Where the
world gathers for metal finishing
Q&As since 1989


-----

Material of Construction for Passivate Tank

Hello,

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.

Thank-you,

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.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - 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, P.E.
Striving to live Aloha
finishing.com - 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 [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.

Thanks

Firdaus Firdaus
- Indonesia, Jakarta
March 16, 2013