Principles of Various Leak Detection Techniques Used in

the Canning Industry

Ovec Systems Limited

LEAK RATE UNITS

1 atms cc / sec = One cubic centimetre of gas, at atmospheric pressure, every second

Leak Types

Gross > 1 atms cc / sec

Medium > 0.01 atms cc / sec or 1x10-2

Micro > 0.000001 atms cc / sec or 1x10-6

Molecular > 0.00000001 atms cc / sec or 1x10-8

Principles of Various Leak Detection Techniques Used in the Canning Industry

PRESSURE DROP / RISE TEST

LIGHT DETECTION TEST

BUBBLE TESTING

DYE PENETRATION

HELIUM MASS SPECTROMETER

PRESSURE TESTING

Pressure rise testPressure drop test

These tests are performed on a system pressurized to a recorded level. The system is sealed and leakage is monitored by checking the rate at which pressure drops or rises. Tests are relatively simple in principle.

METHOD

PRESSURE DROP / RISE 1x10-2 cc/sec

Fairly easy to perform in small test systems.

ADVANTAGES

DISADVANTAGES

Can be used only for systems capable of being pressurized

Difficult to determine location of unacceptable leakage.

More suitable for measuring large rates of leakage.

Short test time

LIGHT DETECTION

Light passing through any pin-holes in the end is detected by a photo sensor.

METHOD

LIGHT DETECTION TEST 1x10-3 cc/sec

On line 100% test

ADVANTAGES

DISADVANTAGES

Poor sensitivity may allow 100% faulty products to go undetected. Some leaks cannot be detected as very few holes have a straight path. Larger leaks may be masked by the tab or rivet.

Relatively low running costs

BUBBLE TESTING

This technique involves the use of air as the tracer gas. One of the many techniques available under this method involves pressurizing one side of the system to be tested with air (tracer gas) and submerging in water. A stream of bubbles will form at the point of leak.

METHOD

BUBBLE TESTING 1x10-5 cc/sec

Bubbles locate leak position

ADVANTAGES

DISADVANTAGES

Bubbles can come from sources other than leaks and give false signals.

Little skill and cost involved.

Procedure is safe in combustible atmospheres.

Appropriate equipment readily available.

Low reliability as water surface tension or impurities may plug the leaks.

Operator and time dependent.

Tested product can't be returned to the line without cleaning.

DYE PENETRATION 1x10-6 cc/sec

This test involves applying a penetrating dye to one side of the surface. After a minimum of 15 minutes the other side is visually examined for the presence of dye by using either a developer solution or ultraviolet light.

Materials are relatively low cost.

METHOD

ADVANTAGES

DISADVANTAGES

Method is more sensitive than bubble, pressure and light testing, but the results can be affected by the geometry of the leakage path.

The dye produces a visual indication of the leak.

Test is destructive.

Procedure is very slow

The dye can plug micro leaks.

Principle of Helium leak testingPrinciple of Helium leak testing

• Seal end in test head

• Evacuate air from both faces

• Pressurise bottom with Helium

• Monitor top face for helium permeation

HELIUM MASS SPECTROMETER 1x10-6 cc/sec

The tracer gas used in this method is inert Helium gas (He). The gas is exposed to one side of the product and the other side is evacuated through the mass spectrometer (detector). If any of the Helium passes through a leak, the spectrometer sensor will detect the presence of Helium atoms. The sensor responds with a signal in proportion to the amount of Helium, and an alarm is triggered.

Not dependant on operator judgment

METHOD

ADVANTAGES DISADVANTAGES

Production-line units involve high initial cost.

This is offset by:

Method is reliable and consistent

Reduction in costly returns

Returning the tested product to the production line

No operator involvement in the testing

Helium is readily available

Mass spectrometer system has sensitivity up to 1 x 10-12 cc/sec

Fast and efficient detection of faulty product

Auto-calibration with reference leaks traceable to international standards

Non destructive

Equipment requires regular maintenance by qualified person.

Summary of Detectable Leak RatesPRESSURE DROP / RISE 1x10-2 cc/sec

LIGHT DETECTION TEST 1x10-3 cc/sec

BUBBLE TESTING 1x10-5 cc/sec

DYE PENETRATION 1x10-6 cc/sec

HELIUM MASS SPECTROMETER 1x10-6 cc/sec

Shelf life for 33cl can 1 hour

Shelf life for 33cl can 10 hrs

Shelf life for 33cl can 6 weeks

Shelf life for 33cl can 15 months

AET 1800 On-line Helium Leak Detector

AET 6000 Off-line Helium Leak Detector

Should you have any questions or require any technical assistance please do not hesitate to contact us:

                                 

Ovec Systems Ltd., 5 Brown Street, Coatbridge, ML5 4AS, Scotland Tel +44 (0)1236 710680 Fax +44 (0)1236 710747

e-mail: info@ovec.co.uk web site: www.ovec.co.uk Reg. SC136128 

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