helium mass spectrometer leak detector in boiler leak detection
The boiler is an energy conversion equipment. The energy input to the boiler includes chemical energy and electric energy in the fuel, and the boiler outputs steam, high temperature water or organic heat carrier with certain heat energy. The hot water or steam produced in the boiler can directly provide heat energy for industrial production and people's life. It can also be converted into mechanical energy by steam power plant or converted into electrical energy by generator. The boiler that provides hot water is called hot water boiler, which is mainly used in daily life and has a small amount of application in industrial production. The boiler that produces steam is called steam boiler, which is often referred to as boiler. It is mostly used in thermal power station, ships, locomotives and industrial and mining enterprises.
In order to solve this problem, helium mass spectrometer leak detector has great advantages in boiler leak detection. The following is a case study of boiler leakage in a power plant.
Conventional leak detection methods
1. Shutdown inspection
The manhole doors on both sides of the boiler were opened to conduct a comprehensive inspection on the internal pipes, and no leakage was found. Therefore, it is preliminarily inferred that the cause of boiler dripping is: as the insulation layer of ceiling pipe is ramming material, during the operation of the unit, the moisture inside the insulation layer gradually evaporates and diffuses outward through the pipeline, and condenses and drips when it encounters cold air.
2. Listen to abnormal sound and observe whether there is steam during operation
During the operation of the boiler, the manhole doors on both sides were opened to check whether there was any abnormal sound. It was found that no leakage sound was heard outside the manhole door; no signs of water vapor were found by using strong light flashlight. The reason is that the temperature in the boiler is high (above 300 ℃), and the pressure is close to 0.1MPa. A small amount of steam will be overheated after leakage, so it can not be seen.
3. Leak detection with compressed air
First, isolate the corresponding system, and then inject compressed air into the reheater and Superheater systems to make the pressure reach 0.5-0.6mpa. Check the superheater and reheater systems. The results show that the pressure of superheater system is stable, while the pressure of reheater system is always unstable. After the start-up of the unit, there is still water dripping on the external insulation aluminum skin of the boiler steam water separator.
Leak detection by helium mass spectrometer
In order to find out the leakage point thoroughly, the helium mass spectrometer leak detector was used to inspect the internal heating surface of the boiler, especially the reheater system. The specific operation steps are as follows:
1. Remove the insulation layer. Remove the insulation layer of the outlet pipe of high temperature reheater for inspection;
2. Inject compressed air and helium into the reheater system. Isolate the corresponding system valves and inject compressed air and helium into the reheater system by nitrogen flushing pipeline;
3. Leak detection. The helium mass spectrometer leak detector is fast, reliable, sensitive and easy to operate. When the pressure of reheater system reaches 0.3MPa, the helium mass spectrometer leak detector is started, and the connecting pipe of the detector is introduced into the boiler. One person holds the detector to check each reheater system pipe, and the other person is responsible for observing the display screen reading of the leak detector. When approaching a certain pipe, the reading of helium mass spectrometer leak detector changes obviously. After that, the insulation was disassembled. When the leakage rate was close to the leakage point, it was found that the leakage rate was obviously jumping in the order of magnitude. At the position close to the weld joint, the slight air flow could be obviously felt with fingers, indicating that there was indeed leakage.
4. Cause analysis of leakage:
(1) Improper operation of original welding. In the original welding process, because the current is too small, the filler wire can not be fully fused with the material to be welded, resulting in incomplete penetration or incomplete fusion, which is the root cause of congenital microcracks. If the welding line energy is too large and the welding speed is too slow, the weld and heat affected zone will overheat and produce coarse martensite structure, which will greatly reduce the comprehensive performance of welded joint.
(2) Post weld heat treatment. The performance of welded joint will be affected if the heat treatment is not carried out in time or the heat treatment process is improper. The welding joint with poor performance will fracture in a short time under the action of thermal stress cycle.
The reason why the helium mass spectrometer leak detector can detect the leakage problem in the boiler is mainly because the tracer gas of helium mass spectrometer leak detector is usually helium, which is small in molecule, light in weight, easy to diffuse, easy to pass through the leak hole, easy to detect and remove; the charge mass ratio of helium ion is small, which is easy to carry out mass spectrometry analysis; Helium is an inert gas with stable chemical properties, which will not corrode and damage any equipment; helium is non-toxic, non condensing and extremely difficult to contain in water. Compared with conventional leak detection methods, helium mass spectrometry leak detection technology has the advantages of fast, accurate, high sensitivity and no damage. Using helium mass spectrometer leak detection technology, when the boiler leaks slightly, it can find the leakage point timely and accurately, and reduce the loss caused by boiler leakage as much as possible, which has more practical value.