Effect of Surface Layers on the Initiation of Internal Pitting Corrosion in Oil and Gas Pipelines

Experiments have been carried out in a high-temperature, high-pressure rotating electrode (HTHPRE) apparatus under 40 conditions to cover the spectrum of conditions found in oil and gas production pipelines in Western Canada. Each experiment was conducted over a period of 100 h. During the experiments, the electrodes were monitored using electrochemical noise technique. After the experiments, the surfaces of the samples were analyzed using scanning electron microscopy (SEM). Potentiodynamic polarization (PP) experiments were also conducted under the same 40 conditions. Based on the electrochemical noise, SEM, and PP data, it was found that the probability of the initiation of pitting corrosion increased with an increase in flow rate, temperature, chloride ion concentration, and anodic polarization, and decreased with an increase in oil wettability, hydrogen sulfide (H₂S) partial pressure, carbon dioxide (CO₂) partial pressure, total pressure, bicarbonate concentration, sulfate concentration, and cathodic polarization. The variation in the probability of initiation of pitting corrosion has been explained based on the type of surface layers formed.