Effect of cathodic polarizations on the failure behavior of epoxy coating/ low alloy steel systems under high hydrostatic pressure

Failure behavior of epoxy coating/low alloy steel systems applied with cathodic polarization at 0.1 MPa and 15 MPa was investigated based on a deep-sea environment simulation test device. The results showed that the diffusion of water into the coating was significantly accelerated by the high hydrostatic pressure under the same polarization potential, and the time of water uptake of the coating that reached saturation was shortened; the coating's physical structure was significantly affected by the high hydrostatic pressure; the generation of highly conductive Fe3O4 was promoted in the corrosion products, which accelerated the metal corrosion process. Under the same hydrostatic pressure, with the negative shift of the polarization potential, the coating protective performance was significantly reduced and metal corrosion was mitigated to a certain extent; the water transport behavior showed a tendency to shorten the time of water uptake of the coating that reached saturation and lengthen the duration of the saturation state, which may be related to a more severe degree of cathodic delamination and the increase of water consumption for cathodic reactions under the coating. In addition, the increase of the weakly conductive alpha-Fe2O3 content in the corrosion products may cause a reduction in the cathodic protection current at the same polarization potential, resulting in the reduction of the protection effect on the metal.