Stainless Steel And Corrosion
Stainless or stain resistant? Stainless steels contain at least 12% chromium and form a thin, invisible protective, corrosion-resistant, passive film on their surface. This film forms spontaneously when the chromium reacts with oxygen in air and water. If the film is damaged or removed during fabrication or polishing, it self-repairs immediately, so long as the surface is clean. If stainless steel corrodes, typically highly localized metal loss or pitting occurs – rarely general or uniform corrosion of the entire surface.
While problems with stainless products are infrequent, the name stainless can be somewhat misleading. It is not actually stainless, but stain resistant – it is a corrosion resistant alloy, not rustproof. Stainless steel may show some forms of corrosion and/or deterioration depending upon the degree of contaminants in its particular environment. Under certain conditions, it can rust unless a program of preventive maintenance is followed.
The environment in and around swimming pools and salt water contain salts which actively attack stainless steel. Heat and humidity increase the corrosive activity of chlorine and bromine salts. In addition, the corrosive action caused by salts that occurs from ice melting agents, such as calcium chloride and sodium chloride, can create the formation of rust. Other chemical reactions that can cause deterioration include carbon picked up from bending or fabricating tools, finishing equipment or steel covered work benches. It is also typical for contractors or masons to use muriatic acid solution on masonry – even the fumes from this liquid can attack stainless steel.
The material’s mechanical finish – satin or mirror – also plays a role in corrosion resistance. Corrosion-causing agents will collect in the fine lines of a satin finish as opposed to the smooth surface of a mirror finish.
Stainless steel is manufactured in various formats and can sometimes be selected to perform better in certain environments or applications. They are identified by T-304, T-316, etc. as well as L Grades (low carbon).
If you experience difficulty with your stainless products, it is likely that there is a contaminant in the environment. The first step is to identify the contaminant and to eliminate it. After that, assure that a preventive maintenance program is in place and being followed.