Investigation on the efficiency of corrosion inhibitor in CO2 corrosion of carbon steel in the presence of iron carbonate scale

In this work, the inhibition efficiency of an imidazoline derivative corrosion inhibitors in CO2 corrosion of carbon steel was investigated in the presence of iron carbonate scale and hydrogen sulfide. The use of corrosion inhibitors is one of the most common controlling techniques for CO2 corrosion of carbon steel in oil and gas industry. One of the imidazoline derivatives was used as a corrosion inhibitor which protects the surface through the film formation mechanism. The investigation material was API 5L X65 carbon steel which was cut from a wet gas transmission pipeline. The internal surface of the pipe was covered with iron carbonate as corrosion product. In order to investigate the inhibitor efficiency, Tafel polarization and electrochemical impedance spectroscopy were done in CO2 -saturated 3.5 wt.% sodium chloride solution. According to the results, the existence of iron carbonate film reduced the inhibition efficiency. Furthermore, it was found that in the presence of H2S gas, the inhibition efficiency was decreased due to the decrease in inhibitor adsorption on the surface.