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EN plating is immediately staining in water service

We are using copper heat exchangers with .001" electroless nickel plating overcoat. We are running a mixture of 9% methanol [affil links]/91% distilled water thru the heat exchanger water channels. We are seeing a discoloration of the plating after just 1 hr of usage. Any ideas what the discoloration is?

Thanks,

Mark
Manufacturing Engineer - Burlington, Massachusetts
2003

Pictures might help (or might not). A quick guess is that the EN is not really .001" thick or has been poorly applied and is porous so the fluid is seeing the copper.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003

Specify a High Phosphorous(11%-13%) Electroless Nickel .001in. Medium and low phosphorous electroless nickel are prone to discoloration in wet environments due to sulfur and other trace amounts of brighteners, stabilizers and exhaultants in the deposit.

Todd Osmolski
- Charlotte, North Carolina, USA

I suggest that you use a high phosphorus Electroless nickel deposit that does not contain divalent sulfur as a stabilizer. I believe that stains occur due to attack on the co-deposited sulfur or other possible other stabilizers used in the plating solution.

Don Baudrand
Consultant - Poulsbo, Washington
(Don is co-author of "Plating on Plastics" [on Amazon or AbeBooks affil links]
and "Plating ABS Plastics" [on Amazon or eBay or AbeBooks affil links])

Three questions: How much phosphorous in the nickel deposit?
and
What is the pH of the cooling agent?
and
What colour is the staining?

Tom Newberry
- Georgetown,Ontario, Canada

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