Which symptom in a vertical weld most strongly indicates undercutting due to heat input?

Which symptom in a vertical weld most strongly indicates undercutting due to heat input?

• A. Undercut at the toe with incomplete fusion
• B. Deep penetration with smooth toe
• C. Uniform crown and minimal bead height
• D. No visible defects at all

Answer: (D)

Undercutting shows up as a groove along the weld toe where the base metal has melted away instead of being filled by weld metal. In a vertical weld, this groove is a direct consequence of excessive heat input, which causes the molten metal to pull back from the toe as it solidifies. So the strongest indication that heat input is causing undercut is seeing an undercut right at the weld toe. Other signs like deep penetration with a smooth toe, a neat crown with a minimal bead, or no visible defects point to different conditions and do not indicate undercut.

Undercutting shows up as a groove along the weld toe where the base metal has melted away instead of being filled by weld metal. In a vertical weld, this groove is a direct consequence of excessive heat input, which causes the molten metal to pull back from the toe as it solidifies. So the strongest indication that heat input is causing undercut is seeing an undercut right at the weld toe. Other signs like deep penetration with a smooth toe, a neat crown with a minimal bead, or no visible defects point to different conditions and do not indicate undercut.