Disk Pressure Tests on polycrystalline Armco iron flat samples provided fracture pressure values within a wide range of applied hydrogen pressure rise rates. FE simulations of the disk bulging and hydrogen transport before fracture have been performed assuming isotropic elastoplasticity. The diffusive and trapped hydrogen concentrations fields in the zone of interest for failure show the effect of the applied pressure rise rate on the coupling between plastic strain and hydrogen transport, and permit to deduce a phenomenological relationship between the failure stress and the hydrogen concentration, as a first approximation to model the embrittlement process. Submodelling with 3D synthetic polycrystals, obeying crystal plasticity, permits to exhibit statistically the effects of local heterogeneities on the hydrogen distribution, and their consequences on the phenomenological failure stress evolution with the hydrogen content.