Impact of Water Content on Corrosion Behavior of CO₂ Transportation Pipeline

Abstract

CO₂ could be transported by pipelines in gaseous, liquid or supercritical phase according to the operating temperature and pressure. Safety concerns might arise from supercritical CO₂ transportation pipeline, especially crossing the densely populated areas. Short-distance gaseous CO₂ pipeline was designed and constructed for an energy company. Water content is critical to understand the corrosion mechanism of CO₂ pipeline. Corrosion behavior of API 5L X65 mild steel exposed to CO₂ stream with different relative humidities (RH), temperatures and pressures was investigated by weight-loss method to determine maximum allowable water content in CO₂ pipeline. The surface morphology of the coupons was examined by scanning electron microscopy (SEM). The results showed that general corrosion rate was stable with increased RH before a separate water phase was observed, and significantly increased when free water was formed for all the test conditions. Localized corrosion or serious general corrosion was observed when the relative humidity was beyond 60%. The upper limit of water content for CO₂ stream should be set at 60% RH for the safety concern of API 5L X65 pipeline on the basis of corrosion study.