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DICHTUNGEN0708Compression set after immersion in H2 and air for 72 haccording to ISO 815-1AChange of volume, weight, tensile strength and elongationof break of different compounds after immersion in H2 for168 h at +23 °C and 70 MPaThe volume change considered here is measured one hour aftertaking the material out of the hydrogen atmosphere. If you comparethe swell 24 hours later, it becomes obvious that the volumechange is not permanent. This indicates that the hydrogen gaslikely did not have any adverse effects on the polymer. Thevolume increase of V9T82 shown in Figure 4 is small and stillwithin the measurement error.4.1.2 INFLUENCE OF THE TEMPERATUREHydrogen seals need to cover a large temperature window fromtypically -40 °C to +85 °C. Results for volume change at room temperatureand at the temperature limits are shown in Figure 5.E8T31 shows higher swell at elevated temperature but stays overallin a small percentage range.Figure 6 shows the change of tensile strength and elongationunder the influence of temperature. Typically, elongation tends toincrease at +85 °C and decrease at -40 °C. However, V9T82, E7T30,E8T24 and EBT25 show almost no change in elongation at break atelevated temperature compared to prior hydrogen immersion. Areason could lie in the higher mobility of the polymer chainswhich allows entrapped hydrogen molecules to escape faster. Thetensile tests were done at room temperature 24 hours after pressurerelief. For tensile strength there is similarly no clear trend visible.Only E8T31 shows a slight increase in tensile strength overtemperature. For ZLT, the previously described slight softening isreduced at higher temperatures. After exposure to -40 °C hydrogen,the polymer shows a small embrittlement. However, it shouldbe investigated if this effect persists after a longer period. Due tothe very dense structure of this polymer, some hydrogen moleculescould still be trapped in the matrix after 24 hours.In essence, the results show that there is no critical influenceon the mechanical properties of the tested elastomers. Comparedto immersion tests in some fluids, the changes observed here arerelatively very small.4.1.3 COMPRESSION SETWhen elastomer seals lose their elasticity over lifetime, leakagecan occur easily. It is therefore vital to understand if the compressionset changes under the influence of hydrogen. The results offive elastomers are shown in Figure 7. Hydrogen has no or even apositive impact which comes most likely from the absence of oxygen.Ageing elastomers in air allows oxygen to attack the polymerchains, which is why a hydrogen atmosphere helps to reduce thiseffect. Small differences like in the case of V9T82 can also originatefrom the higher swell due to hydrogen, which could compensatethe actual compression set.FORSCHUNG UND ENTWICKLUNG4.2 THERMOPLASTIC POLYMERSIn the initial testing phase for thermoplastic polymers, the goalwas to investigate the effect of hydrogen on the volume and mechanicalproperties of the seal material. In Figure 8, the PTFEbasedcompounds show a small noticeable swell independentlyof the filler content. This is due to the sintered structure of PTFEmaterials. When it comes to mechanical properties, only MF2and T05 show an increase in strength and elongation, whereasthe other PTFE compounds show a small embrittlement of lessthan five percent, which is normally not a reason for concern.Z80 is a UHMW polyethylene with a solid thermoplastic matrix,which is why there is almost no weight or volume change, sincethe amount of hydrogen molecules absorbed must be very small.The mechanical properties also show a slight embrittlement belowfive percent.Thermoplastic sealing materials are preferably used when theapplication temperature exceeds the limits of elastomers. Withhigh temperatures, volume increases a bit more, but still belowtwo percent as shown in Figure 9. The increase is slightly smallerin unfilled PTFE, which is T01, due to less diffusion paths for hydrogenalong the fillers.30 O+P Fluidtechnik 2025/01 www.oup-fluidtechnik.de

DICHTUNGENFigure 10 compares the mechanical properties at room temperatureand +130 °C. Z80 is not shown, because its upper temperaturelimit is +80 °C. Overall higher temperatures tend to make thematerials slightly more brittle. This can be observed in MF2, MF6,MF8 and T05 with low percentages. The amount of change howeveris still not at a worrying level. More research is needed to differentiatetemperature aging effects from the influence of hydrogenat elevated temperatures.5 SUMMARY AND CONCLUSIONIn this study the influence of hydrogen on non-metallic sealingmaterials, namely elastomer and plastics, is investigated. Focuslies on the change of mechanical properties, as well as volume,weight and hardness after hydrogen exposure at high pressure.Compression set under hydrogen atmosphere is also studied forelastomers, because it is highly relevant for the sealing performance.The results show no embrittlement of the elastomers tested.Only in the case of one TPU material could a slight softening beobserved. Also, extreme application temperatures of -40 °C and+85 °C show no critical influence on the mechanical properties oftested elastomers. The volume change is below two percent and islargely temporary. However, the results of volume change arehighly dependent on the shape and production method of thesamples. O-Ring samples show less change after hydrogen immersion.This phenomenon should be considered in design andcertification processes. Compression set under hydrogen atmosphereshows no significant deterioration except for one compound,which needs to be studied further.The swell of plastic materials under hydrogen atmosphere inthis study is around one percent and does not depend on the fillerlevel. The change of mechanical properties depends on the specificcompound. Some improve and some decrease, but not morethan five percent, which is usually not a concern. The influence ofhydrogen at high temperature tends to show a slight embrittlementof the polymers investigated. More research is needed todifferentiate temperature aging effects from the influence of hydrogenat elevated temperatures.It is concluded that hydrogen has no significant influence onthe compounds investigated in this study, which are known to bepolymers suitable for hydrogen use. The findings should thereforenot be generalized for all compounds of their material families.Specific testing may be needed to ensure a safe use in hydrogenapplications.0910Volume change of thermoplastic compounds afterimmersion in H2 for 168 h at +23 °C and 70 MPaChange of tensile strength and elongation at break afterimmersion in H2 for 168 h at different temperatures and70 MPaAuthors:Trelleborg Sealing Solutions Germany GmbHSchockenriedstr. 1, 70565 Stuttgart, GermanyPhilipp Hirstein, M. Sc., Philipp.Hirstein@trelleborg.comSandra Kofink, M. Sc., Sandra.Kofink@trelleborg.comTrelleborg Sealing Solutions Americas2509 Bremer Rd, Fort Wayne, IN 46803, United StatesJoel Thompson, M. Sc., Joel.Thompson@trelleborg.comReferences:[1] Bundesministerium für Wirtschaft und Energie: Die Nationale Wasserstoffstrategie,Juni 2020[2] European Commission, A Hydrogen Strategy for a Climate-Neutral Europe,2020[3] IEA, The Future of Hydrogen. Seizing Today‘s Opportunities, 2019[4] https://www.trelleborg.com/de-de/seals/your-industry/hydrogen-sealing(Stand: 30.04.2024)[5] Barrera, O., Bombac, D., Chen, Y. et al.: Understanding and mitigatinghydrogen embrittlement of steels: a review of experimental, modelling and designprogress from atomistic to continuum. J Mater Sci 53, 6251–6290, 2018.[6] DIN EN ISO 17268:2017-03, Gasförmiger Wasserstoff - Anschlussvorrichtungenfür die Betankung von Landfahrzeugen, S.18www.oup-fluidtechnik.de O+P Fluidtechnik 2025/01 31