Top-of-line Corrosion Behavior of X70 Pipeline Steel in HAc-CO2 Environment

Top-of-line corrosion behavior of X70 pipeline steel in HAc-CO2 environment was researched. Simulation laboratory experiment was performed in high temperature and high pressure condensation autoclave to research the effect of HAc concentration on X70 corrosion. SEM and EDS were used to analyze the morphology and characteristics of corrosion scales formed in various HAc concentrations. In addition, the electrochemical behavior of X70 pipeline steel was studied using electrochemical condensation autoclave. With addition of HAc, the corrosion rate increased with the increase of HAc concentration. It was attributed to the fact that HAc degraded the formation of protective FeCO3 scale due to the decrease of pH. In high acetic acid concentration environment, the corrosion potential was shifted toward more positive values, which was due to the increase of cathodic current. It can be deduced that HAc promotes the cathodic process. The adsorbed intermediate product resulted in the inductive loop, which affected the formation and deposit of FeCO3.