O+P Fluidtechnik 1/2025

DICHTUNGENINFLUENCE OF

DICHTUNGENINFLUENCE OF HYDROGEN ON THE MATERIALPROPERTIES OF NON-METALLIC MATERIALSFOR SEALING APPLICATIONSTrelleborg Sealing Solutions offers its comprehensiveH2Pro sealing portfolio of proven components forhydrogen applications across the entire value chain fromproduction, to transport and storage, and end-useFORSCHUNG UND ENTWICKLUNGPhoto: Trelleborg Sealing SolutionsHydrogen entails challenging conditions for all sealing materials. For metals, the effectof hydrogen embrittlement is well known. However, little attention has been paid toelastomers and plastics, which are commonly used as sealing materials. For hydrogenstorage and transport, high pressures and extreme temperature situations must becovered. This paper discusses the influence of hydrogen on mechanical properties,volume and weight change as well as compression set. Additionally, the influence ofextreme application temperatures on mechanical properties is presented. In generalhydrogen has no harmful influence on the compounds presented in this study, whichare known as polymers suitable for hydrogen use.1 INTRODUCTIONThe hydrogen market is experiencing rapid growth due to variousfactors such as the need for low-emission mobility, political supportand funding [1], as well as technological advancements. It isestimated that the hydrogen market‘s turnover could reach 840 billioneuros by 2050, potentially creating 5.4 million jobs [2]. In addition,the share of hydrogen in global final energy consumption isprojected to increase to 19 percent by 2070, which would translateto an annual hydrogen production of 1,084 million tons [3].However, the use of hydrogen poses certain technical challenges,especially in terms of sealing technology, as different requirementsare imposed on seals and materials throughout the entirehydrogen value chain, including production, storage, transportation,and end applications such as fuel cells or combustion [4].The development of hydrogen seals faces a significant hurdledue to the absence of meaningful global industry standards. Thehydrogen industry sometimes utilizes specifications that are intendedfor high-pressure gases in the oil and gas sector, such asNorsok M-710. However, these standards do not accurately representthe actual conditions of hydrogen applications. A comprehensiveanalysis of the standards landscape found that only alimited number of specifications are geared towards elastomersand plastics, which are commonly classified as non-metallic materials.The tests that are typically cited include:n Oxygen ageing (according to ASTM D572)n Ozone ageing (according to ISO 1431)n Hydrogen compatibilityHowever, the fundamental question of how hydrogen impacts thematerial properties of sealing materials is still not answered. Hydrogenis not an aggressive gas, but it diffuses easily into non-metallicmaterials such as elastomers and plastics. It is thereforecrucial to understand how sealing materials are affected by theabsorbed hydrogen molecules. This will help to determine if a26 O+P Fluidtechnik 2025/01 www.oup-fluidtechnik.de

DICHTUNGENcomponent is “hydrogen ready”. If components and systems needto be redesigned to make them fit for hydrogen, it can cause significantcosts in some cases.2 MATERIAL PROPERTIES RELEVANT FORHYDROGEN SEALINGFor metals the effect of hydrogen embrittlement is well-knownand is the subject of many studies. This phenomenon can significantlyreduce the ductility and load-bearing capacity, causingcracking and catastrophic brittle failures at stresses below theyield stress [5]. A frequently asked question from designers whoare used to working with metal is how much sealing materials willembrittle or change under the influence of high-pressure hydrogen.Especially in the field of hydrogen storage and transport, sealsmust be able to withstand extreme temperatures and pressures.When exposed to certain fluids or gases such as hydrogen, elastomersand thermoplastic materials may undergo changes intheir physical and chemical properties, consequently affectingtheir performance and durability. Therefore, it is important to testthe compatibility of the sealing material against hydrogen when itis planned to use them in a hydrogen-related application.First, it is important to know which material properties can beaffected by hydrogen. Secondly, there is a need to understandwhich of these properties are relevant to ensure a good sealingfunction. This study will investigate how the most relevant parameterschange under the influence of hydrogen.2.1 MECHANICAL PROPERTIESMaterial behavior is typically characterized by mechanical propertiessuch as tensile strength, stiffness modulus and elongationat break. These universal characteristics need to be investigatedfor both elastomers and plastics.Another important parameter which is relevant for a reliablesealing function is the change in weight and volume. Due to thesmall size of hydrogen molecules, diffusion into the polymer matrixis inevitable and will cause swell. In real applications, this canbecome critical if the sealing groove is overfilled, leading to damageof the sealing material or the surrounding hardware. However,shrinkage can be more concerning as it can easily cause leakagein sealing applications. Since hydrogen diffuses easily intothe polymer matrix, it will also escape after pressure releases.Therefore, it is vital to differentiate between reversible swell,which is important for the design of a sealing system, and permanentvolume change, which indicates changes in the polymer.If weight loss is present, it means part of the polymer was extractedand is now floating in the hydrogen gas, indicating that materialproperties are most likely changed. Additionally, this couldresult in damaging sensitive downstream systems like fuel cells.Furthermore, for elastomer sealing the change of hardness andcompression set are crucial to understand if hydrogen affects thesealing properties of a compound. For plastics this is not relevant,because the plastic seals are typically activated by pressure, metalsprings or elastomer energizers. Compression set describes theloss of elasticity, meaning the permanent deformation that remainsafter a seal has been compressed over a longer period oftime. When selecting a sealing material, it is important to ensurethat compression set is still in an acceptable range consideringthe influence of the surrounding media.0102Compatibility test pressure chamberChange of volume, weight, tensile strength and elongationat break of different compounds after immersion in H2 for168 h at +23 °C and 70 MPa2.2 TEMPERATURE-RELATED MATERIAL PROPERTIESEspecially for elastomers, the temperature limits are very importantto consider when selecting a compound. At very low temperaturesthe elastomer will not only shrink, but also lose its elasticity,resulting in leakage. The lower temperature limit is determinedby the glass transition temperature T Gand by the T R10value.The latter describes the temperature at which an elastomerhas 10 percent of its elasticity, which is the minimum requirementfor a good sealing function. In combination with high pressures,these limits will increase, commonly known as T G-shift. Formost elastomers the T G-shift lies in the range of two to three Kelvinper 10 MPa pressure increase. Since this phenomenon is independentof the media and not specific for hydrogen only, it willnot be considered in this study.www.oup-fluidtechnik.de O+P Fluidtechnik 2025/01 27