48434

Corrosion resistance : passivation vs electropolishing [Canada] 

April 5, 2008

I'm working with pharmaceutical companies and some of them are requesting that their 316L stainless steel replacement parts are to be electropolished AND passivated after. My understanding is that electropolishing alone is enough since in addition to the surface finishing improvement, you get the cleaning of impurities and the chromium oxide layer as with the passivation process. Therefore, passivation does not add any value. I'm I right?

Regards,

Eric Potvin
process engineer - Québec, Québec, Canada

Hi, Eric, that's a tough one. It has been traditionally stated in authoritative books that electropolishing is the best passivation method. But that was before the days of citric acid passivation,and some of its proponents claim that citric acid passivation can improve the corrosion resistance of electropolished parts. Ask them to send you an independent study proving it.

Regards,

Ted Mooney, P.E.  finishing.com Brick, NJ