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The corrosion behavior of L80 casing steel was studied in a simulating annulus environment using the electrochemical measurement method, immersion test, and tensile test under a high-temperature and high-pressure H2S/CO2 environment. The partial pressure of CO2 (PCO2), the partial pressure of H2S (PH2S), water content, and preloading stress remarkably affected the corrosion behavior of L80 steel. The influence of PCO2 on stress corrosion cracking (SCC) susceptibility has an inflection point of approximately 1.1 MPa. The SCC susceptibility reaches the maximum when the PCO2 is about 1.1 MPa. The SCC susceptibility has a positive correlation to PH2S and water content. The higher water content of the corrosion medium can increase the electrical conductivity of the corrosion medium and promote the corrosion of L80 steel, which can improve the diffusion of hydrogen into steel and promote the SCC of L80 steel. Preloading stress can promote local corrosion, thereby promoting SCC of steel under stress. The dislocation emergence point caused by preloading stress can accelerate the diffusion of hydrogen into steel and increase SCC susceptibility.

To elucidate the effect of surface morphology on corrosion behaviour of coldrolled steel, three-dimensional (3D) surface profiles, average corrosion rate and potential differences (PD) for local areas of cold-rolled steel were investigated using a 3D white-light interference surface profilometer, polarization curves and atomic force microscope. Results showed that the linear relationship between surface roughness Sa and corrosion rate, achieved based on polished steels, was not valid for the as-received interstitial-free steels. An innovative surface parameter, the proportion of active area (Pa), was proposed and verified to have a distinct positive correlation with the corrosion rate of as-received cold-rolled steels. Moreover, it was found that the specimen with different surface textures were involved in diverse corrosion stages, and thus, the corrosion rate was determined by different surface parameters. As a result, a three-stage corrosion evolution, including initial dissolution (stage I), peak levelling (stage II) and general thinning (stage III), was deduced, in which Pa and local PD played predominant roles to stage I and stage II, respectively.

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