JP3238534B2 - In-tube inspection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an in-pipe inspection method for inspecting the inside of a pipe such as a gas pipe.

[0002]

2. Description of the Related Art Conventionally, as a method for inspecting whether foreign matter such as earth and sand has penetrated a pipe such as a gas pipe buried underground, a camera for inspection is inserted into the pipe, and the inside of the pipe is conventionally inspected. The state of the camera is photographed, and the photographed screen is observed to judge whether there is any abnormality, or a self-propelled robot enters the pipe,
Inspection of the condition inside the pipe was conducted (Japanese Patent Laid-Open No. 59-147).
No. 260). Also known is a method of inserting a pig having an outer diameter substantially equal to the inner diameter of the pipe into the inside of the pipe. Further, a method of sending out a sound wave into the inside of the tube and receiving the reflected wave to check the state inside the tube (Japanese Patent Publication No. 51-188)
No. 36) was also known.

[0003]

However, when a camera or a robot is used for the inspection of the inside of the pipe, it cannot be applied when the pipe is complicatedly bent. A mouth is required, and when adapting to an existing pipe, there is a problem that it takes time and labor for excavation work and the like. Furthermore, since the distance that can be inspected at one time is also limited by the length of the electric wires connected to the robot or the like, the number of inspections increases when the inspection distance is long,
Was expensive. Also, when a sound wave is sent into the pipe and the internal state is inspected from the reflected wave, it cannot be easily sensed unless the pipe is completely closed or completely released to the atmosphere. However, there has been a problem that a small change cannot be detected.

[0004]

According to the present invention, in order to solve the above-mentioned problems, a transmitter is inserted into a pipe to be inspected from an end of the pipe which branches off from the pipe to be inspected and opens to the ground. A radio wave having a predetermined frequency corresponding to the inner diameter of the tube to be inspected is transmitted inside the tube to be inspected, and a receiver is inserted into the tube to be inspected from an end of the tube branched from the tube to be inspected and opened to the ground. Is input, the radio wave transmitted from the transmitter is received by the receiver, the received radio wave received by the receiver, the distance between the receiver and the transmitter from the transmitted radio wave transmitted from the transmitter A comparison is made with the value obtained by subtracting the amount of attenuation due to the above, and when the received radio wave is attenuated by a predetermined amount or more, the inside of the tube under test is inserted into the tube under test while the transmitter and the receiver are turned on. Determining that an abnormality has occurred that narrows the cross section of the It was.

[0005]

When a radio wave of a predetermined frequency determined from the inner diameter of the tube is transmitted into the tube, attenuation inside the tube is small, and it is possible to reach a distant place without a drop in intensity. Also, if there is a foreign substance inside the tube and the inside diameter of the tube is reduced on the way due to the foreign substance, the radio wave is greatly attenuated at such a place. So we received the radio wave that passed the inspection point,
If the amount of attenuation of the received radio wave is larger than a predetermined value, by comparing the natural attenuation that occurs from the mere passage distance when there is no abnormality in the pipe such as a reduction in the pipe diameter, and the attenuation of the received radio wave, In this case, clogging or the like occurs inside the pipe, and it can be detected that the inner diameter is reduced.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the inspection method of the present invention will be described below.
A description will be given of a domestic gas pipe buried under a road as an example. Such a household gas pipe under a road is combined with a main pipe 2 buried under the road and a service pipe 4 branched from the main pipe 2 as shown in FIG. A meter 6 is attached to the end of the tube 4, from which it is led into each home.

The inspection is to inspect the internal state of the main pipe 2, and an inspection apparatus for implementing the inspection method is shown in FIG. The inspection device 10 includes a transmitter 12, a receiver 14, a processing device 16, a display device 18, and the like. The transmitter 12 is capable of continuously and variably transmitting radio waves having a frequency of GHz unit, and a transmitting antenna 13 is attached to a leading end of a conductor 21. The receiver 14 includes a receiving unit 15 and an amplifier 17, and a receiving antenna 19 is provided at the tip of a conductor 23 extending from the receiving unit 15.
It is attached in the same way as 2. When a radio wave emitted from the transmitter 12 is received, the signal is amplified and sent to the processing device 16.

The processing unit 16 compares the radio wave received by the receiver 14 with the intensity of the radio wave transmitted by the transmitter 12 (the intensity is input in advance), and detects the amount of attenuation.
The distance input unit 20 is connected, and the antenna 1
The installation intervals of 3, 19 are input, and the attenuation is corrected based on the input value. That is, the amount of attenuation that occurs naturally by passing through the main pipe 2 is corrected. Then, the corrected attenuation amount is sent to the display device 18, and the display device 18 displays the value.

Next, the inspection procedure will be described. First, two meters 6 sandwiching a portion to be inspected are selected, and the service pipe 4 is removed from each meter 6. One of the service pipes removed
The antenna 13 of the transmitter 12 is inserted from the opening end of the main pipe 2 and is fed until the antenna 13 reaches the inside of the main pipe 2.
At that time, the supply of gas to the main pipe 2 may be stopped or may be performed without stopping the supply. If the supply is not stopped, sealing is performed on the open end of the internal pipe 4 so that the gas does not leak outside.

Similarly, the antenna 19 of the receiver 14 is fed to the main pipe 2 from the open end of the service pipe 4 of the meter 6 on the other side. In this way, if the transmitter 12 and the antennas 13 and 19 of the receiver 14 are arranged on both sides of the portion to be inspected of the main pipe 2, the frequency of the transmitter 12 is equal to the speed of light / {1.
A radio wave having a frequency equal to or higher than 706 × the inner diameter of the pipe｝ is transmitted. For example, if the main pipe 2 is a 100A pipe, it is a radio wave of a frequency of 1.67 GHz or more. A radio wave having a frequency equal to or higher than the frequency obtained from this equation has the property of being able to propagate inside the pipe with a small attenuation if the pipe has an inner diameter substituted into the calculation equation.

If a radio wave is transmitted from the transmitter 12 while continuously changing the frequency within a predetermined frequency band, then:
The radio wave passing through the main pipe 2 is received by the receiver 14. The received radio wave is sent to the processing device 16, where it is compared with the intensity of the radio wave transmitted from the transmitter 12 to detect the amount of attenuation. Further, the correction is performed based on the attenuation caused by the distance between the antennas 13 and 19 input from the distance input unit 20. The value is displayed on the display device 18, and the state inside the main branch 2 is inspected. That is, when water, soil, or the like enters the main pipe 2 and the inside of the main pipe 2 is shrunk, the radio wave received by the receiver 14 is attenuated accordingly. Obtaining a substantial amount of attenuation of the radio wave enables an inspection of the closed state of the inside of the main pipe 2.

Next, an experimental example using the above inspection method will be described. The experimental apparatus is shown in FIG. In the experiment, a gas pipe 30 called 100A having an inner diameter of about 105 mm was used. The gas pipe 30 has a length of about 1 m and 50 cm, and transmitter and receiver antennas 32 are installed at both ends with the antennas 32 slightly inserted into the gas pipe 30 respectively.
Radio waves of continuously varied frequencies from z to 5.0 GHz were transmitted, and an obstacle 34 was arranged inside the center. The obstacle 34 has a shape in which a part of a circular thick plate having an outer diameter substantially the same as the inner diameter of the gas pipe 30 is cut out, and the shape and area of the cut-out portion are changed to form the obstacle 3.
4 can change the closed state of the gas pipe 30. Further, an aluminum foil was wound around the surface of the obstacle 34.

More specifically, as a comparative example 1, a radio wave is transmitted from a transmitter without placing an obstacle 34 inside the gas pipe 30, and the radio wave is received by an antenna 32 of a receiver facing the radio wave. Then, an obstacle 34 having a shape covering half of the cross section of the gas pipe 30 was inserted and received in the same manner (Experiment 1).
And ), Obstacle 3 covering 2/3 of the cross section of gas pipe 30
4 and similarly received (experiment 2),
One receiving an obstacle 34 covering the entire cross section of the gas pipe 30 and receiving the same (Experiment 3), and one receiving water with the water placed between the gas pipes 30 (Experiment 4). )
5 types were performed. In Experiment 4, water was placed in a container made of PET resin equal to the cross section of the gas pipe 30, and the water was poured into the gas pipe 30.
Was inserted inside. Hereinafter, the results of Experiments 1 to 4 are shown in FIGS. 4 to 7, and the results of Comparative Example 1 are shown by dotted lines in each figure.

In Experiment 6, the frequency was set to 2.5 GHz, and a condition in which one third of the gas pipe 30 was closed was added. Other conditions were the same as those described above. FIG. 8 shows the results of Experiment 6. From this result, it is possible to set a criterion for determining that a foreign substance is present in the pipe when the attenuation amount is equal to or less than -35 dbm.

FIG. 9 is a graph showing the attenuation constant. This is because the attenuation constant ratio at each frequency when the attenuation constant at 2 GHz in the 100A tube is 1 and the 50A tube
It is a damping constant ratio in a 5A tube. Therefore, 100
Assuming that the attenuation constant at 2 GHz in the A tube is 0.4 dB / m, the difference at each frequency and the difference of the attenuation constant when the inner diameter of the tube is different are obtained from FIG. Find the amount of attenuation.

Further, as an experiment 7, a 1-meter 100A tube was used.
As shown in FIG. 10, a 3 m 100A tube and a 50 cm 10
The receiver was installed by installing a transmitter and a receiver at both ends of a tube in which 0A tubes were alternately connected at right angles. The result is shown in FIG. 11 (the result of a 1 m 100A tube is indicated by a dotted line). From this result, it can be seen that even when the radio wave has many bent portions, the amount of attenuation due to it is small.

As described above, according to the present embodiment, the transmitter 1 is attached to the home meter 6 at two separate locations.
2 and the antennas 13 and 19 of the receiver 14 are inserted and sent into the main pipe 2 to be inspected, and the attenuation of the radio wave transmitted from the transmitter 12 is measured. The closed state of the main pipe 2 up to the receiving antenna 19 can be accurately inspected. Moreover, since radio waves are used, the inspection distance can be set long, and the main pipe 2 can be inspected over a long distance with a small number of inspections. Main branch 2
Even when is complicatedly bent, an accurate inspection can be easily performed with a small amount of attenuation.

In the above embodiment, the gas pipe is inspected, but the application of the inspection method of the present invention is not limited to the gas pipe. Further, the insertion of the antenna 13 or the like does not have to be performed from the connection pipe of the meter 6.

[0019]

According to the inspection method of the present invention, the amount of attenuation of a radio wave transmitted after transmitting a radio wave into a pipe is determined, and an abnormality such as clogging occurring in the pipe is inspected from the attenuation. Therefore, the condition in the tube can be accurately inspected. In addition, because radio waves are used, inspection can be easily performed even when the tube is bent in a complicated manner, and the inspection distance can be set long. it can.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of an inspection method of the present invention.

FIG. 2 is a diagram showing an embodiment of an apparatus according to the inspection method of the present invention.

FIG. 3 is a perspective view showing an experimental example of the inspection method of the present invention.

FIG. 4 is a graph showing experimental results.

FIG. 5 is a graph showing experimental results.

FIG. 6 is a graph showing experimental results.

FIG. 7 is a graph showing experimental results.

FIG. 8 is a table showing experimental results.

FIG. 9 is a graph showing a damping constant ratio.

FIG. 10 is a plan view showing a tube.

FIG. 11 is a graph showing experimental results.

[Explanation of symbols]

 2 main pipe 4 service pipe 6 meter 10 inspection device 12 transmitter 13, 19, 32 antenna 15 reception unit 16 processing device 18 display device 30 gas pipe 34 obstacle

Continuation of the front page (56) References JP-A-53-8190 (JP, A) JP-A-50-91787 (JP, A) JP-A-4-215046 (JP, A) JP-A-60-76660 (JP) , A) Japanese Utility Model Hei 4-68410 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 22/00-22/04

Claims (1)

(57) [Claims] A transmitter is inserted into a pipe to be inspected from an end of a pipe branched from the pipe to be inspected and opened on the ground, and the transmitter is inserted into the pipe to be inspected from the transmitter. Transmit a radio wave of a predetermined frequency corresponding to the inner diameter of the test tube, and in the test tube ,
A receiver is inserted from the end of the tube branched from the tube to be inspected and opened to the ground, the radio wave transmitted from the transmitter is received by the receiver, and the received radio wave received by the receiver is A comparison is made with a correction value obtained by subtracting the amount of attenuation due to the distance between the receiver and the transmitter from the transmitted radio wave transmitted from the transmitter.If the received radio wave is attenuated by a predetermined amount or more, the transmitter and the transmitter are compared. An in-pipe inspection method, characterized in that it is determined that an abnormality that narrows the cross section of the pipe to be inspected has occurred inside the pipe to be inspected while the receiver is turned on.