JP2000346830A - Eddy current flaw-detecting method and its device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an eddy current flaw-detecting method that can detect a flaw with eddy current using a magnetic field of alternating current for magnetizing a material under flaw detection, and has excellent flaw detection function. SOLUTION: In this eddy current flaw-detecting method, a material under flow detection having magnetism is magnetized, the magnetized flaw-detected material is relatively moved to generate induced current on the flaw-detected material, any flaw in the flaw-detected material is detected based on variation of the generated induced current. The material under flow detection is magnetized (c) by alternating current magnetic field (b) with a first frequency (a) in the orthogonal direction to the longitudinal direction of the flaw to be detected, induced current with a second frequency (d) higher than the first frequency is generated on the magnetized material under flow detection, generated induced current is detected (e), variation of the induced current in a prescribed range U for every cycle (f) of the first frequency, of the detected induced current is detected, the flaw in the material under flow detection is detected based on the detected variation of the induced current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for magnetizing a material to be inspected having magnetism, causing an induced current in the material to be magnetized while relatively moving the magnetized material to be inspected, and changing the induced current generated. The present invention relates to an eddy current flaw detection method and an eddy current flaw detection apparatus for detecting flaws in a material to be flaw-detected based on the method described above.

[0002]

2. Description of the Related Art In eddy current flaw detection of magnetic materials, a lot of magnetic noise is generated due to fluctuations in magnetic properties caused by residual stress, plasticity, decarburization / carburization, temperature change near a magnetic transformation point, etc. on the surface layer of the material to be detected. In order to suppress this magnetic noise, when the material to be inspected has an elongated shape such as a steel bar or a steel pipe, a strong magnetic field is generated in the axial direction of the material to be inspected using a penetration coil, and magnetic saturation is often performed. Will be

When the material to be inspected is magnetized in a direction orthogonal to the longitudinal direction of the flaw to be detected, the amount of increase in the flaw detection signal obtained depends on the degree of fluctuation of the magnetic permeability distribution occurring around the flaw. The degree of fluctuation of the magnetic permeability distribution increases when the magnetic flux in the material to be inspected reaches magnetic saturation and a slight difference in magnetic flux density caused by a flaw causes a large fluctuation in relative magnetic permeability. This is "Non-destructive inspection Vol41, No
FIG. 10 shows the flaw signal due to the magnitude of the magnetizing current when the flaw depth is 20, 50, and 70% of the thickness of the material to be inspected. 5 is a graph showing a change in amplitude.

According to this graph, when the magnetizing current is small (around A), the change in the magnetic permeability around the flaw is small and the flaw signal amplitude is also small. When the magnetizing current is increased (near B), the magnetic permeability distribution around the flaw changes rapidly, and the flaw signal amplitude also increases rapidly. Further, when the magnetizing current is increased (near C), the degree of change in the magnetic permeability distribution around the flaw increases, and the flaw signal amplitude becomes maximum. Further, when the magnetizing current is increased, the entire area around the flaw reaches magnetic saturation, the degree of change in the magnetic permeability distribution around the flaw decreases, and the flaw signal amplitude also decreases. This is the case where the magnetizing current is DC, but the same phenomenon occurs when the magnetizing current is AC.

For example, Japanese Patent Publication No. 60-247158 and Japanese Utility Model Publication No. 7-29490 disclose a through coil in order to suppress magnetic noise generated around the Curie point in hot flaw detection of a ferromagnetic material. Is described. In these, the penetration coil is used as a magnetizer, and magnetization is performed in the same direction as the axial direction of the material to be inspected.

On the other hand, Japanese Patent Application Laid-Open No. 6-34747 discloses that the direction of the magnetic field of magnetic saturation is not the axial direction but the circumferential direction of the flaw-detected material, so that the flaws generated in the flaw-detected material are long in the axial direction. Techniques for increasing the detection sensitivity have been disclosed. In this technology, the material to be inspected is sandwiched between opposing magnetic poles,
By applying a magnetic field, magnetization is performed in the circumferential direction of the material to be inspected. Since the magnetic flux density is high in the sound part of the material to be inspected,
Although the relative magnetic permeability is approximately 1, the magnetic flux density is low near the flaw, so that the magnetic permeability is high. For this reason, in the distribution of the magnetic permeability, a portion having a high magnetic permeability is generated around the flaw, and a large signal is obtained in the eddy current flaw detection.

In this technique, by utilizing this, magnetization is performed in the circumferential direction on the material to be inspected, thereby improving the detection sensitivity of flaws that are long in the axial direction of the material to be inspected. When the material to be inspected is hollow and thin, such as a steel pipe, the magnetic flux generated from the magnetic poles arranged on the side of the material to be inspected passes through the inside of the tube wall. And the direction of the magnetic field is the circumferential direction. On the other hand, when the magnetic field is not hollow like a round bar, the magnetic field is set to alternating current, and the magnetic flux passes along the surface layer of the material to be inspected using the skin effect, and the direction of the magnetic field is set to the circumferential direction. Can be done. Further, by using an alternating magnetic field, it is possible to perform flaw detection using magnetic saturation even on a plate material or a structure where magnetic saturation is difficult with direct current.

[0008]

As described above, when an alternating magnetic field is used for magnetization of a material to be inspected, the magnetic flux density in the material to be inspected fluctuates in accordance with the cycle of the magnetization. There is a problem that it is difficult to detect a flaw by simply adding an AC magnetizer to the apparatus. That is, the magnetic permeability changes due to the change in the magnetic flux density due to the magnetization in the material to be detected, and the current induced by the exciting coil changes. Therefore, a large output fluctuation synchronized with the cycle of the magnetization is superimposed on the output of the detection coil, and there is a problem that it is difficult to extract the detection signal of the flaw. The present invention has been made in view of the above-described circumstances, and an eddy current flaw detection method and an eddy current flaw detection apparatus capable of performing eddy current flaw detection using an alternating magnetic field for magnetization of a material to be flawed and excellent in flaw detection are provided. The purpose is to provide.

[0009]

An eddy current flaw detection method according to a first aspect of the present invention is to magnetize a flaw-detected material having magnetism and generate an induced current in the flaw-detected material while relatively moving the magnetized flaw-detected material. In the eddy current flaw detection method for detecting a flaw in the flaw-detected material based on a change in the induced current generated, the flaw-detected material is detected by an AC magnetic field of a first frequency in a direction orthogonal to a longitudinal direction of the flaw to be detected. Is magnetized, and an induced current having a second frequency higher than the first frequency is generated in the magnetized flaw detection material, the generated induced current is detected, and of the detected induced currents, the first The method is characterized in that a change in the induced current in a predetermined range for each frequency cycle is detected, and a flaw in the flaw detection material is detected based on the detected change in the induced current.

In the eddy current flaw detection method according to the second invention, an induced current is generated in the flaw-detected material while the magnetized flaw-detected material is magnetized, and the magnetized flaw-detected material is relatively moved. In the eddy current flaw detection method for detecting flaws in the flaw-detected material based on the change of the flaw-detected material, the flaw-detected material is magnetized by an AC magnetic field of a first frequency in a direction orthogonal to a longitudinal direction of the flaw to be detected. In the flaw detection material, an induced current of a second frequency higher than the first frequency is generated, the generated induced current is detected, and a difference between the detected induced current waveform data and predetermined waveform data is calculated. The method is characterized in that flaws in the material to be detected are detected based on the calculated difference.

The eddy current flaw detector according to the third invention is characterized in that an induced current is generated in the flaw-detected material while the magnetized flaw-detected material is magnetized, and the magnetized flaw-detected material is relatively moved. In the eddy current flaw detector for detecting flaws in the flaw-detected material based on the change of the flaw-detected material, means for magnetizing the flaw-detected material with an AC magnetic field of a first frequency in a direction orthogonal to the longitudinal direction of the flaw to be detected, A means for generating an induced current having a second frequency higher than the first frequency in the material to be inspected magnetized by the means, a means for detecting the induced current generated by the means, and an induction detected by the means. Means for detecting a change in the induced current in a predetermined range for each cycle of the first frequency, of the current, based on the change in the induced current detected by the means, to search for flaws in the flaw-detected material. Characterized by something done

In the eddy current flaw detection method according to the first invention and the eddy current flaw detection apparatus according to the third invention, an induced current is applied to the flaw detection material while the magnetized flaw detection material is relatively moved. Is generated, and a flaw in the flaw-detected material is detected based on the generated induced current change. Means for magnetizing, in a direction perpendicular to the longitudinal direction of the flaw to be explored,
The means for magnetizing and generating the flaw-detected material by the AC magnetic field of the first frequency generates an induced current of a second frequency higher than the first frequency in the magnetized flaw-detected material. The detecting means detects the generated induced current, and the change detecting means detects a change in the induced current in a predetermined range for each cycle of the first frequency among the detected induced currents. Then, based on the detected change in the induced current, a flaw in the material to be detected is searched for. As a result, eddy current flaw detection using an alternating magnetic field for magnetization of the material to be flawed can be performed, and an eddy current flaw detection method and an eddy current flaw detection apparatus excellent in flaw detection can be realized.

An eddy current flaw detector according to a fourth aspect of the present invention is a magnetized flaw-detecting material having magnetism, and generates an induced current in the flaw-detected material while relatively moving the magnetized flaw-detected material. In the eddy current flaw detector for detecting flaws in the flaw-detected material based on the change of the flaw-detected material, means for magnetizing the flaw-detected material with an AC magnetic field of a first frequency in a direction orthogonal to the longitudinal direction of the flaw to be detected, A means for generating an induced current having a second frequency higher than the first frequency in the material to be inspected magnetized by the means, a means for detecting the induced current generated by the means, and an induction detected by the means. Means for calculating a difference between current waveform data and predetermined waveform data,
It is characterized in that the flaws in the flaw-detected material are searched for based on the difference calculated by the means.

In the eddy current flaw detection method according to the second invention and the eddy current flaw detection apparatus according to the fourth invention, an induced current is applied to the flaw-detected material while the magnetized flaw-detected material is relatively moved. Is generated, and a flaw in the flaw-detected material is detected based on the generated induced current change. Means for magnetizing, in a direction perpendicular to the longitudinal direction of the flaw to be explored,
The means for magnetizing and generating the flaw-detected material by the AC magnetic field of the first frequency generates an induced current of a second frequency higher than the first frequency in the magnetized flaw-detected material. The detecting means detects the generated induced current, and the calculating means calculates a difference between the waveform data of the detected induced current and predetermined waveform data. Then, based on the calculated difference, a flaw of the flaw detection material is searched. This allows
Eddy current flaw detection using an alternating magnetic field for the magnetization of the material to be flawed can be performed, and an eddy current flaw detection method and an eddy current flaw detection apparatus excellent in flaw detection can be realized.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing an embodiment. FIG. 1 is a block diagram showing a configuration of an embodiment of an eddy current inspection method and an eddy current inspection device according to the present invention. This eddy current flaw detector divides a reference oscillator 1 and a signal oscillated by the reference oscillator 1 into 1 / n,
The frequency divider 1 creates a signal of the frequency F1, the amplifier 3 amplifies the power of the signal of the frequency F1 created by the divider 2, and the current of the frequency F1 output by the amplifier 3, the frequency F1
And an inverted U-shaped magnetizer 4 for generating an AC magnetic field of The magnetizer 4 generates / absorbs an AC magnetic flux from two ends to form an AC magnetic field, and magnetizes the material to be inspected 8 which is a steel bar in the circumferential direction.

The eddy current flaw detector also includes a reference oscillator 1
Divides the oscillated signal into 1 / m (n> m),
2 (F1 <F2) signal, and an amplifier 6 for power-amplifying the frequency F2 signal generated by the frequency divider 5
And an exciting coil 7 for generating an AC magnetic field of the frequency F2 by the current of the frequency F2 output from the amplifier 6. The exciting coil 7 is held between two ends of the inverted U-shaped magnetizer 4. Since the signals of the frequencies F1 and F2 are each frequency-divided from the signal oscillated by the same reference oscillator 1, they can be completely synchronized.

The eddy current flaw detector is provided between the flaw-detected material 8 and the exciting coil 7, and is provided between the two ends of the magnetizer 4. An amplifier 10 for amplifying a signal and a frequency F from a frequency divider 5
2, a synchronous detector 11 for detecting a detection signal of the detection coil 9 in synchronization with the signal of the detection coil 9, and a waveform recorder 1 for recording waveform data of a sound portion of the material 8 to be detected which is detected by the synchronous detector 11 in advance.
2b, a calculator 12a for calculating the difference between the waveform data detected by the synchronous detector 11 and the waveform data recorded by the waveform recorder 12b, and a display recorder 13 for displaying and recording the calculation result of the calculator 12a. It has. Waveform recorder 12b
And the arithmetic unit 12 a are included in the signal processing unit 12.

Hereinafter, the operation of the eddy current flaw detector having such a configuration will be described. The signal oscillated by the reference oscillator 1 is frequency-divided by the frequency divider 2 into 1 / n, becomes a signal of frequency F 1, and is given to the amplifier 3. Amplifier 3 power-amplifies the signal of given frequency F1. Magnetizer 4 and amplifier 3
When the magnetizing current I1 having the frequency F1 as shown in FIG. 2A flows, a magnetic field-flux density curve (BH curve) of the flaw-detected material 8 is formed near the surface of the flaw-detected material 8 which is a steel bar. Accordingly, the magnetic flux density B at the frequency F1 as shown in FIG.
Is generated and magnetized in the circumferential direction, and a magnetically saturated time region U occurs every half cycle. In FIG. 2B, the magnetic flux density B is shown as an absolute value.

At this time, as shown in FIG. 2C, the relative magnetic permeability in the vicinity of the surface of the material 8 to be inspected becomes low in a time region where the magnetic flux density B is high, and becomes high in a time region where the magnetic flux density B is low. In the time region in which the material to be detected 8 is substantially saturated magnetically, the value becomes low and substantially constant. The section where the relative permeability is low and has a substantially constant value is a time region in which the detection sensitivity of flaws increases due to magnetization. Further, in this time region, the relative magnetic permeability near the surface of the material 8 to be inspected is stable, so that the fluctuation of the induced current by the excitation coil 7 described later is small, and a stable output signal of the detection coil 9 can be obtained. .

On the other hand, the signal oscillated by the reference oscillator 1 is frequency-divided by the frequency divider 5 into 1 / m, becomes a signal of the frequency F2, and is given to the amplifier 6. Amplifier 6 power-amplifies the signal of given frequency F2. When an exciting current I2 output from the amplifier 6 and having a frequency F2 as shown in FIG. 2D flows through the exciting coil 7, an induced current is generated near the surface of the material 8 to be detected. Since the induced current changes under the influence of the relative magnetic permeability near the surface of the material 8 to be detected, the detection signal of the detection coil 9 due to the induced current is synchronized with the relative magnetic permeability as shown in FIG. Change. The eddy current flaw detection device or the flaw-detected material 8 moves in the axial direction of the flaw-detected material 8 in parallel with the execution of each operation described above.

The detection coil 9 detects a magnetic field generated by the induced current of the frequency F2 generated on the surface of the material 8 to be detected and an AC magnetic field of the frequency F1 generated by the magnetizer 4, and supplies the detection signal to the amplifier 10. The amplifier 10 amplifies the applied detection signal and supplies the amplified signal to the synchronous detector 11. Synchronous detector 11
Is a signal of frequency F2 from the given detection signal (FIG. 2).
(D) carrier) and outputs a synchronous detection signal that fluctuates in synchronization with the relative magnetic permeability (FIG. 2 (c)) as shown in FIG. 2 (f).

The synchronous detection signal has a time domain U (FIG. 2).
3B, when there is a flaw, the change becomes the largest, and as shown in FIG. 3A, the flaw portion A and the sound portion B
Significantly occurs. Therefore, by extracting the output of only the time domain U, a flaw signal as shown in FIG. 3B can be easily obtained. As described above, a stable flaw detection signal can be obtained by obtaining the detection signal of the detection coil 9 only in the time region where the magnetic flux density is high in the magnetized portion of the flaw detection material 8.

Hereinafter, the synchronous detector 11 will be described in more detail. FIG. 4 is a block diagram illustrating a configuration example of the synchronous detector 11. In the synchronous detector 11, the multiplier 15 multiplies a detection coil signal, which is a detection signal of the detection coil 9, by a carrier having a frequency F2 provided from the frequency divider 5 (FIG. 1), and FIG. And outputs a multiplied signal as shown in FIG.

If the multiplied signal is a synchronous detector of a general eddy current flaw detector, it is integrated by passing through a low-pass filter. However, in a low-pass filter having a large time constant, the synchronous detection output is a plurality of signals having a frequency F2. Since the average output for the period is obtained, a change in the magnetic permeability in a short time due to a change in the period signal of the frequency F1 cannot be detected. Therefore, the synchronous detector 11 synchronizes with the periodic signal of the frequency F2 in FIG.
Is generated, and the integrator 16 performs integration for each period, thereby enabling synchronous detection of the periodic signal having the frequency F2 in units of one period.

The integrator output as shown in FIG. 5C of the integrator 16 is supplied to the sample-and-hold circuit 17, and the sample-and-hold circuit 17 is inputted immediately before the end of each cycle of the frequency F2. d) sample and hold the output of the integrator by a sample and hold signal as shown in d),
An integrated value, that is, a synchronous detection signal as shown in FIG. For this reason, the synchronous detection signal becomes information one cycle before the periodic signal of the frequency F2, but synchronous detection output for each period is possible. When the sample hold is completed for each cycle, the sample hold circuit 17 receives a reset signal as shown in FIG. 5E and erases the contents of the integration in preparation for the next one cycle of integration.

The integrated signal, the sample hold signal and the reset signal are created with reference to the periodic signal of the frequency F2. Here, an example of the synchronous detection method has been described, but the present invention is not limited to this, and the frequency F
Any method may be used as long as synchronous detection can be performed in a small cycle unit of the second periodic signal.

The sample hold circuit 17 has a frequency F1
The synchronous detection signal is output k times (k = F2 / F1) during one cycle of the periodic signal. It is also possible to directly record the synchronous detection signal on the display recorder 13 and determine the presence or absence of a flaw based on this recording (first and third inventions).
The difference between the reference value of the synchronous detection signal obtained by the sound part and the reference value is calculated to determine whether there is a flaw (second and fourth inventions).

FIG. 6 is a block diagram showing a configuration example of the arithmetic unit 12a and the waveform recorder 12b of the signal processing unit 12.
The arithmetic unit 12a converts the k synchronous detection signals sequentially sent in one cycle of the periodic signal of the frequency F1 from the sample-and-hold circuit 17 into digital signals by the A / D conversion circuit 21, and converts the k synchronous detection signals into digital signals. Are sequentially stored in the register 22. As shown in FIG. 7A, the waveform recorder 12b collects in advance a sound portion of the material 8 to be inspected.
Digital signals of k synchronous detection signals for one cycle of the periodic signal of the frequency F1 are stored in the subtraction reference data storage unit 23, and the time domain where the magnetic flux density is high for one cycle of the periodic signal of the frequency F1 is stored. Are stored in the multiplication reference data storage unit 25.

The k digital signal values stored in the register 22 are each subtracted by the subtraction circuit 24 from the signal value of the sound part stored in the subtraction reference data storage unit 23. At this time, if the k digital signal values stored in the register 22 are digital signal values based on the synchronous detection signal of the sound part as shown in FIG. 7B, the subtracted signal is shown in FIG. A flat waveform as shown in d) is obtained. If the k digital signal values stored in the register 22 are digital signal values based on the synchronous detection signal at the flaw as shown in FIG. 7C, the subtracted signal is
A mountain-shaped waveform as shown in FIG.

The k digital signals subtracted by the subtraction circuit 24 are each multiplied by 0 or 1 by the multiplication circuit 26, and only the time domain having a high magnetic flux density is extracted.
The addition circuit 27 adds one period of the periodic signal of the frequency F1. As a result, the synchronous detection signal of the flaw can be obtained as shown in FIG.
It becomes a detection signal based on the integrated value of the difference as shown in (f), and can be recorded and displayed on the display recorder 13 (FIG. 1). Note that the above-described processing of the signal processing unit 12 is performed by software in a personal computer, but may be similarly performed by hardware. The data stored in the subtraction reference data storage unit 23 may be arbitrary data instead of the data collected in advance by the sound part of the flaw-detected material 8 as described above.

FIG. 8 is a perspective view showing an example of a detection portion when the material to be detected is a relatively thin steel bar 8a. In this example, a coil of the magnetizer 4 is wound with 100 turns of a copper wire, and an alternating current having a frequency of F1 = 1 kHz and 15 A is flowing. The exciting coil 7 has a pancake shape, and an alternating current having a frequency of F2 = 512 kHz flows therethrough.
An induced current is generated near the surface of the steel bar 8a. The detection coil 9 is arranged between the excitation coil 7 and the steel bar 8a. From the relationship between the frequencies F1 and F2, the synchronous detection signal is generated in the above-described signal processing unit 12 within one cycle of the frequency F1.
It is treated and processed as 512 arrays. In this case, if a flaw having a depth of 0.5 mm is detected on the surface of the steel bar 8a, a clear signal waveform indicating the presence of the flaw can be obtained as shown in FIG.

[0032]

According to the eddy current flaw detection method and the eddy current flaw detection apparatus of the present invention, eddy current flaw detection using an alternating magnetic field for the magnetization of the material to be inspected is possible, and the eddy current flaw detection method and eddy current flaw detection excellent in flaw detection. The device can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of an eddy current inspection method and an eddy current inspection device according to the present invention.

FIG. 2 is a waveform chart showing the operation of the eddy current flaw detector according to the present invention.

FIG. 3 is a waveform chart showing the operation of the eddy current flaw detector according to the present invention.

FIG. 4 is a block diagram illustrating a configuration example of a synchronous detector.

FIG. 5 is a waveform chart showing the operation of the synchronous detector.

FIG. 6 is a block diagram illustrating a configuration example of an arithmetic unit and a waveform recorder of a signal processing unit.

FIG. 7 is a waveform chart showing the operation of a calculator and a waveform recorder.

FIG. 8 is a perspective view showing an example of a detection portion of the eddy current inspection method and the eddy current inspection device according to the present invention.

FIG. 9 is a waveform chart showing an example of a flaw detection result by the detection part shown in FIG. 8;

FIG. 10 is a graph showing a change in a flaw signal amplitude depending on a magnitude of a magnetizing current in each case where a flaw depth is different.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reference oscillator 2, 5 divider 3, 6, 10 Amplifier 4 Magnetizer 7 Exciting coil 8 Flaw detection material 9 Detection coil 11 Synchronous detector 12 Signal processing unit 12a Arithmetic unit 12b Waveform recorder 13 Display recorder 15 Multiplier Reference Signs List 16 Integrator 17 Sample hold circuit 23 Subtraction reference data storage unit 24 Subtraction circuit 25 Multiplication reference data storage unit 26 Multiplication circuit 27 Addition circuit

Claims (4)

[Claims] 1. A magnetized flaw-detecting material is magnetized, and an induced current is generated in the flaw-detected material while the magnetized flaw-detected material is relatively moved.
In the eddy current flaw detection method for detecting a flaw of a flaw-detected material, the flaw-detected material is magnetized by an AC magnetic field of a first frequency in a direction orthogonal to a longitudinal direction of the flaw to be detected. Generating an induced current of a second frequency higher than the first frequency, detecting the generated induced current, and detecting, of the detected induced currents, an induced current of a predetermined range for each cycle of the first frequency. An eddy current flaw detection method comprising: detecting a change; and detecting a flaw in the flaw-detected material based on the detected change in the induced current. 2. A magnetized flaw-detecting material having magnetism, an induced current is generated in the flaw-detected material while relatively moving the magnetized flaw-detected material, and based on a change in the induced current generated,
In the eddy current flaw detection method for detecting a flaw of a flaw-detected material, the flaw-detected material is magnetized by an AC magnetic field of a first frequency in a direction orthogonal to a longitudinal direction of the flaw to be detected. Generating an induced current of a second frequency higher than the first frequency, detecting the generated induced current, calculating a difference between the detected induced current waveform data and predetermined waveform data, and based on the calculated difference. An eddy current flaw detection method, wherein flaws in the flaw detection material are detected. 3. A magnetized flaw-detected material is magnetized, and an induced current is generated in the flaw-detected material while the magnetized flaw-detected material is relatively moved, based on a change in the generated induced current.
In the eddy current flaw detector for detecting a flaw in the flaw-detected material, a means for magnetizing the flaw-detected material by an AC magnetic field of a first frequency in a direction orthogonal to a longitudinal direction of the flaw to be detected, and Means for generating an induced current of a second frequency higher than the first frequency in the flaw-detected material, means for detecting the induced current generated by the means, and, among the induced currents detected by the means, Means for detecting a change in the induced current within a predetermined range for each cycle of the first frequency, wherein the means for detecting flaws in the flaw-detected material based on the change in the induced current detected by the means. Eddy current flaw detector. 4. A magnetized flaw-detecting material having magnetism, an induced current is generated in the flaw-detected material while relatively moving the magnetized flaw-detected material, and based on a change in the induced current generated,
In the eddy current flaw detector for detecting a flaw in the flaw-detected material, a means for magnetizing the flaw-detected material by an AC magnetic field of a first frequency in a direction orthogonal to a longitudinal direction of the flaw to be detected, and Means for generating an induced current of a second frequency higher than the first frequency in the material to be detected, means for detecting the induced current generated by the means, waveform data of the induced current detected by the means, Means for calculating a difference between predetermined waveform data, wherein the flaw detection device is adapted to search for flaws in the material to be detected based on the difference calculated by the means.