An Investigation on the Inhibition Behavior of Anodic Inhibitors on St37 Carbon Steel in Closed-Circuit Cooling Water

Abstract

In this study, the effect of hexamine, sodium nitrite, sodium benzoate, and trisodium phosphate corrosion inhibitors concentration on corrosion resistance of St37 carbon steel was studied (at 45 °C in closed-circuit cooling water) using weight loss, electrochemical impedance spectroscopy (EIS) and cyclic polarization tests. For hexamine and trisodium phosphate, with an increase in the concentration of the inhibitors, the corrosion rate decreased significantly. Therefore, the highest corrosion inhibition efficiency (IE%) of hexamine and trisodium phosphate was equal to 62% and 47% for concentrations of 400 ppm and 100 ppm, respectively. On the other hand, there was a critical concentration of sodium nitrite and sodium benzoate to protect carbon steel. For sodium nitrite and sodium benzoate, the highest IE% values were obtained at concentrations of 200 ppm and 5000 ppm, respectively, which were equal to 77% and 74%. According to the results, carbon steel was susceptible to pitting corrosion in the presence of different concentrations of the investigated inhibitors except sodium benzoate. The findings of EIS measurements were consistent with the results of polarization experiments. Overall, it was concluded that for the studied inhibitors, the corrosion control mechanism was charge transfer control in the electrical double layer.