Hydrogen vs helium leak testing

The importance of leak testing in the hydrogen economy

Although cleaner than hydrocarbons when used as a fuel, hydrogen also causes about 10 times more atmospheric warming than CO2 when leaking from infrastructure. Therefore, minimizing hydrogen leaking is of great significance from hydrogen generation to hydrogen storage to hydrogen use. As a result, as the hydrogen economy grows with new investments, accurate leak testing for hydrogen infrastructure becomes even more important.

Helium leak testing

A traditional solution which is trusted in many industries for high accuracy leak detection, including the hydrogen industry, is helium leak testing. Helium leak testing uses helium as a carrier gas, determining a leak rate by finding helium’s leak through rate and using helium detectors such as in gas chromatography-mass spectroscopy (GC-MS) systems.

Some of the main benefits to using helium as a leak test carrier gas include:

• Inert, non-toxic, non-flammable and nonreactive
• Able to flow through micron sized leaks due to small particle size
• Not a common component in atmospheric air and therefore has high detection accuracy

Nonetheless, helium leak tests also have some drawbacks, including:

• The global supply of helium is in limited and thus helium gas is expensive
• Helium detectors are expensive

Because of these reasons, helium leak testing is costly and may not be possible indefinitely as helium global supplies run out over time.

Hydrogen leak testing

An alternative method for high accuracy leak testing with potential to replace some applications of helium leak testing, especially for the hydrogen industry, is hydrogen leak testing. In hydrogen leak testing, hydrogen gas is mixed with an inert gas, typically nitrogen (however helium would also be an option) such that the hydrogen is of a concentration less than 5.7% of the total mix and can be classified as non-flammable via ISO-10156. After creating this hydrogen and inert gas mix, similar to the process in helium leak testing, the leak rates can be determined using hydrogen leak through rates and detectors for hydrogen.

For the hydrogen industry in particular, hydrogen leak testing by using hydrogen as a carrier gas offers advantages such as:

• Affordable and abundant carrier gas
• Non-flammable and inert when mixed below 5.7% of total mix
• Low cost for hydrogen detectors (hydrogen mass spectrometers are 20 times less costly than helium mass spectrometers)
• Very precise leak rates and operating conditions during leak tests, especially for hydrogen gas flow

Designing better helium and hydrogen leak tests

Alicat’s mass flow controllers and pressure controllers can be used to improve helium and hydrogen leak testing accuracy as well as other types of leak tests (such as regular pressure decay and mass flow leak tests).

Noncontinuously flowing leak tests

For noncontinuously flowing helium tests, an Alicat PCD can be attached to a vacuum pump and a helium gas supply with a pressure control line running directly to a DUT chamber and helium mass spectrometer. The DUT chamber is placed under a vacuum using the vacuum pump and then refilled with the helium supply to slightly above atmospheric pressure. As a result, a leakage rate can be determined by testing the leakage flow from the outside to the inside of the DUT using the helium mass spectrometer.

Alternatively, hydrogen leak tests can be executed by first using an Alicat MC-Series or CODA KC-Series mass flow controller to mix hydrogen gas with an inert gas such as nitrogen. Similar to the procedure for noncontinuously flowing helium leak tests, an Alicat PCD can be attached to a vacuum pump and a hydrogen gas supply with a pressure control line running directly to a DUT chamber and a hydrogen mass spectrometer. The DUT chamber is first placed under a vacuum using the vacuum pump and then refilled with the hydrogen gas supply to slightly above atmospheric pressure. As a result, a leakage rate can be determined by testing the flow from the outside to the inside of the DUT using the hydrogen mass spectrometer.

Pressure decay and mass flow hydrogen and helium leak tests

Although less common than the above method for testing a DUT leak rate with either hydrogen or helium, pressure decay and mass flow leak tests can also be designed using both helium and hydrogen as carrier gases.

In pressure decay leak testing using hydrogen or helium, the DUT is pressurized to a given pressure using helium or hydrogen mixed inert gas and isolated from its pressure source by closing an inlet valve. A pressure transducer reads the pressure drop over time, corresponding to a specific leak rate.

There are a few methods of mass flow leak testing using hydrogen or helium.

In the first method, a helium or hydrogen gas supply is connected to a DUT through a flow line with a PC3 pressure controller and either an M-Series or MW-Series mass flow meter. The PC3 is upstream of the mass flow meter and plumbed to sense pressure downstream of the mass flow controller. The pressure controller brings the DUT to a constant pressure using the hydrogen or helium gas supply while the mass flow meter displays the associated helium or hydrogen leak rate. Due to the expense of leaking helium in this type of test, it is likely more suitable for use with hydrogen mixed inert gases.

In the second method, a helium or hydrogen gas supply is connected to a DUT through a flow line with a single MC-Series or MCW-Series mass flow controller maintaining a constant pressure while reading out an associated leak rate in real-time. Compared to the previous mass flow method, this one is less suitable for large volumes with low leak rates and requires more stabilization time to come up to test operating pressure.

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