Influence of soilwater content adjusted by simulated acid rain on corrosion behavior of X80 steel in red soil

The electrochemical behavior and corrosion feature of X80 steel in red soil with different moisture contents adjusted by simulated acid rain were studied by means of potentiodynamic polarization curves, EIS, three-dimensional video microscope, SEM and XRD. Results show that the corrosion rate ([Formula]), corrosion type and corrosion mechanism of X80 steel in red soil irrigating with simulated acid rain were significantly dependent on the soil water content (SWC). By 15% (mass fraction) SWC, the overall corrosion process was controlled by electrochemical activation reaction, the steel surface underwent pitting and filiform corrosion, and [Formula] was small. With the increase of SWC, [Formula] increased, and the corrosion type of the steel surface varied from the localized pitting to the uniform corrosion. When SWC was 25%, a loose and reddish-brown corrosion product layer was formed by the incorporation of soil particles. In the acid rain-saturated soil, the steel surface underwent severe ulcer- like corrosion, the corrosion mechanism varied upon the exposure time. The corrosion process was mainly controlled by a charge-transfer process at the initial stage, but the subsequent corrosion processes were controlled by a combination of activation control and diffusion control after 15 d. In addition to the soil acidity, the condensation phenomenon should be taken into account to understand the corrosive nature of red soil. When X80 steel was exposed in the soil at Nanchang area, the time with moisture film on the steel surface could account for 98.6% of the total exposure time, which means that the corrosion reaction of X80 steel in the acidic red soil could occur at almost any time.