What is a root pass in pipe welds?

• A. The final cap weld that closes the joint
• B. A decorative weld with no structural function
• C. The initial weld layer that establishes root penetration and joint alignment
• D. A post-weld test bead

Answer: (C)

In pipe welding, the root pass is the first weld layer placed at the root of the joint. It fuses the base metals at the root and establishes the initial alignment so the pipes stay correctly positioned as you build the weld up. This layer is all about achieving proper root penetration and a solid start to the seam, providing a base for the subsequent filler passes and the final cap. If the root pass doesn’t penetrate and fuse properly, you can end up with a lack of fusion or incomplete penetration, which weakens the weld and can lead to leaks. The other options describe things that come later in the process (the final cap), are decorative, or aren’t part of the welding sequence, so they don’t define the root pass.