HYDROGEN
Figure 4 – Leakage diagrams according to EN 13555 for material 2 , measured with helium ( left ) and hydrogen ( right ) as a test gas .
to an excellent adaptability to the flange surface , and therefore a good leakage performance . For the fiber-based gasket material 1 , the leakage value for the hydrogen measurements is slightly lower than for the helium measurements when the gasket stress is below 60 MPa . The leakage class L 0 , 01
, which is the limit value of the German TA-Luft regulation , is reached at a gasket stress of 17 MPa for helium , and 15 MPa for hydrogen . For gasket stress levels higher than 60 MPa , the leakage value for helium is slightly lower compared to hydrogen . However , the general trend of the leakage values for the loading and unloading curves are very similar to each other , which indicates that it is not significantly more challenging to seal hydrogen , compared to helium . The second fiber-based gasket material which was tested for this report ( material 2 ) is a gasket material which is exceptionally soft and has an excellent adaptability to the flange surface ( compression according to ASTM F 36 J : 39 %). This material has been designed specifically for reaching extremely low
leakage values even at low gasket stress . So compared to material 1 , material 2 shows an even better leakage performance in the standard helium leakage test according to EN 13555 . The tests in this report show that this behaviour also remains valid for leakage tests with hydrogen . For material 2 , the leakage class L 0 , 01 is already reached at 7 MPa for hydrogen and helium . The leakage curves for the hydrogen and helium measurements are almost identical for low gasket stress until 20 MPa . The leakage rate 10 -6 mg /( m * s ) is reached at an assembly stress of 27 MPa for the helium measurement . For hydrogen measurements with the standard test procedure , 10 -6 mg / ( m * s ) is the detection limit of the mass spectrometer , which is used as a detector in the test apparatus . This explains the increasing difference of the measurements with hydrogen and helium for higher assembly pressures . The leakage rate of the helium measurements is constantly decreasing with higher gasket stress , while the hydrogen measurement cannot fall below the value of 10 -6 mg /( m * s ) due to the detection limit of the hydrogen mass spectrometer . However , the fact that the results for low gasket stress are identical for hydrogen and helium indicates that in this case , the sealing behaviour is also very similar for hydrogen and helium .
Summary
The results of these investigations show that the leakage data measured with helium and hydrogen according to EN 13555 are very similar to each other . These results are also in line with previous reports for graphite and PTFE gaskets that have been published in previous issues of this magazine . Of course , there are many different fiber-based materials with different properties and different leakage performances , so this report cannot fully prove that hydrogen and helium show a similar behaviour in leakage tests for all materials . However , due to the similar composition of fiber-based materials and the results of the materials that have been tested so far , one can assume that the wellestablished helium leakage tests according to EN 13555 can also be used as a basis for calculation for most hydrogen applications .
About the author Anna Berger is a chemist and joined the R & D department of Frenzelit five years ago , after finishing her PhD in Organic Chemistry . She now works as an application engineer for the Industry Division of Frenzelit GmbH and
Figure 5 – Comparison of the loading-curves for the leakage measurements with helium ( blue ) and hydrogen ( green ) for material 2 . The detection limit for the hydrogen measurements is depicted in red . is a member of the ESA Flange Gasket Division .
24 Valve World February 2025 www . valve-world . net