Rapid assessment of stainless steels corrosion by bipolar electrochemistry

This study investigates the influence of applied constant current (0.5–2 A) on the localized corrosion behaviour of 304 and 316 austenitic stainless steels (ASSs), 2205 duplex stainless steel (DSS), and 32750 super duplex stainless steel (SDSS) using bipolar electrochemical (BPE) testing in freely aerated 3.5% NaCl, where each experiment was conducted for a duration of 2 h. The BPE technique induces spatial anodic-cathodic polarization without direct electrical contact, enabling realistic simulation of crevice and pitting corrosion. Among the investigated grades, 304 ASS exhibited the lowest corrosion resistance, showing the highest weight loss (~ 0.069 g/cm²), severe pit coalescence, and deep crevice penetration (~ 610 μm) at 2 A. The addition of Mo in 316 ASS improved performance, reducing weight loss to 0.055 g/cm² and crevice depth to ~ 505 μm. In contrast, 2205 DSS demonstrated significantly enhanced resistance, with weight loss limited to ~ 0.007 g/cm² at 2 A, along with shallow crevices (~ 224 μm) and pitting mainly localized at ferrite-austenite interfaces. The highest resistance was observed in 32750 SDSS, which maintained minimal weight loss (0.004 g/cm²), very shallow crevices (< 100 μm at 2 A), negligible pitting, and the lowest corrosion volume-to-area ratios. Optical profilometry confirmed extensive penetration in 304 ASS and markedly shallower attack in duplex grades. Raman analysis identified α-FeOOH and γ-FeOOH in austenitic steels, indicating sustained active corrosion, whereas γ-Fe₂O₃ dominated in 2205 DSS and 32750 SDSS, reflecting more stable corrosion products and improved localized corrosion resistance.