Polymer Behaviour in High Pressure Hydrogen, Helium and Argon Environments as Applicable to the Hydrogen Infrastructure

Polymers for O-rings, valve seats, gaskets, and other sealing applications in the hydrogen infrastructure face extreme conditions of high-pressure H2 (0.1 to 100 MPa) during normal operation. To fill current knowledge gaps and to establish standard test methods for polymers in H2 environments, these materials can be tested in laboratory scale H2 manifolds mimicking end use pressure and temperature conditions. Beyond the influence of high pressure H2, the selection of gases used for leak detection in the H2 test manifold, their pressures and times of exposure, gas types, relative diffusion and permeation rates are all important influences on the polymers being tested. These effects can be studied ex-situ with post-exposure characterization. In a previous study, four polymers (Viton A, Buna N, High Density Polyethylene (HDPE) and Polytetrafluoroethylene (PTFE)), commonly used in the H2 infrastructure, were exposed to high-pressure H2 (100 MPa). The observed effects of H2 were consistent with typical polymer property-structure relationships; in particular, H2 affected elastomers more than thermoplastics. However, since high pressure He was used for purging and leak detection prior to filling with H2, a study of the influence of the purge gas on these polymers was considered necessary to isolate the effects of H2 from those of the purge gas. Therefore, in this study, Viton A, Buna N, and PTFE were exposed to the He purge procedure without the subsequent H2 exposure. Additionally, six polymers, Viton A, Buna N, PTFE, Polyoxymethylene (POM), Polyamide 11 (Nylon), and Ethylenepropylenediene monomer rubber (EPDM), were subjected to high pressure Ar (100 MPa) followed by high pressure H2 (100 MPa) under the same static, isothermal conditions to identify the effect of a purge gas with a significantly larger molecular size than He. Viton A and Buna N elastomers are more prone to irreversible changes as a result of H2 exposure from both Ar and He leak tests as indicated by influences on storage modulus, extent of swelling, and increased compression set. EPDM, even though it is an elastomer, is not as prone to high-pressure gas influences. The thermoplastics are generally less influenced by high pressure regardless of the gas type. Conclusions from these experiments will provide insight into the influence of purging processes and purge gases on the subsequent testing in high pressure gaseous H2. Control for the influence of purging on testing results is essential for the development of robust test methods for evaluating the effects of H2 and other high-pressure gases on the properties of polymers.