Electro-osmotic control of X80 steel corrosion under HVDC interference

X80 pipeline steel in natural clay soil exhibits a pronounced non-monotonic corrosion kinetic peak under HVDC interference—a phenomenon that deviates significantly from classical electrochemical predictions and challenges existing cathodic protection (CP) design standards. The maximum corrosion rate occurs at 200 V with soil moisture decreasing from 13 wt% to 8 wt% within 8 h. Through decoupled electrochemical and electro-osmotic migration experiments ( n ≥ 3 replicates), we identified electro-osmotic dehydration (EOD) as the dominant mechanism. As water progressively migrates away from the anode/electrolyte interface, soil resistivity increases dramatically by 95%, fundamentally altering electrochemical kinetics. This moisture depletion triggers a critical transition of the rate-determining step from charge-transfer control to ohmic resistance control, explaining why intermediate voltages (150–250 V) generate unexpectedly high corrosion rates despite lower current densities. A coupled Nernst–Planck–Darcy model with saturation-dependent resistivity quantitatively reproduces the non-monotonic trend (prediction error < 7%) and moisture redistribution (error < 4%). The model reveals that corrosion risk concentrates within a specific voltage window under variable soil moisture conditions. These findings establish a multiphysics framework for understanding material degradation in complex electromagnetic environments and provide critical quantitative guidance for pipeline safety assessment in HVDC-affected zones. • Non-monotonic corrosion kinetics of X80 steel are identified under HVDC. • Corrosion rate peaks at 200 V due to electro-osmotic dehydration of soil. • Anodic moisture loss shifts the control from activation to ohmic resistance. • A Nernst-Planck-Darcy model predicts the coupled transport processes. • Kinetic anomalies are quantified through saturation-dependent resistivity.