JP2000275223A - Inspecting tool and its using method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inspecting tool adaptable to a relatively large-diameter underground pile buried in the ground and capable of detecting the corrosion occurring on its peripheral section relatively simply and to detect the corrosion of the underground pile in no contact. SOLUTION: This inspecting tool 20 is provided with a plurality of local coils 21 around a support tool shaft extending in the longitudinal direction, and each local coil has a coil shaft parallel with the support tool shaft. A first connecting circuit 230 connecting all local coils 21 in series and a second connecting circuit 240 connecting them individually are provided between two detection ends of the ground and an output terminal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of inspecting a steel pipe pile buried underground, and a support extending in a longitudinal direction used as a so-called detection coil in a remote field eddy current method or the like for such an inspection. The present invention relates to an inspection tool having a coil around an axis.

[0002]

2. Description of the Related Art In order to prevent corrosion of a steel pipe pile 31 used for a base portion of an LNG tank 30, as shown in FIG. Have been. At present, it is considered that the corrosion of the steel pipe pile 31 in the foundation portion has not progressed so much, so that the steel pipe pile 5 for cathodic protection is left buried without being energized. In recent years, a need has arisen to be able to check the degree of corrosion of the steel pipe pile 31 in the base part. However, since the steel pipe pile 31 in the base part of the LNG tank 30 is directly below the tank, the degree of direct corrosion must be checked. Measuring has heretofore been impossible. Therefore, it has been proposed to estimate the corrosion of the steel pipe pile 31 at the foundation by examining the corrosion state of the steel pipe pile 5 for anticorrosion, which is considered to be substantially the same as the embedding condition.

[0003]

As a method for examining the corrosion state of a steel pipe, there are an ultrasonic method, a remote field eddy current method, and the like. However, the ultrasonic method is problematic in that the inside of the steel pipe pile for electrical corrosion is covered with rust and algae because it is filled with rainwater and left for a long time, so the entire inside of the pile must be cleaned first. There is. Since the length (depth) of the steel pipe pile for cathodic protection was as long as about 26 m, it was practically impossible to clean the entire pile.

[0004] On the other hand, the remote field eddy current test attempts to detect defects such as corrosion based on the following principle. As shown in FIG. 4, when an alternating current is applied to the exciting coil 41 placed in the steel pipe pile 5, an electromagnetic field 42 is directly generated from the exciting coil 41. Since the steel pipe pile 5 is a conductor, an eddy current 43 flows through the pipe body 5 due to the direct electromagnetic field 42, thereby generating an electromagnetic field (referred to as an indirect electromagnetic field 44). If a defect 45 such as corrosion exists in the steel pipe pile 5, a change occurs in the eddy current 43 between the normal portion of the pipe and the defect existing portion. As a result, this effect also appears in the indirect electromagnetic field 44.
By detecting such a change in the indirect electromagnetic field 44 with the detection coil 46, the presence of corrosion (defect 45) can be known. In this remote field eddy current test, the excitation frequency of the excitation coil is reduced to about several tens of Hz to increase the penetration depth of the eddy current, and the interval between the excitation coil and the detection coil is increased to at least two to three times the tube diameter. By doing so, the indirect electromagnetic field can be efficiently detected without the influence of the direct electromagnetic field.

[0005] Such a remote field eddy current method,
Although the corrosion status of the pile can be investigated without contact, the characteristics are easily influenced by the shape of the detection coil. FIG. 5 shows a configuration of a detection coil for inspecting a conventional underground pipe (for example, a pipe for gas supply) by a remote field eddy current method.
(A) and (b). FIG. 5A shows a configuration in which a single coil 50 is provided along the inner peripheral portion of the inspection target. With this configuration, the corrosion at any part of the pile periphery can be detected by one detection as a whole. FIG. 5 (b) includes a plurality of local coils 51 having an axis along the axial direction of the pile to be inspected. In each local coil 51, the coil shape is illustrated. The local coil 51 is provided with a horseshoe-shaped ferrite core 52 as described above. Here, the output of each local coil 51 was configured to be output individually. In this configuration, the corrosion at any part of the pile periphery is
Partial detection with relatively high sensitivity is possible. In addition, in a situation where the entire part is uniformly reduced in thickness and a part of the part is further corroded, the conventional coil can detect only one side corrosion.

Accordingly, an object of the present invention is to provide a detection method which can be applied to a relatively large diameter underground pile buried in the ground, and which can detect corrosion occurring on the periphery thereof relatively easily. It is an object of the present invention to obtain a tool and to obtain a technology capable of detecting corrosion of an underground pile in a non-contact manner.

[0007]

SUMMARY OF THE INVENTION An inspection tool for use in a remote field eddy current test apparatus having a longitudinally extending support shaft and a coil around the support shaft, which can achieve the above object. As described in claim 1, the characteristic configuration of (1) is that an entire detection coil having a main detection area for the whole around the support axis, and a main detection coil for a part around the support axis. And a local detection coil having a detection area. In the inspection tool having such a configuration, the average thinning occurring in the steel pipe pile or the like to be inspected can be detected by the entire detecting coil, and the local thinning coil detects the local thinning. can do.

As described above, in the structure including the two types of coils, a coil having the support shaft as a central axis is employed as the overall detection coil, and As the detection coil, it is preferable to employ a plurality of local coils that are arranged in the circumferential direction around the support shaft and have independent output ends. In this configuration, a coil that can achieve a different type of detection purpose is provided with a relatively simple configuration, and the whole and local portions can be suitably detected.

In the structure having two types of coils, all the local coils arranged in the circumferential direction around the axis of the support as the entire detection coil may be used. Adopt a configuration that is connected in parallel or in series, and use, as the local detection coil, a plurality of local coils that are arranged in the circumferential direction around the support tool axis and each have an independent output end. Is preferred. As the local detection coil, a conventional local coil can be used individually, an output can be obtained from each output terminal, and local thinning can be detected. On the other hand, the entire detection coil has a structure in which a plurality of local coils provided around the support shaft are connected in series or in parallel to obtain an output from a pair of output terminals. By doing so, even in the overall detection, it is possible to perform detection with high sensitivity for each local part, so that more accurate detection can be performed.

As for the individual local coils, each of the plurality of local coils has an outer diameter on which a wire forming the local coil is arranged in an arc shape. A side circular arc portion, a radially extending portion extending in a radial direction around the axis of the support tool from each circular arc end of the outer diameter side circular arc portion, and an inner diameter side end portion of the pair of radially extending portions are connected. It is preferable to be configured with an inner diameter side portion. This local coil is configured such that the wire passes through the outer diameter side arc portion, one radial extension portion, the inner diameter side portion, the other radial portion, continues to the next outer diameter side arc portion, and overlaps in the axial direction. It is said. The local coil of this structure has a structure as shown in FIG. 1B when viewed in the axial direction, but the outer-diameter-side arc portion is densely distributed along the inner surface of the detection target and is adjacent in the circumferential direction. Since the radial portions of the local coils disposed close to each other in the circumferential direction, when used as a detection coil or the like, a high S / N ratio can be detected.

It is preferable that the number of the plurality of local coils equally disposed around the periphery of the support shaft be 5 to 30. If it is smaller than 5, the effect of dividing the circumferential direction to enable detection tends to be low, and if it is larger than 30, the number of channels is too large.

The inspection tool described so far is preferably used as a detection coil in a remote field eddy current test. By providing this inspection tool as a detection coil, a remote field eddy current test capable of performing an inspection with a high S / N ratio can be performed. A device can be obtained.

[0013] Then, the inspection tool described so far,
By using it as a detection coil and performing a remote field eddy current test, it is possible to inspect the corrosion state of a steel pipe pile buried underground.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the configuration of a remote field eddy current test apparatus 1 of the present application will be described. This device configuration is not much different from the conventional type, but the detection coil 2 is different from the conventional type.

As shown in FIG. 1A, the test apparatus 1
A coil support 6 for supporting the coils 2 and 4 in the steel pipe pile 5 to be inspected so as to be movable in the axial direction thereof is provided. It is provided with. The two coils 2 and 4 are provided at a certain distance in the axial direction of the support, and are provided at a distance that the direct electromagnetic field of the excitation coil 4 is not directly detected by the detection coil 2. The apparatus 1 includes a signal generator 7 for outputting a signal for detection timing setting / startup, and an AC for excitation supplied to the excitation coil 4 in synchronization with the signal generated by the signal generator 7. And an exciting coil 4 for directly forming an electromagnetic field by the alternating current supplied from the power amplifier 8. On the other hand, the detection signal detected by the detection coil 2 according to the principle described above is transmitted to the signal generator 7.
A lock-in amplifier 3 for receiving and amplifying the signal in synchronization with the signal generated by the
To extract a phase signal. Then, the signal obtained by the amplifier 3 is
It comprises an output device 9 for receiving as an amplitude signal and a phase signal.

Hereinafter, the configuration of the detector 20 used as the detection coil 2 in the remote field eddy current test apparatus 1 and which is the subject of the present invention will be described with reference to FIGS. FIG. 2 shows a circuit from the detection coil 2 to the lock-in amplifier 3 in FIG. In the present application, there are a first embodiment and a second embodiment.

First Embodiment An inspection tool 20 used as the detection coil 2 in the present application
As shown in FIG. 1 (b), a support tool 6 extending in the longitudinal direction is provided, and around the support tool axis Z1, an entire detection coil 28 having the support tool axis Z1 as a central axis, A plurality of local detection coils are provided around the component axis Z1 in the circumferential direction, and each includes a local coil 21 having an independent output end. Here, each of the plurality of local coils 21 has a coil axis z1 parallel to the support tool axis Z1 (which corresponds to the axial direction of the steel pipe pile 5 to be inspected in the use state). The entire detection coil 28 and the local coil 21 are configured to have independent output terminals. These output terminals are used for output to the lock-in amplifier 3.

The configuration of each of the local coils 21 will be described in detail. Each of the plurality of local coils 21 has an outer diameter at which a wire forming the local coil 21 is disposed in an arc shape (convex on the outer diameter side). Side arc portion 211, radial extension portions 21m, 21m extending in the radial direction around the support tool axis from respective arc ends of the outer diameter side arc portion 211, and a pair of radial extension portions 21m, 21m. And an inner-diameter side portion 21n connecting the inner-diameter-side end portion. In the illustrated example, the inner ends of the radially extending portions 21m are connected linearly by inner diameter sides 21n. That is, these local coils 21 are provided with a configuration along the inner surface of the tube at the outer peripheral portion on the outer diameter side, and are relatively flat in cross-sectional view, and only the arc portion 211 has an arc-shaped rectangular shape. I have. Furthermore, these local coils 21 have the same shape as each other, and are arranged so as to be adjacent to each other with almost no gap between adjacent radially extending portions 21m.
By adopting such a configuration, the peripheral portion of the support 20 is divided equally by the plurality of local coils 21. In the example shown in FIG. 1B, the number of the local coils 21 is twelve.

Second Embodiment As shown in FIG. 2, the detection coil 20 inspection tool 20 of this example includes a support tool axis Z1 extending in the longitudinal direction.
A coil support 6 for supporting a plurality of local coils 21 disposed around the support shaft is provided. Then, each of the plurality of local coils 21 is connected to the support tool axis Z1 (this is the steel pipe pile 5 to be inspected in the use state).
(Coincides in the axial direction of the coil) z1. The inspection tool 20 includes a connection tool 22. The first connection circuit 230 provided in the connection tool 20 connects all the plurality of local coils 21 in series between two detection terminals of the ground and the output terminal. It is configured to be connectable. That is, the wire end 21a from each local coil 21
Are individually connected to the input section 22a of the connector 22, and when the first connection circuit 230 is employed, the entire local coil 21 is connected between the two detection terminals of the ground and the output terminal.
Is a circuit configuration connected in series. The detection signal detected between the ground and the output terminal is sent to the lock-in amplifier 3 and the processing circuit 25 for phase processing provided in the lock-in amplifier 3, and is processed into an amplitude output and a phase output.
The connection tool 22 further includes a second connection circuit 240. The second connection circuit 240 separates each of the plurality of local coils 21 between two detection terminals of the ground and the output terminal. It is configured to be connected to two detection terminals of the ground and the output terminal. That is,
The wire end 21a from each local coil 21 is connected to the input section 22a of the connector 22, and when the second connection circuit 240 is connected, the entire local coil 21 is connected between the two detection ends of the ground and the output terminal. Are individually connected to the circuit. Switching of each local coil is naturally necessary in this case. The detection signal detected between the ground and the output terminal in this way is sent to a predetermined processing circuit 25, where it is processed into an amplitude output and a phase output.

Each local coil 21 has a structure similar to that of the first embodiment described above. When the description is repeated, each of the plurality of local coils 21 includes an outer-diameter-side arc portion 211 on which a wire forming the local coil 21 is disposed in an arc shape, and a respective arc end portion of the outer-diameter-side arc portion 211. And a radially extending portion 21m extending in the radial direction about the axis of the support member, and an inner diameter side portion 21n connecting the inner diameter side ends of the pair of radially extending portions 21m. The radially extending portions 21m are connected linearly between the inner diameter side ends. That is, these local coils 21 are provided with a configuration along the inner surface of the tube at the outer peripheral portion on the outer diameter side, and are relatively flat in cross-sectional view, and only the arc portion 211 has an arc-shaped rectangular shape. I have. Furthermore, these local coils 21 have the same shape as each other, and are arranged so as to be adjacent to each other with almost no gap between adjacent radially extending portions 21m. Therefore, by adopting such a configuration, the peripheral portion of the support 20 is divided equally by the plurality of local coils 21. In the example shown in FIG. 2, the number of the local coils 21 is twelve.

In the example shown in FIGS. 1B and 2, the thickness H of the local coil 21 is about 2.4 cm for the steel pipe pile 5 having an inner diameter of 30.5 cm. Further, the wire diameter (winding diameter is 0.1 mm) of each local coil 21 is set to be about 2,500 turns. The distance between the excitation coil and the detection coil is 750 mm.

The above is the characteristic configuration of the remote field eddy current test device 1 (especially the detection coil 2) in the present application. Hereinafter, a description will be given of an operation procedure when a corrosion inspection operation is performed using this device. . 1 Confirmation of Average Thinning In the aforementioned inspection tool 20, in the first embodiment, the entire detection coil is used, and in the second embodiment, the connection state is changed to the first connection state (the first connection circuit). In the state of connection at 230), the support 6 is moved in the axial direction of the steel pipe pile, and an inspection is performed. By doing so, the excitation frequency 3
Under the conditions (frequency, etc.) of 5 Hz and an excitation voltage of 40 Vp-p,
Corrosion thinning portions (about 0.1 cm) occurring in the steel pipe pile 5 having a wall thickness of 0.69 cm and an inner diameter of 30.5 cm were successfully detected. The information required in this case is the average wall thinning rate of the steel pipe pile 5 in the circumferential direction. In the remote field eddy current method, the disturbance of the magnetic field due to defects is large near the inner surface of the pile. You can ask. Also, if you connect like this,
Since the number of measurement channels can be reduced, the present invention is also effective from the viewpoint of saving device cost and measurement labor. 2 Confirmation of Abnormal Part In the above-described inspection tool 20, the local detection coil is used in the first embodiment, and the connection state is changed to the second connection state (the second connection circuit 240) in the second embodiment. As a result, the support tool 6 is moved in the axial direction of the steel pipe pile 5 in the vicinity of the portion where the thinning is estimated to be large in the above-described inspection state, and the output from each local coil is individually obtained. Perform the inspection. By doing so, it is possible to confirm even the position of the corroded portion locally occurring in the circumferential direction. The detection conditions are almost the same as in the case of 1. 3 Results According to the method of the present invention, the average wall thinning rate in the circumferential direction of the steel pipe pile for corrosion protection can be easily and highly sensitively measured up to the position in the circumferential direction.

[Alternative Embodiment] (A) In the above-described embodiment, an example has been described in which a plurality of local coils are connected in series or in parallel as a whole and are connected in series when handled as an entire detection coil. Alternatively, a plurality of local coils may be connected in parallel as a whole. (B) Further, in the above-described embodiment, the connection is switched between the first connection circuit and the second connection circuit by using the connection tool. It is not necessary to provide the second connection circuit for the purpose only, and it is also possible to simply connect the respective connection ends of the local coils in series or in parallel as a whole to obtain a detection output in the connection completed state. Good. This corresponds to the first embodiment. (C) In the above embodiment, the number of local coils is set to 12, but it may be set to about 6 in consideration of reduction in the number of channels.

[Brief description of the drawings]

FIG. 1 is a diagram showing a use state of a remote field eddy current test device.

FIG. 2 is an explanatory diagram showing a connection relationship between a detailed configuration of an inspection tool and a lock-in amplifier.

FIG. 3 is an explanatory view showing a buried state of a steel pipe pile near a tank.

FIG. 4 is a diagram illustrating the principle of a remote field eddy current method.

FIG. 5 is a diagram showing a configuration of a conventional detector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Eddy current test apparatus 2 Detector coil 3 Lock-in amplifier 4 Excitation coil 5 Steel pipe pile 6 Coil support tool 7 Signal generator 8 Power amplifier 9 Output device 21 Local coil 21l Outside diameter side arc part 21m Radial extension part 21n Inside diameter side part 22 Connector 23 First Connection Circuit 24 Second Connection Circuit 25 Processing Circuit

Claims (7)

[Claims] 1. An inspection tool for use in a remote field eddy current test device, comprising a coil around a support axis extending in a longitudinal direction, wherein a main detection is performed on the whole of the support axis. An inspection tool comprising: an entire detection coil having an area; and a local detection coil having a main detection area with respect to a part around the support tool axis. 2. The whole detection coil is a coil having the support shaft as a center axis, and the local detection coil is disposed in a plurality of positions in the circumferential direction around the support shaft. The inspection tool according to claim 1, wherein the inspection tool is a local coil. 3. The local detection coil, wherein the entire detection coil is configured by connecting a plurality of local coils arranged circumferentially around the support axis in parallel or in series between two detection ends. The inspection tool according to claim 1, wherein a plurality of local coils are provided in the circumferential direction around the support tool axis, and each of the local coils has an independent output end. 4. An outer diameter side arc portion in which the local coil has a local coil axis parallel to the support member axis, and a wire forming the local coil is arranged in an arc shape, and the outer diameter side arc portion A radially extending portion extending in a radial direction around the axis of the support tool from each of the arc ends, and an inner diameter side portion connecting the inner diameter side ends of the pair of radially extending portions. The inspection tool according to 2 or 3. 5. The method according to claim 1, wherein the number of said plurality of local coils equally distributed around the periphery of the support shaft is from 5 to 30.
The inspection tool according to 2, 3, or 4. 6. A remote field eddy current test apparatus comprising the inspection tool according to claim 1, as a detection coil. 7. An inspection for inspecting a thinned portion of corrosion in a steel pipe pile by a remote field eddy current method using the inspection tool according to claim 1, 2, 3, 4, or 5 as a detection coil. Method.