Astro Pak is constantly improving service offerings for helium leak testing. Currently, we perform helium leak testing on small numbers of parts at a time (low volume production) for batch processing or individual tests.
Our current focus is providing accurate, quantitative helium leak testing services for pressure vessels weighing under 100 lbs. However, qualitative testing on low pressure systems is available provided the system can be fully sealed using common stock and/or customer provided hardware. Any system being pressurized must have fittings, seals, caps/plugs, and the system itself be rated to withstand the test pressures prior to pressurization and testing (hydrostatic and pneumatic pressure testing services available) for safety reasons.
Testing for vacuum systems and components is available for systems under 400 L (14.1 ft3) in volume with an internal surface area under 3.0 m2 (32.3 ft2) that can be fully sealed using common stock and/or customer provided hardware. For vacuum systems requiring testing, the internal surfaces must be new or cleaned ( Astro Pak can provide the requisite cleaning services) to ensure accurate results.
What is Helium Leak Testing?
Helium is an inert, stable, and non-condensable gas that is often used as a tracer gas to identify leaks in parts and systems. The very small atomic size allows the helium to easily pass through leaks, and because it is inert, it will not react with virtually any of the materials within the part or system that is being tested. Since helium is only naturally present in the atmosphere in small amounts (~5 ppm), qualitative helium leak testing can be performed in ambient air to test areas that need rewelding, fittings that need tightening, failed gaskets, and other pressure system leak points. It is also used to determine what the total leak of a system is before it is put into service.
For the aerospace industry, the ability to test for leaks with high-level sensitivity is imperative to ensuring mission success, and at times, safety. Failure to identify and repair even small leaks can have detrimental consequences. During regular operations, all aircraft, satellites and rocket systems are subjected to different temperatures, atmospheric pressures and other stressors that can result in more severe leaks. An airplane leaking fuel may have a fire and not reach its destination safely. Space craft missions, with their limited resource supplies, will be compromised if the gas within a tank or primed system leaks out before the mission is complete.
Helium leak detection has been used for many years in the aerospace industry for the following:
- Critical gas lines
- Fuel systems and COPV tanks
- Sealed electronic enclosures
- Missile guidance systems
- Solid rocket booster cone assemblies
- Heat exchangers
- Hydraulic systems
- Cockpit instruments
Helium leak detection methods are also used across a variety of other industries including medical, automotive, and oil and gas processing. Helium leak detectors are used in the quality control of production parts such as medical devices, hydraulic lines, condensers, radiators, manifolds, fuel lines, fittings, and COPV tanks. Pressurized systems such as those found in oil and gas processing and vacuum systems, including vacuum furnaces, isolation glove boxes and laser process equipment, also utilize helium leak detectors to ensure the integrity of those systems prior to start up and as part of their preventative maintenance procedures.
What are the Benefits of Helium Leak Testing?
There are many benefits associated with helium leak testing, which include:
- Leaks can be detected and quantified with a high level of sensitivity
- No adverse impact to the materials being tested due to the inert properties of helium
- The test process is essentially dry and temperature independent
- Microscopic leaks can be fixed before they do significant damage
- Lost production, time and costs can be avoided by repairing leaks before putting the part into service
- Reduced operational and maintenance costs for equipment through preventative maintenance
How Does Helium Leak Testing Work?
Helium leak testing utilizes a Helium Leak Detector, also referred to as a Mass Spectrometer Leak Detector (MSLD), to find a leak inside or outside of a system and then measure the leak rate. The helium leaks in/out of the tested product and is measured by the detector. The detector determines the leak rate based on the helium concentration and flow rate.
A complete Helium Leak Detector system contains the following elements:
- Helium mass spectrometer to detect the mass of the helium
- Vacuum system to maintain sufficiently low pressure for the spectrometer
- Valves which control individual steps of the measuring cycle: evacuation, testing and venting
- Electronic measuring and control systems
- Power sources for individual components – valves, circuits, etc.
- Fixtures, which connect the tested product to the detector
Astro Pak Helium Leak Testing Capabilities
Astro Pak offers various helium leak testing services at its California facility. The method for leak detection is chosen based on the operating conditions of the part or system that is being tested. Proper detection requires that the same pressure conditions are maintained during the test as will be encountered during the actual use of the part.
Vacuum Chamber Capabilities and Specifications:
- 78” DIAMETER X 144” LENGTH. Current capabilities include a base vacuum pressure of 3 X 10E-4 Torr, with a system sensitivity of 7.5 x 10E-12 atm. cc/sec. helium. Astro Pak can also provide pneumatic internal pressurization for a test item- such as a fuel tank, with helium up to 4900 PSIG, while within the vacuum environment.
All helium leak testing efforts at Astro Pak are clearly defined both in specific internal/external test procedures, and in strict accordance with ASME Boiler and Pressure Vessel Code, Section V, Article 10.
Hard Vacuum Leak Testing
The Hard Vacuum Leak Test is one of the most sensitive methods and it is widely used for vacuum system applications. In Hard Vacuum Leak Testing, the test piece or system is tested for leaks from the outside-in. This method is useful for finding leak locations for repair or leak rates, however, it is only designed for testing vacuum systems and parts.
To find leak locations, the test part can be tested by first evacuating air from the inside, and then applying helium to the outside of the part using a small spray probe. If there is a leak in that area, the helium will enter the system and be picked up by the Helium Leak Detector that is connected to the test piece.
To find leak rates, the test part has the air evacuated from the inside and the part is placed in a helium rich environment. The total leak rate can be measured by the Helium Leak Detector connected to the test piece.
Overall Leak Testing
Pressure vessels and parts can be tested using an Overall Helium Leak Testing procedure. Specialized equipment is required to pressurize the vessel or part being tested while in a vacuum environment. The overall leak rate is determined by the amount of helium that is released into the chamber and measured by the Helium Leak Detector. This method is commonly used for space and fuel cell manufacturing and is utilized for determining permeation and pressure retention. Due to the number of variables that are involved in the testing, the Overall Leak Test is the most difficult to perform.
Helium Sniff Testing
Helium Sniff Testing is typically conducted in an open-air setting where the test system is charged with helium and then scanned with a Sniffer probe to detect helium that is escaping from a relatively large leak. A sniff test is generally quick to perform, simply because it can be done in ambient air and only requires a small amount of pressure to be introduced to the part. When using this testing procedure, the leak must be greater than the ambient helium concentration to be detected and generally the results are not for highly accurate leak rates. This method is useful for testing systems that may be too large to place inside a test chamber and for finding relatively large leak locations prior to more accurate testing methods.
The Astro Pak Advantage
With over 60 years of experience in the industry, Astro Pak offers quality precision cleaning services to meet the requirements for hundreds of industry specifications, including those of aerospace contractors, ULA, NASA, the Department of Defense, and many private organizations. Our scientists and experts provide guidance and consultation on precision cleaning to some of the world’s most prestigious institutions. These include JPL, Lawrence Livermore National Laboratory, MIT, Cal-Tech and others. Our Research & Development professionals can develop a customized precision cleaning process that meets nearly any requirement.