Why does the 304 stainless steel pipe leak?
Austenitic stainless steels are extremely sensitive to chloride ion and can occur in a very short time if the temperature and concentration are appropriate. Therefore, the relevant standards and specifications in the clear requirements for austenitic stainless steel pressure vessels for hydraulic pressure test, there are strict requirements on the chloride ion concentration of the water, and after the test to put water clean, dry. In order to avoid residual moisture in the chloride ion corrosion of stainless steel.
This is the mechanism of pitting ion in neutral solution, such as the effect of chlorine ion on the surface of the passivation film, surface damage, and pitting, uneven part of the organization, the structure of the metal inclusions easily become a source of pittingOf course, there are many other forms of corrosion on austenitic stainless steel, such as crevice corrosion, stress corrosion, and so on.
The corrosion resistance of stainless steel is due to the formation of a very thin, adhesive and semi transparent chromium oxide film on the surface of stainless steel. Once this layer of film is destroyed, the chromium in the steel react with oxygen in the atmosphere to recover the film quickly, and mechanical damage can quickly produce a protective film. However, if the chemical erosion by ions, especially chloride ions, will quickly dissolve and corrosion, the result is that the metal surface needle or point, there is a certain depth of small holes, this corrosion is called pitting.
Chloride poisoning. Why chlorine is found in tap water is not explained here.
