The Corrosion Behavior and Mechanism of X80 Pipeline Steel in Saline Soil Influenced by Freezing Induced Phase Transition

Abstract

Sulfate saline soil in cold and arid regions accelerates the deterioration of buried pipelines, but the roles of salt crystallization and ice formation in steel corrosion remain unclear. In this study, the corrosion behavior of X80 steel in sulfate saline soil was investigated under different temperatures, salt contents, and corrosion times using potentiodynamic polarization tests, electrochemical impedance spectroscopy tests, polarized optical microscopy, SEM, XRD, and XPS. The corrosion rate first increased and then decreased with increasing salt content at 20°C and 10°C. Decreasing temperature sharply reduced the corrosion rate, and corrosion was strongly inhibited under frozen conditions. Steel surface corrosion changed from mainly uniform corrosion at 20°C and 10°C to local pitting corrosion at subzero temperatures. The results indicate that dissolved sodium sulfate promotes corrosion before crystallization, whereas mirabilite precipitation and ice formation inhibit corrosion by consuming liquid pore water and restricting ion transfer and oxygen diffusion.