JP4415313B2 - Ultrasonic probe, ultrasonic flaw detection method and ultrasonic flaw detection apparatus - Google Patents

Description

  The present invention relates to an ultrasonic probe for ultrasonic flaw detection of a metal tube, an ultrasonic flaw detection method using the ultrasonic probe, and an ultrasonic flaw detection device, and more particularly to high accuracy up to minute flaws generated in a metal pipe in oblique flaw detection. The present invention relates to an ultrasonic probe capable of performing flaw detection, an ultrasonic flaw detection method and an ultrasonic flaw detection apparatus using the same.

  As the demand for high quality metal pipes used as oil well pipes, line pipes, machine parts, etc. increases, the standards for non-destructive inspection for metal pipes tend to be stricter.

  Conventionally, as a nondestructive inspection method for a metal tube, an ultrasonic flaw detection method for inspecting a defect nondestructively by making an ultrasonic wave incident on the metal tube and detecting a reflection echo from the defect has been performed. Among such ultrasonic flaw detection methods, when inspecting flaws generated on the inner and outer surfaces of the metal tube and inside, and flaws in the welded portion of the metal tube, ultrasonic waves are mainly incident obliquely with respect to the surface of the metal tube. Oblique flaw detection has been applied.

Here, when an ultrasonic wave is incident obliquely on a metal tube, even if the ultrasonic wave (incident wave) incident from the ultrasonic probe is only a longitudinal wave ultrasonic wave, refraction propagates inside the metal tube. It is known that there are longitudinal wave ultrasonic waves (refracted longitudinal waves) and transverse wave ultrasonic waves (refracted transverse waves). If these refracted waves have the relationship shown in FIG. 1 with respect to the incident wave, Snell's law expressed by the following equation (1) holds.
sin θi / Vi = sin θs / Vs = sin θL / VL (1)
However, in the above equation (1), Vi is the velocity of longitudinal ultrasonic waves in the medium I (see FIG. 1), Vs is the velocity of transverse ultrasonic waves in the medium II (see FIG. 1), and VL is the longitudinal velocity in the medium II. The sound velocity of the wave ultrasonic wave, θi means the incident angle of the incident wave, θs means the refraction angle of the transverse wave ultrasonic wave, and θL means the refraction angle of the longitudinal wave ultrasonic wave. In the case of the general oblique flaw detection method, the medium I is water (liquid contact medium) or a resin such as acrylic constituting an ultrasonic probe (oblique probe), and the medium II is an object to be inspected. It is a metal tube.

  As described above, when an ultrasonic wave is incident on the metal tube at an incident angle θi from the ultrasonic probe, the ultrasonic wave is repeatedly reflected on the inner surface and the outer surface of the metal tube as shown in FIG. Propagates inside the tube. If there is a flaw on the inner or outer surface or inside of the metal tube, the reflected ultrasonic wave (reflected echo) does not return to the ultrasonic probe and is received as an echo.

  However, as shown in FIG. 1, when longitudinal and transverse ultrasonic waves coexist in a refracted wave propagating inside the metal tube (medium II), the flaw echo received by the ultrasonic probe becomes longitudinal ultrasonic waves. It is difficult to distinguish whether it is due to shear wave or due to transverse ultrasonic waves. As a result, it is difficult to determine the position of occurrence of a flaw, the received signal waveform becomes complicated, and the SN ratio of the flaw echo decreases. There was a problem.

  In order to solve such a problem, in general, the incident angle θi is set to be larger than the critical angle of the longitudinal ultrasonic wave so that only the transverse ultrasonic wave exists in the refracted wave propagating inside the metal tube. . More specifically, for example, if the medium I is water, the sound velocity Vi of the longitudinal wave ultrasonic wave in the medium I at room temperature is about 1500 m / sec, and the longitudinal wave ultrasonic wave in the medium II (metal tube) Assuming that the speed of sound VL is 5900 m / sec and the speed of sound Vs of transverse ultrasonic waves is 3200 m / sec, the incident angle θi, which is the critical angle of longitudinal ultrasonic waves (θL = 90 °), is about 15 °. Thus, the refraction angle θs of the transverse ultrasonic wave is about 33 °. That is, by selecting an angle of 15 ° or more as the incident angle of the ultrasonic wave, in principle, only the transverse wave ultrasonic wave exists in the medium II.

  However, in the conventional ultrasonic flaw detection method described above, a high t / D metal tube having a large t / D (t is the thickness of the metal tube, D is the outer diameter of the metal tube) of the metal tube to be inspected (for example, , T / D is 20% or more), as shown in FIG. 3, the ultrasonic wave is applied from the outer surface side of the high t / D metal tube at an incident angle θi that is equal to or greater than the critical angle of the longitudinal ultrasonic wave. When incident, the refraction transverse wave propagating inside the metal tube does not reach the inner surface of the metal tube but follows the propagation path to the outer surface, and there is a problem that the inner surface flaw existing on the inner surface of the metal tube cannot be detected. It was.

  As means for solving such a problem, for example, in Patent Document 1, a vibrator (first vibrator) in which the refraction angle θs of the transverse ultrasonic wave inside the metal tube is large (greater than about 35 °) is used. When an ultrasonic probe including a vibrator (second vibrator) whose refraction angle θs is small (less than about 35 °) is used to detect a normal metal tube, the first On the other hand, it has been proposed to use a combination of the first vibrator and the second vibrator when flaw detection is performed on a high t / D metal tube.

  According to the ultrasonic probe described in Patent Document 1, when a high t / D metal tube is flawed, it is possible to cause the refraction transverse wave generated by the second vibrator to reach the inner surface of the metal tube. As described above, since the second vibrator also generates a refraction longitudinal wave, the problem that the position where the flaw is generated cannot be specified, and the received signal waveform becomes complicated, resulting in a decrease in the SN ratio of the flaw echo. The problem will arise.

  By the way, in order to detect minute flaws generated in the metal tube, an acoustic lens whose end face is spherical (or cylindrical) is placed in front of the vibrator (or the end face of the vibrator is made spherical or cylindrical). In some cases, a method of focusing ultrasonic waves in a metal tube is employed (see Non-Patent Document 1). More specifically, when detecting a flaw that is short in the tube axis direction of the metal tube and has a small flaw depth, an acoustic lens having a spherical end surface is used (or the end surface of the vibrator is processed into a spherical shape). ) When detecting flaws having a small flaw depth but continuous in the tube axis direction, an acoustic lens having an end surface of a cylindrical surface shape (a shape in which the cylindrical surface is curved along the circumferential direction of the metal tube) is used ( Alternatively, the end face of the vibrator is processed into a cylindrical surface shape).

  According to the above method, it is possible to increase the intensity of the flaw echo by focusing the ultrasonic wave (for example, to focus on the inner surface of the metal tube) and to detect the flaw echo with a good S / N ratio.

  FIG. 4 is a diagram schematically illustrating an example of propagation behavior of a refraction longitudinal wave and a refraction transverse wave propagating inside the metal tube when an ultrasonic wave (a refraction transverse wave) is focused on the inner surface of the metal tube. FIG. 4 shows a metal tube having a t / D of approximately 20% or more (FIGS. 4A and 4B) and a metal tube having a t / D of approximately 20% or less (about 10%). The propagation behavior of the refraction longitudinal wave and the refraction transverse wave in the case (FIGS. 4C and 4D) is shown.

  As shown in FIG. 4, in the case of a metal tube having t / D of approximately 20% or less, the refracted transverse wave is focused on the inner surface of the metal tube (FIG. 4C) and no refracted longitudinal wave is generated (FIG. 4). 4 (d)) The conditions can be set, but in the case of a metal tube (high t / D metal tube) with a t / D of approximately 20% or more, as described above, the refracted shear wave reaches the inner surface of the metal tube. If it tries to make it (FIG. 4 (a)), a refraction longitudinal wave will also generate | occur | produce (FIG.4 (b)). At this time, a part of the generated refraction longitudinal wave reaches the inner surface of the metal tube in the same manner as the refraction transverse wave, but the refraction longitudinal wave reaching the inner surface of the metal tube propagates at an angle substantially perpendicular to the inner surface of the metal tube. Therefore, multiple reflection occurs on the inner and outer surfaces of the metal tube.

  FIG. 5 is a diagram showing an example of a reflected echo observed when a high t / D metal tube is flawed. As shown in FIG. 5, the inner surface flaw echo by the refraction transverse wave is observed so as to be buried between the multiple reflection echoes of the refraction longitudinal wave. Therefore, it is difficult to detect a minute flaw with a good S / N ratio because a refracted longitudinal wave multiple reflection echo becomes a noise signal that hinders flaw detection. In addition, depending on the thickness of the metal tube, the flaw echo is buried in the multiple reflection echo of the refraction longitudinal wave that appears in a forest shape, so that even a skilled inspector may not be able to identify the appearance of the flaw echo.

  As a method for removing the noise of the multiple reflection echo that stands in the high t / D metal pipe, for example, in Patent Document 2, flaw detection at two frequencies is performed alternately, and the flaw detection waveform at each frequency is subjected to differential processing. Thus, a method of removing multiple reflection echoes has been proposed. More specifically, after detecting flaw echoes and multiple reflection echoes with flaw detection at one frequency, and detecting only multiple reflection echoes with flaw detection at the other frequency, flaws can be obtained by subtracting them. It is a method that tries to extract only echo.

However, the method described in Patent Document 2 has the following problems (a) to (c). That is,
(A) Since it is necessary to collect flaw detection waveforms at almost the same position alternately at two frequencies, the inspection efficiency is reduced to about ½.
(B) When the intensity of the flaw echo is equal to or smaller than the intensity of the adjacent multiple reflection echo and / or when the appearance position of the flaw echo is very close to the appearance position of the multiple reflection echo, the multiple reflection When differential processing is performed on the echo, a part or most of the scratch echo is subtracted, and the scratch echo may not be detected from the waveform after the differential processing.
(C) In order to detect flaws at a plurality of frequencies, a special ultrasonic flaw detector is required, and the inspection cost such as introduction of a dedicated device increases.
Japanese Patent Laid-Open No. 10-90239 JP-A-6-337263 "Ultrasonic flaw detection method" Japan Society for the Promotion of Science, Steelmaking 19th Committee, Nikkan Kogyo Shimbun, p224-p227

  The present invention has been made to solve the problems of the prior art as described above, and an ultrasonic probe capable of highly accurately detecting even a minute flaw in oblique inspection of a metal tube. It is another object of the present invention to provide an ultrasonic flaw detection method and an ultrasonic flaw detection apparatus using the same.

In order to solve the above problems, the inventors of the present invention have made extensive studies and as a result, have obtained the following knowledge. That is,
(A) As described above, a high t / D metal tube is flaw-detected with an ultrasonic probe whose end surface is spherical (or cylindrical surface) (the end of the cross section perpendicular to the axial direction of the metal tube is an arc). In this case, when the refracted transverse wave is focused on the inner surface of the metal tube (FIG. 4A), the simultaneously generated refracted longitudinal wave also reaches the inner surface of the metal tube (FIG. 4B). However, the refracted longitudinal wave that reaches the inner surface of the metal tube is transmitted from a portion located on the ultrasonic wave propagation direction side (left side in FIG. 4) when viewed from the center of the metal tube, and is incident on the outer surface of the metal tube. It is caused by. The ultrasonic wave transmitted from the left side of the paper has a small incident angle on the outer surface of the metal tube, which reduces the refraction angle of the longitudinal ultrasonic wave, and the refracted longitudinal wave reaches the inner surface of the metal tube. To do.

  (B) Therefore, as shown in FIG. 6 (a), the ultrasonic wave propagation direction side (paper surface in FIG. 6 (a)) viewed from the center of the metal tube (the position where the horizontal axis is 0 mm in FIG. 6 (a)). The end portion of the cross section orthogonal to the axial direction of the metal tube of the ultrasonic probe located on the left side) is deviated from the arc shape (hereinafter referred to as “cross-sectional end shape” as appropriate), and the curvature radius thereof Is larger than the portion located on the opposite side (the right side of FIG. 6A) (the arc shape is crushed). As a result, the incident angle of ultrasonic waves and the refraction angle of longitudinal ultrasonic waves transmitted from the left side of the surface of the ultrasonic probe are increased, and the refraction longitudinal waves do not reach the inner surface of the metal tube and do not reach the outer surface of the metal tube. (FIG. 6B). Therefore, it is possible to suppress multiple reflection echoes due to refraction longitudinal waves. As for the refracted shear wave, if the deviation from the arc shape is set as the shape of the entire probe cross-section end while considering to reach the inner surface of the metal tube and converge at a specific position near the inner surface. good.

The present invention has been completed based on the knowledge found by the inventors of the present invention described above.
That is, the present invention is an ultrasonic probe for detecting flaws by obliquely incident ultrasonic waves on a metal tube, and has an end shape in a cross section perpendicular to the axial direction of the metal tube of the ultrasonic probe However, in a refracted wave consisting of longitudinal and transverse ultrasonic waves propagating inside the metal tube, the non-circular shape is designed so that the transverse ultrasonic wave is focused and the longitudinal ultrasonic wave does not reach the inner surface of the metal tube. It is an object of the present invention to provide an ultrasonic probe.

  According to the non-arc-shaped ultrasonic probe according to the present invention, the reflected echo intensity from minute flaws is increased by focusing the transverse wave ultrasonic wave among the refracted waves, and simultaneously generated longitudinal wave ultrasonic waves are generated. Since a propagation path that does not reach the inner surface of the metal tube is traced, multiple reflected echoes due to the longitudinal ultrasonic waves can be suppressed, and high-accuracy ultrasonic flaw detection can be realized.

  “The end shape of the cross section perpendicular to the axial direction of the metal tube of the ultrasonic probe is a non-arc shape” means that the ultrasonic probe is disposed to detect the metal tube. In addition, it means that the end shape of the cross section orthogonal to the axial direction of the metal tube of the ultrasonic probe is a non-arc shape, and an acoustic lens is arranged in front of the transducer. In the ultrasonic probe, this means including the case where the cross-sectional end shape of the acoustic lens is a non-arc shape. Furthermore, as will be described later, in an ultrasonic probe including an array probe configured by arranging a plurality of elements in parallel, by adjusting the delay time of ultrasonic transmission / reception for each element, This also includes the case of simulating a mode in which ultrasonic waves are transmitted from an ultrasonic probe having a non-arc shape.

  Here, in order to design the cross-sectional end shape of the ultrasonic probe so that the transverse wave ultrasonic wave is focused among the refracted waves and the longitudinal wave ultrasonic wave does not reach the inner surface of the metal tube, for example, it is set in advance. Based on the shape of the metal tube (outer diameter, wall thickness, etc.), the sound velocity of the transverse ultrasonic wave in the metal tube, the sound velocity of the longitudinal wave ultrasonic wave in the contact medium, and the focal point of the transverse wave ultrasonic wave in the metal tube, A first step of calculating a propagation path of the ultrasonic wave propagating to the focal point; a propagation path calculated in the first step; and a preset length along the circumferential direction of the metal tube of the ultrasonic probe. Based on the second step of calculating the cross-sectional end shape of the ultrasonic probe, the cross-sectional end shape of the ultrasonic probe calculated in the second step, and the vertical length in the preset metal tube Longitudinal ultrasonic waves propagating inside a metal tube based on the speed of ultrasonic waves If there is a propagation path that reaches the inner surface of the metal pipe among the propagation path of the longitudinal wave ultrasonic wave calculated in the third step and the third step of calculating the propagation path of the horizontal wave, the convergence of the transverse wave ultrasonic wave While changing the point and repeating from the first step to the third step, when there is no propagation path reaching the inner surface of the metal tube, the cross-sectional end shape calculated in the second step is adopted. Four steps may be executed.

  As described above, the ultrasonic probe is an array probe configured by arranging a plurality of elements in parallel, and in a refracted wave composed of longitudinal and transverse ultrasonic waves propagating inside the metal tube. It is also possible to adopt a configuration in which the delay time of ultrasonic transmission / reception is set for each element so that the transverse wave ultrasonic wave is focused and the longitudinal wave ultrasonic wave does not reach the inner surface of the metal tube.

  In order to solve the above-mentioned problem, the present invention is characterized by an ultrasonic flaw detection method characterized by flaw detection using the ultrasonic probe or the ultrasonic probe. Also provided as an ultrasonic flaw detector.

  According to the ultrasonic probe and the like according to the present invention, an excellent effect is achieved that a flaw can be detected with high accuracy even in a minute angle inspection of a metal tube.

  Hereinafter, an embodiment of an ultrasonic probe (ultrasonic flaw detector) according to the present invention will be described with reference to the accompanying drawings as appropriate.

<First Embodiment>
FIG. 7 is a block diagram showing a schematic configuration of the ultrasonic flaw detector according to the first embodiment of the present invention. As shown in FIG. 7, the ultrasonic flaw detector 100 according to this embodiment includes an ultrasonic probe 1, an ultrasonic flaw detector 2, an alarm device 3, and a marking device 4.

  The ultrasonic probe 1 is opposed to the outer surface of the metal tube P, and has an end shape in a cross section perpendicular to the axial direction of the metal tube P (a cross-sectional end shape of a transducer constituting the ultrasonic probe 1). ) In the refracted wave composed of the longitudinal ultrasonic wave U1 and the transverse ultrasonic wave U2 propagating inside the metal tube P, the transverse wave ultrasonic wave U2 is focused and the longitudinal wave ultrasonic wave U1 does not reach the inner surface of the metal tube P. It has a non-arc shape designed by the procedure described later. In order to realize such a non-arc shape with high accuracy as designed, the transducer constituting the ultrasonic probe 1 according to the present embodiment is not a ceramic piezoelectric element typified by PZT, but easily deformed PZT. -Consists of epoxy composite piezoelectric elements.

  The ultrasonic flaw detector 2 according to the present embodiment includes a pulsar 21, a preamplifier 22, a filter 23, a main amplifier 24, and a flaw determination unit 25, and an ultrasonic probe via a coaxial cable C. 1 is connected. The vibrator constituting the ultrasonic probe 1 is excited by a transmission signal from the pulsar 21 every predetermined period, and the ultrasonic wave U is incident on the metal pipe P through the water W as a contact medium. The incident ultrasonic wave U propagates inside the metal tube P as a refracted wave composed of a longitudinal ultrasonic wave U1 and a transverse ultrasonic wave U2, and its reflected echo (such as a flaw echo) is received by the vibrator, and the received signal is an ultrasonic wave. It is transmitted to the flaw detector 2. The received signal is amplified by the preamplifier 22 of the ultrasonic flaw detector 2, filtered in a predetermined frequency band by the filter 23, and further amplified by the main amplifier 24. The output signal from the main amplifier 24 is compared with a predetermined threshold value determined in advance by the flaw determination unit 25. If the output signal exceeds the threshold value, it is determined that there is a flaw, and the alarm device 3 or marking An operation command to the device 4 is output. The alarm device 3 outputs an alarm sound based on the operation command, and the marking device 4 is configured to perform a predetermined marking on the surface of the metal pipe P based on the operation command.

  When flaw detection is performed on the metal pipe P by the ultrasonic flaw detector 100 having the above-described configuration, the metal pipe P is spirally transported (moved in the axial direction while rotating in the circumferential direction). It enables flaw detection over the entire surface. However, the present invention is not limited to this, and it is also possible to adopt a mode in which the ultrasonic probe 1 is rotated in the circumferential direction of the metal tube P while the metal tube P is conveyed straight in the axial direction.

  The ultrasonic flaw detector 100 according to the present embodiment includes t / D (t is the thickness of the metal pipe P, D, for example, a mechanical tube used for automobile parts or a stainless steel pipe used in a high temperature environment). It is possible to make a steel pipe whose outer diameter (the outer diameter of the metal pipe P) is 20% or more suitable for inspection.

  The procedure for designing the cross-sectional end shape of the ultrasonic probe 1 to a non-arc shape will be specifically described below.

FIG. 8 is a flowchart schematically showing a procedure for designing the cross-sectional end shape of the ultrasonic probe. 9A to 9D are explanatory diagrams for explaining a design procedure when a metal pipe (steel pipe) P having an outer diameter of 40 mm and a wall thickness of 10 mm is an inspection target.
As shown in FIG. 8, when designing the cross-sectional end shape of the ultrasonic probe 1, first, (1) the shape (outer diameter, thickness) of the metal tube P, and (2) the metal tube P The speed of sound of a transverse wave ultrasonic wave, (3) The speed of sound of a longitudinal wave ultrasonic wave in the metal tube P, (4) The speed of sound of a longitudinal wave ultrasonic wave in a contact medium (water in this embodiment), and (5) The ultrasonic probe 1 The length of the metal pipe P along the circumferential direction is set as a condition (S1 in FIG. 8). In addition, as the sound velocity of the longitudinal wave ultrasonic wave in the contact medium and the sound velocity of the transverse wave ultrasonic wave and the longitudinal wave ultrasonic wave in the metal tube P, known numerical data corresponding to the type of the contact medium, the material of the metal tube P, and the like are used. Alternatively, experimental data may be collected in advance and used as a set value. In addition, the length along the circumferential direction of the metal tube P of the ultrasonic probe 1 may be set to a length that can provide sufficient transmission / reception sensitivity and can be actually manufactured. In general, although it depends on the shape of the metal tube P, the size of the flaw to be detected, and the material of the vibrator, the value is about 6 to 20 mm.

  Next, (6) after setting the convergence point S (see FIG. 9A) of the transverse ultrasonic wave in the metal tube P (S2 in FIG. 8), the above (1), (2), (4) and (6) Based on the conditions, the propagation path of the ultrasonic wave propagating to the focal point S is calculated (S3 in FIG. 8). Referring to FIG. 9A, the calculation contents will be described in more detail. First, a transverse wave is radiated radially from the focusing point S set on the inner surface P2 of the metal tube P toward the outer surface P1 of the metal tube P. A plurality of propagation paths of the ultrasonic wave U2 (in practice, the transverse ultrasonic wave U2 propagates from the outer surface P1 toward the focusing point S) is drawn. Next, since Snell's law is established at the boundary surface between the outer surface P1 of the metal pipe P and the contact medium W, the incident angle of the incident wave is calculated based on the above conditions (2) and (4), and the super Each propagation path of the longitudinal wave ultrasonic wave U in the contact medium W connected to each propagation path of the sound wave U2 is calculated. Then, an assumed ultrasonic probe is assumed for the initial point (end point opposite to the converging point S) S0 of each propagation path of the ultrasonic wave (longitudinal ultrasonic wave U and transverse wave ultrasonic wave U2) propagating to the converging point S. The initial point S0 is separated from the metal tube P by a distance substantially equal to the offset distance between the child 1 and the metal tube P, and the propagation time of the ultrasonic wave that follows each propagation path (calculated by the length of the propagation path and the sound velocity). Determined to be the same as each other. As described above, the propagation path of the ultrasonic wave (longitudinal wave ultrasonic wave U and transverse wave ultrasonic wave U2) propagating to the focal point S is calculated.

  Next, the cross-sectional end shape of the ultrasonic probe 1 is calculated based on the propagation path calculated as described above and the condition (5) (S4 in FIG. 8). More specifically, the length of a curve obtained by sequentially connecting the initial points S0 of each propagation path or a curve approximated from each initial point S0 (such as least square approximation) is calculated, and this is calculated as (5) above. Compared with the above condition (length along the circumferential direction of the metal tube P of the ultrasonic probe 1), unnecessary propagation paths are omitted from the end so that both are substantially equal in length, and the remaining propagation A curve D calculated from each initial point S0 of the path is defined as the cross-sectional end shape of the ultrasonic probe 1. Note that the example shown in FIG. 9A shows a state in which unnecessary propagation paths are already omitted so as to have a cross-sectional end shape having a length substantially equal to the left and right with respect to the central axis of the metal tube P.

  Next, based on the cross-sectional end shape D calculated as described above and the condition (3) above, the propagation path of the longitudinal ultrasonic wave U1 propagating inside the metal tube P is calculated (S5 in FIG. 8). ). More specifically, as shown in FIG. 9A, the longitudinal wave ultrasonic wave U that follows each propagation path in the contact medium W from each initial point S0 that constitutes the cross-sectional end shape D includes a metal tube P. Since Snell's law is established at the boundary surface between the outer surface P1 and the contact medium W, the refraction angle of the longitudinal wave ultrasonic wave U1 that is refracted and propagates inside the metal tube P is calculated based on the condition (3). Each propagation path of the longitudinal wave ultrasonic wave U1 connected to each propagation path of the longitudinal wave ultrasonic wave U is calculated.

  Next, it is determined whether or not there is a propagation path that reaches the inner surface P2 (see FIG. 9A) of the metal pipe P among the propagation paths of the longitudinal ultrasonic wave U1 calculated as described above (FIG. 8). S6). In the example shown in FIG. 9A, there is a propagation path that reaches the inner surface P2.

  When there is a propagation path that reaches the inner surface P2, the focal point S of the transverse ultrasonic waves is changed (for example, changed at a predetermined pitch along the inner surface P2) (S7 in FIG. 8), and the above-described calculation (FIG. 8). Steps S2 to S5) are repeated. FIG. 9B to FIG. 9D show such a state. By changing the focusing point S along the inner surface P2 of the metal tube P so as to be stepped away from the central axis of the metal tube P, FIG. 9D is obtained. In the state shown, all propagation paths of the longitudinal wave ultrasonic wave U1 do not reach the inner surface P2.

  When there is no longer any propagation path reaching the inner surface P2, the cross-sectional end shape D calculated immediately before (S4 in FIG. 8) is adopted as the cross-sectional end shape of the final ultrasonic probe 1. To do. In the example shown in FIG. 9A, the cross-sectional end shape D when the state shown in FIG. 9D is reached is adopted. More specifically, a cross-sectional end shape is adopted in which the end of each cross section of the ultrasonic probe 1 perpendicular to the axial direction of the metal tube P becomes a curved line D uniformly.

  By the procedure described above, the cross-sectional end shape of the ultrasonic probe 1 is designed to be a non-arc shape (cross-sectional end shape D). The design procedure described above may be executed by the designer drawing it each time, but it is of course possible to execute it automatically by programming, and the latter is more efficient in terms of design efficiency. desirable. Further, in FIGS. 9A to 9D, in order to facilitate the explanation, by analyzing the propagation path of the two-dimensional ultrasonic wave, as in the case of the conventional cylindrical surface shape, the super-orthogonal direction perpendicular to the axial direction of the metal tube P is used. Only the design procedure of the cross-sectional end shape so that the end of each cross-section of the acoustic probe 1 becomes a uniform curve has been described, but by analyzing the propagation path of the ultrasonic wave in three dimensions, Similarly to the spherical shape, it is also possible to design a cross-sectional end shape in which the end of each cross-section of the ultrasonic probe 1 perpendicular to the axial direction of the metal tube P does not form a uniform curve.

  FIG. 10 is a diagram showing an example of the result of designing the cross-sectional end shape of the ultrasonic probe 1 on the basis of the flow chart shown in FIG. 8 described above for high t / D metal tubes of various dimensions. In addition, in FIG. 10, in order to make it easy to understand the difference in the cross-sectional end shape of the ultrasonic probe 1 designed in accordance with various dimensions of the metal tube, each cross-sectional end shape is shown in the horizontal direction and the vertical direction. Plots are translated. As shown in FIG. 10, the object to be inspected according to the present invention is not limited to a metal tube having an outer diameter of 40 mm and a thickness of 10 mm described with reference to FIGS. 9A to 9D, and a high t / D metal tube is used. By applying the design procedure described above to the metal tubes having various dimensions, it is possible to design the cross-sectional end shape of the ultrasonic probe 1 corresponding to the metal tubes having various dimensions.

  In setting the focusing point S of the transverse ultrasonic wave in the metal tube P (S2 in FIG. 8), it is preferable to consider the reflectance of the flaw. More specifically, as shown in FIG. 11, the reflectance of the transverse ultrasonic wave at the flaw (slit-like flaw extending in the axial direction of the metal tube P) depends on the incident angle θ of the transverse wave ultrasonic wave. (If the range of incident angles that can be actually set is considered, the reflectivity increases at about 40 ° to 50 °). Therefore, in order to improve the flaw detection accuracy (increase the intensity of flaw echoes), the incident angle θ is 40 °. It is preferable to design the end shape of the cross section of the ultrasonic probe 1 according to the flowchart shown in FIG. 8 with the focusing point S that can be about ˜50 ° as an initial value.

  FIG. 12 shows flaw detection of 0.1 mm deep flaws existing on the inner surface of a mechanical tube having a high t / D (t / D is 20% or more) by the ultrasonic flaw detection apparatus 100 according to the present embodiment described above. An example of the flaw detection waveform (output signal waveform of the main amplifier 24) obtained at the time of the inspection is shown. As shown in FIG. 12, according to the ultrasonic flaw detector 100 according to the present embodiment, the intensity of reflected echo from minute flaws is increased by focusing the transverse wave ultrasonic wave U2 among the refracted waves (U1, U2). Since the simultaneously generated longitudinal wave ultrasonic wave U1 follows a propagation path that does not reach the inner surface of the metal tube (mechanical tube) P, it is possible to suppress the multiple reflection echo due to the longitudinal wave ultrasonic wave U1, and to improve only the flaw echo. It is possible to detect by the S / N ratio.

  In the present embodiment, the aspect in which the cross-sectional end shape of the transducer itself constituting the ultrasonic probe 1 is a non-arc shape has been described. However, the present invention is not limited to this, and the transducer It is also possible to arrange an acoustic lens made of a resin such as acryl and make the end shape of the cross section of the acoustic lens a non-arc shape designed according to the design procedure described above. When such an aspect is employed, a ceramic piezoelectric element that is difficult to deform, such as PZT, can be used as the vibrator.

<Second Embodiment>
FIG. 13 is a diagram showing a schematic configuration of an ultrasonic flaw detector according to the second embodiment of the present invention. As shown in FIG. 13, an ultrasonic flaw detector 100A according to this embodiment includes an ultrasonic probe 1, an ultrasonic flaw detector (not shown), an alarm device (not shown), and a marking device ( (Not shown). The ultrasonic flaw detector 100A according to the present embodiment includes a probe holder 71, a vertical movement arm 72, a horizontal movement arm 73, a tube following mechanism 74, and an air cylinder 75. Since the ultrasonic flaw detector, the alarm device, and the marking device have the same configuration as that of the first embodiment described above, description thereof is omitted.

  The ultrasonic probe 1 is prepared in advance according to the material of the metal tube (sound velocity of longitudinal wave / transverse wave ultrasonic wave), outer diameter, wall thickness, etc. (see FIG. 8). A suitable one for the metal tube P to be inspected is selected from a plurality of ultrasonic probes, and is manually or automatically loaded into the probe holder 71.

  The probe holder 71 is connected to a tube following mechanism 74 via a vertical movement arm 72, a horizontal movement arm 73, and the like. The tube following mechanism 74 is connected to the air cylinder 75 and is configured to move up and down by the air cylinder 75. When the tube follow-up mechanism 74 moves up and down, the vertical movement arm 72, the horizontal movement arm 73, and the probe holder 71 coupled to the vertical movement arm 72 also move up and down together.

  The relative positional relationship between the ultrasonic probe 1 and the metal tube P is determined in advance by driving the vertical movement arm 72 and the horizontal movement arm 73. If the relative positional relationship between the ultrasonic probe 1 and the metal tube P shifts, the position of the convergence point S of the transverse wave ultrasonic wave in the metal tube P assumed when the cross-sectional end shape of the ultrasonic probe 1 is designed. As a result, the flaw detection ability is reduced. Therefore, in order to accurately set the relative positional relationship between the ultrasonic probe 1 and the metal tube P, it is preferable to use linear guides as the vertical movement arm 72 and the horizontal movement arm 73.

  When flaw detection is performed on the metal pipe P by the ultrasonic flaw detection apparatus 100A having the above-described configuration, spiral conveyance is performed with the tip of the metal pipe P closed with a plug (not shown) for preventing water from entering the inside. While passing through a flaw detection water tank (not shown). At this time, the air cylinder 75 is activated at the timing when the tip of the metal tube P is detected by a predetermined material detection sensor, whereby the tube following mechanism 74, the vertical movement arm 72, the horizontal movement arm 73, and the probe holder 71 are moved. The pipe follow-up mechanism 74 is pressed against the outer surface of the metal pipe P with an appropriate pressure.

  The tube follower mechanism 74 pressed with an appropriate pressure is configured to be movable within a predetermined range in the up, down, left and right directions. It will move up, down, left and right following the backlash. At this time, the vertical movement arm 72, the horizontal movement arm 73 and the probe holder 71 connected to the tube following mechanism also move following the vertical and horizontal directions, and thereby the superstructure loaded in the probe holder 71. The relative positional relationship between the acoustic probe 1 and the metal tube P is kept constant.

  Also with the ultrasonic flaw detector 100A according to the present embodiment, the intensity of reflected echo from minute flaws is increased by the convergence of the transverse wave ultrasonic wave, and the propagation path through which the longitudinal wave ultrasonic wave that occurs simultaneously does not reach the inner surface of the metal tube P is obtained. Therefore, it is possible to suppress the multiple reflection echo due to the longitudinal ultrasonic wave, and it is possible to detect only the flaw echo with a good SN ratio.

  FIG. 13 shows an example in which two ultrasonic probes 1 are arranged so that the ultrasonic wave propagation direction in the metal pipe P is two directions, clockwise and counterclockwise. In order to further improve the efficiency, for example, a plurality of ultrasonic probes 1 whose ultrasonic propagation directions are clockwise and counterclockwise can be arranged along the axial direction of the metal tube P. is there.

<Third Embodiment>
FIG. 14 is a block diagram showing a schematic configuration of an ultrasonic flaw detector according to the third embodiment of the present invention. As shown in FIG. 14, the ultrasonic flaw detector 100B according to the present embodiment includes an ultrasonic probe 1A, a transmission circuit 5, a reception circuit 6, an alarm device 3, and a marking device 4. . In addition, since the alarm device 3 and the marking device 4 have the same configuration as that of the first embodiment, description thereof is omitted.

  The ultrasonic probe 1A according to the present embodiment is disposed so as to face the outer surface of the metal tube P, and a plurality of (for example, 32) micro piezoelectric elements 11 are juxtaposed in a cross section orthogonal to the axial direction of the metal tube P. For example, the array probe is configured to be arranged linearly at intervals of 0.5 mm.

  The transmission circuit 5 includes the same number of pulsars 51 and delay circuits (transmission delay circuits) 52 as the number of piezoelectric elements 11 included in the ultrasonic probe 1A. Each pulsar 51 is connected to each piezoelectric element 11 of the ultrasonic probe 1 </ b> A and to each delay circuit 52. Each piezoelectric element 11 is excited by a transmission signal for each predetermined period from each pulsar 51 connected to each piezoelectric element 11, and an ultrasonic wave U is incident on the metal pipe P through water W as a contact medium. Here, the timing of transmitting a transmission signal from each pulsar 51 can be different for each pulsar 51 according to the transmission delay time set by each delay circuit 52, and as will be described later, By appropriately setting the transmission delay time, a mode in which ultrasonic waves are transmitted from an ultrasonic probe whose cross-sectional end shape is a non-arc shape is simulated.

  The ultrasonic wave U incident on the metal tube P propagates inside the metal tube P as a refracted wave composed of the longitudinal wave ultrasonic wave U1 and the transverse wave ultrasonic wave U2, and the reflected echo is transmitted by the piezoelectric element 11 included in the ultrasonic probe 1A. The received signal is transmitted to the receiving circuit 6.

  The reception circuit 6 includes the same number of preamplifiers 61 and delay circuits (reception delay circuits) 62 as the number of piezoelectric elements 11 included in the ultrasonic probe 1A. The receiving circuit 6 includes an adder 63, a main amplifier 64, and a flaw determination unit 65. Each preamplifier 61 is connected to each piezoelectric element 11 of the ultrasonic probe 1 </ b> A and to each delay circuit 62. The reception signal from each piezoelectric element 11 is amplified by each preamplifier 61 connected to each piezoelectric element 11, and then transmitted by each delay circuit 62 connected to each preamplifier 61. The reception delay time is the same as the transmission delay time of each pulsar 51 connected to the piezoelectric element 11. The output signal of each delay circuit 62 is added by an adder 63 included in the receiving circuit 6 and then amplified by a main amplifier 64. An output signal from the main amplifier 64 is input to a flaw determination unit 65 having the same configuration as that of the flaw determination unit 25 of the first embodiment, and the presence or absence of a flaw is determined.

  Hereinafter, a method for setting the above-described transmission delay time and reception delay time will be described.

  FIG. 15 is an explanatory diagram for explaining a method of setting the transmission delay time and the reception delay time. As shown in FIG. 15, when setting the transmission delay time and the reception delay time, first, the horizontal direction of the non-arc shape D designed by the same procedure as the procedure described in the first embodiment (see FIG. 8). 15 is compared with the length of the ultrasonic probe 1A, and the piezoelectric element 11 to be used is selected so that both are substantially the same length (of the selected piezoelectric element 11). A group is called a selection element group).

  Next, the relative distance between the center coordinates of each piezoelectric element 11 constituting the selected element group and the non-arc shape D is calculated (the relative distance between any one of the piezoelectric elements 11 and the non-arc shape D is calculated as 0). In FIG. 15, the relative distance between the rightmost piezoelectric element 11 and the non-circular arc shape D is 0), and the value obtained by dividing each relative distance by the sound velocity of the longitudinal ultrasonic wave U in the contact medium W corresponds to each piezoelectric element 11. Set as transmission delay time and reception delay time.

  By setting the transmission delay time and the reception delay time by the method described above, the same behavior as when transmitting and receiving ultrasonic waves with an ultrasonic probe whose cross-sectional end shape is a non-circular arc shape D is shown. Become. That is, as shown in FIG. 14, in the refracted wave composed of the longitudinal wave ultrasonic wave U1 and the transverse wave ultrasonic wave U2 propagating inside the metal tube P, the transverse wave ultrasonic wave U2 is focused and the longitudinal wave ultrasonic wave U1 is applied to the inner surface of the metal tube. Will not reach. Therefore, the intensity of the reflected echo from the minute flaw is increased by the convergence of the transverse wave ultrasonic wave U2, and the multiple reflected echo by the longitudinal wave ultrasonic wave U1 that is simultaneously generated can be suppressed. Can be detected.

  In the ultrasonic flaw detector 100B according to the present embodiment, the ultrasonic probe 1A is configured as an array probe, and by setting the delay time of ultrasonic transmission / reception for each piezoelectric element 11 appropriately, the cross-sectional end shape is This configuration can simulate a non-arc shaped ultrasonic probe (non-arc shaped probe). In other words, by using a kind of ultrasonic probe 1A in which the arrangement of the piezoelectric elements 11 is fixed (in the present embodiment, linear arrangement), the delay time of ultrasonic transmission / reception is changed as appropriate. Because it is possible to simulate a non-arc shaped probe, there is no need to prepare a large number of non-arc shaped probes according to the material, outer diameter, wall thickness, etc. of the metal tube P, and the running cost is reduced. It is possible to suppress. Further, since it is not necessary to replace the non-arc-shaped probe according to the material, outer diameter, thickness, etc. of the metal tube P, the time required for the setup change can be shortened, and the inspection efficiency can be improved. Has the advantage.

  In the present embodiment, the case where the array probe in which the piezoelectric elements 11 are linearly arranged is applied as the ultrasonic probe 1A has been described. However, the present invention is not limited to this, and each array is not limited thereto. It is also possible to apply an array probe arranged in an arc shape or a polygonal shape as long as the corresponding ultrasonic transmission / reception delay time is set.

FIG. 1 is an explanatory diagram for explaining a refraction phenomenon of an ultrasonic wave at a boundary surface between media having different sound speeds. FIG. 2 is an explanatory diagram for explaining the propagation behavior of ultrasonic waves in oblique flaw detection of a metal tube. FIG. 3 is an explanatory diagram for explaining a conventional problem in the case of oblique flaw detection of a high t / D metal tube. FIG. 4 is a diagram schematically illustrating a conventional example of the propagation behavior of a refracting longitudinal wave and a refracting transverse wave propagating through the metal tube when an ultrasonic wave (refracted transverse wave) is focused on the inner surface of the metal tube. FIG. 5 is a diagram showing a conventional example of a reflected echo observed when a high t / D metal tube is flawed. FIG. 6 is an explanatory diagram for explaining the propagation behavior of ultrasonic waves when the non-arc-shaped ultrasonic probe according to the present invention is applied. FIG. 7 is a block diagram showing a schematic configuration of the ultrasonic flaw detector according to the first embodiment of the present invention. FIG. 8 is a flowchart schematically showing a procedure for designing the cross-sectional end shape of the ultrasonic probe. FIG. 9A is an explanatory diagram for describing a procedure for designing the cross-sectional end shape of the ultrasonic probe. FIG. 9B is an explanatory diagram for describing a procedure for designing the cross-sectional end shape of the ultrasonic probe. FIG. 9C is an explanatory diagram for describing a procedure for designing a cross-sectional end shape of the ultrasonic probe. FIG. 9D is an explanatory diagram for describing a procedure for designing the cross-sectional end shape of the ultrasonic probe. FIG. 10 is a diagram illustrating an example of a result of designing the cross-sectional end shape of the ultrasonic probe for various t-D metal tubes having various dimensions. FIG. 11 is an explanatory diagram for explaining matters to be considered when setting the focal point of the transverse wave ultrasonic wave in the procedure for designing the cross-sectional end shape of the ultrasonic probe. FIG. 12 shows an example of a flaw detection waveform by the ultrasonic flaw detector according to the first embodiment of the present invention. FIG. 13 is a diagram showing a schematic configuration of an ultrasonic flaw detector according to the second embodiment of the present invention. FIG. 14 is a block diagram showing a schematic configuration of an ultrasonic flaw detector according to the third embodiment of the present invention. FIG. 15 is an explanatory diagram for explaining a setting method of a transmission delay time and a reception delay time in the ultrasonic flaw detector according to the third embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,1A ... Ultrasonic probe 2 ... Ultrasonic flaw detector P ... Metal pipe U ... Ultrasonic wave U1 ... Longitudinal wave ultrasonic wave U2 ... Transverse wave ultrasonic wave

Claims (5)

An ultrasonic probe for detecting flaws by obliquely injecting ultrasonic waves into a metal tube,
The end shape of the cross section perpendicular to the axial direction of the metal tube of the ultrasonic probe has a longitudinal wave and a longitudinal wave that are propagated inside the metal tube. An ultrasonic probe characterized by having a non-circular shape designed so that wave ultrasonic waves do not reach the inner surface of a metal tube. The cross-sectional end shape of the ultrasonic probe is:
Propagation to the focusing point based on the preset metal tube shape, the sound velocity of the transverse wave ultrasonic wave in the metal tube, the sound velocity of the longitudinal wave ultrasonic wave in the contact medium, and the focal point of the transverse wave ultrasonic wave in the metal tube A first step of calculating a propagation path of ultrasonic waves to be
Based on the propagation path calculated in the first step and a preset length along the circumferential direction of the metal tube of the ultrasonic probe, a first shape for calculating the cross-sectional end shape of the ultrasonic probe is calculated. Two steps,
Propagation of longitudinal ultrasonic waves propagating inside the metal tube based on the cross-sectional end shape of the ultrasonic probe calculated in the second step and the sound velocity of longitudinal ultrasonic waves in the metal tube set in advance A third step of calculating a route;
If there is a propagation path that reaches the inner surface of the metal tube among the propagation paths of the longitudinal wave ultrasonic wave calculated in the third step, the focal point of the transverse wave ultrasonic wave is changed, While repeating up to the third step, when there is no propagation path reaching the inner surface of the metal tube, a fourth step adopting the cross-sectional end shape calculated in the second step;
The ultrasonic probe according to claim 1, wherein the ultrasonic probe has a non-arc shape designed by performing the above. An ultrasonic probe for detecting flaws by obliquely injecting ultrasonic waves into a metal tube,
The ultrasonic probe is an array probe configured by arranging a plurality of elements in parallel,
In the refracted wave consisting of longitudinal and transverse ultrasonic waves propagating inside the metal tube, the ultrasonic wave is delayed for each element so that the transverse wave ultrasonic wave is focused and the longitudinal wave ultrasonic wave does not reach the inner surface of the metal tube. ultrasonic probe you characterized in that time is set.   An ultrasonic flaw detection method comprising flaw detection using the ultrasonic probe according to claim 1.   An ultrasonic flaw detector comprising the ultrasonic probe according to claim 1.

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