Formation and Structure of Sulfide Deposits on Carbon Steel Under Free Corrosion Potential

The corrosion of alloy materials in the H₂S environment has considerably limited the growth of oilfield manufacturing. The sour corrosion of iron has frequently been studied, and steel corrosion under the H₂S scheme has been investigated. Many parameters affect the corrosion of carbon steel (CS) in the H₂S natural environment, including a concentration of H₂S, pH, and the temperature, which has significant impacts on the electrochemical responses of the bare metal surface, the formation, and the nature of the created sulfide scale. The latter could be either protective or nonprotective, depending on the formation conditions. This work presents a full experimental investigation for the initial corrosion events of iron/steel at the free corrosion potential for different periods of time in H₂S-saturated solutions of different temperatures where H₂S/N₂ gas was purged into the solutions. The structure, morphology, composition, depth, and ion-concentration of the sulfide film that is established on the pipeline CS (mild carbon steel) in an acidic sour solution was examined using different bulk and surface techniques, e.g., an optical microscope, scanning electron microscopy, and Raman spectroscopy.