Abstract
The influence of CO₂ partial pressure on the corrosion properties, including corrosion rate, morphology, chemical composition, and corrosion depth, of J55 carbon steel in 30% crude oil/brine at 65 °C was investigated. A corrosion mechanism was then proposed based on the understanding of the formation of localized corrosion. Results showed that localized corrosion occurred in 30% crude oil/brine with CO₂. The corrosion rate sharply increased as the CO₂ partial pressure (P co 2 ) was increased from 0 to 1.5 MPa, decreased from P co 2 = 1.5 MPa to P co 2 = 5.0 MPa, increased again at P co 2 = 5.0 MPa, and then reached a constant value after P co 2 = 9.0 MPa. The system pH initially decreased, rapidly increased, and then stabilized as CO₂ partial pressure was increased. In the initial period, the surface of J55 carbon steel in the CO₂/30% crude oil/brine mixtures showed intense corrosion. In conclusion, CO₂ partial pressure affects the protection performance of FeCO₃ by changing the formation of corrosion scale and further affecting the corrosion rate.