JP2002071648A - Method and device for ultrasonic flaw detection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for ultrasonic flaw detection and a device for executing the method allowing the accurate detection of internal flaws over the whole cross section of an inspected part. SOLUTION: A refraction angle controller 9 selects a vibrator group and provides each pulser 5 with timing obtained by adding a corresponding delay time to timing for driving each vibrator 4a by a transmitting delay element 6 corresponding to each vibrator 4a of the selected vibrator group. The driver 4a is driven by each pulser 5 at the timing to transmit ultrasonic beams into a steel pipe 1. An echo signal received by each vibrator 4a is inputted to a receiver 7, and the corresponding delay time is given to the signal inputted to the receiver 7, by a receiving delay element 8 to evaluate the presence of a flaw by a flaw evaluator 12. Scanning is carried out while changing the vibrator group in order. The ultrasonic beams are thereby deflected to perform flaw detection over the whole cross section of a weld part 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic inspection method and an ultrasonic inspection apparatus for detecting a flaw existing in a weld or the like, and more particularly to an ultrasonic inspection method and an ultrasonic inspection for detecting an entire cross section of a thick welded portion. It relates to a flaw detection device.

[0002]

2. Description of the Related Art Various flaws are generated in a welded portion of a welded steel pipe or the like depending on a welding method and conditions, which causes deterioration in the quality of the welded portion. For this reason, non-destructive inspection using X-rays and ultrasonic waves is performed. X-rays can easily detect point-like flaws such as pinholes and slag entrainment, and have many inspection results, but have problems such as low efficiency and high equipment cost.

For this reason, submerged arc welding (SA
W) Ultrasonic flaw detection is performed on the steel pipe, and X-ray inspection is performed only on the portion determined to have a flaw and on both ends of the pipe. Ultrasonic flaw detection is a method suitable for detecting surface flaws such as cracks and fusion defects, and is superior to X-ray inspection in terms of inspection efficiency and equipment cost. And is responsible for the inspection of the entire weld.

As an example, an outline of an online automatic flaw detection method in a manufacturing process of a SAW steel pipe is described in Reference 1 (“Ultrasonic flaw detection method for welded steel pipe”, Quality Control Committee of the Iron and Steel Institute (NDI section)).
Ed., February 22, 1999).
4.3 (pp60-62). This technology arranges multiple probes for detecting internal and external flaws in each of vertical and horizontal flaws so that various flaws generated in the weld can be detected without missing. .

[0005] In online flaw detection, the probe group is formed by using an eddy current or optical seam detector and a seam following mechanism.
The steel pipe is conveyed in a straight line and the entire weld is inspected while always being able to be arranged at a predetermined position from the weld. In this case, in order not to miss the flaw, it is necessary that the ultrasonic beam transmitted and received by the probe group at each position in the longitudinal direction of the tube covers the entire cross section of the welded portion.

An ultrasonic beam transmitted and received by an ultrasonic probe propagates through a material while diffusing at a directivity angle defined by a flaw detection frequency, a transducer diameter, and the like. FIG. 10 is a schematic diagram showing the arrangement of the probe for flaw inspection in the tube axis direction and the ultrasonic wave propagation behavior, wherein 1 is a steel pipe. The steel pipe 1 has a welded portion 2, and an inner surface flaw probe 2 is provided on the outer surface of the steel pipe 1.
Reference numeral 3 is located at a position 0.5 skips from the weld 2 and the outer surface flaw probe 24 is located at a position 1.0 skips.
When the inner surface flaw probe 23 and the outer surface flaw probe 24 are used, the intensity of the ultrasonic beam at the central portion of the welded portion 2 is weakened, and the flaw detection capability is reduced. That is, as shown in FIG. 10, an area A with insufficient flaw detection sensitivity occurs at the center of the welded portion 2. This tendency becomes more pronounced with thicker materials.

Therefore, in the technique described in the above-mentioned document 1, an example of probe setting in steel tube flaw detection (document 1: Table 4.11, p6
As described in 5), for thick materials, it is recommended to install two probes at a distance of 1.0 skip or more from the welded portion 2. FIG. 11 is a schematic diagram showing the arrangement of the probe for flaw inspection in the tube axial direction arranged at the recommended position and the ultrasonic wave propagation behavior, where 1 is a steel pipe. The steel pipe 1 has a welded portion 2. On the outer surface of the steel pipe 1, an inner surface flaw probe 23 is located 1.0 skip from the welded portion 2, and an outer surface flaw probe 24. It is arranged at the position of 5 skips. In FIG. 11, no flaw detection sensitivity shortage region has occurred. This is based on the fact that the ultrasonic beam spreads as the propagation distance increases, but the ultrasonic beam intensity per unit area decreases in proportion to the increase in the propagation distance. The intensity of the reflected echo from the light may also be reduced, and the flaw echo may be buried in the noise signal.

In order to solve the above-mentioned problem, a large number of probes (for example, a probe for an outer surface flaw, an inner surface flaw, a probe for a center flaw, It is desirable to arrange three (the three with the child added). But,
Increasing the number of probes not only increases the number of flaw detectors, but also necessitates the addition of the seam detector and the seam follow-up mechanism, which causes a problem of enormous equipment costs.

In order to solve the above problem, a flaw detection technique using an array probe has recently been proposed. For example, Literature 2 (Non-destructive inspection Vol. 47 No. 1 (1998) pp. 45-
52 "Development of a linear array type ultrasonic flaw detection technique applied to a gas conduit"), a linear scanning type of a beveled array probe, and a beveled array described in JP-A-11-183446. The sector scanning method of the probe corresponds to this. That is, FIG.
And at least two flaw detection areas described in FIG. However, these techniques have the following problems.

In the technique described in the above-mentioned document 2, an acoustic medium made of synthetic resin, called a wedge, for arranging an array probe at a predetermined angle with respect to a flaw detection surface becomes large, and has a thickness of 19 mm. In order to cover the entire cross section of the weld, the length of the contact part between the wedge and the material to be inspected is 150 mm
(Width 20 mm) is reported to be necessary. In order to perform high-accuracy and stable flaw detection, a couplant such as water is required at the contact portion between the wedge and the material to be inspected. It is difficult to keep supplying the couplant. This becomes even more remarkable when the surface of the material to be inspected such as a SAW steel pipe has a curvature.

In the technique disclosed in Japanese Patent Application Laid-Open No. 11-183446, the above problem is relatively small. However, in order to deflect the ultrasonic beam to the refraction angle determined by the wedge shape and change the refraction angle, a large transmission / reception delay time is required. For example, an array probe (wedge material is acrylic; longitudinal wave sound speed 2700 m / s) composed of 16 transducers at a pitch of 1 mm, and a wedge setting refraction angle is 60 ° (incident angle 46 °) and about ± 8 ° To change the refraction angle (incident angle about ± 6 °), a delay time of about 620 ns is required between the vibrators at both ends (= 16 vibrators × sin (6 °) / 2700 m /
s). Generally, an analog delay line is used as a means for delaying a received signal from each transducer. However, there are disadvantages in that the amount of delay is increased, the received waveform is distorted, and the vibration duration is prolonged. Therefore, when performing sector scanning, there is a problem that phase matching on the receiving side is difficult, and it is difficult to perform high-accuracy and high-resolution flaw detection. In addition, when performing sector scanning, there is a problem that a virtual image due to side lobes is easily generated.

The present invention has been made in view of such circumstances, and uses an acoustic medium having a curved contact surface with an array probe, and uses a plurality of ultrasonic transducers of the array probe. 1
Ultrasonic beams are transmitted and received by a group of transducers in one group, this group is sequentially switched, and flaw detection is performed by changing the refraction angle of the ultrasonic beam, thereby detecting internal defects accurately over the entire cross section of the inspected part. It is an object of the present invention to provide an ultrasonic flaw detection method and an ultrasonic flaw detection apparatus for performing the method.

Further, the present invention focuses the ultrasonic beam at each depth in the thickness direction of the material to be inspected by giving a delay time to transmission and reception of each ultrasonic transducer of the group every time the group is switched. It is an object of the present invention to provide an ultrasonic flaw detection method and an ultrasonic flaw detection apparatus which can detect a minute flaw in the entire cross section of a welded portion.

Further, according to the present invention, the shape of the acoustic medium is
Provided is an ultrasonic flaw detector capable of detecting minute flaws without performing transmission / reception delay processing by forming an ultrasonic beam transmitted from an ultrasonic transducer into a shape that converges inside the material to be inspected. The purpose is to do.

[0015]

According to the ultrasonic flaw detection method of the first invention, an acoustic medium is arranged on a surface of a material to be inspected, and an array probe including a plurality of ultrasonic vibrators is moved to the acoustic medium. An ultrasonic flaw detection method for disposing an ultrasonic beam by the ultrasonic vibrator to transmit and receive an ultrasonic beam to detect the inspection target material,
Using an acoustic medium having a curved contact surface with the array probe, an ultrasonic beam is transmitted and received by a transducer group including a plurality of the ultrasonic transducers as one group, and the groups are sequentially switched. In this case, the inspection material is scanned by changing the refraction angle of the ultrasonic beam.

In the ultrasonic flaw detection method according to a second aspect of the present invention, in the first aspect, a delay time is given to transmission and reception of each of the ultrasonic transducers of the group each time the group is switched, and the ultrasonic beam is transmitted to the inspection object. Focusing at a predetermined position.

According to the ultrasonic flaw detector of the third invention, an array probe including a plurality of ultrasonic vibrators is arranged on the surface of a material to be inspected via an acoustic medium, and each of the array probes is separately provided with an ultrasonic vibrator. Each of the ultrasonic oscillators is driven by a connected oscillation circuit to transmit an ultrasonic beam, and the echo signal received by the ultrasonic oscillator is taken into a signal processing circuit to detect a flaw on the inspection object. In the ultrasonic flaw detector, a contact surface of the acoustic medium with the array probe is formed in a curved surface, and a circuit for selecting a plurality of the ultrasonic transducers as one group and the group are sequentially switched. A refraction angle controller having a circuit and a circuit for giving a timing for driving each ultrasonic transducer of the group to each oscillation circuit is provided.

An ultrasonic flaw detector according to a fourth aspect of the present invention is the ultrasonic flaw detector according to the third aspect, wherein a transmission delay element for giving a timing obtained by adding the delay time controlled by the refraction angle controller to the timing to each oscillation circuit; A reception delay element for adding the delay time controlled by the refraction angle controller to the timing at which the acoustic transducer receives the echo signal, and providing the echo signal to the signal processing circuit.

According to a fifth aspect of the present invention, in the ultrasonic flaw detector according to the third or fourth aspect, the acoustic medium is configured to focus an ultrasonic beam transmitted from the ultrasonic transducer inside the inspection object. Characterized by the following shape.

In the first invention and the third invention, since the acoustic medium having a curved contact surface with the array probe is used, the group of ultrasonic transducers involved in ultrasonic transmission and reception is sequentially switched. While maintaining a constant distance from the ultrasonic incidence point to the probe to the part to be inspected, the refraction angle can be changed in the same way as sector scanning, and the entire cross section of the part to be inspected can be detected with high accuracy. it can. In particular, the present invention is useful as an ultrasonic flaw detection method for a welded part that automatically detects a thick welded part and accurately detects an internal flaw. Then, since the ultrasonic beam transmitted and received by each ultrasonic transducer group passes through almost the same place at the contact portion between the acoustic medium and the material to be inspected, it is possible to reduce the length of the acoustic medium. it can. Further, since the refraction angle can be changed only by switching the selected transducer group, flaw detection can be performed without giving a transmission / reception delay to each ultrasonic transducer.

In the second and fourth inventions, transmission and reception delays are provided, so that the ultrasonic beam is prevented from diffusing in the material to be inspected. Further, the delay time can be reduced, the waveform distortion can be minimized, and the generation of a virtual image due to a side lobe can be prevented. Ultrasonic beams can be focused at each depth in the thickness direction only by giving a relatively small transmission / reception delay of up to about 200 nsec for each selected transducer group, enabling detection of minute flaws in the entire cross section of the welded portion. Becomes

An ultrasonic beam transmitted and received from a group of transducers arranged on a curved surface is focused on a position determined by the shape of the curved surface. In the fifth aspect, since the acoustic medium has a shape such that the convergence position is at a predetermined position (for example, the center of the welded portion) inside the test object, the transmission / reception delay processing is not performed (or It is possible to detect minute flaws in the vicinity of the focal point (with only a very small amount of delay).

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. Embodiment 1 FIG. FIG. 1 is a schematic diagram showing an ultrasonic flaw detector according to Embodiment 1 of the present invention, where 1 is a steel pipe. The steel pipe 1 has a weld 2, and a fan-shaped wedge 3 (curvature 50) made of resin such as acrylic is formed on the outer surface of the steel pipe 1.
mm × 15 mm cylinder) and an array probe 4 composed of a plurality of ultrasonic transducers 4 a (length 1 mm × width 10 mm) is arranged on the outer peripheral surface of the wedge 3. Have been. In this embodiment, the array probe 4
Is composed of 32CH, the vertex side is the first CH, and the 90 ° side is the 32nd CH.

A pulser 5 and a transmission delay element 6, and a receiver 7 and a reception delay element 8 are connected to each of the arranged transducers 4a. In this embodiment, an analog delay line is used as the reception delay element 8. The vibrator 4a is driven by the corresponding pulsar 5, and the operation timing of each pulsar 5 is determined by the transmission delay element 6.

Each transmission delay element 6 is connected to a refraction angle controller 9. The refraction angle controller 9 includes a circuit for selecting a vibrator group including a predetermined number of vibrators 4a as one group, a circuit for switching the groups, and a timing for driving each vibrator 4a in the group. Circuit to be applied to pulser 5, transmission delay element 6 and reception delay element 8
And a circuit for providing a delay time to the signal. The transducer group is selected by the refraction angle controller 9, and the selected transmission element 4 a is controlled by the refraction angle controller 9 at the timing of driving each of the transducers 4 a by the corresponding transmission delay element 6. The timing obtained by adding the calculated delay times is given to each pulser 5. By applying a transmission voltage by the pulsar 5 at the above timing, an ultrasonic beam is transmitted from the vibrator 4a into the steel pipe 1.

The reception of a flaw echo or the like is performed as follows. The signal received by each transducer 4 a of the selected transducer group is input to the receiver 7. The signal input to the receiver 7 is output to the adder 10 after the reception delay element 8 is given a delay time controlled by the refraction angle controller 9. The received signals are combined by an adder 10 and amplified by an amplifier 11 to a signal level required for evaluation.
The amplified signal value is compared with a predetermined threshold value by the flaw evaluator 12 to evaluate the presence or absence of flaws.
In the ultrasonic flaw detector according to this embodiment, the angle of refraction incidence on the steel pipe 1 is changed by sequentially switching and scanning, for example, 16 selective transducer groups at predetermined intervals, which contributes to the formation of an ultrasonic beam. Thus, the entire cross section of the welded portion 2 can be detected.

FIG. 1 shows the state of a beam in which the inner surface side is flaw-detected by 0.5 skips and the outer surface side (the side where the array probe 4 is installed) is flaw-detected by 1.0 skips. It is preferable to change the beam irradiation position in multiple steps in the thickness direction so as to detect the entire cross section of the welded portion 2. As will be described later, the present inventors have also conducted a test for flaw detection of the center part of the wall thickness (0.75 skip) in addition to the flaw detection for the inner and outer surfaces.

In this embodiment, the following delay is provided. The unit of the delay time is ns. CH1: 170, CH2: 130, CH3: 90, CH4: 60, CH5: 35, CH6: 20, CH7: 5, CH8: 0, CH9: 0, CH10: 5, CH11: 20, CH12: 35, CH13: 60, CH14: 90, CH15: 130, CH16: 170 Even when the selected transducer group is sequentially switched, the transmission and reception delay times are given in the same pattern. That is, the oscillators 4a at both ends are always 170 ns compared to the oscillator 4a at the center.
Give a degree of delay.

Embodiment 2 In the ultrasonic flaw detector according to the first embodiment, since a 1/4 cylinder is used as the wedge 3, when no transmission / reception delay time is given, the ultrasonic beam transmitted / received by each selected transducer group is the wedge 3 and the steel pipe 1. It converges on the boundary between the two and propagates while diffusing inside the steel pipe 1, and the flaw detection ability is reduced. For this reason, in the first embodiment, the transmission and reception delay corresponding to the distance to the weld 2 is given to focus the ultrasonic beam. However, in order to provide a transmission / reception delay time, a group of transmission delay elements 6 and a group of reception delay elements 8 are required, which makes the electronic circuit complicated and expensive. Although the delay time given in the first embodiment is about 200 nsec at the maximum, problems such as waveform distortion and increase in duration remain as described above.

Therefore, the present inventors have developed an ultrasonic flaw detector which does not require a transmission / reception delay time by examining the shape of the wedge 3 on which the array probe 4 is provided. FIG. 2 is a schematic diagram showing an ultrasonic flaw detector according to Embodiment 2 of the present invention, in which the same parts as those in FIG. 1 are denoted by the same reference numerals. In the second embodiment, the wedge 3 has a shape in which a part of a cylinder having a curvature of 200 mmR is cut out, and the end face on the welded portion 2 side (the ultrasonic beam advancing side) is closer to the end face on the opposite side. It has been enlarged. As a result, the beam is focused at a position of approximately 45 mm along the beam path in the steel pipe 1 without giving a transmission / reception delay time.

A sound absorbing material 13 for suppressing irregular reflection signals inside the wedge 3 is attached to an end face of the wedge 3 on the welded portion 2 side. In addition, the contact surface between the wedge 3 and the steel pipe 1 has a stable contact area except for an area (length: 50 mm × about the width of the wedge 3) necessary and sufficient for an ultrasonic beam transmitted / received by each selected transducer group to pass. A cut is provided to prevent irregular reflection of the sound wave in the wedge 3. In this embodiment, transmission / reception delay is not required, so that the transmission delay element 6 group and the reception delay element 8 group are not required, the electronic circuit is simplified, the manufacturing can be inexpensively performed, and the inexpensive ultrasonic flaw detector is used. Can be provided.

[0032]

EXAMPLES Embodiments 1 and 2 will be described below in more detail with reference to examples. [Example 1] In Example 1, flaw detection was performed using the ultrasonic flaw detector according to Embodiment 1 and switching the group of selected transducers without giving a transmission / reception delay time. By switching the transducer group, the refraction angle is changed, and the ultrasonic beam incident on the steel pipe 1 is deflected. FIG.
3A and 3B are diagrams showing a state in which artificial flaws are provided on a steel plate of mm, FIG. 3A is a side view, and FIG. 3B is a plan view. FIG.
FIG. 4A is a waveform diagram showing a case where the ultrasonic flaw detector according to Embodiment 1 is used to examine the artificial flaw of the steel sheet by the method of Example 1, and FIG. (B) shows a case where the slit on the outer surface is detected, and (c) shows a case where the slit is detected on the inner surface.
Arrows in the figure indicate flaw waveform positions.

The result of detecting the slits on the inner and outer surfaces and the lateral hole at the center of the plate thickness by sequentially switching the group of selected transducers while keeping the distance from the processing position of the flaw of the array probe 4 constant is shown. . The refraction angles at the time of detection of each part are as follows. -Refraction angle when detecting the inner surface slit: about 70 °-Refraction angle when detecting the outer surface slit: about 55 °-Refraction angle when detecting the central side hole: about 63 °

At the same time, a normal oblique flaw detection test was performed.
In this flaw detection test, the refraction angle was fixed at 55 °, the position of the probe was changed according to the flaw depth in the thickness direction of the steel sheet, and flaw detection was performed at a position where the SN ratio was the best. The distance from the flaw was generally set to 0.5 for the inner flaw, 1.0 for the outer flaw, and 0.75 for the center horizontal hole.

FIG. 5 is a graph showing the S / N ratios of the first embodiment and the flaw detection using the oblique flaw detection. In the first embodiment, despite the fact that the distance from the flaw processing position to the array probe 4 is kept constant, flaw detection is performed while changing the refraction angle, thereby making it possible to adjust the distance between the flaw and the normal oblique angle. It can be seen that the same SN ratio as that of the corner flaw detection was obtained. That is, one array probe 4 covers a flaw detection range of three normal angle beam probes. Table 1 shows the difference in sensitivity between the case where the above-described slit flaws on the inner and outer surfaces were detected by a normal probe and the array probe 4 of the present invention.

[0036]

[Table 1]

From Table 1, it can be seen that when the array probe 4 of the present invention was used, the sensitivity difference between the inner and outer surface slit flaws was smaller than in the case of ordinary oblique flaw detection. This is for the following reason. FIG. 6 is a graph showing the correlation between the refraction angle and the relative echo intensity in the range of the refraction angle of 20 ° to 80 °.
In normal oblique flaw detection, the refraction angle is set to be the same and the inner and outer surface flaws are detected by changing the distance from the flaw. Therefore, the sensitivity (relative echo intensity) of the inner and outer surface slits is indicated by points A and B in FIG.
Becomes On the other hand, in the flaw detection according to the first embodiment, since the inner and outer slits are detected by changing the refraction angle while keeping the distance from the flaw constant, the sensitivity of the inner and outer slits is point A and point C, respectively. FIG. 6 shows that the sensitivity difference between points AB is
It can be seen that the sensitivity difference between points AC is small. Therefore, in the present invention, it is possible to perform flaw detection with a small difference in sensitivity between the inner and outer surface flaws, and it is possible to detect flaws of the same size with the same echo intensity regardless of whether they are present on the inner or outer surface. it can.

Further, when scanning is performed by sequentially switching the selected transducer group, the ultrasonic beam transmitted and received by each selected transducer group is 20 mm long on the contact surface between the wedge 3 and the steel pipe 1.
X It has been confirmed by an experiment that the wedge 3 passes through a portion of about the width of the wedge 3. Therefore, by stabilizing the contact state of this portion, flaw detection with good reproducibility can be performed. As described above, by applying the present invention, SA
When performing online flaw detection of a W steel pipe or the like, the number of probes 4 can be significantly reduced.

[Second Embodiment] Next, an ultrasonic flaw detection method according to a second embodiment will be described. In this method, the ultrasonic flaw detector according to Embodiment 1 is used to change the transmission / reception delay time of each transducer 4a selected as a group in accordance with the flaw detection position. In the second embodiment, in the case of flaw detection on the inner surface, a delay time is provided such that ultrasonic waves transmitted and received by the group of selected transducers are focused on the inner surface of the welded portion 2. Gives a delay time such that the beam is focused, and changes the transmission / reception delay time according to the depth of the flaw detection.

FIG. 7 is a graph showing the S / N ratio when the artificial flaw of FIG. 3 is detected by the two methods of Example 2 and the above-described oblique flaw detection. By changing the focus position of the ultrasonic beam in accordance with the depth of the flaw, the SN ratio is improved, and it is possible to detect even a small flaw as compared with the case of FIG. 5 by the method according to the first embodiment. You can see that. Since the beam path to the inner and outer surfaces and the center of the thickness of the material to be inspected changes depending on the thickness of the material to be inspected, the transmission / reception delay time according to the thickness of the material to be inspected and the flaw detection depth in the second embodiment. However, this method is an extremely effective flaw detection method when it is necessary to detect minute flaws.

[Example 3] Ultrasonic flaw detection was performed using the ultrasonic flaw detector according to Embodiment 2 without delay in transmission and reception. FIG. 8 is a graph showing the S when the artificial flaw of FIG. 3 is detected by the method according to the third embodiment and the oblique flaw detection.
It is a graph which shows N ratio. 8, the result of Example 1 (FIG. 5) is slightly inferior to the result of Example 2 (see FIG. 7).
), And an SN ratio comparable to that of normal angle beam inspection, and it can be seen that the invention can be sufficiently applied to online inspection.

FIG. 9 shows a φ processed to a depth of 10 to 80 mm.
It is a graph which shows the depth dependence of the flaw echo intensity (relative echo intensity) obtained from a 3.2 mm side hole. From FIG.
The relative echo intensity independent of the flaw depth is obtained by the method of the second embodiment. In the first and third embodiments, the depth dependence of the echo intensity is smaller than that of the conventional oblique flaw detection method. It can be seen that it has decreased.

As described above, according to the present invention, the welded portion 2 of the steel pipe 1 is provided.
In the method for ultrasonically flaw detection of a flaw existing in a welding part, the distance from the welding part 2 to the probe 4 is kept constant by using one probe from one side of the welding part 2 (two probes from both sides of the welding part). However, only by performing a straight line scan in the welding line direction, it is possible to detect the entire cross section of the welded portion 2 with high accuracy. Further, the ultrasonic beam can be focused at each depth in the thickness direction only by giving a relatively small transmission / reception delay, so that a minute flaw can be detected in the entire cross section of the welded portion 2. By making the shape of the wedge 3 such that the convergence position is at a predetermined position (for example, the center) inside the welded portion 2, the transmission / reception delay processing is not performed (or a very small delay amount is given). Only) can detect a minute flaw near the focal point.

In the above embodiment, the SAW
This section describes the vertical flaw detection (ultrasonic beam incident perpendicular to the weld line) in steel material flaw detection, but the invention is not limited to this. Lateral flaw detection in which the beam is incident obliquely to the weld line It is also possible to apply to.
Further, the present invention is not limited to the flaw detection of the welded portion 2 of the steel pipe 1, but can be applied to ultrasonic flaw detection of a butt welded portion of a steel plate.

[0045]

As described in detail above, in the first and third embodiments, since the acoustic medium having a curved contact surface with the array probe is used, it is involved in transmission and reception of ultrasonic waves. By sequentially switching the group of ultrasonic transducers, it is possible to perform the same refraction angle change as in sector scanning while keeping the distance from the ultrasonic incident point to the probe to the probe constant. It is possible to detect the entire cross section with high accuracy. In particular, the present invention is useful as an ultrasonic flaw detection method for a welded portion for automatically detecting a thick welded portion and accurately detecting an internal flaw. Then, the ultrasonic beam transmitted and received by each ultrasonic transducer group passes through almost the same place at the contact portion between the acoustic medium and the material to be inspected, and the length of the acoustic medium is reduced. be able to. Further, since the refraction angle can be changed only by switching the selected transducer group, flaw detection can be performed without giving a transmission / reception delay to each ultrasonic transducer.

In the case of the second and fourth aspects, transmission and reception delays are provided, so that the ultrasonic beam is prevented from being diffused in the material to be inspected. Further, the delay time can be reduced, the waveform distortion can be minimized, and the generation of a virtual image due to a side lobe can be prevented. The ultrasonic beam can be focused at each depth in the thickness direction only by giving a relatively small transmission / reception delay of up to about 200 nsec for each of the selected transducer groups. It becomes possible.

In the case of the fifth aspect, since the acoustic medium has a shape such that the convergence position is a predetermined position inside the material to be inspected (for example, the center of the welded portion), transmission / reception delay processing is performed. It is possible to detect minute flaws in the vicinity of the focal point even without (or with a very small amount of delay).

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an ultrasonic flaw detector according to Embodiment 1 of the present invention.

FIG. 2 is a schematic diagram showing an ultrasonic flaw detector according to Embodiment 2 of the present invention.

3A and 3B are diagrams showing a state in which artificial flaws are provided on a steel plate having a thickness of 40 mm, wherein FIG. 3A is a side view and FIG. 3B is a plan view.

FIG. 4 is a waveform diagram showing a case where the artificial flaw of the steel sheet is examined by the method of the first embodiment.

FIG. 5 is a graph showing an SN ratio when flaw detection is performed using the two methods of Example 1 and oblique flaw detection.

FIG. 6 is a graph showing a correlation between a refraction angle and a relative echo intensity in a range of a refraction angle of 20 ° to 80 °.

[FIG. 7] FIG. 3 shows two methods of Example 2 and oblique flaw detection.
5 is a graph showing an SN ratio when flaw detection is performed on an artificial flaw.

FIG. 8 is a graph showing the SN ratio when the artificial flaw of FIG. 3 is detected by the method according to the third embodiment and the oblique flaw detection.

FIG. 9 is a graph showing a correlation between a flaw depth and a relative echo.

FIG. 10 is a schematic diagram showing the arrangement of a conventional probe for inspection for a tube axial direction flaw and the ultrasonic wave propagation behavior.

FIG. 11 is a schematic view showing the arrangement of a conventional tube-axial flaw inspection probe and the ultrasonic wave propagation behavior.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel pipe 2 Weld part 3 Wedge 4 Array probe 4a Ultrasonic transducer 5 Pulser 6 Transmitting delay element 7 Receiver 8 Receiving delay element 9 Refraction angle controller 12 Flaw evaluator

Claims (5)

[Claims] 1. An acoustic medium is disposed on a surface of a test object, an array probe including a plurality of ultrasonic transducers is disposed on the acoustic medium, and an ultrasonic beam is transmitted by the ultrasonic transducer. In the ultrasonic flaw detection method for flaw detection of the material to be inspected by transmitting / receiving, an acoustic medium having a curved contact surface with the array probe is used, and a plurality of the ultrasonic vibrators are grouped into one group. An ultrasonic flaw detection method, wherein an ultrasonic beam is transmitted / received by a group of vibrators, and the group is sequentially switched to change the refraction angle of the ultrasonic beam and scan the inspection object. 2. The ultrasonic wave according to claim 1, wherein a delay time is given to transmission and reception of each of the ultrasonic transducers of the group each time the group is switched, so that the ultrasonic beam is focused at a predetermined position on the inspection object. Flaw detection method. 3. An array probe including a plurality of ultrasonic transducers is arranged on a surface of a test object via an acoustic medium,
Each of the ultrasonic transducers is driven by an oscillation circuit connected to each of the ultrasonic transducers to transmit an ultrasonic beam, the echo signal received by the ultrasonic transducer is taken into a signal processing circuit, and the material to be inspected is taken. An ultrasonic flaw detector for detecting flaws, wherein a contact surface of the acoustic medium with the array probe is curved, and a circuit for selecting a plurality of the ultrasonic transducers as one group An ultrasonic flaw detector comprising: a circuit for sequentially switching the group; and a refraction angle controller having a circuit for giving a timing for driving each ultrasonic transducer of the group to each oscillation circuit. 4. A transmission delay element for giving a timing obtained by adding a delay time controlled by the refraction angle controller to the timing to each oscillation circuit, and a timing at which the ultrasonic transducer receives an echo signal, 4. The ultrasonic flaw detector according to claim 3, further comprising: a receiving delay element for adding the echo signal to the signal processing circuit by adding a delay time controlled by a refraction angle controller. 5. The ultrasonic flaw detection device according to claim 3, wherein the acoustic medium has a shape for focusing an ultrasonic beam transmitted from the ultrasonic transducer inside the material to be inspected. apparatus.