Leak Testing (LT)

Helium leak mass spectrometer testing is a way to detect very small leaks across a pressure boundary. The test is conducted with the use of a mass spectrometer, which is calibrated to detect the presence of helium molecules. Helium molecules are very small, so using helium as a tracer gas will find very small leaks that other leak tests may not find. This can be conducted in one of 3 ways: - Detector-probe technique - Tracer-probe technique - Hood technique The detector-probe test is conducted by pressurising a component with helium gas, and then scanning the component “sniffing” for the presence of helium with the detector probe. The mass spectrometer is monitored to verify the presence of helium leakage. The tracer-probe test is conducted by placing the component under a vacuum and connecting it to the mass spectrometer. The tracer probe is then used to “spray” helium around the component under test. If a leak is present, the helium will be drawn into the part due to the differential pressure. The mass spectrometer is monitored to verify the presence of helium leakage. The hood test is conducted by placing the component under a vacuum and connected to the mass spectrometer. A “hood” or “envelope” is then established around a portion of the component under test, such as the tube-sheet bundle of a heat exchanger. The hood, which is normally made of a plastic material or bag, is then filled with helium to test a large area at one time. If a leak is present, the helium will be drawn into the part due to the differential pressure. The mass spectrometer is monitored to verify the presence of helium leakage.

Bubble leak testing is used to find leaks in many different components. The two most common forms of bubble leak testing are the direct-pressure technique and the vacuum-box technique. The direct-pressure technique is conducted by pressurising a component with a gas and then either submerging it in a solution or applying a solution to the outside of the component. If a leak is present, bubbles will form on the surface because of the leaking gas passing through the solution. The vacuum-box technique is conducted on parts that cannot be directly pressurised or where access is not available to both sides of a component. The test is conducted by applying a solution to an area of a pressure-boundary surface and creating a differential pressure across the area, causing the formation of bubbles as leakage gas, such as atmospheric air, passes through the solution.

The Halogen diode detector probe test is a way to conduct a leak test by using a tracer gas and a detector probe to detect the presence of halogen. The detection of halogen across a pressure boundary would indicate the presence of a leak.

Pressure-change testing is conducted to determine the leakage rate across the boundaries of a closed component or system at a specific pressure or vacuum. By monitoring the change in pressure over a period of time, the leakage rate can be determined, either by the loss of pressure in a pressurised system or the increase in pressure in a system under vacuum. The change in pressure can then be compared to a maximum allowable change in either pressure per unit of time, percentage volume, or mass change per unit of time.