Recommended Specimen Dimensions and Boundary Conditions for Measurement of Hydrogen Permeation in Thick Carbon Steel Plates

The present work discusses the influence of specimen dimensions and boundary conditions on the deviation towards 2D diffusion during hydrogen permeation measurements on thick carbon steel plates. It was mathematically found and experimentally confirmed that hydrogen losses through lateral diffusion could significantly affect the validity of laboratory measurements on thick plates, since the common 1D simplification of diffusion equations is no longer valid. Based on a finite element analysis, two options are proposed to minimize the effects of side diffusion on permeation measurements. The first option, which encompasses ISO 17081 criteria, recommends optimum radii for hydrogen charging and extraction surfaces and is valid for a wide range of specimen thicknesses. The second option relies on modification of boundary conditions and consists of applying a hydrogen-diffusion barrier on the specimen side edges. This second option was experimentally tested and validated by means of an oxide layer deposited usi...