plating, anodizing, & finishing Q&As since 1989
We do low quantity periodic passivation of 304 and 316 SS? In order to comply with QQ-P-35C [link is to free spec at Defense Logistics Agency, dla.mil] we apparently have to invest in a humidity chamber or other relatively expensive equipment. I am trying to determine if I could do the copper sulphate [on eBay or Amazon affil link]test instead, but have gotten some information that it is too sensitive and not recommended unless specifically required. Can you tell me if this is true?Peter Frazier
-Murray Hill, NJ
The copper sulphate the ferroxyl tests are sensitive to free iron or oxide surface contamination. However, any decent passivation of 304 or 316 stainless steel should eliminate free iron and iron oxide. The copper sulphate test is tricky and subject to false interpretation on 400 series alloys.
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