In a welded fabrication, which of the following discontinuities is common?

Lack of fusion is a common discontinuity in welded fabrications because it occurs when the weld metal does not properly bond to the base metal or to the previous layers of weld material. This can happen for several reasons, such as improper welding techniques, insufficient heat during the welding process, or contamination of the weld surfaces. The presence of lack of fusion can compromise the integrity and strength of the welded joint, leading to potential failures in structural applications. Identifying and addressing this discontinuity is critical in ensuring the reliability and safety of welded structures.

Shrinkage, seams, and laps may be present in a welded fabrication but do not reflect the specific bonding issues that characterize lack of fusion. Shrinkage relates to the reduction in size as materials cool, seams are merely the joining of metals along their edges, and laps occur when one piece overlaps another but doesn't represent a failure in fusion. Thus, they are less critical concerns compared to the bond integrity represented by lack of fusion.