JP2002228602A - Plastic resin pipe detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To judge the presence or absence of a plastic resin pipe within an embedded gas supply metal pipe. SOLUTION: The gas supply metal pipe DP is irradiated with fast neutrons from a neutron source and neutrons are reflected/transmitted by a plastic resin pipe PE when the plastic resin pipe PE is inserted into the gas supply metal pipe to lose energy to become thermal neutrons. The thermal neutrons are counted for a definite time by a thermal neutron measuring module and the correction of attenuation due to natural decay based on a calender time RTC is performed and the correction value is compared with a predetermined threshold value to judge the presence or absence of the plastic resin pipe.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic resin pipe detecting apparatus, and more particularly to a plastic pipe for supplying city gas into which a plastic resin pipe having substantially the same outer diameter as the inner diameter of the metal pipe is inserted. The present invention relates to a plastic resin tube detection device for non-destructively determining whether or not a metal tube is broken.

[0002]

2. Description of the Related Art At present, in order to efficiently replace non-excavated metal pipes such as steel pipes and cast iron pipes among buried pipes of city gas or the like, an existing metal pipe has an outer diameter substantially equal to the inner diameter of the metal pipe. A method called a FLEX liner method has been developed to insert a plastic resin pipe such as a polyethylene pipe, a cross-linked polyethylene pipe, or a nylon pipe having a crack (Japanese Unexamined Patent Publication No. 2000-62025). Has been proven to be efficient and economical to update, prevent leakage accidents, and supply gas safely.

[0003]

However, in order to supply gas to individual users, it is necessary to connect a plastic resin tube inserted into a gas supply metal tube and a supply tube. It is necessary to know in advance whether or not a plastic resin tube exists in the gas supply metal tube.

[0004] In order to know whether or not a plastic resin pipe is inserted into a gas supply metal pipe buried by the FLEX liner method or the like, it is necessary to insert a plastic resin pipe by the method using a construction history record and a construction history drawing. After investigating whether or not the drilling has been performed, excavate the location, take special measures to prevent gas from leaking to a part of the gas supply metal pipe, and then perform drilling with a dedicated end mill and detect A jig with a magnet called a rod has forced the installer to judge whether there is only a gas supply metal pipe or a plastic resin pipe based on the human feeling of the installer, such as sound and feel.

[0005] In view of such circumstances, the present invention determines whether or not a plastic resin tube is inserted in a gas supply metal tube by using neutron reflection or transmission by a simple operation.
It is an object of the present invention to provide a device for economically detecting a plastic resin tube.

[0006]

In order to achieve the above object, a plastic resin tube detecting device of the present invention is inserted into a metal tube used for gas supply and has an outer diameter substantially equal to the inner diameter of the metal tube. Detects a plastic resin tube that has a neutron source that generates neutrons, and high-speed neutrons emitted from the neutron source are absorbed by a plastic resin tube inserted in a metal tube, and energy is absorbed and caused by deceleration. A thermal neutron detector for detecting thermal neutrons,
Measure the intensity of the thermal neutrons detected by the thermal neutron detector, correct by referring to the neutron radiation attenuation due to the natural decay of the neutron source, and compare with a predetermined threshold to determine the presence or absence of the plastic resin tube. A calculation / determination module for performing determination.

The calculation / judgment module includes a measurement timer for managing the measurement time of thermal neutrons and performing measurement for a fixed time;
A calendar timer for referencing neutron radiation attenuation due to natural decay of the neutron radiation source.

A neutron radiation source and a thermal neutron detector are arranged close to each other, and the presence or absence of the plastic resin tube is determined by measuring the thermal neutrons reflected from the plastic resin tube.

The neutron source and the thermal neutron detector are connected to a metal tube /
A plastic resin tube is disposed so as to sandwich the plastic resin tube, and the presence or absence of the plastic resin tube is determined by measuring the amount of thermal neutrons transmitted through the plastic resin tube.

[0010] In this plastic resin tube detector, high-speed neutrons are constantly generated from the neutron source that generates neutrons described above due to the spontaneous decay of the neutron source. This fast neutron is irradiated to the gas supply metal tube, and the thermal neutron amount is measured for a certain period of time, for example, one minute by a thermal neutron detector disposed in the vicinity.

When there is no plastic resin tube in the gas supply metal tube, since there is no moderator, the conversion efficiency from high-speed neutrons to thermal neutrons is poor, and the value measured by the thermal neutron detector is small. On the other hand, when a plastic resin pipe exists in the gas supply metal pipe, the plastic resin pipe in the gas supply metal pipe acts as a moderator,
Fast neutrons emitted from the neutron beam source are efficiently converted to thermal neutrons, and the value measured by the thermal neutron detector becomes larger than when no plastic resin tube is provided.

On the other hand, such a neutron source has a natural decay.
Is constantly attenuated by, for example, ²⁵²Cf (Califor
In the case of 252), its strength is half in about 2.7 years.
Reduce. Due to this natural collapse, plastic resin tube
Thermal neutron content will also decay with time and change over time
Needs to be corrected.

The amount of thermal neutrons for a certain period of time when a plastic resin tube is present in the gas supply metal tube and when the plastic resin tube does not exist is measured in advance, and the amount of thermal neutrons is corrected in accordance with the change over time, so that the amount of heat in the gas supply metal tube is reduced. It is possible to determine the presence or absence of a plastic resin tube.

The neutron source and the thermal neutron detector are disposed so as to sandwich the gas supply metal tube, and the presence or absence of the plastic resin tube can be similarly determined by measuring the amount of transmitted thermal neutrons. Become.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the plastic resin tube detecting apparatus of the present invention will be described below with reference to the drawings.

The plastic resin tube detecting device of the present invention comprises:
As shown in FIG. 1, a polyethylene pipe or a cross-linked polyethylene pipe inserted into a metal pipe DP such as a steel pipe or a cast iron pipe used for gas supply of city gas or the like and having an outer diameter substantially the same as the inner diameter of the metal pipe or This is for detecting a plastic resin tube PE such as a nylon tube.

The plastic resin tube detector detects neutrons.
The neutron source 1 to be generated (for example, ²⁵²Cf [Califor
252]) and high-speed radiation from the neutron source 1
Plastic tube with neutrons inserted inside metal tube DP
Energy is absorbed by the
Thermal neutron detector 2 for detecting thermal neutrons
The intensity of the thermal neutrons detected at the outlet 2 is measured and the neutron source
Corrected with reference to the neutron beam attenuation accompanying the natural decay of 1,
Plastic by comparing it with a predetermined threshold
Provided in the control unit CNT for determining the presence or absence of the resin pipe PE
And an operation / determination module CPU.

The thermal neutron detector 2 comprises a diode vacuum tube detector having an anode and a cathode (FIG. 2). The neutron source 1 and the thermal neutron detector 2 are provided with a holding member HLD for keeping the positional relationship between the neutron source 1 and the thermal neutron detector 2 constant.
Fixed to The neutron source 1 and the thermal neutron detector 2 are arranged close to each other, and measure the thermal neutrons reflected from the plastic resin tube to obtain the plastic resin tube PE.
Is determined.

The thermal neutron detector 2 is connected to the controller CNT by a signal transmission cable CBL via a terminal TO.
The thermal neutron detector 2 includes a high-voltage generating circuit HVS for enabling the thermal neutron detector 2 to operate in the control unit CNT.
Are connected through the resistors R1 and R2 of the input / output circuit IO to supply a voltage of several hundred volts.

On the other hand, in the thermal neutron detector 2, when thermal neutrons are captured, a pulse corresponding to the number of captured thermal neutrons is output from the thermal neutron detector 2, and the signal transmission cable C
After being converted into a predetermined voltage and a predetermined waveform by the waveform shaping circuit WF including the transistor Tr1 and the resistor R3 via the capacitor C of the input / output circuit IO via the BL, the counter in the calculation / determination module CPU Counted in COUNT.

The calculation / judgment module CPU includes a measurement timer TIMER for managing the measurement time of thermal neutrons and measuring for a fixed time, and a calendar timer for referring to the attenuation of the neutron beam due to the spontaneous decay of the neutron beam source 1. RTC.

Further, the plastic resin tube detecting device has a measurement start switch MS for starting the measurement, a display DSP for displaying the number of accumulated pulses counted by the counter CNT, and a case where the plastic resin tube is inserted into the gas supply metal tube. Is stored for each pipe diameter of the gas supply metal pipe as a threshold value PS for discriminating the case where it is not inserted.
It is provided with an LED 1 for displaying the result of determining the presence or absence of the OM and the plastic resin tube.

In the plastic resin pipe detecting apparatus thus constructed, when the power of the plastic resin pipe detecting apparatus is turned on as shown in FIG. 3, the program in the arithmetic / judgment module CPU incorporated in the control unit CNT starts. (Step 101), the operation / determination module CP
U is automatically initialized (step 102).

The operation waits until the measurement start switch MS is depressed, and the measurement starts when the measurement start switch MS is depressed (step 103).

In the control unit CNT, a pre-programmed time, for example, one minute, is set in the measurement timer TIMER (step 104), and the thermal neutrons are captured by the thermal neutron detection unit 2 during the time set in the measurement timer TIMER. Then, a pulse corresponding to the number of captured thermal neutrons is output from the thermal neutron detection unit 2, passes through the signal transmission cable CBL, passes through the capacitor C of the input / output circuit IO, and has a predetermined voltage at the waveform shaping circuit WF. After being converted into a predetermined waveform, the signal is counted by a counter CNT in the operation / judgment module CPU, and the accumulated pulse number at that time is displayed on a display DSP.
(Steps 105 and 106).

When the time set in the measurement timer TIMER of the calculation / judgment module CPU elapses, the measurement ends (step 107), and the measurement date is read from the calendar timer RTC provided in the control unit CNT (step 1).
08), the number of days elapsed from a reference date set on the program in advance is obtained, and a correction coefficient k due to attenuation due to spontaneous decay of the neutron source 1 is obtained (step 109).

In general, the relationship of the equation (1) is known for the attenuation of radiation, where N ₀ is the initial radiation intensity, t is the elapsed time, and N is the radiation intensity after the time t. Here, λ is called a decay constant and is a unique value depending on the radionuclide.

N = N ₀ e ^{− λ t} (1) k = N / N ₀ (2) Therefore, the correction coefficient k is ^{calculated by the} equations (1) and (2). Can be easily obtained by the combination of

[0029] By dividing the cumulative count PN within a given time by the correction factor k, it is converted into the cumulative count number PN ₀ at the reference date.

On the other hand, RO of the operation / judgment module CPU
In M, a threshold value PS for discriminating between a case where the plastic resin tube is inserted into the gas supply metal tube and a case where the plastic resin tube is not inserted is stored as a reference date value for each tube diameter of the gas supply metal tube. cage, comparing the accumulated count PN ₀ at the threshold PS and the reference date, and determine the presence or absence of plastic resin tube (step 111), and displays the LED1 that is arranged in the controller CNT (step 112).

This embodiment is an example of application using reflected thermal neutrons. As described above, the neutron source 1 and the thermal neutron detector 2 are disposed with the gas supply metal tube DP / plastic resin tube PE interposed therebetween, and The same effect is obtained even when the method is applied by a so-called transmission method for measuring the amount of thermal neutrons transmitted through the resin pipe PE, and it is possible to determine the presence or absence of the plastic resin pipe.

It should be noted that the plastic resin tube detecting device of the present invention is not limited to the above-described embodiment, and it is needless to say that various changes can be made without departing from the gist of the present invention.

[0033]

As is clear from the above description, according to the plastic resin tube detecting apparatus of the present invention, neutrons are generated from a neutron source, and high-speed neutrons emitted from the neutron source are installed in the gas supply metal tube. The thermal neutrons are detected and measured by the thermal neutron detector, where the energy is absorbed and decelerated by the plastic resin tube, and the intensity of the thermal neutrons is determined by referring to the attenuation of the neutron source due to the natural decay of the neutron source. , The presence or absence of the plastic resin pipe can be determined without breaking the gas supply metal pipe.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a plastic resin tube detection device of the present invention.

FIG. 2 is a diagram illustrating a plastic resin tube detection device according to the present invention.

FIG. 3 is a flowchart showing the operation of the plastic resin tube detection device of the present invention.

[Explanation of symbols]

 DP: Metal tube PE: Plastic resin tube 1: Neutron radiation source 2: Thermal neutron detector CPU: Calculation / judgment module TIMER: Measurement timer RTC: Calendar timer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // F16L 1/00 F16L 1/00 L (72) Inventor Toshihide Kawabe 3 Hibarigaokacho, Yaiyama, Kure City, Hiroshima Prefecture No. 18 F term (reference) 2G001 AA04 BA11 BA14 CA04 DA02 FA09 GA01 HA01 JA01 JA11 KA20 LA02 LA05 MA06

Claims (4)

[Claims] An apparatus for detecting a plastic resin pipe (PE) inserted into a metal pipe (DP) used for gas supply and having a substantially same outer diameter as the inner diameter of the metal pipe. A neutron source (1) for generating neutrons, and thermal neutrons generated by deceleration of high-speed neutrons emitted from the neutron source by energy absorption and deceleration by a plastic resin tube inserted in the metal tube. A thermal neutron detector (2) to be detected, and the intensity of the thermal neutrons detected by the thermal neutron detector are measured, corrected with reference to neutron radiation attenuation accompanying natural decay of the neutron source, and predetermined. And a calculation / determination module (CPU) for determining the presence / absence of the plastic resin tube by comparing with a threshold value obtained. . 2. The calculation / judgment module refers to a measurement timer (TIMER) that manages the measurement time of the thermal neutron and performs measurement for a fixed time, and a neutron beam attenuation accompanying a natural decay of the neutron beam source. Calendar timer (R
2. The plastic resin tube detecting device according to claim 1, further comprising: (TC). 3. The method according to claim 1, wherein the neutron radiation source and the thermal neutron detector are disposed close to each other, and the presence or absence of the plastic resin tube is determined by measuring thermal neutrons reflected from the plastic resin tube. The plastic resin tube detection device according to claim 1, wherein: 4. The method according to claim 1, wherein the neutron source and the thermal neutron detector are disposed so as to sandwich the metal tube / the plastic resin tube, and the amount of thermal neutrons transmitted through the plastic resin tube is measured. The plastic resin tube detecting device according to claim 1, wherein the presence or absence of the resin tube is determined.