Letter 12045

Passivation of 304L Stainless Steel Welds 

I have a question regarding the need to passivate welds on a 304L tank assembly. this tank will be exposed to a PH of 3-4. My concern is with the carbon migrating due to the heat of the tig welding. I am currently looking into a mig process called STT which should help the heat affected zone. Will passivation protect the surface only and also, will the PH of the sultion the tank is being exposed to remove the passivation process.

Bob Young
- Lancaster, PA

Bob:

Any time you weld stainless steel the welds, at least, need to be passivated if you want them to be corrosion resistant. What you end up with in the weld and heat zone of the weld are alloys that are totally different than the base metal.

Once you get the welds passivated, they should withstand the pH of 3-4 with no problem, unless you are talking about bleach, HCl or other halide containing material. These can do bad things to stainless and to welds.

pH 3-4 will not destroy the passivation layer unless it is one of the above materials or similar.

Both nitric acid and our citric acid based formulations give good results in passivation of the welds. There are pastes available if the units are too large to dip in tanks. Contact us if we can help.

Lee Kremer Stellar Solutions, Inc. Algonquin, IL, USA

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