What is the Hermetic Leak Test?

We're surrounded by sealed containers. From consumer products to more critical components like pipes, tanks, and technical equipment that must guarantee a complete level of airtightness.

But how do we know that they are actually airtight?

This is what the leak test is about.

What is the Leak Test Used For?

Leak testing is a procedure used to test the ability of a container, such as a tank, pipe, or piping system, to withstand internal pressure without leaking liquid or gas. 

Leak testing can be performed in several ways, including pressurization with gas or a liquid, and using testing methods such as static pressure or dynamic pressure.

Regardless of the method, the first distinction to make is between micro-leak testing and large-leak testing.

Run Extreme
Tests

Discover the new series of Environmental Chambers for controlled climate testing.
Find out more.

Types of Hermetic Leak Test

As the name suggests, the difference between micro losses and large losses is quantitative .

To determine the size of the leak, calculate the volume of air passing through the leak each second at a pressure difference of 1 atmosphere. 

Leak rates greater than 1×10-5 atm-cc/sec are considered large leaks; those less than 1×10-5 atm-cc/sec are considered microleaks.

Typically, fine leak testing uses liquids while coarse leak testing uses tracer gases, but there are procedures that use helium as a tracer even in fine leak testing.

Finally, there is another class of tests that uses dye penetrant, both to detect large and small leaks. This latter type of test also uses a pressure chamber, which we discussed here.

The most common procedures for performing leak tests are outlined by the United States Military Standard, a regulatory body of the U.S. Army that is used as a model by the international community for certain materials tests.

Specifically, the most followed standards are: MIL-STD-202-112 and MIL-STD-883, method 1014.

The Climatic Chamber for the Leak Test

Finally, it is not uncommon for to climate chambers play a role in the procedure surrounding the actual airtightness test.

Climatic chambers can be used in some leak tests when it is necessary to test the resistance of containers to variations in temperature and humidity. In these cases, the sample object in question is first placed inside a climatic chamber where the environmental parameters can be modified, especially temperature andrelative humidity , but also solar exposure or simulated precipitation. 

In this way, it is possible to reproduce more realistic conditions to which certain types of containers will be exposed, such as those designed for extreme environments – think of pipes that pass at considerable underwater depths. 

Can't find the perfect chamber for your rehearsals?

Build your environment directly online, based on your specific needs.
Find out more.

The FDM Environmental Chamber for Leak Testing

The environmental chamber is a type of climatic chamber designed for extreme testing.

When carrying out leak tests, we recommend using this type of chamber which covers all possible environmental conditions and is able to verify how our containers will react even when exposed to the most hostile conditions.

All FDM environmental chambers meet international requirements for climatic tests and are suitable for reproducing the ideal setting for performing the leak test.

For any further questions or concerns, please do not hesitate to contact us.

Do you need a quote or have questions about the product?

Contact us for more information about this product.
Contact Us

Reference Standards

• MIL-STD-883 Method 1014 — Seal test (fine leak + gross leak)
• ISO 10648-2 — Containment enclosures — Classification according to leak tightness
• EN 1779 — Leak testing — Criteria for method selection
• ASTM E2930 — Leak testing of hermetic packages by pressure change
• ISO 9978 — Radiation protection — Sealed radioactive sources — Leak test methods
• SAE ARP1921 — Leak testing of aerospace components

Authoritative Sources

• ASTM E2930.
• ASNT — American Society for Nondestructive Testing.
• ISO 10648-2 — Containment classification leak tightness.

Frequently Asked Questions about the Airtightness Test

What methods of testing for airtightness are there?

Six main methods ordered by increasing sensitivity: (1) Bubble test in water (10⁻⁴ atm cc/s, low cost, inspection); (2) Pressure decay or Pressure rise (10⁻⁴ ÷ 10⁻⁶, small volumes); (3) Tracer gas with 5% H₂ (10⁻⁶ ÷ 10⁻⁸, low cost); (4) Mass spectrometer He (10⁻⁸ ÷ 10⁻¹⁰, standard aerospace); (5) Accumulation test (10⁻⁵ ÷ 10⁻⁷, large volumes); (6) Radioisotope Kr-85 (10⁻¹¹, MIL microcircuits).

When to use pressure decay vs. mass spectrometer?

Pressure decay is preferred for: large volumes (>0.1 L), high volume production line testing, medium/large leaks (>10⁻⁵ atm cc/s), coarse. Mass spectrometer is preferred for: small volumes (

What is a leakage class according to ISO 10648?

ISO 10648-2 classifies containers (glove cabinets, isolator cells) into 4 classes: Class 1, hermetic seal < 2×10⁻³ vol/h (most stringent, radiation protection); Class 2 < 2×10⁻² vol/h (nuclear, biosafety BSL3); Class 3 < 2×10⁻¹ vol/h (standard chemical); Class 4 < 1.0 vol/h (low risk). Testing is performed using constant pressure or constant volume methods according to the standard. High-containment laboratories (pharmaceutical, HPAPI) always require Class 1 or 2.

How do you prepare a component for hermetic testing?

Critical preparation: (1) Thorough cleaning of the external surface with compatible solvents (IPA, acetone) to remove oils/productive traces that could temporarily “plug” the leaks; (2) Thermalization for 30-60 min at test temperature (typically 23°C ±2); (3) Pressurization with helium for 2-4h at 2-5 bar to pack tracer gas inside the cavity (bombing method); (4) Venting and wait time to dissipate residual helium adhered to the surface (prevent false positives).