Who says stainless steel doesn’t rust?

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Brown rust spots (dots) appear on its surface. Stainless steel has the ability to resist oxidation in the atmosphere—that is, its corrosion resistance—but it also has the ability to resist corrosion in media containing acids, alkalis, and salts—that is, its durability. However, its corrosion resistance varies depending on the chemical composition of the steel itself, its microstructure, operating conditions, and the type of environmental medium. Stainless steel can also rust! Brown rust spots (dots) appear on the surface. In a dry and clean atmosphere, stainless steel possesses excellent resistance to rust, but it will still rust when placed in a corrosive environment ； Moreover, not all types of stainless steel are resistant to corrosion and rusting in any environment.   Stainless steel gains its corrosion resistance thanks to an extremely thin, strong, dense, and stable chromium-rich oxide film (protective layer) that forms on its surface, preventing further penetration of oxygen atoms and continued oxidation. Once, for some reason, this film is continuously damaged, oxygen atoms from the air or liquid will keep penetrating in, or iron atoms from the metal will continue to separate, forming loose iron oxide; as a result, the metal surface suffers from continuous rusting. The most common types in daily life are as follows: 1. Electrochemical corrosion – Dust or particles of other metal elements accumulate on the surface of stainless steel; in humid air, the condensation water between these deposits and the stainless steel forms a microbattery, triggering an electrochemical reaction. 2. Organic substances such as juices from fruits and vegetables, noodle soup, sputum, etc., adhere to the surface of stainless steel. In the presence of water and oxygen, these substances form organic acids, which over time cause corrosion of the metal surface. Local corrosion caused by surface adhesion of acidic, alkaline, or saline substances (such as alkaline solutions or lime spray used in wall decoration). 3. In polluted air (such as air containing large amounts of sulfides, carbon monoxide, and nitrogen oxides), when it comes into contact with condensed water, sulfuric acid, nitric acid, and acetic acid are formed, leading to chemical corrosion.   To ensure that the stainless steel surface remains shiny and free from rust, it is recommended to: 1. Regularly clean and scrub the stainless steel surface to remove any deposits and eliminate external factors that could cause corrosion. 2. In coastal areas, stainless steel with good resistance to pitting corrosion, such as grade 316, should be used.  3. Control the chemical composition of stainless steel pipes properly.