Hydrogen permeation in polymer-coated steels: A phenomenological barrier model accounting for coating and interfacial effects

Protective coatings are increasingly considered to be hydrogen barriers for pipeline steels in repurposed natural-gas infrastructure and new hydrogen-dedicated networks. Herein, a phenomenological model is developed to describe hydrogen entry in polymer-coated pipeline steels by coupling coating transport, interfacial transfer, and substrate permeation. An equivalent barrier parameter, A , is introduced into Sieverts’ law to reproduce the same hydrogen flux and subsurface hydrogen concentration in the steel as the full coating–interface–substrate system. The formulation, derived from the hydrogen flux balance and a resistance-in-series framework, explicitly incorporates thickness and transport properties of both coating and steel, and interfacial kinetic contribution. An experimental program was conducted to establish a methodology for determining A and the interfacial resistance, and demonstrate the applicability of the model, highlighting the coating interface as a key factor controlling barrier performance. This framework provides a physically grounded tool for comparing and improving protective coatings for hydrogen applications.