JPH08240568A - Eddy current flaw detection probe - Google Patents

Abstract

PURPOSE: To furthermore enhance the merit of axial defect detection of a bobbin coil type probe and also possess the merit of circumferential defect detectability of a multi-coil type probe. CONSTITUTION: This is an eddy current flaw detection probe 1 comprising in parallel a pair of coils 6, 7 circumferentially wound to be reverse direction to each other, two grooves 8, 9 are formed on a small piece of a ferromagnetic body, and a number of substantially E-shaped cores 10 are shaped, the coils 6, 7 are engaged with the grooves 8, 9 of the cores 10 respectively. The cores 10 are circumferentially substantially equally divided and buried on the circumferential face of a flaw detection part body 4.

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 detection probe for detecting cracks or the like generated in a metal thin tube or the like of a heat exchanger of a nuclear power plant.

[0002]

2. Description of the Related Art When it is difficult to approach a metal tube from the outside like a thin tube of a heat exchanger, a probe is inserted into the metal tube for flaw detection. The conventional probe is a bobbin type probe that enables high-speed flaw detection and has good insertability into a curved pipe section. In this bobbin coil type probe, the lead wire is wound in the circumferential direction of the cylindrical flaw detection portion to form the ECT coil, so that the eddy current flows in the circumferential direction of the metal tube. That is, in eddy current flaw detection,
The eddy current in the metal pipe induced by the coil in the probe is disturbed by the defect in the pipe to detect the defect. However, in the above probe, defects such as cracks in the metal pipe are detected in the circumferential direction of the pipe. If present, the crack direction becomes parallel to the flow direction of the eddy current, so that the eddy current is hardly disturbed and there is a problem that the flaw detection sensitivity is low.

On the other hand, a plurality (in many cases 8
There is also a multi-coil type probe having (an) pancake coil (also referred to as a surface coil). The eddy current due to the pancake coil of this probe is in a relatively narrow range of the metal tube, but since it flows with the tube radial direction as the axis of symmetry, there is a portion that intersects with the circumferential cracks. In the above, there is an advantage that the flaw detection sensitivity is higher than that of the bobbin coil type probe described above.

[0004]

However, the eddy current due to the pancake coil of the above-mentioned multi-coil type probe is strong in the central part of the coil and becomes weaker as it goes away from the central part. Is reduced. That is, in the above-mentioned multi-coil type probe, even if the winding shape and the attachment angle of the pancake coil are changed, since the coil needs to cover the entire circumference of the probe, it is inevitably a certain size or more. As described above, the dead zone or the sensitivity lowering region is generated in the gap. Therefore, in the dead zone and sensitivity lowering area of this probe, there is a possibility of overlooking cracks in the axial direction and short cracks in the circumferential direction in particular, and in consideration of such an accident, the detection limit of the flaw detection probe becomes narrower. Be invited.

There is also a rotating coil type probe in which about 1 to 3 pancake coils are brought into close contact with the tube wall and scanning is performed in a spiral manner while rotating the probe. In this probe as well, the pitch of the pancake coils is also provided. (Usually, the diameter is about the same as the coil diameter, and about 1 mm to 5 mm), the spiral scanning is performed, so that the flaw detection speed is very slow.

In any case, at present, if there is a possibility of a circumferential defect in the metal tube, it is necessary to use not only the bobbin coil type probe but also the multi coil type probe and the rotating coil type probe. However, it takes much time and cost to detect the above defects.

The present invention has been made in consideration of the above situation, and further enhances the axial defect detectability of the bobbin coil type probe, and also detects the circumferential defect detectability of the multi-coil type probe. The object of the present invention is to carry out the flaw detection inspection at the same speed as the bobbin coil type probe, while improving the detectability by providing the advantages of

[0008]

That is, the feature of the eddy current flaw detection probe of the present invention which meets the above object is that a pair of coils wound in the circumferential direction so as to be opposite to each other is used as a flaw detection in a cylindrical or columnar shape. On the basis of the bobbin coil type probe provided in parallel with the main body of the section, two recessed grooves are formed in a small piece of a ferromagnetic material such as ferrite to form a large number of substantially E-shaped cores. The above-mentioned pair of coils are fitted in the respective recessed grooves, and the cores are embedded in the circumferential surface of the flaw detection unit main body in the circumferential direction substantially equally.

[0009]

When the probe of the present invention is inserted into the metal tube, the currents in the circumferential directions opposite to each other flow in the portions facing the two bobbin coils fitted in the groove of the core, while the bobbin coils flow in these bobbin coils. At the portion facing the central convex portion of the sandwiched E-shaped core, a spiral current close to the overcurrent of the pancake coil flows due to the reverse current generated by the bobbin coil.

In addition, in the portion where the upper and lower convex portions of the E-shaped core face, the current meanders over the convex portions of the adjacent cores.

Therefore, in the probe of the present invention, since the current component in the axial direction is generated as described above, the sensitivity to the circumferential defect of the metal tube is improved, and the circumferential current is
Due to the presence of the core, the flow is equal to or higher than that of the conventional bobbin coil type probe, so that it is highly sensitive to axial defects.

Furthermore, since the core is close to the coil, it also has the function of further strengthening the magnetic field generated by the bobbin coil to strengthen the spiral current.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a front view showing an eddy current flaw detection probe according to an embodiment of the present invention. In the figure, 1 is a probe, 2 is a conical guide for improving insertability, 3 is a centering spring, and 4 is flaw detection. Part bodies 5 are flexible tubes, respectively.

As shown in FIGS. 2 and 3, the flaw detection unit main body 4 has a pair of coils 6 and 7 which are wound in the circumferential direction so as to be opposite to each other, and are vertically arranged on the cylindrical main body 4. It is equipped in parallel with.

In the above-described embodiment of the present invention, as shown in FIG. 4, two recessed grooves 8 and 9 are formed in a ferrite plate-like small piece to form a large number of E-shaped cores 10. 2, as shown in FIG. 3, the above-mentioned concave grooves 8 and 9 of these cores 10.
The pair of upper and lower coils 6 and 7 are fitted to each other, and each core 10 is embedded in the circumferential surface of the flaw detection unit main body 4 in the circumferential direction equally.

The number of the cores 10 is eight in this embodiment, but about 8 to 16 cores are circumferentially equally divided into the circumferential surface of the flaw detection unit body 4 and the concave grooves are formed in the same manner as described above. 8, 9
It is also possible to bury it so that it faces outward in the radial direction. Further, although the cross sections of the convex portions 11 to 13 and the columnar portion 14 of the core 10 are squares in this embodiment, they may be circular or other shapes.

Further, the pair of coils 6 and 7 are of the impedance type for both excitation and detection as in the conventional case, so that the inspection can be carried out with only one channel. Only effective to detect.

On the other hand, in order to know the direction of the defect, the position in the circumferential direction, or the spread in the circumferential direction, as shown in FIG. By winding the detection coil 15 around the convex portion 11 as a core, it is possible to detect as the number of the cores 10, that is, eight independent signals.

Further, FIG. 5 is a perspective view showing another example of the core. By forming the core 10 by sequentially shifting the upper, middle, and lower convex portions 11 to 13 in the same circumferential direction, Even with a small number of cores, it is possible to almost eliminate the dead zone of the axial defect of the probe.

Therefore, the probe 1 of the embodiment of the present invention described above.
Is inserted into the metal tube K, as shown in FIG.
In the portions A and A'facing the two bobbin coils 6 and 7 fitted in the concave grooves 8 and 9, electric currents in the circumferential directions opposite to each other flow, while E sandwiched by these bobbin coils 6 and 7 In the portion B facing the central convex portion 11 of the letter-shaped core 10, a spiral current close to the overcurrent of the pancake coil flows due to the reverse current generated by the bobbin coils 6 and 7.

The upper and lower convex portions 1 of the E-shaped core 10 are also provided.
In the portion C that faces 2 and 13, the same convex portion 1 of the adjacent cores
The current meanders over 2'and 13 '.

That is, the probe 1 of the above-mentioned embodiment of the present invention.
Then, since the axial current components are generated in the B and C areas as described above, the sensitivity is good even for the circumferential defect of the metal tube, and the circumferential current in the A area is present in the presence of the core 10. Since it is flowing at a level equal to or higher than that of the conventional bobbin coil type probe, it is highly sensitive to axial defects.
Further, since the core 10 is close to the coils 6 and 7, the magnetic field generated by the bobbin coils 6 and 7 is further strengthened, and the spiral current is also strengthened.

Although the embodiment of the present invention has been described above, the core 10 can be formed of a ferromagnetic material other than ferrite, and the core 10 and the coils 6, 7 and the coils 6, 7 can be detected. It is preferable to dispose thin insulators between the respective coils 15 and.

[0025]

As described above, the eddy current flaw detection probe of the present invention is a probe having a pair of coils wound in the circumferential direction in opposite directions to each other in parallel.
A large number of substantially E-shaped cores are formed by forming two recessed grooves in a small piece of ferrite or the like, and the pair of coils are fitted into the recessed grooves of these cores to detect each core. It is embedded in the circumferential surface of the main body in the circumferential direction so as to be divided into approximately equal parts.While the coil portion generates a circumferential current, the central convex portion of the core generates a spiral current and the upper and lower convex portions It is possible to generate each of the currents that meander in a wavy shape, and the current component in the axial direction is generated.Therefore, the sensitivity to the circumferential defects of the metal tube is improved, and the circumferential current is
Due to the presence of the core, the flow is equal to or more than that of the conventional bobbin coil type probe, so it is highly sensitive to axial defects, and the proximity of the core to the coil further strengthens the magnetic field generated by this bobbin coil. As a result, an excellent effect of increasing the spiral current is obtained.

[Brief description of drawings]

FIG. 1 is a front view showing an eddy current flaw detection probe according to an embodiment of the present invention.

FIG. 2 is a partially cutaway sectional view showing a flaw detection unit main body of the embodiment.

3 is a cross-sectional view taken along line XX of FIG.

FIG. 4 is a perspective view of a core.

FIG. 5 is a perspective view showing another example of the core.

FIG. 6 is a diagram showing a current flow of a metal tube by a probe according to an embodiment of the present invention.

[Explanation of symbols]

 1 probe 2 guide 3 centering spring 4 flaw detection unit main body 5 flexible tube 6,7 coil 8,9 concave groove 10 core 11 central convex portion 12 upper convex portion 13 lower convex portion 14 core columnar portion 15 for detection coil

Front Page Continuation (72) Inventor Ryoichi Yamaguchi 1-7 Kodai, Seika-cho, Soraku-gun, Kyoto Prefecture Nuclear Safety Systems Laboratory (72) Inventor Yoshinori Watanabe 1-7 Kodai, Seika-cho, Soraku-gun, Kyoto Prefecture Nuclear Safety Systems Research Institute (72) Inventor Yutaka Harada 1-3-7 Tosabori, Nishi-ku, Osaka City Nuclear Engineering Co., Ltd.

Claims (1)

[Claims] 1. An eddy current flaw detection probe comprising a pair of coils wound circumferentially in opposite directions on a cylindrical or columnar flaw detection unit body in parallel, and a small piece of a ferromagnetic material such as ferrite. A plurality of substantially E-shaped cores are formed by forming two recessed grooves in the core, and the pair of coils are fitted in the recessed grooves of these cores, and each core is surrounded by the circumference of the flaw detection unit body. An eddy current flaw detection probe characterized in that it is embedded in the surface in a substantially equal manner in the circumferential direction.