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the validity of laboratory measurements on thick plates, since the common 1D simplification of diffusion equations is no longer valid.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 using a heat treatment. The present paper will describe in detail the mathematical modeling and experimental approaches and the basis for our recommendation.

Subject
Pipe surfaces, Barriers, Steel surfaces, Hydrogen permeation, Fluxes, Extraction, Diffusion, Oxide layers, Pipelines, Boundary conditions, Permeation, Steel, Hydrogen
Keywords:
carbon steel, diffusion, hydrogen, hydrogen-induced cracking, hydrogen permeation, modeling
© 2015 NACE International
2015
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