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Leak testing with hydrogen (H2) tracer gas using Leybold Phoenix Quadro Wet

January 20, 2023


Helium tracer gas: the challenge of availability

Due to the current Economic and Geopolitical conditions, the shortage of helium is causing the price to increase (~ 30%), which is becoming a real challenge for facilities using helium as a tracer gas for leak testing. Almost all helium is extracted from natural gas. The supply of helium comes from underground gas fields in the United States and Russia. As an alternative, many facilities are considering using hydrogen (H2) as a tracer gas for leak testing.

The Phoenix Quadro Wet can easily be switched between Mass 2 (hydrogen), Mass 3, and Mass 4 (Helium) by simply pressing a soft key on the front panel display.

After switching to Mass 2 (hydrogen), the Phoenix Quadro Wet can measure leak rates using hydrogen instead of helium.

Safe mixtures of gases for leak testing

Hydrogen is explosive in combination with oxygen, which is why facilities decide to use only a gas mixture of 5% hydrogen and 95% nitrogen, and not 100% hydrogen.  This type of gas mixture is known as forming gas 95/5, which is an effective and safe alternative to helium. 

Using hydrogen as a tracer gas is a low-cost solution compared to helium. It’s readily available, but the base background on any mass spectrometer leak detector will appear higher and unstable. It’s constantly changing compared to helium. 

The earth’s atmosphere contains 5 ppm of helium in the air but less than 0.5 ppm of hydrogen (10 times less).  When using a mass spectrometer leak detector, hydrogen has a higher background compared to helium and can be used for both vacuum and sniffing leak detection methods.

Vacuum and sniffing methods with the Phoenix Quadro Wet

Most facilities where leak testing is being done have several sources of hydrogen, which releases into the environment (batteries for fork trucks, combustion fumes, processing of aluminum, welding processes, and hydrocarbons from oil mist, etc.).

During the vacuum or sniffing leak testing process, hydrogen is desorbed from the environment. Metal surfaces inside the sample under test and the leak detector can develop a thin invisible film of water vapor, which is deposited on the surfaces due to penetration of the humidity.  This water vapor film evaporates under vacuum, and in the mass spectrometer, the water molecules are split and counted as hydrogen, causing a higher and unstable background.


The Phoenix Quadro Wet is one of the market leaders in portable leak detectors with the ability to accurately measure both hydrogen and helium tracer gas.

When using the Phoenix Quadro Wet with Hydrogen or forming gas (95/5), you must first perform an external calibration.  Due to the impact of water vapor from the humidity, you must first give the leak detector sufficient time to warm up (recommended at least 30 minutes).  If the leak detector inlet is closed and the leak detector is in measurement mode, the base background will be very unstable in the most sensitive range because of the water vapor deposited on the inner surfaces of the leak detector (see figure 1.0). 

Phoenix Quadro Wet hydrogen background with inlet blanked off – max sensitivity

  • Unstable background caused by humidity (H2O) desorbed on the inner surfaces of the leak detector during vent cycles
  • Phoenix Quadro Wet hydrogen background: 5.7x10-7 atm cc/s (after 30-minute operation)
Figure: 1.0: vacuum hydrogen ultra

The following leak test examples were done with a Phoenix Quadro Wet using hydrogen under ideal lab conditions.

The smallest detectable leak rate in “vacuum mode” is in the range of ≥ 1x10-6 atm cc/s (see stable hydrogen background (QBG) example 1.1)

Example 1.1 – Quadro wet hydrogen background (QBG)
Overpressure method – Integral leak detection
Vacuum method – Procedure local leak detection (pinpoint)

The smallest detectable leak rate in “sniffing mode” is in the range of ≥ 1x10-5 atm cc/s (see stable hydrogen background (QBG) example 1.2)

Example 1.2 – Quadro wet hydrogen external calibration
Overpressure method – Local leak detection (sniffing)

If someone wants to measure with hydrogen or forming gas (95/5), one must first calibrate the leak detector using an external calibration standard.  The Phoenix Quadro Wet does not include a hydrogen internal calibrated leak.

Calibration with hydrogen

Phoenix Quadro Wet calibrated in vacuum mode with external 100% hydrogen calibrated leak standard

Hydrogen Calibrated Leak Standard Value: 3.94 x10-4 atm cc/s

Phoenix Quadro Wet Actual Leak Rate Value: 3.97x10-4 atm cc/s (very stable leak rate)

Example 1.3 – Quadro wet hydrogen external calibration

Note:  In standard leak detection applications, using hydrogen as a tracer gas the actual leak rates will be higher than the results from leak testing in a lab environment. 

Challenges with using hydrogen as a tracer gas for leak testing

Unfortunately, you will experience longer delays in the overall test time when using hydrogen due to the influence of hydrogen in the test environment and the amount of time required to evacuate the internal system and test chamber down to an acceptable background level to start the leak test. The hydrogen background (QBG) should be approximately 10 times lower than the pass/fail leak rate criteria for an acceptable test.

In summary, if you want to use hydrogen as a tracer gas for leak testing, use the Phoenix Quadro Wet. First, you must consider the environment where the leak testing process will take place and try to reduce the number of hydrogen sources in the area that could lead to a higher and unstable background.  You can consider piping in fresh air or nitrogen or isolating the leak test process with barriers to reduce the overall background due to the environment and vent cycle of the leak detector (results from changing test samples).

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