Numerical simulation of diffusivity of hydrogen in thin tubular metallic membranes affected by self-stresses

Based on the self-stress theory for hydrogen in thin tubular shells, we numerically calculate apparent diffusion coefficients (ADCs) of hydrogen in membranes obtained from the time-lag and half-rise methods under chemopotential- and flux-step boundary conditions. It is found that ADCs differ from the diffusion coefficient under stress-free conditions when either the initial concentration or the chemopotential-step (or flux-step) is taken to be a nonzero value. At the same time, effects of other parameters on values of ADC are discussed as well. The theoretical results are qualitatively consistent with the available experimental data. Our results indicate that a small current will give the minimum error in determining the diffusion coefficient while the initial hydrogen content is nonzero.