Hydrogen gas infrastructure
by Sara McCaslin Sara McCaslin No Comments

The Two Failure Modes That Define Hydrogen Sealing

Hydrogen infrastructure, including electrolyzers, refueling stations, fuel cells, storage and distribution, is rapidly scaling, and seal manufacturers are responding with dedicated hydrogen product lines. But hydrogen is not just “another gas to seal against.” Its molecular size and behavior create two distinct failure modes that do not appear with conventional gases, and a seal rated “hydrogen compatible” on a generic datasheet can still fail in service if the selection does not account for the specific duty cycle.

Failure Mode One: Permeation

Hydrogen has an extremely small molecular size. So small, in fact, that it can diffuse through elastomers far more readily than larger gas molecules; this is a diffusion problem rather than a chemical attack problem: the elastomer is simply not an effective barrier, as opposed to degrading. 

Permeation is a serious issue in hydrogen sealing solutions. It reduces system efficiency by causing hydrogen loss, poses serious safety risks in enclosed spaces, and can, over time, contribute to internal damage as the gas accumulates within the polymer matrix.

FKM generally exhibits lower hydrogen diffusivity than NBR or EPDM, though all common elastomers permeate to some degree. Keep in mind that this is a matter of degree, not absolute barrier vs. non-barrier. There is, however, a better polymer barrier material.

PTFE is virtually inert to hydrogen with markedly lower permeation than any common elastomer, which is why it has become the default choice as pressure and criticality increase

Failure Mode Two: Rapid Gas Decompression (RGD)

Rapid gas decompression (RGD) is the failure mode most specific to hydrogen sealing and the one most likely to be underappreciated by engineers accustomed to conventional gas sealing. In this failure mode, hydrogen molecules that have diffused into the elastomer during sustained high-pressure exposure need time to escape when pressure drops; if depressurization happens faster than the gas can diffuse back out, it becomes trapped and forms internal voids, blisters, or cracks as it expands within the material.

This is also an instance where the failure mode is not solely a chemical compatibility issue. A material can be chemically compatible with hydrogen yet still fail catastrophically under rapid depressurization (RGD) if the duty cycle involves fast pressure drops. This highlights the importance of understanding the kinetics of gas escape and the mechanical response of the seal material.

This is why RGD damage can range from subsurface blistering to structural rupture, especially in high-pressure hydrogen systems such as fueling stations, electrolyzer connections, and pipeline seals. Recognizing these failure modes is essential for preventing field failures during pressure cycling, which are common in applications like rapid fueling or frequent pressure adjustments.

Material Selection Is Not One-Size-Fits-All

Here are some suggested material selections.

EPDM (Ethylene Propylene Diene Monomer)

This is often the default for lower-demand applications, and specifically for alkaline electrolyzers, offering good general hydrogen compatibility and low-temperature flexibility at a reasonable cost. It exhibits excellent low-temperature flexibility, a good compression set, and resistance to alkaline media. However, it has a higher hydrogen gas permeation rate than some other options, namely fluoropolymers such as PTFE. It is primarily used with alkaline electrolyzers (AEL/AEM), water/coolant loops, low-pressure distribution, and low-temperature static seals.

FKM (Fluoroelastomer / Viton)

FKM is favored where chemical resistance matters more broadly (e.g., acidic environments in PEM electrolyzer balance-of-plant). However, it is incompatible with certain hydrogen-adjacent process chemistries, where EPDM may be required instead. It exhibits very low hydrogen permeation compared with synthetic rubbers and has excellent thermal stability across a wide temperature range. However, it becomes brittle at extremely low temperatures, which can lead to leakage during cold thermal cycling. Note that FKM and EPDM are not interchangeable substitutes for each other. It is often used with PEM fuel cells and PEM electrolyzers (oxygen-side/stack sealing), high-temperature gas processing, and high-pressure static connections.

HNBR (Hydrogenated Nitrile Butadiene Rubber )

This material is often specified for fueling-station dispenser seals where low-temperature performance (down to around -40°C) matters, since dispensing frequently involves pre-cooled hydrogen. It has excellent mechanical strength, wear resistance, and extrusion resistance. It is also highly resistant to RGD when compounded properly and retains its flexibility at low temperatures. However, it has a moderate hydrogen permeation rate, and its continuous-use temperature is capped at 300°F. HNBR is commonly used for high-pressure hydrogen valves, compressors, sour gas blends, and pipeline seals, as well as dynamic applications subject to rapid cycling

PTFE (Polytetrafluoroethylene)

PTFE is the default across nearly all pressure tiers once RGD resistance and minimal permeation become priorities. It is inert, low-permeation, and functional across an unusually wide temperature range, though it comes with its own design considerations. It is non-elastic in the sense that it has no inherent memory. It is also prone to creep under continuous pressure loads. Note that it is typically used in energized seal configurations rather than as a standalone elastomer substitute. . It is often used with spring-energized dynamic shaft/stem seals in high-pressure valves, cryogenic liquid hydrogen valves, compressor packing rings, and anti-extrusion back-up rings..

Material Selection and the Duty Cycle

Material selection must consider the actual duty cycle, including pressure cycling frequency, depressurization rates, and temperature swings, rather than relying solely on a generic ‘hydrogen compatible’ rating. For example, two systems operating at the same peak pressure may have vastly different RGD risks depending on their depressurization speed and cycling frequency, which directly impact seal longevity.

Conclusion

Hydrogen sealing involves two key failure modes, permeation and RGD, and understanding these helps engineers feel more equipped to select appropriate materials as infrastructure scales. If you need further assistance finding an effective, reliable sealing solution for your system, contact the sealing experts here at Advanced EMC.

Spring Loaded Seal
by Sara McCaslin Sara McCaslin No Comments

The Overlooked Sustainability Case for Plain Polymer Bearings

Sustainability conversations in engineering tend to focus on the big ideas, such as electrification, renewable energy sourcing, and material recycling, but all at the macro level. On the other hand, component-level design decisions, like bearing selection, are rarely part of that conversation. And this is despite them offering measurable, cumulative impact.

This article will introduce polymer plain bearings as an underexamined contributor to sustainability performance. 

Weight Reduction and Energy Efficiency

Polymer plain bearings are substantially lighter than steel bearings of comparable size and load capacity. In mobile and rotating equipment, that weight reduction translates directly into reduced energy consumption over the equipment’s operating life. Now this is not a marginal, one-time engineering benefit: the weight savings from using a polymer where possible will compound across production volume and service life. This makes the cumulative energy impact larger than it initially appears.  The cumulative energy impact is most obvious in mobile/dynamic equipment.

Elimination of Lubricants 

Many plain polymer bearings are self-lubricating (e.g., PTFE, PEEK, and UHMW PE) either inherently or through the use of solid lubricants incorporated into the bearing material. Such designs do not require grease or oil. This can eliminate a recurring environmental and operational burden by reducing lubricant consumption, disposal, and contamination risks. 

Keep in mind that every eliminated relubrication interval reduces petroleum-based lubricant use, packaging waste, and the handling/disposal requirements associated with spent lubricant. In addition, this reduces the risk of environmental contamination in food, water treatment, and outdoor equipment applications, where lubricant leakage incurs both environmental and regulatory costs. 

The elimination of lubricants through polymer bearings provides an operational sustainability benefit, not just an environmental one. Fewer maintenance interventions for lubrication also reduce associated labor, transportation, and waste streams.

Recyclability and Service Efforts

Certain engineering thermoplastics used in bearings can be recycled at the end of life, including PEEK, POM, and UHMW PE. This is in direct contrast to composite or multi-material metal-bearing assemblies, which are significantly more difficult to separate and reclaim. Keep in mind, of course, that not all polymer-bearing materials are equally recyclable, and reinforced or filled compounds may complicate recycling. This advantage is dependent on the type and grade of polymer selected.

Service life is also a relevant factor: in corrosive, washdown, or moisture-exposed environments, polymer bearings often outlast steel alternatives that require corrosion protection or more frequent replacement. This has the potential to extend the component’s useful life while reducing material turnover. 

Where the Sustainability Case Has Limits

There are boundaries to the sustainability capabilities of plain polymer bearings, however. They are not universally superior. They do have operating envelopes that involve factors such as load capacity, operating temperature, and speed limitations. This means they are not an appropriate substitute for every bearing application. As such, replacing metal bearings with polymer alternatives requires careful evaluation rather than blanket substitution. And while the sustainability case is compelling, it depends on correct application. 

Conclusion

Sustainability in engineering is often achieved through cumulative, component-level decisions rather than singular large-scale initiatives. And that includes the choice of bearings and bearing materials for dynamic machinery and other dynamic applications. Advanced EMC is your resource for engineers evaluating whether a polymer bearing is a viable, sustainability-conscious alternative for your application. Contact us today!