What is the difference between the root pass and fill passes in a groove weld?

What is the difference between the root pass and fill passes in a groove weld?

• A. Root pass uses filler metal to fill remaining gap; fill passes clean up.
• B. The root pass creates the weld root with fusion to base metal; fill passes build up to the final throat thickness with multiple passes.
• C. Root pass is decorative; fill passes are structural.
• D. Root pass is the last pass; fill passes are first.

Answer: (B)

In a groove weld, you start by laying down a root pass that fuses the base metals at the bottom of the groove. This pass establishes the weld root and ensures there is proper penetration into the joint, creating a solid bond with both sides of the metal. After the root is secure, you add one or more fill passes to deposit more welding metal and gradually fill the groove until the weld reaches the full throat thickness required for strength. The final pass, if used, is typically the cap that finishes the surface. So the root pass is about forming the weld root and fusion with the base metal, while the fill passes are about building up the weld height to the final dimensions.

In a groove weld, you start by laying down a root pass that fuses the base metals at the bottom of the groove. This pass establishes the weld root and ensures there is proper penetration into the joint, creating a solid bond with both sides of the metal. After the root is secure, you add one or more fill passes to deposit more welding metal and gradually fill the groove until the weld reaches the full throat thickness required for strength. The final pass, if used, is typically the cap that finishes the surface.

So the root pass is about forming the weld root and fusion with the base metal, while the fill passes are about building up the weld height to the final dimensions.