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topic 42723

Passivating stainless steel tanks

A discussion started in 2006 but continuing through 2019


Q. I will be passivating tanks made of 304 stainless steel.
These tanks are in the 30'h x 50'd size range.
As submersion is not possible, are then any suggestions for a "cascade" type of wash?

Daniel Goll
Marine and industrial cleaning contractor - Vancouver, Washington, USA


A. I would suggest washing the areas of the tank (interior, I presume) that you want to passivate with a citric acid solution. This is much safer than using nitric acid solution. If there are any welded areas, you should remove any heat tint and/or weld discoloration mechanically first (by grinding, sandblasting or glass beading perhaps)for best corrosion protection. You can get the details of the citric acid passivation from ASTM A967 [link by ed. to spec at TechStreet] (I believe) which covers stainless steel passivation. Also there are commercial suppliers of citric acid passivation solutions.

Thomas Kemp
- Erie, Pennsylvania, USA


A. CIP type cleaning (recirculating the passivation solution to a spray ball at the top of the tank) is commonly used to passivate tanks. Let us know if we can help.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
supporting advertiser
McHenry, Illinois
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March 23, 2019 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. 2x2x5 feet open top rectangular tank with hinged lid made from unknown type stainless steel once used for soaking machine parts in stripper. I'd like to use it for wax melting for dipping/preserving beehive woodenware. Would like to clean/treat inside to remove any possible chemical residues that could be imparted into the wax and possibly be harmful to bees. Sandblasting? If so, what blast media best? Sanding/polishing with superfine emery cloth/sandpaper, 3M pads, mechanical buffing wheel, rubbing compound? Acid treatment with nitric, oxalic, or citric acids? What about re-passivation treatments? Any thoughts/comments greatly appreciated. Thank you

Peter Rauert
Beekeeper - Grantham, New Hampshire USA
  ^- Privately contact this inquirer -^

April 4, 2019

If it's decent stainless, it shouldn't have any residue that can't be easily washed off, but you can do some kind of mechanical cleaning (sand blast or whatever) if you like. In any event I would go ahead and passivate with citric acid at the end, just to be sure.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
McHenry, Illinois

April 5, 2019

Q. Thanks Ray: I ordered a gallon of the Citric Acid product with additional rust remover gel. I am using "Barkeeper's Friend" oxalic/citric acids combined with fine abrasive) and 3M pads/polishing bonnet. Tedious work but looking great and I feel better thinking that I am cleaning out any potential contaminants by removing a microscopic layer of the steel. Will be using your product to passivate after I clean it. It's still cool here in NH and I plan to do this outside. Any change in exposure time if temp is 40-50's F? Thanks, Pete

Peter Rauert [returning]
Beekeeper - Grantham, New Hampshire USA

April 10, 2019

A. Peter,
As far as I'm aware, most Bar Keeper's Friend products are just oxalic acid and abrasive, and that's fine for removing rust but abrasives on stainless are just going to remove whatever is left of the passive layer. If it's a good grade of stainless in a low-corrosive environment, it may not matter, but for critical applications, a proper passivation product is recommended.

With the lower temperature, yes, you would need to extend the treatment time. Shoot for 45-60 minutes instead of the 20-30 that you would do at 70 °F.

ray kremer
Ray Kremer
Stellar Solutions, Inc.
McHenry, Illinois

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