Qualification of metallic materials in a hydrogen atmosphere under cyclic loads

The corresponding hydrogen infrastructure is of central importance for the successful ramp-up of the hydrogen economy. This is because the transformation to a hydrogen economy will only succeed if hydrogen can be transported safely from the production and import centers in the north to the consumer centers in the south. In principle, the conditions in Germany are very good due to the well-developed gas network, but hydrogen can have a negative impact on the strength and brittleness of metallic materials, particularly at the connection points of the pipelines. To prevent this, Hartmann Valves GmbH, the German Institute of Rubber Technology and the Institute of Materials Science (IW - Leibniz Universität Hannover) are working on a project funded by the state of Lower Saxony to develop a composite material that is resistant to embrittlement and will enable a permanent seal.

With a length of 500,000 kilometers and numerous gas storage facilities, the gas pipeline network in Germany offers enormous potential for storing hydrogen produced from renewable sources. It is therefore obvious that the existing infrastructure should continue to be used as part of the energy transition and be converted to hydrogen.

However, the mechanical material properties of the metals used - especially at the joints of the pipes - can be reduced when hydrogen is passed through. This can ultimately lead to material failure, which must be ruled out for safety-relevant infrastructure. Materials that are resistant to embrittlement are therefore required, particularly for the so-called "flange connections", which connect the individual components and pipes of the natural gas network.

It is precisely these materials that are being developed as part of the project "Qualification of metallic materials in hydrogen atmospheres under cyclic loads". "In the project, we want to develop a hydrogen-tight flexible coating that remains reliably tight even at higher thermal expansions and vibrations of the hydrogen transport system. This should prevent premature ageing of the steel as a result of hydrogen embrittlement," says Christian Hartmann, Managing Director of project partner Hartmann Valves GmbH.

To this end, the project is pursuing various sub-goals. Firstly, sub-goal 1 is to "qualify" the metallic materials, i.e. test their suitability for hydrogen applications under cyclic stresses. This is intended to develop limit values for the maximum stress.

In sub-objective 2, a dimensionally stable but elastic plastic(nanocomposite) is being developed and tested that can withstand cyclic loading due to its elasticity. A filler is also being developed so that hydrogen cannot penetrate the material. The coating should ultimately ensure that contact between the critical flange connection and the so-called "hydrogen atmosphere" within the pipe is reduced. "The newly developed material is highly impermeable to small molecules such as hydrogen. We achieve this impermeability through specially developed manufacturing processes and the use of suitable innovative materials that have a high barrier effect against hydrogen," says Prof. Ulrich Giese from the German Institute of Rubber Technology, explaining the special features of the project.

In order for the coating process to be successful, sub-objective 3 aims to enable adhesion between the plastic (from sub-objective 2) and the metal on the inside of the fittings. Finally, a fatigue test rig is to be developed in sub-objective 4, which maps cyclical mechanical influences on the material and at the same time takes into account the effect of hydrogen on the material. This will ensure that the newly developed components can be used in existing infrastructure.

Prof. Hans Jürgen Maier from the Institute of Materials Science at Leibniz University Hannover emphasizes the importance of the project for the ramp-up of the hydrogen economy: "With this project, we want to contribute to increasing safety in the storage and transport of hydrogen. In the future, the knowledge gained can serve as a basis for repurposing existing components for hydrogen applications and thus contribute to the development of a safe and resistant hydrogen infrastructure"

The project is being carried out by Hartmann Valves GmbH, the German Institute of Rubber Technology and the Institute of Materials Science (IW) at Leibniz Universität Hannover and is due to be completed by fall 2025. The state of Lower Saxony is funding the project with almost 800,000 euros.