Effect of Temperature on Corrosion Behavior and Mechanism of S135 and G105 Steels in CO2/H2S Coexisting System

The corrosive environment of oilfield condensate water was simulated at different temperatures with CO2/H2S. Weight-loss corrosion tests were conducted on S135 and G105 steels at different temperatures. The corrosion rates of the S135 and G105 were measured at room temperature, 100 degrees C and 180 degrees C. The phase structure of the corrosion products and the corrosion morphologies of the samples were characterized. The results show that the corrosion rates of the S135 and G105 increased at first and then decreased with the increase in temperature. The corrosion rates peaked at 100 degrees C, reaching 0.8463 mm/y and 0.8500 mm/y, respectively. CO2 was the main controlling factor in the corrosion. The corrosion products were FeS and FeCO3. The corrosion rate at room temperature was lower than that at 100 degrees C. The corrosion rate at the temperature of 180 degrees C was the lowest. The corrosion rates of the S135 and G105 were 0.2291 mm/y and 0.2309 mm/y, respectively. CO2 was not the main controlling factor in the corrosion. The corrosion product was FeS. High temperatures aggravated the carbon-steel corrosion further in the environment with the high concentration of CO2 and a loose corrosion-product film formed. The dense and uniform FeS corrosives formed and attached to the surface of the substrate, and inhibited corrosion. Dense and uniform FeS products formed on the surface of the steel with the increase in temperature. A small amount of H2S inhibited the progress of the corrosion.