JPH0451720B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring liquid pressure at measurement points provided at arbitrary intervals along a liquid transport pipeline and detecting leakage based on fluctuations in the measured pressure. It is. The purpose is to provide a method that can detect even minute leaks by taking into account pressure fluctuations caused by changes in pump operating conditions, valve operations, and the like.

Various methods of this type have been proposed in the past, and FIG. 1 is a schematic explanatory diagram of a leak detection device for a liquid transport pipeline in which the method of the present invention is adopted. In the figure, 1 is a liquid transport pipeline, 2 is its departure base, and 3 is its arrival base, and both bases 2 and 3 are equipped with tanks. 4 is a pressure transmitter installed at arbitrary intervals along the pipeline 1, and this pressure transmitter 4 measures the liquid pressure (operating pressure) in the pipeline 1 at the installation point and sends it as an electrical signal. Convert to etc. Reference numeral 5 denotes a telemeter slave station, which transmits the liquid pressure measurement signal from the pressure transmitter 4 to the central control room 6. 7 is the telemeter slave station 5 and the central control room 6
It is a transmission line that connects the two, and the transmission is done by cable or radio. Reference numeral 8 denotes a telemeter master station provided in the central control room, which receives signals from the telemeter slave station 5. 9 is a computer for processing the liquid pressure measurement signal received by the telemeter master station 8;
If a leak is detected here, the alarm indicator 10 will notify you.

In the leakage detection device for liquid transportation pipelines as explained above based on FIG. Then, the liquid pressure is measured at a predetermined sampling time interval at measurement points provided at a predetermined interval, and a difference is calculated between the measured values of the measurement signals that are temporally adjacent to each other. A method for detecting a leak in the pipeline based on a value. There is also a leakage detection method that is improved so that the difference calculation is performed on measured values of the measurement signals at a time interval that is twice or more the sampling time interval. In all of these conventional leak detection methods, a leak is determined when the liquid pressure drop at a certain measurement point is greater than a predetermined value, and pressure fluctuations due to changes in pump operating conditions or valve operation are detected. However, there was a problem in that it could only detect leaks that caused a large pressure drop.

By the way, various recent studies have confirmed that pressure fluctuations due to changes in pump operating conditions, valve operations, etc. can be estimated in advance with high accuracy using the characteristic curve method.

Therefore, the present invention utilizes the idea of this characteristic curve method to estimate pressure fluctuations due to causes other than leakage, and compares the estimated value with the actual measured value.
It attempts to detect leaks.

In other words, in order to solve the above-mentioned conventional problems and achieve the intended purpose, the present invention provides measurement at measurement points provided at arbitrary intervals along a liquid transportation pipeline at minute sampling time intervals. Alternatively, the liquid pressure is continuously measured, and at the time t-Δx ₁ /a (a sound velocity in the liquid pipeline) at the measurement point P ₁ immediately upstream, Δx ₁ away from the obtained measurement point P ₀ . From the pressure measurement value and the pressure measurement value at time t-Δx ₂ /a at measurement point P ₂ immediately downstream, which is Δx ₂ away from P ₀ , calculate the pressure at time t at measurement point P ₀ when there is no leakage. It is characterized by calculating and calculating an estimated value, and detecting a leak by comparing this estimated value with the actual pressure measurement value at measurement point P ₀ at time t, and the details will be explained below. explain.

First, to explain the basic equations adopted in the method of the present invention, from the equation of motion of the liquid in the tube and the equation of continuity, when dx/dt=a, du/dt+g/a dH/dt+g/ausinθ+λ/2D|u
|u=0... When dx/dt=-a du/dt-g/a dH/dt-g/ausinθ+λ/2D|u
|u=0... Here, x: distance measured along the pipeline, t: time, u: flow velocity, a: sound velocity in the pipeline, H: pressure head, g: gravitational acceleration,
θ: pipe inclination angle, λ: pipe friction coefficient, D: pipe inner diameter.

Figure 2 shows the relationship for estimating the pressure at time t at an arbitrary measurement point P ₀ from the pressure measured at measurement points P ₁ and P ₂ immediately above and downstream before time t. It is something. In other words, the coordinate point at measurement time t of measurement point P ₀ is P, the pressure head is H _p , the flow velocity is up, and the measurement point immediately upstream is Δx ₁ away from P ₀ .
The coordinate point of measurement point P ₂ immediately downstream, which is Δx ₂ away from P ₁ , is R,
By using the S pressure head H _R , H _S , the flow rate u _R , u _S and the time Δx ₁ =Δx ₁ /a, Δx ₂ =Δx ₂ /a, from the above equation, U _P −U _R +g/a(Hp−HR)+g/aURsinθ ・Δt ₁ +λ/2D〓UR〓URΔt ₁ =0 Up−Us−g/a(Hp−Hs)−g/aUSsinθ ・Δt ₂ +λ/2D〓 Us〓UsΔt ₂ = 0 Therefore, 2Hp=(HR+Hs)+a/g(UR−Us)−sinθ
(URΔt ₁ +UsΔt ₂ )−λa/2gD (〓UR〓URΔt ₁ −〓Us〓UsΔt ₂ )... Then, the pressure head Hp at the measurement point P ₀ can be obtained.

Here, the pressure head at the measurement point P ₁ at the time t - Δt ₁ before the actual measurement time t of the measurement point P ₀
By measuring HR and the pressure head Hs at measurement point _P2 at time t- _Δt2 , if there is no leakage between that time (t- _Δt1 , t- _Δt2 ) and t, The pressure head Hp at the measurement point P ₀ at time t can be calculated and estimated in advance by Hp=(H _R +Hs)/2 . . . . This equation ignores the second and subsequent terms on the right side of the equation, and a leak of an amount equivalent to the error due to this cannot be detected. In other words, the second and fourth terms on the right side of the equation are the density change due to the compressibility of the liquid and the second term.
Although this is a combination of the flow velocity change due to the difference in time between R and S in the figure, the latter can be minimized by making the measurement points as equally spaced as possible. At this time, the second and fourth terms on the right side of the equation have a value of less than 0.1 m, which is about 10 ^-5 to 10 ^-4 even if the pressure variation is about 1 Kg/cm ² . In addition, the third term on the right side of the equation is a term due to the pipe slope, but in pipes with large slopes, this can be reduced to a sufficiently small value by reducing Δt ₁ and Δt ₂ , that is, by shortening the measurement point interval. Can be done. By the way, to make this value around 0.1m, simθ=0.1
When Δx=500m, and when sinθ=0.02, Δx
= 2500m.

In this way _{, the} pressure _Hp at time _t at measurement point P ₀ is converted to _the measured pressure _H A leak in the pipeline is detected by estimating Hs in advance by calculation and comparing this estimated value with the actual pressure measurement value at time t.

Next, a specific example of the leak detection method described above will be described. From the pressure transmitter 4 at each measurement point shown in FIG. and the data is processed as follows. For example, the pressure data from the i-th measurement point is placed directly in the i-th measurement pressure table.
With a delay of Δt ₁ , Δti−1 is added to the i+1st position in the H _R table.
They are respectively input to the i-1th position of the Hs table with a delay. Furthermore, based on the above formula, the average value of the i-th data of the H _R table and the i-th data of the Hs table is input to the i-th position of the estimation table. Then, the measurement table and the estimation table are compared, and for the i-th data, if the measured pressure is less than the estimated pressure, the i-th leakage flag is set,
If not, reset. Depending on the setting of the leak flag, the computer 9 outputs a leak detection signal and the alarm indicator 10 is activated to report the occurrence of a leak.

Next, an embodiment will be described in which functions as shown in FIG. 3 are added to each of the measurement points. In the figure, 4i is the i-th pressure transmitter,
The signal is input to the additional circuit 11i at the measurement point i, and is also transmitted to the additional circuits (not shown) at the measurement points i-1 and i+1. Said circuit 1
Measurement signals from the pressure transmission products (4i-1) and (4i+1) at measurement points i-1 and i+1 are input to 1i, and the delay circuit 12 with a delay time Δxi- ₁ /a and the delay time Δxi+ ₁ /a are inputted to 1i. Both signals are input to the average value calculation circuit 14 via the delay circuit 13 of a. The average value output from the average value calculation circuit 14 and the actual measured pressure at the i-th measurement point are compared in the comparison circuit 15, and when the latter is smaller, a leakage signal is output, and the computer 9 in the central control room 6 outputs a leakage signal. transmitted to. On computer 9, that i
When a leakage signal comes from the th measurement point, the ith leakage flag is set, and when it does not come, it is reset, and thereafter the same data processing as in the previous embodiment is performed.

As explained above, according to the method of the present invention, the pressure at a certain measurement point in a liquid transportation pipeline at a certain time is estimated from the measurement values at measurement points immediately above and downstream of the measurement point, and this estimated value and Leakage is detected by comparing the actual measured value at a certain time, and since it is performed at minute sampling intervals or continuously, pressure fluctuations due to changes in pump operating conditions or valve operation can be detected. This is a very effective invention, as it can reliably detect even a fairly small amount of leakage without being affected by this.

[Brief explanation of drawings]

Fig. 1 is a schematic explanatory diagram of a leak detection device for a liquid transport pipeline to which the method of the present invention is applied, and Fig. 2 is an explanatory diagram showing the relationship between measurement point distance in the pipeline and measurement time in the method of the present invention. , and FIG. 3 is a block diagram showing a specific example of a part of the same. 1 is a pipeline for liquid transportation, 4 is a pressure transmitter installed at each measurement point, 5 is a telemeter slave station, 8
is the telemeter master station, and 9 is the computer.

Claims (1)

[Claims] 1 At measurement points set at arbitrary intervals along a liquid transportation pipeline, liquid pressure is measured at minute sampling time intervals or continuously, and at a distance of Δx ₁ from the obtained measurement point P ₀ . The pressure measurement value at time t-Δx ₁ /a (a: sound speed in the liquid pipeline) at the measurement point P ₁ immediately upstream,
Time t- at measurement point P ₂ immediately downstream, Δx ₂ away from P ₀
From the pressure measurement value at Δx ₂ /a, calculate the pressure at time t at point P ₀ in the case of no leakage to obtain an estimated value, and calculate this estimated value and P ₀ at time t.
1. A method for detecting a leak in a pipeline for liquid transportation, characterized in that a leak is detected by comparing the measured value of actual pressure at a point.