(1) ASTM A179 cold drawn steel pipe with carbon steel pollution: contact with carbon steel caused by scratches and corrosive media to form the original battery and electrochemical corrosion.
(2) ASTM A179 cold drawn steel pipe cutting: slag, splash and other easy to rust the material attached to the corrosive medium and the formation of the original battery electrochemical corrosion.
(3) Heating: the composition of the flame heating area and microstructure changes and not uniform, and the formation of the original medium of corrosive media and electrochemical corrosion.
(4) ASTM A179 cold drawn steel pipe welding: physical defects in the welding area (undercut, pores, cracks, not fused, not welded, etc.) and chemical defects (coarse grain, grain boundary poor chromium, segregation, etc.) and corrosive media to form the original Battery and produce electrochemical corrosion.
(5) Material: chemical defects of cold drawn steel (uneven composition, S, P impurities, etc.) and surface physical defects (loose, trachoma, cracks, etc.) is conducive to the formation of the original medium with corrosive media and electrochemical corrosion.
(6) Passivation: pickling passivation effect is not good caused by cold-drawn steel pipe surface passivation film is uneven or thin, easy to form electrochemical corrosion.