Which weld is performed before welding on the reference line?

Which weld is performed before welding on the reference line?

• A. Backing weld
• B. Back weld
• C. Root tack
• D. Cap weld

Answer: (A)

The important idea here is that a backing weld is used to support and back up the joint from the opposite side before you lay down the main weld along the reference line. By filling in the root side on the back, you create a solid foundation and heat sink which helps control root penetration and prevents burn-through on the far side. When the reference-line weld is then added, the joint already has backing, making fusion more reliable and the final cap easier to weld with proper contour and strength. Root tack is simply temporary fasteners to hold pieces in place and does not provide the continuous backing needed for a strong root and cap. The cap weld is the final bead placed on top of the joint, not something done before establishing the backing on the opposite side.

The important idea here is that a backing weld is used to support and back up the joint from the opposite side before you lay down the main weld along the reference line. By filling in the root side on the back, you create a solid foundation and heat sink which helps control root penetration and prevents burn-through on the far side. When the reference-line weld is then added, the joint already has backing, making fusion more reliable and the final cap easier to weld with proper contour and strength.

Root tack is simply temporary fasteners to hold pieces in place and does not provide the continuous backing needed for a strong root and cap. The cap weld is the final bead placed on top of the joint, not something done before establishing the backing on the opposite side.