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HYDROGEN
Figure 2 – Leakage diagrams according to EN 13555 for material 1 , measured with helium ( left ) and hydrogen ( right ) as a test gas .
the basis for flange calculations according to leakage data , is measured using helium as a test gas . Helium has the advantage that it is an inert gas which in not reactive and does not burn and can therefore be handled without safety concerns . Helium was also chosen as an ideal gas for leakage tests due to its small atom-size , low density and high volatility . Due to these properties , helium is more challenging to seal compared to most other gases . So , the general assumption is that if a gasket material shows a good sealing performance in a helium leak test , it will show at least a similar or even better leakage performance for other , less challenging media like nitrogen or natural gas . However , for hydrogen this assumption might not be true , as hydrogen is extremely challenging to seal due to its low density and small molecule size . Furthermore , hydrogen can be a safety hazard , as it is a very reactive gas which can burn easily and is potentially explosive . Therefore , it is even more important to minimise the emissions as much as possible by using high performance sealing materials . The aim of this report was to
investigate if the leakage performance of fiber-based gaskets is comparable when hydrogen and helium are used as test gases , or if hydrogen is noticeably more challenging to seal .
Fiber reinforced gasket materials There are many different groups of flat gaskets which are suitable for different application conditions . For example , gaskets based on expanded graphite are suited exceptionally well for challenging applications at elevated temperatures up to 550 ° C and high pressures , while PTFEgaskets are ideally suited for applications that are chemically very challenging . These materials have already been investigated regarding their sealing performance in hydrogen applications in previous articles . For this report , we focused on our fiberbased gasket materials . Fiber-based gaskets are composite materials which are comprised of an elastomer binder , often NBR , reinforcing fibers ( mainly aramid-fibers ) and inorganic functional fillers . These gaskets can typically be used for temperature ranges from -100
Figure 3 – Comparison of the loading-curves for the leakage measurements with helium ( blue ) and hydrogen ( green ) for material 1 to + 200 ° C , are suitable for a wide range of different media and can cover most conventional applications . For this report , we investigated the hydrogen leakage rates of two fiber-based gasket materials . These materials represent the newest generation of NBR-bonded fiber-based gaskets and are characterised by their exceptional adaptability and their extremely good leakage performance in standard helium leakage tests . The aim of this investigation is to evaluate if the leakage behaviour for these materials is comparable when hydrogen is used as a test gas instead of helium .
Comparison of hydrogen and helium leakage tests
For this investigation , the leakage rates of two fiber-based gasket materials were determined according to DIN 13555 using helium and hydrogen as test gases ( material 1 and material 2 ). All tests were performed on an TEMES fl . ai1 test device with mass spectrometric detection at room temperature with a test pressure of 40 bar of either hydrogen or helium using gasket specimens in the dimension DN40 / PN40 ( outer diameter : 92 mm , inner diameter : 49 mm ) in a thickness of 2 mm . For the leakage tests , a surface pressure range of 5 MPa to 160 MPa has been applied in cyclic loading and unloading steps , with a leakage measurement after every loading or unloading step . The resulting leakage diagrams with loading- and unloading-curves for the hydrogen and helium measurements of both materials are depicted in figure 2 and figure 4 . For a better comparability , the loading curves of the helium and hydrogen measurements are shown in a simplified diagram in figure 3 ( material 1 ) and figure 5 ( material 2 ). The first material tested is a gasketmaterial with a high compressibility of 18 % according to ASTM F 36 J , which leads
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