Effects of H₂S on Corrosion Behavior of Carbon Steel in Simulated Oil Storage Tank Bottom Solution

The corrosion behavior of Q235 carbon steel in simulated solution containing H₂S was investigated using the methods of weight loss, electrochemical measurement, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that the increase of H₂S concentration promoted hydrogen evolution reaction, so the corrosion rate of carbon steel increased. The loose and porous corrosion products formed on the steel surface were composed of mackinawite. The corrosion products of carbon steel, which was corroded in sequence in the solution containing H₂S and in the solution containing dissolved oxygen but without H₂S, were divided into two layers. The inner layer was still mainly composed of mackinawite and the outer layer was oxidation product. The oxidation product led to the rupture and shedding of ferrous sulfide film. The existence of ferrous sulfide film provided more protection to carbon steel in the solution containing H₂S than in the solution containing oxygen.