Principles of Various Leak Detection Techniques Used in the Canning Industry Ovec Systems Limited Notes:
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 test Pressure 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 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 Rates PRESSURE 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
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