We TIG weld pipe adapters for food processing in 316L S.S., 10 mm to 100 mm by 2 mm wall, on a welding lathe with a fixed torch and fixtured to purge the inside. We have 2 lengths.
The short are 2 flanges with snouts that are welded together. For the most part these are repeatable. The long have a 1.7 inch length of tubing welded between them.
The weld that is at the exact same place as the short usually welds "bad" while the other end of the tube welds OK. By "bad" - the weld wanders, full penetration is sporadic and it looks like impurities on the surface of the outside weld. The welders keep saying it is impurities on or in the parts or the composition of the material. But we have cleaned, changed materials and parts. So this seems unlikely to me.
Could slight percentage changes in anything in the material (sulfur, silicon, ect.)cause non-repeatable welds?
Ideally we want a weld on the I.D. that requires minimal grinding. Is that possible?
yes it is possible that the silicon or sulphur content is off and affects the weld.
but is it possible the second weld is affected by not allowing the first to cool enough?
or it is possible the purge gas is disturbing the torch gas on the weld that wanders.