Leakage Testing of Gas Meters Designed for Measuring Hydrogen-Containing Gas Mixtures and Pure Hydrogen
Abstract
1. Introduction
1.1. Leak-Testing Methods
- Hydrostatic method—the object (sample) is filled with water. All air must be removed from the system because air is compressible and may distort test results. Pressure is applied using a water pump and maintained for a specified period. Joints, welds, valves, etc., are checked for leaks. A drop in pressure is measured—if there is no pressure loss, the system is considered leak-tight;
- Bubble method—the object (sample) is filled with gas under pressure (e.g., air). In the classic version, the surface is covered with a liquid (e.g., water with detergent). A leak produces visible bubbles. In the immersion version, the object is submerged in a liquid (usually water). Leaks are also revealed by bubble formation;
- Pressure drop method—the object is filled with gas (usually air or nitrogen) to a specified pressure. During the test, the pressure drop over time is monitored. A larger pressure drop indicates a greater leak rate;
- Pressure rise method—the object is filled with gas and placed in a vacuum environment. In the event of a leak, gas escapes and causes a pressure increase outside the object (in the vacuum chamber);
- Vacuum method—a vacuum is created inside the test object (sample). During the test, the internal pressure is monitored. A rise in pressure indicates a leak (gas entering from the outside);
- Tracer gas method—a tracer gas—typically helium or hydrogen (in a mixture with nitrogen)—is introduced inside the test object (or applied outside, if the system is under vacuum), and a detector on the opposite side of the wall registers the presence of the gas that passed through a leak. The sensor detects the tracer gas escaping from the system;
- Mass spectrometry method—the test object is filled with a tracer gas (or placed in a chamber with helium), and a mass spectrometer detects its presence on the opposite side of the wall. Helium is most commonly used due to its inertness, low molecular weight, and low natural concentration in air;
- Thermal conductivity method—This method relies on the fact that different gases have different thermal conductivities. The thermal conductivity of the surrounding gas is monitored—the presence of another gas (from a leak) causes a change. The system is typically filled with a gas of high thermal conductivity (e.g., hydrogen or helium). A sensor measures the thermal conductivity of the gas around it (e.g., using a heated wire Wheatstone bridge). A leak causes a temperature change due to the altered thermal conductivity of the gas mixture;
- Radioisotope method—a radioactive tracer gas or a liquid containing a radioisotope is introduced into or around the object. The presence of the radioactive substance outside the object is detected using ionizing radiation detectors (e.g., Geiger counters, scintillation detectors, or proportional counters);
- Fluorescent dye method—a liquid containing a UV-reactive dye is introduced into the object. Leaking fluid can be visually identified under UV light;
- Ultrasonic method—gas leaking through a small opening produces high-frequency sounds (ultrasound), which are detected by specialized ultrasonic sensors.
1.2. Gas Leakage
- V—internal volume of the gas meter available for the test medium, [m3];
- R—universal gas constant 8.3144 [J/mol·K] (8.3144 [Pa·m3/(mol·K)];
- T—temperature in the gas meter, [K];
- TS—reference temperature, usually 273.15 [K];
- ΔP—pressure drop in the gas meter during Δt, [Pa];
- Δt—time interval between successive registrations of test parameters, [s].
- Pg0—absolute pressure in the gas meter at the start of the test, [Pa],
- Pg1—absolute pressure in the gas meter at the end (after Δt), [Pa],
- Tg0—temperature in the gas meter at the start of the, [K],
- Tg1—temperature in the gas meter at the end (after Δt), [K].
1.3. Available Tests and Calculations Results
- for air: 7.50 × 10−6 Pa·m3/s;
- for helium: 8.50 × 10−6 Pa·m3/s;
- for hydrogen: 2.00 × 10−5 Pa·m3/s.
- for air: 7.50 × 10−2 Pa·m3/s;
- for helium: 7.60 × 10−2 Pa·m3/s;
- for hydrogen: 1.00 × 10−1 Pa·m3/s.
- for air and helium: 1.00 × 100 Pa·m3/s,
- for hydrogen: 1.25 × 100 Pa·m3/s.
2. Materials and Methods
2.1. General Requirements
- v—diffusion rate, [m/s];
- M—molar mass of the gas, [kg/kmol];
- ρ—gas density, [kg/m3].
- Molecular flow occurs when the mean free path of the gas molecules is greater than or comparable to the size of the leak (e.g., the diameter of the hole). This flow regime is typical at very low pressures or in the presence of very small gaps;
- Subsonic flow (incompressible or compressible) occurs when the pressure difference between the inside of the object and the surroundings is small. The velocity of the leaking gas does not exceed the speed of sound. Depending on the size of the leak and the Reynolds number, the flow can be either laminar or turbulent;
- Choked (critical) flow occurs when the pressure inside the vessel is sufficiently higher than the ambient pressure. The gas velocity at the narrowest point of the leak reaches the speed of sound. The flow rate does not increase with further increases in pressure difference—it is limited by the so-called critical flow. Critical flow will occur if the pressure ratio between the inside and outside of the object (Pg0/Pg1) exceeds 1.9 for air, nitrogen, and hydrogen, and 2.0 for helium.
2.2. Samples for Testing
2.3. Test Stand
2.4. Test Method
- All valves in the system were closed, and the gas leakage test meter was installed;
- The CV valve on the gas cylinder containing the test gas was opened, and the pressure on regulator CR was set to approximately 200 kPa (or 500 kPa for industrial gas meters);
- Valves SV1, SV2, and SV3 were opened sequentially to flush the test sample with the test gas (displacing any remaining residues from other media);
- The vent valve SV3 was then closed, and the test gas meter was filled to the required test pressure, allowing the system to stabilize;
- The gas supply was cut off by closing valve SV2. Simultaneously, gas leakage was recorded and monitored along with pressure and temperature inside the gas meter, ambient temperature, and atmospheric pressure over a defined time interval. To enable later reconstruction of the gas outflow, the leak was recorded during the first minute for comparative purposes and to assess the size of the leak.
3. Results
3.1. Selected Results for Domestic Gas Meters
3.1.1. Results for Sample No. 1
3.1.2. Results for Sample No. 7
3.2. Selected Results for Industrial Gas Meters
Results for Sample No. 13
3.3. Collected Results for All Samples
4. Discussion
5. Conclusions
- The rate of gas leakage through a defect is influenced by several factors, including the size and shape of the leak (the length and cross-sectional area of the gas flow path), pressure differential and temperature conditions, gas properties (such as molecular weight, effective particle diameter, and viscosity), as well as the type of flow through the leak and the resulting flow resistance;
- The test results obtained in this study are consistent with leakage test results available in the literature (using mass spectrometry), as well as with theoretical calculations published in scientific sources;
- The standardized methods currently used for leak testing of gas meters intended for natural gas have proven to be sufficient for meters designed to measure natural gas–hydrogen mixtures and pure hydrogen. However, in the case of small leaks (microleaks), it is recommended to modify these test methods by replacing air/nitrogen with hydrogen as the test gas;
- This study also found that nitrogen and helium had similar leakage rates (helium had slightly higher). This suggests that helium is not suitable for pressure drop leak testing and bubble-based immersion leak testing;
- When hydrogen is used as the test gas, explosion risks must be carefully assessed, and appropriate safety measures must be implemented to mitigate potential hazards.
Funding
Data Availability Statement
Conflicts of Interest
Nomenclature
ΔP | pressure drop in the gas meter during Δt, [Pa] |
Δt | time interval between successive registrations of test parameters, [s] |
Pg0 | absolute pressure in the gas meter at the start of the test, [Pa] |
Pg1 | absolute pressure in the gas meter at the end (after Δt), [Pa] |
pmax | maximum working pressure, [Pa] |
v | diffusion rate, [m/s] |
ρ | gas density, [kg/m3] |
T | temperature, [K] |
Tg0 | temperature in the gas meter at the start, [K] |
Tg1 | temperature in the gas meter at the end (after Δt), [K] |
TS | reference temperature, usually 273.15 [K] |
UAG | unaccounted for gas, [GJ] or [m3] |
V | internal volume of the gas meter available for the test medium, [m3] |
W | rate of gas leakage from a tank, [mol/s] or [Pa·m3/s] |
MDPI | Multidisciplinary Digital Publishing Institute |
RES | Renewable Energy Sources |
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Name of the Method | Technique | Location of the Leak | Sensitivity of the Method [Pa·m3/s] | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
10−1 | 10−2 | 10−3 | 10−4 | 10−5 | 10−6 | 10−7 | 10−8 | 10−9 | 10−10 | 10−11 | 10−12 | 10−13 | |||
Hydrostatic | Yes | X | |||||||||||||
Bubble | Classic | Yes | X | X | |||||||||||
Immersion | Yes | X | X | X | |||||||||||
Pressure drop | Not | X | X | ||||||||||||
Pressure increase | Not | X | X | X | |||||||||||
Vacuum | Not | X | X | X | |||||||||||
Tracer gases | Helium | Yes | X | X | X | X | X | X | X | ||||||
Hydrogen | Yes | X | X | ||||||||||||
Halogen | Yes | X | X | X | X | X | |||||||||
Mass spectrometer | Yes | X | |||||||||||||
Thermal conductivity | Not | X | X | X | |||||||||||
Radioactive isotope | Out–in | Not | X | X | X | ||||||||||
In–out | Yes | X | |||||||||||||
Fluorescent dye | Yes | X | |||||||||||||
Ultrasonic | Yes | X | X | X |
Sample | Test Pressure [kPa] | Leakage Ratio to Helium [-] | |
---|---|---|---|
Air | Hydrogen | ||
Flange connection gaskets * | 4000 | n/a | 2.56 |
Soft Gasket Materials ** (FA-NEW GENERATION) from TESNIT® company | 500 | n/a | 1.08 |
Capillary diameter 10 µm *** | n/a | 0.88 | 2.35 |
Capillary diameter 100 µm *** | n/a | 0.99 | 1.32 |
Capillary diameter 1000 µm *** | n/a | 1.00 | 1.25 |
Average leakage against helium | 0.96 | 1.71 |
Gas | Symbol | Molar Mass | Density | Dynamic Viscosity | Effective Particle Diameter |
---|---|---|---|---|---|
(at Normal Conditions) | |||||
[kg/kmol] | [kg/m3] | [µPa·s] | 10−10 [m] | ||
Air | N2 + O2 + … | ≈28.960 | 1.293 | 17.2 | ≈3.70 |
Nitrogen | N2 | 28.014 | 1.146 | 16.5 | 3.64 |
Hydrogen | H2 | 2.016 | 0.082 | 8.4 | 2.89 |
Helium | He | 4.003 | 0.164 | 18.6 | 2.60 |
Carbon dioxide | CO2 | 44.010 | 1.977 | 13.7 | 3.30 |
Methane | CH4 | 16.040 | 0.717 | 10.9 | 3.80 |
Propane | CH38 | 44.097 | 1.970 | 7.5 | 4.30 |
Time [min] | Nitrogen | Helium | Hydrogen | |||
---|---|---|---|---|---|---|
Pressure (Gauge) [kPa] | Temperature [°C] | Pressure (Gauge) [kPa] | Temperature [°C] | Pressure (Gauge) [kPa] | Temperature [°C] | |
0 | 35.0 | 21.1 | 35.0 | 19.6 | 35.0 | 19.4 |
5 | 30.5 | 21.0 | 30.0 | 19.5 | 28.0 | 19.5 |
10 | 24.8 | 21.0 | 24.3 | 19.4 | 22.0 | 19.6 |
15 | 21.0 | 21.0 | 20.5 | 19.4 | 17.8 | 19.7 |
20 | 18.2 | 20.9 | 17.5 | 19.2 | 14.3 | 19.7 |
25 | 15.1 | 20.5 | 14.6 | 19.3 | 11.6 | 19.7 |
30 | 12.8 | 20.4 | 12.3 | 19.3 | 9.8 | 19.7 |
35 | 9.5 | 20.2 | 8.8 | 19.2 | 7.5 | 19.6 |
Leakage rate in first five minutes of the test [Pa·m3/s] | ||||||
- | 6.6 × 10−2 | 7.4 × 10−2 | 1.1 × 10−1 |
Time [min] | Nitrogen | Helium | Hydrogen | |||
---|---|---|---|---|---|---|
Pressure (Gauge) [kPa] | Temperature [°C] | Pressure (Gauge) [kPa] | Temperature [°C] | Pressure (Gauge) [kPa] | Temperature [°C] | |
0 | 75.0 | 19.2 | 75.0 | 20.2 | 75.0 | 19.9 |
5 | 75.0 | 19.2 | 75.0 | 20.2 | 74.6 | 19.9 |
10 | 75.0 | 19.2 | 74.9 | 20.3 | 74.3 | 19.8 |
15 | 74.8 | 19.3 | 74.7 | 20.3 | 74.0 | 19.9 |
20 | 74.7 | 19.4 | 74.5 | 20.2 | 73.6 | 19.9 |
25 | 74.4 | 19.3 | 74.3 | 20.4 | 73.2 | 19.8 |
30 | 74.2 | 19.5 | 74.1 | 20.3 | 73.0 | 19.7 |
35 | 74.0 | 19.2 | 73.9 | 20.2 | 72.6 | 19.8 |
40 | 73.8 | 19.4 | 73.6 | 20.2 | 72.0 | 19.8 |
45 | 73.5 | 19.3 | 73.2 | 20.0 | 71.9 | 19.6 |
Leakage rate in first five minutes of the test [Pa·m3/s] | ||||||
- | 0 | 0 | 6.0 × 10−3 |
Time [min] | Nitrogen | Helium | Hydrogen | |||
---|---|---|---|---|---|---|
Pressure (Gauge) [kPa] | Temperature [°C] | Pressure (Gauge) [kPa] | Temperature [°C] | Pressure (Gauge) [kPa] | Temperature [°C] | |
0 | 400.0 | 19.8 | 400.0 | 21.2 | 400.0 | 20.5 |
5 | 284.0 | 19.9 | 257.0 | 21.2 | 163.0 | 20.6 |
10 | 198.0 | 20.0 | 170.0 | 21.3 | 73.5 | 20.6 |
15 | 139.5 | 20.0 | 116.0 | 21.4 | 38.0 | 20.5 |
20 | 97.0 | 20.2 | 81.0 | 21.3 | 22.0 | 20.4 |
25 | 68.5 | 20.4 | 57.5 | 21.3 | 14.0 | 20.3 |
30 | 49.0 | 20.4 | 42.0 | 21.2 | 8.0 | 20.3 |
35 | 35.5 | 20.5 | 31.0 | 21.2 | 8.0 | 20.4 |
40 | 26.0 | 20.3 | 23.0 | 21.0 | 7.2 | 20.3 |
45 | 21.0 | 20.3 | 18.0 | 20.9 | 6.8 | 20.2 |
Leakage rate in first five minutes of the test [Pa·m3/s] | ||||||
- | 1.3 × 10−1 | 1.5 × 10−1 | 2.6 × 10−1 |
Sample No. | Test Pressure (Gauge) [kPa] | Leakage Rate [Pa·m3/s] | Leakage Ratio to Helium [-] | |||
---|---|---|---|---|---|---|
Nitrogen | Helium | Hydrogen | Nitrogen | Hydrogen | ||
1 | 35 | 6.6 × 10−2 | 7.4 × 10−2 | 1.1 × 10−1 | 0.89 | 1.49 |
2 | 75 | 4.1 × 10−2 | 5.0 × 10−2 | 9.4 × 10−2 | 0.82 | 1.88 |
3 | 75 | 2.1 × 10−2 | 4.0 × 10−2 | 7, 1 × 10−2 | 0.53 | 1.78 |
4 | 35 | 1.1 × 10−2 | 1.3 × 10−2 | 1.5 × 10−2 | 0.85 | 1.15 |
5 | 75 | 2.6 × 10−2 | 3.1 × 10−2 | 5.5 × 10−2 | 0.84 | 1.77 |
6 | 75 | 1.5 × 10−2 | 2.2 × 10−2 | 5.2 × 10−2 | 0.68 | 2.36 |
7 | 75 | 0 | 0 | 6.0 × 10−3 | - | - |
8 | 35 | 7.4 × 10−4 | 7.5 × 10−4 | 1.5 × 10−3 | 0.99 | 2.00 |
9 | 75 | 1.0 × 10−3 | 1.2 × 10−3 | 3.0 × 10−3 | 0.83 | 2.50 |
10 | 35 | 1.7 × 10−2 | 1.5 × 10−2 | 2.2 × 10−2 | 1.13 | 1.47 |
11 | 75 | 4.5 × 10−2 | 5.0 × 10−2 | 1.1 × 10−1 | 0.90 | 2.20 |
12 | 400 | 4.1 × 10−2 | 4.7 × 10−2 | 8, 1 × 10−2 | 0.87 | 1.72 |
13 | 400 | 1.3 × 10−1 | 1.5 × 10−1 | 2.6 × 10−1 | 0.87 | 1.73 |
14 | 400 | 1.5 × 10−1 | 1.6 × 10−1 | 2.7 × 10−1 | 0.94 | 1.69 |
Average leakage against helium | 0.86 | 1.83 |
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Gacek, Z. Leakage Testing of Gas Meters Designed for Measuring Hydrogen-Containing Gas Mixtures and Pure Hydrogen. Energies 2025, 18, 4207. https://doi.org/10.3390/en18154207
Gacek Z. Leakage Testing of Gas Meters Designed for Measuring Hydrogen-Containing Gas Mixtures and Pure Hydrogen. Energies. 2025; 18(15):4207. https://doi.org/10.3390/en18154207
Chicago/Turabian StyleGacek, Zbigniew. 2025. "Leakage Testing of Gas Meters Designed for Measuring Hydrogen-Containing Gas Mixtures and Pure Hydrogen" Energies 18, no. 15: 4207. https://doi.org/10.3390/en18154207
APA StyleGacek, Z. (2025). Leakage Testing of Gas Meters Designed for Measuring Hydrogen-Containing Gas Mixtures and Pure Hydrogen. Energies, 18(15), 4207. https://doi.org/10.3390/en18154207