This is an imperfection at a toe or root of a weld caused by metal flowing on to the surface of the parent metal without fusing to it. It may occur in both fillet and butt welds.
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| Overlap |
Common causes
This is often caused by poor manipulation of the electrode or welding gun, especially when the weld pool is large and 'cold', where the welder allows gravity to influence the weld shape before solidification. Tightly adherent oxides or scale on the metal surface can also prevent the weld metal fusing with the parent metal to cause the overlap imperfection.
Avoidance
Avoidance is achieved through an acceptable level of welder skill and a reduction in weld pool size (obtained by reducing current or increasing travel speed). Adequate cleaning of the parent plate is also important.
Acceptance
Standards rarely allow the presence of this imperfection, unless the length is short (eg BS EN 25817 for moderate quality level D). Overlap can be very difficult to detect, especially if it is extremely small.
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