A welder is fabricating a 6 mm thick mild steel plate assembly. During the final visual inspection, they notice several small, elongated, and sharp-edged discontinuities along the root pass of a fillet weld, particularly in corners or tight areas. This typically indicates:

Question: A welder is fabricating a 6 mm thick mild steel plate assembly. During the final visual inspection, they notice several small, elongated, and sharp-edged discontinuities along the root pass of a fillet weld, particularly in corners or tight areas. This typically indicates:

Answer options:

• Arc blow
• Insufficient preheat ✅ Lack of fusion
• Toe cracks

Correct answer: Lack of fusion

Explanation: Small, elongated, and sharp-edged discontinuities along the root, especially in tight corners, are characteristic of lack of fusion or incomplete penetration, where the weld metal did not properly melt and fuse with the base metal or previous weld bead. Arc blow affects arc stability, insufficient preheat can cause hydrogen cracking, and toe cracks are at the weld toe, not typically along the root pass in this manner.