JPH08313494A - Eddy current test equipment probe - Google Patents

Abstract

PURPOSE: To enhance detection capacity by further enhancing the merit of the axial flaw detection property of a bobbin coil type probe and also providing the merit of the peripheral flaw detection property of a multicoil type probe and further taking in a mutual induction system. CONSTITUTION: In an eddy current test equipment probe parallelly equipped with a pair of exciting coils 6, 7 wound in a peripheral direction so as to become mutually same in direction, two recessed grooves 8, 9 are formed to a small piece of a ferromagnetic material to form a large number of almost E-shaped cores 10 and exciting coils 6, 7 are fitted in the recessed grooves 8, 9 of the cores 10 to embed the cores 10 in the peripheral surface of a flaw detection part main body 4 so as to almost equally divide them in the peripheral direction of the main body 4 and the central protruding parts 11 of the cores 10 are used as winding cores to wind detection coils 15.

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.

Further, the conventional eddy current flaw detection probe is of a self-induction type, in which excitation for generating an eddy current and detection of the generated eddy current are performed by the same coil.

On the other hand, although the mutual induction type is used in the present invention, this is one in which a primary coil for excitation and a secondary coil for detection are separated, and is used in part. However, in the conventional mutual induction method, a voltage output is already generated in the secondary coil for detection even if the metal tube has no defect, and the defect signal is evaluated as a change from the defect-free signal. Therefore, the amount of change in the defect signal is very small as compared with the defect-free signal, which makes it difficult to detect a signal of a minute defect.

The present invention has been made in consideration of the above situation, and further enhances the advantage of the axial defect detection of the bobbin coil type probe, and further improves the circumferential defect detection of the multi-coil type probe. It also has advantages, and aims to perform flaw detection inspection at the same speed as the bobbin coil type probe by improving the detectability by adopting the mutual induction method and arranging the coil and the coil skillfully. It is a thing.

[0010]

That is, the feature of the eddy current flaw detection probe of the present invention which meets the above-mentioned object is that the eddy current flaw detection probe of the present invention is wound around a body of a flaw detection portion having a cylindrical or columnar shape in the circumferential direction in the same direction. A probe provided with a pair of exciting coils in parallel, in which 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 exciting coils are fitted in the concave grooves of the cores, respectively, and the cores are embedded in the circumferential surface of the flaw detection unit main body in the circumferential direction substantially equally, and the central convex portion of the cores is embedded. Each of the detection coils is wound around the core as a winding core.

[0011]

When the probe of the present invention is inserted into the metal tube, the metal tube in the portion facing the two exciting coils,
Currents flow in the same direction as each other. In addition, in the metal tube in the portion where the upper and lower convex portions of the E-shaped core face, the electric current meanders between the convex portions of the adjacent cores, and an eddy current component in the axial direction is generated.

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 current component in the circumferential direction is also present. Therefore, as with the conventional bobbin type coil, the sensitivity to the axial defect is good.

The detection coil for detecting changes in eddy current is wound in a pancake shape with the central convex portion of the core as a winding core. However, when the metal tube is defect-free, the axial magnetic flux is above the core. Since the current flows from the convex portion to the lower convex portion, the radial magnetic flux in the detection coil portion has a value close to zero. On the other hand, when the defect is located between the convex portion on the core and the central convex portion, the balance of the radial magnetic flux is lost, and a magnetic flux circulating between the central convex portion and the lower convex portion is generated. The same effect occurs when the defect is between the central convex portion and the lower convex portion.

Therefore, when there is no defect, the two exciting coils are self-balanced and the magnetic flux of the detection coil is 0. When there is a defect, the magnetic flux is applied to the detection coil from a state where the output voltage is almost zero. As the output voltage is generated and the output voltage can be measured, the detection performance is improved.

[0015]

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

FIG. 1 is a partially cutaway front view showing a main body of a flaw detection portion of an eddy current flaw detection probe according to an embodiment of the present invention, and FIG.
A sectional view taken along line X ', FIG. 3 is a front view of the probe of the embodiment, and FIG.
5 is an exploded view showing the core of the probe, FIG. 5 is a vertical cross-sectional view showing the core portion of the probe, and in FIG. 3, 1 is a probe, 2 is a conical guide for improving insertability, and 3 is a guide.
Is a centering spring, 4 is a flaw detection unit main body, and 5 is a flexible tube.

As shown in FIGS. 1 and 2, the flaw detection unit main body 4 has a pair of coils 6 and 7 wound in the circumferential direction in the same direction as each other on the cylindrical main body 4. It is equipped in parallel with.

Further, in the above-described embodiment of the present invention, as shown in FIGS. 4 and 5, two recessed grooves 8 are formed in the ferrite plate-like small piece.
9 to form a large number of E-shaped cores 10,
As shown in FIG. 1 and FIG. 2, the pair of upper and lower exciting coils 6 and 7 are fitted into the concave grooves 8 and 9 of the cores 10, respectively, and the cores 10 are attached to the peripheral surface of the flaw detection unit body 4. It is buried evenly in the circumferential direction. The detection coils 15 are wound around the base of the central convex portion 11 of each E-shaped core 10 with the convex portion 11 as the center (radial direction of the probe as an axis).

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 main body 4, and likewise the concave grooves. 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.

FIG. 6 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 exciting bobbin coils 6 and 7 fitted in the concave grooves 8 and 9, the circumferential currents in the same direction flow. In the portion B facing the central convex portion 11 of the E-shaped core 10 sandwiched between the bobbin coils 6 and 7, a slight current in the circumferential direction generated by the bobbin coils 6 and 7 flows.

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

That is, the probe 1 of the above-mentioned embodiment of the present invention.
Then, since the axial current component is generated in the C and C'areas as described above, the sensitivity to the circumferential defect of the metal tube is improved, and the circumferential current in the A and A'areas is Because of the presence of the core 10, the flow is equal to or higher than that of the conventional bobbin coil type probe, and therefore, it is highly sensitive to axial defects.

On the other hand, the detection coil 15 for detecting changes in eddy current is wound in a pancake shape with the central convex portion 11 of the core 10 as a core, but as shown in FIG. At this time, since the axial magnetic flux flows from the upper convex portion 12 of the core 10 to the lower convex portion 13, the radial magnetic flux in the detection coil 15 portion becomes a value close to zero.

On the other hand, as shown in FIG. 9, if the defect K ₁ is located between the convex portion 12 on the core 10 and the central convex portion 11, the radial magnetic flux balance shown in FIG. 8 is lost. A magnetic flux circulating between the central convex portion 11 and the upper convex portion 12 as shown in FIG. 9 is generated. This is the same when the defect K ₁ is between the central convex portion 11 and the lower convex portion 13.

Therefore, in the probe of the embodiment of the present invention, as shown in FIG. 8, when the defect K ₁ is not present, the two exciting coils 6 and 7 are self-balanced and the detecting coil 15 is provided.
When the magnetic flux is 0 and there is a defect K ₁ , a magnetic flux is generated in the detection coil 15 as shown in FIG. 9, which causes the output voltage to change from a substantially zero state to a predetermined value. The measurement improves the detectability over the conventional mutual induction probe.

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.

[0028]

As described above, according to the eddy current flaw detection probe of the present invention, the eddy current flaw detection probe is wound in the circumferential direction so as to have the same direction.
A probe equipped with a pair of exciting coils 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 exciting coils are fitted in the recessed grooves of these cores, respectively, and each core is subjected to flaw detection part main body. Is embedded in the circumferential surface of the core in a substantially equal manner in the circumferential direction, and the detection coil is wound around each of the convex portions at the center of the cores as winding cores. On the other hand, in the upper and lower convex portions, it is possible to respectively generate a wavy meandering current and generate an axial current component, which improves sensitivity to circumferential defects of the metal tube,
Moreover, since the circumferential current flows at a level equal to or higher than that of the conventional bobbin coil type probe due to the presence of the core, it is highly sensitive to axial defects, and when there is no defect in the metal tube, the above-mentioned pair of The excitation coil balances the magnetic flux of the detection coil to almost zero, and when there is a defect, the deviation from the zero balance is detected, so even a minute defect signal can be easily discriminated. Compared with the above, the remarkable effect that the detectability is significantly improved is exhibited.

[Brief description of drawings]

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

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

FIG. 3 is a front view of the probe of the example.

FIG. 4 is an exploded view showing a core of the probe.

FIG. 5 is a vertical cross-sectional view showing a core portion of the probe.

FIG. 6 is a perspective view showing another example of the core.

FIG. 7 is a diagram showing a current flow in a metal tube by a probe according to an embodiment of the present invention.

FIG. 8 is a cross-sectional view showing the flow of magnetic flux in the core portion when the metal tube has no defect.

FIG. 9 is a cross-sectional view showing the flow of magnetic flux in the core portion when the metal tube has a defect.

[Explanation of symbols]

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

Front page continuation (72) Inventor Ryoichi Yamaguchi Oita 123 Minami Inazuma, Seika-cho, Soraku-gun, Kyoto Prefecture In-house, Nuclear Safety System Research Co., Ltd. Ina Yatsuma Sub-print 123 Otani, Nuclear Safety Systems Research Institute (72) Inventor Yutaka Harada 1-3-7 Tosabori, Nishi-ku, Osaka City Stock Company Nuclear Engineering

Claims (1)

[Claims] 1. A probe having a pair of exciting coils wound in the circumferential direction so as to be in the same direction on a cylindrical or columnar flaw detection unit main body in parallel, and comprising a ferromagnetic material such as ferrite. A large number of substantially E-shaped cores are formed by forming two recessed grooves in the small piece, and the exciting coils are fitted in the recessed grooves of these cores, so that the cores of the flaw detection unit main body An eddy current flaw detection probe characterized in that it is embedded in a circumferential surface in a substantially equal manner in the circumferential direction, and each of the detection coils is wound with the central convex portion of each core as a winding core.