Detecting leakages in the industrial is really important to ensure performance and safety. Sometimes, even the most pristine of systems can show the signs of leakages. Leak testing is important to control vacuum or pressure, assure the safety of the product, maintain environmental standards, and achieve pressure efficiency.
Leak Testing involves two major aspects – Leak detection and Leak measurement. Pressure plays a vital role in determining the quantity of the gas leak. Every process needs a different vacuum process. These depend upon the volume of the production. The leaks from 1×10-6 mbar*l/s to 1×10-12 mbar*l/s are detected using a helium molecule.
Use of Helium
Mass spectrometer leak detector (MSLD) is a solution to carry out helium leak testing. The gas is used because it is inert, non-condensable, non-flammable, and non-toxic. Other reasons are that helium is not typically present in the atmosphere, it has a small atomic size. In addition, Helium can pass through leaks, effortlessly. Therefore helium is the first choice for leak testing.
The idea of MSLD was first pioneered in the 1940s during the Manhattan Project. With an aim to test nuclear weapons. The commercial use and sell of helium leak testers were started in 1966. A company from France, Alcatel vacuum group introduced ASM 4.
Methods in Helium Leak Testing
The procedure of leak testing involves examining the pressure of inner and outer side of the product. Simultaneously, the amount of gas passing through the leakage is also measured. This procedure is carried out by two methods viz. Vacuum Method and Overpressure Method.
- Vacuum Method: In this method, a search gas (helium gas) is evacuated and sprayed from the outside. When the gas enters through leaks it is detected by a sensor connected to the leak tester. There are two types of tests in Vacuum method, Hoot test and Tracer Probe Test.
- Hood Test: It is an overall leak test, where the product is covered with a hood. Then helium gas is sprayed between the hood and product. This way, the entire object is exposed to the gas. When helium passes through the leaks the sensors are activated. Further, the indicator also detects the leak rate. It is used for small vessels/products.
- Tracer probe test: This test also requires a similar set-up as a hood test, where a jet spray is used to spray helium gas is exposed at the suspected leaks. This test is used for flange connections, seals, weld seams, and others.
- Overpressure Method: The product that is to be examined is filled with helium gas under overpressure. The gas then escapes through the leaks that are present, which is detected by a detector probe. Overpressure method can be implemented by three tests viz. Hood test, the Bombing test and the Detector Probe or Sniffer test.
- Hood Test: Many parameters of this test is are similar vacuum hoot tests like the set-up. It is used for overall examination of the product. Here, a vacuum chamber is used as a hood that is evacuated by an auxiliary pump. The detector is connected to the pump itself. These detectors detect the escaping helium gas through leaks. This method is suitable for products like heat exchangers.
- Bombing Test: This method is used for testing hermetically sealed vessels containing cavity and filled with gas. The helium gas creates a pressure chamber around the product. This create pressure will help helium to penetrate through leaks present in the product. This penetration is referred to as the “bombing”. After this step, the hood test is followed for detection. Even the smallest of leaks are detected by this test.
- Sniffer Test: A detector probe/sniffer, attached to the leak tester is used to examine the whole products. The accuracy of this test depends upon the nature of the search gas.
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