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

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 degrees C, 45 degrees C, 65 degrees C, 85 degrees 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.