There are different corrosion properties of lower gas pipeline in the process of use. Electrochemical corrosion is the biggest threat to buried gas steel tubes. Because the electrochemical corrosion is concentrated, and the speed is fast, once the corrosion occurs, its speed will not slow down will not stop, often resulting in local perforation. Causes of electrochemical corrosion are as follows:

1, due to the soil physical and chemical properties throughout all parts of the pipeline itself metallographic organization structure is different, such as the character of the defect and contains impurities, metal form cold hot working and internal stress generated by the deformation, especially the variation of surface roughness of steel tube and so on reasons, make it easy to part of the metal ionization, positively charged metal ions from the metal, and transferred to the soil, More and more electrons on this part of the tube, more and more negative potential;

2, the other part of the metal is not easy to ionize, relatively positive potential. Thus, electrons flow along the tube from the easily ionized part to the less easily ionized part, and there are gains and losses between the two parts of the metal, resulting in an oxidation-reduction reaction. The segment that loses electrons becomes the anode region and the segment that gains electrons becomes the cathode region. The corrosion current flows from the cathode to the anode, then flows from the anode to the tube, and returns to the cathode through the soil, forming a circuit. In soil as an electrolyte solution, ion migration occurs, with positively charged cations (such as H) tending to the cathode and negatively charged anions (such as OH-) tending to the anode. In the anode area with positive metal ions and negative charged anion electrochemical action, the anode area of metal ions constantly ionized by corrosion, so that the surface of the steel tube cavitation, so that perforation; The cathode remained intact