Inhibition Mechanism of Crevice Corrosion for 304 Stainless Steel by Intermittent Anodic Polarization in Natural Seawater

Marine engineering components of 304 stainless steel inevitably form crevice structures in service, which readily trigger severe crevice corrosion in seawater. Conventional protection strategies, including cathodic protection, organic coatings and corrosion inhibitors, show evident limitations within occluded crevices because of IR drop and mass transfer barriers. In this work, a 10 × 10 array electrode was employed to construct a simulated crevice device with a 0.3 mm gap width. Static immersion tests were carried out in natural seawater collected from Zhanjiang Bay for 75 days, using a blank group and an intermittent anodic polarization group (0.1 V vs. SCE applied for 10 min every 30 min; three independent specimens per group). In situ galvanic potential/current distribution mapping, electrochemical impedance spectroscopy (EIS) and ultra-depth-of-field microscopic observations were performed. Stable oxygen concentration cells were gradually built inside the crevices of blank specimens, producing band-shaped heterogeneous galvanic signals and massive pitting initiation. Intermittent anodic polarization homogenized the crevice internal potential distribution, reduced the galvanic current magnitude and effectively repaired the passive films: the inner crevice film resistance increased from 2.62 × 106 Ω·cm2 to 2.59 × 107 Ω·cm2, and the pitting density decreased markedly. Intermittent anodic polarization ameliorates the occluded electrochemical environment and mitigates crevice corrosion of 304 stainless steel in seawater, offering a potential supplementary strategy for marine stainless-steel components with crevice structures.