Senior Welding Inspector Guide Book

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WORLD CENfRE FOR MATERIALS JOINING TECHNOLOGY

Copyright o 2002, TWI Limited

Training & Examination Services

Granta Park, Great Abington

Cambridge, CB 1 6AL, UK

SENIOR WELDING INSPECTION (WlS 10)

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Section

Title

1)

Terms & Definitions

2)

Duties & Responsibilities

2a)

Duties of a Senior 'Welding Inspector

2b)

QA/QC

3)

Welding Imperfections

4)

Mechanical Testing

5)

Welding Procedures/Welder approval

6)

Materials Inspection

7)

Codes and Standards

8)

Welding Symbols on Drawings

9)

Introduction to 'Welding Processes

0)

Manual Metal Arc Welding

11)

Tungsten Inert Gas Welding

12)

Metal Inert/Active Gas Welding

13)

Submerged Arc Welding

14)

Welding Consumables

15)

Non Destructive Testing

16)

Weld Repairs

17)

Residual Stress & Distortion

18)

Heat Treatment of Steels

19)

Oxy-Fuel Gas Welding & Cutting

20)

Arc Cutting Processes

21)

Welding Safety

22)

Weldability of steels

23)

Fracture Assessments

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Concepts relating to an audit

Audit client Organization or person requesting an audit

Audit program Set of one or more audits planned for a specific time frame and directed towards a specific purpose

Auditee Organization being

audited

(-) Audit 3/2

Lack of fusion caused by the effects of arc blow.

Senior Welding Inspection - Submerged Arc Welding Copyright © 2002 TWI Ltd "

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Summary of Sub Arc \Velding: Equipment requirements: 1) 2) 3) 4) 5) 6) 7) 8)

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A Transformer/Rectifier. (Constant voltage type)

A power and power return cable.

A torch head assembly.

A granulated flux of the correct type/specification and mesh size.

A flux delivery system.

A flux recovery system.

Electrode wire to correct specification and diameter.

Correct safety clothing and good extraction.

Parameters & Inspection Points: 1) AC/DC WFS/Amperage. 3) Flux type and mesh size. 5) Electrode wire and condition. 7) Flux delivery/recovery system. 9) Insulation/duty cycles. 11) Contact tip size/condition.

10) 12)

OCV & Welding Voltage.

Flux condition. (Baking etc.)

Wire specification.

Electrode stick-out.

Connections.

Speed of travel.

2) 4)

Solidification, or centreline cracks. Porosity.

2) 4) 6) 8)

Typical Welding Imperfections: 1)

3)

Lack of fusion. Shrinkage cavities.

Advantages & Disadvantages: (

Advantages:

Disadvantages:

1) 2) 3) 4) 5)

1)

Low weld-metal costs. Easily mechanised. Low levels of ozone production. High productivity (o/t). No visible arc light.

Senior Welding Inspection - Submerged Arc Welding Copyright © 2002 TWI Ltd

2) 3) 4)

5)

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Restricted in positional welding. High probability of arc-blow. (DC+/-) Prone to shrinkage cavities. Difficult penetration control. Variable compositions. (Arc length)

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Questions Submerged Arc Welding Process

QU1.

State the possible problems when using damp and contaminated fluxes in the SAW welding process.

QU2.

State the two flux types used in the SAW welding process.

QU3.

Generally what power source characteristic is required for the SAW welding process?

QU4.

State three main items of SAW fluxes, which require inspection

QU5.

State the advantages and disadvantages of the SAW welding process

Senior Welding Inspection - QU Submerged Arc Welding Process Sec 13 Copyright © 2003 TWI Ltd

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Welding Consumables: Welding consumables are defined as all those things that are used up in the production a weld.

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This list could include many things including electrical energy, however we normally refer to welding consumables as those things used up by a particular welding process.

These are namely: wires

Electrodes

Fluxes

Gases

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When inspecting welding consumables arriving at site, it is important that they are inspected for the following:

1) 2) 3)

Size.

Type or Specification.

Condition.

Senior Welding Inspection -Welding Consumables Copyright © 2002 TWI Ltd

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Consumables for 1VIMA Welding: Welding consumable for MMA consist of a core wire typically between 350 and 450m01 length and from 2.5 - 6mm diameter. Other lengths and diameters are also available. The wire is covered with an extruded flux coating. The core wire is generally of low quality steel (Rimming Steel) as the weld can be considered as a casting, and therefore the weld can be refined by the addition of cleaning, or refining agents in the flux coating. The flux coating contains many elements and compounds that all have a variety of jobs during welding. Silicon is mainly added as a de-oxidising agent (in the form of Ferro silicate), which removes oxygen from the weld metal by forming the oxide Silica. Manganese additions of up 1.6% will improve the strength and toughness of steel. Other metallic and non-metallic compounds are added that have many functions, some of which are as follows:

1) 2) 3) 4) 5) 6) 7) 8)

To aid arc ignition. To improve arc stabilisation. To produce a shielding gas to protect the arc column. To refine and clean the solidifying weld-metal. To form a slag which protects the solidifying weld-metal. To add alloying elements. To control hydrogen content of the weld metal. To form a cone at the end of the electrode, which directs the arc.

Electrodes for MMAJSMAW are grouped depending on the main constituent in their flux coating, which in turn has a major effect on the weld properties and ease of use. The common groups, are given below:

Group

Constituent

Titania Rutile Calcium compounds Basic Cellulose Cellulosic

Senior Welding Inspection -Welding Consumables Copyright © 2002 TWI Ltd

Shield gas

Uses

AWS AS.1

CO 2 CO 2 Hydrogen + CO

General purpose High quality Pipe root runs

E 6013 E 7018 E 6010

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A Typical BS 639 Specification: Reference given in box letter:

E 51 A)

A) Tensile strength:

Symbol

Min Yield Strength 2 N/mm

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B 160

B)

C)

2 0 H

E) F) G)

D)

--

B) Toughness:

Tensile Strength

Nzmrrr'

3

Flat Butt & Fillets + HV Fillets.

4 5

Flat Butt & Fillets Vertical Down + positions of symbol 3 Any position not classified by the above.

First Digit 28 J 0 1 2 3 4 5

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430-550 330 43 380 510-650

51 C) Covering types:

B Basic

BB Basic High Efficiency

C Cellulosic

0 Oxidising

R Rutile Medium Coated RR Rutile Heavy Coated

S Other Types

E) Welding position:

Position

Symbol

All positions

1

All positions except 2

Vertical Down

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THE WELDING INSTITUTE

Second Digit 47 J

Testing Temperature Not specified +20 0 -20 -30 -40

0

1 2 3 4 5

[ D) Electrode Efficiency: l % Recovery to ~he nearest 10% (> = 110)

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F) Electrical characteristic:

Symbol 0 1 2

3 4 5 6 7 8 9

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DC Polarity Polarity as recommended + or­ -

+ + or­ + + or­ +

AC Min OCV Not recommended 500CV 500CV 500CV 700CV 700CV 700CV 900CV 900CV 900CV

G) Hy'~rogen Control: H Indicates Low Hydrogen Potential

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Senior Welding Inspection -Welding Consumables Copyright © 2002 TWI Ltd

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A Typical Electrode Specification to BSEn 499

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A Typical Electrode Specification to AWS A 5.1

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Senior Welding Inspection -Welding Consumables Copyright © 2002 TWI Ltd

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A Typical BSEn 499 Specification: Reference given in box letter:

E 46 3 INi B

35 38 42 46 SO

Min Yield Strength

Nzmrrr' 355 380 420 460 500

Tensile Strength N/rnm2

E%

440-570 470-600 500-640 530-680 560-720

22 20 20 20 18

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A) B) C) D) E) F) G)

A) Tensile strength: Symbol

THE WELDING INSTITUTE

B) Toughness at minimum impact energy 47 Joules: No requirement Z

Min

+20 0 -20 -30

A 0

2 3

-40

4 5

-50 -60

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C) Alloying: (Deposited weld chemical composition) Mn Mo Symbol Ni 2.0 None 0.3-0.6 104 Mo >104-2.0 0.3-0.6 MoMo 104 0.6-1.2 INi 104 1.8-2.6 2Ni 104 >2.6-3.8 3NI 0.6-1.2 Mo INi >104-2.0 0.3-0.6 0.6-1.2 104 INiMo Any other agreed Z composition

D) Covering types: A Acid C Cellulosic R Rutile RR Rutile thick covering RC Rutile/Cellulosic RA Rutile/Acid RB Rutile/Basic B Basic

F) Welding position:

E) Electrical characteristic + recovery % Current type Symbol Recovery % ac +"dc < 105 1 < 105 dc

2 > 105 < 125 ac +dc 3

> 105 < 125 dc

4 > 125 < 160 ac+ de 5

> 125 < 160 dc

6 > 160 ac+dc 7

> 160 dc 8

Symbol I 2

G) Hydrogen Content of deposited weld metal: Max H2 Content Symbol ml/100mgm 5 H5 10 HIO 15 HIS

Position All positions All positions except Vertical Down

3

Flat Butt & Fillets + HV Fillets.

4 5

Flat Butt & Fillets Vertical Down + positions of symbol 3

The strength, toughness, coating of BS 639 plus any light alloying elements of BS EN 499 (If applicable) are the mandatory elements of information that shall be shown on all electrodes. All other information is normally given on the electrode carton.

Senior Welding Inspection -Welding Consumables Copyright © 2002 TWI Ltd

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Inspection Points for MlVIA Consurnables 1: Size:

Wire Diameter & length. ~

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2: Condition:

Cracks, chips & concentricity.

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3: Type (Specification):

Correct specification/code.

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Checks should also be made to ensure that basic electrodes have been through the correct pre-use procedure. Having been baked to the correct temperature (typically 300­ 350°C) for 1 hour and then held in a holding oven at 150°C before being issued to the welders in heated quivers. Most electrode flux coatings will deteriorate rapidly when damp and care should be taken to inspect storage facilities to ensure that they are adequately dry, and that all electrodes are stored in conditions of controlled humidity. Vacuum packed electrodes may be used directly from the carton, only if the vacuum has been maintained. Directions for hydrogen control are always given on the carton and should be strictly adhered to. The cost of each electrode is insignificant compared with the cost of any repair, thus basic electrodes that are left in the heated quiver after the day's shift may potentially be re baked, but would normally be discarded to avoid the risk of H, induced problems.

Senior Welding Inspection -Weiding Consumables Copyright © 2002 TWI Ltd

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Consumables for TIG Welding: Consumables for TIG/GTAW consist of a wire and gas, though tungsten electrodes may also be grouped in this. Though it is considered as a non-consumable electrode process, the electrode is consumed by erosion in the arc, and by grinding and incorrect welding technique. The wire needs to be of a very high quality as normally no extra cleaning elements can be added into the weld. The wire is refined at the original casting stage to a very high quality where it is then rolled and finally drawn down to the correct size. It is then copper coated and cut into 1m lengths. A code is then stamped on the wire with

a manufacturer's, or nationally recognised number for the correct identification of chemical composition. A grade of wire is selected from a table of compositions. The wires are mostly copper coated which inhibits the effects of corrosion. Gases for TIG/GTAWare generally inert. Pure argon or helium gases are generally used for TIG welding. The gases are extracted from the air by liquefaction. Argon is more common in air than helium and thus it is generally cheaper than helium. In the USA vast pockets of naturally occurring helium are found and thus helium gas is more often used in USA. Helium gas produces a deeper penetrating arc than argon. It is less dense (lighter) than air and needs 2 to 3 times the flow rate of argon gas to produce sufficient cover to the weld area when welding down-hand. Argon on the other hand is denser (heavier) than air and thus less gas needs to be used in the down-hand position. We often use mixtures of argon and helium to balance the properties of the arc and the shielding cover ability of the gas. Gases for TIG/GTAW need to be of the highest purity (99.99% pure). Careful attention and inspection should be given to the purging of, and the condition of gas hoses, as it is possible that contamination of the shielding gas can be made through a worn, or withered hose. Tungsten electrodes for TIG welding are generally produced by powder forging technology. The electrodes contain other oxides to increase their conductivity, electron emission and also have an effect on the characteristics of the arc. Sizes of tungsten electrodes are available off the shelf between 1.6 - lOmm diameter. Ceramic shields may also be considered as a consumable item, as they are easily broken. The size and shape of ceramic used depends on the type ofjoint design and the diameter of the tungsten.

Senior Welding Inspection -Welding Consumables Copyright © 2002 TWI Ltd

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Consumables for MIG/lVIAG Welding: Consumables for MIG/MAG welding consist of a wire and gas. The wire specifications used for TIG welding are also used for MIG/MAG welding, as a similar level of quality is required in the wire. The main purpose of the copper coating of steel MIG/MAG welding wire is to maximise current pick-up at the contact tip and reduce the level of coefficient of friction in the liner, with protection against the effects of corrosion being a secondary function.

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Wires are available that have not been copper coated as the effects of copper flaking in the liner can cause many wire feed problems. These wires may be coated in a graphite compound, which again increases current pick up and reduces friction in the liner. Some wires, including many cored wires are nickel coated. Wires are available in sizes from 0.6 - 1.6 mm diameter with finer wires available on a lkg reel though most wires are supplied on a 15kg drum. Common gases and mixtures used for MIG/MAG welding include:

Gas Type

Used for

Characteristic Very stable arc with poor penetration and low spatter levels. Good penetration Unstable arc and high levels of spatter. Good penetration with a stable arc and low levels of spatter.

Pure Argon

MIG

Pure CO 2

MAG

Spray or Pulse Welding of Steels and Aluminium alloys Dip Transfer Welding of Steels

MAG

Dip Spray or Pulse Welding of Steels

Argon + 5 - 20% CO 2 (

Process

.

Argon + 1-2% O 2

MAG

Senior Welding Inspection -Welding Consumables Copyright © 2002 TW[ Ltd

Spray or Pulse Welding of Austenitic or Ferritic Stainless Steels Only

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Active additive gives good fluidity to the molten stainless, and improves toe blend.

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Consumables for Sub Arc Welding: Consumable for Submerged Arc SAW consist of an electrode wire and flux. Electrode wires are normally of high quality and for welding C/Mn steels are generally graded on their increasing Carbon and Manganese content, and the level of de-oxidation. Electrode wires for welding other alloy steels are generally graded by chemical composition in a table, in a similar way to MIG and TIG electrode wires. Fluxes for Submerged Arc Welding are graded by their manufacture and composition. There are 2 normal methods of manufacture known as fused and agglomerated.

1)

Fused fluxes:

Fused fluxes are mixed together and baked at a very high temperature where all the components become fused together. When cooled the resultant mass resembles a sheet of black glass, which is then pulverised into small particles. These particles again resemble small slivers of black glass. They are hard, reflective, irregular shaped, and cannot be crushed in the hand. It is impossible to incorporate certain alloying compounds into the flux such as Ferro manganese, as these would be destroyed in the high temperatures of the manufacturing process. Fused fluxes tend to be of the acidic type, which are fairly tolerant of poor surface conditions, but produce comparatively low quality weld metal in terms of the mechanical properties of tensile strength and toughness.

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Agglomerated tluxes: Agglomerated fluxes on the other hand are a mixture of compounds that are baked at a much lower temperature and are essentially bonded together by bonding agents into small particles. The recognition points of these types of fluxes is easier, as they are dull, generally round granules, that are friable (easily crushed), and can also be very brightly coloured, as colouring agents may be added in manufacture as a method of identification, unlike fused fluxes. Agglomerated fluxes tend to be of the basic type and will produce weld metal that is of much higher quality in terms of strength and toughness. This is at the expense of usability as these fluxes are much less tolerant of poor surface conditions.

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It can be seen that the weld metal properties will result from using a particular wire, with a particular flux, in a particular weld sequence and therefore the grading of SAW consumables is given as a function of a wirelflux combination and welding sequence.

A typical grade will give values for: 1)

2)

Tensile Strength. Toughness (Joules at temp)

2) 3)

Elongation %. Toughness testing temperature.

The re-use or mixing of used and new flux will depend on the class of work being undertaken and is generally addressed in the application standard. All consumables for SAW (wires and fluxes) should be stored in a dry and humid free atmosphere. Basic fluxes may require baking prior to use, and the manufacturers instructions should be strictly followed. On no account should different types of fluxes be mixed together. Senior Welding Inspection -Welding Consumables Copyright © 2002 TWI Ltd

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Questions Consumables

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QU1.

Why are basic electrodes used mainly on high strength materials? And what controls are required when using basic electrodes.

QU2.

What standard is the following electrode classification taken from and briefly discuss each separate part of the electrodes coding E 80 18 M.

QU3.

Why are cellulose electrodes commonly used for the welding of pressure pipelines?

QU4.

Give a brief description of a fusible insert and state two alternative names give for the insert

QU5.

What standard is the following electrode classification taken from and discuss each separate part of the electrodes coding. E 42 3 1Ni B 4 2 H1

Senior Welding Inspection - Consumables Sec 14 Copyright © 2003 TWI Ltd

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Non-Destructive Testing: NDT, or Non Destructive Testing is used to assess the quality of a component without destroying it. There are many methods ofNDT some of which require a very high level of skill both in application and analysis and therefore NDT operators for these methods require a high degree of training and experience to apply them successfully. The four basic methods ofNDT are: 1)

Penetrant testing.

2)

Magnetic particle testing.

3)

Ultrasonic testing.

4)

Radiographic testing.

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A welding inspector should have a working knowledge of all these methods, their

applications, advantages and disadvantages.

NDT operators are examined to establish their level of skill, which is dependant on their

knowledge and experience, in the same way as welders and welding inspectors are examined and tested to establish their level of skill. Various examination schemes exist for this purpose throughout the world. In the UK the CSWIP and PCN examination schemes are those that are recognised most widely.

A good NDT operator has both knowledge and experience, however some of the above

techniques are more reliant on these factors than others.

Senior Welding Inspection - Non-Destructive Testing Copyright © 2002 TWI Ltd

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Penetrant Testing: Basic Procedure: 1)

Surface preparation.

Component must be thoroughly cleaned.

2)

Penetrant application. Penetrant applied and allowed

~o

dwell for a specified time. (Contact time)

3)

Removal of excess penetrant. Once the dwell or contact time has elapsed, the excess penetrant is removed by wiping with a clean lint free cloth, finally wipe with a soft paper towel moistened with liquid solvent. (solvent wipe)

4)

Application of developer. Penetrant that has been drawn into a crack by capillary action will be drawn out of the defect by reverse capillary action.

5)

Inspection.

6)

Post cleaning and protection.

1\ )

Method: (Colour contrast, solvent removable) 1) Apply Penetrant.

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2) Clean then apply Developer.

3) Result.

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Advantage

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Disadvantages

1)

Low operator skill level.

1)

Careful surface preparation required.

2)

Applicable to non-ferromagnetic materials.

2)

Surface breaking flaws only.

3)

Low cost.

3)

Not-applicable to porous materials.

4)

Simple, cheap and easy to interpret.

4)

No permanent record.

5)

Portability.

5)

Potentially hazardous chemicals.

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Senior Welding Inspection - Non-Destructive Testing Copyright © 2002 TWI Ltd

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Senior Welding Inspection - WIS 10 Multi - Choice Question Paper (MSR-SWI-PT-1) N arne:

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Answer all questions t.

What is the flash point of a solvent based product? a. The minimum temperature at which the solvent will be flammable. b. The temperature at which the vapours given off will spontaneously ignite.

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c. The minimum temperature at which the vapours given off will ignite if source of ignition is introduced. d. The temperature at which the dye in a solvent based penetrant losses its capillary action.

2. What primarily governs the rate (speed) of a penetrant entering a surface breaking discontinuity? a. Viscosity. b. Capillary action. c. Wetting ability. d. How the penetrant is applied.

(. 3. Aluminium alloy test specimens that have been tested with penetrant should be thoroughly cleaned after testing because: a. The remaining toxic residue from the test may react with the aluminium causing a fire hazard. b. The acid in the penetrant may cause server corrosion. c. Any remaining alkaline penetrant will leave a red permanent stain on the surface of the aluminium. d. The alkaline content of wet and most emulsifiers could lead to surface pitting, especially in high humidity environments.

WIS 10 Qu paper MSR-SWI-PT- issue 3 Date: 28/05/03

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Which penetrant type does not exist? a. Post-emulsifiable fluorescent. b. Post-emulsifiable visible. c. Dual sensitivity penetrant. d. Dry particulate penetrant.

5.

Why is it bad practice to prepare soft alloy surfaces with a wire brush prior to testing with a penetrant test method? a. It may cause damage to the part. b. It may close any surface breaking discontinuities.

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c. It may contaminate the developer. d. It is not considered to be bad practice. e. Both a and b are correct.

6.

Which of the following NDE method is most likely to detect fatigue cracking? a. Dye penetrant. b. Magnetic particle (a.c. current) c. Ultrasonics. d. It depends on many factors, none of the above can be selected due to the lack of information given. ( -

7.

Which of the following cleaning methods is generally considered unsuitable for pentrant testing without further processing? a. Vapour degreasing. b. Abrasive blasting. c. Solvent cleaning. d. Steam cleaning.

WIS 10 Qu paper MSR-SWI-PT- issue 3 Date: 28/05/03

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8. Which of the following penetrant properties influences capillary pressure? a. Surface tension. b. Wetting ability. c. Dimension of surface breaking flaw. d. All of the above e. Both a and b.

9. Of the following, which are the most important reasons for filtering the UV-A light used for fluorescent penetrant inspection? -,

)

a. To minimise the total light intensity by filtering out the visible light rays. b. To produce better viewing conditions in darkened areas. c. To reduce overall wavelength bands to allow only green fluorescence. d. To prevent personal injury from the more penetrating UV-A rays.

10. How would an ideal emulsification time be established when using post-emulsifiable penetrants? a. By calculation b. By experimentation. c. By measuring the contact angle of the penetrant. (

d. By determining the viscosity of the emulsifier.

11. Generally speaking, which of the following penetrant systems would be the most time consuming to use on the same type of component? a. Solvent based. b. Post-emulsifiable. c. \'Vater-washable. d. All of the above generally would take the same time.

WIS 10 Qu paper MSR-SWI-PT- issue 3 Date: 28/05/03

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12. Which of the following may be used to apply penetrant effectively? a. Spray.

b. Immersion. c. Brush. d. All of the above

13. Dry developer should be applied: a. So that a heavy coat of developer covers all surfaces to be inspected. b. So that a light dusting covers all surfaces to be inspected. c. With a dry soft brush, e.g. paint brush. d. By dipping.

14. Which of the following is not considered good practice when penetrant testing? a. Applying emulsifier by dipping. b. Applying developer by dipping. c. Removing water based penetrant by water spray. d. Applying emulsifier by brush.

15. The profile of the meniscus of a penetrant would be: a. Concave when compared to the meniscus of a penetrant with lower penetration. b. Convex when compared to the meniscus of a penetrant with lower penetration properties.

c. Flat. d. All of the above. 16. Why is it advisable to have an UV-A light source installed at the wash station when

using fluorescent penetrant systems?

a. So that the drying stage can be eliminated to save time. b. To increase the bleed out speed of the penetrant. c. To check the effectiveness of the wash cycle. d. To check that the test components have been adequately covered with penetrant. WIS 10 Qu paper MSR-SWI-PT- issue 3 Date: 28/05/03

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17. Which factor would be used for determining the penetrants contact time required for the test method to be effective? a. Type of discontinuity sought. b. Shape of component. c. Size of component. d. All of the above.

18. Why is the wetting ability a consideration in the design of penetrants? a. Because it has an effect on capillary action. )

b. Because it has an effect on the penetrants coverage of the components surface. c. Both a and b. d. None of the above.

19. Why are contrast penetrants usually red? a. Red provides high definition. b. Red provides high contrast against a white background. c. Red penetrants are more cost effective than other penetrants of different colours. d. Both a and b.

(

20. Which of the following statements is false? a. Penetrant testing can find most types of surface breaking defects. b. Penetrant testing can under most conditions be just as reliable when testing ferritic materials as MPI. c. Penetrant testing can be used to detect fatigue cracks. d. Penetrant testing is less reliable than radiographic testing when attempting to detect minute surface breaking defects.

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21. Which of the following would be the most desirable centre wavelength for the light used in the fluorescent penetrant process. a. 3200A (320nm). b. 3650A (365nm).

c. 4650A (465nm). d. 5960A (596nm).

22. A good commercial penetrant should have a: a. Low flash point. b. High flash point.

c. Flash point less than 55°C. d. A flash point is not relevant.

23. Which of the following materials is often difficult to test with a penetrant test method, due to lack of contrast during final interpretation? a. Ferromagnetic C-Mn steels. b. Aluminium. c. Titanium alloys. d. Cast iron. \.

24. If a penetrant system is halogen free it will contain no: a. Sulphur. b. Dye.

c. Chlorine. d. Solvent.

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25. Which of the following statements is false regarding the use of cracked panels or comparator blocks? a. To establish a standard size of crack, which can be reproduced as, needed. b. To determine the relative sensitivities of two penetrants. c. To determine if a fluorescent penetrant has lost or reduced its fluorescence. d. To determine the degree or method of cleaning necessary to remove penetrant from the surface without removing it from the crack.

26. Which of the following pentrant test methods is the most common found on site work if used on ferromagnetic pipework or pressure vessels?

)

a. Water-washable (Fluorescent). b. Post-emulsifiable (fluorescent). c. Solvent base (contrast) d. Penetrant testing is not used on ferromagnetic materials.

27. When using fluorescent water-washable penetrants, adequate rinsing time is assured by: a. Timing the rinse cycle. b. Scrubbing the part surface. c. Rinsing under UV-A light. ( .. _

d. Using a high-pressure water blast.

28. How long must a penetrant be left on a component before removal? a. As long as possible to ensure good test sensitivity. b. 20 minutes. c. It varies depending on the type of penetrant used, defects to be detected. d. Always between 6 and 20 minutes.

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29. Which of the following are unique to a penetrant test report a. Penetrant used, developer used and dwell time. b. Penetrant used, development time and contrast paint. c. Penetrant used, fluorescent particles and drying time. d. Penetrant used, dwell time and drying time.

30. Which of the following surface breaking defects are best detected using DPI? a. Equiaxed defects. b. Planar defects. (

c. Linear defects. d. All of the above.

(

WIS 10 Qu paper MSR-SWI-PT- issue 3 Date: 28/05/03

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5. Materials which are repelled magnetically are called: a. Paramagnetic. b. Diamagnetic. c. Ferromagnetic. d. Non-magnetic. 6. Which of the following NOT method would be best suited for the detection of surface breaking defects on a austenitic steel weld: a. Dye penetrant. b. Magnetic particle (AC current) )

c. Ultrasonic. d. All of the above. 7. Which of the following are unique to a magnetic particle inspection report: a. Dwell time, magnetic ink, contrast paint b. Couplant, magnetic ink, crack detection unit. c. Magnetic ink, contrast paint, crack detection unit. d. Development time, magnetic ink, contrast paint. 8. An ASME penetrameter may be used in MPI: a. To measure test sensitivity.

(' I

b. To detect the direction of magnetic flux. c. To measure black/fluorescent ink suspensions. d. Both a and b. 9. What is the curie temperature of a ferromagnetic material? a. The temperature at which it becomes radioactive. b. The temperature at which it losses magnetism. c. The temperature at which it becomes magnetic. d. None of the above.

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10. The build up of a non-relevant indication due to a sharp contour change in the test component is referred to as: a. A defect. b. Furring. c. Magnetic writing. d. None of above. 11. Which of the following are important considerations when carrying out MPI? a. Material type. b. Surface condition c. Type of defects sort after. d. All of the above 12. A 5 turn coil around a part being tested produces: a. A longitudinal field. b. A circular field. c. An intermittent field. d. Both a and b depending on current type. 13. Which of the following MPI test methods may be used for the detection of longitudinal defects on a pipes external surface? a. The threader bar method.

(.

b. Rigid coil method. c. Flexible cable wrapped around the pipe making a coil. d. All of the above. 14. Which of the following is considered the most sensitive test method when using MPI. a. Fluorescent particle, wet method. b. Contrast particle, wet method. c. Dry powder method. d. All of the above are considered to be the same sensitivity.

WIS 10 Qu paper MSR-SWI-MT-l issue 3 Date: 28/05//03

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15. Which of the following will produce circular magnetism: a. A.C. yokes. b. Passing current through a coil.

c. Prods. d. All of the above.

16. Which of the following methods would be best suited for the detection of surface breaking defects on duplex stainless steel? a. Dye penetrant.

( J

b. Magnetic particle. c. Radiography. d. The method used depends on the procedure requirements.

17. In accordance with the relevant standard, what is the specific percentage of

fluorescent particles to the base:

a. 1.25%.

b. 0.8 to 3.5%.

c. 0.1 to 0.3%. d. 0.3 to 0.8%. 18. When demagnetising a component in situ in a structure that cannot be easily removed from the parent structure, which of the following techniques is normally used? a. Stroking the component in the same direction using an AC yoke. b. Stroking the component in different directions using a DC Yoke. c. Stroking the component in the different directions using an AC. yoke. d. Stroking the component in same direction using a DC Yoke. 19. When using AC. electromagnets, the strength of the magnet shall be assessed by measuring the lifting power. The lifting power shall be equivalent to or not less than: a. 4.5 kg for poll spacing of 300 mm. b. 2.25 kg for poll spacing of 300 rnrn. c. 18 kg for poll spacing greater than 75 mm. d. The sensitivity of AC. electromagnets is assessed using penetrameters. WIS 10 Qu paper MSR-SWI"MT-l issue 3 Date: 28/05//03

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20. A copper bar is placed inside a 5 mm coil, the amperage required to magnetically saturate it will be: a. In the range of 500 to 100 amps. b. Generally less than steel. c. Not enough information given to give a correct value. d. It is not possible to magnetically saturate a copper bar. 21. Which of the following is the most common method for demagnetising a component?

a. AC. b. DC straight polarity. (

c. HW DC d. The above currents cannot be used for dernagnetising. 2?-. What is coercive force? a. The magnetic force required to magnetically saturate a part. b. The magnetic force required to magnetise a part. c. The reverse magnetic force required to demagnetise a part. d. The reverse magnetic force required to cause the poles of a magnet to rotate

180°.

23. How is the strength of a permanent magnet usually measured? a. By lifting a specified weight of any material.

(

b. By lifting a specified weight of steel. c. By ampere-turns. d. By comparing it against the readings of a magnetometer. e. Both a and b. 24. What sort of magnetic field is produced when using a permanent magnet? . a. Longitudinal. b. Circular. c. Reversing poles. d. None of the above.

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25. When considering AC. yokes, which of the following is applicable? a. Can be used for the detection of both surface and slight sub-surface defects. b. No power source required. c. Must be used with at least a 400 mm pole spacing to ensure adequate coverage. d. None of the above. 26. An example of an instrument use to determine the direction of a magnetic field is

called a:

a. Burmah-Castrol strip. -,

)

b. ASME penetrameter. c. Berthold penetrameter. d. All of the above. e. None of the above. 27. Why is H.W.D.C. often used with dry powders, as opposed to D.C.? a. Because dry powders are not attracted to leakage fields caused by direct current. b. Because the powder retains a residual field with direct current. c. Because greater powder mobility is achieved on the test surface. d. A.C. of H.W.D.C. is not used with dry powders.

28. When checking a weld for defects with a permanent magnet, the magnet should be

) placed:

a. Transversely over the weld to look for longitudinal defects. b. Longitudinal with the weld to look for transverse defects. c. At 45° to the weld to look for both transverse and longitudinal defects at the same time. d. Normally in positions A and B if specification does not state otherwise. 29. Which of the following statements is always true? a. MPI is better than dye penetrant testing. b. Fluorescent inks used in MPI are always green/yellow. c. MPI'can only be used on ferromagnetic materials. d. All of the above.

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30. Which of the following surface breaking defects are best detected using MPI? a. Equiaxed defects. b. Planar defects. c. All types of entrapped gas defects. d. All surface defects are detected using MPI.

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Magnetic Particle Testing: Basic Procedure: l)

Test method for the detection of surface and sub-surface defects in ferromagnetic materials.

2)

Magnetic field induced in component. (Permanent magnet, electromagnet (Y6 Yoke) or current flow (Prods).

3)

Defects disrupt the magnetic flux.

4)

Defects revealed by applying ferromagnetic particles. (Background contrast paint may be required)

Method: 1) Apply contrast paint.

( . ?' 12 % to produce stainless steels, but is 0 ften used in low alloy steels < 5% to increase hardness strength and greatly increase the resistance to oxidation at higher temperatures. Chromium stabilises carbide formation, but promotes grain growth if added in isolation. It is thus often alloyed together with Ni or Mo

Manganese:

Alloyed to structural steels < 1.6% to increase the toughness and strength. It is also used to control solidification cracking in ferritic steels. Alloyed up to 14% in wearlimpact resistant Hadfield steel.

Molybdenum:

Alloyed to low alloy steels to control the effects of creep. It is also used as a stabilising element in stainless steels, and will a limit the effects of grain growth. Alloyed in Cr/Ni/Mo low alloy steels to control an effect called temper embrittlement.

Nickel:

Nickel is alloyed to produce austenitic stainless steels. It may also be added < 9% in the low temperature nickel steels. It promotes graphitisation, but is good grain refiner, and is often used to offset some effects of Chromium. Nickel is very expensive, but improves the strength, toughness, ductility and corrosion resistance of steels.

Niobium:

Carbide former used to stabilise stainless, also in HSLA < .05%

Silicon:

Is alloyed in small amounts < 0.8% as a de-oxidant in ferritic steels. It is alloyed to valve and spring steels, and can also increase fluidity.

Titanium:

Used mainly to stabilise stainless steel, and < .05% in HSLA steels.

Tungsten:

Mainly alloyed to high alloy High Speed Tool steels. This increases the high temperature hardness required of such steels, due to the tempering effect of frictional heat on other steels during cutting.

Vanadium:

Used as a de-oxidant, or as a binary alloy as in HSLA steels < .05%

It should be remembered that most alloying additions increases the ability of a steel to harden by the thermal hardening process. This property is termed "hardenability" Senior Welding Inspection - The Weldability of Steels Copyright © 2002 TWI Ltd

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Crack type:

Hydrogen cracking (cold cracking)

Location:

a. HAZ. Longitudinal b. Weld metal. Transverse or longitudinal

Steel types:

a. All hardenable steels b. HSLA steels & QT Steels Martensite.

Susceptible microstructure:

Causes:

(~)

Hydrogen cracking may occur in the HAZ or the weld metal, depending on the type of steel being welded. Hydrogen may be absorbed into the arc from water on the plates, moisture in the air, paint or oil on the plates or the breakdown of gas shielding etc. An E60 I0 cellulosic electrode uses hydrogen as a shielding gas. Hydrogen will easily dissolve in the molten weld metal, and remain in solution on solidification to austenite. The weld will cool down and transform to ferrite, where the hydrogen has less solubility and will want to diffuse to the HAZ, which will still be austenitic. This occurs rapidly as diffusion is increased with high temperatures. If the HAZ is un­ hardenable it will itself transform to ferrite and the hydrogen, which has some solubility in ferrite, will eventually diffuse out of the weldment. If the HAZ has some hardenability, then the transformation of the HAZ will be from austenite to martensite, which has no solubility for hydrogen. This will result in great internal stress, occurring in a microstructure, which is very brittle. Cracks may occur at areas of high stress concentration, such as the toes of a weld, and move through the hardened HAZ and in extreme cases, the weld metal.

The four minimum critical factors and their values, where hydrogen cracking is likely to occur, are considered to be: a.

Hydrogen content: > 15 ml/l00 gm of deposited weld metal.

b.

Hardness: > 350 VPN.

c.

Stresses: > 0.5 of the yield stress.

d.

Temperature: < 300°C.

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Hydrogen may be absorbed into the arc zone and liquid weld metal from:

Rust, oil, grease, or paint etc. on the plate.

E 6010 electrodes produce

Hz as a shielding gas. "

A long, or an unstable arc .

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':'~"''''.Fo:.~ i~~l~~~~~5;Jjj:

:m~~,~.::.~,~i:

1111~~~~5~~~m:

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.

se

y

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Austenite in HAZ

Weld metal changes phase to

a

ferrite and

Hz diffuses into HAZ H 2 diffusion to HAZ

martensite at 300°C trapping Hz and forcing it out of solution.

Martensitic HAZ

Hz HAZ Cracking

Austenite in HAZ changes to

(

Stress concentrations a. Butt joints.

Stress concentrations

Hz HAZ Cracking lVIartensitic HAZ

b. T joints.

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Prevention of hydrogen HAZ cracking: To control hydrogen cracking in the HAZ it may be necessary to pre-heat the weldment. Pre-heating retards the rate of cooling and suppresses the formation of martensite and other hard structures, which is formed on rapid cooling. It will also allow some of the trapped hydrogen to diffuse back to the atmosphere.

Elements that are to be considered when calculating pre-heat are: a. Hardenability of the joint. (i.e, Ceq) c. Arc energy input.

I, - ')

'--/

b. Thickness of metal and joint type. d. Hydrogen scale, or achievable limit.

Hydrogen induced weld metal cracking is found when welding HSLA (High strength low alloy) steels which are alloyed with micro amounts of titanium, vanadium and/or niobium. (Typically 0.05%) In order to match the weld strength to plate strength, weld metal with increased carbon content is used, as carbon content increases tensile strength. A graph showing the effect of carbon on the properties of plain carbon steels is given below. This results in a hardenable steel weld deposit, in which the austenite of the weld transforms directly to martensite, causing the same conditions as found in the HAZ previously and cracking may now occur within the weld metal.

.,

Prevention of H 2 for these steels is as per H2 HAZ cracking, by the preheating of the weld area, but this is principally to allow any trapped hydrogen the time at temperature to diffuse from the weld & HAZ area back to the atmosphere.

. (

Both HAZ and weld metal H2 cracks are considered as cold cracks « 300°C) and final inspection is often delayed for up to 72 hours as these cracks may appear within this time.

Tensile Strength

.o

Ductility ~

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.2 1.4 1.6 % Carbon

Senior Welding Inspection - The Weldability of Steels Copyright © 2002 TWI Ltd

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It can be clearly seen from the graph that additions of carbon (up to O.83%C) will increase the tens i le strength 0 f plain carbon steel dramaticall y. \Vhilst this wi II serve the purpose of cheaply matching the weld metal strength to the base metal, it will also give the weld metal much higher hardenability. This may now result in H2 cracking in the weld metal, as the weld will transform from austenite - martensite trapping the hydrogen in weld, before it is able to diffuse to the HAZ. It can also be seen from the graph that higher carbon steels have very little ductility, which further complicates the problem. Cracks tend to be transverse, as the main residual stresses are generally in the longitudinal direction, though they may occasionally be longitudinal, or even at 45° to the weld metal.

High strength low ductility weld metal.

Hydrogen induced weld metal cracks.

Prevention of hydrogen cracking in the weld metal of HSLA, or Micro-alloyed steels is very much the same as for hydrogen cracking in the HAZ of other low alloy steels. Summary of prevention methods: a. b. c. d. e. f. g. h. i.

Use a low hydrogen process and/or hydrogen controlled consumables. Maximise arc energy (taking HAZ and weld toughness into consideration). Use correctly treated H2 controlled consumables Minimise restraint. Ensure plate is dry and free from rust, oil, paint or other coatings. Use a constant and correct arc length. Ensure pre-heat is applied and maintained before any arc is struck. Control interpass temperature Ensure welding is carried out under controlled environmental conditions

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Crack type:

Solidification cracking (Hot cracking)

Location: Steel types: Susceptible microstructure:

Weld centre. (longitudinal) All Columnar grains. (In the direction of solidification)

Causes: Solidification cracking, is a hot cracking mechanism that occurs during solidification of welds in steels, having high sulphur content or contaminated with sulphur.

(

--)

Another potential cause is the depth/width ratio of the weld, which in normal welding situations refers to deep narrow welds (cladding applications may produce shallow wide welds, which are also prone to this problem).

~

Therefore if we have a combination of deep narrow welds with a high incidence of sulphur we are great! y increasing the likelihood of hot cracking. As with all cracking mechanisms stress plays a major role in susceptibility. During welding, sulphur in or on the plate may be re-melted and will join with the iron to form iron sulphides. Iron sulphides are low melting point impurities, which will seek the last point of solidification of the weld, which is the weld centreline.

It is here that they form liquid films around the hot solidifying grains, which are themselves now under great stress due to the actions of contractional forces. The bonding between the grains may now be insufficient to maintain cohesion and a crack will result running the length of the weld on its centreline.

(

Prevention of solidification cracking in ferritic steels: To prevent the occurrence of solidification cracking in ferritic steels that contain high levels of sulphur (these steels are said to suffer from Hot Shortness), manganese is added to the weld via the consumable. Sulphur related:

Scrutiny of Mill sheets is essential to assess the materials Sulphur content. A typical maximum level allowed in a low carbon steel specification is 0.05%. Even this seemingly low figure may be excessive for certain high stress/higher carbon applications, or if the depth/width ratio is excessive. Another potential source of Sulphur is paint, oil and grease. This is why temperature Crayons always carry the statement "sulphur free".

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This is a prime reason for thorough cleaning, which becomes of even greater importance when dealing with Austenitic Stainless Steels if material availability dictates the necessity of welding high sulphur steels consumables with a relatively high Manganese content are specified. An example of steel with very high sulphur levels would be a free machining steel. Some of the free machining steels could be considered not weldable in normal circumstances as sulphur levels are so high.

Manganese has the effect of forming preferential manganese sulphides with the sulphur. Mn/S are spherical, solidify at a higher temperature than iron sulphides and therefore are distributed more evenly throughout the weld. The cohesion between the grains is thus maintained and the crack will not occur.

('--")

Careful consideration must be given to the Mn/S ratio, which should be in the region of about 40: 1. Increased carbon content can rapidly increase the required ratio exponentially; thus carbon must be reduced as low as possible, with low plate dilution and low carbon, high manganese filler wires. A summary of prevention methods: a. Use low dilution processes c. Maintain a low carbon content e. Specify low sulphur content of plate g. Thorough cleaning of preparation

b. Use high manganese consumables d. Minimise restraint/stress f. Remove laminations h. Minimise dilution

.Solidification cracking (Sulphur related)

sut~h;de<

Direction of grain solidification Weld centre line with liqnid Iron aronnd the solidifying grains -

Senior Welding Inspection - The Weldability of Steels Copyright © 2002 TWI Ltd

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Effect of Manganese Sulphides formation

Direction of grain solidification

~~

Spheroidal Mn sulphides form between the solidifying grains, maintaining inter-granular strength.

(J

Depth/width ratio related The shape of the weld will also contribute to the possibility of cracking. This may be totally independent from the sulphur aspect but is usually in combination. Processes such as SAW and MAG (using spray transfer) may readily provide these deep/narrow susceptible welds.

\

However it is not the weld volume that is the prime factor but the weld shape as referred to previously. Therefore root runs and tack welds may readily provide the susceptible profile. As root runs are also areas of high dilution (therefore greater sulphur pick up) and more likely to be highly stressed these must always be inspected with solidification cracking in mind.

Senior Welding Inspection - The 'Weldability of Steels Copyright © 2002 TWI Ltd

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Solidification cracking in Austenitic Stainless steels Austenitic stainless steel is particularly prone to solidification cracking.

This is due to:

A comparatively large grain size, which gives rise to a reduction of grain boundary area.

High coefficient of thermal expansion, with resultant high stress.

An atomic structure that is very intolerant of contaminants, such as sulphur,

phosphorous and additional elements such as boron.

The cause and avoidance may be regarded as the same as that of plain carbon steel but

with extra emphasis on thorough cleaning requirements prior to welding.

The welding procedure will have been written to control the balance of austenite and

ferrite in the weld metal. This balance will directly effect the structures tolerance of

contaminants and the resultant grain boundary area. This is why the filler material

specified often does not appear to match the parent material.

Careful monitoring of parameters is required to control dilution to ensure this balance is

maintained.

Senior Welding Inspection - The Weldability of Steels Copyright © 2002 TWI Ltd

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Crack type:

Lamellar tearing.

Location: Steel types: Susceptible microstructure:

Parent material

Any steel type

Low through thickness ductility

Causes:

When welding of joints where high contractional stresses are passed in the through

thickness direction of one of the plates in the joint.

This short transverse direction is lacking in ductility in cold rolled plates, but ductility

is required to accommodate the plastic strain caused by contraction.

(,.

')

A stepped like crack may initiate in the affected plate, just below the HAZ, in a horizontal plane. Micro inclusions of impurities such as sulphides and silicates, which occur during steel manufacture, cause this poor through thickness ductility. When subjected to high short transverse stress this may lead to lamellar tearing

Lamellar tearing. (Ferritic steels)

b. Butt joints.

--.:.

~

'r.~~.

Through thickness contractional strain. =

c. T joints.

Senior Welding Inspection - The Weldability of Steels Copyright © 2002 TWI Ltd

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d. Lap joints.

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Methods of controlling the occurrence of lamellar tearing:

1) Change of weld design

[;

High ductility weld metal

2) Use weld metal buttering layers

3) Minimise restraint

I

Aluminium wire

A pre formed T piece

4)

Use pre formed T piece for critical joints

Senior Welding Inspection - The Weldability of Steels Copyright © 2002 TWI Ltd

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Summary of Weldahility of Steels: Key words: Hydrogen induced HAZ or weld metal cracks. Cause' R~ HAZ cracks Process Consumables Paint, Rust, Grease Delayed inspection. Solubility HAZ o concentrations Diffusion Martensite Critical factors = Transformation Hardness> 350VPN Hydrogen>15ml o > 0.5 yield stress. Temp < 300°C HSLA weld cracks Weld contraction

()

(

Prevention' Pre-heat Minimise restraint Arc energy

High strength metal Transverse crack

High carbon weld Micro alloy Nb T V

Low ductility Longitudinal (J

Hydrogen control Remove coatings Use low Ceq plate

Bake consumable Stable arc length Use hot pass ASAP

Use low H Process y SIS Weld metal Use low H 2 Cons'

2

Solidification cracking in C/Mn steels. Cause' Sulphur. Fe/Sulphides Low melting point film Contraction forces

Weld centreline Loss of cohesion

Contraction Hot shortness

Prevention: High manganese % Control heat input

Control carbon % Change Preparation

Use low dilution Cleaning

Keywords:

Use low restraint Control sulphur %

Lamellar tearing in C/Mn steels. Cause: Poor ductility Plastic strain Contraction Short transverse

Key words: Micro inclusions Segregation

\

Prevention' NDT for laminations Re-design joint

I Through '1' tensile I Buttering layers I Forged T piece

I Chemical analysis

Contraction gap Control heat input

Inter - crystalline corrosion in stainless steels. Key words: Cause: Chromium depletion Temp gradient I Cr Carbide Sensitisation Parallel to weld I In HAZ I Loss of resistance Stabilised

T

Prevention: Low Carbon .03% .Low heat inout

Stabilising elements I Niobium Titanium I Solution anneal

Senior Welding Inspection - The Weldability of Steels Copyright © 2002 TWI Ltd

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Questions Weldability of Steels

QU1.

Briefly discuss the four essential factors for hydrogen cracking to occur

QU2.

State four precautions to reduce hydrogen cracking

QU3.

In which steel type is weld decay experienced? and state how it can be prevented.

QU4.

State the precautions to reduce the chance ofthe occurrence of solidification cracking

QU5.

State four essential factors for lamellar tearing to occur

(~

~

)

Senior Welding Inspection - QU Weldabilityof Steels Sec 22 Copyright © 2003 TWI Ltd

smourssessv a.lnl~8.1JI £'Z

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Fracture Assessments: You are required to:

• Record the sample number • Sketch the fracture surface. • Indicate the fracture initiation points (if known) (

• Show any defects present on the fracture surface • Identify the primary mode of failure. • Identify the secondary mode of failure (if present) • State the location of failure e.g parent material, weld metal or both (ifknown) • Write a conclusion to summarise your findings, providing reasons for the

fracture occurance and evidence.

• Sign and date your report

Senior Welding Inspection - Codes and Standards Copyright © 2002 TWI Ltd

23.1

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