JPH0153732B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for detecting a leak of a liquid to be transported in a pipeline, and more specifically, a method for detecting a leak by accommodating a liquid to be transported, shutting off the pipeline, and suspending operation. and regarding equipment.

As is well known, pipelines buried underground are usually used to transport liquids such as petroleum and chemical products through pipes, but leaks from such pipelines can cause damage to the transported liquid. Not only does it cause a loss of water, but it also poses the risk of ignition, and there is also the risk of contaminating groundwater. Therefore, early detection of leaks from pipelines is essential as well as prevention of leaks. There is.

In pipelines, emergency shutoff valves may be installed at specified intervals. In this case, each shutoff valve is closed, the pressure inside the pipeline in each section is measured, and leakage is detected by checking whether there is a change in pressure after a certain period of time.

By the way, pressure changes are caused not only by leakage but also by
Since it depends on the change in the temperature of the liquid in the pipeline caused by the difference between the external temperature and the temperature of the liquid in the pipeline, the maximum value of the rate of pressure change due to the temperature change of the liquid in the pipeline is predicted, and the maximum A leak is determined when a pressure change rate greater than the specified value appears. However, because it is difficult to accurately determine the range of the rate of pressure change due to temperature change, which serves as a reference, the accuracy of leak detection is extremely poor.

On the other hand, a portion of the liquid to be transported is taken out and put in to keep the pressure in the pipeline constant, and the flow rate of each inflow and outflow is measured, and it is determined that the amount of liquid flowing into the pipeline is greater than the amount corresponding to the temperature change. There is a device that is considered to be a leak in some cases (Special Publication No. 55-23365). In this case as well, it is difficult to accurately measure the amount corresponding to the temperature change, but in cases where the temperature of the liquid in the pipeline can be artificially changed, such as in a heating pipeline, two points at the same temperature can be used. By comparing the flow rates, leaks can be detected with high accuracy. However, the drawback is that it actually takes about 10 hours to reproduce the same temperature state.

The present invention has been made in view of the above-mentioned circumstances, and includes a pipeline leakage detection method and a pipeline leakage detection method capable of quickly and accurately detecting a leakage of liquid in a closed pipeline without being affected by changes in liquid temperature. The purpose is to provide equipment.

According to this invention, a branch path branched from a pipeline, a gate valve that seals fluid in the branch path, and a differential pressure gauge that measures the pressure difference on both sides of the gate valve are provided, forcibly changing the internal pressure of the pipeline by accommodating the liquid to be transported, closing off the pipeline, withdrawing a portion of the liquid from the pipeline, or injecting more liquid into the pipeline; The pressure change rates are determined from the outputs of the differential pressure gauges that change over time starting from two different pipeline internal pressures, and leakage from the pipeline is detected based on a comparison of these pressure change rates. ing.

The present invention will now be described in detail with reference to the accompanying drawings.

First, the present invention will be explained in principle using a graph showing the relationship between time and pressure shown in FIG. 1st
Figure a shows pressure changes due to temperature changes that change over time τ when the temperature of the liquid inside the pipeline is higher than the temperature outside the pipeline. The pressure change in this case is linear (rate of change is constant) for at least several hours, and for example, what is the pressure change rate ΔPθ/Δτ ₁ at time τ ₁ and the pressure change rate ΔPθ/Δτ ₂ at time τ ₂ ? equal. Also,
FIG. 1b shows pressure changes due to leakage of the liquid in the pipeline when the temperature of the liquid in the pipeline does not change.

Generally, the amount of leakage from a pipeline is expressed by the following equation: Q=K√ _IN − _OUT (1). Here, Q is the leakage flow rate, P _IN is the pressure inside the pipe, P _OUT is the pressure outside the pipe, and K is a constant based on the area of the leak hole, the physical property value of the fluid inside the pipe, etc. As is clear from the above equation, the amount of leakage is proportional to the square root of the pressure difference between the inside and outside of the pipe, so when a leak occurs, the leakage flow rate is higher when the pressure inside the pipe is high than when it is low. is large.

Therefore, the pressure change due to leakage of liquid in the pipeline is not linear, and as shown in Figure 1b, for example, the pressure change rate ΔP _l /Δτ ₁ at time τ ₁ is equal to the pressure change rate ΔP l /Δτ 1 at time τ _{2 .} /Δτ larger than ₂ .

In addition, Figure 1c is the above-mentioned Figure 1a and Figure 1b.
, which shows the temperature change of the liquid in the pipeline and the pressure change due to leakage with respect to time τ. Here, if the rate of pressure change at time τ ₁ is ΔP/Δτ ₁ and the rate of pressure change at time τ ₂ is ΔP/Δτ ₂ , then each rate of pressure change ΔP/Δτ ₁ and ΔP/Δτ ₂ is expressed by the following equation, ΔP /Δτ ₁ =ΔPθ／Δτ ₁ +ΔP _l /Δτ ₁ ...(
2) ΔP/Δτ ₂ = ΔPθ/Δτ ₂ + ΔP _l /Δτ ₂ ……(
3) It can be expressed as Comparing the pressure change rates of equations (2) and (3) above, ΔP/Δτ ₁ −ΔP/Δτ ₂ = (ΔPθ/Δτ ₁ +ΔP _l
/Δτ ₁ )−(ΔPθ/Δτ ₂ +ΔP _l /Δτ ₂ )=ΔP _l /Δ
τ ₁ −ΔP _l /Δτ ₂ ...(4) (∵(ΔPθ/Δτ ₁ = ΔPθ/Δτ ₂ ) In addition, leakage can be determined using the following formula: ΔP _l /Δτ ₁ −ΔP _l /Δτ ₂ ≦e (no leak) ΔP _l /Δτ ₁ −ΔP _l /Δτ ₂ > e (with leak) ). However, e is a judgment standard (detection ability) based on pressure meter (differential pressure gauge) error, measurement error, change in physical properties due to pressure change, etc. The present invention focuses on the above points, and has a short In order to detect leakage based on time, the pressure corresponding to time τ ₁ is forcibly changed to the pressure corresponding to time τ ₂ , and leakage is detected based on the difference in the rate of pressure change at each pressure. Furthermore, when determining the rate of pressure change, the pressure of a fluid branched from the pipeline and sealed in the pressure conduit by a gate valve is taken as a reference pressure, and this reference pressure and the pressure inside the pipeline are calculated. The rate of pressure change is determined by measuring the differential pressure that changes with time.

Next, the present invention will be explained based on an embodiment shown in FIG. In FIG. 2, a pipeline 1 can be closed off at a predetermined section by means of shutoff valves 2 and 3. When the liquid in this pipeline is being transported, the shutoff valves 2 and 3 are opened and the main liquid sending pump (not shown) is driven to transport the fluid from the sending side to the receiving side, and when a leak in the pipeline is detected. The fluid transport is stopped at the shutoff valves 2 and 3.
is closed off, and the liquid to be transported is sealed within the closed section of the pipeline 1 at a starting pressure.

The pipeline 1 includes a pressure reducing valve 4 for extracting a portion of the liquid to be transported from the pipeline 1 and a pressurizing device 5 for injecting further liquid into the pipeline 1.
In addition, a pressure introduction section is provided which branches off from the pipeline 1 and has a seal pot 6, a gate valve 7, and a constant temperature pot 8 connected in series.

Further, pressure receiving diaphragms 9 and 10 are provided on both sides of the gate valve 7, that is, on the seal pot 6 and constant temperature pot 8 sides, respectively, and the pressure applied to each diaphragm is guided to a differential pressure gauge 11. The digital printer 12 prints out the differential pressure value measured by the differential pressure gauge 11.

Note that the seal pot 6 is filled with a sealing liquid that is less affected by heat and is different from the liquid to be transported. This sealing liquid is (a) one with a large specific heat (b) one with a small coefficient of thermal expansion (c) one with a large specific gravity (d) one that is liquid at room temperature (-10°C or higher) (e) one that is suitable for the liquid to be transported. On the other hand, it is necessary to select an insoluble material (f) that does not have an adverse effect on the diaphragm, and for example, a 50% ethylene glycol aqueous solution is considered suitable.

In addition, the constant temperature pot 8 is controlled by the pressure (standard pressure) of the liquid sealed in the constant temperature pot 8 by the gate valve 7.
It has a predetermined capacity (20 to 30) and is further covered with a heat insulating material along with the piping after the gate valve 7.

Furthermore, digital printers are designed to eliminate reading errors.

In the leak detection device having such a configuration, when detecting a leak in the pipeline 1, first, the transportation of the liquid in the pipeline 1 is stopped, then the shutoff valves 2 and 3 are closed, and the liquid to be transported is brought to a predetermined pressure. Enclose with. At this time, since the gate valve 7 is open, the pressure on both sides thereof is equal to the sealing pressure.

Then, the gate valve 7 is closed, and the pressure difference on both sides of the gate valve 7 is measured by the differential pressure gauge every 5 minutes for a predetermined period of time, for example, 30 minutes.
1, and print out each of these differential pressure values using the digital printer 12.

Next, the gate valve 7 is opened and liquid is further injected into the pipeline 1 by the pressurizing device 5, or the pressure reducing valve 4 is opened and a part of the liquid is withdrawn from the pipeline 1. The internal pressure of the pipeline 1 is forcibly changed.

Then, the gate valve 7 is closed in the same manner as described above, and the pressure difference on both sides of the gate valve 7 is measured by the differential pressure gauge 11 for a predetermined period of time, and this differential pressure value is printed out by the digital printer 12.

By measuring the change in differential pressure in this way, at least two rates of pressure change in the pipeline with different initial pressures can be obtained. The rate of pressure change at different initial pressures is compared to determine whether there is a leak in the pipeline.

Figure 3 shows that after measuring the pressure change starting from the sealed pressure P ₁ , the pressure is forcibly reduced to P ₂ by the pressure reducing valve 4.
3 is a graph showing the pressure change when the pressure is reduced to 1 and the pressure change is measured again, FIG. 3a shows the pressure change when there is no leakage, and FIG. 3b shows the pressure change when there is a leakage. .

In other words, in the case of Fig. 3a where there is no leakage from pipeline 1, the pressure change depends only on the temperature change of the liquid, so the pressure change rate from P ₁ is ΔP ₁ /Δτ ₁ and the pressure change from P ₂ The ratio ΔP ₂ /Δτ ₂ is equal. On the other hand, in the case of Figure 3b where there is a leak from pipeline 1,
Since the amount of leakage differs depending on the pressure, the rate of pressure change changes momentarily. In particular, since the rate of pressure change is significantly different before and after the pressure inside the pipeline is forcibly changed, the difference can be clearly seen.

FIG. 4 shows another embodiment of the thermostatic pot 8', in which gas is sealed via a diaphragm 13. Since gas is a compressed body, it absorbs pressure changes due to the influence of outside temperature. That is,
By using gas (N2 _, etc.) pressure as the reference pressure, the influence of temperature changes can be further reduced.

Note that although a seal pot and a constant temperature pot are provided in this embodiment, these do not necessarily need to be provided. In other words, the equipment after gate valve 7 that seals in the initial pressure (reference pressure) may be installed in a constant temperature room, or leaks may be detected during periods when there is little change in outside temperature (1 to 2 hours is sufficient for this leak detection). By performing the detection, changes in the reference pressure due to changes in outside temperature can be minimized.

Furthermore, although a diaphragm type differential pressure gauge is used in this embodiment, the present invention is not limited to this, and various other differential pressure gauges may be used. In short, any device may be used as long as it can measure the pressure difference on both sides of the gate valve.

As described above, according to the present invention, leakage of liquid in a pipeline can be detected in a short time without being affected by pressure changes due to changes in liquid temperature. Further, since the device of the present invention uses a differential pressure gauge, it has the advantage that the detection accuracy is about three times higher than that of measuring absolute pressure to determine the rate of pressure change.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between pressure and time used to explain the present invention in principle; FIG. 2 is a system diagram showing an embodiment of the pipeline leak detection method and apparatus according to the present invention; FIG. 3 is a graph showing the relationship between pressure and time used to explain leak detection according to the present invention, and FIG. 4 is a schematic diagram showing another embodiment of the constant temperature pot. 1... Pipeline, 2, 3... Shutoff valve, 4...
...Pressure reduction valve, 5 ... Pressure device, 6 ... Seal pot, 7 ... Gate valve, 8, 8' ... Constant temperature pot, 9,
10...Diaphragm, 11...Differential pressure gauge, 12...
...digital printer, 13...diaphragm.

Claims (1)

[Scope of Claims] 1. The pipeline is closed by accommodating the liquid to be transported at a first pressure, a first rate of pressure change with time is determined, and then the internal pressure of the pipeline is adjusted to the first pressure. The pressure is forcibly changed to a second pressure different from the pressure, the second pressure change rate with time is determined, and based on the comparison between the first pressure change rate and the second pressure change rate. In the method for detecting a leak in the pipeline, the first and second pressures are sealed in a branch path branching from the pipeline, and the pressure between the sealed pressure and the pressure in the pipeline is A method for detecting leakage in a pipeline, characterized in that the first and second pressure change rates are determined by respectively detecting a difference. 2. A shutoff valve that closes off the pipeline and seals in the liquid to be transported at a first pressure, a pressure variable means that forcibly changes the pressure of the liquid to be transported from the first pressure to a second pressure, and the pipeline. a branch passage disposed branching off from the branch passage, a gate valve disposed in the branch passage for sealing the first and second pressures, and a connection between the pressure sealed by the gate valve and the pressure of the pipeline; and a differential pressure gauge for measuring a pressure difference, and the liquid to be transported is supplied to the first and second pipes, respectively.
After the pipe is sealed at a pressure of A pipeline leak detection device that detects line leaks. 3. The pipeline leak detection device according to claim 2, wherein the branch path includes a constant temperature pot having a predetermined capacity. 4. The pipeline leak detection device according to claim 3, wherein the constant temperature pot is filled with gas via a diaphragm. 5. The pipeline leak detection device according to claim 2, wherein the branch path has a seal pot that accommodates a liquid different from the liquid to be transported between the branch point with the pipeline and the gate valve. 6. The pipeline leak detection device according to claim 5, wherein the liquid contained in the seal pot is a liquid that is less affected by heat and is insoluble in the liquid to be transported. 7. The pipeline leak detection device according to claim 2, wherein the differential pressure gauge digitally prints the measured pressure difference using a digital printer.