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topic 3206

Gelling nitric acid for Spot passivation


Q. How would you spot passivate a weld in 316L SS using nitric acid in a suspension, specifically what concentration of nitric acid would be used, what would be the gel substance, and what time period would you recommend.

Any assistance would be appreciated.

Best Regards,

Chris [last name deleted for privacy by Editor]


A. There are commercial products for local passivation of stainless steels after welding. Try asking at a local welding shop. I know that Avesta, a stainless steel company, is one supplier of a passivation paste product.

larry hanke
Larry Hanke
Minneapolis, Minnesota


A. You can perhaps gel the nitric acid with Fumed Silica [linked by editor to product info at Amazon].

My prejudice is I dislike gelled acid for safety reasons. Further, since acids function by reacting with metal, and the gel impedes fresh solution flow to the surface, I think they are less effective than liquid acids. But I would think that you can just follow the regular passivation spec (QQ-P-35 [link is to free spec at Defense Logistics Agency,]) for nitric or nitric-chromic passivation.

Is it impractical to just repassivate the whole welded structure?

Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


A. Chris, You could use Brush Electroplating to selectively passivate the areas that need to be done. Depending on the size of the areas it could go fairly quick.

David Crocker
- Valencia, California

(2003) -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I would be interested to know what gelling or thickening agents or binders can be used for acid pickling which are stable to nitric acid (50% conc.). Most of the gels I tried are not resistant to higher concentrations of nitric acid.

Shashibhushan Vaidya
pretreatment and cleaning chemicals - Mumbai, Maharashtra, India

April 22, 2012 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I am a person involved in pickling & passivation of Stainless Steel. Right now I am doing a conventional method. The process is by the use of hydrofluoric & nitric in a proportion.(Liquid form)
I want to make use of the same proportion in paste/gel form.
So kindly let me know that which ingredient to be used for the above to bind it in paste/gel form without loosing the properties of the product.
I am looking for the binder to make it happen.

- - Bogra, Bangladesh

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