Investigation on Localized Corrosion Resistance of Nickel-based alloy UNS N07718 under Sour conditions of PuGuang Field simulated Environment

Appropriate material selection for high temperature and high hydrogen sulfide/carbon dioxide (H2S/CO2) partial pressure environments within oil and gas wells is essential for a robust corrosion management strategy. Corrosion resistant alloys (CRA) are routinely considered as an alternative to carbon steel for oil and gas applications under such conditions. However, published research relating to CRA passive layer composition and their protective properties in combined H2S/CO2-containing environments is limited, particularly in the presence of chloride ions. This study focuses on understanding the pitting corrosion mechanisms of solution annealed and precipitation hardened UNS N07718. This paper provides an in-depth analysis of the microstructure of both specimens using XRD, SEM/EDX and TEM. Corrosion experiments are conducted in simulated environments analogous to the PuGuang field at 80°C and the testing brine containing chloride and sulfate ions. A combination of elevated temperature/sour gas conditions with electrochemical methods are employed to evaluate the corrosion performance and particularly its localized corrosion performance under the influence of H2S and CO2 partial pressures. Results from potentiodynamic polarization experiments showed an anodic branch that exhibited a complete passivation for both UNS N07718 samples.