What are the maximum melt-through width and height allowed on the backside of a fillet weld?

• A. 5 mm width and 1.5 mm height
• B. 3 mm width and 0.5 mm height
• C. 7 mm width and 2 mm height
• D. 2 mm width and 1 mm height

Answer: (A)

Melt-through on the backside of a fillet weld is the amount of molten metal that penetrates through to the back side of the joint. Keeping this under a set limit prevents burn-through and helps maintain the joint’s strength and integrity. The maximum allowable dimensions are 5 mm in width and 1.5 mm in height. This combination gives enough root fill for a solid weld while limiting how far the heat can push through to the backside, avoiding excessive material loss, distortion, or back-side defects. In practice, you’d inspect after welding and ensure the backside melt-through does not exceed these figures; if it does, you’d adjust technique to stay within the limit. The other options either would permit too much melt-through, risking burn-through and damage, or would imply a smaller maximum than is specified for this standard.