Helium leak test
Principle
Helium is a gas with extremely small molecular weight and strong permeability. The helium leak test uses the high-sensitivity detection function of the helium mass spectrometer to determine the sealing performance of the valve by detecting whether there is helium leakage outside the valve. When the valve is filled with helium, if there is a leakage channel in the valve, helium will seep out of the leak to the outside of the valve. The helium mass spectrometer leak detector can capture extremely small amounts of helium leakage signals, thereby achieving high-precision detection of the valve's sealing.
Operation steps
Preparation
Place the valve in a well-sealed test container or system to ensure that the connection between the valve and the test environment is tight and there is no additional leakage path. For example, in a dedicated helium leak detection laboratory, for a precision small valve, install it in a special sealed test box and connect it to the helium source and helium mass spectrometer leak detector through a pipeline.
Calibrate and preheat the helium mass spectrometer leak detector to put it in normal working condition. The calibration process is a key step to ensure that the leak detector can accurately detect helium leaks, and it needs to be strictly operated in accordance with the instrument's operating instructions.
Helium filling
Inflate the valve with helium at a certain pressure. The helium filling pressure should be set reasonably according to the type, size and test requirements of the valve, and is generally carried out at a lower pressure to avoid damage to the valve or affect its normal working performance. For example, for a medium-sized valve, the helium filling pressure can be set to 0.5 - 1 bar.
During the helium filling process, ensure that the helium fills all parts of the valve evenly. The helium can be diffused by shaking or vibrating the valve appropriately. At the same time, pay attention to controlling the speed of helium filling to avoid excessive pressure fluctuations or other unexpected situations caused by too fast filling.
Detecting leaks
Use a helium mass spectrometer leak detector to scan and detect the outside of the valve. The operator moves the leak detector probe slowly along the surface of the valve to ensure that all possible leaks are covered, such as the sealing surface, valve stem, valve body connection, etc.
When the helium mass spectrometer leak detector detects a helium leak, the instrument will send a signal and display the leak rate. The size of the leak rate reflects the severity of the valve leak, which is generally expressed in terms of the volume or mass of helium leaked per unit time. According to different application scenarios and standard requirements, there are clear regulations on the allowable leakage rate of valves. For example, the allowable leakage rate of valves used in some high-end semiconductor manufacturing equipment may be very low, usually required to be below 10⁻⁹ Pa・m³/s.
If a leak is detected, it is necessary to further determine the leak location. The leak point can be accurately located by applying a small amount of helium on different parts of the valve surface, and then using the leak detector for detection again, observing the change in the leak rate.
Application scenario
The helium leak test is suitable for valves with extremely high sealing requirements, such as in high-tech fields such as nuclear energy, aerospace, and semiconductors. In the field of nuclear energy, the valves in the primary circuit system of nuclear power plants need to withstand high temperature, high pressure and radioactive environment, and have extremely high sealing requirements. Any small leak may cause serious safety accidents. Therefore, a helium leak test is used to ensure the absolute sealing of the valve. In the field of aerospace, the valves in the fuel and oxidizer delivery systems of rocket engines must ensure zero leakage to ensure the launch safety and stable performance of the rocket. The helium leak test is an important means to detect the sealing of these valves. In the semiconductor manufacturing industry, high-purity gases are required in the production process. Minor leaks in valves will contaminate the gas and affect the quality of the chips. Therefore, helium leak tests are widely used to ensure the sealing performance of the valves and meet the strict requirements of the production process.
