# Corrosion Behavior of Stainless Steel in Seawater in the Presence of Sulfide
## 3 Results and Discussion
### Surface Analysis
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline  & \multicolumn{6}{c}{**AISI 304L**} & \multicolumn{6}{c}{**AISI 316L**} \\ \hline
**Element (wt.\%)** & **1** & **2** & **3** & **4** & **5** & **6** & **1** & **2** & **3** & **4** \\ \hline O & 0.58 & 0.65 & 0.77 & 0.63 & 2.65 & 2.36 & 1.69 & 2.45 & 3.15 & 3.36 \\ Na & 28.69 & 28.75 & 29.87 & 36.11 & 6.67 & 5.78 & 34.71 & 34.92 & 4.96 & 3.26 \\ Mg & 0.88 & 0.98 & 0.71 & - & 1.22 & 0.77 & 0.43 & 1.72 & - & - \\ Si & - & 0.16 & 0.17 & - & 0.41 & 0.51 & - & - & 0.30 & 0.30 \\ S & 3.41 & 3.70 & 2.45 & 2.04 & 0.69 & 0.35 & 0.26 & 0.54 & 0.05 & 0.07 \\ Cl & 38.83 & 47.98 & 44.25 & 37.22 & 2.29 & 1.93 & 25.76 & 38.75 & 1.60 & 1.18 \\ Cr & 4.06 & 4.70 & 4.20 & 4.99 & 16.05 & 16.76 & 7.14 & 4.38 & 16.55 & 16.50 \\ Mn & 0.62 & 0.55 & 0.32 & 0.51 & 1.27 & 1.04 & 0.38 & - & 1.05 & 1.41 \\ Fe & 12.00 & 9.82 & 15.67 & 16.69 & 62.30 & 63.72 & 24.74 & 14.81 & 63.63 & 64.88 \\ Ni & 1.41 & 0.87 & 1.36 & 1.80 & 6.46 & 6.78 & 3.60 & 1.94 & 7.01 & 7.21 \\ Mo & - & - & - & - & - & 0.74 & 0.30 & 1.68 & 1.84 \\ K & - & 0.39 & - & - & - & - & 0.38 & 0.41 & - & - \\ Ca & 1.52 & 1.46 & 0.23 & - & - & - & 0.19 & 0.29 & - & - \\ Total & 100.00 & 100.00 & 100.00 & 100.00 & 100.00 & 100.00 & 100.00 & 100.00 & 100.00 & 100.00 \\ \hline \end{tabular}
\end{table} 
Table 8: Elemental composition on marked parts of the surface of AISI 304L and AISI 316L steels after potentiodynamic polarization measurements in seawater with 40 ppm S\({}^{2-}\) ions at 298 K.  
Figure 11: Optical micrographs after potentiodynamic polarization measurements in seawater at 298 K in the presence of 10 ppm of S\({}^{2-}\) for (**a**) AISI 304L and (**b**) AISI 316L (100\(\times\) magnification). Figure 10: Optical micrographs for AISI 304L after potentiodynamic polarization measurements in seawater at (**a**) 288 K and (**b**) 308 K and for AISI 316L at (**c**) 288 K and (**d**) 308 K (100\(\times\) magnification). The size, shape, and density of the pits were strongly affected by the type of stainless steel studied and the experimental conditions, e.g., seawater temperature and S\({}^{2-}\) ion concentrations. Anodic polarization of AISI 304L steel led to the development of a few pits with an average depth of 80-100 \(\upmu\)m and width of about 100 \(\upmu\)m (Figure 12a). Under the same conditions, on the surface of AISI 316L steel, the number and density of pits increased, but their depth and width decreased. As shown in Figure 12b, pits with an average depth of 40-50 \(\upmu\)m and a width of 50 \(\upmu\)m are formed on the surface of AISI 316L steel. The effect of seawater temperature on pit size is shown in Figure 13 for AISI 304L stainless steel. At 288 K, the scanned pit has a diameter of 10-25 \(\upmu\)m and a maximum depth of 50 \(\upmu\)m (Figure 13a). The situation worsens with increasing temperature, and at 298 K (Figure 13b), the depth and width of the pit increase to 70 \(\upmu\)m and 100 \(\upmu\)m, respectively. The situation was the worst at 308 K (Figure 13c), where the pit width and depth remained the same as at 298 K, but the number of pits on the surface increased. In general, it can be said that an increase in temperature does not affect the depth of the pits (at all temperatures, pits have a depth of about 50-70 \(\upmu\)m). However, the number of pits as well as their width, increase significantly (for example, at a temperature increase from 288 to 308 K, the width of the pit increases fourfold, from 25 to 100 \(\upmu\)m). Figure 12: Topographic view of the segment of corroded surfaces in seawater at 298 K after potentiodynamic polarization measurement for (**a**) AISI 304L and (**b**) AISI 316L. The depth and width of pits are determined along the red lines. Figure 14 shows the analysis of pitting damage on the steel surfaces of AISI 304L after the potentiodynamic polarization method in polluted seawater with 10 ppm and 40 ppm of S\({}^{2-}\) ions.