What are the Different Helium Leak Detection Methods?
Leak detection is vital in a plethora of industries, such as aerospace, automotive, pharmaceutical, and the military. When tiny leaks can contaminate medication and cause rockets to explode, it is important to find safe ways to locate and fix those leaking areas.
Helium is typically the best gas for finding leaks because it is small, inert, and non-combustible. This means it can be safely used to test for leaks in a variety of situations (whether for cars, rockets, medicine, etc.). You can learn more about the different industries helium leak detection can be used in here.
While helium can be used in a plethora of situations, the ways helium is applied vary depending on the situation. Different tests are required for evaluating food versus oil and gas. Below we will describe seven of the most common helium leak testing methods and any challenges engineers may have detecting leaks.
Spray Method
The spray method sprays helium on the device under testing (DUT) to detect any leaks that come from inside the test object after the DUT’s interior has been evacuated. These
tests find leaks in large, complex systems where other methods are less safe. It is also simpler and more cost-effective than other methods, requiring less training from those operating the spray guns. The tradeoff is that this method is less sensitive than other methods. While it is safer and cheaper, it will not be able to cover very small leaks.
Vacuum Hood Method
Before starting the vacuum hood method, the tester must evacuate the inside of the test object. Then, they will place a hood on the outside of the DUT and fill the hood with helium gas to detect if helium enters the object in question.
This method can quantify the total leakage of the test object, but finding a leak point is typically done by the spray method. The vacuum hood method is also limited by the size of the vacuum hood, meaning it cannot test larger objects or machinery.
Sniffer Method
The sniffer method begins by pressurizing the inside of the DUT.
Helium is then pumped into a singular port in the device. The pressurization of the DUT will push the helium out of the object if there are any leaks. The sniffer probe will detect this helium to locate any cracks or leaks in the device.
The main problem with the sniffer method is that it can be dependent on the atmosphere it is placed in. If there is helium present in the atmosphere, it could affect the accuracy of the test.
Pressure Accumulation Method
As an alternative to the sniffer method, pressure accumulation covers the test object with a hood, then pressurizes the test object with helium gas. This will cause the leaked helium gas to accumulate, increasing the helium concentration. A detector is then used to locate any abnormal pressure increases that would come from the leak point.
While this method is very precise, it can also be more expensive than other methods. Helium on its own is rapidly growing in price, so adding that cost to the cost of the test and the cleaning system needed to take care of the “contaminated environment” can add up.
Suction Cup Method
Similarly to the sniffer method, this test fills the inside of the DUT with helium. The key difference is,
instead of using a sniffer probe to detect the leak, the suction cup method uses a suction cup to suck the gas from the DUT. This is typically performed on large vacuum containers or other pressure containers that cannot be evacuated or pressurized by the whole body because of a manufacturing process or condition of products. The downside of this method is that they are mainly used for finding the general region where the leaks are, not the exact location.
Bell Jar Method
The bell jar method places the DUT inside the bell jar, then depressurizes
the air. Once this is done, the atmospheric pressure can no longer affect the helium concentration within the jar. After the jar is depressurized, the gas in the chamber is sucked out, and the helium within that gas is detected and judged by a detector. Because it takes the helium out of the whole jar, this method is not ideal for finding the precise location of leaks.
Bombing Method
This method places the DUT in a special chamber to be “bombarded” with helium. Before the helium is used, any excess air is removed from within the chamber, so the pressure and air are controlled when testing for leaked helium. After the helium bombing is completed, every component is tested in a test vacuum chamber to measure how much helium is escaping from each part. The bombing method is useful for finding smaller leaks, since each part is detected individually. That being said, it can be time consuming to complete and it is not ideal for larger leaks.