## 3 Results and Discussion
### Electrochemical Studies
Regarding the LPR measurements, it can be noted that all the mild steel panels were exposed to either WSS or 3.5 wt % NaCl for 96 h, in the presence of inhibitors or not. Bearing in mind the obtained \(R_{\text{P}}\) values (Table 4), it can be assumed that the presence of both \(Na_{2}HPO_{4}\) and \(MBT\) in the electrolytic solutions has as an outcome enhanced corrosion protection of mild steel, as the _Steel-WSS-Na\({}_{2}HPO_{4}\)-MBT_ and _Steel-NaCl-Na\({}_{2}HPO_{4}\)-MBT_ systems exhibit \(R_{\text{P}}\) values higher compared to either the systems without inhibitors (_Steel-WSS-blank_ and _Steel-NaCl-blank_) or to those systems including only one inhibitor. The EIS plots of mild steel panels in the presence or absence of inhibitors after subjection in WSS are demonstrated in Figure 19. Taking into account the EIS Bode curves after 24 h of exposure (Figure 19a), it can be seen that the _Steel-WSS-Na\({}_{2}HPO_{4}\)_ and _Steel-WSS-Na\({}_{2}HPO_{4}\)-MBT_ systems illustrate higher EIS moduli compared to the one of the _Steel-WSS-blank_, indicating that the presence of the Na\({}_{2}\)HPO\({}_{4}\) inhibitor alone or together with MBT into the corrosive environment increases the mild steel corrosion protection. On the contrary, the addition of an MBT compound into the WSS solution does not seem to improve the corrosion protection of the mild steel. Regarding the EIS Bode curves obtained after 96 h of exposure to WSS (Figure 19b), the same results are observed denoting \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{2}{c}{\(E_{\text{OC (V)}}\)} & \multicolumn{2}{c}{\(E_{\text{OC (V)}}\)} \\  & **(Cathodic Branch)** & **(Anodic Branch)** & **(96 h Exposure)** \\  & **(24 h Exposure)** & **(24 h Exposure)** & **(24 h Exposure)** \\ \hline _Steel–WSS–blank_ & \(-0.361\) & \(-0.386\) & \(6.279\) \\ _Steel–WSS–Na\({}_{2}HPO_{4}\)_ & \(-0.303\) & \(-0.374\) & \(2.852\) \\ _Steel–WSS–MBT_ & \(-0.394\) & \(-0.415\) & \(4.731\) \\ _Steel–WSS–Na\({}_{2}HPO_{4}\)–MBT_ & \(-0.253\) & \(-0.463\) & \(6.730\) \\ _Steel–NaCl–blank_ & \(-0.435\) & \(-0.462\) & \(2.822\) \\ _Steel–NaCl–Na\({}_{2}HPO_{4}\)_ & \(-0.586\) & \(-0.406\) & \(1.800\) \\ _Steel–NaCl–MBT_ & \(-0.282\) & \(-0.412\) & \(3.132\) \\ _Steel–NaCl–Na\({}_{2}HPO_{4}\)–MBT_ & \(-0.536\) & \(-0.408\) & \(4.054\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Tabulated values of \(E_{\text{OC}}\) [V vs. Ag/AgCl,KCl(sat)] obtained from the potentiodynamic polarization (PP) technique and of \(R_{\text{P}}\) estimated via the linear polarization resistance (LPR) method acquired for all mild steel panels after subjection in either WSS or 3.5 wt % NaCl in the presence of inhibitors or not. Figure 18: The polarization curves (**a**) cathodic and (**b**) anodic, recorded for mild steel panels after submission in 3.5 wt % NaCl for 24 h: (**filled square**) _Steel–NaCl–blank_, (**filled circle**) _Steel–NaCl–Na\({}_{2}HPO_{4}\)_, (**a filled triangleD**) _Steel–NaCl–MBT_, (**filled triangleU**) _Steel–NaCl–Na\({}_{2}HPO_{4}\)-MBT_. that the introduction of the Na\({}_{2}\)HPO\({}_{4}\) inhibitor alone or together with MBT in to the WSS solution protects the mild steel from corrosion. Considering the EIS plots of mild steel panels in the presence or absence of inhibitors after subjection in 3.5 wt % NaCl (Figure 20), it is clearly seen that after 24 h of exposure (Figure 20), the system _Steel-NaCl-Na\({}_{2}\)HPO\({}_{4}\)-MBT_ illustrates the highest EIS modulus in the low-frequency range, denoting that the presence of the Na\({}_{2}\)HPO\({}_{4}\) inhibitor in accordance with MBT into the corrosive environment increases the mild steel corrosion protection. On the other hand, the insertion of either Na\({}_{2}\)HPO\({}_{4}\) or MBT compounds into the 3.5 wt % NaCl electrolytic solution does not remarkably improve the corrosion protection of the mild steel.