Effect of temperature on the electrochemical pitting corrosion behavior of 316L stainless steel in chloride-containing MDEA solution

Abstract

Here, the effect of temperature on the electrochemical corrosion of 316L stainless steel (SS) in methyl diethanolamine (MDEA) solution with/without 1.0 wt% NaCl in the presence/absence of CO2 was investigated using potentiostatic polarization, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). The electrochemical measurements showed that although the MDEA solution was highly basic, both chloride and temperature played greater roles in the pitting corrosion of 316L SS, similar to plain NaCl solution. The critical pitting temperature (CPT) of 316L SS in MDEA solution with 1.0 wt% NaCl decreased from 67.2 °C to 59.6 °C, and the breakdown potential underwent a negative shift of approximately 400 mV, and the EIS Bode impedance decreased. Furthermore, the breakdown potential shifted negatively with increasing temperature when the temperature was lower than CPT in the MDEA solution containing Cl−; however, the breakdown potential decreased slowly, and its temperature dependence was unclear when the temperature was higher than the CPT. In addition, the passive film resistance of 316L SS in all MDEA solutions decreased as the temperature increased. Particularly for the MDEA solution containing Cl−, the passive film resistance decreased by one order of magnitude when the temperature increased from 50 °C to 60 °C. Although the presence of CO2 in the MDEA solution decreased the passive film resistance, it seemed to reduce the individual corrosion contribution of Cl−. The pitting corrosion process of 316L SS in MDEA solution containing chloride ions was discussed by combining these results with classical pitting mechanisms of stainless steel.