JP5022194B2 - Piping leak detection method - Google Patents

Description

  The present invention relates to a pipe leak point detection method for detecting a leak point in a pipe through which a medium flows.

  For example, in a heating / cooling heat pipe through which a heating / cooling heat medium circulates, a utility pipe buried in the ground, a utility pipe placed on the ceiling / floor / wall of a building, etc. May open and fluid may leak from the inside of the pipe. In such a case, it is necessary to detect the leaked part of the pipe, cut the corresponding section, and replace the old pipe causing the leak with a new one.

  Conventionally, as a technique for detecting a leaking point in a pipe, a microphone is installed at any two points in the piping system (for example, a pair of gas meter inspection holes in the case of a gas pipe), and the leaked sound received by each microphone is detected. There has been a method of analyzing a leak location by obtaining a cross-correlation for a sound wave signal (see, for example, Patent Document 1).

  In addition, in the pipe leak location detection method for detecting leak locations of pipes based on the difference in propagation time of leaked sound wave signals detected by each microphone, leaked sound wave signals detected by each microphone are attached to both ends of the pipe having leak locations. There is also a method in which a low-frequency component is cut by a filter and a noise component is removed, and then an acoustic wave signal is analyzed (see, for example, Patent Document 2).

  In addition, in the pipe leak location detection method for detecting leak locations of pipes based on the difference in propagation time of leaked sound wave signals detected by each microphone, leaked sound wave signals detected by each microphone are attached to both ends of the pipe having leak locations. There is also a method of calculating a cross spectrum after performing Fourier transform, and performing cross-correlation between two sound wave signals after performing smoothing processing and zeroing of unnecessary bands for the amplitude characteristics of the cross spectrum ( For example, see Patent Document 3).

  Furthermore, microphones are attached to both ends of the pipe having the leak location, and the leaked sound wave signal detected by each microphone is classified into a plurality of frequency bands to calculate the correlation coefficient for each frequency band, and the waveform in the frequency band having a high correlation coefficient There is also a method for obtaining a cross-correlation between two sound wave signals after synthesizing (see, for example, Patent Document 4).

JP-A-56-73331 Japanese Patent Laid-Open No. 10-62292 Japanese Patent Laid-Open No. 10-185745 JP-A-11-64151

  However, various noises (for example, background noise, etc.) are mixed in the sound wave signal arriving in the pipe in addition to the leakage sound from the leakage point. Therefore, when the intensity of the leaked sound is weak, the method of simply obtaining the cross-correlation between the two sound wave signals as performed by the pipe leak location detection method described in Patent Document 1 distinguishes the leaked sound from other noises. In some cases, it is difficult to accurately detect the leak position of the pipe.

  Moreover, in patent document 2, in order to improve the discriminability of the leaking sound in piping (namely, in order to improve S / N ratio), the filter process is performed with respect to the original sound wave waveform. However, there is a limit in extracting only the sound waveform of the leaking sound from various sound waveform. Therefore, in the method of Patent Document 2, the sound wave discrimination effect that can be expected unless the intensity of the leaking sound is equal to or higher than a certain level is not seen.

  On the other hand, in Patent Document 3 and Patent Document 4, various signal processing is performed on the intact sound wave signal received in the previous stage of obtaining the cross-correlation. However, since these signal processes are performed based on a very complicated algorithm, there is a problem that it takes time and effort to specify the leaked portion. In addition, although the signal processing is complicated, the S / N ratio of the sound wave signal cannot be sufficiently increased, and thus it is difficult to obtain a detection result with high accuracy as expected.

  Accordingly, the present invention has been made in view of the above-described problems, and the object of the present invention is to leak sound mixed in a sound wave signal in a pipe leak point detection method for detecting a leak point in a pipe through which a medium flows. It is to reduce the influence of noise other than the above and obtain a detection result with high accuracy and reliability.

The characteristic configuration of the pipe leakage point detection method according to the present invention is as follows.
A pipe leak point detection method for detecting a leak point in a pipe through which a medium flows,
The piping includes an inner tube through which a heat medium as the medium flows, an outer tube that surrounds the inner tube, and a plurality of supports that support the inner tube provided between the inner tube and the outer tube. Including members,
When detecting the leak location in the outer tube, a pressurized fluid is injected between the outer tube and the inner tube, and a sound wave signal leaking from the leak location in that state is received.
A step of the pressurized fluid to place the first signal receiving means and the second signal receiving means at a position sandwiching the leakage locations leaks in continuous manner,
The amplitude of the sound wave signal received by the first signal receiving means and the second signal receiving means, respectively, in which pulsed noise and background noise are superimposed on the leaked sound of the pressurized fluid from the leaked location Logarithmically in the time domain,
And obtaining a cross-correlation for the logarithmized sound wave signal, and estimating the leakage location from the result.

In the sound wave signals received by the first signal receiving means and the second signal receiving means, noise such as background noise is mixed in addition to the leaked sound to be detected, and it is difficult to distinguish between them. It is not possible to accurately identify the leakage point of the pipe from the sound wave signal.
However, with the pipe leak location detection method of this configuration, the intensity of the noise component relative to the leaked sound component can be relatively reduced by logarithmizing the received sound wave signal in the time domain. In particular, the effect of reducing the pulsed noise component can be obtained satisfactorily. Thereafter, by obtaining the cross-correlation for the logarithmized sound wave signal in which the intensity of the noise component is relatively reduced, the leaked portion of the pipe can be accurately detected. For example, in the cross-correlation graph, the position where the cross-correlation coefficient shows a peak can be easily identified as a leak location.
As described above, by using the pipe leak location detection method of this configuration, it is easy to determine the leak location, and the leak location can be detected accurately and reliably.

In the piping, pulsed noise may be generated from the support member due to the difference in thermal expansion between the inner tube and the outer tube. If there is a leak location in the outer tube, injecting pressurized fluid between the outer tube and the inner tube will cause the pulse noise to be superimposed on the fluid leak sound along with the background noise, making it difficult to detect the leak location. There is a case. This pulse noise has an unsteady component and has a sound wave waveform different from the background noise.
With the pipe leak location detection method of this configuration, the noise component is effectively reduced with respect to the leaked sound by logarithmizing the sound signal of the leaked sound superimposed with the pulsed noise and background noise that are noise components. can do. Furthermore, by obtaining the cross-correlation for the logarithmized data, the leaked portion of the outer tube can be detected with high accuracy and high reliability.

  In the pipe leakage spot detection method according to the present invention, the pipe is preferably a district cooling and heating pipe having a main pipe as the inner pipe and a sheath pipe as the outer pipe.

In the district cooling and heating pipe, there is a temperature difference between the main pipe through which the heat medium flows and the sheath pipe in contact with a medium such as soil. For this reason, the support member existing between the main tube and the sheath tube is particularly likely to generate pulsed noise due to the difference in thermal expansion between the main tube and the sheath tube.
With the pipe leak location detection method of this configuration, the leak location of the sheath pipe is easily detected by logarithmizing the measured sound wave signal in the district heating pipe that easily generates such pulsed noise. be able to.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the configurations described in the following embodiments and drawings, and various modifications are possible as long as the configurations have the same effects.

(District air conditioning system)
First, an outline of the district air conditioning system will be described. FIG. 1 is a schematic diagram showing a state in which a pipe leakage point detection system 10 for carrying out the pipe leakage point detection method of the present invention is applied to a district cooling / heating pipe 20 used in a district cooling / heating system. FIG. 2 is a cross-sectional view of the district cooling and heating pipe 20 in FIG.

  District air conditioning is a system that performs air conditioning within a certain area using heat discharged from a factory, a garbage incinerator, or the like (heat source), for example. The heat discharged from the heat source is supplied by the medium to the air conditioning facilities of energy consumers in a certain area. For example, as shown in FIG. 1, the district cooling and heating pipe 20 used for supplying the medium is embedded at a predetermined depth (for example, 2 m underground) from the ground. A part of the district cooling and heating pipe 20 is arranged so as to be exposed inside the inspection manhole 30.

  As can be seen from FIG. 2, the district cooling and heating pipe 20 has a double pipe structure including a main pipe 1 and a sheath pipe 2. The main pipe 1 is an inner pipe (inner pipe) through which a heat medium (hot water, cold water, steam, etc.) flows. The main pipe 1 preferably has a certain degree of heat resistance, durability, and corrosion resistance. For example, a cast iron pipe, a copper pipe, a stainless pipe, or the like can be adopted.

  The sheath pipe 2 is an outer pipe (outer pipe) that protects and insulates the main pipe 1 by surrounding the main pipe 1. As shown in FIG. 1, the sheath tube 2 is configured to have an end edge 2 a that is continuous between the two inspection manholes 30 but is closed inside the inspection manhole 30. . The main pipe 1 is exposed from the sheath pipe 2 between the two end edges 2 a inside the inspection manhole 30. A valve 3 for adjusting the flow rate of the heat medium flowing through the main pipe 1 is provided at a location where the main pipe 1 is exposed. In addition, inspection valves 4 a and 4 b are provided in the vicinity of the end edge 2 a of the sheath tube 2. In addition, although the pipe | tube of the material similar to the main pipe 1 can be employ | adopted for the sheath pipe 2, resin pipes, such as a vinyl chloride resin pipe and a polyethylene pipe, are also employable.

  A plurality of support members 5 are provided between the main pipe 1 and the sheath pipe 2. Each support member 5 supports the main tube 1 with respect to the sheath tube 2 while allowing the internal space between the sheath tube 2 and the main tube 1 to communicate in the tube axis direction, for example, FIG. As shown in FIG. 3, the rod 1 is composed of a plurality of rod members extending radially from the periphery of the main pipe 1. The internal space between the sheath tube 2 and the main tube 1 may be filled with a porous heat insulating material (for example, polyurethane foam, polystyrene foam, polyethylene foam, etc.) having air permeability. The support member 5 and the main pipe 1 or the sheath pipe 2 are joined by a conventionally known technique such as welding, adhesion, or screwing. However, the support member 5 is only disposed close to the pipe that is not to be joined. For example, when the support member 5 is joined to the main pipe 1, the support member 5 is disposed close to the sheath pipe 2, and when the support member 5 is joined to the sheath pipe 2, the support member 5 is attached to the main pipe 1. In close proximity to each other. The support member 5 is preferably made of a material having a certain degree of elasticity (for example, a metal material or a resin material).

(Piping leak detection system)
Next, the pipe leak location detection system 10 used for implementing the pipe leak location detection method of the present invention will be described.
When a high-temperature (for example, 120 to 130 ° C.) heat medium flows through the main pipe 1, the main pipe 1 receives heat from the heat medium and becomes a relatively high temperature state. On the other hand, since the sheath tube 2 is in contact with a medium such as soil, it maintains a relatively low temperature state. That is, the main pipe 1 is thermally expanded, but the sheath pipe 2 hardly undergoes changes such as expansion. For this reason, a difference in the amount of thermal expansion occurs between the main pipe 1 and the sheath pipe 2, and this is the reason why the support member 5 that connects the main pipe 1 and the sheath pipe 2 is mainly used. Stress is applied in the tube axis direction. In such a case, the stressed support member 5 bends, and a pulse noise (so-called crackling noise) is generated accordingly. This pulse noise is detected together with the background noise and constitutes a part of the noise component. The pulse-like noise is a noise containing a lot of unsteady components, and can be one of the causes of failure when detecting the leaked portion (damaged portion) P of the sheath pipe 2 of the district cooling and heating pipe 20.

  On the other hand, the pipe leakage point detection system 10 of the present invention includes a first microphone (first signal receiving means) 11, a second microphone (second signal receiving means) 12, and a computer 13. The first microphone 11 and the second microphone 12 are means for receiving various sound waves that arrive inside the district cooling and heating pipe 20. In this embodiment, the 1st microphone 11 and the 2nd microphone 12 are arrange | positioned in the state which each turned to the vicinity of the inspection valves 4a and 4b provided in the edge part 2a of the both sides of the sheath tube 2, respectively.

  When the pipe leakage point detection system 10 is operated, the air cylinder 6 is connected to one inspection valve 4a, and the other inspection valve 4b is closed (shown in black in FIG. 1). In this state, the inspection valve 4a is opened (shown in white in FIG. 1), and compressed air (pressurized fluid) is injected into the sheath tube 2. In such a situation, if there is a leak location P in the sheath tube 2, air leaks from the leak location P and a leak sound is generated. Further, when the heat medium flows through the main pipe 1, as described above, the support member 5 receives the difference in thermal expansion amount and bends to generate pulse noise, which is superimposed on the leaked sound as noise together with the background noise. Will do. Leaked sound (sound wave signal) on which noise including pulse noise and background noise is superimposed is transmitted through the inside of the sheath tube 2 and received by the first microphone 11 and the second microphone 12, respectively. The two sound wave signals received by the microphones 11 and 12 are transmitted to the computer 13, respectively, where the calculation relating to the pipe leakage point detection method of the present invention is executed. Note that these two sound wave signals have a strong cross-correlation with each other as described later, depending on the position of the leaked portion P in the tube axis direction.

(Pipe leak detection method)
The calculation related to the pipe leak location detection method of the present invention performed by the pipe leak location detection system 10 is executed as follows.

  The sound wave signals received by the first microphone 11 and the second microphone 12, respectively, are noises such as pulse noise and background noise mixed in the leaked sound to be detected. For this reason, the raw sound wave signal usually has a high noise level. Therefore, even if the direct correlation is obtained directly from such a raw sound wave signal, it is difficult for a peak for specifying the leaked part to appear, and thus it is difficult to accurately detect the leaked part.

In this regard, in the present invention, the amplitudes of the sound wave signals first received by the first microphone 11 and the second microphone 12 are respectively logarithmized in the time domain. By performing such logarithmic processing, the intensity of the noise component relative to the leaked sound component is relatively reduced. Next, a cross-correlation is obtained for the logarithmic sound wave signal in which the intensity of the noise component is relatively reduced. In the obtained cross-correlation, the position showing the peak of the cross-correlation coefficient corresponds to the leaked portion of the pipe. That is, it is possible to identify the leaked portion of the pipe from the peak position obtained by cross-correlation.
Thus, in the pipe leak location detection method of the present invention, it is easy to determine the leak location, and the leak location can be detected accurately and reliably.

(Example)
Embodiments relating to the pipe leakage point detection method of the present invention will be described below.
FIG. 3 is a graph showing raw data of sound wave signals received by (a) the first microphone 11 and (b) the second microphone 12, respectively. The noise levels of the first microphone 11 and the second microphone 12 used in this example are ± 500 or less. However, the noise level of the actually received sound wave signal is about ± 5000, which is considerably higher than the noise level of the microphones 11 and 12. Further, it can be confirmed that unsteady sound wave signals resulting from pulse noise are superimposed on these sound wave signals in addition to noise such as background noise. This pulse noise is a noise having an unsteady component generated by bending the support member 5 due to the stress applied to the support member 5 in the tube axis direction.

  FIG. 4 is a graph showing the result of logarithmizing the amplitude of the sound wave signal received by each of (a) the first microphone 11 and (b) the second microphone 12 in the time domain. Comparing FIG. 4 with FIG. 3, it can be confirmed in FIG. 4 that the noise component including the pulse noise is relatively reduced with respect to the leaked sound component.

Next, a cross-correlation is obtained for the logarithmic sound wave signal in which the intensity of the noise component is relatively reduced. The results are shown in the graph of FIG. In FIG. 5, the arrow is a position corresponding to an actual leakage location. At the position of this arrow, the cross-correlation coefficient is relatively high and a peak appears. From this, it can be determined that this peak position is a leakage location of the district cooling and heating pipe 20.
Thus, if a cross correlation is calculated | required about the logarithmized sound wave signal, the leak location of the piping 20 for district cooling / heating can be detected comparatively easily with high accuracy and high reliability.

  Incidentally, when the cross-correlation is obtained without performing logarithmic processing on the sound wave signal of FIG. 3, the graph shown in FIG. 6 is obtained. In FIG. 6, the arrow is a position corresponding to an actual leakage location, but the cross-correlation coefficient at this position is low, and it can be said that it is difficult to determine the leakage location of the district cooling and heating pipe 20.

(Another embodiment)
<1> In the apparatus shown in FIG. 1, the first microphone 11 and the second microphone 12 and the computer 13 can be wirelessly connected. With such a configuration, the wiring between the first microphone 11 and the second microphone 12 and the computer 3 becomes unnecessary, and the pipe leakage point detection system 10 can be simplified. Therefore, even if the district cooling / heating pipe 20 to be measured is long or the shape of the district cooling / heating pipe 20 is complicated, the detection work can be smoothly performed because there is no troublesome wiring.

  <2> The first microphone 11 and the second microphone 12 and the computer 3 are each provided with clock means (not shown), and the computer 3 determines the reception time of the leaked sound wave signal in the first microphone 11 and the second microphone 12. It can also be configured to count. With this configuration, since the first microphone 11 and the second microphone 12 and the clock means of the computer 3 are synchronized with each other, accurate time measurement can be performed. The accuracy and reliability of measurement is improved. In addition, since the signal can be continuously measured while the clock is operating, even if one measurement fails, the next measurement can be performed immediately, so that the work efficiency is improved.

  The pipe leakage point detection method of the present invention can be suitably applied to the district cooling and heating pipes exemplified in the above embodiment, but can also be applied to other types of pipes. For example, when detecting leaks in various piping systems such as underground water and sewage piping, various chemical transport pipes installed in factories, etc., and compressed air pipes connected to various machines. The invention can be applied.

The schematic diagram which shows the state which applied the piping leak location detection system for implementing the piping leak location detection method of this invention to the piping for district cooling / heating used for a district cooling / heating system Sectional drawing of district cooling and heating piping in FIG. The graph which shows the raw data of the sound wave signal each received by (a) 1st microphone and (b) 2nd microphone A graph showing the result of logarithmizing the amplitude of the sound wave signal received by each of (a) the first microphone and (b) the second microphone in the time domain. A graph showing the result of cross-correlation for a logarithmic sound wave signal in which the intensity of the noise component is relatively reduced The graph which shows the result of having calculated | required the cross correlation as it was about the sound wave signal of FIG.

Explanation of symbols

1 Main pipe (inner pipe)
2 sheath tube (outer tube)
5 Support member 11 First microphone (first signal receiving means)
12 Second microphone (second signal receiving means)
20 Piping for district heating and cooling P Leakage point

Claims (2)

A pipe leak point detection method for detecting a leak point in a pipe through which a medium flows,
The piping includes an inner tube through which a heat medium as the medium flows, an outer tube that surrounds the inner tube, and a plurality of supports that support the inner tube provided between the inner tube and the outer tube. Including members,
When detecting the leak location in the outer tube, a pressurized fluid is injected between the outer tube and the inner tube, and a sound wave signal leaking from the leak location in that state is received.
A step of the pressurized fluid to place the first signal receiving means and the second signal receiving means at a position sandwiching the leakage locations leaks in continuous manner,
The amplitude of the sound wave signal received by the first signal receiving means and the second signal receiving means, respectively, in which pulsed noise and background noise are superimposed on the leaked sound of the pressurized fluid from the leaked location Logarithmically in the time domain,
A method of detecting a pipe leak location, comprising: obtaining a cross-correlation for the logarithmic sound wave signal and estimating the leak location from the result. The pipe leakage point detection method according to claim 1, wherein the pipe is a district cooling and heating pipe having a main pipe as the inner pipe and a sheath pipe as the outer pipe .

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