The Analysis of Calcium Ions Effect on CO2 Corrosion Using Electrochemical Impedance Spectroscopy

CO2 corrosion is a major threat but it is not widely studied, particularly on the effects of chemical species affecting pitting tendency. One of the suspected species that influence CO2 corrosion is Calcium ions (Ca2+). The project is done to study the effect of Ca2+ in CO2 corrosion towards pitting of X52 mild steel by using electrochemical approach of Electrochemical Impedance Spectroscopy technique. The possible effects were investigated through different concentration of Ca2+ ions in NaCl solution to study the corrosion behavior. For this project, three environments; 3% NaCl, 3% NaCl + 1.5% CaCl2 and 4.6% NaCl solutions (equivalent Cl- concentrations for 3% NaCl + 1.5% CaCl2 and 4.6% NaCl) saturated with CO2 gas at 25oC were tested. The result showed that the corrosion rate increased with increasing concentration of Cl-, but decreased with the presence of Ca2+ ions. Corrosion rate of X52 carbon steel is highest in 4.6% NaCl, CO2 environment at 25oC, followed by 3% NaCl + 1.5% CaCl2 solution and the lowest in 3% NaCl solution. At the same concentration of Cl-, Ca2+ ions decrease the corrosion rate of the X52 carbon steel specimen. The current result showed that Ca2+ inhibited CO2 corrosion rate probably due to scaling formation. However, no pitting corrosion was observed due to short term testing. Further test at longer testing period is necessary in order to observe pitting in this environment.