Whether stainless steel pipe fittings will rust?


First say stainless steel pipe fittings why not be rusty, then say stainless steel why also can rust.

Stainless steel fittings is not easy to rust and the composition of stainless steel has a great relationship. In addition to iron, the composition of stainless steel, chromium, nickel, aluminum, silicon, and so on. Generally, the chromium content of stainless steel is not less than 12%, and even reaches 18%. When chromium and other elements are added to steel, the properties of steel can be changed. For example, the molecular structure of steel is more uniform, and a compact oxide protective film is formed on the surface of steel, which greatly improves the corrosion resistance of stainless steel. Therefore, stainless steel can resist the corrosion of fire, water, acid, alkali and various solutions. Scientists have found that the more uniform the internal structure of steel, the closer the various components become, and the more difficult it is for corrosives to invade. Add a layer of oxide protective coating to the surface, and steel, like armor, is naturally less likely to rust.

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Why does stainless steel rust? People are surprised when brown rust spots appear on the surface of the thin wall stainless steel pipe. They think "stainless steel is not rusting, rusting is not stainless steel, perhaps there is a problem with the steel". In fact, this is a one-sided misunderstanding of stainless steel. Stainless steel will rust under certain conditions.

Stainless steel is formed by its surface of a very thin and strong and fine stable chrome oxide film (protective film), to prevent oxygen atoms continue to infiltrate, continue to oxidize, and obtain the ability to resist rust. For some reason, the film is constantly damaged. Oxygen atoms in the air or liquid will seep in or iron atoms in the metal will separate out, forming loose ferric oxide. The surface of the metal is constantly corroded. This kind of surface film is damaged in many forms, which are commonly seen in daily life:

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Stainless steel surfaces contain dust or foreign metal particles. In moist air, the condensed water between the appendage and stainless steel connects the two to form a micro battery, which triggers an electrochemical reaction. The protective film is damaged, which is called electrochemical corrosion.

Stainless steel surface adheres to organic juice (such as melon, noodle soup, sputum, etc.) In the presence of water and oxygen, organic acids are formed, which corrode the metal surface for a long time.

Stainless steel surface adhesion contains acid, alkali, salt material (such as the alkaline water that decorates a wall, stone ash water spatter), cause local corrosion.

In polluted air (such as atmosphere containing a large amount of sulfide, carbon dioxide and nitrogen oxides), condensate water forms sulfuric acid, nitric acid and acetic acid liquid points, causing chemical corrosion.