CSWIP QUESTION AND ANSWERS
- State three responsibilities and attributes all senior welding inspectors should possess
He is to plan the work i.e. type of inspection and at what times communication with supervisor, and other department / disciplines etc.
Allocation of duties, specifying area of responsibilities
To check if plan and inspectors are functioning correctly and take remedial steps if not.
Honest and sincere to work
To delegate the work
Understanding of problems
Discipline and decisiveness of problems
- Briefly describe two methods by which the quality control department can control the level of inspection?
- Quality control department can control the quality of work by implementing the inspection procedures, during fabrication process at every stage, inspection test plan
Quality control department should engage well trained experienced qualified personal to perform their duties. Selection of person is very important to perform the assigned duties.
- A fabricated product is required to be made with increased toughness. Out line the QA/QC and inspection requirements which must be under taken in order to attain this requirement.
To increase the toughness of the fabricated part,
a. The inspection should verify the mechanical and chemical properties of the material from the laboratory reports, material selection
b. The test result should be compared with the values given, the material specification should conform that the material to be for fabrication shall meet the quality requirements
c. Use of suitable filler materials with alloying content which shall increase the toughness. Welding parameters in which higher heat input and travel speed so that there will be certain increase in the toughness values. The material shall be tested for NDT to ensure the material is defect free
A product being made to a pressure vessel code has a QC requirement that defects should be limited to 80% of the stated values, but the defects between 80% to 100% values should be referred to QC for approval. Give your appreciation of the reason for this
During an audit no material mill certificate was found. How would you proceed?
If MTC is not available ask the supplier to provide it. If it is not available with supplier then the material should be sent to lab for verifying its chemical and mechanical properties.
Why is it desirable to seal in a lamination which found to break during an edge preparation?
Lamination is to be seal welded prior to welding because these areas will open up during welding due to the heat produced while welding.
Describe two method of producing approval procedures
- a. By using pre qualified procedures
- b. By establishing a procedure
- c. By doing mock up or by trial and error method.
In welder approval test should the procedure be explained to the welder?
No, it is not necessary
What is the difference between a welding procedure approval and welder qualification test?
The welding procedure approval test is carried out by a competent welder and the quality of the weld is assessed using non-destructive and mechanical testing techniques. The intension is to demonstrate that the proposed welding procedure will produce a welded joint which will satisfy the specified requirements of weld quality and mechanical properties.
Procedure provides guidelines to the welder in order to produce the sound weld for the given joint
Welder approval test examines a welder skill and ability in producing a satisfactory test weld. The test may be performed with or with out a qualified procedure, (note, without an approved welding procedure the welding parameter should be recorded). Welder approval must be done prior to start the welding on the production site. Welder should be qualified to do the task
What dose a procedure consist of?
- a. Essential variables: A change in welding parameters which effect the mechanical properties of a weld are called essential variables. E.g. process, type of material, electrode, flux, shielding gas, preheating, PWHT, current and voltage etc.,
- b. Non – essential variables: A change in welding parameters which will not affect the mechanical properties of the weld metal, are called non essential variables e.g. Groove angle, method of cleaning etc.
- c. Supplementary variables: The welding procedure shall be attached with PQR to show the evidence that the procedure meets the mechanical properties described by the code specification.
- Give typical extent of approval for a) thickness b) diameter c) process
- i. Thickness when welder is qualified on thickness T he is qualified to weld two times of the thickness (2T)
- ii. Diameter when welder is qualified to weld on diameter D he is qualified to weld the pipe size OD/2 and above
- iii. Process when qualified in a particular process, he is qualified to weld only on that particular process using thickness parameters that are qualified
- State the objective of 1) reduced transverse tensile test 2) radius – reduced transverse tensile test
- a. A reduced transverse tensile test specimen assesses the tensile the joint
- b. A radius reduced transverse tensile test specimen assesses the tensile strength of the weld metal.
- What is the purpose of 1) A all weld tensile test 2) a radius reduce tensile test
- a. An all weld tensile test is to measure the tensile strength of electrodes / flux combinations and quality of the weld metal as deposited.
- b. A radius reduced tensile specimen assesses the tensile strength of the weld metal.
What feature of steel determines its weld ability?
Carbon content – Carbon equivalent
State three factor which contribute to or control the mechanical properties of wrought steel?
Wrought steel gain much refinement during the hot/cold working and many defects are also removed. This improvement is marked in the rolling direction but it usually results in a loss of strength through the thickness
What is the metallurgical production cause of lamellar tearing?
Due to presence on inclusions of sulphur, phosphor, and higher percent of carbon
Dose a wrought plate contain residual stresses due to manufacture?
Give the composition of tool steel?
High carbon steel-0.8% C, 0.9% Mn + Residuals
If a bend test failure has occurred what would be your course of action?
Set aside the piece, take one more test piece and repeat the test. Assess the failure, whether the failure is within the weld metal, weld junction or in the HAZ. A retest is very much needed in cause of failure
In an Organization which has departments of production and design, engineering, how may the function of inspection, quality control and quality assurance be organized?
- a. Quality control inspection: - Observe, measure, report, advice and verify.
- b. Quality control department: - Give requirements, acceptance levels, codes and procedures which shall be followed
- c. Quality assurance: - Set objects, cost, quality level requirements
Calculate the following for a transverse tensile test, a) Yield stress b) % of elongation, if the maximum load applied at failure is 400 kilonewtons. While extension at the failure was 5mm on an original length of 20mm, given the specimen size is 100mm X 100mm in cross section.
Yield stress = Load / original area
= 400.000/100*100 = 10 KN
% elongation = (Final length – Original length) / Original length
= (25 – 20) / 20 = 25%
Can a non – approved welder be employed to perform a welding procedure test?
- In which steel can it be expected that hydrogen induced cracking is found in the weld metal if present at all?
- High Strength Mn steel.
- State four mechanisms of cracking, which may be found in the weld metal of ferritic steel weld metals
- a. Hydrogen induced cracking
- b. Solidification cracking
- c. Solidified pipe or void
- d. Re heat cracking
- State Six methods of procedure for avoiding solidification or center line cracking.
- a. Add manganese to base metal
- b. Increase metal
- c. Reduce welding speed
- d. Reduce amount of parent metal melting by welder technique and reduce amps
- e. Use 1/3 – 2/3 joint preparation
- f. Use cooling bar
- g. Reduce restrain
- h. Use soft weld metal
- i. Use clean metal
- State three methods of procedures for avoiding solidification pipe in weld metal.
- a. Correct depth to width ratio (open V groove)
- b. Correct bead shape
- c. Correct surface chilling effect due to
No slag cover process
Gas not heated
Flow rate too high
Explain the quality of the parent plate may affect the incidence of weld metal cracking?
State the four factors which give the hydrogen cracking and suggest how control can be exercised?
a. Stress, 2) Hardness, 3) Temperature – thickness
- Minimise stress by 1) Presetting 2) Back stitch welding 3) Stringer bead, Joint design (Double side joint), reduce restraining (J preparation – lower induced angle)
- Minimise hardness by – Lower C>E. Limit heat input to 1.7kg /m / ml (avoid grain enlargement), use BS5135 for preheat
- Minimise hydrogen presence in three ways
- Removal by a combination of preheats – Heat input (inter pass temp.) and PWHT (electric not flame).
- Prevent entry by – selection of process, consumable control, surface cleanliness, Welding techniques (short arc)
- Making hydrogen acceptable by control of formation of microstructure. Use an austenitic or nickel weld metal
Why are austenitic SS electrode sometimes specified for the welding of steel which might be subject to hydrogen cracking
Austenitic stainless steel weld can absorb more hydrogen than carbon steel
In what ways does the thickness of the metal influence hydrogen cracking?
Increase the rate of cooling, large volume of hydrogen, greater stress.
In what steel group is PWHT almost always used?
Group 4 – High carbon steel.
Of the high carbon – no alloy, the carbon content is critical; State the % carbon above which the welding becomes very difficult.
Carbon content in excess of .45
State two results, which may be expected from stress relief of welder products.
a. Will reduce internal stress
b. Hydrogen is diffused
c. Grain refinement
What would be the result of using temperature of 1300deg C in heat treatment?
Steels which are overheated i.e. above 1200deg C may suffer a permanent loss of toughness and also form large quantities of mill scale on their surface
State two types of cracking which can result from heat treatment?
a. Stress relief or reheat cracking in steel containing chromium
b. Thermal cracking
What is the main advantage of using austenitic electrodes?
The advantage of using austenitic stainless steel electrodes for repair is that hydrogen entering the weld metal during welding is held in the weld metal and so will not diffuse in to the hardened HAZ; hence hydrogen induced cracking in the HAZ is unlikely to happen.
What is the main problem of weld ability when using 18/8 type austenitic electrode to repair ferritic steels?
a. Solidification cracking
b. Weld decay
c. Reduce the corrosion resistance of weld metal
What is the main advantage of using 29/10 type austenitic electrode to repair ferritic steel?
The defects of dilution will be to lower the alloy content of the weld metal during cooling so it is advisable to use it
Why is it recommended that 29/10 is used for buttering and 18/8 is used to fill when using austenitic electrode for repair?
To avoid cracking it is desirable (at least in joint with high restraint) to butter with an electrode with high dilution tolerance and to make the closing weld with low strength electrode.
Explain why the depth to width ratio is important?
To take care of residual stresses in weld which develop?
a. Longitudinal along the weld
b. Across the weld
c. Through the weld
Out line the metallurgical feature of weld decay?
Weld decay – steels with high carbide forming characteristic such as these will react if the temperature is allowed to dwell about 550degC. If this occurs then the chromium is no longer available for combination with oxygen for reformation of the protective oxide film and corrosion may result.
Weld decay – depletion of chromium carbide in stainless steel.
State three method of avoiding weld decay?
a. Reduce carbon content i.e. 308L
b. Heat treatment 1100deg C and quench
c. To stabilize the steel by added Ti or Nb (to form carbide in preference to Cr carbides)
Why backing gases are often specified when welding stainless steel?
a. To avoid contamination.
b. To prevent formation of porosity
c. To avoid formation of oxides
Why is carbon –di-oxide not normally used as shielding gas when welding mild steel?
When stainless steel is welded to mild steel buttering is recommended why?
a. Seals carbon in
b. To stop dilution
When welding SS to a large root gap (3mm) are often used? Why?
To avoid distortion
What is the essential feature of a stainless steel?
Chromium content. About 11% Cr is the minimum for the formation of SS.
What is the principal reason for the development of residual stresses in weld
Metals contact during solidification and subsequent cooling, but if this contraction is prevented or inhibited residual stresses will develop
Name three directions of residual stresses in weld joint.
Normal welds develop residual stresses.
a. Along the weld – longitudinal residual stresses
b. Across the weld – transverse residual stresses
c. Through the weld – short transverse residual stresses
What causes distortion in welded products?
The action of the residual stresses in welded joints is to cause distortion
MMA (SMAW) defects
- Give four consequences of using excessive current
- Excess spatter, 2) Excess metal profile, 3) Centerline cracking, 4) under cuts.
If excessive arc length
a. UN stable arc, 2) lack of penetration, 3) uneven profile bead.
State the defects which occur when the tack weld is not correctly incorporated into the weld?
Lack of penetration or fusion
Give three consequence of in correct electrode angle?
a. Undercut, 2) spatter, 3) lack of penetration or fusion.
Give one consequence of
a. Too fast a travel speed – lack of penetration or fusion
b. Too slow a travel speed – slag inclusion
What defect I associated with excessively large size electrodes?
Lack of penetration
What defect is caused by inadequate cleaning between runs?
58. What defect can be caused by use of high welding speeds?
a. lack of penetration or fusion 2) Undercut
What defect can be caused by the use of excessive gaps?
Excess penetration or burn through
What is the likely cause of slag in the weld metal?
Slag inclusion: Insufficient Inter – run cleaning, poor bead profile (convex shape)
What is the adjustment must be made in submerged arc welding to reduce the bead width?
a. Lower the voltage
b. Increase the travel speed (if still within the parameter)
What defect can be caused by a plate having poorly cut joint preparation?
Lack of penetration or fusion
A weld is to be made on a close square butt joint with excessively high current. What defect would occur?
Excess weld metal
What is the likely defect to be caused by an excessive flux burden?
What is the critical level of hydrogen in a weld; can it be measured at any time or after stress relief?
a. 5ml per 100gm of weld metal
b. All weld metal hydrogen diffusion test possible but not for the actual weld metal
Describe how and why hydrogen increases the incidence of hydrogen cracking?
Hydrogen in the weld / HAZ builds up internal pressure which could be higher that weld point of metal. Low hydrogen = less stress.
Describe a heat treatment designed to remove hydrogen When must the heat
Why must basic hydrogen controlled electrodes been kept at 10 deg C?
Prevent reabsorbing of hydrogen
What is the cause of lamellar tearing?
Lamellar tearing is a defect in the parent metal of a weld metal due to high through thickness residual stresses and a low through thickness strength and ductility arising from the bands within the steel
Where the lamellar tearing is are found in a weld metal?
The crack is stepped. The crack is parallel to the surface of the plate
How do bands (segregation) within steel influence the incidence of lamellar tearing?
Can susceptibililty to lamellar tearing be assessed by Ultrasonic NDE? NO.
Can lamellar tear be detected by NDE? NO
Three methods to avoid lamellar tearing?
a. Reduce the residual stress by low restraints i.e. by pre setting rather than clamping use of gaps
c. Change in joint design
Name three types of stainless steels?
- Martensitic, 2) Austenitic, 3) Feritic.
State the main weldability problem of the Fe 11% chromium steels?
Why are ferritic SS not generally suitable for welding?
They suffer grain growth with heating and the loss of strength and toughness on welding, severly limits the use of this alloy.
Why are some SS stabilized? Which elements are used?
To avoid depletion of chromium
Titanium and niobium elements are used as stabilizer
Name two methods of avoiding hydrogen cracking in martensitic stainless steel?
a. Control by hydrogen limitation i.e. the use of TIG welding process
b. Control by hardness, normal pre-heat and heat inputs, so select a very low carbon grade.
State the following materials are magnetic.
FeO - 0.1% C - Yes
FeO - 0.8% C -Yes
Fe - 11% Cr -Yes
Fe - 10% Ni -Yes
Fe - 18% Cr, 8% Ni - No
Cu - 10% Ni - No
Stellitite - No
Why do micro alloyed steels suffer hydrogen cracking in the weld metal?
The hydrogen is held in the weld and so hydrogen tends to be located there also
What are the factors which give rise to hydrogen cracking in alloyed steels?
In the HAZ the tensile residual stresses are across the weld, so the hydrogen cracks are along the length of the weld. In weld metal the tensile residual stresses are along the weld, so the hydrogen cracks are across the weld.
What are the two types of SAW flux?
a. Fused, 2) Agglomerated.
Why are hydrogen cracks in the weld metal positioned across the width of the weld?
Hydrogen cracking is typically formed at right angles to the stress and is positively identified by its Trans granular appearance when viewed at X – 100 magnifications. In ferritic steels hydrogen which enters the weld metal during welding moves into the HAZ and due to gas forming characteristics and the residual stress, cracking may result.
Three items which may contribute to excessive hardness in a weldmetal?
Grain size, Quenching, C.E, carbon and alloys.
Two elements cause center-line cracking?
What is the cause of centerline cracking or solidification cracking?
Impurities which are melted out of parent plate and mixed into the weld metal separate out during solidification.
Method of minimizing the solidification cracking?
a. Increase the weld metal
b. Reduce the welding speed
c. Increase the manganese content of the weld pool
d. Use of cooling bars
e. Use of 1/3 – 2/3 joint preparation
f. Use of clean metal
g. Reduce the amount of metal melted out of the parent plate by
i. Skill / technique of the welder
ii. Reduce the current
A crack observed along the center line of the weld. Give two reasons for its formation
When the weld metal has been deposited and its contracts during solidification it is vital that the contraction can be fed by the depression of the outer surface
Contraction fed by the weld metal surface
Give three reasons why pipe may form in the weld metal?
a. Pre-mature freezing of the surface
b. Excessive depth of bead related to width
c. Bad bead shape
Three reasons which contribute to pre- mature freezing of the weld pool surface?
a. No slag covers i.e. the process
b. Gas no heated
c. Flow rate too high
Why ferritic material is usually added to austenitic electrodes?
To avoid center line cracking
Why are austenitic electrodes used for welding carbon manganese steel?
To control the hydrogen level i.e. making the hydrogen level acceptable to avoid hydrogen cracking
When ferrite is added to electrodes what are two possible consequences?
It tends to avoid Solidification cracking, it does induce magnetism and makes the weld metal anodic so reducing the corrosion resistance
Give two advantages of martensitic SS?
a. Magnetic, 2) Abrasion resistant
Why are ferritic SS so named?
Micro structure is ferritic.
Give two reasons why the grain growth which occurs on welding makes these materials unsuited for many welded products i.e. ferritic SS?
As the chromium content is increased, increased quantities of sigma phase is produced which embrittles the steel. Solidification cracking is a problem. Single phase alloying suffer grain growth and with heating and the loss of strength and toughness
Can the enlarged grain size in the HAZ of ferritic SS be refined? If so how?
Yes by peening
Two weldability problems connected with austenitic SS.
a. Cracking, 2) Weld decay
Describe the thermal conditions which give rise to weld decay in austenitic SS weld metals?
550degree C for six seconds
Why are smaller stringer beads usually recommended for SS weldment
To reduce the level of heat input and to avoid cracking
State the special mechanical properties of 25%Cr in Fe alloys?
Ferritic SS: weldability poor due to cracking, brittleness and temper embitterment, it is a single phase alloy which is ferritic at all solid temperatures, so solidification cracking is a problem
What is specification?
It’s a description of what to use in the making of a product i.e. type of material, type of process, type of consumables.
What is the extent of approval in a procedure?
Extent of approval is the range over which certain variables may alert with out requiring new procedure i.e. when there is a limitation in the welding qualification i.e.
a. The minimum and maximum diameter of the pipe that the test sample covers e.g. two inch test piece would allow pipe down to 1” and up to 4”
b. The test may only allow welding of consumables in the same grouping, any other consumables would requires re-test
c. The sue of set electrical characteristics would not allow change with out retest
d. The direction of welding, if changed may required re test
e. Change of material to be tested would require re – testing
When is procedure to be re established?
a. Change of process, direction, material, shielding gas, Joint design, consumables, welding parameters….
State the four factors which must be satisfied for good weld?
a. Fusion (melting) – The metal be melted which requires a high intensity of heat source
b. The process must remove any oxide and other contaminations from the joint faces
c. Contamination by the atmosphere must be avoided
d. The welded joint must possess adequate properties
If you detect arc strike what is the course of action?
It should be grounded smooth and MPI is to be conducted on the location if it is ferrous material. For SS, PT is to be conducted
What are planner defects?
e. Crater cracks
Four mechanical test methods?
c. Nick break
What are the documents required to do a repair?
Approved repair welding procedure, qualified welders, Method of exploration of crack &removal & repair reports.
If visual inspection is not possible how you will ensure the joint is defect free?
It can be examined by appropriate NDT methods like RT, UT, etc…,
What are major defects?
a. Lack of side wall & Inter- run fusion,
d. Lack of penetration & incomplete fusion
What are Minor defects?
Mis – alignment (linear & angular), slag, Porosity etc.
What is the course of action if the weldment has been accepted are rejected?
After inspection the results has to be recorded in a format. If the sample is rejected then the type of defects and its location has to be incorporated in a sketch and the report has to be given for further remedial action.