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304L polished Stainless bent steel pipe rust marks in 2 weeks

We specialize in schedule 40, 4.5" OD pipe bending. We are now getting into bending stainless steel pipe, and we build some bent pipe bollards using 304L Stainless steel. Our customer requested a polished shiny surface finish, therefore we brushed them and then we polish them with polishing component to a shiny bright look.

After we shipped this to our customer in the USA, 2 weeks after, he called us complaining that there was some tiny brownish stain marks on the surface, therefore complaining to us that the steel was rusting, but expecting that being stainless it should not rust.

Why is the stainless steel 304L polished pipe staining so quickly? How can I avoid it or elimminate it? How can my customer clean it, avoiding that it will stain again?

Thanks.

Ruben Martinez
- Monterrey, Nuevo Leon, Mexico
2005

Stainless is stain resistant, not stain proof. When you use the same equipment for SS as you do for iron pipe, you will force tiny amounts of iron into the surface of the SS and it will rust. Since you say "brushed" and tiny rust spots, you very probably used a 410 ss brush which put tiny tiny pieces of the brush into the SS tube. Polishing removes only the easy to get out bits. It will rust! The question is how soon. If you brush it, I doubt if you will ever get it to pass a salt spray test and certainly not a ferroxyl test. Electropolish is about the only way to remedy this, and that may not work. Passivation will help, but it will not pass if you used a power brush on it.

James Watts
- Navarre, Florida
2005

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Passivation after the polishing process is an absolute MUST if you want to prevent corrosion afterwards. I agree with what James says above, but you should be able to get good performance with the right process for polishing and the right process for passivation.

The best overall solution is electropolishing followed by passivation, but that may not be possible for you with long pipes.

Once you get the rust on the pipes it can be removed easily and safely with some safe citric acid based but it can be done.

Let us know if you need help.

Lee Kremer
Stellar Solutions, Inc.

McHenry, Illinois

2005