Active Dissolution and Localized Corrosion Behavior of AISI 316L Stainless Steel in Concentrated Hydrochloric Acid.

AISI 316L austenitic stainless steel is extensively used in petrochemical storage and processing equipment because of its excellent corrosion resistance. However, exposure to concentrated hydrochloric acid severely destabilizes its passive film, promoting active dissolution and localized corrosion. This work investigates the corrosion behavior of AISI 316L stainless steel in hydrochloric acid solutions of 7.2, 9.6, and 12 M at room temperature. Cyclic potentiodynamic polarization (CPP) tests were performed according to ASTM G61, and the corrosion morphology was characterized using optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and metallographic cross-sections. The electrochemical results revealed an active dissolution regime characterized by the absence of a stable passive region and positive hysteresis loops in all HCl solutions, indicating irreversible surface damage and poor repassivation. The corrosion current density increased from the order of 10-1 mA cm-2 in 7.2 and 9.6 M HCl to the order of 101 mA cm-2 in 12 M HCl, demonstrating a significant acceleration of the corrosion kinetics. SEM and cross-sectional analyses confirmed the development of localized pitting corrosion, with pit depths reaching approximately 0.87 mm. The results demonstrate that concentrated hydrochloric acid promotes the coexistence of generalized active dissolution and localized pitting corrosion, while increasing HCl concentration modifies the morphology and propagation mode of the pits.