JP2006337201A - Ultrasonic flaw detection method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic flaw detection method and an apparatus, capable of accurately detecting even defects present in the vicinity of the bottom surface of the object material of flaw detection. <P>SOLUTION: The ultrasonic flaw detection apparatus 100 is provided with a wide-band ultrasonic probe 1, arranged in such a way as to make the ultrasonic waves be incident perpendicularly on the surface of the object material of flaw detection; a high-pass filter 2 for cutting off a low-frequency components, by setting a prescribed cut-off frequency that is higher than the lower limit of the frequency band of ultrasonic waves oscillated by the wide-band ultrasonic probe 1 and is lower than its center frequency, from among frequency components of reflected echoes from the object material of flaw detection received by the wide-band ultrasonic probe 1; and a defect detection circuit 3 for detecting defects present in the object material of flaw detection, by comparing the amplitude of output signals of the high-pass filter 2 with a prescribed threshold. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ultrasonic flaw detection method and apparatus for detecting a defect existing in a flaw detection material such as a plate material, a tube material, and a bar material by ultrasonic vertical flaw detection, and in particular, accurately detects a flaw present near the bottom surface of the flaw detection material. The present invention relates to an ultrasonic flaw detection method and apparatus capable of detection.

  Conventionally, an ultrasonic vertical flaw detection method has been widely used to detect defects such as inclusions present in various flaw detection materials such as steel pipes and steel plates. In the ultrasonic vertical flaw detection method, flaw detection is performed by detecting the presence and size of defects by making ultrasonic waves incident perpendicular to the surface of the material to be inspected and detecting reflection echoes from the defects present in the material to be inspected. Is the method. Here, the ultrasonic wave incident on the flaw detection material is preferable in that the higher the frequency, the better the resolution. On the other hand, if the frequency is too high, the ultrasonic wave is easily attenuated in the process of propagating through the flaw detection material. . Therefore, in consideration of both attenuation and resolution in the material to be inspected, an ultrasonic probe having a wideband frequency characteristic of 2 to 15 MHz is usually used.

  However, when ultrasonic waves are incident on the material to be inspected perpendicularly and propagated inside, excessive reflection echoes are generated on both the surface on which the ultrasonic probe is disposed and the opposite surface (bottom surface). Therefore, it is difficult to detect reflection echoes from minute defects near the surface in terms of resolution (the reflection echoes from the surface of the flaw detection material cannot be distinguished from the reflection echoes from the defect), and there is a dead zone near the surface. There was a problem that existed.

  Various methods have been proposed in the past for the purpose of reducing the dead zone near the surface of the flaw detection material (see, for example, Patent Documents 1 and 2).

  For example, in Patent Document 1, an ultrasonic probe having a frequency of 15 MHz to 50 MHz and a focal length of 12.7 to 38.1 mm is used to transmit an ultrasonic beam in a range of 2 mm subcutaneously including the surface of the flaw detection material. An ultrasonic flaw detection method has been proposed in which a water distance is set so as to converge, and a point converging ultrasonic wave is incident perpendicularly to the surface of the material to be inspected to detect minute defects existing in an area within 2 mm from the surface. ing.

  However, the method described in Patent Document 1 cannot detect a defect existing in a deeper region because only a defect existing in a region within 2 mm from the surface of the flaw detection material is targeted for detection. Therefore, in order to detect all of the material in the thickness direction of the flaw detection material, it is necessary to use another ultrasonic probe different from the above ultrasonic probe, and the number of ultrasonic probes increases. There is a problem that it causes an increase in cost and a decrease in maintainability. In addition, an ultrasonic probe having a high frequency of oscillating ultrasonic waves of 15 MHz to 50 MHz generally has a small transducer size and lowers flaw detection efficiency. Therefore, it can be applied to online high-efficiency continuous flaw detection. It is difficult.

  In Patent Document 2, monitoring is started after a certain period of time has elapsed since the detection of a surface echo (a reflection echo on the ultrasonic incident surface of the flaw detection material), and a bottom echo (the incidence of ultrasonic waves on the flaw detection material is detected). Set the gate to stop monitoring after the scheduled time when the reflection echo on the surface (bottom surface) opposite to the side is detected, and move the ultrasonic probe relatively along the incident surface of the flaw detection material Until the first echo exceeding the threshold is first detected in the gate until the first echo is detected after the surface echo is detected. A method has been proposed in which the time is converted into distance information and a defect is detected from the amount of change in the distance information.

However, since the method described in Patent Document 2 determines the presence of a defect based on the distance information of the first echo exceeding the threshold value, the height of the defect is generally determined from the height of the defect echo (reflection echo from the defect). Unlike the method of determining the size, there is a problem that the size of the defect cannot be evaluated. Further, when flaw detection is performed on a pipe material or the like, a defect is detected from the amount of change in distance information from when the surface echo is detected until the first echo is detected, as in the method described in Patent Document 2. In the configuration, the height of the bottom surface echo varies greatly depending on the ellipticity of the cross section of the tube, eccentricity, thickness deviation, and insufficient follow-up performance of the ultrasonic probe, etc., which may cause false detection of defects. . More specifically, when the threshold value in the gate is made constant, the height of the bottom surface echo changes as described above, so that the position of the bottom surface echo exceeding the threshold value corresponds to one wavelength of the ultrasonic wave. Or, it may fluctuate before a plurality of wavelengths and may be erroneously recognized as a reflected echo from a minute defect present near the bottom surface even though no defect exists.
Japanese Patent Laid-Open No. 4-259853 JP 2003-302381 A

  The present invention has been made to solve such problems of the prior art, and provides an ultrasonic flaw detection method and apparatus capable of accurately detecting defects existing near the bottom surface of a flaw detection material. Is an issue.

  In order to solve the above-mentioned problems, the present invention, as claimed in claim 1, makes the ultrasonic wave oscillated from the broadband ultrasonic probe incident perpendicularly to the surface of the material to be inspected. An ultrasonic flaw detection method for detecting a defect existing in a flaw detection material by receiving a reflected echo from a flaw detection material with the broadband ultrasonic probe, which is received by the broadband ultrasonic probe Of the frequency components of the reflected echo, a predetermined cut-off frequency that is higher than the lower limit value of the frequency band of the ultrasonic wave oscillated by the broadband ultrasonic probe and lower than the center frequency is set to cut off the low frequency component. Then, the present invention provides an ultrasonic flaw detection method characterized by detecting a defect existing in a flaw detection material based on the reflected echo after the interruption.

  According to such invention, the frequency component of the reflected echo received by the broadband ultrasonic probe is higher than the lower limit value of the frequency band of the ultrasonic wave oscillated by the broadband ultrasonic probe and is higher than the center frequency. The lower cutoff frequency is set by setting a lower cutoff frequency, so compared to the case where no cutoff is made (the reflection of the same frequency band as that of the ultrasonic wave oscillated by the broadband ultrasonic probe). It is possible to increase the resolution of the reflected echo (compared to using echo). Therefore, since it becomes easy to distinguish between the reflected echo from the bottom surface of the flaw detection material and the reflection echo from the defect existing in the vicinity of the bottom surface, if a defect present in the flaw detection material is detected based on the reflected echo after the interruption, It is possible to accurately detect defects existing near the bottom surface of the flaw detection material.

  The “broadband ultrasonic probe” in the present invention is an ultrasonic probe having a wide frequency band of oscillating ultrasonic waves, and the frequency distribution of the oscillating ultrasonic waves is analyzed by frequency analysis (FFT or the like). It means an ultrasonic probe in which the ultrasonic energy decreases little over a wide frequency band when measured. For example, when a frequency range in which the energy of the oscillating ultrasonic wave is −6 dB (50%) or more from the maximum value is defined as a frequency band, the frequency band is in a range of about center frequency ± center frequency × 0.6. An ultrasonic probe having a distribution.

  Here, the higher the cutoff frequency, the better in terms of increasing the resolution of the reflected echo. On the other hand, when the cutoff frequency is increased too much, the amplitude (height) of the reflected echo is reduced and the sensitivity is lowered. As described above, the inventors of the present invention diligently studied from the viewpoints of both resolution and sensitivity, and cut to a value of about 80% of the center frequency of the ultrasonic wave oscillated by the broadband ultrasonic probe. It has been found that it is preferable to set the off frequency. Therefore, preferably, as described in claim 2 of the claims, the cut-off frequency is set to a value of 80% of the center frequency of the ultrasonic wave oscillated by the broadband ultrasonic probe.

  In order to solve the above-mentioned problem, the present invention provides a broadband ultrasonic probe arranged so that ultrasonic waves are incident perpendicularly to the surface of the material to be inspected, as claimed in claim 3. Of the frequency components of reflected echoes from the probe and the flaw detection material received by the broadband ultrasonic probe, higher than the lower limit value of the frequency band of the ultrasonic wave oscillated by the broadband ultrasonic probe In addition, a high-pass filter that cuts off low-frequency components by setting a predetermined cut-off frequency lower than the center frequency, and the amplitude of the output signal of the high-pass filter is compared with a predetermined threshold value, so that it exists in the material to be detected The present invention is also provided as an ultrasonic flaw detector comprising a defect detection circuit for detecting a defect to be detected.

  Preferably, as described in claim 4 of the present invention, the cutoff frequency of the high-pass filter is set to a value that is 80% of the center frequency of the ultrasonic wave oscillated by the broadband ultrasonic probe. .

  According to the ultrasonic flaw detection method and apparatus according to the present invention, it is possible to increase the resolution of the reflected echo from the flaw detection material, so that the reflection echo from the bottom surface of the flaw detection material and the reflection from the defect existing in the vicinity of the bottom surface. Echoes can be easily identified, and defects existing near the bottom surface of the flaw detection material can be detected with high accuracy.

  Hereinafter, an embodiment of an ultrasonic flaw detection method and apparatus according to the present invention will be described with reference to the accompanying drawings as appropriate.

  FIG. 1 is a block diagram showing a schematic configuration of an ultrasonic flaw detector according to an embodiment of the present invention. As shown in FIG. 1, an ultrasonic flaw detector 100 according to this embodiment includes a broadband ultrasonic probe (hereinafter referred to as “approx. (Abbreviated as “probe”) 1, a high-pass filter 2 that blocks a low-frequency component by setting a predetermined cut-off frequency for the reflected echo from the flaw detection material received by the probe 1, A defect detection circuit 3 is provided for detecting defects present in the material to be detected by comparing the amplitude of the output signal with a predetermined threshold value. Further, the ultrasonic flaw detection apparatus 100 according to this embodiment includes an oscillator 4 that supplies a pulse signal for oscillating ultrasonic waves from the probe 1, and a reflection echo received from the flaw detection material received by the probe 1. And a receiving amplifier 5 that amplifies and outputs to the high-pass filter 2.

  In the probe 1 according to this embodiment, the oscillating ultrasonic wave has a broadband frequency characteristic of 2 to 15 MHz. More specifically, the actual frequency band of the probe 1 (the band having ultrasonic energy of −6 dB or more with reference to the ultrasonic energy at the center frequency) is the center frequency ± center of the probe 1. Since the frequency is in the range of about 0.6, when the center frequency is 10 MHz, the band is about 4 to 16 MHz. In addition, the probe 1 according to the present embodiment suppresses the wave number of the oscillating ultrasonic wave to 1 to 1.5 waves by selecting the damper material and adjusting the waveform of the pulse signal supplied from the oscillator 4. The resolution is improved.

  When the surface of the flaw detection material has an arc shape like a tube, the ultrasonic wave oscillated from the vicinity of the end of the probe 1 is reflected from the surface of the flaw detection material and enters the flaw detection material. May happen. Therefore, when the surface of the flaw detection material has an arc shape, a convergent probe is used as the probe 1 so that ultrasonic waves oscillated from the vicinity of the end of the probe are also incident on the flaw detection material. It is preferable to make it. In particular, when the flaw detection material is a tube, it is preferable to use a so-called line focus type probe having a focal point along the tube axis direction.

  The high-pass filter 2 oscillates in the probe 1 out of the frequency components of the reflected echo (more specifically, the reflected echo after being amplified by the receiving amplifier 5) received from the flaw detection material received by the probe 1. A predetermined cutoff frequency that is higher than the lower limit value of the frequency band of the ultrasonic wave and lower than the center frequency is set to block low frequency components.

  The resolution of ultrasonic waves is about ½ of the wavelength. Therefore, for example, when the high-pass filter 2 is not provided as in the prior art, if the lower limit value of the frequency band of the ultrasonic wave oscillated by the probe 1 is 4 MHz, the velocity of the longitudinal ultrasonic wave propagating in the steel material is 5900 m. Therefore, the wavelength λ is λ = 5900 m / sec / 4 MHz = 1.48 mm, and the resolution is as large as about 0.79 mm. However, if the high-pass filter 2 is provided and the cut-off frequency is set to 8 MHz, for example, as in the ultrasonic flaw detector 100 according to the present embodiment, the longitudinal wave ultrasonic wave corresponding to the output signal transmitted through the high-pass filter 2 can be obtained. The wavelength λ is λ = 5900 m / sec / 8 MHz = 0.74 mm, and the resolution is as small as 0.37 mm. For this reason, even if a low-frequency component with a large resolution of the ultrasonic wave oscillated by the probe 1 reaches a defect and a reflected echo is generated, the high-pass filter 2 blocks the low-frequency component of the reflected echo. As a result, the resolution is improved as compared with the case where the high-pass filter 2 is not provided.

  FIG. 2 is a diagram schematically showing a schematic configuration of the high-pass filter 2 according to the present embodiment. As shown in FIG. 2, the high-pass filter 2 according to this embodiment includes a CR differentiating circuit including a capacitor C and a resistor R. 3 changes the cutoff frequency of the high-pass filter 2 by variously changing the capacitance of the capacitor C of the high-pass filter 2 shown in FIG. 2 (400 pF, 800 pF, 10000 pF), and the high-pass filter 2 of each condition has 1 to The result of having evaluated the ratio (output ratio) of the output voltage with respect to an input voltage by inputting each electric signal composed of a sine wave having a predetermined frequency in the range of 30 MHz. The vertical axis in FIG. 3 is plotted with the output ratio at the frequency at which the output ratio becomes the maximum value being 100% for each high-pass filter 2 under each condition. Also, the horizontal axis of FIG. 3 indicates the frequency of the electrical signal input to the high pass filter 2.

  As shown in FIG. 3, when the capacitance of the capacitor is 10,000 pF, the frequency band where the output ratio is 70% (−3 dB) or more is about 2.5 to 30 MHz, but in the case of 800 pF, the frequency band is about In the case of 5 to 30 MHz and 400 pF, the frequency is about 8 to 30 MHz, and it has been confirmed that the cutoff frequency of the high-pass filter 2 can be increased as the capacitance of the capacitor is reduced. Note that when a wideband type probe is used conventionally, the receiving amplifier 5 is also required to have a wideband characteristic. Therefore, in addition to a minute DC component and a zero point variation of the pulse signal supplied from the oscillator 4, The fluctuation of the DC component immediately after a large signal (reflection echo) is input remains and is output from the reception amplifier 5. In order to block these direct current components and low frequency components (low frequency components outside the frequency band of the ultrasonic wave oscillated by the broadband ultrasonic probe 1), which are noise factors, between the receiving amplifier 6 and the defect detection circuit 3. Is normally performed using a capacitor, and this corresponds to the case where the capacitor capacity is 10,000 pF. That is, when the capacitor capacity is 10,000 pF, it is equivalent to the conventional configuration in which the high-pass filter 2 is not provided.

  FIG. 4 shows a case where the cut-off frequency of the high-pass filter 2 is set to 2.5 MHz, 5 MHz, 8 MHz, 9 MHz, and 10 MHz, respectively, from the bottom surface of the flaw detection material (SUS304 stainless steel plate material) having a thickness of 8 mm by the water immersion method. The result of measuring the detection sensitivity (height of the reflected echo) of a flat bottom hole having a depth of 4 mm and a diameter of 1.6 mm is shown. The vertical axis in FIG. 4 means that the height of the reflected echo is lower as the dB value is larger. The horizontal axis of FIG. 4 shows the cut-off frequency of the high-pass filter 2 (the frequency on the low frequency side where the aforementioned output ratio is 70% (−3 dB)). The cutoff frequencies of 2.5 MHz, 5 MHz, 8 MHz, 9 MHz, and 10 MHz are 10000 pF (corresponding to the case where the high pass filter 2 is not provided), 800 pF, 400 pF, 200 pF, and 100 pF, respectively. Adjusted by changing.

  As shown in FIG. 4, when the cut-off frequency is 2.5 MHz, the frequency component corresponding to the low frequency region of the ultrasonic wave oscillated by the broadband ultrasonic probe 1 is included among the frequency components of the reflected echo. Since it was not blocked, the height of the reflected echo was 67 dB. However, as the cutoff frequency was increased, the height of the reflected echo was decreased (dB value was increased), and the sensitivity was lowered.

  The higher the cutoff frequency of the high-pass filter 2 is, the higher the resolution of the reflected echo is as described above. On the other hand, when the cutoff frequency is too high, the height of the reflected echo is lowered and the sensitivity is lowered as shown in FIG. Therefore, it is not preferable. Therefore, in consideration of both resolution and sensitivity, the cutoff frequency of the high-pass filter 2 is set to a value that is about 80% of the center frequency of the ultrasonic wave oscillated by the broadband ultrasonic probe 1 (the center frequency is 10 MHz). In this case, it is preferably set to 8 MHz).

  In the defect detection circuit 3, a gate having a predetermined time width is set in the output signal of the high-pass filter 2 described above and located between the surface echo and the bottom echo, and the output signal existing in the gate is set. If there is an output signal with an amplitude exceeding the threshold when the amplitude is compared with a predetermined threshold, it is assumed that there is a defect in the flaw detection material, and an alarm signal or flaw detection result is recorded. An analog signal is output to a recorder (not shown).

  As described above, the ultrasonic flaw detection apparatus 100 according to the present embodiment uses the high-pass filter 2 to determine the frequency of the ultrasonic wave oscillated by the probe 1 among the frequency components of the reflected echo received by the probe 1. Since the predetermined cutoff frequency that is higher than the lower limit value of the band and lower than the center frequency is set to cut off the low frequency component, it is possible to increase the resolution of the reflected echo from the flaw detection material. Accordingly, since the reflected echo from the bottom surface of the flaw detection material and the reflection echo from the defect existing near the bottom surface can be easily identified, the defect detection circuit 3 can detect the defect present in the flaw detection material based on the reflected echo after the interruption. , It is possible to accurately detect defects existing near the bottom surface of the flaw detection material.

  Hereinafter, the features of the present invention will be further clarified by showing examples and comparative examples.

<Example 1>
SUS304 stainless steel plate material (thickness 10 mm) provided with slit flaws with a depth of 0.25 mm from the bottom and a width of 2 mm and a length of 5 mm was used as the material to be inspected, and the center frequency was 10 to 16 MHz on the surface side. An ultrasonic probe having a broadband frequency characteristic of (actual frequency band) was arranged, and flaw detection was performed by allowing ultrasonic waves to be incident perpendicularly to the surface of the material to be inspected by a water immersion method. The cut-off frequency of the high pass filter was set to 8 MHz.

<Comparative Example 1>
Flaw detection was performed under the same conditions as in Example 1 except that the high-pass filter was not provided.

<Evaluation result 1>
FIG. 5A shows a waveform example of a reflected echo (bottom echo) from a healthy bottom surface without slit flaws in the first embodiment, and FIG. 5B shows a reflected echo from a slit flaw in the first embodiment ( An example of a waveform of (defect echo) is shown. As shown in FIG. 5, the defect echo in Example 1 was sufficiently separated from the bottom echo and had a sufficient amplitude (height), and could be detected with high accuracy. On the other hand, FIG. 6A shows a waveform example of a reflected echo (bottom echo) from a healthy bottom surface without slit flaws in the comparative example, and FIG. 6B shows a reflected echo from a slit flaw in the comparative example (bottom echoes). An example of a waveform of (defect echo) is shown. As shown in FIG. 6, the defect echo in the comparative example is not sufficiently separated from the bottom echo and does not have a sufficient amplitude (height), and the defect detection circuit gate and threshold value are set. It was difficult to detect.

  Furthermore, in the waveform shown in FIG. 6A, a waveform A having a large amplitude due to the low frequency component of the ultrasonic wave oscillated by the broadband ultrasonic probe is generated immediately before the bottom surface echo. In the waveform shown in FIG. 5A, a low-frequency component is blocked by the high-pass filter, so that a waveform having a large amplitude as in the waveform A is not generated. In this way, since the low-frequency component is blocked by the high-pass filter, a waveform having a large amplitude other than the defect echo does not occur between the surface echo and the bottom echo, so even if the defect exists near the bottom surface. However, it can be reliably detected by appropriately setting the gate and threshold value of the defect detection circuit.

<Example 2>
A pipe made of duplex stainless steel having an outer diameter of 140 mm and a wall thickness of 10.5 mm provided with slit flaws having a depth from the inner surface of 0.25 mm, a width of 1 mm, and a length of 5 mm is used as the flaw detection material. On the side, a line focus type ultrasonic probe having a center frequency of 10 MHz and a broadband frequency characteristic of 4 to 16 MHz (actual frequency band) and a focal position of 2 inches is disposed, and the outer surface of the material to be inspected is immersed by a water immersion method. Then, flaw detection was performed by vertically injecting ultrasonic waves. The cut-off frequency of the high pass filter was set to 8 MHz.

<Evaluation result 2>
FIG. 7A shows a waveform example of a reflected echo (bottom surface echo) from a sound inner surface without slit flaws in Example 2, and FIG. 7B shows a reflected echo from a slit flaw in Example 2 ( An example of a waveform of (defect echo) is shown. As shown in FIG. 7, even a defect echo from a slit flaw having a width smaller than that of Example 1 is sufficiently separated from the bottom echo and has a sufficient amplitude (height). It was possible to detect with high accuracy.

FIG. 1 is a block diagram showing a schematic configuration of an ultrasonic flaw detector according to an embodiment of the present invention. FIG. 2 is a diagram schematically showing a schematic configuration of the high-pass filter shown in FIG. FIG. 3 shows the results of evaluating the ratio of the output voltage to the input voltage (output ratio) when the capacitor capacity of the high-pass filter shown in FIG. 2 is variously changed. FIG. 4 shows the result of measuring the height of the reflected echo from the defect when the cutoff frequency of the high-pass filter shown in FIG. 1 is variously changed. FIG. 5A shows an example of a waveform of a reflected echo (bottom echo) from a sound bottom surface without slit flaws in the first embodiment of the present invention, and FIG. 5B shows a waveform from a slit flaw in the first embodiment. The example of a waveform of a reflective echo (defect echo) is shown. FIG. 6A shows an example of a waveform of a reflected echo (bottom echo) from a sound bottom surface without a slit flaw in the comparative example, and FIG. 6B shows a reflected echo (defective echo) from a slit flaw in the comparative example. ) Shows an example waveform. FIG. 7A shows an example of a waveform of a reflected echo (bottom echo) from a sound inner surface where no slit flaw exists in the second embodiment of the present invention, and FIG. 7B shows a waveform from a slit flaw in the second embodiment. The example of a waveform of a reflective echo (defect echo) is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Broadband type ultrasonic probe 2 ... High pass filter 3 ... Defect detection circuit 4 ... Oscillator 5 ... Reception amplifier 100 ... Ultrasonic flaw detector

Claims (4)

The ultrasonic wave oscillated from the broadband ultrasonic probe is vertically incident on the surface of the flaw detection material, and the reflected echo from the flaw detection material is received by the wide band ultrasonic probe, so that the inside of the flaw detection material An ultrasonic flaw detection method for detecting defects existing in
Of the frequency components of the reflected echo received by the broadband ultrasonic probe, a predetermined cut that is higher than the lower limit value of the frequency band of the ultrasonic wave oscillated by the broadband ultrasonic probe and lower than the center frequency An ultrasonic flaw detection method characterized in that an off-frequency is set to cut off a low-frequency component, and a defect existing in the flaw detection material is detected based on the reflected echo after the cut-off.   2. The ultrasonic flaw detection method according to claim 1, wherein the cutoff frequency is set to a value that is 80% of a center frequency of an ultrasonic wave oscillated by the broadband ultrasonic probe. A broadband ultrasonic probe arranged so that ultrasonic waves are incident perpendicularly to the surface of the flaw detection material;
Of the frequency components of the reflected echo from the flaw detection material received by the broadband ultrasonic probe, higher than the lower limit of the frequency band of the ultrasonic wave oscillated by the broadband ultrasonic probe and above the center frequency A high-pass filter that sets a predetermined low cutoff frequency and cuts off low-frequency components;
An ultrasonic flaw detection apparatus comprising: a defect detection circuit that detects a defect existing in a flaw detection material by comparing the amplitude of an output signal of the high-pass filter with a predetermined threshold value.   The ultrasonic flaw detector according to claim 3, wherein the cut-off frequency of the high-pass filter is set to a value that is 80% of the center frequency of the ultrasonic wave oscillated by the broadband ultrasonic probe.

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