Letter 5037

In-house passivation 

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We are a job shop specializing in custom railing systems which we build using 304 and 316 stainless. How can we guard the integrity of each joint we weld. There is no passivation practiced- only manual cleaning after grinding and polishing- using sst cleaners.

We do use phosphoric acid solution with electricity to clean the fused joints. Is there any proven method to "passivate" in-house. Sometimes it is specified but we have not been monitored for compliance. Help!!!

Gene Curry
Jerico Metal Specialties - Bloomington, IN

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The best way to passivate depends on your expectations and environment, but it sounds like you could use a Nitric Acid dip to passivate the parts. Don't forget that hot welds will reflow the crystal structure of your stainless, changing the metalurgical properties, so use good welding technique, and always use low-carbon stainless.

The National Association of Corrosion Engineers puts out a very good handbook on corrosion, including lots of info on stainless. I don't know the URL, but they have a site, and the office is in Houston, Texas.

Jeff Watson
- Pearland, TX

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