Effect Of Cr And Pb Pollution On Soil Corrosion Behavior Of Q345Steel

With the development of the industry，soil around China is being polluted by heavy metal in different degrees. Heavy metal in the soil that is slightly contaminated will cause damage to the human, animals and plants; at the same time, it will affect the service life of the metallic pipeline buried in the soil. Along with the increase of contaminated degree, heavy metal will do more serious damage to the animals and plants, However, it is rarely been reported by the media about whether it will affect the corrosion resistance of the metallic pipelines buried in the soil. Heavy metal pollution is an accumulative, irreversible long-term process. The soil around the Lishi sewage irrigation area in Fushun, Liaoning province, was taken as the study object, and the Q345steel that frequently used around the sewage irrigation area was taken as the experimental steel, and focusing on the problem above, the effect of heavy metal Cr and Pb ions on its soil corrosion behaviors and mechanism were studied in this thesis, which in some degree will provide theory and experimental basis on material selection and service life prediction of the underground pipeline in this area.This work investigated how different Cr and Pb ions concentration would affect the corrosion behavior of Q345steel buried in the soil using laboratory simulation immersion experimental method. With the digital camera and SEM, we observed the Macro and micro morphology of the steel before and after removing the corrosion products. Calculated the corrosion rate through weightlessness method and analyzed the corrosion dynamic regulation. The elements and phase composition of the corrosion products was analyzed by EDS and XRD. Tested electrochemical impedance spectroscopy, dynamic polarization curves and Mott-schottky curves, analyzed the electrochemical behavior and properties of the sample with corrosion products after immersion.The result show that: the corrosion form of the Q345steel buried in the undisturbed soil was general corrosion, while it was localized corrosion in the soil contains Cr ions. With the increase of mass fraction of Cr ions, the corrosion products on the surface of the sample increased, the numbers of pitting decreased, the resistance of charge-transfer increased, electric current density of self-corrosion decreased, and the corrosion resistance increased. The main reason of increased corrosion resistance is that the passive film was formed on the surface under the influence of Cr ionsThe corrosion form of the Q345steel immersed in the soil with Pb was general corrosion, the main corrosion products are oxides of Pb and Fe. In the soil contains Pb2+ions, the corrosion rate of the sample slowed down, the resistance of charge-transfer increased, the electric current density decreased, and the corrosion resistance increased. Among the soil solutions with different Pb2+mass fractions (50mg/kg,70mg/kg,90mg/kg,110mg/kg), the corrosion resistance of sample in the soil solution containing70mg/kg was best. Pb2+promoted the formation of oxides of Pb and α-FeOOH, which protected the matrix and was the reason why the corrosion resistance increased.