JP2003028839A - Eddy current flaw detection probe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an eddy current flaw detection probe capable of uniformizing the cross-sectional shape of an exciting coil. SOLUTION: A thin film is wound to form the exciting coil 6 of the eddy current flaw detection probe to easily manufacture the exciting coil 6 having a uniform cross-sectional shape. The cross-sectional shape of the exciting coil 6 is set to a uniform rectangular shape to stabilize the shape of the outer surface of the exciting coil 6. The eddy current flaw detection probe extremely reduced in the characteristics difference between the exciting coils is constituted to enhance the uniformity of a signal level to hold detection accuracy to a high dimension.

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, and is particularly useful when applied to nondestructive inspection of conduits such as heat transfer tubes in various plants.

[0002]

2. Description of the Related Art The eddy current flaw detection method is widely used for nondestructive inspection of metal conduits, which are magnetic materials such as heat transfer tubes, and various eddy current flaw detection probes have been proposed for application thereto. There is. As an eddy current flaw detection probe, there is known a structure in which an exciting coil is provided on a tubular body made of resin or the like, and a film-shaped detection coil is provided on the outer periphery of the tubular body. The exciting coil is formed, for example, by winding a number of thin copper wires arranged in the axial direction and winding them in a radial direction so as to be wound many times, and by adhering the thin wires with an adhesive or the like so as to form a tubular shape. There is.

In the case of an eddy current flaw detection probe in which one to four exciting coils are provided in the circumferential direction of a cylindrical body, a pipe line such as a heat transfer tube is moved in the axial direction while rotating at a predetermined angle in the circumferential direction. , It is designed to inspect each part. Also,
In the case of a multi-coil type eddy current flaw detection probe in which an exciting coil is provided over the entire circumference of a tubular body, the pipe line is moved in the axial direction without being rotated to perform flaw detection in each part.

[0004]

In the conventional eddy current flaw detection probe, the exciting coil is formed by winding a number of thin wires into a tubular shape, and therefore, depending on the contact state of each wire and the overlapping / unwinding state, the exciting coil It is conceivable that the cross-sectional shape of will change. If the cross-sectional shape of the exciting coil changes instead of being rectangular, the shape of the outer surface is not stable, the generated magnetic field has a non-uniform distribution, and the eddy current induced in the flaw-detected portion also becomes non-uniform. In particular, when applied to a multi-coil type eddy current flaw detection probe, there is a possibility that the uniformity of the signal level among the exciting coils is lowered and the detection accuracy is lowered. By reducing the diameter of the thin wire, it is possible to suppress changes in the cross-sectional shape of the exciting coil, but there is a limit to reducing the diameter of the thin wire, and this is not a fundamental solution.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an eddy current flaw detection probe which can make the cross-sectional shape of an exciting coil uniform.

[0006]

The structure of the eddy current flaw detection probe of the present invention for achieving the above object is to generate an eddy current in a member to be measured by an exciting coil for supplying an exciting current, and to cause the eddy current. In the eddy current flaw detection probe for detecting the change in the magnetic flux by utilizing the change in the generated magnetic flux due to the scratch generated in the member to be measured, a thin film is wound to form an exciting coil.

The exciting coil is fixed to the cylindrical body. In addition, a large number of exciting coils are fixed to the cylindrical body in the circumferential direction. In addition, a large number of exciting coils are fixed in a state in which they are present over the entire circumference of the tubular body on a surface intersecting the axis of the tubular body. Moreover, the exciting coil is non-circular.

[0008]

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is an external view of a pipe inspection apparatus equipped with an eddy current flaw detection probe according to an embodiment of the present invention, FIG. 2 is an exploded perspective view of the eddy current flaw detection probe, and FIG. A cross section in the direction crossing the axial direction, a cross section along the line IV-IV in FIG. 3 in FIG. 4, and a detailed external view of the exciting coil in FIG.
FIG. 6 is a side view of the exciting coil, and FIG. 7 is VII-VII in FIG.
A line cross section is shown.

As shown in FIG. 1, in a pipe inspection device 1, an eddy current flaw detection probe 2, a signal transmission unit 3 and the like are linearly connected via a flexible member 4.
The pipe inspection device 1 moves axially in a pipe (not shown), the flexible member is bent at the bent portion of the pipe, and the entire pipe inspection device 1 is inserted along the bent pipe.

As shown in FIGS. 1 and 2, the eddy current flaw detection probe 2 is constructed by providing a large number of exciting coils 6 in the circumferential direction of a cylindrical body 5 made of resin. The detection coil member 7 having the detection coil 9 baked in a film shape is wound around the cylindrical surface of the cylindrical main body 5.

As shown in FIGS. 3 and 4, the cylindrical main body 5 is provided with exciting coils 6 arranged in parallel in parallel with two rows inclined in the axial direction (see FIG. 4). The exciting coil 6 has a cylindrical surface. A large number are fixed so that they exist over the entire circumference in the plane intersecting the axis of the main body 5 (see FIG. 3). The cylindrical main body 5 is formed from a liquid resin by stereolithography, and a groove for disposing the exciting coil 6 is also formed at the same time.

When the pipe inspection device 1 is moved in the pipe in the axial direction, an exciting current is supplied to the exciting coil 6 to generate an eddy current in the pipe. By detecting the magnetic flux caused by the eddy current by the detection coil 9 of the detection coil member 7, the change in the magnetic flux caused by the eddy current is detected by utilizing the fact that the magnetic flux caused by the eddy current changes due to the scratches generated in the pipe. Then, the pipe is inspected.

It is preferable that the large number of exciting coils 6 stabilize the shape of the outer surface, have a uniform distribution of the generated magnetic field, and make the eddy current induced in the portion to be flawed uniform. When applied to the multi-coil type eddy current flaw detection probe 2 shown in the figure, signal level uniformity among the excitation coils 6 is required to maintain detection accuracy.

In order to satisfy such requirements, the exciting coil 6 of the present embodiment is formed by winding copper strip-shaped thin films in multiple layers. That is, as shown in FIGS. 5 to 7, a plurality of copper thin films 11 are wound to form the exciting coil 6, and the exciting coil 6 has a perfect circular shape in a side view (see FIG. 6).
It has become.

In the conventional exciting coil, since the fine wires are arranged in the axial direction, there is a limit in stabilizing the shape of the outer surface. On the other hand, since the thin film 11 is wound to form the exciting coil 6, as shown in FIG. 7, one thin film 11 exists in the axial direction, and a rectangular cross section is formed. As a result, it becomes possible to stabilize the shape of the outer surface, generate a magnetic field having a uniform distribution, and make the eddy current induced in the flaw-detected portion uniform.

Further, since the thin film 11 is wound to form the exciting coil 6, it is not necessary to wind a thin wire several tens of times as in the conventional case, and it is easy to form a uniform rectangular cross section. The shape of the surface can be stabilized. For this reason, when the individual differences of a large number of exciting coils 6 are reduced and applied to the multi-coil type eddy current flaw detection probe 2, the eddy current flaw detection probe 2 having an extremely small characteristic difference between the exciting coils 6 becomes the excitation coil 6 The uniformity of the signal level between them becomes high, and the detection accuracy can be maintained at a high level.

Further, since the exciting coil 6 has a perfect circular shape in a side view, there is no positional restriction in the circumferential direction when the magnetizing coil 6 is assembled into the tubular body 5, and the magnetizing coil 6 has excellent positioning performance and can be easily assembled. You can

The situation of the signal level will be described with reference to FIG. Fig. 8 (a) shows the signal level of the eddy current flaw detection probe 2 having the exciting coil 6, and Fig. 8 (b) shows the signal level of the eddy current flaw detection probe having the exciting coil made by the conventional thin wire. The situation is shown. In the figure, the horizontal axis represents the position of the exciting coil in the circumferential direction of the eddy current flaw detection probe with the tubular body expanded, and the vertical axis represents the signal level. Then, a state in which a scratch is present at the position A in the figure is shown.

As shown in FIG. 8 (a), in the eddy current flaw detection probe 2 provided with the exciting coils 6, the characteristic differences among the large number of exciting coils 6 are small and the signal levels among the exciting coils 6 are highly uniform. Therefore, the signal level is high only at the position A where the scratch is present. Therefore, it becomes easy to specify the position A, and the detection accuracy is improved.

On the other hand, as shown in FIG. 8 (b), in the eddy current flaw detection probe provided with the exciting coil made of a thin wire, the cross-sectional shape of the exciting coil is not rectangular but changes on the outer surface. Since the shape is not stable, the generated magnetic field has a non-uniform distribution and the induced eddy current is non-uniform. For this reason, the uniformity of the signal level between the exciting coils is reduced, and the signal level becomes high even at positions other than the A position where the flaw exists. Therefore, it becomes difficult to specify the position A, resulting in a decrease in detection accuracy.

Therefore, the eddy current flaw detection probe 2 described above is used.
Since the exciting coil 6 having a uniform cross-sectional shape can be easily manufactured, the eddy current flaw detection probe 2 is provided with the exciting coil 6 having uniform characteristics, and excellent detectability can be realized.

Another embodiment of the exciting coil will be described with reference to FIG. FIG. 9 shows a side view of an exciting coil according to another embodiment of the present invention.

In general, the larger the coil, the larger the exciting current. Therefore, it is preferable that the exciting coil used in the eddy current flaw detection probe is large. There is a limit to increasing the diameter of the exciting coil. Therefore, FIG.
The exciting coil 15 shown in (1) is configured by winding the thin film 11 in a non-circular elliptical shape. The exciting coil 15 can be made large without increasing the diameter of the eddy current flaw detection probe by making the exciting coil 15 elliptical and aligning the minor axis direction with the radial direction of the cylindrical body. For this reason,
The exciting current is increased and the coil performance can be improved.

In the case of the conventional exciting coil made of thin wires, since the thin wires are aligned in the axial direction and fixed with an adhesive or the like, if they are made elliptical, they can be joined to each other and affect the outer surface. Will be a factor that affects. In the case of the exciting coil 15 shown in FIG. 9, since the thin film 11 is formed by being wound, there is no factor that affects the outer surface even if it is an ellipse, and thus it is easy to make it non-circular. Therefore, by winding the thin film 11, a structure in which the degree of freedom of the coil shape is increased as compared with the excitation coil manufactured by the conventional thin wire.

Since the thin film 11 is wound to have a structure in which the degree of freedom of the coil shape is increased, the shape of the exciting coil 15 is not limited to an ellipse, and has a linear portion for positioning in the circumferential direction. It is possible to have an arbitrary shape such as a non-circular shape formed on the portion.

In the above-mentioned embodiment, the multi-coil type eddy current flaw detection probe in which a large number of exciting coils are provided in the circumferential direction of the cylindrical main body has been described as an example. It is also possible to provide about four pieces so that the eddy current flaw detection probe can rotate at a predetermined angle. In this case, it is possible to use an exciting coil in which the generated magnetic field has a uniform distribution, the eddy currents induced in the scratches are also uniform, and excellent detectability can be realized.

[0028]

The eddy current flaw detection probe of the present invention generates an eddy current in a member to be measured by an exciting coil that supplies an exciting current, and a magnetic flux resulting from this eddy current is generated in the member to be measured by a flaw. In the eddy current flaw detection probe for detecting the change in magnetic flux by utilizing the change, the thin film is wound to form the exciting coil, so the exciting coil has a uniform rectangular cross-sectional shape, and the shape of the outer surface is It is possible to stabilize the generated magnetic field with a uniform distribution and make the eddy current induced in the flaw-detected portion uniform. As a result, an exciting coil having a uniform cross-sectional shape can be easily manufactured, and excellent detectability can be realized.

In particular, by using a multi-coil type eddy current flaw detection probe in which a large number of exciting coils are provided in the circumferential direction of the cylindrical body, it is possible to obtain an eddy current flaw detection probe with a very small characteristic difference between the exciting coils. As a result, the uniformity of the signal level among the exciting coils becomes high, and the detection accuracy can be maintained at a high level.

Further, since the exciting coil is formed by winding the thin film, it is easy to form the exciting coil in a non-circular shape. By making the exciting coil non-circular (for example, elliptical), the diameter of the eddy current flaw detection probe can be increased. The exciting coil can be made large, and the exciting current can be made large to improve the coil performance.

[Brief description of drawings]

FIG. 1 is an external view of a pipe inspection apparatus including an eddy current flaw detection probe according to an embodiment of the present invention.

FIG. 2 is an exploded perspective view of an eddy current flaw detection probe.

FIG. 3 is a sectional view of the eddy current flaw detection probe in a direction intersecting the axial direction.

FIG. 4 is a sectional view taken along line IV-IV in FIG.

FIG. 5 is a detailed external view of an exciting coil.

FIG. 6 is a side view of an exciting coil.

FIG. 7 is a sectional view taken along line VII-VII in FIG.

FIG. 8 is a graph illustrating a signal level situation.

FIG. 9 is a side view of an exciting coil according to another embodiment of the present invention.

[Explanation of symbols]

1 Piping inspection device 2 Eddy current flaw detection probe 3 Signal transmission unit 4 Flexible member 5 tubular body 6,15 Excitation coil 7 Detection coil member 9 Detection coil 11 thin film

Claims (5)

[Claims] 1. An eddy current is generated in a member to be measured by an exciting coil which supplies an exciting current, and the magnetic flux resulting from this eddy current is changed by a scratch generated in the member to be measured. An eddy current flaw detection probe for detecting a change, wherein an exciting coil is formed by winding a thin film. 2. The eddy current flaw detection probe according to claim 1, wherein the exciting coil is fixed to the cylindrical main body. 3. The eddy current flaw detection probe according to claim 2, wherein a large number of exciting coils are circumferentially fixed to the cylindrical body. 4. The eddy current flaw detection probe according to claim 3, wherein a large number of exciting coils are fixed in a state where they are present over the entire circumference of the tubular main body on a plane intersecting the axis of the tubular main body. 5. The eddy current flaw detection probe according to claim 1, wherein the exciting coil has a non-circular shape.