An apparatus and methodology for the non-destructive measurement of the hydrogen diffusion coefficient of metal structures in situ during operation

摘要

The hydrogen diffusion coefficient (D_H) of a metal is a material property necessary for the modelling of a variety of degradation phenomena which occur due to the presence of hydrogen in metal. Values of D_H in literature can vary even for the same grade of steel, necessitating experimental measurement of this property. While standard laboratory techniques to measure D_H do exist, they are destructive in nature and are not always applicable to old equipment where extracting a coupon is not possible. Hence, there is a motivation to explore means of measuring D_H non-destructively while the equipment is still in operation. This paper explains the authors' idea to utilise the 3D diffusion of hydrogen in order to use adjacent parts of the same surface for both the charging and oxidation of hydrogen. This allows the value of D_H to be measured with access to only one side of operating equipment. A laboratory prototype was constructed to test this method and an experiment was conducted. The diffusion of hydrogen was modelled using COMSOL Multiphysics and the value of D_H optimised using an incremental approach to fit the experimental data. The value of D_H obtained is consistent with values found in the literature for line pipe steels. While the results showed promise, further laboratory work is necessary to build confidence in the process and further challenges need to be overcome for implementation in the field.