Which of the following is considered a common surface defect in welding processes?
Undercut along the weld bead
Welding defects are broadly grouped as surface (external) defects, which are visible on the finished weld, and internal (sub-surface) defects, which lie within the joint and usually need NDT methods (radiography, ultrasonics) to detect. The question asks for a common surface defect, and the correct answer is undercut along the weld bead.
Undercut is a groove or notch melted into the base metal along the toe (edge) of the weld that is not filled by weld metal. It is caused by excessive current, too high a travel speed, an incorrect electrode angle or an overly long arc. It is dangerous because it reduces the cross-section of the base metal and acts as a stress raiser from which fatigue cracks can start, yet it is clearly visible at the surface.
Comparing with the other options:
- Excessive spatter consists of loose metal droplets on the surface; it is a cosmetic/cleanliness issue rather than a structural weld defect.
- Lamellar tearing is an internal, step-like crack that forms beneath the weld parallel to the plate surface, driven by inclusions and through-thickness stresses — a sub-surface defect.
- Incomplete penetration occurs at the root, deep inside the joint, and is not visible from the surface.
Because it is external and readily observed, the recognised common surface defect is undercut along the weld bead.
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