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Passivation of 304L stainless tank in the field.

I want to test and passivate a 304L tank in the field and have been told that I can hydro and passivate at the same time using 3% nitric acid. I'm confused at this point and want to make sure it's done right before putting into service. Any help would be appreciated.

Dave Mosley
QA/QC - Houston
May 8, 2008

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May 21, 2008

I don't know what all is required in doing a hydro test on a new tank (surfactants or other additives) but I would question the effectiveness of that low a dilution of Nitric for providing an adequate passivation.

Tanks and large equipment are routinely passivated using a specially thickened citric acid blend. Thickeners allow for increased contact time on the vertical and inverted surfaces.

Back when I used to use Nitric it was more like 13.6% to 20%.

Todd Turner
- Monroe, Louisiana

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Todd is correct, a thickened "gel" version citric acid passivation solution is commonly used for application like this.

Given your proposal of running a leak test with a passivation solution, I don't see why that couldn't be accomplished with a citric acid based passivation formula. I certainly wouldn't want to see a leak test run with nitric at the concentrations required for passivation, but citric acid is much safer to work with.

Let us know if we can help.

Ray Kremer
Stellar Solutions, Inc.

McHenry, Illinois

June 3, 2008

We are having nitric storage tanks for storing 60% nitric acid of capacity 3000M3. MOC of the tanks is SS304L. I am facing the problem of weld leakage. can you suggest some good way to repair and long lasting weld joints and some type of quality assurance plan to accomplish the good joints.

MADAN MOHAN GUPTA
fertilizers and chemicals - Mumbai, India
June 26, 2008