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"Electroless nickel on steel and stainless steel substrate in marine environment"

March 12, 2010

I protect a piece of threaded steel (or stainless steel) by EN coating (70 µm) against severe corrosion and abrasion in the marine environment. But galvanic corrosion due to insufficient coating adhesion destructs everything.please help me to solve this problem.
Can I use two layered EN coatings, first a heat treated EN layer (above 500)and a second as-deposited EN layer deposited onto first layer?

Rahgozar Isfahani
- Iran

First of two simultaneous responses -- March 13, 2010

I don't think you will have too much luck with a 2-layer approach. The nickel becomes stubbornly passive after heat treat which makes it very difficult to plate over. You can try to reactivate it and continue to plate it, but I think you will have too much trouble with adhesion of the second layer to the first layer. Your adhesion problem over stainless seems to be your main problem that you need to address. Your pretreatment for stainless should be Alkaline Clean, HCl activate, Wood's Nickel Strike, then E-nickel. If that is not what you are doing, you should start with those corrections.

Jon Barrows
Jon Barrows, MSF, EHSSC
Independence, Missouri

Second of two simultaneous responses -- March 15, 2010

Dear Rahgozar Isfahani,

Whichever coating you apply, it will have the same problem as long as you have adhesion problems. You should concentrate on solving the adhesion issue. Any coating which has bad adhesion will come off. 70u EN should withstand the marine conditions relatively long, but only if properly applied.

Best regards,

Harry van der Zanden
Harry van der Zanden
- Budapest, Hungary

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