Test for leaks in a water bath or with trace gas?
Find the right solution for your packaging
LEAK TESTING IN A WATER BATH
Bubble leak testing in a water bath is a visual test method e.g. for leak testing of packaging. The test item is completely immersed in water. If there are leaks, visible air bubbles rise.
LEAK TESTING WITH TRACE GAS
The leak testing with trace gas is done using gas sensors. The test item (packaging) must contain the defined trace gas. If the test item is leaky, the escaping gas is detected by the sensors.
HOW IS THE LEAK TESTING / DETECTION DONE?
Bubble leak test or leak detection systems consist of a transparent water bath into which a test specimen, e.g. a food packaging, is completely immersed, and can be inspected from all sides for any rising air bubbles, i.e. leaks. Ideally, grippers are available to hold the test specimen under water during this process.
The bubble leak test works best the higher the pressure in the test item is compared to the ambient pressure. Then notable streams of air bubbles rise from the leaks to the water surface. At a pressure difference of a few mbar, the surface tension of the water delays or prevents the formation of bubbles. Solid items or components are therefore pressurized with compressed air for water leak testing. Conversely, it is also possible to reduce the ambient pressure in the water chamber: In the sealable water chamber, the air space above the water is evacuated for this purpose.
For a controlled leak testing process, an always consistent pressurization or evacuation as well as testing time under water must be defined and adhered to. The visual checking and attention of the tester is crucial: he/she must notice the rising air bubbles and can thus determine the position of the leak on the test item.
Leak testing equipment with trace gas is available for random sample leak testing and as fully automated inline machines for checking the entire production for leaks. One or more test items (packaging) are positioned in a chamber, a vacuum is created and the trace gas escaping from leaks is detected by sensors.
Food or medical/pharmaceutical products packaged with a modified atmosphere are mainly tested for escaping CO2. It is already present in many packages as part of the modified gas atmosphere. This is different for items or component groups that must have trace gas applied to them. In the most strenuous of leak-tightness requirements, helium or hydrogen serve as trace gases which, with their small molecular size, can pass through even the smallest gaps. For food packaging, such a fine test is rarely necessary. Moreover, the additionally introduced hydrogen makes it difficult to analyse the modified atmosphere for residual oxygen.
Leak tests with trace gas can be automated very easily and thus can also include digital documentation of the testing process. The quality checking is carried out independent of any human inspector and is absolutely standardized. The sensors provide measured values from which an exact leakage rate can be derived.
LEAK TIGHTNESS CLASSIFICATIONS
All packaging materials and conjoined components have tiny openings that can be understood as leaks. Technically, there is no such thing as absolute leak-tightness. Whether a test item (packaging) is “leak-tight” or “leaky” can only be said with reference to the predefined leakage rate. It sets the limit between a tolerable leak and a leak that endangers the function or safety of the product.
Each leak test method has its advantages and disadvantages. It depends on what you want to test, how you define leak-tightness, and how you intend to integrate the testing into your production.
BUBBLE LEAK TEST IN A WATER BATH
Pro
precise localisation of leaks
weak point analysis, to optimise the production process (e.g. seams, sealing points, material condition, assembly faults, etc.)
expensive items can be selectively reworked
Contra
visual inspection by human without exact leakage rate
the tested item may not be able to be returned into production (food packaging)
regular cleaning of the chamber, or water changes required
Especially suitable
for medium to large components with low mould complexity, e.g. stainless steel fittings, fuel tanks, plastic parts, etc.
With the LEAK-MASTER® model series from WITT, you have the choice: bubble leak testing of packaging in a water bath or with CO2 as the trace gas.
LEAK-MASTER® EASY
Optimise your packaging process by detecting leaks with pinpoint accuracy. Bubble leak testing in a water bath is simple and effective with the LEAK-MASTER® EASY leak tester.
Inline leak detection on an industrial scale using trace gas CO2. With LEAK-MASTER® MAPMAX you test your entire production: fully automated and integrated into your packaging line.
Longer shelf life and freshness. This is what packaging of foods, pharmaceutical and cosmetic products is all about. WITT is expert in packaging technology with modified gases and offers gas mixers, gas analysers and leak detectors especially for modified atmosphere packaging MAP.
We are experts in customised solutions in gas process engineering and gas safety technology. We supply gas mixers, leak testers, gas analysers and gas safety technology to the food and beverage industry, the steel industry, the glass industry, the laser industries and many others industries and applications. From product selection and planning to installation, maintenance and repairs, you can rely on our technical support every step of the way.
Leak-tight or leaking? How to find your leakage rate
While components e.g., of a combustion engine may only need to be watertight or “oil-tight”, modified atmosphere packaging for food or pharmaceuticals must not lose any gas. Accordingly, depending on the intended use, leakages on different scales can be tolerated – a component or packaging is considered leak-tight as soon as it fulfils a defined and thus verifiable requirement for its leak-tightness.
The measure of leak-tightness is the leakage rate. It is quoted in the units mbar l/s and abbreviated with the formula symbol qL. Less frequently, the unit of mass flow sccm (standard cubic centimetres per minute), which is independent of pressure and temperature, is used to indicate the leakage rate.
A leakage rate of 1 mbar l/s corresponds to a gas flow of 1 litre per second at a gas pressure of 1 mbar or describes a situation in which in a closed 1 litre container the pressure rises or falls by 1 mbar within one second. With reference to the leakage rate, leaks can be quantitatively recorded, and the following leak tightness classification defined:
Leakage rate qL in mbar l/s
Leak-tightness classification
10-6
viral tigth
10-5
petrol- and oil-tight
10-4
bacteria-tight
10-3
vapour-tight
10-2
watertight (drop)
The definition of permissible leakage depends largely on the nature of the object. At what point does a leak disrupt the function or up to what point is a leak negligible? A look at comparable applications and empirical values from the industry, which provide indications for determining a leakage rate, might help. Once a limit value has been defined, a suitable method for leak testing can be selected on this basis.
Multi-stage leak testing procedures can also be an economical solution: First, a rough leakage test determines whether the test item is approximately leak-tight. If it is, then, a fine leakage test can follow, in which the leakage rate can be determined precisely. This saves unnecessary leak tests and conserves the use of this measurement technology.