It was recalled that, with regard to hydrogen diffusion in metals, it was necessary to consider not only the hydrogen flux driven by the gradient of the hydrogen concentration but also the hydrogen flux driven by the gradient of hydrostatic stress. Such hydrogen diffusion was a multi-physics problem coupling hydrogen diffusion to a stress field. Such hydrogen diffusion analyses were performed for a steel pipe with a crack on an inner surface under internal pressure. On the inner surface of the pipe, the hydrogen concentration calculated using the fugacity of the hydrogen molecules was used as a boundary condition for a hydrogen diffusion equation. The finite element method was employed both for a hydrogen diffusion analysis and for a stress analysis. The hydrogen concentration around a crack tip was obtained by varying the magnitude of the internal pressure and the crack length and examining the relationship between the maximum hydrogen concentration and a non-linear fracture mechanics parameter: the crack-tip opening displacement. A good correlation was found between the maximum hydrogen concentration and the crack tip opening displacement.

Hydrogen Diffusion Analyses of a Cracked Steel Pipe under Internal Pressure. K.Takayama, R.Matsumoto, S.Taketomi, N.Miyazaki: International Journal of Hydrogen Energy, 2011, 36[1], 1037-45