JP5383597B2 - Eddy current inspection apparatus and inspection method - Google Patents

Description

  The present invention relates to an eddy current inspection apparatus and inspection method, and more particularly, to an eddy current inspection apparatus and inspection method suitable for evaluating the thickness of a subject and detecting defects by a pulse excitation type.

  In power plants and the like, the soundness of piping equipment is regularly inspected. Periodic inspections include a thinning inspection for confirming the presence or absence of thinning related to the wall thickness of pipes, and a defect inspection for confirming the presence or absence of defects such as flaws and cracks related to pipe welds. When an ultrasonic flaw detector is used for the thinning inspection, the entire length of the pipe is inspected while the probe is pressed against the pipe and the thickness of the pipe as the subject is measured from the time delay of the reflected wave. In addition to the thinning inspection, the defect inspection is carried out by a visual inspection method, a penetrating flaw detection method and the like. As described above, the thinning inspection and the defect inspection are performed by different inspection methods, but since it is necessary to perform the inspection at the same place, it is difficult to perform both at the same time. As a result, the entire inspection work requires a long time and a great amount of labor.

  In recent thinning inspection, a pulse excitation type eddy current flaw detection method that electromagnetically measures the thickness of a subject has been used. In the pulse excitation type eddy current flaw detection method, a time-varying magnetic field is generated by a pulsed excitation current generated by applying a pulse excitation voltage to an excitation coil of a probe. When the pulse excitation voltage is a rectangular wave, the temporal variation of the magnetic field around the probe indicates that the pulse excitation current waveform has a delay characteristic due to eddy current. Considering the fall of the pulse excitation voltage, the pulse excitation current attenuates more slowly than the pulse excitation voltage. The magnetic flux distribution is changed by this attenuation, and an eddy current is generated in the magnetic material so as to prevent the magnetic flux from changing. In the thickness measurement, after the magnetic flux due to the pulse excitation current is attenuated, the magnetic flux due to the eddy current of the subject is measured, and the thickness is evaluated from the characteristics. In this way, the pulse excitation type eddy current flaw detection method can measure the thickness of pipes and the like in a non-contact manner, so there is no need for incidental operations such as application of contact medium and heat insulation material removal in ultrasonic inspection, especially automatic pipe inspection. It is effective as a technology.

  The eddy current flaw detection method generally performed in the first place continuously applies a sinusoidal excitation current to an excitation coil of a probe by applying a continuous sinusoidal voltage, thereby generating a time-varying magnetic field. In this case, the temporal fluctuation of the eddy current in the magnetic field around the probe is a continuous sine wave. In defect inspection, changes in the amplitude and phase of magnetic flux that fluctuates in time in a continuous sinusoidal shape are measured, and the presence of defects and material changes are evaluated from their characteristics. As described above, it is known that the eddy current flaw detection method that applies a sine wave voltage that is generally performed can measure a defect such as a non-contact or a crack, and particularly has excellent detection sensitivity for a surface defect. . Evaluation of thinning by a method similar to this is applied to a thin object that can be sufficiently penetrated by eddy current.

  Thickness measurement by pulse excitation is the measurement of the thickness of an object made of an electrically conductive material. After a constant current is passed through the emitter coil during the pulse time, the current and related electromagnetic field are turned off at the falling edge of the pulse. It is known that the output voltage between the two receiver coils is measured as a function of time and compared with the attenuation of the reference signal at a known wall thickness (see, for example, Patent Document 1).

  As a defect inspection close to pulse wave excitation, excitation using a non-sinusoidal wave such as a triangular wave, and using a filter or Fourier transform on the detected signal waveform, the response to single frequency sine wave excitation is extracted, and the defect is detected. It detects (for example, refer patent document 2). Measurement over multiple frequencies is performed by changing the extracted sine wave component.

  As a method for inspecting wall thickness and defects at the same time, it is known to measure the wall thickness with an ultrasonic sensor from the inner wall surface and to inspect the defect with an eddy current sensor from the outer wall surface (for example, patent) Reference 3).

Publication 2000-514559 Japanese Patent Laid-Open No. 6-94681 JP-A-61-133856

  However, since the thing of patent document 1 pays attention to the eddy current attenuation | damping by pulse excitation, while the thickness of a thick metal member can be measured, since the information of the defect near a probe position is mixed, it is thinning and Defect measurement becomes difficult. In addition, the method described in Patent Document 2 uses a frequency analysis of the response of non-sinusoidal excitation, which is a method similar to pulse wave excitation, to inspect defects, so when applied to thinning inspection, the thinning of conventional thin tube materials It is considered that the sensitivity performance is equivalent to the inspection. Furthermore, although the thing of patent document 3 can measure a thinning and a defect using an ultrasonic sensor and an eddy current sensor together on both sides of a test object, the surface to be inspected is only on one side of the test object. In some cases, application is difficult.

  An object of the present invention is to provide an eddy current inspection apparatus and an inspection method that can detect defects such as scratches and cracks at the same time while thinning an object can be inspected even with a thick object, thereby improving inspection work efficiency. It is in.

(1) In order to achieve the above object, the present invention is an eddy current inspection apparatus for inspecting a metal object with an eddy current caused by a pulse-like time-varying magnetic field, which has a temporally periodic pulse waveform. A time-varying magnetic field generating means for controlling the exciting current of the exciting coil based on the exciting voltage to generate a time-varying magnetic field, and a transient with respect to the magnetic field change caused by the eddy current generated in the subject by the time-varying magnetic field generating means. The transient information extracting means for extracting the magnetic field information, the periodic information extracting means for extracting the periodic magnetic field information, and the transient magnetic field information extracted by the transient information extracting means A thickness evaluation unit that evaluates the thickness, and a defect evaluation unit that calculates the periodic magnetic field information extracted by the periodic information extraction unit and evaluates defects such as flaws and cracks in the specimen. did Than is.
With this configuration, it is possible to simultaneously measure defects such as flaws and cracks while improving thinning even with a thick specimen, thereby improving inspection work efficiency.

  (2) In the above (1), preferably, the time-varying magnetic field generating means includes a waveform generator that generates an excitation voltage waveform, and a power amplifier that amplifies the excitation voltage waveform and supplies an excitation current to the excitation coil. And a switch for controlling energization and interruption of the excitation current, the waveform generator, and a trigger generator for controlling the switch. The trigger generator outputs a synchronization signal at a constant time period. Connected to the waveform generator to generate a temporally periodic excitation voltage waveform, and connected to the switch to control the energization time and cutoff time of the excitation current, A pulsed magnetic field is generated.

  (3) In the above (1), preferably, the transient information extraction means includes at least one magnetic field detection element, and a sensor unit that acquires a signal of a time-varying magnetic field; The eddy current attenuation information extraction unit extracts eddy current attenuation information using the transient information of the time-varying magnetic field signal as a basis.

  (4) In the above (2), preferably, the eddy current attenuation information extraction unit performs arithmetic processing on the time of energization start time from the time when the excitation current of the switch is cut off and the signal value of the time-varying magnetic field between the times. In addition, eddy current attenuation information is extracted.

  (5) In the above (4), preferably, the eddy current attenuation information extraction unit includes storage means for storing a predetermined reference signal set in advance, and the energization start time is determined from the cutoff time of the excitation current of the switch. The eddy current attenuation information is extracted by comparing the time and the result of the arithmetic processing of the signal value of the time-varying magnetic field between the times with the result of the same arithmetic processing with respect to the reference signal. It is a thing.

  (6) In the above (1), preferably, the period information extracting means includes at least one magnetic field detecting element, and a sensor unit that acquires a signal of a time-varying magnetic field, and a time for energizing or interrupting the excitation current. Based on the periodic information of the time-varying magnetic field signal, an amplitude information extraction unit that extracts amplitude information and a phase information extraction unit that extracts phase information are used.

  (7) In the above (6), preferably, the amplitude information extraction unit includes storage means for storing a predetermined reference signal set in advance, and calculates a difference between the reference signal and the signal value of the time-varying magnetic field. The phase difference extraction unit includes storage means for storing a predetermined reference signal set in advance, and the reference signal and the signal value of the time-varying magnetic field are obtained. Is obtained by calculating the difference in time when the signal value rises or falls and extracts the phase information of the time-varying magnetic field.

(8) In the above (1), preferably, the transient information extraction unit includes at least one magnetic field detection element, and includes a sensor unit that acquires a signal of a time-varying magnetic field, and the periodic information extraction unit includes at least A magnetic field detection element having one magnetic field detection element and acquiring a signal of a time-varying magnetic field, and the magnetic field detection elements used in the transient information extraction means and the periodic information extraction means are the same A thing is used.

  (9) In the above (1), preferably, the transient information extraction unit includes at least one magnetic field detection element, and includes a sensor unit that acquires a signal of a time-varying magnetic field, and the periodic information extraction unit includes at least The magnetic field detection element having one magnetic field detection element and having a sensor unit that acquires a signal of a time-varying magnetic field, and having the characteristics of different magnetic field sensitivities used in the transient information extraction unit and the periodic information extraction unit Is used.

  (10) In the above (1), preferably, the thickness evaluation unit includes storage means for storing the transient magnetic field information for different preset thicknesses, and is extracted by measurement of the subject. The thickness of the object is evaluated by comparing with transient magnetic field information, and the defect evaluation unit stores the periodic magnetic field information for defects such as scratches and cracks having different shapes. And a defect of the subject is evaluated by comparing with periodic magnetic field information extracted by measurement of the subject.

(11) In order to achieve the above object, the present invention provides an eddy current inspection method using an eddy current inspection apparatus that inspects a metal object with an eddy current caused by a pulsed time-varying magnetic field. Using the excitation voltage with a pulse waveform synchronized with the synchronization signal output in step 1, the excitation current of the excitation coil is controlled by a switch to generate a time-varying magnetic field, and the magnetic field changes due to the eddy current generated in the subject. On the other hand, the magnetic field is measured by at least one magnetic field detection element, and eddy current attenuation information obtained by arithmetic processing based on the energization and interruption time of the excitation current is obtained. At the same time, at least one magnetic field detection element is obtained. The magnetic field is measured at, the amplitude information and the phase information obtained by performing arithmetic processing based on the energization or interruption time of the excitation current are obtained, and the eddy current attenuation information is different from a preset value. Compared with eddy current attenuation information with respect to thickness, the thinning of the object is evaluated, and the amplitude information and the phase information are amplitude information and phase information for defects such as scratches and cracks having different shapes. In comparison, the defect of the object is evaluated.
With this configuration, it is possible to simultaneously measure defects such as flaws and cracks while improving thinning even with a thick specimen, thereby improving inspection work efficiency.

According to the present invention, it is possible to simultaneously measure defects such as flaws and cracks while thinning of a thin specimen can be inspected, and the work efficiency of inspection is improved.

1 is a block diagram showing an overall configuration of an eddy current inspection apparatus according to a first embodiment of the present invention. It is a block diagram which shows the structure of the eddy current probe used for the eddy current inspection apparatus by the 1st Embodiment of this invention. It is a perspective view showing one form of piping inspection using an eddy current probe of an eddy current inspection device by a 1st embodiment of the present invention. It is a wave form diagram which shows the signal waveform in the eddy current inspection apparatus by the 1st Embodiment of this invention. It is explanatory drawing of the attenuation | damping waveform of the time-varying magnetic field signal in the eddy current inspection apparatus by the 1st Embodiment of this invention. It is explanatory drawing of the time-varying magnetic field signal waveform by the presence or absence of a defect in the eddy current inspection apparatus by the 1st Embodiment of this invention. It is a wave form diagram which shows the signal waveform in the eddy current inspection apparatus by the 1st Embodiment of this invention. It is explanatory drawing of extraction of the eddy current attenuation | damping information in the eddy current test | inspection apparatus by the 1st Embodiment of this invention. It is explanatory drawing of an example which plate | board thickness evaluated in the thickness evaluation part of the eddy current inspection apparatus by the 1st Embodiment of this invention. It is a wave form diagram which shows the signal waveform in the eddy current inspection apparatus by the 1st Embodiment of this invention. It is explanatory drawing of extraction of the amplitude information in the amplitude information acquisition part in the eddy current inspection apparatus by the 1st Embodiment of this invention, and extraction of the phase information in a phase information acquisition part. It is explanatory drawing of an example which evaluated the defect in the defect evaluation part 20 of the eddy current inspection apparatus by the 1st Embodiment of this invention. It is explanatory drawing of the simultaneous measurement result of the thinning by the eddy current inspection apparatus by the 1st Embodiment of this invention, and a defect. It is a block diagram which shows the whole structure of the eddy current test | inspection apparatus by the 2nd Embodiment of this invention. It is operation | movement explanatory drawing of the eddy current inspection apparatus by the 3rd Embodiment of this invention.

Hereinafter, the configuration and operation of the eddy current inspection apparatus according to the first embodiment of the present invention will be described with reference to FIGS. 1 to 12, the same reference numerals indicate the same parts.
[Time-varying magnetic field signal]
First, the time-varying magnetic field signal used in the eddy current inspection apparatus according to the present embodiment will be described with reference to FIGS.
FIG. 1 is a block diagram showing the overall configuration of the eddy current inspection apparatus according to the first embodiment of the present invention.

  In FIG. 1, the probe control unit 5 outputs information on the position where the eddy current probe 2 is to be moved to the scanning control device 4. The scanning control device 4 controls the scanning mechanism 3 based on the position information and scans the eddy current probe 2. The scanning control device 4 includes an encoder or the like for detecting the position of the eddy current probe 2 moved by the scanning mechanism 3, and outputs a scanning position signal to the probe control unit 5.

  The inspection apparatus 1 receives a time-varying magnetic field signal detected by the eddy current probe 2 at the time of inspection, and evaluates a thickness and a defect as will be described later. In addition, a probe scanning position signal is input to the inspection apparatus 1 from the probe control unit 5. The inspection apparatus 1 outputs the evaluated thickness and defect information to the output unit 21 in association with the scanning position signal and displays the information.

  The eddy current probe 2 includes an excitation coil 6 and sensor units 9 and 10 having magnetic field detection elements 7 and 8 (described later in FIG. 2). In order to generate an eddy current in the subject 11 (described later in FIG. 2), an excitation voltage is generated by the time-varying magnetic field generation means 12 to supply the excitation current to the excitation coil 6. Eddy currents generated in the subject 11 change due to the thickness, scratches, cracks, etc. of the subject, and as a result, the magnetic field distribution changes. Therefore, information corresponding to a change in eddy current can be obtained by measuring the time-varying magnetic field with the magnetic field detection elements 7 and 8.

  In pulse excitation type eddy current flaw detection for measuring wall thickness, the time-varying magnetic field generating means 12 generates a pulsed excitation voltage, supplies the excitation current to the excitation coil, and gives a pulsed time-varying magnetic field, An eddy current is generated in the subject 11. The intensity of eddy current penetrates while decaying exponentially with respect to the thickness direction. The time during which the eddy current permeates penetrates the eddy current with a delay in time as the depth of the subject 11 increases, and a magnetic field that is secondarily generated by the penetrated eddy current circulates on the surface of the subject 11. To do. For this reason, the information on the wall thickness includes a component that is delayed in time when the plate is thick, and a component that is earlier than that in the case where the plate is thick when the plate is thin.

  In order to acquire this phenomenon, the present inspection apparatus 1 includes transient information extracting means 13 for extracting temporal characteristics that occur when eddy currents are attenuated. To obtain eddy current attenuation information. Detailed operation of the transient information extracting means 13 will be described later with reference to FIGS.

  On the other hand, in eddy current flaw detection that detects defects such as scratches and cracks, a sinusoidal excitation current is generally continuously passed through the excitation coil of a probe by applying a continuous sinusoidal voltage to generate a time-varying magnetic field. . In this case, the temporal fluctuation of the eddy current in the magnetic field around the probe also becomes a continuous sine wave, and the defect detection measures changes in the amplitude and phase of the time-varying magnetic field.

  In the case of pulse excitation type eddy current flaw detection, if the pulse excitation waveform is periodic, the waveform can be expressed as a sum of sine waves of a plurality of frequencies by Fourier transform, which is one of mathematical methods. Therefore, single-frequency excitation information is included. Since the output in this case, that is, the information of the time-varying magnetic field obtained by the magnetic field detection elements 7 and 8 can be similarly expressed as the sum of sine waves of a plurality of frequencies using the Fourier transform method, It contains frequency excitation information. The information on the excitation current and time-varying magnetic field of the same frequency component is considered to correspond to the input / output relationship when excitation is performed at that frequency alone, so the waveform is periodic even in pulse excitation type eddy current flaw detection. If so, conventional eddy current flaw detection with a single frequency is possible. Therefore, by acquiring the amplitude information and the phase information in single frequency excitation eddy current flaw detection, it is possible to inspect defects such as flaws and cracks, which are conventionally good at eddy current flaw detection.

  In order to execute this, the inspection apparatus 1 includes periodic information extraction means 15 for extracting periodic information from the signal of the time-varying magnetic field, and the amplitude information extracting unit 16 uses the signal of the time-varying magnetic field. The phase information extraction unit 17 extracts the phase information of the periodic component of the time-varying magnetic field signal. Detailed operation of the period information extracting means 15 will be described later with reference to FIGS.

  The eddy current attenuation information extracted by the transient information extraction unit 13 and the amplitude information and phase information of the periodic time-varying magnetic field extracted by the period information extraction unit 15 are sent to the analysis unit 18.

  Since the eddy current attenuation information extracted by the transient information extracting means 13 includes the thickness information of the subject 11, the thickness is evaluated by performing arithmetic processing in the thickness evaluation unit 19. Detailed operation of the wall thickness evaluation unit 19 will be described later with reference to FIGS.

  In addition, since the amplitude information and the phase information extracted by the period information extraction unit 15 have defect information of the subject 11, the defect is evaluated by performing arithmetic processing in the defect evaluation unit 20. The detailed operation of the defect evaluation unit 20 will be described later with reference to FIGS.

  The evaluation result of the thickness evaluated by the thickness evaluation unit 19 and the evaluation result of the defect evaluated by the defect evaluation unit 20 are displayed and presented by the output unit 21.

Next, the configuration of the eddy current probe 2 used in the eddy current inspection apparatus according to the present embodiment and one form of pipe inspection using the same will be described with reference to FIGS.
FIG. 2 is a block diagram showing the configuration of the eddy current probe used in the eddy current inspection apparatus according to the first embodiment of the present invention. FIG. 3 is a perspective view showing one form of pipe inspection using the eddy current probe of the eddy current inspection apparatus according to the first embodiment of the present invention.

  As shown in FIG. 2, the eddy current probe 2 is composed of an excitation coil 6 and magnetic field detection elements 7 and 8, and is arranged in a non-contact manner on the same examination surface with respect to the subject 11. Pipes installed in the plant may not be accessible from the back side of the subject, and it may be necessary to inspect for thinning and defects from one side.

  The exciting coil 6 uses a coil winding conductor such as enameled wire or formal wire wound around the concentric shaft 22 a plurality of times. A magnetic path (magnetic flux path) may be formed by using a magnetic material such as a ferrite core or an electromagnetic steel plate at the center or the periphery of the exciting coil 6. Alternatively, a plurality of similar coils may be used to increase the magnetic field strength or control the forming magnetic field.

  The magnetic field detecting element 7 constitutes the sensor unit 9 of the transient information extracting means 13 shown in FIG. 1, and a coil, a Hall element, an MI element, a GMR element, a TMR element, an AMR element, a SQUID element, or the like is used. The time-varying magnetic field handled by the transient information extracting means 13 is related to eddy current attenuation, and the magnetic field strength is relatively small. Therefore, when a signal output whose signal output depends on the temporal change rate of the magnetic field is used like a coil, A sufficient signal output voltage may not be obtained. Therefore, it can be said that the Hall element, the MI element, the GMR element, the TMR element, the AMR element, and the SQUID element, which can obtain a signal output with the absolute value of the magnetic field intensity, are magnetic field detection elements that can obtain accuracy in extracting eddy current attenuation information. When the range of the magnetic field strength required for the measurement is wide, the sensor unit may be configured and measured using a plurality of magnetic field detection elements suitable for the range of the magnetic field strength to be measured. In that case, it is preferable to acquire a signal of a time-varying magnetic field by connecting a process for correcting the characteristics of the magnetic field detection element to be used or a filter circuit. Further, since the magnetic field detecting element 7 is arranged near the exciting coil 6 because it is necessary to obtain a small magnetic field signal, the arrangement shown in FIG. Not limited to those.

  The magnetic field detection element 8 constitutes the sensor unit 10 of the period information extraction means 15 shown in FIG. 1, and a coil, a Hall element, an MI element, a GMR element, a TMR element, an AMR element, a SQUID element, or the like is used. The time-varying magnetic field handled by the period information extraction means 15 needs to be measured over a wide magnetic field strength range so that amplitude information and phase information can be acquired. A device with a wider operating range with respect to the magnetic field intensity such as a coil, a Hall element, or an MI element is used than a device with a small operating range with a high resolution with respect to the magnetic field strength, such as a GMR element, a TMR element, an AMR element, or a SQUID element. It can be said that it is easy to do. When the range of the magnetic field strength required for the measurement is wide, the sensor unit may be configured and measured using a plurality of magnetic field detection elements suitable for the range of the magnetic field strength to be measured. In that case, it is preferable to acquire a signal of a time-varying magnetic field by connecting a process for correcting the characteristics of the magnetic field detection element to be used or a filter circuit. In particular, when a coil is used, the output voltage of the coil is obtained by time differentiation of a time-varying magnetic field, so that it is preferable for the subsequent arithmetic processing to perform correction processing such as an integration circuit on the sensor unit. In addition, since the magnetic field detection element 8 needs to obtain a magnetic field signal related to defect information, the magnetic field detection element 8 is disposed at a position suitable for the magnetic field distribution that varies depending on the defect to be measured. In the case of FIG. 2, the coil 8 of the center axis 23 is arranged in the vicinity of the center axis 22 of the excitation coil 6. In this case, a defect is present between the excitation coil 6 and the coil 8 as the magnetic field detection element. Is present, the magnetic field in which the eddy current is greatly disturbed is measured by the coil 8, and a large change is obtained in the amplitude information and the phase information. However, the arrangement is not limited to that shown in FIG. 2 as long as the defect information can be obtained with high sensitivity.

  As shown in FIG. 3, the eddy current probe 2 shown in FIG. 2 is attached to a scanning mechanism 3 serving as a scanner mechanism and can be automatically inspected. The scanning mechanism 3 is attached to a pipe 24 serving as a subject, and scans the outer wall surface of the pipe in the circumferential direction and the axial direction. There is a possibility that the pipe 24 has defects such as a thinning 25 in which the pipe thickness is reduced by a fluid flowing inside the pipe, and a flaw or crack 26 caused by metal fatigue. It is necessary to detect these promptly and take appropriate measures such as repair or replacement. In the inspection, it is preferable to detect these in a short time. Therefore, it is the best inspection method that the thinning and the defect can be detected at the same time as the inspection sensor such as the eddy current probe 2 passes. Therefore, the inspection apparatus 1 shown in FIG. 1 of the present embodiment can rapidly inspect for thinning and defects at the same time, and more quickly for eddy current flaw detection.

Next, signal waveforms in the eddy current inspection apparatus according to the present embodiment will be described with reference to FIG.
FIG. 4 is a waveform diagram showing signal waveforms in the eddy current inspection apparatus according to the first embodiment of the present invention.

  4A shows an excitation voltage composed of positive and negative rectangular waves as a pulse voltage, FIG. 4B shows an excitation current, and FIG. 4C shows time fluctuations obtained by the magnetic field detection elements 7 and 8. Indicates a magnetic field. The horizontal axis is a time axis, and the broken lines in the figure indicate the same time.

  In FIG. 1, the time-varying magnetic field generating means 12 generates an excitation voltage and an excitation current. The time-varying magnetic field generating means 12 includes a waveform generator 26 that can generate an arbitrary waveform and a trigger generator 27 that generates a trigger signal. The trigger generator 27 outputs a trigger signal to the arbitrary waveform generator 26. The waveform generator 26 receives the trigger signal and outputs a preset arbitrary excitation voltage waveform to the power amplifier 28. The power amplifier 28 outputs the pulse excitation voltage waveform amplified by the set magnification to the excitation coil 6 of the eddy current probe 2 and supplies the excitation current. The excitation current can be controlled to be turned on and off by a switch 29 such as a transistor, a thyristor, or a relay, and the control is executed by a signal from the trigger generator 27.

  In contrast to the excitation voltage 30a shown in FIG. 4A, the waveform of the excitation current 30b shown in FIG. 4B gradually increases or decreases due to the influence of the coil inductance. Since the eddy current generated in the subject flows with a delay in time, when the excitation current 30b is cut off, that is, zero, the time-varying magnetic field 30c gradually decreases as shown in FIG. Attenuates to zero. Since the attenuation characteristics change when the thickness of the subject changes, the wall thickness can be evaluated by calculating and evaluating the time-varying magnetic field signal related to the attenuation portion.

Next, the decay waveform of the time-varying magnetic field signal in the eddy current inspection apparatus according to the present embodiment will be described with reference to FIG.
FIG. 5 is an explanatory diagram of the decay waveform of the time-varying magnetic field signal in the eddy current inspection apparatus according to the first embodiment of the present invention.

  FIG. 5 is an enlarged view of the decay waveform of the time-varying magnetic field signal when the thickness of the subject changes. Since the decay time varies between the case where the plate thickness is small and the case where the plate thickness is large, when the time to reach the same magnetic field strength T1 is measured, the arrival time t1 when the plate thickness is small, and the arrival time when the plate thickness is large Time t2 is reached, and the thickness can be evaluated by performing calculation processing and evaluation related to the decay time.

Next, the waveform of the time-varying magnetic field signal depending on the presence / absence of a defect in the eddy current inspection apparatus according to the present embodiment will be described with reference to FIG.
FIG. 6 is an explanatory diagram of time-varying magnetic field signal waveforms depending on the presence or absence of defects in the eddy current inspection apparatus according to the first embodiment of the present invention.

FIG. 6 shows a time-varying magnetic field waveform 32a when there is no defect and a time-varying magnetic field waveform 32b when there is a defect. In eddy current flaw detection based on a single-frequency sine wave, the presence / absence of a defect is detected by utilizing changes in amplitude and phase. Even in pulsating eddy current flaw detection, the same phenomenon can be obtained by analyzing the information decomposed into a single frequency by the Fourier transform, which is a mathematical method. Therefore, as shown in FIG. The phase difference Δt tends to be obtained. Therefore, if the amplitude difference ΔB and the phase difference Δt can be measured without affecting the measurement of the signal 31 of the time difference information 31 related to the eddy current attenuation shown in FIG. 5, the thickness can be measured and the defect can be detected. .
[Transient information extraction means and wall thickness evaluation section]
Next, the configuration and operation of the transient information extraction unit 13 and the wall thickness evaluation unit 19 used in the eddy current inspection apparatus according to the present embodiment will be described with reference to FIGS. 1 and 7 to 9.
FIG. 7 is a waveform diagram showing signal waveforms in the eddy current inspection apparatus according to the first embodiment of the present invention. FIG. 8 is an explanatory diagram of extraction of eddy current attenuation information in the eddy current inspection apparatus according to the first embodiment of the present invention. FIG. 9 is an explanatory diagram of an example in which the plate thickness is evaluated by the wall thickness evaluation unit of the eddy current inspection apparatus according to the first embodiment of the present invention.

  In FIG. 7, FIG. 7A shows an excitation voltage composed of positive and negative rectangular waves as a pulse voltage, FIG. 7B shows a trigger signal, FIG. 7C shows an excitation current, and FIG. (D) shows a time-varying magnetic field obtained by the magnetic field detection element 7. The horizontal axis is a time axis, and the broken lines in the figure indicate the same time.

  The sensor unit 9 including the magnetic field detection element 7 of the eddy current probe 2 described with reference to FIGS. 1 and 2 acquires a time-varying magnetic field 35d illustrated in FIG. In order to extract a magnetic field component for eddy current attenuation with respect to this time-varying magnetic field 35d, it is taken into the calculation unit 14a of the eddy current attenuation information acquisition unit 14 of FIG.

  On the other hand, the trigger generator 27 of the time-varying magnetic field generating means 12 shown in FIG. 1 outputs the trigger signal 35b shown in FIG. 7B to the arbitrary waveform generator 26, and the waveform generator 26 outputs the trigger signal 35b. Then, an arbitrary excitation voltage 35a (FIG. 7A) set in advance is output to the power amplifier 28. The power amplifier 28 outputs the pulse excitation voltage waveform amplified by the set magnification to the excitation coil 6 of the eddy current probe 2, and supplies the excitation current 35c of FIG.

  The calculation unit 14a in FIG. 1 takes in the magnetic field component into the eddy current attenuation by using the trigger signal 35b as information on the cutoff time ts and the energization time te regarding the excitation current 35c of the switch 29 from the trigger generator 27 shown in FIG. Of the variable magnetic field, only the component 36 related to eddy current attenuation can be calculated.

  Thereby, the period information extraction means 15 described later can calculate only the component of the time-varying magnetic field related to the eddy current attenuation irrespective of the time period for acquiring the amplitude information and the phase information.

  Next, eddy current attenuation information extraction processing will be described with reference to FIG. FIG. 8A shows a signal of the time-varying magnetic field shown in FIG. FIG. 8B shows a signal obtained by enlarging the main part of FIG.

  As shown in FIG. 8B, when the plate thickness is changed, that is, when thinning is detected, the attenuation waveform 38b at the time of thinning changes as shown in the figure with respect to the attenuation waveform 38a at the healthy part. .

  The comparison unit 14b performs differential processing on the component related to eddy current attenuation extracted by the calculation unit 14a and the data on the healthy part measurement stored in the storage unit 14c of the eddy current attenuation information acquisition unit 14 to obtain an eddy current. Only the change in the attenuation information can be extracted, and this can be used when an evaluation of a subject having a large plate thickness where the change is minute or when the number of digits of measurement accuracy for thickness measurement is required.

  FIG. 9 shows an example in which the plate thickness is evaluated by the wall thickness evaluation unit 19 based on the eddy current attenuation information obtained by the transient information extraction means 13.

  As shown in FIG. 9A, when the position of the eddy current probe 2 is changed with respect to the subject 39 whose plate thickness is spatially changed, in response to the change in the plate thickness being measured, The eddy current attenuation parameter changes. This parameter value is measured in advance with a comparative specimen having a known plate thickness, and the eddy current parameter is stored in the storage unit 19c.

  FIG. 9B is a graph showing the relationship between the eddy current attenuation parameter and the plate thickness. By using a calibration curve 41 of data measured with a contrast specimen whose thickness is known in advance stored in the storage unit 19c, when the eddy current attenuation parameter is p, the plate thickness a (mm) and the eddy current attenuation parameter are When q, the plate thickness can be quantitatively evaluated such as the plate thickness b (mm).

  The computing unit 19a calculates the rate of change of the magnetic field value for at least two points of time with respect to the time of the waveform indicating the eddy current attenuation component extracted based on the trigger signal, and uses it as a parameter for eddy current attenuation. Can do. For example, if the rate of change is obtained using the values of the magnetic field strengths B2 and B2 'at time t2 and the magnetic field strengths B1 and B1' at time t1, it can be evaluated by approximation with a linear function. In addition, since the attenuation signal is an exponential function, the time characteristic of the attenuation signal can be parameterized by using a parameter representing the exponential function such as power series expansion.

And the comparison part 19b can evaluate a thinning amount or a remaining thickness by comparing the calculation result by the calculating part 19a with the calibration curve 41 memorize | stored in the memory | storage part 19c.
[Period information extraction means and defect evaluation section]
Next, the configuration and operation of the period information extraction unit 14 and the defect evaluation unit 20 used in the eddy current inspection apparatus according to the present embodiment will be described with reference to FIGS.
FIG. 10 is a waveform diagram showing signal waveforms in the eddy current inspection apparatus according to the first embodiment of the present invention. FIG. 11 is an explanatory diagram of extraction of amplitude information in the amplitude information acquisition unit and extraction of phase information in the phase information acquisition unit in the eddy current inspection apparatus according to the first embodiment of the present invention. FIG. 12 is an explanatory diagram of an example in which defects are evaluated by the defect evaluation unit of the eddy current inspection apparatus according to the first embodiment of the present invention.

  10, FIG. 10 (a) shows an excitation voltage composed of positive and negative rectangular waves as a pulse voltage, FIG. 10 (b) shows a trigger signal, FIG. 10 (c) shows an excitation current, and FIG. (D) shows the time-varying magnetic field obtained by the magnetic field detection element 8. The horizontal axis is a time axis, and the broken lines in the figure indicate the same time.

  The sensor unit 10 including the magnetic field detection element 8 of the eddy current probe 2 illustrated in FIG. 1 acquires the time-varying magnetic field 42d illustrated in FIG. In order to extract a periodic magnetic field component with respect to this time-varying magnetic field 42d, it is taken into the calculation unit 16a of the amplitude information acquisition unit 16 and the calculation unit 17a of the phase information acquisition unit 17 in FIG. Here, based on the trigger signal 42b periodically generated from the trigger generator 27 of the time-varying magnetic field generating means 12, the calculation units 16a and 17a take in the periodic time-varying magnetic field component of the time-varying magnetic field. Only the component 43 (FIG. 10D) can be calculated. As a result, the transition period information extraction unit 13 can calculate only the component 43 related to the periodic time-varying magnetic field component regardless of the extraction of the time-varying magnetic field component related to eddy current attenuation.

  FIG. 11 shows a calculation example of extraction of amplitude information by the amplitude information acquisition unit and extraction of phase information by the phase information acquisition unit.

  11A shows a time-varying magnetic field obtained by the magnetic field detection element 8, FIG. 11B shows data to be computed, FIG. 11C shows multiplication data, and FIG. d) shows the calculation processing result. The horizontal axis is a time axis, and the broken lines in the figure indicate the same time.

  A cosine wave 45a and a sine wave 45b (FIG. 11B) having the same period as the period 43 of the trigger signal shown in FIG. 10 are generated by the arithmetic units 16a and 17a of FIG. Signal 44 (FIG. 11A). As shown in FIG. 11C, the cosine wave 45a and the calculation result in a multiplication result 46a, and the sine wave 45b and the calculation result in a multiplication result 46b, each having a harmonic waveform that is approximately twice. On the other hand, when averaged by the filter, as shown in FIG. 11D, the multiplication result 46a becomes the calculation processing result 47a, and the multiplication result 46b becomes the calculation processing result 47b.

  Since the constant value component obtained here is the inner product calculation of the cosine wave 45a and the sine wave 45b, which are data to be calculated, amplitude information and phase information can be extracted. The amplitude information is the mean square of the calculation processing result 47a and the calculation processing result 47b, and the phase information is a declination determined by the calculation processing result 47a and the calculation processing result 47b. The calculation is the same as that of a lock-in amplifier that is a general-purpose measuring instrument. Result. Here, a reference signal such as a healthy part is stored in the storage units 16c and 17c in FIG. 1, and the difference processing is performed by the comparison units 16b and 17b, thereby extracting only the change in amplitude information and phase information. It can be used when an object having a minute defect whose change is minute and the number of digits of measurement accuracy is required.

  In general, in the case of eddy current flaw detection, the calculation processing result 47a is called an X signal and the calculation processing result 47b is called a Y signal. Evaluate defects such as failure and cracking.

  FIG. 12 shows an example in which the defect is evaluated by the defect evaluation unit 20 based on the amplitude information and the phase information obtained by the period information extraction unit 14.

  As shown in FIG. 12A, the eddy current probe 2 is scanned with respect to a subject 49 having a defect 48.

  FIG. 12B shows amplitude information and phase information in a Lissajous diagram. When the eddy current probe 2 is scanned with respect to the subject 49 having the defect 48, in the Lissajous diagram in which the calculation processing result 47a is an X signal and the calculation processing result 47b is a Y signal, the graph is a vertical axis and a horizontal axis. A locus 50a (broken line) as shown in FIG. As the depth of the defect increases, the amplitude 51 and the phase 52 change like a locus 50b (dotted line) and a locus 50c (one-dot chain line). The defect depth and the like are previously measured with respect to the trajectory and stored in the storage unit 20c. The stored locus data can be used as a calibration curve 53 (solid line) in FIG. 12B to compare the signal obtained by actual measurement with the comparison unit 20b to evaluate the depth of the defect.

In addition, when the calibration curve 53 is created as a result of performing the difference from the reference signal by the comparison units 16b and 17b in the phase information acquisition unit 16 and the phase information acquisition unit 17, if the reference signal is a signal of a healthy part, It becomes the difference with the signal, and the difference in the state regarding the healthy part and the defect can be evaluated.
[Simultaneous measurement of thinning and defects]
Next, the results of simultaneous measurement of thinning and defects by the eddy current inspection apparatus according to the present embodiment will be described with reference to FIG.
FIG. 13 is an explanatory diagram of the results of simultaneous measurement of thinning and defects by the eddy current inspection apparatus according to the first embodiment of the present invention.

  As shown in FIG. 13A, a defect 55 having a depth d exists in a subject 54 whose plate thickness is spatially changed. The eddy current probe 2 is spatially moved relative to the subject.

  In this case, an example of the output unit 21 in FIG. 1 is a plate thickness evaluation result 56 and defect signals 57a and 57b shown in FIG. In this inspection apparatus, the transient information acquisition means 13 for measuring the plate thickness and the periodic information acquisition means 14 for acquiring defect information use the trigger signal generated by the time-varying magnetic field generation means 12 to attenuate eddy currents. It is possible to measure the wall thickness and the defect simultaneously by separating the processing time and the periodic time.

  As described above, according to this embodiment, the transient information acquisition unit 13 for measuring the plate thickness and the period information acquisition unit 14 for acquiring defect information are provided, so that the time-varying magnetic field generation unit 12 generates the transient information. By using the trigger signal, the time for eddy current decay and the periodic time can be separated and processed. And, the advantage of the pulse excitation type eddy current flaw detection method that can measure the thickness of a thick metal member can be utilized, and it has the capability of detecting defects such as scratches and cracks, which is the feature of the original eddy current flaw detection method, Even if the inspection position with respect to the subject is the same, the thinning and the defect can be inspected at the same time.

  Next, the configuration and operation of an eddy current inspection apparatus according to the second embodiment of the present invention will be described with reference to FIG. In FIG. 14, the same reference numerals as those in FIG. 1 denote the same parts.

  FIG. 14 is a block diagram showing an overall configuration of an eddy current inspection apparatus according to the second embodiment of the present invention.

  In this embodiment, the magnetic field detecting elements constituting the transient information extracting means 13 and the period information extracting means 14 are constituted by a sensor unit 58 that is unified.

  In the present embodiment, when the magnetic field intensity of the eddy current attenuation information and the magnetic field intensity of the periodic time-varying magnetic field signal are substantially the same range, there is no need to use a magnetic field detection element having a sensitivity of different magnetic field ranges. The detection elements can be the same. As a result, the magnetic field detection elements 7 and 8 in the eddy current probe 2 shown in FIG. 2 are unified, and the volume, area, and number of connections in the probe are reduced, and the subject in a narrow space, Even with a subject having a small radius of curvature, the adhesion of the probe can be maintained.

  In this case, generally, only the magnetic field detection element 7 shown in FIG. 2 is used as the magnetic field detection element of the sensor unit 58. However, depending on the magnetic field intensity to be measured, only the magnetic field detection element 8 can be used.

  As described above, according to the present embodiment, the advantage of the pulse excitation type eddy current flaw detection method that can measure the thickness of a thick metal member can be utilized, and the flaws and cracks that are the features of the original eddy current flaw detection method can be utilized. In particular, even if the inspection position with respect to the subject is the same, the thinning and the defect can be inspected at the same time.

  In addition, the probe adhesion can be maintained even with a subject in a narrow space or a subject with a small radius of curvature.

  Next, the operation of the eddy current inspection apparatus according to the third embodiment of the present invention will be described with reference to FIG. The overall configuration of the eddy current inspection apparatus according to the present embodiment is the same as that shown in FIG. 1 or FIG.

  FIG. 15 is an operation explanatory diagram of the eddy current inspection apparatus according to the third embodiment of the present invention.

  The extraction process of eddy current attenuation information in the eddy current attenuation information acquisition unit 14 will be described with reference to FIG. FIG. 15A shows a signal of the time-varying magnetic field shown in FIG. FIG. 15B shows a signal in which a main part indicated by a broken line 59 in FIG. 15A is enlarged, and a vertical axis indicates a logarithmic scale.

  The present embodiment focuses on the fact that the eddy current attenuation information is an exponential change in the calculation unit 14a of the eddy current attenuation information acquisition unit 14 shown in FIG. 1 or FIG. This is a direct evaluation of the exponent part of the exponential function, that is, the system time constant in system control theory. The signal value of the time-varying magnetic field logarithmically processed at multiple times can be used to evaluate time constant fluctuations with time, and can be used to improve the accuracy of plate thickness evaluation when multiple materials are mixed. .

  As shown in FIG. 15B, when the plate thickness is changed, that is, when thinning is detected, the attenuation waveform 60b at the time of thinning changes as shown in the figure with respect to the attenuation waveform 60a at the healthy part. . With respect to the time of the waveform indicating the eddy current attenuation component extracted based on the trigger signal, the change rate of the magnetic field value can be calculated for at least two points of time, and can be used as a parameter for eddy current attenuation. For example, if the rate of change is obtained using the values of the magnetic field strengths B2 and B2 'at the time t2 and the magnetic field strengths B1 and B1' at the time t1, the time characteristics of the attenuation signal can be parameterized.

Then, by storing healthy part measurement data in the storage unit 14c of the eddy current attenuation information acquisition unit 14 and performing differential processing in the comparison unit 14b, it is possible to extract only the change in the eddy current attenuation information, This method can be used when an object with a large plate thickness that causes a minute change or when the number of digits of measurement accuracy for wall thickness measurement is required.

DESCRIPTION OF SYMBOLS 1 ... Inspection apparatus 2 ... Eddy current probe 3 ... Scanning mechanism 4 ... Scanning control apparatus 5 ... Probe control part 6 ... Excitation coil 7, 8 ... Magnetic field detection element 9, 10 ... Sensor part 11, 39, 49, 54 ... Subject DESCRIPTION OF SYMBOLS 12 ... Time-varying magnetic field generation means 13 ... Transient information extraction means 14 ... Eddy current attenuation information acquisition part 15 ... Period information extraction means 16 ... Amplitude information extraction part 17 ... Phase information extraction part 18 ... Analysis part 19 ... Thickness evaluation part 20 ... Defect evaluation units 30a, 35a, 42a ... Excitation voltages 35b, 42b ... Trigger signals 35c, 42c ... Excitation currents 35d, 42d ... Time-varying magnetic fields

Claims (11)

An eddy current inspection device that inspects a metal object with an eddy current generated by a pulsed time-varying magnetic field,
A time-varying magnetic field generating means for generating a time-varying magnetic field by controlling the exciting current of the exciting coil based on the exciting voltage having a temporally periodic pulse waveform;
Transient information extraction means for extracting transient magnetic field information with respect to changes in the magnetic field due to eddy currents generated in the subject by the time-varying magnetic field generation means; and periodic information extraction means for extracting periodic magnetic field information; ,
A thickness evaluation unit that performs an arithmetic processing on the transient magnetic field information extracted by the transient information extraction means, and evaluates the thickness of the subject;
An eddy current inspection apparatus comprising: a defect evaluation unit that performs arithmetic processing on the periodic magnetic field information extracted by the periodic information extraction unit and evaluates defects such as flaws and cracks of the subject. The eddy current inspection apparatus according to claim 1,
The time-varying magnetic field generating means includes
A waveform generator for generating an excitation voltage waveform;
A power amplifier for amplifying the excitation voltage waveform to supply an excitation current to the excitation coil;
A switch for controlling energization and interruption of the excitation current;
The waveform generator and the trigger generator for controlling the switch,
The trigger generator outputs a synchronization signal at a constant time period, is connected to the waveform generator to generate a temporally periodic excitation voltage waveform, and is connected to the switch to An eddy current inspection apparatus characterized by controlling a current-carrying time and a cut-off time to generate a temporally pulsed magnetic field. The eddy current inspection apparatus according to claim 1,
The transient information extraction means includes
A sensor unit having at least one magnetic field detection element and acquiring a signal of a time-varying magnetic field;
An eddy current inspection apparatus comprising: an eddy current attenuation information extraction unit that extracts eddy current attenuation information using transient information of the time-varying magnetic field signal based on energization and interruption times of the excitation current. The eddy current inspection apparatus according to claim 2,
The eddy current attenuation information extraction unit performs an arithmetic process on the time of energization start time from the cutoff time of the excitation current of the switch and the signal value of the time-varying magnetic field between the times, and extracts eddy current attenuation information. A characteristic eddy current inspection device. In the eddy current inspection apparatus according to claim 4,
The eddy current attenuation information extraction unit includes storage means for storing a predetermined reference signal set in advance,
Compare the time of energization start time from the cutoff time of the excitation current of the switch, the result of computing the signal value of the time-varying magnetic field between the times, and the result of computing the same for the reference signal Thus, the eddy current inspection apparatus is characterized by extracting eddy current attenuation information. The eddy current inspection apparatus according to claim 1,
The period information extracting means includes
A sensor unit having at least one magnetic field detection element and acquiring a signal of a time-varying magnetic field;
Based on the period of time of energization or interruption of the excitation current, the periodic information of the signal of the time-varying magnetic field is used to configure an amplitude information extraction unit that extracts amplitude information and a phase information extraction unit that extracts phase information. A characteristic eddy current inspection device. The eddy current inspection apparatus according to claim 6,
The amplitude information extraction unit includes storage means for storing a predetermined reference signal set in advance,
Obtain the amplitude difference by the difference calculation between the reference signal and the signal value of the time-varying magnetic field, extract the amplitude information of the time-varying magnetic field,
The phase information extraction unit includes storage means for storing a predetermined reference signal set in advance,
An eddy current inspection apparatus characterized in that, by calculating a difference between the reference signal and a signal value of the time-varying magnetic field, a difference in time when the signal value rises or falls is obtained, and phase information of the time-varying magnetic field is extracted. The eddy current inspection apparatus according to claim 1,
The transient information extraction unit includes at least one magnetic field detection element, and includes a sensor unit that acquires a signal of a time-varying magnetic field,
The periodic information extraction means includes at least one magnetic field detection element, and includes a sensor unit that acquires a signal of a time-varying magnetic field,
The eddy current inspection apparatus is characterized in that the same magnetic field detecting elements used in the transient information extracting unit and the periodic information extracting unit are unified . The eddy current inspection apparatus according to claim 1,
The transient information extraction unit includes at least one magnetic field detection element, and includes a sensor unit that acquires a signal of a time-varying magnetic field,
The periodic information extraction means includes at least one magnetic field detection element, and includes a sensor unit that acquires a signal of a time-varying magnetic field,
An eddy current inspection apparatus characterized in that the magnetic field detection elements used in the transient information extraction means and the periodic information extraction means have different magnetic field sensitivity characteristics. The eddy current inspection apparatus according to claim 1,
The wall thickness evaluation unit includes storage means for storing the transient magnetic field information for different wall thicknesses set in advance,
By comparing the transient magnetic field information extracted in the measurement of the subject, the thickness of the subject is evaluated,
The defect evaluation unit includes storage means for storing the periodic magnetic field information for defects such as scratches and cracks having different preset shapes,
An eddy current inspection apparatus characterized by evaluating a defect of a subject by comparing with periodic magnetic field information extracted by measurement of the subject. In an eddy current inspection method using an eddy current inspection apparatus that inspects a metal object with an eddy current caused by a pulsed time-varying magnetic field,
Using a pulsed waveform excitation voltage synchronized with the synchronization signal output at a fixed time period, the excitation current of the excitation coil is controlled by a switch to generate a time-varying magnetic field,
Eddy current attenuation information obtained by measuring the magnetic field with at least one magnetic field detection element and performing arithmetic processing based on energization time and interruption time of the excitation current in response to a change in magnetic field due to eddy current generated in the subject. Get
At the same time, the magnetic field is measured by at least one magnetic field detection element, and amplitude information and phase information obtained by performing arithmetic processing based on the energization or interruption time of the excitation current are obtained.
The eddy current attenuation information is compared with eddy current attenuation information for different preset wall thicknesses to evaluate the thinning of the subject,
The amplitude information and the phase information are compared with amplitude information and phase information for defects such as scratches and cracks having different shapes, and the defect of the object is evaluated. .

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