What is the Helium Leak Test Used For?

In many industrial sectors , the airtightness of instruments and containers is of vital importance

For this reason, many scientific methods have been developed to detect any leaks.

The helium leak test is one of the most reliable and versatile tests for a number of reasons that we will explain in this article.

What is a Helium Leak Test?

One of the most effective ways to test whether an ideally airtight container is actually leaking is to use tracer gases.

Tracer gases are a class of gases with specific characteristics that are introduced into the container and, by diffusing inside it, indicate the presence of openings.

Helium is particularly effective in this regard because it is light, odorless, colorless, and highly penetrating, capable of passing through even the smallest cracks, revealing potential leaks that would otherwise have gone unnoticed. 

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Which sectors are affected by the Helium Leak Test?

Even if we don't think about it, we're surrounded by containers that need to be perfectly airtight to do their job.

For this reason, there are many sectors affected by Helium Leak Testing.

Here are the main ones.

• Automotive Industry: To check for leaks in air conditioning systems, fuel tanks and exhaust systems.

• industry Aerospace: To check the integrity of critical parts, such as fuel tanks and pressurization systems, to prevent leaks into the atmosphere.

• Electronics Industry: To identify any refrigerant gas or fluid leaks in electronic devices, such as refrigerators or air conditioners.

• Chemical and pharmaceutical industry: To check the tightness of containers used for sensitive chemicals or drugs.

• Energy Sector: To verify the integrity of pipeline and tank systems used in the production and transportation of gas or oil.

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How the Helium Leak Test Works

In order to properly perform the helium leak test, it is necessary to have an isolated, controlled and airtight environment.

For this, a thermo-vacuum chamber is often used , which we talked about here.

The sample to be tested is placed inside the chamber. Helium is then injected and the results are observed.

Using a specific instrument, usually a mass spectrometer (which we talked about here), any leaks are detected and located.

The specific procedures for performing helium leak testing are described in a number of international standards. The principal ones are ISO 20484:2017 and ASTM E498/E498M-11.

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The FDM Climatic Chamber for Helium Leak Testing

Like many other laboratory tests we have discussed on these pages, climatic chambers play a complementary but often fundamental role in helium leak testing

There are two functions that climatic chambers can perform in helium leak testing: conditioning and simulation.

Conditioning is when the sample to be analyzed must first be brought to a specific temperature to carry out the test in optimal conditions.

We speak of simulation when temperatures are altered during the test to simulate unfavorable environmental conditions that the sample will face during its life cycle (think of underwater pipes).

The FDM climate chamber is able to perform both tasks perfectly and complements helium leak testing and many other important product and material tests.

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Reference Standards

• MIL-STD-883 Method 1014 — Seal (Fine and Gross Leak) test for microcircuits
• ASTM E499 — Leak testing by Mass Spectrometer Leak Detector in the Detector Probe Mode
• ASTM E493 — Leak testing by Mass Spectrometer in the Inside-Out Tracer Probe Mode
• ISO 20486 — Non-destructive testing — Leak testing — Calibration of reference leaks for gases
• EN 1779 — Non-destructive testing — Leak testing — Criteria for method and technique selection
• SEMI E10 — Specification for Definition and Measurement of Equipment Reliability (includes leak test for vacuum tools)

Authoritative Sources

• ASTM E499 — Helium mass spectrometer leak testing.
• ASNT — American Society for Nondestructive Testing.
• AIV — Italian Association of the Void.

Frequently Asked Questions About Helium Leak Testing

Why use helium as a tracer gas?

Helium is the reference gas for leak testing for four reasons: (1) small atom (radius 31 pm) — passes through leaks that would stop other gases; (2) low atmospheric concentration (5.2 ppm) — low instrumental background noise; (3) inert — does not react with test materials; (4) non-toxic and non-flammable. Typical sensitivity of mass spectrometers : up to 10⁻¹² mbar·L/s (equivalent to one molecule/second).

Difference between fine leak and gross leak?

MIL-STD-883 Method 1014 requires both: Fine Leak Test with helium to detect small leaks (10⁻⁸ ÷ 10⁻⁵ atm cc/s) — the component is pressurized in helium for 2-4 hours at 2-3 bar, then tested in an empty spectrometer. Gross Leak Test with Fluorinert FC-40 or PFE (C₈F₁₈) for large leaks (>10⁻⁴ atm cc/s) — the component is immersed in a volatile liquid at 85°C to generate visible bubbles. Without the gross test, a large leak would be missed because it would “saturate” the spectrometer too quickly.

What are typical pass/fail limits?

MIL-STD-883 standard thresholds: Class S/B hermetic components < 5×10⁻⁸ atm cc/s He; commercial components < 10⁻⁷; pacemakers and implantable devices < 10⁻⁹ (ISO 5841). For fuel cells and batteries: < 10⁻⁶ to prevent moisture ingress. For cryogenic tanks: < 10⁻⁴ for safety. Limit selection is guided by expected service life and internal volume.

How do you calibrate a helium leak detector?

With calibrated reference leaks (sealed microporous metal capillaries, NIST/PTB certified): the detector reads the helium flow rate of the reference leak (typically 10⁻⁷ ÷ 10⁻⁴ atm cc/s) and applies a correction factor. Monthly primary calibration with a master reference; daily secondary calibration with an operational reference. The operator must be ASNT Level II qualified for leak testing according to ISO 9712. All tests are documented in reports with calibration traceability.