ABSTRACT: The electrochemical corrosion behavior of X70 pipeline steel in the wall jet zone was investigated at high temperature and high pressure CO2 environment by jet impingement loop equipment with micro-electrode techniques. The corrosion morphologies and profiles of X70 steel after different corrosion times were characterized by Scanning Electron Microscope (SEM) and 3D optical measurement device. Results showed that the corrosion process of X70 steel was dominated by the anodic dissolution in the first 4 hours (4h), during which the highest corrosion rate was reached. With the increase of the coverage and compactness of corrosion products on the surface, the corrosion resistance of X70 steel increased, and the corrosion rates decreased significantly. Electrochemical Impedance Spectroscopy (EIS) plot was composed of the high-frequency capacitive loop, the medium-frequency capacitive loop and the low-frequency inductive loop. The inductive loop disappeared with the increasing time, which showed that the surface of X70 steel was completely covered by the compact corrosion products. The film resistance Rf and charge transfer resistance Rt increased gradually with time owing to the formation and growth of corrosion scale. The double-layer capacitance Cdl decreased slowly as a function of time, which is mainly attributed to the increase of the thickness of protective layer.
INTRODUCTION CO2 corrosion is a common problem in the oil and gas industry, which can cause failure of pipelines and process equipment, resulting in significant economic loss as well as environmental pollution and ecological damage.1-5 CO2 corrosion is a complex process, and there are numerous factors influencing the corrosion of steels. In particular, the fluid hydrodynamics play a significant role through a complex interrelationship of momentum transfer and mass transfer as well as fluid parameters defining flow field properties with the corrosion reactions of steel.6