QAF011
Rev. 03 Feb. 26, 05
Harvard Technology Middle East
API 570: Piping Inspection Code Inspection, Repair, Alteration & Rerating of In-service Piping Systems (API Exam Preparation Training)
March 5-9, 2005 Abu Dhabi, U.A.E.
Course Instructor(s) Mr. Ron VanArsdale
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To The Participant The Course notes are intended as an aid in following lectures and for review in conjunction with your own notes; however they are not intended to be a complete textbook. If you spot any inaccuracy, kindly report it by completing this form and dispatching it to the following address, so that we can take the necessary action to rectify the matter.
P. O. Box 26608 Abu Dhabi, U.A.E. Tel: +971 2 627 7881 Fax: +971 2 627 7883 Email:
[email protected]
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Disclaimer The information contained in these course notes has been complied from various sources and is believed to be reliable and to represent the best current knowledge and opinion relative to the subject. Harvard Technology offers no warranty, guarantee, or representation as to it’s absolute correctness or sufficiency. Harvard Technology has no responsibility in connection therewith; nor should it be assumed that all acceptable safety and regulatory measures are contained herein, or that other or additional information may be required under particular or exceptional circumstances.
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Table of Contents
Section 1
API 570
Section 2
API 574
Section 3
ASME B16.5
Section 4
ASME B31.3
Section 5
ASME Section V
Section 6
Welding Processes
Section 7
API 578
Section 8
Welding Terminology
Section 9
Welding Discontinuities
Section 10
ASME Section IX
Section 11
Welding Metallurgy
Section 12
Technical Report Writing
Harvard Technology Middle East
COURSE OVERVIEW IE200
API 570: Piping Inspection Code Inspection, Repair, Alteration & Rerating of In-service Piping Systems (API Exam Preparation Training)
Course Title API 570: Piping Inspection Code: Inspection, Repair, Alteration & Rerating of Inservice Piping Systems (API Exam Preparation Training) Course Date/Venue March 05-09, 2005/ Al Hosn Suite, 2nd Floor, Le Royal Meridien, Abu Dhabi, U.A.E. Course Reference IE200 Course Duration 5 days (40 hours as per API recommendations) Course Objectives In order to meet the needs of today's fast changing inspection industry, Harvard Technology (ITAC) has developed the "Piping Inspection Course with API 570 Exam Prep. This comprehensive course is designed to train those individuals who are interested in obtaining the API 570 Piping Inspection Certification. Like the API 653 Exam Prep Course, the student receives in-depth instruction pertaining to passing the API 570 test, as well as insight into the intricacies students may expect to encounter in the working environment. Harvard Technology (ITAC) is proud of its 90%+ pass rate, and we hope to include your staff among our successful candidates. This course is offered as both an in-house and an open enrollment class. Topics include:
Introduction Glossary - Piping Terms Extensive Discussion of API 570 - Inspection, Repair, Alteration, And Rerating Of InService Piping Systems Extensive Discussion of ASME B31.3-Chemical Plant and Petroleum Refinery Piping As related to API 570 Overview of o API 574 - Inspection of Piping, Tubing, Valves and Fittings o ASME B16.5 - As related to API 570 o ASME Section V - As related to API 570 o ASME Section IX - As related to API 570 o NDT- Basic information Welding Processes - General Information Welding Terms - AWS Terminology Weld Discontinuities - General Information Summary and Practice Exam
IE200 IE200-03-05
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Additionally, quizzes are given at the end of each section; homework is handed out at the end of each class day, which consists of 30 questions per day and is reviewed at the beginning of the following day, and a “practice” exam is administered at the end of the course. Harvard Technology (ITAC) is proud of the 90%+ pass rate attained by its students who have sat for the API 570 certification exam. Who Should Attend The course is intended for Inspection Engineers who are seeking API-570 certification. Other engineers, managers or technical staffs who are dealing with Piping Systems will also benefit. Course Instructor Mr. Ron VanArsdale, PE, USA, is the founder of Inspection Training and Consulting Company (ITAC). His duties include conducting training courses for Harvard Technology and ITAC, creating new courses for inspection and other related activities, creating course material, as well as developing custom training programs, customized written practices and providing trouble-shooting consulting services. In the past, Mr. VanArsdale was employed by SGS Industrial Services as the Training Director and the American Welding Society (AWS) as the Curricula and Course Development Manager. In this position he developed various training courses dealing with the AWS Certified Welding Inspector program. He planned, organized, and developed all phases of educational activities for AWS. In addition to these functions, he is a member of the API 653 Questions Committee which devised the API 653 Tank Inspector Certification Examination; as well as a member of the API 570 Questions Committee which is charged with developing the API 570 Piping Inspector Certification Examination. Ron attended San Jacinto College and Texas A&M University, and has a Lifetime Teaching Certificate from the State of Texas. He is an AWS Certified Welding Inspector (CWI), ITAC Level III, an API Certified Aboveground Storage Tank Inspector, and API Certified Piping Inspector, an AWS Certified Welding Educator (CWE) and is an internationally recognized Presenter/Instructor. Additionally, he received the AWS Distinguished Member Award in March, 1989, the AWS CWI of the Year District Award in January, 1993, as well as the AWS District 18 Meritorious Award in September, 1993. He has thirty-three years experience in the erection, maintenance and inspection of buildings, petrochemical facilities, vessels, above-ground storage tanks, piping systems, in addition to teaching welding/inspection education courses. Mr. VanArsdale is professionally affiliated with the American Welding Society, American Society for Nondestructive Testing, American Petroleum Institute, Vocational Industrial Clubs of America, Harvard Technology, American Inspection Society, the National Job Core and has been appointed a Kentucky Colonel by the Governor of Kentucky in recognition of his lifetime contribution to his fellow man. IE200 IE200-03-05
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Required Codes & Standards Listed below are the effective editions of the publications required for the current Piping Inspector Certification Examination. Each student must have these documents available for use during the class. A APPII SSttaannddaarrdd 557700, Piping Inspection Code: Inspection, Repair, Alteration, and Rerating of In-Service Piping Systems,, Second Edition, October, 1998; including, Addendum 1 (February, 2000) and Addendum 2 (December, 2001) and Addendum 3 (August 2003). Global Engineering Product Code API CERT 570 A APPII R Reeccoom mm meennddeedd PPrraaccttiiccee 557744,, Inspection Practices for Piping System Components, Second Edition, June 1998. Global Engineering Product Code API CERT 574 A APPII R Reeccoom mm meennddeedd PPrraaccttiiccee 557788,, Material Verification Program for New and Existing Alloy Piping Systems, First Edition, May 1999
Global Engineering Product Code API CERT 578
A Am meerriiccaann SSoocciieettyy ooff M Meecchhaanniiccaall EEnnggiinneeeerrss ((A ASSM MEE), Boiler and Pressure Vessel Code, 2001 edition with 2002 and 2003 addenda.
i.
A A S M E S o n V AS SM ME ES Seeeccctttiiio on nV V, Nondestructive Examination, Articles 1, 2, 6, 7, 9, 10 and 23 (Section SE-797 only).
ii.
S S o n X Seeeccctttiiio on n IIIX X, Welding and Brazing Qualifications
A Am meerriiccaann SSoocciieettyy ooff M Meecchhaanniiccaall EEnnggiinneeeerrss ((A ASSM MEE)) i. ii.
B B B111666...555, Pipe Flanges and Flanged Fittings, 1996, with 1998 Addenda B B B333111...333, Process Piping, 2002 Edition
Global Engineering Product Code for the ASME package API CERT 570 ASME. Package includes only the above excerpts necessary for the exam. API and ASME publications may be ordered through Global Engineering Documents at 303-397-7956 or 800-854-7179. Product codes are listed above. Orders may also be faxed to 303-397-2740. More information is available at http://www.global.ihs.com. API members are eligible for a 50% discount on all API documents, exam candidates are eligible for a 20% discount on all API documents. When calling to order, please identify yourself as an exam candidate and/or API member. Prices quoted will reflect the applicable discounts. No discounts will be made for ASME documents. For the complete sets of ASME documents including future addenda please contact ASME’s publications department at 1-800-843-2763. In Canada, ASME publications are available through HIS Canada at 1-800-854-7179 or 613-237-4251 Note: API and ASME publications are copyrighted material. Photocopies of API and ASME publications are not permitted. CD-ROM versions of the API documents are issued quarterly by Information Handling Services and are permitted. Be sure to check your CD-ROM against the editions noted on this sheet.
Course Certificate Harvard Technology certificate will be issued to all attendees completing minimum of 75% of the total tuition hours of the course. IE200 IE200-03-05
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Course Fee US $ 2,750 per Delegate. This rate includes Participant’s Pack (Folder, Manual, Hand-outs, etc.), buffet lunch, coffee/tea on arrival, morning & afternoon of each day. Accommodation Accommodation is not included in course fees. However, any accommodation required can be arranged by Harvard Technology at the time of booking. Course Program Day 1 : Saturday 05th of March 2005 0730 - 0800 Registration & Coffee 0800 - 0815 Welcome 0815 - 0900 Introduction 0900 - 0930 Students Take Initial Math Quiz 0930 - 1000 Review Math Quiz Answers 1000 - 1015 Break 1015 - 1045 Overview of Course Outline 1045 - 1230 Review of API 570 Body of Knowledge 1230 - 1330 Lunch 1330 - 1430 API 570 - Sections 1 – Scope 1430 - 1500 API 570 - Sections 2 - References 1500 - 1515 Break 1515 - 1545 API 570 - Sections 3 - Definitions 1545 - 1645 API 570 - Sections 4 - Owner/User Inspection Organization 1645 - 1700 Distribute Homework 1700 End of Day One Day 2 : Sunday 06th of March 2005 0730 - 0830 Review of Day 1 and Homework Answers 0830 - 0930 API 570 - Sections 5 - Inspection And Testing Practices 0930 - 0945 Break 0945 - 1045 API 570 - Sections 6 - Frequency And Extent Of Inspection 1045 - 1130 API 570 - Sections 7 - Inspection Data Evaluation, Analysis, And Recording 1130 - 1200 API 570 -Sections 8 -Repairs, Alterations & Rerating of Piping Systems 1200 - 1230 API 570 - Sections 9 - Inspection of Buried Piping 1230 - 1330 Lunch 1330 - 1400 API 570 - Appendix A - Inspection Certification API 570 - Appendix C - Examples of Repairs API 570 - Appendix D - External Inspection Checklist For Process Piping 1400 - 1410 Administer API 570 Section Quiz 1410 - 1420 API RP 574 - Section 1 - Scope 1420 - 1430 API RP 574 - Section 3 - Definitions IE200 IE200-03-05
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1430 - 1440 1440 - 1450 1450 - 1515 1515 - 1530 1530 - 1540 1540 - 1550 1550 - 1600 1600 - 1615 1615 - 1625 1625 - 1635 1635 - 1645 1645 - 1725 1725 - 1730 1730
API RP 574 - Section 4 - Piping Components API RP 574 - Section 5 - Reasons For Inspection API RP 574 - Section 6 - Inspecting For Deterioration In Piping Break API RP 574 - Section 7 - Frequency And Time Of Inspection API RP 574 - Section 8 - Safety Precautions And Preparatory Work API RP 574 - Section 9 - Inspection Tools API RP 574 - Section 10 - Inspection Procedures API RP 574 - Section 11 - Determination Of Retirement Thickness API RP 574 - Section 12 - Records Administer API 574 Section Quiz Instruction of ASME B16.5 Distribute Homework End of Day Two
Day 3 : Monday 07th of March 2005 0730 - 0830 Review of Day 2 and Homework Answers 0830 - 0845 ASME B31.3 - Chapter 1 - Scope And Definitions 0845 - 0910 ASME B31.3 - Chapter 2 (Part 1) - Design Conditions And Criteria 0910 - 0940 ASME B31.3 - Chapter 2 (Part 2) - Pressure Design of Piping Components 0940 - 1000 ASME B31.3 - Chapter 2 (Part 3) - Fluid Service Requirements For Piping Components 1000 - 1015 Break 1015 - 1040 ASME B31.3 - Chapter 2 (Part 4) - Fluid Service Requirements For Piping Joints 1040 - 1100 ASME B31.3 - Chapter 2 (Part 5) - Piping Flexibility 1100 - 1130 ASME B31.3 - Chapter 3 - Materials 1130 - 1230 ASME B31.3 - Chapter 5 - Fabrication, Assembly And Erection 1230 - 1330 Lunch 1330 - 1430 ASME B31.3 - Chapter 6 - Inspection, Examination And Testing 1430 - 1445 Break 1445 - 1630 ASME Section V - Nondestructive Test Methods 1630 - 1645 ASME Section V Quiz 1645 - 1655 Thought Questions 1655 - 1700 Distribute Homework 1700 End of Day Three Day 4: Tuesday 08th of March 2005 0730 - 0830 Review of Day 3 and Homework Answers 0830 - 0930 Welding Terms 0930 - 0945 Break 0945 - 1045 Welding Procedures 1045 – 1145 Welding Discontinuities 1145 - 1230 ASME Section IX WPS and PQR 1230 - 1330 Lunch IE200 IE200-03-05
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1330 - 1445 1445 - 1500 1500 - 1650 1650 - 1700 1700
Review Procedure Exercise Break ASME Section IX - Welder Certification Distribute Homework End of Day Four
Day 5: Wednesday 09th of March 2005 0730 - 0830 Review of Day 4 and Homework Answers 0830 - 1000 Question and Answer Session 1 1000 - 1015 Break 1015 - 1230 Question and Answer Session 2 1230 - 1330 Lunch 1330 - 1530 Practice Exam 1530 - 1545 Break 1545 - 1630 Presentation of Certificates 1730 End of course
Course Coordinator Ms. Rana Tawfiq,
[email protected]
Tel:
+971-2-6277881,
IE200 IE200-03-05
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Fax:
+971-2-6277883,
Email:
. 26 February 2005
API 570
Piping Inspection Code A AP PII 557700 S Seeccoon nd dE Ed diittiioon n –– O Occttoob beerr, 11999988 Ad dd deen nd du um m 11 -- FFeeb brru uaarryy,, 22000000 A Ad dd deen nd du um m 22 -- D Deecceem mb beerr,, 22000011 A Ad dd deen nd du um m 33 –– A Au uggu usstt,, 22000033 Inspection, Repair, Alteration, and Rerating Of In-Service Piping Systems
Summary and Notes The notes and summary information supplied is the thoughts and opinions of ITAC and does not represent API Committee interpretations. The use of “Key Phrases” is intended as a study guide only.
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API 570 Second Edition - October, 1998 Addendum 1 - February, 2000 Addendum 2 - December 2001
Inspection, Repair, Alteration, and Rerating Of In-Service Piping Systems Foreword This edition of API 570 supersedes all previous editions of API 570. Key phrase ”supersedes previous editions...". 1.0
SCOPE 1.1.1
General API 570 covers inspection, repair, alteration, and rerating procedures for metallic piping systems that have been in-service.
1.1.2
Intent Any organization that uses API 570 should maintain or have access to an authorized inspection agency, a repair organization, qualified engineers, inspectors and examiners. Key phrase "maintain ...agencies and qualified technical personnel".
1.1.3
Limitations Limited to piping that has been placed in-service. Key phrase "placed in service".
1.2
Specific Applications Piping systems for process fluids, hydrocarbons, and similar flammable or toxic fluid services. (Specific services listed in the paragraph.) Page 1- 3
1.2.1
Included Fluid Services 1. 2. 3. 4. 5. 6.
1.2.2
Raw, intermediate, and finished petroleum products. Raw, intermediate, and finished chemical products. Catalyst lines. Hydrogen, natural gas, fuel gas, and flare systems. Sour water and hazardous waste streams above threshold limits. Hazardous chemicals above threshold limits. Key phrase “Services”.
Excluded and Optional Piping Systems Piping systems listed here may be excluded from the specific requirements of API 570, but may be included at the owner's option. Key phrase "owner's option".
1.3
This edition of API 570 (Second Edition, Addenda 1, Addenda 2 and Addenda 3) recognizes API RP 570 “Fitness For Service.” This Recommended Practice is not required by API 570, it is simply allowed if the Owner wants to use it. Key phrase “Fitness For Service”.
2
REFERENCES
3
DEFINITIONS (For the purposes of this standard, the following definitions apply.)
3.1 alteration: A physical change in any component that has design implications affecting the pressure containing capability or flexibility of a piping system beyond the scope of its design. The following are not considered alterations: comparable or duplicate replacement, the addition of any reinforced branch connection equal to or less than the size of existing reinforced branch connections, and the addition of branch connections not requiring reinforcement. 3.2 applicable code: The code, code section, or other recognized and generally accepted engineering standard or practice to which the piping system was built or which is deemed by the owner or user or the piping engineer to be most
appropriate for the situation, including but not limited to the latest edition of ASME B31.3. 3.3 ASME B31.3: A shortened form of ASME B31.3, Chemical Plant and Petroleum Refinery Piping, published by the American Society of Mechanical Engineers. ASME B31.3 is written for design and construction of piping systems. However, most of the technical requirements on design, welding, examination, and materials also can be applied in the inspection, rerating, repair, and alteration of operating piping systems. When ASME B31.3 cannot be followed because of its new construction coverage (such as revised or new material specifications, inspection requirements, certain heat treatments, and pressure tests), the piping Page 1- 4
engineer or inspector shall be guided by API 570 in lieu of strict conformity to ASME B31.3. As an example of intent, the phrase “principles of ASME B31.3” has been employed in API 570, rather than “in accordance with ASME B31.3”. 3.4 authorized inspection agency: Defined as any of the following: a. The inspection organization of the jurisdiction in which the piping system is used. b. The inspection organization of an insurance company that is licensed or registered to write insurance for piping systems. c. An owner or user of piping systems who maintains an inspection organization for activities relating only to his equipment and not for piping systems intended for sale or resale. d. An independent inspection organization employed by or under contract to the owner or user of piping systems that are used only by the owner or user and not for sale or resale. e. An independent inspection organization licensed or recognized by the jurisdiction in which the piping system is used and employed by or under contract to the owner or user. 3.5 authorized piping inspector: An employee of an authorized inspection agency who is qualified and certified to perform the functions specified in API 570. A nondestructive examination (NDE) examiner is not required to be an authorized piping inspector. Whenever the term inspector is used in API 570, it refers to an authorized piping inspector. 3.6 auxiliary piping: Instrument and machinery piping, typically small-bore secondary process piping that can be isolated from primary piping systems. Examples include flush lines, seal oil
lines, analyzer lines, balance lines, buffer gas lines, drains, and vents. 3.7 Critical check valves: Valves that have been identified as vital to process safety and must operate reliably in order to avoid the potential for hazardous events or substantial consequences should a leak occur. 3.8 CUI: Corrosion under insulation, including stress corrosion cracking under insulation. 3.9 deadlegs: Components of a piping system that normally have no significant flow. Examples include the following: blanked branches, lines with normally closed block valves, lines with one end blanked, pressurized dummy support legs, stagnant control valve bypass piping, spare pump piping, level bridles, relief valve inlet and outlet header piping, pump trim bypass lines, high-point vents, sample points, drains, bleeders, and instrument connections. 3.10 defect: An imperfection of a type or magnitude exceeding the acceptable criteria. 3.11 design temperature of a piping system component: The temperature at which, under the coincident pressure, the greatest thickness or highest component rating is required. It is the same as the design temperature defined in ASME B31.3 and other code sections and is subject to the same rules relating to allowances for variations of pressure or temperature or both. Different components in the same piping system or circuit may have different design temperatures. In establishing the design temperature, consideration shall be given to process fluid temperatures, ambient temperatures, heating and cooling media temperatures, and insulation.
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3.12 examiner: A person who assists the inspector by performing specific nondestructive examination (NDE) on piping system components but does not evaluate the results of those examinations in accordance with API 570, unless specifically trained and authorized to do so by the owner or user. The examiner need not be qualified in accordance with API 570 or be an employee of the owner or user but shall be trained and qualified in the applicable procedures in which the examiner is involved. In some cases, the examiner may be required to hold other certifications as necessary to satisfy owner or user requirements. Examples of other certification that may be required are American Society for Non-Destructive Testing SNT-TC1A or CP 189 or American Welding Society Welding Inspector certification. The examiner’s employer shall maintain certification records of the examiners employed, including dates and results of personnel qualifications, and shall make them available to the inspector.
control chemistry or other process variables. Injection points control chemistry or other process variables. Injection points do not include locations where two process streams join (mixing tees). Examples of injection points include chlorine in reformers, water injection in overhead systems, polysulfide injection in catalytic cracking wet gas, antifoam injections, inhibitors, and neutralizers. 3.17 in-service: Refers to piping systems that have been placed in operation, as opposed to new construction prior to being placed in service. 3.18 inspector: An authorized piping inspector. 3.19 jurisdiction: A legally constituted government administration that may adopt rules relating to piping systems. 3.20 level bridle: A level gauge glass piping assembly attached to a vessel.
3.14 imperfections: Flaws or other discontinuities noted during inspection that may be subject to acceptance criteria during an engineering and inspection analysis.
3.21 maximum allowable working pressure: (MAWP): The maximum internal pressure permitted in the piping system for continued operation at the most severe condition of coincident internal or external pressure and temperature (minimum or maximum) expected during service. It is the same as the design pressure, as defined in ASME B31.3 and other code sections, and is subject to the same rules relating to allowances for variations of pressure or temperature or both.
3.15 indication: A response or evidence resulting from the application of a nondestructive evaluation technique.
3.22 mixing tee: A piping component that combines two process streams of differing composition and/or temperature.
3.16 injection point: Locations where relatively small quantities of materials are injected into process streams to
3.23 MT: Magnetic-particle testing.
3.13 hold point: A point in the repair or alteration process beyond which work may not proceed until the required inspection has been performed and documented.
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3.24 NDE: Nondestructive examination. 3.25 NPS: Nominal pipe size (followed, when appropriate, by the specific size designation number without an inch symbol). 3.26 on-stream: Piping containing any amount of process fluid. 3.27 owner/user: An owner or user of piping systems who exercises control over the operation, engineering, inspection, repair, alteration, testing, and rerating of those piping systems. 3.28 owner/user inspector: An Authorized Inspector employed by an Owner-User who has qualified either by written examination under the provisions of Section 4 and Appendix A of API 570 or has qualified under the provisions of A.2, and who meets the requirements of the jurisdiction. 3.29 PT: A liquid-penetrant testing. 3.30 pipe: A pressure-tight cylinder used to convey a fluid or to transmit a fluid pressure and is ordinarily designated “pipe” in applicable material specifications. (Materials designated “tube” or “tubing” in the specifications are treated as pipe when intended for pressure service.) 3.31 piping circuit: A section of piping that has all points exposed to an environment of similar corrosivity and that is of similar design conditions and construction material. Complex process units or piping systems are divided into piping circuits to manage the necessary inspections, calculations, and record keeping. When establishing the boundary of a particular piping circuit, the inspector may also size it to provide a practical package for record keeping and performing field inspection.
3.32 piping engineer: One or more persons or organizations acceptable to the owner or user who are knowledgeable and experienced in the engineering disciplines associated with evaluating mechanical and material characteristics affecting the integrity and reliability of piping components and systems. The piping engineer, by consulting with appropriate specialists, should be regarded as a composite of all entities necessary to properly address a technical requirement. 3.33 piping system: An assembly of interconnected piping that is subject to the same set or sets of design conditions and is used to convey, distribute, mix, separate, discharge, meter, control, or snub fluid flows. Piping system also includes pipesupporting elements but does not include support structures, such as structural frames and foundations. 3.34 primary process piping: Process piping in normal, active service that cannot be valved off or, if it were valved off, would significantly affect unit operability. Primary process piping normally includes all process piping greater than NPS 2. 3.35 PWHT: Postweld heat treatment. 3.36 renewal: Activity that discards an existing component and replaces it with new or existing spare materials of the same or better qualities as the original component. 3.37 repair: The work necessary to restore a piping system to a condition suitable for safe operation at the design conditions. If any of the restorative changes result in a change of design temperature or pressure, the requirements for rerating also shall be satisfied. Any welding, cutting, or grinding operation on a pressurecontaining piping component not
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specifically considered an alteration is considered a repair. 3.38 repair organization: Any of the following: a. An owner or user of piping systems who repairs or alters his or her own equipment in accordance with API 570. b. A contractor whose qualifications are acceptable to the owner or user of piping systems and who makes repairs or alterations in accordance with API 570. c. One who is authorized by, acceptable to, or otherwise not prohibited by the jurisdiction and who makes repairs in accordance with API 570. 3.39 rerating: A change in either or both the design temperature or the maximum allowable working pressure of a piping system. A rerating may consist of an increase, a decrease, or a combination of both. Derating below original design conditions is a means to provide increased corrosion allowance. 3.40 secondary process piping: Smallbore (less than or equal to NPS 2) process piping downstream of normally closed block valves. 3.41 small-bore piping (SBP): Piping that is less than or equal to NPS 2. 3.42 soil-to-air (S/A) interface: An area in which external corrosion will vary depending on factors such as moisture, oxygen content of the soil, and operating temperature. The zone generally is considered to be from 12 inches (305 millimeters) below to 6 inches (150 millimeters) above the soil surface. Pipe running parallel with the soil surface that contacts the soil is included.
3.43 spool: A section of piping encompassed by flanges or other connecting fittings such as unions. 3.44 temper embrittlement: A loss of ductility and notch toughness in susceptible low-alloy steels, such as 1 1/4 Cr and 2 1/4 Cr, due to prolonged exposure to high-temperature service [7000 F to 10700 F (3700 C to 5750 C)]. 3.45 temporary repairs: Repairs made to piping systems in order to restore sufficient integrity to continue safe operation until permanent repairs can be scheduled and accomplished within a time period acceptable to the inspector or piping engineer. 3.46 test point: An area defined by a circle having a diameter not greater than 2 inches (50 millimeters), or a line diameter not exceeding 10 inches (254 millimeters), or not greater than 3 inches (76 millimeters) for larger lines. Thickness readings may be averaged within this area. A test point shall be within a thickness measurement location. 3.47 thickness measurement locations (TMLs): Designated areas on piping systems where periodic inspections and thickness measurements are conducted. 3.48 WFMT: Wet fluorescent magnetic-particle testing. 3.49 alloy material: Any metallic material (including welding filler materials) that contains alloying elements, such as chromium, nickel or molybdenum, which are intentionally added to enhance mechanical or physical properties and/or corrosion resistance. 3.50 material verification program: A documented quality assurance procedure used to assess metallic alloy materials (including weldments and Page 1- 8
attachments where specified) to verify conformance with the selected or specified alloy material designated by the owner/user. This program may include a description of methods for alloy material testing, physical component marking and program record-keeping. 3.51 positive material identification (PMI) testing: Any physical evaluation or test of a material to conform that the material which has been or will be placed into service is consistent with the selected or specified alloy material designated by the owner/user. These evaluations or tests may provide qualitative or quantitative information that is sufficient to verify the nominal alloy composition. 3.52 fitness-for-service assessment: A methodology whereby flaws and conditions contained within a structure
are assessed in order to determine the integrity of the structure for continued service. 3.53 industry-qualified UT shear wave examiner: A person who possesses an ultrasonic shear wave qualification from API or an equivalent qualification approved by the owner/user. 3.54 off-site piping: Piping systems not included within the plot (battery) Limits of a process unit, such as a hydrocracker, an ethylene cracker or a crude unit. Examples of off-site piping include tank farm piping and other lower consequence piping outside the limits of the process unit. 3.55 on-site piping: Piping systems included within the plot limits of process units, such as, a hydrocracker, an ethylene cracker, or a crude unit.
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4
OWNER/USER INSPECTION ORGANIZATION
4.1
General This section establishes an inspection organization to control inspection programs of piping. Key phrase “inspection”.
4.2
Authorized Piping Inspector Qualification Requirements for becoming an "Authorized piping inspector." The term inspector as used by API 570 refers to an authorized piping inspector. See Appendix B for certification requirements. Key phrase “Authorized Piping Inspector”.
4.3
Responsibilities The owner-user shall have overall responsibility for compliance with API 570. The piping engineer is responsible to the owner-user. The repair organization shall be responsible to the owner-user. Key phrase “owner/user”.
5
INSPECTION AND TESTING PRACTICES
5.1
Risk-Based Inspection The paragraph contains a few general statements about an RBI program. This paragraph neither requires or prevents inspection based on RBI. Key phrase "Risk-Based Inspection".
5.2
Preparation This section covers the preparation usually done before the piping inspection begins, such as, permits to enter the area, reviewing history of the system, etc. Key phrase "preparation".
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5.3
Inspection for Specific Types of Corrosion and Cracking Areas that should be inspected for possible problems are listed, see API Recommended Practice 571 for additional information. The areas of deterioration are: • • • • • • • • • • • • 5.3.1
Injection points Deadlegs Corrosion under insulation (CUI) Soil-to-air (S/A) interfaces Service specific and localized corrosion Erosion and corrosion/erosion Environmental cracking Corrosion beneath linings and deposits Fatigue cracking Creep cracking Brittle fracture Freeze damage Key phrase “deterioration”. Injection Points Often subject to accelerated or localized corrosion, more than under normal conditions. Suggestions for establishing injections point circuit, for inspection circuits:
•
•
Upstream 12 inches or three pipe diameters upstream whichever is greater.
•
Downstream The second change in flow direction or 25 feet downstream, beyond the first flow change whichever is less.
Injection nozzles 12 inches upstream of the nozzle and continuing for at least ten pipe diameters downstream of the injection point. TMLs (thickness measurement locations) a. Establish TMLs on fittings b. Establish TMLs on the pipe wall c. Establish TMLs on longer straight piping d. Establish TMLs on both upstream and downstream limits of injection points circuit. The preferred methods of inspection of injection points are radiography and/or ultrasonics. These methods are used to established thickness, not weld quality. Key phrase “injection points”.
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5.3.2 Deadlegs Due to the corrosion rate variation both the active and stagnant end of a deadleg should be inspected. Consideration should be given to removing the deadlegs that serve no useful purpose. Key phrase “deadlegs”. 5.3.3 Corrosion Under Insulation (CUI) External corrosion of an insulated piping system. The corrosion is usually from trapped moisture that may include rain, water leaks, condensation, and deluge systems. The most common form of CIU is localized corrosion of carbon steel and chloride stress corrosion cracking of austenitic stainless steels. Key phrase “CUI”. 5.3.3.1 Insulated Piping Systems Susceptible to CUI a. b. c. d. e.
Areas exposed to overspray from cooling water towers Areas exposed to steam vents Areas exposed to deluge systems Areas subject to process spills, moisture, or acid vapors Carbon steel piping systems operating between 25oF and 250oF f. Carbon steel piping systems above 250oF in intermittent service g. Deadlegs and attachments protruding from insulated systems that may operate at a different temperature than the active line h. Austenitic stainless steel piping systems operating between 150oF and 400oF i. Vibrating piping systems j. Steam traced piping systems k. Piping systems with deteriorated coatings and/or wrappings Key phrase “CUI” 5.3.3.2 Common Locations on Piping Systems Susceptible to CUI a. b. c. d. e. f. g. h. i.
All damaged insulation. Termination of insulation. Missing insulation. Poorly installed insulation. Termination of insulation on vertical piping. Caulking problems. Bulges in insulation, could be an indication of CUI. Low points. Carbon or low-alloy steel flanges, bolting etc., especially if in a high-alloy system. j. Areas where insulation plugs have been removed and not properly sealed. Key phrase “CUI”. Page 1- 12
5.3.4 Soil-to-Air Interface Soil-to-air (S/A) interfaces without cathodic protection shall be included in scheduled external piping inspections. Special interest in this area, note also concrete-to-air and asphalt-to-air have special requirements. Caulking in these areas are often a main concern. Key phrase “S/A”. 5.3.5
Service-specific and Localized Corrosion The three elements of an inspection program: • • •
An inspector with knowledge of the service and where corrosion is likely to occur. Extensive use of NDE. Communication from operations when process upsets occur that may affect corrosion rates.
Examples of service-specific corrosion are listed in the rest of the paragraph. Key phrase “Inspection Program”. 5.3.6 Erosion and Corrosion/Erosion Erosion can be defined as the removal of surface material by the action of numerous individual impacts of solid or liquid particles. Erosion usually occurs in areas of turbulent flow. Inspect the following for erosion/corrosion: a. Downstream of control valves. b. Downstream of orifices. c. Downstream of pump discharges. d. Flow direction change. e. Downstream of piping configurations that produce turbulence. Key phrase “erosion and corrosion”. 5.3.7 Environmental Cracking The topics mentioned here are SCC (Stress Corrosion Cracking) and HIC (Hydrogen Induced Cracking) these types of cracking are results of specific services reacting with the basic metallurgy of the piping. If this type of cracking is found in pressure vessels, then the related piping may have the same problem. Key phrase “cracking”. 5.3.8 Corrosion Beneath Linings and Deposits Usually it is not necessary to remove the linings, internal or external, if there is no evidence of damage. However, if deposits, such as coke, are present, it is important to determine if any active corrosion is beneath the deposits. Key phrase “corrosion”.
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5.3.9 Fatigue Cracking Fatigue cracking is cracking that usually results from cyclic stresses. A piping system may be designed below the static yield strength of the material, but due to the number of heat-up high cycles changing to cool-down low cycles the material may fail. This problem may be detected by PT, MT or (AE) acoustic emission. Key phrase “fatigue cracking”. 5.3.10 Creep Cracking Creep is dependent on time, temperature, and stress. One of the most common examples of creep cracking has been experienced in the industry is in 1 1/4 Cr steels above 9000 F. Creep cracking NDE include PT, MT, UT, RT, and in-situ metallography. Under special conditions AE may be employed. Key phrase “creep cracking”. 5.3.11 Brittle Fracture Failure of piping at lower temperatures, usually below 600 F. Most incidences have occurred during a hydrotest or other over load condition. Special attention should be used when rehydrotesting lowalloy steels (especially 2 1/4 Cr-1 Mo material), because of temper embrittlement, also to ferritic stainless steels. (See API RP 579, Sec. 3). Key phrase “brittle fracture”. 5.3.12 Freeze Damage Inspections should be performed after subfreezing temperatures. Water and aqueous solutions in piping systems may freeze and cause failure because of expansion. Leaks may not be evident until the system thaws. Key phrase “freeze damage”. 5.4
Types of Inspection and Surveillance The basic types of inspection include: • Internal visual inspection. • Thickness measurement inspection. • External visual inspection. • Vibrating piping inspection. • Supplemental inspection. Key phrase “inspection”. 5.4.1
Internal Visual Inspection This type of inspection is not normally performed on piping systems, unless there is large diameter piping involved. Key phrase “internal inspection”.
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5.4.2
Thickness Measurement Inspection Thickness measurements are used for internal condition and remaining thickness of piping systems. Measurements may be taken by inspectors or examiners. Key phrase “thickness measurements”.
5.4.3
External Visual Inspection Items to inspect are listed in this section. Inspections may be performed by inspectors, qualified operating or maintenance personnel. The operating or maintenance personnel shall be qualified through an appropriate amount of training. Key phrase “external visual inspection”.
5.4.4
Vibrating Piping and Line Movement Surveillance This inspection should be performed at junctions where vibrating piping systems are restrained. Key phrase “vibrating”.
5.4.5
Supplemental Inspection Profile radiography, thermography, acoustic emission, acoustic leak detection and ultrasonics can be used where appropriate.
5.5
Thickness Measurement Locations 5.5.1
General TMLs thickness measurement locations are specific areas along the piping circuit where inspections are to be made. This section outlines general TML monitoring and selection. Extremely basic. Key phrase “TML”.
5.5.2 TML Monitoring TMLs should be monitored based on the corrosiveness of the system. Thickness measurements should include measurements at each of the four quadrants on pipe and fittings, with special attention to the inside and outside radius of elbows and tees. Key phrase “TML”. 5.5.3
TML Selection Basic broad rules for TML selection are found in this section, the information found here is extremely basic. Key phrase “TML”.
5.6
Thickness Measurement Methods Piping larger than 1” NPS (Nominal Pipe Size) ultrasonic thickness measuring instruments are accurate. The radiographic profile techniques are preferred for pipe 1” NPS and smaller. When piping temperatures are above 1500 F, a special procedure and equipment must be used. Typical problems when using UT digital instruments are discussed. Key phrase “UT Thickness”. Page 1- 15
5.7
Pressure Testing of Piping Systems Pressure testing is not normally conducted as part of a routine inspection. When this test is used, it should be performed in accordance with ASME B31.3. Piping of 300 series stainless steel should by hydrotested with potable water or steam condensate. A pneumatic pressure test may be used when it is impracticable to hydrotest the system. Such tests must be in compliance with ASME B31.3. Precautions should be used when safety relief valves are installed in the system. Isolation or removal of the safety relief valves may be necessary during the test. Key phrase “pressure test”.
5.8
Material Verification and Traceability This section was updated in the first addenda to specify “alloy material.” All materials, except pure iron, more commonly called “pig iron” are made by using alloying agents. This section also mentions the new API RP 578, Material Verification Program for new an existing alloy piping system.” This testing can be performed by the inspector OR the examiner. Remember, the owner/user will decide on when to use a “PMI (Positive Material Identification) testing program.” Key phrase “alloy material” and “PMI”.
5.9
Inspection of Valves Refer to API Standard 598 for closure pressure tests. Other inspections include external visual examinations, as well as internal inspections if metal loss is suspected. Key phrase “valves”.
5.10
Inspection of Welds In-Service The use of profile radiography is recommended when searching for corrosion or other imperfections in welds that are in-service. Weld imperfections may be the result of original weld fabrication or service. A determination should be made as to what caused the problem. This may be evaluated by: • Inspector judgment. • Certified welding inspector judgment. • Piping engineer judgment. • Engineering fitness-for-service analysis. The following should be considered when assessing the quality of existing welds: 1. Original fabrication inspection acceptance criteria. 2. Extent, magnitude, and orientation of imperfections. 3. Length of time in-service. 4. Operating versus design conditions. 5. Presence of secondary piping stresses. 6. Potential for fatigue loads. 7. Potential for environmental cracking. 8. Weld hardness.
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Note: Some welds may meet original construction criteria but will not perform satisfactorily in-service. In addition to radiography, UT shear wave examination is now allowed. Fitness-for-service monitoring is one application. Key phrase “welds in-service”. 5.11
Inspection of Flanged Joints Check the gaskets and bolting. If the flanges have been clamped and pumped with sealant, check for additional leakage. See API Recommended Practice 574 for procedures when flanges are opened. Key phrase “flanges”.
6
FREQUENCY AND EXTENT OF INSPECTION
6.1
General This extremely general section discusses the RBI concept used to establish a piping circuit inspection strategy. Inspection may be based on the expected forms of degradation, the optimal inspection frequency, extent of inspection and the prevention and mitigation steps to reduce the likelihood and consequence. Key phrase “RBI”.
6.2
Piping Service Classes This section suggests piping be categorized into different classes, or hazard levels, using API Recommended Practice 750 and NFPA (National Fire Prevention Association) 704 as guidelines. Key phrase “service classes”. 6.2.1
Class 1 Class 1 piping is piping whose services have the highest potential of resulting in an immediate emergency if a leak were to occur. Class 1 piping include, but not limited to, the following: 1. Flammable services that may auto-refrigerate and lead to brittle fracture. 2. Pressurized services that may rapidly vaporize during release, creating vapors that may collect and form an explosive mixture, such as C2 (ethylenes), C3 (propylenes), C4 (butanes) streams. Fluids that will rapidly va0orize are those with atmospheric boiling temperatures below 50oF. 3. Hydrogen sulfide (greater than 3 percent weight) in a gaseous stream. 4. Anhydrous hydrogen chloride. 5. Hydrofluoric acid. 6. Piping over or adjacent to water and piping over public throughways. Key phrase “emergency”.
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6.2.2 Class 2 Class 2 piping is usually unit process piping and selected off-site piping that is not included in Class 1 piping. Examples are as follows: 1. On-site hydrocarbons that will slowly vaporize during release such as those operating below the flash point. 2. Hydrogen, fuel gas, and natural gas. 3. On-site strong acids and caustics. Key phrase “process piping”. 6.2.3
Class 3 Class 3 piping contains services that are flammable but do not significantly vaporize and are not located in high-activity areas. Examples are: 1. On-site hydrocarbons that will not significantly vaporize during release such as those operating below the flash point. 2. Distillate and product lines to and from storage and loading. 3. Off-site acids and caustics. Key phrase “Class 3”.
6.3
Inspection Intervals The criteria for inspection intervals are as follows: 1. 2. 3. 4.
Corrosion rate and remaining life calculations. Piping services classification. Applicable jurisdictional requirements. Judgment of the inspector, piping engineer, engineer supervisor, or a corrosion specialist, based on operating conditions, history, current results and special conditions.
The owner-user shall establish inspection intervals for thickness measurements and external visual inspections. Refer to Table 6-1 (page 6-3) for recommended inspection intervals. Inspections should be based on Table 6-1 or half the remaining life determined from the corrosion rates which ever is shorter. Key phrase “inspection interval”. 6.4
Extent of Visual External and CUI Inspections External inspections should be scheduled in accordance with Table 6-1 (page 6-3) using the checklist in Appendix D, EXTERNAL INSPECTION CHECKLIST FOR PROCESS PIPING Alternatively, API RP 580, an RBI system can be used. See Table 6-2 - Recommended Extent of CUI Inspection Following Visual Inspection. Key phrase “visual external inspections”.
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6.5
Extent of Thickness Measurement Inspection As a minimum, a representative sampling of TMLs shall be measured, including various types of components and orientations in each circuit. See 3.2.1 for inspection of injection points. Key phrase “TML”.
6.6
Extent of Small-Bore, Auxiliary Piping, and ThreadedConnections Inspections 6.6.1 Small-Bore Piping Inspection Small-bore piping (SBP) that is primary process piping should be inspected in accordance with all the requirements of API 570. Key phrase “SBP”. 6.6.2
Auxiliary Piping Inspection Inspection of auxiliary SBP is optional, dependent on classification, cracking potential, corrosion, and potential for CUI.
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7
INSPECTION DATA EVALUATION, ANALYSIS AND RECORDING 7.1.1
Remaining Life Calculations Remaining life (years)=
t actual - t required -----------------corrosion rate [inches (millimeters) per year]
Where: t actual = the actual minimum thickness, in inches (millimeters), determined at the time of inspection. t required = the required thickness, in inches (millimeters), for the limiting section or zone. The long term (L. T.) corrosion rate: Corrosion rate (L. T.) = t initial - t actual --------------time (years) between initial and actual inspections The short term (S. T.) corrosion rate: Corrosion rate (S. T.) = t previous - t actual --------------time (years) between previous and actual inspections Long Term and Short Term rates should be compared to see which results in the shortest remaining life as part of the data assessment. Key phrase “corrosion rate”. 7.1.2 Newly Installed Piping Systems or Changes in Service Probable corrosion rates may be determined by use of the following: 1. Corrosion rate of similar service. 2. Owner user’s experience or published data on comparable service. 3. Initial thickness shall be made after 3 months of service by using NDT. Key phrase “corrosion rate”. 7.1.3
Existing Piping Systems Corrosion rates shall be calculated on either a short-term basis, using the two most recent inspections or long-term basis, using original wall thickness and most recent inspection, use the higher result in most cases. Key phrase “corrosion rate”. Page 1- 20
7.2
Maximum Allowable Working Pressure Determination The maximum allowable working pressure (MAWP) for the continued use of piping systems shall be established using the applicable code. Computations may be made if all the following comply with the applicable code: 1. 2. 3. 4. 5.
Upper and/or lower temperature limits for specific materials. Quality of materials and workmanship. Inspection requirements. Reinforcement of openings. Any cyclical service requirements.
See Table 7-1 API 570 uses the “Half-Life” concept Key phrase “MPWA”. 7.3
Minimum Required Thickness Determination The minimum required pipe wall thickness shall be based on pressure, mechanical, and structural considerations using the appropriate design formulae and code allowable stress. Key phrase “minimum thickness”.
7.4
Assessment of Inspection Findings Fitness-for-service techniques may be evaluated by API 579. Key phrase “fitness-for-service assessment”.
7.5
Piping Stress Analysis Piping must be supported and guided so that: 1. its weight is carried safely; 2. it has sufficient flexibility for thermal expansion or contraction; 3. it does not vibrate excessively. Key phrase “stress analysis”.
7.6
Reporting and Records for Piping System Inspection API 574 offers guidance for piping inspection records. Key phrase “records”.
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8
REPAIRS, ALTERATIONS, AND RERATING OF PIPING SYSTEMS
8.1
Repairs and Alterations The principles of ASME B31.3 or the code to which the piping system was built shall be followed for repairs and alterations. Key phrase “ASME B 31.3”. 8.1.3
Welding Repairs (Including on-stream) 8.1.3.1 Temporary Repairs Temporary repairs may be used, full encirclement welded split sleeve or box-type enclosure. Split coupling or plate patch may also be used. Temporary repairs should be removed and replaced at the next available maintenance opportunity. Key phrase “temporary repairs”. 8.1.3.2 Permanent Repairs Replacement pipe may be installed or insert patches (flush patches) may be used if: 1. Full-penetration groove welds are provided. 2. For Class 1 and Class 2 piping systems, the welds shall be 100% radiographed or ultrasonically tested. 3. Patches may be any shape but shall have rounded corners. Key phrase “permanent repairs”.
8.1.4 Nonwelding Repairs (on-stream) Temporary repairs may be made by installing a bolted leak clamp. Pumping of such clamps is allowed. All temporary repairs shall be removed and appropriate actions taken to restore the original integrity of the system. Key phrase “nonweld repairs”. 8.2.1
Procedures, Qualifications, and Records Procedures and welders shall be qualified in accordance with ASME B31.3 or the code to which the piping was built. Key phrase “ASME B31.3
8.2.2
Preheating and Postweld Heat Treatment Preheating shall be in accordance with the applicable code and qualified welding procedure, exceptions must be approved by the piping engineer. Preheating may not be considered as an alternative to environmental cracking prevention. • Postweld Heat Treatment (PWHT) should be in compliance with ASME B31.3 or the code to which the piping was built. Local PWHT may be substituted for 360-degree banding on local repairs. Key phrase “preheating and PWHT”. •
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8.2.3
Designs Butt joints shall be full-penetration groove welds. Fillet welded patches are allowed if approved by the piping engineer. Key phrase “patches”.
8.2.6
Pressure Testing Pressure testing after repairs or alterations may be employed. Nondestructive examination (NDE) shall be utilized in lieu of a pressure test. Key phrase “pressure test”.
8.3
Rerating Rerating piping systems by changing the temperature rating or MAWP may be done only if: 1. Calculations are performed by the piping engineer or the inspector. 2. All reratings shall be in accordance with the requirements of code to which the system was built, newest edition. 3. Current records verify the system is satisfactory and corrosion allowance is provided. 4. Rerated piping systems shall be leak tested. 5. All pressure relieving devices are checked and appropriately set. 6. The piping system rerating is acceptable to the inspector or piping engineer. 7. All piping components are adequate for the new pressure and temperature. 8. Piping flexibility is adequate for design temperature changes. 9. Engineering records are updated. 10. A decrease in minimum operation temperature is justified by impact test results. Key phrase “rerating”.
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9
INSPECTION OF BURIED PIPING
9.1
Types and Methods of Inspection • • • • •
Above-grade visual surveillance Close-interval potential survey Pipe coating holiday survey Soil resistivity Cathodic protection monitoring
Inspection Methods 1. Intelligent pigging 2. Video cameras 3. Excavation Key phrase “buried piping”. 9.2
Frequency and Extent of Inspection 1. The owner-user should, at approximately 6-month intervals, survey the surface conditions on and adjacent to each pipeline path. 2. 5-year intervals for poorly coated pipes with little or no cathodic protection. 3. 5-year intervals for piping not cathodically protected. 4. Piping systems cathodically protected see Section 10 of NACE RP0169 or Section 9 of API RP 651. 5. External and internal inspection intervals see Table 9-1 - Frequency of Inspection for Buried Piping Without Effective Cathodic Protection. Key phrase “buried piping”. 9.2.7 Leak Testing Intervals The leak testing procedure of buried piping systems has been changed, the new procedure calls for an 8 hour test as opposed to the old requirement for 12 hours, repressurization is now to be done at 4 hours after initial pressurization, the 5 percent drop in pressure is still acceptable. Key phrase “pressure test”.
9.3
Repairs to Buried Piping Systems Repairs to coatings, any coating removed for inspection shall be renewed and inspected. Key phrase “buried piping”.
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APPENDIX A - INSPECTOR CERTIFICATION This Appendix covers the examination, grading, and validation of the API 570 exam. Certification and recertification guidelines are also found in this section. Addenda 3 now requires re-testing of each inspector after six years, or during the second renewal. The details have not yet been released.
APPENDIX B - TECHNICAL INQUIRIES This is an avenue to allow communications from interested parties and the API 570 Committee. APPENDIX C - EXAMPLES OF REPAIRS D-1 Repairs See figure D-1 Encirclement Repair Sleeve and Figure D-2 Small Repair Patches. APPENDIX D - EXTERNAL INSPECTION CHECKLIST FOR PROCESS PIPING See page D - 1 for the short external inspection checklist for process piping.
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ITAC Visit our website: www.itac.net
Inspection Training And Consulting Post Office Box 5666 Pasadena, TX 77508-5666 Phone (281) 998-8305 Fax (281) 998-2163
API 570 Quiz 1. API 570 covers inspection of: A. B. C. D.
new construction new tank construction in-service piping in-service vessels
2. CUI is the acronym for: A. B. C. D.
Corrosion Under Insulation Cold Under-ground In-service piping Corrosion Under Inside flow Carpet Under Infra-structure
3. A person who assists the inspector by performing specific NDE on piping systems is termed: A. B. C. D.
NDE technician Inspector assistant Level II inspector Examiner
4. The response or evidence resulting from the application of a nondestructive evaluation technique is termed: A. B. C. D.
A crack Porosity A leak An indication
5. The MAWP is: A. B. C. D.
The maximum internal pressure permitted in the piping system. The minimum internal pressure permitted in the piping system. The maximum external pressure permitted in the piping system. The maximum external stress permitted in the piping system.
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6. A section of piping encompassed by flanges or other connecting fittings is called: A. B. C. D.
A flanged pipe A ready to be installed pipe A spooled piece A fabricated piping assembly
7. If a person has a degree in engineering he is automatically qualified to be: A. B. C. D.
An Authorized Piping Inspector A piping inspector A NDE Level II or III in any technique None of the above
8. A TML is: A. B. C. D.
Thickness Material Laboratory Taiwan Made Label Thickness Measurement Location Time Medium Length
9. The result of excessive cyclic stresses that are often well below the static yield strength of the material is titled: A. B. C. D.
material failure fatigue cracking failure cracking creep cracking
10. Thickness measurements may be taken by ultrasonic instruments or what other method: A. AET B. ET C. MT D. RT 11. Which of the following tests are not normally conducted as part of a routine inspection: A. B. C. D.
UT Thickness Visual Inspection Radiographic profile Pressure tests
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12. Thickness measurements are not routinely taken on ______ in piping circuits. A. B. C. D.
valves straight run pipe fittings deadlegs
13. During the installation of a flanged connection, the bolts should: A. B. C. D.
Extend two threads past their nuts. Extend completely through their nuts. Extend only half way through their nuts. Extend at least .5 inches (1.25 mm) past their nuts.
14. Services with the highest potential of resulting in an immediate emergency if a leak were to occur are in: A. B. C. D.
Class 3 Class 2 Class 1 Owner/user designated system
15. The classification that includes the majority of unit process piping is labeled: A. B. C. D.
Class 3 Class 2 Class 1 Owner/user designated system
16. Services that are flammable but do not significantly vaporize when they leak and are not located in high activity areas: A. B. C. D.
Class 3 Class 2 Class 1 Owner/user designated system
17. What is the remaining life in years of a piping systems whose corrosion rate is .074 inches per year, the actual wall thickness is .370 inches and the minimum required thickness is .1 inches? A. 36.48 years B. 364.8 years C. 3.6 years D 3.6 months
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18. What is the long term corrosion rate of a piping circuit that started at .375 inches and is now .1 inch, the measurements were taken over a five year period. A. B. C. D.
.055 inches per year .005 inches per year .550 inches per year Not enough information given
19. What is the short term corrosion rate of the above piping circuit. A. B. C. D.
.055 inches per year .005 inches per year .550 inches per year Not enough information given
20. A longitudinal crack in an existing piping circuit may be repaired by: A. B. C. D.
installing a full encirclement welded split sleeve welding over the crack welding a box over the cracked area using a full encirclement welded split sleeve, with the approval of the piping engineer
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API 570 Quiz Answer Key 1. C 2. A 3. D 4. D 5. A 6. C 7. D 8. C 9. B 10. D 11. D 12. A 13. B 14. C 15. B 16. A
Paragraph 1.1.1 Paragraph 3.8 Paragraph 3.12 Paragraph 3.15 Paragraph 3.21 Paragraph 3.43 Paragraph A.2.1 Paragraph 3.47 Paragraph 5.3.9 Paragraph 5.6 Paragraph 5.7 Paragraph 5.9 Paragraph 5.11 Paragraph 6.2.1 Paragraph 6.2.2 Paragraph 6.2.3
18. A
Paragraph 7.1.1
17. C Paragraph 7.1.1 Remaining life (years)= t actual - t required -----------------corrosion rate [inches (millimeters) per year] Where: t actual = the actual minimum thickness, in inches (millimeters), determined at the time of inspection. t required = the required thickness, in inches (millimeters), for the limiting section or zone.
The long term (L. T.) corrosion rate: Corrosion rate (L. T.) = t initial - t actual --------------time (years) between initial and actual inspections
19. A
Paragraph 7.1.1
The short term (S. T.) corrosion rate: Corrosion rate (S. T.) = t previous - t actual --------------time (years) between previous and actual inspections
20. D
Paragraph 8.1.3.1
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API 574
Inspection Practices for Piping System Components API Recommended Practice 574 Second Edition, June 1998
Summary and Notes The notes and summary information supplied is the thoughts and opinions of ITAC and does not represent API Committee interpretations. The use of “Key Phrases” is intended as a study guide only.
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Inspection Practices for Piping System Components API Recommended Practice 574 Second Edition, June 1998 Foreword This recommended practice is based on the accumulated knowledge and experience of engineers and other personnel in the petroleum industry. Key phrase “recommended practice". 1
SCOPE API 574 covers the inspection practices for piping, tubing, valves (other than control valves), and fittings used in petroleum refineries and chemical plants.
2
REFERENCES
3
DEFINITIONS
3.1 ASME B31.3: Abbreviation for ASME/ANSI B31.3, Process Piping, published by the American Society of Mechanical Engineers. ASME B31.3 is written for design and construction of piping systems. However, most of the technical requirements on design, welding, examination, and materials also can be applied in the inspection, rerating, repair, and alteration of operating piping systems. When ASME B31.3 cannot be followed because of its new construction coverage, such as revised or new material specifications, inspection requirements, certain heat treatments, and pressure tests, the piping engineer/inspector shall be guided by API 570 in lieu of strict conformance with ASME B31.3. As an example of intent, the term “principles” of ASME
B 31.3 has been employed in API 570 rather than the phrase “in accordance with” ASME B31.3. 3.2 CUI: Corrosion under insulation, which includes stress corrosion cracking under insulation. 3.3 deadlegs: Components of a piping system that normally have no significant flow. Examples include blanked branches, lines with normally closed block valves, lines which have one end blanked, pressurized dummy support legs, stagnate control valve bypass piping, spare pump piping, level bridles, relief valve inlet and outlet header piping, pump trim bypass lines, high point vents, sample points, drains, bleeders, and instrument connections.
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3.4 defect: In NDE usage, a defect is an imperfection of a type or magnitude exceeding the acceptable criteria. 3.5 design temperature: The temperature at which, under the coincident pressure, the greatest thickness or highest rating of a piping system component is required. It is equivalent to the design temperature, as defined in ASME B31.3 and other code sections, and is subject to the same rules relating to allowances for variations of pressure or temperature or both. Different components in the same piping system or circuit may have different design temperatures. In establishing this temperature, consideration shall be given to process fluid temperatures, ambient temperatures, heating/cooling media temperatures, and insulation. 3.6 imperfection: Flaws or other discontinuities noted during inspection that may be subject to acceptance criteria on engineering/inspection analysis. 3.7 injection points: Locations where relatively small quantities of materials are injected into process streams to control chemistry or other process variables. Injection points do not include the locations where two process streams join (mixing tees). Examples of injection points include chlorine in reformers, water injection in overhead systems, polysulfide injection in catalytic cracking wet gas, anti-foam injections, inhibitors, and neutralizers. 3.8 in-service: Refers to piping systems that have been placed in operation as opposed to new construction prior to being placed in service. 3.9 inspector: An authorized piping inspector.
3.10 jurisdiction: A legally constituted government administration that may adopt rules relating to piping systems. 3.11 mixing tees: A component that combines two process streams of differing composition and/or temperature. 3.12 NDE: Nondestructive examination. 3.13 NPS: Nominal pipe size (followed, when appropriate, by the specific size designation number without an inch symbol). 3.14 on-stream: Piping containing any amount of process fluid. 3.15 owner-user: An operator of piping systems who exercises control over the operation, engineering, inspection, repair, alteration, testing, and rerating of those piping systems. 3.16
PT: Liquid penetrant testing.
3.17 pipe: A pressure-tight cylinder used to convey a fluid or to transmit a fluid pressure, ordinarily designated “pipe” in applicable material specifications. (Materials designated “tube” or “tubing” in the specifications are treated as pipe when intended for pressure service.) 3.18 piping circuit: Complex process units or piping systems are divided into piping circuits to manage the necessary inspections, calculations, and record keeping. A piping circuit is a section of piping of which all points are exposed to an environment of similar corrosivity and which is of similar design conditions and construction material. When establishing the boundary of a particular piping circuit, the Inspector may also size it to provide a practical package for record-keeping and performing field inspection.
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3.19 piping engineer: One or more persons or organizations acceptable to the owner-user who are knowledgeable and experienced in the engineering disciplines associated with evaluating mechanical and material characteristics which affect the integrity and reliability of piping components and systems. The piping engineer, by consulting with appropriate specialists, should be regarded as a composite of all entities necessary to properly address a technical requirement. 3.20 piping system: An assembly of interconnected piping, subject to the same set or sets of design conditions, used to convey, distribute, mix, separate, discharge, meter, control, or snub fluid flows. Piping system also includes pipe-supporting elements, but does not include support structures, such as building frames, bents, and foundations. 3.21 PWHT: Post weld heat treatment.
maximum allowable working pressure of a piping system. A rerating may consist of an increase, decrease, or a combination. Derating below original design conditions is a means to provide increased corrosion allowance. 3.24 small bore piping (SBP): Less than or equal to NPS 2. 3.25 soil-to-air (S/A) interface: An area in which external corrosion may occur on partially buried pipe. The zone of the corrosion will vary depending on factors such as moisture, oxygen content of the soil, and the operating temperature. The zone generally is considered to be from 12 inches (30 cm) below to 6 inches (15 cm) above the soil surface. Pipe running parallel with the soil surface that contacts the soil is included. 3.26 spools: A section of piping encompassed by flanges or other connecting fittings, such as unions.
3.22 repair: A repair is the work necessary to restore a piping system to a condition suitable for safe operation at the design conditions. If any of the restorative changes result in a change of design temperature or pressure, the requirements for rerating also shall be satisfied. Any welding, cutting, or grinding operation on a pressure-containing piping component not specifically considered an alteration is considered a repair.
3.27 temper embrittlement: A loss of ductility and notch toughness in susceptible low-alloy steels (e.g., 1 1/4 Cr and 2 1/4 Cr) due to prolonged exposure to high temperature service (between 7000 to 1070 F (3710 C to 5770 C)).
3.23 rerating: A change in either or both the design temperature or the
3.29 WFMT or WFMPT: Wet fluorescent magnetic particle testing.
3.28 thickness measurement locations (TMLs): Designated areas on piping systems where periodic inspections and thickness measurements are conducted.
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4
PIPING COMPONENTS
4.1
Piping Piping can be made from any material that can be rolled and welded, cast, or drawn through dies to form a tubular section. The difference from traditional thickness designations and schedules is indicated. Small bore piping (NPS 2 pipe size and less) is also included. See Table 1 for nominal sizes. Key phrase “piping”.
4.2
Tubing Tubing is generally seamlessly drawn. General information about tubing. Key phrase “tubing”.
4.3
Valves The basic types of valves are gate, globe, plug, ball, diaphragm, butterfly, check, and slide valves. See Figures 1 - 8 for cross section view of each of theses valves. All of Section 4.3 is general basic information about valves. Key phrase “valves”.
4.4
Fittings Fittings are used to connect pipe sections and change the direction of flow or allow the flow in a piping run to be diverted or added to. The basic types of pipe fittings, cast, forged, seamlessly drawn, or formed and welded. Fittings may be flanged, socketwelded, butt welded or threaded. . See Figures 9 - 16 for cross section view of each of theses fittings. All of Section 4.4 and 4.5 is general basic information about pipe fittings. Key phrase “fittings”.
5
REASONS FOR INSPECTION
5.1
General The primary purpose of inspection is to achieve the desired quality assurance and ensure plant safety and reliability. Key phrase "inspection".
5.2
Safety Basic information about common sense piping safety. Key phrase “safety”.
5.3
Reliability and Efficient Operation An added benefit to having a regular inspection program, is that it creates a data bank of information regarding the physical condition of equipment and the rate and causes of deterioration. The user can then establish effective preventative maintenance schedules. This effort should result in reduced maintenance costs and more reliable and efficient operations.
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5.4
Regulatory Requirements Federal, state, and local statutes and regulations may apply to piping installation and inspection. Key phrase “regulatory requirements”.
6
INSPETING FOR DETERIORATION IN PIPING Aboveground piping is subject to atmospheric corrosion; buried piping is subject to soil corrosion. See Figures 17, 18, 19, 20 and 23 for illustrations of corrosion and eroding of piping.”
6.1
General Petro-chemical piping, by nature, often carries highly corrosive materials, it is suggested API IRE Chapter II, Conditions Causing Deterioration or Failures, be reviewed for causes of deterioration. Key phrase “deterioration”.
6.2
Corrosion Monitoring Of Process Piping The most frequent reason for replacing piping is from thinning due to corrosion. A good monitoring system is imperative. Things to consider when establishing a corrosion-monitoring plan: a. Classifying the piping accordance with API 570. b. Categorizing the piping into circuits of similar corrosion behavior. c. Identifying susceptible locations where accelerated corrosion is expected. d. Accessibility of the TML’s for monitoring. Key phrase “corrosion monitoring”. 6.2.1
Piping Circuits The basic factors of pipe wall corrosion are listed. As well as, suggestions for breaking piping systems into circuits, see figure 21 for an example. Key phrase “piping circuits”.
6.2.3
Piping Classifications Factors to consider when classifying piping are, toxicity, volatility, combustibility, location of the piping with respect to personnel and other equipment, and experience and history. Key phrase “classifications”.
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6.3
Inspection For Specific Types Of Corrosion And Cracking General information about the following subjects are found in the rest of this section: a. Injection points. b. Deadlegs. c. Corrosion under insulation (CUI). d. Soil-to-air interfaces. e. Service specific and localized corrosion. f. Erosion and corrosion/erosion. g. Environmental cracking. h. Corrosion beneath linings and deposits. i. Fatigue cracking. j. Creep cracking. k. Brittle fracture. l. Freeze damage. m. Corrosion at support points. n. Dew Point Corrosion.
7
FREQUENCY AND TIME OF INSPECTION
7.1
General The frequency and time of inspection should be determined by the following conditions: • a. The severity of service. • b. The degree of risk. • c. The amount of corrosion allowance remaining. • d. The historical data available. • e. Regulatory requirements. Key phrase “frequency and time”.
7.2
Inspection While Equipment Is Operating Many other conditions in piping systems should be determined while the equipment is operating. On-stream inspection can reduce downtime by the following means: a. Extending process runs and preventing some unscheduled shutdowns. b. Permitting fabrication of replacement piping before a shutdown. c. Eliminating unnecessary work and reducing personnel requirements. d. Aiding maintenance planning to reduce surges in work load. Key phrase “On-stream inspection”.
7.3
Inspection While Equipment Is Shut Down Piping can often be inspected internally during outages. Key phrase “equipment shut down”.
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8
SAFETY PRECAUTIONS AND PREPARATORY WORK
8.1
Safety Precautions This section outlines some generic, extremely basic safety precautions which are probably inferior to your own safety department requirements. Key phrase “safety”.
8.2
Preparatory Work This section should be titled: “The Common Sense Guide to Advance Shut Down Work”. It contains no new or extremely useful information. Key phrase “preparatory work”.
9
INSPECTION TOOLS See Table 2, page 30 of API 570.
10
INSPECTION PROCEDURES
10.1
Inspection While Equipment Is Operating 10.1.1 Visual Inspection 10.1.1.1 Leaks Leaks can be safety or fire hazards, and always result in economic loss. Temporary or permanent repairs can often be made while the lines are in service. Key phrase “leaks”. 10.1.1.2 Misalignment Piping should be inspected for misalignment. Pipe dislodged from supports, vessel wall deformation, pipe supports out of plumb, excessive replacement of bearings, etc., shifting of baseplates, foundation damage, cracks in connecting flanges, expansion joints not performing properly, are all indications of misalignment. Key phrase “misalignment”. 10.1.1.3 Supports Supports are shoes, hangers, and braces, and should be visually inspected for problems. Key phrase “supports”.
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10.1.1.4 Vibration Vibrating or swaying piping should be inspected for cracks, at points of restraint, usually in the areas of anchors, or where small bore pipe is attached to the main line. Key phrase “vibration”. 10.1.1.5 External Corrosion Defects in the protective coatings and insulation will permit moisture to contact the piping. This can result in corrosion and metal loss. Key phrase “external corrosion”. 10.1.1.6 Accumulations of Corrosive Liquids Some liquids are corrosive to steel piping, spills should be cleaned up or neutralized. Key phrase “accumulations of corrosive liquids”. 10.1.1.7 Hot Spots Operating piping at higher than design limits may cause bulging, even to the point of failure. Investigation of these areas is essential. Key phrase “hot spot”. 10.1.2 Thickness Measurements 10.1.2.1 Ultrasonic Inspection UT digital thickness gauges are mentioned with emphasis on high temperature readings. Key phrase “UT thickness”. 10.1.2.2 Radiographic Inspection Wall shot or radiographic profile radiography is discussed in this section, as to the use of the technique, no information about how the technique is performed. Key phrase “radiography”. 10.1.3 Other On-stream Inspections This section mentions “new” methods of inspection; halogen leak detectors, magnetic induction, real-time radiography, neutron radiography, thermography, etc. Key phrase “methods”. 10.2
Inspection While Equipment Is Shut Down 10.2.1 Visual Inspection 10.2.1.1
Corrosion, Erosion, and Fouling
Borescopes are used to inspect piping internally. Key phrase “internal inspection”.
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10.2.1.2 Cracks Inspect the susceptible locations, construction tack welds at other than pressure welds, heat affected areas joining welds, and points of restraint or excessive strain. Include locations that are subject to stress-corrosion cracking, hydrogen cracking, and caustic or amine embrittlement, as well as exposed threads. Key phrase “cracks”. 10.2.1.3 Gasket Faces of Flanges General inspection. Key phrase “flanges”. 10.2.1.4 Valves Inspection techniques for gate valves including the valves being dismantled at specified intervals. Key phrase “valves”. 10.2.1.5 Joints, 10.2.1.5.1 Flanged Joints, 10.2.1.5.2 Welded Joints, 10.2.1.5.3 Threaded Joints, 10.2.1.5.4 Clamped Joints All the listed joints should be inspected, the basic technique is visual examination. Key phrase “joints”. 10.2.1.6 Misalignment Misalignment is caused by: a. Inadequate provision for expansion. b. Broken or defective anchors or guides. c. Excessive friction on sliding saddles, indicating a lack of lubrication or a need for rollers. d. Broken rollers or rollers that cannot turn because of corrosion or lack of lubrication. e. Broken or improperly adjusted hangers. f. Hangers that are too short and thus limit movement or cause lifting of the pipe. g. Excessive operating temperature. Key phrase “misalignment”. 10.2.1.7 Vibration Vibrating or swaying piping should be inspected for cracks, at points of restraint, usually in the areas of anchors, or where small bore pipe is attached to the main line. Key phrase “vibration”. 10.2.1.8 Hot Spots A short discussion of areas over heated on piping is discussed. No mention of thermal photography. Key phrase “hot spots”.
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10.2.2 Thickness Measurements UT digital thickness gauges are mentioned with emphasis on high temperature readings and the use of radiography on nipple thickness. Key phrase “thickness measurement”. 10.2.3 Pressure Tests Pressure tests are leak tests and may be used on the following: a. Underground lines and other inaccessible piping. b. Water and other non-hazardous utility lines. c. Long oil transfer lines in areas where a leak or spill would not be hazardous to personnel or harmful to the environment. d. Complicated manifold systems. e. Small piping and tubing systems. f. All systems, after a chemical cleaning operation. Do not over pressure the system! Various fluids may be used for pressure testing: a. Water with or without an inhibitor, freezing-point depressant, or wetting agent. b. Liquid products normally carried in the system, if non-toxic or flammable. c. Steam d. Air, carbon dioxide, nitrogen, helium, or another inert gas. Salt water can create problems like pitting and corrosion. Pneumatic tests should be conducted strictly in accordance with ASME B 31.3. Key phrase “pressure test”. 10.2.4 Hammer Testing Hammer testing is an old method of testing piping systems, do not use the hammer on cast iron and stress-relieved lines in caustic and corrosive service. Key phrase “hammer test”. 10.2.5 Inspection of Piping Welds Refer to API 570, Section 3.10 which will reference ASME B 31.3 for weld quality. Key phrase “weld quality”. 10.3
Inspection Of Underground Piping Basic information about buried piping, referencing several NACE documents. 10.3.1 Types and Methods of Inspection and Testing 10.3.1.1 Above-Grade Visual Surveillance Extremely basic information about leaking underground piping. Key phrase “leaks”.
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10.3.1.2 Close-Interval Potential Survey This type of survey is used to locate corrosion cells, galvanic anodes, stray currents, coating problems, underground contacts, areas of low pipe-to-soil potentials and other cathodic protection problems. Key phrase “Close-interval potential survey”. 10.3.1.3 Holiday Pipe Coating Survey Basically, a measurement is taken and compared to other areas of the system, coated as opposed to noncoated piping will give different corrosion rates and readings. Key phrase “holiday pipe coating survey”. 10.3.1.4 Soil Resistivity Testing The Wenner method, the soil bar and soil box methods are discussed. Basically, each method measures a voltage drop, caused by a known current flow, across a measured volume of soil. The resistance factor is used in a formula to determine the resistivity of the soil. Key phrase “soil resistivity testing”. 10.3.1.5 Cathodic Protection Monitoring Refer to NACE RP0169 and Section 11 of API Recommended Practice 651. Key phrase “CP monitoring”. Sections 10.3.2 Inspection Methods, 10.3.21. Intelligent Pigging, 10.3.2.2 Video Cameras, 10.3.2.3 Excavation are all basic with little or no useful information. 10.3.3 Leak Testing The basic methods of leak testing underground piping are briefly described in this section. The methods are: a. Pressure decay method. b. Volume in/volume out method. c. Single-point volumetric methods. d. A marker chemical (tracer) method. e. Acoustic emission method. 10.4
Inspection Of New Construction 10.4.1 General Must meet the requirements of ASME B 31.3. Key phrase “ASME B 31.3”.
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10.4.2 Inspection of Materials Materials should be checked for conformance with the codes and specifications that are appropriate for the plant. Checks should be made using material test kits or a nuclear alloy analyzer, (PMI)). Key phrase “ASME B 31.3”. 10.4.3 Deviations No comment. 11
DETERMINATION OF RETIREMENT THICKNESS
11.1
Piping All formulas and data for determining the required wall thickness for piping are found in ASME B 31.3. ASME B 31.3 also takes into consideration the following: a. Corrosion. b. Threads. c. Stresses caused by mechanical loading, hydraulic surge pressure, thermal expansion, and other conditions. The Barlow formula: The Barlow formula can be used provided that the value is less than D/6, or P/SE is not greater than 0.385”. The Barlow formula is as follows: t = PD/2SE Where: t = pressure design thickness for internal pressure, in inches P = Internal design gauge pressure of the pipe, in pounds per square inch D = outside diameter of the pipe, in inches S = allowable unit stress at the design temperature, in pounds per square inch E = longitudinal joint efficiency. Metallic pipe for which t > D/6 or P/SE > 0.385 requires special consideration. Key phrase “Barlow formula”.
NOTE: The Barlow formula has been omitted from B31.3, 2000 addenda. The remaining formulas give practically the same answer. 11.2
Valves And Flanged Fittings Refer to ASME B16.34 for minimum valve wall thickness. Key phrase “ASME B 31.3”.
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12
RECORDS
12.1
General Records should be kept in a detailed and orderly manner. These records will help in evaluating replacement or repair intervals. Key phrase “records”.
12.2
Sketches Sketches have important functions: a. They identify particular piping systems in terms of location, size, material specification, general process flow, and service conditions. b. They inform the mechanical department of points to be opened for visual inspection and parts that require replacement or repair. c. They serve as field data sheets on which can be recorded the locations of thickness measurements, serious corrosion, and sections requiring immediate replacement. These data can be transferred to continuous records at a later date. d. They assist at future inspections in determining locations that urgently require examination. Key phrase “sketches”.
12.3
Numbering Systems Use any convenient means. Key phrase “numbering systems”.
12.4
Thickness Data A record of thickness data may provide a means of corrosion or erosion rates for the piping system. See Figure 25 for an example of sketches and thickness data. Key phrase “thickness data”.
12.5
Review Of Records General information about when to review records. Key phrase “records”.
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API 574 Quiz 1. API 574 covers inspection of: A. B. C. D.
new construction new tank construction piping vessels
2. Cast iron pipe can be joined by: A. B. C. D.
welding compression epoxy resin bell and spigot
3. The primary purpose of inspection is to achieve the desired quality assurance and: A. B. C. D.
ensure plant safety supply the necessary paperwork for outside audits complicate maintenance activities create an avenue for dismissing craftsmen
4. Ultrasonic thickness readings at areas with surface temperatures above ______ are normally higher than actual thickness. A. B. C. D.
1000 F 2000 F 3000 F 2120 C
5. Flame detectors used to indicate a furnace or boiler fire may give erroneous indications on control panels during: A. B. C. D.
Welding or related repairs on piping. Piping alterations in the shop. Ultrasonic inspection. Radiographic inspection.
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6. Leaks in a threaded joint may be caused by: A. B. C. D.
Back-welding the fitting. Lack of thread lubricant. Under-pressuring the part. Changing the direction of flow in the piping system.
7. A leaking threaded joint should not be tightened while the system is in service under pressure because: A. B. C. D.
The craftsman should not be near the threaded connection. Rust or corrosion might be holding the pressure. The joint might be unscrewed. A crack in a thread root might fail.
8. During a pressure test, care should be taken not to: A. B. C. D.
Allow any inert gas into the system. Use water in the system. Overpressure the system. Underpressure the system.
9. Which of the following tests should not be used on cast iron piping: A. B. C. D.
Radiographic test Leak test Ultrasonic test Hammer test
10. The details of inspection of in-service piping are provided in: A. ASME IX B. ASME B31.3 C. API 570 D. ASME B 16.5a 11. t = PD/2SE is the formula for: A. Required Piping Thickness B. Maximum Piping Thickness C. Arbitrary Renewal Piping Thickness D. Average Piping Thickness 12. API RP 574 is a: A. B. C. D.
Code Standard Specification Recommended Practice
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13. During the manufacturing of tubing, the tubing may be welded, but is generally: A. B. C. D.
Riveted. Seamlessly drawn. Wire drawn. Forged.
14. A globe valve is commonly used to: A. Prevent back flow. B. Allow full flow. C. Stop all flow. D. Regulate fluid flow. 15. A check valve is commonly used to: A. Prevent back flow. B. Allow full flow. C. Stop all flow. D. Regulate fluid flow.
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API 574 Quiz Answer Key 1. C 2. D 3. A 4. B 5. D 6. B 7. D 8. C 9. D 10. C 11. A 12. D 13. B 14. D 15. A
Paragraph 1.1 Paragraph 4.5.5 Paragraph 5.1 Paragraph 10.1.2.1 Paragraph 10.1.2.2 Paragraph 10.2.1.5.3 Paragraph 10.2.1.5.3 Paragraph 10.2.3 Paragraph 10.2.4 Paragraph 10.2.5 Paragraph 11.1 Foreword Paragraph 4.2 Paragraph 4.3.3 Paragraph 4.3.8
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ASME B16.5
AN AMERICAN NATIONAL STANDARD
A AS SM ME E//A AN NS SII B B 1166..55aa--11999988 A AD DD DEN ND DA A ttoo A AS SM ME E//A AN NS SII B B1166..55--11999966
Pipe Flanges and Flanged Fittings NPS 1/2 Through NPS 24
Summary and Notes The notes and summary information supplied is the thoughts and opinions of ITAC and does not represent API Committee interpretations. The use of “Key Phrases” is intended as a study guide only.
Page P age 3 - 1
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ASME/ANSI B 16.5a-1998 Addenda to ASME/ANSI B 16.5-1996
Pipe Flanges and Flanged Fittings SECTION 1 - SCOPE 1.1. General ASME/ANSI B 16.5 covers pressure-temperature ratings, materials, dimensions, tolerances, marking, testing, and methods of designating openings for pipe flanges and flanged fitting NPS 1/2 through NPS 24. Key phrase "pipe flanges and fittings". SECTION - 2 PRESSURE-TEMPERATURE RATINGS This section is general information on flange temperature and pressure ratings based on the type of flange, bolting and gasketing. SECTION - 3 SIZE 3.1 Nominal Size The size of flanges are covered by the nominal pipe size, NPS. Key phrase "NPS". Note: The new form for this designation is NPS 6, which was commonly 6” pipe.
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SECTION 4 - MARKING 4.1 General Flanges shall be marked as required in MSS SP-25. Key phrase “marked”. The following shall be marked on the flange: Manufacturer’s name or trademark Material cast - ASTM specification plate - ASTM specification Rating Class Designation (B16 if conforms to this standard) Temperature (none required) Size The letter R if Ring Joint Flange Key phrase “marking”. SECTION 5 - MATERIALS 5.1 General The materials for flanges and flanged fittings have been grouped, see Tables 1 and 2. NOTE the groups are not numbered consecutively. Key phrase “materials”. 5.3 Bolting This section covers general bolting, (Table 1B) high strength bolting, intermediate strength bolting, low strength bolting, bolting to gray cast iron flanges and gaskets, Table 1B. Key phrase “bolting”. SECTION 6 - DIMENSIONS Dimensions for wall thickness, local areas, center-to-center and center-to-end flanges and fittings. Faces and types, lapped joints, raised face, tongue and groove, ring joint, blind flanges and flange facing finishes are generally discussed in this section. Bolt holes, spot facing, welding end preparation reducing flanges, threads and gaskets are also highlighted. Key phrase “dimensions”.
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SECTION 7 - TOLERANCES Tolerances for center-to-center and center-to-end flanges and fittings. Faces and types, lapped joints, raised face, tongue and groove, ring joint, hub dimensions and bore of flanges are generally discussed in this section. Key phrase “tolerances”. SECTION 8 - TEST General test information about testing flanged fittings. Flanges are not required to be hydrostatically tested. Key phrase “tests”.
The rest of this document is tables and diagrams used for reference and dimensions of flanges and flanged fittings.
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ASME B31.3
Process Piping ASME Code For Pressure Piping ASME B31.3 - 2002 Edition
Summary and Notes The notes and summary information supplied is the thoughts and opinions of ITAC and does not represent interpretations. The use of “Key Phrases” is intended as a study guide only.
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Process Piping ASME Code For Pressure Piping ASME B31.3 - 2002 Edition CHAPTER I 300 General Statements This section covers general information about the B31.3 document, if this is the first time the user has seen this document it is of general interest. Key phrase “General information”. 300.1 Scope and Definitions Rules for the Process Piping Code Section B31.3 have been developed considering piping typically found in petroleum refineries; chemical, pharmaceutical, textile, paper, semiconductor, and cryogenic plants; and related processing plants and terminals. Key phrase “Scope”. 300.1.1 Content and Coverage Requirements for materials and components, design, fabrication, assembly, erection, examination, inspection, and testing of pipe. This code applies to piping for all fluids, including: 1. raw, intermediate, and finished chemicals; 2. petroleum products; 3. gas, steam, air, and water; 4. fluidized solids; 5. refrigerants; and 6. cryogenic fluids. Key phrase “Code applications”. 300.2 Definitions The student should read this section in great detail and become familiar with the terms and definitions listed. For welding terms not shown in this section, definitions in accordance with ANSI/AWS Standard A3.0 apply. Key phrase “Definitions”.
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CHAPTER II Design (Included sections and excluded sections, see the API 570 Body of Knowledge.) 301.1 Qualifications of the Designer The qualifications for the designer have now been added. 301.2 Design Pressure The design pressure of each component in a piping system shall be not less that the pressure at the most severe condition of coincident internal or external pressure and temperature (minimum or maximum) expected during service. Consideration must be given to pressure containment or relief in the piping system. Key phrase “Design pressure”. 301.3 Design Temperature The design temperature of each component in a piping system is the temperature at which, under coincident pressure, the greatest thickness or highest component rating is required. Fluid temperatures, ambient temperatures, solar radiation, heating or cooling medium temperatures must be considered. Key phrase “Design temperature”. 301.4 Ambient Effects Ambient effects are in the form of cooling, fluid expansion atmospheric icing all from atmospheric conditions. Key phrase “Ambient”. 301.5 Dynamic Effects Impact, wind, earthquake, vibration and discharge reactions. Key phrase “Dynamic”. 301.6 Weight Effects Live loads and dead loads. Key phrase “Loads”. 301.7 Thermal Expansion and Contraction Effects Loads due to restraints, temperature gradients, expansion characteristics, movements of supports, and anchors, reduced ductility, cyclic, and air condensation. Key phrase “Loads”. 302
Design Criteria (This section has been excluded from the API 570 exam, except for Paragraph 302.3.4 and Table 302.3.4.) 302.3.4 Weld Joint Quality Factor, Ej. This paragraph applies only to the longitudinal weld joint of piping. Girth welds are not addressed in this section. Key phrase “Weld Quality Joint Factor”. Page 4 - 4
Part 2 - Pressure Design of Piping Components See table 326.1. 304.1 Straight Pipe Required Thickness Eq. (2) : tm = t + c tm = minimum required thickness, including mechanical, corrosion, and erosion allowances t = pressure design thickness, as calculated in accordance with para. 304.1.2 for internal pressure or as determined in accordance with para 304.1.3 for external pressure c = the sum of the mechanical allowances (thread or groove depth) plus corrosion and erosion allowances. For machined surfaces or grooves where the tolerance is not specified, tolerance shall be assumed to be 0.5 mm (0.02 in.) in addition to the specified depth of the cut. Key phrase “Required Thickness”. NOTE: The Barlow formula: T = PD 2SE has been removed from the 2000 addenda of B31.3, but is still listed in API 574. 304.1.3
Straight Pipe Under External Pressure (This section has been excluded from the API 570 exam.)
Part 3 - Fluid Service Requirements For Piping Components Material specifications for pipe and tube, API and ASTM. Key phrase “Material specifications”.
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Part 4 - Fluid Service Requirements For Piping Joints 311
Welded Joints Welded joints are allowed for any material which it is possible to qualify welding procedures, welders, and welding operators, see Chapter V, B31.3. Specific requirements for welds for Category D Fluid Service, Severe Cyclic Conditions are mentioned in this section, refer to Table 341.4.2 and Table 341.4.3. Buttwelds with backing rings, socket welds, fillet welds and seal welds may be used, as well as open root welds. Key phrase “Welded joints”.
312
Flanged Joints Note flange ratings and bolting torque. Key phrase “Flanged joints”.
313
Expanded Joints Expanded joints may be used only under specific conditions. Key phrase “Expansion joints”.
314
Threaded Joints The rules for threaded joints are listed. Avoid crevice corrosion, severe erosion, or cyclic loading conditions. Do not use thread sealing compounds when threaded joints are to be seal welded. Give special consideration to vibration and temperature cycling. Key phrase “Threaded joints”.
315
Tubing Joints (This section has been excluded from the API 570 exam.)
Part 5 - Flexibility and Support 319
Piping Flexibility Piping systems shall have sufficient flexibility to prevent thermal expansion or contraction or movements of piping supports and terminals from causing failure, leakage, and excessive thrusts or movements. Displacement strains such as thermal displacement, restraint flexibility, externally imposed displacements are defined in this section. Displacement stresses such as elastic behavior, overstrained behavior must also be considered. Key phrase “Flexibility”. 319.4 Flexibility Analysis (This section has been excluded from the API 570 exam.)
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321
Piping Support The design of support structures are based on acting loads, transmitted into such supports and include weight effects, loads induced by service pressures and temperatures, vibration, wind, earthquake, shock, and displacement strain. Key phrase “Support”. 321.1.1 Objectives The layout and design of piping and its supporting elements shall be directed toward preventing the following: 1. 2. 3. 4. 5. 6. 7. 8. 9.
piping stresses; leakage at joints; excessive thrusts and moments on equipment; excessive stresses in the supporting elements; resonance with imposed or fluid-induced vibrations; excessive interference with thermal expansion and contraction; unintentional disengagement of piping from its supports; excessive piping sag in piping requiring drainage slope; excessive distortion or sag of piping subject to creep under conditions of thermal cycling; 10. excessive heat flow, exposing supporting elements to temperature extremes. Support design is based on location, calculations and engineering judgment. The details of pipe supports are outlined in the rest of this section. Key phrase “Pipe supports”.
Part 6 – Systems (This section has been excluded from the API 570 exam.)
Chapter III Materials 323
General requirements Chapter III states limitations and required qualifications for materials based on their inherent properties. Key phrase “Materials”.
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323.1 Materials and Specifications Materials must conform to listed specifications. Unlisted materials may be used provided they conform to a published specification and meet the requirements of this code. Note materials of unknown specification shall not be used for pressure containing piping components. Reclaimed materials may be used, providing they are properly identified. Most materials have upper and lower temperature limits, see Table 323.2.2. Key phrase “Material specifications”. 323.3 Impact Test Methods and Acceptance Criteria Of special interest is the impact testing methods and acceptance criteria. The procedure and test specimen requirements are listed, see Figure 323.2.2A Minimum Temperatures Without Impact Testing for Carbon Steel Materials and Table 323.3.1 Impact Testing Requirements for Metals. Test temperatures for all Charpy impact tests shall be observed, see paragraph. 323.4 a or b. Acceptance criteria is shown in Table 323.5 The requirements for lateral expansion, weld impact test and other related tests are listed in this section. Key phrase “Impact test”. Chapter IV Standards for Piping Components This section gives the dimensions and ratings of piping components. Key phrase “Dimensions and ratings”.
Chapter V Fabrication, Assembly, And Erection 328.1 Welding Responsibility Each employer is responsible for the welding done by the personnel of his organization and shall conduct the tests required to qualify welding procedures, and to qualify and as necessary requalify welders and welding operators. Key phrase “Responsibility”. 328.2 Welding Qualifications Welders and welding operators must be qualified to ASME Section IX, except as modified by B31.3. The general details are listed in this section. Special attention should be given to sub-paragraph f, this paragraph allows Table A - 1 when matching P-Numbers and SNumbers. Key phrase “Welding qualifications”.
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328.2.2 Procedure Qualification by Others Each employer is responsible for qualifying any welding procedure that personnel of the organization will use. Subject to the specific approval of the Inspector. The Inspector shall be satisfied that: 1. the proposed WPS has been prepared, qualified, and executed by a responsible, organization with expertise in the field of welding; and 2. the employer has not made any change in the welding procedure. Key phrase “Procedure qualification by others”. 328.2.3 Performance Qualification by Others To avoid duplication of effort, an employer may accept a performance qualification made for another employer, provided the Inspector specifically approves. Acceptance is limited to qualification on piping using the same procedure wherein the essential variables are within the limits in Section IX. Key phrase “Performance qualification by others”. 328.2.4 Qualification Records The employer shall maintain a self-certified record, available to the Inspector of procedures and welders employed. Key phrase “Qualification records”. 328.3.1 Welding Materials Filler metal shall conform to Section IX. Others may be used with the owner’s approval if a procedure qualification test is first successfully made. Key phrase “Filler metals”. 328.4 Preparation for Welding Internal and external surfaces to be cut or welded shall be clean and free from paint, oil, rust, scale and other material that can be detrimental to the weld. End preparation is acceptable only if the surface is reasonably smooth and true, and slag is removed. Groove weld details are found in 328.4.2. Alignment shall be aligned within the dimensional limits in the WPS and the engineering design. Key phrase “Weld prep.”.
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328.5 Welding Requirements • • •
• •
Welds shall be made in accordance with a qualified procedure and by qualified welders or welding operators. Each welder shall be assigned an identification symbol. The welds shall be marked or appropriate records shall be filed. Tack welds shall be made with filler metal equivalent to that used in the root pass. Tack welds shall be made by a qualified welder. Tack welds shall be fused with the root pass, cracked tacks shall be removed, bridge tacks shall be removed. Peening is prohibited on the root pass and final pass of a weld. No welding shall be done if there is impingement on the weld area of rain, snow, sleet, or excessive wind, or if the weld area is frosted or wet.
Details of fillet and socket welds, seal welds, welded branch connection welds are given in this section. Key phrase “Weld requirements”. 328.6 Weld Repair A weld defect to be repaired shall be removed to sound metal. Repair welds shall be made using a qualified welding procedure. Key phrase “Weld repair”. 330
Preheating Preheating is used to minimize the detrimental effects of high temperature and severe thermal gradients inherent in welding. Minimum recommended preheat temperatures are given in Table 330.1.1. If the ambient temperature is below freezing, the recommendations in Table 330.1.1 become requirements. The preheat zone shall extend at least 1 inch beyond each edge of the weld. Key phrase “Preheating”.
331
Heat Treatment Heat treatment is used to avert or relieve the detrimental effects of high temperature and severe temperature gradients inherent in welding, and to relieve residual stresses created by bending and forming. General heat treatment requirements include Table 331.1.1 (thickness and material grouping ranges) and must be specified in the WPS. The rest of this section deals with the specific requirements for heat treatment. Key phrase “Heat treatment”.
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Chapter VI Inspection, Examination, and Testing 340
Inspection - General The term “Inspector” refers to the owner’s Inspector or the Inspector’s delegates. It is the owner’s responsibility, through the owner’s Inspector, to verify that all required examinations and testing have been completed and to inspect the piping to the extent necessary to be satisfied that it conforms to all applicable examination requirements of the Code and the engineering design. The Inspector shall have access to any place where work concerned with the piping installation is being performed. The Inspector shall be designated by the owner and shall be the owner, an employee of the owner, an employee of an engineering or scientific organization, or of a recognized insurance or inspection company acting as the owner’s agent. The Inspector shall have not less than 10 years experience in the design, fabrication, or inspection of industrial pressure piping. Key phrase “Inspector”.
341
Examination Examination applies to quality control functions performed by the manufacturer. Inspection does not relieve the manufacturer of the responsibility for: • providing materials, components, and workmanship • performing all required examinations; and • preparing suitable records of examinations and tests for the Inspector’s use. The examiner shall be assured, by examination of certifications, records, and other evidence, that the materials and components are of the specified grades and that they have received required heat treatment, examination, and testing. The examiner shall provide the Inspector with a certification that all the quality control requirements of the code and the engineering design have been carried out. Key phrase “Examination”.
342
Examination Personnel Examiners shall have training and experience commensurate with the needs of the specified examinations (ASNT SNT-TC-1A). Certifications by employers are recognized. Note, for in-process examination, the examinations shall be performed by personnel other than those performing the production work. Key phrase “Examiners”.
343
Examination Procedures Any examination shall be performed in accordance with a written procedure that conforms to ASME Section V. Key phrase “Examination procedures”.
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344
Types of Examination • 100% - complete examination • random - complete examination of a percentage • spot - partial examination • random spot - a specified partial examination of a percentage Key phrase “Examination”. 344.2 Visual Examination Visual examination (VT) is observation of the portion of components, joints, and other piping elements that are or can be exposed to view before, during, or after manufacture, fabrication, assembly, erection, examination, or testing. Visual examination shall be performed in accordance with ASME Section V, Article 9. Key phrase “VT”. 344.3 Magnetic Particle Examination Magnetic Particle (MT) examination shall be performed in accordance with Section V, Article 7. Key phrase “MT”. 344.4 Liquid Penetrant Examination Liquid Penetrant (PT) examination shall be performed in accordance with Section V, Article 6. Key phrase “PT”. 344.5 Radiographic Examination Radiographic (RT) examination shall be performed in accordance with Section V, Article 2. • 100% - applies only to girth and miter groove welds and to fabricated branch connection welds. • Random Radiography - Applies only to girth and miter groove welds. • Spot Radiography - A single exposure radiograph. Key phrase “RT”. 344.6 Ultrasonic Examination Ultrasonic (UT) examination shall be performed in accordance with Section V, Article 5. Note: acceptance criteria is listed in paragraph 344.6.2. Key phrase “UT”. 344.7 In-Process Examination In-process examination includes joint preparation and cleanliness; preheating; preheating; fit-up, joint clearance, and internal alignment; variables specified by the procedure, including filler metal and position; condition of the root pass, slag removal and weld condition between passes; and appearance of the finished joint. The examination is visual. Key phrase “In-process examination”.
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345
Testing Leak test, including hydrostatic, pneumatic or a combined hydrostaticpneumatic test. Details of testing are listed in this section. Key phrase “Leak testing”.
346
Records It is the responsibility of the piping designer, the manufacturer, the fabricator, and the erector, as applicable, to prepare the records required by B 31.3. Examination procedures and examination personnel qualifications records shall be retained for at least 5 years after the record is generated. Key phrase “Records”.
Chapter VII Nonmetallic Piping and Piping Lined With Nonmetals (This section has been excluded from the API 570 exam.)
Chapter VIII Piping for Category M Fluid Service (This section has been excluded from the API 570 exam.)
Chapter IX High Pressure Piping (This section has been excluded from the API 570 exam.)
Appendix A Allowable Stresses And Quality Factors For Metallic Piping And Bolting Materials Table A1 - Table A2 (Note with the introduction of Addenda 96 and 97, many of the stress values have changed.)
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Appendix B Stress Tables and Allowable Pressure Tables for Nonmetals (This section has been excluded from the API 570 exam.)
Appendix C Physical Properties of Piping Materials Table C1 - C8
Appendix D Flexibility and Stress Intensification Factors (This section has been excluded from the API 570 exam.)
Appendix E Reference Standards (This section has been excluded from the API 570 exam.)
Appendix F Precautionary Considerations
Appendix G Safeguarding (This section has been excluded from the API 570 exam.)
Appendix H Sample Calculations for Branch Reinforcement (This section has been excluded from the API 570 exam.)
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Appendix J Nomenclature (This section has been excluded from the API 570 exam.) Appendix K Allowable stresses for High Pressure Piping (This section has been excluded from the API 570 exam.) Appendix L Aluminum Alloy Pipe Flanges Appendix M Guide To Classifying Fluid Services Appendix Q Quality System Program Appendix V Allowable Variations In Elevated Temperature Service
Appendix X Metallic Bellows Expansion Joints (This section has been excluded from the API 570 exam.) Appendix Z Preparation of Technical Inquiries (This section has been excluded from the API 570 exam.) Index This can be an extremely useful tool in looking for items in B 31.3. General notes follow the index.
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ASME B31.3 Quiz 1.
All welding terms found in ASME B31.3 are found in the Code and: A. B. C. D.
2.
A fluid service in which the potential for personnel exposure is judged to be significant: A. B. C. D.
3.
Category M Fluid Service High Pressure Fluid Service Normal Fluid Service Category B Fluid Service
Snow and ice loads due to both environmental and operating conditions are considered: A. B. C. D.
4.
ASME Section IX ASME Section V AWS A2.4 AWS A3.0
Dead Loads Live Loads Environmental Loads Structural Loads
The required thickness of straight sections shall be determined in accordance with Eq. 2, A. B. C. D.
tm = t + d tm = d - t tm = t + c tm = c - t
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5.
Socket welds should: A. be avoided in the piping system B. be used in all welded piping C. be welded using SAW only D. be avoided where crevice corrosion may occur.
6. A Charpy V-notch specimen for impact testing shall be made using a A. B. C. D. 7.
E7018 E7016 E6024 E6010
A welder may pass a performance qualification test for Company A, quit the job, then be hired by Company B, to perform similar work, and not have to retest. A. B. C. D.
11.
by others may be used by the employer only may be used by the use of AWS prequalified, D1.1 type procedures, may be used by the use of API 1104 qualified procedures may be used
A cellulose DCEP Electrode in the AWS A5.1 is: A. B. C. D.
10.
ASME B 31.3 BPV Code, Section IX API 570 Both A and B
Subject to the specific approval of the Inspector, welding procedures qualified: A. B. C. D.
9.
1/2” square cross section 10 M square cross section 10 mm square cross section .505 “ square cross section
Qualification of welding procedures to be used in compliance with ASME B 31.3 shall conform to the requirements of: A. B. C. D.
8.
standard:
True False True only in certain states False, in compliance with ASME B 31.3
Filler metal shall conform to the requirements of: A. B. C. D.
AWS A5.1 Section IX Section V API 570
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12.
Circumferencial welds inside surfaces of groove welds shall be aligned: A. B. C. D.
13.
The root pass and final pass of a weld may not be: A. B. C. D.
14.
peened cleaned stress relieved painted
A threaded joint may be seal welded by a qualified welder if: A. B. C. D.
15.
+ or - 1/16” + or - 1/32” within the dimensional limits in the WPS the fabricator’s discretion
the joint is leaking the joint has straight threads only the joint has tapered threads only all exposed threads are covered
The preheat zone shall extend at least ____ beyond the edge of the weld. A. 10 mm B. 1 inch C. 50 mm D. 3 inches
16.
The owner’s Inspector shall have: A. B. C. D.
17.
an API 570 Certification an AWS CWI Certification an API 510 Certification not less than 10 years experience dealing with piping
In reviewing radiography of a Normal Fluid Service piping weld a crack was noticed. If the pipe wall was .375, what length crack is acceptable? A. none B. T/3 C. 3/16” D. cracks will not show on radiographs
18.
An examiner performing a PT test of a completed weld on the outside of a Category D Fluid Service piping system noted a transverse crack in the root pass: A. B. C. D.
The weld is acceptable The PT test should be repeated The welder should be requalified The PT test will not show this type of discontinuity from the outside.
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19.
Individual slag trapped in a weld in Severe Cyclic Conditions piping system, maximum length may be: A. >TwX3 B. Tw/3 C. 12 T D. 3/23 “
20.
Examiners may be qualified in compliance with: A. B. C. D.
ASME Section IX ASME Section V ASNT SNT-TC-1A API 570
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API ASME B31.3 Quiz Answer Key 1. D 2. A 3. B 4. C 5. D 6. C 7. D 8. A 9. D 10. A 11. B 12. C 13. A 14. D 15. B 16. D 17. A 18. D 19. B 20. C
(Paragraph 300.2 Page 2) (Para. 300.2 b page 5) (Para. 301.6.1 page 13) (Para. 304.1.1 a Page 19) (Para. 311.2.4 Page 35) (Para. 323.3.3 Page 53) (Para. 328.2.1a Page 60) (Para. 328.2.2 Page 60) (Para. 328.2.2g Page 61) (Para. 328.2.3 Page 61) (Para. 328.3 Page 61) (Para. 328.4.3 Page 62) (Para. 328.5.1d Page 63) (Para. 328.5.3 Page 65) (Para. 330.1.4 Page 67) (Para. 340.4 Page 75) (Table 341.3.2 Page 77) (Table 341.3.2 Page 77) (Table 341.3.2 Page 77) (Para. 342.1 Page 82)
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ASME Section V
Nondestructive Examination API 570 - 1998 Edition, including 2000 and 2001 Addenda ASME B31.3 - 2002 Edition
Summary and Notes The notes and summary information supplied is the thoughts and opinions of ITAC and does not represent interpretations
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API 570 Nondestructive Examination API 570 Paragraph 8.2.5 Acceptance of a welded repair or alteration shall include NDE in accordance with the applicable code and the owner-user’s specification, unless otherwise specified in API 570. Note, the applicable code is usually ASME B31.3. ASME B 31.3, Paragraph 342 Examination Personnel Examiners shall have training and experience commensurate with the needs of the specified examinations. (Footnote 1, For this purpose, SNT-TC-1A, Recommended Practice for Nondestructive Testing Personnel Qualification and Certification, may be used as a guide.) The employer shall certify records of the examiners employed, showing dates and results of personnel qualifications, and shall maintain them and make them available to the Inspector. ASME B 31.3 Requirements for Nondestructive Testing Procedures and Personnel Certification. The American Society for Nondestructive Testing, Inc. Recommended Practice SNTTC-1A is recognized for technician qualifications (Examiners) in some NDE techniques. SNT-TC-1A is a document that outlines requirements for Personnel Qualification and Certification in Nondestructive Testing, the main items listed are: Work Experience Training Education Testing In order to qualify as an ASNT Level II, Radiographers must have: 12 Months Job Experience 79 Hours Formal Training High School Graduation Level II Exam, General, Specific and Practical In order to qualify as an ASNT Level II, Ultrasonic Technicians must have: 12 Months Job Experience 80 Hours Formal Training High School Graduation Level II Exam, General, Specific and Practical
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ASME B31.3, Paragraph 343 Examination Procedures Any examination shall be performed in accordance with a written procedure that conforms to one of the methods specified in paragraph 344, including special methods. Procedures shall be written as required in ASME Section V, Article 1, paragraph T-150. ASME B31.3, Paragraph 344 Types of Examination ASME B 31.3, Paragraph 344.1.3 Definitions • • • •
100% - complete examination random - complete examination of a percentage spot - partial examination random spot - a specified partial examination of a percentage
ASME B 31.3, Paragraph 344.2 Visual Examination Visual examination (VT) is observation of the portion of components, joints, and other piping elements that are or can be exposed to view before, during, or after manufacture, fabrication, assembly, erection, examination, or testing. Visual examination shall be performed in accordance with ASME Section V, Article 9. ASME B 31.3, Paragraph 344.3 Magnetic Particle Examination Magnetic Particle (MT) examination shall be performed in accordance with Section V, Article 7.
ASME B 31.3 Magnetic Particle Method
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MT Principles of Operation Basically, an object or localized area is magnetized through the use of AC or DC current. Once the area is magnetized lines of flux are formed. See previous page. Dry iron powder, or iron powder held in suspension is added to the surface of the test piece. Any interruption in the lines of flux will create an indication which can be evaluated. The process may be used on any material that is ferromagnetic. This method of NDE can be used in visible light or with special powders, under black light. Surface discontinues are the most commonly detected indications using this process. This process will detect:
Surface and slightly subsurface defects only! Magnetic Particle Method Study Notes Read ASME Section V, Article 7
Study Notes:
Page Number:
Standard/Code
Calibration requirements
_______________
___________
Yoke weight requirements, both AC and DC
_______________
___________
General MT procedure requirements
_______________
___________
Know where to find:
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ASME B 31.3, Paragraph 344.4 Liquid Penetrant Examination Liquid Penetrant (PT) examination shall be performed in accordance with Section V, Article 6.
Liquid Penetrant Method
PT Principles of Operation Penetrant testing is a family of testing that can be divided into two major groups, visible light and fluorescent or “Black Light” detectable groups. The basic steps of the operation can be seen above. Step 1: the test piece must be cleaned. Step two: the penetrant is applied, a dwell time or soaking time waited. Step three: the excess penetrant is removed. Step four:, the developer applied. Step five: the part is inspected, any indication is evaluated. Step six: the part is post cleaned. This inspection technique relies on the penetrant being pulled into all surface irregularities by capillary action. When the developer is applied, the penetrant is blotted back to the surface making the irregularities visible. The irregularities are then evaluated into three groups, false indications, commonly called handling marks, non-relevant indications and defects. The defects are evaluated to a given standard for acceptance. This process will detect:
Surface defects only! Page 5 - 6
Liquid Penetrant Method Study Notes Read ASME Section V, Article 6
Study Notes:
Page Number:
Standard/Code
Test temperatures
_______________
___________
Surface temperatures
_______________
___________
General PT procedure requirements
_______________
___________
Know where to find:
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ASME B 31.3, Paragraph 344.5 Radiographic Examination Radiographic (RT) examination shall be performed in accordance with Section V, Article 2. • 100% - applies only to girth and miter groove welds and to fabricated branch connection welds. • Random Radiography - Applies only to girth and miter groove welds. • Spot Radiography - A single exposure radiograph. This process will detect:
Surface and subsurface defects! Radiographic Examination
IQI
Shim 17
Weld
1
1 ASTM B
2
RT Principles of Operation Radiography is a nondestructive test method based on the principle of preferential radiation transmission. Areas of reduced thickness or lower density transmit more, and therefore absorb less, radiation. The radiation which passes through a test object forms a shadow image on a film. X-rays are man-made. Subsurface discontinuities which are readily detected by this method are voids, metallic and nonmetallic inclusions, and favorably aligned incomplete fusion and cracks.
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Radiographic Examination Study Notes
Read ASME Section V, Article 2
Study Notes:
Page Number:
Standard/Code
Backscatter acceptability
_______________
___________
Geometric Unsharpness
_______________
___________
IQI information
_______________
___________
Density
_______________
___________
Location Markers
_______________
___________
General RT procedure requirements
_______________
___________
Know where to find:
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ASME B 31.3, Paragraph 344.6 Ultrasonic Examination Ultrasonic (UT) examination shall be performed in accordance with Section V, Article 5. Note acceptance criteria is listed in paragraph 344.6.2. Ultrasonic Method
UT Principles of Operation Ultrasonic testing utilizes high frequency sound waves, well above the range of human hearing, to measure geometric and physical properties in materials. Ultrasonic testing will best detect those more critical planar discontinuities such as cracking and incomplete fusion. UT is most sensitive to discontinuities which lie perpendicular to the sound beam. Because various beam angles can be achieved with transducers and Plexiglas wedges the process can detect laminations, incomplete fusion and cracks that are oriented such that detection with radiographic testing would not be possible. The process has deep penetration ability and can be very accurate. This test method is generally limited to the inspection of butt welds in materials that are thicker than 1/4 inch. This process will detect:
Surface and subsurface defects, will detect some defects not readily detectable by radiography!
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Ultrasonic Testing Study Notes
Read ASME Section V, Article 5
Study Notes:
Page Number:
Standard/Code
Acceptance criteria
_______________
___________
Linear-type discontinuity
_______________
___________
Calibration blocks
_______________
___________
General UT procedure requirements
_______________
___________
Know where to find:
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ASME B 31.3, Paragraph 345.8 - Sensitive Leak Test The test (leak test) shall be in accordance with the gas and bubble test method specified in PBV Code, Section V, Article 10, or by another method demonstrated to have equal sensitivity. ASME Section V, Article 10 - Leak Testing This article gives the general procedure for the performance of leak testing.
Study Notes:
Page Number:
Standard/Code
Procedure Requirements
_______________
___________
Calibration Requirements
_______________
___________
Report
_______________
___________
Know where to find:
Data
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Nondestructive Examination Quiz 1.
_______________ tests leave the test object unchanged and ready to be placed in service, if acceptable. a. b. c. d. e.
2.
_______ inspection is considered to be the primary nondestructive test method. a. b. c. d. e.
3.
Penetrant Ultrasonic Magnetic particle Visual none of the above
Visual inspection must be performed _________________. a. b. c. d. e.
4.
Destructive Nondestructive Bend all of the above none of the above
before welding during welding after welding all of the above none of the above
_________ tests reveals surface discontinuities by the bleedout of a penetrating medium against a contrasting background. a. b. c. d. e.
Penetrant Ultrasonic Magnetic particle Visual none of the above
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5.
The visible dye used in PT produces a vivid _____ indication against a white background. a. b. c. d. e.
6.
The fluorescent dye used in PT produces a ______ fluorescent indication against a light background when observed under an ultraviolet light. a. b. c. d. e.
7.
surface indications cracks overlap all of the above none of the above
The ________ method is used to discover surface or slightly subsurface discontinuities in ferromagnetic materials. a. b. c. d. e.
9.
greenish red neutral all of the above none of the above
PT will not detect ________. a. b. c. d. e.
8.
greenish red neutral all of the above none of the above
penetrant ultrasonic magnetic particle visual none of the above
When the magnetic field is oriented along the axis of the part, it is referred to as ________ magnetism. a. b. c. d. e.
circular diagonal longitudinal all of the above none of the above
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10.
When the magnetic field tends to surround the part perpendicular to its longitudinal axis, it is referred to as ________ magnetism. a. b. c. d. e.
11.
circular diagonal longitudinal all of the above none of the above
A ________ field results when the "yoke" method is used, as shown in figure 11. a. b. c. d. e.
circular diagonal longitudinal all of the above none of the above
Figure 11 12.
A ________ field results when the "prod" technique is used, as shown in figure 12. a. b. c. d. e.
circular diagonal longitudinal all of the above none of the above Figure 12
13.
The major limitation of magnetic particle testing is that it will work only on ________ material. a. b. c. d.
14.
any stainless any copper any lead any ferromagnetic
_______ is a nondestructive test method based on the principle of preferential radiation transmission. a. b. c. d. e.
Penetrant Ultrasonic Magnetic particle Visual none of the above
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15.
The disadvantages of radiographic testing are _________________. a. b. c. d. e.
16.
________ is a nondestructive inspection method which uses high frequency sound waves to measure geometric and physical properties in materials. a. b. c. d. e.
17.
radiation exposure extensive safety training the process may not detect laminations all of the above none of the above
Penetrant Ultrasonic Magnetic particle Visual none of the above
A major limitation of ultrasonic testing is that it requires a ________ because interpretation can be difficult. a. b. c. d.
complex reference guide complex standard test block extensive calibration tests skilled operator
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Nondestructive Examination Answer Key 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.
b d d a b a e c c a c a d e d b d
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Welding Processes
WELDING AND CUTTING PROCESSES Introduction Since the welding inspector is primarily concerned with welding, knowledge of the various joining and cutting processes can be very helpful. While it is not mandatory that the inspector be a qualified welder, any hands-on welding experience is a benefit. In fact, many welding inspectors are selected for that position after working as a welder for some time. History has shown that former welders often make good inspectors. There are certain aspects of the various joining and cutting processes which the successful welding inspector must understand in order to perform the job most effectively. First, the inspector should realize the important advantages and limitations of each process. The individual should also be aware of those discontinuities which may result when a particular process is utilized. Many discontinuities occur regardless of the process used; however, there are others which can occur due to the misapplication of a particular process. These will be discussed for each method and referred to as possible problems. The welding inspector should also have some knowledge of the equipment requirements for each process, because often discontinuities occur which are the result of equipment deficiencies. The inspector should be somewhat familiar with the various machine controls and what effect their adjustment will have on the resulting weld quality. When the welding inspector has some understanding of these process fundamentals, they are better prepared to perform visual welding inspection. This knowledge will aid in the discovery of problems when they occur rather than later when the cost of correction is greater. The inspector who is capable of spotting problems in-process will be a definite asset to both production and quality control. Another benefit of having experience with these methods is that the production welders will have greater respect for the inspector and the inspector’s decisions. Also, a welder is more likely to bring some problem to the inspector's attention if it is known that the inspector understands the practical aspects of the process. So, having this knowledge will help the inspector get better cooperation from the welders and others involved with the fabrication operation. The processes presented here can be divided into two basic groups: welding and cutting. Welding describes a method for joining metals while cutting results in the removal or separation of material. As each of the joining and cutting processes are discussed, there will be an attempt to describe their important features, including:
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process advantages, process limitations, equipment requirements, electrodes/filler metals, techniques, applications, and possible process problems. There are numerous joining and cutting processes available for use in the fabrication of metal products. This fact is supported by the American Welding Society's "Master Chart of Welding and Allied Processes." This chart separates the joining and cutting methods into various categories, namely: Welding Processes and Allied Processes. The Welding Processes are further divided into seven groups: Arc Welding, SolidState Welding, Resistance Welding, Oxyfuel Gas Welding, Soldering, Brazing, and Other Welding. The Allied Processes include: Thermal Spraying, Adhesive Bonding, and Thermal Cutting (Oxygen, Arc and Other Cutting). With so many different processes available, it would be difficult to describe each one within the scope of this course. The following processes will be described: Welding Processes • Shielded Metal Arc Welding • Gas Metal Arc Welding • Flux Cored Arc Welding • Gas Tungsten Arc Welding • Submerged Arc Welding • Plasma Arc Welding • Oxyacetylene Welding Cutting Processes • Oxyfuel Cutting • Air Carbon Arc Cutting • Plasma Arc Cutting • Mechanical Cutting
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Welding Processes Before exploring the various welding processes, it is appropriate to define what is meant by the term "welding." According to AWS, a weld is: "a localized coalescence [joining together] of metals or nonmetals produced either by heating the materials to the welding temperature, with or without the application of pressure, or by the application of pressure alone and with or without the use of filler metal." Therefore, welding refers to the operations used to accomplish this joining. This section will present important features of some of the more common welding processes, all of which employ the use of heat without pressure. As each of these welding processes are presented, it is important to note that they all have certain features in common. That is, there are certain elements which must be provided by the welding process in order for it to be capable of producing satisfactory welds. These features include: some source of energy to provide heating, some means of shielding the molten metal from the atmosphere, and a filler metal (optional with some processes and joint configurations). The processes differ from one another because they provide these same features in various ways. So, as each process is introduced, be aware of how it satisfies these requirements. Shielded Metal Arc Welding (SMAW) The first process to be presented is shielded metal arc welding (SMAW). Even though this is the correct name for the process, it is more referred to as "stick welding." This process operates by heating the metal with an electric arc between a covered metal electrode and the metals to be joined. The arc is created between the electrode and the workpiece due to the flow of electricity. This arc provides heat, or energy, to melt the base metal, filler metal and electrode coating. As the welding arc progresses to the right, it leaves behind solidified weld metal covered by a layer of solidified flux, or slag. This slag tends to float to the outside of the metal since it solidifies after the molten metal has solidified so there is less likelihood that it will be trapped inside the weld zone resulting in a slag inclusion. Another feature is the presence of shielding gas which is produced when the electrode coating is heated and decomposed. These gases assist the flux in the shielding of the molten metal in the arc region. The primary element of the shielded metal arc welding process is the electrode itself. It is made up of a solid metal core wire covered with a layer of granular flux held in place by some type of bonding agent. All carbon and low alloy steel electrodes utilize essentially the same type of steel core wire---a low carbon, rimmed steel. Any alloying is provided from the coating, since it is more economical to achieve alloying in this way.
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The electrode coating is the feature which classifies the various types of electrodes. It actually serves five separate functions: 1.
SHIELDING: decomposes to form gaseous shield for molten metal
2.
DEOXIDIZATION: fluxing action removes oxygen and other atmospheric gases
3.
ALLOYING: provides additional alloying elements for weld deposit
4.
IONIZING: improves electrical characteristics to increase arc stability
5.
INSULATING: solidified slag provides insulating blanket to slow down weld metal cooling rate. (minor effect)
Since the electrode is such an important feature of the shielded metal arc welding process, it is necessary to understand how the various types are classified and identified. American Welding Society Specifications A5.1 and A5.5 describe the requirements for carbon and low alloy steel electrodes, respectively. They describe the various classifications and characteristics of these electrodes. The American Welding Society has also developed a system for the identification of shielded metal arc welding electrodes. The identification consists of an "E", which stands for electrode, followed by four or five digits. The first two or three numbers refer to the minimum tensile strength of the deposited weld metal. These numbers state the tensile strength in thousands of pounds per square inch. For example, "70" means that the tensile strength of the deposited weld metal is at least 70,000 psi. The next number refers to the positions in which the electrode can be used. A "2" means that the molten metal is so fluid that the electrode can only be used in the flat or horizontal fillet positions. A "1" tells us that the electrode is suitable for use in any position. The last number describes the usability of the electrode which is determined by the composition of the coating present on the electrode. This coating will determine its operating characteristics and recommended electrical current---AC (alternating current), DCEP (direct current-electrode positive) or DCEN (direct current-electrode negative). It is important to note that those electrodes ending in "5," "6" or "8" are classified as low hydrogen types. To maintain this low moisture content, they must be stored in their original factory-sealed container or an acceptable storage oven. This oven should be heated electrically and have temperature control capability in the range of o 150o to 350 F. Since this device will assist in the maintenance of a low moisture content (less than 0.2%) it must be suitably vented. Any low hydrogen electrodes which are not to be used immediately should be placed into the holding oven as soon as their air-tight container is opened.
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However, it is important to note that electrodes other than those mentioned above may be harmed if placed in the oven. Some electrode types are designed to have a certain moisture level. If this moisture is eliminated, the operating characteristics of the electrode will deteriorate significantly. Those SMAW electrodes used for joining low-alloy steels may also have an alphanumeric suffix which is added to the standard designation after a hyphen. Suffix to Electrode Designation Major Alloy Element(s) A1 0.5% Molybdenum B1 0.5% Molybdenum-0.5% Chromium B2 0.5% Molybdenum-1.25% Chromium B3 1.0% Molybdenum-2.25% Chromium B4 0.5% Molybdenum-2.0% Chromium C1 2.5% Nickel C2 3.5% Nickel C3 1.0% Nickel D1 0.3% Molybdenum-1.5% Manganese D2 0.3% Molybdenum-1.75% Manganese G* 0.2% Molybdenum; 0.3% Chromium; 0.5% Nickel; 1.0% Manganese; 0.1% Vanadium * Need have minimum content of one element only. The equipment for shielded metal arc welding is relatively simple. One lead from the welding power source is connected to the piece to be welded and the opposite lead goes to the electrode holder into which the welder places the welding electrode to be consumed. The electrode and base metal are melted by the heat produced from the welding arc created between the end of the electrode and the workpiece when they are brought close together. The power source for shielded metal arc welding is referred to as a constant current power supply, having a "drooping" characteristic. This terminology can be more easily understood by looking at the characteristic volt-ampere (V-A) curve for this type of power supply. As can be seen in the typical volt-ampere curves, a decrease in arc voltage will result in a corresponding increase in arc current. This is significant from a process- control standpoint because the arc voltage is directly related to the arc length (distance from electrode to workpiece). That is, as the welder moves the electrode toward or away from the workpiece, the arc voltage is actually being decreased or increased. These voltage changes correspond with changes in the arc current, or the amount of heat created by the welding arc. So as the welder draws the electrode away from the workpiece, the arc length increases which reduces the current, and consequently, the heat to the weld. A shorter arc length results in a higher arc current, and therefore increased heating. So, even though there is a control on the welding
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machine for current, the welder has some capability to instantaneously alter the current at the arc by manipulating the electrode to provide longer or shorter arc lengths. Because the lower curve has less slope than the upper curve, a greater change in arc current is obtained from a given change in arc length (voltage). Modern power supplies utilize controls which vary the open circuit voltage (OCV) and slope to produce a welding current having good operator control and the proper magnitude. Shielded metal arc welding is utilized in most industries for numerous applications. It is used for most materials except for some of the more exotic alloys. Even though it is a relatively old method and newer processes have replaced it in some applications, shielded metal arc welding remains as a popular process which will continue to be greatly utilized by the welding industry. There are several reasons why the process continues to be popular. The equipment is relatively simple and inexpensive. This helps to make the process quite portable. In fact, there are numerous gasoline or diesel engine-driven types which don't rely on electrical input, thus shielded metal arc welding can be accomplished in remote locations. Also, some of the newer solid state power sources are so small and lightweight that the welder can easily carry them to the work. Due to the presence of numerous types of electrodes, the process is considered quite versatile. Finally, with the improved equipment and electrodes available today, the resulting weld quality can be consistently high. One of the limitations of shielded metal arc welding is its speed. The speed is primarily hampered by the fact that the welder must periodically stop welding and replace the consumed electrode with a new one, since they are typically only 14 or 18 inches in length. It has been replaced by other semiautomatic, mechanized and automatic processes in many applications simply because they offer increased productivity when compared to manual shielded metal arc welding. Another disadvantage, which also affects productivity, is the fact that following welding, there is a layer of solidified slag which must be removed. A further limitation, when low hydrogen type electrodes are being utilized, is that they require storage in an appropriate electrode holding oven which will help to maintain their low moisture levels. Now that some of the basic principles have been presented, it is appropriate to discuss some of the discontinuities which may result when the shielded metal arc process is utilized. While these are not the only discontinuities that can be expected, they may result because of the misapplication of this particular process. One of those problems is the presence of porosity in the finished weld. When porosity is encountered, it is normally the result of the presence of moisture or contamination in the weld region. It could be present in the electrode coating, on the surface of the material, or come from the atmosphere surrounding the welding operation. Porosity can also occur when the welder is using an arc length which is too long. This problem of "long- arcing" is especially distressing in the case of low hydrogen electrodes. So, the shorter arc length not only increases the amount of heating produced, but it will also aid in the elimination of porosity in the weld metal.
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Porosity can also result from the presence of a phenomenon referred to as arc blow. While this can occur with any arc welding process, it will be discussed here since it is a common problem which plagues the manual welder. To understand arc blow, one must first know that there is a magnetic field developed whenever an electric current is passed through some conductor. This magnetic field is developed in a direction perpendicular to the direction of the electric current, so it can be visualized as a series of concentric circles surrounding the conductor. This magnetic field is strongest when contained entirely within a magnetic material and resists having to travel through the air outside this magnetic material. Consequently, when welding some magnetic material, such as steel, the field can become distorted when the arc approaches the edge of a plate, the end of a weld or some abrupt change in contour of the part being welded To reduce the effects of arc blow, several techniques can be attempted. They include: 1. 2. 3 4. 5. 6. 7. 8. 9.
10.
Change from DC to AC. Hold as short of an arc as possible. Reduce welding current. Angle the electrode in the direction opposite the arc blow. Use heavy tack welds at either end of a joint, with intermittent tack welds along length of joint. Weld toward a heavy tack or toward a completed weld. Use a back-step technique. Weld away from the ground to reduce back blow; weld toward the ground to reduce forward blow. Wrap ground cable around the workpiece and pass ground current through it in such a direction that the magnetic field set up will tend to neutralize the magnetic field causing the arc blow. Extend the end of the joint by attaching runoff plates.
In addition to porosity, arc blow can also cause: spatter, undercut, improper weld contour, and decreased penetration. Slag inclusions could also occur with SMAW simply because it relies on a flux system for weld protection. With any process utilizing flux, the possibility of trapping slag within the weld deposit is a definite concern. The welder can reduce this tendency by using techniques which allow the molten slag to flow freely to the surface of the metal. Thorough cleaning of the slag from each weld pass prior to deposition of additional passes will also reduce the occurrence of slag inclusions in multipass welds. Since shielded metal arc welding is primarily accomplished manually, numerous discontinuities can result from improper manipulation of the electrode. Some of these flaws are: incomplete fusion, incomplete penetration, cracking, undercut, overlap, incorrect weld size, and improper weld profile.
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Gas Metal Arc Welding (GMAW) The next process to be discussed here is gas metal arc welding. While gas metal arc welding is the AWS designation for the process, it is also commonly referred to as "MIG" welding. It is most commonly employed as a semiautomatic process; however, it lends itself well to mechanized and automatic applications as well. Therefore, it finds itself well suited for robotic welding applications. Gas metal arc welding is characterized by a solid wire electrode which is fed continuously through a welding gun. An arc is created between this wire and the workpiece to heat the base and filler materials. Once molten, the wire becomes deposited in the weld joint An important feature here is the fact that all of the shielding for welding is provided by a protective gas atmosphere which is also emitted from the welding gun from some external source. Gases used include both inert and reactive types. Inert gases such as argon and helium are used for some applications. They can be applied singly, or in combination with each other or mixed with some type of reactive gas such as oxygen or carbon dioxide. Many gas metal arc welding applications utilize carbon dioxide shielding alone, because of its relatively low cost compared to inert gases. The electrodes used for this process are solid wires which are supplied on spools or reels of various sizes. As is the case for shielded metal arc welding electrodes, there is an approved American Welding Society identification system for gas metal arc welding electrodes. They are denoted by the letters "ER," followed by two or three numbers, the letter "S," a hyphen, and finally another number. "ER" designates the wire as being both an electrode and a rod, meaning that it may conduct electricity or simply be applied as a filler metal when used with other welding processes. The next two or three numbers state the minimum tensile strength of the deposited weld metal in thousands of pounds per square inch. So, like the SMAW types, a "70" denotes a filler metal whose tensile strength is at least 70,000 psi. The letter "S" stands for a solid wire. Finally, the number after the hyphen refers to the particular chemistry of the electrode. This will dictate both its operating characteristics as well as what properties are to be expected from the deposited weld. Gas metal arc electrodes typically have increased amounts of deoxidizers such as manganese, silicon and aluminum to assist the shielding gas in the protection of the molten weld metal. Even though the wire doesn't have a flux coating, it is still important to properly store the material when not in use. The most critical factor here is that the wire must be kept clean. If allowed to remain out in the open, it may become contaminated with rust, oil, moisture, grinding dust or other elements present in a weld shop environment. So, when idle, the wire should be kept in its original plastic wrapping and/or shipping container. Even when a spool of wire is in place on the wire feeder, it should be covered with some protective covering when not used for prolonged periods of time. The power supply utilized for gas metal arc welding is quite different from the type employed for shielded metal arc welding. Instead of a constant current type, gas
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metal arc welding uses what is referred to as a constant voltage, or constant potential, power source. That is, welding is accomplished using a preset value of voltage over the a range of welding currents. Gas metal arc welding is normally accomplished using direct current, electrode positive. When this type of power source is combined with a wire feeder the result is a welding process which can be either semiautomatic, mechanized or fully automatic. This reduces the degree of skill required to perform gas metal arc welding. The equipment is more complex than that used for shielded metal arc welding. A complete setup includes a power source, wire feeder, gas source, and welding gun attached to the wire feeder by a flexible cable through which the electrode and gas travel. To set up for welding, the welder will adjust the voltage at the power source and the wire feed speed at the wire feeder. As the wire feed speed is increased, the welding current increases as well. The melt-off rate of the electrode is proportional to the arc current, so the wire feed speed actually controls this feature as well. It was mentioned that this power source is a constant potential type; however, a look at a typical V-A curve will show that the line is not flat but actually has a slight slope. This feature allows the process to function as a semi-automatic type, meaning that the welder does not have to control the feeding of the filler metal as was the case for manual shielded metal arc welding. Another way to describe this system is to call it a "Self-Regulating Constant Potential" system. This is accomplished by the fact that a minor change in the actual arc voltage (caused by a variation in the gun's position with respect to the workpiece) will result in a substantial increase or decrease in the arc current. It can be seen that a decrease in arc voltage (gun moved closer to the workpiece) will produce an instantaneous increase in current. This in turn results in an increase in the electrode melt-off rate which instantaneously burns off additional electrode to bring the arc voltage (length) back to its preset value. Similarly, an increase in the arc voltage (gun moved away from the workpiece) will decrease the current and therefore the electrode melt-off rate. The wire continues to be fed at its preset rate to again provide the original value of arc voltage. This reduces the effect of the operator's manipulation on the welding characteristics, to make the process less operator- sensitive and therefore easier to learn. When the machine adjustments are changed, the result is that the operating characteristics will be drastically altered. Of primary concern is the manner in which the molten metal is transferred from the end of the electrode, across the arc region, to the base metal. With gas metal arc welding, there are four basic modes of metal transfer. They are: spray, globular, pulsed arc, and short circuiting. Their characteristics are so different that it's almost as if there are four separate welding processes. Each specific type has definite advantages and limitations which make it better for some applications than others. The type of metal transfer depends upon
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several factors, including: shielding gas, current and voltage levels and power supply characteristics. One of the basic ways in which these four types differ is that they provide varying amounts of heat to the workpiece. Spray transfer is considered to be the hottest, followed by globular, pulsed arc and finally short circuiting. Therefore, spray transfer is the best for heavier sections and full penetration weld joints, as long as they can be positioned in the flat position. Globular transfer provides almost as much heating and weld metal deposition, but its operating characteristics tend to be less stable, resulting in increased spatter. Pulsed arc gas metal arc welding requires a welding power source capable of producing a pulsing direct current output which allows the welder to program the exact combination of high and low currents for improved heat control and process flexibility. The welder can set both the amount and duration of the high current pulse. So during operation, the current alternates between a high pulse current and a lower pulse current, both of which can be set with machine controls. Short circuiting transfer results in the least amount of heating to the base metal, making it an excellent choice for welding of sheet metal and joints having excessive gaps due to poor fitup. Short circuiting transfer is characteristically colder due to the fact that the electrode actually comes in contact with the base metal creating a short circuit for a portion of the welding cycle. So, the arc is intermittently operating and extinguishing. The brief periods of arc extinction allow for some cooling to occur to aid in reducing the tendency of burning through thin materials. Care must be taken when short circuiting transfer is used for heavy section welding, since incomplete fusion could result from insufficient heating of the base metal. As mentioned, the shielding gases have a significant effect on the type of metal transfer. Spray transfer can be achieved only when there is at least 80% argon present in the gas mixture. CO2 is probably the most popular gas for GMAW of carbon steel, primarily due to its relatively low cost and its excellent penetration characteristics. One drawback which must be realized, however, is that there will be more spatter which may require removal, reducing the overall efficiency. The versatility offered by this process has resulted in its utilization in many industrial applications. GMAW can be effectively used to join or overlay many types of ferrous and nonferrous metals. The use of gas shielding instead of some type of flux reduces the possibility of introducing hydrogen into the weld zone, so GMAW can be used successfully in situations where the presence of hydrogen could cause problems. Due to the lack of a slag coating which must be removed after welding, GMAW is well suited for automatic and robotic welding or other high production situations. This is one of the major advantages of the process. Since there is little or no cleaning following welding, the overall efficiency is greatly improved. This efficiency is further increased by the fact that the continuous roll of wire doesn't require changing as often as the individual electrodes used in SMAW. All of this increases the amount of time in which actual production welding can be accomplished.
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Another benefit of gas metal arc welding is that it is a relatively clean process, primarily due to the fact that there is no flux present. Shops with ventilation problems can find some relief by switching to gas metal arc welding instead of shielded metal arc welding or flux cored arc welding, because less smoke is generated. With the presence of numerous types of electrodes and equipment which has become more portable, the versatility of gas metal arc welding continues to improve. One additional benefit relates to the visibility of the process. Since no slag is present, the welder can more readily observe the action of the arc and molten puddle to improve control. While the use of shielding gas instead of flux does provide some benefits, it can also be thought of as a limitation, since this is the primary way in which the molten metal is protected and cleaned during welding. If the base metal is excessively contaminated, the shielding gas alone may not be sufficient to prevent the occurrence of porosity. GMAW is also very sensitive to drafts or wind which tend to blow the shielding gas away and leave the metal unprotected. For this reason, gas metal arc welding is not well suited for field welding. It is important to realize that simply increasing the gas flow rate above recommended limits will not necessarily guarantee that adequate shielding will be provided. In fact, high flow rates may tend to increase the possibility of porosity because these increased flow rates may actually draw atmospheric gases into the weld zone. Another disadvantage is that the equipment required is more complex than that used for shielded metal arc welding. This increases the possibility that some mechanical problem could cause weld quality problems. Such things as worn gun liners and contact tips can alter the feeding and electrical characteristics to the point that defective welds could be produced. The primary inherent problems have already been explored somewhat. They are: porosity due to contamination or loss of shielding, incomplete fusion due to the use of short circuiting transfer on heavy sections, and arc instability caused by worn liners and contact tips. Although such problems could be disastrous, they can be alleviated if certain precautions are taken. To reduce the possibility of porosity, parts should be cleaned prior to welding and the weld zone protected from any excessive wind using enclosures or windbreaks. If porosity persists, the gas should be checked to assure that there is no moisture present. The problem of incomplete fusion is a real one when we talk about GMAW, especially when short circuiting transfer is being used. This is due in part to the fact that this is a "open arc" process since no flux is used. Without this layer of shielding from the arc, the increased intensity of the arc makes the welder believe that there is a tremendous amount of heating of the base metal. Such a feeling could be very deceiving, so the welder must be aware of the limitation and assure that the arc is being directed where the metal is to be fused.
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Finally, equipment should be well maintained to alleviate the problems associated with unstable wire feeding. Each time a roll of wire is replaced, the liner should be blown out with compressed air to remove particles which could cause jamming. If the problem persists, the liner should be replaced. The contact tip should be changed periodically as well. When it becomes worn, the point of electrical contact changes so that the electrical stickout is increased without the welder knowing it. The electrical stickout is also referred to as the contact tube-to-work distance. Flux Cored Arc Welding (FCAW) The next process to be described is flux cored arc welding. This is very similar to gas metal arc welding except that the electrode is tubular and contains a granular flux instead of the solid wire used for gas metal arc welding It shows the tubular electrode being fed through the contact tip of the welding gun to produce an arc between the electrode and the workpiece. With flux cored arc welding, there may or may not be a shielding gas, depending upon what type of electrode is utilized. Some are designed to provide all of the necessary shielding from the internal flux, while others require additional shielding from an auxiliary shielding gas. As the welding progresses, a bead of solidified weld metal is deposited. Covering this solidified weld metal is a layer of slag, as was the case for shielded metal arc welding. With FCAW, as with other processes, there is a system for identification of the various types of welding electrodes. An identification begins with the letter "E" which stands for electrode. The next number refers to the minimum tensile strength of the deposited weld metal in ten thousands of pounds per square inch, so a "7" means that the weld metal strength is at least 70,000 psi. The next digit is either a "0" or "1". A "0" means that the electrode is suitable for use in the flat or horizontal fillet positions only, while a "1" describes an electrode which can be used in any position. Following these numbers is the letter "T" which refers to a tubular electrode. This is followed by a hyphen and then another number which denotes the particular grouping based upon chemical composition of deposited weld metal, type of current, polarity of operation, whether it requires a shielding gas, and other specific information for the category. With this identification system, it can be determined whether or not a certain classification of electrode requires an auxiliary shielding gas. This is important to the welding inspector since flux cored arc welding can be performed with or without an external shielding gas. Some electrodes are formulated to be used without any additional shielding other than that contained within the electrode. They are designated by the numbers -3, -4, -6, -7, and -8. However, those electrodes having the numerical suffixes -1, -2 or -5 require some external shielding to aid in protecting the molten metal. Both types offer advantages, depending upon the application. For example, the self-shielded types are better suited for field welding where wind could result in a loss of gaseous shielding. Gas shielded types are typically used
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where the need for superior weld metal properties warrants the additional cost. Gases typically used for flux cored arc welding are CO2 or 75% Argon - 25% CO2. The equipment utilized for FCAW is essentially identical to that for GMAW. Some exceptions might be higher current capacity guns and power sources, lack of gas apparatus for self-shielded electrodes, and knurled wire feed rolls. Like GMAW, FCAW utilizes a constant voltage direct current power supply. Depending on the type of electrode, the operation may be DCEP (- 1, -2, -3, -4, -5, -6, and -8) or DCEN (-7). The flux cored arc welding process is a relatively new method compared to other welding processes. Its relatively good performance on contaminated surfaces and the increased deposition rates offered have helped flux cored arc welding to replace SMAW and GMAW for many applications. The process is utilized in all industries where the predominant materials are ferrous. It can be used with satisfactory results for both shop and field applications. Although the majority of the electrodes produced are ferrous (for both carbon and stainless steels) some nonferrous ones are available as well. Some of the stainless types actually employ a carbon steel sheath surrounding the internal flux which also contains granular alloying elements such as chromium and nickel. FCAW has gained wide acceptance because of the many advantages it offers. Probably the most significant advantage is that it provides a high efficiency in terms of the amount of weld metal that can be deposited in a given period of time. It is among the highest for a hand-held process. This is aided by the fact that the electrode comes on continuous reels which increases the "arc time" just as with gas metal arc welding. The process is also characterized by an aggressive, deeply penetrating arc which tends to reduce the possibility of fusion-type discontinuities. Since it is typically utilized as a semi-automatic process, the skill required for operation is less than would be the case for a manual process. With the presence of a flux, whether assisted by a gaseous shield or not, FCAW is capable of tolerating a greater degree of base metal contamination than is GMAW. For this same reason, FCAW lends itself well to field situations where the loss of shielding gas due to winds would greatly hamper GMAW quality. It is important to realize that this process does have certain limitations of which the inspector should be aware. First, since there is a flux present, there is a layer of solidified slag which must be removed before depositing additional layers of weld or before a visual inspection can be made. Due to the presence of this flux, there is a significant amount of smoke generated during welding. Prolonged exposure in unvented areas could prove to be unhealthy for the welder. This smoke also reduces the welder's visibility to the point where it may be difficult to properly manipulate the arc in the joint. Although smoke extractor systems are available, they tend to add bulk to the gun which increases the weight and decreases visibility. They also may disturb the shielding if an auxiliary gas is being used.
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Even though FCAW is considered to be a smoky process, it is not as bad as SMAW in terms of the amount of smoke generated for a given amount of deposited weld metal. The equipment required for FCAW is more extensive than that for SMAW so the initial cost and the possibility of machinery problems does limit its acceptability for some situations. As with any of the processes, FCAW does have some inherent problems. The first has to do with the flux. Due to its presence there exists a possibility that the solidified slag could become trapped in the finished weld. This could be due to either improper interpass cleaning or improper technique. With FCAW, it is critical that the welder travels fast enough so that the arc is always on the leading edge of the molten puddle. When the travel speed is slow enough to allow the arc to be toward the middle or back of the puddle, molten slag may roll ahead of the puddle and become trapped. Another inherent problem involves wire feeding apparatus. As was the case for GMAW, lack of maintenance could cause wire feeding problems which may affect the quality of the weld. Gas Tungsten Arc Welding (GTAW) The next process to be discussed is gas tungsten arc welding which has several interesting differences when compared to those already explained. The most significant feature here is that the electrode used is not intended to be consumed during the welding operation. It is made of pure or alloyed tungsten which has the ability to withstand very high temperatures, even those of the welding arc. Therefore, when current is flowing, there is an arc created between the tungsten electrode and the workpiece. If any filler metal is required, it must be added externally, either by hand or with the use of some mechanical wire feed system. All of the arc and metal shielding is achieved through the use of an inert gas which flows out of the nozzle surrounding the tungsten electrode. The deposited weld bead has no slag requiring removal because no flux is utilized. As with the other processes, there is a system whereby the various types of tungsten electrodes can be easily identified. The designations consist of a series of letters starting with an "E" which stands for electrode. Next comes a "W" which is the chemical abbreviation for tungsten. These letters are followed by letters and numbers which describe the alloy type. Since there are only five different classifications, they are more commonly differentiated using a color code system. The table below shows the classifications and the appropriate color code. AWS Tungsten Electrode Classifications AWS Classification Alloy Color EWP Pure tungsten Green EWTh-1 0.8-1.2% thoria Yellow EWTh-2 1.7-2.2% thoria Red EWTh-3 0.35-0.55% thoria Blue EWZr 0.15-0.40% zirconia Brown
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The presence of the thoria or zirconia aid in improving the electrical characteristics, by making the tungsten slightly more emissive. This simply means that it is easier to initiate an arc with these thoriated or zirconated types than is the case for pure tungsten electrodes. Pure tungsten is quite often utilized for the welding of aluminum because of its ability to form a ball when heated. With a ball instead of a point, there is a lower concentration of current which reduces the possibility of damaging the tungsten. The EWTh-2 type is most commonly used for the joining of ferrous materials. GTAW can be performed using DCEP, DCEN or AC. The DCEP will result in more heating of the electrode, while the DCEN will tend to heat the base metal more. AC alternately heats the electrode and base metal. AC is typically used for the welding of aluminum because the alternating current will increase the cleaning action to improve weld quality. DCEN is most commonly used for the welding of steels. As mentioned, GTAW utilizes inert gases for shielding. Inert means that the gases will not combine with the metal, but will protect it from contaminants. Argon and helium are the two most commonly used inert gases, based on their relative costs and availability compared to other types of inert gases. Some mechanized stainless steel welding applications utilize a shielding gas consisting of argon and a small amount of hydrogen, but this represents a very minor portion of the gas tungsten arc welding which is performed. The equipment required for GTAW has as its primary element a power source like the one used for SMAW; that is, a constant current type. Since there is a gas present, it is now necessary to have apparatus for its control and transmission. An added feature of this welding system, which is not shown, is a high frequency generator which aids in the initiation of the welding arc. In order to alter the welding heat during the welding operation, a remote current control may also be attached. It can be foot-operated or controlled by some device mounted on the torch itself. This is particularly useful for welding thin materials and open root pipe joints, where instantaneous control is necessary. There are numerous applications for GTAW in many industries. It is capable of welding virtually all materials, because the electrode is not melted during the welding operation. Its ability to weld at extremely low currents makes gas tungsten arc welding suitable for use on the thinnest (down to 0.005 inch) of metals. Its typically clean and controllable operation causes it to be the perfect choice for extremely critical applications such as those found in the aerospace, food and drug processing, and power piping industries. The principal advantage of GTAW lies in the fact that it can produce welds of high quality and excellent visual appearance. Also, since no flux is utilized, the process is quite clean; plus there is no slag to remove after welding. As mentioned before, extremely thin sections can be welded. Due to the nature of its operation, it is suitable for welding most metals, many of which are not readily weldable using other welding processes. If joint design permits, these materials can be welded without the use of additional filler metal. When required, numerous types of filler metals exist in wire form for a wide range of metal alloys. In the case where there is
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no commercially-available wire for a particular metal alloy, it is possible to produce a suitable filler metal by simply shearing a piece of identical base metal to produce a narrow piece which can be hand-fed into the weld zone just as if it were a wire. Contrasting these advantages are several disadvantages. First, GTAW is among the slowest of the available welding processes. While it produces a clean weld deposit, it is also characterized as having a low tolerance for contamination. Therefore, base and filler metals must be extremely clean prior to welding. When utilized as a manual process, Gas tungsten arc welding requires a high skill level. This is partially due to the need for two hands--one to manipulate the torch and one to feed the filler metal. GTAW is normally selected in situations where the need for high quality warrants additional cost to overcome these limitations. One of the inherent problems associated with this method has to do with its inability to tolerate contamination. If contamination or moisture is encountered, whether from the base metal, filler metal or shielding gas, the result could be porosity in the deposited weld. When porosity is noted, this is a sign that the process is out of control and some preventive measures are necessary. Checks should be made to determine the source of the contamination so that it can be eliminated. Another inherent problem which is almost totally confined to the GTAW process is that of tungsten inclusions. As the name implies, this discontinuity occurs when pieces of the tungsten electrode become included in the weld deposit. Tungsten inclusions can occur due to a number of reasons, including: 1. 2. 3. 4. 5. 6 7. 8. 9. 10.
Contact of electrode tip with molten metal; Contact of filler metal with hot tip of electrode; Contamination of the electrode tip by spatter; Exceeding the current limit for a given electrode diameter or type; Extension of electrodes beyond their normal distances from the collet, resulting in overheating of the electrode; inadequate tightening of the collet; inadequate shielding gas flow rates or excessive wind drafts resulting in oxidation of the electrode tip; defects such as splits or cracks in the electrode; use of improper shielding gases; and improper grinding of the electrode tip.
Submerged Arc Welding (SAW) The last of the more common welding processes to be discussed is submerged arc welding. This method is typically the most efficient one mentioned so far in terms of the rate of weld metal deposition. SAW is characterized by the use of a continuously-fed solid wire electrode which provides an arc that is totally covered by a layer of granular flux, hence the name "submerged" arc. As mentioned, the wire is fed into the weld zone much the same way as with gas metal arc welding or flux cored arc welding. The major difference, however, is in
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the method of shielding. With submerged arc welding, a granular flux is poured ahead of or around this wire electrode to facilitate the protection of the molten metal. As the welding progresses, in addition to the weld bead, there is a layer of slag and still granular flux covering the solidified weld metal. The slag must be removed and discarded. However, the granular flux can be recovered and reused if care is taken to prevent its contamination. In some cases where the flux must provide alloying for the weld, reuse of the flux may not be advisable. Since SAW utilizes a separate electrode and flux, there are numerous combinations available for specific applications. There are two general types of combinations which can be used to provide an alloyed weld deposit: an alloy electrode with a neutral flux or a mild steel electrode with an alloy flux. Therefore, to properly describe the filler material for Submerged Arc Welding, the American Welding Society identification system consists of designations for both the electrode and flux. The equipment used for submerged arc welding consists of several components. Since this process can be utilized as a fully mechanized or semiautomatic method, the equipment used for each is slightly different. In either case, however, some power source is required. Although most submerged arc welding is performed with a constant voltage power source, there are certain applications where a constant current type is preferred. As with gas metal arc welding and flux cored arc welding, a wire feeder forces the wire through the cable liner to the welding torch. The flux must be moved to the weld zone somehow. For mechanized systems, the flux is generally poured into a hopper above the welding torch and fed by gravity so that it pours either slightly ahead of the arc or around the arc from a nozzle surrounding the contact tip. In the case of semiautomatic submerged arc welding, the flux is forced to the gun using compressed air which makes the granular flux behave similar to a liquid or there is a hopper connected directly to the hand-held gun. Another equipment variation is the choice of alternating or direct current, either polarity. The type of welding current will affect both penetration and weld bead contour. For some applications multiple electrodes can be utilized. The electrodes may be energized by a single power source, or multiple power sources may be necessary. The use of multiple electrodes provides even more versatility for the process. SAW has found acceptance in many industries, and it can be performed on numerous metals. Due to the high rate of weld metal deposition, it has shown to be quite effective for overlaying or building up material surfaces. In situations where a surface needs improved corrosion or wear resistance, it is often more economical to cover a susceptible base metal with a resistant weld overlay. If this application can be mechanized, submerged arc welding is an excellent choice. Probably the biggest advantage of SAW is its high deposition rate. It can typically deposit weld metal more efficiently than any of the more common processes. The submerged arc welding process also has high operator appeal, first because of the lack of a visible arc which allows the operator to control the welding without the need for a filter lens and other heavy protective clothing. The other beneficial
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feature is that there is less smoke generated than with some of the other processes. Another feature of the process which makes it desirable for many applications is its ability to penetrate deeply. The major limitation of SAW is that it can only be done in a position where the flux can be supported in the weld joint. When welding in a position other than the flat or horizontal fillet positions, some device is required to hold the flux in place so it can perform its job. Another limitation is that, like most mechanized processes, there may be a need for extensive fixturing and positioning equipment. As with other processes using a flux, finished welds have a layer of solidified slag which must be removed. If welding parameters are improper, weld contours could be such that this job of slag removal is even more difficult. The final disadvantage relates to the flux which covers the arc during welding. While it does a good job of protecting the welder from the arc, it also prevents him from seeing exactly where the arc is positioned with respect to the joint. With a mechanized setup, it is advisable to track the entire length of the joint without the arc or the flux to check for alignment. If the arc is not properly directed, incomplete fusion could result. There are some inherent problems related to SAW. The first has to do with the granular flux. Just as with low hydrogen SMAW electrodes, it is necessary to protect the submerged arc welding flux from moisture. It may be necessary to store the flux in heated containers prior to use. If the flux becomes wet, porosity and underbead cracking may result. Another characteristic problem of SAW is solidification cracking. This results when the welding conditions provide a weld bead having an extreme width-to-depth ratio. That is, if the bead's width is much greater than its depth, or vice versa, centerline shrinkage cracking could occur during solidification. Plasma Arc Welding (PAW) The next process to be explained is plasma arc welding. A plasma is defined as an ionized gas. With any process utilizing an arc, a plasma is created. However, PAW is so named because of the intensity of this plasma region. At first glance, PAW could be easily mistaken for GTAW because the equipment required is quite similar. The two processes utilize the same type of power source. However when we look closely at the torch itself the difference becomes more obvious. Both the PAW and GTAW torches utilize a tungsten electrode for the creation of the arc. However, with the PAW torch, there is a copper orifice within the ceramic nozzle. There is a high velocity "plasma" gas which is forced through this orifice and past the welding arc resulting in the constriction of the arc. This constriction, or squeezing, of the arc causes it to be more concentrated, and therefore more intense. One way to illustrate the difference in arc intensity between GTAW and PAW would be to use the analogy of an adjustable water hose nozzle. The GTAW arc would be comparable to the gentle mist setting, while the PAW arc
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would behave more like the setting which provides a concentrated stream of water having a greater force. There are two general categories of plasma arc operation, namely the transferred and the nontransferred arc. With the transferred arc, the arc is created between the tungsten electrode and the workpiece. The nontransferred arc, on the other hand, occurs between the tungsten electrode and the copper orifice. The transferred type arc is generally utilized for both welding and cutting of conductive materials, because it results in the greatest amount of heating of the workpiece. The nontransferred type arc is preferred for the cutting of nonconductive materials and for welding of materials when the amount of heating of the workpiece must be minimized. The similarities between GTAW and PAW extend to the equipment as well. The power sources are identical in most respects. However, there are some additional elements necessary, including: plasma control console and a source of plasma gas. The torch, as discussed above, does differ slightly; however, a careful check of the internal configuration must be made to be certain. As indicated, two separate gases are required: the shielding gas and the orifice (or plasma) gas. Argon is most commonly employed for both types of gas. However, welding of various metals might warrant the use of helium or combinations of argon/helium or argon/hydrogen for one or the other gases. The primary applications for PAW are similar to those for GTAW. PAW is utilized for the same materials and thicknesses. PAW becomes the choice where applications warrant the use of a more localized heat source. It is used extensively for full penetration welds in material up to 1/2 inch thick by employing a technique referred to as "keyhole welding. Welding is performed on a square butt joint with no root opening. The concentrated heat of the arc penetrates through the material thickness to form a small keyhole. As welding progresses, the keyhole moves along the joint melting the edges of the base metal which then flow together and solidify after the welding arc passes. This creates a high quality weld, with no elaborate joint preparation and fast travel speeds compared to GTAW. One advantage of PAW, which was mentioned before, is that it provides a localized heat source. This allows for faster welding speeds and therefore less distortion. Since the standoff used between the torch end and the workpiece is typically quite long, the welder has better visibility of the weld being made. Also, since the tungsten electrode is recessed within the torch, the welder is less likely to stick it in the molten metal and produce a tungsten inclusion. The ability to use this process in a keyhole mode is also desirable. The keyhole is a positive indication of complete penetration and weld uniformity. This weld uniformity is in part due to the fact that plasma arc welding is less sensitive to changes in arc length. The presence of its collimated arc will permit relatively large changes in torch-to-work distance without any change in its melting capacity.
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PAW is limited to the effective joining of materials 1 inch or less in thickness. The initial cost of the equipment is substantially greater than that for GTAW, primarily because there is additional apparatus required. Finally, the use of PAW requires greater operator skill than would be the case for GTAW. Among the problems that may be encountered with this process are two types of metal inclusions. Tungsten inclusions may result from high current levels; however, the fact that the tungsten is recessed helps to prevent this occurrence. High current could also result in the copper orifice melting and being deposited in the weld metal. Another problem that may be encountered when keyhole welding is being done is referred to as tunneling. This occurs when the keyhole is not completely filled at the end of the weld, leaving a cylindrical void which may extend entirely through the throat of the weld. When using the keyhole technique, there is also a possibility of getting incomplete fusion since the arc and joint are so narrow. As a result, even small amounts of mistracking can produce incomplete fusion along the joint. Oxyacetylene Welding (OAW) The next process is oxyacetylene welding. While the term oxyfuel welding is also used, acetylene is the only fuel gas capable of producing high enough temperatures for effective welding. With OAW, the energy for welding is created by a flame, so this process is considered to be a chemical welding method. Just as the heat is provided by a chemical reaction, the shielding for oxyacetylene welding is accomplished by this flame as well. Therefore, no flux or external shielding is necessary. The equipment for oxyacetylene welding is relatively simple. It consists of several parts: oxygen tank, acetylene tank, pressure regulators, torch, and connecting hoses. The oxygen cylinder is a hollow high pressure container capable of withstanding a pressure of approximately 2200 psi. The acetylene cylinder on the other hand, is filled with a porous material similar to cement. Acetylene exists in the cylinder dissolved in liquid acetone. Care must be taken since gaseous acetylene is extremely unstable at pressures exceeding 15 psi and an explosion could occur even without the presence of oxygen. Since the acetylene cylinder contains a liquid it is important that it remains upright to prevent spillage. Each cylinder has attached to its top a pressure regulator which reduces the high internal tank pressure to working pressures. Hoses then connect these regulators to the torch. The torch includes a mixing section where the oxygen and acetylene combine to provide the necessary mixture. The ratio of these two gases can be altered by the adjustment of two separate control valves. Normally, for carbon steel welding, they are adjusted to provide a mixture, which is referred to as a neutral flame. A higher amount of oxygen will create an oxidizing flame and a higher amount of acetylene will produce a carburizing flame. After the gases are mixed they flow through a detachable tip. Tips are made in a variety of sizes to allow welding of different metal thicknesses.
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The filler material used for OAW on steel has a simple identification system. Two examples are RG-45 and RG-60. The "R" designates it as a rod, "G" stands for gas and the 45 and 60 relate to the minimum tensile strength of the weld deposit in thousands of pounds per square inch (psi). So 45 designates a weld deposit having a tensile strength of at least 45,000 psi. Although not utilized as extensively as it once was, OAW still sees some usage. Its primary tasks include the welding of thin steel sheet and small diameter steel piping. It is also applied in many maintenance situations as well. The advantages of OAW include some desirable features of the equipment itself. First, it is relatively inexpensive and can be made very portable. This portability relates not only to the compact size but also to the fact that there is no electrical input required. Care should be taken when moving the equipment so that the valves on the cylinders are not damaged. If broken off, a cylinder can turn into a lethal missile. So, whenever transported, the regulators should be removed and the valves covered with special screw-on caps for protection from impact. The process also has certain limitations. For one, the flame does not provide as concentrated a heat source as can be achieved by an arc. Therefore, if a groove weld is being made, the weld preparation should exhibit a thin "feather edge" to assure that complete fusion is obtained at the root of the joint. This lower heat concentration also results in a relatively slow process, so we typically consider OAW best suited for thin section welding. As with any of the welding processes requiring a second hand to feed the filler metal, OAW requires a substantial skill level for best results. There are certain inherent problems associated with OAW. They are primarily related to either improper manipulation or adjustment of the flame. Since the heat source is not concentrated, care must be taken to direct the flame properly to assure adequate fusion. If the flame is adjusted such that an oxidizing flame or carburizing flame is produced, weld metal properties could be degraded, so it is important to have equipment capable of providing uniform gas flow.
Cutting Processes So far the discussion has involved only those methods utilized for joining metals together. Also of importance in metal fabrication are those processes utilized to cut or remove metal. These processes are utilized prior to welding to produce proper part shapes or make specific joint preparations. During or after welding, some of these same processes can also be employed to remove defective areas of welds or to produce a specific configuration if the as-welded shape is not satisfactory for the intended purpose of the part. Oxyfuel Cutting (OFC) The first of these cutting processes is oxyfuel cutting. An oxyfuel flame is used to heat the metal to a temperature at which it will readily oxidize, or burn. Once that temperature has been achieved, a high pressure stream of cutting oxygen is directed
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on the metal's heated surface to produce an oxidation reaction. This stream of oxygen also tends to remove the slag and oxide residue which is produced by this oxidation reaction. Therefore, OFC can be thought of as a type of chemical cutting process The equipment utilized for OFC is essentially the same as that for OAW except that, instead of a welding tip, there is now a cutting attachment which includes an additional lever or valve to turn on the cutting oxygen. The cutting operation also requires a special cutting tip which is attached to the end of the torch. It consists of a series of small holes arranged in a circle around the outside edge of the end of the cutting tip. This is where the oxyfuel gas mixture flows to provide the preheat for cutting. Located in the center of these holes is a single cutting oxygen passage. It should be noted that OFC can be accomplished using several different types of fuel gases, such as: acetylene, natural, propane, gasoline, and MAPP. Each provide various degrees of efficiency and may require slightly modified cutting tips. Other factors which should be considered when selecting the proper fuel gas include: preheating time required, cutting speeds, cost, availability, amount of oxygen required to burn gas efficiently, and ease and safety of transporting fuel containers. Cutting is accomplished by applying heat to the part using the preheat flame which is an oxyfuel mixture. Once the metal has been heated to its kindling temperature, the cutting oxygen is turned on to oxidize the hot metal. The oxidation of the iron produces a tremendous amount of heat. This chemical reaction provides the necessary heat to rapidly melt the metal and simultaneously blow the oxidation products from the joint. The width of the cut produced is referred to as the kerf. The amount of offset between the cut entry and exit points, measured along the cut edge is the drag. Although OFC is utilized extensively by most industries, it is limited to the cutting of carbon and low alloy steels only. As the amounts of various alloying elements increase, one of two things can happen. Either they make the steel more difficult to cut or they may give rise to hardened or heat-checked cut surfaces, or both In most cases, the addition of certain amounts of alloying elements may prevent conventional OFC. In many cases, these elements are oxidation resistant types. In order for an oxyfuel cut to be accomplished, the metal oxide which is produced must melt at some temperature near or below the melting point of the metal. Therefore, in order to cut cast iron or stainless steel with this process, special techniques involving additional equipment are necessary. These techniques include: torch oscillation, use of waster plate, wire feeding, powder cutting, and flux cutting. OFC's advantages include its relatively inexpensive and portable equipment making it feasible for use in both shop and field applications. Cuts can be made on thin or thick sections. Steels up to five feet thick have been cut using this process. When mechanized, OFC can produce cuts of reasonable accuracy. When compared to mechanical cutting methods, oxyfuel cutting of steels is more economical. To improve this efficiency even more, multiple torch systems or stack cutting can be utilized to cut several parts at once.
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One of the limitations of OFC is that the finished cut may require additional cleaning or grinding to prepare it for welding. Another important limitation is that since it utilizes heat, there may be a heat affected zone produced which could exhibit very high hardness. This is especially important if there is a need for machining of this surface. Employment of preheat and postheat will aid in the alleviation of this problem. Also, even though cuts can be reasonably accurate, they still don't compare to the accuracy possible from other mechanical cutting methods. Finally, the flame and hot slag produced result in safety hazards for personnel near the cutting operation. Air Carbon Arc Cutting (CAC-A) Another very effective cutting process is air carbon arc cutting. This process utilizes a carbon electrode to create an arc for heating along with a high pressure stream of compressed air to mechanically remove the molten metal. The equipment utilized for CAC-A consists of a special electrode holder which is attached to a constant current power source and a compressed air supply. This special holder grasps the carbon electrode in small copper jaws, one of which has a series of holes through which the compressed air passes. To achieve a cut, the carbon electrode is brought close to the work to create an arc. Once the arc melts the metal, the stream of compressed air blows away the molten metal to produce a gouge or cut. The electrode holder is attached to some power source as well as a source of compressed air. Any nonflammable compressed gas could be utilized, but compressed air is by far the least expensive, if available. CAC-A has applications in most industries, especially since it works on any material which conducts electricity. Even though it will cut all metals, there may be a requirement for a particular type of electric current and polarity. While we tend to think of its application to remove defective areas of the weld or base metal, it is important to realize that it can be utilized quite effectively as a weld joint preparation tool. For example, two pieces to be butt welded can be aligned with their square-cut edges touching. The CAC-A process can then be employed to produce a uniform U-groove preparation. CAC-A is also used for rough machining of large, complex parts. One of the basic advantages of CAC-A is that it is a relatively efficient method for removal of metal. It also has the ability to cut most types of metals. Since it utilizes the same power sources as those used for some types of welding, the equipment costs are minimal. All that is necessary is the purchase of the special electrode holder which is attached to an existing power source and a compressed air supply. The primary disadvantage of the process is safety-related. It is inherently a very noisy and dirty process. Therefore, the operator may elect to use ear protection to reduce the noise level and breathing filters to eliminate the inhaling of the metal
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particles produced. Another limitation is that the finished cut may require some cleanup prior to additional welding. Plasma Arc Cutting (PAC) The final thermal cutting method for discussion is plasma arc cutting. This process is similar in most respects to PAW except that now the purpose is to remove metal rather than join pieces together. The equipment requirements are similar except that the power utilized may be much higher than that used for welding. The transferred arc type torch is utilized because of the increased heating of the base metal. For mechanized cutting, not only is the torch water-cooled internally, but the actual cutting may take place beneath a water layer to reduce noise and particulate levels. Its primary application is for the cutting of stainless steels since they cannot be cut effectively by oxyfuel cutting. PAC is also useful for the cutting of carbon steels; however, it may not be economical unless the increased cutting speeds will justify the higher initial cost. The advantages include: the ability to cut metals which cannot be cut with OFC, the resulting high quality cut, and increased cutting speeds for carbon steel. One limitation is that the kerf is generally quite large and the cut edges may not be square. Special techniques, such as water injection, can be used to improve this edge configuration if desired. Another limitation is the high cost of equipment as compared to oxyfuel cutting.
Mechanical Cutting Finally, we should briefly mention some of the mechanical cutting methods utilized in conjunction with welding. These methods include, but are not limited to: shearing, sawing, grinding, milling, turning, shaping, drilling, planing, and chipping. These various methods are used for: joint preparation, weld contouring, cutting of parts to be joined, surface cleaning, and removal of defective welds. As a welding inspector, it is important to understand how these methods are used, as their misapplication may have a degrading effect of the final weld quality. For example, many of these methods employ some type of cutting fluid to aid the machining operation. If these fluids are not completely removed from the weld surfaces, problems such as porosity and cracking may result.
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Summary There are numerous joining and cutting processes which can be used in metal fabrication. The welding inspector can more effectively perform the job if the individual has an understanding of the fundamentals of these various processes. With this knowledge, the welding inspector can spot problems before or when they occur so correction becomes more economical. The information provided in this discussion should give the welding inspector a basis upon which can be built to achieve some level of understanding of welding and cutting processes. This technical basis combined with information gained through practical experience will allow the welding inspector to be better prepared to perform visual inspection of welds.
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API 570 Welding Processes Quiz 1.
What welding process is pictured? a. GTAW b. FCAW c. SMAW d. SAW
2.
What welding process is pictured? a. GTAW b. FCAW c. SMAW d. GMAW
3.
What welding process is pictured? a. GTAW b. FCAW c. SAW d. GMAW
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4.
What welding process is pictured? a. GTAW b. FCAW c. SAW d. GMAW
5.
In the SMAW electrode identification system, a "1" in the third position would mean: a. AC & DCEN b. digging arc with deep penetration c. all position electrode d. both a and b e. none of the above
6.
The electrode coating does which of the following: a. acts as a shielding b. acts as a deoxidation agent c. acts as an alloying and ionizing agent d. all of the above
7.
GMAW is characterized by a ________. a. cut length electrode b. flux core electrode c. coated electrode d. solid wire electrode which is fed continuously through a welding gun
8.
Gasses for GMAW can be: a. inert and reactive b. argon or helium for some applications c. inert, mixed with some type of reactive gas d. all of the above
9.
In the electrode identification for GMAW, what does the "S" stand for,in the electrode ER 70S-1? a. Silicon b. Spray arc c. Solid wire d. none of the above
10.
When using GMAW, the type of metal transfer depends on: a. shielding gas b. current and voltage c. power supply characteristics d. all of the above e. none of the above
11.
Spray transfer is considered to be ________.
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a. b. c. d.
the hottest GMAW welding type transfer the least amount of heating to the base metal the process with the highest deposition rate for the process the process that is a program of exact combination of high and low currents
12.
Globular transfer is considered to be ________. a. the hottest GMAW welding type transfer b. the least amount of heating to the base metal c. the process with excellent deposition rate for the process d. the process that is a program of exact combination of high and low currents
13.
Pulsed arc transfer is considered to be ________. a. the hottest GMAW welding type transfer b. the least amount of heating to the base metal c. the process with the highest deposition rate for the process d. the process that is a program of exact combination of high and low currents
14.
Short circuiting transfer is considered to be ________. a. the hottest GMAW welding type transfer b. the least amount of heating to the base metal c. the process with the highest deposition rate for the process d. the process that is a program of exact combination of high and low currents
15.
GMAW is very sensitive to __________, which tends to leave the metal unprotected during welding. a. wind or drafts which tend to blow the shielding gas away b. ultraviolet light waves c. arc lengths d. all of the above e. none of the above
16.
The ________ process has an electrode that is not intended to be consumed during the welding operation. a. SMAW b. GMAW c. FCAW d. GTAW e. none of the above
17.
GTAW can be performed using which of the following polarities? a. DCEN b. DCEP c. AC d. all of the above e. none of the above
18.
_______ and ______ are the two most commonly used inert gasses
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for the GTAW process. a. CO2 and oxygen b. Argon and helium c. Acetylene and oxygen d. none of the above 19.
One of the problems associated with GTAW is: a. inability to tolerate contamination b. it is a slow process c. tungsten inclusions d. all of the above e. none of the above
20.
The ________ process is characterized by the use of a continuously- fed solid wire electrode which provides an arc that is totally covered by a layer of granular flux. a. SMAW b. GMAW c. FCAW d. GTAW e. none of the above
21.
The biggest advantage of SAW is its ________. a. portability b. ability to weld out of position c. high deposition rate d. ability to produce almost no weld defects
22.
A major problem when using the SAW process is ______. a. high deposition rate b. weld contour c. solidification cracking d. none of these
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API Welding Processes Quiz Answer Key 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.
c d a c c d d d c d a c d b a d d b d e c c
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API 578
Material Verification Program for New and Existing Alloy Piping Systems A AP PII R RP P 557788 FFiirrsstt E Ed diittiioon n –– M Maayy,, 11999999
Summary and Notes The notes and summary information supplied is the thoughts and opinions of ITAC and does not represent API Committee interpretations. The use of “Key Phrases” is intended as a study guide only.
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API RP 578 First Edition - May, 1999
Material Verification Program for New and Existing Alloy Piping Systems Foreword This edition of API RP 578 is a recommended practice, not a code or standard. Key phrase “recommended practice...". 1.0
SCOPE 1.1
General API RP 578 covers recommendations for guidelines for material and quality assurance systems to verify the nominal composition of piping.
1.3
Roles and Responsibilities This section lists the responsibilities and players for implementing a material verification program. Key phrase “responsibilities”.
2
REFERENCES
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3
DEFINITIONS (For the purposes of this standard, the following definitions apply.)
3.1 alloy material: Any metallic material (including welding filler materials) that contains alloying elements such as chromium, nickel, or molybdenum, which are intentionally added to enhance mechanical or physical properties and/or corrosion resistance. 3.2 distributor: A warehousing supplier for one or more manufacturers or suppliers of alloy materials or components. 3.3 fabricator: One who fabricates piping systems or portions of a piping system as defined by ASME B 31.3. 3.4 inspection lot: A group of items or materials of the same type from a common source from which a sample is to be drawn for examination. An inspection lot does not include items from more than one heat. 3.5 Level of examination: The specified percentage of the number of components (or weldments when specified) to be examined in an inspection lot. 3.6 lot size: The number of items available in the inspection lot at the time a representative sample is selected. 3.7 material manufacturer: An organization that performs or supervises and directly controls one or more of the operations that affect the chemical composition or mechanical properties of a metallic material. 3.8 material nonconformance: A positive material identification (PMI) test result that is not consistent with the selected or specified alloy.
3.9 material supplier: An organization that supplies material furnished and certified by a material manufacturer, but does not perform any operation intended to alter the material properties required by the applicable material specification. 3.10 material verification program: A documented quality assurance procedure used to assess metallic alloy materials (including weldments and attachments where specified) to verify conformance with the selected or specified alloy material designated by the owner/user. This program may include a description of methods for alloy material testing, physical component marking, and program record-keeping. 3.11 mill test report: A certified document that permits each component to be identified according to the original heat of material from which it was produced and identifies the applicable material specification (including documentation of all test results required by the material specification). 3.12 owner/user: An owner or user of piping systems who exercises control over the operation, engineering, inspection, repair, alteration, testing, and rerating of those piping systems.. 3.13 positive material identification (PMI) testing: Any physical evaluation or test of a material to confirm that the material which has been or will be placed into service is consistent with the selected or specified alloy material designated by the owner/user. These evaluations or tests may provide either qualitative or quantitative information that is Page 7 - 4
sufficient to verify the nominal alloy composition. 3.14 pressure-containing components: Items that form the pressurecontaining envelope of the piping system. 3.15 random: Selection process by which choices are made in an arbitrary and unbiased manner.
4
3.16 representative sample: One or more items selected at random from the inspection lot that are to be examined to determine acceptability of the inspection lot. 3.17 standard reference materials: Sample materials for which laboratory chemical analysis data are available and are used in demonstrating test instrument accuracy and reliability.
EXTENT OF VERIFICATION Summary This section discusses actual verification of materials including the responsibilities, materials to be verified and control of material storage.
5
MATERIAL VARRIFICATION PROGRAM TEST METHODS Summary This section contains recommendations about the objectives of a PMI program, various test methods, equipment calibration and personnel qualifications.
6
EVALUATION OF PMI TEST RESULTS Summary Section 6 is a discussion of the PMI results, as stated by the owner/user, as well as, a nonconformity program.
7
MARKING AND RECORD-KEEPING
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API RP 578 Quiz 1. API RP 578 covers PMI testing of ____________. A. B. C. D.
new construction and in-service materials new tank construction in-service piping in-service vessels
2. Lot size refers to __________. A. B. C. D.
the number of items available in the inspection lot all materials on the job site the area inside the battery limits the material storage area
3. A mill test report __________. A. B. C. D.
is as good as a PMI test always supersedes a PMI test is better than a PMI test should not be considered a substitute for a PMI test
4. PMI testing of a weld “button” _____________. A. B. C. D.
is the only way to test welding electrodes or wires is a test for the quality of a spot weld will insure the base material is compatible with the stored product may be substituted for PMI testing of an electrode
5. Persons performing PMI must be qualified by ______________. A. training and experience B. ASNT C. AWS D. ASTM
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API 578 Quiz Answer Key 1. 2. 3. 4. 5.
A A D D A
Paragraph 1.1. Paragraph 3.6 Paragraph 4.2.4 Paragraph 4.2.6 Paragraph 5.5
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Welding Terminology
WELD JOINT GEOMETRY AND WELDING TERMINOLOGY Introduction The American Welding Society has long realized the need for standardized terms and definitions for use by those actively involved in the fabrication of welded products. In answer to this need, AWS has published the document AWS A3.0, Standard Welding Terms and Definitions. It was developed by the AWS Committee on Definitions and Symbols to aid in the communication of welding information. The standard terms and definitions published in A3.0 are those that should be used in the oral and written language of welding. While these are the standard, or preferred, terms, they are by no means the only terms used to describe various situations. Since the purpose here is to educate, it is felt to be important to mention some of these common terms, even though they are not preferred terminology. When these terms are mentioned, they will appear in parentheses after the preferred words. While most of the terms used apply to the actual welding operation, it is important for the welding inspector to understand other definitions which apply to other related operations. For example, the welding inspector should understand how to describe the various weld joint configurations and those elements of the fitup process requiring comment. After welding is completed, the welding inspector may need to describe the location of some welding discontinuity which has been discovered. If such a discontinuity requires further attention, it is important that the inspector accurately describe the location of the problem so that the welder will know where the repair is to be made.
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Types of Joints Before welding begins, the welding inspector may be required to evaluate the weld joint configuration and fitup. This is one of the most important aspects of welding inspection, because it is possible to detect problems which require correction. When discovered at this stage, these problems can be corrected more economically. So, when a welding inspector is performing this preliminary inspection, it is necessary that he know the differences between the various types of weld joints. A joint is "the junction of members or edges of members which are to be joined or have been joined." There are five basic types of joints, including: butt, corner, T-, lap, and edge. These five joint types get their names from their basic configuration. The butt joint results when the two members to be joined lie in the same plane and they are connected at their edges. With a corner joint, the two members to be joined lie in perpendicular planes and again, their edges are connected. The T-joint is similar in that the two members lie in perpendicular planes, except, now the edge of one member is joined to the planar surface of the other. In a lap joint configuration, the two members lie in parallel planes, but not the same plane. The joint occurs where the two members overlap each other to form a double thickness region, this area is also referred to as the faying surface. The final joint configuration, the edge, also has the two members lying in parallel planes. With this configuration, the two members lie with their planar surfaces in contact so that the actual welding occurs around the perimeter, or outside, of the joint. Parts of the Weld Joint Once the type of joint has been identified, it may be necessary to further describe the exact configuration required. To do this, the welding inspector must be capable of naming the various features of that particular joint. Some of these elements include: joint root, groove face, root face, root edge, root opening, bevel, bevel angle, groove angle, and groove radius. Depending upon the particular type of joint configuration, these features may take on slightly different shapes. A perfect example of this is the joint root, or "that portion of a joint to be welded where the members approach closest to each other. In cross section, the joint root may be either a point, line, or an area." By definition, groove face is "that surface of a member included in the groove." The root face (also commonly called the land, nose or flat) is "that portion of the groove face adjacent to the joint root." The root edge is defined as "a root face of zero width." These elements are often essential variables for welding procedures as well as production welding, so the welding inspector may be required to actually measure them to judge their compliance with applicable drawings or other documents.
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The root opening is described as "the separation between the workpieces at the joint root." The bevel (also commonly referred to as the chamfer) is "an angular edge preparation." The bevel angle is defined as "the angle formed between the prepared edge of a member and a plane perpendicular to the surface of the member." The groove angle is "the total included angle of the groove between workpieces." For a single-bevel-groove-weld, the bevel angle and the groove angle are equal. The final term, groove radius, applies only to J- and U-groove-welds. It is described as "the radius used to form the shape of a J- or U-groove weld." Normally, a J- or U-groove weld configuration is specified by both a bevel (or groove) angle and a groove radius.
Types of Welds There are numerous welds which can be applied to the various types of joints. According to AWS A3.0, there are 18 basic types of welds utilized for arc welding, including: 1) Square-groove weld 2) Bevel-groove weld 3) V-groove weld 4) J-groove weld 5) U-groove weld 6) Flare-bevel-groove weld 7) Flare-V-groove weld 8) Fillet weld 9) Edge weld 10) Edge-flange weld 11) Corner-flange weld 12) Spot weld 13) Seam weld 14) Plug weld 15) Slot weld 16) Surfacing weld 17) Back weld 18) Backing weld With this variety of groove weld geometries available, the welding fabricator can choose the one which best suits his needs. This choice could be based on considerations such as: accessibility, type of welding process being used, method of joint preparation, and adaptation to particular designs of the structure being fabricated. The first seven categories above refer to different groove configurations. Their names imply what the actual configurations look like when viewed in their cross section. All of these groove weld types can be applied to joints which are welded from a single side or both sides. As would be expected, a single-welded joint is "a fusion welded joint that is welded from one side only." A double-welded joint is "a fusion welded joint that is welded from both sides."
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The next category of weld is the fillet weld. This type is possibly the most used of any of the different welds. An important thing to remember is that a fillet weld is not a type of joint. It is a particular type of weld which can be applied to a lap, T- or corner joint. AWS A3.0 defines a fillet weld as "a weld of approximately triangular cross section joining two surfaces approximately at right angles to each other in a lap joint, T-joint, or corner joint." An edge weld is described as "a weld in an edge joint." Two modifications of the edge weld are utilized for flange welds. A flange weld is "a weld made on the edges of two or more members to be joined, usually light gage metal, at least one of the members being flanged." The two common types are the edge- flange weld and the corner-flange weld. The edge-flange weld has both of the members flanged, while the corner-flange weld is used to join two members where only one of the members is flanged. The next weld type of interest is the surfacing weld. As might be expected, this particular type of weld is applied to the surface of a metal. Normally, the primary reason for this application is to provide some barrier against abrasion or corrosion. Often, this approach is more economical than the use of a full thickness of some more expensive material. AWS A3.0 defines a surfacing weld as "a weld applied to a surface, as opposed to making a joint, to obtain desired properties or dimensions.” The final weld types to be discussed are called back and backing welds. From the names, it is apparent that these welds are meant to be applied to the back side of a weld joint. Although they are applied to the same location, they differ depending upon when they are deposited. AWS A3.0 describes a back weld as "a weld made at the back of a single groove weld," and a backing weld as "backing in the form of a weld." Therefore, a back weld is applied after the front side has already been welded, while the backing weld is deposited before welding the front side. Parts of Completed Welds So far, the discussion has been limited to the description of weld joints and types of weld configurations. However, the welding inspector must also be aware of those terms used to describe conditions or features of completed welds. When a completed weld is being inspected, the inspector must be able to describe the conditions which exist when he is required to report his inspection findings. Therefore, it is appropriate to define the various parts of completed groove and fillet welds, since they constitute the bulk of the weld configurations commonly encountered. The groove weld, regardless of its particular configuration, has several primary components. The first part, the weld face, is "the exposed surface of a weld on the side from which welding was done." The junction between the weld face and the base metal surface is referred to as the weld toe. Opposite the weld face is the weld root. The weld root is defined as "the points, as shown in cross section, at which the back of the weld intersects the base metal surfaces." The root surface is the surface of the weld on the side opposite from where the welding was done. Therefore, the root surface is bounded by the weld root on either side. The face reinforcement (also commonly called weld crown) is "the weld reinforcement at the side of the joint from which welding was done." Conversely,
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the root reinforcement is "the weld reinforcement opposite the side from which welding was done." In both cases, this represents that portion of the weld metal which is above the surface of the base metal. These explanations have assumed that this was a single- welded joint, or all welding was performed from one side. In the case where a double-sided-groove is used, both sides of the joint will have a weld face, and the amount of buildup present on both sides will be referred to as the face reinforcement. Just as groove welds have names for their various parts, there is also standard terminology for the parts of a fillet weld. As with the groove weld, the surface of the weld which the inspector will evaluate is referred to as the weld face. The junctions of that weld face with the base metal are called the weld toes. The furthest penetration of the weld metal into the joint is considered to be the weld root. The distance from the weld toe to the joint root is called the leg. One other feature relevant to a fillet weld which is not noted here is the weld throat. In general, this is the shortest distance through the cross section of the weld. The various types of weld throats will be discussed in more detail when sizing convex and concave fillet welds is examined. Fusion and Penetration Terminology There are also terms relating to the fusion and penetration of the weld metal into the base metal. Although these are features which are difficult for the visual inspector to check without further destructive or nondestructive examination, it is still important to understand what the various terms actually mean. In general, fusion refers to the actual melting together of the filler metal and base metal, or of the base metal only. Penetration is a term which relates to the distance that the weld metal has progressed into the joint. The degree of penetration achieved has a direct effect on the strength of the joint and is therefore related to the weld size. Numerous terms exist which describe the degree or location of either fusion or penetration. During the welding operation, the original groove face is melted such that the final boundary of the weld metal is deeper than the original surface. The groove face is referred to as the fusion face since it will be melted during welding. The boundary between the weld metal and base metal is referred to as the weld interface. The depth of fusion is the distance from the fusion face to the weld interface. The depth of fusion is always measured perpendicular to the fusion face. In all cases, the fusion zone, or "the area of base metal melted as determined on the cross section of a weld" is shown as a shaded area.
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There are also several terms which refer to penetration of the weld. Such descriptions are important because the amount of penetration present has a profound effect on the strength of a weld joint. Root penetration is the distance that the weld metal has melted into the joint beyond the joint root. The joint penetration is the distance from the furthest extension of the weld into the joint to the weld face, excluding any weld reinforcement which may be present. For groove welds, this same length is also referred to as the weld size (also commonly referred to as effective throat). For a groove weld with no additional edge preparation, the root penetration and joint penetration are considered to be equal. Weld Size Terminology For the case of a double-groove weld configuration where the joint penetration is less than complete, the weld size is equal to the sum of the joint penetrations from both sides. That is, the weld size is equal to the E1 plus E2. For a complete penetration groove weld, the weld size will be equal to the thickness of the thinner of the two members joined, since there is no credit given for any weld reinforcement present. To determine the size of a fillet weld, we must first know whether the final weld configuration is convex or concave. Convex means that the weld face exhibits some buildup causing it to appear slightly "humped up." This is referred to as the amount of convexity. Convexity in a fillet weld is synonymous with weld reinforcement in a groove weld. If a weld has a concave profile, it means that its face is "dished in." For both configurations, the fillet weld size is determined by the leg length of the largest isosceles (two legs of equal length) right triangle which can be completely included within the cross section of the weld. So, for the convex fillet weld, the leg and size are equal. However, the size of a concave fillet weld is slightly less that its leg length. There are really three different types of weld throats with which to be concerned: theoretical, effective and actual. The first is the theoretical throat. This is the minimum amount of weld which the designer counts on when a weld size is originally specified. The theoretical throat is described as "the distance from the beginning of the joint root perpendicular to the hypotenuse (side of the triangle opposite the right angle) of the largest right triangle that can be inscribed within the cross section of a fillet weld." The effective throat takes into account any additional joint penetration which may be present. So, the effective throat can be defined as "the minimum distance minus any convexity between the weld root and the face of a fillet weld."
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The final dimension, the actual throat, takes into account both the joint penetration as well as any additional convexity present at the weld face. Technically, the actual throat is "the shortest distance between the weld root and the face of a fillet weld." For a concave fillet weld, the effective throat and actual throat are equal, since there is no convexity present. In all of the above cases, it has been assumed that the fillet welds have equal leg lengths. For an unequal leg fillet welds, the fillet weld size is determined by "the leg lengths of the largest right triangle that can be inscribed within the fillet weld cross section." The welding inspector may also be asked to somehow determine the sizes of other types of welds. One example might be a spot or seam weld, where the weld size is equal to the actual nugget size or diameter. This is simply the length of weld metal joining the two members. For an edge or flange weld, the weld size is equal to the total thickness of the weld from the weld root to the weld face. Weld Application Terminology To complete this discussion of welding terms and definitions, it seems appropriate to mention some of the terminology associated with the actual application of welds. Some welding procedures will refer to these details, so the welding inspector should be familiar with their meanings. The first aspect to be covered is the difference among the terms weld pass, weld bead and weld layer. A weld pass is a single progression of welding along a joint. The weld bead is that weld which results from a weld pass. A weld layer is a single level of weld within a multiple-pass weld. A weld layer may consist of a single bead or multiple beads. When a weld bead is deposited, it could have a different name, depending upon the technique which the welder uses. If the welder progresses along the joint with little or no lateral (sideways) motion, the resulting weld bead is referred to as a stringer bead. A weave bead results when the welder manipulates the electrode laterally as the weld is deposited along the joint. The weave bead is typically wider than the stringer bead. Due to the amount of lateral motion used, the travel speed, as measured along the longitudinal axis of the weld, is less than would be the case for a stringer bead. There are several terms which describe the actual sequence in which the welding is to be done. This is commonly done to reduce the amount of distortion caused by welding. Three common techniques are: backstep sequence, block sequence and cascade sequence. The backstep sequence is a technique where each individual weld pass is deposited in the direction opposite that of the overall progression of welding.
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A block sequence is defined as "a combined longitudinal and cross sectional sequence for a continuous multiple pass weld in which separated increments are completely or partially welded before intervening increments are welded." With the block sequence, it is important that each subsequent layer is slightly shorter than the previous one so that the end of the block has a gentle slope. This will provide the best chance of obtaining adequate fusion when the adjacent block is filled in later. A cascade sequence is described as "a combined longitudinal and cross sectional sequence in which weld passes are made in overlapping layers." This method differs from the block sequence in that now each subsequent pass is longer than the previous one.
Summary While numerous terms have been discussed here, that does not imply that these are the only ones which are applied to welding. This does provide some basis upon which the inspector can begin to understand how to describe a weld or some feature of that weld. As the welding inspector gains experience, he will learn to correlate these "textbook" terms with actual physical characteristics. It is only after working with and using these terms that the welding inspector will gain full understanding of how to describe various welding attributes.
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WELD JOINT GEOMETRY AND WELDING TERMINOLOGY
Quiz 1.
The "dictionary" for welding terms is the AWS document ____________. a. b c. d.
2.
A weld "joint" is defined as ____________. a. b. c. d.
3.
any fillet weld any place a weld can be performed the junction of members or edges of members which are to be joined or have been joined the area which is to be welded
A weld "groove face" is defined as _______________. a. b. c. d.
4.
A 2.4 D 1.1 B 1.11 A 3.0
that surface of a member included in the groove the bevels and landing of a weld joint the bevels and adjacent base metal Both b and c
Which of the following is not a type of weld joint? a. b. c. d.
butt joint corner joint lap joint fillet weld
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5.
The surface of the weld on the side opposite from where the welding was done is called the ______________. a. b. c. d.
6.
The exposed surface of a weld on the side from which welding was done is called the ______________. a. b. c. d.
7.
Fusion Dilution zone Penetration Weld
A weld ________ is a single progression of welding along a joint. a. b. c. d.
10.
Fusion Dilution zone Penetration Weld
________ is a term which relates to the distance that the weld metal has progressed into the joint. a. b. c. d
9.
weld face face reinforcement root surface root opening
_________ refers to the actual melting together of the filler metal and base metal, or the base metal only. a. b. c. d
8.
weld face face reinforcement root surface root opening
layer section area pass
A common practice to reduce distortion caused by welding is ____________. a. b. c. d
backstep sequence weld only on one side preheat one side and weld from the other all of the above
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WELD JOINT GEOMETRY AND WELDING TERMINOLOGY
Answer Key 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
d c a d c a a c d a
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Welding Discontinuities
WELD AND BASE METAL DISCONTINUITIES Introduction One of the most important parts of the welding inspector's job is the actual evaluation of welds to determine their suitability for an intended service. During the various stages of this evaluation, he will be looking for any irregularities in the weld or weldment. These inconsistencies are commonly referred to as discontinuities. In general, a discontinuity is described as any interruption in the uniform nature of some item. Therefore, a bump in a highway could be considered to be a type of discontinuity, because it interrupts the smooth, uniform surface of the pavement. In welding, some of the types of discontinuities to be concerned with are such things as: cracks, porosity, undercut, incomplete fusion, etc. Knowledge of these discontinuities is important to the welding inspector for a number of reasons. First, he will be asked to visually inspect welds to determine the presence of any of these discontinuities. If discovered, the welding inspector must then be capable of describing their nature, location and extent. This information will be required to successfully determine whether or not that discontinuity requires repair, as described in the applicable job specifications. If additional treatment is deemed necessary, the welding inspector must be capable of accurately describing the discontinuity to the extent that it can be satisfactorily corrected by production personnel. Before describing these discontinuities, it is extremely important to understand the difference between a discontinuity and a defect. Too often, people mistakenly use the two terms interchangeably. As a welding inspector, you should strive to realize the distinction between the terms discontinuity and defect. While a discontinuity is some feature which introduces an irregularity in an otherwise uniform structure, a defect is a specific discontinuity which impairs the suitability of that structure for its intended purpose. That is, a defect is a discontinuity of a certain type or which occurs in an amount great enough to render that particular object or structure unsuitable for its intended service.
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In order to determine if a particular discontinuity is actually a defect, there must be some standard which defines the acceptable limits of that discontinuity. When its size or concentration exceeds these limits, it is deemed a defect. Therefore, think of a defect as simply a rejectable discontinuity. So, if some feature is referred to as a defect, it implies that it is rejectable and requires some further treatment to bring it into acceptable limits. Depending on the intended service of the part in question, an existing discontinuity may or may not be considered to be a defect. Consequently, each industry utilizes a specific code or standard which describes the acceptable limits for those discontinuities which could affect the successful performance of various parts. Therefore, the following discussion of weld discontinuities will deal with their characteristics, causes and cures, without specific reference to their acceptability. Only after their evaluation in accordance with an applicable standard can a judgment be made as to whether they are acceptable discontinuities or rejectable defects. However, a general discussion about the effect or criticality of certain discontinuities can be addressed. Such a discussion will help in understanding why certain discontinuities are forbidden, regardless of their size or extent, while the presence of minor amounts of others is considered to be acceptable. One way in which this can be explained relates to the specific configuration of that discontinuity. Configurations of discontinuities can be separated into two general groups: linear and non-linear. Linear discontinuities exhibit lengths which are much greater than their widths. Non-linear discontinuities, on the other hand, have length and width dimensions which are essentially the same. When present in a direction perpendicular to the applied stress, a linear discontinuity represents a more critical situation than does a nonlinear type, because it is more likely to propagate and cause a failure. Another way in which the shape of a discontinuity relates to its criticality, or effect on the integrity of a structure, is its end condition. The end condition simply refers to its specific sharpness. In general, the sharper the end of the discontinuity, the more critical it becomes. This is because a sharper discontinuity is more likely to propagate, or grow. Again, this is also dependent on its orientation with respect to the applied stress. Linear discontinuities are most often associated with sharp end condition. So, if there is a linear discontinuity having a sharp end condition lying transverse to the applied stress, this represents the most dangerous situation with respect to the ability of a member to carry some load. If some of the more common discontinuities were to be rated with respect to the sharpness of their end conditions, starting with the sharpest, they would tend to be: cracks, incomplete fusion, slag inclusions, and porosity. This order coincides with the amounts of these discontinuities permitted by most codes. There are only a few instances in which any amount of cracking is allowed. Incomplete fusion may also be forbidden or at least limited to minor amounts. Most codes will permit the presence of small amounts of slag and virtually all will allow some porosity. Depending on the industry and the intended service, these amounts will vary, but in general the sharper the discontinuity, the more its presence is restricted.
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To further explain the importance of the end condition on the severity of a discontinuity, consider the example of how a crack's propagation could be stopped using a technique which you may have seen performed on some noncritical part. The technique referred to here is the placement of a drilled hole at the end of a crack in some material. While this does not correct the cracking, it may stop its further propagation. This is accomplished because the sharp ends of the crack are rounded sufficiently to reduce the stress concentration to the point that the material can withstand the applied load. A final way in which the criticality of a discontinuity is judged relates to the way in which a part or structure will be loaded during service. For example, if a weld forms a part of some pressure boundary, those discontinuities constituting a significantly long leak path will be most damaging. In the case of a structure which will be loaded in fatigue (i.e. cyclic loading) those discontinuities forming sharp notches on the surface of the structure will cause failure more readily than those beneath the surface. That is because they form a stress riser which tends to concentrate, or amplify, the stresses at that point. Such a stress concentration will result in a localized overload condition even though the stress applied to the full cross section may be low. This can be shown by the example of a piece of welding wire which you would like to break. One way of accomplishing this would be to bend the wire back and forth until it finally broke. However, it may take many cycles to produce this failure. If you were to take a similar piece of welding wire, place it on a hard surface, and strike it with the sharp edge of a chipping hammer, you would produce a sharp notch on the wire's surface. Now, only one or two bends would be necessary to result in the failure of that wire, because the notch represents a significant stress concentration. So, for a structure which must withstand fatigue loading, the surfaces should be free of those discontinuities which provide sharp notches. Consequently, parts subjected to fatigue loading in service are often required to have their surfaces machined to very smooth finishes. Abrupt changes in contour are also avoided. For these types of components, one of the most effective methods of inspection is visual. Therefore, you, as a welding inspector, can play an extremely important role in determining how well these components will behave in service. So, in general, you can judge the suitability of these structures for their intended service simply based on the presence and/or sharpness of any surface discontinuities.
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Weld and Base Metal Discontinuities Having provided this background, let's now discuss some of the more common weld and base metal discontinuities. Those with which will be discussed are listed below. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.
cracks incomplete fusion incomplete penetration slag inclusions porosity undercut underfill coldlap convexity weld reinforcement arc strikes tungsten inclusions spatter laminations lamellar tears dimensional
Cracks The first of these discontinuities to be discussed is the crack. This is appropriate, since the crack is generally considered to be the most critical discontinuity which is covered in this chapter. This criticality is due to the fact that cracks are characterized as being linear as well as exhibiting very sharp end conditions. Since the ends of cracks are extremely sharp, there is a tendency for the crack to grow, or propagate, further if some additional stress is applied. Cracks are initiated when the load, or stress, applied to a member exceeds its tensile strength. In other words, there is an overload condition. While the applied load may not exceed the load carrying ability of some member, the presence of some notch, or stress riser, could cause the localized stress at the tip of the stress riser to exceed the tensile strength of the material. In such a case, cracking could occur at this stress concentration. Therefore, cracking is commonly associated with both surface and subsurface discontinuities which provide such a stress riser. Cracks can be categorized in several different ways. One way of grouping cracks is by characterizing them as either hot or cold cracks. This is an indication of when the cracking occurred, or at least the temperature at which the fracture occurred. This is often a way in which it can decided exactly why a particular crack resulted, since some types of cracks are characteristically either hot or cold cracks.
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Hot cracks occur as the metal solidifies, at some elevated temperature. The propagation of these cracks is considered to be intergranular; that is, the cracks occur between individual grains. If the fracture surfaces of a hot crack are observed, various temper colors indicating the presence of that crack at an elevated temperature may be seen. Cold cracks occur after the metal has cooled to ambient temperature. Those cracks resulting from service conditions would be considered cold cracks. Delayed, or underbead, cracks resulting from entrapped hydrogen would also be categorized as cold cracks. The propagation of cold cracks can be either intergranular or transgranular; that is, either between or through the individual grains, respectively. Cracks can also be described by their direction with respect to the longitudinal axis of the weld. Those lying in a direction parallel to the longitudinal axis are referred to as longitudinal cracks. Similarly, those cracks lying perpendicular to the weld's longitudinal axis are called transverse cracks. These directional references apply to cracks occurring in either the weld or base metals. Longitudinal cracks can result from transverse shrinkage stresses of welding or stresses associated with service conditions. Transverse cracks are generally caused by the longitudinal shrinkage stresses of welding acting on weld or base metals of low ductility. Finally, various types of cracks can further be differentiated between by giving a description of their exact locations with respect to the various parts of the weld. These descriptions include: throat, root, toe, crater, underbead, heat affected zone, and base metal cracks. Throat cracks are so named because they extend through the weld along the weld throat, or the shortest path through the weld's cross section. They are longitudinal cracks and are generally considered to be hot cracks. A throat crack can be observed visually on the weld face, consequently the term centerline crack is often used to describe this condition. Joints exhibiting high restraint transverse to the weld axis are susceptible to this type of cracking, especially in situations where the weld cross section is small. So, such things as thin root passes and concave fillet welds could result in a throat cracks, because their reduced cross sections may not be sufficient to withstand the transverse weld shrinkage stresses. Root cracks are also longitudinal; however, their propagation may be in either the weld or base metal. They are referred to as root cracks because they initiate at the weld root or the root surface of the weld. Like throat cracks, they are generally related to the existence of shrinkage stresses from welding. Therefore, they are usually considered to be hot cracks. Root cracks often result when joints are improperly fitted or prepared. Large root openings, for example, may result in a stress concentration to produce root cracks.
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Toe cracks are base metal cracks which propagate from the toes of welds. Weld configurations exhibiting weld reinforcement or convexity may provide a stress riser at the welds' toes. This, combined with a less ductile microstructure in the heat affected zone increase the susceptibility of the weldment to toe cracks. Toe cracks are generally considered to be cold cracks. The stress causing the occurrence of toe cracks could be the result of either the transverse shrinkage stresses of welding, some applied service stresses, or a combination of the two. Toe cracks occurring in service are often the result of fatigue loading of welded components. Crater cracks occur at the termination point of individual weld passes. If the technique utilized by the welder to terminate the arc does not provide for complete filling of the molten weld puddle, the result could be a shallow region, or crater, at that location. The presence of this thinned area, combined with the shrinkage stresses from welding, may cause individual crater cracks or networks of cracks radiating from the center of the crater. When there is a radial array of crater cracks, they are commonly referred to as star cracks. Since crater cracks occur during the solidification of the molten puddle, they are considered to be forms of hot cracks. Crater cracks can be extremely dangerous because there is a tendency for the crack to propagate further. Although the primary cause of crater cracks relates to the technique utilized by the welder to terminate a weld pass, these cracks can also result from the use of filler metals having flow characteristics which produce concave profiles when solidified. An example of this phenomena is the use of those stainless steel covered electrodes bearing designations ending with "-16" (i.e. E308-16, E309-16, E316-16, etc.). This ending designates a titania type coating which will produce a characteristically flat or slightly concave weld profile. Consequently, when these electrodes are utilized, the welder must take extra precautions and fill the craters sufficiently to prevent crater cracks. The next category of crack is the underbead crack. Although related to the welding operation, the underbead crack is located in the heat affected zone instead of the weld metal. As the name implies, it will characteristically lie directly adjacent to the weld fusion line in the heat affected zone. When cross sectioned, underbead cracks will often appear to run directly parallel to the fusion line of a weld bead. Although most commonly found within the metal, they may propagate to the surface to allow for their discovery during visual inspection. Underbead cracking is a particularly dangerous type of crack because it may not propagate until many hours after welding has been completed. For this reason, underbead cracks are sometimes referred to as delayed cracks. Consequently, for those materials which are more susceptible to this type of cracking, final inspection should not be performed until 48 to 72 hours after the weld has cooled to ambient temperature. High strength steels are particularly susceptible to this type of cracking.
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Underbead cracks result from the presence of hydrogen in the weld zone. The hydrogen could come from the filler metal, base metal, surrounding atmosphere or surface contamination. If there is some source of hydrogen present during the actual welding operation, it may be absorbed by the molten weld metal. When molten, the metal can hold a great deal of this atomic hydrogen. However, once solidified, the metal has much less capacity for the hydrogen. The tendency of the hydrogen is to move through the metal structure to grain boundaries in the heat affected zone. At this point, individual atoms of hydrogen may combine to form hydrogen molecules (H2). This gaseous form of hydrogen requires more volume and is now too large to move through the metal structure. These molecules are now trapped. If the surrounding metal does not exhibit sufficient ductility, this internal pressure created by the trapped hydrogen can result in underbead cracking. The welding inspector should be aware of this potential problem and take precautions to prevent its occurrence. The best technique for the prevention of underbead cracking is to simply eliminate sources of hydrogen when welding susceptible materials. With SMAW, for example, low hydrogen electrodes may be utilized. When specified, they should be properly stored in an appropriate holding oven to maintain this low moisture level. If allowed to remain in the atmosphere for prolonged periods, they may pick up enough moisture to cause cracking. Parts to be welded should be cleaned adequately to eliminate any surface sources of hydrogen. Preheat may also be prescribed to help eliminate this cracking problem. Since the heat affected zone is typically less ductile than the surrounding weld and base metal, cracking may occur there without the presence of hydrogen. In situations of high restraint, shrinkage stresses may be sufficient to result in heat affected zone cracking, especially in the case of brittle materials such as cast iron. A particular type of heat affected zone crack which has already been discussed is the toe crack. Cracking may also be present in the base metal itself. These types of cracks may or may not be associated with the weld. Quite often, base metal cracks are associated with stress risers which result in cracking once the part has been placed in service. Radiographically, cracks appear as fine, rather well-defined dark lines which can be differentiated from other linear discontinuities because their propagation path is not perfectly straight, but tends to wander as the crack follows its path of least resistance through the material's cross section. Incomplete Fusion By definition, incomplete fusion is described as the condition where the weld is not completely fused either to the base metal or to adjacent weld passes. That is, the fusion is less than that specified for a particular weld. Due to its linearity and relatively sharp end condition, incomplete fusion represents a significant weld discontinuity. It can occur at numerous locations within the weld zone. Quite often, incomplete fusion also has associated with it slag inclusions. In fact, the presence of slag due to insufficient cleaning may prevent the fusion from occurring.
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It is important to note that some of the examples above depict incomplete fusion which occurs at the weld root. These conditions are most commonly referred to as incomplete penetration since that term better describes the nature and location of these flaws. However, AWS has decided to refer to any discontinuity where adequate fusion has not been attained as incomplete fusion. Incomplete fusion is most often thought of as being some internal weld flaw. However, it can occur at the surface of the weld as well. Another common term for incomplete fusion is cold lap. This term is often used to describe incomplete fusion between the weld and base metal or between individual weld passes. Incomplete fusion can result from a number of conditions or problems. Probably the most common cause of this discontinuity is the improper manipulation of the welding electrode by the welder. Some processes are more prone to this problem because there is not enough concentrated heat to adequately melt and fuse the metals. For example, when using short circuiting transfer GMAW, the welder must concentrate on directing the welding arc at every location of the weld joint where fusion is required. Otherwise, there will be areas which do not exhibit the proper amount of melting, and therefore fusion. In other situations, the actual configuration of the weld joint may limit the amount of fusion which can be attained. Such things as insufficient groove angles and excessive root faces could result in incomplete fusion. Finally, extreme contamination, including mill scale and tenacious oxide layers, could also prevent the attainment of complete fusion. On a radiograph, incomplete fusion will appear as darker density lines which are generally straighter than the images of either cracks or elongated slag. The lateral position of these indications on the film will be a hint as to their actual depth. Incomplete Penetration According to AWS A3.0, incomplete penetration is a nonstandard term. However, as indicated in the discussion of incomplete fusion, incomplete fusion which occurs at the weld root is often referred to as incomplete penetration. So, although incomplete penetration is not the standard terminology, it actually better describes the nature and location of this type of discontinuity. Another way to think of the difference is that incomplete penetration will be related to the root face of the joint. It describes the situation where the weld metal has not completely progressed into the weld root to fuse with the existing root face. Since penetration terminology relates to the weld size, an incompletely penetrated joint will not have the required effective throat, or cross section to transmit the applied loads from one member to the other. Therefore, it is important for the welding inspector to understand what is meant by the term incomplete penetration since it will often be used to describe incomplete fusion at the weld root.
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There is another AWS term, partial joint penetration, which describes the situation where a portion of the weld joint is intentionally left unfused, or penetrated. So, incomplete penetration, or incomplete fusion, should only be applied in cases where the intent was to provide a weld joint having complete penetration or fusion. Incomplete penetration can be caused by the same conditions which result in incomplete fusion; that is, improper technique, improper joint configuration, or excessive contamination. The radiographic image caused by incomplete penetrations will typically be a dark, straight line. It will usually be much straighter than incomplete fusion because it is associated with the original weld preparation at the root. It will normally be centered in the width of the weld. Slag Inclusions Slag inclusions, as the name implies, are regions within the weld cross section or at the weld surface where the molten flux used to protect the molten metal is mechanically trapped within the solidified metal. This solidified flux, or slag, represents a portion of the weld's cross section where the metal is not fused to itself. This can result in a weakened condition which could impair the serviceability of the component. Although slag inclusions are normally thought of as being totally contained within the weld cross section, they are sometimes observed at the surface of the weld as well. Like incomplete fusion, slag inclusions can occur between the weld and base metal or between individual weld beads. In fact, slag inclusions are often associated with incomplete fusion. Slag inclusions can only result when the process being used employs some type of flux shielding. They are most often caused by improper techniques used by the welder. Such things as improper manipulation of the welding electrode and insufficient cleaning between passes can result in the presence of slag inclusions. Often, the improper manipulation of the electrode or incorrect welding parameters could result in undesirable weld profiles which could then hinder cleaning of the slag between passes. Subsequent welding would then cover the trapped slag to produce slag inclusions. Since the density of slag is much less than that of metals, slag inclusions will appear on a radiograph as relatively dark indications, having rather irregular shapes.
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Porosity AWS A3.0 describes porosity as cavity type discontinuities formed by gas entrapment during solidification. Therefore, porosity can be thought of as being voids or gas pockets within the solidified weld metal. Due to its characteristically spherical shape, porosity is normally considered to be the least dangerous discontinuity. However, in cases where a weld must form some pressure boundary to contain a gas or liquid, porosity might then be considered to be more dangerous. This is due to the fact that the porosity might provide a leak path having some significant length. Like cracking, there are several different names given to specific types of porosity. They refer, in general, to the relative locations of several pores or the specific shape of the individual pores. Therefore, such names as uniformly scattered porosity, cluster porosity, linear porosity, and piping porosity are used to better define the occurrence of porosity. In cases where only a single gas pocket is found, it will commonly be described as an isolated pore. Uniformly scattered porosity refers to numerous pores which occur throughout the weld in no particular pattern. Cluster porosity and linear porosity, however, refer to specific patterns of several pores. Cluster porosity describes a number of pores grouped together while the term linear porosity refers to a number of pores which are grouped in a straight line. With these types, the pores are usually spherical in shape. However, with piping porosity, the pores are elongated. For this reason, they may be referred to as elongated or wormhole porosity. Piping-type porosity represents the most dangerous condition if liquid or gas containment is the primary function of the weld, because these elongated pores represent a more significant length of leak path. This condition may also be referred to as a pockmark. Such a condition results when gases are trapped between the molten metal and solidified slag. One situation in which this phenomenon can occur is when the depth of granular flux utilized for SAW is excessive. When this occurs, the weight of the flux may be too great to permit the gas to escape properly. Porosity is normally caused by the presence of contaminants or moisture in the weld zone which decompose due to the welding heat and form gases. This contamination or moisture could come from the electrode, the base metal, the shielding gas, or the surrounding atmosphere. However, variations in the welding technique could also cause this porosity. An example would be the use of an excessively long arc during SMAW with a low hydrogen type electrode. Another example would be the use of excessively high travel speeds with SAW to result in piping porosity. Therefore, when porosity is encountered, it is a signal that some aspect of the welding operation is out of control. It is then time to investigate further to determine what factor, or factors, are responsible for the presence of this weld discontinuity. When porosity is shown on a weld radiograph, it will appear as a well-defined dark region, because it represents a significant loss of material density. It will normally appear as a round indication except in the case of piping porosity. This type of porosity will have a tail associated with the rounded indication.
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Undercut Undercut is a surface discontinuity which occurs in the base metal directly adjacent to the weld. It is a condition in which the base metal has been melted away during the welding operation and there was insufficient filler metal deposited to adequately fill the resulting depression. The result is a linear groove in the base metal which may have a relatively sharp configuration. Since it is a surface condition, it is particularly dangerous for those structures which will be loaded in a fatigue manner. It is interesting to note that for groove welds, the undercut may occur at either the face or root surface of the weld. The visual appearance of undercut at a fillet weld has a definite shadow produced by the undercut when the illumination is properly positioned. Experienced welding inspectors understand this phenomenon and utilize techniques such as laying a flashlight on the base metal surface to result in a shadow being cast in any location where undercut exists. Another technique is to perform final visual inspection of the weldment after painting, especially when the paint being used is a light color such as white or yellow. When viewed under normal lighting, the shadows cast by the presence of undercut are much more pronounced. The only problem with this technique is that the paint must be removed from the undercut area prior to any repair welding to prevent the occurrence of other discontinuities such as porosity. Undercut is normally the result of improper welding technique. More specifically, if the weld travel speed is excessive, there may not be sufficient filler metal deposited to adequately fill depressions caused by the melting of the base metal adjacent to the weld. Undercut could also result when the welding heat is too high, causing excessive melting of the base metal. When noted on a radiograph, undercut will appear as a dark, fuzzy indication at the edge of the weld reinforcement. Underfill Underfill, like undercut, is a surface discontinuity which results in a loss of material cross section. However, underfill occurs in the weld metal of a groove weld whereas undercut is found in the base metal adjacent to the weld. In simple terms, underfill results when there is not sufficient filler metal deposited to adequately fill the weld joint. Like undercut, underfill can occur at both the face and root surfaces of the weld. Underfill at the weld root of pipe welds is sometimes referred to as suckback, because it can be caused by excessive heating of the root pass during deposition of the second pass (or hot pass). As with undercut, when the lighting is properly oriented, there is a shadow produced because of the surface depression.
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The primary cause of underfill is the technique employed by the welder. Excessive travel speeds do not allow sufficient filler metal to be melted and deposited to fill the weld zone to the level of the base metal surface. Coldlap Another surface discontinuity which can result from improper welding techniques is coldlap. Coldlap is described as the protrusion of weld metal beyond the weld toe or weld root. It appears as though the weld metal overflowed the joint and is laying on the adjacent base metal surface. Due to its characteristic appearance, coldlap is sometimes referred to as rollover. As was the case for both undercut and underfill, coldlap can occur at either the weld face or weld root of groove welds. Once again, there is a definite shadow cast when the lighting is properly oriented. Coldlap is considered to be a significant discontinuity since it can result in a sharp notch at the surface of the weldment. Further, if the amount of overlap is great enough, it could hide a crack which may propagate from this stress riser. The occurrence of coldlap is normally due to an improper technique utilized by the welder. That is, if the welding travel speed is too slow, the amount of filler metal melted will be in excess of that amount required to sufficiently fill the joint. The result is that this excessive metal simply lays on the base metal surface without fusing. Some types of filler metals are more prone to this type of discontinuity since, when molten, they are too fluid to resist the forces of gravity. Therefore, they may only be used in positions in which gravity will tend to hold the molten metal in the joint. Convexity This particular weld discontinuity applies only to fillet welds. Convexity refers to the amount of weld metal buildup on the face of the fillet weld. By definition, it is the maximum distance from the face of a convex fillet weld perpendicular to a line joining the weld toes. Within certain limits, convexity is not damaging. In fact, a slight amount of convexity is desirable from a fillet weld strength standpoint. However, when the amount of convexity exceeds some limit, this discontinuity becomes a significant flaw. The fact that additional weld metal is present is not the real problem, unless one considers the economics of depositing more filler metal than is absolutely necessary. The real problem created by the existence of excess convexity is that the resulting fillet weld profile now has sharp notches present at the weld toes. These notches can produce stress risers which could weaken the structure, especially when that structure is loaded in fatigue. Therefore, excessive convexity can be corrected by either removing excess metal from the fillet weld face or by depositing additional weld metal at the weld toes to provide a smoother transition between the weld and base metals.
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The solution to the problem where the convexity present on a reinforcing fillet weld resulted in a stress riser which caused a fatigue crack to initiate during service was to prescribe machining to provide a concave profile which eliminated the stress concentration. Convexity results when welding travel speeds are too slow or when the electrode manipulation is improper. The result is that excess filler metal is deposited and it does not properly wet the base metal surfaces. The presence of contamination on the base metal surface or the use of shielding gases which do not adequately clean away these contaminants can also result in this undesirable fillet weld profile. Weld Reinforcement Weld reinforcement is similar to convexity except that it describes a condition which can only be present in a groove weld. Weld reinforcement is described as that weld metal in excess of the amount required to fill a joint. Two other terms, face reinforcement and root reinforcement, are specific terms which describe the presence of this reinforcement on a particular side of the welded joint. As the names imply, face reinforcement occurs on the side of the joint from which welding was done and root reinforcement occurs on the opposite side of the joint. For a weld joint welded from both sides, the reinforcement on both sides is described as the face reinforcement. Like convexity, the problem associated with this discontinuity lies with the sharp notches that are created instead of the fact that there is more weld metal present than is necessary. The greater the amount of weld reinforcement, the more severe the notches. As the reinforcement angle increases (caused by an increase in the amount of weld reinforcement) there is a drastic decrease in the fatigue resistance of the weld joint. Most codes prescribe maximum limits for the amount of weld reinforcement permitted. However, simply reducing the amount of weld reinforcement does not really improve the situation. Only after performing blend grinding to increase the weld reinforcement angle is the situation really improved. Simple grinding to remove the top of the weld reinforcement does nothing to decrease the sharpness of the notches at the weld toes. Excessive weld reinforcement results from the same reasons a given for convexity, with the actual welding technique being the predominant cause.
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Arc Strikes The presence of arc strikes represents a very dangerous base metal discontinuity. Arc strikes (or arc burns) result when the arc is initiated on the base metal surface away from the weld joint, either intentionally or accidentally. When this occurs, there is a localized area of the base metal surface which is melted and then rapidly cooled due to the massive heat sink created by the surrounding base metal. On certain materials, especially high strength steels, this can produce a localized heat affected zone which may contain martensite. If this brittle microstructure is produced, the tendency for cracking could be great. Numerous failures of structures and pressure vessels can be traced to the presence of a welding arc strike which provided a crack initiation site to result in a catastrophic failure. Arc strikes can provided a crack initiation site which results in the ultimate failure of the specimen. Arc strikes are normally caused by improper welding techniques. Welders should be warned of the dangers of arc strikes. Due to the danger they pose, arc strikes should never be permitted. The welder should not be performing production welding if he insists on initiating the welding arc outside of the weld joint. So, it becomes a matter of discipline. Improper connection of the ground clamp to the work can also result in the production of arc strikes. Another important note applies to the inspection of welds using the prod type magnetic particle method. Since this method relies on the conduction of electricity through the part to produce the magnetic field, the possibility exists that arc strikes could be produced during the inspection if there is not adequate contact between the prods and the metal surface. Although not as severe as welding arc strikes, these arc burns could also produce harmful effects. Tungsten Inclusions Tungsten inclusions are almost always associated with the GTAW process, which utilizes a tungsten electrode to produce an arc, and therefore the heat for the welding. If the tungsten electrode makes contact with the molten puddle, the arc could go out and the molten metal can solidify around the tip of the electrode. Upon removal, the tip of the electrode will most likely break off and could be included in the final weld if not removed by grinding. Tungsten inclusions could also result when the welding current being used for GTAW is in excess of that recommended for a particular diameter of electrode. In such a case, the current density may be great enough that the electrode starts to decompose and pieces may be deposited in the weld metal. This could also occur if the welder does not properly grind the point on the tungsten electrode. If the grinding marks are oriented such that they form rings around the electrode instead of being aligned with its axis, they could form stress risers which might cause the tip of the electrode to break off preferentially.
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Other reasons for the occurrence of tungsten inclusions include: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
contact of filler metal with hot tip of electrode; contamination of the electrode tip by spatter; extension of electrodes beyond their normal distances from the collet, resulting in overheating of the electrode; inadequate tightening of the collet; inadequate shielding gas flow rates or excessive wind drafts resulting in oxidation of the electrode tip; use of improper shielding gas; defects such as splits or cracks in the electrode; use of excessive current for give size electrode; improper grinding of the electrode; or use of too small of an electrode.
Tungsten inclusions are seldom found on the surface of the weld unless the welding inspector has the opportunity to look at an intermediate pass after a piece of tungsten has been deposited. The primary way in which tungsten inclusions are revealed is through the use of radiography. Since tungsten has a greater density than steel or aluminum, it will show up as a definite light area on the radiographic film. Spatter AWS A3.0 describes spatter as metal particles expelled during fusion welding that do not form a part of the weld. We more commonly think of those particles which are actually attached to the base metal adjacent to the weld. However, particles which are thrown away from the weld and base metal are also considered to be spatter. For that reason, another definition might be those particles of metal which comprise the difference between the amount of metal melted and the amount of metal actually deposited in the weld joint. In terms of criticality, spatter may not be of great concern. However, large globules of spatter may have sufficient heat to cause a localized heat affected zone on the base metal surface similar to the effect of an arc strike. Also, the presence of spatter on the base metal surface could provide a localized stress riser which could cause problems during service. The presence of this stress concentration along with a corrosive environment resulted in a form of stress corrosion cracking known as caustic embrittlement. When spatter is present, however, it does detract from the otherwise pleasing appearance of a satisfactory weld.
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Another feature of spatter which could result in problems has to do with the irregular surface which is produced. During inspection of the weld using various nondestructive methods, the presence of spatter could either prevent the performance of a valid test or produce irrelevant indications which could mask real weld flaws. For example, the presence of spatter adjacent to a weld may prevent adequate coupling of the transducer during ultrasonic testing. Also, spatter could cause problems for both the performance and interpretation of magnetic particle and penetrant testing. Spatter can result from the use of high welding currents which can cause excessive turbulence in the weld zone. Some welding processes are considered to characteristically produce greater amounts of spatter than others. For example, short circuiting and globular transfer GMAW tend to produce more spatter than the use of spray transfer. Another feature which will control the amount of spatter produced is the type of shielding gas used for GMAW and FCAW. The use of argon mixtures will reduce the amount of spatter compared to the amount produced when straight CO2 shielding gas is utilized. Lamination This particular discontinuity is a base metal flaw. Laminations result from the presence of nonmetallic inclusions which occur in steel when it is being produced. These inclusions are normally forms of oxides which are produced when the steel is still molten. During subsequent rolling operations, these inclusions become elongated to form stringers. If these stringers are particularly large, they are referred to as laminations. The most massive form of lamination arises from pipe which develops in the upper part of the steel ingot during the final stages of solidification, and which, on infrequent occasions, is not completely cropped off the ingot during rolling to plate or bar. The pipe cavity usually contains some complex oxides, which are rolled out within the laminations. The heat of fusion joining is sufficient to remelt the stringers in the zone immediately adjacent to the weld, and the ends of the stringers may either fuse or they may open up. Laminations may also show up during thermal cutting, where the heat of the cutting operation may be sufficient to open the stringers to the point that they can be visually observed. Another term related to laminations is a delamination. This simply refers to a particular lamination which exhibits some visual separation between layers instead of being a very tight void. Laminations may or may not present a dangerous situation, depending on the way in which the structure is loaded. If the stresses are acting on the material in a direction perpendicular to the lamination, it will severely weaken the structure. However, laminations oriented parallel to the applied stress, may not cause great concern. If a lamination is present on the surface of a weld preparation, it could cause further problems during welding. In such a case, weld metal cracks could propagate from those laminations due to the stress concentration which results.
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Another problem related to the presence of laminations open to the groove face is that they are prime sites for the accumulation of hydrogen. So, during welding this hydrogen could be included in the molten metal and provide a necessary element for the occurrence of underbead cracking. Since laminations are the result of the steel making process itself, there is little that can be done to prevent their occurrence. Purchasing steels having low levels of contaminants will drastically reduce the tendency toward the presence of laminations. However, the welder and welding inspector can do little to prevent their occurrence. About all that can be done is to perform an adequate visual and/or nondestructive examination to reveal the presence of laminations before a piece of laminated material is included in a weldment. The best method for the discovery of laminations other than visual inspection is the use of ultrasonic testing. Radiography will not reveal laminations because there is no change in the radiographic density of a metal even if it is laminated. To illustrate this, imagine the radiography of two 1/4 inch plates place one on top of the other compared to a single 1/2 inch plate. Review of the film would reveal no difference in density, because the radiation is still passing through the same total thickness of metal. Lamellar Tear Another base metal discontinuity of importance is the lamellar tear. It is described as a terrace-like fracture in the base metal with a basic orientation parallel to the rolled surface. Lamellar tears occur when there are high stresses in the throughthickness direction resulting from welding shrinkage. The tearing always lies within the base metal, usually outside the heat affected zone and generally parallel to the weld fusion boundary. Lamellar tearing is a discontinuity most directly related to the actual configuration of the joint. Therefore, those joint configurations in which the shrinkage stresses from welding are applied in a direction which tends to pull the rolled material in its through-thickness or z-axis direction will be more susceptible to lamellar tearing. When a metal is rolled, it will characteristically exhibit lower strength and ductility in this direction as compared to its properties in the longitudinal and transverse directions. Other factors affecting a material's susceptibility to lamellar tearing are its thickness and the degree of contaminants present. The thicker the material and the higher the inclusion content, the greater the possibility of experiencing lamellar tearing. For the onset of lamellar tearing, three conditions must exist simultaneously. They are: stress in the through-thickness direction, susceptible joint configuration, and material having a high inclusion content. So, to prevent the occurrence of lamellar tearing, any one of these elements must be eliminated.
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Since this discontinuity is so closely related to the actual configuration of the weld joint, the experienced welding inspector should be able to spot those situations in which lamellar tearing may occur. Once that is recognized, there is a good possibility that the problem can be avoided. Dimensional Up to this point, all of the discontinuities discussed could be classified as structural type flaws. However, there is another group of discontinuities which can be classified as dimensional irregularities. Dimensional discontinuities are simply size and/or shape imperfections. These irregularities can occur in the welds themselves or in the overall welded structure. Since dimensional discontinuities could render a structure unsuitable for its intended service, they must be considered and checked by the welding inspector. This inspection could consist of the measurement of weld sizes and lengths to assure that there is sufficient weld metal to transmit the applied loads. Other measurements should be made of the entire weldment to assure that the heat of welding has not caused excessive distortion or warpage. Summary Imperfections may exist in the weld and/or base metal. They are generally described as discontinuities. If a certain discontinuity is of sufficient size, it may render a structure unfit for its intended service. Codes normally dictate the permissible limits for discontinuities. Those greater than these limits are termed defects. Defects are discontinuities which require some corrective action. Discontinuity severity is based on a number of factors, including: whether it is linear or nonlinear, the sharpness of its ends, and whether it is open to the surface or not. Discontinuities exist in a number of different forms, including: cracks, incomplete fusion, incomplete penetration, slag inclusions, porosity, undercut, underfill, coldlap, convexity, weld reinforcement, arc strikes, tungsten inclusions, spatter, laminations, lamellar tears, seams/laps, and dimensional. By knowing how these discontinuities can form, the welding inspector may be successful at spotting these causes and prevent the problem from occurring.
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Weld and Base Metal Discontinues Quiz 1.
One of the most important parts of the welding inspector's job is the actual evaluation of welds to determine _______. a. b. c. d. e.
2.
A ________ is some feature which introduces an irregularity in an otherwise uniform structure. a. b. c. d.
3.
defect fault discontinuity none of the above
A ______ is a feature which impairs the suitability of that structure for its intended purpose. a. b. c. d.
4.
their suitability for an intended service appearance rating all of the above none of the above
defect fault discontinuity none of the above
Generally, ________ are considered to be the most critical discontinuity. a. b. c. d.
undercut cracks overlap porosity
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5.
__________ is described as the condition where the weld is not completely fused either to the base metal or to adjacent weld passes. a. b. c. d.
6.
________ describes the situation where the weld metal has not completely progressed into the weld root to fuse with the existing root face. a. b. c. d.
7.
Crack Lamination Porosity Undercut
A discontinuity that appears as though the weld metal overflowed the joint and is laying on the adjacent base metal surface is called ________. a. b. c. d.
10.
Incomplete penetration Incomplete fusion Overlap none of the above
________ is defined as a cavity type discontinuity formed by gas entrapment during solidification. a. b. c. d.
9.
Incomplete penetration Incomplete fusion Porosity none of the above
_________ are regions within the weld cross section or at the weld surface where the molten flux is mechanically trapped within the solidified metal. a. b. c. d.
8.
Incomplete penetration Incomplete fusion Porosity none of the above
incomplete penetration incomplete fusion overlap none of the above
Which of the following is true about laminations? a. b. c. d. e.
a base metal flaw result from the presence of nonmetallic inclusions which occur in steel were formed when the steel was produced all of the above none of the above
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Weld and Base Metal Discontinues Answer Key 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
a c a b b a d c c d
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ASME Section IX
API 570 ASME Section IX ASME Section IX was developed to provide a common location for welding qualifications for the ASME Codes. The intent of Section IX is to provide information on the qualifications of welding procedures and welding personnel for the new construction of boilers and pressure vessels. Section IX is now referenced by other codes such as API 570 and most other API Standards. The organization of Section IX is described in the introduction. Article I is the general article and contains information relative to the remainder of the book. The paragraphs in Article I are numbered QW-100. Article I contains the acceptance criteria, types of tests, etc. Article II deals with welding procedure qualifications. The paragraphs in Article II are numbered QW-200. Article III provides the information needed to qualify welders and operators. The paragraphs in Article III are numbered QW-300. Article IV is titled Welding Data, this article contains the variables, tables and figures used to qualify personnel and procedures. NOTE: Do not go to Article IV unless one of the other articles references you there. Article V, Standard Welding Procedure Specifications (SWPS). This section gives the details for allowing the use of prequalified procedures , as outlined by the American Welding Society. The forward of Section IX contains the following information: Directions for submitting interpretations to ASME, the effective dates of addenda, (Addenda becomes mandatory six months after issue.) and Code cases. Section IX is used to qualify procedures and personnel. The following welding processes are addressed by Section IX: OFW SMAW SAW GMAW FCAW GTAW PAW ESW EGW EBW SW
Oxyfuel Welding Shielded Metal Arc Welding Submerged Arc Welding Gas Metal Arc Welding Flux Core Arc Welding Gas Tungsten Arc Welding Plasma Arc Welding Electroslag Welding Electrogas Welding Electron Beam Welding Stud Welding
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Section II, Part C is the part of Section II that describes welding materials. Section II, Part C, describes: The Processes that may be used with each electrode, recommended storage information, an explanation of the AWS symbols, positions to be used with electrodes and recommended polarity and current. A welding procedure shows compatibility of: Base metals Filler metals Processes Technique When writing a procedure, a good method to use would be to write a sample procedure, weld a test coupon, prepare the test specimen and test them, evaluate the results and document them on and certify the PQR. Considerations involved when writing a procedure include: Economy, the compatibility of the base and weld metal, metallurgical and mechanical properties of the weld, heat treatment requirements, service requirements, welder’s ability and equipment available. The manufacturer must qualify the WPS, maintain the WPS and PQR while welding is being performed and provide a listing of all procedures that may be used on code items. The code forms provided in Section IX are not mandatory, any form may be used provided all the required variables are addressed. The general approaches to procedure qualification is usually in one of two forms: Prequalified procedures These are AWS welding procedures used only for structural welding and do not require testing. The user is limited to specific weld joints and specific weld processes (see AWS D 1.1). ASME Section IX, 2001 Edition, Paragraph QW-100.1 now allows AWS Standard Welding Procedure Specifications (SWPS), as listed in Appendix E or in accordance with Article V. Procedure qualification testing These are API and ASME requirements. Both require actual welding to be performed and destructively tested. ASME procedure qualification testing uses a listing of essential variables in the creation of weld procedures. Essential variables are those in which a change is considered to affect the mechanical properties of the weldment, and shall require requalification of the WPS, ASME IX Paragraph QW - 251.2. Under ASME rules the welding procedure begins with the creation of the WPS. This information is taken from ASME IX and outlines the ranges of materials, electrodes
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and other general aspects. Then the PQR is created, performed and tested and used as proof for the WPS. The WPS can have many supporting PQRs. The basic steps in qualifying a WPS are as follows: • Write a sample around construction parameters and Code variables (QW-250) • Establish a test coupon size (QW-451) • Weld the test coupon using the parameters established. • Monitor all variables and record at least the essential variables on the PQR. If notch toughness is a requirement, a supplementary essential variable must be recorded. • Cut the coupons into specimens (QW-462). • Make the required tests per QW-451. • Evaluate the results against the appropriate criteria found in Article I. • If acceptable, certify the PQR • Approve the WPS for use on Code piping or other Code applications. • Release the approved WPS and PQR for production. The required tests for procedure qualifications are described in QW-202. This paragraph requires 2 tensile tests and 4 bend tests minimum for groove weld qualification. Table QW-451 provides information on coupon size, ranges and test requirements for groove weld qualification. QW-451.1 GROOVE-WELD TENSION TESTS AND TRANSVERSE-BEND TESTS Range of Thickness T of Base Metal Qualified, in. [Note (1)]
Thickness t of Deposited Weld Metal Qualified, in. [Note (1)]
Type and Number of Tests Required Tension and Guided-Bend Tests [Note (4]
Thickness T of Test Coupon Welded, in.
Min.
Max.
Max.
Tension Side Bend Face Bend Root Bend QW-150 QW-160 QW-160 QW-160
Less than 1/16
T
2T
2t
2
...
2
2
1/16 to 3/8, include.
1/16
2T
2t
2
Note (3)
2
2
Over 3/8, but less than 3/4
3/16
2T
2t
2
Note (3)
2
2
3/4 to less than 1 1/2 3/4 to less than 1 1/2
3/16 3/16
2T 2T
2t when t < 3/4 2t when t > 3/4
2 (5) 2 (5)
4 4
... ...
... ...
1 1/2 and over 1 1/2 and over
3/16 3/16
8 (2) 8 (2)
2t when t < 3/4 8 (2) when t > 3/4
2 (5) 2 (5)
4 4
... ...
... ...
NOTES: (1) See QW-403 (.2, .3, .6, .9, .10), QW-404.32, and QW-407.4 for further limits on range of thickness qualified. Also see QW-202 (.2, .3, .4) for allowable exceptions. (2) For the welding processes of QW-403.7 only; otherwise per Note (1) or 2T, or 2t, whichever is applicable. (3) Four side-bend tests may be substituted for the required face- and root-bend tests, when thickness T is 3/8 in. and over. (4) For combination of welding procedures, see QW-200.4. (5) See QW-151 (.1, .2, .3) for details on multiple specimens when coupon thicknesses are over 1 in.
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Locations of weld specimens from plate procedure qualification.
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Locations of weld specimens from pipe procedure qualification.
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Weld procedure specimens, guided bends are also used for welder qualification tests.
Square
Tensile Specimens
Round
Guided Bends Face
Root
Side
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The tests commonly required by ASME Section IX are: Tensile Bends Face Root Side Table QW -451 is the Procedure qualification thickness limits and test specimens requirements. Each groove weld must pass tension tests and transverse bend tests. This table is where the requirements for testing are listed.. After the procedure qualification testing the Welding Inspector must check production welding to ensure welds are being made in compliance with the approved and tested weld procedure. Remember the weld procedure is proof that the weld can be successfully made. The general sequence for procedure qualification testing is as follows: • Select welding variables (write the WPS and PQR) • Check equipment and materials for suitability • Monitor weld joint fit-up as well as actual welding, recording all important variables and observations • Select, identify and remove required test specimens • Test and evaluate specimens • Review test results for compliance with applicable code requirements • Release approved procedure for production • Qualify individual welders in accordance with this procedure • Monitor production welding for procedure compliance
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QW-482 SUGGESTED FORMAT FOR WELDING PROCEDURE SPECIFICATIONS (WPS) (See QW-200.1, Section IX, ASME Boiler and Pressure Vessel Code) Company Name: Welding Procedure Specification No. Revision No. Welding Process(es):
By: Supporting PQR No.(s)
Date: Date: Type(s):
Automatic, Manual, Machine, or Semi-Auto
JOINTS (QW-402) Joint Design Backing (Yes) Backing Material (Type)
Details (No) (Refer to both backing and retainers)
Metal Nonmetalic
Nonfusing Meal Other
Sketches, Production Drawings, Weld Symbols or Written Description should show the general arrangement of the parts to be welded. Where applicable, the root spacing and the details of weld groove may be specified. (At the option of the Mfgr., sketches may be attached to illustrate joint design, weld layers and bead sequence, e.g., for notch toughness procedures, for multiple process procedures, etc.)
*BASE METALS (QW-403) P-No. Group No. OR Specification type and grade to Specification type and grade OR Chem. Analysis and Mech. Prop. to Chem. Analysis and Mech. Prop. Thickness Range: Base Metal: Groove Pipe Dia. Range: Groove Other:
to P-No.
Group No.
Fillet Fillet
*FILLER METALS (QW-404) Spec. No. (SFA) AWS No. (Class) F-No. A-No. Size of Filler Metals Weld Metal Thickness Range: Groove Fillet Electrode-Flux (Class) Flux Trade Name Consumable Insert Other *Each base metal-filler metal combination should be recorded individually
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Sample Procedure Using SMAW variables the following represents a sample welding procedure. This procedure will be written under “ideal conditions”. The production information is as follows: •
A piping system is under construction using welding procedures qualified to ASME Section IX.
•
The pipe wall is 1 inch thick.
•
The base material is SA-106-B.
•
Filler material will be F-3 for the root pass and F-4 for the fill.
•
There are no special service restrictions
The first part is general information supplied by the writer. a detailed sketch of the joint should be included in the space provided or on attached sheets. (QW402.1)
«Base Metals The P-No. is 1 to 1 (See QW-403.1) The Specification, Type and Grade: SA 106 Grade B (Supplied Example) Thickness Range: (QW-403.7 and QW-403.8) Pipe Diameter Range: 2 7/8 inch Outside Diameter and over (QW-452.3)
«Filler Metals (QW-404.4) SFA-5.1 &5.5 (QW-432) AWS No. E-6010 (Supplied Example)
AWS No. E-7018 (Supplied Example)
F-No.: 3 (QW-432)
F-No.: 4 (QW-432)
Weld Metal Thickness Range: (QW-451.1)
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QW-482 (Back) WPS No.
POSITIONS (QW-405)
Rev.
POSTWELD HEAT TREATMENT (QW-407)
Position(s) of Groove Welding Progression: Up Position(s) of Fillet
Temperature Range Time Range
Down
GAS (QW-408) PREHEAT (QW-406)
Percent Composition
Preheat Temp. - Min. Interpass Temp. - Max. Preheat Maintenance
Gas(es)
(Mixture)
Flow Rate
Shielding
(Continuous or special heating where applicable should be recorded)
Trailing Backing
ELECTRICAL CHARACTERISTICS (QW-409) Current AC or DC Amps (Range)
Polarity Volts (Range)
(Amps and volts range should be recorded for each position, and thickness, etc. This information may be listed in a tabular form similar to that shown below. Tungsten Electrode Size and Type (Pure Tungsten, 2% Thorated, etc.) Mode of Metal Transfer for GMAW (Spray arc, short-circuiting arc, etc.) Electrode Wire feed speed range
TECHNIQUE (QW-410) String or Weave Bead Orifice or Gas Cup Size Initial and Interpass Cleaning (Brushing, Grinding, etc.) Method of Back Gouging Oscillation Contact Tube to Work Distance Multiple or Single Pass (per side) Multiple or Single Electrodes Travel Speed (Range) Peening Other
Filler Metal Weld Layer(s)
Process
Class
Dia.
Current Type Polar
Amp Range
Volt Range
Travel Speed Range
Other (e.g., Remarks, Comments, Hot Wire Addition,Technique, Torch Angle, Etc.)
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«Positions (QW-405.1) Welding Progression: (QW-405.3)
«Preheat (QW-406.1) QW-407.1 Special requirements for preheating «Postweld heat treatment (QW-407) none required «Gas (QW-408) none required «Electrical Characteristics (QW-409.4) Current: DC
Polarity: DCRP
Amps: (QW-409.8)
«Technique (QW410.1) String or Weave Bead: Stringer / Weave Cleaning: (QW-410.5) Brush or grind as necessary Method of Back Gouging: (QW-410.6) ACA-A or grind as necessary Peening: (QW-410.26) None allowed
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QW-483 SUGGESTED FORMAT FOR PROCEDURE QUALIFICATION RECORD (PQR) (See QW-200.2, Section IX, ASME Boiler and Pressure Vessel Code) Record Actual Conditions Used to Weld Test Coupon Company Name Procedure Qualification Record No. WPS No. Welding Process(es) Types (Manual, Automatic, Semi-Auto.)
Date
JOINTS (QW-402)
Groove Design of Test Coupon (For combination qualifications, the deposited weld metal thickness will be required for each filler metal or process used.)
BASE METALS (QW-403) Material Spec. Type or Grade P. No. Thickness of Test Coupon Diameter of Test Coupon Other
POST WELD HEAT TREATMENT (QW-407) to P-No.
Temperature Time Other
GAS(QW-408) Gas(es)
FILLER METALS (QW-404) SFA Specification AWS Classification Filler Metal F-No. Weld Meal Analysis A-No. Size of Filler Metal Other Weld Metal Thickness
Percent Composition (Mixture) Flow Rate
Shielding Trailing Backing
ELECTRICAL CHARACTERISTICS (QW-409) Current Polarity Amps. Volts Tungsten Electrode Size Other
POSITION (QW-405)
TECHNIQUE (QW-410)
Position of Groove Weld Progression (Uphill, Downhill) Other
Travel Speed String or Weave Bead Oscillation Multipass or Single Pass (per side) Single or Multiple Electrodes Other
PREHEAT (QW-406) Preheat Temp. Interpass Temp. Other
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QW-483 (Back) PQR No. Tensile Test (QW-150) Specimen No.
Width
Thickness
Area
Ultimate Total Load lb.
Ultimate Unit Stress psi
Type of Failure & Location
Guided-Bend Tests (QW-160) Type and Figure No.
Toughness Tests (QW-170) Specimen No.
Notch Location
Notch Type
Test Temp.
Impact Values
Lateral Exp. % Shear Mils
Drop Weight Break No Break
Fillet-Weld Test (QW-180) Result- Satisfactory: Macro - Results
Yes
No
Penetration into Parent Metal: Yes
No
Other Tests Type of Test Deposit Analysis Other ...................................................................................................................................................... Welder’s Name Tests conducted by:
Clock No.
Stamp No. Laboratory Test No.
We certify that the statements in this record are correct and that the test welds were prepared, welded, and tested in accordance with the requirements of Section IX of the ASME Code. Manufacturer Date
By
(Detail of record of tests are illustrative only and may be modified to conform to the type and number of test required by the Code.)
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ASME Section IX Welder Qualification Welder qualification establishes the skill level for the welder. The test positions are similar to the welding procedure positions. The essential variables for welder qualification are as follows: Position Joint Configuration Electrode Type and Size Process
• • • •
Base Metal Type Base Metal Thickness Technique (Up-hill or Down-hill)
(d) 4G
(b) 2G
(a) 1G
(c) 3G QW-461.3 Groove Welds in Plate -- Test Positions
(a) 1G Rotated (b) 2G
(c) 5G
(d) 6G QW-461.4 Groove Welds in Pipe -- Test Positions Throat of weld vertical
Axis of weld horizontal
Axis of weld vertical
Axis of weld horizontal
45 deg.
(a) 1F
(b) 2F
(d) 4F
(c) 3F QW-461.5 Fillet Welds in Plate - Test Positions
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PERFORMANCE QUALIFICATION - POSITION AND DIAMETER LIMITATIONS (Within the Other Limitations of QW-303) Position and Type Weld Qualified [Note (1)] Qualification Test Weld
Position
Groove Plate and Pipe Over 24 in. O.D.
Plate - Groove
1G 2G 3G 4G 3G and 4G 2G, 3G and 4G Special Positions m(SP)
Plate - Fillet
1F 2F 3F 4F 3F and 4F Special Positions (SP)
F F,H F,V F,O F,V,O All SP,F
Fillet
Pipe 24 in. O.D.
Plate and Pipe
F [Note (2)] F,H [Note (2)] F [Note (2)] F [Note (2)] F [Note (2)] F,H [Note (2)] SP,F
... ... ... ... ... ...
F F,H F,H,V F,H,O All All SP,F
... ... ... ... ... ...
F [Note (2)] F,H [Note (2)] F,H,V [Note (2)] F,H,O [Note (2)] All [Note (2)] SP, F [Note (2)]
Position and Type Weld Qualified [Note (1)] Qualification Test Weld
Position
Groove Plate and Pipe Over 24 in. O.D.
Pipe - Groove [Note (3)] 1G 2G 5G 6G 2G and 5G Special Positions (SP) Pipe - Fillet [Note (3)]
1F 2F 2FR 4F 5F Special Positions (SP)
F F,H F,V,O All All SP,F ... ... ... ... ... ...
Fillet
Pipe 24 in. O.D.
Plate and Pipe
F F,H F,V,O All All SP,F ... ... ... ... ... ...
F F,H All All All SP,F F F,H F,H F,H,O All SP,F
NOTES: (1) Positions of welding as shown in QW-461.1 and QW-461.2. F = Flat H = Horizontal V = Vertical O = Overhead (2) Pipe 2 7/8 in. O.D. and over. (3) See diameter restrictions in QW-452.3, QW-452.4 and QW-452.6
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The general sequence for Welder qualification testing is as follows: • Identify essential variables • Check equipment and materials for suitability •
Check test coupon configuration and position
• Monitor actual welding, to assure that it complies with applicable welding procedure • Select, identify and remove required test specimens • Test and evaluate specimens • Complete necessary paperwork • Monitor production welding
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QW-484 SUGGESTED FORMAT FOR MANUFACTURER’S RECORD OF WELDER OR WELDING OPERATOR QUALIFICATION TESTS (WPQ) See QW-301, Section IX, ASME Boiler and Pressure Vessel Code
Welder’s name Clock no. Stamp no. Welding process(es) used Type Identification of WPS followed by welder during welding of test coupon Base material(s) welded Thickness Manual or Semiautomatic Variables for Each Process (QW-350)
Actual Values Range Qualified
Backing (metal, weld metal, welded from both sides, flux, etc.) (QW-402) ASME P-No. to ASME P-No. (QW-403) ( ) Plate ( ) Pipe (enter diameter, if pipe) Filler metal specification (SFA): Classification (QW-404) Filler metal F-No. Consumable insert for GTAW or PAW Weld deposit thickness for each welding process Welding position (1G, 5G, etc.) (QW-405) Progression (uphill/downhill) Backing gas for GTAW, PAW or GMAW, fuel gas for OFW (QW-408) GMAW transfer mode (QW-409) GTAW welding current type/polarity Machine Welding Variables for the Process Used (QW-360)
Actual Values
Range Qualified
Direct/remote visual control Automatic voltage control (GTAW) Automatic joint tracking Welding position (1G, 5G, etc.) Consumable insert Backing (metal, weld metal, welded from back sides, flux, etc.) Guided-Bend Test Results Guided-Bend Tests Type
( )QW-462.2(Side) Results
( )QW-462.3(a) (Trans. R &F ) Type
( )QW-462.3(b) (Long R & F) Results
Visual examination results (QW-302.4) Radiographic test results (QW-304 and QW-305) (For alternative qualification of groove welds by radiography) Fillet Weld - Fracture test Length and percent of defects Macro test fusion Fillet leg size in. x in. Concavity/convexity Welding test conducted by Mechanical tests conducted by Laboratory test no.
in. in.
We certify that the statements in this record are correct and that the test coupons were prepared, welded and tested in accordance with the requirements of Section IX of the ASME Code. Organization Date
By
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Welding Metallurgy
WELDING METALLURGY Admixture: The interchange of filler metal and base metal during welding, resulting in weld metal of composition borrowed from both. Limited admixture is necessary to complete metallurgical union across the joint. Aging: The recrystallization that occurs over an extended period of time, resulting form austenite or other normally elevated-temperature structure being retained at a temperature and under conditions where it has no permanent stability. The result may be a change in properties or dimension. Under some circumstances, aging can be advantageous. Blowhole: A defect in metal caused by hot metal cooling too rapidly when excessive gaseous content is present. Specifically, in welding, a gas pocket in the weld metal, resulting from the hot metal solidifying without all of the gases having escaped to the surface. Crater cracks: Cracks across the weld bead crater, resulting form hot shrinkage. Heat-affected zone: The portion of the base metal, adjacent to a weld, the structure or properties of which have been altered by the heat of welding. Hot shrinkage: A condition where the thin weld crater cools rapidly while the remainder of the bead cools more slowly. Since metal contracts or shrinks as it cools, and shrinkage in the crater area is restrained by the larger bead, the weld metal at the crater is stressed excessively and may crack. Lamination: An elongated defect in a finished metal product, resulting from the rolling of a welded or other part containing a blowhole. Actually, the blowhole is stretched out in the direction of rolling. Pick-up: The absorption of base metal by the weld metal as the result of admixture. Usually used specifically in reference to the migration of carbon or other critical alloying elements from the base metal into the weld metal. Depending upon the materials involved, this can be an asset and not a liability. Segregation: The tendency of alloying elements, under certain heat conditions, to separate from the main crystalline constituent during transformation and to migrate and collect at the grain boundaries. There they often combine into undesirable compounds.
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Stringers: The tendency of segregated atoms of alloying elements or their compounds to attach to one another in thread-like chains. The problems encountered in welding can be better understood through a basic understanding of metallurgy. The metallurgical effects of welding are the effects of heat. Whether the welds are made by a gas flame, a metal arc, or electrical resistance, the effects on the parent metal are due to heat. Every fusion welding operation involves a logical sequence of thermal or heat events. These include: 1. 2. 3. 4.
Heating of the metal Manipulation of the electrode or torch flame to deposit weld metal Cooling of the weld deposit as well as the base metal Reheating of the entire structure for stress-relieving purposes, in some instances
In every weld, the metal immediately under the flame or arc is in a molten state; the welded section is in the process of cooling off; and the section to be welded has not yet been heated and so is comparatively cool. These various conditions are encountered at the very same instant. As a result of welding, the structure of the welded ferrous metal may become martensitic, pearlitic or even austenitic in nature. The welder who knows metallurgy can predict which structure will be found when the weld has cooled. It is most important to know this because the final condition of the structure after welding is the one that determines the strength, hardness, ductility, resistance to impact, resistance to corrosion and similar mechanical and physical properties of the metal. All these properties may be affected by conditions that exist during the welding operation, so it is well to become acquainted with possible difficulties and see how they may be avoided. To avoid confusion, this discussion will be confined to steel. The effects of heating and cooling will not necessarily be the same for the non-ferrous metals and alloys. In some cases, a considerable difference in temperature ranges and other characteristics exist. The arc welding of steel involves very high temperatures. The resultant weld is essentially cast steel. Since the base metal very close to the weld is comparatively cool, a considerable variation in the grain structure develops within the weld area. As the weld cools will alter the grain structure in both the weld itself and the immediately adjacent base metal, known technically as the heat -affected zone.
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Danger from the Air Unless extreme care to shield the weld metal is exercised during welding, the possibility exists that oxygen or nitrogen or both will be absorbed from the air. What either of these gases can do to weld metal is pitiful. An oxide or nitride coating will form along the grain boundaries. Oxidation along the grain boundaries greatly weakens the weld metal, and greatly reduces the impact strength and also the fatigue resistance of the welded part. Nitrogen forms iron nitrides in chemical composition with the iron, and these make the weld extremely brittle. The extent to which oxides and nitrides penetrate a steel will depend upon the type of steel, the temperature to which it is heated and the length of time it is held at this temperature. Extreme care should be exercised to prevent the penetration of air into high-temperature welding regions. The most satisfactory way to prevent oxide or nitride contamination in metal-arc welding is to make sure that the electrode has a coating that provides adequate shielding. The arc and weld metal may also be shielded by carbon dioxide (CO2) or vapor. In gas tungsten arc welding (GTAW) or gas metal arc welding (GMAW) (inert-gas-arc welding), the inert gas will provide the shielding. With submerged-arc welding, the molten flux that covers the arc does the job. Fluxes or a reducing flame provide the needed protection during gas welding. When the oxyacetylene torch is used for cutting, it is desirable to oxidize the steel. It is rapid oxidation that makes it possible for the flame to sever steel. Besides oxygen or nitrogen, another gas absorbed during welding may have harmful effects on some types of metals and alloys. This gas is hydrogen, and usually comes from moisture in the electrode coating or from the use of hydrogen in the welding flame. The presence of hydrogen in the weld metal will weaken the structure and lead to cracking of the weld. Hydrogen is a contributing cause of underbead cracking. To avoid this harmful weld defect, use low-hydrogen electrodes of the E-xx15, E-xx16 and E-xx18 series. Heat-Affected Zone A weld bead as deposited on the 1/2 inch plate produced a heat-affected zone that extended for about 1/8 in. adjacent to the weld. This zone shows a variation in grain structure adjacent to the weld. This zone shows a variation in grain structure (staring at the bottom) from the normal base metal structure into a band of finer grain structure between the lower and upper critical temperature points and then to a coarse overheated grain structure adjacent to the weld. The extent of the change in the grain structure depends upon the maximum temperature to which the metal is subjected, the length of time this temperature exists, the composition of the steel, and the rate of cooling. The cooling rate will not only affect grain size but it will also affect physical properties. As a rule, faster cooling rates produce a slightly harder, less ductile and stronger steel. For low-carbon steels, the relatively small differences found in practice make insignificant changes in these values. However, with higher carbon content in appreciable amounts of alloying material, the effect may become serious.
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The speed of welding and the rate of heat input into the joint effects change in structure and hardness. On a given mass of base metal, at a given temperature, a small bead deposited at high speed produces a greater hardening than a larger bead deposited at a higher heat input per unit length of joint. This is because small high speed beads cool more rapidly than the larger high heat beads. The effect that heat from welding has on the base metal determines to a great degree the weldability of a metal and its usefulness in fabrication. A metal that is sensitive to heat conditions or heat changes, as in the case of high-carbon and some alloy steels, may require heat treatment both before and after welding. Admixture or Pick-up When a base metal is welded with a filler metal of different composition, the two metals will naturally mix and blend together in the molten weld pool. Consequently, the weld metal will be a mixture of two materials. it will not necessarily be an average of them, however. The amount of base metal picked up in the molten weld pool varies greatly relative to the amount of deposited electrode metal. Some welds are made up principally of base metal, while others are primarily deposited electrode metal. The specific process of welding, the rate of electrode travel, the current selected, the width of the joint, the base metal composition, the plate thickness -- all these factors determine the volume of base metal brought to a molten temperature, and therefore the amount of base metal pick-up or admixture into the weld. In some cases, the deposited metal and the base metal are sufficiently alike in composition that the amount of admixture is of little significance. At other times, admixture is an advantage in that the weld metal is made stronger or otherwise improved by a pick-up of carbon or other needed elements from the base metal. Unfortunately, under some conditions alloying elements or chemical combinations of the base metal tend to concentrate -- to precipitate, or to segregate during the heating and cooling cycle and reform into stringers or other arrangements that harden, embrittle, weaken or otherwise cause inferior welds. Sometimes, the stringer itself is a source of weakness. At other times, the segregation of an element or its loss into the slag or atmosphere "starves" the newly formed weld microstructure of elements needed for certain physical properties. In general, admixture should be limited unless the metals and the processes involved justify a procedure that calls for a specific amount of pick-up. This is discussed further in later chapters on the welding of specific metal groups. To minimize the effects of pick-up, electrode coatings or fluxes are often treated with alloying elements that bring the deposited metal up to the desired composition. These alloying elements replace those that might be destroyed or lost to either parent metal or weld metal during the high-temperature welding operation.
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Carbide Precipitation Sometimes, because of rapid cooling, steels, particularly stainless steels, are not given time to go through all of the temperature changes indicated in the iron-carbon diagram. As a result, a concentration of the solid solution (austenite) is retained at a temperature where it simply has no business existing. This being against nature, so to speak, the dissolved elements will eventually recrystallize. This type of recrystallization is known as aging. Suppose, however, the metal is reheated before recrystallization can occur. In this event, the carbon will crystallize out of the austenite as iron carbide. This phenomena is known as carbide precipitation. Stainless steels of the nickel-chromium variety are austenitic in nature even at room temperatures. When such steels are heated, as by welding operations, carbide precipitation is apt to occur. The carbides, or carbon compounds, are chromium as well as iron. When chromium is used up in this way, in chemical union with the precipitated carbon, the remaining austenite is deficient in the chromium element. The result is a serious reduction in the corrosion-resisting properties of the stainless steel. When the carbides are precipitated in stainless steel, they appear mainly at the grain boundaries. If subjected to corrosion, the carbides along the grain boundaries will be attacked readily. Severe corrosive conditions will cause the grains to lose their coherence and the steel to fail. In making a weld on stainless, there will always be a region some distance back from the weld where the base metal will be at the exact temperature of the precipitation range: 800-1500°F. Consequently, the stainless qualities of the structure will be lost unless steps are taken to prevent precipitation. Austenitic stainless steels may be stabilized against carbide precipitation by the addition of elements known as stabilizers. Such elements are columbium and titanium. These elements have a ready affinity for carbon; they will grab and hold fast the carbon that might otherwise have been attracted to the chromium. Moreover, both titanium and columbium carbide resemble stainless steel in having high resistance to corrosion. Stabilized stainless steels, therefore, will not fail under the combination of heat and corrosive attack. Austenitic stainless steels also are available in several grades with extra low carbon (ELC). Since there is less carbon, the possibility of chromium migration to the grain boundaries is minimized. It is well to remember that the stabilized and ELC austenitic steels will resist carbide precipitation. If the welded stainless is to be subjected to corrosive conditions, particularly at elevated temperatures, the base metal should be a stabilized steel and it should be welded with electrodes or filler rods that have also been stabilized.
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Crater Cracks In some instances, both arc welds and gas welds develop crater cracks. These come from hot shrinkage. The crater cools rapidly while the remainder of the bead is cooling slowly. Since the crater solidifies from all sides toward the center, the conditions are favorable to shrinkage cracks. Such crater cracks may lead to failures under stress -- brittle failures since there is an inclination towards fracture without deformation. The remedy is to manipulate the electrode to fill up the craters when you are welding. Blowholes, Gas Pockets and Inclusions Other common welding defects known as blowholes, gas pockets and inclusions involve problems of electrode manipulation rather than metallurgy. These difficulties are created because of the welder's failure to retain the molten weld pool for sufficient time to float entrapped gas, slag and other forms of material. A blowhole or gas pocket represents a bubble of as in the liquid weld metal. A gas pocket is one that did not reach the surface before the metal began to freeze. Consequently, the gas remains entrapped in the solidified metal. Some gases, particularly hydrogen, are absorbed by the molten metal and are then given off as the metal beings to cool. If the metal is in a molten condition, the gas bubbles make their way to the surface and disappear. If the bubbles are trapped in the growing grains of solid metal, blowholes are the result. Blowholes are particularly prevalent in steels high in sulphur. In this case the entrapped gas is either sulphur dioxide or hydrogen sulphide, the hydrogen being supplied from moisture, the fuel gas (in gas welding), the electrode coating or the hydrogen atmosphere that surrounds the weld in atomic-hydrogen welding. Blowholes may be minimized in the weld area by using a continuous welding technique so that the weld metal will solidify continuously. Most welding operators, through practice, learn to develop welding techniques that will produce a relatively gas-free weld. One of the secrets of such a technique is to keep the molten weld pool at the temperature necessary for the rapid release of absorbed gases. At the same time an unbroken protective atmosphere must be provided over the pool. Modern electrode coatings aid in this problem, for they contain scavenging elements that cleanse the weld pool while it is in molten condition. Inclusions of slag and other foreign particles in the weld present a type of problem similar to gas pockets and blowholes. These inclusions tend to weaken the weld. Slag is frequently entrapped because of the operator's failure to manipulate torch, filler rod or electrode so as to maintain a molten condition long enough to float out all the foreign material. Ordinarily, the liquid slag freezes and forms a protective coating for the weld deposit. On some occasions, however, because of the force of the flame or arc, it is blown into the molten weld pool. The pool freezes before the slag particle or particles can float to the top, thus producing a defective weld.
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Slag inclusions are more common in welds made in the overhead position. The lower density of the slag tends to keep it afloat on the weld pool. In overhead welding, the weld pool first forms at the narrow part of the vee, which is uppermost in the weld. Since the pool tends to drip if kept molten too long, the welder works to have it solidify as rapidly as possible. As a result, inclusions are frequent. This problem in overhead welding can be overcome by using gaseous, non-slagging types of electrodes. Faulty plate preparation contributes to slag inclusions. If edges of V-joints are beveled at too steep an angle and the gap between plates is too small, the weld metal bridges the gap and leaves a pocket at the root in which slag tends to collect. If back of joint is accessible, slag can be removed by back gouging; however, if this operation is omitted, the result is a defective weld. With a J-joint or U-joint, improper arc manipulation may burn back the inside corners and form pockets that can entrap slag or gases. In repair of a broken surface, a groove along the break line should be burned out or ground so as to provide clean surfaces properly angled and spaced. Failure to do so may leave an overhang of base metal or an unfilled crack that can entrap slag or gases. Surfaces to be welded should be thoroughly cleaned of scale, dirt, paint, lubricants, and other chemicals that might contribute to formation of gas or dirt inclusions in the weld. Welds that contain blowholes, gas pockets and inclusions may develop other defects upon hot work. By the action of hot working, the basic defects are exaggerated to form larger defects. For example, if a piece of weld metal containing a blowhole is rolled, the tendency is to flatten and elongate the hole. This develops a long fibrous defect running in the same direction as the piece that is rolled. Such a condition, known as a lamination, will reduce the strength of the metal, particularly in directions at right angles to the lamination.
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Technical Report Writing
TECHNICAL REPORT WRITING LEGAL IMPLICATIONS I.
Preamble Comments A.
The completeness, factual data transmitted and final validity of any equipment inspection depends on the depth and scope of the officially submitted Inspection Report.
B.
The customer's perception of You as a qualified professional is always strongly influenced by what is contained in the report. Remember the "Image" comments earlier? Your report may well be "the make or break" factor about whether you or your company will be favorably considered for future inspection activities.
C.
An unknown factor usually exists relative to the "likes, dislikes and preferences" of the person who receives or acts on your inspection report. Some factors include: 1. 2. 3. 4. 5. 6.
D.
Organization of data Length of report Factual versus theoretical Precise details or general statement. Recommendations or suggestion. Line-item coverage or report by exceptio.
When developing the Inspection Report, consider: 1. 2. 3.
Who will read and/or react to its contents, such as project engineers, superintendents, managers, supervisors, foremen, craftsmen, etc.? Can the report be understood, or will a translator be needed? If repair recommendations or sketches are submitted, how much "hand-holding" is required for them to be understood?
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II.
Date and Signature For a report to be auditable (legitimate by law), it must be dated and signed by the inspector/person involved. Basically, any item worth reporting is worthy of legal validation.
III.
Report Format/Descriptive Contents A.
Many of those reading/reacting to your report simply do not have time to attempt to grasp or correlate those items most useful to their response. Therefore, the report should be factual, concise and reasonably easy to grasp or understand.
B.
An "attention getter", up front statement is always helpful.:
NOTE:
C.
Remember that the person to whom you submit a report is a Client. It may be an "in-house" client for those inspecting equipment owned by their respective employer, or it may be a contract-owner relationship.
Many, if not most, clients will not appreciate, nor perhaps even tolerate, a report that contains "inflammatory" comments. In this context, inflammatory words, comments, opinions or predictions could be anything that, in the event of some future legal action, would place the equipment owner in a precarious, defensive position. Some examples are: 1. 2. 3. 4. 5.
Dangerous Explosion Hazardous Health Problem Unsafe
A simpler explanation would be any comment or wording that could be twisted or used out of context by lawyers in a negligence trial situation. Certainly, the comments listed above are not meant or intended to cause an inspector to prostitute himself or his profession by "soft-pedaling" or ignoring serious problems, plus informing the client whenever problems exist. Each client deserves a true, factual evaluation and condition report. It is possible, however, to structure your report comments in such a fashion that problems can be stated (or client informed) so as to impart various degrees of urgency or involving areas or component items requiring immediate or near term corrective action.
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IV.
Report Vocabulary A.
Each individual most probably has already established, or will establish, his own vocabulary (or word usage) to identify or project his evaluation of conditions noted during the inspection survey. Degrees of corrosion/deterioration exist, plus varying stages or phases of problems involving mechanical equipment, safety, environment, etc., must be described and/or commented upon. Some common descriptive phrases/comments I have become comfortable with are listed below. You will note that it is possible to make many combination statements by grouping certain descriptive words into comments that best describe your personal evaluation. 1. 2. 3. 4. 5. 6. 7.
B.
Very minor, general corrosion. Minor to moderate, etc., etc. Moderate, etc., etc. Moderate to severe, etc., etc. Severe, etc., etc. The results of this inspection survey indicate that repair as follows is recommended. Inspection/evaluation of this equipment indicates it to be in good condition and is considered OK for long term service.
Owner/client user Expectations
You are hired (or used) to determine existing conditions of equipment, assess and evaluate the impact on future reliability, determine corrosion/metal thickness limitations or minimum requirements. You are expected to use your best judgment, expertise, experience and training to develop (perhaps even to recommend), the most cost effective, safest, operationally reliable method/degree of repair necessary to achieve the above conditions. V.
Report Structure A.
Recall earlier comments regarding those who will receive your report plus those who will eventually react to your comments and/or recommendations.
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B.
Methods, data organization, component part separation, etc., suggested for your strong consideration include: 1.
Method of presentation a. Keep the report as brief( but complete) as possible or practical. b. Keep it factual. If theorizing is required, make sure that this approach is recognized. c. Avoid, whenever possible, inflammatory words or comments. d. Be conscious of the economics involved. Don't recommend complete item renewal, when 50% renewal will provide the desired results.
2. NOTE:
Data Organization/Component Part Separation Do not intermingle comments/conditions. Keep comments separated in the report body and on the repair items recommended. Ideally, repair items should be arranged in order, clearly defined and explicit enough, that the list can be given to maintenance personnel who can make proper repairs from the list.
VI.
Review Comments The following are "Basic" in nature, but occasionally can be flexible to fit the needs of a particular situation: A.
Do's 1. 2. 3. 4. 5.
Keep as brief as possible, but present all factual data. A wide flexibility is necessary because of the range of comments required to satisfy numerous conditions. Provide suggestions or recommendations relative to repair if the client requests. Sketches involving repair or procedure details are a mark of competence. Be conscious of the economics involved that could result from your recommendations. Arrange data in an orderly fashion, separated into component parts for ease of reading and understanding. Sign and date report.
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B.
Don'ts 1. 2. 3. 4. 5.
Use inflammatory word, statements or opinions. Present a mass of data all intermingled in one statement. Make it a practice to theorize or guess as to problem cause. Present condition comments or data involving one major piping component into the same statement as data is presented on a completely different major component. Diminish your competency or professional image by a failure to submit a comprehensive, factual, readable report that will, by itself, be a future auditable document.
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