Modelling of Hydrogen Permeability of Structural Materials Through Protective Coating Defect

An efficient reduction of gaseous hydrogen isotope permeation through a metal wall is essential in several applications like hydrogen storage and distribution, hydrogen embrittlement protection, and tritium inventory in future fusion reactors like ITER. Hydrogen permeation barrier films often exhibit lower efficiency than anticipated. It is very difficult to identify and quantify the responsible mechanism since the defects can be of submicrometer dimensions and very sparsely populated. We considered hydrogen permeability through a cylindrical membrane (barrier) in the presence of protective coating defect at the inlet surface of a structural material. For various materials, when the processes of diffusion, desorption and dissolution are limiting, we present the mathematical models in the form of boundary value problems with non-linear and dynamic boundary conditions. On the basis of the implicit difference scheme, a computational algorithm of a boundary value problems solution is developed. Numerical simulation results of hydrogen permeation flux and diffusant distribution are presented. Qualitative regularities of steady state permeability regime establishment and delay times registered experimentally and depending on geometric characteristics of the membrane and physical parameters are identified.