The Role of Iron Sulfide Polymorphism in Localized H_2S Corrosion of Mild Steel

摘要

Localized corrosion in sour fields is a challenge persisting in the oil and gas industry since it has frequently been seen as a cause for catastrophic failures of upstream pipelines. Hence, prediction and mitigation of H_2S localized corrosion of mild steel is of key importance for integrity management. However, our current understanding of H_2S localized corrosion mechanism(s) from numerous studies in both in the laboratory and the field is far from being conclusive. Especially, the environmental conditions that may cause localized H_2S corrosion are unclear. Therefore, defining an experimental condition in the laboratory that can replicate localized corrosion in a sour environment is critical to our understanding of mechanisms of localized corrosion. The focus of the present research was to explore environmental conditions leading to localized H_2S corrosion. It was found that severe localized corrosion was repeatedly observed in experiments, when there was a simultaneous formation of greigite and/or pyrite. Based on those experimental results, a hypothesis for a mechanism of H_2S localized corrosion was proposed.