JP4356549B2 - Ultrasonic flaw detection method and ultrasonic flaw detection apparatus - Google Patents

Description

  The present invention relates to an ultrasonic flaw detection method and an ultrasonic flaw detection device, and more particularly to an ultrasonic flaw detection method and an ultrasonic flaw detection device for flaw detection included in a welded portion formed in the axial direction of a welded steel pipe.

  In a welded portion of a welded steel pipe such as a submerged arc welded (SAW) steel pipe, a defect as shown in FIG. A defect 25 occurring in the welded portion 2 of the welded steel pipe 1 is inherent in the welded portion 25. In other words, the defect 25 does not have an opening on the surface of the weld 2. The defect 25 is, for example, a pinhole or occurs due to insufficient penetration during welding. In order to inspect the presence or absence of such defects in the welded portion, ultrasonic flaw detection such as a tandem flaw detection method as shown in FIG. 14 is performed. In the tandem flaw detection method, a transmission probe 50 and a reception probe 51 are used. The receiving probe 51 is disposed at a position where the echo of the defect 25 of the welded portion 2 propagates, and the receiving probe 51 detects the echo of the defect 25.

  In the tandem flaw detection method, an ultrasonic beam propagates while being reflected by the outer peripheral surface and the inner peripheral surface of a welded steel pipe to be inspected (hereinafter referred to as a welded steel pipe to be inspected) and enters the defect 25 of the welded portion 2. Further, the echo of the defect 25 also propagates while being reflected on the outer peripheral surface and the inner peripheral surface. As the number of reflections increases, the echo attenuates and the defect becomes difficult to detect.

In the ultrasonic flaw detection methods disclosed in Patent Documents 1 and 2 below, an ultrasonic beam is directly incident on a defect in a welded portion without being reflected by the outer peripheral surface and the inner peripheral surface of the inspection target welded steel pipe. Specifically, as shown in FIG. 15, the incident angle α ₀ and the arrangement position N ₀ of the probe 52 are adjusted so that the ultrasonic beam UW is perpendicularly incident on the defect 25. If the ultrasonic beam UW is perpendicularly incident on the defect 25, the echo reflected by the defect 25 returns to the probe 52 without being reflected by the outer peripheral surface and the inner peripheral surface. At this time, the propagation direction of the echo does not deviate from the probe 52. Therefore, the defect detection accuracy can be increased as compared with the tandem flaw detection method.

In the ultrasonic flaw detection method shown in FIG. 15, it is better to accurately determine the incident angle α _{0 of the} ultrasonic beam output from the probe and the arrangement position N _{0 of} the probe according to the welded steel pipe to be inspected. Good. In the ultrasonic flaw detection methods of Patent Documents 1 and 2, the incidence is based on the outer diameter and thickness of the welded steel pipe to be inspected, and the propagation speed of the ultrasonic beam in the probe and the welded steel pipe to be inspected. The angle α ₀ and the arrangement position N ₀ are calculated.

However, in the ultrasonic flaw detection method using the calculated incident angle α ₀ and arrangement position N ₀ , the defect detection accuracy may not be improved for the following reasons.

  (1) A welded steel pipe to be inspected is manufactured by forming a steel plate into an open pipe by bending such as press forming and then welding a joint portion of the open pipe. Therefore, the shape of the cross section perpendicular to the axial direction of the welded steel pipe to be inspected is not a perfect circle, and distortion due to bending occurs. In particular, shape distortion is likely to occur near the weld. The shape on both sides of the welded portion may be asymmetric. In this way, if the cross-sectional shape of the welded steel pipe to be inspected is not a perfect circle, even if flaw detection is performed at the incident angle and arrangement position calculated based on the outer diameter size and the wall thickness dimension of the welded steel pipe to be inspected, The sound beam is not incident perpendicular to the defect. Therefore, the defect detection accuracy does not increase.

  (2) The acoustic anisotropy of the welded steel pipe to be inspected, the temperature of the welded steel pipe to be inspected at the time of flaw detection, the temperature of the probe wedge at the time of flaw detection, and the like affect the propagation speed of the ultrasonic beam. It is difficult to assume the propagation speed value of the ultrasonic beam considering all these conditions. Therefore, even if flaw detection is performed at the calculated incident angle and arrangement position, the ultrasonic beam is not incident perpendicularly to the weld defect.

In short, the incident angle and arrangement position obtained by calculation deviate from the true incident angle and arrangement position at which the ultrasonic beam is incident perpendicularly to the defect. This deviation hinders improvement in defect detection accuracy. In addition, the detection accuracy of the defect may not be improved due to the influence of the mechanical error of the ultrasonic flaw detector. For example, at the time of flaw detection, the welded steel pipe to be inspected is moved in the pipe axis direction by the transport roller while contacting the probe on the welded steel pipe to be inspected. At this time, the welded steel pipe to be inspected vibrates in the horizontal and vertical directions due to looseness of the conveying roller. Due to this vibration, the arrangement position of the probe during the flaw detection may be shifted, or the incident angle of the probe may be shifted from the calculated incident angle.
JP 2003-215115 A Patent No. 3444609 Ultrasonic flaw detection method for welded steel pipes (Edited by the Steel Society Quality Control Committee (NDI Division), p. 60-62)

  An object of the present invention is to provide an ultrasonic flaw detection method and an ultrasonic flaw detection apparatus that can improve the detection accuracy of defects contained in a welded portion formed in the axial direction of a welded steel pipe.

Means for Solving the Problems and Effects of the Invention

An ultrasonic flaw detection method according to the present invention is an ultrasonic flaw detection method for flaw detection in a welded portion formed in the axial direction of a welded steel pipe to be inspected by an oblique flaw detection method, which is the same forming step as a welded steel pipe to be inspected. Preparing a sample welded steel pipe that has the same outer diameter and thickness as the welded steel pipe to be inspected, is inherent in the weld formed in the axial direction, and includes a defect parallel to the thickness direction ; A step of arranging a variable incident angle probe capable of changing the incident angle on the outer peripheral surface of the welded steel pipe, outputting an ultrasonic beam from the variable incident angle probe, and generating the ultrasonic beam as the outer peripheral surface of the sample welded steel pipe And a step of directly receiving the echo reflected by the defect without reflecting on the inner peripheral surface by the incident angle variable probe and changing the incident angle while outputting the ultrasonic beam. the incident angle variable probe while output Change the position of the incident angle variable probe by moving circumferentially child on the outer peripheral surface of the sample welded steel pipe, the angle of incidence echoes defects among the incident angle and the arrangement position has changed is maximum And a step of determining an arrangement position, and a step of flaw-inspecting the welded steel pipe to be inspected at the determined incident angle and arrangement position. Here, the incident angle variable probe may be, for example, an array probe or a probe that can mechanically change the incident angle. The same outer diameter and wall thickness as the inspection target welded steel pipe refer to, for example, the outer diameter of the inspection target welded steel pipe ± 5% and the thickness of the inspection target welded steel pipe ± 5%.

  In the ultrasonic flaw detection method according to the present invention, before flaw detection is performed on a welded steel pipe to be inspected, an incident angle and an arrangement position are determined using a sample welded steel pipe manufactured in the same forming process as the welded steel pipe to be inspected. For example, when the inspection target welded steel pipe is formed by C press, U press, and O press, the sample welded steel pipe is also formed by the same C press, U press, and O press. Moreover, when the inspection target welded steel pipe is formed by roll forming, the sample welded steel pipe is also formed by the same roll forming.

  In short, the sample welded steel pipe has substantially the same cross-sectional shape as the cross-sectional shape in the axial direction of the inspection target welded steel pipe. If shape distortions such as irregularities are generated on the outer peripheral surface of the welded steel pipe to be inspected, the same geometric distortions are also generated at the same location on the outer peripheral surface of the sample welded steel pipe.

  In the ultrasonic flaw detection method according to the present invention, the incident angle of the ultrasonic beam and the arrangement position of the probe are determined using a sample welded steel pipe having substantially the same cross-sectional shape as the inspection target welded steel pipe. Therefore, it is possible to determine the incident angle of the ultrasonic beam and the arrangement position of the probe in consideration of not only the outer diameter and the thickness, but also the distortion of the shape generated by the molding process. If the welded steel pipe to be inspected is detected at the incident angle and arrangement position determined using the sample welded steel pipe, it is possible to prevent the propagation direction of the ultrasonic beam from deviating from the defect in the weld due to the distortion of the shape. As a result, the detection accuracy of defects can be increased. Note that when the incident angle and the arrangement position of the variable incident angle probe are changed while outputting the ultrasonic beam, for example, the ultrasonic beam is intermittently output according to the pulse.

  Preferably, the sample welded steel pipe is made of the same material as the inspection target welded steel pipe.

  In this case, since the sample welded steel pipe is made of the same material as the welded steel pipe to be inspected, the incident angle and the arrangement position can be determined in consideration of acoustic anisotropy.

  Preferably, the flaw detection step includes a step of selecting an oblique probe having a determined incident angle from a plurality of oblique probes having a fixed incident angle, and the selected oblique probe. And a step of flaw detection of a material to be inspected using a child.

  In this case, for example, even if an online ultrasonic flaw detector cannot be equipped with a variable incident angle probe, an oblique angle probe having an incident angle determined using an incident angle variable probe offline can be used online. Can inspect the welded steel pipe to be inspected.

  Preferably, in the flaw detection step, a welded steel pipe to be inspected is flawed using a variable incident angle probe. Here, the variable incident angle probe may be an array probe or a probe that can mechanically change the incident angle.

  Preferably, in the flaw detection step, the welded steel pipe to be inspected is detected while swinging the incident angle of the variable incident angle probe within a predetermined range centered on the determined incident angle.

  Even if the welded steel pipe to be inspected is detected at the incident angle and position determined using the sample welded steel pipe, the ultrasonic beam depends on the temperature of the welded steel pipe to be inspected during the flaw detection and the temperature of the wedge of the probe during the flaw detection. There is a case where the propagation direction of the deviates from the defect. Further, due to a mechanical error of the ultrasonic flaw detector, the arrangement position of the probe with respect to the welded portion may slightly deviate from the determined arrangement position. In the ultrasonic flaw detection method according to the present invention, the flaw detection is performed while swinging the incident angle of the variable incident angle probe within a predetermined range centered on the determined incident angle. Therefore, the deviation in the propagation direction of the ultrasonic beam can be corrected within the range of the incident angle that oscillates. Further, even when a defect inherent in the welded portion is not parallel to the thickness direction but has a slight inclination with respect to the thickness direction, the defect can be detected without overlooking the defect by swinging the incident angle. Therefore, the defect detection accuracy becomes higher.

  Preferably, the determining step determines an incident angle and an arrangement position for each of a plurality of sample welded steel pipes having different materials or sizes. The ultrasonic flaw detection method according to the present invention further includes a step of storing the plurality of determined incident angles and arrangement positions in the management apparatus in association with the sizes and materials of the plurality of sample welded steel pipes. The step of flaw detection is based on the step of retrieving from the management device the incident angle and arrangement position corresponding to the sample welded steel pipe of the same size and material as the welded steel pipe to be inspected, and based on the retrieved incident angle and arrangement position. And a step of flaw detection of the welded steel pipe to be inspected.

  In this case, the incident angle and the arrangement position determined in advance using the sample welded steel pipe before the flaw detection are stored in the management device. When flaw detection is performed on the inspection target welded steel pipe, an incident angle and an arrangement position corresponding to the size and material of the inspection target welded steel pipe may be retrieved from the management device. Therefore, it is not necessary to determine the incident angle and the arrangement position using the sample welded steel pipe immediately before inspecting the inspection target welded steel pipe.

Preferably, in the step of determining the incident angle and the arrangement position, the incident angle of the ultrasonic beam output from the variable incident angle probe is fluctuated, and a plurality of defect echoes are arranged in descending order from the varied incident angle. The step of selecting the incident angle and, for each selected incident angle, moving the variable incident angle probe in the circumferential direction on the outer peripheral surface of the sample welded steel pipe while outputting an ultrasonic beam, Selecting a maximum arrangement position, and determining an incident angle and an arrangement position at which the defect echoes are maximum based on the selected arrangement position for each incident angle.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

1. 1. First embodiment 1.1. Configuration of Ultrasonic Flaw Detector With reference to FIG. 1A, an ultrasonic flaw detector 10 according to an embodiment of the present invention uses the array probes 15A and 15B to detect a welded portion 2 of a welded steel pipe 1 to be inspected. As shown in FIG. 1A, the inspection target welded steel pipe 1 may be placed on a V-shaped transport roller 20 or may be installed on a V-shaped mount.

  The ultrasonic flaw detector 10 includes a lift frame 11, a rail 12, an arm 13, a probe holder 14, array probes 15 </ b> A and 15 </ b> B, a control device 16, and a seam that detects the position of the welded portion 2. And a detector 17.

  The elevating frame 11 and the arm 13 move the array probes 15A and 15B to predetermined arrangement positions. The lift frame 11 has a seam detector 17 attached to the center position of the lower surface thereof, and rails 12 attached to both ends of the lower surface. The elevating frame 11 is raised or lowered by hydraulic pressure or electric power. The elevating frame 11 moves up and down corresponding to the outer diameter of the welded steel pipe 1 to be inspected to bring the array probes 15A and 15B into contact with the outer peripheral surface of the welded steel pipe 1 to be inspected.

  The elevating frame 11 can be further rotated within a predetermined range in the circumferential direction of the inspection target welded steel pipe 1. During ultrasonic flaw detection, the elevating frame 11 rotates so that the seam detector 17 is positioned directly above the weld 2. For example, when the welded steel pipe 1 to be inspected is rotated clockwise from the state of FIG. 1A and the welded portion 2 is shifted from right below the seam detector 17, the lifting frame 11 is rotated clockwise, and the seam detector 17 stops at a position directly above the weld 2. Thereby, the distance between the welded portion 2 and the array probes 15A and 15B during the ultrasonic flaw detection is kept constant.

  The arm 13 moves the array probes 15A and 15B held by the probe holder 14 in the horizontal direction and the vertical direction. The arm 13 includes a horizontal arm member 131 and a vertical arm member 132. The horizontal arm member 131 moves in the horizontal direction along the rail 12 by electric drive. The vertical arm member 132 has the probe holder 14 at the lower end. The vertical arm member 131 moves in the vertical direction.

  The control device 16 controls the lift frame 11, the arm 13, and the array probe 15. The control device 16 determines the arrangement positions of the array probes 15A and 15B, and moves the array probes 15A and 15B to the determined arrangement positions by the lifting frame 11 and the arm 13. Further, the incident angle of the ultrasonic beam for detecting the defect 25 of the welded portion 2 is determined.

  Referring to FIG. 1B, array probe 15A includes a wedge 151 and a plurality of transducers CH1 to CH32. The vibrators CH <b> 1 to CH <b> 32 are arranged in a line in the order of the vibrator number along the circular arc portion on the upper surface of the wedge 151. Specifically, among the plurality of transducers CH1 to CH32, the transducer CH1 is disposed on the top. Subsequently, the vibrators CH2 and CH3 are arranged in the order of the vibrator numbers, and the vibrator CH32 is arranged at the bottom. The vibrators CH1 to CH32 receive a pulse output from the control device 16 and transmit an ultrasonic wave. A plurality of transmitted ultrasonic waves are combined to form an ultrasonic beam. Further, the transducers CH1 to CH32 receive the echo. The array probe 15B has the same configuration as the array probe 15A.

  The control device 16 includes swinging units 180A and 180B, echo receiving units 190A and 190B, a determining unit 166, and a hard disk 170. The swinging part 180A and the echo receiving part 190A correspond to the array probe 15A, and the swinging part 180B and the echo receiving part 190B correspond to the array probe 15B. The swinging units 180A and 180B have the same configuration, and the echo receiving units 190A and 190B have the same configuration.

  The swinging unit 180A causes the array probe 15A to output ultrasonic beams having various incident angles. The swing unit 180A includes pulsers PL1 to PL32, transmission delay elements TD1 to TD32, and a swing instruction unit 169. The pulser PLn (n = 1 to 32) outputs a pulse for exciting the corresponding transducer CHn. For example, the pulser PL1 outputs a pulse to the vibrator CH1, and the pulser PL2 outputs a pulse to the vibrator CH2.

  The swing instructing unit 169 selects a plurality of pulsers PL that output pulses from the pulsers PL1 to PL32, and further determines the timing for outputting pulses to the selected pulsers PL. In other words, the swing instruction unit 169 can swing the incident angle of the ultrasonic beam output from the array probe 15A. Specifically, the swing instruction unit 169 performs the following operation.

The swing instructing unit 169 selects 16 consecutive pulsers PL. Specifically, the swing instruction unit 169 selects pulsars PLk to PLk + 15 (k = 1 to 17). Here, k is a count value, and the swing instruction unit 169 increments or decrements. The count value k is stored in a memory (not shown) in the swing instruction unit 169. After selecting the pulsar PL, the swing instruction unit 169 determines the delay times of the transmission delay elements TDk to TDk + 15 corresponding to the pulsars PLk to PLk + 15 based on the delay time table shown in Table 1. The delay time table is stored in the hard disk 170.

  In Table 1, the delay time indicates that the wavefront of the ultrasonic beam UW, which is a synthesized wave of ultrasonic waves output from the pulsars PLk to PLk + 15, connects the lower surface center portion of the transducer CHk and the lower surface center portion of the transducer CHk + 15. It is set to be parallel to the straight line. The delay times T1 to T7 have the relationship of Expression (1).

  0 <T1 <T2 <T3 <T4 <T5 <T6 <T7 (1)

  For example, the swing instruction unit 169 sets the count value k = 1 and selects the pulsars PL1 to PL16. In other words, transducers CH1 to CH16 are selected as transducers that output ultrasonic waves. Subsequently, the swing instruction unit 169 determines the delay times of the transmission delay elements TD1 to TD16 to the times shown in Table 1. Specifically, the delay elements TD1 and TD16 have a delay time T7, and the delay elements TD2 and TD15 have a delay time T6. The delay elements TD7 and TD8 have a delay time of zero.

  Subsequently, the pulsars PL1 to PL16 output pulses based on the determined delay time. Referring to FIG. 2A, pulsers PL7 and PL8 output pulses earliest, and thus transducers CH7 and CH8 first output ultrasonic waves among transducers CH1 to CH16. Subsequently, the transducers CH6 and CH9 output ultrasonic waves, and then the transducers CH5 and CH10 output ultrasonic waves. Similarly, each transducer CH sequentially outputs ultrasonic waves, and finally the transducers CH1 and CH16 output ultrasonic waves. By shifting the output timing of the ultrasonic wave of each selected transducer, the wavefront of the ultrasonic beam UW, which is a combined wave of the ultrasonic waves of each transducer, is changed to the center of the bottom surface of the transducer CH1 and the center of the bottom surface of the transducer CH16. Parallel to the string 100 connecting the parts. The ultrasonic beam UW is output from the point N1 on the lower surface of the wedge 151 into the inspection target welded steel pipe 1. The incident angle at this time is α1.

  Subsequently, the swing instruction unit 169 sets the count value k = 2 and performs the same operation. At this time, as shown in FIG. 2B, the transducers CH2 to CH17 output ultrasonic waves. The output timing of ultrasonic waves from the transducers CH2 to CH17 follows Table 1. Specifically, the transducers CH8 and CH9 first output an ultrasonic wave, and the transducers CH2 and CH17 finally output an ultrasonic wave. As a result, the wavefront of the ultrasonic beam UW is parallel to the string 101 connecting the lower surface center portion of the transducer CH2 and the lower surface center portion of the transducer CH17. Also at this time, the ultrasonic beam UW is output from the point N1. When the incident angle is α2, α1 <α2.

  The swing instruction unit 169 sequentially increments the count value k and performs the same operation. When k = 17, as shown in FIG. 2C, the transducers CH17 to CH32 output ultrasonic waves at the timing shown in Table 1. The ultrasonic beam UW at this time is also output to the inspection target welded steel pipe 1 from the point N1. If the incident angle at this time is α17, then α17> α2.

  With the above operation, the swing instruction unit 169 increments the count value k, so that the incident angle of the ultrasonic beam UW can be swung. After k = 17, the swing instruction unit 169 may decrement k.

  Further, the increment and decrement of the count value k may be repeated within a predetermined range. For example, the increment and decrement may be repeated in the range of the count value k = 3-5. In this case, the incident angle can be swung around the incident angle when the count value k = 4.

  Even if the count value k is sequentially changed, the output ultrasonic beam UW is always output from the point N1. This is because the wavefront of the ultrasonic beam UW is parallel to any chord of the arc portion on the upper surface of the wedge 151. In short, the point N1 is the center of the circle of the arc portion.

  Returning to FIG. 1A, the ultrasonic beam UW output from the point N1 of the array probe 15A is reflected by the defect 25 in the welded portion 2, and returns to the array probe 15A as a defect echo. The echo receiver 190A analyzes the flaw detection result based on the echoes returned to the array probe 15A.

  The echo receiving unit 190A includes a plurality of receivers RE1 to RE32, a plurality of receiving delay elements RD1 to RD32, an adder 163, an amplifier 164, and an evaluator 165. The receiver REn and the reception delay element RDn correspond to the transducer CHn. For example, the receiver RE1 and the reception delay element RD1 correspond to the transducer CH1.

  The vibrators CHk to CHk + 15 output ultrasonic waves by the swing unit 180A, and an ultrasonic beam UW is output from the array probe 15A. At this time, each transducer CHk to CHk + 15 receives the returned echo and converts it into an electrical signal. Receivers REk to REk + 15 receive signals output from corresponding transducers CHk to CHk + 15. The receiving delay elements RDk to RDk + 15 receive signals from the corresponding receivers REk to REk + 15 and delay them by the delay times shown in the delay time table of Table 1. Signals output from the delay elements RDk to RDk + 15 are added by the adder 163.

  As shown in Table 1, the delay time of the transmission delay element TDk and the delay time of the reception delay element RDk are the same. By making the delay time at the time of pulse output and the delay time at the time of echo reception the same, the signal added by the adder 163 becomes an accurate flaw detection result.

  The signal output from the adder is amplified by the amplifier 164 and output to the evaluator 165. The evaluator 165 receives the signal output from the amplifier 164 and displays the waveform of the signal on a display (not shown) as a flaw detection result. The evaluator 165 further determines the presence or absence of a defect based on the flaw detection result. The signal waveform indicates the echo intensity. Therefore, the evaluator 165 determines that there is a defect if there is an echo intensity equal to or greater than a predetermined value.

  The determining unit 166 determines the incident angle of the ultrasonic beam UW when flaw detection is performed on the inspection target welded steel pipe 1. Further, the arrangement positions of the array probes 15A and 15B at the time of flaw detection are determined.

1.2. Ultrasonic flaw detection method In the ultrasonic flaw detection method according to the present embodiment, before flaw detection is performed on the welded steel pipe 1 to be inspected, the sample welded steel pipe 200 that is known in advance to contain the defect 25 is detected. . The ultrasonic flaw detector 10 determines the incident angle and the arrangement positions of the array probes 15A and 15B for flaw detection of the inspection target welded steel pipe 1 based on the flaw detection result of the sample welded steel pipe 200. The welded steel pipe 1 to be inspected is manufactured by the following manufacturing process. An open pipe is formed by bending a steel plate by a known bending method such as C press, U press, O press or roll forming. The formed open pipe seam is welded by a well-known welding method to obtain a welded steel pipe 1 to be inspected. After welding, the welded steel pipe 1 to be inspected is flawed by the ultrasonic flaw detection method described below.
Details of the ultrasonic flaw detection method according to the present embodiment will be described below.

  With reference to FIG. 3, first, a sample welded steel pipe 200 is prepared, and the prepared sample welded steel pipe 200 is placed on the roller 20 (S1). The sample welded steel pipe 200 has substantially the same outer diameter and thickness as the inspection target welded steel pipe 1 and is manufactured in the same molding process as the inspection target welded steel pipe 1. For example, when the inspection target welded steel pipe 1 is bent by a C press, U press, and O press, a welded steel pipe bent by the same C press, U press, and O press is prepared as the sample welded steel pipe 200. When the inspection target welded steel pipe 1 is processed by the roll forming process, a welded steel pipe processed by the same roll forming process is prepared as the sample welded steel pipe 200. In short, the sample welded steel pipe 200 has substantially the same cross-sectional shape as the cross-sectional shape of the inspection target welded steel pipe 1 in the axial direction. For example, when the cross-sectional shape of the welded steel pipe 1 to be inspected is not a perfect circle and there is distortion due to bending at a certain location, the same location of the cross-sectional shape of the sample welded steel pipe 200 also has distortion due to bending. The sample welded steel pipe 200 is made of the same material as the inspection target welded steel pipe.

  The sample welded steel pipe 200 includes a defect 25 inherent in the weld 2. The defect 25 is parallel to the thickness direction of the sample welded steel pipe 200. The defect 25 does not have an opening on the surface of the weld. The defect 25 is artificially created.

  Subsequently, the lifting frame 11 and the arm 13 of the ultrasonic flaw detector 10 are adjusted, and the array probes 15A and 15B are brought into contact with the outer peripheral surface of the sample welded steel pipe 200 (S2). At this time, the seam detection unit 17 is disposed immediately above the welded portion 2.

  After the placement, the defect 25 is detected by the array probes 15A and 15B, and the incident angle and the placement position are determined (S3 to S7). Specifically, the incident angle and the arrangement position are changed while outputting the ultrasonic beam UW, and the incident angle and the arrangement position at which the echo of the defect 25 is maximized are determined from the changed incident angle and arrangement position. The incident angle and the arrangement position are determined for each array probe. Hereinafter, a method of determining the incident angle and the arrangement position of the array probe 15A will be described, but the method of determining the incident angle and the arrangement position is the same for the array probe 15B.

An ultrasonic beam UW is output from the array probe 15A into the sample welded steel pipe 200 (S3). At this time, the initial incident angle is set so that the ultrasonic beam UW is directly incident on the defect 25 without being reflected by the outer peripheral surface and the inner peripheral surface of the sample welded steel pipe 200, and the ultrasonic beam UW is output. The initial incident angle may be a value calculated from the outer diameter of the sample welded steel pipe or the like, or may be an empirical value obtained by conventional experience. Here, the count value of the initial angle of incidence and k _0.

After outputting the ultrasonic beam UW, the incident angle of the ultrasonic beam UW is changed by the rocking unit 180 (S4). Specifically, the swing instruction unit 169 increments or decrements the count value k _0. Within the range of the oscillating incident angle, three incident angles with high echo intensity of the defect 25 are selected in descending order of intensity (S5). The incident angle is selected by the determination unit 166. Let the three selected incident angles be α ₁₀₁ , α ₁₀₂ , and α ₁₀₃ .

Subsequently, the incident angle of the array probe 15A is fixed at the incident angles α ₁₀₁ , α ₁₀₂ , and α ₁₀₃ , and the arrangement position of the array probe 15A is changed. Specifically, as shown in FIG. 4, the incident angle is fixed at α ₁₀₁ , and the array probe 15 </ b> A is moved in the circumferential direction while being in contact with the outer peripheral surface of the sample welded steel pipe 200. At this time, the intensity of the defect echo is highest at the arrangement position where the propagation direction of the ultrasonic beam UW is most perpendicular to the defect 25.

The determination unit 166 selects an arrangement position where the defect echo intensity is highest at each incident angle α _{101 to} α ₁₀₃ as an arrangement position at the incident angle (S6). For example, of the position N11~N13 in FIG. 4, if the most echo intensity is higher at position N12, determination unit 166 selects the position N12 as the arrangement position of the incident angle alpha _101. At this time, the determination unit 166 stores the echo intensity of the defect 25 at the position N12. For the incident angles α ₁₀₂ and α ₁₀₃ , the arrangement position with the highest defect echo intensity is determined.

After selecting the arrangement position of each incident angle, the determination unit 166 selects the highest intensity arrangement position and incident angle from the defect echo intensities at the arrangement position determined in step S6. The determination unit 166 determines the selected incident angle and arrangement position as the incident angle and arrangement position when flaw-detecting the inspection target welded steel pipe 1 (S7). For example, when the defect echo intensity at the position L2 of the incident angle α ₁₀₁ is the highest, the determination unit 166 determines the incident angle of the array probe 15A when the inspection target welded steel pipe 1 is flawed as α ₁₀₁ , and the array probe. The arrangement position of the child 15A is determined as the position L2.

  In addition, the incident angle and arrangement position of the array probe 15B are also determined by the operations in steps S3 to S7.

  Moreover, the operator of the ultrasonic flaw detector 10 may perform selection of the incident angle in step S5, selection of the arrangement position in step S6, and determination of the incident angle and arrangement position in step S7. Specifically, the operator may select or determine the incident angle and the arrangement position while displaying the flaw detection result of the defect 25 on the evaluator 165. In this case, in step S <b> 7, the operator inputs the selected or determined incident angle and arrangement position to the ultrasonic flaw detector 10. The determination unit 166 determines the input incident angle and arrangement position as the incident angle and arrangement position when the inspection target welded steel pipe is flawed.

  After determining the incident angle and the arrangement position, the sample welded steel pipe 200 is removed from the roller 20 and the inspection target welded steel pipe 1 is conveyed onto the roller 20 (S8). After the conveyance, the ultrasonic flaw detector 10 performs ultrasonic flaw detection on the inspection target welded steel pipe 1 (S9). At this time, the ultrasonic beam UW is output at the incident angle and arrangement position of the array probe 15A and the incident angle and arrangement position of the array probe 15B determined in step S7.

  In the ultrasonic flaw detection method according to the present embodiment, the incident angle and the arrangement position are determined by the sample welded steel pipe 200 before flaw detection is performed on the inspection target welded steel pipe 1. Since the sample welded steel pipe 200 is manufactured by the same molding process as the welded steel pipe 1 to be inspected, the cross-sectional shape of the sample welded steel pipe 200 is almost the same as that of the welded steel pipe 1 to be inspected. Therefore, the incident angle and the arrangement position are determined in consideration of local unevenness and bending distortion of the shape of the welded steel pipe 1 to be inspected.

  Furthermore, since the sample welded steel pipe 200 is made of the same material as the inspection target welded steel pipe 1, the incident angle and the arrangement position are determined in consideration of acoustic anisotropy. Therefore, if the inspection target welded steel pipe 1 is flawed at the determined incident angle and arrangement position, it is possible to prevent a decrease in flaw detection accuracy due to the influence of local shape distortion and acoustic anisotropy. Therefore, the welded part 2 can be detected with high accuracy.

  Further, since the incident angle and the arrangement position are determined for each of the array probes 15A and 15B, even if the shape near the welded portion 2 of the welded steel pipe 1 to be inspected is asymmetric, defects are accurately detected by each array probe. Can detect flaws.

  Further, the incident angle and the arrangement position are changed while outputting ultrasonic waves to the sample welded steel pipe, and the incident angle and the arrangement position at which the echo of the defect 25 is maximized are determined from the changed incident angle and arrangement position. Therefore, the incident angle and the arrangement position can be determined so that the ultrasonic beam is incident as perpendicular to the defect 25 as possible.

2. Second Embodiment If the angle of incidence is swung within a predetermined range during flaw detection on a welded steel pipe to be inspected, the flaw detection accuracy for defects in the welded portion can be further improved.

  Specifically, in step S9 in FIG. 3, ultrasonic flaw detection is performed while the incident angle is swung within a predetermined range centered on the determined incident angle. For example, as shown in FIG. 5, when the determined incident angle is 47 deg, ultrasonic flaw detection is performed while swinging the incident angle within a range of 47 ± 3 deg, that is, 44 deg to 50 deg.

  The swing instruction unit 169 instructs the swing of the incident angle. If the incident angle is 47 deg when the count value k = 9, the incident angle is 50 deg when the count value k = 11, and the incident angle is 44 deg when the count value k = 7, the swing instruction unit 169 counts. The incident angle is swung in the range of the value k = 7 to 11. As a result, the incident angle of the ultrasonic beam UW during flaw detection varies in the range of 44 deg to 50 deg.

  Even if the incident angle and the arrangement position of the sample welded steel pipe 200 are determined, the propagation direction of the ultrasonic beam UW may deviate from the defect 25 due to a mechanical error of the ultrasonic flaw detector 10. Further, the propagation direction of the ultrasonic beam UW is also shifted depending on the temperature of the welded steel pipe 1 to be inspected at the time of flaw detection and the wedge 151 of the array probe. In the ultrasonic flaw detection method according to Embodiment 2, the incident angle during flaw detection is swung by a predetermined range around the determined incident angle. Therefore, even if the ultrasonic beam UW is displaced due to the mechanical error, temperature, or the like, the displacement can be corrected by swinging the incident angle. In short, the ultrasonic beam UW can be incident on the defect 25 substantially perpendicularly by oscillating the ultrasonic beam within an incident angle range where a deviation of the ultrasonic beam UW is expected. Therefore, the flaw detection accuracy is improved.

3. Third Embodiment The incident angles and arrangement positions determined by the sample welded steel pipes 200 of a plurality of sizes and materials may be registered in the ultrasonic flaw detector 10 as a database.

The ultrasonic flaw detector 10 according to the present embodiment stores the setting table shown in Table 2 on the hard disk 170.

  Referring to Table 2, in the setting table, incident angles and arrangement positions corresponding to materials, outer diameter dimensions, and wall thickness dimensions are registered. Note that the inspection standard of the flaw detection inspection, the flaw detection sensitivity, the fluctuation range of the incident angle during the flaw detection, and the like are also registered in the setting table. The incident angle and the arrangement position corresponding to the material, the outer diameter, and the wall thickness are determined by repeating steps S1 to S7 in FIG. 3 using a plurality of sample welded steel pipes 200 having different sizes and materials. Registered in the setting table. Input to the setting table may be performed by an operator using an input device (not shown), or may be performed by the determination unit 166.

  Referring to FIG. 6, when flaw detection is performed on welded steel pipe 1 to be inspected, welded steel pipe 1 to be inspected is installed on roller 20 (S10). Further, the material, outer diameter, and thickness of the inspection target welded steel pipe 1 are input to the ultrasonic flaw detector 10 (S11). Input of these values may be performed by an operator using an input device (not shown).

  The determination unit 166 in the ultrasonic flaw detector 10 searches the setting table for an incident angle and an arrangement position corresponding to the input material, outer diameter, and thickness (S12). After the search, the determination unit 166 determines the detected incident angle and arrangement position as the incident angle and arrangement position at the time of flaw detection (S13).

  The ultrasonic flaw detector 10 detects the welded steel pipe 1 to be inspected at the incident angle and arrangement position determined in step S13 (S14).

  If a plurality of incident angles and arrangement position data are registered in the setting table, it is not necessary to detect the sample welded steel pipe 200 before each inspection target welded steel pipe 1 is detected. Therefore, inspection efficiency is improved. The plurality of sample welded steel pipes 200 are manufactured in the same forming process as the corresponding inspection target welded steel pipe 1.

4). Fourth Embodiment Although an ultrasonic flaw detector installed online can attach an oblique probe with a fixed incident angle, there are cases where an array probe cannot be attached. In this case, the ultrasonic flaw detector 10 is installed off-line, and the incident angle and the arrangement position are determined using the array probes 15A and 15B. An oblique probe having an incident angle determined offline is mounted on an online ultrasonic flaw detector, and the welded steel pipe to be inspected is detected online.

The ultrasonic flaw detector 10 stores an oblique probe table shown in Table 3 on the hard disk 170.

  Referring to Table 3, the probe number of the oblique probe corresponding to the incident angle is registered in the oblique probe table.

  Referring to FIG. 7, the operations from step S1 to step S7 are the same as those in FIG. However, the ultrasonic flaw detector 10 is installed offline. After determining the incident angle and the arrangement position in step S7, the ultrasonic flaw detector 10 searches the oblique probe table for the oblique probe corresponding to the determined incident angle (S20).

  The on-line ultrasonic flaw detector mounts the bevel probe having the probe number searched in step S20 (S21). The bevel probe may be mounted by an operator. After mounting, the welded steel pipe to be inspected is conveyed to an online roller (S22). The online ultrasonic flaw detector arranges the bevel probe at the arrangement position determined in step S7 (S23), and performs ultrasonic flaw detection (S24).

  In FIG. 7, the ultrasonic flaw detector 10 has selected the oblique angle probe, but the operator may select the oblique angle probe based on the incident angle determined in step S7.

5. Fifth Embodiment In the first to fourth embodiments, the defect 25 of the sample welded steel pipe 200 is detected and the incident angle and the arrangement position are set. However, the cross-sectional shape of the inspection target welded steel pipe 1 is a perfect circle. Assuming that there is, the incident angle and the arrangement position may be calculated.

  In this case, there is a high possibility that the ultrasonic beam UW output at the calculated incident angle will deviate from the defect 25. Therefore, as in the second embodiment, the incident angle fluctuates during ultrasonic flaw detection.

  With reference to FIG.8 and FIG.9, the outer diameter dimension and wall thickness dimension of the inspection target welded steel pipe 1 are input into the ultrasonic flaw detector 10 (S31). The input may be input by an operator from an input device (not shown), or may be automatically input from a computer or the like connected via a network.

The determining unit 166 calculates the refraction angle D1 based on the input outer diameter dimension and wall thickness dimension (S32). As shown in FIG. 9, it is assumed that the inspection target welded steel pipe 1 has an outer diameter dimension of D, a wall thickness dimension of t, and a cross-sectional shape of a perfect circle. Further, it is assumed that a surface defect exists in the thickness direction including the center point P ₀ of the thickness t. Note that the intersection of the thickness direction and an outer peripheral including the point P ₀ and the point N0. In this case, ultrasonic beams UW is incident on the point P _0, and, as the ultrasonic beam UW is incident perpendicular to the thickness direction including a point P _0, to calculate the refraction angle D1. In this case, the refraction angle D1 is calculated by the equation (2).

D1 = sin ⁻¹ (1- (t / D)) (2)

  Here, D is the outer diameter dimension input in step S31, and t is the wall thickness input in step S31.

  In addition, the intersection of the ultrasonic beam UW and the outer periphery of the inspection target welded steel pipe 1 in FIG. 9 is a point N1. Based on the point N1, the arrangement positions of the array probes 15A and 15B are calculated (S32).

  Subsequently, the determination unit 166 calculates an incident angle using the refraction angle calculated in step S332 (S33). Specifically, the determination unit 166 calculates the incident angle α from Expression (3) based on Snell's law.

α = sin ⁻¹ (sin (D1) × V ₀ / V ₁ ) (3)

Here, V ₀ is the longitudinal wave velocity of the ultrasonic beam UW in the wedge 151, and V ₁ is the transverse wave velocity of the ultrasonic beam UW in the inspection target welded steel pipe 1. Longitudinal sound readings V ₀ and shear wave sound speeds V ₁ use past experience values and the like. The determination unit 166 determines the arrangement position and incident angle calculated in steps S32 and 33 as the arrangement position and incident angle at the time of flaw detection.

  After calculating the arrangement position and the incident angle, the inspection target welded steel pipe 1 is installed on the roller 20 (S34). The ultrasonic flaw detector 10 arranges the array probes 15A and 15B at the arrangement position calculated in step S32 (S35). After the placement, the inspection target welded steel pipe 1 is flawed (S36). At this time, as in the second embodiment, ultrasonic flaw detection is performed while swinging the incident angle within a predetermined range centered on the determined incident angle. The swing instruction unit 169 instructs the swing of the incident angle.

  The difference in echo intensity of the defect 25 between the case where the incident angle of the array probes 15A and 15B is obtained using the sample welded steel pipe 200 and the case where the incident angle is obtained by the equations (2) and (3). investigated.

  The sample welded steel pipe 200 was manufactured as follows. The TMCP steel plate was bent by a C press, U press, and O press to form an open pipe, and then the joint was welded by a multi-electrode submerged arc welding method. The outer diameter of the sample welded steel pipe 200 was 660 mm, and the wall thickness was 18 mm. After the welding, as shown in FIG. 10, an artificial defect 25 was produced in the formed weld 2. The defect 25 was made into a cylindrical hollow having an outer diameter of 1.6 mm and a length of 5 mm, and was produced so that the axial direction of the defect was parallel to the thickness direction.

  Using the formulas (2) and (3), the arrangement positions and the incident angles of the array probes 15A and 15B were calculated. As a result, the incident angle α = 47.5 deg.

  Subsequently, the array probes 15A and 15B were arranged on the sample welded steel pipe 200, and the incident angle was swung while outputting the ultrasonic beam UW. At this time, the value determined based on Expression (2) was used as the arrangement position. Specifically, the point N1 in FIG. 9 is determined by Expression (2). The array probe 15A was installed on the determined point N1, and the array probe 15B was installed at a point symmetrical to the point N1 with the defect 25 as the symmetry axis. The distance S along the outer peripheral surface from the point N0 to the point N1 was about 98 mm.

  While oscillating the incident angle, the echo intensity of the defect 25 at each oscillated incident angle was investigated. Specifically, the incident angle was swung in the range of 43 deg to 49 deg. The frequency at the time of flaw detection was 5 MHz. FIG. 11 shows the survey results. While the calculated incident angle is 47.5 deg, the incident angle at which the echo intensity of the array probe 15A is maximized is 48.5 deg, and the echo intensity of the array probe 15B is maximized. The incident angle was 48.0 deg. In other words, the incident angle at which the echo intensity of the array probes 15A and 15B is maximized is different from the calculated incident angle. The cross-sectional shape of the sample welded steel pipe 200 is not a perfect circle, and there are local bending distortions and irregularities, and the acoustic intensity of the material, and the echo intensity at an incident angle deviated from the calculated incident angle. Is considered to be the largest.

  As a result of the above investigation, when the welded steel pipe 1 to be inspected is flawed, it is considered that the defect detection accuracy is improved by determining the incident angle and the arrangement position with the sample welded steel pipe 200 before flaw detection.

  The sample welded steel pipe 200 having the defect 25 shown in FIG. 10 was detected with the array probe 15A. At this time, the incident angle of the ultrasonic beam was swung in the range of 48.5 deg to ± 3.0 deg, the sample welded steel pipe 200 was repeatedly detected 10 times, and the echo intensity of the defect 25 was measured. Further, while the incident angle of the ultrasonic beam was fixed at 48.5 deg, the sample welded steel pipe 200 was repeatedly detected 10 times, and the echo intensity of the defect 25 was measured.

  The flaw detection results are shown in FIG. In the figure, ◯ indicates the result of flaw detection with the incident angle being swung, and X indicates the result of flaw detection with the incident angle fixed. The vertical axis shows the relative value of the echo intensity when the first echo intensity detected by fluctuating the incident angle is “1”.

  From FIG. 12, when flaw detection was performed with the incident angle being fluctuated, the echo intensity for each flaw detection frequency was almost the same. On the other hand, when the flaw detection was performed with the incident angle fixed, the echo intensity varied for each flaw detection. As a result, the echo intensity was more stable when flaw detection was performed with the incident angle varied than when flaw detection was performed with the incident angle fixed. Therefore, it is considered that the flaw detection accuracy can be improved by flaw detection by swinging the incident angle.

  In the above embodiment, the array probe is used as the variable incident angle probe capable of changing the incident angle, but another variable variable incident angle probe may be used. For example, instead of the array probe, a probe that can mechanically change the incident angle may be used.

  Further, the defect 25 of the sample welded steel pipe 200 may not be an artificial one. For example, a welded steel pipe having a defect 25 discovered by ultrasonic flaw detection in the past may be used as the sample welded steel pipe.

  While the embodiments of the present invention have been described above, the above-described embodiments are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately modifying the above-described embodiment without departing from the spirit thereof.

  The ultrasonic flaw detection method and the ultrasonic flaw detection apparatus according to the present invention can be widely used for nondestructive inspection of welded steel pipes, and in particular, can be used for nondestructive inspection of welded steel pipes used as oil well pipes or line pipes. .

1 is a schematic diagram showing the configuration of an ultrasonic flaw detector according to a first embodiment of the present invention. It is a functional block diagram which shows the detail of the control apparatus shown in FIG. It is the schematic for demonstrating the rocking | fluctuation operation | movement of the incident angle of the ultrasonic beam output from an array probe. It is another schematic diagram for explaining the swinging operation of the incident angle of the ultrasonic beam output from the array probe. It is another schematic diagram for explaining the swinging operation of the incident angle of the ultrasonic beam output from the array probe. It is a flowchart for demonstrating the ultrasonic flaw detection method by the 1st Embodiment of this invention. It is the schematic for demonstrating step S6 in FIG. It is the schematic for demonstrating the ultrasonic flaw detection method by the 2nd Embodiment of this invention. It is a flowchart for demonstrating the ultrasonic flaw detection method by the 3rd Embodiment of this invention. It is a flowchart for demonstrating the ultrasonic flaw detection method by the 4th Embodiment of this invention. It is a flowchart for demonstrating the ultrasonic flaw detection method by the 5th Embodiment of this invention. It is the schematic for demonstrating step S32 in FIG. It is the schematic which shows the defect dimension in the sample welded steel pipe used in the Example. It is a figure which shows the relationship between the incident angle of an ultrasonic beam, and the echo intensity of a defect. It is a figure which shows the result of having investigated the detection accuracy of the defect when flaw-detecting by swinging an incident angle and flaw-detecting with a fixed incident angle. It is the schematic which shows the defect inherent in the welding part of the conventional welded steel pipe. It is the schematic for demonstrating the conventional tandem flaw detection method. It is the schematic for demonstrating the ultrasonic flaw detection method which injects an ultrasonic beam perpendicularly into the defect in a welding part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inspection target welded steel pipe 2 Welding part 10 Ultrasonic flaw detector 11 Lifting frame 12 Rail 13 Arm 14 Probe holder 15A, 15B Array probe 16 Controller 17 Seam detector 20 Carrying roller 25 Defect 131 Vertical arm member 132 Horizontal Arm member 166 Determining unit 169 Oscillating instruction unit 170 Hard disks 180A, 180B Oscillating units 190A, 190B Echo receiving unit 200 Sample welded steel pipe 200 Welded steel pipe CH1 to CH32 to be inspected Vibrator

Claims (8)

An ultrasonic flaw detection method in which defects included in a weld formed in the axial direction of a welded steel pipe to be inspected are flaw-detected by an oblique flaw detection method,
Produced by the same molding step as said object welded steel pipe has the same outer diameter and wall thickness inspected welded steel pipe, inherent in the weld, providing a sample welded steel pipe comprising the defect parallel to the thickness direction And a process of
Arranging an incident angle variable probe capable of changing the incident angle on the outer peripheral surface of the sample welded steel pipe; and
An ultrasonic beam is output from the variable incident angle probe, and the ultrasonic beam is directly incident on the defect without being reflected by the outer peripheral surface and the inner peripheral surface of the sample welded steel pipe, and an echo reflected by the defect is detected. Receiving with the variable incident angle probe ;
The incident angle is changed by changing the incident angle while outputting the ultrasonic beam, and moving the variable incident angle probe on the outer circumferential surface of the sample welded steel pipe while outputting the ultrasonic beam. by changing the position of the variable probe, and determining the angle of incidence and position the echo is maximized in the defect from the incident angle and the arrangement position changed,
And flaw detection of the inspection target welded steel pipe at the determined incident angle and arrangement position. The ultrasonic flaw detection method according to claim 1,
The sample welded steel pipe is made of the same material as the inspection target welded steel pipe. The ultrasonic flaw detection method according to claim 1 or 2,
The flaw detection step includes
Selecting an oblique probe having the determined incident angle from a plurality of oblique probes having fixed incident angles;
An ultrasonic flaw detection method comprising: flaw detecting the welded steel pipe to be inspected using the selected oblique angle probe. The ultrasonic flaw detection method according to claim 1 or 2,
The ultrasonic flaw detection method characterized in that the flaw detection step involves flaw detection of the inspection target welded steel pipe using the variable incident angle probe. The ultrasonic flaw detection method according to claim 4,
In the flaw detection step, the inspection target welded steel pipe is flawed while the incident angle of the incident angle variable probe is swung within a predetermined range centered on the determined incident angle. Flaw detection method. The ultrasonic flaw detection method according to any one of claims 1 to 5,
The determining step determines an incident angle and an arrangement position for each of a plurality of sample welded steel pipes having different materials or sizes,
The ultrasonic flaw detection method further includes
Storing the plurality of determined incident angles and arrangement positions in a management device in association with the size and material of the plurality of sample welded steel pipes,
The flaw detection step includes
A step of retrieving from the management device an incident angle and an arrangement position corresponding to a sample welded steel pipe of the same size and material as the size and material of the welded steel pipe to be inspected;
And flaw detection of the inspection-target welded steel pipe at the searched incident angle and arrangement position. The ultrasonic flaw detection method according to any one of claims 1 to 6,
The step of determining the incident angle and the arrangement position includes:
Varying the incident angle of the ultrasonic beam output from the incident angle variable probe, and selecting a plurality of incident angles in descending order of the echo of the defect from the varied incident angles;
For each selected incident angle, the variable angle of incidence probe is moved circumferentially on the outer peripheral surface of the sample welded steel pipe while outputting the ultrasonic beam, and the defect echo is maximized. Selecting a placement position;
And a step of determining the incident angle and the arrangement position at which the echo of the defect is maximized based on the selected arrangement position for each incident angle. A process of bending a steel plate to form an open pipe;
Welding the open pipe seam to produce a welded steel pipe;
A method for manufacturing a welded steel pipe, comprising the step of flaw-detecting the welded steel pipe by the ultrasonic flaw detection method according to any one of claims 1 to 7.

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