For a non-destructive testing method to measure leakage of fluids or gases in evacuated or pressurized systems, many turn to leak testing. Being able to effectively find and quantify leaks is vital in a broad range of industries and research centers, from the production of high-performance gaskets to the safe usage of vacuum chambers within a microbiology lab.
Leak Detection Process
Choosing the most suitable testing method for a particular component or piece of equipment can be tricky, as there are a large number of varied applications for leak detection.
This article will outline the process of leak detection, how to carry it out successfully and the advantages of Helium leak detectors, such as Leybold’s Phoenix 4.
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For those working with vacuums, a leak detector is vital. There are a number of reasons for this, with the most important being for the protection of staff and the laboratory environment.
This issue is of particular concern in nuclear and microbiology research, but there are countless other industries that engage with hazardous materials that must not be allowed to enter the external environment.
Another popular reason for carrying out leak testing is for quality assurance. The reliability of items such as fire extinguishers and shock absorbers is greatly affected by their leak rates.
In fields where manufacturers are required to meet compliance provisions or other regulatory standards, leak detection is frequently a vital stage in the manufacturing process.
Lastly, in a point that is more applicable to industry than research, leak testing is needed to ensure that machines and systems are maintained at operational readiness.
The presence of unwelcome leaks in any vacuum system can cause damage to equipment and machinery, lowering their effectiveness and causing disruption to product flow.
After confirming that leak testing is required, the next stage is to select the most suitable method to be employed. The key factor in determining this is the leak rate, which is typically measured in millibar liters per second. (mbar L/s).
For reference, the leak rate of a tap which drips once per second is around 0.17 mbar L/s, while the leak rate of a car tire leaking at a fairly standard rate of 0.2 bar in 6 months is 4x10-5 mbar L/s.
The below table displays a variety of frequently used leak detection methods, alongside the lowest leak rates they can detect.
Methods of Leak Detection
Methods of leak testing fall into two categories: vacuum method or overpressure method.
During the vacuum method (also referred to as “Outside-In Testing”), the test vessel or component is positioned in a chamber with a tracer gas and linked to a leak detector which creates a vacuum by pumping the air out.
The leak detector then determines the quantity of tracer gas that leaks into the test component.
Vacuum method, integral leak testing
An alternative method is to spray tracer gas over any potential leak points in the test component. Any tracer gas the detector then picks up indicates the site of a leak.
Vacuum method, local leak detection
Overpressure (or “Inside-Out”) is carried out in reverse - The test component is pressurized with a tracer gas and positioned within a test chamber linked to a leak detector, which determines the quantity of tracer gas leaking out of the test component.
Overpressure method, integral leak detection
An overpressure mode also enables “sniffing” methods, in which a handheld probe is used to determine the site of any leaking tracer gas.
Overpressure method, local leak detection
The best way to choose a suitable leak detection method is to opt for one that is in line with the final use of the test piece. To illustrate, to test a pressure vessel, one should use an overpressure method, while to test a vacuum chamber, a vacuum method is most appropriate.
Likewise, if a component is only required to be water-tight, then it may be adequate to simply employ a water pressure test. Where rigorous tests are required to locate or quantify a leak, a Helium leak detector should be employed.
Advantages of Helium Leak Detection
Helium leak detection, employing Helium 4 as a tracer gas, has arisen as the most advanced leak detection technology. This method can measure minute leak rates well into the 10-12 mbar L/s range – a leak rate equal to a tap dripping approximately once in a millennium.
The most appropriate tracer gas is Helium, which is the second smallest gas molecule after Hydrogen. In contrast with Hydrogen, it is chemically inert and non-flammable.
Thanks to its small size and the ease with which it can be detected, it can be employed to detect leaks several orders of magnitude smaller than opposing technologies can.
Proper calibration of equipment is vital during a process as sensitive as Helium leak testing.
As Helium is found at concentrations of approximately 5 ppm in the lower atmosphere, it is important that measures are taken to confirm background Helium levels, and to identify other sources of Helium, such as permeation and “false” leakage from pockets or fissures within the test component.1
As a general rule, in order to locate or quantify a leak, the Helium background should be at least two order of magnitude lower than the leak rate being examined.
In order to calibrate machines used for sensitive testing, “test” leaks, delicately calibrated instruments which leak Helium at a known, constant rate, are frequently employed. Thankfully, the majority of modern leak detectors can carry out this calibration in an automated manner.
Sample of background helium signal
Leading the revolution of Helium leak detection, Leybold has introduced the Phoenix 4 line, its fourth generation of Helium detectors. The three Phoenix models, each developed for different uses, have been developed to deliver higher levels of accuracy and speed.
Phoenix 4 Vario, Quadro and Magno
Every Phoenix 4 Helium detector boasts a tuned mass spectrometer which can detect Hydrogen 2 and Helium isotopes 3 and 4 to detect and quantify leaks at levels as low as 5x10-12 mbar L/s. In addition to this, enhanced measurement systems can deliver more rapid response times than ever.
With the help of an easy-to-operate touchscreen interface, intuitive in-built software and the ability to store parameter sets for various test parts, the Phoenix 4 circumvents a number of the standard issues faced in leak testing.
No other portable detector available today offers the Phoenix 4 range’s simple Wi-Fi-based login, or easy use of a smartphone or tablet without the need for any software or app download.
This reference document was based on Leybold’s free webinar “The Do’s and Don’ts of Leak Testing and Detection”, produced by Leybold’s in-house leak detection expert Mike Ridenour.
References and Further Reading
- Helium concentration in the Earth’s lower atmosphere. Oliver, B. M., Bradley, J. G. & Farrar, H. Geochim. Cosmochim. Acta 48, 1759–1767 (1984).
- Leak Detectors - Leybold. Available at: https://www.leybold.com/en/products/measurement-and-instrumentation/leak-detectors-1/
This information has been sourced, reviewed and adapted from materials provided by Leybold.
For more information on this source, please visit Leybold.