Effect of CO2 partial pressure on the corrosion behavior of J55 carbon steel in 30% crude oil/brine mixture

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 (Pco2) was increased from 0 to 1.5 MPa, decreased from Pco2 = 1.5 MPa to Pco2 = 5.0 MPa, increased again at Pco2 = 5.0 MPa, and then reached a constant value after Pco2 = 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.