Sealing Solutions for H2 Storage

Liquid hydrogen (LH2) is stored at lowest temperatures in cryogenic tanks. Effective insulation and sealing of the tanks is essential. Parker Prädifa offers a wide range of sealing systems made of diverse low-temperature materials for reliable sealing of LH2.

A cryogenic tank serves to store liquid hydrogen (LH2) at -253 °C. Reliable sealing, for instance of the pressure and safety valves or the openings needed for filling or extracting hydrogen, is possible only with specialty sealing solutions. The same applies to sealing the entire line systems and related connectors and valves of the cryogenic tank system. The cryogenic conditions prevent the use of classic rubber or rubber-elastic sealing solutions. Solutions using specialty PTFE or metallic materials are preferably utilized instead. Combined with seal designs specifically developed for cryogenic conditions, these materials enable low-leakage sealing solutions that are not prone to glass-hard embrittlement in cryogenic conditions.

The PTFE sealing solutions preloaded with steel springs (FlexiSeals®) specifically developed by Parker Prädifa or the resilient metal sealing solutions (e.g., C-rings) are perfectly suited for sealing of liquid hydrogen at -253 °C.

After compression, gaseous hydrogen can be stored under high pressure. Irrespective of the type and size of the pressure tanks their leaktightness is of utmost importance.

Gaseous hydrogen can be compressed and stored under high pressure of up to 700 bar and more. Various types of compressors such as piston, cylinder, and diaphragm compressors for high pressures and screw-type compressors for lower pressure ranges are used, depending on volume and pressure requirements. Avoidance of contamination of the hydrogen to be compressed, for instance by lubricants, requires sealing solutions with low friction and low wear in an environment with minimal lubricants.

The compressed hydrogen is subsequently filled into pressure tanks for storage and transportation. The range of storage solutions extends from pressurized gas cylinders to mobile on-board pressure tanks in passenger cars and commercial vehicles to stationary high-pressure tanks with high capacities.

A reliable sealing solution resisting high pressures, explosive decompression, and high temperature fluctuations is required, irrespective of the type and size of the storage tank. The materials used have to exhibit high mechanical strength in order to withstand the risk of gap extrusion in high-pressure conditions. At the same time, low permeation is important to minimize diffusion losses and to prevent the risk of explosive decompression of the material in the event of a sudden pressure drop.

Hydrogen can also be stored and transported by means of liquid carriers known as LOHC (liquid organic carriers) or solid carriers such as metal hydrides. Parker Prädifa offers suitable solutions for the related sealing requirements.

As carrier materials for storing gaseous hydrogen, solids such as metal hydrides or liquids known as  LOHC (liquid organic carriers) are used.

LOHC are liquid organic compounds such as certain thermal oils that chemically bond with hydrogen and exhibit similar storage behavior as gasoline or diesel. Consequently, similar to conventional fuels, the hydrogen stored by means of such carriers can be handled by using existing infrastructure in combination with suitable sealing solutions made of LOHC-compatible materials.  

Storage of gaseous hydrogen in compact solid carriers uses metal hydrides. By means of catalysts and/or pressure, the hydrogen, dissolved in a metal or metal alloy, is stored and released again by reducing pressure and/or by applying heat. Sealing the solid carrier storage systems and their peripheries requires low-leakage sealing solutions to prevent potential safety risks due to hydrogen escaping from the storage system, for instance in poorly ventilated environments.   

For both dynamic and static sealing of threaded connections, valves, housings, etc. of H2 storage systems, seals made of EPDM, butyl, or TPU materials meeting the exacting sealing requirements are available.