Root concavity in which the inside surface of the root pass is drawn back into the joint, leaving a groove below the inner pipe surface, most often in the overhead zone around six o'clock. It reduces thickness at the root and shows on radiographs as a darker band along the root. Causes include too much heat, slow travel overhead, a wide gap and excess purge pressure on TIG roots.
You've got suck-back at the bottom of every joint, speed up through six and push the rod in more.
Also heard as
- suckback
- root concavity
- concave root
Related terms
Root pass
The first weld pass in a joint, laid at the root, which sets the quality of everything above it.
Purge
Inert gas flowed inside a pipe or behind a joint to keep the back of the weld from oxidizing.
Icicles
Slang for drips of excess root metal hanging inside a pipe from too much heat or too wide a gap.
RT
Radiographic testing: imaging a weld's interior with X-rays or gamma rays on film or a digital detector.