All metals and the reaction of oxygen in the atmosphere, the surface oxide film. Unfortunately, ordinary stainless steel pipe in the formation of iron oxide on the oxidation continues, the rust continues to expand, eventually forming holes. You can use paint or oxidation-resistant metal (eg, zinc, nickel and chromium) plating to ensure the carbon steel surface, but, as people know, this protection is only a film. If the protective layer is damaged, the following steel began to rust.
　　Stainless steel pipe depends on the corrosion resistance of chromium, but because chromium is a component of steel, so the method of protection is different.
　　Add in the amount of chromium reached 10.5%, the atmospheric corrosion resistant steel increased significantly, but higher chromium content, although still improve corrosion resistance, but not obvious. Because chromium is alloying of steel processing, the surface oxide is similar to the type of change has become pure chromium metal oxides formed on the surface. This tight adhesion of the chromium-rich oxide surface protection to prevent further oxidation. This thin oxide layer, through which you can see the surface of the natural sheen of steel, the stainless steel has a unique surface. Moreover, if the damaged surface, the exposed steel surface and the atmospheric response to self-repair, re-formation of this "passive film", continue to play a protective role.
　　Therefore, all stainless steel have a common characteristic, namely chromium content of 10.5% or more.
　　And building construction applications, the stainless steel pipe types are usually only six. They contain 17 to 22% of chromium, a good steel also contains nickel. Molybdenum can be added to further improve the atmospheric corrosion, particularly corrosion resistance to chloride-containing atmosphere.