A Unified Kinetic Framework for Hydrogen Permeation and Thermal Desorption in Steels: Sensitivity Analysis and Practical Implications

Electrochemical permeation and thermal desorption spectroscopy (TDS) are widely used to characterize hydrogen transport and trapping in steels, but are commonly interpreted through separate modelling approaches. This work presents a unified one-dimensional kinetic framework for the coupled simulation of hydrogen permeation, room-temperature free desorption, and thermal desorption. Lattice diffusion is coupled with explicit McNabb–Foster trapping and detrapping kinetics for multiple effective trap populations characterized by their density and binding energy. The formulation enables the consistent transfer of hydrogen distributions and trap occupancies between successive simulation stages, thereby linking hydrogen uptake, retention, and release within a single framework. The kinetic equations are expressed in concentration form, employ the Eyring transition frequency, and recover the Oriani relationship as the equilibrium limit. Sensitivity analyses show that stationary permeation flux is governed primarily by charging concentration and specimen thickness, whereas permeation transients and residual hydrogen content are strongly affected by trapping. Thermal desorption peak temperature and shape depend on trap energy, trap density, diffusion length, and hydrogen distribution, demonstrating that peak position is not a unique measure of trap strength. Kissinger plots remain highly linear under all investigated conditions, although the recovered energies systematically underestimate the nominal trap energies and should therefore be interpreted as effective desorption parameters. An application to an industrial ferritic stainless steel demonstrates the practical use of the framework for interpreting complex TDS spectra and estimating effective trapping parameters. The framework provides a computationally efficient tool for integrated interpretation of hydrogen transport, trapping, and thermal desorption in steels.