All metals react with oxygen in the atmosphere and form oxide films on the surface. Unfortunately, iron oxide formed on ordinary carbon steel continues to oxidize, causing corrosion to expand and eventually form holes. Electroplating can be used to ensure the surface of carbon steel using paint or oxidation resistant metals such as zinc, nickel and chromium, but, as it is known, this protection is only a kind of film. If the protective layer is damaged, the steel below will rust.
The corrosion resistance of stainless steel composite pipes depends on chromium, but because chromium is one of the components of steel, the protection methods are different.
When the amount of chromium is 10.5%, the corrosion resistance of steel increases significantly, but the corrosion resistance can still be improved, but it is not obvious, though the chromium content is higher. The reason is that when chromium is used for alloying steel, the type of surface oxide is changed into a surface oxide similar to that formed on pure chromium metal. This tightly adhered chromium rich oxide protects the surface from further oxidation. The oxide layer is very thin, through which it can see the natural luster of the steel surface and make the stainless steel composite tube have a unique surface. Moreover, if the surface is damaged, the exposed steel surface will repair itself with the atmospheric reaction, reformed the "passivation film" and continue to play a protective role.
Therefore, all stainless steel composite pipes have a common characteristic, that is, chromium content is above 10.5%.
There are usually only six kinds of steel related to the application of building structures. They contain 17 to 22% chromium, and the better steel contains nickel. Adding molybdenum can further improve atmospheric corrosiveness, especially chloride containing atmospheric corrosion.
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