JP2003262621A - Ultrasonic inspection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonic inspection method which can select a few inspection refraction angles, made to correspond to a wall thickness of a material to be inspected, the degree of diffusion of an ultrasonic beam or the like, and by which a calibration work is easily carried out. <P>SOLUTION: In the ultrasonic inspection method, an artificial flaw is inspected at a prescribed refraction angle, and a distance between a weld section 2 and an array probe 4 is set based on the inspection result, and each echo intensity is detected, in the case a prescribed number of artificial flaws are inspected at a plurality of refraction angles, in such a state that the distance is kept constant, and the inspection refraction angles are selected, based on the detected echo intensity. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic flaw detection method for flaw detection on a welded portion of a material to be inspected.

[0002]

2. Description of the Related Art Various flaws are generated in a welded portion such as a welded steel pipe depending on the welding method and conditions, which causes deterioration of the quality of the welded portion. Therefore, nondestructive inspection using X-rays and ultrasonic waves is performed. X-rays can easily detect spot defects such as pinholes and slag inclusions, and have many inspection results, but there are problems such as low efficiency and high equipment cost.

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

As an example, an outline of an online automatic flaw detection method in the manufacturing process of a SAW steel pipe is described in Reference 1 ("Ultrasonic flaw detection of welded steel pipe" Iron and Steel Institute Quality Control Subcommittee (NDI Division).
Ed., Published on February 22, 1999).
4.3 (pp60-62). This technology has a plurality of probes for detecting internal flaws and external flaws for each of the vertical flaws and the horizontal flaws, and it is possible to detect various flaws occurring in the welded portion without missing them. . In this case, in order not to miss the flaw, it is necessary that the ultrasonic beam transmitted and received by the probe group covers the entire cross section of the welded portion at each position in the longitudinal direction of the pipe.

The ultrasonic beam transmitted and received by the ultrasonic probe propagates in the material while being diffused at a directivity angle defined by the flaw detection frequency and the diameter of the transducer. FIG. 5 is a schematic view showing the K-form arrangement and ultrasonic wave propagation behavior of a probe for axial flaw inspection, in which 1 is a steel pipe. The steel pipe 1 has a welded portion 2. On the outer surface of the steel pipe 1, the inner surface flaw probe 23 is located at a position 0.5 skip from the welded portion 2, and the outer surface flaw probe 24 is 1. It is located at the 0 skip position. When the probe 23 for the internal flaw and the probe 24 for the external flaw are used, the ultrasonic beam intensity at the central portion of the welded portion 2 becomes weak and the flaw detectability is deteriorated. That is, as shown in FIG. 5, the flaw detection sensitivity insufficient region A occurs in the central portion of the welded portion 2. This tendency becomes more pronounced for thicker materials.

Therefore, in the technique described in Document 1, an example of probe setting in steel pipe flaw detection (Document 1: Table 4.11, p6
As described in 5), in thick-walled materials, it is recommended to install two probes at a distance of 1.0 skip or more from the weld portion 2. FIG. 6 is a schematic view showing the arrangement and ultrasonic wave propagation behavior of the pipe axial direction flaw inspection probe arranged at the recommended position, where 1 is a steel pipe. On the outer surface of the steel pipe 1, the inner surface flaw probe 23 is arranged at a position of 1.5 skips from the welded portion 2, and the outer surface flaw probe 24 is arranged at a position of 1.0 skips. In FIG. 6, the flaw detection sensitivity insufficient region does not occur. This utilizes 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, so there is a defect. The intensity of the reflected echo from the device also decreases, and the flaw echo may be buried in the noise signal.

In order to solve the above-mentioned problems, a large number of probes (for example, a probe for external flaws, a probe for internal flaws, and a probe for central flaws) are provided at positions where the ultrasonic wave propagation distance to the welded portion 2 is short. It is desirable to place 3) with children added. However, increasing the number of probes not only increases the number of flaw detectors, but also requires the addition of a seam detector, a seam tracking mechanism, and the like, which causes a problem of enormous equipment cost.

The inventors of the present application filed Japanese Patent Application No. 2000-2564.
No. 16 proposed an ultrasonic flaw detection method that can reduce the number of probes and detect internal flaws accurately over the entire cross section of a weld. This is to arrange an array probe including a plurality of ultrasonic transducers on a material to be inspected through a wedge having an arcuate curved surface, and sequentially switch the transducer groups that form a plurality of ultrasonic transducers into one group. Is a method of scanning the material to be inspected by changing the refraction angle of the ultrasonic beam.

Further, the inventors of the present application disclosed in Japanese Patent Laid-Open No. 2002-2
In Japanese Patent No. 2714, two or more array probes are arranged with a welded portion sandwiched therebetween, and in particular, by arranging them in the welding line direction at least by shifting the size of the array probe, ultrasonic waves are simultaneously transmitted. Disclosed is an ultrasonic flaw detector capable of reliably detecting a longitudinal flaw in the entire cross section of a welded portion even in a steel pipe conveyed at high speed without causing any interference.

Generally, in automatic ultrasonic flaw detection for quality control and assurance at the manufacturing site, time-division flaw detection is carried out in order to simplify equipment and reduce costs. FIG. 7 is a plan view showing the arrangement of the probes in UOE steel pipe flaw detection. In this UOE steel pipe flaw detection, A
4 of 1-A2, B1-B2, C1-C2 and D1-D2
A pair of probes and four ultrasonic flaw detectors connected to them are used. The probes B1-B2 and D1-D2 detect vertical flaws and lateral flaws on the outer surface, and A1-A2 and C1-C2 detect inner flaws.

In this flaw detection, for example, 1) A1 probe vertical transducer is used for coupling check and sensitivity correction is performed. 2) A1 probe bevel transducer is used for flaw detection of the welded portion 2. 3) A2 probe vertical transducer is used for coupling check and sensitivity correction is performed. 4) A2 probe bevel transducer is used for flaw detection of welded portion 2. 5) A1 probe bevel transducer. To the A2 probe bevel transducer, the sensitivity check and the flaw monitoring gate check are repeated based on the ultrasonic waves that are transmitted. Therefore, when the basic repetition frequency of the ultrasonic flaw detector is 10 KHz, the repetition frequency for each procedure is 2 KHz.

Assuming that the array probe repeats three kinds of refraction angle variations (for example, refraction angles of 50 degrees, 60 degrees, and 70 degrees), the vertical flaw detection required for the coupling check function is added to 4 Become a procedure / transducer. When a pair of probes are arranged to face each other on a straight line, it is necessary to alternately transmit and receive because ultrasonic waves transmitted and received by the opposing probes do not interfere, and (4 procedures / probe) x 2 probes Child + {V transmission (1 procedure)}
= 8 to 9 procedures.

In the case of the ultrasonic flaw detector disclosed in Japanese Unexamined Patent Publication No. 2002-22714 described above, when a pair of array probes are arranged to face each other with a welding portion interposed therebetween, the flaw repetition frequency is compared with that of a normal probe. And it will be about half. When the number of refraction angle variations in each array probe, that is, the number of procedures increases, the flaw detection repetition frequency for each procedure decreases. If the repetition frequency for each procedure is lowered, there is a risk of overlooking small flaws and flaws when the steel pipe is transported at high speed.

Therefore, in the ultrasonic flaw detector,
The array probe, which is placed across the weld, is shifted in the welding line direction to improve the flaw detection repetition frequency / procedure. By arranging them so that they are displaced in the welding line direction, there is no interference even if ultrasonic waves are transmitted at the same time, and it is possible to increase the transmission repetition speed of each ultrasonic wave. The following Table 1 shows the results of determining the flaw detection repetition frequency / procedure when the probe and the arrangement of the probe are changed.

[0015]

[Table 1]

It can be seen from Table 1 that when the array probes arranged with the welded portion sandwiched therebetween are displaced in the welding line direction, the flaw repetition frequency / procedure is increased to that of a normal probe.

The ultrasonic flaw detection method using the above-mentioned ultrasonic flaw detection device has the following problems. First, in the above-described array probe including a plurality of ultrasonic transducers, there is a problem of how to set the inspection procedure of the entire cross section of the welded portion by the procedure (refraction angle).

FIGS. 8 to 10 are views showing ultrasonic wave propagation behavior in a UOE steel pipe. FIGS. 8 and 9 and 10 show ultrasonic wave propagation behaviors when an UOE steel pipe having an outer diameter of 800 mm, a wall thickness of 7.5 mm, an outer diameter of 1000 mm and a wall thickness of 38 mm is flaw-detected by an array probe. , Shows the propagation behavior when the refraction angle from the array probe is changed in steps of 2 degrees. Of the solid lines showing the ultrasonic beam propagation, the central line shows the beam center, and the other two lines show the diffusion due to the directivity (directivity angle 4 degrees) of the ultrasonic beam.

As is clear from FIGS. 8 to 10, the number of deflection angle deviations required for flaw-free inspection of the entire cross section of the welded portion is determined by the thickness of the material to be inspected and the degree of diffusion of the ultrasonic beam. Change depending on.

It is possible to calculate the rough procedure number (refraction angle variable number) by using a technique such as numerical analysis. However, in this method, the number of procedures is changed according to the variation of ultrasonic propagation velocity due to the difference in the manufacturing conditions of the material to be inspected, the existence of sonic anisotropy, the roundness when the material to be inspected is a steel pipe, etc. Not enough to make a final decision. Further, when the number of procedures increases, as described above, the flaw detection repetition frequency / procedure decreases, and there is a possibility that a minute flaw may be missed. Therefore, even when arranging a pair of array probes with the welded part sandwiched in between and displaced in the welding line direction, the minimum possible thickness can be accommodated depending on the thickness, roundness, ultrasonic beam divergence, etc. of the material to be inspected. We need a way to derive a number of steps.

Further, when a pair of array probes are arranged so as to be shifted in the direction of the welding line with the welded portion sandwiched therebetween, there are the following problems in the calibration work using artificial flaws machined into a comparative test piece or the like. 1) Calibration work is complicated. When arranging a pair of array probes on a straight line that intersects with the welding line, align the pair of array probes with the artificial flaws on the front faces of the opposing probes to perform the calibration work (welding part and probe). Adjusting the separation distance from the tentacle, adjusting the sensitivity, and adjusting the position and width of the defect monitoring gate)
Could be done. However, in the case of arranging a pair of array probes so as to be displaced in the welding line direction, after performing a calibration operation by aligning a predetermined artificial flaw with the front surface of one of the probes, the artificial flaw of the other probe is arranged. It was necessary to shift it to the front side and perform the calibration work for the other probe.

In the case of a calibration work using a fish-like comparison test piece cut out to a length of about 1 m, the work of adjusting the artificial flaw to the probe position can be easily performed because the comparison test piece is relatively lightweight. it can. However, in the case of calibration work using a steel pipe having a length of 10 m as a comparative test piece, it is necessary to move a steel pipe having a weight of 10 tons in millimeters and align the artificial flaw with the probe position, which makes the work complicated. In order to improve the efficiency and efficiency, it is desirable to minimize the number of flaw alignments.

2) It is not possible to perform sensitivity check and flaw monitoring gate position check based on the ultrasonic waves that propagate through. In the method of arranging the probe as shown in FIG. 7, the opposing probe is used to perform sensitivity check and flaw monitoring based on the intensity of ultrasonic waves propagating through the inspection material and appearance position information. Checking the gate position. In the configuration in which the pair of array probes are displaced in the welding line direction, there is a problem that the sensitivity check by the transmission ultrasonic waves and the flaw monitoring gate position check cannot be performed.

The present invention has been made in view of the above circumstances, and maintains a constant distance between the weld and the probe,
A predetermined number of artificial flaws are provided in the welded part of the test material that is the same or very similar in material and shape to the material to be inspected, and the flaw detection refraction angle is selected based on the echo intensity detected by flaw detection of the artificial flaw at multiple refraction angles. Therefore, the thickness, roundness,
An object of the present invention is to provide an ultrasonic flaw detection method capable of easily selecting a small number of flaw detection refraction angles in accordance with the material, the degree of ultrasonic beam diffusion, and the like.

Further, according to the present invention, the distance between the welded portion and the probe is determined based on a result of flaw detection of an artificial flaw provided on a test material at a predetermined refraction angle, and the plurality of refraction angles are set to the above-mentioned refraction angles. By including the specified refraction angle, if the position where the echo intensity of the flaw reaches its peak is set to the distance between the weld and the probe, the wall thickness, roundness, material and degree of ultrasonic beam diffusion It is an object of the present invention to provide an ultrasonic flaw detection method that can detect flaws with higher sensitivity, because the flaw can be correctly irradiated with the ultrasonic beam depending on the situation.

Further, the present invention includes the step of selecting the refraction angle when the echo intensity of each artificial flaw is equal to or more than the preset threshold value, so that when the selected refraction angle is the flaw detection refraction angle, An object of the present invention is to provide an ultrasonic flaw detection method capable of detecting flaws to be detected by reducing the number of flaw detection refraction angles.

Furthermore, the present invention includes the step of selecting, as a flaw detection refraction angle, a combination of refraction angles at which the maximum echo intensity is detected for each artificial flaw among the selected refraction angles. Since the number will be further reduced,
It is an object of the present invention to provide an ultrasonic flaw detection method capable of improving flaw detection repetition frequency / procedure, detecting micro flaws, and reliably detecting flaws even when a material to be inspected is transported at high speed. .

Further, the present invention includes the process of preferentially selecting a refraction angle at which a high echo intensity is detected for a preselected artificial flaw among the refraction angles selected, so that the flaw detection refraction angle number is Since it is further reduced, the flaw detection repetition frequency / procedure is further improved, even minute flaws can be detected, and ultrasonic flaw detection that can reliably detect flaws to be detected even when the inspected material is conveyed at high speed The purpose is to provide a method.

And, in the present invention, a process of arranging a pair of probes on a straight line intersecting with a welding line of the welded portion to detect and calibrate an artificial flaw, and a pair of the probes to the welding line. In a direction parallel to the above, at least displaced by the size of the probe, by including the step of flaw detection of the welded portion,
At the time of calibration, the calibration work can be facilitated, and the sensitivity check and flaw monitoring gate position check can be performed. During flaw detection of the material to be inspected, the flaw repetition frequency / procedure can be improved and even minute flaws can be detected. An object of the present invention is to provide an ultrasonic flaw detection method capable of reliably detecting flaws even when the material to be inspected is transported at high speed.

Further, the present invention provides an ultrasonic flaw detection method capable of changing the refraction angle easily and at high speed by using an array probe having a plurality of ultrasonic transducers as the probe. The purpose is to do.

[0031]

In the ultrasonic flaw detection method of the first invention, an ultrasonic beam is transmitted from a probe capable of flaw detection at a plurality of different refraction angles to a welded portion of a material to be inspected, and the probe is used. In the ultrasonic flaw detection method for flaw detection of the welded portion based on the received echo signal, while maintaining a constant distance between the welded portion and the probe, a predetermined number of artificial flaws at a plurality of refraction angles. The process of detecting the echo intensity in case of flaw detection,
The method is characterized by including a process of selecting a flaw detection refraction angle based on the detected echo intensity and a process of flaw detection of a welded portion of a material to be inspected based on the selected flaw detection refraction angle.

In the first aspect of the present invention, artificial flaws provided beforehand based on the standards such as ISO and API, the thickness of the material to be inspected, the outer diameter and the roundness, and the approach limit distance of the probe are used as the welded portion. By selecting the flaw detection refraction angle based on the results of flaw detection at multiple refraction angles while keeping the distance to the probe constant, the thickness, roundness, material and ultrasonic wave of the material to be inspected are selected. A small number of flaw detection refraction angles can be easily selected according to the degree of beam divergence, and the flaw detection repetition frequency / procedure is improved. The artificial flaw is provided on the test material or the test material whose material and shape are the same or very similar to those of the test material.

In the ultrasonic flaw detection method of the second aspect of the invention, in the first aspect of the invention, the distance between the welded portion and the probe is determined based on the result of flaw detection of the artificial flaw provided in advance at a predetermined refraction angle. The plurality of refraction angles include the predetermined refraction angles. In the second aspect of the invention, the position where the echo intensity of the flaw reaches a peak is set to the distance between the weld and the probe, so that the thickness, the roundness, the material, the degree of ultrasonic beam diffusion, etc. can be adjusted. The flaw can be correctly irradiated with the ultrasonic beam, and flaw detection can be performed with higher sensitivity.

An ultrasonic flaw detection method according to a third aspect of the invention is characterized in that, in the first or second aspect of the invention, it includes a step of selecting a refraction angle when the echo intensity of each artificial flaw exceeds a preset threshold value. And

In the third aspect of the invention, a refraction angle that is equal to or more than a preset threshold value is selected in accordance with the standards such as ISO and API applied to the material to be inspected and the type and degree of the flaw to be detected. By including the process, when the selected refraction angle is set as the flaw detection refraction angle, it is possible to reduce the number of refraction angles used for flaw detection and detect flaws to be detected.

In the ultrasonic flaw detection method according to the fourth aspect of the present invention, a combination of the refraction angles at which the maximum echo intensity is detected for each artificial flaw is selected from the refraction angles selected in the third aspect as the flaw detection refraction angle. It is characterized by including a process. In the fourth aspect of the invention, since the flaw detection refraction angle number is further reduced, the flaw detection repetition frequency / procedure is improved, minute flaws can be detected, and flaws can be reliably detected even when the material to be inspected is conveyed at high speed. can do.

The ultrasonic flaw detection method according to the fifth aspect of the present invention includes the step of preferentially selecting a refraction angle at which a high echo intensity is detected for a preselected artificial flaw among the selected refraction angles. It is characterized by including. In the fifth aspect of the invention, since the flaw detection refraction angle number is further reduced, the flaw detection repetition frequency / procedure is further improved, minute flaws can be detected, and even when the material to be inspected is conveyed at high speed, it can be detected reliably. Can detect flaws.

In the ultrasonic flaw detection method of the sixth invention, a plurality of probes capable of flaw detection at different refraction angles are arranged on both sides of the welded portion of the material to be inspected, and the ultrasonic beam is welded from the probe. In the ultrasonic flaw detection method of transmitting to a portion, the probe based on an echo signal received by the probe, the pair of probes is arranged on a straight line intersecting with the welding line of the welding portion, A step of detecting and calibrating the artificial flaw, and a step of arranging the pair of probes in a direction parallel to the welding line with a displacement of at least the size of the probe and detecting the welded part. Is characterized by.

According to the sixth aspect of the invention, since the pair of probes are arranged on a straight line intersecting with the welding line of the welded portion during the calibration performed statically or quasi-statically, the calibration work becomes easy and The sensitivity check and the defect monitoring gate position check can be performed based on the intensity and appearance position information of the ultrasonic waves that propagate through the material to be inspected. Even if the flaw repetition frequency / procedure is lowered by arranging the pair of probes facing each other, adjustment of the separation distance between the weld and the probe, sensitivity adjustment, adjustment of the position and width of the flaw monitoring gate, etc. There is no hindrance to the calibration work. During flaw detection and dynamic calibration of the material to be inspected, the pair of probes are arranged so as to be offset from each other in a direction parallel to the welding line, so that the flaw repetition frequency / procedure is improved and minute flaws can be detected. Therefore, the flaw can be reliably detected even when the material to be inspected is transported at high speed.

A seventh invention is characterized in that, in any one of the first to sixth inventions, the probe is an array probe having a plurality of ultrasonic transducers. In the seventh aspect, the refraction angle can be changed easily and at high speed.

[0041]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below with reference to the drawings showing the embodiments thereof. Embodiment 1. FIG. 1 is a schematic diagram showing an ultrasonic flaw detector applied to Embodiment 1 of the present invention, in which 1 is a steel pipe. The steel pipe 1 has a welded portion 2, and on the outer surface of the steel pipe 1, a fan-shaped wedge 3 made of a resin such as acrylic or polystyrene resin (curvature 50 mm × width 15 mm
4) is arranged, and the array probe 4 composed of a plurality of ultrasonic transducers 4a (length 1 mm × width 10 mm) is arranged on the outer peripheral surface of the wedge 3. Ultrasonic transducer 4a
As, a piezoelectric vibrator such as lead niobate-based porcelain, lead titanate-based porcelain, and lithium niobate-based porcelain, or a composite piezoelectric vibrator in which the porcelain-based piezoelectric vibrator and a resin such as an epoxy resin are combined. To use. In this embodiment, the array probe 4 is composed of 64CH, the apex side is the 1st CH, and the 90 ° side is the 64th CH.

A pulser 5, a transmission delay element 6, and a receiver 7 are provided in each of the ultrasonic transducers 4a thus arranged.
And the receiving delay element 8 are connected. In this embodiment, an analog delay line is used as the receiving delay element 8. The ultrasonic transducers 4a are driven by the corresponding pulsers 5, and the operation timing of each pulser 5 is
It 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 that selects a transducer group including a preset number of ultrasonic transducers 4a as one group, and a circuit that switches the group.
It includes a circuit for giving each pulser 5 a timing for driving each ultrasonic transducer 4a of the group, and a circuit for giving a delay time to the transmission delay element 6 and the reception delay element 8.
The ultrasonic transducer group is selected by the refraction angle controller 9,
For each selected ultrasonic transducer 4a, the timing obtained by adding the delay time controlled by the refraction angle controller 9 to the timing for driving each ultrasonic transducer 4a by the corresponding transmission delay element 6 is Given to pulsar 5. By applying the transmission voltage by the pulser 5 at the above timing, the ultrasonic beam is transmitted from the vibrator 4a into the steel pipe 1.

Reception of a flaw echo or the like is carried out as follows. Each ultrasonic transducer 4 of the selected ultrasonic transducer group
The signal received by a 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 the adder 10 and amplified by the amplifier 11 to a signal level required for evaluation. The amplified signal value is compared with a predetermined threshold value by the defect evaluator 12 to evaluate the presence / absence of a defect. In the ultrasonic flaw detector according to the present embodiment, the angle of incidence on the steel pipe 1 is increased by sequentially switching, for example, 16 selected ultrasonic transducer groups at a predetermined interval, which contribute to ultrasonic beam formation. Instead, the entire cross section of the welded portion 2 can be detected.

FIG. 1 shows the state of the beam in which the inner surface side is flaw-detected with 0.5 skips and the outer surface side (array probe 4 installation side) is flaw-detected with 1.0 skips. It is preferable to change the beam irradiation position in multiple stages in the thickness direction of 1 to detect the flaw on the entire cross section of the welded portion 2.

In the present embodiment, the following delay is given. The unit of 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 ultrasonic transducer groups are sequentially switched, the transmission / reception delay times are given in the same pattern. That is, the ultrasonic transducers 4a at both ends always have the ultrasonic transducers 4 at the center.
A delay of about 170 ns is given to a.

In the present embodiment, one probe (two from both sides of the welded portion 2) is used from one side of the welded portion 2 to keep the distance from the welded portion 2 to the probe 4 constant. However, the entire cross section of the welded portion 2 can be detected with high accuracy simply by linearly scanning in the welding line direction. Then, the ultrasonic beam can be focused at each depth in the wall thickness direction only by giving a relatively small transmission / reception delay, and it becomes possible to detect microscopic flaws in the entire cross section of the welded portion 2.

Further, when the timing of transmitting and receiving ultrasonic waves in each ultrasonic transducer 4a is controlled by the transmission delay time control and the reception delay time control, it is possible to select a group of ultrasonic transducers 4a and perform switching scanning without selecting them. The refraction angle can be changed. Whether the refraction angle deflection is performed by switching scanning of the group of ultrasonic transducers 4a or by delay time control is determined in consideration of the shape of the array probe 4 and the range of refraction angle polarization.

The inspection specifications of the material to be inspected are generally determined for each material to be inspected by the standards such as ISO and API. Defects used for sensitivity adjustment include notches and drill holes on the inner and outer surfaces that are machined in the central portion of the welded portion 2, and lateral holes that are machined in the central portion in the thickness direction. Also,
For the gate position and width adjustment, the above-described flaws and flaws such as notches and drill holes that are processed in the weld toe are used.

Array probe 4 arranged on one side of welded portion 2
When the above-mentioned flaw is detected, the refraction angle is changed. When the test piece is a flat plate, the outer surface can be detected at a refraction angle of about 55 degrees by detecting the inner surface at a refraction angle of 70 degrees. The number of refraction angles (the number of divisions between refraction angles 55 to 70 degrees) necessary for inspecting the entire cross section of the welded portion 2 without omission is the degree of diffusion of the ultrasonic beam and the size of flaws to be detected. It depends on the curvature, wall thickness, outer diameter, and roundness of the UOE steel pipe.

A method for determining the flaw detection refraction angle number will be specifically described below. FIG. 2 is a plan view showing a state where artificial flaws are provided on the comparative test piece used in the present embodiment. In the figure, a to d are vertical holes, e is a horizontal hole, f to g are outer surface notches, and h to i are inner surface notches. The artificial flaw is ISO
And API, the thickness of the steel pipe 1, the outer diameter and the roundness, the approach limit distance of the array probe 4, and the like.

The procedure for flaw detection on the artificial flaw of FIG. 2 using the ultrasonic flaw detector according to this embodiment is as follows.
The inner surface notch flaw i provided on the comparative test piece (1) having an outer diameter of 800 mm and a wall thickness of 7.5 mm was flaw-detected by 1.5 skips at a refraction angle of 66 degrees (ultrasonic wave propagation behavior shown in FIG. 8A), The position where the echo intensity of the flaw reaches its peak is set as the probe-weld portion distance. Further, the inner surface notch flaw i provided in each of the comparative test pieces (2) having an outer diameter of 1000 mm and a wall thickness of 38 mm was flaw-detected with 0.5 skips at a refraction angle of 66 degrees (the ultrasonic wave propagation behavior shown in FIG. 9A). , The position where the echo intensity of the flaw reaches a peak is set as the probe-weld distance. Here, in the comparative test piece (1), the approach limit distance of the array probe is about 5
Since it is 0 mm, the array probe cannot be brought close to the distance for detecting the inner surface notch flaw i with 0.5 skip, so the flaw was detected with 1.5 skip.

With the set probe-weld portion distance maintained, flaws from a to h in FIG. 2 were detected. The results are shown in Tables 2 and 3. Table 2 shows the result of flaw detection on the comparative test piece (1), and Table 3 shows the result of flaw detection on the comparative test piece (2). In the table, ◯ indicates that the flaw echo intensity exceeds a predetermined threshold value, and ⊚ indicates that the echo intensity is maximum. The refraction angle "1" in the table corresponds to 70 degrees, and as the number in the table increases, the refraction angle decreases in steps of approximately 2 degrees. The threshold value is determined according to the standard applied to the steel pipe 1 and the type and degree of flaws to be detected. For example, when the ultrasonic beam is transmitted to a vertical hole having a diameter of 3.2 mm and the echo intensity is 100%, the echo intensity of 50% is set as the threshold value.

[0054]

[Table 2]

[0055]

[Table 3]

From Tables 2 and 3, when the flaw detection is performed at a refraction angle exceeding a predetermined threshold and indicated by ◯, the comparison test piece (1) is detected at six refraction angles (six steps). This means that the comparative test piece (2) will detect flaws at seven different refraction angles (seven steps). When these are used as flaw detection refraction angles, they are refraction angles that are equal to or greater than a threshold value set in advance corresponding to the standards such as ISO and API applied to the steel pipe 1 and the type and degree of flaws to be detected. It is possible to reduce the number of flaw detection refraction angles and detect flaws to be detected.

Then, considering the degree of diffusion of the ultrasonic beam, the size of the flaw to be detected, the transport speed of the material to be inspected, etc.,
According to the following rules, the flaw detection refraction angle number can be further narrowed down. 1) For each flaw, select the combination of refraction angles at which the maximum flaw echo intensity is detected. In Table 3, five types of refraction angles of flaw detection refraction angles “3”, “4”, “5”, “8”, and “9” are selected, and can be reduced from the above-mentioned 7 procedures to 5 procedures. . In this case, the flaw detection refraction angle number is further reduced, the flaw detection repetition frequency / procedure is improved, and minute flaws can be detected, and flaws are not overlooked even when the steel pipe 1 is transported at high speed.

2) Reselection is performed so that the number of refraction angles used for flaw detection is minimized with respect to the refraction angle group in which the flaw echo intensity is equal to or higher than a predetermined threshold value. In the case of Table 3, when three refraction angles of "3", "5", and "9" are selected, all flaw echoes can be detected with the intensity equal to or higher than the threshold value. In the case of Table 2,
When two refraction angles of “3” and “5” are selected, it becomes possible to detect all flaw echoes with an intensity equal to or higher than the threshold value. In this case, the flaw detection refraction angle number is minimized, the flaw detection repetition frequency / procedure is further improved, even minute flaws can be detected, and flaws are not overlooked even when the steel pipe 1 is transported at high speed.

The flow for minimizing the flaw detection refraction angle number is shown below. a) In a predetermined flaw (in the present embodiment, the 1.6 mm diameter vertical hole a is given the highest priority), the refraction angle that maximizes the flaw echo intensity is selected. b) In the case where there is a flaw in which the refraction angle of a) does not exceed the threshold value, the flaw selected according to the priority order (in the case of the present embodiment,
In Tables 2 and 3, the artificial flaws on the upper side have a high priority), and the refraction angle that is equal to or larger than the threshold value is selected. c) When the echo intensity becomes equal to or higher than the threshold value for all the flaws, the selection of the refraction angle is finished. d) When there are a plurality of selection branches, a refraction angle having a high echo intensity is selected for a flaw having a higher priority.

Note that the flow is not limited to the above, as long as a small number of refraction angles capable of detecting all flaw echoes with an intensity equal to or higher than a threshold value can be selected.
However, when the number of refraction angles is reduced, there is a merit that the flaw detection repetition frequency / procedure is improved, but when the actual flaw of the welded portion 2 is different from the artificial flaw and is inclined in the thickness direction of the steel pipe 1, When an error more than expected is included due to various factors such as seam copying, there is a demerit that the reproducibility of flaw detection decreases. Therefore, it is necessary to determine the flaw detection refraction angle number in consideration of the degree of divergence of the ultrasonic beam, the flaw size to be detected, the transport speed of the steel pipe 1, the steady accuracy of seam scanning control, and the like.

Embodiment 2. FIG. 3 is a plan view showing a state in which the steel pipe 1 is calibrated before being flaw-detected by using the ultrasonic flaw detector according to the second embodiment. In the figure, the same parts as those in FIG. 1 are designated by the same reference numerals. . The flaw detection unit 15 includes the pulser 5, the transmission delay element 6, the receiver 7, the reception delay element 8, the refraction angle controller 9, the adder 10, the amplifier 11, and the flaw evaluator 12 described above. The pair of array probes 4 includes the welded portion 2
It is arranged in a state of being supported by the supporting portion 14 on a straight line orthogonal to the welding line. In the case of flaw detection and calibration of artificial flaws, ultrasonic waves are alternately transmitted and received from the pair of array probes 4 to select the refraction angle shown in the first embodiment. When confirming the echo intensity and the appearance position of the ultrasonic waves propagating through the steel pipe 1, ultrasonic waves are transmitted from one array probe 4 and received by the other array probe 4, and calibration is performed based on the result. To do. At this time, the refraction angles set by the two array probes 4 are the same.

In the present embodiment, a pair of array probes 4 are arranged so as to face each other on a straight line orthogonal to the welding line, and an artificial flaw is positioned on the front surface of the array probe 4 to perform accurate calibration. It can be carried out. Then, the calibration work becomes easy, and the sensitivity check and the defect monitoring gate position check can be performed.

FIG. 4 is a plan view showing a state in which the steel pipe 1 is flaw-detected by using the ultrasonic flaw detector according to the present embodiment.
In the figure, the same parts as those in FIG. 3 are designated by the same reference numerals. The pair of array probes 4 has a dimension (length of the ultrasonic transducer 4a) of the array probe 4 in a direction parallel to the welding line of the welded portion 2.
In the state of being displaced as described above, it is supported and arranged by the support portion 14. This arrangement improves the flaw detection repetition frequency / procedure. Therefore, even a small flaw can be detected, and even when the steel pipe 1 is transported at high speed, the flaw can be surely detected.

In the present embodiment, the arrangement of the probe 4 is changed manually during calibration and during flaw detection, but the arrangement may be changed automatically by driving a motor or the like.

In the first and second embodiments, the case where the steel pipe 1 is used as the material to be inspected has been described, but the present invention is not limited to this. It can also be applied to ultrasonic flaw detection.

In the first embodiment, the case where the wedge 3 has a fan shape has been described, but the present invention is not limited to this.

Furthermore, in the first and second embodiments,
The case where the array probe 4 including a plurality of ultrasonic transducers is used as a probe capable of performing flaw detection at different refraction angles has been described, but the present invention is not limited to this, and a mechanical device such as a motor may be used. Alternatively, a probe whose refraction angle can be changed may be used.

[0068]

As described above in detail, in the case of the first invention, the distance between the weld and the probe is kept constant,
Since the flaw detection refraction angle is selected based on the echo intensity detected by flaw detection of the artificial flaw with a plurality of refraction angles, a small number can be selected according to the thickness of the material to be inspected, the roundness and the degree of ultrasonic beam diffusion. The flaw detection refraction angle can be easily selected,
The inspection repetition frequency / procedure can be improved.

In the case of the second invention, the distance between the welded portion and the probe is determined based on the result of flaw detection of the artificial flaw at a predetermined refraction angle, so that the position where the echo intensity of the flaw reaches a peak is determined. By setting the distance, it is possible to correctly irradiate the flaw with the ultrasonic beam in accordance with the thickness, the roundness, the material, the degree of the ultrasonic beam diffusion, etc., and it is possible to detect flaws with higher sensitivity.

In the case of the third aspect of the invention, since it includes the process of selecting the refraction angle when the echo intensity of each artificial flaw is equal to or greater than the preset threshold value, when the selected refraction angle is the flaw detection refraction angle, It is possible to detect flaws to be detected by reducing the number of flaw detection refraction angles.

In the case of the fourth invention, the process of selecting, as the flaw detection refraction angle, the combination of the refraction angles at which the maximum echo intensity is detected for each artificial flaw among the selected refraction angles is included. The number is further reduced, the flaw detection repetition frequency / procedure is improved, and minute flaws can be detected, and flaws can be reliably detected even when the material to be inspected is transported at high speed.

In the case of the fifth aspect of the invention, among the selected refraction angles, the step of preferentially selecting the refraction angle at which a high echo intensity is detected for the preselected artificial flaw is included, so that the flaw detection refraction angle number is Further, the flaw detection repetition frequency / procedure is further improved, and minute flaws can be detected, and flaws that should be surely detected can be detected even when the material to be inspected is conveyed at high speed.

According to the sixth aspect of the invention, the pair of probes are arranged on a straight line intersecting with the welding line of the welded portion, the artificial flaw is flaw-detected and calibrated, and the pair of probes are welded. By arranging in a direction parallel to the line at least displaced by the size of the probe and inspecting the welded portion, the calibration work is facilitated at the time of calibration, and the sensitivity check and flaw monitoring gate are performed. Position checking can be performed. When the inspection of the material to be inspected is performed, the inspection repetition frequency / procedure is improved, and even small flaws can be detected.
Even when the material to be inspected is transported at high speed, it is possible to reliably detect the flaw.

In the case of the seventh invention, since the array probe having a plurality of ultrasonic transducers is used as the probe, the refraction angle can be easily and rapidly changed.

[Brief description of drawings]

FIG. 1 is a schematic view showing an ultrasonic flaw detector applied to a first embodiment of the present invention.

FIG. 2 is a plan view showing a state where artificial flaws are provided on a comparative test piece used in the first embodiment of the present invention.

FIG. 3 is a plan view showing a state in which a steel pipe is calibrated before being flaw-detected by using the ultrasonic flaw detector according to Embodiment 2 of the present invention.

FIG. 4 is a plan view showing a state in which a steel pipe is flaw-detected using the ultrasonic flaw detector according to Embodiment 2 of the present invention.

FIG. 5 is a schematic diagram showing the arrangement and ultrasonic wave propagation behavior of a conventional tube axial direction flaw inspection probe.

FIG. 6 is a schematic view showing the arrangement and ultrasonic wave propagation behavior of a conventional tube axial direction flaw inspection probe.

FIG. 7 is a plan view showing an arrangement of probes in UOE steel pipe flaw detection.

FIG. 8 is a diagram showing ultrasonic wave propagation behavior in a UOE steel pipe.

FIG. 9 is a diagram showing ultrasonic wave propagation behavior in a UOE steel pipe.

FIG. 10 is a diagram showing ultrasonic wave propagation behavior in a UOE steel pipe.

[Explanation of symbols]

1 steel pipe 2 welds 3 wedges 4 array transducer 4a Ultrasonic transducer 5 Pulsa 6 Transmission delay element 7 receiver 8 Delay element for reception 9 Refraction angle controller 12 flaw evaluator

Claims (7)

[Claims] 1. An ultrasonic beam is transmitted from a probe capable of flaw detection at a plurality of different refraction angles to a weld portion of a material to be inspected, and the weld portion is flaw-detected based on an echo signal received by the probe. In the ultrasonic flaw detection method, with the distance between the weld and the probe kept constant,
The process of detecting the echo intensity when detecting a predetermined number of artificial flaws with multiple refraction angles, the process of selecting the flaw detection refraction angle based on the detected echo intensity, and the process of detecting the material to be inspected based on the selected flaw refraction angle A method for ultrasonic flaw detection, comprising a step of flaw detection of a welded portion. 2. The distance between the welded portion and the probe is determined based on the result of flaw detection of a pre-formed artificial flaw at a predetermined refraction angle, and the plurality of refraction angles are the predetermined refraction angle. The ultrasonic flaw detection method according to claim 1, further comprising: 3. The ultrasonic flaw detection method according to claim 1, further comprising a step of selecting a refraction angle when the echo intensity of each artificial flaw exceeds a preset threshold value. 4. The method according to claim 3, including a step of selecting, as a flaw detection refraction angle, a combination of refraction angles at which the maximum echo intensity is detected for each artificial flaw among the selected refraction angles. Ultrasonic flaw detection method. 5. The method according to claim 3, further comprising the step of preferentially selecting a refraction angle at which a high echo intensity is detected for a preselected artificial flaw among the refraction angles selected.
Ultrasonic flaw detection method described. 6. A probe capable of performing flaw detection at a plurality of different refraction angles is arranged on both sides of a welded portion of a material to be inspected, and an ultrasonic beam is transmitted from the probe to the welded portion to detect the probe. In an ultrasonic flaw detection method for flaw detection of the welded portion based on the echo signal received by the child, a pair of probes are arranged on a straight line intersecting the welding line of the welded portion, and flaws of the artificial flaw are calibrated and calibrated. An ultrasonic flaw detection method comprising a step and a step of arranging a pair of probes in a direction parallel to the welding line with a displacement of at least the dimension of the probe and detecting the weld portion. . 7. The ultrasonic flaw detection method according to claim 1, wherein the probe is an array probe including a plurality of ultrasonic transducers.