What is the maximum single undercut length allowed?

• A. 1.6 mm
• B. 2.0 mm
• C. 0.8 mm
• D. 2.2 mm

Answer: (A)

Undercut along the weld toe weakens the joint by removing material from the base metal, creating a notch that can concentrate stress. Codes set acceptance limits for how large this imperfection can be. For a single undercut, the maximum length allowed is 1.6 mm (about 1/16 inch). This means a single continuous undercut shorter than or equal to 1.6 mm is acceptable (assuming no other defects exceed limits). If the undercut extends longer than 1.6 mm, it would fail the inspection criteria for undercut.

When inspecting, you measure along the weld toe from the edge into the undercut to determine its length; multiple shorter undercuts are evaluated individually, but the single undercut length limit applies to each continuous instance.

The other options exceed typical code limits or, in the case of a shorter value, are simply not the maximum allowed.