JP3141708B2 - Gas pipeline leak detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a leak detecting device for detecting a gas leak in a gas pipeline for transporting a fluid such as natural gas.

[0002]

2. Description of the Related Art Fluids transported by pipelines include gases such as liquids and gases. 2. Description of the Related Art In a liquid transport system for transporting liquid, various types of liquid leakage detection devices that detect liquid leakage by detecting the internal pressure of a pipeline have been developed and are actually installed in the pipeline. FIG. 6 is a graph showing a change state of the internal pressure of the pipeline when a liquid leaks from the pipeline in such a system. In FIG. 6, a is a point closest to the leak point, and b is a point slightly away from the leak point. And c indicate the farthest point, st indicates the start of liquid leakage, and en indicates the end of leakage. As can be seen from FIG.
At the liquid leakage start time st and the liquid leakage end time en, a relatively large pressure fluctuation occurs depending on the amount of leakage, and propagates to the points b and c. Therefore, by detecting this pressure change, it is possible to relatively easily and reliably detect the leakage of the liquid.

[0003] However, since gas is more compressible than liquid, even if a leak occurs at one point in the pipeline, the magnitude of the generated pressure wave is small and the attenuation when propagating upstream and downstream of the pipeline. Because of the high rate, attempts to detect at another point in the pipeline will either be quite disturbed, or the pressure wave will be too small to be detected. Furthermore, the pressure waves generated by the leak and propagating through the pipeline are very small, as described above, and are difficult to distinguish from pressure fluctuations that occur during operation of the pipeline. Therefore, if the above-described liquid leak detection device is directly applied as a gas leak detection device, frequent malfunctions occur during the operation of the pipeline,
In addition, there was a possibility of overlooking the actual leak.

[0004] Therefore, several gas leak detection methods rooted in such gas-specific properties have been adopted or proposed, examples of which are shown below. (1) A method using a gas detector that measures a leaked gas component to determine that the gas is leaking. (2) A method of detecting a gas leak by providing a pressure detector at a departure base, a destination base of a gas pipeline or in the middle of a pipeline, and comparing a pressure detected by the pressure detector with a preset lower limit set value. . However, the above (1) and (2) have the following problems. That is, with respect to (1), it is difficult to monitor the entire pipeline because it is necessary to install a large number of gas detectors except for monitoring using a patrol car. The method is not suitable for monitoring the entire pipeline. In the case of (2), gas leakage is indirectly determined, and it is difficult to detect gas leakage unless a large amount of gas is leaked.

As a device capable of detecting gas leakage over the entire pipeline with extremely high accuracy, for example, a gas line leakage detecting device disclosed in Japanese Patent Application Laid-Open No. 63-30737 shown in FIG. is there. The gas line leak detection device disclosed in the publication has pressure guiding pipes 1 and 2 attached at two points (first and second points) of a gas pipeline 11 through which gas flows, and a resistance element is connected to the pressure guiding pipe 2. 3 and a capacitance element 4 are arranged in series, and a differential pressure detector 5 for measuring a pressure difference between a pressure of the gas pipeline obtained from the pressure guiding pipe 1 and a pressure through the resistance element 3 and the capacitance element 4 is provided. Differential pressure detector 5
Is to detect gas leakage by a leakage detection algorithm based on the output signal of

Here, the reason why the resistance element 3 and the capacitance element 4 are necessary will be described below. The pressure wave generated due to the leak
The velocity propagating upstream and downstream of the pipeline is approximately equal to the sound velocity of the gas in the pipe, and is about 300 to 400 m / s. In addition, the distance between the first point and the second point in FIG. 7 is, for example, about 5 m from the relationship with the site area of the installation position. If the CPU passes the signal of the differential pressure detector 5 through a leak detection algorithm to detect a pressure wave caused by the leak, the analog voltage signal of the differential pressure detector 5 is first converted into a digital signal and then passed through the leak detection algorithm. Will be. Further, a method of removing high-frequency noise contained in a digital signal on the leak detection algorithm side by using a statistical method such as a moving average is often adopted.

Now, consider the case where there is no capacitance element 4 and no resistance element 3 as shown in FIG. The time required for the pressure wave generated by the leak to pass through the first and second points in the figure is
The propagation velocity of about 300 to 400 m / s, and the distance between the first point and the second point of about 5 m from about 0.013 to 0.01
7 sec. Therefore, for example, if the frequency at which the analog voltage signal of the differential pressure detector 5 is digitally sampled is 25 Hz, the relationship between the actual pressure wave waveform and the sampling value is as shown in FIG. Pressure wave cannot be sampled. Further, even if the sampling frequency is increased and the waveform of the pressure wave is captured, the waveform becomes a high-frequency impulse-like waveform as shown in FIG. 10, and such a waveform is passed through a leak detection algorithm to obtain a moving average. If such statistical processing is performed, it is averaged together with high-frequency noise as shown in FIG. 11, and cannot be distinguished from noise.

[0008] Therefore, as shown in FIG.
The provision of the resistance element 3 forms a pseudo first-order lag element, and the output of the differential pressure detector 5 has a step-like waveform as shown in FIG. With such a signal output, even if statistical processing such as moving average is performed in the numerical algorithm, as shown in FIG. 13, the signal value after the statistical processing before reaching the pressure wave and the signal value after reaching the pressure wave are significant. Difference can be easily detected, and even a considerably small pressure wave can be detected.

[0009]

However, Japanese Patent Application Laid-Open No.
In the gas line leak detection device disclosed in Japanese Patent No. 30737, when the normal pressure of the pipeline fluctuates greatly per hour as shown in FIG. 14, even if the pressure wave does not reach the installation point of the device. Differential pressure occurs (however, instead of a step-like waveform when the pressure head wave arrives,
If the pressure fluctuation is large, the differential pressure value exceeds the measurement range of the differential pressure gauge as shown in FIG. 15, and it becomes impossible to constantly monitor the pipeline for leakage. I will.

[0010] To explain this point in more detail, the reproducibility of the currently most accurate differential pressure detector over the measurement range is about 0.1%.
On the order, also considering that the magnitude of the pressure wave to be catch now a number mmH ₂ O ~ number 10 mm H ₂ O, to measure the pressure wave with high accuracy, the measurement range of the differential pressure gauge -1500~ + 1500mmH must be in the order of ₂ O. Conversely, if the measurement range is as large as this, the minimum value of the reliable measurement value is about 1.5 mmH ₂ O, which makes it possible to sufficiently measure a minute pressure wave. However, for example, the pressure in the pipeline main line is about 5 kg per hour
/ Cm ² G, the capacity of the capacity element 4 is 60 liters, and the resistance element 3 is Cv value [Cv value:
US gpm (US gallons / minute) indicates the flow rate of 60 ° F clear water when the differential pressure across the valve is 1 psi. ] Is set to 0.0035, the differential pressure value in the differential pressure detector 5 is about 2000 to 2500 mmH ₂ O per hour, and exceeds the measurement range of the differential pressure detector 5 as shown in FIG. , The monitoring of the pressure wave becomes impossible.
This means that an impulse-like waveform as shown in FIG.
Since the capacitance of the capacitance element 4 for converting into a step-like waveform as shown in FIG. 2 is too large, and the Cv value of the resistance element 3 is too small, it reacts sensitively to pressure fluctuation in the pipeline main pipe. This is because

If the size of the capacitance element 4 is reduced and the Cv value of the resistance element 3 is increased in order to prevent this, the trend component becomes insensitive to pressure fluctuations in the main pipe of the pipeline. As shown, the measurement range problem is solved. For example, if the Cv value of the resistance element 3 is 0.014 and the capacity of the capacitance element 4 is 3 liters, the normal pressure of the pipeline is 5 kgf / hour.
/ Cm ² G changes even if the trend component
As shown in the figure, it becomes 1.5 mmH ₂ O per hour, and if it is about this, without exceeding the measurement range of the differential pressure gauge,
It is possible to constantly monitor pipelines with large pressure fluctuations. However, this time, the response to the pressure wave also becomes small, so that a step-like pressure wave as shown in FIG. 12 cannot be created, and the leak detection algorithm cannot distinguish the high-frequency noise from the high-frequency noise and can detect the pressure wave caused by the leak. Will be gone.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and a gas pipeline leak detecting device capable of detecting gas leak even when the normal pressure of the pipeline fluctuates greatly over time. The purpose is to get.

[0013]

SUMMARY OF THE INVENTION A gas pipeline leak detecting device according to the present invention is provided in a pressure guiding tube installed in a gas pipeline, and gives a first-order lag to a pressure wave of a gas introduced into the pressure guiding tube. enter pressure shaping unit, a differential pressure detector for detecting a difference between the pressure of the gas introduced directly from the gas pressure and the gas pipeline which is output from the pressure shaping unit, a differential pressure signal of the differential pressure detector According to the input signal.
Resistors and capacitors that give a first-order lag to the resulting waveform
A waveform shaping means including an electric circuit having a circuit , and sampling an output signal of the waveform shaping means at a predetermined cycle, and a moving average value of the sampling data and the latest sampling
Determine the difference from the data and compare this difference with the threshold.
And a judgment means for judging the presence / absence of gas leakage.

The differential pressure detector and the waveform shaping means
Between the high-frequency component of the voltage output of the differential pressure detector
In which a filter means for removing the filter is interposed .

[0015]

In the gas pipeline leak detecting device constructed as described above, the pressure shaping means gives a first-order lag to the pressure wave of the gas introduced into the pressure guiding tube. When the working pressure fluctuates at a constant width per unit time, the product of the rate of change of the gas pressure and the time constant of the first-order lag between the pressure given the first-order lag and the gas pressure directly derived from the gas pipeline. A proportional pressure difference occurs. Further, the differential pressure detector detects a difference between the gas pressure output from the pressure shaping means and the pressure of the gas directly guided from the gas pipeline, and the waveform shaping means inputs a differential pressure signal of the differential pressure detector , and Depending on the input signal
First-order lag is given to the waveform formed . Further, the judging means samples the output signal of the differential pressure detector at a predetermined period, and compares the moving average value of the sampled data with the latest sample.
Find the difference from the ring data and compare this difference with the threshold
To determine the presence or absence of gas leakage by.

Further, the filter means outputs the output signal of the differential pressure detector.
Removes high frequency components from signals, compressors, governors, etc.
To remove noise such as driving noise.

[0017]

[Embodiment 1] FIG. 1 is a block diagram of one embodiment of the present invention. The gas pipeline 11 is provided with a pressure guiding pipe 13 downstream of the gas leak point 12, and the pressure guiding pipe 13 branches into branch pipes 14 and 15 on the way. One branch pipe 15 is provided with a resistance element 16 and a capacitance element 17 following the resistance element 16 (hereinafter, the resistance element 16 and the capacitance element 17 subsequent thereto are collectively referred to as a pressure shaping element). And the capacitance element 1
A differential pressure detector 21 for detecting a pressure difference between a pressure at a point 19 of the pressure guiding pipe led from 7 and a pressure at a point 20 of the other branch pipe 14 is provided.

The differential pressure detector 21 is connected to an amplifier circuit 23 having a filter function, and the filter function removes high frequency noise components. In this embodiment, the cutoff frequency is set to 12.
This corresponds to a high cut filter of 5 Hz. A waveform shaping element 25, which is an electric circuit for converting the signal 51 having a somewhat low frequency waveform as shown in FIG. 3 into a signal 55 having a step-like waveform as shown in FIG. 4, is connected to the amplifier circuit 23. Have been. This waveform shaping element 25
Is not particularly limited as long as it converts the input signal into a step-like waveform. In this embodiment, the variable resistor 25a shown in FIG.
5b and operational amplifier 25c (input impedance about 2M
Ω).

Further, the waveform shaping element 25 is connected to an A / D conversion circuit 27 for converting an analog signal from the waveform shaping element 25 into a digital signal.
7 is connected to a CPU 29 which digitally samples a digital signal from the A / D conversion circuit 27 and determines gas leakage by a numerical operation algorithm for leakage detection. The numerical calculation algorithm for leak detection is not particularly limited, but for example, the following A1 is conceivable. Here, P is a differential pressure detection signal, i is the i-th sampling, Δt is a sampling interval (this is not particularly necessary if the sampling interval is constant), and C is a threshold. The meaning of this algorithm is as follows. That is, n
The average value of the sampled data from the previous time to the previous time, in other words, the moving average value of the sampled data is compared with the latest sampled data. High-frequency noise is reduced or eliminated by the moving average process.

Next, the operation of the above embodiment will be described. When a leak occurs at the gas leak point 12 in FIG.
The pressure wave generated there propagates at a speed substantially equal to the sound speed of the fluid in the pipeline, and is introduced into the pressure guiding pipe 13 and the branch pipe 14.
Is input to the differential pressure detector 21 at the point 20 via On the other hand, the pressure at the point 19 of the pressure guiding pipe via the pressure shaping element does not immediately become the same pressure value as at the point 20 because of the pressure shaping element, but gradually decreases from the pressure value before reaching the pressure wave. It will approach the pressure value after reaching. For example, if the Cv value of the resistance element 16 of the pressure shaping element is 0.014,
If the capacity of the capacity element 17 is 3 liters,
The output of the differential pressure detector 21 for measuring the differential pressure between the pressure and the point 19 depends on the magnitude of the pressure wave when the pressure wave reaches the pressure guiding pipe 13. For example, the magnitude of the pressure wave is about 10 mmH ₂ O. Then, as shown in FIG. 3, a relatively low-frequency signal 51 having a duration of about 3 seconds is obtained.

If a pressure shaping element having the above-described degree is selected, as described in the above-mentioned subject, the trend that occurs even if the ordinary pressure of the pipeline changes by 5 kgf / cm ² G per hour. Components are 1.5m per hour
mH ₂ O (see FIG. 18). With this level, the measurement range of the differential pressure gauge is not exceeded, and it is possible to constantly monitor a pipeline having a large pressure fluctuation.

Next, the signal having the waveform shown in FIG.
3 and 1 by the filter function of the amplifier circuit 23.
High-frequency noise components of 2.5 Hz or more are removed. For example, taking the signal of FIG. 3 as an example, the signal 53 which is a high-frequency noise component is removed, the signal 51 caused by the pressure wave due to gas leakage is not removed, and the waveform shaping element 25 is not changed.
Sent to The reason for employing this filter function is as follows. That is, if there is no filter function, the signal 53 which is a noise component in FIG. 3 is sent to the waveform shaping element 25 as it is, and this signal 53 is converted into a step-like pressure waveform as described later. This is because the noise component cannot be distinguished from the noise component, and the noise component is erroneously recognized as the noise component. Therefore, it is meaningful to connect the pressure waveform element, the filter, and the waveform shaping means in this order.

Next, the output of the amplifier circuit 23 is sent to the waveform shaping element 25. This circuit converts the signal 51 having a waveform of about 3 seconds shown in FIG. 3 into a signal 55 having a step-like waveform having a duration of about 20 seconds as shown in FIG. The conversion into such a step-like waveform is shown in FIG.
When the signal 51 having the waveform shown in (1) is processed by the algorithm A1 having a relatively rough sampling interval corresponding to the time required from the occurrence of the leak to the detection / warning, it is averaged together with the noise, and accurate leak detection is impossible. However, if the signal 55 has a step-like waveform as shown in FIG. 4, it is possible to identify the noise 55 even after adding the moving average process in the algorithm A1. Next, the signal 55 is sent to the A / D converter 27 and is converted into a digital signal having a certain period. This digital signal is sampled at a predetermined sampling cycle (in this embodiment, the sampling cycle is set to 0.04 seconds), and the CPU 29 executes a numerical calculation algorithm A1 for leak detection to determine a gas leak. You.

As described above, according to the present embodiment, even in a gas pipeline having a large pressure fluctuation, when a leak occurs, detection is performed with respect to a leak detection algorithm having a step of performing statistical processing. can be supplied easily step-shaped signal, it is possible to make the leak detection gas pipelines easily and accurately captures accurately the timing of the leakage occurrence.

Embodiment 2 FIG. FIG. 5 is a block diagram of another embodiment of the present invention. In the first embodiment, an example in which the pressure outlet is provided at one place is shown. In the present embodiment, in addition to the pressure guide pipe 13, a pressure guide pipe 31 is connected to the gas pipeline 11, and two pressure outlets are provided. It was made. As described above, according to the present invention, one or two outlets of the pressure guiding pipe can be accommodated.

In the above embodiment, an example having both a resistance element and a capacitance element has been described. However, the present invention may be applied to a case having either a capacitance element or a resistance element. In this case, the missing element is replaced with a pressure guiding pipe from the gas pipe to the differential pressure detector 21.

In the above embodiment, the circuit for converting the input signal into a step-like waveform is shown as the waveform shaping element 25. However, a hold circuit for holding the peak state of the input signal for a certain period of time may be used. Good. The time constant in this case is the holding time.

Further, if the time constant of the pressure shaping element is within the range of 0.1 second to 5 seconds in the measurement range of a normal gas pipe pressure fluctuation or a generally used differential pressure detector, a pressure wave due to leakage is detected. In addition, it is possible to prevent scale-out due to pressure fluctuation of the normal pressure. In the above embodiment, the cutoff frequency of the filter function is set to 12.5 Hz.
However, the frequency may be 5 Hz or more depending on the installation location of the detector, the type of the noise source, the operating condition, and the like, and the noise of the compressor and the governor can be removed at this level. In the above embodiment, the time constant of the waveform shaping means is set to 20 seconds.
If it is longer than second, the time delay of the detection of the pressure wave can be ignored.

[0029]

As described above, according to the present invention, the wave in the present invention, the waveform shaping means, formed by the differential pressure signal of the differential pressure detector
The first order delay is given to the shape, so even for gas pipelines with large fluctuations in normal pressure, the leak detection algorithm, which has a process of performing statistical processing when a leak occurs, has an easy-to-detect step shape. Signal can be supplied, and leak detection of the gas pipeline can be quickly, easily and accurately performed.

Further , the differential pressure detector is
Since high frequency components are removed from the output signal,
Elimination of noise such as driving noise of the compresa enables false detection
Is reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is an explanatory diagram of a circuit configuration example of a waveform shaping element according to the embodiment.

FIG. 3 is an explanatory diagram of a signal waveform output from a differential pressure detector.

FIG. 4 is an explanatory diagram of a signal waveform output from a waveform shaping element.

FIG. 5 is a block diagram of another embodiment of the present invention.

FIG. 6 is a graph showing a change state of the internal pressure of the pipeline when a liquid leaks from the pipeline.

FIG. 7 is a block diagram of a conventional gas line leak detection device.

FIG. 8 is a block diagram of a conventional gas line leak detection device.

FIG. 9 is a graph showing a relationship between a waveform of an actual pressure wave and a sampling value in a conventional example.

FIG. 10 is a graph showing a waveform of a pressure wave captured by increasing the sampling frequency in a conventional example.

11 is a graph showing a waveform obtained by performing a statistical process such as a moving average on the waveform shown in FIG. 10;

FIG. 12 is a graph showing a waveform when a first-order lag is given to a pressure wave in a conventional example.

FIG. 13 is a graph showing a waveform when a statistical process such as a moving average is performed on the waveform shown in FIG. 12;

FIG. 14 is a graph showing a change state of a normal pressure of a pipeline.

FIG. 15 is a graph showing a change state of a differential pressure when the pressure fluctuation shown in FIG. 14 occurs.

FIG. 16 is a graph showing a change state of the differential pressure when the capacitance of the capacitance element is increased and the Cv value of the resistance element is decreased.

FIG. 17 is a graph showing a change state of the differential pressure when the capacitance of the capacitance element is small and the Cv value of the resistance element is large.

FIG. 18 is a graph showing a change in the differential pressure when the Cv value of the resistance element 3 is 0.014 and the capacity of the capacitance element 4 is 3 liters.

[Explanation of symbols]

Reference Signs List 11 gas pipeline 16 resistance element (constitutes pressure shaping means together with capacitance element 17) 17 capacitance element (constitutes pressure shaping means together with resistance element 16) 21 differential pressure detector 23 amplifier circuit 25 waveform shaping element 27 A / D converter 29 CPU

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Mitsuyuki Goto 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Yuichi Nogami 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan (56) References JP-A-63-30737 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01M 3/28 G01M 3/24

Claims (2)

(57) [Claims] 1. A pressure shaping means provided in a pressure guiding pipe installed in a gas pipeline to give a first-order lag to a pressure wave of a gas introduced into the pressure guiding pipe; and a gas pressure output from the pressure shaping means. a differential pressure detector for detecting a difference between the pressure of the gas introduced directly from the gas pipeline, enter the differential pressure signal of the differential pressure detector, the form by the input signal
Resistors and capacitors that give first-order lag to the resulting waveform
Waveform shaping means comprising an electric circuit having: a sampling means for sampling the output signal of the waveform shaping means at a predetermined cycle, and a moving average value of the sampled data and the latest sample
Find the difference from the ring data and compare this difference with the threshold
And a determining means for determining the presence or absence of gas leakage by performing the above process. 2. The apparatus according to claim 1, wherein filter means for removing high-frequency components from the voltage output of said differential pressure detector is interposed between said differential pressure detector and said waveform shaping means. Gas pipeline leak detection device.