Why stainless steel welded pipe surface rust?

Stainless steel welded pipe part of the surface of the “rust” phenomenon is normal, with the Centerway to understand.

“Although in theory the welded pipe is not rust, but rust is not a welded pipe, may be a problem with the steel. Such views on the welded pipe belongs to the lack of understanding or understanding of one-sided. In fact, the welded pipe will rust under certain conditions. Theoretically, the welded pipe has the ability to resist atmospheric oxidation - that is, stainless steel, but also has the ability to resist corrosion in the medium containing acid, alkali, salt - that is, corrosion resistance. But the size of its corrosion resistance is with the steel itself chemical composition, plus mutual state, use conditions and the type of environmental media and change. Such as 304 steel pipe, in the dry clean atmosphere, there is absolutely excellent corrosion resistance, but it will be moved to the seaside areas, in the sea spray containing a large amount of salt, long-term so it will rust; and 316 steel pipe is good performance. Therefore, not any kind of welded pipe, in any environment can resist corrosion, not rust. Stainless steel welded pipe rust is mainly reflected in the surface of the brown rust spots (points) and other phenomena.

Welded pipe rust is mainly rely on its surface to form a layer of very thin and solid dense stable chromium-rich oxide film (protective film), to prevent the continued penetration of oxygen atoms, continue to oxidize, and obtain the ability to resist rust and corrosion. Once there is some reason such as transportation, collision, and other items in contact, this film has been constantly damaged, air or liquid oxygen atoms will continue to penetrate or metal iron atoms continue to separate out, the formation of loose iron oxide, metal surface is also subjected to constant corrosion. This surface film is damaged in many forms, daily use in addition to the above reasons are as follows:

Welded pipe surface deposits containing other metal elements of dust or dissimilar metal particles of adhesion, in the humid air, adhesion and condensation between the welded pipe, will be connected to a microcell, triggering an electrochemical reaction, the protective film is damaged, known as electrochemical corrosion.

Welded pipe surface adhesion of organic sap (such as vegetables, noodle soup, phlegm, etc.), in the presence of water and oxygen, constitutes an organic acid, a long time, the organic acid corrosion of the metal surface.

Welded pipe surface adhesion containing acid, alkali, salt substances (such as alkaline water, lime splash decoration wall), causing localized corrosion.

In the polluted air (such as containing a large number of sulfides, carbon oxides, nitrogen oxides in the atmosphere), condensation, the formation of sulfuric acid, nitric acid, acetic acid liquid point, causing chemical corrosion.

All of the above can cause the destruction of the protective film on the surface of the welded pipe to cause corrosion, resulting in the surface of the steel pipe to produce color rust, spots (points) and other “rust” phenomenon.