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Hydrogen places different demands on seals than many conventional gases. Not because every elastomer is immediately chemically affected, but because hydrogen, due to its small molecular size, can permeate more quickly, escape more easily through minimal gaps and create additional stress on O-rings and other seals during pressure fluctuations.
That is why an O-ring for hydrogen systems requires more than just a standard material choice. Pressure, temperature, media purity, gland design, compression set, hardness, backup rings and compound validation all play a role. Especially in high-pressure hydrogen, refuelling stations, compressors and storage applications, it is important to look not only at the material family, but at the complete application.
At O-ring-stocks.eu, we help select O-rings and sealing materials for hydrogen applications. From electrolyzers and compressors to hydrogen storage, pipelines, refuelling stations and fuel cells.
O-rings are used in many places throughout the hydrogen chain. Think of valves, filters, couplings, sensors, pumps, pressure regulators, manifolds, tank bosses, dispensers and balance-of-plant components around electrolyzers and fuel cells. The load varies greatly from one component to another.
In an electrolyzer environment, moisture, temperature and chemical secondary media can be important. In a compressor, dynamic movement, heat generation and rapid pressure changes play a larger role. In storage and refuelling stations, the challenges mainly involve high pressure, low temperature, pressure cycles and leak-tightness. A hydrogen O-ring must therefore always be selected based on the application, not just the material.
For low- and medium-pressure sections, an elastomer O-ring can be a suitable solution. At extreme pressure, with cryogenic hydrogen or in dynamic sealing applications, PTFE, thermoplastic seals, spring-energized seals or metal seals are sometimes more logical.
Hydrogen is a small molecule. As a result, it can diffuse through elastomers more easily and escape more quickly through small openings or an unfavourable fit. A seal that performs well with air, nitrogen or water is therefore not automatically suitable for Hâ‚‚ service.
The main points of attention are:
Especially with high-pressure hydrogen, the design of the seal is just as important as the material. A suitable compound can still fail if the groove geometry, gap size, depressurisation or support is not correct.
Permeation is one of the best-known challenges in hydrogen sealing. Hydrogen can dissolve into the elastomer, diffuse through the material and emerge again on the other side. The extent to which this happens differs per material and compound. EPDM, FKM, NBR, HNBR, FFKM and PTFE all behave differently under Hâ‚‚ exposure.
In addition, rapid gas decompression, also referred to as RGD or explosive decompression, is an important failure mechanism. At high pressure, for example in a hydrogen compressor, hydrogen can be absorbed into the elastomer. If the system pressure then drops quickly, the trapped gas wants to expand. This can lead to blistering, internal cracks or damage to the O-ring.
At high pressure, extrusion also plays a role. The O-ring can then be pressed into the gap between two metal parts. In such situations, harder compounds, correct groove dimensions and PTFE backup rings are often necessary. Especially in static high-pressure connections, valves, filters and tank components, this can be decisive.
At low temperature, the problem changes. Elastomers become stiffer and lose part of their resilience. With liquid hydrogen, around cryogenic temperatures, classic elastomer O-rings are usually not the right primary seal. In that case, the choice often shifts towards PTFE, thermoplastic or metal seals.
There is no universal “best” O-ring material for hydrogen. The right choice depends on pressure, temperature, medium, movement, cleanliness requirements, pressure fluctuations and the available compound data.
EPDM can be interesting in low- to medium-pressure sections, wet environments and certain balance-of-plant applications. The material often has good low-temperature properties and performs strongly in water- and steam-like environments. At the same time, EPDM can allow relatively high hydrogen permeation, which means it is not automatically the best choice when minimal permeation is the leading requirement.
FKM / Viton often has lower hydrogen permeation than EPDM and performs strongly at higher temperatures and in chemically broader applications. Even so, FKM must be assessed carefully in high-pressure hydrogen. During rapid decompression or severe pressure cycles, swelling or internal damage can occur, depending on the compound and design.
HNBR is mechanically strong and wear-resistant. This can make it interesting in applications with higher pressure or mechanical load. Compound validation is important, however, because the available open data per HNBR compound is limited and behaviour under RGD, ageing and dynamic load can vary greatly.
NBR can be usable in some hydrogen applications, but is usually not the first choice for critical Hâ‚‚ systems with high pressure, broad temperature windows or demanding service-life requirements. Suitability must always be assessed at compound level.
FFKM offers very broad chemical resistance and is suitable for demanding environments where temperature, purity or chemical load are dominant. Due to the high cost and compound-dependent Hâ‚‚ performance, FFKM is mainly logical when the application truly justifies it.
PTFE is chemically very inert and is often used for backup rings, seats, jackets or spring-energized seals. PTFE behaves differently from elastomers and does not have a classic elastomer RGD mechanism, but it can be sensitive to creep or cold flow. It is therefore especially strong when the design is adapted to this.
AFLAS / FEPM can be relevant in chemically more demanding process environments, for example around alkaline media, steam, amines or wet process gas sections. Validation remains necessary for extreme hydrogen pressure or rapid pressure cycles.
In the production phase, for example in electrolyzers, O-rings are mainly found in balance-of-plant components. Think of filters, pumps, valves, measurement ports, separators and maintenance covers. The seal often has to deal with moisture, temperature, proximity to oxygen or electrolytic media here.
In hydrogen compressors, seals are subjected to heavier loads. Dynamic movement, heat, wear, pressure build-up and depressurisation make standard O-rings less straightforward. In many compressor applications, PTFE or thermoplastic seal concepts, possibly with spring energisation, are more suitable than a standard elastomer O-ring.
In storage and pressure vessels, O-rings are used in valves, tank bosses, sensors, filters, connectors and service points. High pressure, temperature cycles and microleakage are important points of attention here. Backup rings, harder compounds and validated gland geometry are often required.
In pipelines, couplings and fittings, the focus is mainly on installation reliability, vibration resistance and leak-tightness. O-ring face seals, ORFS couplings and compact high-pressure connections require precise fitting and material selection.
In hydrogen refuelling stations, O-rings are used in nozzles, receptacles, breakaways, filters, high-pressure valves, sensors and dispensers. This environment combines high pressure, low temperature, many cycles and strict safety requirements. That makes it one of the most demanding application areas for hydrogen seals.
In fuel cells, O-rings are found in control valves, purge valves, drain valves, sensors, manifolds and balance-of-plant components, among others. The pressure here is often lower than in storage or refuelling stations, but purity, moisture, temperature and service life remain important.
Validation is essential for hydrogen seals. Material names such as EPDM, FKM or HNBR provide an initial direction, but they do not yet say enough about actual performance in a specific application.
For high-pressure hydrogen, standards and test frameworks around Hâ‚‚ permeation, material compatibility, refuelling stations, valves and system leak tests are relevant, among others. Think of ISO 19880-7 for rubber O-rings in high-pressure hydrogen refuelling stations, DVGW ZP 5101 for Hâ‚‚ permeation assessment of elastomers and ISO 11114-2 as a qualitative compatibility basis for non-metallic materials.
It is important that material tests are not a complete replacement for component or system tests. A compound may appear suitable on paper, but can still fail due to incorrect groove dimensions, rapid depressurisation, temperature cycles or dynamic load. For critical hydrogen applications, supplier data on permeation, RGD/ED, compression set, low temperature and leakage after cycles is therefore strongly recommended.
Are you working on a hydrogen system and want to know which O-ring or seal is suitable? Then it is wise to first map out the application technically. Think of medium, pressure, temperature, pressure fluctuations, movement, groove dimensions, cleanliness requirements and desired service life.
O-ring-stocks.eu helps select O-rings and sealing materials for hydrogen applications. We advise on material selection, compound direction, backup rings and practical availability.
Contact us for advice on O-rings for hydrogen systems or discuss your application directly with a specialist.
That depends on the application. Pressure, temperature, medium, pressure fluctuations, groove design and compound validation determine which O-ring is suitable. EPDM, FKM, HNBR, FFKM, PTFE and AFLAS can all be relevant, but not for the same application.
EPDM can be suitable in certain low- to medium-pressure applications and wet environments. However, the material can allow relatively high hydrogen permeation. That is why EPDM must always be assessed at compound level and by application.
FKM / Viton can be interesting because of its low permeation and good temperature resistance. At high pressure and during rapid decompression, caution is needed because RGD damage or swelling can occur. Validation is therefore important.
Rapid gas decompression occurs when gas under high pressure penetrates an elastomer and then expands due to a rapid pressure drop. This can cause blisters, cracks or internal damage in the O-ring.
Backup rings are especially relevant at high pressure, large pressure differences or when there is a risk of extrusion. They mechanically support the O-ring and help prevent the material from being pressed into the gap.
Not automatically. With high-pressure hydrogen, compound validation, hardness, groove geometry, gap control, RGD resistance and test data are important. A standard O-ring without Hâ‚‚ validation is usually not a safe starting point.
Common materials include EPDM, FKM, HNBR, FFKM, PTFE and AFLAS/FEPM. In cryogenic or highly critical applications, thermoplastic or metal seals may be more suitable.
