JP2006329868A - Electromagnetic ultrasonic flaw detection method and apparatus thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electromagnetic ultrasonic flaw detection method and apparatus capable of removing transmission frequency component noise by a magnetostrictive electromagnetic ultrasonic sensor. <P>SOLUTION: A current of an additional magnetic field by burst waves is synchronized with a normal waveform and an inverted waveform of a bias magnetic field. SH waves by the normal waveform and SH waves by the inverted waveform are alternately transmitted. By determining the difference between the SH waves by the normal waveform and the SH waves by the inverted waveform when reflected waves from a flaw are received by an electromagnetic ultrasonic sensor for reception, it is possible to suppress transmission noise and achieve an increase in the level of reflected waves from the flaw. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ultrasonic flaw detection method and apparatus using an electromagnetic ultrasonic sensor, and more particularly to an electromagnetic ultrasonic flaw detection method and apparatus using a magnetostrictive drive type electromagnetic ultrasonic sensor.

  In facilities that handle high-temperature and high-pressure fluids such as power plants, it goes without saying that ensuring safety is an important issue. To this end, the facilities' structures are regularly inspected to ensure their soundness. For this reason, visual inspection using a video camera and ultrasonic inspection using a piezoelectric probe have been conventionally applied to such facilities.

  Here, in any inspection, it is necessary to stop the operation of the power plant or the like during the inspection period. At this time, shortening of the inspection period is strongly required from the viewpoint of economy. Thus, efforts have been made to reduce the inspection time by automating the inspection apparatus and remotely operating the sensor position.

  However, in recent years, from the standpoint of further pursuing safety, inspection requirements have spread to complicated shapes and narrow parts of structures, and it has become difficult to reduce inspection time depending on mechanical operation and control. It was. Therefore, in recent years, a technique for propagating (propagating) ultrasonic waves over a long distance within an inspection object and flaw-detecting a wide area with a single operation has attracted attention in recent years, and EMAT is an example of a sensor for that purpose. There is an electromagnetic ultrasonic sensor called (Electromagnetic Acoustic Transducer).

  By the way, this electromagnetic ultrasonic sensor also has two types of magnetostrictive drive type EMAT and Lorentz type EMAT. Here, the magnetostrictive drive type EMAT will be described, which uses the magnetostrictive effect of the magnetic material as the name suggests. In this case, the magnetostrictive effect is a phenomenon in which when a magnetic field is applied to a magnetic material, a stress in the direction of the magnetic field appears on the magnetic material. Therefore, the magnetostrictive drive type EMAT is an inspection object. Expansion and contraction due to the magnetostriction effect is periodically generated in a part of the magnetic material, and ultrasonic waves are generated in the inspection object itself along with the expansion and contraction.

  Therefore, an example of the magnetostrictive drive type EMAT will be described in more detail with reference to FIG. 8. This is constituted by the bias field electromagnet 10 and the meandering coil 12, as shown in the figure. First, an electromagnet 10 for a bias magnetic field is obtained by winding a coil 13 around a horseshoe-shaped core 11 made of a high permeability magnetic material to form an electromagnet. Next, the meandering coil 12 is shown in detail in FIG. In addition, the conductor 14 is meandered at a constant interval L on a plane.

  If the bias field electromagnet 10 and the meandering coil 12 are arranged on the surface of the inspection object O while maintaining the positional relationship shown in FIG. 8, when the inspection object O is a magnetic material, the SH wave ( A horizontal shear wave can be generated. Here, the SH wave is an elastic wave that oscillates in a direction perpendicular to the propagation direction of the wave and parallel to the incident surface. In this case, the elastic wave is an ultrasonic wave.

  Next, the operation of the magnetostrictive drive type EMAT shown in FIG. 8 will be described with reference to FIG. Here, FIG. 10 is a schematic view of FIG. 8 as viewed from above. When a current is passed through the coil 13 so that the north pole of the bias field electromagnet 10 is on the left side, the bias magnetic field in the direction indicated by the arrow is shown. B is generated. Here, assuming that a current flows through the meandering coil 12 in the directions indicated by the arrows a1 and a2, the magnetic field of the surface layer portion of the inspection object O is as shown in FIG.

  Here, first, as shown in FIG. 11, the bias magnetic field B forms a uniform magnetic field from the north pole side to the south pole side of the x axis. On the other hand, the magnetic field generated by the meandering coil 12 appears in the y-axis direction and becomes an additional magnetic field with respect to the bias magnetic field B. At this time, the direction of the meandering coil 12 is reversed every time the meandering coil 12 is meandered. As an additional magnetic field A2, a vector can be displayed. At this time, the magnetic field due to the current in the direction of the arrow a1 is the additional magnetic field A1, and the magnetic field due to the current in the direction of the arrow a2 is the additional magnetic field A2.

  Therefore, these vector sums become a composite magnetic field V1 and a composite magnetic field V2, respectively. When the vector sum of these composite magnetic fields V1 and V2 is viewed as a whole sensor, only the x-axis direction component remains, and as a result, as shown in the drawing, due to the magnetostrictive effect in the inspection object O that is a magnetic material. Distortion D occurs.

  At this time, the directions of the vectors of the composite magnetic fields V1 and V2 change each time the meandering coil 12 meanders. Accordingly, as shown in FIG. 12, a distortion having a different direction is locally generated in the inspection object O in accordance with the x-axis direction component of the composite magnetic field, and vibration due to the distortion induces an SH wave.

  Therefore, by supplying an alternating current signal having a frequency corresponding to the ultrasonic wave to be generated to the meandering coil 12, an ultrasonic wave propagating through the inspection object O in the y-axis direction can be obtained. Can be operated as

  On the other hand, when the ultrasonic wave propagates through the inspection object O from the y-axis direction, distortion due to the elastic wave is generated in the bias magnetic field B, and the elastic wave is generated in the meandering coil 12 by the magnetostriction effect of the inspection object O that is a magnetic material. Since an alternating voltage having the same frequency as that of the first frequency is induced, it can be operated as a receiving sensor.

  As described above, since this electromagnetic ultrasonic sensor transmits and receives ultrasonic waves using only electromagnetic action, application of a contact medium and pressing of the sensor, which are indispensable for flaw detection by a piezoelectric probe, are performed. Is unnecessary, and there is no risk of uncertainties associated with them, so that it is rich in quantitativeness and excellent in reproducibility.

However, on the other hand, there is a problem that the detection sensitivity of the electromagnetic ultrasonic sensor is two orders of magnitude lower than that of the piezoelectric probe. Therefore, in order to improve this point, an inspection method using an electromagnetic ultrasonic sensor combined with a signal processing technique has been proposed in the past. As an example, an electromagnetic ultrasonic sensor for reception is provided in front of the electromagnetic ultrasonic sensor for transmission. The conventional technology is designed to reduce the random noise and improve the detection sensitivity by measuring the transmitted wave in addition to the reflected wave and calculating the cross-correlation of both the reflected wave and the transmitted wave. It has been proposed (see, for example, Patent Document 1).
JP 2003-294714 A

  The above prior art does not take into consideration that the transmission frequency component tends to be noise, and has a problem in removing noise due to the transmission frequency component.

  As described above, since the conventional technique correlates with the transmission wave, it is possible to reduce random noise. However, since the transmission frequency component does not occur at random, it cannot be removed even if correlation is taken.

  An object of the present invention is to provide an electromagnetic ultrasonic flaw detection method and an electromagnetic ultrasonic flaw detection apparatus in which transmission frequency component noise can be removed by a magnetostrictive electromagnetic ultrasonic sensor.

  The object is to control the phase of an ultrasonic waveform transmitted from the electromagnetic ultrasonic sensor in an ultrasonic flaw detection method using an electromagnetic ultrasonic sensor, observe two types of reflected waveforms having different phases, and This is accomplished by performing signal processing for calculating the difference between the reflected waveforms and displaying it.

  At this time, a magnetostrictive drive type electromagnetic ultrasonic sensor may be used as the electromagnetic ultrasonic sensor, and the ultrasonic wave transmitted from the electromagnetic ultrasonic sensor may be a shear wave, and the electromagnetic ultrasonic wave may be used. The phase of the ultrasonic waveform transmitted from the acoustic wave sensor may be 180 ° different.

  Further, at this time, the phase may be changed by changing the direction of the bias magnetic field of the magnetostrictive drive type electromagnetic ultrasonic sensor, and the generation point of the ultrasonic wave is the maximum value point and the minimum value of the bias magnetic field. It may be synchronized with the time.

  Further, the above object is to provide an ultrasonic flaw detection apparatus using an electromagnetic ultrasonic sensor, a means for controlling the phase of an ultrasonic signal transmitted from the electromagnetic ultrasonic sensor, and two types of reflection by ultrasonic signals having different phases. It is also achieved by including means for observing a wave, means for calculating a difference waveform between the two kinds of reflected waves, and means for displaying the difference waveform.

  At this time, the electromagnetic ultrasonic sensor is a magnetostrictive drive type electromagnetic ultrasonic sensor, and the ultrasonic wave transmitted from now on may be a shear wave, and at this time, the magnetostrictive drive type electromagnetic ultrasonic sensor May be constituted by a bias magnetic field electromagnet and an additional magnetic field meandering coil, and the direction of the bias magnetic field may be changed by passing an alternating current through the coil of the bias magnetic field electromagnet.

  Further, at this time, the above object can be achieved even if means for displaying the current waveform of the bias magnetic field coil and the transmission waveform of the ultrasonic wave and means for adjusting the transmission timing of the ultrasonic wave are provided. Here, a signal delay device may be used to adjust the transmission timing.

  According to the present invention, since two types of waveforms with different phases are measured and the difference between the two waveforms is observed, it is possible to improve detection sensitivity and suppress electrical noise, and perform highly accurate flaw detection. be able to.

  Hereinafter, an electromagnetic ultrasonic flaw detection method and an electromagnetic ultrasonic flaw detection apparatus according to the present invention will be described in detail with reference to illustrated embodiments.

  FIG. 1 is a block diagram of an electromagnetic ultrasonic flaw detector according to an embodiment of the present invention. In this figure, the transmission electromagnetic ultrasonic sensor 1 and the reception electromagnetic ultrasonic sensor 2 have been described with reference to FIG. The magnetostrictive electromagnetic ultrasonic sensor includes a bias magnetic field electromagnet 10 and a meandering coil 12.

  At this time, the bias field electromagnet 10 is obtained by uniformly winding an insulated wire around a core 11 obtained by cutting a soft magnetic material into a horseshoe shape to form a coil 13, and the meandering coil 12 has six stages of enameled wires. They are arranged in a plane and then covered with a plastic sheet.

Here, first, the transmission electromagnetic ultrasonic sensor 1 is supplied with an AC bias voltage V _B and a burst wave W _B. In this case the bias voltage V _B is supplied via the power amplifier 4 from the sine wave generator 3, the burst wave W _B is supplied from the transmission unit of the burst wave transceiver 5.

Then, as the bias voltage V _B at this time, the frequency is e.g. 100Hz sine wave signal is used as the burst wave W _B, the frequency is for example 375KHz signal is used, wherein the burst wave transceiver transmitting portion 5 is made a sine wave voltage supplied from the sine wave generator 3 via a signal delay device 6 to generate a burst wave W _B as a trigger.

Thus, frequency current is supplied bias magnetic field 100Hz sine wave to the coil 13 of the transmitting electromagnetic ultrasonic wave sensor 1, so that the current use additional magnetic field generated by the burst wave W _B is supplied to the serpentine coil 12 . At this time, the output of the sine wave generator 3 and the output of the burst wave transmitter / receiver 5 are supplied to the AD converter 8 for monitoring.

On the other hand, the bias voltage V _B, which is the output of the power amplifier 4, is also supplied to the receiving electromagnetic ultrasonic sensor 2, so that a sinusoidal bias magnetic field current is also applied to the coil 13 of the receiving electromagnetic ultrasonic sensor 2. To be supplied. At this time, the reception signal R detected by the meandering coil 12 of the reception electromagnetic ultrasonic sensor 2 is taken into the signal amplifier 7, and the amplified waveform AR is supplied to the reception unit of the burst wave transmitter / receiver 5. W is input to the AD converter 8.

  Therefore, the AD converter 8 AD-converts this signal waveform W and inputs it to the computer 9, and as a result, necessary information is displayed on the monitor 10. At this time, as described above, the output of the sine wave generator 3 and the output of the burst wave transmitter / receiver 5 are also AD-converted by the AD converter 8 and input to the computer 9.

  Next, the operation of the electromagnetic ultrasonic measurement apparatus according to this embodiment will be described. In this embodiment, the phase of the transmission waveform is controlled as shown as step 101 in the block diagram of FIG. At this time, as described with reference to FIG. 1, the sine wave generator 3 generates a sine wave signal and a rectangular wave signal having an arbitrary frequency, for example, a frequency of 100 Hz, and generates a bias voltage and a trigger.

  First, the bias voltage is applied to the bias magnetic field coil 13 of the transmission electromagnetic ultrasonic sensor 1 via the power amplifier 2, and as a result, the bias magnetic field current shown in FIG. The electromagnet 10 is excited, and an alternating bias magnetic field B is generated on the surface layer portion of the inspection object O as shown in FIG.

At this time, the trigger output from the sine wave generator 3 is also input to the signal delay device 6 as shown in FIG. Therefore, the signal delay device 6 uses the input trigger as a reference signal, controls the delay time and inputs it as an external trigger to the burst wave transmitter / receiver 5, and generates a burst wave B _W in synchronization with the external trigger. This is applied to the transmission meandering coil 12, whereby a burst waveform current flows through the transmission meandering coil 12 as shown in FIG. 3, and as shown in FIG. 4, the additional magnetic field generated by the transmission meandering coil 12. A1 occurs in the surface layer portion of the inspection object O.

  The relationship between the current of the bias magnetic field coil 13 necessary for exciting the bias magnetic field B and the current of the transmitting meandering coil 12 necessary for exciting the additional magnetic field A1 is as shown in FIG. As shown in FIG. 1, the current of the bias magnetic field coil 13 can be observed by the monitor 10 from the monitor bias signal output from the sine wave generator 3, and the transmission meander coil that excites the additional magnetic field A1. Similarly, as shown in FIG. 1, the current 12 can be observed by the monitor 10 from the monitoring burst wave output from the burst wave transceiver 5.

In this embodiment, as is apparent from FIG. 3, the additional magnetic field current, that is, the burst waveform is applied to the transmitting meandering coil 12 in synchronization with the time when the current for exciting the bias magnetic field B exhibits the maximum value and the minimum value. Thus, the delay time of the signal delay device 6 is set so that the current of 1 is supplied, so that the bias magnetic field B is alternately changed from the N pole to the S pole at the time between each waveform of the burst wave B _W , or Invert from S pole to N pole.

  FIG. 4 shows a comparison of the directions of distortion caused by the reversal of the bias magnetic field B side by side, and FIG. 4 shows that the direction of the composite magnetic field V1 is changed by reversing the magnetic poles of the bias magnetic field B. It can be seen that the direction of is reversed and the phase of the SH wave is 180 ° different. In FIG. 4, the additional magnetic field A2 described in FIG. 11 and the resultant composite magnetic field V2 are omitted.

  Hereafter, the observed waveform of the SH wave generated at the timing when the bias magnetic field B changes from the N pole to the S pole (N pole → S pole) is referred to as a normal rotation waveform, and the bias magnetic field B is changed from the S pole to the N pole (S Assuming that the observed waveform of the SH wave generated at the timing of changing from the pole to the N pole is an inverted waveform, the waveform on the receiving side is observed in steps 102 and 103 in FIG.

  Now, as a result of the excitation of the transmitting electromagnetic ultrasonic sensor 1 of FIG. 1, an SH wave propagating through the inspection object O appears, and the SH wave is directly below the receiving meandering coil 12 of the receiving electromagnetic ultrasonic sensor 2. If it reaches, a change appears in the magnetic flux of the coil 12 due to the magnetostriction effect, which is converted into a voltage signal, and the received waveform R is taken into the burst wave transmitter / receiver 5 as the amplified waveform AR via the signal amplifier 7, As a result of the signal band limitation and amplification performed by the receiving unit, the signal waveform W is converted into a digital signal by the AD converter 8 and taken into the computer 9.

  At this time, in step 102, the normal waveform of the signal waveform W is observed, and in step 103, the inverted waveform of the signal waveform W is observed. Therefore, the computer 9 performs signal processing on the signal waveform W converted into a digital signal as shown in step 104, and displays the result on the monitor 10 as shown in step 105.

  At this time, as part of the waveform signal processing in step 104, the computer 9 stores the digital signal of the normal waveform and the digital signal of the inverted waveform in the memory. Next, a normal waveform and an inverted waveform digital signal at the same time t are extracted from the normal waveform and inverted waveform digital signals stored in these memories, and the difference between the digital values is calculated. The waveform signal value. Then, the result of this signal processing is displayed on the monitor 10 as a difference waveform at time t.

  Next, with respect to the operation of this embodiment, as shown in FIG. 5, a substantially rectangular magnetic plate material in which a slit-like defect F is previously formed in the vicinity of one end thereof is used as an inspection object O. A case where the transmitting electromagnetic ultrasonic sensor 1 and the receiving electromagnetic ultrasonic sensor 2 are arranged so as to face the defect F as shown in the figure will be described in the vicinity of the other end.

  Then, as described with reference to FIG. 3, the transmission electromagnetic ultrasonic sensor 1 alternately transmits the SH wave based on the normal waveform of the bias magnetic field B and the SH wave based on the inverted waveform, and the reflected wave from the defect F Is received by the receiving electromagnetic ultrasonic sensor 2, and the result of displaying the SH wave with the normal waveform and the inverted waveform observed at this time on the monitor 10 is shown in FIG. It can be confirmed that the SH wave of the normal rotation waveform shown by the solid line and the SH wave of the inverted waveform shown by the broken line are level-inverted, and the phase of the signal is 180 ° different. It turns out that the normal rotation waveform shown and the inversion waveform shown with the broken line overlap, and both waveforms are in phase.

  Further, FIG. 7 shows the result of calculating the difference between the normal waveform and the inverted waveform in FIG. 6, that is, the differential waveform. From this figure, the signal amplitude is approximately doubled in the reflected wave from the defect F. On the other hand, the transmission noise is greatly suppressed. Therefore, by taking the difference between the normal waveform and the inverted waveform, the transmission noise can be suppressed and the signal component from the defect F is 2 at the maximum. It can be seen that the level is doubled.

  Therefore, according to this embodiment, noise due to the transmission frequency component of the magnetostrictive electromagnetic ultrasonic sensor can be suppressed, and a large level signal can be obtained from the defect F. As a result, the S / N is improved. In addition, improvement in ultrasonic flaw detection accuracy can be obtained.

1 is a block diagram showing an embodiment of an electromagnetic ultrasonic flaw detection method and an electromagnetic ultrasonic flaw detection apparatus according to the present invention. It is a control block diagram by one Embodiment of this invention. It is explanatory drawing of the current waveform in one Embodiment of this invention. It is operation | movement explanatory drawing of one Embodiment of this invention. It is arrangement | positioning explanatory drawing of the sensor by one Embodiment of this invention. It is a normal rotation waveform and inversion waveform diagram for demonstrating operation | movement of one Embodiment of this invention. It is a difference waveform diagram for demonstrating operation | movement of one Embodiment of this invention. It is a perspective view which shows an example of a magnetostriction drive type | mold electromagnetic ultrasonic sensor. It is explanatory drawing of the meander coil in an example of a magnetostriction drive type | mold electromagnetic ultrasonic sensor. It is a top surface sectional view showing an example of a magnetostriction drive type electromagnetic ultrasonic sensor. It is explanatory drawing which shows the relationship between the bias magnetic field and additional magnetic field in an example of a magnetostriction drive type | mold electromagnetic ultrasonic sensor. It is explanatory drawing of the generation | occurrence | production and propagation state of a horizontal shear wave by an example of a magnetostriction drive type | mold electromagnetic ultrasonic sensor.

Explanation of symbols

1: Electromagnetic ultrasonic sensor for transmission 2: Electromagnetic ultrasonic sensor for reception 3: Sine wave generator 4: Power amplifier 5: Burst wave transceiver 6: Signal delay device 7: Signal amplifier 8: AD converter 9: Computer 10 : Monitor 10: Electromagnet for bias magnetic field 11: Core 12: Coiled coil 13: Coil for bias magnetic field a1, a2: Arrow B: Bias magnetic field A1, A2: Additional magnetic field V1, V2: Compound magnetic field O: Inspection object F: Defect V _B : Bias voltage AR: Amplified signal W: Signal waveform B _W : Burst waveform

Claims (13)

In the ultrasonic flaw detection method using an electromagnetic ultrasonic sensor,
Controlling the phase of an ultrasonic waveform transmitted from the electromagnetic ultrasonic sensor, observing two types of reflected waveforms with different phases, performing signal processing for calculating a difference between the two types of reflected waveforms, and displaying A characteristic electromagnetic ultrasonic flaw detection method. In the invention of claim 1,
An electromagnetic ultrasonic flaw detection method, wherein the electromagnetic ultrasonic sensor is a magnetostrictive drive type electromagnetic ultrasonic sensor. In the invention of claim 1,
An ultrasonic ultrasonic flaw detection method, wherein the ultrasonic wave transmitted from the electromagnetic ultrasonic sensor is a shear wave. In the invention of claim 1,
An electromagnetic ultrasonic flaw detection method, wherein phases of ultrasonic waveforms transmitted from the electromagnetic ultrasonic sensor differ by 180 °. In the invention of claim 2,
An electromagnetic ultrasonic flaw detection method characterized in that the phase is changed by changing the direction of a bias magnetic field of the magnetostrictive drive type electromagnetic ultrasonic sensor. In the invention of claim 5,
The electromagnetic ultrasonic flaw detection method, wherein the generation time of the ultrasonic wave is synchronized with the maximum value time and the minimum value time of the bias magnetic field. In an ultrasonic flaw detector using an electromagnetic ultrasonic sensor,
Means for controlling the phase of an ultrasonic signal transmitted from the electromagnetic ultrasonic sensor;
Means for observing two kinds of reflected waves by ultrasonic signals having different phases;
Means for calculating a difference waveform of the two kinds of reflected waves;
An electromagnetic ultrasonic flaw detector comprising: means for displaying the difference waveform. In the invention of claim 7,
The electromagnetic ultrasonic flaw detector is characterized in that the electromagnetic ultrasonic sensor is a magnetostrictive drive type electromagnetic ultrasonic sensor. In the invention of claim 8,
The ultrasonic ultrasonic flaw detector characterized in that the ultrasonic wave transmitted from the electromagnetic ultrasonic sensor is a shear wave. In the invention of claim 8,
The magnetostrictive drive type electromagnetic ultrasonic sensor comprises an electromagnet for bias magnetic field and a meandering coil for additional magnetic field, and an electromagnetic ultrasonic flaw detector. In the invention of claim 7,
An electromagnetic ultrasonic flaw detector characterized in that the direction of a bias magnetic field is changed by passing an alternating current through a coil of the bias magnetic field electromagnet. In the invention of claim 7,
Means for displaying the current waveform of the bias magnetic field coil and the transmission waveform of the ultrasonic wave;
An inspection apparatus comprising: means for adjusting the transmission timing of the ultrasonic wave.   13. The inspection apparatus according to claim 12, wherein a signal delay device is used to adjust transmission timing.

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