JP5222080B2 - Ultrasonic flaw detection method, ultrasonic flaw detection program used in the method, and recording medium on which the program is recorded - Google Patents

Description

  The present invention relates to an ultrasonic flaw detection method using surface SH waves, and more particularly to an ultrasonic flaw detection method based on image processing of an ultrasonic wave reception waveform signal.

  Conventionally, as an ultrasonic flaw detection method, a flaw detection method using a longitudinal wave or a transverse wave of an ultrasonic wave is known. In places where the incident method of ultrasonic waves is limited, for example, floor concrete buried steel sheets in nuclear power plants, only a part of the steel sheet surface can be exposed from the floor concrete. Or, there may be a case where the measurement cannot be performed by entering from the end face. In such a case, flaw detection can be performed by making an ultrasonic wave incident from the surface of the subject and propagating along the surface of the subject. As ultrasonic waves, there are longitudinal waves and transverse waves, and transverse waves include SV waves and SH waves. An oblique flaw detection method using longitudinal waves or SV waves and an ultrasonic flaw detection method using SH waves (for example, Patent Documents 1 to 3) are known. In the oblique flaw detection method using longitudinal waves, ultrasonic waves cannot be propagated so far due to loss due to the conversion of vibration modes into transverse waves on the surface. The oblique flaw detection method using the SV wave whose ultrasonic vibration direction is perpendicular to the surface of the subject propagates the ultrasonic wave far away if there are surface deposits or structures such as paint on the surface of the subject. I can't. On the other hand, the SH wave can propagate to a certain distance (1 m or more) without being affected by the surface deposits. Even if the SH wave can be propagated far away, the propagation distance may be insufficient depending on the measurement site. In such a case, in order to increase the propagation distance, it is conceivable to use a large SH wave element.

  However, the ultrasonic wave element for the SH wave is obtained by cutting the element for the longitudinal wave along the expansion / contraction direction of the element, and the SH wave probe that is actually manufactured is the largest due to a problem in manufacturing technology. But it is about 4 cm wide. Therefore, even if the maximum size SH wave probe is used, the propagation distance is limited, and the propagation distance may be insufficient.

Therefore, it is conceivable to expand the received waves by using a plurality of ultrasonic probes, digitally capturing the received waves of each ultrasonic probe, and using a phased array method in which synthesis processing is performed ( Patent Document 3). The phased array method is a method that gives the transmission and reception times the difference in propagation time that is theoretically calculated based on the ultrasonic wave propagation speed according to the distance from each probe to the target defect. is there.
JP-A-9-80031 Japanese Patent Laid-Open No. 9-318605 JP 2007-322350 A

  However, the ultrasonic flaw detector using the phased array method does not take into account the difference in the distance of implementation, the displacement of the probe arrangement, the manufacturing error of each probe, etc. For example, in an extreme case, it may occur that the reflected waves (echoes) cancel each other at the peaks and valleys. In particular, the surface SH wave probe is not generally mass-produced in large quantities, and there are variations in dimensions and the like for each probe, and there are variations in performance.

  The present invention provides an ultrasonic flaw detection method capable of flaw detection at a relatively distant place using a surface SH wave probe even in a place where flaw detection is difficult with longitudinal waves and SV wave ultrasonic waves, and an ultrasonic wave used in the method. The main object is to provide a flaw detection program and a recording medium on which the program is recorded.

In order to achieve the above object, the present invention provides, as a first means, a step of arranging a plurality of surface SH wave probes at appropriate positions on the surface of the subject, and each of the plurality of surface SH wave probes. Digital signal processing by a computer of the ultrasonic wave reception waveform signal obtained from the computer, and the digital signal processing by the computer of the ultrasonic wave reception waveform signal is obtained from each of the plurality of surface SH wave probes. A step of displaying a sound wave reception waveform signal on a monitor, a step of converting an ultrasonic wave reception type signal other than a reference ultrasonic wave reception waveform signal into a complex frequency spectrum among the respective ultrasonic wave reception waveform signals, and the reference become in order to correct the time difference between the peak of the peak and other ultrasonic receiving waveform signals of the ultrasonic reception waveform signal, versus time displacement input through the input means Performing a phase correction calculation on the complex frequency spectrum based on the input value to perform, reconverting each complex frequency spectrum after the phase correction calculation into an ultrasonic reception signal having time as a variable, The ultrasonic flaw detection comprising the steps of: synthesizing the reconverted ultrasonic reception waveform signal and the reference ultrasonic reception waveform signal; and displaying the synthesized ultrasonic reception waveform on a monitor. Provide a method.

  In the present invention, it is preferable that the second means further includes a step of determining deterioration of a defect to be detected from a peak height of the synthesized waveform in the first means.

  Each step of the digital signal processing is executed by a computer using a dedicated ultrasonic flaw detection program, and the program is provided by being recorded on a computer-readable recording medium.

  According to the present invention, the difference in the distance between the defect of the subject and each of the surface SH wave probes, the variation in characteristics due to the manufacturing error of each surface SH wave probe, etc., and the surface SH wave probe to the subject. A difference in reception time in the ultrasonic reception waveform signal that appears due to variations in the arrangement of the touches is removed by individual adjustment and added to obtain a waveform with higher intensity. Therefore, even if the distance from each surface SH wave probe to the defect of the subject is large and the reflected wave is weak, the echo height (reflected wave intensity) of the synthesized waveform can be greatly monitored by appropriate waveform synthesis. It can be displayed and easily recognized visually.

  The best mode for carrying out the present invention will be described below with reference to FIGS.

  FIG. 1 is a system configuration diagram for carrying out an ultrasonic flaw detection method according to the present invention. This system example transmits a control signal to a plurality of surface SH wave probes 1a to 1e and surface SH wave probes 1a to 1e and receives a reflected wave signal from the surface SH wave probes 1a to 1e. A multi-channel transmission / reception device 2, an A / D converter 3, a control computer 4 for controlling the multi-channel transmission / reception device 2, and a digital device connected so as to be able to receive the output from the multi-channel transmission / reception device 2. And an oscilloscope 20. In the illustrated example, there are five surface SH wave probes, but the number is not limited to five.

  As shown in FIG. 2, the multi-channel transmission / reception device 2 includes transmission / reception units 2 a to 2 e corresponding to the surface SH wave probes 1 a to 1 e, respectively. Each of the transmission / reception units 2a to 2e has a built-in pulse generation circuit 2f to 2j, receives a control signal related to the pulse voltage and the pulse generation timing from the control computer 4, and each of the pulse generation circuits 2f to 2j A pulse signal with a predetermined timing and voltage is sent. Each of the surface SH wave probes 1a to 1e generates a surface SH wave (ultrasonic wave) by applying a pulse voltage.

  The surface SH waves oscillated from the surface SH wave probes 1a to 1e propagate along the surface of the subject 5 and are reflected by the defect 5a of the subject (such as a thinning depression due to corrosion or the like). The reflected waves are received by the surface SH wave probes 1a to 1e. The reflected waves (echoes) received by the surface SH wave probes 1a to 1e are converted into voltages and received by the corresponding transmitting / receiving units 2a to 2e.

  The surface SH wave probes 1 a to 1 e are installed at appropriate positions on the surface of the subject 5. In general, a surface SH wave dedicated contact medium is applied to the surface of the subject 5 to which the surface SH wave probes 1 a to 1 e are fixed in order to propagate ultrasonic waves to the subject 5.

  When the surface SH wave probes 1a to 1e are individually arranged, for example, the surface SH wave probe 1a is arranged at a rough position, a pulse voltage is applied to the surface SH wave probe 1a, and the reflected wave is digitally converted. In the state displayed on the oscilloscope 20, the position of the surface SH wave probe 1a is shifted to search the position where the received waveform capable of recognizing the defect appears on the digital oscilloscope 20, and the position where the received waveform capable of recognizing the defect appears. A surface SH wave probe 1a is installed.

  In general, as the distance from the surface SH wave probe to the defect increases, the echo height of the received waveform that can be recognized as a defect decreases, but the noise increases, so the surface appears at a position where the echo height appears as high as possible. An SH wave probe is arranged. In addition, the surface SH wave probe is used to propagate the generated transverse wave to the subject via the highly viscous contact medium, so that the echo height is more stable than other oblique angle probes. The force of kg must continue to be pushed for several tens of minutes, but if a stable echo height is obtained by continuing to push, the adhesion to the subject increases, and the surface SH wave probe is easily moved. I can't. Therefore, it is necessary to position the surface SH wave probe at a position where the echo height appears as high as possible in an unstable echo height state.

  As described above, the plurality of surface SH wave probes 1a to 1e are individually disposed at appropriate positions. After arranging each of the plurality of surface SH wave probes 1a to 1e at appropriate positions in this way, the surface SH wave probes 1a to 1e are attached to the subject 5 using a dedicated fixture (not shown). It can be fixed so as to be pressed against the subject 5. Such a fixture includes, for example, when the subject 5 is a steel plate, a magnet that can be strongly magnetically attached to the steel plate that is the subject, and a pressing means that presses each of the surface SH wave probes 1a to 1e. Can be provided. The surface SH wave probe in the illustrated example uses a lead zirconate titanate piezoelectric element having a frequency of 0.5 MHz and an ultrasonic transducer size of 40 mm (height) × 40 mm (width). In addition, the code | symbol B shows a concrete structure in FIG.

  As shown in FIG. 2, the ultrasonic reception waveform signals (real-time waveform signals) of the reflected waves received by the transmission / reception units 2a to 2e are unnecessary in the low-pass filter 3a and the high-pass filter 3b in the A / D converter 3. After the high frequency component and the low frequency component are removed, the signal is amplified by the amplifier 3c, the analog input is converted into a digital signal by the A / D conversion unit 3d, and is output and stored in the memories 6a to 6e of the control computer 4 respectively. The The amplification factor of the amplifier 3c can be set by the control computer 4.

  As shown in FIG. 2, the control computer 4 includes memories 6 a to 6 e and 6 f, a CPU 7, a monitor 8, an input unit 9, a hard disk 10, and the like. An ultrasonic flaw detection program for digitally processing the received ultrasonic waveform signal is recorded. The ultrasonic flaw detection program can be installed on the hard disk of the control computer 4 from a computer-readable recording medium on which the program is recorded. In the illustrated example, the control computer uses a notebook personal computer.

  Below, the control flow by an ultrasonic flaw detection program is demonstrated with reference to the functional block diagram of FIG. 2, the flowchart of FIG. 3, and the graph of FIGS. For the sake of simplicity, the case of two signals will be described in the flowchart of FIG.

  The ultrasonic reception waveform signals (real time waveform signals) converted into digital signals and stored in the memories 6a to 6e are displayed on the monitor 8 (FIG. 2) by the real time waveform display means 11a to 11e ( Step S1). The graph of FIG. 4 is a graph showing two ultrasonic reception waveform signals (real-time waveform signals), with the horizontal axis representing time (μs) and the vertical axis representing reflected wave (echo) intensity (dB). In the graph shown in FIG. 4, it can be seen that the peak of the waveform 2 is shifted to the right by the time shift amount Δt with respect to the peak of the reference waveform 1.

  The time shift amount Δt is detected by the operator reading from the time display on the horizontal axis of the monitor 8. The detected time shift amount Δt is input by the operator through the input means 9 and stored in the memory 6f.

  The ultrasonic reception waveform signal (real time waveform signal) of the waveform 2 is subjected to DTFT conversion (discrete time Fourier transform) by the FFT algorithm by the conversion means 12 (step S2). FIG. 5 shows a complex frequency spectrum of the waveform 2 converted into the frequency domain by the DTFT conversion. In FIG. 5, the horizontal axis is frequency (MHz), and the vertical axis is intensity.

  Next, in order to correct the time lag between the peak of the waveform 1 and the peak of the waveform 2, the time shift means 13 reads out the time lag amount Δt from the memory 6f, and the time shift unit 13 reads the time lag from the complex frequency spectrum obtained by DTFT conversion. The phase correction calculation is performed by shifting the time by the time shift amount Δt in the region (step S3). The time shift of the discrete time data using the complex frequency spectrum is described by the following equation (1) by the theorem. The phase correction calculation is performed on the complex frequency spectrum by substituting the time shift amount Δt read from the memory 6f for Δt on the right side in the following equation (1).

y (t + Δt) = Y (f) exp (2πfiΔt) (1)
Where t: time
f: Frequency Δt: Time shift amount y (t): Time series data Y (f): Frequency spectrum
i: Imaginary unit Next, the re-conversion unit 14 performs inverse DTFT conversion on the frequency spectrum of the waveform 2 that has been time-shifted in step 3 by the FFT algorithm (step S4). FIG. 6 is a graph in which the waveform 2 re-converted into the time domain by inverse DTFT conversion and converted into time series data is displayed together with the reference waveform 1. In the graph of FIG. 6, the horizontal axis is the time axis. From the graph of FIG. 6, it can be seen that the time lag of the maximum peak signal is removed compared to the graph of FIG.

  Next, the waveform synthesizing unit 15 synthesizes the waveform 1 and the waveform 2 shown in FIG. 6 (step S5), and the synthesized waveform display unit 16 displays the synthesized waveform on the monitor 8 (step S6). FIG. 7 shows the synthesized waveform.

  As a comparative example, FIG. 8 shows a waveform obtained by synthesizing waveform 1 and waveform 2 of FIG. It can be seen that the peak of the waveform in FIG. 7 is displayed larger than in FIG.

  As is apparent from the above description, according to the present invention, the amount of time shift can be adjusted by looking at the real-time waveform displayed on the monitor. Therefore, the difference in the reception time in the reception signal that appears due to the difference in the distance between the surface SH wave probes 1a to 1e and the defect of the object, the variation in the characteristics of the surface SH wave probes 1a to 1e, the variation in the arrangement, etc. The received signal having a higher strength can be obtained by individually removing and adding the signals. Even if the distance to the defect is large and the reflected wave is weak, the synthesized waveform can be enlarged and displayed on the monitor by appropriate waveform synthesis.

  In the above embodiment, some of the received waveform signals may be synthesized without synthesizing all of the waveform signals received by the plurality of surface SH wave probes. For example, the surface SH waves can be transmitted from the five surface SH wave probes 1a to 1e, and the received waveform signals received by the three surface SH wave probes 1a to 1c can be synthesized. As a result, only a waveform having a large peak can be extracted from a plurality of real-time waveforms displayed on the monitor and synthesized, so that a waveform having a larger peak height can be synthesized.

  Note that if there is still a time shift amount Δt ′ between the waveform 2 converted into the time domain by the inverse DTFT conversion in step S4 and converted into time series data, and the waveform 1, the time shift amount Δt ′ is set as follows. Further, it is possible to add to the control program a time lag amount detecting means obtained by obtaining a cross-correlation function between the re-converted waveform 2 waveform signal and waveform 1 waveform signal. In general, the cross-correlation function C (t) between the signal waveform g (i) and the signal waveform h (i) can be obtained by the following calculation formula (2).

一方の波形をずらした時間（遅れ時間）の関数として表したものが相関関数であるから、相互相関関数の値がもっとも大きい時間から時間ずれ量Δｔ’を算出することができる。そうして求めた時間ずれ量Δｔ’を用いることにより、上記ステップ２〜ステップ５と同様の操作により、さらに時間ずれを調整して波形を合成することも可能である。

Since the correlation function is what is expressed as a function of the time (delay time) in which one waveform is shifted, the time shift amount Δt ′ can be calculated from the time when the value of the cross-correlation function is the largest. By using the time shift amount Δt ′ thus determined, it is possible to further synthesize the waveform by further adjusting the time shift by the same operation as in steps 2 to 5 above.

  Further, the relationship between the echo height of the synthesized waveform and the depth of the defect of the subject may be compiled into a database, and the depth of the subject's defect may be displayed on the monitor 8 from the echo height at the maximum peak of the synthesized waveform. However, the presence / absence of deterioration and the degree of deterioration may be determined. Further, the distance from the surface SH wave probe to the defect of the subject may be displayed on the monitor 8 from the time of the synthesized waveform.

  In the above embodiment, an example in which the surface SH wave probes are individually arranged has been described. However, a probe array in which a plurality of surface SH wave probes are incorporated and fixed can also be used. In this case, the plurality of surface SH wave probes may include those that do not receive the reflected wave or are weak even if they are received depending on the arrangement. In such a case, the reflected wave is received. If the waveform is not displayed on the monitor without being displayed, it is synthesized by excluding those with small peaks, or by selecting several synthesized waveforms from the reflected waveform data displayed on the monitor. Synthesis is possible.

1 is a perspective view showing a system configuration example for implementing an ultrasonic flaw detection method according to the present invention. It is a functional block diagram for demonstrating the process of the ultrasonic reception waveform signal in the system configuration | structure of FIG. It is a flowchart which shows the control flow in the digital signal processing of the ultrasonic flaw detection method which concerns on this invention. It is one of the monitor images for demonstrating the ultrasonic flaw detection method which concerns on this invention. It is one of the monitor images for demonstrating the ultrasonic flaw detection method which concerns on this invention. It is one of the monitor images for demonstrating the ultrasonic flaw detection method which concerns on this invention. It is one of the monitor images for demonstrating the ultrasonic flaw detection method which concerns on this invention. It is a waveform display graph for demonstrating the comparative example with the ultrasonic flaw detection method which concerns on this invention.

Explanation of symbols

1a-1e Surface SH wave probe
2 Multi-channel transceiver 3 A / D converter 4 Control computer 5 Subject

Claims (4)

Arranging a plurality of surface SH wave probes at appropriate positions on the surface of the subject;
Digital signal processing of an ultrasonic wave reception waveform signal obtained from each of the plurality of surface SH wave probes by a computer,
Digital signal processing by the computer of the ultrasonic reception waveform signal,
Displaying on the monitor an ultrasonic reception waveform signal obtained from each of the plurality of surface SH wave probes;
Of each of the ultrasonic reception waveform signals, converting an ultrasonic reception type signal other than the reference ultrasonic reception waveform signal into a complex frequency spectrum;
In order to correct the time lag between the peak of the ultrasonic reception waveform signal serving as the reference and the peak of the other ultrasonic wave reception waveform signal, the complex frequency is based on the input value corresponding to the time lag input through the input means. Performing a phase correction calculation on the spectrum;
Reconverting each complex frequency spectrum after the phase correction calculation into an ultrasonic reception signal having time as a variable;
Synthesizing the reconverted ultrasonic reception waveform signal and the reference ultrasonic reception waveform signal;
And displaying the synthesized ultrasonic reception waveform on a monitor. The ultrasonic flaw detection method according to claim 1, further comprising a step of determining deterioration of the subject from a peak height of the synthesized waveform. An ultrasonic flaw detection program for causing a computer to execute each step of the digital signal processing according to claim 1. A computer-readable recording medium on which the ultrasonic flaw detection program according to claim 3 is recorded.

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