Stainless steel gets its corrosion resistance from a chromium oxide layer on the surface. Introduce free iron. From a shared grinding disc, a contaminated wire brush, or airborne particles from nearby carbon steel work. And that layer breaks down locally, leading to rust spots or, in aggressive environments, pitting corrosion. In food-grade and chemical plant fabrication, this is not a cosmetic issue.
How contamination happens in a shared workshop ¶
The most common contamination routes are grinding sparks from carbon steel work landing on stainless surfaces, shared wire brushes carrying embedded carbon steel particles, and shared grinding discs used on both materials. Airborne iron particles from MIG welding on carbon steel can also settle on stainless surfaces and cause rust spots after passivation. In a busy workshop, these risks are present even when individual welders are careful.
Dedicated bay and tooling as the practical solution ¶
The most reliable prevention is physical separation. At our Kawasaki workshop, the TIG bay fitted out in June 2026 is used exclusively for stainless and aluminium work. It has its own set of grinding discs, wire brushes, and clamps, all colour-coded and stored separately. The bay operates at slight positive air pressure relative to the adjacent carbon steel bay, which reduces airborne particle ingress. Stainless workpieces are stored on dedicated racks with rubber contact points to avoid iron transfer from steel shelving.
Post-weld treatment: pickling and passivation ¶
Even with good contamination control, post-weld treatment is standard practice for food-grade and chemical plant stainless. Pickling paste (typically a nitric-hydrofluoric acid mixture) removes the heat tint and any surface contamination from the weld area. Passivation with nitric acid or citric acid solution then restores the chromium oxide layer. In Japan, the handling and disposal of pickling chemicals is regulated under the Waste Management and Public Cleansing Act. We use a licensed waste contractor for spent pickling materials.
If your stainless fabrication is destined for a food-grade or chemical plant environment, ask us about our contamination control procedures and post-weld treatment options when you send your enquiry.