Letter 37051

Rinsing after stainless steel passivation [Mexico] 

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What are the minimum requirements of water (pH, hardness, conductivity, etc.) to wash stainless steel after performing any manufacturing process and for passivation purposes?

Sergio Ortiz
filtration - Monterrey, Nuevo Leon, Mexico

Your question is quite broad to be answered in a couple lines, but you are right to be concerned on this matters. Water quality can directly affect the quality of products. The water quality will depend a lot on the application (medical, aerospace, semiconductor, etc).
In the case of citric/nitric passivation, according ASTM A-967 [link is to info about spec at TechStreet] final rinse water should not exceed total dissolved solids of 200 ppm. I even believe this is too much. I think softened and 10 micron filtered water is ok for general purposes. R.O. is preferred. pH of rinse water must also be controlled to a "neutral" range to avoid product carrying acid residue to the customer.
If the application is critical, such as semiconductor industry, ultrapure deionized (DI) water is a must, as well as monitoring purity of parts. So you can see the application must be considered to know what water class is needed.

Manuel Sández
High purity Components Manufacturing - Hermosillo, Sonora, Mexico

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