Hydrogen leak testing method.

We have made ourselves aware with the pressure decay and bubble leak testing methods and other production automation, machine cutting techniques in our last articles. Both the processes are simple, inexpensive and easily automated. However both these methods have significant shortcomings such as the inability to determine the location of leaks and limited sensitivity etc.

A relatively new leak testing technology known as hydrogen leak testing addresses these shortcomings faced in pressure decay and bubble methods. This method actually works as an enhancement to pressure decay systems or as a substitute method. The apparatus and the test procedures for pressure decay and hydrogen leak testing technique are however similar.

This hydrogen leak testing method makes use of a robust, self-calibrating and maintenance-free microelectronic probe that is extremely sensitive and 100% selective to hydrogen. The test gas which is a non-flammable mix of hydrogen and nitrogen is then injected into the test object, and leakage is detected in a variety of ways: In an accumulation chamber where the test object is enclosed, the presence of hydrogen is measured over a certain time interval to determine the total leakage. Alternatively, a hydrogen probe can scan the object’s exterior, either manually or robotically, to pinpoint the location of leaks.

A very useful method, hydrogen leak testing is done on objects rejected by the pressure decay system which are then subsequently tested offline by a separate hydrogen-based leak detection system. Prior to the extensive use of hydrogen method, helium leak testing method was used to address the shortcomings of other leak testing methods. But helium leak testing method proves to be a expensive and moreover the tracing gas helium used in the method is very expensive gas too.

Common Leak Testing Methods.

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.

Why is leak testing essential in automation manufacturing industries?

Leak testing is a vital part of every quality assurance testing for broad range of industries. In fact, for many suppliers of the automation engineering systems and assembly machine equipments industry, leak testing is very integral part of production. Hundred percent of the machinery parts of automation industry are tested against a leak standard.

The leak testing process involves measuring of the leak rate of a part or product. Let’s find out why leak testing process is a critical one in manufacturing and production automation industries. Here I have listed some common ones:-

1. The process of leak testing ensures that the various toxic, corrosive or flammable chemicals and substances are contained tightly within an object.

2. The testing process makes sure that the elements that are present outside the equipment or object for example water cannot get inside the products or mix with the products.

3. In the automotive industry the process of leak testing ensures that the level of gas or liquid that are essential for the proper functioning of the systems, such as hydraulic valves, brakes, air conditioners etc are maintained within that system for the required period of time.

Leak testing process is carried out by several methods like Pressure Decay Method where the test object is pressurized with air and monitored with a pressure gauge, Water Dunk testing method where amount of bubbles per minute signifies the size of the leak, Testing With Tracer Gases that includes Hydrogen Helium leak testing etc which I will be discussing deeply in my next article. But each method offers the specific advantages and certain drawbacks too. Though practically nothing can be absolutely tight, but the leak testing process will ensure that the part or equipment meets a carefully established specification for maximum allowable leakage.