JP5127573B2 - Ultrasonic flaw detection apparatus and method - Google Patents

Description

  The present invention relates to an ultrasonic flaw detection apparatus and method for detecting an internal defect of a subject by transmitting an ultrasonic wave to the inside of the subject by receiving a refraction phenomenon caused by a medium different from the subject and receiving a reflected wave from the inside of the subject. In particular, an ultrasonic flaw detection apparatus and method suitable for detecting a defect from the inside of a subject far from the ultrasonic probe installation position by using an array probe to multiplexly reflect transverse waves inside the subject. About.

  Conventionally, an ultrasonic method (ultrasonic flaw detection method) has been used as a non-destructive inspection method for solids that allow the propagation of longitudinal and transverse waves, such as steel materials generally used as power plant structures. As one of the ultrasonic flaw detection methods, there is a transverse wave oblique flaw detection method using a refraction phenomenon caused by a medium called a shoe or a wedge. Generally, in the shear wave oblique angle flaw detection method, a synthetic resin such as acrylic or polystyrene is used as a shoe material, and the shape thereof is a triangle (wedge shape). By causing refraction at the boundary between the object and the subject, an ultrasonic wave of a predetermined mode (transverse wave) can be obtained. Further, by adjusting the wedge-shaped angle of the shoe, it is possible to obtain a transverse wave ultrasonic wave that propagates at a desired angle.

  Here, one of the reasons for using a transverse wave for ultrasonic flaw detection of a structure is that the reflection efficiency in the subject is good. Structures usually have surface defects (cracks) such as cracks. To detect such surface defects, ultrasonic waves are incident directly above the crack. Instead, a method of making an ultrasonic wave incident from an oblique direction (an oblique flaw detection method) is often used. This is intended to receive an ultrasonic wave reflected from a defect with an ultrasonic probe at a higher intensity by applying an ultrasonic wave from an oblique direction. At this time, the reflectance of the ultrasonic wave hitting the defect from the oblique direction is almost 100% for the transverse wave (when the propagation direction of the ultrasonic wave is transmitted within a range of about 35 to about 55 degrees with respect to the subject surface. ), The longitudinal wave is about 20%, and the transverse wave can receive signals with higher intensity. For these reasons, transverse wave oblique ultrasonic waves are often used to detect defects inside structures.

  As a piezoelectric vibrator constituting an ultrasonic probe, there are one that generates a longitudinal wave and one that generates a transverse wave. A contact medium is used to transmit ultrasonic waves from the ultrasonic probe (or shoe) to the subject. Longitudinal ultrasonic waves can penetrate the liquid, but transverse waves do not penetrate the liquid with sufficient intensity. For this reason, in order to transmit the transverse wave vibration directly to the subject, it is necessary to use a contact medium having a very high viscosity. In ultrasonic flaw detection of a structure, it is common to use a liquid contact medium (water, oil, glycerin, etc.) that is easy to apply and remove in consideration of workability related to application and removal of the contact medium.

  Considering such workability, in ultrasonic flaw detection of a structure, a method using a refraction phenomenon by a shoe, not a transverse wave transducer that directly transmits a transverse wave vibration to a subject, that is, a longitudinal wave propagating in the shoe is shoeed. A flaw detection method for converting into a transverse wave at the boundary between the object and the subject is widely used.

  As a conventional shear wave oblique angle flaw detection method, a single piezoelectric vibrator is installed on a shoe with a certain angle. In this case, the transverse wave that can be generated by the refraction phenomenon is limited to one angular direction. Therefore, in order to change the ultrasonic wave propagation direction from 40 degrees to 50 degrees, for example, it is necessary to change to a shoe having a different angle (or sound speed).

  As a countermeasure against such a problem, a method of using an ultrasonic array probe and a shoe in combination has been proposed. A phased array method can be applied by using an ultrasonic array probe.

  Here, since the phased array method is also called an electronic scanning method or an electronic scanning method, for example, a so-called array probe in which a plurality of ultrasonic generating elements made of piezoelectric vibrators are arranged in an array shape is used. An electrical signal that triggers the generation of ultrasonic waves is given to each element of this array probe with a predetermined time delay, and the ultrasonic waves generated from each element are superimposed to form a composite wave, thereby inspecting Conditions such as the transmission angle and reception angle of ultrasonic waves to the body, the transmission position and reception position, or the position where the combined wave interferes and strengthens each other, that is, the focal position, can be changed at high speed by electrical control. This is an ultrasonic flaw detection method that can be used.

The reason for electrically scanning the flaw detection conditions using the array probe in this way is that the ultrasonic transmission / reception angular position and focus can be freely changed over a wide angle range. This is because by selecting the angle, position, and focal point at which the reflected wave from the reflection source (defect, etc.) inside or on the body can be received more strongly, the defect that is the reflection source can be easily found. By using a child, the angle at which the transverse ultrasonic wave is transmitted can be made plural, and the shoe replacement work is unnecessary, but in order to change the angle by the phased array method using the array probe, It is necessary to sufficiently reduce the size of the piezoelectric vibrator constituting the array probe. For example, it is known that the interval (pitch) between the piezoelectric vibrators is set to be longer than 1/4 of the wavelength of the subject and shorter than 1/2 (see, for example, Patent Document 1).

US Pat. No. 4,363,115

  As described above, conventionally, when the transverse wave oblique flaw detection method is realized by using the phased array method using the array probe, it is said that it is necessary to make the pitch of the piezoelectric elements constituting the array probe fine. It was. For example, when carbon steel is flaw-detected with a transverse wave at a frequency of 5 MHz, if the transverse wave sound velocity of the carbon steel is 3200 m / second, the wavelength is 0.64 mm, and the element pitch is, for example, 0.32 mm. When the size of the piezoelectric vibrator is reduced, the sensor opening of the entire array probe is reduced, and the sensitivity of the entire sensor is lowered. In addition, since the piezoelectric transducers become finer, the electrical impedance of the piezoelectric transducers increases, making it difficult to achieve electrical matching. Therefore, the sensitivity of each transducer that makes up the array probe There is a problem that the sensitivity of the entire array probe is further lowered.

  In addition, since the size of the entire array probe is reduced, it is necessary to move the position of the array probe when testing the subject, and there is a problem that the inspection time becomes longer.

  The purpose of the present invention is to increase the size of the piezoelectric transducers constituting the array probe, thereby increasing the aperture of the entire array probe, improving electrical matching, and generating a highly sensitive signal. It is an object of the present invention to provide an ultrasonic flaw detection apparatus and method that can be obtained and can perform a wide range of inspections in a short time by using a large array probe.

(1) In order to achieve the above object, the present invention generates ultrasonic waves generated from an ultrasonic probe to a subject through a shoe having a sound velocity slower than that of the subject. An ultrasonic flaw detection apparatus for inspecting the subject, wherein the ultrasonic probe uses an array probe in which a plurality of piezoelectric transducers are arranged in an array, and the transverse wave oblique ultrasonic wave When the incident angle is 35 to 55 degrees, the element pitch of the plurality of piezoelectric vibrators is larger than 0.75 times the wavelength of the transverse wave propagating through the subject and smaller than 2.35 times. .
With this configuration, by increasing the size of the piezoelectric transducers that make up the array probe, the aperture of the entire array probe can be increased, and electrical matching can be improved to obtain highly sensitive signals. And a large array probe enables a wide range of inspections in a short time.

  (2) In the above (1), preferably, the shoe is provided with a step for constraining the position of the ultrasonic array probe to the end face of the subject.

(3) In order to achieve the above object, the present invention applies ultrasonic waves generated from an ultrasonic probe to a subject through a shoe having a sound velocity slower than that of the subject. An ultrasonic flaw detection method for inspecting the subject generated and using an array probe in which a plurality of piezoelectric vibrators are arranged in an array as the ultrasonic probe, When the incident angle of the sound wave is 35 degrees to 55 degrees, the element pitch of the plurality of piezoelectric vibrators is larger than 0.75 times the wavelength of the transverse wave propagating through the subject and smaller than 2.35 times. The ultrasonic array probe is installed on the subject, and both the signal obtained at the flaw detection location and the signal obtained at other than the flaw detection location in the same subject are displayed. Is.
By such a method, the size of the piezoelectric vibrator constituting the array probe is increased, so that the aperture of the entire array probe is increased, and electrical matching is improved, thereby obtaining a highly sensitive signal. And a large array probe enables a wide range of inspections in a short time.

  (4) In the above (3), preferably, the multiple reflection signals are added or averaged and combined and displayed using information on the incident direction of the ultrasonic wave and the thickness of the subject.

  According to the present invention, the size of the piezoelectric vibrator constituting the array probe is increased, so that the opening of the entire array probe is increased, electrical matching is improved, and a highly sensitive signal is generated. A large array probe that can be obtained enables a wide range of inspections in a short time.

Hereinafter, the configuration and operation of an ultrasonic flaw detector according to an embodiment of the present invention will be described with reference to FIGS.
First, the outline of the ultrasonic flaw detector according to the present embodiment will be described with reference to FIG.
FIG. 1 is a schematic view of an ultrasonic flaw detector according to an embodiment of the present invention. FIG. 1B is an enlarged view of the AA cross section of FIG.

  The ultrasonic flaw detector according to the present embodiment includes an ultrasonic array probe 104, a piezoelectric vibrator 106 constituting the ultrasonic array probe 104, a shoe 105 attached to the ultrasonic array probe 104, and an inspection target. The transmitting / receiving unit 107 that transmits ultrasonic waves to the subject 101 and receives the reflected signal from the subject 101, the data storage unit 108, and the display unit 109 that displays the received signal. Yes.

Here, an example of the subject of the ultrasonic flaw detector according to the present embodiment will be described with reference to FIG.
FIG. 2 is an explanatory diagram of an example of a subject of the ultrasonic flaw detector according to one embodiment of the present invention.

  A subject 101 shown in FIG. 1 is a plate-like subject having a step, and specifically, as shown in FIG. 2, a fork 805 for attaching a turbine blade 801 to a turbine rotor 804 has this shape. It corresponds to. A fork 805 is formed at the base of the turbine blade 801. The fork 805 is attached to the turbine rotor 804. At this time, the pin 802 is inserted into the pin hole 803 formed in the fork 805 and the turbine rotor 804, so that both are fixed. As shown, the fork 805 has a plate shape with a step. The surface on which the ultrasonic array probe and the shoe can be installed is limited to the upper surface 810 of the fork.

  Again, in FIG. 1, the subject 102 shown in FIG. 1 is represented as a flat plate-shaped cross-sectional view for the sake of simplicity. In order to inspect such an elongated subject, the transverse wave ultrasonic wave 111 transmitted by the ultrasonic array probe 104 and the shoe 105 is subjected to multiple reflection in the subject 101 a plurality of times, and the shape changing unit 102 (FIG. 2 is equivalent to the pin hole 803 in FIG.

  In this embodiment, in addition to the turbine blade mounting part (fork), in ultrasonic flaw detection such as flat plates and pipes, ultrasonic inspection is performed due to interference with the shape of the subject and structures existing around the subject. When it is difficult to bring the child close enough to the expected position of the defect, the ultrasonic probe is installed at a position away from the expected position of the inspection by reflecting the oblique wave ultrasonic waves in the subject multiple times. The present invention can also be applied to flaw detection.

  As shown in FIG. 1, the ultrasonic array probe 104 is installed on an inclined medium called a shoe 104, and the shoe 104 is installed on the subject 101. In this embodiment, it is assumed that the surface on which the ultrasonic array probe 104 and the shoe 105 can be installed is limited to the upper surface 112 of the subject 101 (in FIG. 2, the surface is limited to the surface 810). Suppose you are).

  The shoe 105 is made of a material whose sound speed is lower than that of the subject and whose density is low, and for example, a synthetic resin such as acrylic, polystyrene, or polyimide is used. In addition, a medium for transmitting longitudinal ultrasonic waves called a contact medium is interposed between the ultrasonic array probe 104 and the shoe 105 and between the shoe 105 and the subject 101. For example, water, machine oil, glycerin or the like is used as the contact medium.

  The piezoelectric vibrator 106 constituting the ultrasonic array probe 104 is connected to the transmission / reception unit 107, and a longitudinal wave is generated from the piezoelectric vibrator 106 inside the shoe 105 by a drive signal sent from the transmission / reception unit. The longitudinal wave ultrasonic wave 111 propagated in the shoe 105 is then converted into a transverse wave by a refraction phenomenon at the boundary between the shoe 105 and the subject 101 and propagated in the subject 101 as the transverse wave ultrasonic wave 111. The transverse ultrasonic wave that has been subjected to multiple reflections in the subject and reflected by the shape changing portion 102 or the defect 103 is refracted again at the boundary between the subject 101 and the shoe 105 and converted into a longitudinal wave. It propagates as a wave ultrasonic wave, is received by the piezoelectric vibrator 106 of the ultrasonic array probe 104, and is converted into an electric signal. The electric signal of the reception wave is received by the transmission / reception unit 107 and displayed on the display unit 109 as a reception signal. The received signal is stored as a reference signal in the storage unit 108 as necessary.

Next, the detailed configuration of the ultrasonic flaw detector according to the present embodiment will be described with reference to FIG.
FIG. 3 is a system block diagram showing the configuration of the ultrasonic flaw detector according to one embodiment of the present invention.

  The piezoelectric vibrator 106 constituting the ultrasonic array probe 104 is, for example, as an example of an ultrasonic generator, a piezoelectric ceramic or a composite piezoelectric body in which a thin rod of the piezoelectric ceramic is embedded in a polymer material ( (Also called composite). The piezoelectric vibrators (or elements) 106 are usually arranged at equal intervals, and the distance (element pitch) 120 between the piezoelectric vibrators 106 is important in determining the performance of the ultrasonic array probe 104. . Conventionally, the element pitch is generally set to 0.5 times or less of the wavelength of the ultrasonic wave propagating in the subject. However, in this embodiment, the wavelength of the transverse wave propagating through the subject is 0. It has the feature of increasing from .75 times to 2.35 times. The size of the element pitch 120 will be described later with reference to FIGS.

  The transmission / reception unit 107 includes a pulsar 107A, a receiver 107B, a delay time control unit 107C, a data recording unit 107D, a computer 107E, a connector 107F, and a switch 107G. While controlling the timing of the drive signal output from the pulsar 107A, the delay time control unit 107C controls the input timing of the received signal by the receiver 107B, whereby the operation of the ultrasonic array probe 104 by the phased array method is controlled. To be obtained. The data recording unit 107D functions to process the reception signal supplied from the receiver 107B and supply it to the display unit 109.

  The storage unit 108 records the flaw detection data recorded by the transmission / reception unit 107, and in particular stores flaw detection data (received signal) in a region (healthy portion) that is assumed to be free of defects as reference data 108A. In addition, the shape data 108B of the subject is stored and supplied to the computer 107E.

  The display unit 109 is a means for displaying a reception signal corresponding to an ultrasonic reception angle (in this example, since the transmission direction and the reception direction are the same, the transmission angle and the reception angle are the same). As an example, an example is shown in which received signals when ultrasonic waves are transmitted and received in the range from the start angle 611 to the end angle 610 are displayed in a sector shape with the angle in the circumferential direction and the one-way propagation distance in the axial direction. Such a method for flaw detection by changing the transmission angle of the ultrasonic wave is called a sector scan method in the phased array method.

  When the transmission angle is scanned from the start 611 to the end 610, the reflection signals 601A and 601B from the shape changing unit 102 of the subject and the reflection signal 602 assumed to be due to the defect are received, and a sector shape is obtained as in the flaw detection image 109A. Are displayed as areas of different colors or darkness according to the strength of the received signal.

  Here, in order to compare with the in-flaw detection image 109A, the reference data stored in the storage unit 108 may be read into a computer and displayed side by side with the in-flaw detection image as the sound portion image 109B. Thus, by comparing the healthy part image 109B and the flaw-detecting image 109A, the reflection signals 601A and 601B from the shape change part appear in both the healthy part image 109B and the flaw-detecting image 109A. It is possible to easily identify that the reflected signal 602 that is assumed to appear only in the flaw-detecting image 109A, and to determine the presence or absence of a defect in a short time.

Next, the reason why the element pitch is increased in the ultrasonic flaw detector according to the present embodiment will be described with reference to FIGS.
FIG. 4 is a system block diagram showing the configuration of the ultrasonic flaw detector according to one embodiment of the present invention.

  Hereinafter, the principle that the element pitch can be increased when a defect from the inside of the subject far from the ultrasonic probe installation position is detected by multiply reflecting the transverse wave inside the subject will be described.

  When inspecting a member where the installation surface 810 of the ultrasonic probe is limited, such as a fork (fork 805 in FIG. 2) of a turbine blade mounting portion to be inspected in this embodiment, a steel material or the like is used. Requires a method of flaw detection in which an ultrasonic wave is incident on the subject, multiple reflected in the subject, the ultrasonic wave is propagated far from the ultrasonic probe, and a reflected wave from the defect is received. In this case, in order to receive the energy of the incident ultrasonic wave with higher intensity, the transverse wave is advantageous in that the round-trip passing rate is larger than the longitudinal wave.

  On the other hand, the ultrasonic array probe 104 is composed of a plurality of regularly arranged piezoelectric vibrators (elements), and the angle range in which ultrasonic waves can be transmitted is the interval between the piezoelectric vibrators (elements). It is known that it greatly depends on the pitch.

  FIG. 4 shows an example of a numerical calculation result of an ultrasonic sound field formed by ultrasonic array probes having different element pitches. FIG. 4A shows an example in which the element pitch is the same as the wavelength of the ultrasonic wave propagating in the subject (element pitch = 1 wavelength), and FIG. 4B shows the element pitch propagating in the subject. This is an example in the case of half the wavelength of the ultrasonic wave.

  As shown in FIG. 4A, when the element pitch is large, ultrasonic waves are generated in the diagonally downward right direction (arrow 1202) in addition to the desired diagonally downward left direction (arrow 1201). I understand.

  On the other hand, as shown in FIG. 4B, when the element is small, only the desired ultrasonic wave (arrow 1201) is confirmed.

  In the example shown in FIG. 4A, the desired ultrasonic wave (arrow 1201) is called a main lobe, and the other ultrasonic wave (arrow 1202) is called a grating lobe.

Assuming that the angle of the main lobe is α and the element pitch that is the interval between the piezoelectric vibrators is p, the condition of the element pitch (p) at which no grating is generated is known to be given by the following expression (1). (See, for example, Masayasu Ito and Tsuyoshi Mochizuki, “Ultrasonic Diagnostic Equipment” Corona, Inc. (2002, first edition, first print), page 48).

The meaning of the expression (1) represents the maximum value of the element pitch p of the ultrasonic array probe when performing flaw detection transmitted in the direction of the angle α with ultrasonic waves (wavelength λ). When the equation (1) is transformed, the relationship between the angle α of the main lobe and the ratio p / λ of the element pitch p and the wavelength λ becomes as in the equation (2).

  FIG. 5 is a plot of equation (2) as a graph (curve 1403).

  From FIG. 5, it is better to use the transverse wave of 35 to 55 degrees in order to propagate the transverse wave into the subject with energy efficiency. That is, when the angle α of the main lobe is set to 35 to 55 degrees (region C), the maximum value of the element pitch p is 0.64 times the wavelength and 55 degrees when the incident angle is 35 degrees. It can be seen that the incident wavelength is 0.55 times the wavelength (region D). As described above, when the specification of the ultrasonic array probe is determined by using the equation (1) (or the equation (2)), when the flaw detection is performed in the subject at a lateral wave oblique angle of 35 to 55 degrees, the element pitch is It is necessary to make it 0.55 times or less of the wavelength.

  However, when the element pitch is reduced, as described above, the sensitivity of the signal is lowered due to the reason that the sensor opening of the entire ultrasonic array probe is reduced. In this embodiment, since a long path is propagated by multiple reflection in the subject, it is desirable that the sensitivity be as high as possible.

Note that the grating lobe is a phenomenon peculiar to the ultrasonic array probe, and is generated when the generation conditions are met. In the ultrasonic array probe, setting the main lobe to the angle α means that the phase of the ultrasonic wave transmitted in the direction of the angle α is set to the same phase. However, depending on the size of the element pitch, a phenomenon occurs in which the phases of the ultrasonic waves at different angles ψ are aligned by n × 2π times. In this way, the angle direction in which the phase is aligned as an integer multiple of 2π instead of the phase difference is 0 is called a grating lobe, and the grating angle ψ in which the phase is aligned at n times 2π can be written as in Expression (3). it can.

  Here, θ0 is a refraction angle of the transverse wave due to the refraction of the shoe, and there is a relationship of sin θ0 = sin (φ × V2 / V1) where the inclination angle of the shoe is φ. V1 is the longitudinal wave velocity of the shoe, and V2 is the transverse wave velocity of the subject.

  Here, the principle of taking a value larger than the element pitch defined by Equation (1) by limiting to ultrasonic flaw detection using multiple reflection of oblique angle transverse wave ultrasonic waves will be described.

  In the present embodiment, attention is paid to the angular dependence of the energy efficiency of the transverse wave with respect to the three quantities. The first is the angle dependency of the transverse wave passage rate from the shoe to the subject.

  Here, FIG. 6 shows the passage rate RTL (1303) when the longitudinal wave (110) passes as the transverse wave (111) from the synthetic resin shoe to the subject. It can be seen that when the transverse wave transmission angle αt is larger than 35 degrees, the transverse wave transmittance RTL has a large value.

  The second is the transverse wave reciprocation rate for transverse wave defects. In FIG. 6, the transverse wave reciprocation rate is plotted and shown.

  In consideration of the angular dependence of these two quantities, when the reflection efficiency (transverse wave reciprocation rate) at the defect is taken into consideration, the energy when the transverse wave transmission angle αt shown in region B is in the range of 35 degrees to 55 degrees It can be seen that the ultrasonic wave is transmitted from the shoe to the subject with high efficiency and reflected by the defect and can be received by the ultrasonic probe. Conversely, when the transverse wave transmission angle αt is in the region A, both when the ultrasonic wave is transmitted from the shoe to the subject and when the ultrasonic wave is reflected by the defect and returns to the ultrasonic probe. In the case of, energy loss is large. Therefore, as long as the grating lobe generation angle ψn is within the range of the region A, it can be considered that the influence of the grating lobe is small.

  The third is the angle dependency of the directivity of the piezoelectric vibrator (element) constituting the ultrasonic array probe. An ultrasonic wave generated from an ultrasonic probe having a finite size has a spread called directivity.

  FIG. 7B shows the directivity of ultrasonic waves, and has a distribution as shown by a curve 1601. FIG. 7B shows a case in which an ultrasonic wave is transmitted in an angle 45 ° (θ0 = 45) diagonally downward to the left with a refraction angle θ0 by the shoe. At this time, after the direction of the arrow 1602, the intensity of the ultrasonic wave is extremely small. If an angle at which the intensity is 1/10 with respect to the directivity peak value at the angle θ0 is defined as γ0, γ0 is given by an approximate expression such as Expression (4). The angle distribution represented by the curve 1601 is called directivity of one piezoelectric vibrator (element), and depends on the refraction angle θ0 by the shoe, the wavelength λ of the subject, and the element pitch p as shown in the equation (4). Amount. FIG. 7A shows the transverse wave transmittance RTL.

  The grating lobe generation angle ψn by the ultrasonic array probe is expressed by equation (3), and the grating lobe generation angle ψn has the directivity (1602 in FIG. 7B) of one piezoelectric vibrator (element). If it is out of range, the influence of the grating lobe can be regarded as small.

  As described above, in this embodiment, even if the element size is increased and the condition for generating a grating lobe is satisfied, the angle ψn at which the grating lobe propagates is set in the region A, or the piezoelectric vibration By setting it outside the directivity range of one child (element), the influence of the grating lobe is substantially suppressed.

  8, 9, and 10, when the transverse wave refraction angle θ0 by the shoe is 35 degrees, 45 degrees, and 55 degrees, the transverse wave refraction angle θ0, the grating lobe generation angle ψn, and the angle γ0 representing the spread of the piezoelectric vibrator are shown. This is an example of calculating the ratio p / λ between the element pitch p and the transverse wave wavelength λ in the subject. This covers the range where the reciprocation rate of the transverse ultrasonic wave is 100%, and in this embodiment, it is assumed that θ0 is used in the range of 35 to 55 degrees.

  From FIG. 8 (θ0 = 35 degrees), the angle γ0 representing the spread of the piezoelectric vibrator is larger than the grating lobe generation angle ψn−1, that is, the grating lobe generation angle ψn−1 is the region 1601 in FIG. From this condition, the condition that p / λ is larger than 0.75 is derived. Further, the condition that p / λ is smaller than 2.35 is derived from the condition that the grating lobe ψ1 does not occur. Similarly, the conditions for p / λ are derived from FIGS. 9 and 10, both of which are within the range of the conditions obtained from FIG. 8. In this embodiment, the ultrasonic array probe is used. If the distance (element pitch) between the piezoelectric vibrators constituting the is greater than 0.75 times the wavelength propagating through the subject and less than 2.35 times, the influence of the grating lobe can be suppressed, In addition, the element pitch can be increased.

  8 to 10, acrylic (longitudinal wave sound velocity 2730 m / s) is assumed as a shoe, steel material (longitudinal wave sound velocity 5900 m / s, transverse wave sound velocity 3200 m / s) is assumed as an object, and 5 MHz is assumed as an ultrasonic frequency. However, the value varies greatly depending on the ultrasonic sound velocity of the shoe. FIG. 5 shows an example in which the transverse wave passage rate from the shoe to the subject is calculated for both the case where the longitudinal wave sound velocity of the shoe is 3000 m / s and 2000 m / s.

  FIG. 11A shows the transverse wave passing rate from the shoe to the subject when the longitudinal sound velocity of the shoe is 3000 m / s, and FIG. 11B shows the case where the longitudinal wave sound velocity of the shoe is 2000 m / s. The transverse wave passing rate from the shoe to the subject is shown.

  This is because the speed of sound of the synthetic resin used as the shoe material is normally distributed in the range of 2000 to 3000 m / s. In both cases of FIGS. 11A and 11B, it can be confirmed that the passing rate of the transverse wave is small when the transverse wave transmission angle αt is smaller than 30 degrees. Therefore, the content of the present invention can similarly obtain the effects of the invention even when the sound speed of the shoe varies depending on the material of the shoe.

Next, the flaw detection method using the ultrasonic flaw detector according to the present embodiment will be described with reference to FIG.
FIG. 12 is a flowchart showing the contents of the flaw detection method by the ultrasonic flaw detector according to the embodiment of the present invention.

  First, a combination of the ultrasonic array probe 104 and the shoe 105 is placed on the subject 101 (step S701).

  Next, it is selected whether the signal obtained in the same subject is used as a reference signal (step S702). In the case of NO, for example, the signal of the healthy part of the comparison specimen having the same shape and material of the subject is selected. Call to the computer 107E (step S703).

  On the other hand, if YES is selected, the ultrasound array probe 104 is moved on the probe scanning surface 112 on the subject 101, and the sound portion signal is recorded and stored in the storage portion 108 (step S704). ). Thereafter, the sound part signal is called to the computer 107E (step S705).

  Next, flaw detection is performed on the subject 101 (step S706), and a healthy part signal and a signal during flaw detection are displayed on the display unit 109 (step S707).

  The flaw detection signal and the healthy part signal are compared (step S708), and if there is no difference in the signal appearance pattern, the flaw detection position is determined to be healthy (step S709). If there is a difference, it is determined that there is a possibility of a defect (step S710). Thus, by comparing with the healthy part, it is possible to easily determine the presence or absence of a defect.

  As described above, according to the present embodiment, when the distance from the ultrasonic probe installation position to the defect is long, the element pitch is larger than 0.75 times the wavelength in the subject, and 2.35. By combining the ultrasonic array probe 104 and the shoe 105 and transmitting the transverse wave ultrasonic wave into the subject, the sensor aperture of the ultrasonic array probe is enlarged, Sensitivity is improved, sufficient signal intensity can be maintained even when multiple reflections are made inside the subject, and defects located far from the ultrasonic probe can be detected. This causes a problem that it becomes difficult to determine the defect due to the reception of complex signals due to multiple reflections. However, it is easy to determine the presence or absence of defects by displaying the sound part signal and the flaw detection signal. Can be. Thereby, highly sensitive ultrasonic flaw detection can be realized, and the time required for ultrasonic flaw detection including defect determination can be shortened.

  Moreover, as an ultrasonic probe, it is larger than 0.75 times the wavelength of the transverse wave propagating through the subject and smaller than 2.35 times, so that it is compared with about half of the conventional wavelength. By using a piezoelectric vibrator that is 1.5 to 4.5 times larger in size, a high-sensitivity signal can be obtained, and by performing a wide range of flaw detection at once, the time required for flaw detection can be reduced. It can be shortened.

Next, the configuration and operation of an ultrasonic flaw detector according to another embodiment of the present invention will be described with reference to FIGS.
FIG. 13 is a schematic view of an ultrasonic flaw detector according to another embodiment of the present invention. FIG. 14 is a flowchart showing the contents of a flaw detection method using an ultrasonic flaw detector according to another embodiment of the present invention.

  This embodiment is different from the embodiment shown in FIGS. 1 and 12 in the display method of the flaw detection result (reception signal) on the display unit 109, that is, the method of multiple reflection display. In the first embodiment, a method of displaying an ultrasonic wave propagation direction (angle) and a received signal on an arc or a fan shape is adopted.

  In the present embodiment, the reception signal obtained by multiple reflection inside the subject is displayed in correspondence with the shape of the subject in order to facilitate identification of the reflected wave from where. is there. That is, using the information on the incident direction of the ultrasonic wave and the thickness of the subject, the multiple reflection signals are added or averaged and combined and displayed.

  FIG. 13 shows a display example of flaw detection results according to this embodiment. Transverse ultrasonic waves are transmitted in the range from arrow 611 to arrow 610 by the ultrasonic array probe. At this time, an ultrasonic wave 1001 propagating in a certain angle direction θ1 and an ultrasonic wave 1003 propagating in another direction θ2 will be described as an example. In ordinary sector scan display, the intensity of the signal corresponding to the distance L (θ1) at the angle θ1 is displayed as an image at the black point 1002A, and the intensity of the signal corresponding to the distance L (θ2) at the angle θ2 is displayed as an image at the white point 1004A. Was. The amplitude value of the signal is obtained from the corresponding point (1002B, 1004B) of the A scan data with the distance (or time) on the horizontal axis and the amplitude value (or intensity) on the vertical axis. On the line segment extending in the direction (angles θ1 and θ2), the received signal is displayed on the pixel corresponding to the distance (L) in shades and colors according to the amplitude value (or intensity). Here, the amplitude value is an amount that takes both positive and negative values, and the intensity is an amount that takes a non-negative value taking an absolute value.

  In this embodiment, a geometric propagation path 1001C due to multiple reflection of ultrasonic waves corresponding to the transmission direction θ1 and a path 1003C for θ2 are obtained from the shape data 108B of the subject stored in the storage unit 108. The amplitude (or intensity) is displayed as a pixel at a point (1002C, 1004C) corresponding to the distance L on the broken line. However, in the normal fan-shaped display, the line segments 1001 and 1003 do not intersect after extending in a radial manner, but when they are displayed by a multiple reflection path like the points 1002C and 1004C in FIG. In some cases, the polygonal lines intersect. In this case, the added value or average value of the amplitude values of the intersecting points or the intensity average value or added value is displayed.

  Next, a flaw detection result display method according to this embodiment will be described with reference to FIG.

  First, flaw detection is performed while changing the ultrasonic transmission direction θ (step S1101), flaw detection data corresponding to each θ is recorded, and the data is read out to the computer (step S1102).

  Next, the shape data of the subject is read from the storage unit into the computer (step S1103). At this time, since the flaw detection data is data of time and amplitude, the time is multiplied by the speed of sound in the subject and further reduced by half (step S1104).

  Next, imaging corresponding to the angle θi is started (step S1105). A multiple reflection propagation path at an angle θi is calculated for the object shape (step S1106), and an amplitude value (or intensity) is temporarily recorded as a pixel value with respect to the one-way distance L (step S1107). Then, it is determined whether it is in the vicinity of the multiple reflection by θi and the intersection of the path by another angle (step S1108). (Step S1109). When the iterative process for the distance L is completed, the recorded pixel value is displayed (step S1110).

  After passing through the steps so far, the process proceeds to the next angle θi + 1, and the same processing is repeated for the angle θ, whereby the flaw detection data for all angles can be displayed. Finally, the flaw detection result and the subject shape are displayed together and the process ends (step S1111).

  According to the display method described above, a complex reflection that is multiple-reflected within the subject is obtained by combining or averaging the multiple reflected signals by using the information on the incident direction of the ultrasonic wave and the thickness of the subject, and then displaying the resultant by averaging. It is possible to display the flaw detection defect that becomes the propagation path according to the shape of the subject, it becomes easy to determine which reflection source the reflected signal is from, it is easy to determine the presence or absence of the defect, and flaw detection It is possible to reduce the time required for

Next, another configuration of the ultrasonic array probe used in the ultrasonic flaw detector according to each embodiment of the present invention will be described with reference to FIGS.
15 to 17 are perspective views showing other configurations of the ultrasonic array probe used in the ultrasonic flaw detector according to each embodiment of the present invention.

  In each of the above-described embodiments, as the ultrasonic array probe 104, as shown in FIG. 15, a large ultrasonic array probe 201 that covers the probe scanning surface 112 widely can be used. In this case, a large shoe 202 is also used.

  In this case, as the ultrasonic array probe 201, as shown in FIG. 16, an ultrasonic array probe 401 in which piezoelectric transducers 402 are arranged in a line may be used, and as shown in FIG. Alternatively, a matrix type array probe 501 in which a plurality of piezoelectric vibrators 502 are arranged in a plurality of rows may be used.

  The matrix type array probe 501 shown in FIG. 17 has two advantages compared to the ultrasonic array probe 401 in which the piezoelectric vibrators 402 shown in FIG. 16 are arranged in one row. First, since the ultrasonic transmission direction can be arbitrarily changed three-dimensionally, the ultrasonic array probe main body can be mechanically moved in order to obtain a signal from a healthy part or a defect. This is unnecessary and can be detected at high speed. Second, the focal point formed by the ultrasonic array probe becomes a point focus 503, which can increase the signal intensity as compared with the case of the line focus 403 formed by the one-dimensional array of probes 401. It becomes possible.

Next, another configuration of the shoe used in the ultrasonic flaw detector according to each embodiment of the present invention will be described with reference to FIG.
FIG. 18 is a front sectional view showing another configuration of a shoe used in the ultrasonic flaw detector according to each embodiment of the present invention.

  In each of the above-described embodiments, as shown in FIG. 18, as a shoe 105 combined with an ultrasonic array probe, a sound absorbing material 303 for suppressing multiple reflections of ultrasonic waves in the shoe, In order to facilitate the alignment of the sensor combining the ultrasonic array probe 104 and the shoe 105 on the probe scanning surface 112, a step 301 is formed in an L shape along the corner portion of the subject 101. May be provided. According to the level difference 301, the position of the ultrasonic probe with respect to the subject (the position in the left-right direction in FIG. 3) can be easily adjusted, and the ultrasonic probe can be easily installed, The effect of shortening the time of the sonic flaw detection can be obtained.

According to this example, since the step is used for restraining the ultrasonic array probe to the end surface of the subject on the shoe, positioning when the array probe is installed on the subject is facilitated. The time required for flaw detection can be shortened.

1 is a schematic view of an ultrasonic flaw detector according to an embodiment of the present invention. It is explanatory drawing of an example of the test object of the ultrasonic flaw detector by one Embodiment of this invention. 1 is a system block diagram showing a configuration of an ultrasonic flaw detector according to an embodiment of the present invention. 1 is a system block diagram showing a configuration of an ultrasonic flaw detector according to an embodiment of the present invention. It is explanatory drawing which concerns on the conventional method. It is a principle explanatory view of an ultrasonic flaw detector according to an embodiment of the present invention. It is a principle explanatory view of an ultrasonic flaw detector according to an embodiment of the present invention. It is a principle explanatory view of an ultrasonic flaw detector according to an embodiment of the present invention. It is a principle explanatory view of an ultrasonic flaw detector according to an embodiment of the present invention. It is a principle explanatory view of an ultrasonic flaw detector according to an embodiment of the present invention. It is a principle explanatory view of an ultrasonic flaw detector according to an embodiment of the present invention. It is a flowchart which shows the content of the flaw detection method by the ultrasonic flaw detector by one Embodiment of this invention. It is the schematic of the ultrasonic flaw detector by other embodiment of this invention. It is a flowchart which shows the content of the flaw detection method by the ultrasonic flaw detector by other embodiment of this invention. It is a perspective view which shows the other structure of the ultrasonic array probe used for the ultrasonic flaw detector by each embodiment of this invention. It is a perspective view which shows the other structure of the ultrasonic array probe used for the ultrasonic flaw detector by each embodiment of this invention. It is a perspective view which shows the other structure of the ultrasonic array probe used for the ultrasonic flaw detector by each embodiment of this invention. It is front sectional drawing which shows the other structure of the shoe used for the ultrasonic flaw detector by each embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Subject 102 ... Shape changing part 103 of subject ... Defect 104 ... Ultrasonic array probe 105 ... Shoe 106 ... Piezoelectric vibrator (element)
107: Transmission / reception unit 108 ... Storage unit 109 ... Display unit 801 ... Turbine blade 802 ... Pin 803 ... Pin hole 804 ... Turbine rotor 805 ... Fork

Claims (4)

An ultrasonic flaw detector that inspects the subject by generating ultrasonic waves generated from an ultrasonic probe through a shoe having a sound velocity slower than that of the subject, generating a transverse wave oblique angle ultrasonic wave on the subject,
As the ultrasonic probe, an array probe in which a plurality of piezoelectric vibrators are arranged in an array is used,
When the incident angle of the transverse wave oblique ultrasonic wave is 35 to 55 degrees, the element pitch of the plurality of piezoelectric vibrators is larger than 0.75 times the wavelength of the transverse wave propagating through the subject 2.35. Ultrasonic flaw detector characterized by being smaller than double. The ultrasonic flaw detector according to claim 1,
2. The ultrasonic flaw detector according to claim 1, wherein the shoe includes a step for constraining the position of the ultrasonic array probe to the end face of the subject. An ultrasonic flaw detection method for inspecting the subject by generating a transverse wave oblique ultrasonic wave on the subject through a shoe having a sound speed slower than that of the subject, the ultrasonic wave generated from the ultrasound probe,
As the ultrasonic probe, an array probe in which a plurality of piezoelectric vibrators are arranged in an array is used, and when the incident angle of the transverse wave oblique ultrasonic wave is 35 degrees to 55 degrees, the plural The ultrasonic array probe is placed on the subject using an element pitch of the piezoelectric vibrator having a pitch greater than 0.75 times and less than 2.35 times the wavelength of the transverse wave propagating through the subject. An ultrasonic flaw detection method characterized by displaying both a signal obtained at a flaw detection location and a signal obtained at a location other than the flaw detection location in the same subject. The ultrasonic flaw detection method according to claim 3,
An ultrasonic flaw detection method characterized in that multiple reflection signals are added or averaged and combined and displayed using information on the incident direction of ultrasonic waves and the thickness of the subject.

Images