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Why does stainless steel rust? Causes and preventive solutions

November 15, 2023

Stainless steel has the ability to resist atmospheric oxidation, it will not rust, and it also has the ability to corrode in media containing acid, alkali, and salt--that is, corrosion resistance. However, its corrosion resistance changes with the chemical composition of the steel itself, its additive state, usage conditions and environmental medium types. Like 304 steel pipes, in the atmosphere of dry cleansing, absolute good resistant to tarnishing ability is arranged. But if it is moved to riviera, in containing the sea fog of a large amount of salts, will soon get rusty, while 316 steel pipes perform very well. Therefore, not any kind of stainless steel can resist corrosion and rust in any environment.


Stainless steel relies on the formation of an extremely thin, strong, fine, and stable chromium-rich oxide film (protective film) on its surface to prevent the continued penetration and oxidation of oxygen atoms, thereby obtaining the ability to resist corrosion. Once this film is continuously damaged for some reason, oxygen atoms in the air or liquid will continue to penetrate or iron atoms in the metal will continue to separate out, forming loose iron oxide, and the metal surface will be continuously corroded. There are many forms of damage to this surface film, and the common ones are as follows:


1. Dust containing other metal elements or attachments of heterogeneous metal particles accumulate on the surface of stainless steel. In humid air, the condensed water between the attachments and stainless steel connects the two into a micro-battery, triggering an electrochemical reaction, the protective film is damaged, which is called electrochemical corrosion.


2. Organic juices (such as vegetables, noodle soup, phlegm, etc.) adhere to the surface of stainless steel. In the presence of water and oxygen, they form organic acids. For a long time, the organic acids will corrode the metal surface.


3. The surface of stainless steel contains acids, alkalis, and salts (such as alkaline water and lime water splashed on walls), causing local corrosion.


4. In polluted air (such as an atmosphere containing a large amount of sulfides, carbon oxides, and nitrogen oxides), when encountering condensed water, sulfuric acid, nitric acid, and acetic acid liquid points are formed, causing chemical corrosion.


All of the above situations can cause damage to the protective film on the stainless steel surface and cause corrosion. Therefore, to ensure that the metal surface is permanently bright and protected from rust, we recommend:


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


2. 316 stainless steel should be used in seaside areas. 316 material can resist seawater corrosion.


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