# Corrosion Behavior of Stainless Steel in Seawater in the Presence of Sulfide
## 3 Results and Discussion
### Polarization Measurements
Increasing the temperature from 288 to 308 K resulted in a significant increase in current densities in the active anodic and passive regions, while the cathodic effect was not very pronounced. In addition, higher temperatures did not have a pronounced effect on the corrosion potentials but significantly lowered the primary passive potentials, decreased the passive potential range, and reduced the pitting potentials. All these results (Table 5) clearly show that temperature adversely affects the corrosion behavior of AISI 304L and AISI 316L stainless steels, which is consistent with the data in the literature for seawater and other aggressive environments [31, 32, 46, 47, 48, 49, 60, 61]. The temperature was found to affect pitting potential  
Figure 6: Potentiodynamic polarization curves for AISI 316L stainless steel in seawater at different (**a**) temperatures and (**b**) S\({}^{2-}\) concentrations (at 298 K). values more than chloride concentration. Moreover, an increase in temperature up to 90 \({}^{\circ}\)C in Cl\({}^{-}\) ion-containing electrolytes decreased the pitting potential by more than 200 mV [31; 61]. In the active potential range, the presence of S\({}^{2-}\) ions (up to 40 ppm) shifted \(E_{\text{corr}}\) by \(\approx\)100 mV on the active (cathodic) side for both samples and increased the \(i_{\text{corr}}\) more than twice (from 2.56 to 5.85 \(\upmu\)A cm\({}^{-2}\) for AISI 304L and from 1.26 to 3.20 \(\upmu\)A cm\({}^{-2}\) for AISI 316L). Moreover, in the passive potential region, the presence of S\({}^{2-}\) ions increased the current densities in the passive and transpassive regions and significantly lowered the primary passive potentials, the passive potential region, and the pitting potentials, which were observed with increasing temperature. This suggests that the presence of S\({}^{2-}\) ions negatively affects the corrosion behavior of stainless steels in saltwater environments. As already mentioned, this effect was observed in the presence of inorganic sulfide [13; 14; 15; 48; 49; 50; 51; 52; 53; 54] and in the presence of biogenic sulfide (known in the literature as SRB) [15; 54; 55; 56; 57; 59; 40; 41; 42; 43; 44; 45; 52] in various media (seawater, artificial seawater, aggressive environments with Cl\({}^{-}\) ions, then in artificial wastewater, in the oil industry, etc.). In investigating the corrosion behavior of AISI 304L steel, [PERSON] et al. found that the \(E_{\text{corr}}\) of specimens in artificial seawater remains fairly constant (about \(-\)0.17 V), while \(i_{\text{corr}}\), after 42 days of exposure, shows a slight decrease (from 3.9 to 3.2 \(\upmu\)A cm\({}^{-2}\)) due to the formation of conditioning layers and passive oxide layers. However, under the influence of inorganic sulfide ions, \(E_{\text{corr}}\) experiences a negative shift of about 100 mV (\(-\)0.28 V), while \(i_{\text{corr}}\) is about twice as large (about 8.3 \(\upmu\)A cm\({}^{-2}\)) [15]. The increased corrosion rate of stainless steels is mainly due to the accelerated conversion of metal oxides to metal sulfides by the inorganic sulfide, which has been confirmed by various surface analysis techniques [15; 54; 51; 48]. However, the conversion of metal oxides to metal sulfides by inorganic sulfide is slower than by biogenic sulfide (in the presence of active SRB) [15; 54]. In the literature, organic sulfides and corrosive sulfide intermediates have been found to be involved in the sulfurization process using biogenic sulfides [15; 54; 55; 56; 57; 40]. Despite extensive research, the mechanism of the complex action of biogenic sulfides is still not fully understood. The results for AISI 316L show that in the temperature range 288 to 308 K, the passivation current rises from \(\approx\)2 to \(\approx\)7.5 \(\upmu\)A cm\({}^{-2}\), while the addition of 10 ppm sulfide causes an increase in \(i_{\text{p}}\) from \(\approx\)4 to \(\approx\)9 \(\upmu\)A cm\({}^{-2}\) (Table 5).