How to test thin gas lines faster with Helium detection?
Helium leak testing is indeed a non-destructive test method with high sensitivity and a wide dynamic range. Since helium leak detection works with test gas, it is governed by the laws of fluid mechanics. High internal flow resistances of individual test objects can severely impair the effectiveness of helium leak detection. This is especially true for long, thin gas pipes used, for example, for the construction of high-purity media supply systems or coil-wound heat exchangers.
Leak detection by spraying with helium
After connecting and evacuating the gas line, the outer surfaces are sprayed with helium using a finely adjustable spray-gun. Helium enters the gas line through leaks and can be transported to the detection device. The response time during the measurement is determined by the volume of the gas line and the effective pumping speed of the helium gas test setup.
Helium spray test with tracer gas. An exemplary experimental setup consists of an ASM 340 leak detector with ASM View software. At both ends of each specimen, type TPR 280 Pirani tubes with a TPG 262 DualGauge measurement instrument are used as pressure gauges.
The effective pumping speed for helium is made up of the helium pumping speed of the leak detector used, the flow resistances of the gas line as well as the piping components forming the connection between the leak detector and the gas line.
Conventional helium leak detectors reach their maximum sensitivity in what is known as “fine leak mode“ at a comparatively low test pressure.
For this experiment, a cuboid-shaped container with a volume of 1.5 liters and gas lines with a length of 7 meters and 20 meters and an inside diameter of 4 mm were used.
With the cuboid, a background signal of 10-9 mbar · l/s is achieved within roughly one minute. On a gas line, the remaining helium content of the air can only be pumped out of the gas pipe very slowly due to the high flow resistance of the pipe and the background signal stabilizes at a value of 5 · 10-8 mbar · l/s. When the thin gas pipe is measured, the background signal is thus higher by a factor of 50 than when measured on a flow optimized component. In order to achieve an identical signal-to-noise ratio, a test leak of 5 · 10-6 mbar · l/s is used for the gas pipe.
Read more about this state of the art technology in the attached application report.
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