Corrosion, especially the localized corrosion of carbon steel, in sour systems (H2S dominant) has progressively become a greater concern to the oil and gas industry as a result of production from increasingly sour environments. In this study, the effects of chloride ion concentration on the localized H2S corrosion were initially investigated, followed by the investigation of the corrosion of carbon steel in the presence of elemental sulfur, which is often present in sour systems. Attempts were also made to determine if classic galvanic theory can be applied to explain the propagation of localized corrosion in sour systems.
A series of experiments were performed to study high chloride concentration effects on the initiation and propagation of localized H2S corrosion. Localized corrosion events were detected in both chloride-free and high chloride concentration conditions. The results suggest that chloride ion may not be the direct cause of initiation of localized H2S corrosion. Instead, high concentrations of chloride ions significantly decreased overall general H2S corrosion.
The corrosion of carbon steel in the presence of elemental sulfur was also studied. Elemental sulfur was shown to cause catastrophic corrosion of carbon steel when water is present. The addition of salts significantly accelerates the corrosion. From the experimental results, it has been concluded that an electrochemical process is the dominant corrosion mechanism of elemental sulfur corrosion, and that solution conductivity plays a very important role. Based on the experimental data, an electrochemical model is proposed for elemental sulfur corrosion.
Propagation of localized corrosion in an H2S system was also studied using an artificial pit technique. From the experimental results, it was determined that standard galvanic theory cannot be used to explain the propagation of localized corrosion in H2S systems.