Corrosion Product Films as Natural Barriers for Hydrogen Energy Pipelines: Structure-Permeation Correlations

Ensuring the integrity of hydrogen-blended natural gas (HBNG) infrastructure is pivotal for the sustainable hydrogen energy landscape, yet the surface interactions governing hydrogen embrittlement remain a critical challenge. This study presents a multiscale quantitative characterization of the film structure and hydrogen permeation kinetics of corrosion product films (CPFs), primarily composed of FeCO₃, by integrating X-ray micro-computed tomography (micro-CT), in situ high-pressure gaseous hydrogen permeation testing, and molecular dynamics (MD) simulations. Our findings elucidate that hydrogen traverses the CPFs predominantly in molecular form, with interconnected pores functioning as low-impedance "short-circuit" diffusion pathways. Kinetic evaluations indicate that the CPF densification over an extended duration drives the pressure exponent n from 0.783 to 0.901, marking a fundamental mechanistic shift from mixed molecular/atomic control to a dominant molecular barrier-controlled regime. Furthermore, a structural influence factor α and a quantitative correlation model are developed to accurately describe the attenuation of hydrogen flux induced by film densification. This work uncovers the potential of CPFs as natural hydrogen barriers, and also provides a robust theoretical framework for material compatibility evaluation and hydrogen embrittlement mitigation in HBNG infrastructure.