Helium Leak Rate

Detection Principle

Helium serves as the preferred tracer gas because its small atomic size allows it to pass through microscopic gaps that would block larger molecules. The test specimen is pressurized with helium or placed in a vacuum chamber where escaping gas is measured by a mass spectrometer. This spectrometer detects the unique charge-to-mass ratio of helium ions, providing a highly sensitive measurement of the flow rate.

This technique can identify leaks that are several orders of magnitude smaller than those detectable by water immersion or bubble emission tests.

Standard Limit

Manufacturing specifications for battery pack cooling plates often require a helium leak rate below a specific threshold to prevent coolant escape. If the coolant leaks, it can cause electrical short circuits and initiate thermal runaway within the high-voltage module. For long-term battery storage, hermetic cell seals must meet even stricter leak rate standards to prevent moisture from entering and degrading the electrolyte.

Sourcing teams specify these leak rate limits in supply agreements to ensure component quality and long-term reliability.

Calibration Control

Accurate measurement requires daily calibration of the leak detection system using a certified reference leak bottle. This calibration ensures that changes in ambient temperature or spectrometer filament aging do not skew the measured leak rates. Operators must also monitor background helium levels in the test area, as accumulating tracer gas can cause false positive readings.

Maintaining a well-ventilated testing environment is therefore critical for securing consistent and repeatable leak rate measurements.