Effects of Chloride and Dissolved Oxygen on Pitting Corrosion of Cr-Mn Austenitic Stainless Steels in Drilling Environments (C2026-00186)

Shuai Ren, Krutibas Panda

For decades, Cr-Mn austenitic stainless steels (SS) have been widely used in manufacturing various components of the bottom hole assembly (BHA) for oil and gas drilling. In addition to being non-magnetic and offering high strength and toughness, these materials must also exhibit excellent corrosion resistance to prevent material failure in harsh drilling environments. In this study, the effects of chloride and dissolved oxygen in drilling fluids on the susceptibility of pitting corrosion were investigated using electrochemical methods in simulated drilling environments. The results show that increasing chloride concentration raised the susceptibility to pitting corrosion; however, the underlying mechanism varies depending on the molybdenum (Mo) content in the steel. For the steel with relatively low Mo content, chlorides primarily increase pitting susceptibility by hindering the re-passivation process. In contrast, for the steel with higher Mo content, chlorides promote susceptibility by facilitating the initiation of pits. While oxygen generally facilitates the formation and stability of passive films, its presence in this study was found to increase the risk of pitting corrosion. This dual effect was discussed, and the underlying mechanism was elucidated. These findings provide valuable insights for alloy qualification and material selection in oil and gas drilling applications.