Effect of H2S on Fe corrosion in CO2-saturated brine

摘要

The effect of H2S at ppm level concentrations on iron corrosion in 3 wt% NaCl solutions saturated with CO2 in the temperature range of 25-85 degrees C is examined using electrochemical and surface science techniques. Small H2S concentrations (5 ppm) have an inhibiting effect on corrosion in the presence of CO2 at temperatures from 25 to 55 degrees C. At 85 degrees C, however, 50 ppm H2S is needed to provide significant corrosion inhibition. At higher H2S concentrations, the corrosion rate increases rapidly, while still remaining below the rate for the H2S-free solution. Characterization of the iron surfaces after corrosion was carried out using X-ray photoelectron spectroscopy and X-ray diffraction. A sulfur peak (S2p) is observed at a binding energy of 161.8 eV in all cases, attributable to disulfide (S-2(2-)) formation. Corrosion protection in the temperature range 25-55 degrees C can be attributed to Fe(II) bonded to S and O. At 85 degrees C, protection of the iron surface is most likely due to FeS2 formation. Morphological changes on the iron surface after exposure to H2S containing solutions were observed by SEM. A thin protective film was seen after exposure to solutions containing 5 ppm H2S at 25 degrees C, while at 85 degrees C, with the addition of 50 ppm H2S to CO2-saturated brine solution, a dense protective film was formed on the iron surface.