JP6058436B2 - Eddy current flaw detector and eddy current flaw detection method - Google Patents

Description

  Embodiments described herein relate generally to an eddy current flaw detector and an eddy current flaw detection method.

  Non-destructive inspection methods are used for in-service inspection of furnace internal structures, and representative examples include visual inspection (VT), ultrasonic inspection (UT), and eddy current inspection (Eddy). Current Testing (ECT). Among these, VT and ECT are used for surface inspection, and UT is used for volume inspection. If there is a flaw instruction, the flaw sizing is performed by a more detailed UT.

  However, many in-furnace structures have narrow and complicated welds with a small radius of curvature. For such a part, it is difficult to control the incident angle of the ultrasonic wave, and since the attenuation is large, high-precision sizing is difficult. On the other hand, in recent years, a pulsed eddy current testing method (PECT), which is an inspection method using a propagation phenomenon of eddy current generated in a body to be inspected by using a pulse wave for ECT, has been proposed.

  The principle of PECT will be described. First, a rectangular current is supplied to the exciting coil. Immediately after the current is cut off, a three-dimensional eddy current distribution is formed in the body to be inspected according to the frequency component contained in the pulse wave.

  At this time, since the supply of the magnetic field that has induced the eddy current distribution is stopped, a transient change occurs thereafter. This transient change is attenuation according to the frequency component and propagation of eddy current in the depth direction of the inspection object.

  In addition, the lower the frequency component, the lower the attenuation factor and the deeper the skin depth. Therefore, the propagation of the low-frequency component eddy current even if time elapses until the eddy current of the high-frequency component existing on the surface of the test object attenuates to a negligible level. The information on the deep part can be detected without being affected by the eddy current on the surface layer of the object to be inspected.

  Furthermore, since a pulse magnetic field can be applied in a non-contact manner and an eddy current signal can be detected, the possibility of sizing can be expected even for a narrow and complex shaped part.

  A technique for measuring the pipe wall thickness using such a principle is described in, for example, Japanese Patent Laid-Open No. 2005-106823 (Patent Document 1).

JP 2005-106823 A

  In the technique described in Patent Document 1, a pulse magnetic field is applied using sensor elements arranged in an array to detect a transient change in eddy current generated in an object to be inspected. In addition, an approximate expression using a polynomial is applied to the detected eddy current signal, and the thickness of the object to be inspected is estimated from the coefficient of each order term.

  This known technique utilizes the characteristics determined by the circuit system including the above-described features of PECT and the inspection object. That is, it is a technique for estimating the thickness from the characteristics of the entire region where the pulse eddy current is induced.

  On the other hand, since conventional PECT does not detect signal changes in the local time of propagating eddy currents, it can be applied to objects in which changes in local eddy current distribution occur with a time difference like flaws. There are challenges when doing so. That is, in order to measure the depth of the flaw, it is necessary to detect a transient change in the eddy current distribution generated at both ends of the flaw.

  In addition, transient changes in the eddy current distribution that occurs in the deep part of the flaw are difficult to detect unless the eddy current intensity is sufficient. Therefore, when using PECT for nondestructive inspection, a position far from the surface of a large structure or the like ( There is a problem in that the inspection accuracy can be maintained even for an inspection object that requires flaw detection at a deep position. That is, it is necessary to appropriately detect the eddy current intensity generated in the deep part of the flaw existing at a deep position.

  The present invention has been made in consideration of the above-described circumstances, and an object thereof is to provide an eddy current flaw detection apparatus and an eddy current flaw detection method capable of sizing flaws by pulse excitation eddy current flaw inspection.

  In addition, another object of the present invention is to enable flaw sizing by pulse excitation eddy current flaw inspection, and to inspect the inspection target that requires flaw detection at a deep position during the sizing. An object of the present invention is to provide an eddy current flaw detection apparatus and a eddy current flaw detection method that can be maintained.

In order to solve the above-described problem, an eddy current flaw detector according to an embodiment of the present invention is configured such that two or more exciting coils that excite a pulsed magnetic field to form an eddy current can be arranged in the same plane in a subject. The at least one detection element from an excitation means for supplying a pulsed current to each of the excitation coils of the excitation body and at least one detection element for detecting a transient distribution change of the eddy current Detection means for receiving a voltage signal detected by each of the above, a gripping means for gripping the excitation body and the detection body, and scanning the excitation body and the detection body, and a voltage signal detected by the detection means . Among the maximums of the sum of two or more points obtained by calculating the sum of changes in the difference between the upper envelope and the lower envelope of the waveform, it appears at the position where the maximum value of two points continuous in the scanning direction appears. Based on While calculating the position of the flaw existing in the inspection object, the depth of the flaw in the inspection object existing at the position to be calculated is based on the temporal change of the center frequency in the frequency spectrum of the voltage signal detected by the detection means. And a calculation means for controlling the excitation means such that an eddy current formed by a pulse current supplied to each of the excitation coils is superimposed with a time difference in the subject. It is characterized by comprising.

In order to solve the above-described problem, the eddy current flaw detection method according to the embodiment of the present invention is configured such that two or more exciting coils that excite a pulsed magnetic field and form an eddy current can be arranged in the same plane in the inspected body. The at least one detection element from an excitation means for supplying a pulsed current to each of the excitation coils of the excitation body and at least one detection element for detecting a transient distribution change of the eddy current A detection means for receiving a voltage signal detected by each of the detection means, and a position for calculating the position of the flaw existing in the inspected body based on information obtained from the waveform of the voltage signal received by the detection means Calculation extraction means for calculating the depth of the flaw in the body to be inspected present on the basis of the temporal change of the center frequency in the frequency spectrum of the voltage signal, the excitation body, the detection body, And an eddy current flaw detection method performed using an eddy current flaw detector comprising the control means for controlling the excitation means, wherein the excitation means supplies a pulsed current to each of the excitation coils, The detection means receives the voltage signal detected by each of the at least one detection element, and the computation extraction means receives the voltage signal waveform received in the step of receiving the voltage signal. Of the local maximum of two or more points obtained by calculating the sum of changes in the difference between the envelope and the lower envelope, the local maximum of two points in the scanning direction of the excitation body and the detection body While calculating the position of a flaw existing in the inspected body based on the appearance position of the flaw, the depth of the flaw in the inspected object existing at the calculated position is calculated in the frequency spectrum of the voltage signal. A step of calculating based on a temporal change in frequency, and when the control means does not cause a temporal change in the center frequency in the frequency spectrum of the voltage signal, the scanning of the excitation body and the detection body is stopped, and the excitation Supplying a pulsed current having a time difference to each of the coils, and controlling the excitation body, the detection body, and the excitation means so that the eddy current is superimposed with a time difference in the inspected body; It is characterized by comprising.

  According to the present invention, a local change in eddy current distribution caused by a flaw can be detected in pulse excitation eddy current flaw inspection (PECT), and flaw sizing becomes possible. In addition, it is possible to maintain the inspection accuracy even for an inspection object that requires flaw detection at a deep position when sizing a flaw.

The functional block diagram which shows the structure of the eddy current flaw detector which concerns on embodiment of this invention. Explanatory drawing explaining the example of arrangement | positioning of the exciting coil applied with the eddy current flaw detector which concerns on embodiment of this invention. Explanatory drawing which showed an example of the detection signal measured in the eddy current flaw detector which concerns on embodiment of this invention. Explanatory drawing which showed an example of the detection signal measured in the eddy current flaw detector which concerns on embodiment of this invention. It is explanatory drawing explaining the method of identifying the detection time of the deep end part of a flaw by the eddy current flaw detector which concerns on embodiment of this invention, (A) is a time chart of a detection voltage, (B) is a flaw deep end part. The frequency spectrum figure of the detection voltage when an eddy current reaches to. It is explanatory drawing explaining the method of identifying the detection time of the deep end part of a flaw by the eddy current flaw detector which concerns on embodiment of this invention, and the frequency spectrum figure of the detection voltage when an eddy current does not reach a flaw deep end part . Explanatory drawing which shows the 1st example of the time difference provision pattern of the pulse current which the eddy current flaw detector which concerns on embodiment of this invention supplies to an exciting body. Explanatory drawing which shows the 2nd example of the time difference provision pattern of the pulse current which the eddy current flaw detector which concerns on embodiment of this invention supplies to an exciting body. Explanatory drawing which shows the 3rd example of the time difference provision pattern of the pulse current which the eddy current flaw detector which concerns on embodiment of this invention supplies to an exciting body. Schematic which shows an example of the calibration test piece used in the eddy current flaw detector which concerns on embodiment of this invention.

  An eddy current flaw detection apparatus and an eddy current flaw detection method according to an embodiment of the present invention will be described with reference to the drawings. In the following description, words indicating directions such as up, down, left, and right are based on the illustrated state or the normal use state.

  The eddy current flaw detection apparatus and the eddy current flaw detection method according to the embodiment of the present invention can be applied to general inspection of metal structural materials such as a reactor pedestal, a reactor bottom, or a metal pipe, for example. This is a technique that can identify the depth of the generated flaw.

  Further, in the eddy current flaw detection apparatus and the eddy current flaw detection method according to the embodiment of the present invention, it is possible to appropriately detect the eddy current intensity generated in the deep part of the flaw existing deeper in the inspection target, Even for an object to be inspected for which it is necessary to appropriately detect the eddy current intensity generated in the deep part of the flaw existing in a deeper position such as a metal structure, the inspection accuracy can be maintained without lowering.

  FIG. 1 is a functional block diagram showing a configuration of an eddy current flaw detector 10 which is an example of an eddy current flaw detector according to an embodiment of the present invention.

  The eddy current flaw detector 10 generates eddy currents (traveling waves) that propagate toward the inside of the inspection object 1 at a plurality of locations on the surface of the inspection object 1, and the inspection object 1 is in accordance with the principle of wave superposition. Compared with conventional PECT, the eddy current intensity in deeper regions in the metal structure is controlled by controlling the timing and magnitude of the excitation current so that the eddy current becomes stronger in the depth range where the flaw detection is desired. This is an eddy current flaw detector capable of identifying the depth of a flaw existing at a deeper position of the inspection object 1.

  The eddy current flaw detection apparatus 10 is an apparatus for inspecting the presence or absence of a flaw 2 of the object 1 by pulse excitation eddy current flaw inspection (PECT). For example, a plurality of eddy current flaw detection apparatuses 10 (shown in FIG. 1) are arranged in the same plane. In the example, the excitation body 12 having excitation elements such as the excitation coils 11 (11a to 11c), the gripping means 13, the excitation means 14, and a plurality (three in the example shown in FIG. 1) are detected. A detection body 16 having elements 15 (15a to 15c), a detection means 17, a calculation extraction means 18, a control means 19, and a display means 21 are provided.

  The exciting coil 11 (11a to 11c) is supplied with a pulsed current (exciting current) from the exciting means 14 to excite a pulsed magnetic field in the device under test 1 to form an eddy current.

  The exciter 12 has a plurality of exciting elements such as three exciting coils 11a to 11c arranged in the same plane and is gripped by the gripping means 13 in a three-dimensionally movable state. .

  The gripping means 13 grips the exciter 12 and the detector 16. The gripping means 13 has a function of moving the exciter 12 and the detector 16 to a desired point on the surface (inspection surface) of the device under test 1 while holding the exciter 12 and the detector 16 and within the three-dimensional space. The position and orientation information of the excitation coils 11 a to 11 c (excitation body 12) and the detection elements 15 a to 15 c (detection body 16) with the set origin O as a reference is recorded and transmitted to the control means 19.

  The exciting means 14 is electrically connected to the exciting coils 11a to 11c. The exciting means 14 generates a pulsed current and supplies the generated pulsed current to the exciting coils 11a to 11c as an exciting current.

  The detection element 15 (15a to 15c) detects an eddy current distribution change due to a transient spread of the eddy current formed in the device under test 1 by the exciter 12. The number and arrangement of the detection elements 15 are appropriately determined in consideration of detection resolution and a range in which flaws can be detected by one scan. As the detection element 15, various detection elements capable of detecting a magnetic field such as a coil, a Hall element, and an MR sensor can be applied.

  The detection body 16 has a plurality of detection elements such as three detection elements 15a to 15c, for example, and is gripped by the gripping means 13 in a three-dimensionally movable state. In addition, the detection body 16 can also be applied in the state accommodated integrally with the excitation body 12 (for example, the sensor 43 shown by FIG. 4 mentioned later).

  The detection means 17 is electrically connected to each detection element 15a-15c. The detection means 17 detects an electrical signal generated in each of the detection elements 15a to 15c, and transmits the detected electrical signal to the calculation extraction means 18 as a detection signal. The detection means 17 has an amplifier and a filter, and appropriately amplifies and removes the detected electric signal and transmits it to the calculation extraction means 18.

  The calculation extraction unit 18 is electrically connected to the excitation unit 14, the detection unit 17, and the control unit 19. The calculation extraction means 18 receives information indicating what excitation current is supplied from the excitation means 14, receives a detection signal (electric signal) from the detection means 17, and receives excitation signals 11 a to 11 c (excitation bodies) from the control means 19. 12) and position information of the detecting elements 15a to 15c (detecting body 16) and a predetermined waveform analysis processing execution command are received.

  Upon receiving these information and commands, the operation extraction means 18 performs a predetermined waveform analysis process (details will be described later) on the detection signal (electrical signal) transmitted from the detection means 17, thereby inspecting the object to be inspected. Sizing flaw 2 that may exist in body 1. The result of the predetermined waveform analysis processing performed by the arithmetic extraction means 18 is given to the control means 19.

  The control means 19 is electrically connected to the gripping means 13, the excitation means 14, the calculation extraction means 18, and the display means 21, and controls the gripping means 13, the excitation means 14, the calculation extraction means 18, and the display means 21. To do.

  The control means 19 gives a movement command to the gripping means 13 and moves the exciter 12 and the detector 16 independently to desired points on the surface (inspection surface) of the object 1 to be inspected. Further, the control means 19 gives a position information transmission command and receives the position information of the excitation coils 11a to 11c (excitation body 12) and the detection elements 15a to 15c (detection body 16) acquired by the gripping means 13. Position information of the excitation coils 11a to 11c (excitation body 12) and the detection elements 15a to 15c (detection body 16) received by the control means 19 is given to the calculation extraction means 18.

  The control means 19 gives an excitation current control command to the excitation means 14 to turn on / off (ON / OFF) the excitation current (excitation pulse) generated by the excitation means 14, the magnitude, the rise time of the pulse, and the rise of the pulse. Control fall time, width, period, etc. In the eddy current flaw detector 10, the pulse current (FIGS. 8 to 10) with a time difference can be supplied to the exciting coils 11a to 11c by the control.

  The control means 19 gives the position information of the excitation coils 11a to 11c (excitation body 12) and the detection elements 15a to 15c (detection body 16) to the calculation extraction means 18 and executes a predetermined waveform analysis process on the calculation extraction means 18. Give a directive to The result of the predetermined waveform analysis processing performed by the arithmetic extraction means 18 is given to the display means 21 via the control means 19 and displayed on the display means 21.

  In the eddy current flaw detector 10, the arrangement of the exciting coils 11 constituting the exciter 12 is not limited to a linear shape (one line) as shown in FIG. 1, and can be arbitrarily arranged.

  FIG. 2 is an explanatory view for explaining an arrangement example of the excitation coils 11 applied in the eddy current flaw detector 10.

  For example, as shown in FIG. 2, as another arrangement of the excitation coil 11, the excitation coils 11a to 11e can be arranged in a cross shape. In addition to these, they may be arranged in a circular shape, an array shape, or the like.

  Next, the pulse excitation eddy current flaw inspection (PECT) of the inspection object 1 performed using the eddy current flaw detector 10 will be described.

  When the excitation coil 11 is positioned on the inspection surface of the device under test 1, the excitation means 14 supplies the excitation coil 11 with a pulse current I (t) represented by the following equation (1). When the pulse current I (t) is supplied to the exciting coil 11 as an exciting current, the detection of the magnetic field signal by the detecting element 15 is started.

  The exciting means 14 supplies a pulse-shaped applied current I (t) generated from a Fourier series having a coefficient calculated from the skin depth δ as an exciting current to the exciting coil 11, so that the depth of the device under test 1 is increased. An eddy current having substantially the same magnitude in the vertical direction can be induced immediately after the pulse current is cut.

  Subsequently, as a eddy current flaw detection method according to the embodiment of the present invention, a flaw 2 sizing method in a pulse excitation eddy current flaw detection (PECT) of the inspection object 1 performed using the eddy current flaw detection apparatus 10 will be described.

[Identification of the position of scratch 2]
FIG. 3 is an explanatory view showing an example of a detection signal measured in the eddy current flaw detector 10.

Here, the broken line V ₁ is a detection signal when there is no flaw, and the solid line V ₂ is a detection signal when there is a flaw.

The detection signals V ₁ and V ₂ correspond to the voltage signal of the detection element 15, are amplified and filtered by the detection unit 17, and are sent to the calculation extraction unit 18.

In operation extraction unit 18 performs a Fourier transform on the detection signals _V 1, _{V 2,} determine the frequency spectrum of the detection signal _V 1, _{V 2.} Further, in the process of obtaining the frequency spectra of the detection signals V ₁ and V ₂ , the frequency spectrum can be obtained by limiting to (t, t + Δt) which is the minute section 41 shown in FIG. Δt is variable, and the temporal change of the frequency spectrum can be obtained by sweeping the Fourier transform target section in the time domain from the start to the end of measurement.

Further, the operation extraction means 18 obtains the upper envelopes UE ₁ and UE ₂ and the lower envelopes LE ₁ and LE ₂ of the detection signals V ₁ and V ₂ , and further, the upper envelopes UE ₁ and UE ₂ and the lower envelopes A difference 42 between LE ₁ and LE ₂ (hereinafter referred to as “envelope difference”) 42 is obtained. Further, the calculation extraction means 18 calculates the difference in the preceding and following scan steps with respect to the upper envelopes UE ₁ and UE ₂ , the lower envelopes LE ₁ and LE ₂ , and the envelope difference, The envelope difference change with respect to the sensor position change and the sum (area) of the envelope difference change are obtained.

  FIG. 4 is an explanatory diagram for explaining a method for identifying a flaw position in the eddy current flaw detector 10.

  FIG. 4 shows an example of one-dimensional (x-axis direction) scanning. Reference numeral 43 denotes an exciter 12 and detector 16 housed in a casing (hereinafter simply referred to as “sensor”).

When the sensor 43 passes over the flaw 2, the total sum of changes in the envelope difference is maximized due to the presence of the flaw 2 at a plurality of specific coordinates. For example, in the example shown in FIG. 5, the maximum value of the sum of the envelope difference changes appears at two points of coordinates x ₁ and x ₂ . In this case, the position x _{0 of the} flaw 2 is specified as the midpoint of the coordinates x ₁ and x ₂ at which the sum of the envelope difference changes becomes maximum, that is, x ₀ = (x ₁ + x ₂ ) / 2. The calculation extracting means 18 performs the calculation for identifying the position of the flaw 2.

  It should be noted that the coordinates and the number of the coordinates at which the sum of the envelope difference changes becomes maximum vary depending on the structure of the sensor 43 and the shape of the flaw. The number of coordinates at which the total sum of envelope difference changes is maximized is not limited to two and may be three or more. In that case, the local maximum values of two consecutive points are extracted, and calculation is performed assuming that a flaw 2 exists at the midpoint of the two extracted local maximum values.

[Identification of Defect 2 Depth]
FIG. 5 is an explanatory diagram for explaining a method for identifying the detection time of the deep end 2b (FIG. 4) which is the deepest position of the flaw 2 by the eddy current flaw detector 10, and FIG. 5 (A) is a detection signal with respect to time. FIG. 5B is a graph (detection voltage time chart) showing a change in (detection voltage), and FIG. 5B shows a change in detection signal (detection voltage) with respect to the frequency when the eddy current reaches the flaw deep end 2b. It is a graph (frequency spectrum figure of a detection voltage).

Here, Δt shown in FIG. 5A is a minute time corresponding to Δt shown in FIG. Reference numeral R ₁ denotes a time region from when the eddy current reaches the front end 2 a, which is an end on the surface side of the flaw 2, until Δt elapses, and R ₃ denotes an eddy that has reached the front end 2 a. This is a time region from when the current propagates in the depth direction until it reaches the deep end 2b of the flaw 2 until Δt elapses, R ₂ is a time region between R ₁ and R ₃ , and R ₄ is R ₃ or later of the time domain. Furthermore, V _{R1 to} V _R4 are frequency spectra of detection voltages in the time domains R _{1 to} R ₄ , respectively.

When the calculation extraction unit 18 specifies the coordinates x ₁ and x _{2 at} which the total sum of the envelope difference changes becomes a maximum by the above-described procedure, the calculation extraction unit 18 then sets the coordinates at which the total sum of the envelope difference changes becomes a maximum. obtaining a frequency spectrum obtained by performing a Fourier transform at intervals of time width Δt with respect to the detection signal (detection voltage) in the coordinate x ₁ or x ₂ identified. Further, the arithmetic extraction unit 18 obtains a time change of the frequency spectrum of the detected voltage by setting the target section of Fourier transform as a time region from the start of measurement to the end of measurement and sweeping the target section.

As shown in FIG. 5B, during the time regions R _{1 to} R ₃ , that is, the eddy current propagates in the depth direction from the front end 2a (FIG. 4), and the deep end 2b (FIG. 4). to the until it reaches the center frequency of the frequency spectrum _{V R1,} V _R2, V _R3 of the detection voltage is shifted in frequency from the center frequency f ₀ of the pulsed excitation current applied to the exciting coil 11 (excitation pulse) F ₀ + Δf. In addition, between these time regions R _{1 to} R ₃ , the center frequency does not change and only the amplitude is attenuated.

In the time domain R _{3 and} thereafter, that is, in the time domain R ₄ , an eddy current signal that is not affected by the flaw 2 is also detected. _Therefore , the center frequency of the frequency spectrum VR ₄ of the detected voltage is the center frequency f of the excitation pulse. Shift to _zero .

In the eddy current flaw detector 10, the center frequency is shifted to f ₀ + Δf under the influence of the flaw 2 (front end 2a), and then the eddy current propagating in the depth direction is deeper than the deep end 2b. By observing the phenomenon that the center frequency of the frequency spectrum of the detection voltage shifts back to the center frequency f ₀ of the excitation pulse and returns, the eddy current is affected by the scratch 2 The time during which the eddy current propagates in the depth direction of the flaw 2 is measured.

  By performing such measurement, the eddy current flaw detector 10 allows the length 2 of the flaw 2 in the depth direction (from the front end portion 2a to the deep end portion 2b) when the flaw 2 exists in the inspection object 1. (Length) can be measured (calculated). When measuring the length of the flaw 2 in the depth direction, correction calculation is performed in consideration of the propagation speed at which the eddy current propagates through the object 1 and the inclination of the sensor.

  The propagation speed at which the eddy current propagates through the device under test 1 and the mathematical information of the correction calculation are given in advance so that the calculation extraction means 18 can calculate them. At this time, the propagation speed at which the eddy current propagates through the device under test 1 can be calculated in advance using, for example, a test piece 50 (FIG. 10) described later.

On the other hand, when the position of the depth end portion 2b of the flaw (Figure 4) is in a deep position from the surface, i.e., when the time domain R ₃ which are shown in FIG. 5 (A) is present in more right, the detected voltage In some cases, a change in the center frequency over time of the frequency spectrum (shift from the center frequency f ₀ + Δf to f ₀ ) cannot be detected.

  FIG. 6 is an explanatory diagram for explaining a method of identifying the detection time of the deep end 2b (FIG. 4) which is the deepest position of the flaw 2 by the eddy current flaw detector 10, and the eddy current reaches the flaw deep end 2b. It is a graph (frequency spectrum figure of a detection voltage) which shows change of a detection signal (detection voltage) with respect to a frequency when not doing.

As shown in FIG. 6, the frequency spectrum of the detected voltage is propagated to 2 not come eddy current, center frequency under the influence of the flaw 2 is shifted from f ₀ to f _{0 +} Delta] f, then the influence of the flaw 2 While the signal is being received, the amplitude gradually decreases with the passage of time (propagation of eddy current) at the position where the center frequency is f ₀ + Δf.

If the position of the depth end portion 2b of the flaw (Figure 4) is in a deep position from the surface, i.e., if the time domain interval of R ₂ is a long time domain R ₁ and R ₃ is large, as shown in FIG. 5 (B) As the time elapses, the amplitude of the detected voltage may become so small that it cannot be observed before the shift phenomenon of the center frequency from f ₀ + Δf to f ₀ is detected. In this case, the depth of the scratch 2 cannot be calculated.

Therefore, in the eddy current flaw detector 10, before the shift phenomenon of the center frequency from f ₀ + Δf to f ₀ with the passage of time is detected, the amplitude of the detected voltage becomes so small that it cannot be observed. In this case, a pulse current having a time difference is supplied to each of the exciting coils 11a to 11c.

  The eddy current flaw detector 10 controls the timing of generating a plurality of eddy currents in the device under test 1 by controlling the pulse currents supplied to the respective excitation coils 11a to 11c. Is superimposed in the process of propagation. By superimposing a plurality of eddy currents inside the object 1 to be inspected, it is possible to cause a phenomenon in which eddy currents propagating inside the object 1 to be inspected interfere with each other and strengthen each other. Thus, it is possible to obtain a detection voltage having a large amplitude even at a deeper position inside the device under test 1.

  More specifically, the control means 19 gives a stop command to the gripping means 13, while giving an excitation current control command to the excitation means 14 to stop scanning by the sensor 43 (excitation body 12 and detection body 16). In this state, a pulse current having a time difference is supplied to the exciter 12.

7 to 9 are explanatory views showing first to third examples of a time difference application pattern of pulse currents supplied to the exciter 12 by the eddy current flaw detector 10. Reference numerals I _{a to} I _c shown in FIGS. 7 to 9 represent pulse currents of the excitation coils 11a and 11c, respectively. The pulse of the excitation current I _a ~I _c shown in FIGS. 7-9, as an example, pulse height, and the pulse width indicates the case the same.

  For example, as shown in FIG. 8, the time difference providing pattern is a pattern in which the pulse current supply timing of the excitation coil 11b is delayed from the pulse current supply timing of the other excitation coils 11a and 11c (delay pattern). There is.

  Further, the time difference application pattern is not limited to the delay pattern of the excitation coil 11b shown in FIG. 8, and the pulse current supply timing of the excitation coil 11b shown in FIG. Arbitrary time differences such as a pattern that precedes the current supply timing (preceding pattern) and a pattern that sequentially delays the exciting coils 11a, 11b, and 11c shown in FIG. Is possible.

  The time difference Δt given here is variable depending on the time during which the detection signal shown in FIG. 3 is completely attenuated, and can be given a specific value or swept within a variable range.

  For example, as shown in FIG. 6, when the center frequency of the frequency spectrum of the detection voltage does not change, the control unit 19 generates a stop command for the gripping unit 13 and a time difference application pattern for the excitation unit 14 and Δt. The excitation current control command for designating the range is given and the selection of the time difference pattern and the Δt range adjustment are repeated until the center frequency of the frequency spectrum of the detection voltage changes, and data is acquired.

  Finally, the calculation extraction means 18 uses the relative positional relationship between the flaw 2 and the sensor, the detection time of the flaw deep end 2b, and the propagation speed of the eddy current in the inspection object 1 identified so far. To identify the length of the flaw in the depth direction.

[Calibration specimen]
FIG. 10 is a schematic view showing a test piece 50 which is an example of a calibration test piece used in the eddy current flaw detector 10.

The test piece 50 is made of a material that is the same as or substantially the same as the material to be inspected 1 (a material that can be identified with at least the conductivity σ and the permeability μ when considering the inspection accuracy required by the user). For example, it has at least one step. That is, the test piece 50 has a plurality of portions (steps) having different thicknesses, and is formed in a step shape having n steps (n is a natural number of 2 or more). Here, reference numeral d ₁ is the thickness of the first stage, code d _n is the thickness of the n stages.

At the time of calibration, the sensor 43 (exciter 12 and detector 16) is arranged on the test piece 50 to obtain a frequency spectrum and envelope. Here, pulsed eddy current identified time to propagate to the bottom surface 51, (the thickness d ₁ of the calibration _specimen, ..., d _n) propagation distance for calculating the propagation velocity from.

  Note that the test piece 50 is not necessarily configured in a stepped shape having a plurality of steps, but is configured in a stepped shape having at least two steps from the viewpoint of improving the calculation accuracy of the propagation velocity in the inspection object 1.

  Further, from the viewpoint of further increasing the calculation accuracy of the propagation velocity in the device under test 1, it is desirable to increase the number n of the test pieces 50 as much as possible. The propagation speed of the eddy current in the inspected object 1 is finally used to identify the length of the flaw 2 in the depth direction, so it is desired to know the length of the flaw 2 in the depth direction more accurately. In this case, it is desirable to increase the number of stages n of the test piece 50 and calculate the propagation speed of the eddy current in the inspection object 1 with higher accuracy.

  As described above, according to the eddy current flaw detection apparatus 10 and the eddy current flaw detection method for the object 1 to be inspected using the eddy current flaw detection apparatus 10, the propagation eddy current that could not be detected by the conventional pulsed eddy current flaw detection (PECT) is detected. Since signal changes in local time can also be detected, PECT can be performed on an object such as a test object 1 that causes a change in local eddy current distribution, such as flaw 2, and the test object. Scratch 2 can be sized with respect to 1.

Further, according to the eddy current flaw detection apparatus 10 and the eddy current flaw detection method for the object to be inspected 1 using the eddy current flaw detection apparatus 10, the sizing of the flaw 2 by the pulse excitation eddy current flaw inspection is performed. Since the depth position where a plurality of eddy currents propagating through the inside is strengthened can be controlled by controlling the excitation current, the center frequency can be obtained even for the inspected object 1 that needs to detect a deep position. A sufficient detection voltage for observing the shift phenomenon from f ₀ + Δf to f ₀ can be obtained. Therefore, even when the inspection object 1 that requires flaw detection at a deep position is inspected (the flaw 2 is sized), the shift phenomenon of the center frequency in the frequency spectrum of the detected voltage can be accurately grasped. Inspection accuracy can be maintained.

  It should be noted that the present invention is not limited to the above-described embodiment as it is, and can be implemented in various forms other than the above-described examples in the implementation stage, and various modifications can be made without departing from the spirit of the invention. Can be omitted, added, replaced, or changed. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 1 ... Test object, 2 ... Scratch, 2a ... Scratch front end part, 2b ... Scratch deep end part, 10 ... Eddy current flaw detector, 11 (11a-11e) ... Excitation coil, 12 ... Excitation body, 13 ... Grasping means , 14 ... Excitation means, 15 (15a to 15c) ... detection element, 16 ... detection body, 17 ... detection means, 18 ... calculation extraction means, 19 ... control means, 21 ... display means, 41 ... minute section, 42 ... envelope Line difference, 43 ... Sensor, 50 ... Test piece, 51 ... Bottom of test piece, V _R1 ... Frequency spectrum of detection voltage in time domain R ₁ , V _R2 ... Frequency spectrum of detection voltage in time domain R ₂ , V _{R3 ...} the frequency spectrum of the detected voltage in the time domain _{R 3,} the frequency spectrum of the detected voltage in V _{R4 ...} time domain _{R 4,} the excitation current flowing through the I a _... exciting coil 11a, the flow to the I b _... exciting coil 11b Excitation current, the excitation current flowing through the I c _... exciting coil 11c to be.

Claims (10)

Excitation means for supplying a pulsed current to each of the excitation coils of an exciter configured to excite two or more excitation coils that form an eddy current by exciting a pulsed magnetic field in the body to be inspected;
Detection means for receiving a voltage signal detected by each of the at least one detection element from a detection body having at least one detection element for detecting a transient distribution change of the eddy current;
Gripping means for gripping the exciter and the detector, and scanning the exciter and the detector;
Of the maximum of the sum of two or more points obtained by calculating the sum of changes in the difference between the upper envelope and the lower envelope of the waveform of the voltage signal detected by the detection means, the maximum of the sum is obtained with respect to the scanning direction. While calculating the position of a flaw existing in the subject based on the appearance position of two consecutive local maximum values, the detection means detects the depth of the flaw in the subject existing at the calculated position. Calculation extraction means for calculating based on the time change of the center frequency in the frequency spectrum of the voltage signal
Control means for controlling the excitation means so that the eddy current formed by the pulsed current supplied to each of the excitation coils is superimposed with a time difference in the body to be inspected. Eddy current flaw detector. The gripping means can three-dimensionally scan the excitation body and the detection body,
The control means stops the gripping means when the time change of the center frequency does not occur as a result of the calculation by the calculation extraction means during the scanning, and the eddy current is superimposed with a time difference in the subject. 2. The eddy current flaw detector according to claim 1, wherein the excitation means is controlled as described above. The control means continuously changes the time difference of the pulsed current supplied to each of the exciting coils, and repeats the change of the time difference and the calculation of the frequency spectrum until the time change of the center frequency occurs. The eddy current flaw detector according to claim 1 or 2, wherein the excitation means and the calculation extraction means are controlled. The calculation extraction means is based on a time during which the eddy current propagates in the depth direction through the flaw in the inspection subject and a speed at which the eddy current given in advance propagates through the flaw in the inspection subject in the depth direction. The depth of the flaw in the body to be inspected, and from the time change of the frequency spectrum of the voltage signal received by the detection means, the peak of the frequency spectrum of the voltage signal received by the detection means The eddy current is a time obtained by measuring a time during which a frequency taking a value is maintained in a state of being shifted by a predetermined amount with respect to a center frequency of a pulsed current supplied to the exciting coil. The eddy current flaw detector according to any one of claims 1 to 3, wherein the flaw is calculated as a time for propagation in the depth direction. The speed at which the eddy current propagates in the depth direction through the object to be inspected is a value calculated in advance using a calibration test piece made of a material having at least the same conductivity and permeability as the object to be inspected. The eddy current flaw detector according to claim 4. The calibration test piece has a plurality of planes having an area on which the exciting coil and the detection element can be placed together, and each of the planes is parallel to the bottom surface and has a distance from the bottom surface. The eddy current flaw detector according to claim 5, which is different. 2. The calculation extraction unit, when obtaining the frequency spectrum, performs a Fourier transform on a time domain divided by an arbitrary minute time domain, and observes a time change of the frequency spectrum. The eddy current flaw detector according to any one of 1 to 6. The calculation extraction unit calculates a midpoint of the appearance positions of two maximum values that are continuous in the scanning direction, and sets the calculation result as a position of a flaw existing in the body to be inspected. The eddy current flaw detector according to any one of claims 1 to 7. 9. The pulse-shaped applied current supplied to the exciting coil is a pulse-shaped applied current generated from a Fourier series having a coefficient calculated from the skin depth. The eddy current flaw detector described in the paragraph. Excitation means for supplying a pulsed current to each of the excitation coils of an exciter configured to excite two or more excitation coils that form an eddy current by exciting a pulsed magnetic field in the body to be inspected; A detecting means for receiving a voltage signal detected by each of the at least one detecting element from a detecting body having at least one detecting element for detecting a transient distribution change of the eddy current; While calculating the position of the flaw existing in the inspected object based on information obtained from the waveform of the voltage signal, the depth of the flaw in the inspected object existing at the calculated position is calculated in the frequency spectrum of the voltage signal. An eddy current flaw detector comprising a calculation extraction means for calculating based on a change in center frequency with time, and a control means for controlling the excitation body, the detection body, and the excitation means is used. An eddy current testing method that performs,
The excitation means supplying a pulsed current to each of the excitation coils;
The detection means receiving the voltage signal detected by each of the at least one detection element;
The maximum of the sum of two or more points obtained by calculating the sum of changes in the difference between the upper envelope and the lower envelope of the waveform of the voltage signal received in the step of receiving the voltage signal by the calculation extraction means. Among these, the position of the flaw that exists in the inspected body is calculated based on the appearance positions of two local maximum values that are continuous in the scanning direction of the excitation body and the detection body. Calculating the depth of the flaw in the subject to be inspected based on the time change of the center frequency in the frequency spectrum of the voltage signal;
When the control means does not cause a time change of the center frequency in the frequency spectrum of the voltage signal, scanning of the excitation body and the detection body is stopped, and a pulsed current having a time difference is applied to each of the excitation coils. Eddy current flaw detection method comprising: supplying and controlling the exciter, the detector, and the exciter so that the eddy current is superimposed with a time difference in the subject. .

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