JP2002131172A - Method for detecting leakage of gas in pipeline - Google Patents

Abstract

PROBLEM TO BE SOLVED: To distinguish the fluctuation of pressure due to the leakage of gas from the fluctuation of pressure occurring during a normal operation period and accurately detect the leakage of gas. SOLUTION: The method for detecting the leakage of gas is composed of a step in which the pressure of fluid in a pipeline is measured within determined time intervals at specified positions of the pipeline, and the start of propagation of the pressure fluctuation is detected, a step in which a plurality of values of pressure are measured during a constant period after detecting the stat of propagation of the pressure fluctuation, and a gradient A of variation of the values of pressure within the constant period is calculated, a step in which a plurality of values of pressure are measured during a period longer than the constant period after detecting the start of propagation of the pressure fluctuation, and a gradient B variation of the values of pressure within the constant period is calculated, a step in which a judgement is carried out whether the ratio A/B between the gradient A and the gradient B is more than a threshold value or not.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas leak detecting method 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 various gases and other gases in addition to liquids. 2. Description of the Related Art In a liquid transport system that transports a liquid through a pipeline, various types of liquid leakage detection devices that detect the leakage of the liquid by measuring the internal pressure of the pipeline have been developed and installed in the pipeline.

FIG. 2 is a graph showing how the internal pressure of a pipeline changes with time when a liquid leaks from the pipeline in such a liquid transport system. In the figure, the curve a shows the pressure fluctuation at the point closest to the leak point, the curve b shows the pressure fluctuation at a point slightly away from the leak point, and the curve c shows the pressure fluctuation at the point farthest from the leak point. I have. In addition, st represents a liquid leakage start time point, and en represents a liquid leakage end time point.

As can be seen from FIG. 2, at point a, relatively large pressure fluctuations occur at the leak start time st and the leak end time en, and these pressure fluctuations are accompanied by a slight time delay and the attenuation of the fluctuation amount, and Propagated to point and point c.

[0005] As described above, since the propagation of pressure fluctuations extends over a wide range, it is possible to relatively easily and reliably leak liquid by detecting a change in pipe pressure over time even at a point distant from the leak point. Can be detected.

However, since gas is more compressible than liquid, even if a leak occurs at one point in the pipeline, the fluctuation in the pressure inside the pipe is small, and it is difficult to detect gas leakage at the leak point, and the pressure is low. Since the fluctuation rate of the pressure fluctuation when the fluctuation propagates upstream and downstream of the pipeline is large, even if an attempt is made to detect a gas leak at a point distant from the leakage point, the pressure fluctuation is too small and the detection is even more difficult.

[0007] It is also difficult to distinguish pressure fluctuations that occur during operation of the pipeline.

Therefore, if the above-described liquid leak detecting device is applied as it is to a gas leak detecting device, there is a possibility that a gas leak may be overlooked during the operation of a pipeline.

As described above, as a conventional technique for detecting a gas leak that cannot be detected by the liquid leak detecting device, a method using a gas line leak detecting device disclosed in Japanese Patent Application Laid-Open No. 63-30737 is disclosed. (Prior Art 1). The gas line leak detection device includes a pressure guiding pipe attached to the gas line, which includes at least one of a capacitance element and a resistance element, and a differential pressure detecting unit that detects a differential pressure between specific locations of the pressure guiding pipe. One or more gas leak detection algorithms are stored in advance, and the detection signals from the differential pressure detecting means are sequentially sampled at a predetermined cycle, and one or a plurality of appropriate gas leak detection algorithms are sampled from the sampling data. Gas leakage data acquiring means for acquiring relative value data relating to gas leakage based on the data, and gas leaking from the gas line using the relative value data acquired by the gas leakage data acquiring means. Judgment means for judging whether or not the operation is performed.

The gas line leak detecting device will be described with reference to FIG. 3. At two points A and B at a certain distance from a gas pipeline 21 through which gas flows, a pressure guiding pipe 2 is provided.
2 and 23, a resistance element 24 and a capacity element 25 are arranged in series on the pressure guiding pipe 22, and the capacity element 25 and the pressure guiding pipe 22 are connected. And a differential pressure detector 26 for measuring a differential pressure between the pressure of the pressure sensor and the pressure through the resistance element 24 and the capacitance element 25. A leak detection algorithm is provided based on the output signal of the differential pressure detector 26. This detects gas leakage.

The speed at which the pressure fluctuation generated due to the gas leakage propagates up and down the pipeline is approximately equal to the sound speed of the gas in the pipe, and is about 300 to 400 m / sec. In addition, the distance between the point A and the point B in FIG. 3 is, for example, about 5 m from the relationship with the site area of the installed position. In the gas line leak detection device of FIG. 3, considering the case where the resistance element 24 and the capacitance element 25 are not provided, the time required for the leading pressure wave generated by the leak to pass between the point A and the point B is as described above. From the velocity of the pressure head wave and the distance between the two points, about 0.012 to 0.017 sec.
Becomes

When trying to capture the waveform of the pressure fluctuation in such a short time, even if the sampling pitch is increased and the waveform of the pressure fluctuation is captured, the waveform is as shown in the graph of FIG. , A pulse-like waveform that terminates the high-frequency response instantaneously. Then, if such a waveform is passed through a leak detection algorithm and subjected to statistical processing such as moving average, the waveform is averaged together with high-frequency noise and cannot be identified as noise.

A gas line leak detection device disclosed in Japanese Patent Application Laid-Open No. 63-30737 is provided to solve such a problem, and includes a resistance element 24 and a capacitance element 25.
, A pseudo first-order lag element is formed, and the waveform of the pressure fluctuation detected by the differential pressure detector 26 becomes a step-like waveform as shown in the graph of FIG.

With such a waveform, even if statistical processing such as moving average is performed in the gas leak detection algorithm, the signal value after the statistical processing before the pressure fluctuation reaches and the signal value after the pressure fluctuation reaches , It is easy to find a significant difference from the signal value after the statistical processing, and it is possible to detect even a small pressure fluctuation.

As another conventional technique for detecting the leakage of gas, there is a technique (prior art 2) disclosed in Japanese Patent Application Laid-Open No. H6-129941. A method for detecting the arrival time of a pressure front wave based on this technology is a method for detecting the arrival time of a pressure front wave that propagates as a medium with the fluid due to an event that causes a fluid pressure fluctuation in a pipeline, Measuring a characteristic value related to the fluid pressure in the pipeline; converting the measured characteristic value to an electrical signal; storing and retaining the electrical signal over a predetermined time; Determining the arrival time of the leading pressure wave from the electrical signal for a predetermined time by using a statistical method, the arrival time of the leading pressure wave.

The arrival time of such a pressure head wave (pressure fluctuation) is detected by pressure detectors provided at two places separated from each other in the pipeline, and the occurrence position of an event such as gas leakage is estimated based on the time difference. Is what you do.

[0017]

However, the above-mentioned conventional methods for detecting gas leaks in pipelines include the following:
There are the following problems. Prior art 1 and prior art 2
In both cases, it is possible to capture the pressure fluctuation caused by the flow fluctuation of the fluid in the pipeline, but the pressure fluctuation caused by the gas leakage and the pressure fluctuation generated by the pressure reducing valve operation etc. performed during normal operation Is difficult to distinguish.

The waveform of the pressure fluctuation when the pressure fluctuation due to the gas leakage reaches the place where the differential pressure detector is installed, as shown in the graph of FIG. Although the waveform gradually recovers to a constant pressure, the waveform of the pressure fluctuation generated by the operation of the pressure reducing valve or the like is a waveform in which the pressure gradually decreases with time as shown in FIG.

In the above-mentioned prior art, the differential pressure signal is sampled at regular time intervals, and the variation of the slope of the approximate straight line calculated from the obtained differential pressure value group is monitored. Since it is a method of judging that the leakage has occurred when exceeding, the waveform of FIG. 6 and the waveform of FIG.
The slope of the approximate straight line becomes similar, and it is difficult to distinguish between pressure fluctuation caused by gas leakage and pressure fluctuation generated during normal operation.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and is capable of distinguishing between pressure fluctuations caused by gas leakage and pressure fluctuations generated during normal operation. Therefore, an object of the present invention is to provide a method for detecting gas leakage in a pipeline that can accurately detect gas leakage.

[0021]

SUMMARY OF THE INVENTION A gas leak detecting method for a pipeline according to the present invention measures the pressure of a fluid in the pipeline at a specific location of the pipeline at predetermined time intervals, and measures the propagation of pressure fluctuation. Detecting a start, and determining a gradient A of a pressure value change within the time from a plurality of pressure values measured within a certain time after the start of the propagation of the pressure fluctuation is detected; Obtaining a gradient B of a pressure value change within the time from a plurality of pressure values measured within a certain period of time after the start of the fluctuation propagation is detected, and a gradient A and a gradient B; And determining whether or not the ratio A / B exceeds a threshold value, thereby detecting gas leakage.

Further, the step of detecting the start of the propagation of the pressure fluctuation includes the step of obtaining an average value of the pressure within a predetermined time, and the step of determining the absolute value of the difference between the average value and the latest measured pressure value as a threshold value. And a step of determining whether or not the number exceeds the threshold.

In the method for detecting gas leakage in a pipeline according to the present invention, the start of propagation of pressure fluctuation is detected, and the gradient of a change in pressure value within a certain period of time near the start point of the pressure fluctuation is determined. Since the presence or absence of gas leakage is determined based on the ratio of the gradient of the pressure value change over a longer period of time, pressure fluctuation based on gas leakage and pressure fluctuation based on operational factors such as operation of the pressure reducing valve And gas leakage in the pipeline can be accurately grasped.

[0024]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a gas leak detection system diagram for explaining an embodiment of a gas leak detection method for a pipeline according to the present invention. The gas pipeline 1 is provided with a pressure guiding pipe 3 downstream of the gas leak point 2. The pressure guiding pipe 3 is branched into a branch pipe 4 and a branch pipe 5 on the way, and the branch pipe 4 has a resistance element 6 and a capacitance element 7 (the resistance element 6 and the capacitance element 7 are referred to as a mechanical pressure shaping element). Are provided in this order. The branch pipe 5 has a resistance element 6 and a capacitance element 7 that are connected to the pressure at a point A where the pressure guiding pipe 3 of the pipeline 1 that is guided through the branch pipe 5 is attached.
Pressure detector 8 for detecting the differential pressure with the pressure guided through
Is provided.

An amplifier circuit 9 having a filter function is connected to the differential pressure detector 8. In the amplifier circuit 9, a high-frequency noise component in the differential pressure signal detected by the differential pressure detector 8 is detected. Is removed.

The amplifying circuit 9 includes an electric waveform shaping element 10
Is connected to the electric waveform shaping element 10.
An electric circuit for converting a signal of a low frequency waveform into a step-like waveform is incorporated.

The electrical waveform shaping element 10 is connected to an A / D conversion circuit 11 for converting an analog signal from the electrical waveform shaping element 10 into a digital signal. A computer 12 which samples a digital signal from the D conversion circuit 11 and judges a gas leak by a numerical operation algorithm for gas leak detection based on the gas leak detecting method for a pipeline according to the present invention.
Is connected.

The numerical calculation algorithm for detecting gas leakage includes a part for detecting the start of propagation of pressure fluctuation and a part for detecting whether the detected pressure fluctuation is caused by gas leakage, or by operating a pressure reducing valve. It consists of two steps of judging from the shape of the waveform whether it has occurred, and the pressure fluctuation due to gas leakage is detected based on the two-step criterion.

First, the start of pressure fluctuation propagation is determined based on the following equation (1).

[0031]

(Equation 1)

The meaning of the above equation (1) is as follows.

That is, the average value of the sampling data of the differential pressure detection signal from the nth previous time, in other words, the moving average value of the sampling data of the differential pressure detection signal, and the sampling data of the latest differential pressure detection signal If the difference between the two exceeds the threshold value C, it is determined that pressure fluctuation has occurred. The sampling interval is constant.

Next, when the value on the left side of the equation (1) exceeds the threshold value C, it is determined based on the following equations (2) to (4) whether or not the value is caused by gas leakage.

[0035]

(Equation 2)

[0036]

(Equation 3)

[0037]

(Equation 4)

In equation (2), A indicates the start of pressure fluctuation detection (the difference between the moving average value of sampling data and the latest data is the threshold C in the detected step-like pressure fluctuation waveform). M) until the end of detection (when the difference between the moving average value of the sampling data and the latest data returns to a constant value equal to or less than the threshold value C). It shows the maximum value of the slope based on arbitrary continuous k sampling points among the sampling points, and shows the maximum value of the local slope of the waveform. B in equation (3) indicates the maximum value of the slope at m sampling points, and indicates the maximum value of the entire slope of the waveform.

If the number of samplings for calculating the local inclination is 5 points and the number of samplings for calculating the overall inclination is 125 points, the waveform of the pressure fluctuation generated by the operation of the pressure reducing valve or the like is as shown in FIG. Since the waveform has a gentle slope as shown by, A and B have similar slopes. On the other hand, since the waveform of the pressure fluctuation due to the gas leakage has a locally greatly inclined waveform as shown in FIG. 6, A has a larger inclination than B.

Accordingly, the value of A / B shown in the equation (4) is small when the pressure reducing valve is operated or the like and is large when the gas is leaked. Gas leakage can be detected.

In the description of the embodiment of the present invention, as a step of detecting the start of the propagation of the pressure fluctuation, the absolute value of the difference between the average value of a plurality of pressure values within a fixed time and the latest measured pressure value is used. Although the step of determining whether the value exceeds the threshold has been described as an example, as a step of detecting the start of propagation of pressure fluctuation, a step of performing statistical processing such as a moving average,
The differential pressure signal is sampled at regular time intervals, and the variation of the slope of the approximate straight line calculated from the obtained differential pressure value group is monitored,
It may be a step of determining whether or not the variation exceeds a certain threshold, or another method may be applied.

[0042]

According to the present invention, it is possible to discriminate whether the pressure fluctuation is caused by the operation or the gas leak, so that the gas leak in the pipeline can be accurately detected.

[Brief description of the drawings]

FIG. 1 is a gas leak detection system diagram for explaining an embodiment of a pipeline gas leak detection method of the present invention.

FIG. 2 is a graph showing how the internal pressure of the pipeline changes over time when a liquid leaks from the pipeline in the liquid transport system.

FIG. 3 is an explanatory view of a conventional gas line leak detection device.

FIG. 4 is a graph of a pressure fluctuation waveform detected when a resistance element or a capacitance element is not installed in a conventional gas line leak detection device.

FIG. 5 is a graph of a waveform of a pressure fluctuation detected by the conventional gas line leak detection device shown in FIG.

FIG. 6 is a graph of a waveform of pressure fluctuation caused by gas leakage.

FIG. 7 is a graph of a pressure fluctuation waveform generated by operating a pressure reducing valve or the like.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 gas pipeline 2 gas leak point 3 pressure guiding pipe 4, 5 branch pipe 6 resistance element 7 capacitance element 8 differential pressure detector 9 amplifier circuit 10 electrical waveform shaping element 11 A / D conversion circuit 12 computer

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Hideki Kanai Tokyo Gas Co., Ltd. F-20 terms 1-5-20, Minato-ku, Tokyo 2F030 CA04 CB02 CC13 CE02 2G067 AA11 BB11 CC04 DD02 EE05 3J071 AA02 BB11 EE19 EE24 EE37 FF01

Claims (2)

[Claims] At a specific point in a pipeline, a pressure of a fluid in the pipeline is measured at predetermined time intervals to detect a start of propagation of the pressure fluctuation, and a start of the propagation of the pressure fluctuation is detected. From a plurality of pressure values measured within a certain time after the time, a step of obtaining a gradient A of the pressure value change within the time, and a step of obtaining a gradient A of the pressure change within the certain time after the start of the propagation of the pressure fluctuation is detected. Obtaining a gradient B of a pressure value change in the time from a plurality of pressure values measured in a long time, and a ratio A between the gradient A and the gradient B;
Determining whether or not / B is greater than a threshold value by detecting gas leakage in the pipeline. 2. The method according to claim 1, wherein the step of detecting the start of the propagation of the pressure fluctuation includes the step of obtaining an average value of the pressure within a predetermined time, and the step of detecting an absolute value of a difference between the average value and the latest measured pressure value. 2. A method for detecting gas leakage in a pipeline according to claim 1, further comprising a step of determining whether or not the gas leakage exceeds the threshold value.