Most stainless weld defects trace back to three things: cleaning, shielding and parameters.

1) Porosity: oil, moisture or rust on base metal or filler, insufficient shielding gas or excessive flow (turbulence entraining air), wind without shielding. Fix: thorough cleaning, check the gas path, add wind screens, bake filler per specification. 2) Lack of fusion / penetration: small bevel angle, large root face, low current, too fast travel, poor interpass cleaning. Fix: design the joint for the thickness, follow WPS/PQR, control interpass temperature and cleaning. 3) Heat tint: insufficient gas coverage or poor trailing shield. Tinted areas have reduced corrosion resistance and need pickling/passivation; critical parts should be welded without tint. 4) Distortion: use back-step and symmetrical welding with fixturing on thin sheet; straighten after welding if needed.

Acceptance: visual plus PT/RT/UT where required; for corrosion-critical parts, pickle and passivate after welding and run a blue-dot test. Weld quality comes from process discipline, not from rework.