The effect of temperature, CO2, H2S gases and the resultant iron carbonate and iron sulfide compounds on the sour corrosion behaviour of ASTM A-106 steel for pipeline transportation

Highlights: • The sour corrosion behaviour of ASTM A-106 Grade A pipeline steel are highly dependent on temperature. • FeCO₃ and FeS compounds do not have sufficient stability to protect the metal surface at higher temperatures. • By increasing temperature, the tafel curves move towards higher corrosion current density. • The presence of H₂S formed oxidation agents such as bisulfide (HS⁻) and S⁻² sulfide in the electrolyte. • Due to the presence of H₂S, the corrosion rate of the steel in the environment was increased five times. -- Abstract: In this investigation, extracted products corrosion behaviour of sour environment in oil and gas industry was studied. Of the important aspects of these products is the presence of significant amounts of CO₂ and H₂S in the solution of the sour products. The corrosion mechanism could also be involved during the extraction, transportation and purification of the sour products. Therefore, the corrosion behaviour of ASTM A-106 Grade A carbon steel, used for the transportation of oil and gas, in the presence of H₂S and CO₂ and at different temperatures, was studied by potentiodynamic polarization, electrochemical impedance spectroscopy techniques, and Scanning Electron Microscope (SEM) equipped with Electron Dispersive Spectroscope (EDS). Corrosion tests were conducted on the alloy in solutions with 3 wt% NaCl saturated with CO₂ gas in the presence/absence of 200 ppm H₂S gas at temperatures of 25 °C, 45 °C, 65 °C, 85 °C. Results showed that increasing the temperature of the solution substantially increased the corrosion rate of the steel under investigation. As well, the presence of both gases of CO₂ and H₂S enhanced the corrosion rate. EDS results also showed that iron carbonate and iron sulfide compounds do not have sufficient stability at high temperatures to protect the metal surface against corroding agents. And they could not form a uniform coating on the steel surface.