Galvanic Corrosion Behavior of Dissimilar Metal Coupling in Highly Acidic Environments

A high temperature and high sour environment of 150℃, 1.0 MPa H₂S partial pressure, 1.5 MPa CO₂ partial pressure, and 200 000 mg/L Cl^- was simulated. Electrochemical tests and immersion corrosion tests were conducted in a high temperature and high pressure autoclave, and the corrosion products formed on the metal surface were analyzed by scanning electron microscopy (SEM) and energy disperse spectroscopy (EDS), which aimed to investigate the galvanic corrosion behavior between nickel-based alloy 718 and 35CrMo/20CrMnTi/2A12, respectively. The results showed that the galvanic corrosion rate after coupling with dissimilar metal was positively correlated with the potential difference between the two different metals,however, there was no significant effects on the mechanism of corrosion and corrosion products. The large potential difference such as 718-2A12 coupling should be avoided during structural design of downhole tools.