When welding stainless, generally 304 and 316, I have noticed lately that the tip of the tungsten gradually seems to go from a sharp point to more of a mushroom when welding. When I start welding with the sharp point I get a beautiful weld, but as the end of tungsten starts to change, the weld pool starts to wander and I lose the nice fine ripples. Material is generally 1.6 mm stainless with either a thoriated or multi-strike tungsten, 2.4mm dia. Seems worse when on pulse, although the multi-strike lasts longer on pulse than the thoriated. Typically I can get one weld round a 2" pipe before I need to regrind. Using Pure Argon (Air Liquide) and a gas lens.