[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [New Search]
On 21 Apr 2005 at 20:32, Keith Park wrote: > I know there are different grades, I just dont consider any steel that can > rust stainless.... I call it high carbon steel. I think that all stainless steel alloys still consist of more than 50% iron. Even real stainless can rust. The different elements in many stainless alloys coexist in crystals of the separated metals. The chromium and nickle crystals form a clear oxide film quickly which prevents further corrosion, but pure iron crystals at the surface will still rust, especially if the part has been machined and cut thru some of the pure iron crystals. Passivation is a process which selectively eats away any exposed iron from a stainless part. It's a common treatment for machined stainless parts which must stand up to adverse weather conditions. Passivation consists of a hot acid bath which the parts are immersed in for a few minutes, and then rinsed off. As part of a summer job many years ago, I ran a passivation bath for a few days. I had no idea at the time what I was doing, and the main thing that I remember about it was that the bath was heated by steam radiators which were also in the tank. The radiators themselves were stainless, but the pipes leading to them were just iron, so we had to haul the radiators out about once a shift just to replace the pipes when they started to leak because of being eaten away. The steamfitter who did the actual pipe replacements made a big impression on me when he explained how stupid it was that the people in charge were too cheap to buy a few feet of stainless pipe, which would have paid for itself in just a couple of days of not having to shut down the bath for an hour every shift. -- ******************************* Jim Adney, jadney@vwtype3.org Madison, Wisconsin, USA ******************************* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~