Stainless steel welded pipes are called stainless steel welded pipes due to their high resistance to corrosion and the corrosive nature of their surroundings. There are many theories to explain the passivation of stainless steel welded pipe.
Explanation from the chemical theory
Due to the action with the medium, there will be a layer of Cr20-based film on the surface, that is, the clocking film, so that the stainless steel huang tube is considered to have corrosion resistance. This type of film is characterized by thin, generally only a few microns, chromium content is greater than 10.5%, the specific gravity of this type of film is greater than the specific gravity of the metal matrix, indicating that the film is very dense. This can effectively protect the metal matrix from corrosion, because this kind of film is very difficult to be corrosive medium damage. Electronic Theory Explanation.
It is believed that the bellicose state of the metal is related to the unfilled electron layer. The iron-chromium alloy stainless steel humongous tube is passivated because chromium tries to absorb electrons and iron (Fe) atoms lose electrons. Some scholars believe that when the chromium content in the ferrochromium alloy solid solution reaches 1/8 (i.e., 12.5%), the electrode potential can jump from 0.56 V to +0.2 V. The increase in electrode potential makes the metal in the electrolyte more stable, that is, less prone to corrosion. The above theory is based on the role of bearing in mind. In fact, due to the diversity and complexity of the material environment, in order to improve and consolidate the corrosion resistance of the material, it is necessary to add other alloying elements under certain conditions. For example, the addition of nitrogen (N) elements will make the corrosive product M002 close to the base rest, to promote the passivation of the substrate; the addition of people, N) elements will make the stainless steel tube surface of the chemical film contains u0, not with the corrosive medium phase, thereby improving the corrosion resistance of the material; the addition of people nitrogen (N) elements will make the material's corrosion resistance, because the passivation film is rich in Cr2N, thereby increasing the concentration of chromium in the passivation film.
