Corrosion behavior of Q235 under dynamic simulated seawater and online monitoring using resistance probes

The harsh service environment of offshore engineering equipment exposes its metallic piping systems to severe risks of localized corrosion. This study addresses the challenge of corrosion monitoring for carbon steel in seawater pipeline systems by developing an online monitoring setup that dynamically simulates the seawater pipeline environment, and systematically conducts real-time monitoring and mechanistic analysis of the corrosion behavior of Q235 carbon steel. By coupling resistance probe online monitoring with the conventional corrosion coupon method, a predictive model for dynamic corrosion rate was established, and, using X-ray diffraction (XRD) along with microscopic morphology characterization techniques (SEM and 3D confocal microscopy), the evolution of corrosion products and their impact on monitoring accuracy were elucidated. The results indicate that the corrosion products of Q235 carbon steel in dynamic simulation of seawater conditions are predominantly Fe 3 O 4 (accounting for over 90%). The accumulation of corrosion products caused the relative deviation between resistance probe measurements and corrosion coupon results to increase from 23.19% in the initial stages to 148.09% in later stages, prompting the proposal of a logarithmic function-based data correction model, with the correction model expressed as: . This model provides a theoretical basis for optimizing the engineering applicability of monitoring techniques in dynamic corrosion environments, and, combined with quantitative analysis of pit depth, reveals how micro-region electrochemical heterogeneity at the product layer-substrate interface exacerbates localized corrosion.