# Corrosion Behavior of Stainless Steel in Seawater in the Presence of Sulfide
## 1 Introduction  
Marine environments can be very challenging for metallic structural materials due to factors such as high salinity, water velocity, temperature, and biological activities [1; 2; 3; 4; 5]. The corrosion of alloys in seawater has serious effects on the reliability and service life of marine equipment, causing severe damage to structures, materials, equipment, port facilities, and ships, which is a major concern for scientists and engineers [6; 7; 8]. In addition to the adverse effects of chlorides and other halide ions naturally present in seawater, pollutants can also have a significant impact on the corrosion of metals. Corrosion and pollution are interrelated processes, as many pollutants produced by burning fossil fuels accelerate corrosion, and corrosion products such as rust, oxides, and salts pollute water. Both processes negatively affect the quality of the environment and the durability of marine structures and building materials [7; 9]. Pollution also leads to climate change, which can alter environmental conditions and increase the risk of corrosion failures, altered precipitation patterns, and the corrosioness of coastal regions, with added stresses on marine systems [9; 10]. Anthropogenic activities increase the generation of CO\({}_{2}\), H\({}_{2}\)S,and NH\({}_{3}\). Such contaminants may originate from natural geochemical processes, biological and bacteriological processes in seawater, and anthropogenic sources such as industrial waste discharge, oil and gas production, or scattered anoxic sediments [11; 12; 13; 14]. Among these compounds, hydrogen sulfide (H\({}_{2}\)S) is a highly toxic compound that accelerates the deterioration of steel structures in a process known as sour water corrosion. While hydrogen sulfide is always present in anaerobic seawater, studies have shown that sulfides are also widespread in aerobic surface waters, usually at concentrations 4-6 orders of magnitude lower than in anoxic regions. In both anaerobic and aerobic water, hydrogen sulfide occurs as a dissolved gas [H\({}_{2}\)S(g)], as its dissociated ions, bisulfite (HS\({}^{2-}\)) and sulfide (S\({}^{2-}\)), and as dissolved metal-sulfide complexes [12; 13]. Metals and alloys used in oil and gas extraction and purification processes also suffer from severe corrosion due to the presence of sulfur-containing ions such as S\({}_{2}\)O\({}_{3}\)\({}^{2-}\), SO\({}_{3}\)\({}^{2-}\), S\({}_{2}\)O\({}_{4}\)\({}^{2-}\), and HS\({}^{-}\) together with H\({}_{2}\)S [1; 2]. H\({}_{2}\)S is the most critical pollutant in seawater and can reach levels of 50 ppm or more in heavily polluted coastal or harbor waters [11]. Dissolved-free sulfides have been found to be very aggressive species towards many different metals and alloys, including various types of steels, copper and copper alloys, titanium and its alloys, etc. [11; 15; 16]. [PERSON] investigated the corrosion of Cu-Ni alloys in sulfide-contaminated seawater and found that the presence of dissolved sulfide in seawater leads to the formation of a porous copper sulfide corrosion product, which interferes with the normal growth of the protective oxide film and enables the initial high corrosion rate in aerated seawater [17]. [PERSON] et al. [18] studied the corrosion of CuNiFeMn alloys in sulfide-polluted and unpolluted natural seawater and found an accelerated corrosion attack at a sulfide concentration of 4 ppm. The presence of sulfur oxyanions deep in the corrosion layer leads to structural defects and the formation of poorly compact and porous corrosion product layers with low corrosion protection. [PERSON] [19] studied the corrosion of different types of steel in NaCl solution saturated with H\({}_{2}\)S and observed that saturation of the chloride solution with H\({}_{2}\)S gas further reduced the corrosion resistance of the steels since the presence of H\({}_{2}\)S impeded passivation and lowered the breakdown potentials of all the steels studied.