In my last article we talked about the leak testing process and why is it a critical one in manufacturing and production automation industries. Let’s find out in this article what are the different processes and in how many ways this leak testing process is carried out. A variety of leak testing methods are available, but the simpler methods have been the most popular. Methods prevalent in every industry include water dunk testing and pressure decay. Each of these methods offers the advantage of minimal investment, but each also has major drawbacks.
Bursting the bubble Leak testing method.
Process:
This process includes dunking of an object into water to determine if and where an object has a leak. When an object is immersed, bubbles form at the source of the leak as a result of air pressure. The amount of bubbles forming at the source of any special purpose machinery is measured and this amount of bubbles per minute signifies the size of the leak.
Disadvantages:
1. This method provides minimal quality assurance as a very small leak might make a few miniscule bubbles. Also whether air bubbles rise to the surface or stick to the test object depends on surface tension.
2. The method operator’s involvement is also one of the factors that may determine the accuracy and efficiency of the test conducted on various automation systems. In this method, the operator’s perspective can be limited as he may not be able to see small leaks on the opposite side of the object.
3. Since water dunking method involves the use of the water itself, many products can’t be immersed in water due to the risk of corrosion or contamination.
Pressure Decay Leak Testing Method.
Process:
Another most common method for leak testing is pressure decay. In this method, the test object is pressurized with air and monitored with a pressure gauge. A drop in pressure signifies a leak; the greater the pressure drop, the larger the leak. This method is convenient, in that it’s dry and easily automated. However, pressure decay testing cannot be used to pinpoint the location of a leak, and its accuracy depends on the temperature, size and material of the test object.
Disadvantages:
1. Temperature inside the object can be a factor that decreases the efficiency of this leak testing method. As air is compressed inside the object, its temperature rises. The pressure will not stabilize until the temperature stabilizes. Any additional temperature that may come either from the hand or any outside element can throw off the test results.
2. This leak testing method works best with objects that are made up of rigid materials than flexible materials. Products made of rubber or flexible plastic counteract the drop in pressure by reducing their volume.
3. Pressure decay testing is much preferred for objects with small test volumes. This may not be the best choice for testing large objects, such as gasoline tanks, because they take too long to pressurize.
One more method that is being used in the recent years called Helium Hydrogen leak testing or testing with tracer gases has proven to be the most effective one for measuring and detecting leaks in both small and large objects. We will discuss about this method in detail but in my next article.
