Solid...shoots down the internal gas expansion theory
We had a discussion here a while back about the effects of bead blasting and the residual "impregnated" impurities. Especially for GTAW. Somewhat sensitive to any such residues.
Also, what tungsten are you using? Don't remember seeing that yet.
So, tungsten, gas flow (hose leaks? pressure- not too high, not too low), polarity -DCEN, Amps, grounding (on a lathe? ground should be straight to the welded part so you don't go through bearings for multiple reasons), clean (Stainless wire brush, Acetone is our friend, brush, Acetone is our friend, brush, did we talk about Acetone??), OH, what are you using for filler? Is the base metal all the same and do you know the specs on it?
And, always a chance of contaminated shielding gas. About once every couple of dozen cylinders depending upon which supplier I use.
Any one and/or combination of will cause problems as described.
He Is In Control, Have a Great Day, Brent