Questions related to Welding/ Weld defects/Post heating/Post weld heat treatment/ Electrode/Filler wire.
1. Q:- What do you mean by following type of welding?
- SMAW B. TIG
Answer:- A. SMAW : - Shielded Metal Arc Welding.
- TIG : - Tungsten Inert Gas Welding.
2. Q:- Mention the contents of TIG welding set?
Answer:- A. Torch : Consist of hose for argon gas / welding lead / ceramic nozzle/ collet / tungsten rod as
cathode to create arc.
- Regulator with Pressure Gauge (HP & LP) & flow meter.
- Argon cylinder – Gr.2 / Gr.1 depending upon requirements of the job.
- Transformer / Rectifier.
- Filler wire
3. Q:- While welding of pipe trunnion to pipe/reinforcement pad you have to put a hole or leave some portion of welding why?
Answer:
For venting of hot gas which may get generated due to welding.
4. Q:- What is the thumb rule to calculate Current required for Welding?
Answer:
20±Current (Amp) = [Diameter of Electrode (mm) X 40]
5. Q:-What is the minimum thickness of cs pipe that requires stress relieving to be done as per B31.3?
Answer: - 19.05 mm thk.
6. Q:-Which is the Electrode & filler wire used for welding of following materials?
- Alloy steel
- ASTM A335PI
- ASTM A335P2
III. ASTM A335P11
- ASTM A335P5
- ASTM A335P9
- Stainless steel
- ASTM A312TP304
- ASTM A312TP304L
III. ASTM A312TP304H
- ASTM A312TP308
- ASTM A312TP310
- ASTM A312TP316
VII. ASTM A312TP316L
VIII. ASTM A312TP316H
- ASTM A312TP321
- ASTM A312TP321H
Answer: -
Covered Electrode Bare electrode
Alloy Steel
- ASTM A335PI E7018 E70 S-1B
- ASTM A335P2 E8018-B1 ---
III. ASTM A335P11 E8018-B2 ER515
- ASTM A335P5 E502 ER502
- ASTM A335P9 E505 ER505
Stainless Steel
- ASTM A312TP304 E308 ER308
- ASTM A312TP304L E308L ER308L
III. ASTM A312TP304H E16-6-2 ER16-8-2
- ASTM A312TP308 E309 ER309
- ASTM A312TP310 E310 ER310
- ASTM A312TP316 E316 ER316
VII. ASTM A312TP316L E316L ER316L
VIII. ASTM A312TP316H E16-8-2 ER16-18-2
- ASTM A312TP321 E347 ER347
- ASTM A312TP321H E16-6-2 ER16-8-2
7. Q:-What are the common welding defects?
Answer: -
- Lack of penetration.
- Lack of fusion.
- Undercut.
- Slag inclusion.
- Porosity.
- Crack.
- Faulty weld size & profile.
- Distortion.
- Lack of penetration.
This defect occurs at the root of the joint when the weld metal fails to reach it or weld metal fails
to fuse completely the root faces of the joint. As a result, a void remains at the root zone, which
may contain slag inclusions.
Cause: -
- Use of incorrect size of electrode in relation to the form of joint.
- Low welding current.
- Faulty fit-up and inaccurate joint preparation.
- Lack of fusion.
Lack of fusion is defined as a condition where boundaries of unfused metal exist between the
Weld metal & base metal or between the adjacent layers of weld –metals.
Cause: -
- Presence of scale, dirt, oxide, slag and other non-metallic substance which prevents
the weld metal to reach melting temperature.
- Improper deslagging between the weld pass.
Precaution: -
- Keep the weld joint free from scale, dirt, oxide, slag and other non- metallic substance.
- Use adequate welding current.
- Deslag each weld pass thoroughly.
- Place weld passes correctly next to each other.
- Undercut
This defect appears as a continuous or discontinuous groove at the toes of a weld pass and is
located on the base metal or in the fusion face of a multipass weld. It occurs prominently on the
edge of a fillet weld deposited in the horizontal position.
Cause: -
- Excessive welding current.
- Too high speed of arc travel.
- Wrong electrode angle.
Rectification: -
The defect is rectified by filling the undercut groove with a weld pass. If undercut is deep &
contains slag, it should be chipped away before rewelding.
- Slag Inclusion
Non–metallic particles of comparatively large size entrapped in the weld metal are termed
as slag inclusion.
Cause: -
- Improper cleaning of slag between the deposition of successive passes.
- Presence of heavy mill scale, loose rust, dirt, grit & other substances present on the
surface of base metal.
Precaution: -
- Clean the slag thoroughly between the weld pass.
- Keep the joint surface (especially gas cut surface) and bare filler wire perfectly clean.
- Avoid undercut & gaps between weld pass.
- Use proper welding consumables.
- Porosity
The presence of gas pores in a weld caused by entrapment of gas during solidification is
termed as porosity. The pores are in the form of small spherical cavities either clustered locally
or scattered throughout the weld deposit. Sometimes entrapped gas give rise to a single large
cavity called Blowholes.
Cause: -
- Chemically imperfect welding consumables, for example, deficient in deoxidiser.
- Faulty composition of base material or electrode, for example, high sulphur content.
- Presence of oil, grease, moisture and mill scale on the weld surface.
- Excessive moisture in the electrode coating or submerged-arc flux.
- Inadequate gas shielding or impure gas in a gas –shielded process.
- Low welding current or too long an arc.
- Quick-freezing of weld deposit.
- Crack
Fracture of the metal is called crack. Two types of cracks: - Cold crack & Hot crack.
Cold crack usually occur in HAZ of the base metal when this zone becomes hard and brittle due
to rapid cooling after the weld metal has been deposited & sufficient hydrogen has been
absorbed by the weld metal from the arc atmosphere.
Precaution: -
- Use of low carbon equivalent materials.
- Higher heat input during welding.
- Preheating.
- Use of low hydrogen electrode.
- Faulty weld size and profile
A weld is considered faulty if it has lack of reinforcement, excessive reinforcement or irregular
Profile.
- Distortion
Because a weldment is locally heated (by most welding processes), the temperature
distribution in the weldment is not uniform and changes take place as welding processes.
Typically, the weld metal and the base metal heat-affected zone immediately adjacent to it are
at a temperature substantially above that of the unaffected base metal. As the molten pool
solidifies and shrinks, it begins to exert shrinkage stresses on the surrounding weld metal and
heat-affected zone area. When it first solidifies, this weld metal is hot, relatively weak, and can
exert little stress. As it cools to ambient temperature, however, the shrinkage of the weld metal
exerts increasing stress on the weld area and eventually reaches the yield point of the base
metal and the heat-affected zone. Residual stresses in weldments have two major effects. First,
they produce distortion, and second, they may be the cause of premature failure in weldments.
Distortion is caused when the heated weld region contracts no uniformly, causing shrinkage in
one part of the weld to exert eccentric forces on the weld cross section.
The distortion may appear in butt joints as both longitudinal and transverse shrinkage or
Contraction, and as angular change (rotation) when the face of the weld shrinks more than the
root.
Distortion in fillet welds is similar to that in butt welds: transverse and longitudinal shrinkage as
well as angular distortion results from the unbalanced nature of the stresses in these welds.
8. Q:- What is mean by ‘PWHT’? Why it is required?
Answer: -
“POST WELD HEAT TREATMENT” This is done to remove residual stress left in the joint which may
cause brittle fracture.
9. Q:-Why pre-heating is done on some pipe before starting welding?
Answer: -
To slow down the cooling rate.
10. Q:-Why post-heating is done on some pipe after the welding is over?
Answer: -
To maintain uniform homogeneous structure.
11. Q:-What is the pre-heat temperature for carbon steel above 19.05MM thk.
Answer: -
Pre –heat temperature for carbon steel above 19.05 mm is 80 C.°
12. Q:- Is post heating required for carbon steel material above 19.05MM thk.
Answer: -
No. Post heating is not required for carbon steel material of any thickness.
13. Q:-What is the soaking temperature during stress reliving for carbon steel material?
Answer: -
C)°20±C. (°Soaking temperature for carbon steel material during stress reliving is 620
14. Q:- What is the soaking period during stress relieving for carbon steel material?
Answer:- Soaking period for carbon steel material during stress relieving is 1hr.
Q:- What is the rate of heating & cooling during stress relieving for carbon steel material?
Answer: -
The rate of heating & c/hr.°cooling for carbon steel material during stress reliving is 150
16. Q:-What is the pre-heat temperature during stress reliving for alloy steel materials?
Answer: -
Pre-heat temperature for AS materials is 180 C.°
17. Q:-What is the soaking temperature during stress relieving for alloy steel material?
Answer: -
C).°20±C(°Soaking temperature for alloy steel material is 720
18. Q:-What is the soaking period during stress reliving for alloy steel material?
Answer: -
Soaking period for alloy steel material is 2hrs.
19. Q:-What is the rate of heating & cooling during stress reliving for alloy steel material?
Answer: -
The rate of heating & C/hr.°cooling for alloy steel material is 100
20. Q:-What is the post heat temperature for alloy steel material?
Answer: -
Post heat temperature for alloy steel material is 300 C.°
21. Q:-What is a four or five digit coding for electrode as per AWS classification SFA 5.1?
Answer: -
E X X X X X
X X X X
The minimum UTS of Welding position. Type of coating
the undiluted weld metal and current condition.
in psi. ( UTS – Ultimate tensile strength).
22. Q:-Where the use of electrode E7018 is recommended?
Answer: -
The use of electrode E7018 is recommended for welding the following: -
- For high strength steel.
- For high thickness carbon steel plates.
- Higher carbon equivalent material.
23. Q:-Why the electrode E7018 is called low hydrogen electrode?
Answer:-
The low hydrogen electrodes have in their coating ingredient, which produces carbon di-oxide during
melting. This CO2 gives a gaseous shielding for the metal and prevents atmospheric hydrogen from
entering in arc atmosphere. By this way the weld metal has low level of hydrogen.
24. Q:-What should be the content of chlorine in water while conducting hydrotest for CS & SS pipes?
Answer: -
For CS – 250 PPM.
For SS – 30 PPM.
25. Q:-Draw the stress-reliving diagram for carbon steel & Alloy steel material?
Answer: -
Soaking period ( 1hr. for C.S & 2hrs. for AS)
(Note: - The stress reliving diagram remain same
for both AS & CS. The difference is only
in soaking temperature.)
Time
Temperature
26. Q:-What is the test positions for fillet & groove welding in case of plate & pipes?
Answer: -
Test positions for Fillet welds: -
Plate positions: -
- Flat Position 1F : - Plates so placed that the weld is deposited with its axis horizontal & its
throat vertical. Refer sketch (a).
- Horizontal Position 2F : - Plates so placed that the weld is deposited with its axis horizontal on
the upper side of the horizontal surface and against the vertical
surface. Refer sketch (b).
- Vertical Position 3F : - Plates so placed that the weld is deposited with its axis vertical. Refer
sketch (c).
- Overhead Position 4F : - Plates so placed that the weld is deposited with its axis horizontal on
the underside of the horizontal surface and against the vertical surface.
Refer sketch (d).
Pipe positions: -
to horizontal and rotated during°A. Flat Position 1F : - Pipe with its axis inclined at 45
Welding so that the weld metal is deposited from above and at the point
of deposition the axis of weld is horizontal and the throat vertical. Refer
sketch (a).
- Horizontal Position 2F : - Pipe with its axis vertical so that the weld is deposited on the upper
side of the horizontal surface and against the vertical surface. The axis
of the weld will be horizontal and the pipe is not to be rotated during
Welding. Refer sketch (b).
- Horizontal Position 2FR: - Pipe with its axis horizontal and the axis of the deposited weld in the
vertical plane. The pipe is rotated during welding. Refer sketch (c).
- Overhead Position 4F : - Pipe with its axis vertical so that the weld is deposited on the underside
of the horizontal surface and against the vertical surface. The axis of
the weld will be horizontal and the pipe is not rotated during welding.
Refer sketch (d).
- Multiple Position 5F : - Pipe with axis horizontal and the axis of the deposited weld in the
vertical Plane. The pipe is not to be rotated during welding. Refer
sketch (e).
Test positions for Groove welds: -
Plate positions: -
- Flat Position 1G : - Plate in a horizontal plan with the weld metal deposited from above.
Refer sketch (a).
- Horizontal position 2G : - Plate in a vertical plane with the axis of the weld in horizontal.
Refer sketch (b).
- Vertical position 3G : - Plate in vertical plane with the axis of the weld vertical. Refer sketch (c).
- Overhead Position 4G : - Plate in a horizontal plane with the weld metal deposited from
underneath. Refer sketch (d).
Pipe Positions: -
- Flat Position 1G : - Pipe with its axis horizontal and rolled during welding so that the weld
metal is deposited from above. Refer sketch (a).
- Horizontal Position 2G : - Pipe with its axis vertical and the axis of weld in a horizontal plane.
Pipe shall be not be rotated during welding. Refer sketch (b).
- Multiple Position 5G : - Pipe with its axis horizontal and the welding groove in vertical plane.
Welding shall be done without rotating the pipe. Refer sketch (c).
to horizontal. Welding shall be done°D. Multiple Position 6G : - Pipe with its axis inclined at 45
without rotating the pipe. Refer sketch (d).
27. Q:-Draw the Groove details for 6G position in pipe?
°2 ½±°75
0.5 MM±1 MM
1 MM±2.5MM
Joint details for 6G Position.
28. Q:-Draw the Groove details for 2G & 3G position in case of plates?
Answer: -
to 70°60°
10 MM THK.(Max.)
2 TO 3.2MM
2 TO 3.2 MM
2MM°45
3MM°to 70°60
12 MM THK. & Above.
2 TO 3.2
2 TO 3.2 MM
Joint details for 3G Position Joint details for 2G Position
(vertical joint). (Horizontal Joint).
29. Q:- What is the effect if the quantity of hydrogen induced in weld metal is more?
Answer:-
When hydrogen is more in weld metal, it tends to make the material brittle & subsequently leads to
cracking. These cracks are called hydrogen induced cracking or delayed crack. To avoid this the
C for one hour in mother oven°C to 300°electrode before using is backed at 250 & then cooled down
C in the same oven°to 100 & finally transferred to portable oven for use where temperature is to 70°maintained at 60°
