Hydrogen Tech World February 2023 | Page 37

[ sealings ]

1.00E-01

Mass leakage

But does that also apply to hydrogen ?

Leakage ( ml / min ) Leakage ( mg /( s · m ))

1.00E-02

1.00E-03

1.00E-04

1.00E-05

FA-STANDARD

FA-NEW GENERATION

1.00E-06

0 5 10 15 20 25 30 35 40 45 Internal pressure ( bar )

Volume leakage

1.00E + 01

FA-STANDARD 1.00E + 00 1.00E-01 1.00E-02 1.00E-03 1.00E-04 1.00E-05

FA-NEW GENERATION

1.00E-06 1.00E-07 1.00E-08

0 10 20 30 40 50 Internal pressure ( bar )

Fig . 2 . Helium ( dashed line ) and hydrogen ( full line ) leakage curves for FA-NEW GENERATION ( red ) and FA-STANDARD ( blue ) at 30 MPa installation surface stress

employs a mass spectrometer for the fine leakages with a sensitivity equivalent to the latter test .

Note that all the aforementioned standard test methods call upon either nitrogen or helium gas as the test medium ( non-hydrogen environments ). In general , it is commonly accepted that if the sealability threshold is determined for helium or nitrogen , this would be valid as well for methane ; in practice , it is admitted that a gasket material with an L0.1 tightness class for helium could serve to tightly seal other gases too .

New test system for determining H ₂ leakage

From DONIT R & D Application Engineering labs , a gasket testing setup for hydrogen permeability emerged in 2021 ( Figure 1 ). Its design is based on a further improvement of the VDI2440 / 2200 standard . This well-established standard can now be extended to the testing of sealing materials for their hydrogen permeability and resistance .

Gasket materials for He & H ₂ gases

Gasket permeability to helium or hydrogen was performed on representative soft gasket materials : TESNIT ^® BA-U ( FA-STANDARD ) and TESNIT ^® BA-SOFT ( FA-NEW GENERATION ). These materials are based on aramid fiber with NBR .

FA-STANDARD represents gasket material with low compressibility of 6 – 9 %, well-suited for gas ( air , methane , propane , butane ) installations , while FA-NEW GENERATION represents a material with compressibility of ~ 25 %, high adaptability and sealability with very good thermomechanical properties .

Mass and volume leakages of FA-STANDARD and FA-NEW GENERATION were determined under 30 MPa of surface stress and 5 – 40 bar internal pressure . Figure 2 shows the comparison between leakage values of helium and hydrogen as mass and volume leakage of FA-NEW GENERATION . The gasket was installed with 30 MPa surface pressure . The leakage

Table 2 . Data of some fluids

Hydrogen H ₂

2 289 1.1 1.4 Helium He 4 260 1 1 Nitrogen N ₂

28 364 1.4 0.37

Hydrogen Tech World | Issue 8 | February 2023 37