JP6688687B2 - Nondestructive inspection device and nondestructive inspection method - Google Patents

Description

  The present invention relates to a nondestructive inspection device and a nondestructive inspection method for performing a nondestructive inspection of a subject using electromagnetic induction.

  As described in Patent Documents 1 to 6, in an eddy current flaw detector using electromagnetic induction, a sine wave generator, a drive circuit for driving an exciting coil, a sensor including an exciting coil and a detecting coil, and amplification for amplifying the output of the detecting coil. A device calibrated with an analysis circuit including a circuit and a synchronous detection circuit has been proposed and used.

FIG. 22 is a diagram showing an example of a conventional sensor.
As shown in FIG. 22, the sensor is an exciter formed by winding an exciting coil 101 around an exciting core 102 made of a magnetic material such as silicon steel plate or ferrite for the purpose of applying a strong magnetic field to the subject. 2, the exciting coil 101 is excited by a sine wave having a constant voltage. The detection coil 104 is arranged inside the excitation coil 101.
In the sensor having such a configuration, based on the output of the detection coil 104, the change of the eddy current generated in the deep portion of the subject can be detected by means of the synchronous detection or the like, and the detection of the wall thinning or the scratch can be performed from the outside of the tube. it can.

Japanese Patent No. 3753499 Japanese Patent No. 3266128 JP, 2010-48552, A Japanese Patent No. 3896489 JP, 2010-54352, A Patent No. 4756409

  However, the actual subject 2 is often a tube body 2a having both magnetism and conductivity. Such a tube body 2a is covered with a heat insulating material 2b such as glass wool and calcium silicate, and the outside thereof is made of aluminum, zinc-plated iron plate or tin-plated iron plate, conductive or magnetic such as stainless steel, or conductive and magnetic, It is often covered with a dew-proofing material 2c made of a metal body having both of the above.

  When the tube body 2a is a metal tube or the like having both magnetism and conductivity, the exciting alternating magnetic field hardly penetrates into the subject 2 due to the eddy current effect. In particular, when the tube body 2a is magnetic, it is strongly influenced by the frequency, and the attenuation becomes extremely large as the frequency becomes higher. As a result, the exciting alternating magnetic field is extremely unlikely to penetrate into the inside of the subject 2.

  Further, since the tube body 2a serving as the subject 2 is covered with the thick heat insulating material 2b, the distance between the tube body 2a serving as the subject 2 and the sensor, that is, the lift-off must be increased. As a result, the output of the detection signal becomes extremely small.

  Further, the dew-proofing material 2c is consequently arranged in the immediate vicinity of the sensor and is strongly affected by the eddy current. In this case, when the dew-proofing material 2c is a metal body having both magnetism and conductivity, the influence becomes extremely large.

Further, in the actual subject 2, the shape is not uniform in the tube axis direction, the length is finite, and a flange or the like is attached to the end in many cases.
Also, the heat insulating material 2b is often deformed over the years, and its thickness is often different. In addition, the heat insulating material such as calcium silicate is often halved and bound with a magnetic and conductive tin-plated iron wire, etc., and its position may not be specified from the outside. Many. Further, in many cases, the dew-proofing material 2c is also caulked together with a plate-like material, and the caulking portion has a structure in which the dew-proofing materials overlap each other, so that the influence of the eddy current becomes large. In addition, the dew-proofing material 2c having a finite length is aligned and coupled in the pipe axis direction, and that portion is often beaded. Further, the dew-proof material 2c is often mechanically deformed.

  As a result, due to these influences, it becomes difficult to ensure the accuracy of detection of the thickness, thickness reduction, scratches, etc. of the tube body 2a of the subject 2.

  Therefore, an object of the present invention made is that even if the subject body is covered with a dew-proofing material or a heat insulating material having both magnetism and conductivity and the distance between the sensor and the subject body, that is, the lift-off is large, An object of the present invention is to provide a non-destructive inspection device and a non-destructive inspection method capable of accurately inspecting a sample body.

The present invention adopts the following means in order to solve the above problems.
That is, the nondestructive inspection device of the present invention, an exciting coil facing the subject body, a detection coil facing the subject body, a signal processing unit for detecting the amplitude and phase of the voltage generated in the detection coil, A non-destructive inspection device that excites the subject body by applying an alternating signal to the excitation coil, and detects a magnetic field change including a magnetic flux due to an eddy current generated in the subject body by the detection coil. The exciting coil is provided such that the central axis of the exciting coil is inclined with respect to the central axis of the detecting coil and intersects the central axis of the detecting coil, and the exciting coil is provided on the side close to the detecting coil. The first end portion is arranged at a position farther from the subject body than the detection sensor end portion on the side closer to the subject body in the detection coil.
With such a configuration, when the first end portion of the exciting coil is located closer to the subject body than the detection sensor end portion, among the magnetic force lines emitted from the exciting coil, the magnetic force lines extending in the direction away from the subject body are more Since many of them interlink with the detection coil, the sensitivity decreases. On the other hand, by separating the first end of the exciting coil from the body of the subject rather than the end of the detection sensor, more magnetic lines of force of the magnetic field of the exciting coil toward the body of the subject are interlinked with the detection coil. It is possible to cancel the magnetic flux heading in the direction away from the main body of the subject and suppress the decrease in sensitivity.

Further, the exciting coil may be arranged such that a second end of the exciting coil farther from the detection coil protrudes toward the subject body side than the detection sensor end of the detection coil.
With such a configuration, the exciting magnetic flux generated by the exciter is concentrated on the subject body side, and the detection sensitivity is improved.

Further, the detection coil is arranged in a central portion, the excitation coil is provided in a plurality in the outer peripheral portion of the detection coil at intervals in the circumferential direction, and the central axis of the plurality of excitation coils is the central axis of the detection coil. May be provided so as to concentrate and intersect at the same position.
With such a configuration, only one position concentrates the exciting magnetic flux.
Here, in the structure as shown in FIG. 22, inside the reverse U-shaped core 102 for strengthening the magnetic flux of the exciting coil 101, the same reverse U-shaped core for strengthening the magnetic flux interlinking with the detection coil 104 is also provided. Are arranged. In such a configuration, for example, when the sensor 1 is scanned from left to right in FIG. 22, when the specific point Px of the subject 2 goes from the outer peripheral side of the exciting coil 101 and the detecting coil 104 to the inner peripheral side, When the coil 101 and the detection coil 104 move from the inner circumference side to the outer circumference side, the exciting coil 101 and the detection coil 104 are passed twice. That is, as shown in FIG. 23, the output waveform W of the detection coil 104 indicating a flaw or the like of the subject 2 has two peaks Wm or valleys, which may lead to an erroneous determination of the flaw or the like. There are drawbacks.
On the other hand, as described above, since the central axes of the plurality of exciting coils are provided so as to concentrate and intersect at the same position of the central axes of the detecting coils, only one position concentrates the exciting magnetic flux. It is possible to prevent erroneous determination of the position of a meat portion, a scratch, or the like.

Further, the intersecting position of the central axes of the plurality of exciting coils and the central axes of the detecting coils may be set to be on the outer peripheral side of the subject body.
In this way, the crossing position of the central axis of the exciting coil and the central axis of the detecting coil is set to be on the outer peripheral side of the subject main body, so that the magnetic force lines from the plurality of exciting coils are directed to the outer periphery of the subject main body. They meet on the side, and from there they enter the body of the subject in the direction normal to the subject. In this way, there are many components in which the magnetic force lines are perpendicularly incident on the subject body. As a result, the magnetic field concentrates in the vicinity of the body of the subject, and the eddy current generated in the direction along the surface of the body of the subject increases, so that the detection sensitivity is enhanced.

Further, the subject body is cylindrical, columnar, any one of spherical, the excitation coil, the coil axis direction of the second end side, along the surface of the subject body, It may be provided so as to be inclined so as to gradually approach the subject body side from the inner circumference side close to the detection coil toward the outer circumference side.
In this way, when the subject body is cylindrical, columnar, or spherical, by placing the exciting coil along the surface of the subject body, the exciting magnetic flux inside the subject body Can penetrate deeply.

The signal processing unit further includes a reference coil electromagnetically coupled to the exciting coil, the signal processing unit detects the magnetic field as an alternating signal voltage of the detection coil, and an amplitude and a phase of the alternating signal voltage are referred to as the reference signal. You may make it detect on the basis of the amplitude and phase of the voltage which generate | occur | produces in a coil.
With such a configuration, it is possible to suppress the effects of lift-off, which is the distance between the sensor and the subject body, and temperature changes.

Further, the amplitude value of the reference coil may be compared with a predetermined reference value, and negative feedback processing may be performed so as to approach the reference value.
With such a configuration, it is possible to more stably suppress the lift-off, which is the distance between the sensor and the subject body, and the influence of temperature change.

Further, the exciting coil is excited by an alternating signal of a plurality of frequencies, the signal processing unit, the amplitude of the voltage generated in the detection coil obtained for each of the plurality of frequencies, the simultaneous equations taking in the phase difference as a variable It may be used to estimate the thickness of the subject body.
With such a configuration, disturbance factors such as the thickness of the dew-proof material and the heat insulating material that cover the subject body can be eliminated, and the thickness of the subject body can be estimated.

In addition, the signal processing unit uses the simultaneous equations in which the amplitude of the voltage generated in the detection coil, the phase difference, and the higher-order value higher than the square of the coordinate value of the measurement position are taken as variables, and the thickness of the subject. May be estimated.
With such a configuration, disturbance factors such as the thickness of the dew-proof material and the heat insulating material that cover the subject body can be eliminated, and the thickness of the subject body can be estimated.
Here, the coordinate value of the measurement point may be an XY coordinate value, a polar coordinate value, a coordinate value obtained by combining a distance and an angle, and the distance may be not only a spatial distance but also a creeping distance along the creeping surface of the object, It is sufficient if the measurement position can be uniquely specified.

Further, the excitation coil is excited by an alternating signal of a plurality of frequencies, the signal processing unit, for each of the plurality of frequencies, the amplitude of the voltage generated in the detection coil, the phase difference, and the coordinate value of the measurement position. The thickness of the subject body may be estimated by using a simultaneous equation in which higher-order values higher than the square are taken as variables.
With such a configuration, disturbance factors such as the thickness of the dew-proofing material and the heat insulating material covering the subject body can be eliminated, and the thickness of the subject body can be estimated with higher accuracy.

Further, a plurality of coordinate axis values may be used as the coordinate values, and a simultaneous equation including a product of the plurality of coordinate values or a higher-order term equal to or more than the square of the product may be used.
With such a configuration, disturbance factors such as the thickness of the dew-proof material and the heat insulating material that cover the subject body can be eliminated, and the thickness of the subject body can be estimated.

  Further, the signal processing unit, the first value to be set in the region including the site to be calibrated, and the second value to be set in the region including the site to be measured, the simultaneous equations captured as variables. It may be used to estimate the thickness of the subject body.

  A fast Fourier transform (FFT) may be used as the means for detecting the amplitude and phase.

  Further, a burst signal that rises exponentially and falls exponentially may be used as the alternating signal for exciting the exciting coil.

  The frequency or combination of frequencies of the alternating signal that excites the exciting coil may be selected from a frequency sequence that is a prime multiple of a predetermined reference frequency.

  Further, the present invention is a nondestructive inspection method in a nondestructive inspection apparatus as described above, wherein an alternating signal is applied to the exciting coil while the exciting coil is opposed to the subject body. By exciting the sample body, the voltage output from the detection coil is input to the measurement processing unit according to the magnetic field change including the magnetic flux due to the eddy current generated in the object body, and is input by the signal processing unit. The thickness of the subject body is estimated by detecting the amplitude and phase of the voltage.

  With such a configuration, even if the distance between the sensor and the subject body, that is, the lift-off state is large, the subject body can be inspected accurately.

  According to the present invention, the subject body is covered with a dew-proofing material or a heat insulating material having both magnetism and conductivity, and even if the distance between the sensor and the subject body, that is, the lift-off is large, The inspection can be performed with high accuracy.

It is a figure which shows the structure of the nondestructive inspection apparatus which concerns on the 1st Embodiment of this invention. It is a figure which shows the sensor which comprises the said nondestructive inspection apparatus. It is a figure which shows the detail of the exciter in the said sensor. It is a figure which shows the relationship between a subject and a sensor in the Example of this invention. In the 3rd Example of this invention, the input waveform of the exciting coil which synthesize | combined the sine wave of 5 frequencies is shown. In the 3rd Example of this invention, the detection coil output waveform at the time of exciting an exciting coil by said 5 frequencies is shown. 6 is a graph showing an example of measurement by a single frequency, simultaneous three-dimensional equation, according to a conventional technique. It is a graph at the time of using 2 frequencies (55,95Hz) in the Example of using multiple frequencies in the 2nd Embodiment of this invention. It is a graph at the time of using 3 frequencies (55,95,115Hz) in the Example of using multiple frequencies in the 2nd Embodiment of this invention. It is a graph at the time of using 4 frequencies (55,95,115,355Hz) in the Example of using multiple frequencies in the 2nd Embodiment of this invention. It is the graph which compared the case where four frequencies (55,95,115,355Hz) were used, and the case by the prior art in the pipe axial direction in the Example of using multiple frequencies in the 2nd Embodiment of this invention. It is the graph which compared the case where four frequencies (55,95,115,355Hz) were used, and the case by a prior art in the Example using multiple frequencies in the 2nd Embodiment of this invention in the circumferential direction. . It is a three-dimensional display graph at the time of using 4 frequencies (55,95,115,355Hz) in the Example of using multiple frequencies in the 2nd Embodiment of this invention. It is a graph which shows the coordinate value in the 3rd Embodiment of this invention, and the measurement result of the Example which took in more than the square value as an element variable. It is a graph which compared the measurement result of the Example which took in the coordinate value in the 3rd Embodiment of this invention, and its square or more as an element variable, and the prior art in the pipe axis direction. It is a graph which compared the measurement result of the Example which took in the coordinate value in the 3rd Embodiment of this invention, and its square or more as an element variable, and the prior art in the circumferential angle direction. It is the graph which carried out the three-dimensional display of the coordinate value in the 3rd Embodiment of this invention, and the measurement result of the Example which took in more than the square value as an element variable. It is a graph which shows the measurement result of the Example which used the multiple frequency and coordinate value in the 4th Embodiment of this invention, and took in more than the square of it as an element variable. In the 4th Embodiment of this invention, it is the graph which carried out the three-dimensional display of the measurement result of the Example which took in the use and coordinate value of multiple frequencies, and its square or more as an element variable. In the 5th Embodiment of this invention, it is a graph which shows the measurement result of the Example at the time of making the angle Y = 0 degree and 120 degrees when making the circumferential direction of the pipe used as a test object the Y-axis a variable. . It is a graph which shows the measurement result of the Example in case the area variable W = 0 and 1 is made into the variable in the 5th Embodiment of this invention. FIG. 3 shows a sensor according to the prior art. It is a figure which shows the example of the output waveform in the conventional sensor.

Embodiments for carrying out a nondestructive inspection device and a nondestructive inspection method according to the present invention will be described below with reference to the accompanying drawings.

(First embodiment)
FIG. 1 is a diagram showing a configuration of a nondestructive inspection device according to a first embodiment of the present invention. FIG. 2 is a diagram showing a sensor that constitutes the nondestructive inspection device. FIG. 3 is a diagram showing details of the exciter in the sensor.
As shown in FIG. 1, the nondestructive inspection device includes a sensor 1 and a measuring device (signal processing unit) 4.

  Here, the subject 2 to be inspected is a tubular tube body (subject body) 2a, a heat insulating material 2b that covers the outer peripheral portion of the tube body 2a, and a dew-proof material 2c that covers the outer peripheral side of the heat insulating material 2b. And are equipped with. 1 and 2, the subject 2 shows only a part of the portion above the central axis of the cross-sectional views.

The tube body 2a is made of metal having both magnetism and conductivity.
The heat insulating material 2b is made of a material having a non-magnetic property and a non-conductive property such as calcium silicate and glass wool, and has a predetermined thickness.
The dew-proof material 2c is made of a metal material having at least one of conductivity and magnetism, such as aluminum, a zinc-plated iron plate (so-called galvanized iron) or a tin-plated iron plate, and stainless steel.

As shown in FIG. 2, the sensor 1 includes an exciter 12 and a detector 11.
The sensor 1 is provided with a detector 11 in the central portion and a plurality of exciters 12 on the outer peripheral portion of the detector 11.

The detector 11 includes a detection coil 112. The detection coil 112 is an air-core coil and is arranged in the central portion of the sensor 1.
Here, the detection coil 112 may be provided with a core material made of a magnetic material such as ferrite in the central portion, but since the exciting magnetic flux is directly attracted to the core material, the magnetic field is disturbed. This effect is great when the lift-off (distance between the subject 2 and the sensor) must be large. Therefore, in such a case, it is preferable that the core coil is not provided and the detection coil 112 is an air-core coil.

  Such a detector 11 is arranged with the detection coil 112 facing the subject 2 with the central axis Ck of the detection coil 112 aligned with the normal line of the subject 2.

  As shown in FIGS. 2 and 3, each exciter 12 includes an exciting core 121, an exciting coil 122, and a reference coil 123.

The exciting core 121 is made of a magnetic material such as ferrite. The exciting core 121 has a first core portion 121a and a second core portion 121b extending orthogonally from one end of the first core portion 121a, and has a substantially L shape.
Here, in the exciting core 121, the second core portion 121b is formed longer than the first core portion 121a. The exciting core 121 is arranged so that the first core portion 121a faces the inner peripheral side of the detector 11 and the second core portion 121b faces the outer peripheral side.
Further, in the exciting core 121, the second core portion 121b is directed from the one end of the first core portion 121a on the inner peripheral side toward the outer peripheral side toward the subject 2 side along the outer periphery of the tubular subject 2. It is formed to gradually approach.

  Further, the exciting coil 122 is provided on the side of the second core portion 121b far from the detection coil 112 with respect to the inner peripheral side end portion (first end portion) 122a of the detection coil 112 on the side of the first core portion 121a close to the subject 2. An outer peripheral side end (second end) 122b is provided so as to protrude toward the subject 2 side along the central axis Ck of the detection coil 112. Further, the outer peripheral side end portion 122b of the exciting coil 1222 is provided closer to the subject 2 than the end surface (detection sensor end portion) 11f of the detector 11 facing the subject 2 is.

  The exciting coil 122 is wound around the outer peripheral sides of the first core portion 121a and the second core portion 121b of the exciting core 121, and is connected to each other in series.

  Here, in FIG. 1, two exciters 12 are arranged on the left and right with the detector 11 as the center. Not limited to this, three or more exciters 12 may be arranged radially around the detection coil 112.

  The reference coil 123 is wound inside the exciting coil 122 at the tip of the first core portion 121a. The reference coil 123 may be wound outside the exciting coil 122.

The exciting coil 122 and the reference coil 123 are electromagnetically connected to the exciting core 121, respectively. Further, between the plurality of exciters 12, the excitation coil 122 and the reference coil 123 wound around the plurality of excitation cores 121 are connected in series.
Further, all the exciting coils 122 are excited so that the directions of the magnetic force lines are in phase at the position of the detector 11. As a result, the direction of the magnetic force line at a certain moment becomes, for example, downward as shown in FIG. 2 by overlapping with the central axis Ck of the detection coil 112, and the exciting coil 122 is arranged by selecting the winding direction, winding start, winding end, or the like. Has been done.

  In this way, the exciting core 121 including the exciting coil 122 and the reference coil 123 is arranged such that the central axis Cr of the first core portion 121a intersects with the central axis Ck of the detector 11 on the subject 2 side. . The exciting core 121 is arranged such that the central axis Cr of the exciting core 121 intersects with the central axis Ck of the detector 11 at the same position between the plurality of exciters 12. Furthermore, the crossing position of the central axis Cr of the exciting core 121 of the plurality of exciters 12 and the central axis Ck of the detector 11 is the target object 2 for which the thickness, scratch, etc. are finally detected. It is preferable to set it so as to be located on the inner peripheral side of the surface of the sample 2 and on the outer peripheral side of the outer surface 2f of the tube body 2a.

  Further, in the exciting coil 122, the outer peripheral side end 122b far from the detection coil 112 projects toward the subject 2 side more than the inner peripheral side end 122a, and the subject 2 from the end face 11f of the detector 11 facing the subject 2 is detected. It is located closer to. In this way, the exciting magnetic flux generated by the plurality of exciters 12 is concentrated on the subject 2 side with respect to the end surface of the sensor 1 facing the subject 2. The lines of magnetic force generated by the exciting cores 121 of the plurality of exciters 12 are curved in an arc shape, so that the magnetic field lines of the central axis Cr of the exciting core 121 and the central axis Ck of the detector 11 are geometrically intersected with each other. At the inner peripheral side of the subject 2, the direction (center axis Ck direction) orthogonal to the outer surface of the subject 2 is faced. Further, since the second core portion 121b of the exciter 12 is arranged along the outer periphery of the subject 2, the exciting magnetic flux acts as if it penetrates deeply into the tube body 2a. In this way, the exciting magnetic flux perpendicular to the subject 2 can be generated, so that the sensor 1 with high sensitivity can be configured. Such a sensor 1 is particularly effective when the subject 2 has a cylindrical shape, a cylindrical shape, or a spherical shape.

  Further, in the detector 11, the inner peripheral side end portion 122 a of the exciter 12 is arranged at a position farther from the subject 2 than the end face 11 f closer to the subject 2. When the inner peripheral side end portion 122a of the exciter 12 is located closer to the subject 2 than the end surface 11f of the detector 11, the direction of the magnetic force lines emitted from the exciting coil 122 away from the subject 2 (upward in FIG. 2). The magnetic field lines Ms toward () are interlinked more with the detection coil 112, and the sensitivity is lowered. Therefore, by separating the end face 12f of the exciter 12 from the subject 2 rather than the detector 11, more magnetic force lines Mr toward the subject 2 side of the magnetic force lines of the exciting coil 122 are interlinked with the detector 11 and the subject 11 is detected. It is possible to suppress the decrease in sensitivity by canceling out the magnetic flux in the direction away from the subject 2 that causes the decrease in sensitivity without being affected by 2.

  As shown in FIG. 1, the measuring device 4 includes a computer 405, a display / recorder 406, a digital / analog converter (DAC) 401, a power amplifier 402, a multiplexer 403, and an analog / digital converter (ADC) 404. ing.

  The measuring device 4 converts a digital signal generated by the computer 405 that combines sine waves having a plurality of frequencies or a sine wave digital signal having a single frequency into an analog signal by a digital-analog converter 401. The converted analog signal is amplified by the power amplifier 402 and excites the exciting coil 122.

The measuring device 4 excites the exciting coil 122 with an alternating voltage and receives the voltage generated in the reference coil 123 and the voltage generated in the detection coil 112 as a measurement signal.
The output of the detection coil 112 is converted into a digital signal by the analog / digital converter 404 via the multiplexer 403 and supplied to the computer 405.
Further, the output of the reference coil 123 is input to the analog / digital converter 404 via the multiplexer 403, converted into a digital signal, and input to the computer 405.

  The computer 405 calculates the amplitude and phase of the output signal of the reference coil 123 and the output signal of the detection coil 112, which have been converted into digital signals, by Fast Fourier Transform (FFT).

Generally, a sine wave signal can be uniquely expressed by a combination of its frequency, amplitude and phase. The output value of the detection coil 112 often changes due to fluctuation factors such as temperature and voltage fluctuations. Therefore, by comparing the output of the reference coil 123, which is subject to fluctuations such as temperature and voltage fluctuations, with the detection coil 112, and the output of the detection coil 112, highly accurate data acquisition is possible.
More specifically, the amplitude of the output of the detection coil 112 is represented as an amplitude ratio with the output of the reference coil 123 as the denominator. Further, the output phase of the detection coil 112 is represented as a phase difference based on the output phase of the reference coil 123. As a result, an accurate measurement output can be obtained.

Further, the exciting magnetic flux in the exciter 12 is affected by the temperature change of the DC resistance value of the exciting coil 122 and the temperature change of the magnetic permeability of the exciting core 121. Therefore, the excitation magnetic flux itself is detected by the reference coil 123, the absolute value of the amplitude obtained by the fast Fourier transform is compared with a preset reference value, and the excitation signal is set so that the difference becomes as close to zero as possible. It is controlled by the computer 405. That is, the computer 405 may digitally perform negative feedback.
In general, it is very difficult to apply an analog negative feedback to an inductive load such as the exciting coil 122 because it easily oscillates due to a large phase rotation. However, if digital negative feedback is applied, the multiplexer 403 is a kind of high-speed sampling, and stable negative feedback is possible by sampling control.

According to the above-described nondestructive inspection device and nondestructive inspection method, the exciting coil 122 has the center axis Cr of the exciting coil 122 inclined with respect to the center axis Ck of the detecting coil 112 and the center of the detecting coil 112. It is provided so as to intersect the axis Ck. Further, the intersecting position of the central axis Cr of the exciting coil 122 of the exciter 12 and the central axis Ck of the detecting coil 112 of the detector 11 is closer to the sensor 1 on the outer peripheral side than the surface of the tube body 2a. Is set. In this way, the magnetic force lines Mr from the plurality of exciting coils 122 meet on the outer peripheral side of the tube body 2a and then enter the tube body 2a in the normal direction of the tube body 2a. As a result, the component in which the magnetic force lines Mr are perpendicularly incident on the tube body 2a increases, and the magnetic field concentrates near the tube body 2a. As a result, the eddy current generated in the direction along the surface of the tube body 2a becomes large, so that the detection sensitivity is improved.
Further, the inner peripheral side end 122a near the detection coil 112 is arranged at a position farther from the pipe body 2a than the detection sensor end 11f on the side closer to the pipe body 2a in the detection coil 112. As a result, among the magnetic force lines of the exciting coil 122, more magnetic force lines Mr toward the tube body 2a side are interlinked with the detection coil 112, and the magnetic flux toward the direction away from the tube body 2a is offset to suppress the decrease in sensitivity. You can
Further, the exciting coil 122 is arranged such that the outer peripheral side end portion 122b on the side far from the detection coil 112 projects toward the tube body 2a side more than the end portion of the detection coil 112. With such a configuration, the exciting magnetic flux generated by the exciter 12 is concentrated on the tube body 2a side, and the detection sensitivity is improved.
Therefore, even if the pipe body 2a is covered with the dewproof material 2c and the heat insulating material 2b having both magnetism and conductivity, and the distance between the sensor 1 and the pipe body 2a, that is, the lift-off is large, The inspection can be performed with high accuracy.

Further, since the coil axis direction of the second core portion 121b on the outer peripheral side end portion 122b side of the exciter 12 is along the outer peripheral portion of the subject 2, the exciting magnetic flux is applied to the subject 2 even when the lift-off is large. It is possible to penetrate into the deep layer.
Therefore, even if the tube body 2a has a cylindrical shape, a cylindrical shape, or a spherical shape, it is possible to enhance the sensitivity and accuracy of the measurement / inspection of the subject 2 in the sensor 1.

Further, in the sensor 1, the detection coil 112 is arranged in the central portion, and the excitation coils 122 are provided in the outer peripheral portion of the detection coil 112 with a plurality of intervals in the circumferential direction, and the central axes Cr of the plurality of excitation coils 122 are detected. The coils 112 are provided so as to concentrate and intersect at the same position on the central axis Ck of the coil 112. By thus exciting the same position in a concentrated manner by the plurality of exciting coils 122, the thickness t of the tube body 2a of the subject 2 can be detected with higher accuracy.
With such a configuration, the exciting magnetic flux generated by the plurality of exciting coils 122 configuring the exciter 12 is concentrated at one point on the tube body 2a side, and the position of the thinned portion, scratch, etc. is erroneously determined. You can suppress it.

  Further, the computer 405 further includes a reference coil 123 electromagnetically coupled to the exciting coil 122, and the computer 405 generates in the reference coil 123 the amplitude and phase of the voltage generated in the detection coil 112 by exciting the exciting coil 122. The voltage amplitude and phase are detected as a reference. As a result, lift-off, which is the distance between the sensor 1 and the subject 2, and the influence of temperature change can be suppressed.

  In the above embodiment, the method of detecting the wall thickness of the tube body 2a of the subject 2 by the computer 405 based on the output signal from the sensor 1 is not limited at all.

(Second embodiment)
Next, a second embodiment of the nondestructive inspection device and the nondestructive inspection method according to the present invention will be described. In the second embodiment described below, the same components as those in the first embodiment will be designated by the same reference numerals in the drawings, and the description thereof will be omitted.
In the second embodiment, the structures of the sensor 1 and the measuring device 4 are not changed from those of the first embodiment. In this embodiment, an example of a specific method of detecting the wall thickness of the tube body 2a of the subject 2 with the computer 405 will be disclosed.

The computer 405 detects the thickness t of the tube body 2a of the subject 2 as follows, for example.
In the nondestructive inspection device, the measuring device is calibrated at a specific point where the thickness of the subject 2 is known, and based on the calibration value, the sensor 1 is moved along the outer surface of the subject 2 while being detected at a plurality of locations. To go. As a method of calibration, first, a measurement element such as an amplitude ratio and a phase difference is used as a variable, an equation for estimating the thickness of the subject 2 is created from this, and measurement is performed at the calibration point where the thickness of the subject 2 is known. The simultaneous equations in which the element values and the known wall thickness values are substituted into the above equations are solved to find the contribution coefficient or constant that is given to the object thickness of each element variable. As a result, the coefficients and constants of the thickness estimation equation are determined, that is, the subject thickness estimation equation is established. The object thickness at each measurement point is obtained by substituting the element measurement values at the measurement point into the object thickness estimation equation.
More specifically, the computer 405 formulates simultaneous equations based on the output signals from the detection coil 112 and the reference coil 123 at the calibration point. The computer 405 determines the coefficients and constants of the estimation equation for estimating the thickness t of the tube body 2a of the subject 2 by solving the simultaneous equations. In this case, the computer 405 may solve the simultaneous equations online to estimate the thickness t. However, from the viewpoint of measurement speed, only the amplitude ratio and the phase difference and the coordinate value indicating the measurement point are online. It is also possible to take the data acquisition of 1 and solve the simultaneous equations off-line to estimate the thickness t at that point.
Here, the coordinate value may be an XY coordinate value, a polar coordinate value, a coordinate value obtained by combining a distance and an angle, and the distance may be not only the spatial distance but also the creepage distance along the creepage surface of the object, Anything that can be uniquely specified may be used.

  Here, as the equation for estimating the thickness t of the pipe body 2a, it is preferable to use an estimation equation including an element value that gives a variation to the estimation of the thickness t of the pipe body 2a. It was found that it is effective to use the amplitude ratio and the phase difference measured at a plurality of different frequencies as the element values.

Generally, the amplitude ratio and the phase difference change in response to fluctuations in disturbance factors such as the thickness of the dew-proofing material 2c and the like, the thickness of the heat insulating material 2b, and the end effect, in addition to the thickness t of the tube body 2a. If these disturbance factors are U, the amplitude ratio A and the phase difference P are expressed by equations (1) and (2).

If both sides of the equation (1) are multiplied by e, both sides of the equation (2) are multiplied by b, and both sides are subtracted and rearranged, the equation (3) is obtained.

Here, if the coefficients and constants of the equation (3) are a, b, and c, the general equation (4) is obtained.

According to the above equation (4), it is possible to estimate the thickness t of the subject 2 by eliminating the unknown disturbance factor U. The influences of the thickness of the dew-proofing material, the thickness of the heat insulating material, the end effect, etc. differ depending on the frequency to be measured. Here, assuming that the amplitude ratio and the phase difference measured at the frequency f1 are A1, P1 and those measured at the frequency f2 are A2 and P2, for the two disturbance factors U and V, (5) to Expression (7) is established.

Here, the equations in which V is eliminated from the equations (5) and (6), and the equations in which V is eliminated from the equations (5) and (7) result in the above equations (1) and (2). If the coefficients are a, b, c, d, then the following equation (8) is established.

According to the above equation (8), the thickness t can be estimated by removing the two unknown disturbance factors U and V. Similarly, if the amplitude ratio at the frequency f1 and the phase difference are A1, P1, the amplitude ratio at the frequency f2, and the phase difference is A2, P2, etc., the pipe wall thickness t is ( It can be expressed by equation (9).

  The respective coefficients and constants can be obtained by solving the following simultaneous equations using the known value of t and the measured value at the calibration point.

There are various methods of solving simultaneous equations by determinant, but when calculating with a computer, there is little concern about digit cancellation, and the intuitive Cramer method is convenient, so the following is shown.
For the estimation of the pipe wall thickness t by the equation (9), the nine-element simultaneous equation (10) is solved by the nine-point calibration, the respective coefficients a, b, c of the equation (9) are obtained, and these are converted into the equation (9). Substituting it, and further substituting the amplitude ratio and phase difference of each frequency at the measurement point into the equation (9), it is sufficient to obtain t.

In the solution method by the Cramer method, the determinant (11) that becomes the denominator is first obtained. The determinant (11) is a determinant with all 9s in the ninth column. The value z of this determinant is determined. In order to obtain the value z of such a determinant, for example, a spreadsheet program such as Excel (registered trademark) of Microsoft Corporation can be used. In such a spreadsheet program, the value z of the determinant can be obtained by implanting the left side of equation (11) into cells of 9 rows × 9 columns and applying the MDETERM function.

For the determinant corresponding to the numerator for obtaining the coefficient a, the tube wall thickness t at the calibration point is input in the first column, and m is obtained from equation (12).

Similarly, for the coefficient b, the t value is input to the second column, and n is obtained from the equations (13) to (14).

Similarly, each coefficient is obtained by the following equation (15).

  In this way, the thickness t of the tube body 2a of the subject 2 can be estimated by using the above equation (9) using a plurality of frequencies.

  As described above, the exciting coil 122 is excited by the alternating signals of a plurality of frequencies, and the measuring apparatus 4 acquires simultaneous amplitudes and phase differences of the voltage generated in the detecting coil 112 for each of a plurality of frequencies as simultaneous equations. Is used to estimate the thickness of the tube body 2a. With such a configuration, disturbance factors such as the thickness of the dew-proofing material 2c and the heat insulating material 2b covering the tube body 2a can be eliminated, and the thickness of the tube body 2a can be estimated.

(Third Embodiment)
Next, a third embodiment will be described. While the second embodiment uses the measured values of the amplitude ratio and the phase difference at a plurality of frequencies as the element variables for estimating the wall thickness of the subject 2, the third embodiment faces the subject 2. The position coordinate value of the sensor and a higher-order variable equal to or higher than its square are used as element variables for estimating the wall thickness of the subject 2. This is because the wall thickness of the pipe main body 2a, the thickness of the heat insulating material 2b, the thickness of the dew-proofing material 2c, the end effect, etc. are often expressed as a higher-order function of the position coordinates of the sensor. We have found that it is possible to improve the accuracy of thickness estimation. By transforming the equations (1) and (2), equations (16) and (17) are obtained.

Equation (18) is obtained by adding and organizing both sides.

In equation (18), if the coefficients are rewritten as a, b, c, etc., equation (19) is obtained.

The thickness of the heat insulating material, the thickness of the dew-proofing material, the distance between the dew-proofing material and the detection coil, the end effect, etc., which affect the amplitude ratio and the phase difference, are often difficult or unknown to measure from the outside. However, they are often regarded as a higher-order function of the measurement position, that is, the coordinate value of the measurement point. On the other hand, the coordinate values of the measurement points can of course be measured from the outside. Then, the method of incorporating the coordinate values of the measurement points into the simultaneous equations and estimating the thickness of the subject 2 was found. As the coordinate values of the measurement points, the distance in the tube axis direction of the subject 2 is X, the angle in the circumferential direction is Y, and as an example, if X is a function up to the 4th order and Y is a function up to the 2nd order, U can be expressed. , (20) is obtained. This U is expressed as a higher-order function of coordinate values by integrating various disturbance factors such as the thickness of the dew-proofing material, the thickness of the heat insulating material, and the end effect.

By substituting the expression (20) into the expression (19) and rewriting it with coefficients such as a, b, and c, the expression (21) can be obtained.

The coefficients and constants of this thickness estimation formula are determined by establishing the simultaneous equations described above from the measured values at the calibration points. Then, by using these values and substituting the measured values and position coordinates at that point into the equation (21), it becomes possible to estimate the wall thickness of the subject 2 at that point.
In this way, the thickness t of the tube body 2a of the subject 2 can be estimated by using the above equation (21) based on the higher-order function of the position coordinates.

  As described above, the measuring device 4 uses the simultaneous equations in which the amplitude and the phase difference of the voltage generated in the detection coil 112 and the higher-order value equal to or more than the square of the coordinate value of the measurement position are taken as variables, and Estimate the thickness. With such a configuration, disturbance factors such as the thickness of the dew-proofing material 2c and the heat insulating material 2b covering the tube body 2a can be eliminated, and the thickness of the tube body 2a can be estimated.

(Fourth Embodiment)
In this embodiment, the equation (9) showing the second embodiment in which the amplitude ratio and the phase difference by a plurality of frequencies are used as element variables and the third embodiment using the higher-order function of the position are shown (21). ) Is used in combination with the amplitude ratio and the phase difference at a plurality of frequencies, the position coordinate of the sensor, and a higher-order function higher than its square as element variables.
As an example, if two frequencies are used and up to the fourth power of X and up to the square of Y are used, Equation (22) is obtained. The coefficients and constants of this thickness estimation formula are determined by establishing the simultaneous equations described above from the measured values at the calibration points. It is possible to estimate the wall thickness of the subject 2 at that point by substituting the measured values and position coordinates at that point into the expression (22) using these.

Specifically, if equation (22) is written in the form of simultaneous equations, equation (23) is obtained.

The determinant used as the denominator for solving the simultaneous equations by the Cramer's method is the equation (24).

The determinant that is the numerator of the coefficient a is equation (25).

Similarly, the numerator of the coefficient b is the equation (26).

Similarly, the numerator of the last constant term k becomes the equation (27).

From this, a. b, ..., K, etc. are obtained by the equation (28).

  In this way, each coefficient and constant of the thickness estimation formula are obtained, and by using these, the measured value and position coordinate at that point are substituted into the formula (22), the tube body of the subject 2 at that point is calculated. The thickness t of 2a can be estimated.

  Furthermore, when coordinate values are represented by numerical values of a plurality of coordinate axes, their interaction may be large. In that case, a product of these coordinate axis values, or a higher-order function of those products, in the above example, X * Y, and a higher-order term equal to or greater than the square of X * Y, are used as variables in simultaneous equations. By importing it, it becomes possible to estimate the subject thickness with higher accuracy.

  In this way, the thickness t of the tube body 2a of the subject 2 can be estimated with high accuracy by using the above formula (22) that uses a combination of a plurality of frequencies and higher-order functions of position coordinates. .

  As described above, the exciting coil 122 is excited by the alternating signals of a plurality of frequencies, and the measuring apparatus 4 acquires the amplitude and phase difference of the voltage generated in the detecting coil 112 and the coordinate value of the measuring position, which are acquired for each of the plurality of frequencies. The thickness of the tube main body 2a is estimated by using simultaneous equations in which high-order values equal to or more than the square of and are taken as variables. With such a configuration, disturbance factors such as the thickness of the dew-proofing material 2c and the heat insulating material 2b covering the tube body 2a can be eliminated, and the thickness of the tube body 2a can be estimated with higher accuracy.

(Concrete example)
Here, a double tube including an outer tube and an inner tube is taken as an example of the subject, and a specific example will be examined.
The amplitude ratio Amp and the phase difference Pha, which are measured values, are considered to be a function of the inner tube thickness t2, the outer tube thickness t1, and the gap Gap between the two. Therefore, if they are expressed by a linear expression, the equations (31) and (32) are obtained. Becomes

By transforming these, equations (33) and (34) can be obtained.

By transforming (33) + (34) and rearranging, Equation (35) is obtained.

Here, if it is rewritten by using the coefficients a, b, c, etc., the equation (36) is obtained.

  Here, if t1 and Gap are known, there is no problem, but the inner tube thickness t1 changes so much that it cannot be expressed unless it is a six-dimensional expression of the radius R along the outer surface from the center of the outer surface of the inner tube. To do. It is assumed that the inner tube thickness t1 changes mainly on the inner surface. As a result, it is considered that the distance between the inner surface of the outer tube and the outer surface of the inner tube, that is, the gap Gap, also changes intricately in the order of the sixth order.

  Therefore, the outer tube thickness t1 was also estimated by a sixth-order equation of the radius R, and a good result was obtained. The 6th-order equation is not complicated because it only takes in the 6th-order term as a variable and the estimation equation is substantially a linear first-order equation.

Here, if the outer tube thickness t1 and the gap Gap can be approximated by a sixth-order equation of the radius R, the equations (37) and (38) are obtained.

By substituting these equations (37) and (38) into the equation (36), the equation (39) is obtained.

From this, equation (40) is obtained.

Here, if each coefficient is written again as a, b, c, etc., the equation (41) is obtained.

  The inner tube thickness t2 will be estimated based on this (41).

The inner tube thickness t2 is estimated by the equation (41) by solving a nine-element simultaneous equation by nine-point calibration, obtaining the coefficients a, b, c, etc. of the equation (41), and using them, the amplitude ratio of the measurement points, From the phase difference and the radius, t2 may be obtained by substituting it into the equation (41).

The determinant used as the denominator is a determinant in which all 9s in the ninth column in the equation (42) are set.
Since the terms of each degree of R can be calculated by inputting only the radius R, it is easy to substantially input three variables of Amp, Pha, and R.

For the determinant corresponding to the numerator for obtaining the coefficient a, the inner tube thickness at the calibration point is input in the first column, and m is obtained by the equation (44).

Similarly, for the coefficient b, the value t2 is entered in the second column, and n is calculated by the equation (45).

The coefficients c, d, e, f, g and h are obtained in the same manner, and the last i is given the t2 value in the ninth column and u is obtained by the equation (46).

From this, each coefficient is obtained by the following equation (47).

(Fifth Embodiment)
In this embodiment, in actual measurement, calibration is performed at a specific site (region) without measuring over the entire region of the subject, and when measuring another specific site (region), the actual measurement is performed as a variable. The case where two different values are input instead of the coordinate values is shown.

In the examples shown in the above embodiments, the longitudinal direction of the subject (pipe) is the X axis, the tube axial distance of the subject and the angle when the circumferential direction of the pipe is the Y axis are variables, Calibration points are taken at a plurality of points (for example, 0 °, 105 °, 120 °, −120 °, 45 °, etc.). In this measuring method, when 3 frequencies (55 Hz, 95 Hz, 115 Hz) are taken as the measurement frequencies, a total of 6 (3 × 2 = 6) measured values are obtained as the amplitude ratio and the phase difference.
In this case, 6 + 1 = 7 or more measurement values at different positions are necessary for calibration (when there are two combinations of exactly the same measurement values, the value of the determinant becomes zero and the simultaneous equations become indefinite and cannot be solved. Therefore, the measured values at seven positions substantially different from each other on the X axis are necessary (coordinate values).
Further, if it is expressed as a quadratic expression of Y as an influence of the angle of the Y axis, Y ² , Y, a constant term and 2 + 1 = measurement values (coordinate values) at 3 or more different angles are used for calibration. It is necessary for.
Therefore, as a result, it is necessary to solve a 9-element simultaneous equation of 6 + 2 + 1 (constant term) = 9.

The measurement method for performing such calibration is good when it is desired to measure in a wide range of measurement, for example, in the range of Y = 0 ° to 120 °, but in the actual measurement, calibration is performed in the 0 ° direction and the pipe of the subject is calibrated. In some cases, only the position in the Y-axis direction (for example, 120 ° direction) where the influence of the caulking portion of the outer cover iron plate that forms the area is likely to be large is measured.
In the present embodiment, in this way, when calibrating at a specific site and measuring other specific sites, not the actual coordinate values but two different values are input as variables, and simultaneous equations are established. In this case, as the Y axis, only the 1st power of Y may be taken and the angles such as Y = 0 ° and Y = 120 ° may be input, but the calibration region including the portion to be calibrated (calibration portion) is set to 0 ( It is possible to input a variable (hereinafter, referred to as a region variable W) in which W = 0) and a region including a site (measurement site) to be measured is 1 (W = 1).

The reason why the variable may be a value such as W = 0 or 1 instead of the angle unit such as Y = 0 ° or 120 ° is as follows.
That is, in the simultaneous equations, the unit of each variable is to incorporate (calculate) into the simultaneous equations as a calibration point, and to estimate (measure) the numerical value such as the target wall thickness using the coefficient value obtained by solving the simultaneous equations. If the units of these variables are the same, the unit may be any unit. For example, in the case of a primary coordinate value variable, a coefficient obtained by calibrating by inputting a variable value in mm as a dimension into a simultaneous equation is compared with a coefficient obtained by inputting a variable value in m. Then, the latter (variable value in m unit) is 1000 times the former (variable value in mm unit), but the result obtained by multiplying the coefficient value and the variable value is the same. Therefore, if the unit of the variable value to be used is the same in the case of calibration and the estimation calculation (measurement) of the target numerical value, the result of the final estimation calculation (measurement) will be the same.
However, when calculating the determinant for solving simultaneous equations, multiplication and addition / subtraction are involved, so select the unit of each variable as much as possible so that there is no fear of precision loss in computer calculations. Is desirable in actual calculation.

When the angles such as Y = 0 ° and 120 ° are taken in as variables without using the region variable, as described above, for example, the caulked portion of the outer cover iron plate that forms the pipe of the subject in the direction of Y = 120 °. However, due to the influence, the measured values (amplitude ratio, phase difference) may be extremely different. For example, when measuring at an angle of Y = 0 °, calibration is performed at this position, so the measured value of the subject can be accurately obtained. For example, near Y = 10 °, the position of Y = 0 ° is obtained. Rather than being affected by the position of Y = 120 °, the measured value of the subject may appear thicker. Similarly, in the vicinity of Y = 110 °, the measured value of the subject may be low due to the influence of the position of Y = 0 °.
On the other hand, if the coordinate variable of the calibration site is, for example, the region variable W = 0 and the coordinate variable of the measurement site is, for example, the region variable W = 1 as variables, the above influence is not required.
Specifically, for example, when the subject is a pipe having a length of 10 m, the region where the tube axis distance from one end is around 2 m is W = 0 as a calibration region, and the tube axis distance from one end is around 8 m. Is measured as W = 1.
Further, for example, assuming that there are two pipes as the subject, one pipe A can be set as a calibration region with W = 0, and the other pipe B can be set as a measurement region with W = 1 for measurement.

Here, in the case where the angle when the circumferential direction of the pipe to be inspected is the Y axis is a variable, if the Y axis is up to the square of Y, at least three angles, for example, 0 ° , 90 °, 120 ° must be input. Therefore, in addition to Y = 0 ° and 120 °, it is necessary to input an intermediate value of Y = 90 ° (not necessarily 60 ° which is the median of Y = 0 ° and 120 °).
On the other hand, when the area variable is used as the variable, only two values of W = 0 and W = 1 are required, and an intermediate value such as 0.6 is not necessary.

Here, in the above, the coordinate variable of the calibration site is, for example, area variable = 0, and the coordinate variable of the measurement site is, for example, area variable = 1. However, the coordinate variable of the calibration site is, for example, area variable = 1, and the measurement site The coordinate variable may be, for example, area variable = 0.
However, in the former case, the coordinate variable of the calibration site is set to the region variable W = 0, and the coordinate variable of the measurement site is set to the region variable W = 1 regardless of the measurement value (amplitude ratio, phase difference) of the captured measurement region. This is convenient because the coefficient values, which are the solutions of simultaneous equations for the amplitude ratio, the phase difference, etc., do not change.

Hereinafter, embodiments will be described with reference to the drawings. FIG. 4 shows a configuration in an example of the first exemplary embodiment of the present invention, and the same configurations as the configurations described so far are designated by the same reference numerals.
As the test object 2, it was used for 30 years or more, and the dewproof material 2c deteriorated and had holes, and rainwater penetrated into the tube body 2a, and the outer surface of the pipe body 2a was corroded and thinned. Here is an example:
The tube main body 2a of this sample is largely corroded in the Y = 0 ° direction of FIG. 4 and its periphery. Further, the heat insulating material 2b is a new calcium silicate having a thickness of 50 mm, the dew proofing material 2c is a new tin-plated iron plate having a thickness of 0.3 mm, and the four-layer crimped portion 2d is in the Y = 180 ° direction. Was measured.

The specifications of the sensor 1 of this embodiment are as follows.
A ferrite core is used as the exciting core 121, the cross-sectional area is 170 square mm, the central length of the first core portion 121a of the L-shaped exciting core 121 is 95 mm, and the central length of the second core portion 121b of the exciting core 121 is 145 mm. did. Further, as the reference coil 123, a formal wire having a diameter of 0.3 mm was wound 120 times, and as the exciting coil 122, a formal wire having a diameter of 1 mm was wound 210 times over the entire lengths of both long and short legs.

  The detector 11 is an air-core coil having a diameter of 48 mm and a height of 35 mm, and a formal wire having a diameter of 0.2 mm is wound 5400 times. With the detector 11 as the center, the two exciters 12 were arranged so that the tip portions (inner peripheral side end portions 122a) were located at a radius of 30 mm. The center distance of the outer peripheral side end 122b of the two exciting coils 122 farther from the detector 11 is 265 mm, and the outer peripheral side end 122b close to the subject 2 is the end face of the detector 11 closer to the subject 2. It was arranged in a substantially inverted V shape so that it was closer to the subject 2 by 30 mm than 11f.

  Further, in the calibration and measurement, two exciting coils 122 are connected in series, and a synthetic wave having a peak value of 3 V, which is a synthetic wave of sine waves of 35, 55, 95, 115, and 355 Hz, and the magnetic field near the detection coil 112 is the above-mentioned. The two exciting coils 122 were excited so as to have the same phase. The selection of this frequency was made to be a prime multiple of 5 Hz as a radix, and consideration was given to reduce the probability that harmonics fall into other frequency regions as much as possible. The angle between the axis of the detection coil 112 and the axis of the exciting coil 122 is 50 °. This independent composite waveform of 5 frequencies was sampled at 8192 points, and the amplitude ratio and phase difference for each frequency were detected and recorded by fast Fourier transform (FFT).

  FIG. 5 shows the excitation voltage waveform of the excitation coil, and FIG. 6 shows the output voltage waveform of the detection coil. If all the 8192 sampling points are shown, it becomes difficult to see the waveform, so only the first 2000 points are shown. Since the excitation signal is generated digitally as shown in FIG. 5, it is possible to form a burst signal that rises exponentially and falls exponentially, and a continuous wave is sampled to perform fast Fourier transform ( When performing FFT, it is possible to omit the filter that is normally required to prevent aliasing.

  In the actual measurement, the tube axis direction of the subject 2 is set as the X axis, and the stepping motor automatically scans at 2.84 mm / step, and the circumferential direction of the subject 2 is from + 120 ° to −120 ° every 15 °. It was changed manually, and 17 data were acquired.

FIG. 7 shows an example of measurement at a single frequency of 55 Hz, which is a conventional technique, and Table 1 shows a three-dimensional simultaneous equation expressed in a tabular form, coefficients and constants obtained by solving the simultaneous equation, position coordinates of calibration points, The measured values of the amplitude ratio and the phase difference at that point are shown.
As the tube wall thickness of the subject 2, assuming that it is unknown from the outside, a nominal value of 5.8 mm was used at all calibration points except the reference value. As a reference value, a carbon steel pipe having the same outer diameter of 115 mm and a thickness of 4.4 mm made of the same material and free from corrosion or the like was used. The calibration conditions were the same in all the following examples. The coefficients and constants of a, b, and c obtained by solving this simultaneous equation of three elements are shown in the upper part of Table 1. The estimated thickness at each measurement point was obtained by multiplying the measured values of the amplitude ratio and phase difference at that point by this coefficient.
The results are shown in the graph of FIG. This graph shows data of 17 lines scanned in the X-axis direction at intervals of 15 ° from + 120 ° to −120 °. Regardless of the nominal value of 5.8 mm, there is a large variation of 3 mm to 10 mm and poor accuracy. Only the measurement result can be obtained. The main reason for this is that when the circumferential angle exceeds +/− 90 °, the seam of the dew-proofing material, that is, 2d in FIG. 4, approaches the outside of the L-shaped core of the exciting coil 122, that is, 121b. This is because the wall thickness is observed to be large, and because the length of the pipe body 2a is finite, the pipe wall thickness is observed to be thin at the end because of the end effect.

  FIG. 8 shows an example of the second embodiment of the present invention, in which two frequencies of 55 Hz and 95 Hz are used as a plurality of frequencies, two combinations of amplitude ratios and phase differences are used, and five points of calibration are performed. Fig. 7 shows an example of a 5-element simultaneous equation using points. As shown in FIG. 8, the variation in the wall thickness of the tube is improved to 3.5 mm to 7.5 mm.

  FIG. 9 is another example of the second embodiment of the present invention, in which three frequencies of 55, 95, and 115 Hz are used as a plurality of frequencies, and a 7-element simultaneous equation is used. As shown in FIG. 9, the estimation result of the pipe wall thickness is improved to 5 to 6.8 mm.

FIG. 10 is another example of the second embodiment of the present invention, in which four frequencies of 55, 95, 115 and 355 Hz are used as a plurality of frequencies, nine calibration points, and a nine-element simultaneous equation is used. Here is an example. As shown in FIG. 10, a maximum accuracy of 5 to 6.3 mm can be achieved with sufficient accuracy. Table 2 shows the 9-element simultaneous equations expressed in a tabular form in this case, each coefficient obtained by solving the simultaneous equations, constants, and calibration points.

  FIG. 11 shows the circumferential angle in the tube axis direction at a single frequency of 55 Hz, which is a conventional technique, and at four frequencies of 55, 95, 115, and 355 Hz, which is an example of the second embodiment of the present invention. This is a comparison in the 0 ° direction. As shown in FIG. 11, it is apparent that the end effect is largely corrected and improved.

  FIG. 12 shows a case where the central axis of the tube is X = 500 mm and the thickness variation in the circumferential direction is a single frequency of 55 Hz according to the related art and a case of four frequencies which is an example of the second embodiment of the present invention. It is a comparison. As shown in FIG. 12, it is clear that the influence of the seam of the dew-proof material, 2d in FIG. 4, is remarkably improved.

  FIG. 13 shows the case of 4-frequency, 55, 95, 115, 355 Hz, 9-element simultaneous equation calibration that is an example of the second embodiment of the present invention, in which the tube axis direction is the X axis and each circumference is the Y axis. 3 is a 3D graph represented by contour lines with the tube wall thickness as the Z axis. As shown in FIG. 13, the corrosion state of the pipe body 2a is accurately represented.

  In the 9-element simultaneous equations in Table 2, all the wall thicknesses at the calibration points were calibrated at the nominal value of 5.8 mm, but as a result, it is possible that the location that was not originally 5.8 mm was calibrated as 5.8 mm. Therefore, based on the graph of FIG. 9 or the result of FIG. 13, the points of different pipe wall thickness values other than the original calibration points are again calibrated again using the obtained values. As a result, it becomes possible to depict the exact form of corrosion that converges.

Table 3 shows the simultaneous equations and the calibration points of the example of the third embodiment of the present invention in a tabular form. The element values are up to the fourth power of the tube axis distance X as the coordinate values of the measurement points, and the circles. The figure shows a 9-element simultaneous equation in the case of capturing up to the square of the circumference angle.

  FIG. 14 shows a measurement example calibrated by the simultaneous equations of nine elements by a change in pipe wall thickness in the pipe axis direction. As shown in FIG. 14, the pipe wall thickness is measured from 2.6 mm to 7.2 mm, which is an improvement over FIG. 7, which is an example of measurement by the three-dimensional simultaneous equations of the related art.

FIG. 15 is a graph showing the wall thickness value in the X direction of the tube axis distance at Y = 0 °, and the three-dimensional simultaneous equation of a single frequency, which is a conventional technique, and the second or higher order coordinate values, which are the embodiments of the present invention. This is a comparison of cases of simultaneous equations with 9 elements including polynomials of degree. As shown in FIG. 15, the end effect is alleviated.
FIG. 16 is a comparison of changes in the circumferential angle direction when X = 500 mm. As shown in FIG. 16, the influence of the four-layer overlapping portion 2d of the dew-proofing material is reduced.
FIG. 17 is a three-dimensional graph. As shown in FIG. 17, it is possible to clearly detect the corroded portion.

Table 4 shows an example of the fourth embodiment of the present invention, and shows an example in which the use of multiple frequencies and the variable capture of the square of coordinate values or more are combined. That is, the amplitude value and the phase difference at a plurality of frequencies of 55 Hz and 95 Hz respectively incorporate the coordinate value and the square of the square axis and up to the fourth power of the tube axis distance X and up to the second power of the circumferential angle Y11. The case of the simultaneous equations is shown. FIG. 18 shows a measurement example calibrated by this 11-element simultaneous equation by the change in the wall thickness in the pipe axis direction. As shown in FIG. 18, it is further improved as compared with FIG. FIG. 19 is the three-dimensional graph display. As shown in FIG. 19, the appearance of corrosion of the pipe body 2a is clearly detected.

Next, an example of the fifth exemplary embodiment of the present invention will be described.
Here, it is assumed that the pipe of the subject has a seam of a zinc-plated iron plate for calibrating the pipe at a site of Y = 120 °.

  For such an object, the actual coordinate values are not taken in, and the tube axis distance X, which is the length from the end of the object, is changed only in the direction of Y = 0 ° and the calibration is performed by the simultaneous equation of seven elements. I went. Then, the measurement was performed by taking in the amplitude ratio and the phase difference at three frequencies (55 Hz, 95 Hz, 115 Hz) in the Y = 120 ° direction in which there is an influence of the outer cover due to the joint of the zinc-plated iron plate.

The results are shown in Table 5 and FIG.

In FIG. 20, the thick line is the measured value of the subject in the calibrated Y = 0 ° direction, and the thin line is the measured value of the subject in the Y = 120 ° direction where there is an influence of the external body. .
As shown in FIG. 20, the measured value of the subject in the Y = 120 ° direction, which is affected by the outer body, is not influenced by the outer body, and the calibrated object in the Y = 0 ° direction is measured. The measured value (5.8 mm) is significantly different.

  On the other hand, with respect to the same subject, W was taken as a region variable, the calibration site (Y = 0 °) was set to W = 0, and the measurement site (Y = 120 °) was set to W = 1 for calibration. Then, the amplitude ratio and the phase difference of three frequencies (55 Hz, 95 Hz, 115 Hz) were captured at one point of X = 500 mm, and the measurement was performed.

The results are shown in Table 6 and FIG. In FIG. 21, the thick line is the measured value of the subject in the calibrated Y = 0 ° direction, and the thin line is the measured value of the subject in the Y = 120 ° direction where the external body influences. .

As shown in FIG. 21, the measured value shows a value close to the actual value of 5.8 mm without being affected by the outer jacket even in the Y = 120 ° direction where the outer shell is influenced by the seams. .
In this case, only one point of Y = 120 °, X = 500 mm, and W = 1 is taken into the simultaneous equation as the measurement site, but even if the values of a plurality of points, for example, the value of X = 300 mm is additionally taken as W = 1, good. In that case, the number of points taken in with W = 0 is reduced accordingly.

Table 7 shows the case where the angles Y = 0 ° and 120 ° when the circumferential direction of the pipe to be inspected is the Y axis are variables and the region variables W = 0 and 1 are variables. The coefficients obtained by solving the simultaneous equations are compared with each other.

As shown in Table 7, when the Y direction is the circumferential direction of the pipe to be inspected, the angles Y = 0 ° and 120 ° are variables, and the region variables W = 0 and 1 are variables. In the case, the coefficients and the constants a to f and h are the same in both cases, and when the area variable W = 0 or 1 is used, the coefficient g is added.
From this, it is shown that the coefficient value of the calibration point remains unchanged even if the area variable W = 1 is taken in at Y = 120 ° of the measurement site, and accurate measurement can be performed.
Furthermore, if the variable value at the point of Y = 120 ° is taken into the calibration without using the region variable W, the variable value having the influence of the outer body will be taken into the calibration, and the validity of the calibration itself is impaired. However, this measurement method can overcome such drawbacks.

Here, in the above description, only one point of the region variable W = 1 was taken into the simultaneous equation as the measurement site in the direction of Y = 120 ° and the tube axis distance of X = 500 mm. Even if the tube axis distance is 300 mm, the area variable W may be additionally taken in as W = 1.
In this case, with the tube axis distance of X = 300 mm, it is possible to reduce the number of calibration points taken as the area variable W = 0.

  According to the present invention, as shown in the embodiments of the present invention, a subject body made of carbon steel or the like having both magnetism and conductivity is also provided with both magnetism and conductivity through a thick heat insulating material for increasing lift-off. Even if it is covered with a dew-proofing material such as galvanized iron, the large lift-off and removal or mitigation of the effect of the outer covering material, and the thickness of the subject body from the outside of the outer covering material It is possible to measure and detect corrosion, scratches, etc., and in particular, it can be effectively used for safety / maintenance of facilities and equipment, preventive maintenance and the like.

1 Sensor 2 Subject 2a Tube Main Body (Subject Main Body)
2b Heat insulating material 2c Dewproof material 2d Caulking section 4 Measuring device (signal processing section)
11 Detector 11f End face (end of detection sensor)
12 Exciter 112 Detection coil 121 Excitation core 122 Excitation coil 122a Inner peripheral side end (first end)
122b Outer peripheral side end (second end)
123 reference coil Ck central axis Cr central axis

Claims (15)

An exciting coil facing the subject body that is one of a cylindrical shape, a cylindrical shape, and a spherical shape ,
A detection coil facing the subject body,
A signal processing unit that detects the amplitude and phase of the voltage generated in the detection coil,
A non-destructive inspection apparatus for exciting the body of the subject by applying an alternating signal to the exciting coil, and detecting a change of a magnetic field including a magnetic flux due to an eddy current generated in the body of the subject by the detection coil,
The exciting coil is provided such that the central axis of the exciting coil is inclined with respect to the central axis of the detecting coil and intersects the central axis of the detecting coil, and the exciting coil has a first side close to the detecting coil. The end portion is arranged at a position farther from the subject body than the detection sensor end portion on the side closer to the subject body in the detection coil ,
Further, in the exciting coil, a second end portion on the side far from the detection coil projects toward the subject body side from the detection sensor end portion of the detection coil, and the detection coil side is closer to the subject body. The nondestructive inspection device is arranged so as to be closer to the subject body than the end portion of the detection sensor . The detection coil is arranged in the central portion,
A plurality of the exciting coils are provided on the outer peripheral portion of the detection coil at intervals in the circumferential direction,
The non-destructive inspection device according to claim 1 , wherein the central axes of the plurality of exciting coils are provided so as to concentrate and intersect at the same position of the central axes of the detection coils. The non-destructive structure according to claim 2 , wherein the intersecting positions of the central axes of the plurality of excitation coils and the central axes of the detection coils are set to be on the outer peripheral side of the subject body. Inspection device. The exciting coil has a coil axial direction on the side of the second end that gradually moves toward the subject body from the inner circumference side close to the detection coil toward the outer circumference side so as to follow the surface of the subject body. The nondestructive inspection device according to claim 2 or 3 , wherein the nondestructive inspection device is provided so as to be inclined so as to approach. Further comprising a reference coil electromagnetically coupled to the exciting coil,
The signal processing unit detects the magnetic field as an alternating signal voltage of the detection coil, and detects an amplitude and a phase of the alternating signal voltage with reference to an amplitude and a phase of a voltage generated in the reference coil. The nondestructive inspection device according to any one of claims 1 to 4 . The non-destructive inspection device according to claim 5 , wherein the amplitude value of the reference coil is compared with a predetermined reference value, and negative feedback processing is performed so as to approach the reference value. Exciting the exciting coil with an alternating signal of a plurality of frequencies,
The signal processing unit estimates the thickness of the subject body by using a simultaneous equation obtained by acquiring the amplitude and phase difference of the voltage generated in the detection coil for each of the plurality of frequencies as variables. The nondestructive inspection device according to any one of claims 1 to 6 . The signal processing unit estimates the thickness of the subject by using the simultaneous equations in which the amplitude, the phase difference of the voltage generated in the detection coil and the higher-order value of the square value of the coordinate value of the measurement position or more are taken as variables. nondestructive inspection apparatus according to any one of claims 1 6, characterized by. Exciting the exciting coil with an alternating signal of a plurality of frequencies,
The signal processing unit uses a simultaneous equation acquired for each of the plurality of frequencies, the amplitude and phase difference of the voltage generated in the detection coil, and a higher-order value higher than the square of the value of the measurement position as variables. The non-destructive inspection device according to any one of claims 1 to 6 , wherein the thickness of the subject body is estimated. According to claim 8, wherein using the plurality of coordinate axes values as a coordinate value, using the simultaneous equations comprising the product of the plurality of the coordinate values, or higher-order terms of the above square of the product as a variable Non-destructive inspection equipment. The signal processing unit uses a simultaneous equation in which a first value set in a region including a part to be calibrated and a second value set in a region including a part to be measured are taken as variables. the nondestructive inspection apparatus according to any one of claims 1, wherein the estimating the thickness of the subject body 6. The nondestructive inspection device according to any one of claims 7 to 11 , wherein a fast Fourier transform (FFT) is used as the means for detecting the amplitude and the phase. As the alternating signal to excite the exciting coil, nondestructive inspection according to any one of claims 7 to 11, characterized by using a burst signal rises exponentially, and falls exponentially apparatus. As a combination of frequency or the frequency of the alternating signal to excite the exciting coil, non according to claims 7 and selects from a predetermined reference number times the frequency column element of the frequency in any one of the 11 Destruction inspection device. A nondestructive inspection method in non-destructive inspection apparatus according to any one of claims 1 to 14,
A magnetic field change including a magnetic flux due to an eddy current generated in the subject body by applying an alternating signal to the exciting coil to excite the subject body in a state where the exciting coil faces the subject body. Input the voltage output from the detection coil to the measurement processing unit according to
The nondestructive inspection method, wherein the signal processing unit estimates the thickness of the subject body by detecting the amplitude and phase of the input voltage.

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