EXPERIMENTAL INVESTIGATION OF THE EFFECTS OF EXPOSURE TO PRESSURIZED HYDROGEN ON GENERAL USE POLYMER-BASED O-RING SEALS

Abstract

The utilization of hydrogen as an energy carrier has become particularly attractive in the lastdecades. Hydrogen use as an energy carrier along with the use of renewable energy sources presents the possibility of developing energy infrastructure with minimum environmental impact by decreasing greenhouse gas emissions. Nevertheless, material interactions between hydrogen gas and polymer materials lead to changes in mechanical properties that can compromise the performance of components over time, leading to gas leakages and increasing concerns regarding the economic viability of hydrogen use as well as concerns about the inherent risks associated with technology. For these reasons, understanding material compatibility with hydrogen gas is exceptionally important since numerous components and systems across all aspects of hydrogen infrastructure are vulnerable to hydrogen assisted material degradation. This study demonstrates that hydrogen-induced degradation in FKM NBR and EPDM under prolonged high-pressure exposure is governed not by monotonic strength loss, but by pressure-dependent competition between swelling-induced internal stress and hydrogen- assisted viscoelastic relaxation, which manifests most clearly under displacement- controlled tensile loading. An experimental system was designed and commissioned to safely conduct these experiments. The experimental system includes sensors for automated safety shutoff, remote controls, and data acquisition system. Specimens were exposed to gaseous hydrogen at pressures ranging from 55 to 482 bar for 200 hours at room temperature, followed by uniaxial tensile testing and hardness measurement. Raw force– time and deformation–time responses were analyzed alongside normalized force and deformation metrics to isolate pressure-dependent effects while accounting for specimen variability. Tensile strength was calculated, and results are reported as mean ± standard deviation. Similarly, material hardness was measured and reported as mean ± standard deviation. Additionally, material imaging and computational methods were used to characterize changes in morphology to the material as a consequence of exposure to pressurized hydrogen gas. These results showed that exposure of the selected polymer xiv formulations to a hydrogen environment pressurized at varying levels undergo structural changes at a molecular level through the effects of hydrogen dissolution and the subsequent depressurization. Two main effects were observed on the material samples analyzed: plasticization by gas infiltration and chemical aging through cross-link bond scission. The results reveal that hydrogen exposure does not produce a monotonic degradation in tensile strength. Instead, all materials exhibit pressure-dependent and non-monotonic responses arising from competing mechanisms including swelling-induced internal stress, transient plasticization, and viscoelastic relaxation under displacement-controlled loading. NBR and EPDM retain tensile integrity across the investigated pressure range, though with altered stiffness evolution and increased variability at higher pressures, while FKM exhibits the highest susceptibility due to its highly permeable network. These findings highlight the importance of evaluating full tensile response histories, rather than peak strength alone, when assessing elastomer suitability for high-pressure hydrogen sealing applications.