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How to remove unwanted galvanic plating from stainless steel valves

April 4, 2009

Our company specializes in processing equipment for the food industry.

We have a problem regarding hygienic valves from one of our customers.
The interior of these seat valves is blue/black when it should be a shiny stainless steel surface.
We have never come across this problem before and hope that someone of your members would be able to help us.

Our customer has been using NaOH and acids for cleaning purposes, often at temperatures round 90 degrees C (190F).
Our guess is that the production facility has had problems with galvanic current due to improper grounding of the pipework and that the result is ion plating.

What would be the easiest way to restore the valve surfaces again?

Ja-Olov Forslund
- Lund, Sweden

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First of two simultaneous responses --

There is a possibility that what you are seeing could also be an advanced form of rouging. When very bad it gets black. Are they using hot DI water in the system?
If it is rouging you can remove this, although the shiny surface may not come back.
Electrical attack CAN produce this, also. If this is the case you probably have to electropolish it.

Lee Kremer
Stellar Solutions, Inc.

McHenry, Illinois

April 15, 2009

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Second of two simultaneous responses --

Mechanical methods would work almost regardless of surface contamination nature. In order to use a chemical method, identification of contaminant is a must. This can be made by trial and error or sending the valve to a well equipped lab.

Guillermo Marrufo
Monterrey, NL, Mexico
April 16, 2009