INTRODUCTION In the cleaning industry, components and systems must be leak tested to ensure that cleaning leakages are below specified limits. THE THREE BASIC FUNCTIONS OF LEAK TESTING ARE 1)....
In the cleaning industry, components and systems must be leak tested to ensure that cleaning leakages are below specified limits.
THE THREE BASIC FUNCTIONS OF LEAK TESTING ARE
1) determining if there is leakage or not (detection),
2) measurement of leak rate and
3) leakage location.
There are many methods and types of test equipment for solving these problems, but unfortunately there is no single technique that fits every situation. Each test method is suitable only for a specific leak rate or for fixed forms and technologies. In most instances where leak detection is used, explicit leak rate measurement is not required, but the system must be able to recognize if the leak rate is above or below a specified level. This reference limit depends on the maximum acceptable leak rate, consistent with the reasonable working life expectation for final products, and, especially in certain countries, on rules and regulations constraints
2 LEAK TESTING METHODS
A leak can be defined as an unintended crack, hole or porosity in an enveloping wall or joint, which must contain or exclude different fluids and gases allowing the escape of closed medium. Critical leak spots in closed systems are usually connections, gaskets, welded and brazed joints, defects in material, etc.
2.1 WATER IMMERSION BUBBLE TEST METHOD
The water-immersion bubble test, also called "bubble testing" or "dunking", is a traditional and relatively primitive technique of leak detection. It consists of immersing a charged or pressurized part, usually with high-pressure dry air or nitrogen, in a water tank and watching for escaping bubbles. The larger and more frequent the bubbles, the bigger the leakage.
2.2 SOAP SOLUTION BUBBLE TEST
Instead of submersing the part in water, the pressurized unit to be tested is sprayed with a soap solution and the operator is able to see the bubbles formed by gas escaping from where the leak is. Soap solutions are available in many different types. Some have a brush applicator and others have a dabber (an absorbent ball attached to a stiff wire inside of the cap.) Some brands may even have a spray applicator to quickly cover large areas of tubing in a short amount of time. This is an advantage but is also messy and time consuming to clean up. Some soap solutions even have an antifreeze base to prevent them from freezing in the winter time. Others may have a lower density to make them even more sensitive to very tiny leaks. This method has a higher sensitivity than water immersion.
2.3 PRESSURE DECAY TEST
This method consists of pressurizing the system with a high pressure gas, usually dry air or nitrogen. Then the part is isolated from the gas supply and, after a stabilizing period, its internal pressure is monitored over time. The pressure drop Δp is measured in the time Δt. If the pressure in the system drops fast, there is a large leak present in that component or section of the system. If the system’s pressure drops slowly, there is a small leak present. If the pressure remains the same, that component is leak-free.
2.4 VACUUM DECAY TEST OR PRESSURE RISE TEST
A vacuum decay test or pressure rise test works in the opposite way of the pressure decay test. This method involves evacuating the part to suitably low pressures and, after stabilizing the pressure, measuring the increase in pressure caused by test media entering the part. Only parts that are able to withstand external pressure can be tested in this way(e.g. thin-walled plastic parts cannot be tested due to the danger of collapsing).
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