###### Abstract
Based on the electrochemical measurements, they concluded that, even though they observed \"a lower corrosion potential and a higher polarization resistance\" when the medium contained CaCO\({}_{3}\), there was a period of dephosphorylation, followed by pit formation after 500 mV (vs. SCE). They pointed out that this occurred because the mixed carbonate was more porous and, thus, more susceptible to Cl\({}^{-}\) ion permeability, in comparison to FeCO\({}_{3}\)[9]. [PERSON] et al. [10] studied the effect of Ca\({}^{2+}\) on CO\({}_{2}\) corrosion in a glass cell in stagnant conditions at 0.05 MPa CO\({}_{2}\), 80 \({}^{\circ}\)C with 1% \(w\)/\(w\) NaCl with different concentrations of Ca\({}^{2+}\) (between 0 and 10,000 ppm) and an initial concentration of Fe\({}^{2+}\) of 10 ppm, for a 7-day period. They reported that the corrosion rate decreased over time when the Ca\({}^{2+}\) concentration varied between 0 and 100 ppm. Based on this, they pointed out that the formation of a protective FeCO\({}_{3}\) layer occurred with no significant interference by Ca\({}^{2+}\). However, for higher Ca\({}^{2+}\) concentrations (between 1000 and 10,000 ppm), the corrosion rate was higher. In a subsequent study, [PERSON] et al. [11] studied the effects of Ca\({}^{2+}\) ions on the formation and protectiveness of the FeCO\({}_{3}\) layer in aqueous solutions for the CO\({}_{2}\) corrosion of G10180 steel. They reported a localized corrosion in the presence of high concentrations, and that Ca\({}^{2+}\) was responsible for the initiation of localized attacks, rather than Cl\({}^{-}\), since they did not observe any indications of pitting for the Ca\({}^{2+}\) solution. Moreover, they observed that at 10,000 ppm Ca\({}^{2+}\) and 600 rpm, there were no indications of pitting. [PERSON] et al. [6] pointed out that, in 1984, [PERSON] and [PERSON] [12] conducted one of the first studies to assess the effects of Ca\({}^{2+}\) and Mg\({}^{2+}\), along with other ions, on the CO\({}_{2}\) corrosion of API 5L X52 steel. They conducted potentiodynamic sweeps for three different Ca\({}^{2+}\) concentrations, 0, 400, and 1200 ppm, at 20 \({}^{\circ}\)C, 1 bar partial pressure of CO\({}_{2}\), over a pH range of 5.80-7.39 for two days. They reached the conclusion that the formation of FeCO\({}_{3}\) protective layers enriched with Ca\({}^{2+}\) led to a drop in the corrosion rate of mild steel. In the review by [PERSON] et al. [6], they mentioned the work of [PERSON] et al. [13]. They stated that the corrosion rate decreased in the \"short term\" in the presence of Ca2+ and Mg2+; however, there was no special difference for the long-term exposure. [PERSON] et al. [14] found that the corrosion rate, in an electrolyte agitated at 1% _w/w_ NaCl saturated by CaCO3 (160 ppm Ca2+) and with CO2 at 80 \({}^{\circ}\)C, was lower during the first 60 h of exposure, with respect to the corrosion rate in a medium without CaCO3 (1% NaCl + NaHCO3). After this period, the rate relation was reverted. [PERSON] et al. [5] studied the role of Ca2+ ions on the CO2 corrosion of X65 steel in a stagnant medium. For this purpose, tests were conducted at 80 and 150 \({}^{\circ}\)C for 96 h using two different solutions, 3% _w/w_ NaCl and 1.54% _w/w_ NaCl + 1.83% _w/w_ CaCl2-H2O to maintain the same Cl\({}^{-}\) concentration in both cases. The addition of Ca2+ at 80 \({}^{\circ}\)C accelerated pit growth and these effects diminished at 150 \({}^{\circ}\)C.  
[PERSON] et al. [15] investigated the effect of Ca2+ on an already-formed FeCO3 protective layer on L80-1 Cr steel, and its influence on the corrosion behavior in an aqueous solution saturated by CO2 at 1% _w/w_ NaCl in 0, 100, 1000, and 10,000 ppm Ca2+ (from CaCl2-H2O) at atmospheric pressures and at 80 \({}^{\circ}\)C under stagnant conditions. Throughout this experience, they observed three stages. During the first stage, the sample was left to corrote until Fe2+ ions super-saturated the solution, thus promoting FeCO3 precipitation.