JPH0961376A - Method for detecting joint position of buried metal pipe with electromagnetic wave, and method for inspecting joint of metal pipe with electromagnetic wave - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the joint of a buried metal pipe having a curved part, and shorten the detecting time by exciting an electromagnetic wave to the buried metal pipe with a transmitting device, and propagating it in the metal pipe. SOLUTION: When an electromagnetic wave is supplied from a transmitting device 6 to an exciting part 3 through a coaxial cable 7, the electromagnetic wave of the mode corresponding to the electric field by a probe 5 is excited to propagate the electromagnetic wave through a buried metal pipe 1 in the same mode as a circular waveguide. When the electromagnetic wave is propagated through the metal pipe 1, the electromagnetic wave is leaked to the outside from the position of a joint 2. Thus, the leaked electromagnetic wave is received by a receiving device 9 through an antenna 8, thereby, the joint 2 can be detected. When the antenna 8 having a high directivity is used in this case, the direction of the antenna 8 is properly changed while moving it along the metal pipe 1 to detect the peak, thereby, the position of the joint 2 can be precisely detected by the direction of the antenna 8 corresponding to the peak.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of detecting a joint position of a buried metal pipe by using electromagnetic waves, and a method of inspecting a joint state of a buried metal pipe or an exposed metal pipe.

[0002]

2. Description of the Related Art As a conventional main method for detecting the position of a joint of a buried metal pipe, there is the following method. A method of detecting a joint position by moving a base body provided with a detection coil in an embedded metal pipe whose joint position is to be detected, and changing the inductance of the base body. (Japanese Patent Examination 5-5755
No. 3 gazette) A high frequency voltage is applied to the outer surface of the buried metal pipe whose joint position is to be detected to propagate through the pipe wall, and the time taken for the voltage reflected by the joint to return to the application point is measured to measure the joint. How to detect the position of. (JP-A-2-187683)

[0003]

In the above method, since the base body having the detection coil has to be moved in the embedded metal pipe, the detection operation is difficult and the detection is difficult in the embedded metal pipe having the curved pipe portion. Takes a long time, and the detectable distance is relatively short. On the other hand, in the method, in addition to being able to detect only the joint to be inspected closest to the position for each position to which the high-frequency voltage is applied, the high-frequency voltage is applied to a position relatively close to the joint to be inspected. There is a need to do it. The present invention aims to solve such problems.

[0004]

In order to solve the above-mentioned problems, according to the present invention, an electromagnetic wave is excited in a buried metal pipe by a transmitter to propagate the electromagnetic wave in the buried metal pipe and a receiver is arranged along the buried metal pipe. We propose a method to detect the joint position by moving and receiving the electromagnetic wave leaking from the joint with a receiver.

Further, according to the present invention, the transmitting device excites an electromagnetic wave into the metal tube to propagate the electromagnetic wave in the metal tube, and the receiving device receives the electromagnetic wave leaking from the joint to be inspected.
We propose an inspection method that estimates the state of the joint to be inspected based on the electromagnetic wave reception level.

In the above inspection method, when the metal pipe having the joint to be inspected is a buried metal pipe, it is proposed to perform the inspection after applying the above-mentioned joint position detecting method.

In the above joint position detecting method, the joint position is detected by the peak of the reception level of the electromagnetic wave by the receiver.

[0008]

Embodiments of the present invention will now be described with reference to the accompanying drawings. FIG. 1 conceptually shows a first example of an embodiment for carrying out the inspection method of the present invention. Sign 1
Is a metal pipe, in this example the metal pipe is a buried metal pipe,
The joint 2 to be inspected is provided in the embedded portion. A portion of the buried metal pipe 1 which is standing on the ground is cut, and an exciting portion 3 is formed in the opening. The excitation unit 3 is configured as a coaxial-circular waveguide converter in which a probe 5 is provided on a lid 4 attached to the opening so as to project.
And a coaxial cable 7 for connection. Reference numeral 8 is an antenna, 9 is a receiving device, and 10 is a coaxial cable. A worker searches for electromagnetic waves leaking from the buried metal pipe 1 side while moving the antenna 8.

In the above structure, when an electromagnetic wave is supplied from the transmitter 6 to the exciter 3 by the coaxial cable 7, the electromagnetic wave in the mode corresponding to the electric field generated by the probe 5 is excited, and thus the buried metal tube 1 has a circular waveguide. Electromagnetic waves can be propagated in the same mode as.

When an electromagnetic wave is propagated in the buried metal pipe 1,
The electromagnetic waves leak outside at the joint 2. That is,
Electromagnetic waves leak through a rubber ring or a gasket when the joint 2 is a mechanical joint, a gasket when the joint is a flange joint, and a non-conductive member 11 such as a seal material when the joint is a screw joint.

Therefore, the joint 2 can be detected by receiving the electromagnetic wave thus leaked by the receiving device 9 via the antenna 8 as described above. Since the electromagnetic wave propagates in the buried metal pipe 1 over a relatively long distance and slightly leaks at each joint, a plurality of joints 2 in series can be detected by exciting the electromagnetic wave at one location. Then, the position of the joint 2 can be detected by the peak of the reception level of the electromagnetic wave by the receiving device 9. At this time, when the antenna 8 has a sharp directivity, the antenna 8 is appropriately moved while being moved along the embedded metal pipe 1 (a route estimated from materials such as drawings as a route in which the embedded metal pipe 1 is embedded). If the peak is detected by changing the direction, the position of the joint 2 can be accurately detected by the direction of the antenna 8 corresponding to the peak, and the influence of external noise is reduced. However, by using an omnidirectional or weakly directional antenna 8, it is possible to detect the position that moves along the buried metal pipe 1 and shows the peak of the reception level as the position directly above the joint 2.

On the other hand, the amount of electromagnetic waves leaking from the joint 2 increases as the tightening of the joint 2 becomes loose. Therefore, the loose state of the joint can be detected by the reception level.
That is, when the reception conditions such as the distance and the direction to the antenna 8 are similar in the specific joint 2, the reception level of the electromagnetic wave leaking from the joint 2 changes depending on the loose state. Compared with the measured past reception level data, if there is no change, it means that there is no slackness, and if it is large, it means that slackness has occurred. Can be estimated.

In order to estimate the looseness of the joint of the metal pipe from the reception level, it is necessary that the reception conditions are the same as described above. If the metal pipe is a buried metal pipe, the antenna 8 is used. The characteristics such as the distance and direction with the same are of course the same, and the characteristics for electromagnetic waves in the surrounding area where the metal tube is embedded must also be constant. It is difficult to estimate the looseness of the joint from the level. However, even if the metal pipe is a buried metal pipe, it is possible to estimate the looseness of the joint by the above-mentioned operation when all the above conditions are satisfied or in the case of an exposed metal pipe in which the receiving condition can be easily made the same. .

FIG. 2 conceptually shows a second example of the embodiment for carrying out the inspection method of the present invention. In the second example, as compared with the first example, only the structure of the excitation unit 3 is shown. However, the other configurations are the same, the same reference numerals are given, and the description is omitted. That is, the excitation unit 3 of this second example is
Similar to the first example, the probe 15 and the loop are attached to the lid 14 of the branch opening 13 on the lateral side of the tee 12 which is installed in advance in the portion of the embedded metal pipe 1 that is the embedded metal pipe that is standing above the ground. (Not shown) is configured to protrude into the tee 12, and in this configuration, the embedded metal pipe 1
There is an advantage that the exciting unit 3 can be configured without cutting the. A concrete example of the excitation unit 3 will be described below.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 3 shows a concrete embodiment of the excitation unit 3, and the same components as those shown in FIG. 2 are designated by the same reference numerals. In FIG. 3, reference numeral 16 is a support,
Reference numeral 17 is a lock nut, which is connected by a screw portion 18. Screw part 1 of lock nut 17
8a is inserted inward from a mounting hole 19 formed in the center of the lid 14, and is screwed and tightened with a screw portion 18b of a support body 16 disposed inside, so that the periphery of the mounting hole 19 of the lid 14 is locked with a lock nut. It is assumed that the collar portion 17 of 17 and the support body 16 hold it and fix it. Prior to such screwing, the tip of the coaxial cable 7 is inserted into the lock nut 17, the center lead 21 is projected, and the braid of the shield wire 22 is expanded along the clamp 23. Washer 2 on the tip side of
4, the gasket 25 is interposed, and the expanded shield wire 22 is brought into pressure contact with the inner wall of the support 16 by the above-mentioned tightening to be in the attached state. On the other hand, a linear probe 15 is joined to the tip end side of the center lead 21, and the probe 15 is supported at the center position of the support 16 by an insulator 26.
In such a configuration, the screw portion 26a of the lid 14 can be closed by screwing the screw portion 26a of the lid 14 into the screw portion 26b of the opening portion 13 on the side of the tee 12 and tightening the screw portion 26b. Located in tee 12. Reference numeral 27 is an O-ring-shaped shield material.

In the above structure, when an electromagnetic wave is supplied from the transmitter 6 to the exciter 3 by the coaxial cable 7, the electromagnetic wave in the mode corresponding to the electric field generated by the probe 15 is excited in the tee 12, and the tee 12 causes the buried metal tube 1 to be buried. Propagate to. In this way, the gas-buried metal pipe 1 can propagate electromagnetic waves in the same mode as the circular waveguide metal pipe. That is, in the case of the figure, an electromagnetic field of TM ₀₁ mode is formed and propagates in the buried metal tube 1.

[0017]

Since the present invention is as described above, it has the following effects as compared with the above-mentioned prior art. Since it is not necessary to insert and move the detection coil into the pipe, it is possible to detect even with a joint of an embedded metal pipe having a curved pipe portion, and the time required for detection is short, and it is possible to detect over a relatively long distance. Excitation of electromagnetic waves at one location makes it possible to detect a plurality of continuous joints over a relatively long distance. When the propagation characteristics of electromagnetic waves around the joint are similar, the joint can be inspected for looseness or the like.

[Brief description of drawings]

FIG. 1 conceptually shows a first example of an embodiment for carrying out the inspection method of the present invention.

FIG. 2 conceptually shows a second example of the embodiment for carrying out the inspection method of the present invention.

FIG. 3 is a cross-sectional view showing a specific example of an excitation unit for carrying out the inspection method of the present invention.

[Explanation of symbols]

 1 Metal Pipe (Buried Metal Pipe) 2 Joint 3 Excitation Part 4, 14 Lid 5, 15 Probe 6 Transmitter 7, 10 Coaxial Cable 8 Antenna 9 Receiver 9 Non-Conductive Member 12 Tee 13 Branch Opening 16 Support 17 Lock Nut 18a, 18b Threaded portion 19 Mounting hole 20 Collar portion 21 Center lead 22 Shield wire 23 Clamp 24 Washer 25 Gasket 26a, 26b Threaded portion 27 O-ring shaped shield material

Claims (5)

[Claims] 1. A joint by causing a transmitter to excite electromagnetic waves in a buried metal pipe to propagate in the buried metal pipe, move the receiver along the buried metal pipe, and receive electromagnetic waves leaking from the joint by the receiver. A method for detecting the position of a joint of a metal pipe by electromagnetic waves, characterized by detecting the position 2. The method for detecting the joint position of a metal pipe by electromagnetic waves according to claim 1, wherein the joint position is detected by the peak of the reception level of the electromagnetic wave by the receiving device. 3. A transmitting apparatus excites an electromagnetic wave into a metal tube to propagate the electromagnetic wave in the metal tube, and an electromagnetic wave leaking from a joint to be inspected is received by a receiving apparatus, and the state of the joint to be inspected is determined by the reception level of the electromagnetic wave. A method of inspecting a metal pipe joint by electromagnetic waves, which is characterized by estimating 4. The embedded metal pipe is used as the metal pipe, the receiving device is moved along the embedded metal pipe, and the electromagnetic wave leaking from the joint to be inspected is received by the receiving device to detect the joint position. The method of inspecting a joint for a metal pipe by electromagnetic waves according to claim 3, wherein the state of the joint to be inspected is estimated based on the reception level. 5. The method for inspecting a joint of a metal pipe by electromagnetic waves according to claim 4, wherein the joint position is detected by a peak of a reception level of the electromagnetic wave by the receiving device.