What is the basic principle of using suckback to repair a GTAW root?

What is the basic principle of using suckback to repair a GTAW root?

• A. Sitting on a section of excessive reinforcement will eventually cause the material to pull in removing the reinforcement
• B. Pushing material forward to add reinforcement
• C. Applying external cooling to shrink the weld
• D. Shaping the root with filler material only

Answer: (A)

Suckback relies on the molten weld metal’s behavior to flatten the root by pulling excess material back into the weld as you finish the root pass. In GTAW root repair, you control heat input so that as you near the end of the root, the arc is reduced and the pool remains just long enough to pull the surface tension of the liquid metal back toward the joint. This draws out and smooths any excess reinforcement, leaving a flatter, flush root instead of a crown. It’s not about pushing more filler forward, cooling to shrink, or shaping the root with filler alone—the effect comes from letting the molten metal pull back into the weld.