by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Hydrogen Embrittlement and Seal Permeation

What Every Engineer Needs to Know

The hydrogen economy is scaling fast, with global demand for hydrogen expected to double between 2021 and 2030 (Statista). And the growing demand for fuel cells, electrolyzers, pipelines, and green energy storage is all driving demand for hydrogen-compatible hardware.

Here is the problem engineers are facing: hydrogen is uniquely aggressive. It is the smallest molecule in existence, and it attacks both metallic components and elastomeric seals through. That is why it is dangerous for engineers to treat hydrogen as a typical gas and attempt to reuse designs from natural gas or nitrogen service.  Doing so is just setting up a system for premature and potentially catastrophic failure.

Given the importance of the topic, the blog post focuses on hydrogen embrittlement and seal permeation, including the causes and industry best practices for addressing their effects in a hydrogen sealing solution.

Hydrogen Embrittlement in Metal Seals

At metal surfaces, H₂ dissociates into atomic hydrogen at metal surfaces. This atomic hydrogen then diffuses into the metal’s crystal lattice, where it accumulates at grain boundaries, dislocations, and stress concentrations.

While the metal’s yield strength remains unchanged, its ductility and fracture toughness decrease. The metal part can then fail without warning at stresses far below what a standard tensile test would suggest is safe. This phenomenon is particularly dangerous. 

The metals most susceptible to hydrogen embrittlement are high-strength steels above ~1,000 MPa; BCC crystal structures (ferritic and martensitic steels); and hardened fasteners like Grade 12.9, which are notorious. On the other hand, the more resistant metals include austenitic stainless steels (304L, 316L) and nickel-based alloys, as their FCC crystal structure resists hydrogen diffusion more effectively.

One of the best practices for addressing hydrogen embrittlement in metal seals is to use materials with reduced strength levels where conditions allow. For example, steel with an ultimate tensile strength of 800 MPa often outperforms 1,400 MPa steel when it is used in H₂ service. And for wetted components, engineers often opt for austenitic stainless steel. 

Another approach is to control hydrogen-generating manufacturing processes (acid pickling, electroplating) per ASTM A143. Parts can also be baked at about ~190°C within hours of processing to drive out the absorbed hydrogen.

Finally, minimizing stress concentrations on metal seals is another effective approach. The impact of these stress concentrations is significantly greater in hydrogen service.

Seal Permeation and Rapid Gas Decompression with Elastomeric Seals

Elastomeric seals can also be sensitive to hydrogen, but through a different mechanism. Because of their small atoms, hydrogen dissolves into and diffuses through elastomeric seal materials at rates far exceeding other common gases. The permeation is made worse in the presence of elevated pressure and temperature, where a seal can become fully saturated with hydrogen.

When system pressure drops during shutdown or a relief event, dissolved hydrogen tries to exit the elastomer faster than it can diffuse out of the surface, a process known as  RGD (Rapid Gas Decompression). The result is the elastomeric seals experiencing internal nucleation, blistering, and explosive tearing from the inside out. In short, a seal that survives thousands of cycles can be destroyed by a single fast depressurization event.

The most direct way to mitigate the effects of elastomeric seal permeation is to use a material that effectively resists it. Several options are summarized below.

  • FFKM (Kalrez, Perlast) — Excellent: Best all-around performance in H₂ service; highest cost
  • PTFE (spring-energized seals) — Good: Very low permeation rate; requires a different design approach than standard elastomeric seals
  • EPDM — Good: Surprisingly strong RGD resistance; widely used in fuel cell systems
  • FKM (Viton) — Moderate: Adequate at lower pressures but evaluate carefully for high-pressure cycling applications
  • NBR / Silicone — Avoid: High hydrogen permeability; not suitable for H₂ service

Other best practices include controlling the decompression rate by utilizing engineered bleed-down or staged depressurization. In addition, face seals instead of radial seals tend to work better in high-pressure applications. Backup rings are another tool to use, limiting extrusion and preferving the seal geometry. Finally, design the seals in compliance with NORSOK M-710 or ISO 23936-2. Keep in mind that data sheets alone are not sufficient for high-pressure hydrogen duty

Conclusion

Neither hydrogen embrittlement nor seal permeation is a mystery as both are well-characterized and manageable. The engineers who will struggle are those who reach for familiar materials and assume the physics is the same. Here at Advanced EMC, we encourage engineers to know the mechanisms behind these failure modes related to hydrogen service, then select deliberately and test accordingly. And Advanced EMC is here to help you every step of the way. Contact one of our seal solution experts today to explore what your options are and put industry best practices to use.

Best Materials for Spring Energized Seals | Advanced EMC Technologies
by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Why Spring-Energized PTFE Seals Work in So Many Applications

Spring-energized PTFE seals work incredibly well. Engineers know that when designing equipment for truly hostile operational environments, whether facing cryogenic cold, aggressive media, or extreme pressure cycling, the reliability of the seal is absolutely critical. Traditional seals frequently fail under such harsh conditions, suffering from issues such as chemical attack, thermal degradation, or permanent deformation. The proven industrial solution for conquering these critical limitations lies in the PTFE spring-energized seal.

In this blog post, we discuss exactly why PTFE spring-energized seals work so well, including the use of PTFE and spring-energizers, along with a discussion of where these seals are used.

Where Spring-Energized Seals Conquer Extreme Conditions

Before discussing why these seals work so well, it would be wise to quickly review the many different industries and applications in which they have proven themselves. PTFE spring-energized seals have become indispensable across almost every challenging industrial sector because of their unique performance characteristics. Advanced EMC provides solutions for industries including Oil & Gas/Energy, Medical Devices, Aerospace & Defense, Automotive, and Food, Dairy, and Pharmaceutical.

In Oil & Gas and Energy, seals must handle extremely high pressures, sometimes up to 25 kpsi. They must also maintain integrity when exposed to chemically aggressive media such as sour gas and acid gases. In these applications, the PTFE jacket resists the chemicals while the energized springs help keep the seal in place.

For Aerospace & Defense, especially in cryogenic space applications, seals must survive conditions where temperatures drop below -250°C. Traditional elastomeric seals often shrink and lose sealing force at these cryogenic temperatures. PTFE spring-energized seals compensate for thermal contraction and are suitable for applications such as cryogenic fuel transfer and rocket engines. Virgin PTFE and high-purity filled PTFE variants also exhibit minimal outgassing, meeting NASA/ESA standards for use in a vacuum.

In the Medical Device and Pharmaceutical industries, reliability and purity are paramount. Virgin PTFE is both FDA- and USDA-approved. These seals are crucial in fluid management systems, surgical instruments, and diagnostic equipment. They withstand aggressive sterilization processes, including high-temperature Clean-In-Place (CIP) and Sanitize-In-Place (SIP) procedures, due to PTFE’s high thermal stability and chemical inertness. PTFE is also hydrophobic, repelling water and making it easier to clean complex geometries.

The Material Foundation: Why PTFE?

Polytetrafluoroethylene (PTFE), also know as Teflon®, is a synthetic fluoropolymer of tetrafluoroethylene. This material forms the resilient seal jacket, providing excellent chemical and thermal performance. Pure PTFE is almost completely chemically inert, meaning it resists attack from aggressive media such as acids, solvents, and reactive gases, minimizing the risk of degradation or swelling. It is also hydrophobic and non-wetting.

In addition, PTFE boasts an operating temperature range: it is thermally stable enough for continuous service up to 500°F, and certain specialized compounds can function reliably in cryogenic conditions as low as -450°F. PTFE also has the lowest coefficient of friction of any known solid and is naturally self-lubricating, which means it performs well in dry or non-lubricated applications. All of these are reasons to choose PTFE as the seal jacket in a spring-energized seal.

PTFE Spring-Energized Seals Work So Well

The core principle of a spring-energized seal lies in its architecture: a polymer seal jacket housing an internal metallic spring energizer. The spring’s primary job is to apply a continuous force against the sealing surface. This initial force ensures a consistent seal is maintained, especially at low system pressures.

The energizer’s constant force provides permanent resilience to the seal jacket, compensating for operational issues that would cause conventional seals to fail, including:

  • Jacket wear
  • Hardware misalignment and eccentricity
  • Dimensional changes due to thermal contraction or expansion
  • Misalignment

When system pressure increases, the pressure begins to supplement the spring force. This drives the seal lip against the mating surface, resulting in a tighter, highly efficient barrier. The spring design also ensures that the seal maintains force over time, eliminating the problem of permanent deformation or compression set seen in elastomers.

Engineers can select from various spring types to suit specific needs. The V spring (V ribbon spring energized seal) is an excellent candidate for cryogenic and vacuum applications, where coil springs (spiral pitch springs) work well, where low friction and high pressure are involved, typically in medium-speed applications. The helical flat spring is adapted to a wide range of pressures, from high pressure all the way down to vacuum conditions. An elastomeric O-ring energizer can be used when the use of metal must be avoided, and is adapted well to extreme pressures.

Conclusion

Robust, reliable sealing is absolutely necessary in mission-critical operations, regardless of the industry. Spring-energized PTFE seals provide a superior engineering solution. By combining the chemical inertness, wide temperature range, and low friction of PTFE with the persistent mechanical force of a metallic spring, these seals eliminate issues like compression set and loss of sealing force over time. They flex, adapt, and hold their seal integrity even when conditions shift fast.

For applications that demand unparalleled performance where failure is not an option, PTFE spring-energized seals work extremely well as they provide the durability, adaptability, and precision required. When specifying a PTFE spring-energized seal, never take for granted the finish of the mating surface. Advanced EMC Technologies offers expert polymer sealing solutions, leveraging more than 100 years of combined experience. Contact Advanced EMC today to learn how spring-energized seals can improve the reliability and lifespan of your system.