CORROSION BEHAVIOR OF 6.5%Cr STEEL IN HIGH TEMPERATURE AND HIGH PRESSURE CO2 ENVIRONMENT

In the oil and gas industry, CO2 in reservoirs generally causes severe corrosion of C steel in pipelines. Adding Cr to C steel can enhance CO2 corrosion performance by a factor of at least 3, and even up to 10 times and more, whilst maintain a cost penalty less than 1.5 times that of C steels. Corrosion behavior of 6.5% Cr steel in high temperature and high pressure CO2 environment is investigated in this work. The corrosion rate of 6.5%Cr steel at 80 degrees C and 0.8 MPa is measured by autoclave. The surface and cross-sectional morphology is studied by SEM, and the enrichment of Cr in the corrosion scale is investigated by EDS. The change of LPR and EIS results with corrosion time is studied by high temperature and high pressure electrochemical tests. According to the test results of ion concentration in the solution, the mechanism of corrosion scale growth is discussed. The results show that the corrosion rate of 6.5%Cr steel is 0.72 mm/a. The Cr enriches in the corrosion scale, and the Cr/Fe ratio is higher than 5:1. Under different corrosion time, the concentration of Cr3+ in the solution is always low, which demonstrates that Cr seldom enters into solution.