Formation characteristic of CO2 corrosion product layer on the surface of P110 steel was investigated in simulated oilfield environment using mass-loss experiment,potentiodynamic polarization curve,impedance spectroscopy,and SEM micrograph analysis.Samples of different times up to 240 h were tested during exposure.Corrosion product was primarily composed of Fe(Ca,Mg)(CO3)2,which was distinguished by two layers.With an increase in the exposure time,the charge transfer resistance and polarization resistance increased progressively,the uniform corrosion rate decreased,and the corrosion reaction was controlled by the diffusion process instead of the activation process.All phenomena were attributed to the formation of the protective corrosion product layer.More compact and lower porosity of the layer made it more difficult to transfer and diffuse through the corrosion product layer for the charges and ions.Similar results were obtained by electrochemical test and mass-loss experiment. Formation characteristic of CO2 corrosion product layer on the surface of P110 steel was investigated in simulated oilfield environment using mass-loss experiment, potentiodynamic polarization curve, impedance spectroscopy, and SEM micrograph analysis. Samples of different times up to 240 h were tested during exposure. Corrosion product was primarily composed of Fe (Ca, Mg) (CO3) 2, which was distinguished by two layers. With an increase in the exposure time, the charge transfer resistance and polarization resistance increased progressively, the uniform corrosion rate decreased, and the corrosion reaction was controlled by the diffusion process instead of the activation process. All phenomena were attributed to the formation of the protective corrosion product layer. More compact and lower porosity of the layer made it more difficult to transfer and diffuse through the corrosion product layer for the charges and ions. Similar results were obtained by electrochemical test and mass-loss experiment.