Investigation of the pitting corrosion characteristics of 304L stainless steel in sulfuric acid solutions with chloride ions

During the production and transportation processes in refining pipelines, corrosive species such as sulfides and chlorides can degrade the passivation film on the surface of stainless steel, resulting in localized corrosion within the pipelines. Under the initial pH value of 4 and a chloride ion concentration of 0.02 mol/L, real-time monitoring was employed to maintain the pH value constant during the corrosion process. Via electrochemical testing, the corrosion morphology and surface film properties were characterized to investigate the effects of hydrogen sulfide concentration and temperature on the pitting corrosion behavior of 304L stainless steel in chloride- and hydrogen sulfide-containing solutions under constant pH conditions. The introduction of hydrogen sulfide disrupted the original dense structure; the newly formed sulfides, owing to their loose crystalline structure, increased the porosity of the passivation film and significantly reduced its stability, thereby rendering the stainless steel more prone to corrosion. As hydrogen sulfide concentration increased, the solution conductivity also rose, while the charge transfer resistance (Rct) of the inner passivation layer decreased to 2.89 × 10⁴Ω·cm-2, the stability of the inner passivation layer gradually deteriorated, diffusion effects intensified, the formation of pit nuclei leads to a reduction in the energy barrier, thereby facilitating the occurrence of the corrosion reaction. The depth and width of pitting corrosion pits increased significantly with increasing hydrogen sulfide concentration. Under high-temperature conditions, the self-corrosion current density increased, and the passivation film gradually transformed toward a more iron-rich sulfide composition, generating sulfides with a looser and more porous structure. This led to diminished corrosion resistance of 304L stainless steel, enhanced corrosion propensity, and more rapid onset of pitting corrosion.