Multi-factor corrosion model of TP110TS steel in H2S/CO2 coexistence and life prediction of petroleum casings

Abstract

The failure of petroleum casings due to the combined effects of CO2/H2S corrosion and internal pressure has become a main concern during the exploitation of high-temperature, high-pressure, and high-corrosion gas fields. Therefore, establishing a corrosion evolution model is crucial for accurately predicting the service life of casings. In this study, an analytical model describing the corrosion rate of casing steel TP110TS under different CO2/H2S partial pressures and applied stresses was established, combined with the mechanical-chemical effect. The weightlessness method was used to determine the model parameters from the experimental results using a multiple regression. Based on the elasticity, a service life prediction model considering mechanical property attenuation and casing stress fluctuation was established from the assumption of uniform thickness thinning. The effects of internal pressure and CO2/H2S partial pressures on the service life were analyzed. The corrosion rate initially decreased with time. However, the stress increased as the wall thickness decreases from corrosion. The stress-promoting corrosion effect gradually manifested, and the corrosion rate rapidly increased. The higher the internal pressure and H2S/CO2 partial pressure, the shorter was the service life of the casing. In the H2S/CO2 coexistence environment, the influence of H2S partial pressure was more significant than that of CO2.