Granular, dark gray to black oxide that forms on the root side of stainless steel, nickel alloy or titanium welds when the hot back side meets air. The chromium-depleted, porous crust destroys corrosion resistance and can hide cracks and lack of fusion, so sugared roots are normally rejected and cut out. Back purging prevents it, and special fluxes are used on open roots where purging is impossible.
Root's sugared from three to nine, the purge must have died, that joint's a cutout.
Straw or light blue on the back of stainless is usually acceptable; gray or black sugar is a reject on most piping jobs.
Also heard as
- sugar
- sugared root
- oxidized root
Related terms
Purge
Inert gas flowed inside a pipe or behind a joint to keep the back of the weld from oxidizing.
GTAW
Gas tungsten arc welding: an arc from a non-consumable tungsten electrode under inert gas, known as TIG.
Root pass
The first weld pass in a joint, laid at the root, which sets the quality of everything above it.
Cup
The ceramic or glass nozzle on a TIG torch that directs shielding gas; also a MIG gun nozzle.