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Leak Testing: Guide to helium leak testing

Explore the Leak Testing Section Guide to the fundamentals of Helium Leak Testing
Leak Testing is used to ensure quality, tested
and proven parts are supplied into the market. What is helium leak testing?
The use of leak testing equipment eliminates
failures in the field. Helium is used to find small leaks or possibly larger leaks in bigger volumes. The helium is used as a
tracer gas and its concentration is measured.
Explore this section to find out more about the
how TQC can help you with your leak testing
requirements Why use helium for leak testing?
Overview
Helium is one of the smallest gas molecules and is inert, (remember your periodic table from Chemistry?).
General Information Being inert it is relatively safe to use (rather than hydrogen) and will not react with any of the materials
Basic Principles within the part to be tested. In most helium leak testing applications, one uses a mass spectrometer
tuned to detect helium although it is possible to use a residual gas analyser. Helium leak testing can be
Useful Leak Specification Guidelines generally be between one thousand and one million times more sensitive than using pressure decay
Leak Test Machines techniques.

Air Decay
What are the benefits of Helium Leak Testing?
High Pressure (Over 6 Bar)
Low Pressure (0 to 6 Bar) Using this technique you can leak test to find smaller leaks than with other test processes, using a largely
Vacuum temperature independant, dry technique. This should result in a longer product life. There are 2 basic
techniques; high vacuum testing which allows leak test thresholds to be set down as low as 1x10-
Helium 12mbar.l.sec-1, or sniffing which is generally used for helium leaks down to 1x10-6mbar.l.sec-1. For
Guide to Helium Leak Testing
reference 1 cubic millimetre per second is approximately 1x10-3mbar.l.sec-1. or 1cc is approximately
1mbar litre per second.
Using a Mass Spectrometer
Sniffing Most tests use readily available Balloon Gas (yes, this is what is put in kiddies balloons!). On rare
occasions certifiably pure gas is used. On a safety note, please remember that bottled helium contains no
Other Test Methods
oxygen and is therefore an asphyxiant. It is worth remembering that leakage is a flow of fluid from a higher
Novel Leak Testing Techniques pressure to a lower pressure through a fault in an assembly or manufactured part.
High Vacuum Methods
The high vacuum technique requires that the test volume to which the instrument is connected is at high
Water Submersal
vacuum i.e. less than 10mbar absolute pressure. Can the part or assembly withstand this pressure? It is
Leak Testing Services possible to test a part at high pressure and high vacuum at the same time. You need to arrange these
pressures either side of the leaking boundary. This may mean putting the part under test inside a leak tight
Standard Equipment chamber.
Series 10 Standard Leak Testing Fixture
Series 20 Standard Leak Testing Fixture When testing using helium, it is possible to flood the mass spectrometer with helium if there is a large
leak. In most instances, where there are many minutes between each test, this is not a problem, one just
Series 40 Standard Leak Testing Fixture waits for the instrument to clean itself up.
Twin Station Series 40 Standard Leak
Testing Machine One can also either sniff or spray helium. Helium Sniffing is used where the part can be pressurised
Series 40 Standard Leak Testing above atmospheric and a helium sniffer gun is manually positioned round the part. Spraying is where the
Machine with Interchangeable Fixtures part can be evacuated and helium is manually sprayed over the outside of the part.
Automatic Sealing Connectors
Background Helium concentration
Case Studies
Automotive Brake Leak and Flow Helium can and will get everywhere if it can. It gets quite difficult sometimes to determine where the helium
Testing
is coming from. There is approximately 5 ppm Helium in the atmosphere. If the part under test is filled with
Automotive Bedplate Leak Test Machine helium it is important that the test charge is taken away and not just released into the immediate area. For
Battery Tray Leak Test Machine just a few tests, the helium can be diluted in the immediate area. For more frequent testing, this may mean
piping the extracted test gas away to the outside of the building on the downwind side and well clear from
Chilled Beam Leak Test doors or windows that could allow it back in.
Flexible Leak Test Facility
To locate helium leaks one usually either sprays or sniffs, the latter being the norm in high volume testing.
Fuel Tank Leak Testing
When using a helium sniffer, one starts with 5 ppm and would usually look to detect an increase of a
Helium Leak Test Bench further 5 ppm.
Helium Leak Testing of Automotive Fuel
Pipes
High Pressure Audit Leak Testing One can use this detectable rise in helium concentration to test parts inside a shroud where the test
System with Datalogging pressure is at or near atmospheric pressure. By circulating the air within the shroud and passing it by a
High Speed Leak Testing of Pipe Fittings mass spectrometer in sniffing mode, you can set an alarm limit at say 8ppm. Again it is important to flush
using Air and Helium or extract away any contaminated air once the test has completed.
High Speed Leak Testing of Plastic Vial
for the Medical Industry Helium leak testing at Lower Limits
Leak Test Facility for Water Valves
When testing at 1 x10-9 and below one may need to do additional things to be able to complete a viable
Leak Test Cell with Robotic Handling
test. One may need to purge away any clinging helium left in the part to be tested or the test chamber. For
Casting Leak Testing of Engine Blocks example, with the chamber and part open to atmosphere before the test, they are exposed to a helium
Medical Filter Leak Test Machine concentration of 5 ppm. The helium can cling to various surfaces and affect the results of the test. So, one
may need to "wash" away any clinging helium in the chamber and part in a gas containing no helium.
Medical Showerhead Leak Test Machine
Plastic Fuel Rail Leak and Burst Test The sequence might be:
Machine
Plastic Sump Pipe Leak Test and 1. evacuate both the part and chamber
Assembly 2. back fill the test volume with certified clean dry nitrogen
Small Medical Device Leak Test 3. re-evacuate
Machine
4. fill the part with the test gas
Twin Station Leak Test Machine for Oils
Sumps
Helium leak testing at high production rates
V6 Cylinder Head Leak Test Machine
V6 Engine Leak Test Machine When high volume production requires high vacuum, you must also consider the time taken to pump down
V8 Cylinder Head Leak Test Machine to the required level of vacuum, this can be significant. At higher production rates, having much shorter
time to test a part, large leakers may be a problem. The flooding of the leak test instrument with helium
V8 Engine Block Leak Test Machine
may take several minutes for the helium to reduce to a level where testing can recommence. To reduce
Valve Block Leak Test Machine the effect of a large leaker one can; build up to the full test pressure in stages, build up to the full
Vauxhall Leak Test Machine concentration, flush the mass spec with a gas with no helium present or pre-screen using an air decay
technique before helium testing. Air decay pre screening will allow known larger leakers to be to be
Weapon Leak Test Machine removed prior to helium leak testing.

When testing at high speed it is important to reduce the test time to its minimum. To do this one may have
to employ a number of techniques to; reduce the test volume (by infilling voids and ensuring minimum pipe
run volumes), nitrogen flush, etc. Of course at high speed the automatic handling of the product and
automatic connection play a large part.
Tooling & Pipework

If one is intending to helium leak test a part; it is important to note that the tooling and pipework used to
create the test volume and helium gas supply must be leak tight to higher degree than the leak test
threshold. This means that careful engineering of the seals is necessary, particularly where complicated
seals are required (e.g. right angled seals for 2 perpendicular faces). One must also use helium leak tight
valves and pipework and pay particular attention to the sizing of the vacuum pipework.

Helium mixing, helium recovery and helium re-use

When testing large volumes, at higher pressures and at high speed, the quantity of helium being used may
become significant. There are a number of techniques to reduce the consumption of the helium gas. First
of these is to mix the helium with another lower cost gas either nitrogen or compressed air. This is only
possible where the sensitivity of the test is not compromised by the mixing process.

The second of these is to re-use the gas from one test by extracting it from the device and then pushing it
into the next device. This can often be implemented by a combination of a vacuum pump and simple air
cylinder arrangement if the volume is not too large. Between cycles it is possible to use the mass
spectrometer to monitor the concentration of helium that is being reused; when the concentration falls
below an acceptable level it is dumped and a new charge of helium is used.

The third technique is helium recovery. Here one extracts the helium into an intermediate holding vessel to
be compressed back to high pressure to recover the helium.

To find out more about how we can help you with your helium leak testing requirements:

We build all machines in-house, applying our 25+ years experience in specialised test and automated
handling machines experience to the engineering projects we undertake. We offer customer support,
backup and service call-out for all projects, whatever the size.

Get in touch with us to discuss your requirements and we will be happy to offer our professional advice
and visit you at your site.

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Email us or call us on 0115 950 3561
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