Corrosion behavior of low‐alloy steel used for pipeline at vapor‐saturated CO2 and CO2‐saturated brine conditions

Abstract

Immersion experiment was carried out to investigate the CO2 corrosion behavior of low‐alloy steel used for pipeline at vapor‐saturated CO2 and CO2‐saturated brine conditions by revealing microstructure, corrosion rate, corrosion phases, surface/cross‐section morphology, and elements distribution. The results demonstrate that mass losses at both conditions are approximately linear to corrosion time with log scale, and the corrosion rate at vapor‐saturated CO2 condition is greatly lower than that at CO2‐saturated brine condition. The main corrosion phases consisting of inner layer and outer layer are Cr‐rich compounds and FeCO3 crystals, respectively. Corrosion products on the coupon surface produced at vapor‐saturated CO2 condition are formed locally, while the ones produced at CO2‐saturated brine condition deposit on the coupons surface homogeneously. That distinction is caused by the difference of formation process of corrosive solution. According to the experimental results, corrosion mechanisms of low‐alloy steel at both conditions are discussed to illustrate CO2 corrosion behavior.