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Does the Stainless Steel Tube Must not Rust?

Date:2019-06-19    keywords:stainless, steel, tube, rust

The stainless steel tube does not easily rust and has a great relationship with the composition of the stainless steel. In addition to iron, stainless steel has chromium, nickel, aluminum, silicon, and the like. Generally, the chromium content of stainless steel is generally not less than 12%, and even high is even 18%. When chromium or other elements are added to the steel, the properties of the steel can be changed. For example, the molecular structure of the steel is more uniform, and a dense oxide protective film is more easily formed on the surface of the steel, thereby greatly improving the corrosion resistance of the stainless steel. Therefore, stainless steel can resist the corrosion of fire, water, acid, alkali and various solutions, and does not rust. Scientists have found that the more uniform the internal structure of steel, the more closely the various components are connected, the more difficult it is to invade corrosion, and the addition of an oxide protective film on the surface, just like putting armor on steel, naturally It is not easy to rust.

When brown rust spots (dot) appeared on the surface of stainless steel pipes, people might be amazed: "Stainless steel is not rusted, rust is not stainless steel, and there may be problems with steel." In fact, this is a one-sided misconception about the lack of understanding of stainless steel. Stainless steel will also rust under certain conditions.

Stainless steel has the ability to resist atmospheric oxidation - that is, rust, and also has the ability to corrode in acids, alkalis, and salts - that is, corrosion resistance. However, the degree of corrosion resistance varies with the chemical composition of the steel itself, the state of interaction, the conditions of use, and the type of environmental medium. For example, 304 steel pipe has absolutely excellent rust resistance in a dry and clean atmosphere, but it is moved to the coastal area, and it will soon rust in sea fog containing a lot of salt; while 316 steel pipe will perform. good. Therefore, it is not any kind of stainless steel that is resistant to corrosion and rust in any environment.

Stainless steel is a very thin and strong and stable chromium-rich oxide film (protective film) formed on the surface to prevent the oxygen atoms from continuing to infiltrate and continue to oxidize, thereby obtaining the ability to resist rust. Once for some reason, the film is constantly destroyed, oxygen atoms in the air or liquid will continue to infiltrate or iron atoms in the metal will be continuously separated, forming loose iron oxide, and the metal surface will be continuously rusted. There are many forms of such surface film damage, and the following are common in daily life:

1. The surface of the stainless steel contains dust or other metal particles attached to other metal elements. In humid air, the condensed water between the attached material and the stainless steel connects the two into a micro battery, triggering an electrochemical reaction. The protective film is destroyed, which is called electrochemical corrosion.

2. The surface of the stainless steel adheres to the organic juice (such as melon, noodle soup, glutinous rice, etc.), and in the case of water and oxygen, constitutes an organic acid, and the organic acid corrodes the metal surface for a long time.

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

4. In polluted air (such as containing a large amount of sulfide, carbon oxide).

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