Why is stainless steel rust? When the stainless steel tube surface appear brown rusty spot (or points), big surprised: people think "stainless steel is not rusty, rust is not stainless steel, is likely to be the problem of steel". In fact, this is a one-sided erroneous view of the lack of understanding of stainless steel. Stainless steel also rusts under certain conditions.

      Stainless steel has the ability to resist atmospheric oxidation - that is, non-rust, and also has the ability to corrode in the medium of acid, alkali and salt - that is, corrosion resistance. However, its corrosion resistance is changed by its chemical composition, the state of reinforcement, the conditions of use and the type of environmental media. The 304 steel pipe, in the dry clean atmosphere, has an excellent resistance to rust, but moves it to the coastal area, which will soon rust in the sea fog that contains a lot of salt. The 316 steel pipe is performing well. Therefore, not any kind of stainless steel, can resist corrosion and rust in any environment.

     Stainless steel is formed on the surface of a layer of a very thin and fine and stable solid rich chromium oxide film (protective film), prevent oxygen to infiltration, continue to oxidation, and ability to resist corrosion. Once you have some reason, this film has been continuously destroyed, air or liquid oxygen in the original child will constantly infiltration or metallic iron atom separation out unceasingly, forming loose iron oxide, gold Surface are also constantly rust. There are many forms of damage to this surface film, and there are many of them in daily life:

    1. Deposited on the surface of the stainless steel contain other metals attached or heterogeneous metal particles of dust of the content, in the humid air, attachments and condensed water between the stainless steel, will both together as a micro battery, triggers the electrochemical reaction, protective film is damaged, to call the electrochemical corrosion.

    2. The stainless steel surface adheres to organic juices (such as melons, soups, sputum etc.), and in the case of water oxygen, the organic acids are formed, and the organic acids are used to corrode the metal surface for a long time.

    3. Surface adhesion of stainless steel contains acid, alkali and salt substances (such as alkaline water in the wall of decoration and splash of lime water), causing local corrosion.

    4. In the polluted air (such as the atmosphere with a large amount of sulphide, oxidized carbon and nitrous oxide), it can be used to form sulfuric acid, nitric acid and acetic acid, causing chemical corrosion.