Rouging

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.[2]

There are three classes of rouging: Class I, Class II, and Class III.[3]

Class I – stainless steel surface and the Cr/Fe ratio[clarification needed] of the metal surface beneath such deposits usually remain unaltered.
Class II – Iron particles originating in-situ on unpassivated or improperly passivated stainless steel surfaces. By their formation the Cr/Fe ratio of the metal surface is altered.
Class III – Iron oxide (or scale) which forms on surfaces in high temperature steam systems. The Cr/Fe ratio of the protective film is usually altered.

## References

1. ↑ Rivera, Hadziselimovic, Lopolito (2017-02-15). "Preventive and Corrective Maintenance for Rouge in Stainless-Steel Equipment". Equipment and Processing Report. Equipment and Processing Report-02-15-2017 10 (2). http://www.pharmtech.com/preventive-and-corrective-maintenance-rouge-stainless-steel-equipment. Retrieved 2019-04-12.
2. ↑ "Rouging". http://corrosion-doctors.org/MatSelect/rouging.htm.
3. ↑ "Rouging of Stainless Steel in High-Purity Water", Corrosion: Environments and Industries, ASM International, 2006, pp. 15–22, doi:10.31399/asm.hb.v13c.a0004103, ISBN 9781627081849

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