The helium mass spectrometer leak detection method is based on the basic principle of helium partial pressure measurement using a helium mass spectrometer leak detector, to accurately measure the helium leakage of the tested object. When there is a leak on the protruding surface of the inspected part, the helium gas and its components will leak out from the leak. After the leaked air enters the helium mass spectrometer leak detector, due to the selective identification ability of the helium mass spectrometer leak detector, only the helium gas in the gas is divided into pressure data signal values. On the basis of obtaining the helium gas data signal value, the leak hole to helium leakage amount can be obtained according to the standard leak hole verification method.

Based on the different associations between the storage location of the leak gas and the inspected object during the entire leak detection process, helium mass spectrometry leak detection can be divided into vacuum method, positive pressure method, vacuum working pressure method, and back pressure method. The following summarizes the basic principles, advantages, disadvantages, and inspection standards of these four helium mass spectrometry leak detection methods.

When using the vacuum method for leak detection, an auxiliary vacuum pump or leak detector must be used to evacuate the sealed chamber inside the tested product. Helium gas should be applied to the outer surface of the tested product using a helium hood or gas generator. When there are leaks on the surface of the tested product, helium gas will enter the interior of the tested product according to the leaks, and then enter the helium mass spectrometer leak detector to accurately measure the leakage of the tested product. According to the different methods of applying leaked gas, the vacuum method can be divided into vacuum injection method and vacuum helium hood method. The vacuum spraying method uses a spray gun to generate helium gas from the gas generator on the outer surface of the inspected product, which can accurately locate the leakage hole; The vacuum helium hood method uses a helium hood with a certain degree of sealing function to cover all the tested products, and fills the hood with a certain concentration of helium gas, which can accurately measure the total leakage rate of the tested products.

The characteristics of vacuum method are high sensitivity in inspection, precise positioning, and the ability to complete leak detection for large vessels or complex structured products.

The drawback of the vacuum method is that it only completes the leakage rate test of one atmospheric pressure difference, which cannot accurately reflect the true leakage situation of the product under pressure.

The quality standards for vacuum method include QJ3123-2000 "Vacuum Leak Detection Method for Helium Mass Spectrometry Analysis" and GB/T 15823-2009 "Helium Leakage Inspection", which are mainly used for vacuum sealing function regulations, but do not apply to products in pressure work, such as indoor space themed moving components, liquid hydrogen tank trucks, environmental monitoring system machinery and equipment.

Positive pressure helium mass spectrometry leak detection

When using the positive pressure method for leak detection, it is necessary to fill the sealed chamber inside the tested product with helium gas at a pressure higher than one atmosphere. When there are leaks on the surface of the tested product, the helium gas will be buried in the holes and enter the surrounding ambient air on the outer surface of the tested product. Then, the suction gun method is used to check the increase in helium concentration in the surrounding ambient air of the tested product, thereby achieving accurate measurement of the leakage of the tested product. According to different methods of collecting helium gas, the positive pressure method can be divided into the positive pressure suction chicken gun method and the positive pressure accumulation method. In the positive pressure suction chicken gun method, a leak detector suction gun is used to scan the outer surface of the inspected product, which can accurately locate the leak hole; The positive pressure accumulation method uses a helium hood with a certain degree of sealing function to cover all the tested products, and uses a leak detector suction gun to accurately measure the change in helium concentration inside the helium hood before, after, and after a certain time range, completing the precise measurement of the total leakage rate of the tested products.

The characteristic of the positive pressure method is that it does not require auxiliary vacuum system software and can accurately locate and complete inspections under all pressures.

The shortcomings of the positive pressure method are low sensitivity in testing, high measurement uncertainty in testing results, and significant harm to natural environmental standards in fertilization.

The quality standards for the positive pressure method include QJ3089-1999 "Helium Mass Spectrometry Positive Pressure Leak Detection Method" and QJ2862-1996 "Helium Mass Spectrometry Suction Gun Cover Box Leak Detection Test Method for Pressure Vessel Welds", which are mainly used for leak detection of large capacity high-pressure sealed vessel products, such as high-pressure helium cylinders and cabin door leak detectors.

Vacuum working pressure method helium mass spectrometry leak detection

When using the vacuum working pressure method to detect leaks, the inspected product must be placed in a vacuum sealed room as a whole. The vacuum sealed room is connected to the auxiliary pumping time system software and the leak detector. The inflation port of the inspected product is led out of the vacuum sealed room according to the connecting pipeline, and then connected to the helium gas source. When there are leaks on the surface of the inspected product, helium gas will enter the vacuum sealed room according to the leaks, and then enter the helium mass spectrometer leak detector to accurately measure the total leakage rate of the inspected product.

The characteristic of vacuum working pressure method is high sensitivity in inspection, which can complete the leakage rate inspection of all pressures and reflect the true leakage situation of the inspected item.

The drawback of the vacuum working pressure method is that the leakage detection system software is complex, and the vacuum sealing chamber must be designed according to the volume and shape of the inspected product. It must be indicated here that during the entire leakage testing process, it is required to ensure that there is no leakage in the inflation pipeline socket, or to use a unique design to place all inflation pipeline connection sockets outside the vacuum sealed chamber.

The testing standard for vacuum working pressure method includes GB/T 15823-2009 "Helium Leakage Inspection", which is mainly used for sealing products with simple construction and low working pressure, such as relays, high-pressure pumping pipelines, rocket fuel storage tanks, wireless antennas, responders, and whole satellite products.

Back pressure helium mass spectrometry leak detection method

When using the back pressure method for leak detection, the tested product is placed in a high-pressure helium chamber and soaked for several hours or days. If there are leakage holes on the surface of the tested product, helium gas is pressurized into the internal sealing chamber of the tested product according to the leakage holes, causing the working pressure of helium in the internal sealing chamber to increase. Subsequently, remove the inspected product, blow off the residual helium gas on the surface, and then place the inspected product into a vacuum vessel connected to a leak detector. The helium gas inside the sealed chamber of the inspected product will leak into the vacuum vessel through the leak hole, and then enter the helium mass spectrometer leak detector to accurately measure the total leakage rate of the inspected product. The leakage rate value obtained by the leak detector accurately measures the leakage rate, and the equivalent circuit standard leakage rate of the tested product must be calculated and converted according to the formula.

The characteristic of the back pressure method is high sensitivity in inspection, which can complete the leakage inspection of small and medium-sized sealed vessel products and achieve large-scale quantitative inspection.

The disadvantage of the back pressure method is that it cannot carry out leakage of large and medium-sized sealed vessels, otherwise due to the large capacity of the sealed inner cavity, the charging time will be too long. In addition, each precise measurement of leakage rate matches the leakage rate of two equivalent circuit specifications. After fine inspection, other methods must be used for rough inspection to eliminate the possibility of large leaks.

The specific leak detection standards for back pressure method include QJ3212-2005 "Helium Mass Spectrometry Back Pressure Leak Detection Method" and GJB360A-1996 "Electronic and Electrical Component Test Method Method 112 Sealing Test", which are mainly used for testing various electronic component products.