Hydrogen Compatibility of Commercial Silicone Elastomer Seals: Multiscale Mechanical and Surface Characterization Following High-Pressure Hydrogen Exposure

Commercial silicone O-rings were exposed to hydrogen pressures up to 7000 psi for 192 h and evaluated using mechanical, data-driven, and microstructural characterization. ASTM D1414-based O-ring tensile testing was complemented by multivariate and functional analyses, while surface evolution was quantified using SEM-based image analysis and spatial statistics. Inclusion of an unexposed 0 psi mechanical control revealed a non-monotonic exposure-associated response. Several hydrogen-exposed groups exhibited greater ultimate elongation, tensile toughness, and structural loading work than the unexposed control, whereas these quantities decreased at 7000 psi relative to selected lower-pressure exposed groups. Welch ANOVA identified significant overall group effects for tensile strength, ultimate elongation, toughness, and structural loading work. The normalized tensile-curve shapes and several stiffness-related descriptors showed smaller relative differences than the failure-related properties. These results demonstrate that hydrogen exposure was associated with changes in deformability and failure response, but the tensile data alone do not establish the molecular mechanism responsible for these changes. Quantitative SEM analysis revealed pressure-associated differences in localized morphology and spatial organization, including a tendency toward reduced dark-feature number density and variation in the magnitude and length scale of feature clustering among the analyzed conditions, without evidence of catastrophic surface degradation in the examined SEM fields. Overall, the investigated silicone exhibited non-monotonic exposure-associated changes in mechanical response together with localized pressure-associated surface evolution, without evidence of catastrophic surface degradation in the analyzed SEM fields. These findings provide comparative post-exposure material-response data for commercial silicone O-rings under high-pressure hydrogen conditions.