JPH06103291B2 - Pipe inspection device by remote field eddy current method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a pipe by a remote field eddy current method for inspecting the corrosion state of the outer peripheral surface of a pipe body without digging underground pipes such as gas pipes. Body inspection device

(Prior Art) Conventionally, for example, among gas pipes, a small-diameter steel pipe with a diameter of 2 inches or 3 inches buried in the ground is generally used as a branch pipe, and the total length of the whole country reaches tens of thousands of kilometers. . Of these, the branch pipes laid after the 1970s are plastic lining pipes, etc., so there is no concern about corrosion, but the branch pipes laid before that are coated with asphalt jute, so This means that the anticorrosion effect due to the coating covering deteriorates over time, and the outer peripheral surface of the branch pipe corrodes.

Conventionally, as the outer peripheral surface inspection means, there has been a tubular body inspection device by a remote field eddy current method using a probe 51 as shown in FIG. According to this device, the transmission coil 52
7 and the receiving coil 53, each of which is provided at a predetermined distance of about twice the diameter of the pipe to be inspected, is inserted into the inner diameter of the pipe 54 to be inspected, and the principle of inspection shown in FIG. When a magnetic flux is generated from the transmitting coil 52 by passing an alternating current of a predetermined frequency of about 45 Hz to the transmitting coil 52 as shown in Fig. 5, a direct magnetic field 55 is formed by this magnetic flux, and the tubular body 54 is formed by the formed direct magnetic field 55. Since an eddy current 56 flows in the tube 54, the eddy current 56 forms an indirect magnetic field 57 in the tube 54, while
The direct magnetic field 55 due to the magnetic flux from 52 is canceled by the indirect magnetic field 57 generated in the tube body 54, and the influence of the direct magnetic field 55 is almost eliminated at the position of the receiving coil 53.
Focuses on the fact that only the indirect magnetic field 57 can be detected. If there is a scratch 58 such as corrosion on the outer peripheral surface of the pipe body 54 to be inspected, the eddy current 56 changes, so that the receiving coil
The indirect magnetic field 57 detected by 53 changes, and the alternating electrical signal output from the receiving coil 53 is output as an electrical signal corresponding to the scratch 58, but generally the outer peripheral surface of the pipe body 54 to be inspected is corroded. If there is a scratch 58, the phase of the electric signal output from the receiving coil 53 advances, so that the phase of the alternating current of a predetermined frequency supplied to the transmitting coil 52 and the phase of the electric signal output from the receiving coil 53. It was possible to inspect the size of the scratch 58 on the outer peripheral surface of the pipe body 54 to be inspected by obtaining the difference.

(Problems to be Solved by the Invention) Generally, the branch pipe of the above-described gas conduit is shown in FIGS.
Corrosion of the branch pipe is connected by a joint 61 as shown in the figure, and the coating applied to the joint portion at the time of burying is inferior in corrosion resistance compared to the central portion of the pipe body, etc. There is a tendency that the progress is fast in the adjacent portion.
However, in the case of the conventional pipe inspection apparatus by the remote field eddy current method using the probe 51 having one transmitting coil 52 and one receiving coil 53, as shown in FIG. Since the joint 61 influences the propagation of the eddy current 56 at the positions sandwiching the
There is a problem that the indirect magnetic field 57 detected by the receiving coil 53 becomes unstable and it becomes impossible to accurately inspect the outer peripheral surface shape near the joint 61.

Therefore, in the present invention, two receiving coils are arranged around the transmitting coil, or a probe in which two transmitting coils are arranged around the receiving coil is used, and one of the two receiving coils is provided, or The technical problem to be solved is to enable accurate inspection of the outer peripheral surface shape of the pipe body near the joint by switching and selecting one of the two transmission coils corresponding to the position of the joint. Is.

(Means for Solving the Problems) A first technical means for solving the above problems is to generate a magnetic field directly by passing an alternating current of a predetermined frequency to a transmitting coil inserted in a metal tube to directly generate a magnetic field. An eddy current is caused to flow through the eddy current to generate an indirect magnetic field due to the eddy current, and the indirect magnetic field due to the eddy current is detected by the receiving coil arranged at a predetermined distance from the transmitting coil, and the detected indirect magnetic field is detected. A tube by the remote field eddy current method for flaw detection on the outer surface of the tube body based on the difference between the phase of the electric signal and the phase of the alternating current applied to the transmission coil by outputting the electric signal from the receiving coil. The body inspection device, while the transmission coil is arranged in the center,
A flexible probe in which the receiving coil is arranged at a symmetrical position spaced apart from the transmitting coil by a predetermined distance coaxially with the transmitting coil, and the same two probes electrically connected to the two receiving coils. One of the receiving coils, a changeover switch for electrically selecting corresponding to the position of the connection joint of the pipe to be inspected, an alternating current for supplying an alternating current of the predetermined frequency to the transmitting coil, and the probe The electric signal from the receiving coil that detects the indirect magnetic field corresponding to the eddy current in a state where the alternating current is being applied to the transmitting coil in the process of being inserted into the inner diameter portion of the pipe to be inspected and moved. Input, the phase of the alternating current supplied to the transmission coil and the phase of the electrical signal are compared to calculate a phase difference, and a table corresponding to the outer surface shape of the tubular body based on the phase difference. And the outer surface shape recognition means for outputting a signal, and to a configuration in which a display means for displaying the outer contour of the enter the pipe body said display signal output from the outer surface shape recognition means.

A second technical means is a pipe inspection apparatus by a remote field eddy current method, in which the receiving coil is arranged in the center and at a symmetrical position coaxially with the receiving coil and separated from the receiving coil by a predetermined distance. A flexible probe in which the transmitting coil is arranged, and one of the two transmitting coils electrically connected to the two transmitting coils, corresponding to the position of the connection joint of the pipe to be inspected. A changeover switch to be electrically selected, an alternating current power source for supplying an alternating current of the predetermined frequency to the transmission coil through the changeover switch, and a process in which the probe is inserted into the inner diameter portion of the tube to be inspected and moved. While the AC current is being supplied to the transmission coil, the electric signal from the reception coil that has detected the indirect magnetic field corresponding to the eddy current is input, and the transmission coil is supplied with electricity. After comparing the phase of the alternating current with the phase of the electric signal to calculate the phase difference, the outer surface shape recognizing means for outputting a display signal corresponding to the outer surface shape of the tubular body based on the phase difference, The display signal output from the outer surface shape recognizing means is input to display means for displaying the outer surface shape of the tubular body.

(Operation) According to the tubular body inspection apparatus by the remote field eddy current method configured as described above, one of the two receiving coils mounted around the transmitting coil in the probe inserted into the pipe to be inspected, or the receiving coil. One of the two transmission coils mounted centering on the is connected to the position of the joint which is a connecting member of the pipe to be inspected, that is, a transmission coil to which an alternating current of a predetermined frequency is applied, and a vortex. After selecting by the changeover switch so that the receiving coil for detecting the indirect magnetic field generated by the current is not located in the state of sandwiching the joint, the alternating current of the predetermined frequency is transmitted from the alternating current power source in the process of moving the probe. When the coil is energized, a magnetic field is directly generated by the magnetic flux of the transmission coil, and an eddy current flows through the tube body to be inspected by the direct magnetic field. The receiving coil, which is arranged at a predetermined distance from the transmitting coil, detects the indirect magnetic field generated by the eddy current and outputs an electric signal corresponding to this indirect magnetic field. The external surface shape recognizing means, which receives the electric signal, compares the phase of the alternating current supplied from the alternating-current power source to the transmitting coil with the phase of the electric signal output from the receiving coil to obtain the difference, The outer surface shape of the pipe to be inspected is recognized based on the phase difference, and a display signal corresponding to the recognized outer surface shape is output to the display means.
Since the display means that has input the display signal displays the outer surface shape of the pipe to be inspected based on this display signal, it is necessary to immediately inspect whether the outer surface of the pipe to be inspected has a flaw such as corrosion. You can

(Example) Next, the Example of this invention is described, referring drawings.

FIG. 1 is a partial sectional front view showing a configuration of a probe 1 inserted into an inner diameter portion of a pipe to be inspected such as a branch pipe of a gas conduit. As shown in the figure, the probe 1 has a transmitter coil 2 at the center of the drawing, and receiver coils 3A and 3B are provided on the left and right of the transmitter coil 2, respectively. In the probe 1, the transmitting coil 2 and the receiving coils 3A and 3B are coaxially arranged on the flexible elastic shaft 4, and the straight pipe to be inspected is bent at a right angle from the original. The probe 1 can also be inserted through the inspection tube body. A plurality of aligning wires 5 are attached to the outer peripheral portion of the transmission coil 2 so as to be in contact with the inner diameter surface of the pipe to be inspected and to align the axis of the transmission coil 2 with the center axis of the inner diameter portion of the pipe to be inspected. ing. On the other hand, a plurality of resin beams 6 that hold the coils 3A and 3B and are in contact with the inner diameter surface of the pipe to be inspected are attached to the outer peripheral portions of the receiving coils 3A and 3B. The aligning wire 5 and the beam 6 can be slid in the axial direction of the inner diameter portion of the pipe to be inspected.

The elastic shaft 4 is formed in a flexible tube shape so as to have a bendability of 90 degrees or more as described above,
The transmitting coil 2 and the receiving coil are provided inside the elastic shaft 4.
A lead wire (not shown) connected to each of 3A and 3B is inserted, and the lead wire is connected to an electric circuit described later.

The transmission coil 2 is wound around a bobbin 8 with enameled wire or the like about 600 times, and its winding end is connected to the lead wire. On the other hand, the receiving coils 3A and 3B
In this example, about 12 small receiving coils 10 each having a thin enamel wire wound, for example, 500 times are arranged on a concentric circle on a relatively small bobbin 9 as shown in FIG. And a small receiver coil
10 Each winding end is connected to the lead wire.

The outer circumferences of the transmitting coil 2 and the receiving coils 3A and 3B configured as described above are protected by synthetic resin or other protective cases 11 and 12.
Is covered with.

FIG. 3 is a block diagram of an electric circuit to which the transmitting coil 2 and the small receiving coils 10 of the receiving coils 3A and 3B are electrically connected.

As shown in FIG. 3, the transmission coil 2 of the probe 1 is connected to the output amplification circuit 21, and an alternating current of, for example, 45 HZ is supplied from the output amplification circuit 21 to the transmission coil 2 at a predetermined output. An AC signal oscillation circuit 22 is provided to oscillate the 45 Hz AC signal, and the oscillation circuit 22 is connected to the output amplification circuit 21.

On the other hand, two receiving coils are provided so that the transmitting coil 2 and the receiving coil 3A or 3B are not in a state of sandwiching the joint 61 of the pipe body 54 to be inspected as shown in FIG.
A changeover switch 23 for selecting one of 3A and 3B is provided, and when the receiving coil 3A is selected, the indirect magnetic field generated by the eddy current 56 shown in FIG. The electric signal from the receiving coil 3A upon detection is input to the input amplifier circuit 24 connected to the changeover switch 23. The input amplification circuit 24, to which the above electric signal is input, amplifies the input electric signal at a predetermined amplification factor and then outputs it as a received AC signal to the phase detection circuit 25.

The phase detection circuit 25 electrically connected to the input amplification circuit 24 and the AC signal oscillation circuit 22 is an AC signal transmission circuit 22.
The phase of the alternating current signal oscillated by and the phase of the received alternating current signal output from the input amplifier circuit 24 are detected, and an electric signal corresponding to each detected phase is output to the phase difference calculation circuit 26. The phase difference calculation circuit 26, when the electric signal corresponding to the above two types of detected phases is input, calculates the phase difference based on the input electric signal, and then outputs the signal corresponding to this phase difference to the outer surface shape recognition circuit 27. Output. External shape recognition circuit 27
Receives the signal corresponding to the phase difference, recognizes the shape of the outer peripheral surface of the pipe body to be inspected based on this signal, and outputs the chart signal corresponding to the shape. The chart recorder 28 connected to the outer surface shape recognition circuit 27 records and displays the shape of the outer peripheral surface of the pipe to be inspected by inputting the chart signal.

When inspecting a flaw on the outer peripheral surface of the pipe to be inspected by the pipe inspection device by the remote field eddy current method configured as described above, as shown in FIG. 10 (A), the transmitter coil 2 and the receiver coils 3A, 3B are used. Is arranged, the receiving coil 3B is selected by the changeover switch 23, and when the transmitting coil 2 and the receiving coils 3A and 3B are arranged as shown in FIG. 10B, the receiving coil 3A is selected and then the transmitting coil is selected. The coil 2 is oscillated by the AC signal oscillation circuit 22 and the 45 Hz AC current amplified by the output amplification circuit 21 is supplied. As a result, the seventh
As shown in the figure, an eddy current 56 flows in the tube 54 to be inspected by the direct magnetic field 55 generated by the magnetic flux generated in the transmission coil 2, and an indirect magnetic field 57 is generated by this eddy current 56. This indirect magnetic field
Since an induced voltage is induced in the preselected receiving coil, for example, 3A by 57, the induced voltage is input from the receiving coil 3A to the input amplification circuit 24 as an electric signal. The input amplifier circuit 24 amplifies the input electric signal and outputs it to the phase detection circuit 25 as a received AC signal. The phase detection circuit 25 detects the phase of the received AC signal and the phase of the AC signal oscillated by the AC signal oscillation circuit 22, and outputs an electric signal corresponding to each phase to the phase difference calculation circuit 26. The phase difference calculation circuit 26 calculates the difference between the two types of phases, and outputs a signal based on this phase difference to the outer surface shape recognition circuit 27. The outer surface shape recognition circuit 27, which has received the above signal, outputs a chart signal corresponding to the outer surface shape of the inspected pipe body 54 to the chart recorder 28, so that the outer peripheral surface shape of the inspected pipe body 54 is recorded in the chart recorder 28. , For example, when there is a scratch on the outer peripheral surface, the corrugated 29 has a convex shape 30 as shown in FIG.
Is displayed in. For this reason, the inspector uses the chart recorder 28
It is possible to find a flaw on the outer peripheral surface of the pipe body 54 to be inspected by observing the shape of the outer peripheral surface of the pipe body 54 to be inspected displayed on.

As shown in FIG. 1, the probe 1 has a transmitter coil 2
Although the receiving coils 3A and 3B are arranged at symmetrical positions with respect to the center of the drawing, as another probe example, as shown in FIG. 4, the transmitting coils 2A and 2B are arranged at symmetrical positions with respect to the receiving coil 3. You may arrange. In that case, as shown in FIG. 5, the changeover switch 23A for selecting one of the two transmission coils 2A and 2B is connected to each of the transmission coils 2A and 2B. When the transmitting coils 2A, 2B and the receiving coil 3 are arranged at the positions shown in FIG. 11 (A), the transmitting coil 2A is selected by the changeover switch 23A, and as shown in FIG. 11 (B). When the transmission coils 2A and 2B and the reception coil 3 are arranged at the positions, the transmission coil 2B is selected by the changeover switch 23A. The changeover switch 23A is connected to the output amplifier circuit 21. On the other hand, the receiving coil 3 is directly connected to the input amplifier circuit 24. Then, in addition to the output amplification circuit 21 and the input amplification circuit 24 shown in FIG. 5, the AC signal oscillation circuit 22, the phase detection circuit 25, the phase difference calculation circuit 26, the outer surface shape recognition circuit 27, and the chart recorder 28 are respectively configured. ,
The operation is the same as the configuration and operation of that shown in FIG.

As is apparent from the above embodiment, the probe 1 is provided with the receiving coils 3A and 3B at symmetrical positions with respect to the transmitting coil 2, or the probe 1A is provided with the transmitting coils 2A and 2B at symmetrical positions with respect to the receiving coil 3. Equipped with a changeover switch
Since it is configured to be switchable and selectable by 23, 23A, the transmitter coil 2 or 2A, 2B and the receiver coil 3, which are selected when inspecting the pipe body with the joint 61 sandwiched as shown in FIG. Alternatively, 3A and 3B are not positioned, and the tubular body can be inspected up to the outer peripheral surface shape near the joint 61.

(Effects of the Invention) As described above, according to the present invention, the receiving coil is arranged at the symmetrical position with respect to the transmitting coil, or the probe having the transmitting coil at the symmetrical position with respect to the receiving coil is formed. Since the transmitting coil and the receiving coil do not sandwich the joint of the pipe to be inspected, either the receiving coil or the transmitting coil can be selected by the changeover switch. It becomes possible to find a flaw on the outer peripheral surface, and it is possible to prevent gas leakage due to corrosion of a branch pipe or the like.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional front view illustrating the configuration of a probe according to an embodiment of the present invention, FIG. 2 is a front view of a small receiving coil that constitutes a receiving coil, FIG. 3 is an electric circuit diagram, and FIG. FIG. 5 is a partial cross-sectional front view illustrating the configuration of a probe according to another embodiment.
Fig. 6 is an electric circuit diagram when the probe of Fig. 4 is used.
FIG. 7 is an inspection state diagram when a probe is inserted into a pipe to be inspected to inspect the outer peripheral surface of the pipe to be inspected, FIG. 7 is an explanatory diagram of an inspection principle, FIG. 8 is an explanatory diagram of conventional problems, FIG. 9 is a diagram showing an example of a flaw display on the pipe to be inspected by the chart recorder. 10 (A) and 10 (B) are layout diagrams of the probe 1 having two receiving coils with respect to the pipe body to be inspected, FIG. 11 (A),
FIG. 11 (B) is a layout view of the probe 1A having two transmitting coils with respect to the pipe body to be inspected. 1,1A …… Probe 2,2A, 2B …… Transmission coil 3,3A, 3B …… Reception coil 21 …… Output amplifier circuit 22 …… AC signal oscillation circuit 23,23A …… Changeover switch 24 …… Input amplifier circuit 25 …… Phase detection circuit 26 …… Phase difference calculation circuit 27 …… Outer surface shape recognition circuit 28 …… Chart recorder

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuji Hosohara 4-1225 Tsukagoshi, Warabi-shi, Saitama No. 713 Touken New Heights (72) Inventor Takashi Kikuta 5-1, Hirano-cho, Higashi-ku, Osaka, Osaka In Osaka Gas Co., Ltd. (72) Inventor Takao Yamagishi 5-1, Hirano-cho, Higashi-ku, Osaka-shi, Osaka Osaka Gas Co., Ltd. (72) Inventor Yu Yamada 19-18 Sakurada-cho, Atsuta-ku, Nagoya-shi, Aichi Prefecture Toho Gas Co., Ltd.

Claims (2)

[Claims] 1. A magnetic field is directly generated by passing an alternating current of a predetermined frequency through a transmission coil inserted in a metal tube to cause an eddy current to flow in a tube wall, and an indirect magnetic field is generated by the eddy current. By detecting the indirect magnetic field due to the eddy current with a receiving coil arranged at a predetermined distance from the transmitting coil and outputting an electric signal corresponding to the detected indirect magnetic field from the receiving coil, A pipe body inspection apparatus for detecting an outer surface of a pipe body based on a difference between a phase and a phase of an alternating current applied to the transmission coil, wherein the transmission coil is arranged in the center while the transmission coil is arranged. And a bendable probe in which the receiving coils are arranged at symmetrical positions spaced apart from the transmitting coil by a predetermined distance, and the two receiving coils electrically connected to the two receiving coils. A changeover switch for electrically selecting one of the signal coils corresponding to the position of the connection joint of the pipe to be inspected, an AC power supply for supplying an alternating current of the predetermined frequency to the transmission coil, and the probe. The electric signal from the receiving coil that detects the indirect magnetic field corresponding to the eddy current in a state where the alternating current is being applied to the transmitting coil in the process of being inserted into the inner diameter portion of the pipe to be inspected and moved. Is input, and the phase difference is calculated by comparing the phase of the alternating current and the phase of the electric signal applied to the transmission coil, and a display corresponding to the outer surface shape of the tubular body is based on the phase difference. A remote field comprising: an outer surface shape recognizing unit that outputs a signal; and a display unit that inputs the display signal output from the outer surface shape recognizing unit and displays the outer surface shape of the tubular body. Tube inspection apparatus according to the flow method. 2. A magnetic field is directly generated by passing an alternating current of a predetermined frequency through a transmission coil inserted in a metal tube to cause an eddy current to flow in the tube wall, and an indirect magnetic field is generated by the eddy current. By detecting the indirect magnetic field due to the eddy current with a receiving coil arranged at a predetermined distance from the transmitting coil and outputting an electric signal corresponding to the detected indirect magnetic field from the receiving coil, What is claimed is: 1. A pipe body inspection apparatus for detecting an outer surface of a pipe body based on a difference between a phase and a phase of an alternating current supplied to the transmission coil, wherein the reception coil is arranged in the center while the reception coil is arranged. And a flexible probe in which the transmitting coils are respectively arranged at symmetrical positions spaced apart from the receiving coil by a predetermined distance, and two probes that are electrically connected to the two transmitting coils. A changeover switch for electrically selecting one of the receiving coils corresponding to the position of the connection joint of the pipe to be inspected, and an AC power supply for supplying an alternating current of the predetermined frequency to the transmitting coil through the changeover switch. In the process in which the probe is inserted into the inner diameter portion of the tube to be inspected and moved, the inductive magnetic field corresponding to the eddy current is detected from the receiving coil in a state where the alternating current is being applied to the transmitting coil. The phase difference is calculated by inputting the electric signal and comparing the phase of the alternating current and the phase of the electric signal supplied to the transmitting coil, and based on the phase difference, the external shape of the tubular body is determined. An external surface shape recognizing unit that outputs a corresponding display signal, and a display unit that inputs the display signal output from the external surface shape recognizing unit and displays the external surface shape of the tubular body. Tube inspection apparatus according to over preparative field eddy current method.