JP7277391B2 - Ultrasonic inspection device and ultrasonic inspection method - Google Patents

Description

The present invention relates to an ultrasonic inspection apparatus and an ultrasonic inspection method, and more particularly to an ultrasonic inspection apparatus and an ultrasonic inspection method for volumetric inspection of welded parts and base material parts of pressure vessels and pipes.

Component maintenance in power plants is necessary to maintain normal operation. Therefore, the role played by non-destructive inspection technology is highly important. Especially in nuclear power plants, it is important to ensure the integrity of reactor primary system equipment such as the reactor pressure vessel (RPV) and recirculation system piping. Ultrasonic testing (UT) is mainly required for welds. In addition, in the special inspection for grasping the deterioration state of the plant due to aging, base material inspection in the core region of the reactor pressure vessel is also required. An ultrasonic inspection apparatus that performs UT usually has a so-called probe, which is a device for transmitting and receiving ultrasonic waves while in contact with the flaw detection surface of the object. A probe usually has one or more piezoelectric elements (vibrators) capable of mutually converting electrical energy and acoustic energy.

Typically, in the inspection area of carbon steel, such as the base metal and weld seams of pressure vessel bodies, circumferential and axial cracks are assumed to be defects to be detected. For example, in the UT standard (Non-Patent Document 1) for in-service inspections of light water reactors, longitudinal wave vertical ultrasonic waves and refraction angles of two or more angles (typically 45° and 60°). In addition, it is also necessary to irradiate oblique shear wave ultrasonic waves from four directions as much as possible: the top and bottom directions in the axial direction of the pressure vessel, and the CW and CCW directions in the circumferential direction of the pressure vessel.

In response to such inspection requests, it is inefficient to perform inspections while changing the direction of the probe by changing the probe many times. A device with touchers may be used.

Patent Document 1 discloses a super ultrasonic sensor that enables flaw detection at a plurality of angles and directions at once using a member in which a plurality of probes with different refraction angles are incorporated in one holder (hereinafter referred to as a flaw detection head). A sonography device is disclosed. The ultrasonic inspection apparatus of Patent Document 1 includes a plurality of probes that transmit and receive ultrasonic waves by bringing the contact surface into contact with the flaw detection surface of the object, and a holder that holds the plurality of probes. A probe has a flaw detection head coupled to a holder via an elastically deformable elastic member. Even against a curved flaw detection surface of a pressure vessel, pipe, etc., the contact surface of each probe can be independently tilted along the flaw detection surface by elastic deformation of the elastic member, so that the flaw detection surface and each contact surface It has a structure that suppresses the formation of a gap between the Further, in more general inspection apparatuses, a so-called gimbal mechanism is often used as a mechanism that allows each probe to tilt independently.

JEAC 4207-2016 Regulations for Ultrasonic Testing for In-Service Inspections of Equipment for Light Water Nuclear Power Plants, Japan Electric Association Nuclear Standards Committee

JP 2015-75409 A

However, the use of a flaw detection head in which many probes are arranged and integrated inevitably increases the overall size of the flaw detection head, which poses a problem that the shape of the flaw detection surface to which the flaw detection head can be applied is limited. In addition, due to the large size, interference with structures such as pipe nozzles and support members in the vicinity of the inspection range is likely to occur, and ultrasonic waves cannot be irradiated from the desired angle and direction within the inspection range. The range of possibilities expands. For example, if one longitudinal wave vertical probe and two 45° and 60° shear wave oblique angle probes are arranged facing each other to perform oblique angle inspection in two directions at the same time, the probes By arranging five probes, the area (footprint) occupied by the flaw detection head is approximately five times that of the case of one probe.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and its object is to enable simultaneous detection of multiple angles and multiple directions while suppressing an increase in the undetectable range with a compact flaw detection head configuration. To provide an ultrasonic inspection apparatus and an ultrasonic inspection method that can improve the efficiency of

In order to achieve the above object, the present invention provides an array probe having a wedge in which a vibrator array composed of a plurality of piezoelectric elements is arranged parallel to a tangential plane on a flaw detection surface of a test object. selects a predetermined number of piezoelectric element groups from the plurality of piezoelectric elements, controls the transmission timing of the plurality of ultrasonic waves transmitted from the piezoelectric element group, and generates a composite wave composed of the plurality of ultrasonic waves. a control device for scanning the propagation direction, scanning the transmission direction of the composite wave in the front-rear direction of the array probe, and mode conversion of the composite wave incident on the flaw detection surface via the wedge, thereby It is characterized in that it is possible to excite transverse waves having equal intensity in the longitudinal direction of the array into the specimen.

According to the present invention, a compact flaw detection head configuration of one array probe equipped with a wedge for exciting transverse waves of equal intensity in the front and back direction of the probe by mode conversion suppresses an increase in the undetectable range. At the same time, it is possible to improve the efficiency of inspection by enabling simultaneous detection of multiple angles and multiple directions.
Problems, configurations, and effects other than those described above will be clarified by the following description of the embodiments.

It is a figure showing composition of an ultrasonic inspection device in a 1st embodiment of the present invention. FIG. 2 is a diagram showing an example of a display screen of the display device according to the first embodiment of the present invention, and is a diagram showing an A-scope; FIG. 4 is a diagram showing an example of a display screen of the display device according to the first embodiment of the present invention, and is a diagram showing a sector screen; FIG. 4 is a diagram showing an example of a probe moving mechanism according to the first embodiment of the present invention, and is a front view of the probe moving mechanism; FIG. 4 is a diagram showing an example of a probe moving mechanism according to the first embodiment of the present invention, and is a plan view of the probe moving mechanism; FIG. 1 is a plan view showing an array probe structure according to a first embodiment of the present invention; FIG. FIG. 4B is a cross-sectional view (cross-sectional view along AA shown in FIG. 4A) showing the array probe structure in the first embodiment of the present invention; It is a front view showing the array probe structure and its arrangement in the prior art. FIG. 2 is a plan view showing an array probe structure and its arrangement in the prior art; FIG. 2 is a front view showing an image of ultrasonic wave propagation direction control based on delay patterns in the first embodiment of the present invention; 4 is a graph showing refraction angle dependence of intensities of longitudinal waves and transverse waves generated in a steel material by a laser point sound source. FIG. 4 is a conceptual diagram for explaining phase shift angles of wavefronts of composite waves formed by elementary source waves transmitted from two piezoelectric elements in the first embodiment of the present invention. 5 is a graph showing an example of specific calculation results of the phase shift angle of the composite wave wavefront in the first embodiment of the present invention; FIG. 10 is an explanatory diagram relating to an apparent aperture width in the prior art; It is an explanatory view relating to the apparent aperture width in the present invention, and is a front view explaining the apparent aperture width in the first embodiment of the present invention. 5 is a graph showing the transmission/reception efficiency of longitudinal waves with respect to the direction of propagation of composite waves possessed by each piezoelectric element in one embodiment of the present invention. 1 is a front view showing a typical wedge shape in the first embodiment of the invention; FIG. 1 is a plan view showing a typical wedge shape in the first embodiment of the invention; FIG. FIG. 4 is a plan view showing an example of wedge shape for comparison with a typical wedge shape in the first embodiment of the present invention; FIG. 2 is a plan view showing a part of the configuration of an apparatus in which two probes in the first embodiment of the present invention are arranged in a T shape and oblique flaw detection is performed simultaneously in four directions; FIG. 4 is a side view of the probe for explaining the influence of multiple reflected waves in the wedge, which is a concern when performing vertical flaw detection with the array probe according to the first embodiment of the present invention; FIG. 4 is an image diagram of a flaw detection waveform for explaining the influence of multiple reflected waves in a wedge, which is a concern when performing vertical flaw detection with the array probe according to the first embodiment of the present invention; FIG. 10 is a plan view (planar perspective view) showing an array probe structure according to a second embodiment of the present invention; FIG. 10 is a side view (side perspective view) showing the array probe structure in the second embodiment of the present invention; FIG. 15B is a cross-sectional view (CC cross-sectional view shown in FIG. 15A) showing the array probe structure in the second embodiment of the present invention; FIG. 10 is a front view for explaining a difference in path between vertical flaw detection and oblique flaw detection with the array probe according to the second embodiment of the present invention;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing the configuration of an ultrasonic inspection apparatus according to this embodiment. Here, as an object to be inspected, the circumferential weld line of the body of the reactor pressure vessel will be described as an example, but the present invention can also be applied to the inspection of welded parts and base material parts of piping.

The ultrasonic inspection apparatus of this embodiment includes a transducer array 2 having a plurality of piezoelectric elements 1 arranged in a line, and the transducer array arranged parallel to a tangential plane on the test surface. An array probe 4 having wedges 3 to be arranged, a probe moving mechanism 5, a couplant supply device 6, a control device 7, a calculator 8, a display device 9, and an input device 10 are provided. The calculator 8 is composed of a computer or the like, the display device 9 is composed of a display or the like, and the input device 10 is composed of a mouse, a keyboard, a touch panel or the like.

The plurality of piezoelectric elements 1 oscillate by a plurality of driving signals from a pulser 11 of the control device 7 to be described later, transmit a plurality of ultrasonic waves, and combine them to form a composite wave 16 . By controlling the timing of transmitting a plurality of ultrasonic waves, the direction of propagation of the composite wave 16 can be varied in any desired direction. When this composite wave 16 is vertically incident on the surface of the object 20 through the wedge 3, a longitudinal wave 17 propagates in the plate thickness direction of the object 20. FIG. On the other hand, when the composite wave 16 is obliquely incident on the surface of the subject 20, a transverse wave 18 is generated in the subject due to mode conversion and propagates obliquely in the subject at an angle according to Snell's law. The wedge 3 is made of a resin material such as acrylic, polystyrene, or polyimide, and the space between the wedge 3 and the surface of the subject 20 is filled with liquid such as water as a contact medium.

In this embodiment, in order to acoustically couple the wedge 3 and the subject 20 by the water gap method (water film method), a pump mounted on the couplant supply device 6 is used to fill the gap between the surfaces of the wedge 3 and the subject 20. An example of supplying a couplant with a thickness of about 0.3 mm to about 1 mm will be shown. Also good.

As shown in FIG. 1, when there is a crack 23 on the inner surface of the inspection range 22 for the welded portion 21 of the test object 20, the reflected wave 18a reflected by the crack 23 is received by the piezoelectric element 1 via the wedge 3. . The piezoelectric element 1 converts the received reflected wave into a waveform signal and outputs the waveform signal to the receiver 12 of the control device 7, which will be described later.

The control device 7 has a pulser 11 , a receiver 12 , a delay control section 13 , a mechanical control section 14 and a data recording section 15 . The delay control unit 13 and the mechanical control unit 14 are composed of processors and the like that execute processing according to programs, and the data recording unit 15 is composed of memory and the like. The delay control unit 13 outputs a delay pattern corresponding to the propagation direction of the composite wave to the pulser 11 and the receiver 12 in accordance with the instruction from the computer 8 . The mechanical control unit 14 generates a signal to drive the motor mounted on the probe moving mechanism 5 according to the command from the computer 8, and the encoder mounted on the probe moving mechanism 5 detects the amount of rotation of the motor. Receive corresponding signals to control the position of the probe.

The pulsar 11 controls the output timing of a plurality of drive signals to be output to the plurality of piezoelectric elements 1 based on the delay pattern. Thus, sector scanning is performed to change the propagation direction of the composite wave. At this time, by performing transverse wave sector scanning including two types of refraction angles (typically 45° and 60°) required by the standard symmetrically in the front and back direction of the array probe 4, one mechanical Oblique flaw detection in two directions and two angles is completed by regular probe scanning, and the efficiency of inspection is improved. In addition, by performing longitudinal wave sector scanning at a refraction angle of about 0° corresponding to longitudinal wave vertical flaw detection, all ultrasonic transmission directions required for flaw detection in the circumferential or axial direction of the object can be satisfied. can be done.

The receiver 12 adjusts the input timing of the waveform signal from the piezoelectric element 1 and synthesizes the waveform signal based on the delay pattern. Thereby, the propagation direction of the reflected wave is adjusted so as to correspond to the propagation direction of the composite wave.

The waveform signal synthesized by the receiver 12 is converted into waveform data by an analog-digital converter (not shown) and recorded by the data recording unit 15 . The data recording unit 15 records the waveform data in association with the delay pattern (or information on the direction of propagation of the corresponding composite wave and ultrasonic waves generated in the subject). Waveform data consists of a combination of reception time and signal strength.

The computer 8 creates a flaw detection image based on the waveform data recorded by the data recording unit 15 and information on the direction of propagation of the corresponding synthetic waves and intra-subject ultrasonic waves. Specifically, a reflection position is assumed based on the information on the propagation direction of the composite wave and intra-subject ultrasound and the reception time, and the pixel position is selected according to the reflection position, and the pixel position is selected according to the signal intensity. A flaw detection image is created by varying the hue, saturation, or brightness.

The display device 9 displays the waveform data recorded by the data recording section 15, as shown in FIG. 2A, for example. The horizontal axis corresponds to the reception time of the ultrasonic waves, which is converted into a path distance from the incident point on the surface of the subject 20 in the ultrasonic transmission direction based on the speed of sound in the ultrasonic mode and displayed. This allows an inspector to evaluate the presence and location of flaws. FIG. 2A is an example of a screen configuration that simultaneously displays a waveform 300 of vertical flaw detection (refraction angle θ = 0°) by longitudinal waves, waveforms 301a and 302b with a transverse wave oblique angle of 45°, and waveforms 302a and 302b with a transverse wave oblique angle of 60°. is shown. Waveforms 301a and 302a are obtained by obliquely transmitting transverse waves to the front of the array probe 4, and waveforms 301b and 302b are waveforms obtained by obliquely transmitting transverse waves to the rear of the array probe 4. FIG. In FIG. 2A, the waveforms of 301b and 302b are represented by dashed lines, but any display such as different colors may be used as long as they can be distinguished from 301a and 302a. Of course, the waveforms may be displayed in different small windows instead of overlapping the waveforms as shown in FIG. 2A.

Further, the display device 9 displays the inspection image created by the computer 8, as shown in FIG. 2B, for example. This allows the inspector to evaluate the dimensions and properties of the flaw. FIG. 2B shows a longitudinal wave sector image 311 with a refraction angle of about 0° corresponding to vertical flaw detection by longitudinal waves, and oblique angle transmission of transverse waves to the front of the array probe 4 in oblique flaw detection by transverse waves. A screen configuration for simultaneously displaying a transverse wave sector image 312a corresponding to the transmission of the transverse wave to the rear of the array probe 4 and a transverse wave sector image 312b corresponding to oblique transmission of the transverse wave to the rear of the array probe 4 is shown. Since the longitudinal wave sector image 311 and the transverse wave sector images 312a and 312b have different sound velocities of ultrasonic waves used for flaw detection, the computer 8 calculates pixel positions in consideration of differences in sound velocities of the respective ultrasonic modes.

In addition, a moving trajectory diagram (not shown) of the probe based on an encoder signal mounted on the probe moving mechanism 5, which will be described later, is displayed.

An example of the probe moving mechanism 5 will be described with reference to FIGS. 3A and 3B. The probe moving mechanism 5 is an XY scanner that two-dimensionally scans the probe, and is a device for obtaining a C-scan image. For example, an arc-shaped track 100 attached along the circumferential weld line 21 of the object 20 and a movably provided A circumferential movement device 101, an axial movement device 102 provided in the circumferential movement device 101 and sliding in a direction perpendicular to the track 100 (the direction of the arrow D2 in FIGS. 3A and 3B), and an axial movement It has a probe holding mechanism 103 attached at a predetermined offset to the device 102 .

The circumferential scanning device 101 includes a pinion 111 that meshes with a rack 110 formed on the outer peripheral side of the track 100, a motor (not shown) that rotates the pinion 111, and an encoder (not shown) that detects the amount of rotation of the motor. and As the pinion 111 rotates, the circumferential movement device 101 moves along the track 100 . Along with this, the probe holding mechanism 103 (that is, the array probe 4) moves in the circumferential direction of the subject.

The axial movement device 102 includes a pinion (not shown) that meshes with a rack 112 formed on the arm 103, a motor (not shown) that rotates the pinion 111, and an encoder (not shown) that detects the amount of rotation of the motor. and move the arm 103 in a direction perpendicular to the track 100 . By moving the arm 103, the position of the probe pressing mechanism 103 in the axial direction of the object, that is, in the direction perpendicular to the circumferential weld line 21 can be adjusted.

Further, the probe holding mechanism 103 includes a probe holder 114 that holds the array probe 4 and urges the probe holder 114 toward the subject to hold the array probe 4 on the outer surface of the subject. An urging mechanism (for example, a spring, pneumatic cylinder, or hydraulic cylinder, although details are not shown) for pressing against (flaw detection surface), and a probe rotation mechanism 115 capable of rotating the probe by 90° together with the probe holder. have. A contact medium supply hose 116 is connected to the array probe 4 , and the contact medium is supplied from the contact medium supply device 6 to the gap between the array probe 4 and the object 20 .

It should be noted that the probe moving mechanism 5 described here is an example, and any device configuration may be used as long as the probe can be two-dimensionally scanned around the welding line of the object 20. and

The structure of the array probe 4, which is the main part of this embodiment, will be described. 4A and 4B are diagrams showing the structure of the array probe 4 in this embodiment. FIG. 4A is a plan view of the internal structure seen through from the upper surface of the array probe, and FIG. 4B is a cross-sectional view taken along the line AA in FIG. 4A.

The array probe 4 of this embodiment is based on a linear array structure having a transducer array 2 in which a plurality of piezoelectric elements 1 are linearly arranged in one row. The transducer array 2 is placed on the upper surface of a flat wedge 3 having a thickness h, and the wedge 3 is installed with a gap height g (0.3 to 1.0 mm) from the surface of the object. , is housed within the casing 400 . At both longitudinal ends of the wedge, sound absorbing material 402 (such as cork or rubber-based material) is provided to absorb incident sound energy and reduce ultrasonic echoes within the wedge. The casing 400 and the wedge 3 are provided with a couplant supply hole 401, and the couplant supplied from the couplant supply device 6 through the hose 116 fills the gap between the wedge 3 and the test object 20. Acoustically coupled with the subject 20 by the water gap method.

Since the wedge 3 made of a resin material and the object 20 made of steel have different acoustic impedances, sound pressure loss occurs when ultrasonic waves travel back and forth between the wedge 3 and the object 20 . A coefficient representing this efficiency is the sound pressure round-trip transmission rate T. FIG. When the wedge 3 and the object 20 are acoustically coupled by the water gap method, the acoustic impedance with the couplant also affects. It is known that if the gap height g is set to be a multiple of half the wavelength of the couplant, the effect of the couplant can be almost ignored. theory, and cannot be ignored for a pulse wave with a wide frequency band. Moreover, the gap height changes depending on the curvature and unevenness of the object surface. Since it is not realistic to control the gap height g in the submillimeter order, it is necessary to assume that ultrasonic sound pressure loss occurs between the wedge 3 and the couplant and between the couplant and the test object 20 . Under this premise, rather than directly contacting the piezoelectric element (acoustic impedance of about 10 to 30×10 ⁶ kg/m ² s) and the couplant (acoustic impedance of about 1.5 to 2×10 ⁶ kg/m ² s), , and a wedge 3 made of a resin material having an intermediate acoustic impedance (acoustic impedance of about 2.5 to 3.5) is sandwiched between them.

Here, a coordinate system is defined to facilitate the following description. The point where the Z axis passes through the center of the transducer array 2 and the normal direction of the transducer array 2 is vertically downward, and the point where the Z axis passes through the surface of the subject 20 is defined as an origin O. , the arrangement direction of the piezoelectric elements 1, that is, the front-rear direction of the array probe 4 is the Y-axis, and the longitudinal direction of the piezoelectric elements, that is, the width direction of the array probe 4 is the X-axis. The tangent plane at the point O on the object surface is the XY plane, and the transducer array 1 is arranged parallel to this tangent plane by the wedge 3 at a distance h.

When performing flaw detection by generating transverse waves in the object as in the present embodiment, generally, even an array probe, like a single-element fixed-angle probe, is inclined diagonally. An inclined wedge-shaped wedge 500 is used. 5A and 5B show a typical structure of a conventional transverse wave excitation array probe. FIG. 5A is a front view seen from the side of the probe, and FIG. 5B is a plan view seen from the top of the probe. An array probe 501 in which a plurality of piezoelectric elements 1 are arranged in a line is placed on a subject through a wedge-shaped wedge 500 . The reason for inclining the wedge at the wedge-like inclination angle α is to make the composite wave 16 of the longitudinal waves in the wedge that generate the transverse waves 18 of the object by mode conversion as strong as possible. , cannot excite a strong transverse wave 18 toward the rear of the array probe. Therefore, although it is possible to perform oblique flaw detection at two angles or more with a single array probe, another array probe 501a and the wedge-shaped wedge 500a must be arranged opposite to each other, which doubles the footprint of the entire flaw detection head (L×W in FIG. 5B) and causes an increase in the undetectable range.

The wedge 3 of the array probe 4 in the first embodiment of the present invention shown in FIGS. 4A and 4B is rotated 180° about the normal to the center of the transducer array 2 without being inclined. It is a rotationally symmetrical shape that has the same shape (except for the contact medium supply hole 401). Therefore, when the transverse wave 18 is obliquely transmitted in front of the array probe 4 and when the transverse wave 18 is obliquely transmitted behind the array probe 4, the transverse waves can be excited with the same intensity. . Although the details will be described later, when the width of the piezoelectric elements of the array is sufficiently small, the difference in intensity of the composite wave 16 between when the wedge is tilted and when the wedge is not tilted is not so large, and the aperture width a of the entire transducer array is set to an appropriate size. , it is possible to excite the composite wave 16 and the transverse wave 18 with the same intensity as when the wedge is tilted. Therefore, if the array probe 4 in the first embodiment of the present invention is used, oblique flaw detection and vertical flaw detection in two directions and two angles can be performed at once with a compact flaw detection head with only one array probe. Therefore, it is possible to improve the efficiency of inspection while suppressing an increase in the untestable range.

The vibrator array 2 is formed by arranging a plurality of piezoelectric elements 1 having a width e and a length l (this number is n) arranged at an element pitch p. The element pitch p is made small enough to suppress pseudo ultrasonic beams called grating lobes that occur when the phases of ultrasonic waves transmitted from each piezoelectric element are aligned in a direction different from the intended direction. I have a need. A guideline for this element pitch p is determined by the following formula (1).

p≦λ _M /(1+Sinθ _max ). (1)

Here, λ _M is the shear wave wavelength in the subject, and θ _max is the maximum refraction angle of the shear wave 18 in the subject. Using the maximum element pitch p that satisfies Equation (1), the aperture width a of the entire transducer array can be reduced to It is possible to increase the intensity of the composite wave 16 and the transverse wave 18 caused by mode conversion. When the maximum refraction angle is θ _max =90°, the element pitch p should be λ _M /2 or less. For example, since the wavelength of a 2.25 MHz transverse wave in steel (sonic velocity of 3.23 km/s) is about 1.4 mm, the element pitch is preferably 0.7 mm or less.

FIG. 6 shows an image diagram of ultrasonic wave propagation direction control based on the delay pattern. By controlling the output timing of a plurality of drive signals 410 that are respectively output to the plurality of piezoelectric elements 1, the wavefront 16b of the composite wave 16 is formed as an envelope of the source wave (longitudinal wave) 16a radiated from each piezoelectric element. do. This composite wave 16 propagates in the direction of an arbitrary incident angle φ according to the delay pattern. At the incident point I on the surface of the object, the wave is mode-converted into a transverse wave 18, bent according to Snell's law, and propagated in the direction of the refraction angle θ within the object. Reference numeral 18a denotes a transversal wave mode-converted from the source wave 16a, and 18b denotes a wavefront of the transversal wave 18 formed as an envelope curve of 18a. By reversing the slope of the drive signal, a transverse wave can be excited toward the rear of the probe with the same refraction angle θ.

The wedge 3 in this embodiment forms a longitudinal wave composite wave 16 once in the wedge and converts it into a transverse wave 18 by mode conversion. The purpose is to stably excite sensitive transverse waves. Even in the case of direct contact, it is known that a transverse wave is generated by mode-converting the longitudinal edge wave generated from the end of the piezoelectric element 1. However, the intensity of the transverse edge wave is generally weak, It strongly depends on the surface state, and the directivity is also extremely dependent on the angle of refraction compared to the longitudinal edge wave. Although the directivity of this transverse edge wave has not yet been fully formulated, the field of laser UT that instantaneously heats a localized area of the surface of an object with a laser beam and excites ultrasonic waves as a point sound source. A theoretical solution is sought in . FIG. 7 shows, for reference, the refraction angle dependence of the intensity of longitudinal waves and transverse waves generated from a point sound source in a steel material. The horizontal axis represents the propagation direction of the ultrasonic wave, and the refraction angle θ with respect to the direct downward direction of the point sound source.The vertical axis represents the relative sound pressure of the ultrasonic wave generated from the laser point sound source. A dashed line is the longitudinal wave directivity. Longitudinal waves show a general directivity similar to a cosine curve with the maximum in the direct downward direction (θ = 0°). On the other hand, the transverse wave exhibits extreme refraction angle dependence with two peaks near 30° and 45° with no sound pressure directly below. For example, when a transverse wave is sector-scanned in the range of 40° to 75° (range including typical refraction angles of 45°, 60°, and 70°), a large sensitivity difference of about 9 dB occurs. When the array probe is brought into direct contact with the subject, the transverse edge wave generated in the subject from the end of the piezoelectric element also exhibits directivity similar to the directivity of the transverse wave shown in FIG. In the case of scanning, there is a problem of stability in addition to the above-mentioned lack of absolute intensity and high dependence on surface conditions. Therefore, in the present embodiment, a transverse wave is excited by mode-converting a composite wave of longitudinal waves generated in the wedge via the wedge 3 . By using a wedge made of a resin material that has an acoustic impedance intermediate between that of the piezoelectric element and that of the couplant, the sound pressure round-trip transmission rate is slightly improved, and an improvement in sensitivity can also be expected.

In this embodiment, it is important to form a high-intensity and stable composite wave 16 within the wedge, and it is necessary to set an appropriate wedge thickness h. As the wedge thickness h increases, the intensity of the composite wave decreases due to sound scattering attenuation within the wedge, and the footprint of the entire array probe including the wedge also increases. On the other hand, if the wedge thickness h is too small, a sufficiently smooth composite wavefront cannot be formed, and transverse wave excitation due to mode conversion of the composite wave is unstable.

An appropriate wedge thickness h will be described with reference to FIG. FIG. 8 is a conceptual diagram for explaining the smoothness (size of unevenness) of the wavefront of a composite wave formed by elemental waves (edge waves) transmitted from two piezoelectric elements. Only two piezoelectric elements and a part of the wedge 3 are extracted from the first embodiment of the present invention. When trying to form the wavefront 16b of the composite wave 16 in the direction of the incident angle φ, the actual wavefront is an uneven wavefront that traces the two source waves 16a, and is represented as a tangent to the two source waves 16a. At the intersection _Q3 of the two source waves 16a, there is a maximum distance difference of δ in the propagation direction of the composite wave from the virtual wavefront 16b. Given the element pitch p, the incident angle φ, and the wedge thickness h, the maximum distance difference δ of the composite wave front is expressed by the following equations (2) to (4). Also, the value obtained by dividing δ by the wavelength λ _W in the wedge and multiplying it by 2π (360°) is defined as the maximum phase shift angle Δ of the composite wave front by Equation (5).

δ＝r ₀ (1-Cos dφ) (2)
dφ≡∠Q ₃ EI = Arcsin(( ^p2 + _r02 - ^r12 )/( _2pr0 )) ( ₃ ⁾
_r1 = _r0 - pSinφ (4)
Δ≡2πδ/ _λW (5)

As an example, using polyetherimide (longitudinal wave speed of sound 2.43 km/s) as the wedge material, the specific phase when the element pitch p is set to 1/2 the wavelength λ _M of the transverse wave in the steel material according to formula (1) FIG. 9 shows the calculation result of the deviation angle. The horizontal axis is the wedge thickness normalized by the wavelength in the wedge, h/λ _W , and the vertical axis is the maximum phase shift angle Δ. It is shown repeatedly. The smaller the refraction angle θ, that is, the smaller the incident angle φ, the larger the phase shift angle Δ even with the same wedge thickness. Assuming that the maximum allowable phase shift angle Δ is Δ≤10° so that the sinusoidal amplitude change is less than 2%, the minimum wedge thickness h/λ _W for the range of refraction angles θ≥45° is 1.4. becomes.

From the above considerations, considering some errors, the wedge thickness h required to form a smooth composite wavefront that can stably convert the mode to a transverse wave is 1.5 times or more the wavelength of the longitudinal wave in the wedge. It is preferable to ensure Since the thickness of the protective film of a general array probe is designed around 1/4 wavelength, wedges (protective films) are consciously designed to enable stable mode conversion to transverse waves. It needs to be thickly designed.

10A, 10B and 11, the shear wave 18 excited by the prior art tilted wedge array probe configuration shown in FIGS. 5A and 5B and the shear wave 18 shown in FIGS. A condition for making the intensity of the transverse waves 18 excited by the configuration of the array probe 4 of Embodiment 1 of the present invention approximately equal and the difference in the footprint length L at that time will be described. 10A and 10B are explanatory diagrams of the apparent aperture width a′ in the conventional technology and the embodiment of the present invention, FIG. 10A is an explanatory diagram of the apparent aperture width a′ in the conventional technology, and FIG. 10B is an explanatory view of the apparent aperture width a′ in the embodiment of the present invention. is. FIG. 11 shows the longitudinal wave transmission/reception efficiency (reciprocating directivity) with respect to the propagation direction of the composite wave possessed by each piezoelectric element.

It is known that the magnitude of the signal amplitude of ultrasonic echoes in oblique flaw detection is roughly proportional to the apparent aperture width a'. The relationship between the apparent aperture _width a ₁ ' and the actual aperture width a ₁ of the prior art _shown in FIG. The relationship is shown in Equation (7).

_a1 ' = _a1 (Cosθ/Cosφ) (6)
_a2 ' = _a2 '' (Cosθ/Cosφ) = _a2Cosφ (Cosθ/Cosφ) = _a2Cosθ (7)

Here, a ₁ and a ₂ are the actual aperture widths of the transducer array, φ is the incident angle of the composite wave 16 , and θ is the refraction angle of the transverse wave 18 . Comparing equations (6) and (7), it can be seen that in order to make the apparent aperture width the same as in the conventional technique in the probe configuration of this embodiment, the size of the actual aperture should be increased by 1/Cosφ times. I understand. However, since each of the piezoelectric elements 1 also has directivity in the transmission/reception efficiency of the ultrasonic wave, in order to compensate for the decrease in sensitivity caused by transmitting the composite wave at an angle of incidence φ from the normal direction of the piezoelectric element 1, It is desirable to increase the actual aperture width. FIG. 11 shows the reciprocating longitudinal wave directivity of the piezoelectric element 1 when the material of the wedge 3 is polyetherimide and the vibrator width is 0.5 mm, which is less than half the wavelength. The greater the incident angle φ of the composite wave, the lower the transmission/reception efficiency. For example, if the material of the wedge 3 is polyetherimide and a shear wave with a refraction angle of 60° is excited in the steel material, the incident angle φ is about 41°, so the transmission/reception efficiency due to the directivity of the piezoelectric element is 0.73 times (-2.7dB). be. In this case, if the actual aperture is increased by 1/0.73=1.37 times that of the probe configuration of the prior art, the decrease in sensitivity due to the directivity of the piezoelectric element 1 can be canceled. Since the aforementioned apparent aperture width correction coefficient is 1/Cos41°=1.33, the actual aperture should be multiplied by 1.37×1.33=1.8.

Based on the difference in the actual aperture mentioned above, the minimum footprint lengths L ₁ and L ₂ of the probe configuration required for two-way oblique angle testing are calculated using the following formulas (8) and (9). be done.

L ₁ ≧ 2a ₁ (Cosφ + SinφTanφ) (8)
_L2 ≥ _a2 + 2h Tanφ (9)

Here, with the shear wave refraction angle of 60° as the reference, when the incident angle φ = 41° and a ₂ =1.8a ₁ are designed, L ₁ ≥ 2.65a ₁ , L ₂ ≥ 1.8a ₁ +1.7h, and h is as small as about 1.5 times the wavelength of the longitudinal wave in the wedge, L ₂ ≤ L ₁ , and the footprint can be made smaller than the conventional technology while maintaining the flaw detection sensitivity.

Finally, with reference to FIGS. 12A, 12B, and 13, wedge shape devising for reducing pseudo echoes due to multiple reflected waves 116 of the composite wave 16 generated in the wedge 3 will be described. 12A and 12B are explanatory diagrams showing typical wedge shapes in the first embodiment of the present invention. Of the probe configuration, only the parts necessary for explaining the propagation path of the multiple reflected waves 116 in the wedge are extracted and drawn, and for example, the sound absorbing material at the edge of the wedge is omitted. FIG. 12A is a front view seen from the side of the wedge, and FIG. 12B is a plan view seen from the upper surface of the wedge. As shown in the figure, the typical wedge shape in the present invention has a three-dimensional end surface inclination such that the projected view from the side is a trapezoid and the projected view from the top is a parallelogram, and the transducer array It has a rotationally symmetrical shape with the normal line at the center of 2 as an axis. As shown in FIG. 12A, the composite wave 16 transmitted to the left of the wedge for oblique inspection is reflected by the bottom surface of the wedge and then incident on the left end surface of the wedge. Since the wedge end surface is inclined by an angle β in the thickness direction of the wedge, the angle of the multiple reflected waves 116 deviates in the thickness direction, and is at a different angle from the propagation direction of the composite wave with respect to the transducer array 2. As a result, reception efficiency decreases and pseudo echoes are reduced. In addition, as shown in FIG. 12B, since the wedge end face is inclined at an angle γ in the wedge width direction even when viewed from above, the multiple reflected waves 116 reflected from the wedge end face deviate in the wedge width direction, Since the composite wave 16 is no longer incident on the array 2 at an angle greatly different from the propagation direction, the reception efficiency is lowered, and together with the inclination in the thickness direction, the pseudo echo can be effectively reduced.

FIG. 13 shows, for comparison, a case in which the projected view from the top is trapezoidal. In this case, the multiple reflected wave 116 reflected from the wedge end face returns in a direction parallel to the propagation direction of the composite wave 16 when reflected from the opposite end face. Therefore, a parallelogram is preferable to a trapezoid as the projection shape viewed from above. When the only purpose is to reduce the echo in the wedge, it is not necessary to have a rotationally symmetrical shape. A rotationally symmetrical shape is more preferable because the positions and magnitudes of pseudo echo signals generated by multiple reflected waves change in some cases, which may cause problems in identifying echoes.

By using the array probe provided with the transverse wave excitation wedge described above, it is possible to suppress an increase in the undetectable range and simultaneously detect flaws at a plurality of angles and in a plurality of directions, thereby improving inspection efficiency.

In this embodiment, as shown in FIGS. 3A and 3B, an apparatus configuration for simultaneous two-direction flaw detection using one array probe 4 has been described as an example, but as shown in FIG. It is also conceivable to use a device configuration in which two array probes having a structure are arranged in a T-shape to perform flaw detection in four directions at the same time. In this case, instead of increasing the overall footprint, flaw detection can be performed more efficiently, and the probe rotation mechanism 115 becomes unnecessary. In particular, it is suitable as an apparatus for inspecting a base material of a pressure vessel in which the inspection range of the object to be inspected is wide in the axial direction.

A second embodiment of the present invention will be described with reference to the drawings. Since the configuration of the probe is the same as that of the first embodiment except for a part of the configuration of the probe, the description of common parts will be omitted and only the difference will be described.

Using FIGS. 15A and 15B, the influence of multiple reflected waves in the wedge, which is a concern when performing vertical flaw detection with the array probe 4 in the first embodiment, will be described. FIG. 15A is a conceptual diagram showing the propagation paths of the longitudinal wave 17, the composite wave 16, and the multiple reflected waves 116 when the crack 23 at the depth position d is detected by vertical flaw detection, and FIG. 15B is obtained at this time. An example of an echo appearing in a vertical flaw detection waveform 300 is shown. In vertical flaw detection, the composite wave 16 is transmitted parallel to the plate thickness direction of the wedge 3 to excite the longitudinal wave 17. Therefore, unlike the oblique flaw detection, the multiple reflected waves 116 within the wedge reach the transducer array 2. On the other hand, since it is incident from the same direction as the propagation direction of the composite wave, the pseudo echoes 302a and 302b due to the multiple reflected waves in the wedge are much larger than in the oblique flaw detection, and are too large to be ignored compared to the echo 301 from the flaw. I have a concern. If the wedge is extremely thin, the dead zone caused by the pseudo echo due to the multiple reflected waves will rapidly decrease in echo amplitude due to reflection loss during multiple reflection, and will be limited to a limited area on the external surface of the object. In the embodiment of the present invention, which requires a thickness of about 1.5 times the wavelength in order to stably excite transverse waves by mode conversion, there is a possibility of causing problems in flaw detection.

As an excellent method for solving the dead zone problem during vertical flaw detection in fixed-angle probes, a two-element probe with split transmission and reception is known. This is done by dividing the transducer into one for transmission and one for reception, and inserting an acoustic isolation plate made of sound-absorbing material such as cork between the transducers. It shields the propagation path of ultrasonic waves and prevents the generation of pseudo echoes due to multiple reflected waves within the wedge.

In an array probe, it should be possible to eliminate the dead zone during vertical flaw detection by separating the transducer group for transmission and the transducer group for reception and inserting an acoustic isolation plate between them. However, for example, when an acoustic isolation plate is inserted parallel to the longitudinal direction of the piezoelectric element so as to divide the transducer array 2 shown in FIGS. It becomes a wall that shields part of the wedge, causing various problems such as reduced sensitivity, sound field distortion, and an increase in multiple reflection echoes inside the wedge.

Therefore, in the second embodiment of the present invention, the array probe structure shown in FIGS. 16A to 16C is used to solve the dead zone problem in vertical flaw detection without affecting oblique flaw detection as much as possible. 16A is a plan perspective view of an array probe according to a second embodiment of the present invention, FIG. 16B is a side perspective view of the array probe viewed from the direction of arrow B in FIG. 15A, and FIG. FIG. 15B is a cross-sectional view of the array probe taken along the line CC shown in FIG. 15A; In this array probe, a part of the transducer array 2, typically the piezoelectric element 1 in the center of the transducer array 2, is divided into two in the longitudinal direction of the transducer, and each is divided into two different pulsers/receivers. It is characterized in that an acoustic isolation plate 500 is inserted in the wedge between the vibrators that are connected and electrically independent, and that is parallel to the arrangement direction of the array for acoustic isolation. To simplify the explanation, all the piezoelectric elements are numbered 1 to 24, but there is no intention to limit the number of elements in the embodiment of the present invention to 24.

Of the two-divided transducer group, one is for transmission (element numbers 7 to 12, for example), and the other is for reception (element numbers 19 to 24, for example), and oblique angle inspection is performed. By doing so, it is possible to perform vertical flaw detection excluding multiple reflected waves in the wedge, as in the case of the two-element probe. On the other hand, when performing oblique-angle flaw detection using shear waves, the two-divided transducer is treated as a virtual one, and element numbers 19 to 24 are driven with the same delay time pattern as element numbers 7 to 12. do. The direction of propagation of the composite wave is parallel to the acoustic isolator and is not blocked by the acoustic isolator. Shear waves 18 can be excited into the subject 3 with a sensitivity comparable to that of an array of morphologies.

Due to the restriction of grating lobe suppression, when the element pitch p is the same as that of the probes of FIGS. 4A and 4B, the number of elements for obtaining the same aperture width a increases by the number of divided transducers. If all the array transducers are simply divided into two, the number of elements is double that in the case of not dividing. However, the number of transducers in the array probe is limited to a finite number by the specifications of the pulser/receiver mounted on the control device 7 that controls the transmission and reception of ultrasonic waves. In order to do so, it is necessary to reduce the number of divided transducers and increase the aperture width a of the entire array. As a measure of the number of elements to be divided, the length b of the region where the transducer is divided into two with respect to the aperture width a of the entire array is determined based on the following equation (10).

b≦0.5a (10)

The grounds for this value will be briefly described with reference to FIGS. 10B and 17. FIG. FIG. 17 is a conceptual diagram for explaining the difference between the path length _w1 in the case of perpendicular flaw detection of the test object 20 having a plate thickness T and the path length _w2 in the case of oblique flaw detection with a refraction angle θ. The signal amplitude V of echoes from large cracks is proportional to the apparent aperture a ₂ ' shown in FIG. 10B and inversely proportional to the ultrasonic path length W ₁ or W ₂ shown in FIG. The apparent aperture a ₂ ' is Cos θ times the actual aperture width a ₂ (≦1) according to equation (7). Further, the path length w of the ultrasonic wave covering the entire plate thickness is obtained by the equation (12) using the plate thickness T and the refraction angle θ.

w=T/Cosθ (11)

Therefore, the magnitude of the echo signal amplitude V follows the following equation (12).

_V∝a2 ′/w=( _a2 /T) ^Cos2θ (12)

For example, when oblique-angle detection is performed with a larger refraction angle θ=60° among the refraction angles required by the standard, and when vertical flaw detection is performed (θ=60°), the signal amplitude for vertical flaw detection is oblique-angle It becomes four times larger than the signal amplitude of flaw detection. Considering the difference in transmittance, etc., the actual sensitivity difference is even greater. Therefore, the aperture area for performing vertical flaw detection with the same level of sensitivity as oblique flaw detection may be 1/4 or less of the oblique flaw detection. In the vertical flaw detection by the probe in this embodiment, the aperture area is halved by splitting the transmission and reception. A guideline is 1/2 or less of the width a (relationship of formula (10)). 16A to 16C are cases where b=a/3, and the number of elements to obtain the same aperture width a as in the case of no division is 4/3 times (1.33 times). Larger apertures can be obtained.

With the probe structure described above, the maximum aperture width for oblique-angle inspection is secured with a limited number of elements, and oblique-angle inspection is performed with high sensitivity. Flaw detection can also be performed.

In addition, the present invention is not limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiments have been described in detail in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the described configurations. In addition, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. Moreover, it is possible to add, delete, or replace a part of the configuration of each embodiment with another configuration.

REFERENCE SIGNS LIST 1 piezoelectric element 2 vibrator array 3 wedge 4 array probe 5 probe movement mechanism 7 controller 16 synthetic wave 18 transverse wave 20 test object 21 weld line 23 crack

Claims (6)

an array probe having a wedge in which a transducer array composed of a plurality of piezoelectric elements is arranged parallel to a tangential plane on the flaw detection surface of the object;
selecting a predetermined number of piezoelectric element groups from the plurality of piezoelectric elements, controlling transmission timing of the plurality of ultrasonic waves transmitted from the piezoelectric element group, and controlling a propagation direction of a composite wave composed of the plurality of ultrasonic waves; and a controller for scanning the
The transmission direction of the composite wave is scanned in the front-rear direction of the array probe, and the mode conversion of the composite wave incident on the flaw detection surface through the wedge causes the composite wave to enter the subject in the front-rear direction of the array probe. It is possible to excite a transverse wave with an intensity equal to
A part of the transducer group in the transducer array is divided into two in the transducer longitudinal direction, and is acoustically isolated by an acoustic isolation plate inserted into the wedge, and the divided transducer group is divided into two groups. 1. An ultrasonic inspection apparatus characterized in that vertical flaw detection is performed using one transducer as a transmitting transducer and the other as a receiving transducer . In the ultrasonic inspection apparatus according to claim 1,
An ultrasonic inspection apparatus according to claim 1, wherein the thickness of said wedge is 1.5 times or more the wavelength of the longitudinal wave in said wedge, and its shape is rotationally symmetrical about a normal line at the center of said transducer array. In the ultrasonic inspection apparatus according to claim 2,
The wedge has a parallelogram shape when viewed from the top and a trapezoid when viewed from the side. An ultrasonic inspection apparatus, characterized in that it is arranged so that its direction is parallel to the longitudinal edges of said parallelogram. In the ultrasonic inspection apparatus according to any one of claims 1 to 3 ,
An ultrasonic inspection apparatus according to claim 1, wherein a length b of a region dividing the transducers into two with respect to an aperture width a of the entire transducer array satisfies b≦0.5a. In the ultrasonic inspection apparatus according to any one of claims 1 to 4 ,
By having an additional array probe having a structure similar to that of the array probe, and arranging the two array probes so that their directions are perpendicular to each other, four oblique directions can be obtained without moving the probe. An ultrasonic inspection apparatus capable of performing corner flaw detection. An ultrasonic inspection method using the ultrasonic inspection apparatus according to any one of claims 1 to 5 , wherein vertical flaw detection and oblique flaw detection in two or more directions and two or more angles without moving the probe An ultrasonic examination method characterized by carrying out.

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