JPH05180804A - Inspecting method for buried piping - Google Patents

Abstract

PURPOSE:To detect the two-dimensional position of an object place of a defect, such as corrosion loss in thickness or a through hole, or a joint by means of a flaw detection sensor. CONSTITUTION:A flaw detection sensor 2, in which a transmitting coil 3 and a receiving coil 4 being spaced apart by a predetermined distance from each other are provided, is moved in a buried piping 1 so as to detect the object places. At the same time, the electromagnetic wave 10 transmitted from the transmitting coil 3 is received by the receiving coil in a position sensor 12 on the ground so as to detect the position of the flaw detection sensor 2.

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 corrosion condition of a buried pipe such as a city gas supply pipe.

[0002]

2. Description of the Related Art A remote field eddy current inspection method is one of inspection methods for inspecting a corrosion condition of a buried pipe or detecting a joint or the like. In this inspection method, a flaw detection sensor in which a transmitting coil and a receiving coil are separated by a predetermined distance is made to travel in a buried pipe by a traveling device capable of measuring a distance,
Detects defects such as corrosion wall thinning and through holes or target points such as joints by changing the propagation time of electromagnetic waves from the transmitting coil to the receiving coil, and also measures the target points such as the above defects by the running distance of the flaw detection sensor. Is.

[0003]

Since the measurement of the position based on the traveled distance is based on the one-dimensional scale, the position where the defect is detected cannot be accurately measured as the two-dimensional position when the pipe is curved. ..

Therefore, in the case of repairing a pipe portion where such a defect is detected by excavation, wasteful excavation is performed or other pipes that happen to be close to the excavated portion are mistakenly recognized. In some cases, such inconvenience may occur. For example, in a flaw detection of a curved pipe D as shown in FIG. 3, when a flaw detection sensor detects a defect at a point B separated by a distance L from the point A, the above-mentioned point is required unless the curvature of the pipe D is considered. B is erroneously detected as a point C on a straight line from the point A, which is adjacent to the pipe E. The present invention aims to solve such problems.

[0005]

In order to solve the above-mentioned problems, the present invention detects a target location by running a flaw detection sensor having a transmitting coil and a receiving coil separated by a predetermined distance in an embedded pipe. At the same time, there is proposed a method for inspecting a buried pipe in which an electromagnetic wave from the transmitting coil is received by a receiving coil of a position sensor on the ground to detect the position of a flaw detection sensor.

The present invention proposes, in the above method, a method for inspecting a buried pipe in which a flaw detection sensor is caused to travel in a buried pipe by a traveling device capable of measuring a distance.

[0007]

[Function] By running the flaw detection sensor in the buried pipe, it is possible to detect defects such as corrosion thinning and through holes, or target points such as joints, and at the same time as detecting such defects,
By detecting the position of the transmission coil, that is, the flaw detection sensor by the position sensor on the ground, the position of the target location can be accurately measured as a two-dimensional position.

The position sensor can detect the position continuously while moving along with the flaw detection sensor, or can be predicted by the running distance of the flaw detection sensor when the target point is detected. It is also possible to move the position sensor near the position and detect the position of the flaw detection sensor described above.

[0009]

Embodiments of the present invention will now be described with reference to the drawings.
FIG. 1 illustrates the concept of the method of the present invention. Code 1
Is a buried pipe buried in the soil, and reference numeral 2 is a flaw detection sensor that travels in the buried pipe 1 to detect defects such as corrosion wall thinning and through holes or target points such as joints. The flaw detection sensor 2 has a transmission coil 3 and a reception coil 4 which are installed at a predetermined distance from each other, and travels in a buried pipe 1 by a traveling device (not shown) via a cable 5 which can be pushed and pulled back. It is configured to let. Further, this traveling device is provided with distance measuring means (not shown) such as a rotary encoder for measuring the payout and pullback distance of the cable 5.

FIG. 2 shows the structure and principle of flaw detection of the flaw detection sensor 2 of FIG. A plurality of receiving coils 4 are arranged in an annular shape, and the transmitting coil 3 is composed of a single coil. Reference numeral 6 is an oscillator that generates an AC signal for flaw detection, and this signal is supplied to the transmission coil 3 via the amplifier 7 and simultaneously input to the lock-in amplifier 8 as a reference signal. The received signal from the receiving coil 4 is input to the lock-in amplifier 8 together with the reference signal, the lock-in amplifier 8 obtains a phase difference from the reference signal, and the phase difference output is recorded in synchronization with the distance measuring means. The data is output to the total 9 and recording is performed corresponding to the distance of the flaw detection sensor 2.

All of the plurality of receiving coils 4 may be input to the lock-in amplifier 8 as independent channels, or the plurality of receiving coils 4 may be connected in series or in parallel for a small number of groups. It is also possible to configure a small number of channels and to input to the lock-in amplifier 8 for each channel. In the latter configuration,
This brings about an effect of reducing the number of channels in the lock-in amplifier 8 and the recorder 9.

In the above structure, a part of the electromagnetic wave 10 emitted from the transmitting coil 3 propagates to the receiving coil 4 through the pipe wall of the pipe 1. At this time, the propagation time changes if there is a thickness reduction 11 as shown in the figure, a defect such as a through hole, or a detection target portion such as a joint. This change in propagation time can be captured by the lock-in amplifier 8 as a change in the phase of the signal from the receiving coil 4 corresponding to the detection target location. Therefore,
The change in the phase of such a signal can be detected by the output of the lock-in amplifier 8, that is, the recording of the recorder 9 to detect the target portion and its contents.

Since the frequency of the electromagnetic wave used in the above inspection method, that is, the so-called remote field eddy current inspection method is as low as ~ Hz, this electromagnetic wave is pipe 1
Easily leaks to the outside. Therefore, by detecting the leaked electromagnetic wave on the ground by the receiving coil of the position sensor 12, the position of the transmitting coil 3, that is, the position of the flaw detection sensor 2 can be detected. The detection of the position of the transmission coil 3 is
This can be done by using a suitable position sensor 12 with a receiving coil, for example a piglometer.

[0015]

As described above, according to the present invention, the flaw detection sensor detects defects such as corrosion thinning and through holes or target points such as joints, and at the same time, transmits electromagnetic waves from the transmission coil, which is a component of the flaw detection sensor, to the ground. Since it is possible to detect a two-dimensional position by detecting with a position sensor in such a case, in the case of repairing a pipe part where such a defect is detected by excavation, useless excavation or This has the effect of not causing the inconvenience of erroneously recognizing another pipe that happened to be close to the drilled location.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of the method of the present invention.

FIG. 2 is an example diagram of a flaw detection sensor used in the method of the present invention.

FIG. 3 is a conceptual diagram showing an inconvenience that occurs when flaw detection and position detection are performed only by a flaw detection sensor.

[Explanation of symbols]

 1 buried pipe 2 flaw detection sensor 3 transmission coil 4 reception coil 5 cable 6 oscillator 7 amplifier 8 lock-in amplifier 9 recorder 10 electromagnetic wave 11 thinning

Claims (2)

[Claims] 1. A flaw detection sensor in which a transmission coil and a reception coil are separated from each other by a predetermined distance is run in an embedded pipe to detect a target location, and at the same time, an electromagnetic wave from the transmission coil is received by a position sensor on the ground. A method for inspecting a buried pipe, characterized in that the position of a flaw detection sensor is detected by a coil. 2. The method for inspecting a buried pipe according to claim 1, wherein the flaw detection sensor is configured to travel inside the buried pipe by a traveling device capable of measuring a distance.