Corrosion Behaviors of X80 Steel in Typical Soil Environments along the Second West-East Gas Pipeline

The corrosion behaviors of X80 steel in typical soil environments along the Second West-East Gas Pipeline were investigated using the methods of indoor testing of buryed specimens, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). The results show that all the impedance spectra present a characteristic of two capacitance loops with two time constants of the X80 steel exposed to three types of soil for 60 d and the corrosion rate decreased with the time of X80 steel exposed to alkaline soil of Yumen and Yichuan, however, the corrosion rate of X80 steel in acid soil of Zhangshu showed the reverse trend. The corrosion mode is pitting corrosion for X80 steel exposed to three types of soil for 60 d. In the soil environment with relative low moisture, the reason for pitting corrosion is the formation of concentration cell on the X80 steel surface caused by the discontinuous distribution of the liquid phase electrolyte.