JPH0961377A - Method for inspecting buried metal pipe with electromagnetic wave - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the leaking position of electromagnetic wave in a buried metal pipe by comparing the electromagnetic wave received by a receiving device with the electromagnetic wave transmitted by a transmitting device in modulation signal to determine the time difference. SOLUTION: An electromagnetic wave is excited in a buried metal pipe 1 at an exciting part 2 on the transmitting device 6 side, and the electromagnetic wave leaked from the corrosion hole 10 of the metal pipe is probed while moving the antenna 8 on the receiving device 7 side in this state. The position of the corrosion hole 10 is detected on the ground by receiving the electromagnetic wave leaked from the corrosion hole 10 in this way. A processing device 11 compares the electromagnetic wave transmitted by the device 6 with the electromagnetic wave detected by the device 7 to determine the propagation time of the electromagnetic wave from the exciting position or the exciting part 2 formed on the opening end of the metal pipe 1 to the corrosion hole 10 where the leak is detected with the device 7 and the distance between them. Thus, the modulation to the transmitted electromagnetic wave is performed to determine the propagation time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting a buried metal pipe by using electromagnetic waves to detect the positions of corrosion holes and joints formed in the buried metal pipe.

[0002]

2. Description of the Related Art A detection method using electromagnetic waves has been proposed as one of methods for detecting corrosion holes formed in a buried metal pipe such as a gas pipe. This detection method is a method of detecting a corrosion hole from the ground by exciting the electromagnetic wave in the buried metal tube, propagating it in the same manner as a circular waveguide, and receiving the electromagnetic wave leaking from the corrosion hole.

FIG. 3 schematically shows a conventional structure to which this method is applied. Reference numeral 1 is an embedded metal pipe to be inspected, and a portion of the embedded metal pipe 1 standing on the ground is cut. The excitation part 2 is formed at the open end of the excitation part 2. The excitation unit 2 is configured as a coaxial-circular waveguide converter in which a probe 4 is provided on a lid 3 attached to the open end,
A transmitter 6 is connected to the excitation unit 2 via a coaxial cable 5. Reference numeral 7 is a receiving device, and 8 is an antenna connected to the receiving device 7 via a coaxial cable 9.

In the above construction, the transmitter 1 side continuously excites an electromagnetic wave by the exciter 2, and in this state, the worker on the receiver 7 side moves the antenna 8 while corroding the corrosion hole of the buried metal pipe 1. The electromagnetic wave leaking from 10 is searched. Corrosion holes 10 such as those formed in the buried metal pipe 1 in this way
By receiving the electromagnetic wave leaking from the corrosion hole 10
The position of can be detected from the ground.

When the presence of corrosion holes 10 such as corrosion holes in the buried metal pipe 1 is detected in this manner, the buried metal pipe 1
Repairing is performed from the inner surface of the so that the corrosion hole 10 is closed with resin or the like.

[0006]

Although the above-mentioned detection method using electromagnetic waves can detect the position of the corrosion hole with high accuracy, it cannot detect the path of the embedded metal pipe 1, and therefore the embedded metal pipe cannot be detected. The distance from the reference position appropriately set to 1 to the corrosion hole cannot be measured. Therefore, it is not possible to obtain data such as the distance necessary for repairing the corrosion hole from the inside of the buried metal pipe with resin or the like by the above method alone. The present invention aims to solve such problems.

[0007]

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. A method of performing an inspection by moving an electromagnetic wave leaking from an electromagnetic wave leakage point in a buried metal pipe by a receiving device, wherein an electromagnetic wave excited in the buried metal pipe is modulated, and an electromagnetic wave received by the receiving device and a transmitting device are modulated. The time difference is obtained by comparing the electromagnetic waves transmitted by the method in the modulated signal, and the propagation time corresponding to the distance excluding the propagation distance from the excitation point to the leakage point is subtracted from this time difference, and the We propose to obtain the distance of the buried metal pipe from the excitation point to the leakage point by measuring the propagation time.

In such a method, the position of the corrosion hole can be detected from the ground by detecting the electromagnetic wave leaking from the corrosion hole generated in the buried metal pipe, and the electromagnetic wave received by the receiving device can be detected. And, measuring the time difference by comparing the electromagnetic waves transmitted by the transmitter in the modulated signal, from this time difference, by subtracting the propagation time corresponding to the distance excluding the propagation distance from the excitation point to the leakage point,
By measuring the propagation time of the electromagnetic wave from the excitation point to the leakage point, the distance of the buried metal pipe from the excitation point to the leakage point can be obtained.

In the above method, the time difference can be measured by the phase difference between the modulated signals of the electromagnetic wave detected by the receiver and the electromagnetic wave transmitted by the transmitter.

Further, in the above method, the distance resolution can be enhanced by applying the pulse compression method when transmitting the electromagnetic wave in the transmitting device and receiving the electromagnetic wave in the receiving device.

[0011]

Embodiments of the present invention will now be described with reference to the accompanying drawings.

FIG. 1 conceptually shows a first example of a mode for carrying out the inspection method of the present invention. In this example, the structure of the excitation unit 2 is different from the conventional structure shown in FIG. The other similar configurations are denoted by the same reference numerals. Of course, even if the same reference numerals are given, they do not necessarily have the same configuration.

Reference numeral 1 denotes an embedded metal pipe to be inspected. In this example, unlike the above-mentioned conventional one, the excitation unit 2 does not cut the portion of the embedded metal pipe 1 standing on the ground, and is installed in advance. The probe 15 and the loop (not shown) are attached to the lid 14 of the branch opening 13 on the lateral side of the tee 12 to project into the tee 12,
With this configuration, there is an advantage that the excitation unit 2 can be configured without cutting the embedded metal pipe 1. A concrete example of the excitation unit 2 will be described later.

The exciter 2 is constructed as a coaxial-circular waveguide converter having the above-mentioned configuration, and a transmitter 6 is connected to the exciter 2 via a coaxial cable 5. The transmitter 6 supplies a signal to the exciter 2 after performing appropriate modulation as described below using a signal having a frequency higher than the cutoff frequency when the buried metal tube 1 to be inspected is regarded as a circular waveguide as a carrier. It is configured to be possible. Reference numeral 7 is a receiving device, and 8 is an antenna connected to the receiving device 7 via a coaxial cable 9.

In the above structure, the transmitter 1 side excites an electromagnetic wave into the embedded metal pipe 1 at the excitation unit 2, and the worker on the receiver 7 side moves the antenna 8 while moving the antenna 8 in this state. The electromagnetic wave leaking from the corrosion hole 10 is searched. By thus receiving the electromagnetic wave leaking from the corrosion hole 10 generated in the buried metal pipe 1, the position of the corrosion hole 10 can be detected from the ground. That is, when the antenna 8 is omnidirectional or weakly directional,
Move the antenna 8 along the embedded metal pipe 1 (the route that is estimated from materials such as drawings as the route in which it is embedded),
The position showing the peak of the reception level can be detected as the position directly above the corrosion hole 10. If the antenna 8 has a sharp directivity, the position directly above can be detected with higher resolution and the influence of external noise is reduced.

Reference numeral 11 denotes a processing device. The processing device 11 compares the electromagnetic wave transmitted by the transmitting device 6 with the electromagnetic wave detected by the receiving device 7 to excite the excitation point, that is, the opening end of the buried metal pipe 1. The propagation time and the distance of the electromagnetic wave from the excitation unit 2 configured as described above to the corrosion hole 10 where leakage is detected by the reception device 7 are obtained.

In order to compare the electromagnetic wave transmitted by the transmitting device 6 with the electromagnetic wave detected by the receiving device 7 to obtain the propagation time, the electromagnetic wave to be transmitted is modulated. For modulation of electromagnetic waves, various modulation methods such as pulse modulation, amplitude modulation, frequency modulation, and code modulation can be applied, and the time difference between the electromagnetic waves thus modulated and transmitted and the received electromagnetic waves is Well-known appropriate methods such as direct time measurement, time measurement by detecting a phase difference, and time measurement by detecting a shift amount of a correlation coefficient can be applied. Further, in these cases, a pulse compression method used for the purpose of improving S / N in radar and ultrasonic measurement can be applied, that is, in this case, the electromagnetic wave to be transmitted is
Modulation of linear FM (chirp wave), Barker code, M sequence code, complementary sequence code, etc. is performed.

In the above structure, the signal St, which has been subjected to a predetermined modulation, is fed from the transmitter 6 to the exciter 2 through the coaxial cable 5 in accordance with a command from the processor 11 to be excited and propagated in the buried metal pipe 1. At the same time, a signal St similar to the excited electromagnetic wave is output to the processor 11 for comparison with the received signal. On the other hand, a signal Sr of the electromagnetic wave received by the receiving device 7 leaking from the corrosion hole 10 of the buried metal pipe 1
Is output to the processing device 11 for comparison with the transmission signal after pre-processing such as amplification as necessary.

Then, the processor 11 compares the transmission signal St with the reception signal Sr and measures the time difference between them. For the measurement of the time difference, an appropriate method as described above can be used according to the modulation method. For example, when the modulation is pulse modulation, a method of directly measuring the time difference between pulses is used. When the modulation is amplitude modulation, the time difference is calculated by measuring the phase difference between the modulated signals of the transmission signal St and the reception signal Sr. A method of calculating a time difference by detecting a deviation amount of a correlation coefficient can be applied to an appropriate modulation including a method and code modulation.

During the time difference between the transmission signal St and the reception signal Sr obtained as described above, the exciter 2 moves to the corrosion hole 10
In addition to the propagation time of the corresponding electromagnetic wave to a path L up to the path l ₁ from the transmitter 6 to the excitation unit 2, the path l ₂ from the transmitter 6 to the processing unit 11, a receiving device 7 from the antenna 8 Path l ₃ to the processing device 11 via the corrosion hole 1
Since the propagation time of the signal corresponding to each path l ₄ from 0 to the antenna 8 is mixed, the time difference obtained as described above corresponds to the path L from the excitation unit 2 to the corrosion hole 10. It is not the propagation time of electromagnetic waves.

However, the propagation times of the signals corresponding to the paths l ₁ , l ₂ and l ₃ do not change and can be measured in advance.
Since the distance of the path l ₄ is the sum of the buried depth of the buried metal pipe 1 and the height of the antenna 8 from the ground, the former can be known from the piping construction drawing of the buried metal pipe 1, and the latter can be measured. Can be obtained by Therefore, by adding / subtracting the propagation times of the signals corresponding to the paths l ₁ , l ₂ , l ₃ , and l ₄ with respect to the time difference obtained by the above-described measurement, the path from the excitation unit 2 to the corrosion hole 10 The propagation time of the electromagnetic wave corresponding to L can be obtained.

In this way, the propagation time of the electromagnetic wave corresponding to the path L from the excitation unit 2 to the corrosion hole 10 can be obtained, and therefore the distance of this path L can be calculated.

As described above, the position of the corrosion hole 10 can be detected from the ground by detecting the electromagnetic wave leaking from the corrosion hole 10 generated in the buried metal pipe 1, and the reception device 7 receives the electromagnetic wave. By comparing the generated electromagnetic wave and the electromagnetic wave transmitted by the transmission device 6 in the modulated signal, the time difference is measured, and the propagation time of the electromagnetic wave from the excitation unit 2 to the corrosion hole 10 which is the leak point is measured from the time difference. Since the distance of the embedded metal pipe 1 from the excitation unit 2 to the corrosion hole 10 can be obtained, for example, the inside of the embedded metal pipe 1 is made of resin or the like to be used for the corrosion hole 1 by using a pig or the like.
Repairs that block 0 can be performed efficiently.

In the first example, the exciting part 2 is constructed by using a tee installed in advance on the rising part of the buried metal pipe 1, but the buried metal pipe 1 is cut as in the conventional case. It goes without saying that it can be appropriately configured, for example, in the cutting portion.

[0025]

FIG. 2 shows a concrete example of the excitation unit 2, and the same components as those shown in FIG. 1 are designated by the same reference numerals. In FIG. 2, reference numeral 16 is a support, 17
Is a lock nut, and these are connected by a screw portion 18. Screw part 18a of the lock nut 17
Is inserted inward from a mounting hole 19 formed in the center of the lid 14 and screwed with a screw portion 18b of a support body 16 arranged inside to tighten the periphery of the mounting hole 19 of the lid 14 to the lock nut 17. The brim portion 20 and the support body 16 are sandwiched between them to be in a fixed state. Prior to such screwing, the tip of the coaxial cable 6 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 the transmitter 6 supplies the electromagnetic wave modulated by the coaxial cable 5 to the excitation unit 2, 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 to be buried. Propagate to the tube 1. In this way, the gas-buried metal tube 1 can propagate electromagnetic waves in the same mode as the circular waveguide buried metal tube. 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.

Although the corrosion hole has been described above as the electromagnetic wave leakage point in the buried metal pipe, the electromagnetic wave also leaks at the joint, so the present invention can also be used for detecting this joint point.

[0028]

Since the present invention is as described above, it has the following effects as compared with the above-mentioned prior art. Not only can the position of an electromagnetic wave leakage point such as a corrosion hole or a joint in the embedded metal pipe be detected, but the distance from the reference position set appropriately in the embedded metal pipe to the leakage point can be measured. Therefore, it is possible to confirm whether or not the buried metal pipe is installed by being greatly bent between the reference position and the leakage point, and repairing corrosion holes etc. from the inside of the buried metal pipe with resin etc. It can be done efficiently.

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

FIG. 3 is an explanatory view conceptually showing a conventional inspection method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Embedded metal pipe 2 Excitation part 3,14 Lid 4,15 Probe 5,9 Coaxial cable 6 Transmitter 7 Receiver 8 Antenna 10 Corrosion hole 11 Treatment device 12 Tee 13 Branch opening 16 Support 17 Lock nuts 18a, 18b Screw Part 19 Mounting hole 20 Collar part 21 Center lead 22 Shield wire 23 Clamp 24 Washer 25 Gasket 26a, 26b Screw part 27 O-ring shaped shield material

Claims (5)

[Claims] 1. A transmitter transmits an electromagnetic wave to a buried metal pipe to propagate it inside the buried metal pipe, and a receiver moves along the buried metal pipe to receive an electromagnetic wave leaking from an electromagnetic wave leakage point in the buried metal pipe. In the method of inspecting by receiving by the device, the electromagnetic wave excited in the buried metal pipe is modulated, the electromagnetic wave received by the receiving device and the electromagnetic wave transmitted by the transmitting device are compared in the modulated signal to obtain the time difference, and this time difference From the excitation point to the leakage point, the propagation time corresponding to the distance from the excitation point to the leakage point is subtracted, and the electromagnetic wave propagation time from the excitation point to the leakage point is measured. Inspection method for buried metal pipes by electromagnetic waves, characterized in that pipe distances are obtained 2. The method for inspecting a buried metal pipe with an electromagnetic wave according to claim 1, wherein the time difference is measured by a phase difference between the modulated signal of the electromagnetic wave detected by the receiving device and the modulated signal of the electromagnetic wave transmitted by the transmitting device. 3. The method for inspecting a buried metal pipe with an electromagnetic wave according to claim 1, wherein a pulse compression method is applied when transmitting the electromagnetic wave in the transmitting apparatus and receiving the electromagnetic wave in the receiving apparatus. 4. The method for inspecting a buried metal pipe by electromagnetic waves according to claim 1, wherein the electromagnetic wave leakage point is an opening having a repair such as a corrosion hole. 5. The method for inspecting a buried metal pipe by electromagnetic waves according to claim 1, wherein the leakage point of the electromagnetic waves is a joint.