Study on H_2S/CO_2 Corrosion Behaviors of Low-Cr Acid Resistant Casing Steel

H2S/CO2 corrosion behaviors of 3Cr110S steel were studied with high temperature and high pressure and H2S stress corrosion cracking(SSC) test by use of scanning electron microscope(SEM),energy disperse spectroscopy(EDS),X-Ray diffraction(XRD) and transmission electron microscope(TEM).The results show: Under the simulated high temperature and high pressure H2S/CO2 corrosion conditions,H2S electrochemical corrosion dominates the corrosion course,and the uniform corrosion rate of 3Cr110S steel is 0.127 2 mm/a,furthermore,the local corrosion is very slight.When the applied stress is 72% and 80% actual yield strength(AYS),all test specimens of 3Cr110S steel have not been found cracked which reveals the superior SSC resistance.The larger orientation difference between lath microstructures of 3Cr110S tempered sorbite micro-structure,granular carbide about Cr precipitating at the grain boundary or in crystal grain,dislocation tangle as well as dislocation pinning of the dispersion carbonide,all of those hinder severely SSC cracks to propagate.