Will Stainless Steel Sanitary Valves and Fittings Not Rust?

Many people simply think that stainless steel will not rust, rust doesn't occur in stainless steel.
Ordinary carbon steel reacts with oxygen in atmosphere, and forms oxide film on the metal surface. The oxidation continues so that corrosion will expand, and form corrosive layers until it is rotten. Of course, people can use paint or metals which are oxidation resistant(such as zinc, nickel and chromium) to electroplate so as to protect the surface of carbon steel, but this protective layer is only a thin layer of film, if the layer is destroyed, the steel inside will begin to rust.

However, the processing of stainless steel sanitary valve fittings is different. when chromium of stainless steel reaches about 12%, it will contact with atmospheric and form a layer of passive film (Cr2O3) on its surface, which is dense chromium oxidation. Chromium oxidation can protect the surface of the stainless steel sanitary valve fittings, especially prevent the steel from further oxidation. This oxide film is extremely thin through which you can see the natural gloss of the steel surface, and that makes stainless steel a unique surface properties. If the surface oxide film is destroyed, the exposed steel surface will react with the oxygen in the atmosphere, re-form passive film and continue to protect the steel. Therefore, under the guidance of this theory, many people think that stainless steel sanitary valve fittings will not rust. But actually different kinds of rust occur in many sites due to the different humidity, which is normal.