The stainless steel is not easy to rust has the very big relations with the stainless steel ingredient. In stainless steel ingredient besides iron, but also has the chromium, the nickel, the aluminum, the silicon and so on. The common stainless steel chromic quantity is not lower than 12% generally, high even achieves 18%. (we use in 316 steel pipes chromium content should after 16%-18%) the steel joins elements and so on chromium, can change the steel the performance, like the example steels molecular structure is evener, produces compact oxide compound protective film in the steel superficial change and so on, thus sharpens the stainless steel anti-corrosive ability greatly. Therefore the stainless steel can arrive at the fire resistance, the water, the acid, the alkali and each kind of solution to its corrosion, is not rusty. The scientist discovered that the steel internal structure is evener, each kind of component relates closely, the corrosive substance invasion is more difficult, in addition the surface adheres to stick cohere oxide compound protective film, looks like to the steel and iron puts on the helmet and armor to be the same, was not naturally easy to rust. Why does the stainless steel also rust? When the stainless steel tube-surface presents the brown rusty stain (spot) time, the people big feeling is surprised: Thought that “the stainless steel does not rust, rusted is not the stainless steel, possibly was the steel had the problem”. Actually, this is lacks the understanding to the stainless steel one one-sided wrong view. The stainless steel will also rust under certain condition. The stainless steel has the resistance air oxidation ability---Namely the rustless property, simultaneously also has in contains the acid, the alkali, in the salty medium is corrosion ability---Namely corrosion resistance. But its corrosion resistance abilitys size is along with its steel itself chemical composition, the Canadian mutually condition, the exploitation conditions and the ambient medium type changes. If 304 steel pipes, in the dry clean atmosphere, have absolutely the fine anti-corrosion ability, but transfers to it the seashore area, in includes in the massive salty share sea fog, very quick will rust; But 316 steel pipe good behavior. Therefore, is not any kind of stainless steel, the ability corrodes under any environment, does not rust. The stainless steel is one which forms depending on its surface is extremely thin and the firm close stable rich chromium oxide film (protective layer), prevents the oxygen atom to continue permeating, to continue to oxidize, but obtains the anti-corrosion ability. Once has some kind of reason, this kind of thin film encountered destroyed unceasingly, in the air either the liquid the oxygen atom unceasingly will permeate or in the metal the hard atom separation comes out, to form the loose ferric oxide unceasingly, the metal surface also receives rusts away unceasingly. This kind of surface film receives the destruction the form to be many, in the daily life sees has the following several kinds: 1. the stainless steel surface stores is including other of metallic element dust or the different races metal pellet attachment, in the moist air, condensed water between the attachment and the stainless steel, the two Lian Cheng a microcell, initiated the electrochemistry response, the protective film has received the destruction, said that it said the electrochemistry corrosion. 2.the stainless steel surface adherency organic matter juice (for example melons vegetables, hot water, phlegm and so on), in have in the water oxygen situation, constitution organic acid, long time organic acid to metal surface corrosion. 3. the stainless steel surface adherency includes the acid, the alkali, the salts material (for example repair wall lye, limewater splattering), causes the localized corrosion 4.In has in the pollution air (for example to include massive sulfide, oxidized carbon, nitrogen oxide atmosphere), meets the condensed water, forms the sulfuric acid, the nitric acid, the acetic acid fluid spot, causes the chemical etching.