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Passivation Staining on 17-4 PH Stainless Steel

Q. We are having an issue when swab passivating 17-4 PH SS with nitric. We do also have citric but some of our customers require the nitric. Typically the swab passivation is done on the laser marking or assembly level welds. The components themselves are fully passivated prior to assembly. However, when the swab passivation is done we are seeing a significant lightening in color within the area and a darker distinct water type mark bordering the area of the swab passivation. We are using the same solution from the tanks originally used to passivate these parts. We are also doing our best to make sure solution remains wet while on the surface. The only way we've found to remove the staining/mark is to glass bead blast it off...which of course requires re-passivation. Does anyone have any information on what could be occurring here or any advice on how to avoid this issue? Any information would be greatly appreciated.

May 10, 2012

A. We think that swab passivating with nitric acid solution can cause stains because nitric evaporates very quickly leaving less concentrated solution on some locations. I suggest use gels for local cleaning and passivation. Contact us for information on make-your-own passivating and pickling nitric acid gels.

Anna Berkovich
Russamer Lab

Pittsburgh, Pennsylvania

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