Weld oxidation is a corrosion site — not just a colour problem

Heat tint on stainless is a chromium-depleted oxide layer. It looks cosmetic, but it is where pitting starts, especially in chloride service or hygienic lines. The practical requirement is mechanical removal plus passivation for visible tint, and full pickling for heavier oxide or where the specification calls for it. On site, the contractor should state the method, the rinse water quality and the final check (blue-spot or ferroxyl test) — not just 'cleaned after welding'.