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Why Stainless Steel Tubes Pipes Will Rust?Posted on 03-25-2012 - 492 Views
Why stainless steel tube will rust? When the stainless steel tube's surface appear brown rusty spot (point), people was surprised: stainless steel can't be covered with rust, pipes covered with rust, usually, we call it –“stainless steel tube”, and they Maybe think that the quality of the stainless steel tube has a problem. Actually, this is a wrong view, because people have little understanding about the stainless steel tube. Stainless steel also will rust in certain conditions
Stainless steel has the ability to resist oxidation atmosphere—resist rust, also has the ability of corrosion resistance in acid, alkali, salt-namely corrosion resistance. However, the strength of corrosion resistance will be changed with its own chemical composition damaged. It is according to the use of conditions and environment. Such as 304 steel, in a dry and clean atmosphere have excellent corrosion resistance. But in the coast, the stainless steel will be covered by fog which contains a lot of sea salt and soon will be rusted. Under the same conditions, 316 steel tube is performing well.
Therefore, not any kind of stainless steel can resist corrosion and rust in any environment.
Stainless steel can resist corrosion and rust, because its surface have formed a thin layer of fine and strong, stable, rich chromium oxidation film(protection film)which can prevent to the oxygen atom and oxidation.
Once there are some reason, this protection film will be destructed, the air or oxygen in liquid can unceasingly infiltrate or metal atoms constantly analysis from iron, forming loose ferric oxide, the metal surface also are constantly rusted .There are many formation that damage to the surface protection film .In our daily lives, usually have the following kinds:
1. The stainless steel surface accumulates the dust which contained other metal elements or attached other metal particles. In the moist air, the condensed water between objects and stainless steel, combine them into a small battery, causing the electrochemical reactions protective film to be changed, says: the electrochemical corrosion.
2. Stainless steel surface attached juice (such as organic melons, vegetable, noodles soup, phlegm, etc), where there is water, oxygen constitute organic acid, after a long time, the organic acid would corrode the metal surface.
3. Stainless steel surface attach some things which contains acid, alkali, salt material (such as the alkaline water and the lime water of the buck decorate wall), cause local corrosion.
4.The air which contains a lot of sulfur, carbon dioxide, nitrogen oxide ,when encountered the condensed water, will form sulfuric acid, nitric acid, acetic acid liquid point and cause chemical corrosion.