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.

About

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. Spacecraft 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
Antennas
Heat exchangers
Hydraulic systems
Valves
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 on 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

Ultrasonic Cleaning:

This technique uses cavitation which is induced by high frequency sound waves to agitate the cleaning solution aiding in dislodging particles. It is particularly effective for precision parts cleaning of complex parts with threads, rough surfaces and blind interior spots that are inaccessible by other cleaning methods. Ultrasonic cleaning typically employs aqueous, semi-aqueous and solvent-based cleaning systems and detergents. This combination removes contaminants at nearly a microscopic level, with higher sound frequencies generally able to remove finer particles.

High-Pressure Spray Cleaning:

This procedure utilizes the kinetic energy of a water jet to “blast” the particles and soils from a surface. It is most often used in conjunction with detergents or surfactants to chemically loosen or solubilize the soils in order for the water jet to more effectively remove the contaminants from the surface. The ability to vary the water pressure, nozzle size and/or spray pattern allows this method to be easily customizable for different materials of construction and soil compositions.

Flush Cleaning:

Using a turbulent velocity, cleaning liquids are flooded through the interior of tubes, pipes, and other internal pathways to flush the contaminants out of the hardware or component as it rotates. This method is particularly useful for precision cleaning of components of varying shape and size for which high-pressure sprays are not useful.

Vacuum Bakeout:

This methodology uses vacuum baking to volatilize hydrocarbon contaminants and remove hydrocarbons that are entrapped in the pores of sensitive equipment. It also reduces the outgassing rates to acceptable levels for aerospace instrumentation.