Stainless Passivation Alternatives?

[crthomps]

I had a question regarding passivation: hypothetically, if I was in a 'pickle' and did not want to send the stainless product to another shop to get passivation treatment, is there another equivalent method that can be performed in house? I know that pickling gets rid of all impurities on the surface and passivation gives the surface a protective surface through baths in nitric acid.
However, I recently read that stainless passivates in air (and rinse in demineralized water) over a 24 hour period, and the oxide layer is quite similar to that of normal passivation. Is this true? If so, would it be plausible to use a pickling agent then allow to passivate over the next 24 hours in air and rinsed in demineralized water?

 

[sreid]

My understanding was that passivation selectively etched iron from the surface leaving a chrome enriched surface.

There is always a chrome oxide on the stainless surface. So exposure to air followed by rinsing would be the same as doing nothing. It seems to me.

 

[israelkk]

According to ASTM A 967 Chemical Passivation Treatments for Stainless Steel Parts. Pickle is the process to remove heat tint and oxidation according to this standard.

Part that were pickled to remove the heat tint and oxidation does not need a passivation because the acid used to remove the the heat tint and oxidation is stronger than the acid to perform passivation on a clean ans iron free surface.

The process where acid is used to remove the free iron particles is called in ASTM A 967 passivation and no further treatment is necessary.

 

[EdStainless]

Both pickle and passivation will remove surface Fe contamination. If that is your primary goal then you are fine.
In a good passivation treatment you also enhance the thickness of the surface oxide layer as well as the apparent Cr/Fe ratio. This will not happen in pickling. These acids are not oxidizing enough.

For most applications the pickled and rinsed surface will be just fine. It will be clean which is usually the major point.


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