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Ted Mooney, P.E. RET
Pine Beach, NJ
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for Metal Finishing since 1989
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Passivation of stainless steel to remove rust from garden furniture
Q. Dear Sir or Madam,
We are the manufacturer of the garden furniture which is made from teak and stainless steel. Our company is established in Thailand and exports our products to European Countries. We learned that the stainless steel needs pickling and passivation treatment to protect the stainless contaminated by oxide. However, we face the serious problem that the rust occurs on the finished product (stainless steel). We used only Nitric acid to clean the oxide, is that the appropriate solution or do we need something else or method to protect our product?
Regards,
- Bangkok, Thailand
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A. Buppha: There are a lot of questions about what you did in the pretreatment, what grade of stainless steel, etc. However, if you passivated correctly with either nitric acid or citric acid formulations you should not have a rusting problem under normal conditions. If the product was exposed to salt spray it can still eventually rust, however. If you have rusted finished product that you need to remove rust from, there are a number of good products to do this that are safe and easy to use without the hazards of nitric acid (which is not the best at removing rust). citric acid based formulae are good for this and very safe to use under normal conditions. Adv.   Lee Kremer Stellar Solutions, Inc.  McHenry, Illinois  A. You do not say what type of stainless steel you are using. This could have big implications on any treatment, but my first thought would be to electropolish the steel with a sulfuric acid/phosphoric acid mixture. This will not only give a bright finish it will also put down a phosphate passivation coating that will help prolong the life of the reflective surface. the easiest stainless steels to electropolish are 200 and 300 series, although some are better than others. 400 series stainless can be done, but with more variable and not as good results  Trevor Crichton R&D practical scientist Chesham, Bucks, UK |
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