Rust on Stainless Steel

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I fabricated and installed a 24' stainless steel gate about 6 months ago. It is now poping up with rust everywhere...does anyone know of a good way to remove the rust and keep the rust from returning. I also put a coat of permalac over the gate before it was installed.

Thanx to all who can help!

[Rasper]

red,

I use HCL to remove rust from steel, plain or stainless. The most convienient form of it is swimming pool acid. It's the right strength too. I use it right out of the bottle, or dilute with water if I want to be a little cautious and move a bit slower. You'd have to take off that Permalac I would think. Sounds like that may be a lacquer. If so, lacquer thinner would do it. As far as preventing more rust, that would depend on why the rust is there. If it is just particles of plain steel that got imbedded into the stainless from contact with tools or from scraping against work tables or such, the acid would go a long way towards eliminating that. If it is caused by a change in the composistion of the stainless itself, due to being held at somewhere approaching dull red for more than a couple of minutes, you would have to heat treat it. I have a limited knowledge of metalurgy - what I know I get out of the definitive book on working stainless published by International Nickel back in about 1949 - but what I do to eliminate this problem is to heat the stainless to about 1900 degrees (past red to almost yellow) and then quench it in water. Seems to work. But for a gate? Maybe just give it an acid bath once in a while until it gets tired of rusting. Must be a nice gate. Post a photograph. I'd like to see it.

Richard

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Richard - Thanx for the information. I will try your method...Where do you purchase HCL? I talked to a person in California that sells a passivation weld cleaner and is quite expensive. I believe that something like that is more of a cleaning tool for weld burns than actually a method of rust removal.

I am sending along an attachment of the gate - sort of a wide angle view. For this project, I made a 24 foot driveway gate, a smaller pedectrian gate and a custom bench.

Thanx for you help.

Red

[Rasper]

Red,

Get swimming pool acid. Comes in gallon milk jugs from Home Depot or any place that sells pool supplies. Wear eye protection. Acid is serious stuff. And it eats concrete; it's what bricklayers use to clean the mortar off their finished brick walls. Put down drip protection on the driveway.

Make sure you test a small patch before commiting yourself.

Passivation would, I believe, address the issue I mentioned of an actual metallurgical change in the stainless. I'm going to look that up - you got me interested - and I'll let you know what I find.

Tell me, is the rust all over, or just near the welds?

That gate is a beauty. Thanks for the photo.

Richard

[Rasper]

Okay, here's a link to a paper by Lincoln Welders on the subject of carbon precipitation in stainless. Go to section 3.3, which is titled Austentic Stainless Steels, which I certainly assume yours is. Section 3.3.1 is entitled Sensitization. See if that fits your case.

http://content.lincolnelectric.com/p...ure/c64000.pdf

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Richard - The rust is just starting to pop in many random areas. It could be poping up like that because of carbon steel contamination or by not getting a thick enough coating of Permalac onto the gate before it was installed.

I'm going to the Lincoln weld site now to read the paper you suggested.

Thanx for your help on this...this whole issue has been very upsetting.

[cprocess]

The reason that stainless steel (SS) rusts, is from oxidation of the iron on the surface. This iron must be removed by "passivating", which removes the iron from the surface of the SS. Since this process involves toxic chemicals such as nitric acid and chromic acid, I would definitely NOT recommend trying this at home, as noxious fumes are generated during this process. Once the iron is removed from the surface, the chromium in the SS is more prevalent on the surface, which is much more resistant to oxidizing than iron. An alternative to passivating would be electropolishing, which leaves a very bright finish, similar to chrome plate. If you look at the surface of the SS under a powerful microscope, you would see many peaks and valleys (similar to a stock market graph). Electropolishing electrolytically dissolves the peaks to match the level of the valleys, resulting in a smooth bright finish. This process also involves toxic chemicals such as sulfuric acid and phosphoric acid so should not be done at home. This process removes the iron from the surface of the SS as well, so retards the rusting process.
Hope this information helps!
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