Leak testing is a crucial process in various manufacturing industries to ensure product integrity and safety—but it can be challenging to ensure a reliable, repeatable leak test.
One of the many potential challenges when leak testing is the compression heat effect, which can lead to inaccurate results if not properly accounted for when using pressure-based leak detection methods. Understanding and mitigating this effect is vital for ensuring test accuracy and preventing false measurements.
What is compression heat effect? Why is it important?
Temperature can affect your leak test in many different ways, including part/fixture temperature, environmental temperature, and test air temperature. The test air temperature must be the same temperature as the part under test and the fixture, and account for any changes in environmental temperatures due to climate, etc. This temperature can be controlled in various ways, e.g., by installing a heat exchanger in the leak testing machine or by sealing it off from environmental influences.
However, even if you have controlled your temperature, the compression heat effect must be considered. When filling a test specimen with test air, the existing atmospheric air in the test specimen is compressed (sometimes referred to as the “air pump effect”). This compression raises the temperature of the material in the test specimen (see the compression heat formula below).
The compression heat formula (here using an example of a component with compression to 5 bar rel.)
can be used to help predict the pressure increase.
The heated compressed air then cools down again due to the heat dissipation of the DUT. This causes a pressure drop to occur immediately after filling, which could be measured as a false leak—unless it is properly compensated or stabilized.
How to compensate for compression heat effect
There are various ways to compensate for the compression heat effect. Below are some of the most common ways manufacturers can control these effects to ensure an accurate, reliable leak test.
Ensure adequate stabilization time
One way to avoid the compression heat effect is to ensure adequate stabilization time to compensate for compression heat before the leak measurement takes place.
During leak testing, if pressure readings are taken too soon after pressurization, this heat-induced pressure increase can lead to false leaks or mask genuine leaks. Using proper stabilization time allows the gas temperature to equilibrate with the component’s surroundings, reducing the thermal expansion effects. The correct stabilization time depends on many factors of the DUT and can only be set correctly by testing it.
Consider tracer gas leak testing methods
If there is not adequate time for stabilization in meeting your target cycle time, you may want to consider tracer gas leak test methods instead of air leak testing.
Tracer gas leak testing methods, such as helium or forming gas (a mixture of 5% hydrogen / 95% nitrogen) leak detection, offer higher sensitivity with minimal thermal interference. These methods detect gas escaping from a sealed component rather than measuring pressure changes, making them less susceptible to compression heat effects.
Need help refining your leak test? Contact the leak test experts
It is worth noting that the degree of compression heat effect will vary depending on factors such as gas type, material properties, and environmental conditions. If you are having trouble refining your leak testing process, the innomatec team is here to help!
innomatec has over 40 years’ experience assisting leading manufacturers worldwide in designing and enhancing their leak tests for optimal accuracy and reliability. Contact us to discuss your leak test today.
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