Investigation of Individual and Synergistic Effects of Salinity and Temperature on CO2 Corrosion Performance of Low Carbon API N80 Steel

The simultaneous presence of CO2-saturated water with natural oil in the transmission pipeline system, often made from steel, is inevitable. Therefore, in the present study, three brine salinities (low salinity, medium salinity, and high salinity) and six different temperatures (35, 45, 55, 65, 75, 85 °C) in CO2-saturated brines containing NaCl, CaCl2, MgCl2, Na2SO4 and KCl were employed to study the individual and synergistic effects of brine salinity and temperature on CO2 corrosion of low carbon API N80 steel. According to Tafel polarization tests results, in the 35-65 °C temperature range, increasing the brine salinity resulted in a decrease in the corrosion rate; however, from 65 to 85 °C, by increasing the salinity from low to high, the corrosion rate increased. In all brine salinities, increasing the temperature resulted in the corrosion rate enhancement to a maximum value and then a decrease was observed. Electrochemical impedance spectroscopy and Tafel tests results agreed. Weight loss method was also performed to validate the electrochemical technique and the results confirmed the electrochemical data. According to the quantitative analysis (using the analysis of variance experimental design method), the synergistic action of salt concentration and temperature was higher than the individual action of them and among temperature and salt concentration, the most influential parameter was temperature. Furthermore, according to qualitative analysis results, which was used to predict the direction of variations, the synergistic effect of temperature and salt concentration in all 6 temperatures and both medium and high salt concentrations was accelerating.