JPH06138096A - Eddy current flaw detection probe and flaw detection method using the probe - Google Patents

Abstract

(57) [Summary] [Purpose] In an insertion type eddy current flaw detection probe, regardless of the direction or length of cracks in metal pipes, etc.
Highly sensitive and high-speed flaw detection, and even a spiral flaw detection does not require a rotating mechanism, the probe is compact and simple, and if it is easy to insert into curved pipes, durable, and maintainable. Close. [Structure] An insertion type eddy current probe in which a plurality of coils 9a, 9b, 9c wound substantially parallel to the respective cross-sections of the probe 1 are arranged on a plurality of axial cross-sections that are equally divided in the circumferential direction. Using the coils 9a, 9b, 9c, an alternating current is applied to each of the coils 9a, 9b, 9c in order from the adjacent ones so that a radial magnetic field rotating in the circumferential direction is generated on the object to be inspected. The eddy current generated on the peripheral surface of the inspection object is detected.

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 in a metal thin tube of a heat exchanger of a nuclear power plant, and a flaw detection method using the probe. is there.

[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, since the lead wire is wound in the circumferential direction of the cylindrical probe to form a coil, the eddy current flows in the circumferential direction of the metal tube. That is, in eddy current flaw detection, an eddy current in a metal tube induced by a coil in the probe is disturbed by a defect in the tube to detect the defect. When the defect (1) exists in the circumferential direction of the tube, 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 probe is strong at the center of the coil and becomes weaker as it goes away from the center, so the sensitivity decreases near the coil and the middle of the coil. However, there is a problem that it is not suitable for flaw detection of a crack having a short length existing in the intermediate portion. Also, there is a rotating coil type probe in which about 1 to 3 pancake coils are closely attached to the tube wall and scanning is performed in a spiral shape while rotating the probe.
Also in this probe, since it has a rotating mechanism, the structure becomes large and complicated, and there is a problem in insertability into the curved tube portion, durability, maintainability, and the like.

The present invention has been made in view of the above-mentioned actual situation, and detects defects such as cracks in a metal pipe or the like at high speed and with high sensitivity regardless of the direction or length of the defect. It is an object of the present invention to provide an eddy current flaw detection probe that can be manufactured, has a simple structure, and is excellent in insertability into a curved tube portion, durability, and maintainability.

[0006]

That is, the feature of the eddy current flaw detection probe of the present invention which meets the above-mentioned object is that the center of the probe is used in a cylindrical or columnar insertion type eddy current flaw detection probe inserted into a metal tube or the like. On a plurality of axial cross-sections including a shaft and dividing the probe into substantially equal parts in the circumferential direction, a plurality of coils passing near both sides of the probe and wound substantially parallel to the respective cross-sections were arranged. Where it is. Further, the eddy current flaw detection method of the present invention uses the eddy current flaw detection probe of the present invention, in which an alternating current is applied to each of the coils with a phase delay from adjacent ones, and the probe is inserted. Generates a radial magnetic field that rotates in the circumferential direction,
An eddy current generated on the peripheral surface of the object to be inspected by the magnetic field is detected by each of the coils or another coil.

[0007]

In the eddy current flaw detection probe of the present invention or the flaw detection method of the present invention using the same, since the magnetic field can be rotated and spiral scanning can be performed without rotating the probe itself, the probe becomes large. Therefore, the insertability into the curved pipe portion, the durability, and the maintainability are kept good. Since the scanning detects the eddy current generated on the peripheral surface of the object to be inspected by the magnetic field, regardless of whether the crack or the like is generated in the circumferential direction or the axial direction, the sensitivity is increased to detect flaws. In addition, since the eddy current is generated together with the rotating magnetic field, there is no region of poor sensitivity as in the conventional multi-coil type probe. Further, in the scanning for rotating the magnetic field, a magnetic field rotation speed of 1000 rps can be obtained by flaw detection with an alternating current of 1 kHz, for example, which is several hundred times faster than the conventional rotating coil type probe. Inspection is possible.

[0008]

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 of an embodiment of the present invention. In the figure, (1) is a cylindrical probe body, (2) is a conical guide for improving insertability, and (3) is centering. Brush (may be a leaf spring), (4) shows a coil assembly, (5) shows a lead wire, and (6) shows a flexible tube for protecting the lead wire. In the present invention, the probe includes the central axis (A) of the probe (1) as shown in FIG.
Three axial sections (7a), (7b), which are equally divided into 6 by °
As shown in FIG. 3 or FIG. 4 (a), (b), on (7c), passing through both sides (8), (8) of the probe formed thicker than the other part in the coil assembly (4), And three coils (9a), (9b), (9) wound substantially parallel to the above-mentioned cross sections (7a), (7b), (7c).
c) is provided. Each coil (9a),
Each of (9b) and (9c) is connected to an oscillator (not shown) that delays the phase of the alternating current and sends it to the adjacent coils in sequence. That is, in this embodiment, each of the coils (9a), (9b), (9c) serves both for excitation and for detection.

FIG. 5 shows an eddy current flaw detection probe according to the second embodiment of the present invention. In addition to the structure of the first embodiment, in addition to the coil assembly (4), the coil (9a), (9b) and (9c) are provided exclusively for excitation, and a bobbin coil (10) for detection is provided behind them.
It has a configuration in which

On the other hand, the eddy current flaw detection method of the present invention uses the probe as described above and uses the coils (9a), (9b),
In (9c), alternating currents are sequentially passed from the adjacent ones by the oscillator (not shown) with a phase delay of 2π / 3, and as shown in FIG. 8 and FIG. Radial magnetic fields (H ₁ ) to (H _x ) that rotate in the circumferential direction are generated on the inspection object (K), and as shown in FIG. 9, the magnetic fields (H ₁ ) to (H _x ) cause An eddy current (11) is generated on the peripheral surface of the inspection object (K), and the eddy current (11) is detected by the coils (9a) to (9c) or the bobbin coil (10). .

This will be described in detail with reference to FIGS. 4 and 6-9. In FIG. 4, I = I ₀ is applied to the coil (9a).
When an alternating current represented by sin ωt is applied, the coil (9a)
At the center of the arrow, as shown in FIG. 6, H ₁ = in the direction of the arrow (B).
A magnetic field represented by H ₀ sin ωt is generated. Here, H ₀ is a constant, ω is the angular velocity of the alternating current, and t is time.

Assuming that the BB direction is applied to the x axis and the directions orthogonal to the BB direction and the AA direction are applied to the y axis, the direction of the magnetic field (H ₁ ) is shown in FIG. Thus, the x-axis direction is set.

Next, the coil (9b) and the coil (9c) shown in FIG. 4 have the same size as the coil (9a) and the phases thereof are 120 ° (2π / 3) and 240 ° (4π / 3), respectively. ) When a delayed current is passed, H ₂ = H ₀ sin (ω
t-2π / 3), and H ₃ = H ₀ sin (ω) in the coil (9c).
A magnetic field represented by t-4π / 3) is generated, and the magnetic fields (H ₂ ), (H ₃ ) are, as shown in FIG. 7, the x-axis which is the direction of the magnetic field (H ₁ ) and 120 ° and 240 ° respectively
Occurs in the direction of.

When the above magnetic fields (H ₁ ), (H ₂ ), and (H ₃ ) are divided into x component and y component, respectively, and the suffixes x and y are added, the margins are as shown below.

[0015]

[Equation 1] Finally, when three magnetic fields are combined and the magnetic field due to the coil assembly is obtained, as shown in Equation 2 below,

[0016]

[Equation 2] Becomes From both equations and the equation of sin ωt ² + cos ωt ² = 1 as shown in the following Equation 3,

[0017]

[Equation 3] And the direction of the magnetic field is as shown in FIG.

[0018]

[Equation 4] It rotates at the number of rotations of

[0019]

[Equation 5] Is the street. When the coil assembly in the above-mentioned set state is inserted into the tube (K) which is a conductor as shown in FIG. 9,
Inside the tube, as shown in the figure, a magnetic field (H) is generated on the circumference.
An eddy current that moves according to the rotation of the direction is generated, and flaw detection is possible by detecting this.

In the flaw detection probe of the present invention or the flaw detection method using the same, however, the magnetic field (H ₁ ) to (H _x ) is rotated without rotating the probe itself to form a spiral shape. Since the scanning can be performed, it is possible to prevent the probe from increasing in size by eliminating the need for a rotation mechanism, and to maintain good insertability into a curved pipe section, durability, and maintainability. In addition, the scanning by the rotation of the magnetic field is about 4 to 6 rps in the conventional rotating coil type probe, but 1000 rps is detected if the flaw is detected with an alternating current of 1 kHz
It is possible to obtain the number of rotations of the rotary coil type probe, which enables high-speed inspection several hundred times that of the rotary coil type probe.

Further, the eddy current flaw detection probe of the present invention not only enables high-speed inspection equal to or higher than that of the conventional bobbin coil type probe as described above, but the flaw detection also detects eddy currents generated on the peripheral surface of the object to be inspected. Since it is for detection, defects such as cracks can be detected with high sensitivity regardless of whether it is in the circumferential direction or the axial direction, and the eddy current is generated together with the rotating magnetic field. It is also suitable for detailed inspections, as it does not have a region with low sensitivity like a probe.

Therefore, the eddy current flaw detection probe of the present invention is
It is capable of performing detailed inspections of the total length and length of many pipes at high speed, and is ideal for maintenance inspection of many pipes such as heat exchangers of nuclear reactors.

Although the embodiments of the present invention have been described above, the number of the coils may be two or four or more as long as the same rotating magnetic field can be obtained, and the shape of the coil is not necessarily circular. It does not need to be wound into a shape. Further, the arrangement of the bobbin coil is not limited to the above-mentioned position as long as it can detect the eddy current, and the shape, the quantity, the relative arrangement, etc. of various parts constituting the probe, such as the shape of the guide, Various changes can be made without departing from the scope of the present invention.

[0024]

As described above, according to the present invention, a plurality of coils wound substantially parallel to the respective axial cross sections that divide the probe into substantially equal parts in the circumferential direction are arranged. Using an insertion type eddy current flaw detection probe, an alternating current is applied to each of the above coils in order to gradually delay the phase from the adjacent ones to generate a radial magnetic field rotating in the circumferential direction on the object to be inspected. The eddy current generated on the peripheral surface of the object to be inspected is detected, and the probe itself does not rotate, but the magnetic field is rotated to perform a spiral scan,
As a result, it is possible to prevent the probe from increasing in size by eliminating the need for a rotating mechanism, and to maintain good insertability into a curved pipe section or the like, durability, and maintainability. Moreover, the scanning by the rotation of the magnetic field described above can obtain a rotation speed of 1000 rps by detecting flaws with an alternating current of 1 kHz, which enables high-speed inspection several hundred times that of the conventional rotary coil type probe.

Further, in the eddy current flaw detection probe of the present invention, since flaw detection detects an eddy current generated on the peripheral surface of the object to be inspected, defects such as cracks are present in either the circumferential direction or the axial direction. Since it is possible to perform flaw detection with high sensitivity, and since the eddy current is generated together with the rotating magnetic field, it is suitable for detailed inspection without the area of poor sensitivity as in the conventional multi-coil type probe.

That is, the eddy current probe of the present invention is capable of performing a detailed inspection of the total length and the total number of many pipes at high speed, and is most suitable for the maintenance inspection of many pipes such as a heat exchanger of a nuclear reactor. Can be said to be.

[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 an explanatory view showing an axial cross section of the embodiment.

FIG. 3 is an explanatory diagram showing a coil of the example.

FIG. 4 (a) is an explanatory view showing the coil of the embodiment as seen from the axial direction of the probe. (B) It is explanatory drawing which looked at the same coil from the direction orthogonal to the axis of a probe.

FIG. 5 is a front view showing an eddy current flaw detection probe according to a second embodiment of the present invention.

FIG. 6 is an explanatory view of rotation of a magnetic field (perspective view).

FIG. 7 is an explanatory diagram of rotation of a magnetic field.

FIG. 8 is an explanatory diagram of rotation of a magnetic field.

FIG. 9 is an explanatory diagram showing an object to be inspected, a magnetic field, and an eddy current caused by the magnetic field.

[Explanation of symbols]

(1) Probe body (2) Guide (3) Centering brush (4) Coil assembly (5) Lead wire (6) Flexible tube (7a) Probe axial section (7b) Probe axial section (7c) Probe axis Section (8) Both sides of probe (9a) Coil (9b) Coil (9c) Coil (10) Bobbin coil (11) Eddy current (H ₁ ) to (H _x ) magnetic field (A) Central axis of probe

Claims (2)

[Claims] 1. A cylindrical or columnar insertion type eddy current flaw detection probe to be inserted into a metal tube or the like, on a plurality of axial cross-sections including a central axis of the probe and dividing the probe into substantially equal portions in the circumferential direction. An eddy current flaw detection probe characterized in that a plurality of coils wound around both sides of the probe and wound substantially parallel to the respective cross-sections are arranged. 2. A plurality of axial cross sections including a central axis of a cylindrical or columnar probe and dividing the probe into substantially equal parts in the circumferential direction, passing near both sides of the probe and being substantially parallel to the respective cross sections. Using an insertion type eddy current flaw detection probe having a plurality of coils wound around
An alternating current is made to flow from one next to the other by sequentially delaying the phase to generate a radial magnetic field that rotates in the circumferential direction on the inspection object with the probe inserted, and the vortex is generated on the peripheral surface of the inspection object by the magnetic field. An eddy current flaw detection method, wherein an electric current is detected by each of the above coils or another coil.