JP5003275B2 - Ultrasonic flaw detection apparatus and ultrasonic flaw detection method for tubular body - Google Patents

Description

  The present invention relates to an ultrasonic flaw detection apparatus and an ultrasonic flaw detection method for a tubular body, and more particularly to an ultrasonic flaw detection apparatus for a tubular body for accurately detecting minute defects generated in a welded portion of a welded steel pipe by ultrasonic flaw detection. And an ultrasonic flaw detection method.

  In welded steel pipes, the quality of the welded part is very important, and in the manufacturing process, on-line flaw detection is generally performed by ultrasonic oblique flaw detection. In this method, ultrasonic waves are incident obliquely on the inspection surface of the test material, and internal and external surface defects and internal defects of the test material are detected from reflected waves reflected by the defects. In general, for example, in an ERW pipe, a reflection method using an ultrasonic beam having a refraction angle of 45 ° at 5 MHz is applied. Detected.

  On the other hand, recently, quality requirements for welded steel pipes have become stricter, and detection of defects smaller than conventional ones has been required. For example, cold-welded defects and minute penetrators are used for electric-welded pipes, and blow holes are used for laser-welded pipes. These defects have a very small size of several tens to several hundreds of micrometers. In addition, the generation position may occur anywhere along the weld line from the inner surface to the outer surface, and the incident point and return point of the ultrasonic beam differ depending on the position of the defect. Because of these influences, there are many cases where detection cannot be performed by a conventional ultrasonic flaw detection method, and a technique capable of detecting with higher accuracy is required.

  The following conventional techniques have been disclosed as methods for detecting minute defects in a welded steel pipe. In Patent Document 1, a point focus type probe having a frequency of 8 MHz or more is used for oblique flaw detection to improve the detection capability for the penetrator. In Patent Document 2, a focus beam is formed by an array probe to improve detection ability, and a blow hole can be detected by scanning from the inner surface side to the outer surface side of the welded portion by sector scanning. Yes.

  Moreover, in patent document 3, the frequency of an ultrasonic wave is 25 MHz or more and 500 MHz or less, and it makes it enter into a welding part from the pipe outer surface side with an incident angle of 0 degree or more and 20 degrees or less, and fine FeO below several micrometers forms a group. It makes it possible to detect a contaminated cold welding defect. Furthermore, in Patent Document 4, a plurality of point focus type probes having a frequency of 20 MHz to 80 MHz are used and arranged so that the focusing position is a pitch of 3 mm or less from directly above the seam, thereby detecting a blowhole of 0.1 mm or more. I can do it.

  In [Disclosure of the Invention], the following Patent Document 5 and Non-Patent Document 1 are cited, and are described together here.

JP 60-205356 A Japanese Patent Laid-Open No. 11-183446 Japanese Patent Laid-Open No. 61-111461 Japanese Patent Laid-Open No. 7-35729 JP-A-4-274756 Edited by Japan Iron and Steel Institute "Ultrasonic flaw detection series (II) Ultrasonic flaw detection of welded steel pipes" 1988, pp. 28-31

  However, the above-described disclosed technique still has the following problems. First, in the method of Patent Document 1, since the beam width of the focused ultrasonic wave is narrow, in order to perform flaw detection so as not to overlook the entire region in the depth direction of the welded portion (the thickness direction of the steel pipe), a large number of channels are required. There is a problem that the equipment cost is high because it is necessary and the position adjustment when the tube size is changed is very troublesome. Also, if the defect shape is not a blowhole shape but a planar shape such as a penetrator or cold weld and the position is inside the wall thickness, it is difficult to detect because the reflected wave goes in a direction different from the incident direction. is there.

  In the method of Patent Document 2, only one array probe is required, and the setting for changing the size can be performed electronically. Therefore, although the former problem shown in Patent Document 1 is not present, the latter problem still remains. It remains unresolved. Also, in the electronic scanning that solves the former problem, the geometric calculation of the propagation path of the ultrasonic transmission beam and reception beam is based on the assumption that the steel pipe is a perfect circle. In the lot in which the thickened portion 1a is generated on the inner surface of 1, the reflection path is changed and there is a problem that electronic scanning cannot be performed.

  Furthermore, when the defect shape is planar as described above, the width of the defect viewed from directly above the seam is very thin, for example, because the seam portion is upset in the ERW pipe. Even in the method 4, the reflected wave from the defect is actually very weak and difficult to detect in many cases. Further, since about 1 to 2 mm in the vicinity of the surface echo becomes a dead zone due to the reverberation of the surface echo, there is a problem that it cannot be detected when the position of the defect is in the vicinity of the outer surface.

  As described above, a technique for detecting a micro defect of about several hundred μm or less generated in a welded portion in the pipe axis direction of a welded steel pipe can be performed by a C-scan method in which a test sample obtained by cutting a welded portion is measured off-line. However, there has not yet been established a technique for detecting defects having a size of several hundreds of μm or less in a non-destructive manner and with high accuracy and stability online.

  The present invention has been made in view of the above circumstances, and is a case in which a minute defect having a thickness of about several hundreds μm or less located inside the thickness of a welded portion such as an electric resistance welded tube is generated on the inner surface. However, it is an object of the present invention to provide an ultrasonic flaw detection apparatus and an ultrasonic flaw detection method for a tubular body that enable detection from the inner surface to the outer surface without leakage.

The invention according to claim 1 of the present invention is configured to receive a part of or all of a reflected wave reflected by a welded part and a wave transmitting part that makes ultrasonic waves incident on a weld surface of a welded part of a pipe body in a tube axis direction. A transmitter / receiver unit, wherein the transmitter unit and the receiver unit are composed of different transducer groups on one or more array probes for flaws arranged in the circumferential direction of the tube, A wall thickness measurement probe for measuring the wall thickness distribution of the pipe body, and a tube array using the flaw detection array probe based on the wall thickness distribution measured by the wall thickness measurement probe. Propagation path calculation means for calculating a propagation path of ultrasonic waves for scanning in the body thickness direction, and based on the calculated propagation path, the transmitting section and the receiving section on the flaw detection array probe and by controlled so to change the corresponding transducer groups in, characterized by comprising a control unit for controlling the scanning in the thickness direction of the tubular body Body is an ultrasonic flaw detector.

In the invention according to claim 2 of the present invention, a part of or all of the reflected wave reflected by the welded part and the wave sending part that enters the ultrasonic wave with respect to the weld surface of the welded part in the tube axis direction of the pipe body. A transmission / reception unit comprising a group of different transducers on one or more array probes for flaw detection, wherein the transmission unit and the reception unit are arranged in the tube circumferential direction. When the tube body is flaw-detected with an ultrasonic flaw detector of the tube body equipped with, based on the measured wall thickness distribution, based on the measured wall thickness distribution, using the flaw detection array probe, An ultrasonic propagation path for scanning in the thickness direction of the tubular body is calculated, and vibrations corresponding to the transmitting section and the receiving section on the flaw detection array probe are calculated based on the calculated propagation path. and by controlled so to change the element group, an ultrasonic flaw detection method of the tubular body, characterized in that scanning in the thickness direction of the tube.

  According to the present invention, it becomes possible to detect a minute defect of about several hundreds μm or less located inside the thickness of a welded portion such as an electric resistance welded tube having an increased thickness on the inner surface from the inner surface to the outer surface without leakage. The quality of welded steel pipes will be dramatically improved by improving the welding process so that micro defects that affect the mechanical properties of the welded part of the welded steel pipe do not occur, and by making it possible to select in the manufacturing process so that defects do not flow out. And can be used under conditions that are severer than before.

  First, the inventor investigates the reflection characteristics of the defect to be detected, and detects the incident angle of the ultrasonic wave to the defect and the reflected ultrasonic wave reflected by the defect in order to detect the minute defect. The optimum range of reflection angle was obtained. Details are described below.

[Analysis of reflection characteristics of defects]
Microdefects such as penetrators and cold-welding defects existing in the welded parts of ERW welded steel pipes, which are the subject of the present invention, are crushed and thinned in the pipe circumferential direction because the welded pipes are manufactured by upsetting the welded parts On the other hand, the pipe thickness (tube diameter) direction and the pipe axis direction, that is, the pipe axis is assumed to be a flat shape extending in the weld surface and having an area.

  Therefore, the relationship between the defect size and the reflection directivity was theoretically examined, and the result shown in FIG. 10 was obtained. Here, the results shown in FIG. 10 correspond to the tube thickness direction at frequencies of 10 MHz, 15 MHz, and 20 MHz, respectively, as shown in FIG. It is obtained by theoretically calculating the signal intensity at each reflection angle under the conditions of a defect size of 0.1 mm, 0.2 mm, 0.4 mm, and 0.8 mm (corresponding to the direction). Note that the vertical axis of FIG. 10 indicates a normalized relative value with a signal intensity of 45 °, which is a regular reflection angle, as a reference value 1. In any case, the signal intensity of the reflected wave reflected in the −45 ° direction where the ultrasonic wave is incident is very low, which is about 0.2 or less in the regular reflection direction of 45 °. In any case, it can be seen that the 45 ° direction which is the regular reflection direction is the strongest.

  At 20 MHz with a defect size of 0.8 mm having the sharpest directivity under this calculation condition, the angle at which the signal intensity is half (value 0.5 in FIG. 10) is 40 ° to 50% with respect to the signal intensity at the regular reflection angle. It is the range of °. As described above, since the directivity differs depending on the defect size, the range of the incident angle of the received beam with respect to the welded portion may be determined according to the size of the defect to be detected. For example, in order to detect a larger defect without lowering the sensitivity, the incident angle of the received beam with respect to the welded portion is desirably an angle close to 45 °, for example, to reduce the signal strength decrease of a 0.8 mm defect by half at 15 MHz. Is preferably in the range of 39 ° to 52 °. On the other hand, for example, when a small defect of only 0.4 mm or less at 15 MHz is targeted, a range of 33 ° to 61 ° is also preferable.

  From the above analysis, it was found that the reflected signal of the ultrasonic wave at the defect has a high signal intensity with the regular reflection direction as a peak. It is most preferable to receive the ultrasonic waves in the regular reflection direction, but if the reflection intensity is 50% of the peak, it can be detected sufficiently, so if ultrasonic waves reflected in the angular range corresponding to that range are received. I found it good.

  According to the result of the reflection directivity having a defect size of 0.4 mm at a frequency of 15 MHz shown in FIG. 10, the reflection angle at which the reflection intensity is 50% or more of the peak is 33 to 61 °, and thus the regular reflection angle. A range of −12 ° to + 16 ° is a preferable range on the basis of 45 °. In addition, when a defect size of up to 0.8 mm is targeted at a frequency of 20 MHz, a range of −5 to + 5 ° with respect to the regular reflection angle is a preferable range. Moreover, although the above-mentioned example showed the reflection angle characteristic at an incident angle of 45 ° to the defect, the same result can be obtained for the incident angle characteristic when the opposite reflection angle is 45 °. Even if the incident angle is other than 45 °, substantially the same characteristics can be obtained as long as the incident angle range can satisfy the condition of mode conversion loss described later.

  And the content which examined the structure of the ultrasonic sensor based on the reflective characteristic of this defect is demonstrated below.

[Tandem configuration]
According to the knowledge of the defect reflection characteristics as described above, in order to receive an ultrasonic wave reflected within a predetermined angle range centering on the specular reflection direction at the defect, the receiving ultrasonic probe is transmitted. It is preferable to adopt a so-called tandem arrangement that is arranged at a position different from the wave ultrasonic probe. However, it is necessary to arrange a plurality of probes in order to inspect in the tube thickness thickness direction (tube diameter direction) of the welded portion using the point focus type probe as in Patent Document 1 without disconnection. There is. In addition, in order to detect a smaller defect, it is aimed to increase the aperture diameter for focusing the beam. It is very difficult in terms of engineering and cost to realize this as a device configuration.

  Therefore, in the present invention, an array probe is used, and the transmission unit and the reception unit are different in tandem configuration. By using the array probe, by sequentially changing the transducer group of the transmission unit and the transducer group of the reception unit, and / or the refraction angle at the time of transmission and the refraction angle at the time of reception, The focused position of the ultrasonic beam can be scanned from the inner surface side to the outer surface side (or from the outer surface side to the inner surface side in either direction) in the tube thickness direction of the welded portion, from the inner surface side to the outer surface side. Flaw detection is possible without dead zone. Further, since the array probe is used, the scanning range and the focusing position can be easily changed even if the size of the tube is changed, and the setting adjustment in advance becomes very simple. As described above, the transducers of the array probe are selected so as to be arranged in tandem, and inspection without missing in the thickness direction is realized.

  This tandem configuration has the advantage of improving sensitivity by receiving reflected waves in a predetermined angle range with respect to the regular reflection direction. In addition to this, there are other sensitivity improvement effects as described below. In order to detect defects reliably, the inventors have found that a tandem configuration is desirable.

  FIG. 12 is a diagram schematically illustrating a comparison between a non-tandem configuration and a tandem configuration. FIG. 12A shows a case where a welded portion is flawed by a general reflection method using an array probe and having the same transmitting portion and receiving portion. Ultrasound is emitted from the transducer group of the array probe, refracts on the outer surface of the tube, enters the inside of the tube, and reaches the weld. If there is a defect, it will be reflected and incident on the transducer group that has been transmitted along the same path as during transmission and received. Here, when receiving a wave, in addition to the reflected wave from the defect, reverberation inside the array probe, irregular reflection due to the surface roughness of the outer surface of the tube, reflected by the outer surface of the tube, and the array probe and its holding The reflected wave at the section, the surface roughness of the inner surface of the tube, and the reflected wave at the bead cutting residue are directed to the array probe. As described above, in the case of a general reflection method, these unnecessary reflected waves, that is, noises are superimposed on the defect signal and received, so that detection of a state in which the signal sensitivity and the S / N ratio are poor is detected. Is going. Moreover, the noise removal is very difficult.

  On the other hand, FIG. 12B shows a case of a tandem configuration using different transducer groups for transmission and reception. Ultrasound is emitted from a group of transducers for transmitting the array probe, refracts on the outer surface of the tube, enters the tube, and reaches the weld. If there is a defect, it is reflected there, and at this time, it travels most strongly in the regular reflection direction, then reflects on the inner surface of the tube, reaches the outer surface of the tube, refracts, enters the receiving transducer group, and is received . In order to follow such a path, reverberation inside the array probe, irregular reflection due to the surface roughness of the outer surface of the tube, reflection at the outer surface of the tube, reflection at the array probe and its holding part, etc., surface roughness of the inner surface of the tube All reflections from the sheath cutting residue are directed to the transmitting transducer group, but do not reach the receiving transducer group. That is, the signal received by the receiving transducer group in the tandem configuration is not superposed with noise echoes caused by the irregular reflection of ultrasonic waves and is hardly affected by noise, and is generally shown in FIG. Compared with a simple reflection method, an extremely high S / N can be obtained, and the effect of taking a reflected wave in the regular reflection direction and the effect of noise reduction can be obtained, thereby facilitating detection of a micro defect. .

  FIG. 13 is an example of a flaw detection result comparing the one tandem method and the tandem method in which transmission / reception waves that do not have a tandem configuration are performed by the same probe.

  The tube to be inspected used for comparison is provided with three types of drill holes DH as shown in FIG. That is, φ1mm drill holes (Fig. 14 (a)) drilled in the orthogonal direction with respect to the surface consisting of the thickness direction and the pipe axis direction at three locations in different thickness directions, and penetrated with φ1.6mm in the thickness direction Drill hole (FIG. 14 (b)) to be drilled, and drill hole (FIG. 14 (c)) penetrating through the tube axis direction at φ1.6 mm.

  FIG. 13A shows flaw detection image data according to the conventional method, and FIG. 13C shows flaw detection image data according to the present invention. In order to explain the detection status of flaw detection images (a) and (c), FIG. (A) is a diagram schematically showing, (d) is a diagram schematically showing (c) which is a flaw detection image in the present invention. In the image data (a) and (c), the higher the signal intensity, the whiter the data is displayed.

  As described above, it has been found that the tandem configuration improves the detection performance over the conventional method. However, it has been found that there are some difficulties in applying to a tube with curvature. The solution will be described below.

  As can be seen from this result, noise due to the surface roughness of the inner surface is strongly generated in one search method, and the echo from the tip of the φ1 mm drill hole (see FIG. 14A) simulating a minute defect is buried in the noise. The detection is difficult. In particular, the reflection from the inside of the wall is very weak and is hardly detected. On the other hand, in the tandem method, the noise due to the surface roughness on the inner surface side is weakened, and it can be clearly detected including the inside of the wall thickness without affecting the echo from the tip of the φ1 mm drill hole.

  As described above, it has been found that the tandem method improves the detection performance as compared with the one-search method. However, it has been found that there are some difficulties in applying to a tubular body having a curvature and sometimes having a thickened portion on the inner surface. The solution will be described below.

[Examination of mode conversion loss]
As described above, it has been found that high sensitivity can be sufficiently achieved by the tandem configuration. However, in order to maintain the high sensitivity of the tandem configuration, the signal intensity is attenuated due to the "mode conversion loss" when the ultrasonic wave propagates inside the steel pipe and is reflected by the inner and outer surfaces of the pipe and defects. You must not do it. The mode conversion loss is a phenomenon in which the ultrasonic wave incident on the steel pipe is a transverse wave ultrasonic wave, but is converted into a longitudinal wave ultrasonic wave depending on reflection conditions, and as a result, the signal intensity is attenuated and the detection sensitivity is lowered. This phenomenon will be described with reference to the drawings.

  FIG. 15 is a diagram for explaining mode conversion loss in a flat steel plate. FIG. 15A shows flaw detection (hereinafter also referred to as tandem flaw detection) in a tandem configuration of a flat steel plate. When a transverse wave ultrasonic wave is incident on a flat steel plate and its refraction angle is θ, the incident angle θa on the welding surface is (90 ° −θ) in the flat steel plate. Further, the incident angle θb to the bottom surface is θ. Here, in steel, when a transverse wave ultrasonic wave is reflected at a welded portion, a steel plate bottom surface, or the like, and incident at an incident angle of about 33 ° or less, the longitudinal wave ultrasonic wave is converted into a dotted line direction by mode conversion in reflection. It is known that it will occur.

  For example, as shown in FIG. 15A, when θ is large (about 57 ° or more), θa becomes small (about 33 ° or less), and mode conversion occurs due to reflection of the welded portion. As described above, when θ is small (about 33 ° or less), mode conversion does not occur due to reflection of the weld, but θb is about 33 ° or less, and mode conversion occurs. When such a mode conversion from a transverse wave to a longitudinal wave occurs, the ultrasonic intensity in the tandem flaw detection direction becomes weak, and as a result, the detection sensitivity decreases. A phenomenon in which the ultrasonic wave undergoes mode conversion from a transverse wave to a longitudinal wave during reflection and the intensity of the transverse wave ultrasonic wave is attenuated is referred to as mode conversion loss. Here, FIG. 15C shows the change in the reflection intensity when the ultrasonic wave corresponding to the incident angle is reflected twice by the welding surface and the inner surface when reflecting, as shown in FIG. If the incident angle is in the range of 33.2 ° to 56.8 ° as a theoretical value, no mode conversion loss occurs.

  In the case of a flat steel plate, the relative angle between the array probe surface and the flat steel plate upper surface is constant regardless of the location. Therefore, in order to scan the welding surface with an ultrasonic beam, a transmitting portion and a receiving portion are used. Even if the transducers that make up the sensor are moved, mode conversion is possible if the relative angle of the array probe surface to the flat steel plate upper surface and the angle of the transmitted beam with respect to the probe surface are studied at an arbitrary position. The refraction angle condition for determining whether or not loss occurs can be easily determined.

  However, it will be described with reference to FIG. 16 that tandem flaw detection of a steel pipe is not as simple as a flat steel plate due to the influence of curvature. As in the case of the flat steel plate described above, as shown in FIG. 16A, when the angle of the weld surface is set to a reference angle of 0 °, ultrasonic waves are incident on the steel pipe so as to have a refraction angle θ. think of. The incident point (incident position) on the outer surface of the steel pipe is a position where the angle formed by the normal direction of the outer surface at the incident point and the weld surface is θ1. The incident angle θa to the welding surface at this time is not (90 ° −θ) but (90 ° −θ−θ1). Similarly, the incident angle θb to the bottom surface is not θ, but is (θ + θ2).

  In this example, since θ1 <θ2, the range of the refraction angle at which no mode conversion loss occurs is narrowed by θ2 at the maximum compared to flat steel plates. As an example, in a steel pipe having a wall thickness t / outer diameter D = 3.4%, for example, if the refraction angle is about 45 °, θ2 is about 4 °. The range of refraction angles at which no loss occurs is narrowed to 37 ° to 53 °. Note that θ2 is in the range of about 1.7 ° to 11.25 °, considering the size of a steel pipe that can be realistically considered.

  In addition, when t / D is from the smallest value to about t / D = 5%, a considerable amount of main steel pipe size can be covered, and when t / D = 5%, θ2 is 6.8 °. In this case, the range of the refraction angle is 40 ° to 50 °.

  Furthermore, considering that the array transducer is generally linear and the steel pipe has a curvature, as shown in FIG. 16B, an ultrasonic beam is emitted from the array transducer as in the case of a flat steel plate. When the wave is transmitted at a constant angle (90 ° with respect to the probe surface in the figure), the incident angle to the steel pipe does not become a constant angle, and therefore the refraction angle does not become constant. In order to perform tandem flaw detection, the beam scan width from the array transducer is double the wall thickness, and the above steel tube with t / D = 3.4% is taken as an example so that the refraction angle is 45 ° at the center. Even if the probe is arranged on the surface, the refraction angle changes from 31 ° to 62 ° within the scan width, exceeding the range where no mode conversion loss occurs.

  Therefore, considering the curvature of the steel pipe due to the above problem, the steel pipe is tandemly detected with high sensitivity unless the beam is controlled so that the refraction angle is within a certain range so that mode conversion loss does not occur on the weld surface and bottom surface. It is not possible. When the incident angle to the welded surface of the tube and the inner surface of the tube is converted into a refraction angle in consideration of the above θ2, the refraction angle is 35 with respect to the theoretical value of the incident angle when t / D is the smallest value. The angle is between ゜ and 55 degrees.

  In other words, if the measurement position is moved by scanning the ultrasonic beam, the ultrasonic incident angle (refractive angle) to the steel pipe will be changed, so whether or not the angle at which mode conversion loss occurs will occur. However, the method was not established.

  The inventor has realized that the incident angle is set by the scanning line determination method described below as an example so that no mode conversion loss occurs.

  Hereinafter, a procedure for setting the refraction angle to a refraction angle range in which mode conversion loss does not occur will be described.

1) Determine the refraction angle and determine the position and angle of the array probe.
1) -1: The refraction angle θ is determined in consideration of the incident angle θa to the weld surface. The incident angle on the theoretical weld surface where no mode conversion loss occurs is 33.2 ° ≦ θa ≦ 56.8 °, and within this range, the weld surface is scanned over the inner surface of the pipe in the thickness direction. At this time, the incident angle on the welding surface is not constant and may change. Therefore, here, in order to facilitate the calculation, an example in which the refraction angle θ is made constant is shown. Here, the incident angle θa to the weld surface is θa = 90 ° −θ−θ1, and θ1 varies depending on the position in the thickness direction of the weld in the range of 0 to θ2 (for example, θ1 on the inner surface side). = Θ2 and θ1 = 0 on the outer surface side). For example, when θ2 = 4 ° and a refraction angle of 45 °, θa = 41 ° to 45 °. Further, if the refraction angle is 47 ° when entering the vicinity of the tube thickness center of the welded portion, θa = about 45 ° at the center portion in the thickness direction of the welded portion, and θa = 43 in scanning on the inner and outer surfaces. It is in the range of ° to 47 °.
1) -2: A beam transmitted from a transducer located at the center of the array probe in a direction perpendicular to the probe surface is super transverse wave at a predetermined refraction angle (for example, 45 °). The position of the array probe so that the sound wave enters from the outer surface side of the steel pipe and enters the inner surface side end (or outer surface side end) of the welding surface at a predetermined incident angle (for example, 41 ° in the above example). And determine the angle.

2) The position where the scanning line transmitted / received from each transducer of the array probe enters the outer surface of the tube is determined.
2) -1: There are various methods of determination. For example, the target transducer (or a position between the transducers) is scanned on the outer surface of the tube, and is determined by the transducer position, the outer surface scanning position, and the outer surface tangent. The refraction angle θ is calculated, and the incident position on the outer surface where θ becomes the value determined in 1) −1 is determined. Specifically, a scanning line is defined by connecting each point on the outer surface from each transducer (for example, each point is arranged at equal intervals or arbitrary intervals on the outer circumference) with a straight line, and the refraction angle θ for each of these scanning lines. Is calculated, and a scanning line having the same or the closest value of θ as the predetermined refraction angle is selected and set as the incident position of the scanning line.
2) -2: Geometrically determine the propagation path after pipe incidence from the transducer position, the incident position on the outer surface determined in 2) -1, and the pipe shape (diameter and thickness), and enter the weld surface. Determine the position.

  3) Positioning is performed at the center of the array probe in the above 1), and the above processing is performed with a constant refraction angle. Therefore, 2) on the welding surface symmetrically with respect to the scanning line at the center of the array probe. The combination (pair) of routes of the propagation path (scan line) obtained in -2. This pair is used as a transmission / reception scanning line, and is used as the central transducer for each of the transmission / reception units (the transducer group of the transmission / reception units is formed around this transducer) . If the number of transducer groups is an even number, the center position is corrected to the boundary of the transducers and the above processing is performed. Further, although the calculation is made here with the refraction angle θ constant, it may be calculated with the incident angle θa to the weld surface constant, or both θ and θa can be changed.

  Although details will be described later, if the transducer group is appropriately controlled or an array probe having a curvature is used, the incident angle and the refraction angle can be within a theoretical range in which no mode conversion loss occurs. The refraction angle suitable for flaw detection with a transverse wave can be applied in the range of approximately 30 ° to 70 °. However, considering the angular dependence of the sound pressure reflectivity when the transverse wave is reflected on the defect and the inner surface, total reflection is considered. A range of approximately 35 ° to 55 ° is more desirable. Furthermore, it may be in the range of 40 ° to 50 ° in consideration of stability. In addition, it is most desirable that the refraction angles of the transmitted wave and the received wave are the same, but since the reflection directivity of the defect is broad, the present invention can be applied even if they are different within the range of the reflection directivity.

  In the above description, the case where the thickened portion does not occur on the inner surface, that is, the case where the pipe body is a perfect circle has been described, but in an actual tubular body, the thickened portion may occur on the inner surface depending on the lot. , It may not be a perfect circle. In such a case, in addition to the above-described procedure for calculating the path with a perfect circle, the flaw detection array probe 5 and the wall thickness measurement array probe 50 as illustrated in FIG. With the device configuration provided, the inner surface shape is obtained, and the route is determined based on the result. That is, as shown in FIG. 1B, the thickness distribution is measured by the thickness measuring array probe 50 provided immediately above the welded portion (seam) 2, and the inner surface shape is determined from the result. And based on this result, as shown in FIG.1 (c), the reflection path | route in an inner surface is calculated | required and a tandem flaw detection is implement | achieved.

  Specifically, the wall thickness is measured, and the inner surface shape is calculated by, for example, a polynomial approximation. Then, the propagation path after the wave transmission is calculated as being a perfect circle, and the intersection point with the previously determined inner surface (shape approximate expression) is obtained. Further, the reflection path is obtained based on the inner surface angle (differentiation of the shape approximation formula), and the refraction path is obtained as a perfect circle.

[Control of constant incident angle]
When applying a tandem array probe to a tube having a curvature, a general array probe is linear and is arranged with respect to the circumferential surface. When the position on the array of the transducer group constituting the wave portion changes, the incident angle to the tube body changes in certain transmission / reception and other transmission / reception. This phenomenon is shown in FIG. 17 showing an example of a propagation path in the tubular body. It can be seen that transmission and reception are established in the solid beam, but the relationship between transmission and reception is not established in the other broken beams because the refraction angles are different.

  In other words, even if the transmitting section is housed in the array probe, the receiving section is located outside the array probe (shown by the broken line in the figure), and within the range of the array probe. Therefore, it becomes impossible to arrange the transducer group of the transmission unit and the reception unit so as to have a tandem configuration. The inventor kept the incident angle of at least one of the transmission side and the reception side, preferably both, at a constant angle through scanning. If it does so, since the refraction angle inside pipes, such as a steel pipe, will become constant, the above problems will hardly arise.

  For example, even in the case of FIG. 2 using an array probe similar to that in FIG. 17, by making the refraction angle constant, all combinations of transmission parts and reception parts can be accommodated in the array probe. Further, if the refraction angle is made constant, for example, if the outer surface side inner surface side of the steel pipe is a perfect circle, there is an advantage that the positional relationship between the transmitted wave and the received wave can be easily obtained geometrically. Furthermore, even if there is a change in the thickness of the steel pipe and the inner surface side is not a perfect circle, if either the transmitting side or the receiving side has a constant refraction angle, the path that is incident on the welding surface and reflected is reflected. Since the outer surface side of the steel pipe is a perfect circle, it can be easily obtained, and the path ahead can be determined theoretically or experimentally in consideration of the shape of the inner surface side.

  The means for making the incident angle constant can be realized by controlling each transducer of the transducer group used for the transmission unit and the reception unit from the array probe. The selection of the transducer group may be performed by the above-described method, but details regarding other controls will be described later.

  As another means, the array probe itself may be formed in a shape having substantially the same curvature as that of the tube, and the vibrator may be controlled.

[Ultrasonic beam focusing conditions]
Although the height of a minute defect such as a penetrator is as small as several hundred μm or less, the reflection intensity can be increased by concentrating the transmitted beam and the received sensitivity on the defect by focusing. The inventor has derived a condition for detecting a minute defect by using a focusing coefficient J represented by the following equation. The focusing coefficient J is a value indicating an increase in sound pressure at the focusing position.

  Here, D is the aperture width of the vibrator, F is the focal length, and λ is the wavelength. In Expression (1), the focal length F and the wavelength λ are values converted into water.

  FIG. 18 is a diagram showing an experimental example in which the focusing ability required in the present invention is investigated. In this experiment, we used a sample obtained by slicing an ERW welded part including a micro penetrator every 2 mm across the seam, and focused on the seam using a point focus probe with various focusing coefficients. In addition, C-scan flaw detection was performed on the weld. Here, the range of the focusing coefficient is determined by the measurement result of the C scan, but the focusing coefficient has an advantage that it can be treated as an index value that can be evaluated equivalently even if the ultrasonic flaw detection method is different. The result of the scan can be applied as it is.

  FIG. 18A shows the result of obtaining the relationship between the focusing coefficient and S / N from the C-scan result, and shows that the higher the focusing coefficient J, the better the S / N of the defect echo. As a result of cross-sectional observation of the defect, the height of the defect F (size in the radial direction of the steel pipe) was about 100 μm.

  In general, at least S / N = 6 dB is required for online flaw detection, and preferably 10 dB or more is required. Therefore, from the figure, it was found that if a defect similar to the defect F or a small defect is to be detected, the necessary focusing coefficient is 5 dB or more, preferably 10 dB or more.

  According to the reflection characteristics shown in FIG. 10 described above, since the reflection angle is equivalent to −45 ° in the conventional technology that does not have a tandem configuration, the reflection intensity can be obtained only about 20% of the tandem configuration. That is, in the conventional technique, the sensitivity is inferior to about 14 dB with respect to the tandem configuration. Therefore, in order to obtain an equivalent S / N, a focusing coefficient of about 20 dB is required. Further, considering that the influence of disturbance noise is inevitable in the prior art, it is necessary to further improve the focusing coefficient. Thus, it has been found that it is more effective to combine the tandem configuration of the present invention and beam focusing.

  Similarly, the result of obtaining the relationship between the beam diameter and S / N is FIG. 18B. From the figure, it was found that the required beam diameter is 0.7 mm or less, preferably 0.5 mm or less.

  As for the upper limit of each focusing coefficient and the lower limit of the beam diameter, the range of the upper limit of the frequency is about 20 MHz to 50 MHz and the upper limit of the opening width is 20 mm as an actually feasible range in oblique flaw detection of a steel pipe. Since the lower limit range of the focal length is about 20 mm to 40 mm, the focusing coefficient is 24 dB to 50 dB, and the beam diameter is 30 μm to 0.32 mm. When the frequency exceeds 20 MHz, the attenuation of the ultrasonic signal intensity increases in propagation in steel. Therefore, if the upper limit of the frequency is 20 MHz, the upper limit of the focusing coefficient is 40 dB, and the lower limit of the beam diameter is 74 μm. This is a preferred range.

  For example, if the water distance is 20 mm and the path length in the steel is 38 mm, the focal length F is 20 mm + (38 mm / underwater sound speed 1480 m / S × steel wave transverse sound speed 3230 m / S) = 103 mm, and the frequency is 15 MHz, the wavelength λ is 1480 m. / S / 15 MHz = 0.1 mm, and the aperture width D for obtaining a focusing coefficient of 10 dB is obtained from the following equation (2).

  From Expression (2), the opening width D is determined as D = 11.3 mm. Therefore, if the transducer pitch of the linear array probe is 0.5 mm, for example, the number of transducers in the transducer group is calculated as 11.3 / 0.5 = about 22.

  The number of transducers in the transducer group can be obtained from the beam size obtained as described above, but if this is a constant value, the closer to the weld, the shorter the focal length, so the beam width becomes narrower and fine scanning is performed. The pitch becomes necessary, and the focal length becomes longer toward the side farther from the welded portion, resulting in a problem that the focusing ability is deteriorated.

  Therefore, it is preferable to set the number of transducers of the transmitting transducer group and the receiving transducer group to be smaller as it is closer to the welded portion and larger as it is farther from the welded portion. In this way, the closer to the welded portion, the narrower the opening width at the time of simultaneous excitation, so the beam width does not become too narrow even if the focal length is short. Since the aperture width is wide, the focusing coefficient can be increased even when the focal length is long, and the detection ability does not deteriorate. Accordingly, since the focusing characteristics from each transducer group can be made uniform, flaw detection can be performed with uniform detection sensitivity from the inner surface side to the outer surface side.

  However, since the focusing coefficient J includes the focal length F and the aperture width D as parameters, if the focusing coefficient is set to be constant or within a predetermined range, the focus does not change due to the measurement position due to scanning. The opening width can be set according to the distance. Thus, by using the focusing coefficient, there is an effect that the calculation according to the movement of the scanning position becomes very easy.

  Furthermore, if the linear array probe is provided with an acoustic lens, and the focal length of the acoustic lens is set shorter as it is closer to the welded portion and longer as it is farther from the welded portion, the transmission beam focused in the tube axis direction and Received sensitivity is obtained, and high detectability can be obtained. Since an acoustic lens is used, the focal length can be easily changed by simply exchanging the lens, and setting adjustment when the tube size is changed is also easy.

Embodiments according to the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram for explaining the principle of the present invention. The configuration of the present invention is a configuration including an array probe 50 for thickness measurement in addition to the array probe 5 for tandem flaw detection as shown in FIG.
As shown in FIG. 2, the array probe 5 for tandem flaw detection performs flaw detection by propagating ultrasonic waves inside the steel pipe. An ultrasonic wave is transmitted from the wave transmission unit 6 so that the diameter of the transmission beam 8 is set in accordance with the detection target with respect to the welding surface of the tube axis direction welded part 2 of the tube body 1, Reflected by the minute defect 3 on the welding surface, a part or all of the reflected wave (received beam 9) is received by the receiving unit 7. The transmitting unit 6 and the receiving unit 7 are composed of different transducer groups on one or more array probes 5 arranged in the circumferential direction of the tube. Then, as shown in FIG. 3, control is performed so as to change the transducer group corresponding to the transmitting unit and the receiving unit on the array probe, or to change the angle of the array probe. The tube is scanned in the thickness direction, and the diameter of the ultrasonic beam with respect to the weld surface is maintained in the above range.

  In FIG. 3, in step 1 indicating the start of scanning, the transducer group in the vicinity of the center of the linear array probe is used to align the focusing position (focal position) on the inner surface of the steel pipe of the welded portion, and 0.5 skip is performed. The flaw detection method is used. At this time, transmission and reception are performed by the same transducer group. Next, in step 2, the transmitting transducer group is shifted to the welded portion side, the received transducer group is shifted to the far side from the welded portion, and the focal position is slightly above the steel pipe inner surface side of the welded portion (steel pipe By setting to the outer surface side, flaw detection is performed inside the wall a little above (outer surface side of the steel pipe) from the inner surface of the steel pipe of the weld by tandem flaw detection.

  Subsequently, in Step 3, the transmitting transducer group is shifted to the welded portion side and the received transducer group is shifted to the opposite side of the welded portion, and the flaw detection position in the welded portion is moved to the outer surface side of the steel pipe. I do. In the figure, only steps 2 and 3 are shown. However, in consideration of the focal point size of the ultrasonic wave (the beam size at the focal position), the flaw detection defect (leakage) and the effective flaw detection without overlapping are actually performed. In addition, the number of transducer groups to be shifted is determined so that a part of the ultrasonic beam overlaps. Finally, step 4 indicates the end of scanning, and flaw detection is performed on the outer surface side of the welded portion by a 1.0-skip reflection method using a group of transducers far from the welded portion. While repeating Steps 1 to 4, the relative position between the steel pipe and the linear array probe is mechanically scanned in the pipe axis direction, so that the entire length of the welded portion (from the outer surface side to the inner surface side) can be detected. It can be carried out.

  As shown in FIG. 1B, the array probe 50 for measuring the thickness is arranged in a direction substantially orthogonal to the welding surface immediately above the welded portion (seam) 2. Moreover, the array probe 50 for thickness measurement should just be the magnitude | size which can measure the thickness of the area | region (area | region where a thickened part generate | occur | produces) where the thickness changes in the inner surface of a steel pipe, and thickness change What is necessary is just to make it the same magnitude | size as the area | region which generate | occur | produces.

  Then, several consecutive transducers among the transducers of the wall thickness measurement array probe 50 are simultaneously excited, and ultrasonic waves are transmitted in a direction substantially directly below the transducers. In this way, the transmitted ultrasonic wave is partially reflected on the outer surface of the tube and received on the side of the array probe 50 for thickness measurement, but the rest is incident on the inside of the tube, and the inner surface of the tube. And is received by the wall thickness measurement array probe 50. By measuring the difference in propagation time of the reflected wave between the outer surface and the inner surface at this time, it is possible to measure the thickness of the portion where the ultrasonic wave is incident. The thickness distribution of the tube is measured by changing the position of the transducer for transmitting and receiving the wave in the wall thickness measuring array probe 50 and scanning the incident position of the ultrasonic wave in the tube circumferential direction. From this result, the inner surface shape can be calculated.

  Based on the inner surface result thus obtained, the tandem flaw detection probe 5 can perform uniform scanning in the thickness direction of the welded portion by tandem flaw detection. Is calculated geometrically. In accordance with the incident position, the incident angle, the refraction angle, etc. calculated in the propagation path thus obtained, the tandem flaw detection probe 5 as shown in FIG.

  FIG. 4 is a diagram showing a functional configuration example of the ultrasonic flaw detector according to the present invention. As a configuration, a functional unit for calculating the inner surface shape is added to a functional unit for performing tandem flaw detection.

  The functional units for performing tandem flaw detection include a flaw detection linear array probe 5, a subject size input unit 30, an array probe storage unit 31, a transmission / reception control unit 32, a gate position storage unit 33, and an array transmission rule storage unit. 34, an array reception rule storage unit 35, an array transmission unit 36, an array reception unit 37, a gate unit 38, a determination threshold value input unit 39, and a defect determination unit 40.

  The functional units for calculating the inner surface shape are a linear array probe 50 for thickness measurement, a transmission / reception control unit 51 for thickness measurement, a gate position storage unit 52 for thickness measurement, and an array transmission rule storage unit for thickness measurement. 53, a wall thickness measurement array reception rule storage unit 54, a wall thickness measurement array transmission unit 55, a wall thickness measurement array reception unit 56, a wall thickness measurement gate unit 57, and an inner surface shape calculation unit 58.

  First, the function part of tandem flaw detection will be described. In the object size input unit 30, values of the outer diameter and thickness of the steel pipe that performs tandem flaw detection are input from an operator or a process computer. Further, data of the inner surface shape calculated before performing the tandem flaw detection is input from the inner surface shape calculating unit 58. The array probe storage unit 31 stores the frequency, transducer pitch, and number of transducers of the array probe 5.

  In the transmission / reception control unit 32, the position of the transmission array probe, the number of transmission scanning lines, the number of transmission beams of each scanning line, according to the size of the steel pipe, the specifications of the array probe, and the inner surface shape. The path, the number of transducers of the transmission transducer group for each scanning line, the position of the transducer group for transmission, the focal length, and the deflection angle are calculated, and the delay time of each transducer is calculated for each scanning line. Each value determined in this way is referred to herein as an array transmission rule.

  In the transmission / reception control unit 32, the position of the array probe, the number of reception scanning lines, and the path of the reception beam of each scanning line according to the size of the steel pipe, the specification of the array probe, and the inner surface shape. The number of transducers of the receiving transducer group for each scanning line, the position of the receiving transducer group, the focal length, and the deflection angle are calculated, and the delay time of each transducer is calculated for each scanning line. Each of the above values determined in this way is referred to herein as an array reception rule. Furthermore, a defect detection gate position is determined based on the beam path calculated by the transmission / reception control unit 32 and stored in the gate position storage unit 33.

  Here, the array reception rule may be determined based on the previously obtained array transmission rule, or conversely, the array reception rule may be determined first and the array transmission rule may be determined based thereon. The array transmission rule and the array reception rule determined in this way are stored in the array transmission rule storage unit 34 and the array reception rule storage unit 35, respectively, and used for the following transmission / reception control.

  The array transmission unit 36 selects a transmission transducer group based on the array transmission rule stored in the array transmission rule storage unit 34, and generates a transmission pulse with a delay time added to each element. The array receiving unit 37 selects a transducer group for receiving waves based on the array receiving rule stored in the array receiving rule storage unit 35, adds a signal with a delay time to each element, and generates a flaw detection waveform. obtain. The gate unit 38 extracts a gate position signal stored in the gate storage unit 33.

  The defect determination unit 40 compares the defect determination threshold value input to the determination threshold value input unit 39 with the signal intensity in the gate, and determines that the defect is a defect if the signal intensity is equal to or greater than the threshold value. When the flaw detection for one scanning line is completed in this way, the next transducer group for transmission is selected based on the array transmission rule stored in the array transmission rule storage unit 34, and the flaw detection is performed in the same manner as described above. Repeat. In addition, regarding the determination of the defect, the defect may be determined when the signal intensity is equal to or more than a threshold value a plurality of times.

  Next, a functional unit for calculating the inner surface shape will be described. In the thickness measurement transmission / reception control unit 51, the size data input by the subject size input unit 30 is input via the transmission / reception control unit 32, and according to the data, the position of the thickness measurement linear array probe, Calculate the array transmission rule for wall thickness measurement and the array reception rule for wall thickness measurement, such as the path of the transmission / reception beam, the number of transducers of the transducer group of each scanning line, the position of the transducer group, the focal length, and the deflection angle. .

  Further, the thickness measurement gate position is determined by determining the gate position for detecting the outer surface reflection wave and the inner surface reflection wave for the wall thickness measurement based on the beam path calculated by the wall thickness measurement transmission / reception control unit 51. Store in the storage unit 52.

  The wall thickness measurement array transmission rule and the wall thickness measurement array reception rule thus determined are stored in the wall thickness measurement array transmission rule storage unit 53 and the wall thickness measurement array reception rule storage unit 54, respectively. It is used for transmission / reception control for the following wall thickness measurement.

  The wall thickness measurement array transmission unit 55 selects a transducer group for transmission based on the wall thickness measurement array transmission rule stored in the wall thickness measurement array transmission rule storage unit 53 and transmits it from each element. A pulse is generated and scanned in the tube circumferential direction. The wall thickness measurement array receiver 56 selects a receiving transducer group based on the wall thickness measurement array reception rule stored in the wall thickness measurement array reception rule storage unit 54 and receives each element. Wave signals are added, and a signal waveform for thickness measurement is obtained at each scanning position. The thickness measurement gate unit 57 extracts the signal of the gate position stored in the thickness measurement gate position storage unit 52, and obtains a signal including an external reflection wave and an internal reflection wave.

The inner surface shape calculation unit 58 obtains the thickness at each scanning position from the difference in propagation time between the outer surface reflected wave and the inner surface reflected wave, and calculates the thickness distribution. Further, the inner surface shape is derived from the result.
The inner surface shape derived in this way is output from the inner surface shape calculation unit 58 to the transmission / reception control unit 32.

  Here, the processing corresponding to the inner surface thickening is performed in the procedure as shown in FIG.

  That is, first, in step S1, the wall thickness distribution in the tube circumferential direction is measured using the wall thickness measuring array probe 50 arranged at an incident angle of 0 ° directly above the seam 2. The array probe for wall thickness measurement is arranged almost directly above the welded part, and a tube group consisting of several to several tens of transducers in the array probe for wall thickness measurement is used. Ultrasonic waves are transmitted so that the incident angle on the outer surface is 0 °. The transmitted ultrasonic wave is reflected on the outer surface of the tube, propagates inside the tube, and is reflected on the inner surface. The reflected wave on the outer surface and the inner surface is received by the array probe for thickness measurement, and from the waveform, the inner surface shape calculation unit finds the thickness at the incident position from the difference in propagation time. Further, since the ultrasonic wave is scanned in the tube circumferential direction, the thickness distribution in the tube circumferential direction can be calculated by obtaining the wall thickness at each scanning position. At that time, the beam is set in a direction toward the center of the tube. Note that a deflection angle may be set, or the opening angle may be narrowed to widen the directivity angle. An example of the measurement result is shown in FIG. The X coordinate on the horizontal axis is the horizontal position coordinate of the outer surface with the center of the tube as the origin coordinate. The position where the X coordinate is 0 corresponds to the weld. The vertical axis represents the value of the wall thickness when moving from the X coordinate of the outer surface toward the center. If it is a perfect circle, it shows a uniform value, but here there is a thickened part on the inner surface, so the thickness increases at a position shifted to both sides from the welded part, and it becomes thinner at the outer side. Recognize.

  Next, in step S2, the inner surface shape is determined. Specifically, first, (1) each incident position on the outer surface side of the beam at the time of wall thickness measurement is obtained from the position relationship between each scanning line on the array probe 50 and the steel pipe 1. Next, (2) each coordinate of the portion that hits the inner surface of the beam is obtained from each incident position and the thickness obtained in step S1. Next, (3) the inner surface shape is approximated by a polynomial or a spline function from these coordinates. The results are shown in FIG. The horizontal axis is the same as in FIG. The vertical axis Y-coordinate indicates the position coordinate of the inner surface in the vertical direction with the tube center as the origin. The shape shown in FIG. 7 is obtained by inverting the shape shown in FIG. In FIG. 7, if it is a perfect circle, it becomes an arc having the maximum Y coordinate when X = 0, but it is not a perfect circle because it is not an arc shape.

  Next, in step S3, a path is calculated as a perfect circle. Specifically, first, (1) the array probe 50 for measuring the thickness is arranged so that the beam of the central portion hits the inner surface. Next, (2) coordinates of each transducer of the oblique angle flaw detection array probe 5 are obtained. Next, (3) each position on the array 5 of each scanning line for oblique angles is obtained from the coordinates of each transducer and the number of simultaneous excitation elements. Next, (4) each incident position on the pipe outer surface side where the incident angle (= refraction angle) of each scanning line is constant is the size of the steel pipe 1, the sound speed of water 4 and steel, and the oblique angle obtained in (3). From each position of each scanning line on the array 5, it is obtained based on Snell's law. Next, (5) from each incident position on the pipe outer surface side and the steel pipe size, the steel pipe is regarded as a perfect circle, and the path to the seam portion 2 is determined for each scanning line. Next, (6) the angle at which the beam incident on the seam part is regularly reflected is obtained, and the beam path toward the inner surface is determined for each scanning line.

  The focal length of each scanning line is obtained from (4) the deflection angle of each element number and (5) from the steel intermediate distance from the array probe 5 to the seam 2 and the water distance.

  Next, in step S4, an intersection point between the inner surface approximation formula and the beam path obtained in step S3 (5) is determined for each scanning line. Next, in step S5, a reflection path is obtained based on the inner surface angle. Specifically, (1) the angle of the inner surface at the intersection is obtained from the differential value of the inner surface approximate expression, and the angle incident on the inner surface is determined for each scanning line. Next, (2) a beam path reflected from the inner surface and directed toward the outer surface is determined for each scanning line from the angle of incidence on the inner surface. Next, (3) the coordinates of the portion incident on the outer surface are determined for each scanning line. Next, (4) the angle of incidence on the outer surface is determined for each scanning line.

  Next, in step S6, assuming that the steel pipe is a perfect circle, the refraction path based on Snell's law is determined for each scanning line from the size of the steel pipe, the speed of sound of water and steel, and the angle of step S5 (4) To decide.

  Next, in step S7, (1) a position incident on the array probe 5 is obtained for each scanning line, and a tandem pair transducer group (transducer number) of each scanning line is determined. Next, (2) the angle of incidence on the array probe 5 is determined for each scanning line, and the deflection angle when receiving each scanning line is determined. Next, (3) the distance in the steel and the water distance from the seam 2 to the array probe 5 are obtained for each scanning line, and the focal length when receiving each scanning line is obtained.

  Next, in step S8, the delay time of each transducer of each scanning line for transmission and reception is obtained from the deflection angle and focal length of each scanning line.

  The calculation method can be realized by a method disclosed in known documents such as Patent Document 2 and Non-Patent Document 1, but here, as an example, a basic concept of a specific calculation is shown in FIG. It demonstrates with reference to a numerical formula. First, the coordinates {Xf, Yf} of the focal position are obtained as follows, where the center position of the transducer group is the origin of coordinates, the focal length is F, and the deflection angle is θ.

    Xf = F · sinθ, Yf = −F · cosθ

  Next, assuming that the transducer pitch is P and the number of transducers in the transducer group is n (where n is an even number), the coordinates {Xp (i), Yp (i)} of each transducer are obtained.

    Xp (i) =-n.p / 2-p / 2 + p.i, Yp (i) = 0 (i = 1 to n)

  Further, the distance Z (i) between the focal position and each transducer and the maximum value Zm thereof are obtained as follows.

Z (i) = SQRT {(Xf−Xp (i)) ² + (Yf−Yp (i)) ² } (i = 1 to n)
Zm = max {Z (i)} (i = 1 to n)

  Finally, the delay time Δt (i) is obtained by the following equation. C is the speed of sound.

    Δt (i) = (Zm−Z (i)) / C (i = 1 to n)

  The above shows the basic concept of calculation, and the center position of the transducer group does not necessarily have to be the coordinate origin for each scanning line. Moreover, although the number n of vibrators has been described as an even number, it may be an odd number. In the case of an odd number, it is needless to say that the above formula can be applied if it is partially changed. In actual calculation, the coordinates of each element of the array probe are determined in advance, the coordinates of the focal position are obtained according to the focal length and the deflection angle, and the distance Z (i) between the focal position and each transducer. Should be asked.

  The difference in sensitivity between the case where the inner shape is corrected and the case where the inner shape is not corrected by drilling a φ1.6 mm drill hole in the thickness direction for the sample with the thickening on the inner surface side by the above method It was confirmed. The experimental results are shown in FIG. When the inner surface shape is not corrected, the sensitivity is greatly reduced on the outer surface side from 1 / 2t (half the tube thickness), and the sensitivity difference is about 20 dB. On the other hand, if the inner surface shape is measured, the propagation path of tandem flaw detection is corrected based on the measurement result, flaw detection conditions are set, and measurement is performed, the sensitivity difference can be improved within 6 dB. It could be confirmed.

  In this embodiment, the flaw detection conditions are calculated by first determining the incident point of each scanning line and then calculating sequentially. However, the present invention is not limited to this. For example, after determining the focal position, the focal position is determined. Alternatively, the path with the shortest propagation time may be searched for each transducer.

  Although the array probe for tandem flaw detection has been described as a linear array probe, it may be an array probe having a curvature, even if the shape is not a linear array type, or a single probe. For example, the welding surface may be divided into an inner surface side and an outer surface side, and a probe for inspecting the inner surface side and two probes for inspecting the outer surface side may be used. The scanning in the thickness direction of the weld surface is performed electronically, but the probe may be mechanically moved or rotated. In the case of a configuration of a plurality of probes, it may be configured by appropriately combining a combination of a linear array probe and a probe having a curvature, electronic scanning and mechanical operation. Good.

The figure explaining 1st Example of this invention The figure which shows the mode of the bevel flaw detection in 1st Example The figure which shows the example of the procedure of scanning similarly The figure which similarly shows the function structural example of the ultrasonic flaw detector based on this invention The flowchart which shows the process sequence of 1st Example. The figure which shows an example of the wall thickness measured in the 1st Example The figure which shows an example of the inner surface shape determined in the 1st Example Diagram explaining the delay time given to each transducer The figure which shows the difference of the effect by the presence or absence of this invention in the sample whose internal wall thickness is large Diagram explaining the relationship between defect size and reflection directivity Diagram explaining reflection characteristics Diagram showing a comparison between non-tandem and tandem configurations The figure which shows the comparative example of the conventional method and the tandem flaw detection method which take non-tandem constitution The figure explaining the drill hole provided in the inspection pipe Diagram explaining mode conversion loss in flat steel plate Diagram explaining mode conversion loss in steel pipe Diagram showing an example of a propagation path in a tube The figure which shows the experiment example which investigated the focusing ability required in this invention

Explanation of symbols

1 ... Steel pipe 2 ... Welded part (Seam)
DESCRIPTION OF SYMBOLS 3 ... Defect 4 ... Water 5 ... Linear array probe for flaw detection 6 ... Transmitter transducer group 7 ... Receiver transducer group 8 ... Transmit beam 9 ... Receive beam 30 ... Subject size input part DESCRIPTION OF SYMBOLS 31 ... Array probe memory | storage part 32 ... Aperture width control part 33 ... Gate position memory | storage part 34 ... Array transmission rule memory | storage part 35 ... Array reception rule memory | storage part 36 ... Array transmission part 37 ... Array receiving part 38 ... Gate part 39 ... Determination threshold value input unit 40 ... Defect determination unit 50 ... Linear array probe for wall thickness measurement

Claims (2)

A wave transmitting portion that makes ultrasonic waves incident on the welding surface of the welded portion in the tube axial direction of the tubular body, and a wave receiving portion that receives a part or all of the reflected wave reflected by the welded portion. A wave transmitting portion and a wave receiving portion are composed of different transducer groups on one or two or more flaw detection array probes arranged in the circumferential direction of the tube, and
A thickness measuring probe for measuring the thickness distribution of the tube;
Propagation path for calculating ultrasonic propagation path for scanning in the thickness direction of the tube using the array probe for flaw detection based on the thickness distribution measured by the thickness measurement probe A calculation means;
Based on the calculated propagation path, the probe said on wound array probe transmitting section and with due controlled so to change the corresponding transducer groups on the wave receiver, the scanning in the thickness direction of the tubular body A control unit for performing control,
An ultrasonic flaw detection apparatus for a tubular body, comprising: A wave transmitting portion that makes ultrasonic waves incident on the welding surface of the welded portion in the tube axial direction of the tubular body, and a wave receiving portion that receives a part or all of the reflected wave reflected by the welded portion. A tube is an ultrasonic flaw detector having a wave section and a wave receiving section, each of which includes a transmitter / receiver section including different transducer groups on one or more flaw detection array probes arranged in the circumferential direction of the pipe body. When testing your body,
Measure the wall thickness distribution of the tube,
Based on the measured thickness distribution, using the array probe for flaw detection, calculate the propagation path of ultrasonic waves for scanning in the thickness direction of the tube,
Based on the calculated propagation path, the probe said on wound array probe transmitting section and with due controlled so to change the corresponding transducer groups on the wave receiver, the scanning in the thickness direction of the tubular body An ultrasonic flaw detection method for a tubular body characterized by: