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Key words: valve; seal; leakage; detection I. Introduction Valve is an important control component in fluid conveying system. It is widely used in petrochemical, thermal power, nuclear power and other industries. Accurate detection of valve leakage is of vital importance to industrial production. Role [1]. The pressure leak detection methods of valves in domestic and foreign patent documents mainly include: bubble method, soap bubble method, special tracer method, water pressure method, ultrasonic method [2], pressure drop method, valve internal leakage temperature method [3].
Second, several different valve leak detection methods 2.1 bubble method using the bubble method for valve leak detection, fill the valve with a certain pressure of the leak gas after the valve into the liquid, the gas enters the surrounding liquid through the leak hole Bubbles, where bubbles form, are where the leaks exist. It is usually observed at a close distance to see if bubbles are generated.
In the patent CN205785696, a camera is arranged in the water tank 1 to realize remote observation of whether the valve in the water tank 1 has air bubbles. In the patent CN106052969A, when the bubble 25 is generated in the water tank liquid 27, the air detector 20 outputs a signal generated by the bubble, and automatic detection of bubble generation is realized.
2.2 Soap bubble method When the valve is leak-detected by the soap bubble method, after the valve is filled with a certain pressure of the leaking gas, the soap liquid is applied to the place where the leak is suspected, and the part where the soap bubble is formed is the portion where the leak hole exists. It is usually observed manually by bubbling and judging the size of the bubble.
In the patent CN105954015A, the camera is used to photograph the state of the soapy water in the sealing portion of the valve 100, and the control system 7 compares the received soapy water state image of the sealed portion with the image of the qualified soapy water state stored therein to achieve whether the valve leaks and the degree of valve leakage. Automatic judgment.
2.3 Special tracer method When the valve is leak-detected by the special tracer method, the valve is filled with a certain pressure of the leaking fluid containing special tracer. When the special tracer escapes from the leak, special use The detecting device of the tracer finds the position of the leak. The most common special tracer is helium, which is tested with a helium mass spectrometer leak detector.
When leaking a valve for a conventional use, a special tracer substance is mixed into the fluid to be tested for leak detection. In patent CN104977139A, an isotope tracer material (such as carbon-14, helium) is uniformly mixed with the cold water liquid in the cold water circuit of the converter valve, and the tracer material in the air around the converter valve is detected by a nuclear detection counter. In patent CN107655636A, a color liquid is injected into the valve housing, and the sealed valve housing is lowered below the water surface of the water tank to observe the color change of the water in the water tank, and the leakage point is identified by color contrast. In the patent CN108279096A, the iodine solution is injected into the upper chamber of the valve body 31. If the sealing property of the valve 30 is defective, the iodine solution will leak to the glutinous rice paper 17 in the lower chamber to make the glutinous rice paper 17 appear blue, and observe The color change of the rice paper 17 determines the sealing property of the valve 30. In patent CN202720099A, the valve is filled with a mixture of hydrogen and nitrogen. When the valve leaks, the gas sensor generates an electrical signal output after being detected by hydrogen gas and uploads it to the PLC. The PLC compares the measured leakage amount with the standard value.
For leak detection of some special-purpose valves, the fluids controlled by them can be directly used as tracer substances. For example, in patent CN104913886A, the Freon valve uses Freon with a halogen detector for leak detection. In the patent CN107727324, the natural gas valve uses natural gas and natural gas. The detection sensor performs leak detection. In the patent CN204666317A, the gas valve uses methane and carbon monoxide in the gas to cooperate with the methane inspection probe and the carbon monoxide detection probe for leak detection. In the patent CN205138736A, the acid-base valve uses the acid solution and the PH display device for leak detection. .
2.4 Water pressure method When using the water pressure method to check the valve, first fill the inside of the valve with water, then use the water pump to fill the water inward, and observe that there is no water leakage around the valve. It is usually observed directly by hand to see if water has leaked out.
In the patent CN205580687A, a sump 4 is arranged on the bottom side of the SVC valve block, a water absorbing sponge 5 is embedded in the sump 4, and a water-soluble fluorescent yellow powder is arranged on the water absorbing sponge 5, and when the water leaks into the sump 4, the water absorbing sponge 5 Inhalation of water leakage, leakage and contact with water-soluble fluorescent yellow powder, visible yellow-green fluorescence can be seen by ultraviolet radiation, so that the staff can clearly observe the water leakage through the naked eye in the far and dark environment. In the patent CN107702866A, a leakage detection module (short-circuit detection) unit is composed of two metal guide pieces H201, H202 and a sensitivity adjusting resistor. When two metal guide pieces are not detected when the water leakage state is detected, when the water leakage occurs, two The guides are short-circuited, and the corresponding MCU I/O changes from high level to low level. This falling edge will trigger the MCU to send an alarm signal to warn the valve of leakage.
2.5 Ultrasonic method When the valve is leak-detected by the ultrasonic method, the audible frequency portion of the leaked sound is partially cut off, and only the ultrasonic portion is amplified to detect the leak. Usually, the worker directly uses the ultrasonic detector to determine whether there is leakage according to whether the meter pointer is swung or not. The frequency conversion technology can also be used to convert the ultrasonic signal into a signal that can be heard by the human ear.
In patent CN106033021A, the amplitude/amplitude display analysis software displays the amplitude spectrum of the acoustic signal at each frequency in the environment where the ultrasonic probe is located, by observing or monitoring whether the ultrasonic signal of the fixed frequency in the figure is obviously enhanced, or by judging Whether the amplitude of the frequency ultrasonic signal exceeds a preset value, it is safe, remote, and real-time to determine whether the steam safety valve has a steam leak.
2.6 Pressure drop method When using the pressure drop method for valve leak detection, connect the compressor to the valve, and then press it. When the pressure rises to a certain value, stop the pressure, and close the valve for a period of time. If the pressure drops sharply, It can be judged that the leak rate is large, and if the pressure does not change much, the leak rate is considered to be small or there is no leak. Usually the staff directly uses the pressure gauge to determine the presence or absence of leakage based on the change in the pressure gauge pointer reading.
In the patent CN108332958 A, the high pressure gas cylinder 5, the second pressure gauge 6, the second shutoff valve 7, the first pressure sensor 12, the test station 20, the second pressure sensor 13, and the fifth shutoff valve 14 are sequentially connected by a pipe. The airtightness of the electromagnetic pneumatic shutoff valve on the test station 20 is judged by the pressure difference between the first pressure sensor 12 and the second pressure sensor 13.
2.7 Valve internal leakage temperature method When the valve has a working fluid leakage, especially a high temperature valve or a low temperature valve, the heat generated by the working medium or the absorbed heat will cause the wall temperature to rise or fall. If the valve leakage remains unchanged, a section After the time, the heat transfer process tends to be stable, and the heat is dissipated or absorbed and the wall temperature is maintained at a certain value. When the valve leak detection method is used to detect the leak of the valve, the temperature sensor around the valve is installed on the valve to measure the ambient temperature around the valve. It is used as a characteristic parameter to detect whether the valve is leaky. After the instrument data is analyzed, the leak inside the valve is judged.
In patent CN102478445A, by detecting the temperature of the outer wall surface of the pipe before the valve, the temperature of the outer wall surface of the pipe after the valve, and the ambient temperature, the heat dissipation heat Q of the pipe is calculated, thereby calculating the flow velocity and flow rate of the fluid in the pipe, and obtaining the leakage of the working fluid of the valve. flow. In the patent CN102323013A, a temperature sensor is arranged on the valve, and the valve is judged whether or not the valve leaks by comparing the information measured by the temperature sensor with the temperature information measured by the temperature sensor that is not leaked beforehand.
Third, the end of each valve leak detection method has different advantages and disadvantages, in the detection of leaks for a specific purpose of the valve, according to the actual leak detection conditions and need to achieve the leak detection requirements, such as the length of time, cost Choose the appropriate leak detection method by how high or low, how easy it is to operate, whether to determine the leak point, whether to determine the leak rate, and whether it pollutes the environment.
references:
[1] å•é¦–æ¥ .Discussion on valve leakage detection method[J].Guangdong Chemical Industry,2011,38(6):210.
[2]Deli Lijun, Nie Wei. Waveform Analysis of Ultrasonic Testing of Chemical High Pressure Valve Housing[J]. Nondestructive Testing, 2003, 27(5): 44-45.
[3]Huang Zhangjun, Li Luping, et al. Quantitative Detection and Diagnosis of Internal Leakage of Steam Turbine Valves in Power Plants[J]. Turbine Technology, 2016, 58(2): 149-152.
About the author: Huang Chuanxia, ​​1988, female, Han, Jiangsu, China Association of Jiangsu Association examiners, masters.
Abstract: This paper introduces the basic principles of several different valve leak detection methods, and briefly introduces several different valve leak detection methods in Chinese patents.