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What causes blue discoloration of stainless steel

2004

Hi,

Can anybody tell me why a 304 stainless steel tank discolors and gets the light blue stains? .This tank contains dairy products. From time to time it is sterilized (vapor, 1300C for 30 minutes), and cleaned (sodium carbonate / washing soda [affil links] or sodium with a diluted acid).

The discoloration is superficial and can be wiped out using brush, cleaning agent or scotch-brite.

Thanks,

Shraga Yaron
- Hod Hasharon, Israel

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I believe it is some kind of chromium oxides.

Good luck

Khair Shishani
aircraft maintenance - Al Ain, UAE
2004

How do you get a vapor to 1300C? The blue normally is from oxidation caused by the high temperature and oxygen in the air. Organic material will bake on at this temp and will cause the blue to be very hard to remove as it is now an organo-metallic.

James Watts
- Navarre, Florida
2004