Explain the process of passivation in stainless steel and why it is crucial for corrosion resistance in industrial environments.

Passivation in stainless steel is the spontaneous formation of a thin, chromium-oxide rich, passive layer on the surface of the steel when exposed to oxygen. Stainless steel's corrosion resistance is primarily due to the presence of chromium. When chromium is exposed to oxygen, it reacts to form chromium oxide (Cr2O3). This chromium oxide layer is extremely thin (typically a few nanometers thick), tightly adherent, and self-repairing. If the passive layer is scratched or damaged, it will quickly reform in the presence of oxygen. This self-healing property is what gives stainless steel its excellent corrosion resistance. Passivation is crucial for corrosion resistance in industrial environments because it protects the underlying steel from corrosive agents such as acids, chlorides, and high temperatures. Without passivation, stainless steel would be susceptible to corrosion, particularly in aggressive industrial environments. The passivation process can be enhanced by chemical treatments, such as immersion in nitric acid or citric acid solutions. These treatments remove any surface contaminants and promote the formation of a uniform and stable passive layer. For example, stainless steel piping used in a chemical plant to transport corrosive chemicals relies on the passive layer to prevent corrosion and maintain the integrity of the piping system. If the passive layer is compromised, for example, by welding without proper passivation procedures, the steel can become susceptible to localized corrosion, such as pitting or crevice corrosion.