AWS Certified Welding Inspector — FundamentalsWelding MetallurgyEasy
A welding inspector is conducting an examination of a carbon steel weld. The inspector observes a discontinuity characterized by a depression in the base metal adjacent to the toe of the weld, often appearing as a groove. The weld metal itself is sound. What type of weld discontinuity has been observed?
- AUnderfill
- BOverlap
- CIncomplete Penetration
- DUndercut
Show answer & explanationAnswer & explanation
Correct answer: D. Undercut
Undercut is a groove melted into the base metal adjacent to the toe or root of a weld and left unfilled by weld metal. It is a common discontinuity often caused by excessive current, too high travel speed, or incorrect electrode angle. The description of a depression in the base metal adjacent to the toe fits undercut perfectly.
Why the other options are wrong
- A. Underfill is a depression on the face or root surface of the weld, below the level of the adjacent base metal.
- B. Overlap is when weld metal extends beyond the toe or root of the weld, without fusing to the base metal.
- C. Incomplete penetration is when the weld metal does not extend through the full thickness of the joint.
Undercut (Weld Discontinuity)
A groove melted into the base metal adjacent to the toe or root of a weld and left unfilled by weld metal.
- Located in the base metal, next to the weld toe or root.
- Appears as a sharp groove or depression.
- Caused by excessive heat, high travel speed, or incorrect technique.
- Reduces the load-carrying capacity of the joint.
Memory trick: Undercut is a 'cut under' the weld, a groove by its side.