Corrosion behavior of X100 pipeline steel and its heat-affected zones in simulated Korla soil solution under alternating current interference

In recent years, many accidents caused by alternating current (AC) corrosion have been reported. AC corrosion has become a serious potential damage to buried steel pipelines. The X100 pipeline steel is a very promising material for long-distance gas pipelines, and Korla soil is a typical saline-alkali soil of West China. The coarse-grained heat-affected zone (CGHAZ) and the intercritically reheated coarse-grained heat-affected zone (ICCGHAZ) were simulated by a Gleeble thermomechanical processing machine through different thermal cycle times, peak temperatures, and cooling rates. Electrochemical corrosion measurements, immersion experiments and surface analysis techniques were used to characterize the corrosion behavior of the base metal, CGHAZ, and ICCGHAZ of the X100 pipeline steel in simulated Korla soil solution under AC interference. The X100 pipeline steel base metal, CGHAZ, and ICCGHAZ exhibited active dissolution in the simulated Korla soil solution under AC interference, and the average corrosion rate increased with the increase in AC density. The amplitude of the polarization potential oscillation caused by AC interference and the microstructure had an important influence on the corrosion rate and corrosion morphology of the X100 pipeline steel base metal, CGHAZ and ICCGHAZ. Under the interference of 5 mA·cm^‒2 AC density, the X100 pipeline steel base material shows the most negative corrosion potential and the largest average corrosion rate, while the ICCGHAZ shows the most positive corrosion potential and the smallest average corrosion rate. Under the interferences of 20 and 50 mA·cm^‒2 AC densities, the ICCGHAZ of X100 pipeline steel shows the most negative corrosion potential and the largest average corrosion rate, while the base metal shows the most positive corrosion potential and the smallest average corrosion rate. Under the interference of 20 mA·cm^‒2 AC density, the X100 pipeline steel is locally corroded. CGHAZ and ICCGHAZ have obvious grain boundary corrosion, whereby GCHAZ grain boundary corrosion morphology is slit-shaped, and ICCGHAZ grain boundary corrosion morphology is continuous pores.