LEAK TESTING OF COMPONENTS

Hydrogen Tanks
DESCRIPTION OF TECHNICAL CHALLENGE
Fuel cell vehicles (FCVs) typically use Type IV tanks for hydrogen storage. TypeIV tanks are composite tanks of carbon fiber with a polymer liner. Storage
pressure are typically in the range of 350 – 700 bar. Hydrogen tanks for FC
buses often use 350 bar hydrogen tanks, passenger vehicles mainly use 700
bar storage pressure.
Safety regulations (ISO/TS 15869) require that hydrogen tanks are tested forleakage / permeation. Permeation rates are measured as Normal liter ofH2/time in hr/volume of the tank. Different standards define slightly different
maximum allowable permeation rates. Any leak rate that is higher than themaximum allowable permeation rate is consider a leak. Typical maximum
allowable permeation rates range in the 10-2 mbar l/s decade. However,
manufacturers often achieve permeation rates of about ten times lower
permeation, i.e. in the 10-3 mbar l/s range. Hence, leak rate limits are set in the10-3 … 10-2 mbar l/s range.

THE INFICON SOLUTION

Type IV composite tanks are typically usedfor hydrogen storage in fuel cell vehicles.

Integral testing of tank body
The required leak rates may indicate that these could be detected with pressure
leak testing (pressure decay). However, this proofs to be impossible due to therather large volume of the parts. Any minimal change in temperature during thetesting cycle – even with temperature compensation - will result in a rather largechange in pressure, either causing a false positive or hiding a potential leak.
For tank testing applications during the production process, the vacuum
chamber method and the accumulation chamber method differ slightly in testingtime and investment cost. The choice between the two methods should bebased on the size of the test sample, the used test gas mixture and the testing
application.
Hydrogen tanks are typically tested via helium vacuum chamber leak testing toachieve short cycle times and high throughput. Due to the large volume of thetanks and the rather large allowable leak rates, typically helium mixed with air
is used as tracer gas. The hydrogen tank is filled with a small amount of helium
first and then backfilled with air to operating pressure so that the resulting gas
mixture in the tank contains about 5 – 10% helium. The hydrogen tank is thenplaced in a vacuum chamber. The chamber is evacuated and once the final
vacuum pressure is reached, an LDS3000 leak detector is connected to thevacuum chamber and helium escaping from the hydrogen tank is detected by
the LDS3000. The threshold leak rate needs to be adapted to the used helium
concentration in the tracer gas. The used tracer gas can be reclaimed forconsecutive testing.

Hydrogen tank bodies are tested by
vacuum chamber testing for highthroughput manufacturing.

LEAK TESTING OF COMPONENTS
HYDROGEN TANKS

Hydrogen tanks may also be tested by accumulation leak testing with slightly
lower productivity. Accumulation testing allows for the use of either helium,
typically again mixed with air to save cost, or forming gas, a non-flammable 5%hydrogen in 95% nitrogen gas mixture. The hydrogen tank is filled with therequired amount of tracer gas first. The hydrogen tank is then placed in an
accumulation chamber. In case of a leak, the escaping tracer gas will cause arise of concentration in the accumulation chamber. This rise in concentration isdetected by an LDS3000 AQ leak detector and an alarm is given if a thresholdleak rate is exceeded. The threshold leak rate needs to be adapted to the usedhelium concentration in the tracer gas. The used tracer gas can be reclaimed forconsecutive testing.

Hydrogen tank bodies are also tested inan accumulation chamber in lower
throughput manufacturing.

Leak testing of assembled hydrogen tanks
Once the hydrogen tank body is assembled with fittings and connectors thesejoints are tested for leaks typically by hydrogen sniffing. Also welds of different
parts of the body can be tested this way.
For the sniffing test the assembled hydrogen tank is filled with forming gas – a
non-flammable 5% hydrogen in 95% nitrogen gas mixture. The sniffer probe of a
Sensistor Sentrac hydrogen leak detector is then guided along potential leaklocations. If forming gas escapes from any leaks, it is detected by the sniffer probe
and the leak detector will alarm. This allows for the leaks to be exactly locatedand the leak location can be reported to any rework stations.
Assembled hydrogen tanks are often
tested by hydrogen sniffing.

BENEFITS OF LEAK TESTING WITH TRACER GASHigh reliability of leak detection
Repeatable and reproducible process
Results traceable to national standards
No influence of temperature or humidity
Selection of solutions for cost vs throughput

For more information, please visit us atwww.inficonautomotive.com
or call your nearest sales representative.

www.inficon.com

reachus@inficon.com

Due to our continuing program of product improvements, specifications are subject to change without notice.
miaq00en-03 (2007)©2020 INFICON