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topic 3270

nickel sulfamate-failure of corrosion test


(1999)

I have some problems concerning corrosion resistance test on nickel sulfamate. I coated 4130 steel test panels with 0.002 inch nickel sulfamate and it did not pass the 200 hours salt spray test. I will appreciate to get some advices about the reasons of this failure and what I have to improve to pass the test.

Arie Yogev
- Israel


(1999)

There are two possibilities.

1]There is porosity in the test piece material which is causing pitting in the coating.

2]There are problems with the solution (this is a very difficult solution to maintain in good condition, especially if it is not used on a regular basis). It could need carbon filtering to remove impurities. Check the pH is in specification and/or carry out a full analysis. You need very good agitation in the bath.

With a flat plate you may be getting gas pitting due a poor 'flow off' of gas bubbles at the surface.

regards

Trevor Amos
coating technology - Southampton, UK


(1999)

My bet is that it was plated at a moderately high current density without a thief frame or box so you get very high plate thickness at the outsides and very little at the center of the plate. As stated before, the tank should be in excellent balance with considerable agitation for best results.

James Watts
- Navarre, Florida



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