Effect of Cl− accumulation on corrosion behavior of steels in H2S/CO2 methyldiethanolamine (MDEA) gas sweetening aqueous solution

•Effect of Cl− contents on corrosion behaviors of steels in H2S/CO2 MDEA solution was studied.•The self-designed HT autoclave has been used to perform the weight-loss experiment.•Anode reaction mechanism Schematic was proposed.•The schematic of Cl− catalytic and competitive absorption mechanism were portrayed.

Effects of Cl− accumulation on corrosion behavior of the three steels (20,304L and 316L) in H2S/CO2 MDEA desulfuring aqueous solution was investigated by using a HT (high temperature) autoclave, and the corrosion products were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction technique (XRD). Electrochemical measurements such as polarization curve and electrochemical impedance spectroscopy were adopted to analyze the effects of Cl− concentration on the corrosion. Weight loss tests showed that corrosion rate of three steels (20, 304L and 316L) appeared as a reversal “v” shape and reached the peak at 20,000 mg/L Cl− content. SEM, EDX and XRD results showed that the corrosion scales were mainly FeS, FeS2 and FeCO3, and the corrosion process was mainly controlled by H2S, furthermore, CO2 corrosion further weakened as the chlorine ions content increased. Electrochemical studies suggested that, with the rise in chlorine ions content, the corrosion potential shifted negatively, and the activation and dissolution of mental anode accelerated, which can be attributed to the penetration and absorption effect of chloride ion. In addition, chlorine ions competitive absorption also played an important role in corrosion process. Therefore, to prolong the service life of desulfuring equipment, it is suggested that 20 steel not be used in units and facilities with large acid gas load at high temperature and the mass concentration of chloride ion content in the desurfuring MDEA solution should be controlled at a low level with the consideration of its complex effect.

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