JP2009257794A - Rotary eddy current flaw detection probe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rotary eddy current flaw detection probe capable of detecting the flaw in the whole direction of the deep layer part of a thin-walled metal by one scanning. <P>SOLUTION: A first exciting coil group is formed of a pair of exciting coils 31a and 31b and a pair of other exciting coils 32a and 32b while a second exciting coil group is formed of a pair of exciting coils 33a and 33b and a pair of other exciting coils 34a and 34b. The respective pairs of two exciting coils produce magnetic fields in opposite directions. The exciting current of the first exciting coil group and the exciting current of the second exciting coil group are different by 90° in phase. The exciting coils of the first exciting coil group and the second exciting coil group produce rotary eddy currents in an inspection target M2 and the eddy currents in the vicinity of the surface of the inspection target M2 are set off to be reduced. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a rotating eddy current flaw detection probe using a rotating magnetic field.

The conventional eddy current flaw detection probe is suitable for flaw detection of a metal such as a relatively thin steel plate, but it is difficult to flaw a deep portion of a thick metal. Therefore, an eddy current flaw detection probe capable of flaw detection inside a thick metal has been proposed (see Patent Document 1).
FIG. 7 shows a configuration of a conventional eddy current flaw detection probe suitable for flaw detection of a thick metal. 7 (a) is a plan view, FIG. 7 (b) is a cross-sectional view of the X1 portion of FIG. 7 (a) in the direction of the arrow, and FIG. 7 (c) is the X2 direction coil of FIG. 7 (a). It is a side view.
A circular (pancake-shaped) detection coil 13 is arranged on the inspection surface of the metal object M1 so that the coil surface is parallel to the inspection surface, and the excitation coil 11a has a rectangular coil surface on both sides of the detection coil 13. 11b and 12a, 12b are arranged so that the coil surfaces are perpendicular to the inspection surface.
An exciting current in the reverse direction is supplied to the exciting coils 11a and 11b, and an exciting current in the opposite direction is supplied to the exciting coils 12a and 12b. An exciting current in the same direction is supplied to the exciting coils 11b and 12b, and an exciting current in the same direction is supplied to the exciting coils 11a and 12a.

When the four exciting coils 11a to 12b are excited as described above, eddy currents induced on the surface of the inspection object M1 by the four exciting coils are canceled out and reduced, so that the detection coil 13 has a strong surface. It is possible to detect the eddy current in the deep portion of the object M1 without being affected by the eddy current.
However, the eddy current flaw detection probe of FIG. 7 is difficult to detect when the direction of the flaw is perpendicular to the scanning direction of the probe.

On the other hand, a probe has also been proposed that can detect scratches in all directions by one scan of the eddy current flaw detection probe regardless of the direction of the scratch (see Patent Document 2).
An eddy current flaw detection probe capable of detecting scratches in all directions will be described with reference to FIG. 8A is a plan view, FIG. 8B is a cross-sectional view of the X1 portion of FIG. 8A in the arrow direction, and FIG. 8C is the arrow direction of the X2 portion of FIG. 8A. FIG. 8D is a diagram for explaining the rotating magnetic field.
The exciting coil 21b is inserted into the exciting coil 21a, and the coil surfaces of both exciting coils are orthogonal to each other and are arranged to be perpendicular to the inspection surface of an object to be inspected (not shown). Between the excitation coil 21a and the excitation coil 21b and the inspection surface, a circular (pancake-shaped) detection coil 22 is arranged so that the coil surface is parallel to the inspection surface. Excitation currents that are 90 degrees out of phase flow through the excitation coil 21a and the excitation coil 21b. As shown in FIG. 8D, the direction of the eddy current generated on the inspection surface changes 360 degrees during one period T and changes 360 degrees. Can be detected.
The eddy current flaw detection probe shown in FIG. 8 can detect flaws in all directions on the surface of the object to be inspected, but flaw detection in the deep layer is difficult.

JP 2006-10665 A JP 2002-131285 A

  In view of the problems of the conventional eddy current flaw detection probe, the present invention provides an eddy current flaw detection probe that generates (induces) a rotating eddy current in a test object to detect flaws in all directions. An object of the present invention is to provide a rotating eddy current flaw detection probe capable of flawing flaws in the deep layer.

In order to achieve the object of the present invention, the rotating eddy current flaw detection probe according to claim 1 is a group of exciting coils in which the coil axes of two pairs of exciting coils coincide and the coil surfaces are perpendicular to the inspection surface of the object to be inspected. N (an integer of 2 or more) group and a detection coil whose coil surface is parallel to the inspection surface of the object to be inspected, and two excitation coils in each excitation coil group are arranged on both sides of the detection coil, respectively. The coil axes of the groups intersect at the center of the detection coil and are arranged at intervals of “2π / 2N” degrees, the two excitation coils of each pair of each excitation coil group generate a magnetic field in the opposite direction, and the excitation current is The phase is different by “2π / 2N” degrees for each excitation coil group.
The rotating eddy current flaw detection probe according to claim 2 is characterized in that the N is 2 in the rotating eddy current flaw detection probe according to claim 1.
The rotating eddy current flaw detection probe according to claim 3 is the rotating eddy current flaw detection probe according to claim 1, wherein the N is 3.

The rotating eddy current flaw detection probe of the present invention can detect flaws in all directions of the deep layer portion of the object to be inspected by one scanning of the probe and can also determine the depth and direction of the flaws. It is possible to detect a scratch on the object to be inspected in a short time and to increase the detection accuracy.
In the rotating eddy current flaw detection probe according to the present invention, when the number of exciting coil groups is three, the detection sensitivity of a flaw does not decrease even in an intermediate portion between the exciting coil group and the exciting coil group.

  An embodiment of the present invention will be described with reference to FIGS.

FIG. 1 shows the configuration of a rotating eddy current flaw detection probe. FIG. 1A is a plan view when a rotating eddy current flaw detection probe is arranged on the inspection surface of a metal object to be inspected, and FIG. 1B is a cross-sectional view of the Y1 portion of FIG. FIG.1 (c) is the figure which abbreviate | omitted the coil support member 41 in FIG.1 (b).
The excitation coil section includes a first excitation coil group including a pair of square excitation coils 31a and 31b and another pair of square excitation coils 32a and 32b, a pair of square excitation coils 33a and 33b, and another pair of squares. And a second exciting coil group consisting of the exciting coils 34a and 34b. The four coils of the excitation coils 31a, 31b, 32a, and 32b have the same coil axis (center axis) Z1, and the coil surface (the surface surrounded by the windings and perpendicular to the coil axis) is the metal MUT. They are arranged so as to be perpendicular to the inspection surface (the coil axis is parallel to the inspection surface). Similarly, the four coils of the exciting coils 33a, 33b, 34a, and 34b are also arranged so that the coil axis Z2 coincides and the coil surface is perpendicular to the inspection surface of the metal object M2. The first excitation coil group and the second excitation coil group are arranged so that the coil axis Z1 and the coil axis Z2 are orthogonal to each other.
The circular (pancake-shaped) detection coil 37 is arranged so that the coil axis is perpendicular to the inspection surface of the object M2 to be inspected (the coil surface is parallel) and coincides with the intersection of the coil axis Z1 and the coil axis Z2. It is. That is, the detection coil 37 is arranged such that the center of the coil surface is the intersection of the coil axis Z1 and the coil axis Z2.
Each excitation coil and detection coil 37 of the first excitation coil group and the second excitation coil group are attached to the support member 41.

Next, the excitation current that flows through each excitation coil of the first excitation coil group and the second excitation coil group will be described.
First, in the case of the first excitation coil group, an excitation current is passed through the pair of excitation coils 31a and 31b so that the magnetic fields generated by both excitation coils are in opposite directions (reverse polarity). Similarly, the other pair of exciting coils 32a and 32b also pass an exciting current so that the magnetic fields generated by both exciting coils are in opposite directions (reverse polarity). In that case, the excitation coils 31b and 32b on the side (inner side) close to the two pairs of detection coils 37 generate magnetic fields in the same direction, and the excitation coils 31a and 32a on the side (outer side) far from the two pairs of detection coils 37 also. Generate a magnetic field in the same direction.
Similarly, in the case of the second exciting coil group, the magnetic fields generated by the two exciting coils are reversed in the pair of exciting coils 33a and 33b, and the two exciting coils are also generated in the other pair of exciting coils 34a and 34b. An exciting current is passed so that the magnetic field to be reversed is in the opposite direction. In this case, the excitation coils 33b and 34b on the side (inner side) close to the two pairs of detection coils 37 generate a magnetic field in the same direction, and the excitation coils 33a and 34a on the side farther (outer side) of the two pairs of detection coils 37 also. Generate a magnetic field in the same direction.

The excitation current of the first excitation coil group and the excitation current of the second excitation coil group are 90 degrees out of phase. For example, the excitation coil 31a of the first excitation coil group and the excitation coil 33a of the second excitation coil group have an excitation current phase difference of 90 degrees, and the excitation coil 31b and the excitation coil 33b also have an excitation current phase difference of 90 degrees. . The same applies to the other exciting coils.
As described above, the two excitation coils in each pair of the first and second excitation coil groups generate magnetic fields in opposite directions. The excitation current of the first excitation coil group and the excitation current of the second excitation coil group are 90 degrees out of phase.

In the rotating eddy current flaw detection probe shown in FIG. 1, the eddy currents generated in the inspection object M2 by each pair of excitation coils of the first excitation coil group are reversed in direction and are canceled near the surface. Similarly, eddy currents generated in the inspected object M2 by each pair of exciting coils of the second exciting coil group are canceled and reduced near the surface. On the other hand, since the excitation current of the first excitation coil group and the excitation current of the second excitation coil group are 90 degrees out of phase, the eddy current generated in the object M2 is a rotating eddy current.
Therefore, the rotating eddy current flaw detection probe shown in FIG. 1 generates a rotating eddy current in the inspection object M2, so that it is possible to detect scratches in all directions by one scan of the probe. Further, since the eddy current near the surface of the object to be inspected is canceled, it is possible to detect a flaw in the deep layer portion of the object to be inspected without being affected by a large eddy current near the surface.

  In order to generate a reverse magnetic field in the two excitation coils of each pair of each excitation coil group, for example, the excitation coils 31a and 31b of the first excitation coil group, those having the same winding direction are used for both excitation coils. In addition, power sources having opposite phases (180 degrees different) may be connected to both excitation coils separately, or coils having opposite winding directions may be used, and the same power source may be connected to both excitation coils. In addition, it is possible to use a method of generating a magnetic field in the reverse direction in two commonly used coils.

FIG. 2 shows an arrangement example of a plurality of exciting coil groups of the rotating eddy current flaw detection probe.
FIG. 2A is an example of a rotating eddy current flaw probe having two sets of exciting coil groups (same as the rotating eddy current flaw probe in FIG. 1).
The rotating eddy current flaw detection probe shown in FIG. 2A includes a first excitation coil group including a pair of excitation coils 31 and another pair of excitation coils 32, a pair of excitation coils 33, and another pair of excitation coils 34. A second exciting coil group is arranged. Both excitation coil groups are arranged so that the coil axes Z1 and Z2 are orthogonal to each other. Therefore, in the case of FIG. 2A, the pair of exciting coils 31 of the first exciting coil group and the pair of exciting coils 33 of the second exciting coil group are also orthogonal to each other. Similarly, the coil surfaces of the other pair of exciting coils 32 of the first exciting coil group and the other pair of exciting coils 34 of the second exciting coil group are orthogonal to each other.
The two excitation coils in each pair of each excitation coil group are excited so as to generate magnetic fields in opposite directions (reverse polarity). The excitation currents of the first excitation coil group and the second excitation coil group are 90 degrees out of phase.

FIG. 2B is an example of a rotating eddy current flaw detection probe in which three sets of exciting coil groups are arranged.
In FIG. 2B, a third exciting coil group having a coil axis Z3 is added to the rotating eddy current flaw detection probe shown in FIG. The third excitation coil group includes a pair of excitation coils 35 and another pair of excitation coils 36, and has the same configuration as the first and second excitation coil groups. The coil axes Z1, Z2, and Z3 intersect at an angle of 60 degrees. The excitation currents of the first, second, and third excitation coil groups are 60 degrees out of phase with each other.
In the rotating eddy current flaw detection probe shown in FIG. 2A, since the eddy current generated in the middle part (near 45 degrees) of the coil axes Z1 and Z2 is small, the detection sensitivity of the scratches at that part is low. However, the rotating eddy current flaw detection probe of FIG. 2B can eliminate the decrease in detection sensitivity of the rotating eddy current flaw detection probe of FIG. 2A by adding the third exciting coil group.
The example in which the exciting coil groups are 2 groups (groups) and 3 groups (groups) has been described. However, when the coil groups are N (2 or more) groups, the coil axis is set to “360 degrees (2π) / 2N. And the phase of the excitation current of each excitation coil group is different by “360 degrees (2π) / 2N”.

Next, a flaw detection test performed using the rotating eddy current flaw detection probe of FIG. 1 will be described with reference to FIGS.
In the flaw detection test, SUS316L with a wall thickness of 25 mm was used as an object to be inspected, and the object to be inspected was subjected to electric discharge machining of scratches having a width of 0.5 mm, a length of 40 mm and a depth of 10, 12, 15, 20 mm It was.
The dimensions of one excitation coil of the rotating eddy current flaw detection probe are 10 mm in length, 30 mm in width, 30 mm in height, and the dimensions of the detection coil are 6 mm in diameter and 1 mm ² in winding cross-sectional area. The test frequency was set to 10 kHz.
The test was performed by scanning the rotating eddy current flaw detection probe along the center of the scratch in the direction of the scratch, and scanning both ends of the scratch in a direction perpendicular to the scratch.

FIG. 3 shows the amplitude characteristics of the zero-phase component and the 90-degree phase advance component of the scratch signal when the rotating eddy current flaw detection probe is scanned in the scratch direction (the scratch angle is 0 degrees with respect to the scanning direction). The figure shows the normalized amplitude.
FIG. 3A shows a case where the rotating eddy current flaw detection probe of FIG. 1 is excited so that the magnetic fields generated by two pairs of two exciting coils (for example, the exciting coils 31a and 31b) are in the same direction. FIG. 3B shows a case where excitation is performed so that the magnetic field is in the opposite direction.

In FIGS. 3A and 3B, “a” indicates a case where the depth of the scratch is 10 mm, “b” indicates a case where the depth of the scratch is 15 mm, and “c” indicates a case where the depth of the scratch is 20 mm.
In the case of FIG. 3A, the amplitude and phase of the scratch signal (output of the detection coil 37) are not significantly different even if the depth of the scratch is changed. On the other hand, in the case of FIG. 3B, the amplitude of the scratch signal changes corresponding to the depth of the scratch, and the phase of the scratch signal becomes slower as the scratch becomes deeper. Therefore, in the case of FIG. 3B, when the rotating eddy current flaw detection probe of FIG. 1 is excited so that the magnetic fields generated by the two excitation coils of each of the four pairs are in opposite directions, the amplitude of the scratch signal and It can be seen that the phase corresponds to the depth of the scratch.

FIG. 4 shows the amplitude characteristics of the zero-phase component and the 90-degree phase advance component of the scratch signal when the rotating eddy current flaw detection probe is scanned in the direction perpendicular to the scratch (the scratch angle is 90 degrees with respect to the scanning direction). . The figure shows the normalized amplitude.
FIG. 4A shows a case where the rotating eddy current flaw detection probe of FIG. 1 is excited so that the magnetic fields generated by two pairs of two exciting coils (for example, the exciting coils 31a and 31b) are in the same direction. FIG. 4B shows a case where excitation is performed so that the magnetic field is in the opposite direction.
In FIGS. 4A and 4B, “a” indicates a case where the depth of the scratch is 10 mm, “b” indicates a case where the depth of the scratch is 15 mm, and “c” indicates a case where the depth of the scratch is 20 mm.

In the case of FIG. 4A, the amplitude and phase of the scratch signal are not significantly different even if the depth of the scratch is changed. On the other hand, in the case of FIG. 4B, the amplitude of the scratch signal changes corresponding to the depth of the scratch, and the phase of the scratch signal becomes slower as the scratch becomes deeper. Therefore, in the case of FIG. 4B, when the rotating eddy current flaw detection probe of FIG. 1 is excited so that the magnetic fields generated by the two pairs of two exciting coils are in opposite directions, the amplitude of the scratch signal and It can be seen that the phase corresponds to the depth of the scratch.

FIG. 5 shows the depth of the scratch and the amplitude characteristic of the scratch signal (FIG. 5A) when the rotating eddy current flaw detection probe is scanned in the scratch direction (the scratch angle is 0 degrees with respect to the scanning direction). Depth and phase characteristics (FIG. 5B) are shown. The figure shows the normalized amplitude and phase.
In the figure, black circles indicate the case where the rotating eddy current flaw detection probe of FIG. 1 is excited so that the magnetic fields generated by two pairs of two exciting coils (for example, the exciting coils 31a and 31b) are in the same direction. A white circle indicates a case where excitation is performed so that the magnetic field is in the opposite direction.

5A, the change in the amplitude with respect to the change in the depth of the scratch is greater when the magnetic fields of the two exciting coils are in the opposite direction than when the magnetic fields of the two exciting coils are in the same direction. For example, the difference in amplitude between the scratch depth of 20 mm and 10 mm is about 1.25 times when the magnetic field is in the same direction, and is about twice when the magnetic field is in the reverse direction. Therefore, when the magnetic fields of the two exciting coils are in opposite directions, the amplitude of the scratch signal corresponds to the depth of the scratch.
5B, when the magnetic fields of the two exciting coils are in the same direction, the phase of the scratch signal hardly changes even if the scratch depth changes, but the magnetic field is reversed. In the case of the direction, if the depth of the scratch changes, the phase of the scratch signal also changes greatly. Therefore, when the magnetic fields of the two exciting coils are in opposite directions, the phase of the scratch signal corresponds to the depth of the scratch.

FIG. 6 shows a flaw depth and a flaw signal amplitude characteristic (FIG. 6A) when a rotating eddy current flaw detection probe is scanned in a direction orthogonal to the flaw (the flaw angle is 90 degrees with respect to the scanning direction). Scratch depth and phase characteristics (FIG. 6B) are shown. The figure shows the normalized amplitude and phase.
In the figure, black circles indicate the case where the rotating eddy current flaw detection probe of FIG. 1 is excited so that the magnetic fields generated by two pairs of two exciting coils (for example, the exciting coils 31a and 31b) are in the same direction. A white circle indicates a case where excitation is performed so that the magnetic field is in the opposite direction.

Looking at the amplitude characteristics of FIG. 6A, the change in amplitude with respect to the change in the depth of the scratch is greater when the magnetic fields of the two exciting coils are in the opposite direction than when the magnetic fields of the two exciting coils are in the same direction. For example, the difference in amplitude between the scratch depth of 20 mm and 10 mm is about 1.25 times when the magnetic field is in the same direction, and is about twice when the magnetic field is in the reverse direction. Therefore, when the magnetic fields of the two exciting coils are in opposite directions, the amplitude of the scratch signal corresponds to the depth of the scratch.
6B, when the magnetic fields of the two exciting coils are in the same direction, the phase of the scratch signal hardly changes even if the depth of the scratch changes, but the magnetic field is reversed. In the case of the direction, if the depth of the scratch changes, the phase of the scratch signal also changes greatly. Therefore, when the magnetic fields of the two exciting coils are in opposite directions, the phase of the scratch signal corresponds to the depth of the scratch.

  From the amplitude characteristics and phase characteristics of the flaw signal shown in FIGS. 5 and 6, the rotating eddy current flaw detection probe shown in FIG. 1 can detect flaws in all directions in the deep layer of the object to be inspected by one scan of the probe. It can also be seen that the depth and direction of the scratch can also be determined.

It is the top view and sectional drawing of the rotation eddy current flaw detection probe which concern on the Example of this invention. It is a figure explaining the positional relationship of the exciting coil of the rotating eddy current flaw detection probe which concerns on the Example of this invention. FIG. 3 shows the amplitude characteristic of a scratch signal when the rotating eddy current flaw detection probe of FIG. 1 is scanned in the scratch direction (the scratch angle is 0 degree with respect to the scanning direction). FIG. 3 shows the amplitude characteristic of a scratch signal when the rotating eddy current flaw detection probe of FIG. 1 is scanned in the direction of 90 degrees with a scratch (the scratch angle is 90 degrees with respect to the scanning direction). FIG. 2 shows the depth of the scratch, the amplitude characteristic and the phase characteristic of the scratch signal when the rotating eddy current flaw detection probe of FIG. 1 is scanned in the scratch direction (the scratch angle is 0 degree with respect to the scanning direction). FIG. 2 shows the depth of the scratch, the amplitude characteristic and the phase characteristic of the scratch signal when the rotating eddy current flaw detection probe of FIG. 1 is scanned in the direction of 90 degrees with the scratch (the scratch angle is 90 degrees with respect to the scanning direction). It is the top view and sectional drawing of the conventional eddy current flaw detection probe which detects the crack of the deep layer part. It is the top view and sectional drawing of the conventional rotating eddy current flaw detection probe.

Explanation of symbols

31a to 36a Excitation coils 31b to 36b Excitation coil 37 Detection coil M2 Inspected objects Z1 to Z3 Coil shaft

Claims (3)

  An excitation coil group in which the coil axes of two pairs of excitation coils coincide and the coil surface is perpendicular to the inspection surface of the object to be inspected is an N (an integer of 2 or more) group, and the detection coil whose coil surface is parallel to the inspection surface of the object The two pairs of exciting coils of each exciting coil group are arranged on both sides of the detecting coil, and the coil axes of each exciting coil group intersect at the center of the detecting coil and are arranged at intervals of “2π / 2N” degrees. The two excitation coils in each pair of each excitation coil group generate magnetic fields in opposite directions, and the excitation current has a phase difference of “2π / 2N” for each excitation coil group. Current testing probe.   2. The rotating eddy current flaw detection probe according to claim 1, wherein the N is 2.   2. The rotating eddy current flaw detection probe according to claim 1, wherein said N is three.

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