The development of hydrogen as a key element for the energy transition also raises questions: About safety and danger of handling and use of hydrogen, and about suitable and innovative ways of storing it.
Sealing of hydrogen
Hydrogen is the most abundant element in the universe. On earth it is predominantly found in compounds (water, hydrocarbons).
Under normal conditions, hydrogen is gaseous. The gas consists of diatomic H2 molecules. It is light and non-toxic, colorless, tasteless and odorless. However, hydrogen is also highly flammable and has the ability to embrittle materials.
Selection of suitable gasket materials
Not only during transport and storage, but also during the operation of plants in which hydrogen is used as a medium, the use of suitable gasket materials is essential for long-term safe and reliable sealing. In addition, media losses not only represent a safety risk, but also cause costs and contribute to global warming.
When selecting sealing materials - regardless of the medium - there are basically two aspects to be considered: The effects of the medium on the leakage of the gasket or seal and the resistance of the sealing material to the medium.
Tightness testing
Gaskets should be chemically resistant, long-term mechanically stable, and reduce media losses to a minimum to enable safe, reliable, and economical operation of equipment including pipe flanges, vessels, valves, etc.
The small size of the hydrogen molecule makes its sealing very challenging when it comes to leakage behavior.
SIGRAFLEX gaskets are and have already been used successfully for many years to seal hydrogen. In order to be able to make well-founded statements on the leak tightness of SIGRAFLEX for hydrogen applications and on the use of sealing characteristics determined with helium also for hydrogen, SGL Carbon had AMTEC Messtechnischer Service GmbH carry out leakage measurements with pure hydrogen in accordance with EN 13555.
The results show that the leakage rates of hydrogen and helium are similar. This means that SIGRAFLEX gasket materials are suitable for safe and reliable sealing of hydrogen. In addition, gasket factors determined with helium as the test medium can also be used for the standard calculation for flange connections for sealing hydrogen.
Are you interested in the measurement results in detail?
Sealing of hydrogen with SIGRAFLEX®, technical information
Chemical resistance
SIGRAFLEX is chemically resistant to hydrogen in the temperature range from -269 °C (-452 °F) to about 900 °C (1,652 °F).
As reinforcement for our gasket sheets, we exclusively use thin smooth or tanged foils made of austenitic stainless steels, in particular CrNi steel 1.4404 (316L), which are among the standard materials for hydrogen technologies.
Due to the installation situation as a flat gasket in the flange, the stainless steel foils are in compression and tensile stresses are negligible. SIGRAFLEX flat gaskets are not susceptible to hydrogen corrosion. They are chemically resistant.
Long-term stability
SIGRAFLEX flexible graphite is manufactured without the use of adhesives and binders. The material does not age or become brittle. Only high-purity natural graphite flakes are used as raw material, thus also minimizing contamination. Its high purity has a significant positive effect on the corrosive resistance.
SIGRAFLEX graphite gasket materials - whether used as die formed packing rings or flat gaskets - are the optimum choice for hydrogen applications. They help to reduce the emission of hydrogen in the long-term, as well as to ensure safe operation of plants and equipment.
When it comes to selecting graphite gasket sheets with long-term stability and optimum leak tightness, we particularly recommend the use of SIGRAFLEX HOCHDRUCK PRO, SIGRAFLEX UNIVERSAL PRO or SIGRAFLEX MF®.
Hydrogen storage
The hydrogen economy faces major challenges: In addition to increasing production volumes and improving the transport infrastructure, these also include long-term and short-term as well as energy-efficient storage. For only in this way can hydrogen find widespread use, as a raw material as well as an energy carrier for industry and mobility.
The storage of hydrogen in pressure gas and liquefied gas tanks has already proved successful. Increasingly, however, more "mobile" processes are gaining in importance, using materials that are suitable as hydrogen carriers or absorption storage. These include metals and metal alloys, carbon, and zeolites. These support the energy distribution concept of hydrogen technology.
New processes often require innovative materials, and this also applies to the storage of hydrogen. When properties such as thermal conductivity, temperature resistance or chemical resistance are required, graphite products from SGL Carbon come into play.
Metal hydride storage (absorption storage) utilizes the ability of metals and metal alloys to adsorb gaseous hydrogen. The hydrogen atoms are deposited in the interstitial sites in the metal lattice; metal hydrides are formed. The metal embrittlement mentioned above is based on the same principle. The hydrogen can be released again by adding heat.
Hydride storage systems have a relatively high mass and hydrogen absorption and release are comparatively slow. However, these disadvantages are outweighed by the safety of the bonded hydrogen (no high storage pressure). The systems are already being used successfully today in special applications such as submarines.
Improved performance of hydride storage systems
Flexible graphite has several key advantages that can be used to improve the performance of absorption storage systems for hydrogen:
- Thermal conductivity
- Hydrogen compatibility
- Purity
- Temperature stability
- Corrosion resistance
This relates to hydrogen charging and discharging, especially the duration of charging and discharging cycles, and heat distribution.
We offer different expanded graphite products for hydrogen storage:
- SIGRATHERM® lightweight boards
- SIGRATHERM GFG graphite powder
- SIGRATHERM flexible graphite foil
- SIGRATHERM graphite expandate
Depending on the requirements of the storage system, our experts will select the suitable material from our portfolio together with you. Contact us!
Components
Further application area
SIGRAFLEX® HOCHDRUCK PRO
SIGRAFLEX® UNIVERSAL PRO
SIGRAFLEX® MF®
SIGRAFLEX MF is best in class when it comes to the separating behavior of graphite flat gaskets. In addition, it meets the very highest demands in terms of mechanical properties, sealability and operational reliability.
Materials
Our products made from flexible graphite – whether foils, sheets, boards or powder – are chemically resistant to hydrogen, long-term stable and show purity and temperature stability. Furthermore, the SIGRAFLEX materials allow for safe, leak tight and reliable sealing of hydrogen.
Find the optimum graphite gasket material!
Let our Product Finder Flexible Graphite guide you to the optimum gasket material for your application.
Brochures, technical data and information sheets as well as approvals and test reports on our SIGRAFLEX products can be found in our Download Center.
