What are the Common Welding Defects?

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:
(A) Use of incorrect size of electrode in relation to the form of joint.
(B) Low welding current
(C) 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 or between the adjacent layers of weld metals.

Cause:
(A) Presence of scale, dirt, oxide, slag 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 afillet weld deposited in the horizontal position.

Cause:
(A) Excessive welding current
(B) Too high speed of Arc travel
(C) 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:

(A) Improper cleaning of slag between the deposition of successive passes.
(B) Presence of heavy mill scale, loose, rust, dirt, grit & other substances present on the surface of base metal.

Precaution:

(A) Clean the slag thoroughly between the weld pass.
(B) Keep the Joint surface (especially gas cut surface)and bare filler wire perfectly clean.
(C) Avoid undercut & gaps between weld pass.
(D) Use proper welding consumables.

Porosity:

The presence of gas pores in a weld caused by entrapment of gas during solidfication 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:

(A) Chemically imperfect welding consumables, for example, deficient in deoxidiser.
(B) Faulty composition of base material or electrode, for example, high sulphur content.
(C) Presence of oil, greese, moisture and mill scale on the weld surface.
(D) Excessive moisture in the electrode coating or submerged -arc flux.
(E) Inadequate gas shielding or impure gas in a gas-shielded process.
(F) Low welding current or too long an Arc.
(G) Quick Freezing of weld deposit.

Crack:

Fracture of the metal is called crack. Two types of cracks:-

Cold 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:

(A) Use of low carbon equivalent materials.
(B) Higher heat input during welding.
(C) Preheating.
(D) Use of low hydrogen electrode