Welding/ Weld Defects/Post Weld Heat Treatment/Electrode/Filler Wire

Q#1: What do you mean by following type of welding?
(A) SMAW, ( B) TIG

Ans: SMAW: Shielded Metal Arc Welding
TIG: Tungsten Inert Gas Welding

Q#2: While welding of pipe trunion to pipe / reinforcement pad you have to put a hole or leave some portion of welding why?

Ans: For venting of hot gas which may get generated due to welding.

Q#3: What is the thumb rule to calculate Current required for welding?
Ans: Current( Amp) = ( Diameter of Electrode(mm) X 40)

Q#4: What is the minimum thickness of CS pipe that requires stress relieving to be done as per B 31.3 ?
Ans: 19.05mm thk.

Q#5: What are the common welding defects?
Ans: 1: Lack of Penetration
2: Lack of fusion
3: Under cut
4: Slag Inclusion
5: Porosity
6: Crack
7: Faulty weld size & Profile
8: Distortion


A: Lack of penetration:
This defects occurs at the roof 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 inclusion.

Cause: (A) : Use of incorrect size of electrode in relation to the form of joint
(B): Low welding undercut
(C): Faulty fit-up and inaccurate joint preparation

B: Lack of fusion:
Lack of fusion is defined as a condition where boundaries of unfused metal exist between the weld metal a base metal or between the adjacent layers of weld metals.

Cause:

A) Presence of scale, dirt, oxide, slage and other non-metallic substance which prevents the weld metal to reach melting temperature.

B) Improper deslagging between the weld pass.
Precaution:-
A) Keep the weld joint free from scale, dirt, oxide, slag and other non-metallic substance.
B) Use adequate welding current
C) Deslag each weld pass thoroughly
D) Place weld passes correctly next to each other

Under Cut:
This defect appears as a continuous or discontinuous groove at the toes of a weld pass and 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:
A) Excessive welding current
B) Too high speed of arc travel
C) Wrong electorde 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.