Eddy current flaw detection method

Abstract

To provide an eddy current flaw detection method that can easily obtain an amount of lift-off of an eddy current flaw detection probe.SOLUTION: In an eddy current flaw detection method, the detection method has the steps of: preparing a first Lissajous waveform S1 on the basis of a lift-off signal when getting an eddy current flaw detection probe 1 close to a test piece, computing an angle θ between a tangent line A1 of a start point P1 in a first Lissajous waveform L1 and each straight line B connecting each object point Q to the start point P1, and preparing a lift-off characteristic serving as a relationship between the angle θ and a lift-off amount H of the eddy current flaw detection probe 1; and preparing a second Lissajous waveform L2 on the basis of a lift-off signal when getting the eddy current flaw detection probe 1 close to a tested piece 6, computing an angle θ' between a tangent line A2 of a start point P2 in the second Lissajous waveform L2 and a straight line C connecting an end point R to the start point P2, and obtaining a final lift-off amount H' of the eddy current flaw detection probe 1 relative to the teste piece 6, using the computed angle θ' and the previously described lift-off characteristic.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an eddy current inspection method using an eddy current inspection probe. [Background technology]

[0002] In the eddy current inspection method, an eddy current inspection probe (hereinafter simply referred to as a probe) having at least one coil is used to inspect an object to be inspected. More specifically, the probe is brought close to the object to be inspected, and an AC magnetic field is generated by the coil of the probe to induce eddy currents in the object to be inspected. If a defect exists in the object to be inspected, the eddy currents are disturbed, and a detection signal is obtained based on the change in impedance of the coil caused by the disturbance of the eddy current, and the presence or absence of a defect is evaluated based on the detection signal.

[0003] Since the detection sensitivity changes depending on the lift-off amount (distance) of the probe from the object under test, it is important to check the placement of the probe. However, when inspecting a narrow section or a site adjacent to a structure, or when the probe is operated remotely, it is difficult to visually check the placement of the probe. For this reason, a method has been proposed in which the lift-off amount of the probe from the object under test is measured by utilizing a lift-off signal generated by the lift-off of the probe from the object under test (see, for example, Patent Document 1).

[0004] In Patent Document 1, when the probe is moved away from the test piece, the transition of the lift-off amount of the probe with respect to the test piece is obtained, and the transition of the X component (the same component as a specific phase) or the Y component (the component that differs by 90 degrees from the specific phase) of the lift-off signal is obtained, and a lift-off characteristic that is the relationship between the probe lift-off amount and the X component or the Y component of the lift-off signal is created. This lift-off characteristic has a first lift-off characteristic in which the X component or the Y component of the lift-off signal increases as the probe lift-off amount increases from zero to a predetermined value (e.g., 1 mm), and a second lift-off characteristic in which the X component or the Y component of the lift-off signal decreases as the probe lift-off amount increases beyond the predetermined value.

[0005] Then, when the probe is brought closer to the object under test, the transition (specifically, the maximum value and final value) of the X-component or Y-component of the lift-off signal is acquired, and the final lift-off amount of the probe with respect to the object under test is calculated using the first lift characteristic or the second lift characteristic selected based on the transition (the maximum value and final value) and the final value of the X-component or the Y-component of the lift-off signal. This makes it possible to check the placement of the probe. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 5476588 Summary of the Invention [Problem to be solved by the invention]

[0007] In Patent Document 1, a lift-off characteristic, which is the relationship between the lift-off amount of the probe and the X-component or Y-component of the lift-off signal, is created in advance, and the lift-off amount of the eddy current flaw detection probe for the test object is calculated using this lift-off characteristic. However, the X-component and the Y-component of the lift-off signal change depending on the phase setting. Therefore, it is necessary to fix the phase setting or to create in advance multiple lift-off characteristics corresponding to multiple phase setting candidates.

[0008] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide an eddy current inspection method that can easily determine the lift-off amount of an eddy current inspection probe. [Means for solving the problem]

[0009] In order to achieve the above object, a representative embodiment of the present invention is an eddy current inspection method using an eddy current inspection probe, comprising the steps of acquiring a transition in the lift-off amount of the eddy current inspection probe when the eddy current inspection probe is brought closer to a test piece, creating a first Lissajous waveform based on a plurality of lift-off signals acquired at that time, calculating angles between a tangent to a starting point of the first Lissajous waveform and each straight line connecting each target point to the starting point, and creating a lift-off characteristic which is a relationship between the angles and the lift-off amount of the eddy current inspection probe, and creating a second Lissajous waveform based on a plurality of lift-off signals acquired when the eddy current inspection probe is brought closer to the test piece, calculating an angle between a tangent to a starting point of the second Lissajous waveform and a straight line connecting an end point to the starting point, and using the calculated angle and the lift-off characteristic to determine a final lift-off amount of the eddy current inspection probe for the test piece. Effect of the Invention

[0010] According to the present invention, the lift-off amount of an eddy current flaw detection probe can be easily obtained. [Brief description of the drawings]

[0011] [Figure 1] 1 is a diagram illustrating a configuration of an eddy current flaw detector according to a first embodiment of the present invention. [Diagram 2] 2 is a flowchart showing an eddy current flaw detection method according to the first embodiment of the present invention. [Diagram 3] FIG. 2 is a diagram illustrating a first Lissajous waveform in the first embodiment of the present invention. [Figure 4] FIG. 4 is a diagram illustrating lift-off characteristics in the first embodiment of the present invention. [Diagram 5] FIG. 4 is a diagram illustrating a second Lissajous waveform in the first embodiment of the present invention. [Figure 6] 5 is a flowchart showing an eddy current flaw detection method according to a second embodiment of the present invention. [Figure 7] FIG. 11 is a diagram illustrating a first Lissajous waveform in the second embodiment of the present invention. [Figure 8] FIG. 11 is a diagram illustrating a second Lissajous waveform in the second embodiment of the present invention. [Figure 9] 10 is a flowchart showing an eddy current flaw detection method according to a third embodiment of the present invention. [Figure 10] FIG. 11 is a diagram illustrating a first Lissajous waveform in the third embodiment of the present invention. [Figure 11] FIG. 11 is a diagram illustrating lift-off characteristics in the third embodiment of the present invention. [Figure 12] FIG. 13 is a diagram illustrating a second Lissajous waveform in the third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] A first embodiment of the present invention will be described with reference to the drawings.

[0013] FIG. 1 is a diagram showing the configuration of an eddy current flaw detector in this embodiment.

[0014] The eddy current flaw detection apparatus of this embodiment comprises an eddy current flaw detection probe 1 (hereinafter simply referred to as probe 1) having at least one coil (not shown), a moving device 2 that moves the probe 1, a control device 3 that controls the coil of the probe 1, a computer 4 connected to the moving device 2 and the control device 3, and a monitor 5 connected to the computer 4.

[0015] The moving device 2 has, for example, an arm that supports the probe 1 and a motor that moves the arm. The computer 4 controls the moving device 2 to move the probe 1 relative to the inspected object 6 (or the test object) and obtain the position of the probe 1 relative to the inspected object 6 (or the test object).

[0016] The control device 3 has, for example, an electric circuit connected to the coil of the probe 1. The computer 4 controls the control device 3 to generate an AC magnetic field by the coil of the probe 1 brought close to the object under inspection 6, thereby inducing an eddy current in the object under inspection 6. If a defect exists in the object under inspection 6, the eddy current is disturbed, so the control device 3 obtains a detection signal based on a change in impedance of the coil caused by the disturbance of the eddy current, and outputs the obtained detection signal to the computer 4.

[0017] The monitor 5 displays the position of the probe 1 and the detection signal acquired by the computer 4. An inspector evaluates the presence or absence of defects based on the detection signal displayed on the monitor 5.

[0018] In the eddy current inspection method of the present embodiment, a lift-off amount of the probe from the object 6 is measured by utilizing a lift-off signal generated by lift-off of the probe 1 from the object 6. The details will be described with reference to Figs. 2 to 5. Fig. 2 is a flow chart showing the eddy current inspection method of the present embodiment. Fig. 3 is a diagram showing a first Lissajous waveform in the present embodiment. Fig. 4 is a diagram showing lift-off characteristics in the present embodiment. Fig. 5 is a diagram showing a second Lissajous waveform in the present embodiment.

[0019] The eddy current flaw detection method of this embodiment has a pre-process (steps S11, S12, S13) in which the probe 1 is used on the test piece, and a post-process (steps S14, S15, S16) in which the probe 1 is used on the inspected object 6. Here, the phase setting is not changed between the pre-process and the post-process, and for convenience, a case will be described as an example in which the first Lissajous figure and the second Lissajous figure are the same.

[0020] In step S11, the computer 4 controls the moving device 2 to move the probe 1 closer to the test piece and acquires the transition of the lift-off amount H of the probe 1 relative to the test piece (in other words, a plurality of lift-off amounts H). The computer 4 controls the control device 3 to acquire a plurality of lift-off signals respectively corresponding to the plurality of lift-off amounts H.

[0021] In step S12, the computer 4 creates a first Lissajous waveform S1 (see FIG. 3) based on the multiple lift-off signals acquired in step S11. In detail, the first Lissajous waveform S1 is created by plotting the multiple lift-off signals in a coordinate system with the X component of the lift-off signal as the horizontal axis and the Y component of the lift-off signal as the vertical axis. The start point P1 of the first Lissajous waveform S1 corresponds to the lift-off signal when the probe 1 is sufficiently separated from the test piece, and the X component and the Y component are zero. Each target point Q of the first Lissajous waveform S1 corresponds to another lift-off signal.

[0022] In step S13, the computer 4 calculates the angle θ between the tangent A1 to the starting point P1 in the first Lissajous waveform S1 and each straight line B connecting each target point Q to the starting point P1, and creates lift-off characteristics (see FIG. 4) which are the relationship between the angle θ and the lift-off amount H of the probe 1. The computer 4 stores the created lift-off characteristics in the memory area 7. The slope of the tangent A1 to the starting point P1 is calculated using the starting point P1 and the target point Q in its vicinity.

[0023] In step S14, the computer 4 controls the moving device 2 to move the probe 1 closer to the object under test 6, and also controls the control device 3 to obtain a plurality of lift-off signals.

[0024] In step S15, the computer 4 creates a second Lissajous waveform S2 (see FIG. 5) based on the multiple lift-off signals acquired in step S14. The start point P2 of the second Lissajous waveform S2 corresponds to the lift-off signal when the probe 1 is sufficiently separated from the object under test 6, and its X component and Y component are zero. The end point R of the second Lissajous waveform S2 corresponds to the lift-off signal when the probe 1 is brought close to the object under test 6.

[0025] In step S16, the computer 4 calculates the angle θ' between the tangent A2 to the start point P2 in the second Lissajous waveform S2 and the straight line C connecting the end point R to the start point P2, and determines the final lift-off amount H' of the probe 1 with respect to the inspected object 6 using the calculated angle θ' and the lift-off characteristics stored in the memory area 7. The monitor 5 displays the final lift-off amount H' of the probe 1 determined by the computer 4. This allows the inspector to check the arrangement of the probe 1.

[0026] As described above, in this embodiment, a lift-off characteristic, which is the relationship between the lift-off amount of the probe 1 and the angle θ, is created, and the final lift-off amount of the probe 1 for the test object 6 is obtained using this lift-off characteristic. If the phase setting is changed between the pre-process in which the probe 1 is used for the test object and the post-process in which the probe 1 is used for the test object 6, the direction of the Lissajous waveform (i.e., the X component and Y component of the lift-off signal) changes, but the above-mentioned angle θ does not change. Therefore, it is not necessary to fix the phase setting, and it is also not necessary to create multiple lift-off characteristics corresponding to multiple phase setting candidates. Therefore, the lift-off amount of the eddy current flaw detection probe 1 can be easily obtained.

[0027] A second embodiment of the present invention will be described with reference to Figs. 6 to 8. Fig. 6 is a flow chart showing an eddy current flaw detection method in this embodiment. Fig. 7 is a diagram showing a first Lissajous waveform in this embodiment. Fig. 8 is a diagram showing a second Lissajous waveform in this embodiment. In this embodiment, parts equivalent to those in the first embodiment are given the same reference numerals, and descriptions thereof will be omitted as appropriate.

[0028] The eddy current flaw detection method of this embodiment has a pre-process (steps S11, S12, S17) in which the probe 1 is used on the test piece, and a post-process (steps S14, S15, S18) in which the probe 1 is used on the inspected object 6. Here, the phase setting is not changed between the pre-process and the post-process, and for convenience, a case will be described as an example in which the first Lissajous figure and the second Lissajous figure are the same.

[0029] In step S11, the computer 4 controls the moving device 2 to move the probe 1 closer to the test piece and acquires the transition of the lift-off amount H of the probe 1 relative to the test piece (in other words, a plurality of lift-off amounts H). The computer 4 controls the control device 3 to acquire a plurality of lift-off signals respectively corresponding to the plurality of lift-off amounts H.

[0030] In step S12, the computer 4 creates a first Lissajous waveform S1 (see FIG. 7) based on the multiple lift-off signals acquired in step S11.

[0031] In step S17, the computer 4 calculates the angle φ between the tangent A1 to the starting point P1 in the first Lissajous waveform S1 and the tangent D to each target point Q, and creates lift-off characteristics (not shown) which are the relationship between the angle φ and the lift-off amount H of the probe 1. The computer 4 stores the created lift-off characteristics in the memory area 7.

[0032] In step S14, the computer 4 controls the moving device 2 to move the probe 1 closer to the object under test 6, and also controls the control device 3 to obtain a plurality of lift-off signals.

[0033] In step S15, the computer 4 creates a second Lissajous waveform S2 (see FIG. 8) based on the multiple lift-off signals acquired in step S14.

[0034] In step S18, the computer 4 calculates the angle φ' between the tangent A2 to the start point P2 and the tangent E to the end point R in the second Lissajous waveform S2, and determines the final lift-off amount H' of the probe 1 with respect to the inspected object 6 using the calculated angle φ' and the lift-off characteristics stored in the memory area 7. The monitor 5 displays the final lift-off amount H' of the probe 1 determined by the computer 4. This allows the inspector to check the arrangement of the probe 1.

[0035] As described above, in this embodiment, a lift-off characteristic, which is the relationship between the lift-off amount of the probe 1 and the angle φ, is created, and the final lift-off amount of the probe 1 for the test object 6 is obtained using this lift-off characteristic. If the phase setting is changed between the pre-process in which the probe 1 is used for the test object and the post-process in which the probe 1 is used for the test object 6, the direction of the Lissajous waveform (i.e., the X and Y components of the lift-off signal) changes, but the above-mentioned angle φ does not change. Therefore, it is not necessary to fix the phase setting, and it is also not necessary to create multiple lift-off characteristics corresponding to multiple phase setting candidates. Therefore, the lift-off amount of the eddy current flaw detection probe 1 can be easily obtained.

[0036] A third embodiment of the present invention will be described with reference to Figs. 9 to 12. Fig. 9 is a flow chart showing an eddy current flaw detection method in this embodiment. Fig. 10 is a diagram showing a first Lissajous waveform in this embodiment. Fig. 11 is a diagram showing lift-off characteristics in this embodiment. Fig. 12 is a diagram showing a second Lissajous waveform in this embodiment. In this embodiment, parts equivalent to those in the first embodiment are given the same reference numerals, and descriptions thereof will be omitted as appropriate.

[0037] The eddy current flaw detection method of this embodiment has a pre-process (steps S11, S12, S19) in which the probe 1 is used on the test piece, and a post-process (steps S14, S15, S20) in which the probe 1 is used on the inspected object 6. Here, the phase setting is not changed between the pre-process and the post-process, and for convenience, a case will be described as an example in which the first Lissajous figure and the second Lissajous figure are the same.

[0038] In step S11, the computer 4 controls the moving device 2 to move the probe 1 closer to the test piece and acquires the transition of the lift-off amount H of the probe 1 relative to the test piece (in other words, a plurality of lift-off amounts H). The computer 4 controls the control device 3 to acquire a plurality of lift-off signals respectively corresponding to the plurality of lift-off amounts H.

[0039] In step S12, the computer 4 creates a first Lissajous waveform S1 (see FIG. 10) based on the plurality of lift-off signals acquired in step S11.

[0040] In step S19, the computer 4 calculates the distance L between the starting point P1 and each target point Q in the first Lissajous waveform S1, and creates lift-off characteristics (see FIG. 11) which are the relationship between the distance L and the lift-off amount H of the probe 1. The computer 4 stores the created lift-off characteristics in the memory area 7.

[0041] In step S14, the computer 4 controls the moving device 2 to move the probe 1 closer to the object under test 6, and also controls the control device 3 to obtain a plurality of lift-off signals.

[0042] In step S15, the computer 4 creates a second Lissajous waveform S2 (see FIG. 12) based on the multiple lift-off signals acquired in step S14.

[0043] In step S20, the computer 4 calculates the distance L' between the start point P2 and the end point R of the second Lissajous waveform S2, and determines the final lift-off amount H' of the probe 1 with respect to the inspected object 6 using the calculated distance L' and the lift-off characteristics stored in the memory area 7. The monitor 5 displays the final lift-off amount H' of the probe 1 determined by the computer 4. This allows the inspector to check the arrangement of the probe 1.

[0044] As described above, in this embodiment, a lift-off characteristic, which is the relationship between the lift-off amount of the probe 1 and the distance L, is created, and the final lift-off amount of the probe 1 for the test object 6 is obtained using this lift-off characteristic. If the phase setting is changed between the pre-process in which the probe 1 is used for the test object and the post-process in which the probe 1 is used for the test object 6, the direction of the Lissajous waveform (i.e., the X component and Y component of the lift-off signal) changes, but the above-mentioned distance L does not change. Therefore, it is not necessary to fix the phase setting, and it is also not necessary to create multiple lift-off characteristics corresponding to multiple phase setting candidates. Therefore, the lift-off amount of the eddy current flaw detection probe 1 can be easily obtained. [Explanation of symbols]

[0045] 1 Eddy current testing probe 6. Test subject

Claims

1. In an eddy current inspection method using an eddy current inspection probe, a step of acquiring a transition of the lift-off amount of the eddy current inspection probe when the eddy current inspection probe is brought close to a test piece, creating a first Lissajous waveform based on a plurality of lift-off signals acquired at that time, calculating an angle between a tangent to a start point of the first Lissajous waveform and each straight line connecting each target point to the start point, and creating a lift-off characteristic which is a relationship between the angle and the lift-off amount of the eddy current inspection probe; creating a second Lissajous waveform based on a plurality of lift-off signals acquired when the eddy current testing probe is brought closer to the object to be inspected, calculating an angle between a tangent to a starting point of the second Lissajous waveform and a straight line connecting an end point to the starting point, and determining a final lift-off amount of the eddy current testing probe with respect to the object to be inspected using the calculated angle and the lift-off characteristics.

2. In an eddy current inspection method using an eddy current inspection probe, a step of acquiring a transition of the lift-off amount of the eddy current inspection probe when the eddy current inspection probe is brought close to a test piece, creating a first Lissajous waveform based on a plurality of lift-off signals acquired at that time, calculating an angle between a tangent of a start point and a tangent of each target point in the first Lissajous waveform, and creating a lift-off characteristic which is a relationship between the angle and the lift-off amount of the eddy current inspection probe; creating a second Lissajous waveform based on a plurality of lift-off signals acquired when the eddy current inspection probe is brought closer to the object to be inspected, calculating an angle between a tangent to a starting point and a tangent to an end point of the second Lissajous waveform, and determining a final lift-off amount of the eddy current inspection probe with respect to the object to be inspected using the calculated angle and the lift-off characteristics.

3. In an eddy current inspection method using an eddy current inspection probe, a step of acquiring a transition of the lift-off amount of the eddy current inspection probe when the eddy current inspection probe is brought close to a test piece, creating a first Lissajous waveform based on a plurality of lift-off signals acquired at that time, calculating a distance between a start point and each target point in the first Lissajous waveform, and creating a lift-off characteristic which is a relationship between the distance and the lift-off amount of the eddy current inspection probe; creating a second Lissajous waveform based on a plurality of lift-off signals acquired when the eddy current inspection probe is brought closer to the object to be inspected, calculating the distance between the start point and the end point of the second Lissajous waveform, and determining a final lift-off amount of the eddy current inspection probe with respect to the object to be inspected using the calculated distance and the lift-off characteristics.

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