Effect of temperature, chloride and dissolved oxygen concentration on the open circuit and transpassive potential values of 316L stainless steel at high-temperature pressurized water

The electrochemical performance of 316L stainless steel was investigated in high-temperature pressurized NaCl solutions. Variations of the transpassive potential (Et) and open circuit potential (OCP) of steel were analyzed using an experimental design strategy versus three factors namely temperature (T) (30 °C-350 °C), chloride [Cl−] concentration (10 ppb-1000 ppb) and dissolved oxygen (DO) concentration (0 ppb-200 ppb) by conducting a short series of experiments. The 3D response surface plots of the electrochemical responses (Et and OCP) versus each factor were constructed and the optimum value of each factor was obtained from the designed matrix of the experiments and the 3D response surface plots based on the most positive Et and OCP values. The optimum conditions in which the most positive Et of steel can be achieved were found as follow: T ≈ 30 °C, [Cl−] ≈ 10 ppb and [DO] ≈ 200 ppb. The most positive OCP values however, were observed when the values of the analyzed factors were as follow: T ≈ 140 °C, [DO] ≈ 200 ppb and [Cl−] ≈ 10 ppb. Finally, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) were used for further analysis of the steel samples exposed to high-temperature NaCl solutions under different experimental conditions.