hydrochloric acid added to a stainless tank 1

[vipereyes]

Hi all,

We have a small 316 SS tank that we use for passivating small stainless components with a 50/50 mix of water and Nitric acid 42BE.

A new employee changed out the tank last night and added Hydrochloric acid to the water instead of Nitric acid. By time the acid was pumped out, it had etched/pitted the tank.

It doesn’t appear that any of the pitting is too deep, and this is probably a stupid question, but can we still use the tank for Nitric acid?

I wasn’t sure if the stainless tank had some sort of protective layer that the hydrochloric has eaten away leaving it unsuitable for our passivation process.

Thanks for your help!

 

[rustbuster]

You should be able to re-passify the surface, nitric acid should be effective for re-passivation.

 

[unclesyd]

As stated above the reintroduction of HNO3 after a through rinsing will passivate the tank in progress. The surface will be very sensitized after the exposure to HCl so you may get a little rust which need s to be removed before any production parts are introduced into the bath.

If you do please post.

 

[strider6]

Stainless steel resistance to corrosion rely on a superficial passive layer.. in an oxidant solution, like nitric acid, the passive layer is restored..
have a look at this page of BSSA for Nitric Acid passivation:

http://www.bssa.org.uk/topics.php?article=68

also

http://www.euro-inox.org/pdf/map/Passivating_Pickling_EN.pdf

http://www.corrosionist.com/cleaning_stainless_steel.htm

s


Corrosion Prevention & Corrosion Control

 

[vipereyes]

Thank you for the input everyone. And the passivation website was very informative.

Kim

 

[EdStainless]

If some areas have been roughened a lot you may need to go in with mechanical polishing and smooth them out some. If it is too rough it could catch debris and cause marking/streaking issues.

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[tomwalz]

Were it I, I would check the welds especially carefully.

Thomas J. Walz
Carbide Processors, Inc.

http://www.carbideprocessors.com

Good engineering starts with a Grainger Catalog.

 

[EdStainless]

The reason for special attention on the welds is that the fabrication welds will have a residual ferrite in them. and that ferrite is attacked very quickly in HCl.
If you saw roughening of the base metal you may have lost a significant amount of metal out of the welds.

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