Occurrence of stainless steel rust

  • 2021-12-10
Stainless steel will rust under certain conditions. Stainless steel has the ability to resist atmospheric oxidation, that is, rust resistance. At the same time, it also has the ability to resist corrosion in media containing acid, alkali and salt, that is, corrosion resistance. However, its corrosion resistance changes with its own chemical composition, interaction state, service conditions and environmental medium type. For example, 304 steel pipe has absolutely excellent corrosion resistance in a dry and clean atmosphere, but if it is moved to the coastal area, it will soon rust in the sea fog containing a lot of salt; 316 steel pipe performs well. Therefore, not any kind of stainless steel can resist corrosion and rust in any environment.

Stainless steel is a very thin, firm, fine and stable chromium rich oxide film (protective film) formed on its surface to prevent the continuous infiltration and oxidation of oxygen atoms, so as to obtain the ability to resist corrosion. Once the film is continuously damaged for some reason, oxygen atoms in air or liquid will continuously penetrate or iron atoms in metal will continuously separate out, forming loose iron oxide, and the metal surface will be continuously corroded. There are many forms of destruction of the surface film.

1. There are dust containing other metal elements or attachments of dissimilar metal particles on the surface of stainless steel. In humid air, the condensate between the attachments and stainless steel connects them into a micro battery, which leads to electrochemical reaction and damage to the protective film, which is called electrochemical corrosion.

2. Organic juice (such as melons and vegetables, noodle soup, phlegm, etc.) adhered to the surface of stainless steel constitutes organic acid in the presence of water and oxygen. For a long time, the corrosion of organic acid on the metal surface will be reduced.

3. The adhesion of stainless steel surface contains acid, alkali and salt substances (such as alkali water and lime water splashing on the decoration wall), causing local corrosion.

4. In polluted air (such as atmosphere containing a large amount of sulfide, carbon oxide and nitrogen oxide), sulfuric acid, nitric acid and acetic acid liquid points are formed in the presence of condensate, causing chemical corrosion.

The above conditions can cause the damage of the protective film on the surface of stainless steel and lead to corrosion. Therefore, in order to ensure that the metal surface is permanently bright and not corroded, we suggest:

1. The decorative stainless steel surface must be cleaned and scrubbed frequently to remove attachments and eliminate external factors causing modification.

2. 316 stainless steel shall be used in coastal areas, which can resist seawater corrosion.

3. The chemical composition of some stainless steel pipes in the market can not meet the corresponding national standards and can not meet the 304 material requirements. Therefore, it will also cause rust, which requires users to carefully select the products of reputable manufacturers.

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