JP3130129B2 - Eddy current flaw detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an eddy current flaw detector which is one of non-destructive inspection devices.

[0002]

2. Description of the Related Art For example, there is an eddy current flaw detector for performing a maintenance inspection of a heat exchanger tube. FIG. 6 is a schematic structural explanatory view of an eddy current flaw detection device for inspecting a plate-like inspection object 12A. In FIG. 6, a coil 11 is wound around a core 10A, and a current is supplied to the coil 11 from an AC power supply 14. Then, this coil 11 is
When approaching A, an eddy current 13 is generated in the inspection object 12A. When the defect 15 exists in the inspection object 12A,
Since the impedance changes, by detecting this, the presence of a defect is detected. That is, as shown in the equivalent circuit of FIG. 9, when the defect 15 exists, the impedance of the impedance element 18 changes and the voltage Vo
Also change. This change is detected and a defect is detected.

FIG. 7 is a schematic structural explanatory view of an insertion type eddy current inspection device for inspecting a cylindrical inspection object 12B. In FIG. 7, coils 11A and 11B are wound around a core 10B in parallel with each other. Core 10B is inspected 1
When inserted into the test object 2B, an eddy current is generated in the test object 12B. When a defect exists in the inspection object 12B, the impedance changes as described above, and the defect is detected by detecting the impedance.

FIG. 8 is a schematic structural explanatory view of a through-type eddy current flaw detector for inspecting a columnar inspection object 12C. In FIG. 8, the core 10C has a cylindrical shape.
In the same manner as in the example, the coils 11A and 11B are wound in parallel with each other. When performing the inspection, the core 10C
The test object 12C is inserted into the inside, and a defect is detected by a change in impedance as described above.

[0005] Examples of the penetrating eddy current flaw detector include:
There is one described in JP-A-63-15154. In the eddy current flaw detection device described in this publication, two detection coils are wound stepwise and inclined with respect to the axial direction of a cylindrical inspection object. As an example of an eddy current flaw detector for a flat object to be inspected, there is one described in Japanese Patent Application Laid-Open No. 3-94152.

[0006]

In the above-described interpolation type eddy current flaw detection apparatus, as shown in FIG.
Is generated in the circumferential direction of the cylindrical test object 20. Therefore, a defect in the direction in which the eddy current 13 is interrupted,
Although the 0 axial defect 21 can be easily detected, the circumferential defect 22 is difficult to detect because it is parallel to the eddy current 13.

Therefore, there is an eddy current detector described in Japanese Utility Model Publication No. 55-97448. In other words, a coil is wound around each of the teeth of a circular saw-shaped magnetic body on which a number of teeth are formed, and these coils are arranged so that the directions of the generated magnetic flux are opposite to each other between the adjacent teeth. It is wound. Then, two circular saw-shaped magnetic bodies wound with coils as described above are provided, and the teeth of one magnetic body and the teeth of the other magnetic body are viewed from the axial direction of the magnetic body,
It is configured to be staggered. With this configuration, the axial defect and the circumferential defect can be similarly detected.

However, in the eddy current flaw detector described in the above publication, as described above, the coils must be wound around the teeth of the circular saw-shaped magnetic body so that the winding directions are opposite to each other. The configuration is complicated and the manufacturing process is complicated. Furthermore, even if the distance between the teeth is narrowed to improve the detection accuracy, it is difficult to narrow the distance between the teeth because of the coil wound around each tooth.
It has been difficult to improve the detection accuracy.

Further, as described in JP-A-61-198055 and JP-A-63-298053, a configuration in which a large number of detection pancake coils are arranged in a staggered manner on the surface of a cylindrical magnetic body. Some are. However,
Even in such a staggered configuration, a large number of detection coils are used, so the configuration is complicated,
The manufacturing process was complicated. Further, similarly to the above, even if it is attempted to improve the detection accuracy by narrowing the interval between the coils, it is difficult to narrow the interval between the coils, and it is difficult to improve the detection accuracy. .

Therefore, if the inspection speed is reduced, the detection accuracy can be improved. However, in this,
This is not desirable because it increases the time and labor required for the inspection.

SUMMARY OF THE INVENTION An object of the present invention is to realize an insertion type or through-type eddy current flaw detection apparatus which has a simple structure, is easy to manufacture, and can improve the flaw detection accuracy without lowering the inspection speed.

[0012]

The present invention is configured as follows to achieve the above object. A plurality of rows of coils are wound in the circumferential direction of a cylindrical or columnar magnetic body,
These coils generate an eddy current in the test object,
In an eddy current flaw detection device that detects a change in the impedance of these coils and performs flaw detection on an object to be inspected, each of a plurality of rows of coils alternates between a portion extending in the circumferential direction and a portion extending in the axial direction of the magnetic material. And the comb-shaped coils are arranged in a staggered pattern with respect to each other.

Preferably, two rows of comb-shaped coils are arranged on the magnetic material, and the comb-shaped patterns of these comb-shaped coils are configured to be shifted from each other by about a quarter period. Preferably, the magnetic body has a columnar shape, and is configured to perform a flaw detection of a cylindrical inspection object. Preferably, the magnetic body has a cylindrical shape, and is configured to perform a flaw detection of a columnar test object. Preferably, a plurality of rows of comb-shaped grooves are formed on the peripheral surface of the magnetic body, and a winding is arranged in these comb-shaped grooves to form a comb-shaped coil. Further, preferably, three rows of comb-shaped coils are arranged on the magnetic material, and the comb-shaped patterns of these comb-shaped coils are configured so as to be shifted from each other by about 1/6 cycle.

[0014]

A comb-shaped eddy current having the same shape as that of the comb-shaped coil is generated in the test object. Thereby, the axial defect and the circumferential defect are detected with high accuracy. Further, there may be a case where an axial defect exists at a position corresponding to an axial portion of one comb-shaped coil of the inspection object. In this case,
The axial defect corresponds to the circumferential portion of the other comb-shaped coil and can be detected. Similarly, of the test object,
At the location corresponding to the circumferential part of one comb-shaped coil,
Circumferential defects may be present. In this case, the circumferential defect corresponds to the axial portion of the other comb-shaped coil, and thus can be detected. Further, narrowing of the comb-shaped pattern of the comb-shaped coil is easier than in the conventional example, and the accuracy of defect detection can be improved by the narrowing.

[0015]

FIG. 1 is a schematic structural view of an interpolation type eddy current testing apparatus according to an embodiment of the present invention. The core 10 is made of a phenolic resin, and is a tubular, that is, a cylindrical object to be inspected. For example, the core 10 has a diameter corresponding to the inner diameter of the tube and an appropriate length so that it can be inserted into a heat transfer tube. . The comb-shaped coil 23A and the comb-shaped coil 2
3B are arranged. These comb-shaped coils 23A and 23B are formed by a portion extending in the circumferential direction of the core 10 and the core 1
The portions extending in the axial direction of 0 are alternately arranged to form a comb shape. Further, the comb-shaped coils 23A and 23B are staggered with their comb-shaped patterns shifted from each other by about a quarter period. That is, the circumferential distance x between the axial portion A0 of the coil 23A and the axial portion B0 of the coil 23B is about one half of the length of the circumferential portion, that is, the comb-shaped pitch y. . The coil 23
A and 23B are connected to the cable 24, and FIG.
This constitutes a bridge circuit as shown in FIG.

An eddy current 25 is generated in the device under test 12 by the comb-shaped coil 23A as shown in FIG. That is,
A portion corresponding to the portion where the coil 23A extends in the circumferential direction 27 generates an eddy current in the circumferential direction, and a portion corresponding to the portion extending in the axial direction generates an eddy current in the axial direction. The eddy current generated by the comb-shaped coil 23B is the same as in the example shown in FIG.

FIG. 3 is a diagram showing eddy currents 25A and 25B generated in the test object 20 by the coils 23A and 23B. Since an eddy current having a shape as shown in FIG. 3 is generated in the test object 12, the axial defect 21 and the circumferential defect 2
2 can be detected similarly. Further, as shown in FIG. 4, the axial defect 21 may correspond to the axial portion of the eddy current 25A. In this case, the defect 21 can be detected by moving the core 10 and moving the eddy current 25B to the position of the defect 21. Similarly, the circumferential defect 22 may correspond to the circumferential portion of the eddy current 25A. Also in this case, the defect 22 can be detected by moving the core 10 and moving the eddy current 25B to the position of the defect 22.

FIG. 5 is an overall configuration diagram of the example shown in FIG. 1, for example, showing a state in which an eddy current flaw detector is inserted into a heat exchanger heat transfer tube 20 which is an object to be inspected. In FIG. 5, the eddy current flaw detector includes an introduction part 10D and a connection case part 1.
0E and a protective sleeve 28,
Comb-shaped coils 23A and 23B are arranged in 0D. The introduction portion 10D has a sufficient axial length to stabilize the posture of the coils 23A and 23B, and has a conical tip. Thereby, insertion into the heat transfer tube 20 becomes easy. Also, the protective sleeve 28
Is for covering and protecting the coils 23A and 23B.

The lead wires 29A and 29B at the winding start and end portions of the comb-shaped coils 23A and 23B pass through the slit 35, are led to the connection case 10E side, and are connected to the relay terminal 30. The introduction part 10D and the connection case part 10E are connected by the screw part 34. The protective sleeve 28 is pressed and fixed to the connection case 10E by tightening the screw 34.

The relay terminal 30 is connected to the cable 24, and a stop ring 31 is attached to one end of the cable 24. The retaining ring 31 is for preventing the cable 24 from coming off the connection case 10E. The other end of the cable 24 is connected to the detector 32
The detector 32 detects a defect in the heat transfer tube 20. The detection signal from the detector 32 is supplied to a recorder 33 such as a pen-written oscillograph, for example.
Be recorded.

As described above, according to one embodiment of the present invention, the comb-shaped coils 23A and 23B
Are arranged in a zigzag, so that an eddy current flaw detector capable of detecting the axial defect and the circumferential defect of the inspected object with a simple configuration and easy manufacture is realized. Also, since the pitch y of the comb-shaped coil can be narrowed more easily than in the conventional example, the narrowing of the pitch y can improve the flaw detection accuracy without lowering the inspection speed. .

In the method of arranging the comb-shaped coils 23A and 23B on the peripheral surface of the core 10, a comb-shaped groove may be formed on the peripheral surface of the core 10 to arrange the coils 23A and 23B. The coil previously formed in a comb shape may be bonded to the peripheral surface of the core 10 with an adhesive. Further, in the above-described embodiment, two comb-shaped coils are arranged on the core 10;
You may comprise so that three or more comb-shaped coils may be arrange | positioned. For example, when three comb-shaped coils are arranged, the comb-shaped patterns may be arranged so as to be shifted by about 1/6 cycle. Further, the above-described example is an example of an interpolation type eddy current flaw detector, but the present invention is not limited to the interpolation type eddy current flaw detector, but is applicable to a penetration type eddy current flaw detector.

[0023]

As described above, according to the present invention, the following effects can be obtained. Plural rows of coils are wound in the circumferential direction of a cylindrical or columnar magnetic body, and these coils generate an eddy current in the object to be inspected, detect a change in impedance of these coils, and detect a change in the impedance of the coil. In the eddy current flaw detection device that performs flaw detection, each of the plurality of rows of coils has a comb shape having a portion extending in the circumferential direction and a portion extending in the axial direction of the magnetic body alternately, and these comb coils are mutually connected. They are arranged in a staggered pattern. Therefore, it is possible to realize an eddy-current flaw detector capable of detecting the axial defect and the circumferential defect of the inspection object with high accuracy while having a simple configuration and easy manufacturing. Also, since the comb pattern of the comb coil can be narrowed more easily than the conventional example, the narrowing of the comb pattern can further improve the flaw detection accuracy without lowering the inspection speed. Can be.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an interpolation type eddy current testing apparatus according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an eddy current generated by a comb-shaped coil 23A.

FIG. 3 is an explanatory diagram of an eddy current generated in a test object 12;

FIG. 4 shows defects 21 and 2 caused by eddy currents 25A and 25B.
FIG. 4 is an explanatory diagram showing that the number 2 can be detected.

FIG. 5 is a diagram showing the entire configuration of the example shown in FIG. 1, showing a state in which an eddy current flaw detector is inserted into a heat exchanger heat transfer tube.

FIG. 6 is a schematic configuration diagram of an eddy current flaw detection device for a flat inspection object.

FIG. 7 is a schematic configuration diagram of a conventional interpolation type eddy current testing device.

FIG. 8 is a schematic configuration diagram of a conventional through-type eddy current flaw detection device.

FIG. 9 is an equivalent circuit diagram of the eddy current flaw detector.

FIG. 10 shows a defect 22 that is difficult to detect with a conventional eddy current flaw detector.
FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Core 10D Introducing part 10E Connection case part 12 Inspection object 20 Heat transfer tube 21 Axial defect 22 Circumferential defect 23A, 23B Comb coil 24 Cable 25A, 25B Eddy current 28 Protective sleeve 29A, 29B Lead wire 30 Relay terminal 31 Stop ring 32 Detector 33 Recorder 34 Screw 35 Slit

Continuation of the front page (72) Inventor Kazuhiro Suzuki 3-2-1, Sachimachi, Hitachi-shi, Ibaraki Hitachi Engineering Co., Ltd. (56) References JP-A-50-17693 (JP, A) JP-A-54-99489 (JP, A) Japanese Utility Model 63-177747 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 27/72-27/90

Claims (6)

(57) [Claims] A plurality of rows of coils are wound around a cylindrical or columnar magnetic body in a circumferential direction, an eddy current is generated in an object to be inspected by these coils, and a change in impedance of these coils is detected. In the eddy current flaw detection device that performs flaw detection of an object to be inspected, each of the plurality of rows of coils has a comb shape having a circumferentially extending portion and an axially extending portion of the magnetic material alternately. An eddy current flaw detection device, wherein the shaped coils are arranged in a staggered pattern. 2. The eddy current flaw detector according to claim 1,
Two rows of comb-shaped coils are arranged on the magnetic material, and the comb-shaped patterns of these comb-shaped coils are approximately one-fourth of each other.
An eddy current flaw detection device characterized by a period shift. 3. The eddy current flaw detector according to claim 2,
The eddy current flaw detection device is characterized in that the magnetic body has a cylindrical shape and performs flaw detection on a cylindrical test object. 4. The eddy current flaw detector according to claim 2,
The eddy current flaw detection device is characterized in that the magnetic body has a cylindrical shape and performs flaw detection on a columnar test object. 5. The eddy current flaw detector according to claim 1,
On the peripheral surface of the magnetic body, a plurality of rows of comb-shaped grooves are formed, and windings are arranged in these comb-shaped grooves,
An eddy current flaw detector, wherein a comb-shaped coil is formed. 6. The eddy current flaw detector according to claim 1,
Three rows of comb-shaped coils are arranged on the magnetic material, and the comb-shaped patterns of these comb-shaped coils are approximately one-sixth of each other.
An eddy current flaw detection device characterized by a period shift.