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Seamless steel pitting

First, the concept of seamless steel pitting

As described above, the seamless steel pipe excellent in corrosion resistance due to oxide film on the steel surface forming an invisible, making it a passive state. Forming the passivation film is exposed to the atmosphere because the steel upon reaction with oxygen, or a consequence of the contact with other oxygen-containing environment. If the passive film is damaged, seamless steel pipe corrosion will continue to go on. In many cases, the passive film is destroyed only in localized metal surface, corrosion role is the formation of small holes or pits, like corrosion pits produce irregular distribution of the material surface.

Second, the factors that cause pitting of seamless steel pipe

Pitting is likely to be the presence of a compound with the depolarizer chloride ions. Seamless steel tubes and other passive metals pitting often due to some aggressive anions partial destruction of the passive film. Protection high corrosion resistance of passive state usually requires an oxidizing environment, but this is just pitting conditions occur. Pitting media is Cl-, Br-, I-, ClO4- solution in the presence of Fe3 +, Cu2 +, Hg2 + and other heavy metal ions or containing H2O2, O2, etc. Na +, Ca2 + chloride solution of an alkali and alkaline earth metal ions.

Pitting rate increases with increasing temperature. For example, in a concentration of 4% to 10% sodium chloride solution, weight loss reached the maximum pitting caused at 90 ℃; for more dilute solution, maximum occurs at higher temperatures.


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