What is the consequence of too little weld penetration?

Too little weld penetration results in the weld sitting on top of the base metal without adequately fusing with it. This can lead to weak joints that may not withstand stresses or loads as effectively as a properly penetrated weld. Insufficient penetration means that the weld lacks the depth needed to ensure a strong bond between the welded pieces, which compromises structural integrity and can lead to failures in service.

In contrast, if a weld penetrates too deeply, it could potentially burn through the base metal, creating holes or weakening the material, which is a different issue altogether. Insufficient penetration does not create a flat surface flush with the base metal, but instead creates a raised profile, thus distinguishing it from the choice indicating that the weld will be even with the base metal. While unevenness can occur due to various factors in welding, it is a separate concern from the direct effects of inadequate penetration.