Gas Liquid Interface Corrosion Behavior of X65 Steel in CO2 and H2S Corrosive Environment

X65 carbon steel is widely used in subsea gathering and transportation pipelines. In the gathering and transportation process, the natural gas medium is complex and often contains corrosive gases such as H2S and CO2. Due to the use of wet gas transportation, condensate water was formed, resulting in serious corrosion perforation accidents of pipelines. In this work, through the experiments of high - temperature and high - pressure reactor, the corrosion mechanism of gas phase, liquid phase and gas - liquid interface were analyzed, which provided a basis for the formulation of corrosion prevention and control measures for X65 steel wet gas gathering and transmission pipeline. Moreover, high - temperature and high - pressure reactor experiments were carried out with X65 steel in the presence of CO2, H2S and Cl - respectively. Each experiment was carried out for 7 d for gas - liquid interface corrosion, and the characteristics of corrosion products were analyzed by surface analysis technologies, such as scanning electron microscope (SEM) and X - ray diffraction (XRD). Results showed that with the injection of CO2 and H2S, the local corrosion rate increased in three regions of gas phase, liquid phase, and gas - liquid interface. In the presence of CO2 and H2S, the order of corrosion rate was liquid phase corrosion rate > gas phase corrosion rate > interface corrosion rate. Under the condition of gas - liquid interface, X65 steel formed anode below the interface and cathode above the interface, so that the local corrosion rate of liquid phase was faster.