JP5306919B2 - Ultrasonic flaw detection method and apparatus - Google Patents

Description

  The present invention relates to an ultrasonic flaw detection method and apparatus. More specifically, the present invention relates to an ultrasonic flaw detection method (short method) in which a longitudinal wave diffracted wave generated by incidence of ultrasonic waves on the wound tip using a bevel probe and a vertical probe is received on the shortest path. The present invention relates to an improvement in the path diffracted wave method (Short Path of Diffraction).

  The present inventors have previously developed a simple and highly accurate SPOD method using vertical and oblique probes for transmission and reception as a crack depth measurement method in an ultrasonic flaw detection test. In flaw detection, it was confirmed that the crack depth can be measured with high accuracy (see Patent Document 1).

  This SPOD method is a method in which an ultrasonic wave is incident on an inspection object obliquely by an oblique probe, and a longitudinal wave diffracted wave generated at the edge of the wound is received by a vertical probe directly above the wound. The flaw height is obtained from the arrival time difference between the diffracted wave directly from the edge of the flaw toward the vertical probe and the diffracted wave once reflected toward the bottom surface. According to this SPOD method, since the path of the ultrasonic beam is short, it can be used for stainless steel and Inconel (registered trademark of Special Metals Corporation) with large crystal grains and large ultrasonic attenuation. The height of the flaw can be measured easily and with high accuracy. Moreover, not only the arrival time difference between the direct wave and the indirect wave of the diffracted wave generated at the edge of the scratch, but the height of the edge can be easily calculated and the height of the scratch can be calculated easily. This is a promising flaw detection method because it has various advantages such as accurate measurement without experience and skill.

International Publication WO2007 / 004303

  However, according to the conventional SPOD method, the sensitivity is good at a point where the beam center axis of the oblique angle probe and the beam center axis of the vertical probe intersect (referred to as an intersection point in this specification). However, there is a problem that the intensity of the echo corresponding to the reflector / scratch decreases as the reflector / scratch deviates from the intersection. For example, when focusing on the periphery of the back opening, the sensitivity is good for a shallow slit, but the deep slit has a problem that the echo intensity is greatly attenuated and the sensitivity is deteriorated. For this reason, the crack tip to be detected in the full-thickness volume inspection in the thick inspection object may be missed depending on the position in the thickness direction. Therefore, in order to apply to an actual machine, it is desirable that the detection sensitivity does not change so much in the thickness direction of the inspection object, that is, the detection sensitivity does not decrease.

  On the other hand, in order to apply the ultrasonic flaw detection method to a full-thickness volume inspection, it is necessary to detect the tip regardless of the crack tip position in the thickness direction of the inspection object. For this reason, when the conventional SPOD method is applied to the full-thickness volume inspection, a considerable amount of the probe is required so that the intersection point coincides with the reflection position (scratch position / reflector position). Since recombination is required, a plurality of mechanical scans with different probe intervals and refraction angles are required, but such inspection procedures are impractical for nondestructive inspection of actual machines. For this reason, the echo intensity obtained by the SPOD method greatly depends on the depth of the flaw, and the echo intensity greatly decreases as the flaw becomes deeper. Then, it is difficult to apply the conventional SPOD method when it is unclear where and how deep there is a flaw. In addition, vertical flaw detection cannot detect a flaw at the tip of a vertical fatigue crack.

  In addition, the opening crack or internal crack generated in the main pipe of the actual machine does not necessarily propagate perpendicularly to the inner surface of the pipe, but the strength of the end echo required for crack depth measurement due to the crack inclination. Changes greatly. For example, according to the experiments by the present inventors, when measuring the depth of a crack tilted by the conventional oblique flaw detection method, the surface of the crack reflected from the surface of the crack as a tilt crack with a tilt angle of 50 °. When the angle formed by the central axis of the sound wave approaches 90 °, there is a problem that specular reflection at the crack surface becomes remarkable and the end echo and the opening echo cannot be separated. Furthermore, it is considered that this kind of crack depth measurement also has an influence of ultrasonic frequency. However, conventionally, it has not been clarified whether the SPOD method can be applied to the measurement of the depth of an inclined crack, and whether it has an advantage over other measurement methods. It was difficult to determine whether to apply the SPOD method in a state in which the situation was unknown.

  The present invention is a method for suppressing a difference in detection sensitivity in the thickness direction of an inspection object in the SPOD method, that is, a method for reducing sensitivity reduction in the thickness direction as much as possible and enabling detection with substantially the same sensitivity even when the depth changes. The purpose is to provide. Another object of the present invention is to provide a method that can reliably detect an echo corresponding to a crack tip in the SPOD method regardless of the magnitude of the frequency and the presence or absence of a crack inclination.

  In order to achieve this object, the ultrasonic flaw detection method according to the first aspect of the present invention uses a phased array, performs vertical transmission with some vibration elements of the phased array, and performs oblique transmission with some vibration element groups. The range in which the facet array is installed is divided into a mesh shape within the range where the faced array is installed, and at least in each of the sections within the range of the ultrasonic beam for vertical transmission, the plurality of vibration elements are oblique. Aperture synthesis processing for adding the A-scope waveform signal received at the angle is performed over the entire imaging range by performing electronic scanning with the interval between the transmitting and receiving vibration elements kept constant, and synthesized by the aperture synthesis processing. An arbitrary object to be inspected can be obtained by performing luminance modulation processing for converting the amplitude value of the A scope waveform at the position of each section into a luminance value and displaying it on the corresponding pixel of the image display means. And so as to construct a B-scope image of the surface.

  According to a second aspect of the present invention, in the ultrasonic flaw detection method according to the first aspect, a receiving vibration element group that performs oblique reception is disposed on both sides of a transmitting vibration element that performs vertical transmission. Yes.

  Further, the transmission vibration element and the reception vibration element group may be adjacent to each other, and in some cases, the transmission vibration element may be included in a part of the reception vibrator. It is preferable that a gap of at least one element is disposed between the receiving vibration element group.

  Furthermore, an ultrasonic flaw detection apparatus according to a fourth aspect of the invention includes a phased array in which a plurality of small vibration elements are arranged in a line, and a part of vibration elements of the phased array performs vertical transmission and a part of vibration. The element group performs oblique angle reception, and the range in which the specimen is imaged is divided into a mesh shape within the range where the faced array is installed, and at least for each division within the range of the ultrasonic beam for vertical transmission A control device for receiving an A scope waveform signal at an oblique angle by a plurality of the vibration elements and performing electronic scanning over the entire imaging range with a constant interval between the transmission / reception vibration elements, and for each position of each section An aperture synthesis process is performed in which the A scope waveform signals received at an oblique angle by a plurality of the vibration elements are added so that the waveforms overlap each other, and at the position of each section synthesized by the aperture synthesis process. An imaging processing apparatus for constructing a B-scope image of an arbitrary cross section to be inspected by performing luminance modulation processing for converting the amplitude value of the A-scope waveform into a luminance value and displaying it on a corresponding pixel of the image display means; I am doing so.

  According to a fifth aspect of the present invention, in the ultrasonic flaw detector according to the fourth aspect of the present invention, reception vibration element groups that perform oblique reception are arranged on both sides of a transmission vibration element that performs vertical transmission. is there.

  Furthermore, in the ultrasonic flaw detector of the present invention, the transmitting vibration element and the receiving vibration element group may be adjacent to each other, and in some cases, the transmitting vibration element is included in a part of the receiving vibrator. However, it is preferable that a gap of at least one element is disposed between the transmitting vibration element and the receiving vibration element group. .

  According to the ultrasonic flaw detection method and the ultrasonic flaw detection apparatus according to claim 1 and 4, electronic scanning is performed while changing the focal position of the oblique reception beam in the depth direction of the specimen at least within the range of the ultrasonic beam for vertical transmission. As a result, the same waveform as the SPOD method is obtained, and the distance amplitude characteristic is corrected by aperture synthesis processing to this waveform, thereby acquiring the luminance of each pixel in the cross-sectional image construction region and constructing the B scope image of the SPOD method. As a result, the B scope image in the flaw detection range can be efficiently constructed by the SPOD method, and the echo intensity can be received strongly without depending on the slit depth. As shown in FIG. A difference in detection sensitivity in the thickness direction of the inspection object can be suppressed, and a decrease in sensitivity in the thickness direction can be reduced. In addition, it is possible to find the tip of a crack that is difficult to find with efficient signal processing of the received waveform. Therefore, it can be applied to the volume inspection of the total thickness of the thick structure and can be inspected with higher sensitivity than the conventional SPOD method. Here, flaws and defects to be inspected are scratches such as cracks opening on the back surface (or inner surface) opposite to the surface on which the probe of the specimen is installed, or closed scratches. Needless to say, it is not limited to obtaining a B-scope image, and it is also possible to obtain the tip of an opening scratch (a crack that opens toward the surface side where the probe is placed and progresses toward the back surface side). Furthermore, closed flaws near the surface layer can be clearly imaged as B-scope images.

  In addition, it meets the flaw detection conditions because electronic scanning is performed with a constant interval between the transmitting and receiving elements while receiving oblique angles with multiple vibrating elements in the depth direction of the specimen within at least the ultrasonic beam range of vertical transmission. The incident ultrasonic beam is incident and there is no fear of missing a flaw. Therefore, the SPOD method of the present invention can be applied to an inspection object / test body in which it is unknown where and how deep there is a flaw.

  Further, the inventors' experiments have revealed that the measurement of the depth of an inclined crack has an advantage over the case of the oblique flaw detection method. It was confirmed that the echo corresponding to the crack tip could be reliably detected regardless of the magnitude of the frequency and the presence or absence of the crack slope.

  Further, according to the ultrasonic flaw detection method and apparatus according to claims 2 and 5, since the receiving element is provided on both sides of the transmitting element, a symmetrical instruction overlap occurs, noise is canceled, and the end echo is Since the S / N ratio is improved and the instructions that appear obliquely for the reception of the oblique angle overlap and the overlapping portions are in phase, the instructions are symmetric, and although the vertical inspection is not vertical inspection, A similar image closer to the actual reflector can be obtained.

  Furthermore, according to the ultrasonic flaw detection method and apparatus according to claims 3 and 6, since there is a gap / non-operating vibration element between the transmitting element and the receiving element, geometrically vertical and oblique angles are effective. Is established. If the distance between the transmitting vibrating element and the receiving vibrating element and the number of non-operating vibrating elements are appropriate, the SPOD method is effective.

It is a principle figure of the ultrasonic flaw detection method concerning this invention. It is a top view which shows embodiment of arrangement | positioning of a transmission / reception element, (A) shows the example of 1 transmission element, (B) shows the example of multiple transmission element. It is a block diagram which shows the basic composition of the ultrasonic flaw detector concerning this invention. The cross-sectional image with respect to a crack defect is shown, (A) is a cross-sectional image with respect to the crack-like defect obtained from the calculation result by the simulation method developed by the present inventors, and (B) is an experiment of the crack-like defect. A cross-sectional image based on the results, (C) is a principle diagram showing the SPOD method. It is a graph which shows the result of having compared the edge part echo intensity by the conventional SPOD method and the ultrasonic flaw detection method of this invention. It was confirmed that the tip of a fatigue crack (maximum depth of 12 mm) in a stainless steel block with a thickness of 38 mm that cannot be detected by vertical flaw detection using a general phased array flaw detector can be detected by the ultrasonic flaw detection method of the present invention. (A) is a schematic diagram showing a measurement system, and (B) is a B scope image showing measurement results. It is explanatory drawing which shows the propagation path of the ultrasonic wave in the conventional SPOD method. It is explanatory drawing which shows the determination of the propagation path between two points. It is explanatory drawing which shows the propagation path containing many reflections. It is a figure explaining the reciprocal relationship of an angle probe, (A) shows a transmission state, (B) shows a reception state. It is explanatory drawing of the diffraction in a slit front-end | tip. It is a figure explaining the real propagation path and virtual propagation path in using reciprocity theorem. It is a figure which shows the slit shape of the test body used in the experiment for verifying the simulation method which the present inventors developed, (A) is several depths to the test body of thickness 25mm, width 40mm, and length 250mm. (B) shows a sample having a thickness of 25 mm, a width of 40 mm, and a length of 300 mm, in which cracks of several inclination angles are formed. It is explanatory drawing which shows the mechanical scanning direction of a probe. Experimental results showing the frequency-of _{L 1} and _{L 2} echo for different depths slit, (A) is a 2MHz, (B) is 5 MHz. The relationship between the L ₁ echo intensity and the cross axis position (intersection position of the central axis of the ultrasonic beam for vertical transmission and the central axis of the ultrasonic beam for oblique reception) obtained from the experimental results at a frequency of 5 MHz is shown. It is a graph. In the simulation calculation results showing a _{L 1} and _{L 2} echo for different slit depths, (A) is a 2MHz, (B) is 5 MHz. Obtained by simulation over configuration calculation results in the frequency 5 MHz, the L ₁ echo strength and transverse position (intersection of the central axis of the ultrasonic beam central axis and the oblique angle reception of the ultrasonic beam in the vertical transmission) It is a graph which shows a relationship. It is a B-scope image of the slit which was obtained by the experimental result in frequency 5MHz, and was inclined by the longitudinal wave oblique-angle flaw detection. It is a B-scope image of the slit by the SPOD method obtained by the experimental result in frequency 5MHz. It is a B-scope image of the slit which inclined by the SPOD method obtained by the simulation calculation result in frequency 5MHz. It is a B-scope image of the slit by the SPOD method (refraction angle 30 degree) obtained by the simulation calculation result in frequency 5MHz. It is a figure explaining the aperture synthetic | combination process with respect to the conventional SPOD method, (A) shows a scanning state, (B) shows before and after composition of A scope waveform. B scope images before and after aperture synthesis processing, (A) at 2 MHz and (B) at 5 MHz. Is a graph showing changes in L ₁ echo intensities before and after the aperture synthesis processing. It is explanatory drawing which shows the calculation model used for the simulation method which the present inventors developed. It is a graph showing the relationship between the slit depth and intensity of the L ₁ echo and end echo before and after the aperture synthesis processing. It is a perspective view explaining the test body which has a fatigue crack. Obtained by the transmission and reception patterns of FIG. 2 (A), a B-scope image showing the L ₁ and L ₂ echo for different slit depths. Is a graph showing changes in L ₁ echo intensity for slit depth in the case of using the phased array technique. The B scope image with respect to a fatigue crack is shown, (A) and (B) were obtained by the transmission / reception pattern of FIG. 2 (A), (C) was obtained by the transmission / reception pattern of FIG. 2 (B). Is.

  Hereinafter, the configuration of the present invention will be described in detail based on embodiments shown in the drawings.

  1 and 2 show an embodiment of an ultrasonic flaw detection method according to the present invention. This ultrasonic flaw detection method uses a phased array 1, performs vertical transmission with some vibration elements of the phased array 1 and receives oblique angles with some vibration element groups, and a range in which the faced array 1 is installed Then, an echo 3r, that is, an A scope waveform signal received at an oblique angle by a plurality of vibration elements 1r for each of the sections 2 within the range of the ultrasonic beam 3t for vertical transmission at least in the range 20 to be imaged of the specimen. The aperture synthesis process for adding is performed electronically with the interval between the transmitting and receiving vibration elements 1t and 1r being kept constant, so that the entire area of the imaging range 20 is overlapped and synthesized by the aperture synthesis process. A luminance modulation process for converting the amplitude value of the A scope waveform at the position of each section 2 into a luminance value is performed and displayed on the corresponding pixel of the image display means, whereby the B cross section of an arbitrary cross section to be inspected is displayed. So that to construct the-loop image. That is, the luminance of each pixel of the B scope image is acquired by the aperture synthesis process. In the specification, the transmission vibrator is referred to as a transmission vibration element 1t, and the reception vibrator is referred to as a reception vibration element 1r. The inactive vibrating element 1g forms a gap between the transmitting / receiving vibrating elements 1t and 1r.

  FIG. 3 shows an embodiment of an apparatus for performing the above-described ultrasonic flaw detection method. This ultrasonic flaw detector has a phased array 1 in which a plurality of small vibration elements (hereinafter, simply referred to as elements) are arranged in a line, and causes a part of the vibration elements of the phased array 1 to perform vertical transmission and perform vertical transmission. The range in which the test piece is imaged within the range where the faced array 1 is installed is divided into a mesh shape within at least the range of the ultrasonic beam for vertical transmission. A control device 4 that receives an A-scope waveform signal at an oblique angle with a plurality of vibration elements for each section and performs electronic scanning over the entire imaging range while maintaining a constant interval between the transmission and reception vibration elements, and the position of each section Aperture synthesis processing is performed in which the A scope waveform signals received at an oblique angle by a plurality of vibration elements are added so that the waveforms overlap each other, and the A scope waveform at each position synthesized by aperture synthesis processing is modulated. An imaging processing device 5 for constructing a B-scope image of an arbitrary cross section to be inspected by performing luminance modulation processing for converting a value into a luminance value and displaying it on a corresponding pixel of the image display means 7, and having reciprocity SPOD method while changing the intersection (focal point) position of the vertical transmission beam and the oblique reception beam in the depth direction of the specimen by changing the refraction angle of the oblique probe and the distance between the incident points using electronic scanning By obtaining the same waveform and correcting the distance amplitude characteristics by aperture synthesis processing to this waveform, the brightness of each pixel in the cross-sectional image construction region is acquired and a B scope image is constructed.

  The ultrasonic flaw detector 10, for example, performs aperture synthesis on a control device (transmission / reception circuit) 4 connected to the phased array 1 via a connector 9 and an A scope waveform signal received at an oblique angle by a plurality of receiving transducers 1 r. The image processing apparatus 5 that performs the image composition processing for generating the B scope image after performing the processing, and the necessary software such as system software and UI software for executing the predetermined processing are stored in the ROM or other storage means. The central processing unit 6 and the touch panel display 7 are controlled. The control device 4 serving as a transmission / reception circuit includes a transmission / reception switching circuit 11, a transmission circuit 12, a reception amplifier 14, and a transmission / reception control circuit 13. The transmission / reception control circuit 13 causes the transmission / reception switching circuit 11, the transmission circuit 12, and the reception amplifier 14 to be connected. It is controlled. The A scope signal received by each receiving element 1r at the position of each section 2 of the imaging range 20 of the test body partitioned and coordinated in a mesh shape is an A / D conversion circuit of the imaging processing device 5. 15 is input to the parallel arithmetic circuit 16, and after performing aperture synthesis processing, image synthesis processing for generating a B scope image is performed. Reference numeral 8 in the figure denotes a bus.

  Here, the control device 4 individually controls the delay time of the pulse voltage applied to each oscillating element of the phased array 1 so as to easily control focusing and deflection of the ultrasonic beam, and a part of the phased array 1. By transmitting a plurality of vibration elements 1r at least for each section 2 within the range of the ultrasonic beam 3t for vertical transmission. Control is performed so that 3r (A scope waveform signal) is received at an oblique angle and electronic scanning is performed over the entire imaging range with the interval between the transmitting and receiving vibration elements 1t and 1r being kept constant. As a result, overlapping of the ultrasonic beams 3t for vertical transmission occurs, and vertical transmission and oblique angle reception are repeated for the same section 2. In general, the transmission / reception control circuit 13 of the control device 4 has the focal point coincident with the arbitrary section 2 with respect to the group of the plurality of receiving vibration elements 1r of the phased array 1 according to the delay time pattern obtained in advance. Control to do. For example, the faced array 1 is placed on a specimen, the flaw detection range 20 is divided into a mesh shape within the set range, and coordinates are set. Each coordinate (each section) and each oblique angle receiving vibration element 1r are set. The delay time pattern for focusing on each section is obtained and stored from the geometrical positional relationship with. That is, if the coordinates of the points of each section 2 are determined, the above-described geometric relationship is determined. In addition, since the position of the phased array 1 is recorded simultaneously by an encoder (not shown), the coordinates of each of the sections 2 can be recognized as being on one coordinate axis. For this reason, even if the flaw detection range 20 is moved by mechanically scanning the installation position of the phased array 1, the coordinates of the respective sections 2 can be matched. Therefore, oblique angle reception is performed in all thickness directions by the plurality of receiving vibration elements 1r at the position of each section 2 within the range of the spread of the vertical beam 3t, that is, the position corresponding to the pixels constituting the B scope image. (In other words, aperture synthesis) is repeated each time the active vibration elements 1t and 1r are shifted by one element in the scanning direction (length direction of the faced array) while maintaining the distance therebetween. The A scope waveform is redundantly acquired for each of the sections 2. The A scope waveform signal received by each receiving vibration element 1r is input to the imaging processing device 5 and converted into a digital signal by the A / D circuit 15 of the device, and then a memory (not shown) for each section 2 or the like. Are sequentially stored in the storage means.

  Note that even if the oblique angle reception and thus the aperture synthesis process is performed on a region 2 where there is no energy, that is, the section 2 outside the range of the ultrasonic beam 3t for vertical transmission, there is no effect of aperture synthesis, and processing time is wasted. Therefore, in consideration of the spread of sound (directivity), oblique angle reception and aperture synthesis are performed focusing on the section 2 within the range of the vertical transmission beam. Since how the beam spreads (directivity) can be easily predicted based on the size and frequency of the vibrator, the range in which aperture synthesis is performed can be determined in consideration of the expected beam spreading method. In the present invention, while vertical transmission is performed using some elements of the element group of the phased array 1, oblique reception is performed using some elements, but the measurement system is linear. If present, due to reciprocity, the same waveform as the short path diffracted wave method (SPOD method) in which a longitudinal wave diffracted wave generated by incident ultrasonic waves on the wound tip is received through the shortest path can be obtained.

  In the case of the phased array of the present embodiment, a non-operating vibration element 1g is provided between the transmission vibration element 1t and the reception vibration element 1r, and the transmission vibration element 1t and the reception vibration element 1r are provided. A certain interval (non-operating area) is provided. In this case, the oblique flaw detection can be realized easily and reliably because the receiving vibration element 1r is separated from the transmission vibration element 1t even at a deep point in the flaw detection area. In order to achieve geometrical vertical transmission and oblique angle reception, it is simple and effective to provide a non-operating region that becomes a gap between the transmitting vibration element 1t and the receiving vibration element 1r. The larger the distance between the element 1t and the receiving vibration element 1r, the better the effect of the SPOD method. Here, increasing the number of transmitting vibration elements 1t, that is, increasing the size of the transmitting vibrator 1t increases the S / N ratio so that a weak instruction such as an instruction of the tip of a fatigue crack can be identified. This is one of the effective means for improving. For example, an indication of the tip of a fatigue crack that could not be observed by vertical flaw detection using a conventional phased array probe can be identified by increasing the number of transmitting vibration elements 1t. Note that the number of vibration elements 1g in the non-operating region depends on the thickness of the specimen, and the number of elements is appropriately set. In the case of this embodiment, when the number of elements of the phased array probe to be used is 64, for example, as shown in FIG. 2, the receiving vibration element 1r group has 10 elements and the transmission vibration element 1t has 1 to 9 vibration elements. The number of elements in the non-operating area is set to 1 to 5, and the receiving vibration element 1r group is arranged for each 10 elements with the non-operating area interposed on both sides of the transmitting vibration element 1t. However, the non-operating region between the transmitting vibration element 1t and the receiving vibration element 1r is not necessarily provided, and the group of the transmitting vibration element 1t and the receiving vibration element 1r may be adjacent to each other. Depending on the case, the transmitting vibration element 1t may be included so as to overlap the group of the receiving vibrator 1r.

  In addition, it is preferable to arrange a group of receiving vibration elements 1r that perform oblique reception on both sides of the transmitting vibration element 1t that performs vertical transmission. In this case, the S / N ratio of the end echo L1 is improved, and as shown in FIG. 4B, an instruction that is close to a point is obtained due to the overlapping of symmetrical instructions. However, in some cases, reception may be performed in which the receiving vibration element 1r group is disposed only on one side. In this case, since there is no overlapping of symmetrical instructions, as shown in FIG. 4 (A), the instruction includes an oblique line, but it still cannot detect the presence and position of a flaw. is not.

  The imaging processing device 5 performs aperture synthesis processing for adding the A scope waveform signals received at an oblique angle by the plurality of vibration elements 1r for each position of each section 2 so that the waveforms overlap each other, and each synthesized by aperture synthesis processing A B-scope image of an arbitrary cross section to be inspected is constructed by performing luminance modulation processing for converting the amplitude value of the A scope waveform at the position of the section 2 into a luminance value and displaying it on the corresponding pixel of the image display means. .

  In the aperture synthesis process, the parallel arithmetic circuit 16 extracts the amplitude value of the flight time in each beam path from the waveform data for each receiving vibration element 1r, and adds it to the image memory corresponding to the section 2 of the flaw detection range. The same processing is applied to the waveform data obtained by the other receiving vibration element 1r, and the peak values of many reflected waveforms are added in the same phase, thereby relatively increasing the signal intensity. As a result, if there is a flaw in the section 2, the waveforms are added to increase the amplitude value of the waveform, and if there is no flaw, the waveforms are not added, so the amplitude does not change. That is, the peak values of a large number of reflected waveforms from the defect are added in the same phase, and a clear defect image / pixel is obtained by luminance modulation processing. In the background image in which no flaw exists, since the waveform to be added does not exist, the amplification of the waveform value does not occur, and the background level is relatively reduced. Therefore, a clear B-scope image is synthesized by performing these processes on all meshes in the imaging process area.

  Here, since the wave exiting the transmitting vibration element 1t spreads and propagates in the test body, the energy becomes weaker as it deviates from the central axis of the ultrasonic beam. Therefore, the delay of the received signal and the attenuation of the energy intensity become more prominent as the position of the scratch / reflector is located far from the position directly below the transmitting / receiving vibration element 1r. However, since the vertical transmission position is shifted by one element by electronic scanning and the oblique transmission is repeated throughout the range of the ultrasonic transmission beam 3t in the vertical direction, the aperture synthesis for the same section 2 is repeated. Repetition of the process further amplifies the received signal with the waveform, while the received signal without the waveform (background image without flaws) does not change, so the echo indicating that the background level has not been reduced relatively Make the strength clear. This is effective when detecting a flaw or the like at a deep position in a thick inspection object. When a small transducer is used, the spread of the ultrasonic beam for vertical transmission becomes larger, and at the bottom side, the attenuation of energy increases and the attenuation of echoes also increases, resulting in poor sensitivity. However, the bottom side where the spread of the ultrasonic beam 3t becomes larger, the repetition of the aperture synthesis process for the same section 2 increases, and the received signal having a waveform is amplified, and the echo intensity is attenuated by reducing the relative background level. Can be made clear. In addition, the aperture synthesis process has an effect of correcting the spread of instructions due to the diffusion of ultrasonic waves. On the other hand, since a strong signal is originally obtained on the surface side of the test body where the spread of the ultrasonic beam 3t is small, it is not necessary to repeat aperture synthesis. Of course, when enlarging the size of the transducer and increasing the energy of the ultrasonic beam for vertical transmission, the beam spread is reduced due to the high directivity of the beam, but directly under the transmitting vibration element 1t (vertical transmission). If a reflector such as a flaw or crack exists on the center axis of the ultrasonic beam, a strong received signal and A scope waveform signal are acquired, so the echo from the flaw on the bottom side is attenuated. Even if it does not, the signal strength is not greatly impaired.

The B (brighthess) scope image performs luminance modulation that converts the amplitude of the reflected wave into brightness intensity on the time axis, and further scans the probe to draw the probe position information and the time-luminance signal in two dimensions. Then, a tomographic image of an arbitrary cross section to be inspected is displayed. Specifically, a value corresponding to the beam path of the point on the waveform synthesized by the aperture synthesis process is stored in the memory as a pixel value, that is, a luminance at each recording point. Based on the luminance at each pixel, a B scope image is created and displayed on the display device. This process is performed for each data recording point (corresponding to a pixel) in the B scope image (the luminance of each pixel is acquired by the aperture synthesis process). In this embodiment, the A scope waveform affected by a certain point on the B scope image is extracted based on the half-value width of the directivity of the probe.
That is, the B scope image is constructed by acquiring the luminance of each pixel in the cross-sectional image construction region.

  The above-described embodiment is an example of a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the gist of the present invention. For example, in the present embodiment, the case of obtaining a B-scope image of a crack such as a crack opened on the back surface (or the inner surface) opposite to the surface on which the probe is installed or a closed wound is mainly obtained. Although explained, it is needless to say that it can also be applied to the case of finding the tip of an opening flaw (a crack that opens on the surface side where the probe is placed and progresses toward the back surface side). Close flaws can be clearly imaged as B-scope images. In addition, although the region of the non-operating element 1g is provided between the vertical transmission vibration element 1t and the oblique reception vibration element 1r, the non-operational area may not be provided depending on circumstances.

  Furthermore, in this embodiment, the oblique angle reception and the aperture synthesis processing are performed on each section 2 within the range of the vertical transmission ultrasonic beam 3t. Scanning is performed by performing electronic control so that the intersection (intersection axis point) between the central axis of 3t and the central axis of the oblique angle receiving ultrasonic beam 3r is on each section partitioned in a mesh shape. Also good. Also in this case, if there is a reflector such as a flaw directly under the vertical transmission vibrating element 1t, the oblique reception signal becomes strong. The effect of suppressing the echo intensity reduction is comparable to that of the above-described embodiment.

  In the ultrasonic flaw detection apparatus and flaw detection method according to the SPOD method of the present invention configured as described above, the difference in detection sensitivity in the thickness direction of the inspection object is suppressed, that is, the decrease in sensitivity in the thickness direction is reduced. This was confirmed by simulation. Moreover, it was confirmed that the echo corresponding to the crack tip can be reliably detected in the SPOD method of the present invention regardless of the magnitude of the frequency and the presence or absence of the inclination of the scratch.

  First, the simulation method will be described. The amplitude and propagation direction of the ultrasonic waves radiated from the probe change due to refraction when passing through the flaw detection surface, reflection at the crack surface and the bottom of the specimen, and diffraction at the crack tip. In addition, since mode conversion occurs in each process, there are an infinite number of propagation paths.

Here, the SPOD method is a method in which a longitudinal wave diffracted wave generated by obliquely entering an ultrasonic wave into a crack is received directly above the crack using an oblique probe. Therefore, among the infinite number of propagation paths, the propagation paths that contribute to the received waveform of the SPOD method are limited to the six ways shown in FIG. A solid line in the figure indicates a longitudinal wave, and a broken line indicates a transverse wave. As an example, L2 ′ represents a propagation path in which a longitudinal wave incident on a specimen is mode-converted into a transverse wave at the tip of a crack-like defect and then converted into a longitudinal wave at the bottom and received. The propagation path was determined according to Fermat's principle. Now, considering the case where the propagation path between the point 0 of the medium 1 and the point F of the medium 2 is determined as shown in FIG.
Since the above equation is non-linear, it is necessary to determine the angle by successive approximation or the like. In this embodiment, the Newton-Raphson method is used. Differentiating Equation 1 yields Equation 2 below.
By applying successive approximation to the above equation so that δx = 0, θ0 and θ1 can be calculated.

Next, a method for calculating the received waveform will be described. In this experiment, assuming that the specimen is a flat plate and there is a slit simulating a crack-like defect in the far field of the oblique probe, geometrical optical diffraction theory (waves such as electromagnetic waves and light) are assumed. Geometrical Theory of Diffraction (GTD) that can be applied more generally by combining geometrical optics that handles the propagation of light geometrically with rays and wavefronts, and diffraction theory at the tip of crack-like defects, etc. A method of calculating a received waveform based on the above will be described.
First, an equation for obtaining changes in the amplitude and phase of ultrasonic waves due to repeated refraction and reflection at the boundary surface will be described. Next, the far field of the oblique probe is shown, and the diffraction at the slit tip inside the solid is also shown. Finally, a calculation formula for obtaining the received waveform is derived using these relationships.

(Change in amplitude and phase due to refraction and reflection)
When there is no attenuation due to the material of the specimen, the amplitude of the ultrasonic wave radiated from the point sound source is attenuated in inverse proportion to the distance according to the energy conservation law. FIG. 9 shows an acoustic ray of an ultrasonic wave that is incident on the test body starting from a point sound source and propagates by being repeatedly reflected n times on the upper and lower boundary surfaces of the test body. The change in amplitude and phase in this case can be expressed by the following Equation 3.
However,
It is. Here, i represents an imaginary unit, un and un are amplitudes of displacement speeds and displacement speed vectors, and dn is a unit vector representing a vibration direction. Rp, θp, cp, and kp represent the length, refraction angle or reflection angle, sound speed, and wave number, respectively, of the p-th acoustic line segment. Further, t _p-1 and p indicate the transmittance or reflectance between the sound ray segments p-1 and p.

(Long-distance sound field of an oblique probe)
The sound field generated by the oblique probe uses the Reciprocity Theorem to calculate the signal when using the oblique probe (Kotaro Mano, theory of ultrasonic propagation inside a solid) And application to ultrasonic flaw detection, Railway Technology Research Report, No. 276, 1962.). The acoustic impedance of the wedge made of resin is small compared to the piezoelectric ceramic that is the vibrator, so the vibrator surface performs a piston motion like a rigid body at the time of transmission, and almost reflects the incident wave in a state of being stationary at the time of reception. You can think of it. Therefore, the displacement speed of the vibrator surface can be expressed by the following formula 6.
Here, u0 and u0 ′ represent the displacement velocity vector of the transducer surface in the transmission process and the reception process, respectively, and u0 represents the amplitude of the displacement velocity. n is a unit normal vector of the transducer surface, and it is assumed that the entire transducer vibrates with a constant amplitude u0 in the normal direction.
A transmission process and a reception process are shown in FIG. Point Fn is an arbitrary point in the specimen. In the transmission process, the vibrator moves as a piston, and ultrasonic waves are radiated to the test body and enter the point Fn after being reflected several times. On the other hand, in the reception process, the point Fn becomes a virtual point sound source, and ultrasonic waves are radiated into the wedge through several reflections. Since a reciprocal relationship is established between these two processes, the amplitude un of the ultrasonic displacement speed at the point Fn radiated from the oblique probe can be obtained by the following formula 7 using the above formula 6.
Here, ρ represents the density of the specimen, t0 and t0 ′ represent surface forces generated on the transducer surface in the transmission process and the reception process, respectively, and S represents the transducer surface. t0'n represents a component perpendicular to the transducer surface of the surface force generated on the transducer surface completely stationary by the ultrasonic wave radiated from the point sound source, and is expressed by the following Equation 8.
Here, ω is the angular frequency, θ0 is the refraction angle when the ultrasonic wave is incident on the wedge from the point sound source, ξ and ζ are the longitudinal wave incident angle and the transverse wave reflection of the ultrasonic wave propagated in the wedge to the transducer surface, respectively. It is a horn. From Equations 7 and 8, the sound field at the point Fn generated by the oblique probe can be calculated by surface integration on the transducer surface.

(Diffraction from slit tip)
As shown in FIG. 11, a diffracted wave when a plane wave having an amplitude uin is incident on the tip of the slit can be expressed by the following Equation 9.
Here, dd and λd are unit vectors and wavelengths indicating the vibration direction of the diffracted wave, k is a wave number vector, and r is a distance vector from the slit tip. D represents a diffraction coefficient, and four combinations are conceivable depending on modes of incident waves and diffracted waves. As an example, the diffraction coefficient regarding the longitudinal wave incident wave and the longitudinal wave diffracted wave is expressed by the following Expression 10.
Here, a and aD represent directions of incident waves and diffracted waves, respectively. The functions and constants in the formula are as follows.
Here, cL, cT, and cR are longitudinal, transverse, and Rayleigh wave velocities, respectively, and K is an integral used in the Wiener-Hopf method. Since Equation 10 diverges infinitely when aD = π ± a, correction is necessary.

(Calculation of received waveform)
As shown in FIG. 12, a boundary surface SF is considered around the slit tip, and a reciprocal relationship is used between this boundary surface and the transducer surface SP of the receiving probe. The path until the transmitted wave is diffracted at the slit tip and received is represented by R, and the ultrasonic wave transmitted from the receiving probe propagates in the same path as the path R and enters the slit tip. The route is represented by V. At this time, the reciprocal relationship of the following formula 12 holds for the two boundary surfaces SF and SP.
Here, tR, uR and tV, uV represent the surface force and the displacement velocity vector in the path R and the path V, respectively. If it is considered that the transducer surface performs a piston motion at the time of transmission and is almost stationary at the time of reception, it is assumed that uR = 0 and uV = n on the transducer surface SP. Here, the amplitude of uV is 1. As a result, the above equation 12 is
It becomes. The left side of the above equation is obtained by integrating the component perpendicular to the vibrator of the surface force with the vibrator surface SP, and can be regarded as the waveform I received by the vibrator. If the radius b of the boundary surface SF is sufficiently larger than the wavelength, a plane wave relationship such as tR = ρcuR or tV = −ρcuV can be used. Further, uR and uV on the boundary surface SF can be calculated by using Expression 7, and the right side of Expression 13 can be expressed by Expression 14 finally using the stationary phase method.
Here, ρVm, cVm, and f represent the density, sound velocity, and frequency of the specimen, respectively. Further, n represents the number of refractions or reflections along the path T until the transmission wave enters the slit tip from the vibrator, and m represents the number of refractions or reflections along the path V. The subscripts T and V represent variables of the paths T and V, respectively. uT0 and uV0 can be expressed by the following Equation 15 and Equation 16, where the length of one side of the square transducer of the transmission probe is 1T and the length of one side of the square transducer of the reception probe is 1V.
Finally, the received waveform in the time domain can be calculated by inverse Fourier transforming the product of Equation 14 and the Fourier transform of the pulse waveform determined by the flaw detector.

  As described above, the calculation method of the received waveform has been formulated. Therefore, the above-described calculation method is a simulation tool that has been developed by the present inventors (a simulation tool that can predict the flaw detection result of a single transducer probe at high speed even on a laptop computer (Hayashiyama, Naohio Yamada, Hiroyuki, Takashi Ogata, Development of simulation tools for improving the accuracy and efficiency of ultrasonic flaw detection tests (1st report), incorporated in the Chuo Electric Power Research Institute report Q07004, 2008.)) SPOD The simulation of the two-probe method such as the TOFD method was enabled. Since the prediction result obtained by this simulation tool was in good agreement with the actual flaw detection result, its validity could be confirmed (see FIGS. 4A and 4B).

Next, the simulation method described above was verified.
(experimental method)
First, in order to verify the developed simulation method, an experiment was performed using a test body having a slit having a depth of 2 mm to 15 mm and a test body having a slit having a depth of 5 mm and an inclination angle of 50 ° to 90 °. The material of the test body is stainless steel (SUS316), and the shape and arrangement of the test body and the slit are as shown in FIGS. 13 (A) and 13 (B). Probes having the same nominal center frequency (hereinafter simply referred to as frequency) were used for transmission and reception, and as shown in FIG. For the test specimens with slits having different inclination angles, the probe was scanned in two directions from the A side to the B side and from the B side to the A side. In order to investigate the influence of the difference in frequency, probes having general frequencies of 2 MHz and 5 MHz were used. Both vibrator diameters are 10 mm. The wedge has a STB longitudinal wave refraction angle of 45 ° and is made of acrylic. In the oblique flaw detection for comparison with the SPOD method, an oblique probe having a frequency of 5 MHz, a transducer size of 10 mm × 10 mm, and a longitudinal wave refraction angle of 45 ° was also used. A linear scale encoder (manufactured by MTL) was used for position measurement during probe scanning, and A scope waveforms were acquired at intervals of 0.5 mm to draw B scope images. A commercially available ultrasonic flaw detector (TOMOSCAN III) was used for flaw detection data acquisition, and glycerin paste was used for the contact medium.

(Results and discussion)
(Effect of frequency)
FIGS. 15 (A) and 15 (B) show experimental results of B scope images obtained when a 2 MHz probe is used for transmission and reception and 5 MHz is used for a specimen having slits with different depths. . Here, the probe interval was set so that the intersecting point of the vertical and oblique probes was located 10 mm (FP = 10 mm) from the bottom surface (FP = 0 mm) and the thickness direction of the specimen. Comparing the cases of 2 MHz and 5 MHz from the figure, clearer L1 and L2 echoes are obtained at 5 MHz, and the bottom echo (BW in the figure) is stronger at 2 MHz than both echoes. This is due to the directivity of the probe. Therefore, a 5 MHz probe is desirable when the influence of scattering attenuation is small. When using a low-frequency probe due to the influence of scattering attenuation, it is necessary to note that the intensity ratio of the L1 and L2 echoes to the bottom echo greatly changes in addition to the decrease in S / N ratio and temporal resolution. is there. As for the cross axis position, the L1 echo of the slit with the tip close to the cross axis point is the strongest, and the intensity of the L1 echo at 5 MHz in FIG. 15B is the maximum value when FP = 0 mm and FP = 10 mm. The numerical values normalized by Fig. 16 are shown in FIG. Unlike the value by the longitudinal wave oblique angle probe described for reference (LA45 in the figure), it becomes difficult to detect the L1 echo away from the intersection point.

  The calculation results corresponding to the above experimental results are shown in FIGS. The calculation time of the B scope image for one slit was about 5 seconds on a personal computer equipped with Xeon (registered trademark of Microsoft Corporation) with a clock frequency of 3.06 GHz. In the formulation of the calculation method of the received waveform, the transducer was formulated as a square for simplicity of calculation of the sound field, whereas in the experiment, a circular transducer was used. Except for the near field on the central axis of the circular vibrator, the influence of the shape of the vibrator on the pulse sound field is small. Therefore, in the simulation of the same figure, the vibrator size was set to 10 mm × 10 mm. The difference in the beam path length of the L1 and L2 echoes from the simulation agrees well with the experimental results, and as shown in FIG. 15, the tendency of the magnitude relationship between the L1 and L2 echoes and the bottom echo to change greatly depending on the frequency is shown in FIG. You can also see. Since the calculation results are qualitatively consistent with the experimental results, the developed simulation tool can be fully utilized for grasping the features of the SPOD method different from other flaw detection methods and examining the measurement conditions.

(Echo of inclined crack)
The effect of crack inclination on flaw detection results was investigated. First, for reference, FIG. 19 shows the result of longitudinal wave oblique angle flaw detection on a specimen having slits with different inclination angles. As shown in this figure, when the angle between the slit surface and the ultrasonic central beam approaches 90 °, as in the case of a slit with an inclination angle of 50 °, the specular reflection at the slit surface becomes prominent. It becomes impossible to separate. On the other hand, the flaw detection result of the SPOD method when FP = 10 mm is as shown in FIG. 19 and 20 show the results when a probe having a frequency of 5 MHz is used. In the case of the SPOD method, it can be confirmed from the figure that the L1 and L2 echoes can be separated from the difference in the reception path, although the incident angle to the slit surface is the same as that in the case of the oblique flaw detection. FIG. 21 shows the calculation result corresponding to FIG. From both figures, the indication of the L1 echo becomes stronger as the specular reflection condition is approached. The calculated results are in good agreement with the experimental results in the separability of echoes and the echo intensity depending on the tilt angle of the inclined slit. From the experiment and calculation results, it was confirmed that the SPOD method has an advantage in measuring the depth of an inclined crack compared to the conventional oblique flaw detection. FIG. 22 shows the calculation result when the refraction angle of the oblique angle probe is 30 degrees and the intersection point is set near the slit tip. From this result, separation of both echoes is confirmed, and it can be seen that the magnitude relationship between the two echoes changes due to the difference in refraction angle.

  From the above, it was confirmed that the manufactured simulation tool was sufficiently effective for prediction of the flaw detection result of the SPOD method for the inclined crack and examination of flaw detection conditions. That is, it was confirmed that the method can be sufficiently applied to the evaluation of the influence of the test frequency and the inclination of the crack-like defect on the inspection result.

  Next, the usefulness of the ultrasonic flaw detection method and apparatus of the present invention was confirmed by the simulation method described above.

(Aperture synthesis processing using phased array technology)
First, performance prediction was performed by simulation. In the SPOD method, the same waveform is obtained due to reciprocity when the oblique probe is used for transmission and the vertical probe is used for reception, and when the probe is replaced, if the measurement system is linear. Further, data can be efficiently acquired by electronic scanning of the phased array. Using reciprocity and electronic scanning, we studied the modification of distance amplitude characteristics using a simulation tool. The calculation model shown in FIG. 26 was set with reference to experiments with test specimens having slits with different depths in the verification of the simulation method described above. The width of the element of the phased array probe with a frequency of 5 MHz was 1 mm, and the thickness of the test body having slits with depths of 2, 5, 10, and 15 mm was 25 mm. One element was used for transmission and eleven elements were used for reception, and nine elements were provided between them. The A scope waveform for each element obtained in the group of receiving vibration elements 1r was subjected to aperture synthesis processing so that the focal point would be the tip of each slit.

  One probe method using the maximum value of L1 echo when electronically scanned with the above model and a longitudinal wave oblique angle probe (frequency 5 MHz, transducer size 10 mm × 10 mm) instead of a phased array probe The maximum value of the end echo in the case of mechanical scanning was obtained by simulation. These maximum values are compared and shown in FIG. For comparison, the figure shows the maximum value of the end echo when aperture synthesis processing is performed on the result of the longitudinal wave oblique angle probe. From the figure, it was confirmed by simulation that the distance amplitude characteristic is corrected as compared with the case of FIG. 25 in which the flaw detection result of the SPOD method is simply processed.

(experimental method)
In order to verify the simulation results described above, the specimen having slits with different depths used in the verification of the above-described simulation technique and the 38 mm thick stainless steel (SUS316 having a fatigue crack provided by the mechanical test shown in FIG. ) Experiments were conducted using two test specimens. The maximum depth of the four fatigue cracks is 7 mm to 15 mm. The frequency of the phased array probe is 5 MHz. The number of elements is 64, the opening area of each element is 0.8 mm × 10 mm, and the pitch is 1 mm. The probe was equipped with a 30 mm-high polystyrene flaw detection wedge. One-dimensional mechanical scanning was performed at the center of the specimen using a scanner, and B-scope image data was recorded at the position where the L1 echo was confirmed. In addition to an ultrasonic phased array flaw detector (trade name: Matrixeye EX manufactured by Toshiba Corporation) that has an aperture synthesis processing function for acquiring flaw detection data, general ultrasonic waves are used to compare the SPOD method with the conventional pulse echo method. A phased array flaw detector (trade name OmniscanMX) was also used. Water was used as the contact medium. As shown in FIG. 1 and FIG. 2, the transmission / reception pattern 1 (FIG. 2 (A)) and 2 ( FIG. 2 (B)) was determined. As a result, 1 or 9 elements 1t were used for transmission, and a total of 20 elements 1r were used on both sides of the transmitting vibration element 1t for reception. The number of elements between the transmitting vibration element 1t and the receiving vibration element 1r group was set to 5 or 1. The reason why the receiving vibration element 1r group is arranged on both sides is to obtain an instruction symmetrical to the aim of improving the S / N ratio of the L1 echo. Although the calculation model of FIG. 26 and the experimental conditions are different, it has been confirmed by simulation that the expected effect can be obtained even under these conditions. Matrixeye can display the B scope image in real time by performing aperture synthesis processing at high speed using the parallel arithmetic circuit and four A / D converters that incorporate the pixel values in the B scope image from the A scope waveform received by each element. (Haraichi Karasawa, Hideo Isobe, Takayuki Hamajima, 3D Aperture Synthesis (3D-SAFT) Array and 9 Cases, Nondestructive Inspection, Vol.56, No.10, 520-524, 2007). The number of pixels set in this measurement is 512 and 64 in the vertical and horizontal directions, respectively, and the spatial resolution is 0.07 mm and 1 mm in the vertical and horizontal directions.

(Experimental result)
FIG. 29 shows a B-scope image obtained with the transmission / reception pattern 1 for the test specimen with slits. L1 and L2 echoes are observed, and the receiving vibration elements 1r are arranged symmetrically on both sides of the transmitting vibration element 1t, so that the instructions of both echoes appear symmetrically. FIG. 30 shows the maximum amplitude of the L1 echo of each slit. In FIGS. 24 (A) and 24 (B), the distance amplitude characteristic was not corrected despite the aperture synthesis processing, but 40% of the maximum value was obtained by using the ultrasonic flaw detection method of the present invention. It was confirmed that it could be corrected within the range. Therefore, it was confirmed that by utilizing the flaw detection method according to the present invention, not only the efficiency improvement that a B-scope image of the SPOD method can be constructed but also the distance amplitude characteristic can be corrected. In addition, it was confirmed that the L1 and L2 echoes were separated even for the inclined crack-like defect in which the edge echo and the opening echo could not be separated by the conventional oblique flaw detection.

Next, flaw detection was carried out on the fatigue cracked specimen. Prior to measurement by SPOD method, vertical flaw detection by pulse echo method was performed using Omniscan.
The electronic scan was a linear scan, and the number of simultaneous transmitting / receiving vibration elements 1r was increased to 16. However, the tip of any fatigue crack could not be captured. On the other hand, FIG. 31 shows a B-scope image when a fatigue crack is detected by the SPOD method in the transmission / reception pattern 1. Three of the four fatigue cracks could easily grasp the crack tip as shown in the area surrounded by the broken line in FIG. 31 (A), but one was clearly as shown in FIG. 31 (B). I couldn't get the correct tip instructions. This is probably because the tip is closed compared to the other three. Therefore, flaw detection was performed with the transmission / reception pattern 2 of FIG. This B scope image is shown in FIG. As can be seen in comparison with FIG. 31 (B), a clear indication of the crack tip can be confirmed. That is, the indication of the tip of the fatigue crack that could not be observed by vertical flaw detection using a conventional phased array probe can be identified by increasing the number of transmitting vibration elements 1t. As means for improving the S / N ratio of a weak instruction such as an instruction at the tip of a fatigue crack, it is effective to increase the opening area of ultrasonic transmission / reception, for example, increase the number of transmitting vibration elements 1t. Turned out to be one of.

  From the results of the above experiments, the effectiveness of the present invention in confirming the difference in detection sensitivity in the thickness direction of the inspection object was confirmed by a demonstration experiment.

DESCRIPTION OF SYMBOLS 1 Phased array 1t Transmission vibration element 1r Reception vibration element 1g Non-operation vibration element 2 The point which imaged the range to image the test body in the shape of a mesh 3t Ultrasonic beam of vertical transmission 3r Echo received obliquely 4 Control device 5 Imaging processor 20 Range of specimen image

Claims (6)

Using a phased array, vertical transmission is performed with some vibration elements of the phased array and oblique reception is performed with some vibration element groups, and the range in which the specimen is imaged in the range where the faced array is installed Is divided into a mesh shape, and aperture synthesis processing for adding A scope waveform signals received at an oblique angle by a plurality of the vibration elements for each of the sections within the range of the ultrasonic beam for vertical transmission is performed at intervals of the transmission / reception vibration elements. A luminance modulation that converts the amplitude value of the A scope waveform into a luminance value at the position of each section synthesized by the aperture synthesis process by performing electronic scanning while keeping the image constant. An ultrasonic flaw detection method characterized in that a B-scope image of an arbitrary cross section to be inspected is constructed by performing processing and displaying it on a corresponding pixel of an image display means. The ultrasonic flaw detection method according to claim 1, wherein the receiving vibration element group that performs oblique angle reception is disposed on both sides of the transmitting vibration element that performs the vertical transmission. The ultrasonic flaw detection method according to claim 1 or 2, wherein a gap of at least one element is disposed between the transmitting vibration element and the receiving vibration element group. A phased array in which a plurality of small vibration elements are arranged in a row, a part of the phased array that performs vertical transmission, a part of the vibration element group that performs oblique reception, and the faced array includes: The range in which the specimen is imaged in the installed range is divided into a mesh shape, and the A scope waveform signal is received at an oblique angle by a plurality of the vibration elements for each of the sections in the range of the ultrasonic beam transmitted at least vertically. A control device that performs electronic scanning over the entire imaging range while maintaining a constant interval between the transmitting and receiving vibration elements, and the A scope waveform signal that is obliquely received by a plurality of the vibration elements for each position of each section Is performed so that the waveforms overlap each other, and a luminance variation for converting the amplitude value of the A scope waveform at the position of each section synthesized by the aperture synthesis processing into a luminance value is performed. Corresponding image processing apparatus and the ultrasonic flaw detection apparatus in which comprises constructing a B-scope image of an arbitrary cross section of the test object by displaying the pixels of the image display means is subjected to processing. The ultrasonic flaw detector according to claim 4, wherein the reception vibration element group that performs oblique angle reception is disposed on both sides of the transmission vibration element that performs the vertical transmission. 6. The ultrasonic flaw detection method according to claim 4, wherein at least one non-operational vibration element is disposed between the transmission vibration element and the reception vibration element group.