Stainless steel surface coatings has also influenced its use in commercial kitchens and food processing plants. Stainless steels do not suffer uniform corrosion, like carbon steel, when exposed to wet environments. Unprotected carbon steel rusts readily when exposed to the combination of air and moisture. The resulting iron oxide surface layer (the rust) is porous and fragile. Since iron oxide occupies a larger volume than the original steel this layer expands and tends to flake and fall away exposing the underlying steel to further attack. In comparison, stainless steels contain sufficient chromium to undergo passivation, spontaneously forming a microscopically thin inert surface
SAE 904L stainless steel SAE 904L stainless steel 904L is an austenitic stainless steel. In comparison to 316L, its molybdenum addition gives it superior resistance to localized attack (pitting and crevice corrosion) by chlorides and greater resistance reducing acids and in particular its copper addition gives it useful corrosion resistance to all concentrations of sulphuric acid. Its high alloying content also gives it greater resistance to chloride stress corrosion cracking, but it is still susceptible. Its low carbon content makes it resistant to sensitization by welding and which prevents intergranular corrosion. It has applications in piping systems, pollution control equipment, heat exchangers, and bleaching