JPS6141940A - Detection of fluid leak position - Google Patents

Abstract

PURPOSE:To detect a leak position of fluid speedily and accurately by calculating an effective value of sound pressure in plural frequency ranges and also calculating the ratios of effective values of sound pressure of respective frequency ranges to that of the whole frequency range. CONSTITUTION:A leak signal detected by an AE (Acoustic Emission) sensor 1a is amplified 2a and 3a and inputted to an arithmetic unit 7 through band-pass filters 4aa-4ak, effective voltmeters 5aa-5ak, and A/D converters 6aa-6ak. The filter 4aa allows a signal detected almost over the entire frequency range of an AE signal of about 0.01-1MHz to pass and the obtained signal is processed 7 to calculate the standardized effective value of sound pressure in the whole frequency range. Other filters 4ab-4ak have frequency ranges obtained by dividing the whole frequency range into (k-1) sections and effective values of sound pressure in their respective ranges are calculated 7. Then, the ratios of effective values of sound pressure of respective ranges to that in the whole range are compared to calculate the distance from the AE sensor to the leak position.

Description

[Detailed Description of the Invention] [Industrial Utilization] The present invention utilizes the sound generation phenomenon at the time of fluid leakage,
The present invention relates to a method of detecting a fluid leak position from changes in the frequency spectrum pattern.

[Prior art] One of the methods for detecting fluid leakage from a fluid distribution system is to detect the sound produced when fluid leaks.
E (Acoustic Em+5sion1 There is a method of detecting the opening signal using a sensor.

For example, in the J3 pressure tube reactor, in order to detect coolant leakage due to defects in the inlet pipes leading to each pressure tube, AE sensors are attached to piping, etc., which are structures to be monitored. A system configuration is adopted that monitors the sound emitted due to leakage.

The conventional detection method is lf? The system detects the sound pressure level of the sound emitted due to i leakage, and issues an alarm if the sound pressure level becomes abnormally high. Of course, in fluid circulation systems, etc., there are also environmental noise components such as active sound sources such as circulation pumps and the sound of fluid flowing, so accurate detection cannot be made based only on the magnitude of the detected sound pressure level itself. ,
Taking these into consideration, a method is adopted in which the influence of the above-mentioned environmental noise components is subtracted, and the presence or absence of leakage is detected from the magnitude of the subtracted signal level. Such a conventional technique is described in, for example, Japanese Patent Laid-Open No. 146684/1984.

[Problems to be Solved by the Invention] However, in such conventional technology, an abnormality is basically detected at a monitoring point based on the magnitude of the sound pressure level of the sound emitted due to leakage, as described above. Even if the presence or absence of fluid leakage can be detected, the location of the leakage cannot be specified. This is because the sound pressure level changes depending on the size of the discharge hole, the state of fluid leakage, the distance from the leakage location to the monitoring point (AE sensor mounting position a), and the like.

For this reason, the prior art has the disadvantage that if a pipe breaks at a location that cannot be easily observed, the location of the leak cannot be determined unless all pipes are inspected, and it takes time to respond to the accident. Particularly when the structure to be monitored is the cooling system of a nuclear reactor, it is strongly desired to be able to detect the occurrence of a leak and identify the location of the leak at the same time from the perspective of minimizing radiation exposure. There is.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the prior art and perform some kind of signal processing on the signal from the AE sensor, so that the AE sensor can be easily detected from the installation point to the fluid leakage location. Therefore, when applied to the cooling system piping of a nuclear reactor, for example, workers can immediately locate the leak without entering the containment vessel. It is an object of the present invention to provide a method for detecting the position of a fluid leak, which can significantly reduce radiation exposure of workers, and enable quick and efficient response to accidents.

[Means for Solving the Problems] The present invention, which can achieve the above-mentioned objects, is such that the frequency spectrum of the sound emitted due to leakage is It is devised to take advantage of the fact that the position changes, and to quickly and accurately extract position data without using complicated equipment such as a frequency analyzer that requires a long processing time.

That is, the present invention divides a signal from an AE sensor attached to a structure to be monitored into a plurality of frequency bands using a filter, calculates the effective sound pressure value in each band, and calculates the sound pressure in all frequency bands. The AE is determined by the ratio of the sound pressure effective value of each frequency band to the pressure effective value.
This is a fluid leak position detection method configured to obtain the distance from the sensor mounting position to the leak position.

When a fluid such as a high-pressure coolant leaks from a pipe or the like, ultrasonic waves are generated and propagate through structures such as the pipe. The ultrasonic waves used at this time are usually in a frequency band of several MHz or less.

Therefore, in general, the method of the present invention as described above is carried out by specifying in advance a desired four divisions (range) in a frequency band of about 0.01 to I MTo.
0kHz.

! QCI ~200 large, 200~300kHz,
This is carried out by specifying in advance four divisions of bands from 300 to 1000 kiloliters.

[Function] The effective value of the sound pressure of the emitted sound generated due to leakage is attenuated as it propagates through piping, etc., and the rate of this is particularly significant in the high frequency range. In other words, the detected leakage amount spectrum changes depending on the distance from the leakage position to the mounting position of the AE sensor. Therefore, the total frequency band is divided into multiple bands, the effective sound pressure value is divided into m foils over the entire frequency band, and the ratio of the effective sound pressure value of each divided frequency band is calculated using AE. If the correlation with the distance from the sensor to the leak position is actually measured and determined in advance, the distance to the In leak position can be determined by comparing the ratio of the effective sound pressure value for each frequency band with the above correlation at the time of leak detection. It is possible to detect distance.

[Example] Hereinafter, the present invention will be explained in more detail based on the drawings. FIG. 1 is a block diagram showing an example of an apparatus suitable for implementing the method of the present invention, and FIG. 2 is an explanatory diagram showing the mounting position of the AE sensor. Must be monitored! A large number of AE sensors la are installed in a structure (for example, piping of a fluid circulation system, etc.).

lb, ・ can be attached. In this example, the second
As shown in the figure, fluid from main piping 10 flows into manifold 1
1 and flows into a large number of inlet pipes 12a, 12b, etc., each population 11! r12a,
The waveguide rod 13 is connected to the connection part of 12b, .
AE sensors la, lb,... are installed at the base end of each.
・is installed. 1% i? A circulation pump 14 and the like are attached to 2-, which become a noise source for each AE sensor.

Since the leakage signal that is normally input to the AE sensors la, ..., 1n is a signal in the frequency band of about 0.01 to I MHz, it is necessary to use a sensor that can convert ultrasonic vibrations in that frequency band into electrical signals. It may be of any type, and piezoelectric elements are usually used.

For example, assume that a leakage point 15 occurs in the inlet pipe 12a. A
The leakage signal detected by the E sensor 1a is transmitted to the preamplifier 2a.
and is amplified by the main amplification gain 3a. These amplified signals are passed through band pass filters 4aa, . . . , 4, respectively.
ak and effective voltmeter 5aa, ..., 5ak, and A/I) (ynalog digital) change 1jJ@Baa,
・, 5 consisting of a mini computer etc. via 6ak
Input to 12 calculator 7. Here, the bandpass filter 4aa
is to pass a signal detected over almost the entire frequency band of AE flaw signal from 0.01 to I MHz,
The obtained signal is converted into an effective voltage value by an effective value meter 5aa, converted into a digital signal by an A/D converter 6aa, and then inputted to an arithmetic unit 7, thereby converting the normalized sound in all frequency bands. The effective pressure value is calculated.

The other band-pass filters 4ab, . , ...,
5ak, and the voltage is A/D converted @6ab,
-, 6ak are converted into digital signals and input to the arithmetic unit 7, respectively. As mentioned above, it is usually good to divide the entire frequency band into about 4, so the value of 5 is selected as the value. If the number of divisions is too small, the detection accuracy of distance data will decrease, which is undesirable. If the number of divisions is too large, it is expected that the detection accuracy will improve, but the device configuration will become extremely complicated and the cost will increase, which is not very preferable.

Now, in calculation @s7, it is calculated whether there is a difference between the past value and the current value for each frequency band, and if a significant difference occurs in a certain frequency band, it can be determined that leakage has occurred. You can do it.

At the same time, calculate the ratio of each sound pressure effective value in each frequency band to the normalized sound pressure effective value in all frequency bands calculated as above. Calculated by instrument 7. For example, Figure 3A,
B and C are graphs showing power spectra of leakage signals when leakage occurs. Here, the vertical axis is normalized as (maximum value of power). Same figure A
Figure B shows the case where the AE sensor is located very close to the leakage position, and Figure B shows the case where the A and E sensors are located 5m away from the leakage position, and Figure C shows the case where the A and E sensors are located 15rngl away from the leakage position. As is clear from a comparison of the figures, the effective value of the sound pressure of the countersunk sound is attenuated when it travels through pipes, etc., but the degree of attenuation is particularly pronounced in the high frequency range.

Therefore, if the correlation between the ratio of the effective value of sound pressure in each band and the distance to the leakage position is determined in advance by an experiment and stored in a minicomputer, etc., the sound pressure for each band obtained as described above can be calculated. By storing the ratio of effective values and comparing it with certain data, the distance from the mounting position of the AE sensor to the leakage position If can be determined. Since standardized effective values are used as position detection data, accurate detection is possible without being affected by the size of the leakage hole or the sound pressure level itself due to the distance to the leakage location. It is.

Although the configuration and operation of only the AE sensor 1a and the circuits connected to it have been explained here, in reality, many other AE sensors lb, ..., In are installed, and they are not shown in the diagram. As shown in FIG. 2, similar circuits are connected to each AE sensor, and each AE sensor detects the occurrence of leakage and the detection of the leakage position by the same operation.

By the way, the maximum value of the power spectrum decreases as the distance increases. Therefore, the presence or absence of leakage can be detected by the level average of the power spectrum, but if the distance is 20 m or more from the leakage position, the level approaches the noise level, and it becomes difficult to even detect the presence or absence of leakage. However, even in such a state, the spectrum of the detected signal changes reliably, so according to the method of the present invention, it is possible to determine the presence or absence of leakage and the distance from the mounting position of the AE sensor to the leakage position. It is.

Although a preferred embodiment of the present invention has been described in detail above, it goes without saying that the present invention is not limited to this configuration, and that various modifications are possible.

For example, in terms of equipment, if a multiplexer or the like is inserted between the main amplification type and the band-pass filter to switch the (N) of each AE sensor in a time-sharing manner, the band-pass filter, the effective value It is also possible to significantly reduce the number of installed A/D* converters.

[Effects of the Invention] Since the present invention is a method for detecting the position of a fluid leak configured as described above, it is possible to detect the position of a fluid leak with a relatively simple device configuration, whereas the conventional technology could detect only the presence or absence of a leak. It is possible to quickly and accurately detect the location of a fluid leak, which reduces the time it takes to respond to an accident.As a result, it is possible to prevent serious accidents in the structures that need to be monitored, and to improve the use of the system. It can have excellent effects such as improving efficiency and increasing worker safety.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of a device suitable for carrying out the present invention, FIG. 2 is an explanatory diagram showing an example of an installation state of the AE sensor, and FIG. 3A. B and C are diagrams each showing an example of a leakage sound spectrum. Ia, -, 1n=AE sensor, 4 a a g '''
r4nk bandpass 74 router, 5aa, ・=,
5nk-effective value meter, 6aa, -, 6nk...A
/ D converter, 7 performance, 10 - main piping, 11 manifold, 12a, 12b...inlet pipe, 13... wave guide rod. Patent applicant Power Reactor and Nuclear Fuel Development Corporation Agent
Shigeru Mi 1st 1rIIJ Figure 2 Figure 3! 1A* from the leak position: Om 3 meters distance from the leak position: 5 m Distance from the leak towing position: 15 m

Claims (1)

[Claims] 1. The signal from the AE sensor attached to the structure to be monitored is divided into multiple frequency bands by a filter, and the effective sound pressure value in each band is determined,
A method for detecting a fluid leak position, characterized in that the distance from the mounting position of the AE sensor to the leak position is determined based on the ratio of the sound pressure effective value in each of the frequency bands to the sound pressure effective value in all frequency bands.