JPH0949825A - Eddy-current flaw detecting probe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the peripheral-direction defect detecting ability of a bobbin coil type probe to the same degree as that of the peripheral-direction defect detecting ability of a multicoil type probe without sacrificing the axial-direction defect detecting property of the probe and, at the same time, to improve the defect detecting ability of the probe in a thin tube by incorporating a mutual induction system in the probe. SOLUTION: In an eddy-current flaw detecting probe, exciting coils 6 and 7 wound in the peripheral direction so that the coils 6 and 7 can be directed in the same direction are arranged in parallel with each other. Numerous main cores 10 each of which is formed in an E-shape by forming two recessed grooves 8 and 9 on the surface of a small piece of a ferromagnetic material are formed and, at the same time, the cores 10 are buried at regular intervals in the peripheral surface of the main body 4 of the flaw detecting section of the probe and detection coils 15 are formed by using the central processing sections 11 of the cores 10 as winding cores. In addition, the central projecting sections 11 are joined to magnetic field converging cores 16.

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 a defect such as a crack generated in a thin tube in an inspection of a thin tube of a heat exchanger of a nuclear power plant.

[0002]

2. Description of the Related Art When it is difficult to detect flaws from the outside of a thin tube, such as a thin tube inside a heat exchanger, the probe is inserted inside the thin tube to detect flaws. It is a bobbin coil type probe that enables high-speed flaw detection and has good insertability into a curved pipe section. In this bobbin coil type probe, a conductor wire is wound in the circumferential direction of the cylindrical flaw detection portion to form a coil, so that an eddy current generated in the thin tube flows in the circumferential direction of the thin tube.

There is also a pancake type coil for the purpose of inducing an axial eddy current in a thin tube. As one of them, the rotating coil type probe which scans the inner circumference of the thin tube spirally scans the inside of the thin tube with one coil, so that there is no dead zone or sensitivity lowering area. It has the same sensitivity to cracks.

On the other hand, there is also a multi-coil type probe in which coils are arranged on the outer circumference of the probe by linear scanning, and this multi-coil type probe is local to the thin tube, but it induces an eddy current in the axial direction. Directional cracks are relatively easy to detect.

The above is a so-called self-induction type which detects a change in the impedance of the coil. A method called a mutual induction type in which both the excitation coil and the detection coil are provided and the voltage excited in the detection coil is detected. Some of them are also used (see, for example, JP-A-63-298052).

[0006]

However, in the above bobbin coil type probe, when a crack exists in the circumferential direction in the thin tube, the eddy current induced in the thin tube is in the circumferential direction with respect to the thin tube, so that the crack and the eddy current are generated. Are parallel to each other, and if the cracks are minute, the eddy current is not easily affected by the cracks. Therefore, the bobbin coil type probe has a drawback that the detection sensitivity for circumferential cracks is low.

On the other hand, in the rotary coil type probe, since the probe spirally scans the inside of the tube, it takes a long time to detect a flaw in one thin tube. This is because spiral scanning is performed with the coil diameter as the pitch, and the pitch is usually 1 to
Because it is 5 mm.

Further, in the multi-coil type probe, the eddy current due to the coil is maximum at the center of the coil and becomes weaker as the distance from the coil increases. Therefore, the intensity of the eddy current is minimized at the center between the coils, and the detection sensitivity is reduced. In other words, in this multi-coil type probe, even if the coil shape and installation angle are changed, the coil must cover the entire circumference of the probe, so the size inevitably becomes larger than a certain amount, and the dead zone or the sensitivity in the gap. There are areas of degradation. In this dead zone or in the area of reduced sensitivity,
There is a possibility that axial cracks and minute circumferential cracks may be overlooked, resulting in a decrease in detection limit.

Further, in the mutual induction type probe, the defect signal is detected as a change in the output voltage of the detection coil, but even if the thin tube is not defective, the output voltage exists in the detection coil. Therefore, if the defect is small, the amount of change in voltage is also small and it becomes difficult to detect the defect.

An object of the present invention is to provide an eddy current flaw detection probe which copes with the above situation and improves the detectability of minute defects in the circumferential direction without impairing the detectability of axial defects.

[0011]

That is, the feature of the eddy current flaw detection probe of the present invention for solving the above-mentioned problems is that the flaw detection unit main body formed in a cylindrical shape or a cylindrical shape and a substantially E-shaped ferromagnetic material are used. In such a manner that a plurality of main cores are embedded in the circumferential surface of the flaw detection unit main body at substantially equal intervals in the circumferential direction with the convex portions facing outward and in a parallel state, and the main cores are fitted into the two grooves of the main cores, respectively. A pair of excitation coils wound around the flaw detection unit body in the circumferential direction and substantially parallel to each other; and a number of detection coils wound around the central convex portion of the main core as a core. The main core is provided with the same number of magnetic field converging cores as the main core fixed to the tip of the central convex portion and the surface of which is positioned near the peripheral surface of the flaw detection unit body.

Further, in the flaw detection probe of the present invention, the magnetic field converging core is provided with a shaft portion formed in the circumferential direction of the flaw detection portion main body and from both ends of the shaft portion in the axial direction up and down direction of the flaw detection portion main body, respectively. It is also possible to form it into a substantially H-shape by having a protrusion.

Further, in the flaw detection unit body, it is also preferable that the magnetic field converging core is provided on the outer peripheral side of the excitation coil and the detection coil is provided on the central side of the excitation coil.

[0014]

In the eddy current flaw detection probe according to the present invention, it is possible to generate an eddy current in the axial direction at the same time as generating an eddy current in the circumferential direction in the thin tube. Both circumferential defects can be detected.

Further, as described in detail in the embodiments, since the principle is self-balancing, it is only necessary to detect the deviation from 0 output when there is no defect. Therefore, the fluctuation of the output voltage due to the minute defect in the thin tube is detected. Easy to detect. Further, unlike the rotating coil type probe, the inspection speed is increased because the spiral scanning is not performed.

[0016]

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

FIG. 1 is a partially cutaway sectional view showing a flaw detection unit body of an eddy current flaw detection probe according to an embodiment of the present invention, and FIG.
1 is a sectional view taken along line XX ′ in FIG. 1, FIG. 3 is a front view of a probe according to the present invention, FIG. 4 is an exploded perspective view showing a main core of the probe, and FIG. 5 is a main core portion of the probe. FIG. 3 is a longitudinal sectional view, in FIG. 3, 1 is a probe, 2 is a conical guide for improving insertability, 3 is a centering spring,
Reference numeral 4 indicates a cylindrical flaw detection unit main body, and 5 indicates a flexible tube.

A large number of E-shaped ferromagnetic main cores 10 are provided in the flaw detection unit main body 4, and their convex portions 11 to 13 are directed outward as shown in FIGS. Further, they are embedded in the circumferential surface of the flaw detection unit main body 4 in a parallel state at equal intervals in the circumferential direction.

The two grooves 8 and 9 of the main core 10 have 1
The pair of excitation coils 6 and 7 are wound in parallel with each other in the same direction in the circumferential direction of the flaw detection unit body 4. As shown in FIGS. 1 and 2, the positions of the excitation coils 6 and 7 are set closer to the center of the probe 1 than the magnetic field converging core 16 described later.

Further, as shown in FIG. 4, a magnetic field converging core 16 made of a magnetic material or a ferromagnetic material having a substantially H-shape in plan view is fixed to the tip of the convex portion 11 at the center of the main core 10. ing. The magnetic field converging core 16 and the upper and lower convex portions 12 and 13 of the main core 10 have outer circumferential surfaces that are on the same circumferential surface, and are also on the same circumferential surface as the circumferential surface of the flaw detection unit body 4. Is formed. The outer surfaces of the magnetic field converging core 16 and the upper and lower convex portions 12 and 13 are formed in an arc shape so as to match the peripheral surface of the flaw detection unit body 4 as shown in FIG.

Further, as shown in FIGS. 2, 4 and 5, the detection coil 15 is provided on the central convex portion 11 of the main core 10.
Is wound around and the detection coil 15 is arranged closer to the probe center side than the excitation coils 6 and 7. In addition,
The detection coil 15 and the magnetic field converging core 16 are provided for all eight main cores 10.

When the probe of the embodiment of the present invention is inserted into the metal capillary K, however, as shown in FIG. 6, the portions A and A'confronted by the pair of excitation coils 6 and 7 have the same orientation. A current flows in the circumferential direction. Further, in the portion B facing the magnetic field converging core 16, a slight amount of current in the circumferential direction flows due to the excitation coils 6 and 7.

In the portions C and C'confronted by the upper convex portion 12 and the lower convex portion 13 of the main core 10, the electric current meanders between the convex portions 12 and 13 of the adjacent cores. That is, in the eddy current probe of the present invention, an axial current component is generated in the C and C'portions due to the above meandering, so that the sensitivity is improved even for the circumferential defect of the thin tube and the circumferential direction of the A and A'portions. Since the current flows sufficiently due to the presence of the main core 10, it is highly sensitive to axial defects.

On the other hand, as shown in FIG. 7, if the thin tube is defect-free, the axial magnetic flux flows from the convex portion 12 to the lower convex portion 13 (or the opposite direction) and passes through the central convex portion 11 in the radial direction. The magnetic flux is almost zero. Therefore, the output voltage value of the detection coil 15 is almost zero.

On the other hand, as shown in FIG. 8, when there is a circumferential defect K ₁ in the narrow tube, the eddy current bypasses the circumferential defect, and as a result, the radial magnetic flux as shown in the figure is generated.
This radial magnetic flux flows into the central convex portion 11 via the magnetic field converging core 16, and thus an electromotive force is generated in the detection coil 15. Therefore, the defect can be detected.

Therefore, in the eddy current probe of the present invention, when the capillary is defect-free, the pair of excitation coils 6 and 7 self-balance, and the output of the detection coil 15 is 0 in principle.
When there is a defect in the thin tube, the output voltage of the detection coil is almost zero.
To a predetermined value. Therefore, the output fluctuation can be easily measured, and the detectability is improved as compared with the conventional mutual induction probe.

In this embodiment, the magnetic field converging core 16 is
As shown in FIG. 4, a shaft portion 16b formed in the circumferential direction of the flaw detection unit body 4 and the flaw detection unit body 4 from both ends of the shaft portion 16b.
Is substantially H-shaped with the protrusions 16a projecting upward and downward in the axial direction, the axial magnetic flux is bent by the presence of the protrusions 16a into a circumferential magnetic flux. This is to increase the axial eddy current as a result.

In the present embodiment, a total of eight main cores 10 are installed on the outer circumference of the flaw detection unit main body 4 at an angle of 45 °, but a larger number of main cores 10 may be arranged at equal intervals. Further, although the cross sections of the convex portions 11 to 13 and the columnar portion 14 of the main core 10 are quadrangular in this embodiment, other shapes such as a circle can be adopted.

Next, a second embodiment of the present invention will be described. 9 is a partially cutaway sectional view showing a main body of a flaw detection portion of an eddy current flaw detection probe according to another embodiment of the present invention, and FIG.
-X 'line sectional drawing, FIG. 11 is an exploded perspective view showing the main core of the probe, and FIG. 12 is a vertical sectional view showing the main core portion of the probe.

The structure of the probe of the second embodiment is almost the same as that of the previous embodiment except that the magnetic field converging core 16 has a rectangular shape and the outer peripheral surfaces of the excitation coils 6 and 7 are the core 1.
0 is located on the same plane as the upper and lower convex portions 12 and 13, which is a difference from the first embodiment. The other same components are denoted by the same reference numerals and the description thereof will be omitted.

The rectangular magnetic field converging core 16 has protrusions 1 for increasing the axial eddy current as in the first embodiment.
Although there is no 6a, since the projections 16a are not provided, the excitation coils 6 and 7 are arranged closer to the outer peripheral side of the flaw detection unit body 4 than in the first embodiment, and the distance between the detection coil 15 and these excitation coils 6 and 7 is increased. It can be increased. For this reason, it is possible to reduce the magnetic flux that directly leaks from the excitation coils 6 and 7 to the detection coil 15, and as a result, the output voltage of the detection coil 15 when there is no defect becomes closer to 0 and is consumed as the leakage magnetic flux. Since the component is applied to the thin tube, it has an advantage of increasing the eddy current in the thin tube.

Although the embodiments of the present invention have been described above, the distance between the adjacent magnetic field converging cores 16 in both the first and second embodiments is 0.5 mm, but they may be closer. Further, it is effective to improve the detectability by interposing an insulator such as a mylar film or a polyimide film between the main core 10 and each coil.

[0033]

As described above, in the eddy current flaw detection probe according to the present invention, it is possible to generate an eddy current in the axial direction at the same time as generating an eddy current in the circumferential direction in the thin tube. Since it is possible to detect small defects in both the axial direction and the circumferential direction, and in principle, self-balance, it is sufficient to detect the deviation from 0 output when there is no defect, which is caused by the minute defects in the thin tube. The output voltage fluctuation can be easily detected, and unlike the rotating coil type probe, the spiral scanning is not performed, so that the inspection speed is high, which has the remarkable effect of reducing the burden on the worker.

[Brief description of drawings]

FIG. 1 is a partially cutaway sectional view showing a flaw detection unit body of an eddy current flaw detection probe according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line XX ′ in FIG.

FIG. 3 is a front view of an eddy current flaw detection probe according to the embodiment.

FIG. 4 is an exploded perspective view showing a main core portion of the eddy current flaw detection probe according to the embodiment.

FIG. 5 is a vertical sectional view showing a main core portion of the eddy current flaw detection probe according to the embodiment.

FIG. 6 is a view showing an eddy current induced in a thin tube by the eddy current flaw detection probe according to the example.

FIG. 7 shows an eddy current flaw detection probe according to the same embodiment,
It is sectional drawing which shows the flow of the magnetic flux of the main core part when a thin tube is defect-free.

FIG. 8 shows an eddy current flaw detection probe according to the same embodiment,
It is sectional drawing which shows the flow of the magnetic flux of the main core part when there is a defect in a thin tube.

FIG. 9 is a partially cutaway sectional view showing a flaw detection unit body of an eddy current flaw detection probe according to a second embodiment of the present invention.

10 is a sectional view taken along line XX ′ of FIG.

FIG. 11 is an exploded perspective view showing a main core portion of the eddy current flaw detection probe according to the embodiment.

FIG. 12 is a vertical cross-sectional view showing a main core portion of an eddy current flaw detection probe according to the example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 probe 2 guide 3 centering spring 4 flaw detection part main body 5 flexible tube 6, 7 excitation coil 8, 9 concave groove 10 main core 11 central convex portion 12 upper convex portion 13 lower convex portion 14 main core columnar portion 15 detection coil 16 Magnetic field converging core 16a Protrusion 16b Shaft

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshinori Watanabe 123 Otani, Minami-Ina-Yatsuma-Fuji, Seika-cho, Soraku-gun, Kyoto Prefectural Institute for Nuclear Safety Systems (72) Inventor Yutaka Harada Hajime Tosabori, Nishi-ku, Osaka City 3-3 No. 7 in Nuclear Engineering Co., Ltd. (72) Inventor Junri Shimane 1-3-7 Tosabori, Nishi-ku, Osaka City In Nuclear Engineering Co., Ltd.

Claims (3)

[Claims] 1. A cylindrical or columnar flaw detection unit main body and a substantially E-shaped ferromagnetic body, with the convex portions facing outward and arranged in parallel with each other to surround the circumferential surface of the flaw detection unit main body. A large number of main cores embedded in the direction substantially at equal intervals, and
A pair of substantially parallel excitation coils wound in the circumferential direction around the flaw detection unit body so as to fit in the grooves of the strip,
The same number of detection coils as the main core wound around the central convex portion of the main core as a winding core, and fixed to the tip of the central convex portion of the main core, the surface of which is near the peripheral surface of the flaw detection unit body. An eddy current flaw detection probe comprising the positioned main cores and the same number of magnetic field converging cores. 2. The magnetic field converging core has a shaft portion formed in the circumferential direction of the flaw detection unit main body, and projections projecting vertically from both ends of the shaft portion in the axial direction of the flaw detection unit main body. The eddy current flaw detection probe according to claim 1, wherein the eddy current flaw detection probe is formed in a substantially H shape. 3. The eddy current flaw detection probe according to claim 1, wherein in the flaw detection unit main body, a magnetic field converging core is provided on the outer peripheral side of the excitation coil, and a detection coil is provided on the central side of the excitation coil. .