Hydrogen embrittlement study of epoxy-coated X60 pipeline steel using a modified disc pressure test and phase-field modelling approach

The effectiveness of epoxy-based coatings in mitigating hydrogen embrittlement of X60 steel was evaluated using a modified Disc Pressure Test under hydrogen pressure. Both rupture pressure and displacement were used to quantify degradation using a hydrogen embrittlement index. The uncoated specimens exhibited a marked reduction in rupture pressure and, in particular, deformation capacity. The application of epoxy coatings significantly reduced the embrittlement indexes, leading to intermediate behaviour between the reference test (in helium) and uncoated hydrogen conditions. However, fractographic analysis revealed predominantly brittle features, indicating that the coatings delayed but did not fully inhibit hydrogen-assisted fracture. A coupled hydrogen transport phase-field fracture model reproduced the experimental trends. Simulations indicated that the behaviour of the coated specimens is not only attributed to bulk permeability but also requires consideration of interfacial resistance effects that reduce the effective hydrogen flux at the steel surface.