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Material of Construction for Passivate Tank


What kind of tank would you recommend for a Nitric passivation tank.

It will contain 25% Nitric and 2-3% sodium dichromate

It will operate at a temperature of 120-130F.


Micheline Forth
Finishing Company - Rincon, Georgia, USA
May 1, 2008

May 2, 2008

Hi, Micheline. If you search the site with the term "material nitric tank" you will see several previous discussions. But I would go with 316L stainless steel. The best alternative and much cheaper is molded (no welds!) polyethylene. Although you could buy a resistant tank liner, I don't think I'd use a steel tank because of the widely rapid attack in the event of a spill or a liner leak.


Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

May 2, 2008

Thank-you for your response Ted.

That is what we purchased over a year ago and it has been a nightmare.
I could write a book on everything that has gone wrong since we purchased this system.
The main thing is deterioration of the tank at an alarming rate.
I do test my tank every week and can assure you that my concentrations have been good, except for iron. Due to the deterioration I have had to change my tank very often.
My personal belief is that the manufacturer made a mistake and I got some steel parts in my tank.
I wondered if anybody has any suggestions. Could it be electrical?
Please Help.

Micheline Forth
- Rincon, Georgia, USA

Now that you've reminded me, I see the earlier discussion of this under letter 45942.

Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey
May 7, 2008

HI Micheline

You didn't give the tank's size ... if it is available as a moulded PE tank, then ask the supplier (so-called Engle Process) to make it heavier ... yes, this can be easily done by him ... up to 3/8" thickness. any internal welding must be avoided as this will cause stress cracking.

Alternatively, a dual laminate construction using PVC:FRP.

freeman newton portrait
Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).

May 7, 2008

Q. At the time of (HNO3) passivation of grade 316L stainless steel, we use a circulation pump that is not stainless steel but cast or carbon steel.


My questions:
1. Is the pump used to be stainless steel?
2. If the pump material is cast, will there be any influence on the products that will be passivated.


Firdaus Firdaus
- Indonesia, Jakarta
March 16, 2013

A. Hi Firdaus. Sorry, this will be unsatisfactory and possibly dangerous. Nitric acid is very aggressive towards iron and steel. Plus, you will consume a lot of nitric acid dissolving the iron in your pump instead of dissolving the traces of iron on your parts. Use a stainless steel or plastic pump. Good luck.


Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey
March 21, 2013

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