## 3 Results and Discussion
In this mechanism, the corrosion relation involved is:  
\[\text{Fe}^{0}\leftrightarrow\left[\text{Fe}^{2+}\right]+2\text{e}^{-} \tag{3}\]  
[ ] represents interstitial ions, indicating that iron oxidation leads to interstitial iron ions and an excess of electrons in the FeCO\({}_{3}\) encrustations. By applying the law of mass action to Equation (3), Equation (4) is obtained:  
\[\text{K}=\left[\text{Fe}^{2+}\right]\text{e}^{2} \tag{4}\]  
where the product of interstitial ion and electron square concentrations must be constant. It is reasonable to assume that protons can be incorporated into the encrustation through the protonation of carbonate ions in the system. This leads to iron ion vacancies that, in turn, lead to a higher concentration of interstitial iron ions and, thus, to a greater encrustation permeability [33]. [PERSON] stated that a cation, such as protons, is introduced into the system; by analogy, in our work, we hold that the Na\({}^{+}\) cation behaves in a similar way, generating specific defects in the crystal system and favoring a higher porosity in the corrosion products. In our work, conducted under dynamic conditions with a cylinder rotating at 600 rpm at 65 \({}^{\circ}\)C and saturated by CO\({}_{2}\), we found the following decreasing order in the carbon steel corrosion rate:  
2% NaCl + 1380 ppm CaCl\({}_{2}\) > 2% NaCl > 2% NaCl + 1360 ppm Na\({}_{2}\)CO\({}_{3}\) > 2% NaCl + 1.25 g/L CaCO\({}_{3}\) > 1450 ppm of NaCl > 1380 ppm CaCl\({}_{2}\) > 1360 ppm Na\({}_{2}\)CO\({}_{3}\) > 500 ppm CaCl\({}_{2}\) > 424 ppm Na\({}_{2}\)CO\({}_{3}\) > 1.25 g/L CaCO\({}_{3}\). Chlorides favor the carbon steel corrosion process due to their affinity of this anion to iron, especially in an acidic medium. In our case study, the pH of the solution with 2% NaCl saturated by CO\({}_{2}\) at atmospheric pressure is 4.4. Additionally, it is well-known that solutions containing CO\({}_{2}\) in contact with low-alloy steel create a corrosion product protective layer on the material, basically formed by siderite (FeCO\({}_{3}\)) [34; 35]; however, the presence of certain ions, essentially chlorides, interfere with the formation of the protective layer, causing its dissolution [36] and resulting in an increase in the corrosion rate. Moreover, the presence of Na\({}^{+}\) promotes the action of chlorides. A plausible explanation for the corrosion rate increase is that Na\({}^{+}\) ions from NaCl in solution are incorporated into the crystal system of FeCO\({}_{3}\), creating new crystal defects, Na\({}^{+}\) ions, placing themselves in interstitial positions and creating Fe\({}^{2+}\) vacancies to keep the electroneutrality of the siderite [37; 38]. In accordance with the above mentioned results, a simplified sequence of the reactions with a pH < 4.5 might be:  
\[2\text{ NaCl}+\text{CO}_{2}+\text{H}_{2}\text{O}\to 2\text{ HCl}+\text{Na}_{2}\text{CO}_{3} \tag{5}\]  
\[(1-\text{x})\text{ FeCO}_{3}+\text{xNa}_{2}\text{CO}_{3}\rightarrow\text{Fe}_{(1- \text{x})}\square_{\text{x}}[\text{Na}_{2\text{x}}]\text{CO}_{3} \tag{6}\]  
where \(\square\) are Fe\({}^{2+}\) vacancies and [ ] are Na\({}^{+}\) interstitial ions. This contamination mechanism of the siderite crystals in the presence of NaCl leads to the instability of the protective layer, making it porous and increasing the Fe\({}^{2+}\) dissolution in the solution. This can be seen in Table 1; when only NaCl is apparent, the pH is acidic and CR is equal to 5.01 mmpy, showing the effect, first by Equation (5) and supported by Equation (6). However, when NaCl + Na\({}_{2}\)CO\({}_{3}\) is present, CR is equal to 4.41 mmpy (assay 3), which leads us to think that the reaction mechanism is deactivated, mainly because the reaction of Equation (5) is inhibited. This can be confirmed when we consider that, when NaCl is absent (assay 7), CR is equal to 1.81 mmpy.