With time, all grades of stainless steel will corrode in the right environment unless properly protected. The accepted industry standard is to passivate stainless steel as the last step in the manufacturing process by dipping it in or wiping it with acids such as citric or nitric. The resultant chromium oxide film is a function of metal chromium content, acid used, temperature, and exposure time to the acid. Unfortunately, the oxide layer is not permanent, as it can be damaged during normal plant operations by exposure to harsh chemicals, physical abrasion, or stress due to expansion and contraction.
When the oxide film on the surface is continuously destroyed, it loses its ability to form new oxide films. Once the film is destroyed it exposes the metal to corrosive elements such as organic and inorganic acids, alkalis, and halides. Halides, especially chlorides, are a serious factor causing stainless steel to rust because they destroy passivating films. Chlorides are all around us, in sea and saltwater lakes, household cleaners, and disinfectants. When left exposed to these products for extended periods of time with no adequate cleaning, stainless steel will corrode and tarnish.