When welding different thicknesses in a single joint, what pass strategy reduces defects and improves fusion?

• A. Cap first, then root pass.
• B. Skipping root pass.
• C. Only use one pass.
• D. Root pass to penetrate, then fill passes, ending with cap.

Answer: (D)

When different thicknesses are welded in one joint, start with a root pass to penetrate and fuse the joint at the root. This establishes a solid foundation where the thick portion can be properly welded through, preventing lack of fusion at the root and helping control the heat input as you move to thicker sections. After establishing the root, add fill passes to build up the weld metal gradually, which allows you to manage heat input, avoid burn-through on the thinner side, and ensure adequate penetration along the entire joint. Finish with a cap pass to create a smooth, fully fused surface and proper weld crown. This sequence reduces common defects and gives consistent fusion across varying thicknesses. Skipping the root pass, using only one pass, or placing the cap first would not reliably achieve root fusion or sufficient build-up, increasing the risk of defects.