Rouging is a form of corrosion found in stainless steel.
[1] It can be due to iron contamination of the stainless steel surface due to welding of non-stainless steel for support columns, or other temporary means, which when welded off leaves a low chromium area.
Class II – Iron particles originating in-situ on unpassivated or improperly passivated stainless steel surfaces.
Class III – Iron oxide (or scale) which forms on surfaces in high temperature steam systems.
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