Selecting the right seals and gaskets for hydrogen infrastructure is critical due to the unique challenges posed by hydrogen’s small molecular size, high diffusivity, and potential for embrittlement. The primary criteria for selection include leak prevention, thermal stability, and chemical resistance, with adherence to standards such as ISO 19880-3 ensuring safety and performance.

**Leak Prevention**
Hydrogen’s low molecular weight and high diffusivity make it prone to leakage through microscopic gaps in seals and gaskets. Elastomers and thermoplastics must exhibit low permeability to minimize hydrogen escape. Materials like fluorocarbon elastomers (FKM) and perfluoroelastomers (FFKM) are often preferred due to their dense molecular structure, which reduces hydrogen permeation.

Permeability is quantified in terms of the material’s transmission rate, typically measured in cm³·mm/(m²·day·atm). For instance, FKM exhibits a hydrogen transmission rate approximately 10 times lower than nitrile rubber (NBR), making it more suitable for high-pressure hydrogen applications. ISO 19880-3 specifies permissible leakage rates for hydrogen components, requiring seals to maintain integrity under cyclic pressure conditions.

Compression set resistance is another key factor. Seals must retain elasticity over time to prevent gaps from forming under compression. Materials with low compression set values, such as ethylene propylene diene monomer (EPDM) or FFKM, are preferred for long-term applications.

**Thermal Stability**
Hydrogen infrastructure often operates across a wide temperature range, from cryogenic conditions in liquid hydrogen storage to elevated temperatures in fuel cells or reforming processes. Seals and gaskets must maintain performance without degrading or losing elasticity.

For cryogenic applications, polytetrafluoroethylene (PTFE) and modified PTFE blends are common due to their ability to remain flexible at temperatures as low as -200°C. However, PTFE’s cold flow characteristics can lead to seal extrusion under pressure, necessitating reinforced designs.

At high temperatures (above 150°C), conventional elastomers like NBR or hydrogenated nitrile butadiene rubber (HNBR) may degrade. FFKM and silicone-based materials offer better thermal stability, with some grades capable of withstanding temperatures up to 300°C. Thermal aging tests, as outlined in ASTM D573 or ISO 188, are used to evaluate material performance over time.

**Chemical Resistance**
Hydrogen itself is relatively inert, but infrastructure often involves exposure to other chemicals, such as lubricants, coolants, or process gases. Seals must resist swelling, cracking, or chemical attack to maintain integrity.

FFKM and PTFE excel in chemical resistance, particularly against aggressive media like sulfuric acid or ammonia, which may be present in hydrogen production or storage systems. EPDM is resistant to polar fluids like water or steam but performs poorly with hydrocarbons. Compatibility charts, such as those provided in ASTM D471, guide material selection based on exposure conditions.

Hydrogen embrittlement of elastomers is less common than in metals but can occur in certain polymers exposed to high-pressure hydrogen over extended periods. Testing under simulated service conditions, as per ISO 23936-2, helps identify susceptible materials.

**Material Selection Guidelines**
The following table summarizes key properties of common sealing materials for hydrogen applications:

| Material | Temperature Range (°C) | Hydrogen Permeability | Chemical Resistance | Compression Set Resistance |
|-------------------|------------------------|-----------------------|---------------------|----------------------------|
| FKM | -20 to +200 | Low | Excellent | Good |
| FFKM | -30 to +300 | Very Low | Outstanding | Excellent |
| EPDM | -50 to +150 | Moderate | Good (polar fluids) | Good |
| PTFE | -200 to +260 | Very Low | Outstanding | Poor (cold flow) |
| HNBR | -40 to +150 | Moderate | Good | Fair |

**Standards and Testing**
ISO 19880-3 provides comprehensive guidelines for hydrogen components, including seals and gaskets. Key requirements include:
- Leakage rates not exceeding 0.25 Ncm³/hr per cm of seal diameter at 1.5 times working pressure.
- Material compatibility verified through exposure testing (minimum 1,000 hours).
- Cyclic pressure resistance (minimum 5,000 cycles) to simulate real-world conditions.

Additional standards, such as ASTM D1414 for compression set testing or ASTM D395 for compression deflection, ensure material robustness. Dynamic sealing applications, like those in compressors or valves, may require further validation under ISO 3601 for O-rings or ISO 6194 for rotary shaft seals.

**Conclusion**
Selecting seals and gaskets for hydrogen infrastructure demands a balance of low permeability, thermal stability, and chemical resistance. Fluorinated elastomers and high-performance thermoplastics like PTFE are often the best choices, validated through rigorous testing per ISO and ASTM standards. Proper material selection ensures long-term reliability and safety in hydrogen systems, mitigating risks associated with leakage or premature failure.