The failure behaviour of a commercial highly pigmented epoxy coating under marine alternating hydrostatic pressure

•The failure process of the coating was accelerated by the alternating pressure.•The water diffusion in the coating was promoted significantly by the pressure.•The pigment/binder interface was deteriorated greatly by the alternating pressure. A commercial epoxy coating, incorporated with inert pigments, was aged in a sodium chloride (3.5wt.%) solution under alternating hydrostatic pressure (AHP), compared with that under atmospheric pressure (AP). By the fitting analysis of the impedance data with equivalent electric circuits (EEC), the failure process was accelerated and got complicated under AHP. The evolution of water absorption by gravimetric tests indicated that water diffusion deviated from typical Fickian diffusion to case II diffusion. A leaching process of pigments was observed by scanning electron microscopy (SEM) and no shift of chemical bonds was monitored by Fourier transform infrared spectroscopy (FT-IR). The AHP accelerated the coating physical failure, and the chemical structures of the coating did not change during the experiment.