JPS5846694B2 - gas loweikenchihouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a detection method for detecting gas leakage from a gas transport pipe that occurs when pinholes, cracks, etc. occur in the transport pipe during gas transport.

Several methods are being considered for detecting gas leaks, but all of them involve only bi-hourly monitoring.

The present invention is a detection method for constantly monitoring the presence or absence of gas leakage during gas pipeline transportation.

When a crack occurs in a transport pipe due to some reason, gas is suddenly ejected from the crack.

Particularly in the case of high-pressure gas, rapid gas injection generates elastic wave energy in the vicinity of the injection port.

The generated elastic waves include those that propagate in the medium such as gas inside the pipe, those that propagate outside the pipe, and those that propagate along the pipe wall.There is a method for detecting elastic waves in the transport pipe. Possible methods include a method of detecting elastic waves propagating in the medium inside the pipe and a method of detecting elastic waves propagating on the outer wall of the pipe.

The former mainly detects elastic waves using an ultrasonic microphone or the like, and the attenuation of the elastic waves is relatively small, with an attenuation rate of about 10 dB/100 m.

Therefore, even if the detection sensitivity of the detector is somewhat low, it can be easily detected.

However, the former detection method has the following drawbacks and is difficult to put into practical use industrially.

That is, (1) in the case of transport pipes, it is difficult to attach and remove the detector, and especially in the case of a breakdown, it is impossible to repair it.

2. Easy to undergo chemical reactions such as corrosion.

3. Directly influenced by fluid objects such as pressure and flow in the fluid.

For these reasons, it is impossible to use it in the field.

The latter method (namely, the method of attaching the detector to the wall of the outer tube) does not have the above disadvantages, and the attachment can be easily managed later.

However, when this method is applied to buried pipes, there is a drawback that the attenuation rate of elastic wave energy increases.

For example, when the frequency of an elastic wave is 10kHz, the attenuation rate of an aboveground pipe is about 10dB/100m, but the attenuation rate of a buried pipe is about 40dB/100, and the attenuation rate of a buried pipe is compared to that of an aboveground pipe. It is about 30dB/100m louder.

Therefore, it is relatively easy to detect leaky elastic waves in above-ground pipes, but it has been considered difficult to detect them in buried pipes because of their large attenuation.

The present invention solves the above-mentioned drawbacks of the prior art, and its purpose is to dissipate the acoustic wave energy generated by gas leakage and propagating through the wall of the gas transport pipe as far as possible in a buried gas transport pipe. Detection is performed using a vibration detector attached to the outer wall of the gas transport pipe. Therefore, when installing the vibration detectors, the interval between them should be as large as possible, the number of vibration detectors should be minimized, and the number of vibration detectors should be minimized. To provide a gas leak detection method capable of constantly operating, constantly monitoring gas leaks at minimum cost and expense, and detecting gas leaks as soon as they occur.

A feature of the present invention that achieves this object is to convert the energy of elastic waves generated by gas leakage in a buried gas transport pipe and propagating through the pipe wall of the gas transport pipe into vibrations attached to the outer wall of the gas transport pipe. In the method of detecting gas leakage from a gas transport pipe by using a detector, the resonant frequency of the vibration detector is 3 to 12 kHz, and the vibration detectors are installed on the outer wall of the gas transport pipe at intervals of 300 to 400 m. A gas leak detection method is provided.

The gas leakage detection method according to the present invention performs detection not in all frequency bands of elastic waves caused by leakage but in a predetermined frequency band.

That is, 100 to 200 from the leak point? ? Unlike the frequency distribution when detecting at a point separated by Z and the frequency distribution of elastic wave energy at the leak point, the frequency component of the elastic wave energy that is maximum at the leak point is hardly detected at the detection point.

This is thought to be because the attenuation of the elastic waves propagating along the surface pipe wall of the gas transport pipe differs depending on the frequency, and the attenuation rate becomes larger at high frequencies.

Furthermore, the level of external noise is large at low frequencies, making it difficult to identify the desired signal.

For the above reasons, 100~
200? ? Even at a long distance in Z, it can be determined that the signal level is sufficiently large compared to external noise and that signal capture is possible.

Here, in order to explain the present invention in detail, the results of a gas leakage experiment will be described.

In this experiment, a buried pipe (pipeline) with a diameter of 2007nr/Lφ was used, and a gas body was used as the fluid.

Is the pipeline gas pressure 50Ky/c/? Hold it at L and make a hole with a diameter of 2 mmφ, and gas will blow out from this hole.
It looked like a gas leak would occur.

FIG. 1 is a characteristic diagram according to this experimental example, showing the frequency distribution of elastic wave energy propagating through the tube wall at a gas leak point, where f represents the frequency and e represents the elastic wave energy level.

From Figure 1, the elastic wave energy near the gas leak point is 80
It can be seen that the maximum energy density is near kHz, and as the frequency moves higher or lower, the energy density rapidly attenuates.

Figure 2 is also a characteristic diagram according to this embodiment, and is a diagram showing the frequency distribution at a point 150 m away from the leakage point of the elastic wave energy propagating through the pipe wall, and 21 is an elastic wave propagating due to gas leakage. The frequency distribution of energy, 22 is the frequency distribution of noise energy when there is no leakage, f is the frequency,
e represents the elastic wave energy level.

In FIG. 2, the peak of energy density near 30 kHz that was seen in FIG. 1 disappears, and a peak appears near 10 kHz, with a gentle attenuation in both directions.

This is thought to be because, as shown in FIG. 3, which will be described later, the attenuation rate of the elastic waves propagating through the buried pipe suddenly increases as the frequency increases.

In FIG. 2, the frequency range in which the solid line elastic wave energy level 21 is higher than the broken line noise energy level 22 is from 3 kHz to 12 kHz.

In the frequency range other than the above range, the noise energy level 22 exceeds the elastic wave energy level 21 in both the low frequency range and the high frequency range.

Therefore, the frequency range in which gas leakage can be detected at a long distance from the gas leakage point, for example at a distance of 100m or more, is 3kHz to 12kHz.
Limited to Hz.

Also, the detected elastic wave energy level was low 1.0
-3 Gal or less.

It is simply impossible to detect such minute elastic wave signals with commonly used broadband vibration detectors.

FIG. 3 is also a characteristic diagram based on this experimental example, showing the attenuation characteristics of the elastic wave energy propagating through the tube wall depending on each frequency, where d represents the distance from the gas leak point, and e represents the elastic wave energy.

In the example shown in Figure 3, when the distance from the gas leak point is 120 m, most of the elastic energies of the frequencies are grouped together, and the energy level is 2 X I F" Ga i (Gal is C
rrL15eC2).

At longer distances, the low frequency energy component becomes larger, and when the detection point is 150 m, the elastic wave energy distribution characteristics become as shown in FIG.

The problem here is that when detecting a signal on the pipe wall, especially when the pipe is buried like in this embodiment and the gas outlet is small, the detection level of elastic wave energy is very low.

Fig. 4 is also a characteristic diagram based on this first experimental example, showing the attenuation characteristics of the above-ground pipe and the buried pipe of the elastic wave energy with a frequency of 10 kHz propagating through the pipe wall, where 41 is the characteristic of the above-ground pipe, and 42 is the characteristic of the above-ground pipe. Characteristics of the buried pipe, d is the distance from the gas leak point, e
represents the elastic wave energy level.

That is, the detection level of elastic wave energy in the case of a buried pipe is 1×10 ”Gal at a frequency of 10 kHz.

In the case of above-ground pipe under the same conditions, it is 1X10'Gal.

Therefore, since the vibration detectors currently on the market cannot detect gas leakage, the inventors developed a vibration detector for detecting minute elastic waves and completed the present invention.

FIG. 5 is a cross-sectional view of one embodiment of the above-mentioned vibration detector.
52 is a transducer made of piezoelectric ceramics, 53 is a weight, 54 is a metal vibrating piece, 55 is an impedance converter for removing external noise, and 56 is a cable.

This vibration detector utilizes mechanical resonance between a metal vibrating piece 54 and a weight 53, and in this embodiment, the resonance sharpness is designed to be about 400.

In addition, this vibration detector has a resonance frequency of 3kHz to 12kHz.
It is within the range of Hz.

(3 kHz, 5 kHz, 8 kHz in experiments)
I did it.

) The output sensitivity of the detector at these resonance points is 2X 1
0"-8V/Gal and 150??Z from the gas leak point
An output sensitivity of 1 to 10 .mu.cm was obtained as a detection sensitivity at a distant point.

(However, the measurement conditions were a gas pressure of 50 Kq/i, a gas leak diameter of 2 mm, and a frequency of 8 kHz.

) This level of output sensitivity is within the signal level that allows the amplifier to work with sufficient precision, and is also within the range that allows for subsequent signal processing.

By installing a plurality of the above elastic wave detection detectors at intervals of about 300 to 400 m in the longitudinal direction of the pipeline, continuous leakage monitoring of the pipeline becomes possible.

In addition, in the case of buried pipes, the attenuation rate of elastic wave energy is much higher than in above-ground pipes, so if a gas leak occurs, the difference in output level between each detector will be large, making it relatively easy to locate the leak point. can be discovered.

FIG. 6 shows an embodiment of the gas leakage detection method according to the present invention.
61 is a sensor, 62 is an impedance converter, 63 is a vibration detector, 64 is an amplifier, 65 is a bandpass filter,
66 is an A-D converter, 67 is a comparator, and 68 is an alarm device.

It is also possible to deploy such detectors at intervals of 300 to 400 meters, compare the level difference of their output signals with a comparator, and use a telemeter to notify the monitoring room of a gas leak alarm via an alarm device. be.

As explained above, the gas leakage detection method according to the present invention can detect the energy of elastic waves of various frequencies that are generated due to gas leakage in a buried gas transport pipe and propagate through the wall of the gas transport pipe. , since the vibration detector has a resonant frequency that resonates with elastic waves in the frequency range of 3 to 12 kHz, which is higher than the noise energy level and propagates at a low attenuation rate to a distance of 100 m or more, it is detected. , when installing the vibration detector, the interval should be 300~
To obtain the effect of being able to be extremely large at 400 m, minimizing the number of units installed, constantly operating vibration detectors to constantly monitor gas leaks at minimum cost and expense, and detecting gas leaks immediately as they occur. Can be done.

[Brief explanation of the drawing]

Figure 1 is a characteristic diagram showing the frequency distribution of elastic wave energy propagating through the pipe wall at a gas leak point, and Figure 2 is a characteristic diagram showing the frequency distribution of elastic wave energy propagating through the pipe wall at a point 150 m away from the leak point. Figure 3 is a characteristic diagram showing the attenuation characteristics of elastic wave energy propagating through the pipe wall depending on each frequency. Figure 4 is a characteristic diagram showing the attenuation characteristics of elastic wave energy propagating through the pipe wall in ground pipes and underground pipes. Characteristic diagram showing the attenuation characteristics by
FIG. 5 is a sectional view showing a resonant vibration detector according to an embodiment of the present invention, and FIG. 6 is a block diagram showing a detection method according to an embodiment of the present invention. 21... Frequency distribution of elastic wave energy, 22
...Frequency distribution of noise energy, 41...
...Characteristics of above-ground pipes, 42...Characteristics of buried pipes,
51... Main body, 52... Transducer, 53... Weight, 54... Metal vibrating piece, 55, 62... impedance converter,
56...Cable, 61...Sensor,
63...Vibration detector, 6 Bandpass filter, 6 67°°゛...Comparator, 4...Amplifier, 65...6...
・A-D converter, 68... Alarm device.

Claims (1)

[Claims] 1. The energy of elastic waves generated by gas leakage in a buried gas transport pipe and propagating through the pipe wall of the gas transport pipe is
In the method of detecting gas leakage of the gas transport pipe by detecting it with a vibration detector attached to the outer wall of the gas transport pipe, the resonance frequency of the vibration detector is 3 to 12 kHz,
A gas leakage detection method characterized in that the vibration detectors are attached to the outer wall of the gas transport pipe at intervals of 300 to 400 m.