JP2006275906A - Leakage inspection method and system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simple and low cost leakage inspection method by effectively removing an influence of a temperature change in a container in leakage inspection of the container such as a pipe, and also to provide its system. <P>SOLUTION: The leakage inspection method includes a pressure increase and reduction process for increasing or reducing pressure of the container to inspect leakage, and a pressure measuring process for measuring the pressure P<SB>j</SB>of the container and pressure change (dP(t)/dt)<SB>t=tj</SB>for times t<SB>j</SB>(j=0, 1, 2 to n, and n is a natural number of two or more). The leakage inspection method enables the detection of the leakage of the container on the basis of a specific leakage coefficient k or an amount equivalent to it by substituting the pressure and pressure change measured in the pressure measuring process in an equation to calculate the specific leakage coefficient k and the equivalent amount. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a leakage inspection method and apparatus used for diagnosing the state of a container including a pipe supplying gas or liquid, and more particularly to a leakage inspection method for detecting leakage of gas or liquid from the container. And an apparatus.

Buildings such as homes and factories are equipped with containers containing many pipes, and these contain various gases or liquids such as city gas, liquefied petroleum gas, drinking water, refrigerants for air conditioning and gas / solutions for plants. It is used to supply or store various parts of the building.
However, containers including these pipes are gradually deteriorated by long-term use due to mechanical or chemical action, and in some cases, openings are generated in the container walls or the airtightness of the joints is lost. Or the gas or liquid introduced into the container may leak.

Conventionally, leak inspection related to containers such as pipes is performed by closing the container and injecting gas or liquid from an inlet port provided in a part of the container such as a supply port and a discharge port and communicating with the inside of the container. After the pressure is higher than the outside of the tube, the pressure change in the container is measured over a predetermined time.
In the measurement result, for example, when the pressure shows a decreasing tendency, it is assumed that gas or liquid is flowing out of the container, and it is determined that there is an opening such as a crack in a part of the wall surface of the container. Was.

However, the change in pressure in the closed container is not simply caused by leakage, but also changes depending on the influence of temperature change in the container.
For this reason, accurate inspection requires measurement in consideration of the effects of temperature fluctuations. Conventionally, when measuring changes in the pressure of a container, simple measurements such as simultaneously measuring the temperature change in the container are performed. Since there is no device, the time when the temperature change is small is selected and measured, which causes a significant decrease in the efficiency of the inspection work.

In the following Patent Document 1, a pressure measuring method and apparatus capable of compensating for a temperature change is proposed.
In the invention according to Patent Document 1, in the pressure measurement method for measuring the internal pressure of a pipe that supplies gas or liquid, the pipe internal pressure of the pipe is adjusted to be the same as the pressure outside the pipe, and the pipe is closed. Measure the amount of pressure change inside the pipe due to temperature change, or correct the pressure change in the pipe based on the measured temperature of the gas or liquid in the pipe or the amount of change in the measured temperature of the pipe. Is to remove the influence of.
Japanese Patent No. 3484253

In small-capacity gas pipes for general households, leak inspection can be performed in a relatively short time, so the temperature change has a substantially constant slope throughout the inspection time, that is, the second derivative with respect to time of temperature is It is possible to assume zero. Therefore, before or after leak inspection, the pipe internal pressure of the pipe is adjusted to be the same as the pressure outside the pipe to close the pipe, and the amount of pressure change inside the pipe due to temperature change is measured. Based on the above, it is possible to eliminate the influence of the temperature change during the leakage inspection time.
However, in large-capacity piping facilities such as apartment houses, hospitals, schools, etc., a long time is required for leakage inspection, and therefore the gradient of temperature change may vary within the inspection time. For this reason, there is a case where the influence of the temperature change cannot be removed by using the result obtained by adjusting the internal and external pressures of the pipes to be the same before or after the leakage inspection. Furthermore, when detecting the temperature of the pipe itself, as the pipe capacity increases, the tendency for the temperature change to differ depending on the location of the pipe increases, and it is difficult to achieve sufficient temperature compensation. is doing.

  In the invention relating to Patent Document 1, the operation of adjusting the pipe internal pressure to be the same as the pressure outside the pipe is usually realized by opening the pipe to open air. If an attempt is made to balance the pressure inside and outside the pipe without using this means of opening, a large-scale device or a precise measuring device is required. In addition, since a large volume of fuel gas piping releases a large amount of combustible gas into the atmosphere, it is dangerous to open the piping to the atmosphere to make the pressure inside the tube equal to the atmospheric pressure. Furthermore, since air is introduced into the piping by opening the piping to the atmosphere, an air purge operation is required before resuming use after inspection. With large capacity piping, the air purge operation is very large and difficult. Needless to say, the container cannot be opened to the outside air even in the leak inspection of the container storing toxic gas, corrosive gas and the like.

In order to solve the problem of the temperature effect in the leakage inspection, the present inventor in Japanese Patent Application Laid-Open No. H10-228707, the pressurizing or depressurizing step of pressurizing or depressurizing the container to be inspected for leakage according to a predetermined time sequence, A pressure measurement step for measuring a pressure change, calculating a correlation between the signal measured in the pressure measurement step and a reference signal corresponding to the time series, and based on the correlation, the leakage of the container is calculated. A leakage inspection method characterized by detecting was proposed. Thereby, the leakage inspection method which can remove effectively the influence of the temperature change in a container can be provided.
Japanese Patent Application No. 2004-42272 (Application Date: February 19, 2004)

  However, in the above-described leakage inspection method using the correlation method, a highly reliable leakage inspection is possible, but it is necessary to strictly control the time of the pressure increasing / decreasing process of the container, which makes the apparatus somewhat complicated. Costs are incurred. Further, since the temperature influence is removed by time integration, there is a disadvantage that a long inspection time is inevitably required.

  The problem to be solved by the present invention is to solve the above-mentioned problems, effectively remove the influence of temperature change in the container in the leakage inspection of a pipe or the like, and to provide a simple and low-cost leakage inspection method and Is to provide a device.

In order to solve the above-mentioned problem, the invention according to claim 1 is a pressure-increasing / depressurizing step of pressurizing or depressurizing a container to be inspected for leakage, and a time t _j (j = 0, 1, 2,... N.n. _Includes a pressure measurement step of measuring the pressure P _j and the pressure change (dP (t) / dt) _{t = tj} in the container at a natural number of 2 or more, and the pressure measured in the pressure measurement step Leakage inspection characterized by substituting the pressure change into the following equation to calculate a leakage coefficient k or an equivalent amount, and detecting leakage of the container based on the leakage coefficient k or the equivalent amount Is the method.
k = -G / D
(However,
G≡Σ _{j = 0} ⁿ {(1 / P _j ) · (dP (t) / dt) _{t = tj} / L _j ⁽ⁿ⁾ (t _j )},
D≡Σ _{j = 0} ⁿ {ΔP _j / L _j ⁽ⁿ⁾ (t _j )}
And
here,
ΔP _j ≡P _j −P _atm (P _atm is the pressure outside the container),
L _j ⁽ⁿ⁾ (t) ≡ (t−t ₀ )... (T−t _j−1 ) (t−t _{j + 1} ). (T−t _n ),
It is. )
The “equivalent amount” used in the present invention means not only the leakage coefficient k but also a numerical value having a correlation with the leakage coefficient k, such as an inverse number of the leakage coefficient k and a value proportional to the k.

  Further, in the invention according to claim 2, in the leakage inspection method according to claim 1, when the leakage coefficient k or the equivalent amount is within a predetermined value range, it is determined that “no leakage”. Features.

  The invention according to claim 3 is a leakage inspection apparatus using the leakage inspection method according to claim 1 or 2.

In the invention according to claim 1, while pressurizing or depressurizing the container to be inspected for leakage, at time t _j (j = 0, 1, 2... N, n is a natural number of 2 or more) the pressure P _j and pressure change (dP (t) / dt) t = tj are measured, the difference approximation equation of n order differential coefficient based on the n-order interpolating polynomial, calculated leakage coefficient k by substituting the measured values is doing. When the temperature does not change, that is, when the first derivative of the temperature is zero, it is the situation assumed by the conventional pressure type leak inspection, and the leakage coefficient k is measured by measuring the pressure and the pressure change once. Can be requested. When the temperature is linearly changed, that is, when the first derivative is not zero but the second derivative is zero, the temperature change is estimated before or after the leakage inspection including the above-mentioned Patent Document 1. The method of providing a period is a situation that is normally assumed. By measuring the pressure and the pressure change at least twice, the leakage coefficient k can be obtained without the influence of temperature fluctuation. In the present invention, the leakage coefficient k can be obtained by removing the temperature effect for a temperature change in which the differential coefficient up to the nth floor is generally not zero. Further, instead of the leakage coefficient k, a numerical value having a correlation with the leakage coefficient k can be calculated as an “equivalent amount”, and the equivalent amount can be used.

In the present invention, the initial pressure P _j in the pressure increasing / decreasing process and the time t _j (j = 0, 1, 2,. Optional except for restrictions. For this reason, it is not necessary to strictly control the pressure increasing / decreasing step and the pressure measuring step using a computer or the like. It does not matter if the pressure is increased or decreased with a manual pump, etc., and the value of the pressure increase / decrease may vary, and the pressure measurement time t _j does not need to exactly match a predetermined time sequence, and the measurement is performed manually. It doesn't matter if the time varies. Therefore, it is possible to configure the leakage inspection apparatus at a very low cost, and it is possible to perform a high degree of temperature compensation corresponding to the nth derivative of the temperature change.

Furthermore, since the pressure P _j has only a restriction that D is not zero, the initial pressure of the leak test, that is, P _0, and the pressure P _n immediately before the end of the leak test can be freely selected. Therefore, by setting equal P ₀ and P _n the pipe internal pressure in normal use, it is possible to omit the pressurization process for P ₀ and P _n. Compared with the case where the temperature influence is checked by making the pressure in the pipe equal to the atmospheric pressure before or after the leakage inspection, the inspection time can be greatly shortened.

  In the invention according to claim 2, when the leakage coefficient k or the equivalent amount is within the range of the predetermined value, it is possible to detect leakage more simply by determining “no leakage”.

  According to the invention of claim 3, by using the leakage inspection method according to claim 1 or 2, it is possible to provide a leakage inspection apparatus that can easily and inexpensively detect leakage by eliminating the influence of temperature change. It becomes.

Hereinafter, the detailed principle of the present invention will be described based on examples.
FIG. 1 models a leakage state of a container such as a pipe, which is a target of a leakage inspection method according to the present invention.
Assuming that gas exists in the container and indicates the state of the gas, it is assumed that the gas pressure P, the gas temperature T, the gas mass M in the container, the average molecular weight m of the gas, and the volume V ₀ in the container. .
The equation of state for the gas in the container is given by the following equation (1).
PV ₀ = MRT / m (1)

Given the time variation of the state quantity of the gas in the container, by differentiating both sides of Equation (1) time, by dividing both sides by PV _0, the following equation (2) is obtained.
1 / P · dP / dt = −πa ⁴ / (8 μΔLV ₀ ) · (P−P _atm ) + 1 / T · dT / dt (2)
However, the leakage is equivalently expressed as a gas leaking from the pinhole having the radius a. viscosity coefficient of μ gas, [Delta] L is the length of the pinhole, P _atm means a container outside the pressure (usually atmospheric pressure).

Here, k = −πa ⁴ / (8 μΔLV ₀ ) is defined as the leakage coefficient k representing the magnitude of leakage. Further, assuming that the pressure difference between the inside and outside of the container is ΔP = P−P _atm , Expression (2) is expressed by the following expression.
1 / P · dP / dt = −k · ΔP + 1 / T · dT / dt (3)

The present invention is characterized in that the presence or absence of leakage is determined by calculating the leakage coefficient k in the above equation (3) while performing a pressurizing / depressurizing step of pressurizing or depressurizing a container to be inspected for leakage.
The pressurizing / depressurizing step can be selected in any state. For example, as shown in FIG. 2, the time t _j (j = 0, 1, 2, ... n, where n is a natural number of 2 or more), the pressure P in the container and the time change (dP (t) / dt) of the pressure are measured n + 1 times. Although spacing of the measurement time need not be equally spaced, avoiding pressurizing and transient response period during decompression, after the inside of the gas reaches a steady state, it is preferable to place each measurement time t _j . In FIG. 2, the portion where the pressure changes exponentially before each time t _j is the transient response.

When the function y (t) takes a value y _j at time t _j (j = 0, 1, 2,... N, where n is a natural number of 2 or more), an nth-order Lagrangian interpolation that approximates the function y (t). The polynomial is the following n-order polynomial L _j ⁽ⁿ⁾ (t) ≡ (t−t ₀ ) ·· (t−t _j−1 ) (t−t _{j + 1} ) ·· (t−t _n )
Y _n (t) = Σ _{j = 0} ⁿ {y _j · L _j ⁽ⁿ⁾ (t) / L _j ⁽ⁿ⁾ (t _j )} (4)
Given in. The n-th derivative of this polynomial is d ⁿ y _n / dt ⁿ = Σ _{j = 0} ⁿ {n! Y _j / L _j ⁽ⁿ⁾ (t _j )} (5)
It is.

Now, the pressure in the container at time t _j (j = 0, 1, 2,... N, where n is a natural number of 2 or more) is P _j , and the time change in pressure is (dP (t) / dt) _{t = tj} When the pressure difference ΔP _j = P _j −P _atm inside and outside the container is used, the following equation is established from the equation (3) between the measured values.
g _j = −k · ΔP _j + f _j ... (6)
However, for simplicity, g _j ≡1 / P _j · (dP (t) / dt) _{t = tj} ,
f _j ≡1 / T _j · (dT / dt) _{t = tj}

Substituting g _j in equation (6) for y _j in equation (5),
Σ _{j = 0} ⁿ {n! G _j / L _j ⁽ⁿ⁾ (t _j )} = − k · Σ _{j = 0} ⁿ {n! ΔP _j / L _j ⁽ⁿ⁾ (t _j )} + Σ _{j = 0} ⁿ {n! F _j / L _j ⁽ⁿ⁾ (t _j )} (7)
Is obtained. The second term on the right side of equation (7) represents a difference approximation equation of the nth derivative of the function f (t). If f (t) satisfies the condition that the nth or higher derivative is zero, that is, if the n + 1 or higher derivative of the temperature T (t) is zero, this term is zero. ,
Σ _{j = 0} ⁿ {n! G _j / L _j ⁽ⁿ⁾ (t _j )} = − k · Σ _{j = 0} ⁿ {n! ΔP _j / L _j ⁽ⁿ⁾ (t _j )}
That is, Σ _{j = 0} ⁿ {1 / P _j · (dP (t) / dt) _{t =} t _j / L _j ⁽ⁿ⁾ (t _j )} = − k · Σ _{j = 0} ⁿ {ΔP _j / L _j ^{( n)} (t _j )} (8)
Holds. Accordingly, the leakage coefficient k is given by the following equation.
k = -G / D (9)
(However,
G≡Σ _{j = 0} ⁿ {1 / P _j · (dP (t) / dt) _{t = tj} / L _j ⁽ⁿ⁾ (t _j )},
D≡Σ _{j = 0} ⁿ {ΔP _j / L _j ⁽ⁿ⁾ (t _j )}
It is.

  In the above formula (9), it is assumed that the time differential of the (n + 1) th or higher temperature is zero. Strictly speaking, this assumption is not always satisfied with real temperature changes. However, the error caused by the fact that the n + 1-th derivative is not zero is an n + 1-order high-order minute term. The influence of fine temporal high frequency fluctuations included in the temperature fluctuation can be removed by signal processing to be described later. For moderate low frequency fluctuations, the value of the higher-order derivative is small. (9) It can be considered that the precondition of the equation is approximately satisfied.

FIG. 3 shows an example of a leakage inspection apparatus according to the present invention.
A measurement pipe 3 is connected to a container 1 such as a pipe via a connection port 2. The connection port 2 normally uses a maintenance / inspection valve installed in a pipe or the like, or a gas cock plug in a fuel gas pipe. The pressure in the container is measured by a gauge pressure sensor 4 connected to the measurement pipe 3. A valve 5 is connected to the other end of the measurement pipe 3, and the inspector operates the valve 5 to connect the measurement pipe 3 to a manual double ball pump 6, or atmospheric pressure. Control whether to release or block. The output of the gauge pressure sensor 4 is input to the control circuit 7. The control circuit 7 incorporates an A / D converter, a memory, a timer, etc. (all not shown), converts the signal of the gauge pressure sensor 4 into a digital signal and takes it in, and calculates the pressure change. The time t _j when these measurements are performed is stored, and the leakage coefficient k is calculated by performing the above-described calculation. Further, the control circuit 7 is connected to the display device 8. The display device 8 instructs the operator to operate the double ball pump 6 or the valve 5 in accordance with a signal from the control circuit 7, and displays the pressure in the container 1, the leakage inspection result, and the like. Reference numeral 9 denotes a leak hole generated in the container 1.

The gauge pressure sensor 4 measures the difference between the pressure in the container 1 and the atmospheric pressure. Since the fluctuation of the atmospheric pressure is usually several percent at most, the pressure P _j and the pressure change (dP (t) / dt) _{t = tj} are calculated from the output of the gauge pressure sensor 4 assuming that the atmospheric pressure is constant. be able to. Of course, it is possible to calculate _Pj more accurately if a configuration is adopted in which an atmospheric pressure sensor is separately installed, an absolute pressure sensor is used instead of a gauge pressure sensor, or an atmospheric pressure at the time of inspection is manually input. Needless to say. Moreover, it is good also as a structure which measures the differential pressure | voltage between the reference | standard containers installed separately using a differential pressure sensor as a pressure sensor. Note that the connection position of the pressure sensor is not limited to the place shown in FIG. 3, and can be directly connected to another pipe or the like extending from the container 1.

  Next, a procedure for calculating the leakage coefficient k in the control circuit 7 will be described. In the control circuit 7, a CPU and a memory circuit (not shown) are incorporated, and by operating them with a predetermined algorithm, calculation of the leakage coefficient k and leakage determination based on the leakage coefficient k are performed.

The control circuit 7 is preprogrammed with a pressure increasing / decreasing pattern in the case of using an n-order interpolation polynomial, and an instruction is appropriately displayed by the operator so that the pattern is roughly executed. For example, an instruction is given to pressurize to a certain pressure, and measurement of the internal pressure of the container is started at an appropriate timing with a margin for convergence of the transient response after the operation is completed. The pressure is measured for a certain period, and the pressure change (dP (t) / dt) is calculated from this data. Any known algorithm may be used as the calculation algorithm, but it is advantageous to use linear fitting based on the least square method that is simple in calculation and can remove high-frequency noise. The calculated pressure change (dP (t) / dt) _{t = tj} is stored in the memory together with the actual measurement value P _{j of} the pressure and the measurement time t _j which is the median value of the pressure measurement period. However, for the purpose of reducing the influence of noise from a measuring instrument or the like, the pressure within the measurement period may be averaged as the actual measurement value P _j of the pressure.
Note that the patterns programmed in advance are not limited to one pattern even if they have the same order (n). Therefore, an optimum pattern is programmed in accordance with the condition to be inspected. Alternatively, a plurality of patterns may be stored in advance, and an appropriate pattern may be selected from them according to the target conditions.

When the measurement and calculation of n + 1 times are completed, the leakage coefficient k is calculated using the above equation (9). And when the calculated absolute value of k is below a specific numerical value, it is determined that there is no leakage from the container.
About the specific numerical value used as a judgment criterion of leakage, the leakage coefficient k can be conceptually defined as k = −πa ⁴ / (8 μΔLV ₀ ). Viscosity coefficient) and pressure sensor performance are taken into consideration.

The leakage coefficient k is the reciprocal of the time constant created by the container volume and leakage. The amount calculated to determine leakage is not limited to k. The degree of leakage is expressed as the leakage time constant 1 / k, or the leakage volume per unit time is calculated and displayed by measuring the container volume V ₀ or giving it separately. Can be expressed in various amounts. It is clear that the use of these quantities does not change the essence of the invention.
As a means for pressurizing and depressurizing the container 1, any pressure increasing / decreasing means such as an electric pump can be used. The reason why the double ball pump 6 is used in this embodiment is to reduce the cost as much as possible. The manual type valve 5 is used for the same reason. It goes without saying that the control circuit 7 can control the pressure-increasing / decreasing means and valves and their operation timings to automatically inspect them.

The present invention is not limited to the above description, and as described in Patent Document 1, storage means for storing various measurement mode programs related to leakage inspection, display means such as liquid crystal, KEY board, etc. Needless to say, a known technique in this field, such as a technique related to the input means, can be added.
Further, various extended functions can be added by utilizing the properties of the interpolation polynomial. For example, the pressure increase / decrease pattern stored in advance in the inspection apparatus is not limited to the same order (n), and patterns of a plurality of orders can be stored. In this case, it is possible to perform leakage inspection while changing the order n of the interpolation polynomial, analyze the change in the result due to the order, and determine what order polynomial can be used to approximate the temperature change under the inspection condition. Yes, if this function is used, the reliability of the test results can be further increased.

  According to the present invention, it is possible to provide a simple and low-cost leakage inspection method and apparatus that effectively removes the influence of temperature changes in a container in a leakage inspection of a container such as a pipe.

It is a figure which shows the model of the leakage state in a container. It is the schematic which shows the pressurization / decompression process in a container. It is the schematic of the leakage inspection apparatus of this invention.

Explanation of symbols

1 Container 2 Connection 3 Pipe for Measurement 4 Gauge Pressure Sensor 5 Valve 6 Double Ball Pump 7 Control Circuit 8 Display Device 9 Leakage Hole

Claims (3)

A pressurizing / depressurizing step for pressurizing or depressurizing the container to be inspected for leakage, and the pressure P _j and the pressure in the container at time t _j (j = 0, 1, 2,..., N is a natural number of 2 or more). A pressure measurement step of measuring change (dP (t) / dt) _{t = tj} ,
The pressure measured in the pressure measuring step and the change in pressure are calculated as a leakage coefficient k or an equivalent amount calculated by the following equation, and the container is calculated based on the leakage coefficient k or the equivalent amount. Leakage inspection method characterized by detecting leakage of water.
k = -G / D
(However,
G≡Σ _{j = 0} ⁿ {(1 / P _j ) · (dP (t) / dt) _{t = tj} / L _j ⁽ⁿ⁾ (t _j )},
D≡Σ _{j = 0} ⁿ {ΔP _j / L _j ⁽ⁿ⁾ (t _j )}
And
here,
ΔP _j ≡P _j −P _atm (P _atm is the pressure outside the container),
L _j ⁽ⁿ⁾ (t) ≡ (t−t ₀ )... (T−t _j−1 ) (t−t _{j + 1} ). (T−t _n ),
It is. )   2. The leakage inspection method according to claim 1, wherein when the leakage coefficient k or the equivalent amount is within a predetermined value range, it is determined that there is no leakage. A leakage inspection apparatus using the leakage inspection method according to claim 1.

Images