What causes the following weld defects? (i) Undercut (ii) Slag inclusion (iii) Porosity (iv) Excessive penetration – NABTEB QUESTION

(i) Undercut

– A too rapid rate of travel of electrode or blow pipe.
– Use of wrong electrode or blow pipe.
– It can be caused by excessive heat built up.

(ii) Slag inclusion

– Using too low current to weld.
– Using too large electrode.
– Fast metal surface can cause it.

(iii) Porosity

– Using damp or wet electrode
– Welding on dirty surface of metal like rust, grease, water etc.

(iv) Excessive penetration

– Using too high welding current.
– Slow rate of travel of electrode or blow pipe.
– Bad edge preparation or wide root gap.
– Too much concentration of heat.