JPH0587669A - Pipe-leakage inspecting method - Google Patents

Abstract

PURPOSE:To obtain a pipe-leakage inspecting method, which can remove disturbances such as flowing sound and mechanical sound generated in the pipe without especially stopping a plant and can perform accurate judgment without much skill. CONSTITUTION:The sound pressures at two appropriate points A and B of a pipe (a) are detected with sound-pressure sensors 1 and 3. The frequency bands lower than the specified value are removed from the sound signals in sound-pressure measuring devices 2 and 4. The sound-pressure components in the remaining high-frequency band is compared with a reference value, and the presence or absence of leakage is judged. The correlation coefficient is computed from the sound-pressure data at two points with a correlator 5. Thus, a leaking point C is judged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pipe leakage inspection method for determining whether or not there is a leak from a pipe for transporting water, oil or the like in a chemical plant or the like.

[0002]

2. Description of the Related Art Conventionally, in order to determine whether or not there is a leak from a pipe, the flow of water, oil, etc. is stopped in the pipe in the section where the leak inspection is carried out, and disturbances such as flow noise and mechanical noise generated in the pipe The leak inspection was carried out with the influence of the above as small as possible.

[0003]

As described above, in the conventional leak inspection method, the flow of water, oil, etc. in the pipe in the section where the leak inspection is to be carried out must be stopped before the inspection. Is expensive and not easy, and
Since the plant was stopped, the productivity was also significantly reduced, and it was not possible to carry out frequent inspections.

Further, even if the inspection is carried out by the conventional leakage inspection method without stopping the flow of water, oil, etc., the influence of disturbances such as flow noise and mechanical noise generated in the pipe is great, and accurate inspection is required. It was impossible to do.

Furthermore, even if the inspection is carried out by stopping the flow of water, oil, etc. in the pipes in the section where the leakage inspection is carried out,
Disturbances such as flow noise and mechanical noise from pipes in other sections cannot be completely removed, it is not easy to distinguish between leakage noise and disturbance, and skill is required to determine the presence or absence of leakage. Nevertheless, there were still cases where misidentification or inaccurate judgment could not be made.

The present invention has been made in view of the above problems, and an object thereof is to remove disturbances such as flow noises and mechanical noises generated in piping without stopping the plant. Further, the present invention provides a pipe leakage inspection method which does not require so much skill and can make an accurate determination.

[0007]

In order to achieve the above object, the pipe leakage inspection method of the present invention detects the sound pressures at two points of the pipe in the section where the leakage inspection is performed, and the sound pressures below a predetermined value are detected. For the sound pressure obtained by removing the frequency component of, the presence or absence of leakage is determined by comparing the waveform and intensity of the sound pressure with a reference value, and the leakage point is calculated from the propagation time difference of the leakage sound at the two points. It is a thing.

In the conventional pipe leakage inspection method, the reason why the flow of water, oil, etc. in the pipe is stopped and the inspection is carried out is to remove disturbances such as flow noise and mechanical noise as much as possible. If disturbances such as sound and mechanical noise can be removed, even if water, oil, etc. are flowing in the pipe, a leak inspection can be performed.

Therefore, frequency analysis was performed on disturbances such as flowing sounds and mechanical sounds and leakage sounds. The result is shown in FIG.

As can be seen from FIG. 1, disturbances such as flowing sounds and mechanical sounds exist in a low frequency band of 5 kHz or less, while leak sounds also exist in a high frequency band of 5 kHz or more. Also, the attenuation of the sound propagating in the pipe becomes greater as the frequency becomes higher, but it is 10 kHz even at a point about 20 m away from the leak point.
Components up to about z propagate sufficiently. Therefore, by using a high-frequency filter that removes the low-frequency band of 5 kHz or less, disturbances such as flowing noise and mechanical noise can be removed, and almost only leak noise can be detected, and water, oil, etc. are flowing in the pipe. Even then, a leak inspection can be performed.

From the above consideration, the sound pressure obtained by detecting the sound pressure in the pipe at appropriate two points of the pipe in the section where the leakage inspection is performed and removing the frequency component of the sound pressure below a predetermined value When the sound pressure is equal to or higher than the reference value, it can be determined that there is a leak.

Then, the propagation time difference (Δt) of the leak sound is calculated from the sound pressure data at these two points, and the leak point can be determined from the following equation (see FIG. 2). L = (D ± V · Δt) / 2 (1) where L; distance from sound pressure detection point to leakage point,
D: Distance between sound pressure detection points, V: Propagation velocity of leakage sound.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The pipe leakage inspection method of the present invention will be described more specifically with reference to the drawings.

The pipe leakage inspection method of the present invention is carried out using an apparatus as shown in FIG. This device has two points (A, B) of the pipe a in the section where the leakage inspection is carried out.
The sound pressure sensor 1 and the sound pressure measuring device 2 are installed at the point A, the sound pressure sensor 3 and the sound pressure measuring device 4 are installed at the point B, and the correlator 5 is installed at a predetermined point.

The sound pressure sensors 1 and 3 are similar piezoelectric acceleration sensors, and in the case of this embodiment, 40 in the case of water.
A pressure sensitivity of 300 to 400 mV / G at 0 Hz and a pressure sensitivity of 1000 to 1200 mV / G in the case of oil were used. Here, the difference in pressure sensitivity is due to the use of the sound pressure sensor having a different mounting form, and is merely for the sake of convenience. To reduce the sensitivity to low frequency components that account for most of the disturbance, resistors 6 and 7 of about 10 kΩ are connected to the ends of the sound pressure sensors 1 and 3 as shown in FIG.

The sound pressure measuring instruments 2 and 4 are also the same,
Preamps 8 and 9, log amps 10 and 11,
It consists of data loggers-12 and 13.

The sound pressure signals detected by the sound pressure sensors 1 and 3 are supplied to the preamplifiers 8 and 9 as shown in FIG.
5kH by built-in high frequency filter-14,15
After the low frequency band below z is removed, the voltage is amplified.

Then, the voltage level is logarithmically compressed by the log amplifiers 10 and 11, and in the case of water, the vibration acceleration 1.
0 × 10 ^{−7 to} 4.0 × 10 ⁻⁵ G is output as a voltage signal in the range of 1 to 2 V, and in the case of oil, 4.0 × 10 ^{−8 to} 1.0 ×
A voltage signal of 10 ⁻⁵ G is output in the range of 1 to 2V.

The data loggers 12 and 13 display the voltage signals converted as described above on the displays 16 and 17 and record them as sound pressure data in a memory card or the like.

The voltage output signals from the preamplifiers 8 and 9 can be confirmed by the headphones 18 and 19, and are also sent from the output terminals 20 and 21 to the correlator 5.

As shown in FIG. 5, the correlator 5 takes in the two voltage signals sent from the output terminals 20 and 21 of the sound pressure measuring instruments 2 and 4 from the input terminals 22 and 23, and the sampling circuit 26, It converts into a digital signal by 27.

Then, the cross-correlation coefficient of the leak sound at the points A and B, that is, the propagation time difference (Δt) is calculated from the two digital signals by the microcomputer 28,
The leak point C is detected by performing the calculation of the equation (1).
The calculation result is displayed on the display 29 and recorded by the printer 30.

The pipe leakage inspection method of the present invention is performed as follows using the above apparatus.

First, the sound pressure sensors 1 and 3 and the sound pressure measuring instruments 2 and 4 are installed at appropriate two points A and B of the pipe a in the section where the leakage inspection is to be performed.

Sound pressure detection is continued for a predetermined time, and sound pressure data at points A and B2 are collected. At this time, since the low frequency band of 5 kHz or less is removed by the high frequency filters-14 and 15, disturbances such as flowing sound and mechanical sound are almost removed, and only the sound pressure component in the high frequency band remains.

Then, the presence or absence of leakage is determined by comparing the sound pressure component in the high frequency band with the reference sound pressure set on the basis of the waveform and the strength of the sound pressure previously obtained when there is no leakage.

When it is determined that there is a leak, the correlator 5 calculates the propagation time difference (Δt) of the leak sound from the sound pressure data at the points A and B2, calculates the above equation (1), and leaks. The point C is detected.

Next, the effectiveness of the pipe leakage inspection method of the present invention will be described with reference to experimental examples.

(Experimental Example 1) An experiment was conducted using an apparatus as shown in FIG. This device has two standing parts 3 on the pipe 31.
2, 33 are provided, and one end is used as the outlet 34,
A leak hole 35 is formed at a predetermined point of the pipe 31. The upper end of the standing portion 32 is used as an inflow port 36, and another pipe 37
The heavy oil A is introduced into the pipe 31 from the inlet 36 at a predetermined pressure through the hose 38, and is discharged from the outlet 34. A disturbance generator 42 including a tape recorder 39, an amplifier 40, and a vibrator 41 is installed at the upper end of the standing portion 33. Then, the sound pressure sensors 43 and 44 are connected to the pipe 31.
The sound pressure measuring instruments 45 and 46 and the correlator 47 detect leak sound and calculate leak points.

Oil pressure is 5 kg / cm ² , flow rate is 6 l / h
r, pipe 37 diameter 6 inch (150 mm), leak hole 3
5 diameter 1.0mm, the distance between the sound pressure sensor 43,44 is 15
The disturbance generator 42 was not operated. The frequency band filter used is one that removes frequencies other than 5 to 10 kHz.

The output frequency spectra of the sound pressure sensors 43 and 44 at this time are as shown in FIG. 7, and the correlation waveforms are as shown in FIG. It can be seen that in the correlation waveform, a leak sound peak that is practically sufficient is generated.

(Comparative Example 1) An experiment was conducted under the same conditions by using the same apparatus as in Experimental Example 1. However, the frequency band filter used is one that removes frequencies other than 1 to 10 kHz.

The output frequency spectra of the sound pressure sensors 43 and 44 at this time were as shown in FIG. 7, and the correlation waveforms were as shown in FIG. It can be seen that an undesired peak, which is considered to be due to the resonance of the pipe, is generated in the correlation waveform.

(Experimental Example 2) An experiment was conducted under the same conditions as the experimental example 1 except that the disturbance generator 42 was operated. Here, the frequency spectrum of the generated disturbance is as shown in FIG. The frequency band filter used is one that removes frequencies other than 5 to 10 kHz.

The output frequency spectra of the sound pressure sensors 43 and 44 at this time are as shown in FIG. 11, and the correlation waveforms are as shown in FIG. Peaks are generated in both the leaked sound and the disturbance in the correlation waveform, but there is a large difference in the peak level between the leaked sound and the disturbance, so that they can be easily distinguished from each other, and there is a point showing the maximum peak value. The leak point can be calculated.

(Comparative Example 2) An experiment was conducted using the same apparatus as in Experimental Example 2 under the same conditions. However, the frequency band filter used is one that removes frequencies other than 1 to 10 kHz.

The output frequency spectra of the sound pressure sensors 43 and 44 at this time were as shown in FIG. 11, and the correlation waveforms were as shown in FIG. Multiple peaks corresponding to the leaked sound and the disturbance are generated in the correlation waveform, and the peak levels of the leaked sound and the disturbance are approximately the same, so it is not possible to easily distinguish the two and the leak point It is impossible to calculate.

From the above experimental results, by using a high frequency band filter of 5 to 10 kHz, it is possible to significantly remove the disturbance, and even if the distance between the sound pressure sensors is 15 m, the sound pressure and the leakage sound are practically sufficient. It was found that the location could be detected.

[0039]

According to the pipe leakage inspection method of the present invention, 5
Disturbances such as flow noise and mechanical noise can be significantly removed by removing the sound pressure component in the low frequency band below kHz, so no leakage inspection is required even when water or oil is flowing in the piping. obtain.

According to the pipe leakage inspection method of the present invention,
Distinguishing between the leak sound and the disturbance becomes easy, less skill is required to determine the presence or absence of the leak, and false recognition is reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing frequency characteristics of leakage sound and disturbance.

FIG. 2 is an explanatory diagram for calculating a leak point.

FIG. 3 is an explanatory view of an apparatus for carrying out the pipe leakage inspection method of the present invention.

FIG. 4 is a configuration diagram of a sound pressure sensor and a sound pressure measuring device.

FIG. 5 is a block diagram of a correlator.

FIG. 6 is an explanatory diagram of an apparatus for testing the pipe leakage inspection method of the present invention.

7A and 7B are diagrams showing an output frequency spectrum of a sound pressure sensor when there is no disturbance, where FIG. 7A is at point A and FIG. 7B is at point B. FIG.

FIG. 8 is a diagram showing a correlation waveform when a frequency filter of 5 to 10 kHz is used when there is no disturbance.

FIG. 9 is a diagram showing a correlation waveform when there is no disturbance and a frequency filter of 1 to 10 kHz is used.

FIG. 10 is a diagram showing a frequency spectrum of disturbance.

11A and 11B are diagrams showing an output frequency spectrum of the sound pressure sensor in the case where there is a disturbance, where FIG. 11A is a point A and FIG.
It is at the point.

FIG. 12 is a diagram showing a correlation waveform when there is a disturbance and a frequency filter of 5 to 10 kHz is used.

FIG. 13 is a diagram showing a correlation waveform when there is a disturbance and a frequency filter of 1 to 10 kHz is used.

[Explanation of symbols]

 1 Sound pressure sensor 2 Sound pressure measuring device 3 Sound pressure sensor 4 Sound pressure measuring device 5 Correlator a Piping

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Housuke Ishikawa 1-11, Kanda Izumicho, Chiyoda-ku, Tokyo Fuji Underground Information Co., Ltd.

Claims (3)

[Claims] 1. A sound pressure obtained by detecting sound pressure at two points in a pipe and removing a frequency component of the sound pressure below a predetermined value, and comparing the waveform and the strength of the sound pressure with a reference value to cause leakage. It is determined whether or not there is a leak, and the leak point is calculated from the propagation time difference of the leak sound at the two points. 2. The pipe leakage inspection method according to claim 1, wherein the predetermined value is 5 kHz. 3. The reference value is a reference value based on a waveform and intensity of sound pressure which is obtained in advance when there is no leakage.
Alternatively, the pipe leakage inspection method according to claim 2.