JPH08219933A - Method for detecting leakage of gas from gas duct - Google Patents

Abstract

PURPOSE: To obtain a method for detecting leakage of city gas in a service pipe without requiring any digging work of ground. CONSTITUTION: A gas meter 3 is provided with a pressure sensor 5 and installed on a leakless duct 2. The pressure sensor 5 measures the pressure difference when no gas flows through the duct and when gas flows through the duct and the flow rate of gas is also measured. The pressure difference is integrated for a predetermined time and stored along with the flow rate as initial values. Subsequently, the flow rate and the pressure difference are measured every time when the gas is used. The pressure difference is integrated for a predetermined time and the flow rate is corrected. The integrated value subjected to flow rate correction is then compared with the initial integration value thus detecting leakage of gas. Since leakage of gas from a duct coupling the gas meter 3 and a main or branch line 1 can be detected without requiring any digging work, manpower can be reduced and since leakage is monitored every time when the gas is used, safety is enhanced. Furthermore, since an integrated pressure drop is subjected to comparison, microfluctuation in the pressure of gas being supplied from the main or branch line 1 can be averaged and detection miss or erroneous detection can be prevented.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for detecting gas leakage from a gas conduit.

[0002]

2. Description of the Related Art For example, as a conventional method for detecting leakage of a conduit from a main branch pipe to a gas meter of a customer, that is, a supply pipe and an inner pipe (serving pipe) in a pipeline of city gas, Boring on the ground where is buried,
It is common to use a gas detector or sniff odor to check for leakage.

[0003]

However, the conventional method as described above has a problem in that excavation work such as boring is required, which requires manpower. Then, this invention aims at solving such a subject.

[0004]

In order to solve the above-mentioned problems, the present invention provides a gas sensor with a pressure sensor,
This gas meter is installed in a leak-free conduit at that time, and at this time, the pressure sensor measures the pressure difference between when gas is not flowing and when gas is flowing. Integrate the difference for a predetermined time,
The integrated value and flow rate are stored as initial values, and after that,
Each time the gas is used, the flow rate and the pressure difference are measured, and the pressure difference at these points is integrated for a predetermined time and the flow rate is corrected, and the flow rate corrected integrated value is compared with the initial integrated value to prevent leakage. It proposes a method for detecting leakage of gas to be detected.

[0005]

[Operation] When there is no leakage from the conduit, such as when laying the conduit, when the gas is flowing at a constant flow rate,
By measuring the flow rate and pressure with a gas meter and determining the difference between the pressure when gas is not flowing, the pressure difference due to the pressure loss of the conduit when there is no leakage from the conduit, and the data of the flow rate at that time are calculated. It can be obtained as an initial value.

Then, the flow rate and the pressure are measured with a gas meter for each subsequent use of the gas, the pressure difference and the flow rate at that time are obtained, and the pressure difference is corrected by the flow rate.
It is possible to compare with the pressure difference of the initial value. That is, when there is no leakage from the pipe, there is no change with the pressure difference of the initial value,
If there is leakage, it will be larger than the initial value. Therefore,
These comparisons allow detection of leaks from the conduit each time the gas is used.

Since the pressure difference is not compared only at a certain point in time but is integrated for a predetermined time and the integrated values are compared,
Instantaneous fluctuations in the source pressure and the like can be averaged, erroneous detection due to instantaneous fluctuations can be prevented, and leakage detection accuracy can be improved.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the accompanying drawings. FIG. 1 conceptually shows an example of a gas pipeline system to which the present invention is applied. This shows a city gas pipeline system which is drawn from a main branch pipe to a customer. Reference numeral 1 is a main branch pipe, and reference numeral 2 is a domestic pipe, that is, a pipe branching from the main branch pipe 1 and drawn into the customer, a supply pipe from the branch point of the main branch pipe to the road boundary, and a gas from the road boundary to the consumer gas. It is a conduit including the inner pipe to the entry side of the stopper. Reference numeral 3 is a gas meter, 4 is a gas appliance, and a pressure sensor 5 is provided in the gas meter 3 either internally or externally. The flow rate measuring unit of the gas meter 3 is indicated by reference numeral 6. Reference numeral 7 is a monitoring device, and the monitoring device 7 is configured to monitor the leakage from the service pipe 2 by using the flow rate signal from the flow rate measuring unit 6 of the gas meter 3 and the pressure signal from the pressure sensor 5 as inputs.

In the present invention, when there is no leakage from the service pipe 2 such as when the above-mentioned conduit system is newly installed, when gas is flowing at a constant flow rate due to use of the gas appliance 4, The monitoring device 7 calculates the difference in the reaching pressure to the gas meter 3 due to the pressure loss of the service pipe 2 from the flow rate signal from the flow rate measuring unit 6 of the gas meter 3 and the pressure signal from the pressure sensor 5. That is, the monitoring device 7 calculates the pressure difference by the difference between the pressure signal when the gas is flowing and the pressure signal from the pressure sensor 5 at the time when the gas is not flowing before that time. The pressure difference is calculated, for example, every few seconds, and the calculated value is integrated for a predetermined time within a range in which the flow rate does not change. Then, the monitoring device 7 stores the integrated value and the flow rate in the storage means as initial values.

Next, when the gas is used after that, the monitoring device 7 measures the flow rate and the pressure every time the gas is used, finds the pressure difference in the same manner as described above, and monitors this for the predetermined time. Only integrate. When the flow rate is different from the initial flow rate, it is based on the well-known relationship between the flow rate of the gas flowing through the pipe and the pressure difference, that is, when the gas has a low pressure, the pressure difference is proportional to the square of the flow rate. , The flow rate of the pressure difference is corrected. Then, the monitoring device 7 compares the integrated value of the pressure difference for which the flow rate correction has been performed this time with the initial integrated value, and if the integrated value of this time is larger, it is determined that there is a leak from the pipe, and an alarm is issued. The corresponding processing of is performed.

Next, the method of the present invention will be described with theoretical support. First, in FIG. 1, it is assumed that a leak occurs at a point L, the portion of the service pipe 2 from the main branch 1 to the leak point L is A, and the portion from the leak point L to the gas meter 3 is B.
And And when the gas supply pressure from the main branch pipe 1 is Y, and the gas of flow rate Q is flowing using the gas appliance 4,
The pressure loss of each of the portions A and B is a and b. FIG. 2 is an explanatory diagram showing changes in pressure in the portion of the service pipe 2 from the main branch pipe 1 to the gas meter 3. (1) When there is no leakage from the leakage point L The pressure that reaches the gas meter 3 when the gas is not used in the gas instrument 4, that is, the pressure of the gas measured by the pressure sensor 5 of the gas meter 3 is as shown in FIG. It is Y as shown by the solid line. Since the pressure loss including the portions A and B when the gas with the flow rate Q is used is a + b 2, the pressure of the gas measured by the pressure sensor 5 at this time is shown by the one-dot chain line in FIG. As such, it is Y- (a + b). Therefore, in the monitoring device 5, Y- {Y- (a +
b)} = a + b, the pressure difference due to the pressure loss can be calculated. In the monitoring device 5, the pressure difference is integrated for a fixed time T, and the integrated value, ∫ ₀ ^T (a + b) dt, is used as an initial value,
It is stored together with the flow rate Q. (2) When there is a leakage of flow rate Qm from the leakage point L The pressure reaching the gas meter 3 when the gas is not used in the gas instrument 4, that is, the measured pressure is Y−a ×
(Qm ² / Q ² ) This is derived based on the relationship that the pressure difference of the gas flowing through the pipe is proportional to the square of the flow rate when the gas has a low pressure as described above. Similarly, the measured pressure when the gas with the flow rate Q is used for the gas appliance 4 is Y- as shown by the chain double-dashed line in FIG.
It becomes {a × (Q ² + Qm ² ) / Q ² + b}. Therefore, in the monitoring device 5, the pressure difference corresponding to the following equation for calculating these differences is calculated. ^{Y- (Qm 2 / Q 2)} × a- [Y- {a × (Q 2 + Qm 2) /
Q ² + b}] = {(Q ² + 2QQm) / Q ² } × a + b Then, the monitoring device 7 integrates the pressure difference obtained in the same way as above for a fixed time T to obtain an integrated value ∫ ₀ ^T [{( Q ² +
2QQm) / Q ^2} seek × a + b] dt. As shown in, the flow rate Q of the gas is the same as the flow rate stored as the initial value in the storage unit of the monitoring device 5, so the integrated value of the pressure difference obtained in step 3 is used as the initial integrated value without performing flow rate correction. Compare with. The difference between these integrated values corresponds to the following equation, and ∫ ₀ ^T [{(Q ² + 2QQm) / Q ² } × a +
b] dt−∫ ₀ ^T (a + b) dt = ∫ ₀ ^T [(2QQm / Q ² ) ×
a] dt, and the value of this expression is always positive. Therefore, the integral value when there is a leak from the leak point L is larger, and the leak can be detected by determining this.

Under the condition that the gas supply pressure Y from the main branch pipe 1 does not fluctuate, as shown in the above equation, the pressure difference when there is a leak and the pressure difference when there is no leak are integrated. Leakage can be detected by comparing only the value at a certain time, not the value, but under actual conditions where the gas supply pressure fluctuates but is small, the pressure difference due to leakage increases. However, there is a possibility that it may not be detected because it is offset by an increase in the gas supply pressure, or conversely, a decrease in the gas supply pressure may be erroneously detected as an increase in the pressure difference due to leakage. Therefore, as described above, if the pressure difference when there is a leak and the pressure difference when there is no leak are compared by the integral value for a predetermined time, the minute upper and lower sides of the gas supply pressure are averaged, and the above-mentioned inconveniences occur. Can be prevented.

In the above case, the gas flow rate at the time of leak detection is the same as the initial state, but even if the gas flow rate is different, the flow rate correction is performed based on the above-described relationship between the gas pressure difference and the flow rate. Therefore, leakage can be detected as follows. That is, here, under the condition (1), the gas flow rate at the time of leakage detection is set to Qk. (1) When there is no leakage from the leakage point L The pressure difference at the flow rate Q is a + b (1). Pressure difference when the flow rate Qk is ^{(Qk 2 / Q 2) (} a + b)
… (2). Therefore, in order to make these pressure differences the same, equation (2) may be multiplied by Q ² / Qk ² as a flow rate correction coefficient. (2) When there is a leakage of the flow rate Qm from the leakage point L The pressure difference at the flow rate Q is a × (Q ² + Qm ² ) / Q ² + b (3) The measured pressure when the flow rate is 0 is Y- (Qm ² / Q ² ) × a (4) Further, the measured pressure at the flow rate Qk is Y- {a × (Qk ² + Qm ² ) / Q ² + b × (Qk ² / Q ² )}
Since it becomes (5), the pressure difference at the flow rate Qk is (4)-(5)
By the calculation of a × (Qk ² + 2QkQm) / Q ² + b × (Qk ² / Q ² ) ...
It becomes (6). As in the case where there is no leakage, the pressure difference at this flow rate Qk is multiplied by Q ² / Qk ² as a flow rate correction coefficient to obtain (Q ² / Qk ² ) {a × (Qk ² + 2QkQm) / Q ² + b ×
(Qk ² / Q ² )} = a + b + a × ² Qk Qm / Qk ² (7)
And the pressure difference corrected by the flow rate can be obtained. In this way, the pressure difference (7) at the flow rate Qk corrected by the flow rate, Q ² /
Comparing with (2) corrected by multiplying Qk ^2, that is, a + b ... (8), that is, calculating the difference between them, (7)-(8) =
a + b + a × 2QkQm / Qk 2 - (a + b) = a × 2QkQm
/ Qk ² and this value is always positive, so the leakage point L
When there is a leak from the integrated circuit, the integrated value becomes larger, and therefore by judging this, the leak can be detected.

[0014]

As described above, the present invention has the following effects. Without excavating the ground, it is possible to detect gas leakage from a gas meter to a main pipe such as a main branch pipe, thereby reducing manpower. Safety can be improved because leakage can be monitored each time gas is used. Since the pressure loss is compared by the integrated value, it is possible to average the minute fluctuations in the gas supply pressure from the main pipe etc.
Leakage detection Leakage and erroneous detection can be prevented.

[Brief description of drawings]

FIG. 1 is a system diagram conceptually showing an example of a gas conduit system to which the present invention is applied.

FIG. 2 is an explanatory diagram showing a change in pressure in a portion of a service pipe from a main branch pipe to a gas meter shown in FIG.

[Explanation of symbols]

 1 branch pipe 2 service pipe 3 gas meter 4 gas appliance 5 pressure sensor 6 flow rate measurement unit 7 monitoring device

Claims (2)

[Claims] 1. A gas meter is provided with a pressure sensor, the gas meter is installed in a leak-free conduit at that time, and at this time, the pressure sensor measures the pressure difference between when gas is not flowing and when gas is flowing. Measure and measure the flow rate of the gas, integrate this pressure difference for a predetermined time, store the integrated value and the flow rate as initial values, and then measure the flow rate and the pressure difference each time the gas is used. A method for detecting leakage of gas from a gas conduit, characterized in that the pressure difference at the point of time is integrated for a predetermined time, the flow rate is corrected, and the leak is detected by comparing the flow rate-corrected integrated value with the initial integrated value. 2. The method for detecting leakage of gas from a gas pipe according to claim 1 or 2, wherein the gas pipe to be leak-detected is a pipe from a main branch of a city gas pipe system to a gas meter of a customer.