Interview questions

June 24, 2016 | Author: Joseph George | Category: N/A
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Welding , Mechanical Interview Questions...

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QUESTIONS 1. NDT 1. What are the commonly used NDT methods in oil fields? RT, UT, MPI, LPT 2. Briefly describe the methods of RT, UT, PT & MT? MPI Consider a bar magnet. It has a magnetic field in and around the magnet. Any place that a magnetic line of force exits or enters the magnet is called a pole. A pole where a magnetic line of force exits the magnet is called a north pole and a pole where a line of force enters the magnet is called a south pole. When ever there is a discontinuity in the magnetic field, the magnetic field spreads out when it encounter the small air gap created by the crack because the air cannot support as much magnetic field per unit volume as the magnet can. When the field spreads out, it appears to leak out of the material and, thus, it is called a flux leakage field. If iron particles are sprinkled on a cracked magnet, the particles will be attracted to and cluster not only at the poles at the ends of the magnet but also at the poles at the edges of the crack. This cluster of particles is much easier to see than the actual crack and this is the basis for magnetic particle inspection. MPI can be used applied where, component being inspected must be made of a ferromagnetic material such iron, nickel, cobalt, or some of their alloys. A dipole is an object that has a magnetic pole on one end and a second equal but opposite magnetic pole on the other. The Source of Magnetism All matter is composed of atoms, and atoms are composed of protons, neutrons and electrons. The protons and neutrons are located in the atom's nucleus and the electrons are in constant motion around the nucleus. Electrons carry a negative electrical charge and produce a magnetic field as they move through space. A magnetic field is produced whenever an electrical charge is in motion. The strength of this field is called the magnetic moment Diamagnetic metals have a very weak and negative susceptibility to magnetic fields. Diamagnetic materials are slightly repelled by a magnetic field and the material does not retain the magnetic properties when the external field is removed. eg. copper, silver, and gold, are diamagnetic. Paramagnetic metals have a small and positive susceptibility to magnetic fields. These materials are slightly attracted by a magnetic field and the material does not retain the magnetic properties when the external field is removed. Paramagnetic properties are due to the presence of some unpaired electrons and from the realignment of the electron orbits

caused by the external magnetic field. Paramagnetic materials include magnesium, molybdenum, lithium, and tantalum. Ferromagnetic materials have a large and positive susceptibility to an external magnetic field. They exhibit a strong attraction to magnetic fields and are able to retain their magnetic properties after the external field has been removed. Ferromagnetic materials have some unpaired electrons so their atoms have a net magnetic moment.

LPT Penetrant Testing, or PT, is a nondestructive testing method that builds on the principle of Visual Inspection. PT increases the “seeability” of small discontinuities that the human eye might not be able to detect alone. Fluorescence Fluorescence is the process wherein a molecule absorbs a photon of radiant energy at a particular wavelength and then quickly re-emits the energy at a slightly longer wavelength. Working a. In penetrant testing, a liquid with high surface wetting characteristics is applied to the surface of a component under test. b. The penetrant “penetrates” into surface breaking discontinuities via capillary action and other mechanisms. c. Excess penetrant is removed from the surface and a developer is applied to pull trapped penetrant back the surface. d. With good inspection technique, visual indications of any discontinuities present become apparent. Type of Penetrant Material by type a. Fluorescent b. Visible Type of Penetrant Material by Method a. Water Washable b. Postemulsifiable - Lipophilic c. Solvent Removable d. Postemulsifiable – Hydrophilic Characteristics of Penetrant Material Penetrants are formulated to possess a number of important characteristics. To perform well, a penetrant must: Spread easily over the surface being inspected. Be drawn into surface breaking defects by capillary action or other mechanisms. Remain in the defect but remove easily from the surface of the part. Remain fluid through the drying and developing steps so it can be drawn back to the surface.

Be highly visible or fluoresce brightly to produce easy to see indications. Not be harmful to the inspector or to the material being tested.

Sensitivity Levels Penetrants are also formulated to produce a variety of sensitivity levels. The higher the sensitivity level, the smaller the defect that the penetrant system is capable of detecting. The five sensitivity levels are: Level 4 - Ultra-High Sensitivity Level 3 - High Sensitivity Level 2 - Medium Sensitivity Level 1 - Low Sensitivity As the sensitivity level increases, so does the number of non relevant indications. Therefore, a penetrant needs to be selected that will find the defects of interest but not produce too many non relevant indications. Developers a. b. c. d.

Dry Powder Wet, Water Soluble Wet, Water Suspendable Wet, Non-Aqueous

3. Which method is suitable for the testing of high thickness metals? 4. What are the advantages of RT over UT and UT over RT? 5. What is the advantage of PT over MT? 6. How will u demagnetize a test piece?

7. Which code and article describe the Visual Inspection? ASME Sec-V Article 9 - VISUAL EXAMINATION A written procedure, when required in accordance with T-150, shall include at least the following: (a) how visual examination is to be performed; (b) type of surface condition and criteria for surface cleaning; (c) cleaning instructions or reference to cleaning procedures: (d) method or tool for surface preparation, if any; (e) whether direct or remote viewing is used;

(f) special illumination, instruments, or equipment to be used, if any; (g) sequence of performing examination, when applicable; (h) data to be tabulated, if any; (i) report forms or general statement to be completed. Physical Requirements Personnel shall have an annual vision test to assure natural or corrected near distance acuity such that they are capable of reading standard J-1 letters on standard Jaeger test type charts for near vision. Equivalent near vision tests are acceptable. Direct visual examination may usually be made when access is sufficient to place the eye within 24 in. of the surface to be examined and at an angle not less than 30 deg. to the surface to be examined. Mirrors may be used to improve the angle of vision, and aids such as a magnifying lens may be used to assist examinations. Illumination (natural or supplemental white light) for the specific part, component, vessel, or section thereof being examined is required. The minimum light level shall be 50 footcandles. 8. What do you mean by random inspection? 9. Which NDT method will be the most suitable for detecting the lack of side wall fusion ? Why? 10. What is the acceptable range of density for RT films? 11. How will u calibrate a AC Yoke? II.

WELDING

1. Which is the most commonly used welding process? 2. Which are the most commonly used welding electrodes for flow lines? 3. Explain the letter designation system for E 7018-1 4. What is the difference between 7018 and 7018-1 electrodes? 5. What are the major types of weld cracks and what are the reason for the occurrence of cracks? Solidification cracks, crater cracks, delayed cracks, HIC cracks Maintain the required preheat temperature Baking and Holding the electrodes at required temperatures

6. As a welding inspector what can u do to prevent the weld cracks? 7. Why are u preheating the electrodes? What will happen if u keep a low hydrogen electrode in open air for 4 hours and then used for welding a LTCS material? 8. What are the advantages of P Numbers? Can I weld P no 1 material to PNo 34 material without any problems? P No are assigned to reduce the no of welding procedure specifications P No: 34 is CuNi(70/30) 9. What is the difference between preheating & heat treatment ? What are the advantages of heat treatment? 10. Which progression of welding would u prefer for 6” Sch 80 pipeline? Why? 1. III. MATERIAL 1. What are the materials used for LTCS piping, Flanges and fittings? Pipe 333 Gr 6 , Flange 350 LF2 and Fittings A 420 …. 2. What is the acceptable carbon , sulphur percent in API 5L Gr. B PSL-1 C= 0.28 Mn= 1.20 P=0.030 S=0.030 Carbon equivalent= only when specified Charpy Impact test not required PSL-2 C= 0.22 Mn= 1.20 P=0.025 S=0.015 Carbon equivalent=0 .43%(IIW formula) 3. What is the difference between PSL-1 and PSL-2?

Api 5L specification establishes requirements for two product specification levels (PSL 1 and PSL 2). These two PSL designations define different levels of standard technical requirements. PSL 2 has mandatory requirements for carbon equivalent, notch toughness, maximum yield strength, and maximum tensile strength. 4. What is the carbon equivalent and its acceptance limit? 5. What property will change if u are adding more carbon into the steel? Carbon Carbon in steel forms iron carbide (Fe3C) in the matrix. The larger size of the carbide compound pins the layers within the metal matrix and makes it much more difficult for the material to yield. This raises the tensile, yield strength, and hardness of the steel considerably. Silicon Silicon is added mainly as a deoxidizer. Manganese Manganese is used in small amounts in most steels to deoxidize, desulfurize, and improve material properties. Any manganese remaining after formation of MnO and MnS will form manganese carbide (Mn3C) which strengthens and toughens the matrix. Molybdenum Molybdenum is another carbide forming element, and is added to most alloy steels from .5% to 1.5%. Molybdenum improves yield strength and resistance to high temperature creep (deformation due to high temperature and stress). It also helps to maintain the strength of the steel after it undergoes stress relief. Molybdenum is added to stainless steels to reduce pitting (highly localized corrosion) in corrosive environments. Chromium Chromium is added to increase the strength, wear resistance, heat resistance, corrosion resistance, and hardness of steel. Chromium is also a carbide former, and forms chromium carbide (Cr3C). In steels, chromium can also form complex carbides, Fe2CrC and Cr2FeC. In stainless steel 12-18% Cr is added. Nickel While nickel does not form any carbide in a steel matrix, hardenability, ductility and toughness are all improved when nickel is added. Nickel is added to austenitic stainless steels (300 series) in concentrations of 7-35%. Nickel is also an important element found in the materials used for storage of cryogenic fluids. An

alloy containing 9% nickel is used to fabricate the inner vessel in liquid nitrogen, argon, and oxygen tanks. Vanadium Vanadium is a strong carbide former, and increases the hardenability of the steel. Vanadium is expensive, so it is usually used in percentages of less than .2%. This element reduces the grain size and increases the toughness of the material. Vanadium steels are used to make axles, connecting rods, hand tools, and engine crankshafts. Titanium Titanium is a strong carbide former that will also form oxides and nitrides. A large use of titanium is to stabilize certain grades of the stainless steels. Titanium combines with any carbon in the matrix to form carbides before chromium carbide precipitation can occur. When chromium forms carbides, the corrosion resistance of the material will deteriorate. Titanium also helps to reduce grain growth in high strength steels, improving strength and toughness. 6. What will u do if u want to increase the ductility of carbon steel? 7. Which CS material is more vulnerable to H2 induced weld metal cracks? 8. Which welding electrode do u use for welding LTCS pipes & Why?

9. What is the benefit of PWHT? a) Tempering of martensite that may have resulted from the welding, this will restore the ductility b) Reduction of residual stress which present in the welds c) Increases the corrosion resistance d) Diffusion of hydrogen in the welds

Aramco Questions? Describe yourself What are the activities you have done last week. Preparation for the procedure qualification Preparation of some procedures Preparation of ITP Material certificate review Welder qualification

WHAT are the inspection you will do for tie-in  Initially the approval for the tie-in has taken or not check  Then the tie-in procedure and ITP for the tie has approved or not  The tie-in location identified and the thickness survey has done and the lamination check has done  If hottapping the drawing shall be approved  Approval for the hottapping taken  Approval for material for the hottapping connection  Welders are qualified  Fitting the split tee or weldolet and the welding check  MPI on welds or UT  Fit the valve and hydrotest the full assembly  Check the assembly is working, like complete removal of the cutter  Check the service conditions are ok  Check the safety requirements are ok(like escape route, communication etc)  Cut the pipe and retrive the coupon, check the retrieval ok For the welded tie-in after the bevelling conduct MPI or PT on bevel ends Weld and take radiography of welds Where possible do hydrotest If hydrotest is not possible do service leak test What about hottapping How do you do the material inspection? Check material is from the approved vendors if not the vendors approval has taken? Corss check with the purchase order with MTC what is ordered is delivered Check the MTC with the project specification and the codes? Chemical combination, Mechanical Properties and the heat treatment and the manufacturing process Any supplimentrary requirement for the project Like NCAE , HIC testing, addition NDT etc, Check the physical condition of the material Any damages ? like dents , bulging , corrosion, cracks and pitting Check the dimension What are the things you will check for the piping material inspection? Did you come across the pipe ovality? API 5L pipe out of roundness upto 1% of OD, this has been seen in the APL 5L Pipes especially welded pipes. What are the check you have done for the tray installation?

How do you do the trays performance testing? What are the different kind of trays? Bubble cap, Valve trays, How do you do the welder qualification? What is HIC Testing? HIC Testing of material resistance in the sour service environment. Test is done based on NACE-TM-0284 Section the specimen and check the following:  Crack length ratio  Crack thickness ratio  Crack Sensitivity Ratio Acceptance criteria: Crack Length Ratio < 15% Crack thickness ratio < 5% Crack Sensitivity Ratio < 2%

What is the color coding of the Gaskets? What is the roughness required for flanges as per the code B31.9? What is the rejection rate for welders? What is your weakness? What is the strength? What is the min covering required for the ug piping (Sand padding)? I mtr What is sour service? What are precautions to be taken for the sour services? What is dissimilar welding? How do you select the welding material? What is category D fluid service? How to avoid the effects in the service? Or avoid HIC? What is slag? Slag inclusions are oxides and nonmetallic solid materials trapped in the weld metal or at the weld metal interfaces. What is the name called for the angle side of a weld? What is the name called for out side surface of a weld?

What is SFA no What are the AWS codes u used? How do you check the lateral tee connection fit-up What is FCAW Flux cored arc welding

What is the min. % of welding to be completed before the removal of external clamp? 50% For internal clamps 100% of the weld to be completed prior to the clamp removal As per API 1104 what is the maximum misalignment possible? 3mm Your doubts? What is my role there? What is the chances for the promotion? How often this will do? Is there any chance of getting overtime? Any special allowance? KNPC What is a welding procedure? Dissimilar welding? CS to P5 material RT technique Where we use Double wall technique? How to calculate the thickness using the radiography? Design calculation of Pressure vessel? What are the corrosion u have find? How did u check the corrosion? Heat exchanger corrosion inspection? Check the inside shell and end cover, check the tube sheets, If there is significant corrosion on the tube cut one tube and see the conditions. Heat treatment? PWHT? What is the criteria for PWHT?

What is the basis of considering the ½ thickness, when considering the scattered pitting? Design Min temperature and Max tem. How is calculating? Design Calculation for vessels? For Circumferential Stress

For Longitudinal Stress

t = minimum required thickness of shell, in. P = internal design pressure (see UG-21), psi R= inside radius of the shell course under consideration, 15 in. S = maximum allowable stress value, psi (see UG-23 and the stress limitations specified in UG-24) E = joint efficiency for, or the efficiency of, appropriate joint in cylindrical or spherical shells, or the efficiency of ligaments between openings, whichever is less. What are the test to be done for the PQR?. Mandatory test. Tensile Test (two nos) Bend Test Macro Optional tests Impact test Hardness Ferrite test What are differences in section IX and API 1104?.

Section IX

API 1104

Section IX of the ASME Boiler and Pressure Vessel Code relates to the qualification of welders, welding operators, brazers, and brazing operators, and the procedures employed in welding or brazing in accordance with the ASME Boiler and Pressure Vessel Code and the ASME B31 Code for Pressure Piping.

Covers the gas and arc welding of butt, fillet, and socket welds in carbon and lowalloy steel piping used in the compression, pumping, and transmission of crude petroleum, petroleum products, fuel gases, carbon dioxide, nitrogen and, where applicable, covers welding on distribution systems. It applies to both new construction and in-service welding. The welding may be done by a shielded metal-arc welding, submerged arc welding, gas tungsten-arc

welding, gas metal-arc welding, flux-cored arc welding, plasma arc welding, oxyacetylene welding, or flash butt welding process or by a combination of these processes using a manual, semiautomatic, mechanized, or automatic welding technique or a combination of these techniques This standard also covers the procedures for radiographic, magnetic particle, liquid penetrant, and ultrasonic testing, as well as the acceptance standards to be applied to production welds tested to destruction or inspected by radiographic, magnetic particle, liquid penetrant, ultrasonic, and visual testing methods. Procedure Qualification Welder Qualification

What are the test needed for the welder qualification as per the sec IX?. Why 410s is used for the try construction?. Which is the weakest joint in a tank?. What are the welding electrodes used?. In a pipeline what are the location needed to for the thickness survey?. How the settlement reading are taking and what is the acceptance level. What is the permissible tolerance for the verticality of tank as per 653. How do you test PVRV? In procedure qualification the acceptance of tensile value based on which code? ASTM std. for IQI? How Painting Inspection done? Surface preparation, Coating, Holiday testing etc What are code used for the painting

Selection of material for the sour service? What are the density range acceptable for the film? 2 to 3 How to check the Film Quality. For the annular plate what are the NDT to be taken?

Purpose of WPS and PQR The purpose of the Welding Procedure Specification (WPS) and Procedure Qualification Record (PQR) is to determine that the weldment proposed for construction is capable of having the required properties for its intended application.

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