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Sealing Selection for Hydrogen Applications
When considering the vast array of hydrogen applications, several critical requirements for sealing systems emerge. These requirements can vary in importance depending on the specific application. Key factors include:
- Low permeation and/or leakage
- Good pressure resistance
- Good chemical resistance
- Temperature resistance
- Long service life
- Technical cleanliness and purity
Low permeation and/or leakage for hydrogen applications
Seals are never completely gas-tight, which is particularly crucial for flammable gases like hydrogen. Hydrogen's small molecular size increases its permeation rate and risk of interfacial leakage compared to other gases. Effective sealing designs must address:
- Suitable sealing area design with the required surface quality
- Seal design that generates sufficient contact pressure to close micro-channels
- Selection of a sealing compound with low permeation
Pressure resistance
High pressures can lead to extrusion or rapid gas decompression of sealing materials. Rapid gas decompression occurs when pressurized gas diffuses into the sealing material and expands rapidly during a sudden pressure drop, causing material failure. Extrusion happens when the sealing material is pushed into the gap between sealing surfaces, shearing off if inner strength is exceeded. Solutions include:
- Reducing gap size through design
- Using backup rings
- Selecting materials with good mechanical strength, such as our TPU compound P5009 (see table)
Chemical resistance for hydrogen applications
Most sealing materials exhibit good chemical resistance to hydrogen. Swelling observed in materials under hydrogen pressure is due to hydrogen diffusion, not chemical interaction. This is usually a reversible process unless excessive stress, like rapid gas decompression, occurs. Additionally, sealing systems often need to resist other media like coolants, lubricants, or electrolytes, which can pose greater challenges than hydrogen itself.
Cleanliness and purity for hydrogen applications
The performance of sealing systems also depends on their chemical purity. Contaminants or foreign particles from the sealing system can clog delicate components in hydrogen applications, such as fuel cells, leading to reduced performance or corrosion. Ensuring pure compounds and additional cleaning steps in the manufacturing process is crucial for sensitive applications.
Temperature resistance for hydrogen applications
Low-temperature resistance
Applications involving cryogenic hydrogen storage or transport demand sealing systems with excellent low-temperature resistance. Elastomeric materials can become brittle below their glass transition temperature, losing their elasticity and sealing performance. For temperatures below ‑60 °C, specialty elastomer compounds are required, and for even lower temperatures, PTFE or metal sealing solutions are used.
High-temperature resistance
For applications with temperatures above 250 °C, such as reaction furnaces or pyrolysis systems, elastomeric materials are unsuitable. PTFE sealing solutions may be used up to around 300 °C, but for higher temperatures, metallic sealing solutions are necessary.
Service life for hydrogen applications
Long-term reliability is paramount for sealing systems. Thermal, chemical, and mechanical aging can degrade material properties over time. Selecting suitable compounds with adequate reserves can ensure reliable performance for 10 to 15 years or longer, despite the inevitable aging processes.
The original article can be found on Parker's website.
Gallagher Fluid Seals is a premier distributor for Parker Sealing. For more information about seals for hydrogen applications, contact us today.
