Post on 30-Mar-2015
transcript
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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