Cold-drawn steel pipe will also rust under certain conditions. However, the corrosion resistance of the steel varies with its chemical composition, additive state, service conditions and the type of environmental medium. Cold-drawn seamless steel pipe is formed by a thin, solid, compact and stable chromium-rich oxide film (protective film) on its surface, which prevents oxygen atoms from penetrating into and oxidizing continuously, and obtains the ability to resist corrosion. Once for some reason, the film is constantly destroyed, oxygen atoms in air or liquid will continuously infiltrate or iron atoms in metal will continuously separate out, forming loose iron oxide, and metal surface will be constantly corroded. There are many forms of destruction of the surface film.
1. The surface of cold-drawn seamless steel pipe is deposited with dust containing other metal elements or adhesives of different metal particles. In moist air, the adhesives and condensate water between stainless steel and stainless steel connect them into a micro-battery, which leads to electrochemical reaction, and the protective film is destroyed. It is called electrochemical corrosion.
2. The surface of cold-drawn seamless steel pipe is adhered with organic juice (such as melon, vegetable, noodle soup, phlegm, etc.). Under the condition of water and oxygen, organic acid is formed, and for a long time, organic acid corrodes the metal surface.
3. The adherence of cold-drawn seamless steel pipe surface to acid, alkali and salt substances (such as alkali water and lime water splashing on decoration walls) causes local corrosion.
4. In polluted air (such as atmosphere containing large amounts of sulfide, carbon dioxide and nitric oxide), sulfuric acid, nitric acid and acetic acid are formed in the presence of condensate, which leads to chemical corrosion.
All of the above can cause the surface protective film damage of cold-drawn seamless steel tube and lead to corrosion. Therefore, in order to ensure that the metal surface is permanently bright and not corroded, we recommend:
1. The surface of decorative cold-drawn seamless steel tubes must be cleaned and scrubbed regularly to remove the attachments and eliminate the external factors causing the modification.
2. Seamless cold-drawn 316 steel pipes should be used in coastal areas. 316 steel pipes can resist seawater corrosion.
3. The chemical composition of some cold-drawn seamless steel tubes in the market can not meet the corresponding national standards, and can not meet the material requirements of 304. Therefore, it will also cause rust, which requires users to carefully choose products from reputable manufacturers.
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