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Stainless Steel "rust" marks on paint
On Tue, 27 Mar 2007 17:35:18 GMT, Don W
wrote: Bruce wrote: The acid treatment was "passivating". My experience is that unless the stainless is polished to a mirror bright finish you will get staining. All the bits have to be polished; Assuming that it is a bolt on fitting the bolts and washers that are exposed to sea water need to be polished. I've been making things out of stainless and putting them on boats for quite a number of years and I have found that if the part has all the welds ground smooth (so the welding ripples don't show), no pin holes or voids in the weld and then polished bright I seldom get staining. If I don't do this I always get staining. snip... Bruce in Bangkok (brucepaigeatgmaildotcom) Hi Bruce, I've just recently started building stainless parts for my two sailboats. I'm using 316 SS and 316L SS exclusively and passivating with Citrisurf which is a strong citric acid. It can also be used for electropolishing, and I intend to try using it for that in the future. Google "Citrisurf". It is supposed to be better and more environmentally friendly than nitric acid paste. Several of the welders that post to sci.engr.joining.welding have used it with good results. I've only started using it about six months ago, so the stuff I've built has not been out in the salt spray long enough to tell how good the passivation was. Don W. Don, I've tried things ranging from purpose made passivating stuff to vinegar. At the moment I am using a tile cleaner sold, here in Thailand in every supermarket, that is 20% hydrochloric acid. One comment I probably should make is that all the passivation chemicals work by dissolving (eating) some material from the surface of the piece being worked on. Of course this is how it works, removing all the oxides and other rubbish from the just welded surfaces. BUT, it also etches the nice shiny surface of the expensive piece of stainless you just welded. My experience is that if you don't polish the etched surface back to a mirror finish you still get staining. In another message I mentioned some dinghy lifting brackets I made that stained. They had been left in acid overnight and were perfectly clean but with a matt finish when I installed them -- thought the matt finish would hold the paint better -- wrong. Bruce in Bangkok (brucepaigeatgmaildotcom) -- Posted via a free Usenet account from http://www.teranews.com |
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