Chromium content in stainless steel tubes

　　The corrosion resistance of stainless steel tubes depends on the chromium. When the amount of chromium added is 10.5%, the atmospheric corrosion resistance of the steel pipe is remarkably increased, but when the chromium content is higher, although the corrosion resistance is still improved, it is not obvious. The reason is that when chromium is used to alloy steel, the type of surface oxide is changed to a surface oxide similar to that formed on pure chromium metal. This tightly adhering chromium-rich oxide protects the surface from further oxidation. This oxide layer is extremely thin, through which you can see the natural luster of the steel surface, giving the stainless steel a unique surface. Moreover, if the surface layer is damaged, the exposed steel surface will react with the atmosphere to repair itself, and the "passivation film" is reformed to continue the protection.

　　Therefore, all stainless steel pipes have a common characteristic, that is, the chromium content is more than 10.5%.

　　Steel pipes for building construction, all of which contain 17 to 22% chromium, and preferred steel pipes also contain nickel. The addition of molybdenum further improves atmospheric corrosivity, particularly corrosion resistance to chloride-containing atmospheres.

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