Hydrogen compatibility of rubber seals for converting natural gas pipelines to hydrogen service: A molecular dynamics approach

The conversion of natural gas pipelines into hydrogen pipelines represents an effective strategy under the global energy transition and low-carbon goals. However, natural gas pipeline systems exposed to hydrogen environments exhibit material compatibility problems (e.g., hydrogen embrittlement and seal failure), inducing gas release, explosion, etc. The mass transfer process of hydrogen molecules proceeds with direct adsorption and dissolution on polymer surfaces, then matrix entry, thereby causing rubber seal failure via mechanical property degradation, swelling, and microstructural damage. This study proposes a molecular dynamics-based approach to assessing rubber seal compatibility in hydrogen pipeline transportation environments. Molecular dynamics (MD) in combination with the grand canonical Monte Carlo (GCMC) method serves to simulate hydrogen molecule adsorption and diffusion movements in rubber materials. The solubility coefficient obtained from the Henry's law adsorption method and the diffusion coefficient obtained from the Einstein equation determine the permeability coefficient, a crucial indicator for rubber hydrogen compatibility. The approach is applied to assess the compatibility of two typical sealing materials: hydrogenated nitrile butadiene rubber (HNBR) and ethylene propylene diene monomer rubber (EPDM), demonstrating that HNBR with a lower permeability coefficient offers better resistance to hydrogen. The hydrogen permeability coefficient of EPDM is measured to be 124.58% greater than that of HNBR at 5 MPa and 293 K.