Why does stainless steel flange rust?

Why does stainless steel flange rust? Stainless steel flange has the ability to resist atmospheric oxidation and corrosion in the medium containing acid, alkali and salt. However, the size of stainless steel flange corrosion resistance changes with its own chemical composition, interaction state, service conditions and environmental medium type.

For example, the stainless steel flange has absolutely excellent corrosion resistance in the dry and clean atmosphere, but when   stainless steel flanges moved to the seaside area, it will soon rust in the sea fog containing a lot of salt, while the 316 flange is outstanding. Therefore, not any kind of stainless steel flange can resist corrosion and rust in any environment.

Stainless steel flange is a thin and stable chromium rich oxide film (protective film) formed by its appearance to avoid the continuous entry and oxidation of oxygen atoms and obtain the ability of corrosion resistance. Once there is a certain reason, the stainless steel flange film is constantly damaged, and oxygen atoms in air or liquid will enter or iron atoms in metal will be separated continuously, forming loose iron oxide, and the metal surface will be constantly rusted.

There are many ways in which the surface film is damaged. The stainless steel flange following are common in daily life: there are dust containing other metal elements or attachments of dissimilar metal particles on the surface of stainless steel flange. In humid air, the condensate between the attachments and stainless steel flange connects them into a micro battery, which leads to electrochemical reaction, and the protective film is damaged, which is called electrochemical corrosion.

The surface of stainless steel flange adheres to organic juice (such as melons and vegetables, noodle soup, phlegm, etc.), which constitutes organic acid in the case of water and oxygen. For a long time, the corrosion of organic acid on the surface of metal. The surface of stainless steel contains acid, alkali and salt substances (such as alkali water and lime water splashing for decorating the wall), causing local corrosion. In the polluted air (such as the atmosphere containing a lot of sulfide, carbon oxide and nitrogen oxide), stainless steel flange forms sulfuric acid, nitric acid and acetic acid liquid points in the presence of condensate, causing chemical corrosion.