JP2013234886A - Ultrasonic flaw detection method and device by tofd method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic flaw detection method and device by a TOFD method, capable of remarkably increasing an SN ratio of diffracted waves from foreign matter (for example cracks) by remarkably reducing noise generated inside a test body or on a surface layer thereof.SOLUTION: (1) By a sector scanning of a phased array probe 15b, the direction of an incident ultrasonic wave beam (incident wave S1) is changed, intersecting axes point depth D from the surface of a test body 3 at intersecting axes point X where central axes of ultrasonic wave beams of a transmission-side probe 12 and a reception-side probe 14 are intersected with each other is sequentially changed, and a plurality of diffracted waves S2 corresponding to a plurality of intersecting axes point depths D are received by the reception-side probe 14. (2) A combined waveform S3 of the diffracted waves S2 are created by overlapping a plurality of diffracted waves with one another.

Description

  The present invention relates to an ultrasonic flaw detection method and apparatus using the TOFD method.

  As a means for inspecting the inside of a test body with an ultrasonic beam, ultrasonic flaw detection by the TOFD method has been conventionally known (for example, Patent Documents 1 and 2).

JP 2004-117137 A JP 2011-149888 A

FIG. 1 is a schematic diagram of ultrasonic flaw detection by the TOFD method.
In the TOFD method, two oblique angle probes 1 and 2 are arranged facing each other at regular intervals to transmit and receive an ultrasonic beam. When there is no crack 4 inside the test body 3, only the lateral wave A propagating on the surface and the bottom echo C reflected on the back surface are obtained. On the other hand, when the crack 4 exists, the diffracted wave B at the crack end 5 is received. From the propagation time of the diffracted wave B, the depth of the crack end 5 can be obtained geometrically.

However, when the crack end 5 is in the vicinity of the surface layer portion, the lateral wave A and the diffracted wave B of the crack end 5 interfere with each other, and it is difficult to clearly identify the crack end 5. .
Hereinafter, this problem will be described.

FIG. 2 is a diagram showing a specific example of ultrasonic flaw detection by a conventional TOFD method. In this figure, a phased array probe 7 is mounted on a longitudinal wave wedge member 6 (hereinafter referred to as a wedge) for a steel material having a nominal refraction angle of 45 degrees, and the two wedges 6 are arranged to face each other. ing. The reason why the phased array probe 7 is mounted is to arbitrarily change the refraction angle of the ultrasonic beam by sector scanning. The center position of each element of the phased array probe 7 is arranged on the slope of the wedge 6 having a height of 20.8 mm from the wedge surface contacting the specimen 3 and 11.2 mm from the center position of the two wedges 6. An example is shown.
In this example, two flaw detection examples in which the intersection point 8 is connected to positions 1 mm and 2 mm immediately below the surface of the test body 3 will be considered. The longitudinal wave refraction angle at this time is geometrically 54 degrees and 62 degrees. In the flaw detection waveform at this time, a lateral wave A propagating on the surface and a diffracted wave B from the crack are obtained.

FIG. 3 is a schematic diagram showing a waveform when the intersection point depth is 1 mm, and FIG. 4 is a waveform diagram when the intersection point depth is 2 mm. In these drawings, (A) shows a lateral wave and a diffracted wave, and (B) shows a synthesized wave.
As shown in FIG. 3 and FIG. 4A, the lateral wave propagating on the surface (dotted line) and the diffracted wave at the crack tip at the intersection (solid line) each have a waveform of 2 waves at 10 MHz. However, the flaw detection waveform obtained by the conventional TOFD method is a single waveform obtained by synthesizing these two waveforms, as shown in FIGS.

  As described above, it is very difficult to separate the lateral wave and the diffracted wave when the intersecting point depth is 1 mm or 2 mm, and it is difficult to obtain crack depth information.

  The present invention has been developed to solve the above-described problems. That is, the object of the present invention is to reduce the noise generated in the test specimen or in its surface layer, and to significantly increase the SN ratio of the diffracted wave from a foreign substance (for example, a crack). It is to provide a flaw detection method and apparatus.

According to the present invention, in a state where the distance between the transmission probe and the reception probe is kept constant, an ultrasonic beam is incident on the inside of the test body by the transmission probe, and the ultrasonic beam is input by the reception probe. An ultrasonic flaw detection method using a TOFD method for receiving a diffracted wave of
The transmission probe and the reception probe consist of a wedge and a phased array probe mounted thereon,
The direction of the incident ultrasonic beam is changed by the sector scan of the phased array probe, and the cross-axis point where the central axis of the ultrasonic beam of the transmitting probe and the receiving probe intersects from the specimen surface A plurality of diffracted waves corresponding to a plurality of cross-axis point depths are received by the reception probe by sequentially changing the cross-axis point depths,
There is provided an ultrasonic flaw detection method using a TOFD method, wherein a composite waveform of diffracted waves is created by superimposing the plurality of diffracted waves.

In addition, according to the present invention, in a state where the distance between the transmission probe and the reception probe is kept constant, an ultrasonic beam is incident on the inside of the test body by the transmission probe, and the ultrasonic probe is input by the reception probe. An ultrasonic flaw detector using a TOFD method for receiving a diffracted wave of a sound beam,
The transmission probe and the reception probe consist of a wedge and a phased array probe mounted thereon,
Furthermore, a control device for controlling the transmission probe and the reception probe is provided.
The direction of the incident ultrasonic beam is changed by the sector scan of the phased array probe, and the cross-axis point where the central axis of the ultrasonic beam of the transmitting probe and the receiving probe intersects from the specimen surface A plurality of diffracted waves corresponding to a plurality of cross-axis point depths are received by the reception probe by sequentially changing the cross-axis point depths,
There is provided an ultrasonic flaw detector using a TOFD method, wherein a composite waveform of diffracted waves is created by superimposing the plurality of diffracted waves.

According to the method and apparatus of the present invention, (1) the direction of the incident ultrasonic beam is changed by sector scanning of the phased array probe, and the ultrasonic beams of the transmission probe and the reception probe are changed. The crossing point depth from the specimen surface of the crossing point where the central axis intersects is sequentially changed, and a plurality of diffracted waves corresponding to a plurality of crossing point depths are received by the receiving probe. 2) Since a composite waveform of diffracted waves is created by superimposing a plurality of diffracted waves, the noise that changes in the phase generated in the test specimen or in the surface layer thereof is greatly reduced, and foreign substances (for example, cracks) existing in the test specimen are reduced. The SN ratio of the diffracted wave from the (crack) can be greatly increased.

It is a schematic diagram of the ultrasonic flaw detection by TOFD method. It is a figure which shows the specific example of the ultrasonic flaw detection by the conventional TOFD method. It is a schematic diagram which shows a waveform in case an intersection point depth is 1 mm. It is a schematic diagram which shows a waveform in case an intersection point depth is 2 mm. 1 is an overall configuration diagram of an ultrasonic flaw detector according to the present invention. 1 is an overall flowchart of an ultrasonic flaw detection method according to the present invention. It is a figure which shows the propagation path of an ultrasonic beam in case an intersection point depth is 4 mm. It is a figure which shows the propagation path of an ultrasonic beam in case an intersection point depth is 6 mm. It is a figure which shows the synthetic | combination waveform of 20 diffracted waves which changed the intersection point depth. It is a figure which shows the synthetic | combination waveform calculated | required by synthesize | combining each flaw detection waveform and the flaw detection waveform obtained by the TOFD flaw detection in each crossing axis depth which was set when the intersection point depth D is 2 mm. It is a figure which shows the synthetic | combination B scope (left figure) and synthetic | combination A scope (right figure) of a synthetic | combination waveform in case an intersection point depth is 1.0, 1.5, and 2.0 mm. It is the figure which extracted the diffraction wave in the notch tip from a synthetic waveform, and calculated | required the depth geometrically from propagation time. It is the schematic diagram which applied the conventional TOFD method inside the test body. It is the schematic diagram which applied this invention inside the test body.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In each figure, common portions are denoted by the same reference numerals, and redundant description is omitted.

FIG. 5 is an overall configuration diagram of an ultrasonic flaw detector according to the present invention.
The ultrasonic flaw detector 10 of the present invention is configured so that an ultrasonic beam (incident wave S1) is placed inside the test body 3 by the transmission probe 12 in a state where the distance between the transmission probe 12 and the reception probe 14 is kept constant. ) And an ultrasonic flaw detector by the TOFD method that receives the diffracted wave S2 of the ultrasonic beam by the receiving probe 14.

  In this figure, an ultrasonic flaw detector 10 of the present invention includes a transmission probe 12, a reception probe 14, a control device 16, a display device 18, and an image processing device 20.

  The transmission probe 12 and the reception probe 14 are composed of a longitudinal wave wedge member 15a (hereinafter referred to as longitudinal wave wedge) and a phased array probe 15b mounted thereon. By the sector scan of the child 15b, focused flaw detection for focusing the ultrasonic beam can be performed.

The control device 16 controls the transmission probe 12 and the reception probe 14, and the ultrasonic beam (incident wave S1) incident from the transmission probe 12 is detected by the sector scan of the phased array probe 15b. 3, and the intersection point depth D of the intersection point X from the surface of the test body 3 is sequentially changed.
Further, the control device 16 receives a plurality of diffracted waves S2 corresponding to the intersection point depth D by the reception probe 14, and creates a composite waveform S3 of the diffracted waves S2 by superimposing the plurality of diffracted waves S2. .

The display device 18 is a display device and displays a combined waveform S3 of the diffracted wave S2.
The image processing apparatus 20 extracts a diffracted wave S4 of a foreign substance (for example, a crack) from the combined waveform S3 and geometrically determines the depth of the foreign substance from the propagation time.

FIG. 6 is an overall flowchart of the ultrasonic flaw detection method according to the present invention.
In the ultrasonic flaw detection method of the present invention, an ultrasonic beam (incident wave S1) is applied to the inside of the test body 3 by the transmission probe 12 while the distance between the transmission probe 12 and the reception probe 14 is kept constant. The ultrasonic flaw detection method according to the TOFD method in which the diffraction probe S2 is received by the reception probe 14 and the diffraction wave S2 of the ultrasonic beam is received.

  In FIG. 6, the ultrasonic flaw detection method of the present invention includes steps ST1 to ST6.

In ST1, the ultrasonic beam (incident wave S1) incident from the transmission probe 12 is focused on the intersection point X inside the test body 3 by the sector scan of the phased array probe 15b and the change of the intersection point X. And the intersection point depth D of the intersection point X from the surface of the test body 3 is changed.
In other words, in transmission / reception of ultrasonic beams having the same refraction angle, the refraction angle is changed, and the intersection point depth D is sequentially changed.

The change in the intersection point depth D is preferably performed at a pitch of 0.1 mm or more and 1.0 mm or less in a desired measurement range. Moreover, the number of the intersection point depths D is preferably 5 or more and 100 or less, and more preferably 20 or more and 50 or less. If the intersection point depth D exceeds 100, the inspection time becomes long.
In the examples described later, 41 different intersection depths D are implemented at a pitch of about 0.25 mm.

In ST2, the reception probe 14 receives the diffracted wave S2 corresponding to the intersection point depth D.
ST1 and ST2 are repeatedly performed by sequentially changing the intersection point depth D, and a plurality of diffracted waves S2 corresponding to the plurality of intersection point depths D are received.

In ST3, the control device 16 superimposes a plurality of diffracted waves S2 to create a combined waveform S3 of the diffracted waves S2.
In ST4, the display device 18 displays a plurality of diffracted waves S2 and their combined waveform S3.
In ST5, the image processing apparatus 20 extracts the diffracted wave S4 of the foreign matter from the combined waveform S3.
In ST6, the depth of the foreign matter is obtained geometrically from the propagation time of the diffracted wave S4 by the image processing device 20.

Hereinafter, the principle of the present invention will be described in detail.
FIG. 7 is a diagram showing a propagation path of an ultrasonic beam when the intersection point depth is 4 mm.
In this figure, it is assumed that a foreign substance (for example, a crack) exists at a depth of 2 mm.
Assuming that the center position of the transmitting side piezoelectric element is the point O, the central axis of the ultrasonic beam transmitted from the point O passes through a and goes to the point of intersection b having a depth of 4 mm. Here, at the point a, the path of the ultrasonic beam is determined under the condition that Snell's law of refraction holds. That is, the following expression (1) is established.
sin (θ _i ) / sin (θ _r ) = v _W / v _T (1)
Here, θ _i is the incident angle at the wedge, θ _r is the refraction angle at the specimen, v _{W is} the speed of sound of the wedge, and v _T is the speed of sound in the specimen.

On the other hand, a lateral wave is generated at the point a, and the ultrasonic beam propagating on the surface of the specimen is received by the receiving probe through the position of the central axis of the ultrasonic beam at the point a ′. However, the wave refracted on the surface of the specimen is directed to the point b, but since no sound source position (for example, a foreign object) exists at the point b, no diffracted wave is generated and no echo (diffracted wave) is received.
The above is the result of the study on the central axis of the ultrasonic beam, and the propagation time of the lateral wave is the path of the central axis of the ultrasonic beam where the maximum echo height can be obtained. On the other hand, the ultrasonic beam propagates with a spread around the central axis having the highest sound pressure. Considering the spread of this ultrasonic beam, the path of the diffracted wave from the sound source existing at a depth of 2 mm is examined. That is, it becomes a propagation path through c where Snell's law is established, and becomes a propagation path of Oc-d-c'-O '.

FIG. 8 is a diagram illustrating a propagation path of an ultrasonic beam when the intersection point depth is 6 mm.
Also in this figure, it is assumed that a foreign substance (for example, a crack) exists at a depth of 2 mm.
As shown in FIG. 8, the distance between a and a ′ where the lateral wave propagates becomes longer and the propagation time of the lateral wave becomes longer, whereas the propagation of the diffracted wave at the sound source position of the crack of the same depth. You can see that the time is the same.
That is, by performing flaw detection with the crossing point changed in the depth direction, the propagation time of the lateral wave changes, while the flaw detection waveform (diffracted wave S2) in which the propagation time of the diffracted wave from the crack does not change. You can get many. When the obtained flaw detection waveforms (diffracted waves S2) are superimposed, lateral waves whose propagation times change are weakened each other, and diffracted waves S4 from cracks whose propagation times do not change are strengthened, and the SN ratio is remarkably improved. The flaw detection waveform is obtained. Therefore, it is possible to accurately obtain depth information even for a crack near the surface.

FIG. 9 is a diagram showing a combined waveform of 20 diffracted waves with varying intersection point depths.
This figure is a composite waveform obtained by adding up all 20 diffracted waves in which the intersection point depth is changed from 0.5 mm to 10 mm at intervals of 0.5 mm in the apparatus of FIG. It is assumed that the waveform of the lateral wave and the crack diffracted wave obtained at each intersection point depth is equivalent to that in FIG.
From FIG. 9, it is clear that the lateral wave and the diffracted wave of the crack can be identified, and the SN ratio is remarkably improved as compared with FIG.

  Examples of the present invention will be described below.

FIG. 5 described above is a configuration diagram of the transmission probe 12 and the reception probe 14 used in the confirmation test.
The longitudinal wave wedge 15a of the transmission probe 12 and the reception probe 14 has a shape in which two wedges for longitudinal waves of 45 degrees in refraction angle are matched to a symmetrical shape, and an ultrasonic beam is placed on the target symmetry axis. An acoustic dividing surface 13 for preventing transmission is provided. Further, an inclined portion for mounting the phased array probe 15b is provided around the point O and the point O '.

  The longitudinal wave wedge 15a was equipped with a phased array probe 15b (element spacing 0.6 mm) of 32 channels at 10 MHz. The reason why the phased array probe 15b is used is that the beam is sector-scanned and the intersection point X is provided at an arbitrary depth D.

The axis of symmetry of the longitudinal wave wedge 15a is divided into 40 equal parts between a depth of 0.1 mm and a depth of 10 mm immediately below the surface of the test body 3, and 41 intersecting axes are provided. TOFD flaw detection was performed.
In this confirmation test, focused flaw detection in which the ultrasonic beam (incident wave S1 and diffracted wave S2) is focused at each intersection X is used.

  As test body 3, electric discharge machining notches having a depth of 0.4, 0.5, 0.75, 1.0, 1.5, and 2 mm were processed on a flat plate, and a test for evaluating a diffracted wave at the lower end of the notch was performed. . In the ultrasonic flaw detection, the probes 12 and 14 were scanned in the direction orthogonal to the longitudinal direction of the notches with respect to the respective notches, and the waveform of the diffracted wave S2 was collected. That is, 41 flaw detection images having different intersection points X were obtained for each notch. By superimposing these images, the effect of the present invention was confirmed, and the measurement accuracy of the lower end position of the crack (that is, the crack depth measurement accuracy) was verified. Scanning in the direction perpendicular to the length of the notch is to measure the depth by using a geometric condition in which the beam path of the diffracted wave is shortest when the crack is at the center position of the probes 12 and 14. Because.

(Test results)
FIG. 10 shows a flaw detection waveform obtained by TOFD flaw detection at each set cross axis depth when the cross axis depth D is 2 mm, and a composite waveform obtained by combining these flaw detection waveforms. FIG.
In this figure, each flaw detection image at a representative intersection point depth (0.1 mm, 0.6 mm, 1.1 mm, 1.6 mm, 2.1 mm, 2.6 mm and 3.1 mm) is represented by 41 This is compared with the flaw detection image according to the present invention in which the flaw detection image is synthesized. It is difficult to clearly identify the diffracted wave at the tip of the notch from the flaw detection images at any intersection depth, and it is difficult to measure the crack depth. On the other hand, the diffracted wave image of the crack tip clearly appears in the flaw detection image according to the present invention at the lower right, and it can be seen that the crack depth can be measured.

FIG. 11 is a diagram showing a composite B scope (left diagram) and a composite A scope (right diagram) of the composite waveform when the notch depth is 1.0, 1.5, and 2.0 mm.
From this figure, it can be seen that the lateral wave and the diffracted wave can be clearly separated.

FIG. 12 is a diagram in which a diffracted wave at the tip of the notch is extracted from the resultant combined waveform, and the depth is obtained geometrically from the propagation time. In this figure, the horizontal axis represents the notch depth and the vertical axis represents the propagation time difference.
From this figure, it can be seen that the measured value is in good agreement with the calculation result obtained geometrically, and the diffracted wave at the tip of the notch is accurately captured by the composite waveform according to the present invention.

  In Example 1 described above, the lower end position of the notch is measured, but it is clear that the measured echo measures the diffracted wave at the lower end of the notch, and is also effective for measuring the upper and lower ends of the buried crack. Obviously. Although applied to a crack in the surface layer portion, the present invention is effective not only for a crack in the surface layer portion but also for an internal crack.

FIG. 13 is a schematic diagram in which the conventional TOFD method is applied to the inside of the test specimen, and FIG. 14 is a schematic diagram in which the present invention is applied to the inside of the test specimen. In this figure, ● indicates a position where the sound field intensity is 50%, Δ indicates a position where it is 25%, and a broken line indicates a groove shape.
FIG. 13 shows an example of a sound field by the conventional TOFD method. Detection of a crack in a range away from this sound field becomes difficult to detect by moving away from the central axis of the ultrasonic beam.
On the other hand, FIG. 14 shows an example according to the present invention. In the present invention, since the intersection point depth is sequentially changed, flaw detection can be performed at a plurality of intersection points whose refraction angles are changed by phased array flaw detection. As a result, the flaw detection area increases, and by adding the obtained images to obtain the image of the present invention (the combined waveform of the diffracted waves), the diffracted wave of the crack obtained in the same beam path is emphasized, On the other hand, randomly generated noise is reduced by adding together, and as a result, the SN ratio can be significantly increased.

  According to the method and apparatus of the present invention described above, (1) the direction of the incident ultrasonic beam (incident wave S1) is changed by the sector scan of the phased array probe 15b, and the transmission probe 12 and the reception are received. The crossing point depth D from the surface of the test body 3 at the crossing point X at which the central axis of the ultrasonic beam of the probe 14 intersects is sequentially changed, and a plurality of crossing point depths are obtained by the receiving probe 14. A plurality of diffracted waves S2 corresponding to the length D are received, and (2) a plurality of diffracted waves S2 are superimposed to create a composite waveform S3 of the diffracted waves S2, so that a phase generated inside the test body 3 or on its surface Can be greatly reduced, and the SN ratio of the diffracted wave from a foreign substance (for example, a crack) existing inside the specimen 3 can be greatly increased.

  In addition, this invention is not limited to embodiment mentioned above, Of course, it can change variously in the range which does not deviate from the summary of this invention.

1, 2 Bevel probe, 3 specimens, 4 cracks, 5 crack ends,
6 wedges, 7 phased array probe, 8 intersection points,
10 ultrasonic flaw detector, 12 transmission probe, 13 acoustic dividing plane,
14 reception probe, 15a wedge member for longitudinal wave (wedge for longitudinal wave),
15b phased array probe,
16 control device, 18 display device, 20 image processing device,
A lateral wave, B diffracted wave, C bottom echo, D intersection depth,
X intersection point, S1 incident wave, S2 diffracted wave, S3 combined waveform, S4 diffracted wave

Claims (7)

With the distance between the transmission probe and the reception probe kept constant, an ultrasonic beam is incident on the inside of the test body by the transmission probe, and the diffracted wave of the ultrasonic beam is received by the reception probe. An ultrasonic flaw detection method using a TOFD method,
The transmission probe and the reception probe consist of a wedge and a phased array probe mounted thereon,
The direction of the incident ultrasonic beam is changed by the sector scan of the phased array probe, and the cross-axis point where the central axis of the ultrasonic beam of the transmitting probe and the receiving probe intersects from the specimen surface A plurality of diffracted waves corresponding to a plurality of cross-axis point depths are received by the reception probe by sequentially changing the cross-axis point depths,
An ultrasonic flaw detection method using a TOFD method, wherein a composite waveform of diffraction waves is created by superimposing the plurality of diffraction waves.   2. The ultrasonic wave by the TOFD method according to claim 1, wherein a diffracted wave from a foreign substance inside a specimen is extracted from a composite waveform of the diffracted wave, and a depth of the foreign substance is obtained geometrically from a propagation time. Flaw detection method.   The ultrasonic flaw detection method by the TOFD method according to claim 1, wherein the method is applied to measurement of a crack near the surface of a specimen and separates a diffracted wave from a crack end portion and a lateral wave propagating through a surface layer portion. .   The ultrasonic flaw detection method by the TOFD method according to claim 1, wherein in transmission / reception of ultrasonic beams having the same refraction angle, the refraction angle is changed, and the intersection point depth is sequentially changed.   The change of the intersection point depth is a pitch of 0.1 mm or more and 1.0 mm or less in a desired measurement range, and the number of intersection point depths is 5 or more and 100 or less. An ultrasonic flaw detection method by the TOFD method according to claim 1. With the distance between the transmission probe and the reception probe kept constant, an ultrasonic beam is incident on the inside of the test body by the transmission probe, and the diffracted wave of the ultrasonic beam is received by the reception probe. An ultrasonic flaw detector by the TOFD method,
The transmission probe and the reception probe consist of a wedge and a phased array probe mounted thereon,
Furthermore, a control device for controlling the transmission probe and the reception probe is provided.
The direction of the incident ultrasonic beam is changed by the sector scan of the phased array probe, and the cross-axis point where the central axis of the ultrasonic beam of the transmitting probe and the receiving probe intersects from the specimen surface A plurality of diffracted waves corresponding to a plurality of cross-axis point depths are received by the reception probe by sequentially changing the cross-axis point depths,
An ultrasonic flaw detector using a TOFD method, wherein a composite waveform of diffracted waves is created by superimposing the plurality of diffracted waves. A display device for displaying the combined waveform of diffracted waves;
5. An ultrasonic flaw detector using the TOFD method according to claim 4, further comprising: an image processing device that extracts a diffracted wave of foreign matter from the synthesized waveform and geometrically determines the depth of the foreign matter from a propagation time. .

Images