Modelling the influence of trapping on hydrogen permeation in metals

• A modelling study for diffusion of hydrogen with traps is presented.
• Hydrogen permeation cannot be described by a constant effective diffusivity.
• Diffusivity depends widely on hydrogen concentration and traps.
• Charging and discharging process show asymmetry.

Hydrogen permeation (diffusion) is strongly influenced by the local hydrogen concentration and by the density and depth of traps. Consequently hydrogen diffusion cannot be described by a constant effective diffusivity as suggested in standards and several papers.A modelling study for diffusion of hydrogen in metals with traps is presented. Simulations are performed for a charging and discharging process, showing a remarkable asymmetry. The actual chemical diffusivity ranges over several orders of magnitude depending on the hydrogen concentration as well as the density and depth of traps. Consequently, the concept of effective diffusivity outlined in standards and many publications fails.