## 4 Conclusions  
In order to evaluate the corrosion resistance of surfaces with high electrochemical impedance, the method of electrochemical impedance spectroscopy (EIS) is suitable, especially to study the degradation of metals covered with organic layers (paints). Moreover, in this study all the experimental data for the six alloys immersed in three corrosion environments could be processed with only three equivalent cell types. According to the EIS experimental data:  
* the _C45 samples_ exhibit a double layer structure with high polarization resistance and low corrosion rate when exposed to rainwater (RW). When exposed to Black Sea water (BSW), due to the aggressiveness of the chlorine ions, the steel, especially the iron, is rapidly attacked, consequently, the polarization resistance is 3.3 times lower and the corrosion rate is higher. In the fire extinguishing solution (FES), the equivalent circuit used is characteristic to a corrosive metal coated with a porous non-conducting layer in which the corrosion process is carried out under a mixed, kinetic and diffusion control. The estimated corrosion rate of the C45 samples exposed to FES is close to the value which corresponds to BSW;
* more than 10 times higher than that presented by the II-ZN/Fe and III-Mn samples. The sample with the lowest corrosion resistance is the III-Mn sample which was coated with an Mn\({}_{3}\) (PO\({}_{4}\))\({}_{2}\) + Fe + Ni-based solution. The corrosion rates of phosphate samples are higher when exposed to BSW, compared to RW, also, the I-Zn phosphate sample provides the best corrosion protection, while the III-Mn phosphate sample the lowest. In FES, the II-Zn/Fe sample appears as the sample with the highest corrosion resistance, while the I-Zn sample is the second. * the _phosphate and oil immersed samples_ (OPS) show a very low corrosion rate in OPS/RW system. In the case of OPS/RW and OPS/FES systems, the circuit used describes a double-layer physical  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \multirow{2}{*}{**System**} & \multirow{2}{*}{ \begin{tabular}{c} **R\({}_{\text{s}}\)** \\ **\(\Omega\)-cm\({}^{2}\)** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **C\({}_{\text{ext}}\)** \\ **F/cm\({}^{2}\)** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **R\({}_{\text{ext}}\)** \\ **\(\Omega\)-cm\({}^{2}\)** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **CPE** \\ **Q** \\ **S-s\({}^{\text{th}}\)/cm\({}^{2}\)** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **R\({}_{\text{in}}\)** \\ **R\({}_{\text{in}}\)** \\ **P/cm\({}^{2}\)** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **C\({}_{\text{dl}}\)** \\ **F/cm\({}^{2}\)** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **R\({}_{\text{ct}}\)** \\ **\(\Omega\)-cm\({}^{2}\)** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **R\({}_{\text{ct}}\)** \\ **\(\Omega\)-cm\({}^{2}\)** \\ \end{tabular}  } & \multirow{2}{*}{ \begin{tabular}{c} **R\({}_{\text{ct}}\)** \\ **F/cm\({}^{2}\)** \\ \end{tabular}  } & \multirow{2}{*}{\ \begin{tabular}{c} **R\({}_{\text{ct}}\)** \\ **\(\Omega\)-cm\({}^{2}\)** \\ \end{tabular}  } & \multirow{2}{*}{
\begin{tabular}{c} **system with kinetic and diffusion mixed corrosion rate control. The capacities (expressed by the constant phase elements CPE1 and CPE2), the resistances (R\({}_{\text{ext}}\) and R\({}_{\text{ct}}\)) and the Warburg constant (W) obtained for OPS samples in both corrosion environments are in the same range. Given the very low values of the constant W, the diffusion impedance (ZW) is very high. The sum of kinetic (R\({}_{\text{ct}}\) + R\({}_{\text{ext}}\)) and diffusional (ZW) components leads to a very high polarization resistance and a significant reduction in corrosion rate, moreover, the instantaneous diffusion rate is 114 um/year in seawater, while in FES it is of 243 um/year. the _phosphate and rubber painted samples_ (PPS) were analyzed with a circuit that describes a three-layer physical state, with kinetic control of the corrosion rate.