Effect of hydrogen traps on hydrogen permeation in X80 pipeline steel —— a joint experimental and modelling study

Abstract

The permeation of hydrogen in the X80 steel was studied in this paper through thermal desorption spectroscopy, stepwise hydrogen permeation experiments and finite element modelling. Firstly, one kind of shallow trap and deep traps in X80 steel were identified through thermal desorption spectroscopy and the corresponding binding energies were obtained. According to the experiment and simulation, the deep hydrogen traps can significantly retard the first hydrogen permeation process but have almost no effect during the following charging. The X80 steel used in hydrogen compressed natural gas pipelines is exposed to hydrogen for long periods and deep traps are filled, its hydrogen permeation process is more in line with the stepwise hydrogen charging. Therefore, the stepwise hydrogen charging experiments were performed and the apparent diffusion coefficients (Dapp) and the hydrogen trap density involved in the hydrogen permeation transient (N1) were obtained using three different thickness samples. Then, a quantitative relationship in X80 steel was fitted between the N1 and the variation of hydrogen concentration. Based on the quantitative relationship and the hydrogen trap binding energies, a hydrogen permeation model in X80 steel was established. By comparing the hydrogen permeation curves obtained by our model under different boundary conditions with experiment curves, it is found that the constant concentration boundary condition model can better describe the hydrogen permeation kinetic in X80 steel under electrochemical hydrogen charging. As a result, this model can be used to predict the distribution of hydrogen in X80 steel, laying the foundation for predicting the occurrence of hydrogen embrittlement in pipeline steels.