We fuse 1.25" Diameter 316L to 316L tubing; .083 wall, without filler and we have recently been experiencing microcracks that fail Pressure test (200 psig). We used to use 304 and occasionally 316, problems were very infrequent. The joint is a square groove without backing or purge gas. 50% Penetration. The surface must be flush w/o post weld finishing. Hence, no filler.
Capt'n Tom
Capt'n Tom