Letter 25045

Chromed stainless steel corrosion  

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We have recently experienced corrosion problems with hard chrome plated stainless steel (431S29) in a salt water environment, the corrosion is not severe but is still visible (green spots). Is this likely to be deterioration of the chrome or the stainless steel? How can we rectify the problem? There is no nickel base below the chrome - would this have a detrimental effect? Your advice / help would be greatly appreciated.

Robert Robertson
oilfield products - Aberdeen, Aberdeenshire, Scotland

I don't think chromium corrosion products would be green. Green is usually associated with nickel salts, so I'd say it is the stainless steel that is corroding. Hard chromium is not very good as a corrosion-resistant coating because the coating is cracked. If you need corrosion-resistance you would be best served by an electroless nickel plating. Whether you need chrome on top of the electroless nickel or not would depend on other application details more than upon corrosion resistance requirements.

Ted Mooney, P.E.  finishing.com Brick, New Jersey

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