Lack of penetration has a lot of harm, the first is to reduce the effective area of the weld, the joint strength is lowered. Second, the harm caused by the lack of penetration stress concentration is large, lack of penetration severely reduce the fatigue strength of the weld. Lack of penetration may become a source of cracks, it is an important cause of weld failure.
There are the main reason to cause welding torch appears incomplete penetration, for example, groove weld joint angle is small, the gap is too small blunt edge is too thick, welding speed is too fast, weldment cooling too fast, not fully fused between the bath and the base metal.
