JP5341028B2 - Eddy current flaw detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an eddy current testing method capable of confirming adhesion when pressing a probe to a surface to be tested even if a curvature radius of the surface to be tested is unknown. <P>SOLUTION: An operation control part 40 finds out a lift-off allowable area A on a lissajous plane from a detection signal generated until an eddy current probe 3 is adhered closely to a plane of a test body 20A and a detection signal generated when adhering the eddy current probe 3 closely to a curved surface of a test body 20B. Further, the operation control part 40 compares a signal on the lissajous plane which is generated in a process for adhering the eddy current probe 3 closely to a body to be tested with the lift-off allowable area A to evaluate lift-off quantity generated when pressing the eddy current probe 3 to an arbitrary curved surface. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention relates to an eddy current flaw detection method, and more particularly to an eddy current flaw detection method suitable for use in eddy current flaw detection on an inspection surface having a curvature.

  The principle of the eddy current flaw detection method is that an eddy current is induced in a test object by an alternating magnetic field generated by the coil for a conductive test object, and the defect is determined from the impedance change of the coil caused by the eddy current disturbance due to the defect. It evaluates the presence or absence of. In the eddy current flaw detector, a signal is also generated by a change in lift-off, which is the distance between the probe and the object to be inspected. It is possible to measure lift-off by using this characteristic. On the other hand, as a probe, a multi-coil probe in which a plurality of coils that can be measured over a wide range and inspected a curved surface are regularly arranged has been developed (for example, see Non-Patent Document 1).

  In the eddy current flaw detection method, the detection sensitivity changes depending on the distance (lift-off) between the probe and the object to be inspected. Therefore, the probe needs to be appropriately disposed on the object to be inspected before the flaw detection. Although this state can be confirmed visually, it may be difficult to visually confirm a narrow part or a part adjacent to a structure. In addition, the same applies to remote operation.

  As a countermeasure, there is known one that estimates the distance from an object to be inspected by using an eddy current flaw detection probe that can obtain a lift-off signal (see, for example, Patent Document 1).

JP 2007-147525 A

Proceedings of the 8th Surface Inspection Symposium p.139-142 (2005)

  Although the thing of patent document 1 evaluates the adhesiveness at the time of arrange | positioning a probe to a to-be-inspected object, it is an effective means when the curvature of the to-be-inspected surface which arrange | positions a probe is known. On the other hand, it is conceivable that the lift-off signal characteristics may change depending on the bending state of the probe for a part where the curvature is unknown, and may not be applicable. For this reason, when the radius of curvature of the surface to be inspected is unknown, another means is required.

  An object of the present invention is to provide an eddy current flaw detection method capable of confirming adhesion when a probe is pressed against a surface to be inspected even when the radius of curvature of the surface to be inspected is unknown.

(1) In order to achieve the above object, the present invention uses an eddy current probe in which a plurality of coils are regularly arranged on a substrate and the same material as an object to be inspected, and uses a specimen that simulates a flat surface and a curved surface. From the detection signal generated until the eddy current probe is brought into close contact with the plane of the specimen and the detection signal generated when the eddy current probe is brought into close contact with the curved surface of the specimen, a lift-off allowable region is obtained on the Lissajous plane. The lift-off amount when pressing the eddy current probe against an arbitrary curved surface is evaluated by comparing the signal on the Lissajous plane generated in the process of bringing the eddy current probe into close contact with the object to be inspected. Is.
With this method, even when the radius of curvature of the surface to be inspected is unknown, it is possible to confirm the adhesion when the probe is pressed against the surface to be inspected.

  (2) In the above (1), preferably, the lift-off allowable region includes a first detection signal generated when the eddy current probe is brought into close contact with a plane of the test body, and the vortex on the curved surface of the test body. The second detection signal generated when the current probe is brought into close contact, the point of the first detection signal on the Lissajous plane where the probe is in close contact, and the second detection signal at the position where the probe is in close contact The point obtained by bringing the eddy current probe closer to the lift-off Xmm to the plane of the specimen on the Lissajous plane and the eddy-current probe closer to the lift-off Xmm to the curved surface of the specimen It is obtained from a point and a straight line approximation obtained from the point.

(3) In the above (1), preferably, the lift-off allowable region includes a first detection signal generated when the eddy current probe is brought into close contact with the plane of the specimen, and a probe on the plane of the specimen. adhesion is, a second detection signal when scanning toward the curved portion maintaining a tight Chakujo state, and a third detection signal generated when releasing the curved or Lapu lobes of the specimen, the test specimen The probe is made close to the lift-off plane of Xmm, and this distance is maintained and obtained from the fourth detection signal generated when scanning the curved surface.

According to the present invention, even when the radius of curvature of the surface to be inspected is unknown, the adhesion when the probe is pressed against the surface to be inspected can be confirmed.

It is a block diagram of the eddy current probe used for the eddy current flaw detection method by one Embodiment of this invention. It is a block diagram which shows the structure of the eddy current flaw detector which implements the eddy current flaw detection method by one Embodiment of this invention. In the eddy current flaw detection method by one Embodiment of this invention, it is explanatory drawing when a probe approaches a flat test surface. In the eddy current flaw detection method by one Embodiment of this invention, it is explanatory drawing when a probe approaches a flat test surface. In the eddy current inspection method by one Embodiment of this invention, it is explanatory drawing when a probe is bent gradually. In the eddy current inspection method by one Embodiment of this invention, it is explanatory drawing when a probe is bent gradually. In the eddy current inspection method by one Embodiment of this invention, it is explanatory drawing when a probe is bent gradually. It is explanatory drawing at the time of scanning a probe with respect to the part where the curvature of a to-be-inspected object changes in the eddy current flaw detection method by one Embodiment of this invention. It is explanatory drawing at the time of scanning a probe with respect to the part where the curvature of a to-be-inspected object changes in the eddy current flaw detection method by one Embodiment of this invention. In the eddy current flaw detection method according to one embodiment of the present invention, it is an explanatory diagram when the probe that is in close contact with the curved surface portion is gradually separated from the surface to be inspected. In the eddy current flaw detection method according to one embodiment of the present invention, it is an explanatory diagram when the probe that is in close contact with the curved surface portion is gradually separated from the surface to be inspected. It is explanatory drawing of the content of the detection signal by the state of a to-be-inspected object and a probe in the eddy current flaw detection method by one Embodiment of this invention. It is a flowchart which shows the content of the eddy current flaw detection method by one Embodiment of this invention. It is explanatory drawing of the eddy current flaw detection method by one Embodiment of this invention. It is a block diagram which shows the structure of the eddy current testing apparatus which implements the eddy current testing method by other embodiment of this invention. It is a flowchart which shows the content of the eddy current flaw detection method by other embodiment of this invention.

Hereinafter, an eddy current flaw detection method according to an embodiment of the present invention will be described with reference to FIGS.
First, the configuration of the eddy current probe used in the eddy current flaw detection method according to the present embodiment will be described with reference to FIG.
FIG. 1 is a configuration diagram of an eddy current probe used in an eddy current flaw detection method according to an embodiment of the present invention. FIG. 1A is a plan view, and FIG. 1B is a front view.

  The multi-coil probe 3 used in this embodiment is one in which a plurality of coils 1 are regularly attached to a flexible substrate 2, and the probe itself bends to adhere to the curvature of the surface to be inspected, and a signal due to the bending is generated. Occur.

  In the eddy current flaw detection probe 3, for example, the detection signal 1ch generates a magnetic field with the coil 1A1 and detects a signal with the coil 1A2. The detection signal 2ch generates a magnetic field at the coil 1B1 and is detected by the coil 1B2. This enables the inspection of the region corresponding to the switching coil width to be performed at a high speed by one scan.

Next, the configuration of the eddy current flaw detection apparatus that performs the eddy current flaw detection method according to the present embodiment will be described with reference to FIG.
FIG. 2 is a block diagram showing a configuration of an eddy current flaw detection apparatus that performs an eddy current flaw detection method according to an embodiment of the present invention. The same reference numerals as those in FIG. 1 indicate the same parts.

  The eddy current flaw detector is composed of a multi-coil probe 3, a moving unit 30, and an arithmetic control unit 40. Further, test bodies 20A and 20B for obtaining an allowable value of the distance (lift-off) between the probe and the surface to be inspected are used. The test body 20A has a flat surface and is made of the same material as the actual inspection part or a member having the same electric / magnetic characteristics. The test body 20B has a circular arc-shaped groove having a predetermined curvature formed on the surface thereof, and is made of the same material as the actual inspection part or a member having the same electric / magnetic characteristics.

  The moving unit 30 moves the multi-coil probe 3 while changing the distance between the test bodies 20 </ b> A and 20 </ b> B, and is controlled by the calculation control unit 40. The moving unit 30 can also bring the multi-coil probe 3 into close contact with the test bodies 20A and 20B. As indicated by a broken line A, the moving unit 30 can gradually bring the multi-coil probe 3 closer to the surface of the test body 20A and can be brought into close contact with the surface of the test body 20A. Further, as indicated by a broken line B, the moving unit 30 moves the multi-coil probe 3 onto the test body 20B, gradually brings the multi-coil probe 3 closer to the surface of the test body 20B, and further the surface of the test body 20B. Can be adhered to. When the multi-coil probe 3 is in close contact with the arc-shaped groove of the test body 20B, the multi-coil probe 3 is bent according to the curvature of the groove. Furthermore, as shown by the broken line C, the moving unit 30 can gradually move away from the state in which the multi-coil probe 3 is in close contact with the test body 20B. At this time, the moving unit 30 moves while maintaining the bent state of the multi-coil probe 3.

The arithmetic control unit 40 generates a magnetic field by the coil 1A 1 shown in FIG. 1 of the eddy current flaw detection probe 3, for example. At this time, the signal detected from the coil 1A2 shown in FIG.

Next, the principle of lift-off measurement in the eddy current flaw detection method according to the present embodiment will be described with reference to FIGS.
A mutual induction type standard comparison type eddy current flaw detection probe having an excitation coil and a detection coil generates a detection signal corresponding to the distance (lift-off) between the probe and the surface to be inspected. As shown in FIG. 1, the multi-coil probe 3 on the flexible substrate 2 fitted with a plurality of coils regularly is in close contact with the curvature of the inspected surface by the probe itself is bent, but the signal due to bending Occur.

  Hereinafter, the signals due to lift-off and probe bending will be described.

First, with reference to FIG. 3 and FIG. 4, changes in the detection signal of the probe when the probe approaches the flat inspection surface in the eddy current flaw detection method according to the present embodiment will be described.
FIG. 3 and FIG. 4 are explanatory diagrams when the probe approaches the flat inspection surface in the eddy current flaw detection method according to the embodiment of the present invention. The same reference numerals as those in FIG. 1 indicate the same parts.

As shown in FIG. 3, in the inspection, for installing the probe 3 to the surface to be inspected, the surface is away from the plate-shaped specimen 20A (state 1), to move the probe 3 in the direction of arrow A, the test There is a state (state 2) in which the body 20A is brought into close contact with and close to the body 20A. The detection signal of the probe 3 generated during this time is a signal due to lift-off.

  Here, FIG. 4 shows a detection signal generated by the pair of the coil 1An and the coil 1A (n + 1). In FIG. 4, the horizontal axis indicates the X component, and the vertical axis indicates the Y component. Assuming that (state 1) is (origin 5), the lift-off signal draws a locus toward (point 6) indicating (state 2).

Next, changes in the detection signal of the probe when the probe is gradually bent in the eddy current flaw detection method according to the present embodiment will be described with reference to FIGS.
5-7 is explanatory drawing when a probe is bent gradually in the eddy current flaw detection method by one Embodiment of this invention. The same reference numerals as those in FIG. 1 indicate the same parts.

As shown in FIG. 5, when the state changes from (state 1) to state 3 where the probe is bent to a certain curvature, the detection signal is as shown in FIG. That is, if (state 1) is (origin 5), (state 3) changes linearly toward (point 7). This is because, as shown in FIG. 7, by the probe bends, the distance of the exciting coil 1An and the detection coil 1A (n + 1) is changed. Since the magnetic field 8 attenuates as the distance from the exciting coil 1An increases, the detection signal also changes as the probe bends. Further, since this change is not accompanied by generation or distribution of eddy current, the detection signal changes linearly as shown in FIG.

Next, changes in the detection signal of the probe when the probe is scanned over a portion where the curvature of the object to be inspected changes in the eddy current flaw detection method according to the present embodiment will be described with reference to FIGS. To do.
8 and 9 are explanatory diagrams when the probe is scanned over a portion where the curvature of the object to be inspected changes in the eddy current flaw detection method according to the embodiment of the present invention. The same reference numerals as those in FIG. 1 indicate the same parts.

As shown in FIG. 8, with respect to the test body 20 'that changes or smooth the flat portion to curved, to place the probe 3 in the flat portion. This state is the same as (State 2) in FIG. The probe 3 scans the curved surface portion in close contact with the surface to be inspected. The radius of curvature of the surface changes to gradually decrease. As shown in FIG. 8, a state in which the probe 3 is scanned to the curved surface portion is referred to as (state 4).

As shown in FIG. 9, the detection signal in this case changes linearly from (Point 6) indicating (State 2) to (Point 10). This is because the change due to the bending of the probe is shown as described above with reference to FIG. Further, since the eddy current generated in the test body 20 ′ does not attenuate or change its distribution, it changes linearly from (Point 6) to (Point 10).

Next, changes in the detection signal of the probe when the probe in close contact with the curved surface portion is gradually separated from the surface to be inspected in the eddy current flaw detection method according to the present embodiment will be described with reference to FIGS.
FIG. 10 and FIG. 11 are explanatory views when the probe in close contact with the curved surface portion is gradually separated from the surface to be inspected in the eddy current flaw detection method according to one embodiment of the present invention. The same reference numerals as those in FIG. 1 indicate the same parts.

As shown in FIG. 10, a state in which the probe 3 is in close contact with the curved specimen 20B is referred to as (state 4), and a state in which the probe 3 is gradually separated is referred to as (state 5). The detection signal at this time moves from (Point 10) to (Point 7) as shown in FIG. Since (State 5) is the same as (State 2) described above, (Point 7) indicating both states overlap.

Next, with reference to FIG. 12, detection signals according to the state of the inspection object and the probe in the eddy current flaw detection method according to the present embodiment will be described together.
FIG. 12 is an explanatory diagram of the contents of a detection signal depending on the state of the inspection object and the probe in the eddy current flaw detection method according to the embodiment of the present invention.

  In summary, it can be seen that the detection signal shows a characteristic change depending on the state of the inspection object and the probe.

  The state (point 5) in which there is no object to be inspected and the probe is extended is set as a reference (this indicates setting to the origin of the detection signal). As shown in FIG. 11, the locus of the detection signal from (point 5) to (point 7) in the direction of arrow 12 is such that the radius of curvature decreases from the state in which the probe is extended without the object to be inspected. This is a detection signal when turning. The trajectory in the direction of arrow 13 from (Point 6) to (Point 10) indicates a state in which the probe bends in accordance with the curvature of the object to be inspected in a state where the probe is in close contact with the object to be inspected. (Point 6) changes to (Point 10) as the radius of curvature decreases from the state in which the probe is on the plane. The detection signal that moves between the two characteristics is a detection signal generated by lift-off of the probe and the object to be inspected. Corresponding to the direction indicated by the arrow 14, the lift-off becomes small and adheres to the object to be inspected on the line between (Point 6) and (Point 10).

  By preparing the characteristics of the detection signal according to the state of the inspection object and the probe in advance, it is possible to grasp the contact state when the probe is installed even for a part where the curvature of the inspection object is not known. .

Next, the contents of the eddy current flaw detection method according to the present embodiment will be described with reference to FIGS. 13 and 14.
FIG. 13 is a flowchart showing the contents of an eddy current flaw detection method according to an embodiment of the present invention. FIG. 14 is an explanatory diagram of an eddy current flaw detection method according to an embodiment of the present invention.

  In this embodiment, (Point 5), (Point 6), and (Point 10) in FIG. 12 are determined by the following procedure.

  First, in step S10, the calculation control unit 40 sets the origin of the detection signal in a state where the probe is extended at a position away from the object to be inspected. This setting is called balance setting or NULL setting in eddy current inspection. This set value is (point 5).

  Thereafter, in step S15, the arithmetic control unit 40 controls the moving unit 30 to move the probe so that the probe is brought into close contact with the specimen 20A shown in FIG. 2, and record the detection signal generated in this process. . The test body 20A has the same material as that of the actual inspection part, or has the same electrical and magnetic characteristics. (Point 6) is determined by this detection signal.

Next, in step S20, the arithmetic control unit 40 uses the test body 20B shown in FIG. 2, to record a detection signal of a state of being in close contact with the probe on a curved surface. Thereby, (point 10) is determined.

  Next, in step S25, the arithmetic control unit 40 approximates a straight line between (point 6) and (point 10).

  Next, in step S30 and step S35, the arithmetic control unit 40 measures the value of the allowable lift-off value in the same procedure. These points are defined as (Point 6 ') and (Point 10'). Specifically, the detection signal is measured in the process of bringing the probe close to the lift-off Xmm to the flat part of the test body 20A, and the detection signal is measured in the process of bringing the probe close to the lift-off Xmm of the curved part of the test body 20B. If the allowable value Xmm of lift-off is, for example, 1 mm, it can be measured by placing a 1 mm spacer on the specimen. When the detection signal corresponding to the lift-off distance is recorded in the measurement for determining (Point 6) and (Point 10), it is not necessary to measure again, and the data for the lift-off of 1 mm is obtained from the data (Point 6 ' ), (Point 10 ').

  In step S40, the arithmetic control unit 40 approximates (point 6 ') obtained in step S30 and (point 10') obtained in step S35 by a straight line.

  Further, in step S45, the arithmetic control unit 40 determines a region A surrounded by (point 6), (point 10), (point 10 ′), (point 6 ′), and (point 6) on the Lissajous plane. .

  The characteristics obtained in this way are as shown in FIG. A region surrounded by (Point 6), (Point 10), (Point 10 '), (Point 6'), and (Point 6) is a lift-off allowable region A based on the lift-off allowable value.

In the above description, (Point 7) has been discussed, but what is actually required is (Point 6), (Point 10), (Point 10 '), (Point 6'), (Point Since the region is surrounded by 6), (Point 7) is not necessarily obtained. When obtaining (Point 7), a detection signal generated in the process of separating from the specimen 20B is recorded while maintaining the probe shape bent along the curved surface.

  Next, when actually inspecting the object to be inspected using the eddy current probe, first, in step S50, the arithmetic control unit 40 sets the origin in a state of being arranged in the vicinity of the part to be inspected by the moving unit 30. To implement. In order not to be affected by the object to be inspected, the probe needs to be at a distance sufficiently away from the object to be inspected. It is desirable to separate 30 mm or more.

  In step S55, the calculation control unit 40 measures a signal on the Lissajous plane generated in the process of bringing the eddy current probe 3 into close contact with the object to be inspected. Further, in step S60, the arithmetic control unit 40 determines the measured signal and the lift-off region A described above. Compare. The inspection is possible if it is within the lift-off allowable region determined by the test body, and if not, the retry is made.

  With the above procedure, the lift-off when the eddy current probe is pressed against an arbitrary curved surface can be evaluated.

  As described above, according to the present embodiment, since the inspection signal by the eddy current flaw detection for the object to be inspected from the flat surface to the curved surface can be recorded in advance, the probe can be used even for the part where the curvature of the object to be inspected is not known. It is possible to grasp the close contact state when installed.

Next, an eddy current flaw detection method according to another embodiment of the present invention will be described with reference to FIGS. 15 and 16.
FIG. 15 is a block diagram showing a configuration of an eddy current flaw detection apparatus that performs an eddy current flaw detection method according to another embodiment of the present invention. The same reference numerals as those in FIG. 2 indicate the same parts. FIG. 16 is a flowchart showing the contents of an eddy current flaw detection method according to another embodiment of the present invention.

  The test body 20 </ b> C used in the present embodiment has a shape that gradually changes from the flat surface portion 23 to the curved surface portion 24. The test body 20C has the same material as that of the actual inspection section, or has the same electrical / magnetic characteristics. In order to record a detection signal generated in the process of bringing the probe 3 into close contact with the flat surface portion, the flat surface portion 23 is used. Thereby, (point 6) is determined. Next, the probe is moved from the flat surface portion 23 to the curved surface portion 24 in a close contact state. Thereby, the detection signal from (Point 6) to (Point 10) and (Point 10) are determined.

  In FIG. 16, first, in step S10, the arithmetic control unit 40 performs balance installation of measuring instruments. That is, the origin of the detection signal is set with the probe extended at a position away from the object to be inspected. This set value is (point 5).

  Then, the test body 20C shown in FIG. 15 is used. This specimen has a shape that gradually changes from a flat surface to a curved surface.

Next, in step S15, the arithmetic control unit 40, closer to probe the flat portion 23 of the trial Kentai 20C, measuring a first detection signal in the process of adhering (in FIG. 14 (point 6)).

Next, in step S20 ′, the arithmetic control unit 40 controls the moving unit 30 to perform scanning toward the curved surface portion 24 while keeping the probe in close contact with the flat surface portion 23 of the specimen 20C. The second detection signal (point 10 in FIG. 14) is measured.

Next, in step S35 ′, the calculation control unit 40 detects the third detection signal ((dot in FIG. 14) when the probe is lifted off to the lift-off Xmm from the curved surface portion 24 of the specimen 20C while the probe is bent. 10 ′) is measured.

  Next, in step S40 ', the arithmetic control unit 40 obtains a fourth detection signal (point 6' in FIG. 14) generated when the probe is brought close to the lift-off Xmm on the flat surface portion of the specimen.

  Further, in step S45, the arithmetic control unit 40 determines a region A surrounded by (point 6), (point 10), (point 10 ′), (point 6 ′), and (point 6) on the Lissajous plane. .

  Next, when actually inspecting the object to be inspected using the eddy current probe, first, in step S50, the arithmetic control unit 40 sets the origin in a state of being arranged in the vicinity of the part to be inspected by the moving unit 30. To implement. In order not to be affected by the object to be inspected, the probe needs to be at a distance sufficiently away from the object to be inspected. It is desirable to separate 30 mm or more.

  In step S55, the calculation control unit 40 measures a signal on the Lissajous plane generated in the process of bringing the eddy current probe 3 into close contact with the object to be inspected. Further, in step S60, the arithmetic control unit 40 determines the measured signal and the lift-off region A described above. Compare. The inspection is possible if it is within the lift-off allowable region determined by the test body, and if not, the retry is made.

  With the above procedure, the lift-off when the eddy current probe is pressed against an arbitrary curved surface can be evaluated.

As described above, according to the present embodiment, since the inspection signal by the eddy current flaw detection for the object to be inspected from the flat surface to the curved surface can be recorded in advance, the probe can be used even for the part where the curvature of the object to be inspected is not known. It is possible to grasp the close contact state when installed.

DESCRIPTION OF SYMBOLS 1 ... Coil 2 ... Flexible board 3 ... Multi-coil probe 20 ... Test body 30 ... Moving part 40 ... Control calculating part

Claims (3)

It is the same material as the object to be inspected and the eddy current probe in which a plurality of coils are regularly arranged on the substrate, and using a test body that simulates a flat surface and a curved surface,
From the detection signal generated until the eddy current probe is brought into close contact with the plane of the test body and the detection signal generated when the eddy current probe is brought into close contact with the curved surface of the test body, a lift-off allowable region is obtained on the Lissajous plane,
Comparing a signal on the Lissajous plane generated in the process of bringing the eddy current probe into close contact with the object to be inspected and the lift-off allowable region, the lift-off amount when the eddy current probe is pressed against an arbitrary curved surface is evaluated. Eddy current flaw detection method. The eddy current flaw detection method according to claim 1,
The lift-off allowable region is
A first detection signal generated when the eddy current probe is brought into close contact with the plane of the specimen;
A second detection signal generated when the eddy current probe is brought into close contact with the curved surface of the test body;
A straight line obtained by a point at a position where the probe of the first detection signal is in close contact with the Lissajous plane and a point at a position where the probe of the second detection signal is in close contact;
A linear approximation obtained from the point where the eddy current probe is brought close to the lift-off Xmm on the plane of the specimen on the Lissajous plane, and the point where the eddy current probe is brought close to the lift-off Xmm on the curved surface of the specimen. An eddy current flaw detection method characterized by: The eddy current flaw detection method according to claim 1,
The lift-off allowable region is
A first detection signal generated when the eddy current probe is brought into close contact with the plane of the specimen;
Brought into close contact with the probe in the plane of the specimen, and a second detection signal when scanning toward the curved portion maintaining a tight Chakujo state,
A third detection signal generated when releasing the curved or Lapu lobes of said specimen,
An eddy current flaw detection method characterized in that it is obtained from a fourth detection signal generated when a probe is brought close to the plane of the test body to a lift-off Xmm, and this distance is maintained and the curved surface is scanned.

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