Corrosion behavior of scratched coated steel structures in marine atmospheric environments

To examine the corrosion behavior of scratched coatings in marine atmospheric environments, this study developed a multiphysics coupling model to evaluate the effects of scratch geometry (linear, circular, elliptical, and cross-shaped), defect size, temperature, and relative humidity. The simulations indicate dual-stage kinetic effects of temperature and humidity. In the initial stage, higher temperatures enhanced ionic diffusion and accelerated the onset of substrate corrosion, while higher humidity increased electrolyte film thickness and promoted mass transfer. Over longer exposure, enhanced transport also promoted the formation of oxidation products, increasing surface coverage and inhibiting sustained substrate corrosion. Consequently, the predicted substrate corrosion thickness decreased with increasing temperature and humidity over the one-year simulation period, whereas coating thickness reduction increased. Geometry strongly affected localized corrosion. For cross-shaped scratches, the corrosion rate decreased as the intersection angle increased. Among the representative geometries, linear scratches showed the lowest substrate corrosion risk, while elliptical and circular defects produced higher localized corrosion intensity. Elliptical scratches exhibited the highest temperature sensitivity (−3.31%/°C), followed by linear (−2.86%/°C) and circular (−1.29%/°C) scratches. Humidity sensitivity was highest for linear scratches (−5.54%/%RH), followed by elliptical (−5.33%/%RH) and circular (−4.10%/%RH) scratches.