## 3 Methods  
The study of structural materials corrosion in solutions was carried out in both static conditions and with agitation. In the experiments with agitation, a periodical agitation of the solution was carried out once a day for 1 h by a submerged mixing device at the rate of \(\approx\)600 RPM. The technique of the experiment with agitation is described in detail in our previous works [32; 33]. The sheet metal samples were welded by ANO-4 electrodes 2 mm\({}^{2}\) in diameter with a welding current of 40 A. Then, the surface was mechanically cleaned and the 10 cm\({}^{2}\) plates were cut out. The obtained 10 cm\({}^{2}\) plates were placed into the solution (Table 2) and exposed for 1-62 days. The pH of the model solution was about 11.2-11.5 and changed slightly over time. At the same time, two parallel experimental series were performed in dynamic mode and three in static mode. Corrosion rate monitoring was \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Control Parameters** & \multicolumn{3}{c}{**Material Grade**} \\ \hline \multirow{3}{*}{**Components**} & **U7** & **St3** & **ANO-4** \\ \cline{2-4}  & **GOST** & **GOST** & **GOST** \\  & **1435–99** & **380–2005** & **5.1215–72** \\ \hline As & - & up to 0.08 & - \\ \hline C & 0.66–0.73 & 0.14–0.22 & up to 0.10 \\ \hline Cr & up to 0.2 & up to 0.3 & - \\ \hline Cu & up to 0.25 & up to 0.3 & - \\ \hline Fe & base & base & base \\ \hline Mn & 0.17–0.33 & 0.4–0.65 & 0.6–0.8 \\ \hline Ni & up to 0.25 & up to 0.3 & - \\ \hline N & - & up to 0.008 & - \\ \hline P & up to 0.03 & up to 0.04 & up to 0.035 \\ \hline S & up to 0.028 & up to 0.05 & up to 0.035 \\ \hline Si & 0.17–0.33 & 0.05–0.17 & up to 0.18 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Composition of the studied structural materials. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Sample No.**} & **Sample** & \multicolumn{2}{c}{**Saline Media Composition, wt. \%**} & \multicolumn{2}{c}{**Initial Corrosion Rate Per**} \\ \cline{3-5}  & **Material** & **Na\({}_{2}\)CO\({}_{3}\)** & **NaHCO\({}_{3}\)** & **NaCl** & **.104** \\ \hline \multirow{2}{*}{1} & \multirow{2}{*}{St3} & 4.2 & 33.6 & 3.5 & 3.4 \\  & & 4.2 & 33.6 & - & 1.8 \\ \hline \multirow{2}{*}{2} & \multirow{2}{*}{U7} & 4.2 & 33.6 & 3.5 & 1.2 \\  & & 4.2 & 33.6 & - & 0.95 \\ \hline \multirow{2}{*}{3} & \multirow{2}{*}{Weld joint} & 4.2 & 33.6 & 3.5 & 3.2 \\  & & St3-St3 & 4.2 & 33.6 & - & 2.13 \\ \hline \multirow{2}{*}{4} & \multirow{2}{*}{Weld joint} & 4.2 & 33.6 & 3.5 & 3.42 \\  & & St3-U7 & 4.2 & 33.6 & - & 2.4 \\ \hline \multirow{2}{*}{5} & \multirow{2}{*}{Weld joint} & 4.2 & 33.6 & 3.5 & 3.3 \\  & & U7-U7 & 4.2 & 33.6 & - & 2.10 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Summary data on the study of structural materials corrosion resistance. implemented by weighting by the use of the analytical balance VLO-200 (Russia). The reaction rate was determined by the loss in weight of the plate for the specified time period:  
\[\upsilon=\frac{\Delta\mathrm{m}}{S\cdot\Delta\tau} \tag{3}\]  
where:  
\(\upsilon\)--corrosion rate;  
\(\Delta\mathrm{m}\)--sample mass variation;  
\(S\)--sample area;  
\(\tau\)--exposure time. The concentration of iron in the solution was determined via the spectrophotometric method [29]. Spectrophotometric determination of iron (III) in solution was carried out by the use of strongly colored complexes with thiocyanate ions. Photometric analysis was performed on the KFK-3 instrument (Russia) at a wavelength of 480 nm (when the maximum absorption of the thiocyanate ion was observed). Photometry was carried out according to a two-beam scheme using a comparison solution with a cuvette length of 2 cm. Quantitative determination was performed using a pre-constructed calibration dependence with standard solutions. This method is very sensitive and allows to confidently determine the concentrations of iron (III) ions up to \(10^{-5}\) mol/L.