Corrosion behavior of SM 80SS tube steel in stimulant solution containing H2S and CO2

Scanning electron microscopy, X-ray diffraction and electrochemical measurement technique were applied to investigate the corrosion of SM 80SS tube steel in stimulant solution with carbon dioxide (CO2) and hydrogen sulfide (H2S) at variable conditions of PCO2/PH2SPCO2/PH2S and temperature. The results suggest that there exists a synergism of sweet corrosion and sour corrosion on the steel surface, corrosion attack increases in the initial stage and then decrease with the increase of PCO2PCO2 or PH2SPH2S; serious corrosion occurs in the PCO2/PH2SPCO2/PH2S ranged from 31 to 520. In addition, the fitted parabola function equation Y = 0.47873 + 0.04014X – (3.23788E−5)X2 is established, and the most serious corrosion is 600 for PCO2/PH2SPCO2/PH2S. Under the moderate contents of PCO2PCO2 and PH2SPH2S, the corrosion scale consists of FeS0.9 and FeCO3; for relatively high PH2SPH2S, additive product FeS comes into being at high temperature such as T = 150 °C, product FeO(OH) is found in the corrosion scale. The H2S corrosion has a significant effect on the whole reaction process and iron sulfide is superior to precipitating on the steel surface compared with iron carbonate. In addition, the surface scales of iron sulfide almost act as a diffusion barrier and inhibit the corrosion by a coverage effect strongly depending on H2S concentration by EIS measurement.