Session: 12-01: Hydrogen Energy, Alternative Fuels, Bioenergy, and Biofuels

Paper Number: 130823

130823 - Leak Tightness of Valves for the Hydrogen Industry 

Abstract: 

The emerging hydrogen industry requires an infrastructure for the transportation and storage of hydrogen. This includes the need for valves suitable for the handling of gaseous or liquified hydrogen. However, conventional metal and polymer-based valves are often not suitable for hydrogen applications due to the permeation of gaseous hydrogen into the sealing material of the valve. In most alloys and steels, this can lead to hydrogen embrittlement, which can cause the seal to fail under cyclic loading. In the case of polymers, pressure drops will cause the embedded hydrogen to expand and thus can cause cracks to form, destroying the sealing. Further challenges in sealing technology for hydrogen are the wide temperature and pressure ranges and the low hydrodynamic viscosity of hydrogen.

Metallic sealings are robust against cracking due to pressure drops and, in the case of austenitic stainless steels, resistant to hydrogen embrittlement. However, the low viscosity of hydrogen poses a great challenge to the tightness of the valve. Known methods to describe leakage of metallic sealings typically assume liquids or ideal gases. However, these methods are not able to deal with the leakage of pressurized gaseous hydrogen, as the ideal gas approximation is not valid under the conditions in metallic seals. For these reasons, there is a need for research into the tightness of valves against hydrogen.

This work introduces a simulation describing the leakage of hydrogen in a rough metallic sealing gap. It considers the contact mechanics and the leakage model developed by B. N. J. Persson. This model is based on the surface power spectral density and makes it possible to calculate the leakage considering the elastoplastic deformation of the roughness asperities.

The flow model implemented in this work is based on an orifice equation, which has been modified for real gases. The calculated leak rates for different surfaces are then compared with experimental results.

The leakage experiments are performed by measuring the pressure drop over time on reference valves with different sealing surfaces, which must be attached to a well-defined reference volume. These leak tests are performed using inert forming gas, which is a mixture of hydrogen and nitrogen, as a replacement for pure hydrogen for safety reasons. Using a hydrogen detector, it is possible to detect even very small leakage rates.

Due to this simulation validation, it is possible to show whether existing methods of leakage calculation on metallic seat valves in pneumatic systems are also suitable for hydrogen. The presented methods can be used to develop and optimize metallic seals for hydrogen applications.

Presenting Author: Felix Fischer RWTH Aachen University

Presenting Author Biography: Felix Fischer completed a Bachelor's degree in Physics from 2014 to 2017 and a Master's degree in Theoretical Solid State Physics from 2017 to 2019 at RWTH Aachen University.
Currently, since 2019, he serves as a research associate at the Institute for Fluid Power Drives and Systems at RWTH Aachen University, specializing in Tribology.
As part of the VDMA research grant "Air2H2", Mr. Fischer conducts research on developing and evaluating the leak-tightness of valves used in the hydrogen industry. His research centers around investigating the influence of rough surfaces in seals on valve tightness and longevity.

Authors:

Felix Fischer RWTH Aachen University
Katharina Schmitz RWTH Aachen University