(1) The ASTM A179 cold-drawn steel pipe is contaminated by carbon steel: scratches and corrosive media are caused by contact with carbon steel, forming primary batteries and electrochemical corrosion.


(2) ASTM A179 cold-drawn steel pipe cutting: molten slag, splash and other rusty substances adhere to corrosive medium and form electrochemical corrosion of primary battery.


(3) Heating: The composition and microstructure of the flame heating zone vary unevenly, and corrosive and electrochemical corrosion media are formed.


(4) ASTM A179 cold-drawn steel pipe welding: physical defects (bottom cutting, blowhole, cracks, unfused, unwelded, etc.) and chemical defects (coarse grains, grain boundary chromium difference, segregation, etc.) and corrosive medium form original batteries and produce electrochemical corrosion.


(5) Material: Chemical defects (non-uniform composition, S, P impurities, etc.) and surface physical defects (loose, trachoma, cracks, etc.) of cold-drawn steel are conducive to the formation of original media with corrosive media and electrochemical corrosion.


(6) Passivation: poor acid pickling passivation results in uneven or thin passivation film on the surface of cold-drawn steel pipes, which is easy to form electrochemical corrosion.