Multiple ways of mass spectrometry
Edit / Yang Wenliang
A hydrogen leak Profile
A mixed gas of 5% hydrogen and 95% nitrogen is used as a tracer gas for leak detection, which is called a hydrogen-nitrogen mixed gas leak detection method, or a hydrogen leak detection method. Whether leak location or leak test applications, this leak detection method has been widely used in various industry sectors. This low concentration of hydrogen and nitrogen mixed gas is non-toxic and non-corrosive, non-flammable and non-hazardous. The price is very low and it is easy to buy from various gas suppliers. Hydrogen-nitrogen mixed gas leak detection technology can detect leaks as low as 5*10-7 mbar/s, equivalent to 0.1 g/y. Its gas use cost is only 1/10 to 1/20 of helium. It is the development trend of leak detection technology.
Hydrogen as a tracer for leak detection has many unique advantages. Hydrogen is the smallest and lightest element in nature, and hydrogen is the lightest of all gases. Since hydrogen molecules move faster than other molecules, the use of safe low-concentration hydrogen as a tracer gas allows for faster response times and better leak detection accuracy. Further, the diffusion of hydrogen molecules is the best of all elements, the use of nitrogen gas mixture of hydrogen leak detection method does not require very demanding environment of the background, without the same as helium leak detection chamber to provide a dedicated leak.
Second, the introduction of cockroach leak detection technology
1. Vacuum box type inspection method
â– Fill the workpiece to be inspected with high pressure nitrogen and keep pressure. The pressure sensor of the system confirms whether there is a big leak.
â– Vacuum the vacuum box to the set pressure;
â– The workpiece is evacuated;
â– The workpiece is filled with helium;
â– æ°¦ Detector detects the change in enthalpy concentration in the vacuum chamber.
2, sniffer type inspection method
â– Fill the workpiece to be inspected with high-pressure nitrogen and keep pressure. The pressure sensor of the system confirms whether there is a large leak;
â– The workpiece is evacuated;
â– The workpiece is filled with helium;
â– Scan the possible leak points one by one with the inhaler probe and observe the change in the enthalpy concentration value to find the location of the leak.
3, cover type inspection method
â– Fill the workpiece to be inspected with high-pressure nitrogen and keep pressure. The pressure sensor of the system confirms whether there is a large leak;
â– Cover the workpiece to be inspected with a metal cover;
â– The metal cover is evacuated;
â– The workpiece is evacuated;
â– The metal cover is filled with helium;
â– æ°¦ leak detector to detect the change in radon concentration in the metal cover;
Third, the vacuum system leak detection method
1. Pressure-holding leak detection method
step:
(1) Set up isolation valves and pressure gauges in the completed system piping.
(2) Pass nitrogen (N2) to the system and pressurize to a preset holding pressure, usually 30~60psi. After that, close the front and rear isolation valves and relieve the pressure outside the isolation valve system.
(3) Observe the pressure gauge indication of the system and mark it.
(4) The maintenance condition is about 1 hour or more (the length of time depends on the size of the system and the leakage rate of demand).
(5) See if the indicator of the pressure gauge has dropped to determine the presence or absence of leakage.
Disadvantages:
(1) can only be used as a preliminary leak reference.
(2) Time-consuming.
(3) It is often not allowed due to the temperature difference of the system.
2, leak detection method
Use a thicker liquid such as soapy water, apply it to the part to be tested, and observe whether the foam is produced or not.
step:
(1) Inject nitrogen gas into the system to be tested and pressurize about 30~60 psi.
(2) Spray the leak detection fluid to the component or joint where the leak may be predicted.
(3) Observe whether or not bubbles are generated, and the size of the bubbles will depend on the leak rate.
(4) Dry the leak detection solution.
Disadvantages:
(1) Initial leak detection
(2) The leak detection fluid may contaminate the pipe fittings. If the leak detection fluid is not wiped clean, the pipe fittings may rust.
3, helium leak detection method
(1) Negative pressure method:
1 Close the pipeline system to be tested and connect one end to the helium leak detector.
2 According to the operation method of the helium leak detector, the pipeline system to be tested is pumped to the target test vacuum.
The 3-way piping system squirts the gas to the point to be measured from top to bottom and looks at the reaction of the leak detector (pointer indication or alarm).
Note: If a leak is displayed at one location, in order to reconfirm, a vacuum seal can be applied to it and the test repeated.
(2) Positive pressure method:
1 Start the helium leak detector according to the method of use and establish a certain vacuum.
2Inject helium into the pipeline of the system to be tested and pressurize to 30 ~ 60 psi.
3 Place the leak detector probe at the pipe to be tested to detect the leak.
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