JP4596326B2 - Ultrasonic flaw detection method and apparatus for internally finned tube - Google Patents

Description

The present invention relates to an ultrasonic flaw detection method and apparatus for an internally finned tube, and in particular, even if the inner surface shape of the tube is not uniform in the tube circumferential direction, a minute defect (cracked minute defect) extending in the tube axis direction. The present invention relates to an ultrasonic flaw detection method and apparatus capable of reliably detecting a).

  As a steel pipe used in an ethylene production plant, the purpose is to increase heat transfer efficiency. The inner surface of the steel pipe has a triangular cross-thread shape and is straight in the pipe axis direction (usually 8 to 12). A so-called inner finned tube in which fins are formed is known.

  FIG. 1 is a schematic cross-sectional view showing an example of the inner finned tube. As shown in FIG. 1, the internally finned tube P is formed of peaks (fins) M and valleys R whose inner surfaces are alternately provided in the circumferential direction. Such an internally finned tube P is usually made of a high Cr-high Ni Fe-based alloy as a raw material, and is manufactured by a hot extrusion tube manufacturing method typified by a centrifugal casting method or a Eugene Sejurne method.

  However, in the case of manufacturing the above inner finned pipe P by the hot extrusion pipe manufacturing method, the high Cr-high Ni Fe-based alloy is inferior in hot workability. There is a characteristic that the shape of the top is difficult to be a predetermined shape. For this reason, measures such as increasing the extrusion ratio are taken so that the shape of the peak portion M becomes a predetermined shape. In this case, however, the minute portion extending in the tube axis direction is almost at the center of the valley bottom portion Rs. A cracked flaw-like defect K may occur.

  If the occurrence of such a defect K is missed, a serious accident may occur during use of the pipe P. Accordingly, it is necessary to take measures such as inspection before product shipment to clean and remove the defect K, and the ultrasonic flaw detection method is applied as a highly efficient non-destructive inspection method for this purpose.

  However, when applying the ultrasonic flaw detection method, as shown in FIG. 2, a normal steel pipe in which fins are not formed on the inner and outer surfaces (that is, the inner and outer surfaces are concentric in the pipe circumferential direction and are circular arc surfaces having the same curvature radius). As in the case of inspecting a steel pipe), if an ultrasonic beam is incident at an acute incident angle θ (generally 35 to 55 °) with respect to the valley bottom Rs, it is extremely difficult to reach the vicinity of the valley bottom Rs. Reflective echoes (from the side surfaces of the ridge M) (shape echoes) from excessive fins are generated. For this reason, it is difficult to distinguish from a reflection echo (defect echo) from a minute defect K existing in the approximate center of the valley bottom Rs. As a result, there is a problem that the defect K cannot be detected reliably.

なお、表１における谷部肉厚は、前述した図１に符号ｔで示す部位の厚みに相当する。また、表１における山部高さは、前述した図１に符号ｈで示す部位の厚みに相当する。 More specifically, the inventors of the present invention conducted a flaw detection test for artificial defects (notches) provided in the valley bottom Rs under the flaw detection conditions shown in Table 1 and FIG.

Note that the valley thickness in Table 1 corresponds to the thickness of the portion indicated by the symbol t in FIG. Moreover, the peak height in Table 1 corresponds to the thickness of the portion indicated by the symbol h in FIG.

  As a result of the flaw detection test, as shown in FIG. 4, a 15% notch (notch with a depth of 0.9 mm (15% of valley thickness 6 mm = 0.9 mm)) and a 12.5% notch (with a depth of 0.1 mm). If it is 75 mm (12.5% of valley wall thickness 6 mm = 0.75 mm), the height of the shape echo is the noise level (N) and the height of the defect echo is the signal level (S) The S / N ratio of 2 is not less than 2, but the 5% notch (depth 0.3mm (5% of valley thickness 6mm = 0.3mm) notch is detected because the SN ratio is much lower than 2. As described above, the conventional ultrasonic flaw detection method can detect a minute defect that exists in the approximate center of the valley bottom due to the generation of an extremely large shape echo. There was a problem that was difficult.

  Furthermore, the position (time axis) at which the shape echo is detected changes due to the uneven thickness of the tube (particularly, uneven thickness of the valley). For this reason, when there is uneven thickness in the tube, there is a case where the shape echo enters the flaw detection gate set for detecting the defect. At this time, if the height of the shape echo is sufficiently smaller than the height of the defect echo, there is no problem by increasing the threshold value for detecting the defect echo. Since the difference is small, the shape echo that enters the flaw detection gate may be erroneously recognized as a defect echo. As a result, there is a problem that it is difficult to automatically determine the defect.

  Here, the inventor of the present invention has proposed, for example, methods and apparatuses disclosed in Patent Documents 1 and 2 as an ultrasonic flaw detection technique using an internally finned tube as a flaw detection material.

  As shown in FIG. 5, the technique described in Patent Document 1 uses an internally finned tube in order to minimize the shape echo from the side surface of the peak M that is an obstacle to identifying the defect echo from the defect K. An ultrasonic beam from the outer surface side of the tube at an incident angle θ (θ = 90 to 70 °) substantially orthogonal to the diameter line L of the tube passing through the center of the valley bottom portion Rs with respect to the center of the valley bottom portion Rs of the inner surface of P. Is incident.

  In the method described in Patent Document 1, when the inner surface shape of the internally finned pipe P is substantially uniform in the pipe circumferential direction, specifically, the valley wall thickness t (see FIG. 1 described above) of the valley bottom Rs is substantially the same. If they are the same, no problem will occur. However, if the inner surface shape is uneven in the tube circumferential direction, that is, if the tube wall thickness t of the valley bottom Rs is not uniform, it is difficult to distinguish between the shape echo from the side surface of the peak M and the defect echo from the defect K. It has been found that there is a drawback that the defect K cannot be detected at all when it is remarkable.

  On the other hand, the technique described in Patent Document 2 is based on an angle (90 to 70 °) substantially perpendicular to the diameter line of the tube passing through the center of the valley bottom with respect to the center of the valley bottom of the inner surface of the internally finned tube. An ultrasonic beam is incident from the outer surface, and the detected flaw detection signal is binarized and divided into signals of multiple levels, displayed on a B scope, and this B scope display image is image-processed to generate at the bottom of the valley It is a technology to detect the defect.

According to the technique described in Patent Literature 2, when the depth of the defect is large, it is possible to distinguish the defect echo from the shape echo on the image. However, when the depth of the defect is small, it is difficult to identify both echoes, and there is a risk of erroneous determination of the defect. Furthermore, since imaging and image processing are required, there is a drawback that it is difficult to apply to high-speed inspection, and the cost of the processing apparatus increases.
Japanese Patent Laid-Open No. 10-274643 JP-A-11-217114

The present invention has been made to solve the problems of the prior art described above, and the inner surface shape of the internally finned tube having protrusions continuous in the tube axis direction on the tube inner surface is not uniform in the tube circumferential direction. Even in such a case, the ultrasonic wave of the internally finned tube that makes it possible to reliably detect a minute defect extending in the tube axis direction (for example, a cracked minute defect generated at the valley bottom of the inner surface of the internally filled tube). It is an object of the present invention to provide a flaw detection method and an ultrasonic flaw detection apparatus used for carrying out this method.

In order to solve the above-mentioned problems, the present invention provides an ultrasonic probe installed on the outer surface side of a tube with an inner surface fin formed by crests and valleys whose inner surfaces are alternately provided in the circumferential direction. The ultrasonic flaw detection method detects a defect extending in the tube axis direction at the valley bottom of the inner surface of the tube by performing oblique angle ultrasonic flaw detection while relatively moving the tube in the circumferential direction of the tube. Two ultrasonic probes are arranged along the tube axis direction and at a distance larger than the length of the defect to be detected in the tube axis direction, and the two ultrasonic probes, The flaw detection signal output from one ultrasonic probe and the flaw detection signal output from the other ultrasonic probe are differentially calculated, and the defect is determined based on the differential signal obtained by the differential calculation. the ultrasonic testing method of the internal surface fin tube and detecting It is intended to provide.

According to such an invention, since the two ultrasonic probes are arranged on the outer surface side of the tube at a distance from each other along the tube axis direction, the ultrasonic beam transmitted from each ultrasonic probe is transmitted to the inner surface. At the flaw detection position (position in the tube circumferential direction of the tube) where a reflected echo (shape echo) is generated by reaching the projection side surface of the finned tube , both of the flaw detection signals output from the ultrasonic probes are internal fins. Equivalent shape echoes from the projection of the attached tube will be included. Further, since the interval between the two ultrasonic probes is larger than the length of the defect to be detected in the tube axis direction, only the flaw detection signal output from one or the other ultrasonic probe is used. A reflection echo (defect echo) from the defect is included. Accordingly, the differential signal obtained by differentially calculating the flaw detection signal output from one ultrasonic probe and the flaw detection signal output from the other ultrasonic probe includes a defect echo. The shape echo is subtracted to reduce its height. As a result, the S / N ratio (height of defect echo / height of shape echo) of the differential signal is improved.

  In addition, even if the appearance of the shape echo is not uniform in the pipe circumferential direction due to the fact that the inner surface shape of the pipe is not uniform in the pipe circumferential direction, each super Since the flaw detection signal output from the acoustic probe includes a non-uniform shape echo in the equivalent tube circumferential direction, the height of the shape echo contained in the differential signal obtained by differentially calculating both is still Will be reduced. Therefore, even if the inner surface shape of the tube is not uniform in the tube circumferential direction, the S / N ratio of the differential signal is improved.

  Since the present invention detects defects based on such differential signals, it can reliably detect minute defects extending in the tube axis direction even when the inner surface shape of the tube is not uniform in the tube circumferential direction. Is possible.

  In the present invention, the incident angle of the ultrasonic beam transmitted from each ultrasonic probe (incident angle with respect to the valley of the inner surface of the tube, corresponding to θ in FIG. 2) is the same as that of a general oblique flaw detection. What is necessary is just to set to about 35-55 degree.

As described above, the present invention is based on the premise that both of the flaw detection signals output from the ultrasonic probes include the same shape echoes from the protrusions of the internally finned tube . However, in reality, the propagation of the ultrasonic beam transmitted from each ultrasonic probe is caused by the error in the mounting position of each ultrasonic probe or the tube shape being different in the tube axis direction. As a result of the distances being different from each other, the position (time axis) of the shape echo included in the flaw detection signal output from each ultrasonic probe may be shifted. If the positional deviation of the shape echo becomes excessively large, the shape echo remains in the differential signal, and there is a problem that the S / N ratio cannot be improved reliably.

In order to reduce the influence of such positional deviation of the shape echo, the amplitude of the differential signal obtained when the material to be inspected is an internally finned tube in which the defect does not occur is reduced to a predetermined value or less. The flaw detection signal output from the one ultrasonic probe or the flaw detection signal output from the other ultrasonic probe is preferably delayed in time.

According to such a preferable aspect, the amplitude of the differential signal obtained when the material to be inspected is an internally finned tube having no defect is reduced so as to be smaller than a predetermined value (in other words, each ultrasonic probe). Flaw detection output from one ultrasonic probe so that the amplitude of the differential signal when the flaw detection signal output from the probe does not include a defect echo but only a shape echo is smaller than a predetermined value) Since the signal or the flaw detection signal output from the other ultrasonic probe is time-delayed, it is possible to reduce the influence of the positional deviation of the shape echo and improve the S / N ratio more reliably.

  The time delay of the flaw detection signal is determined by the transmission timing of the ultrasonic beam transmitted from one (or the other) ultrasonic probe to the transmission timing of the ultrasonic beam transmitted from the other (or one) ultrasonic probe. This can be done by delaying the transmission timing. Alternatively, the transmission timings of the ultrasonic beams transmitted from both ultrasonic probes can be made the same, while any one of the output flaw detection signals can be input to an appropriate delay circuit. .

  Further, in the present invention, output from each ultrasonic probe is caused by a difference in sensitivity of each ultrasonic probe, an error in the mounting position, a difference in tube shape in the tube axis direction, and the like. The height of the shape echo included in the flaw detection signal may be different. If the difference in height between the shape echoes becomes excessively large, the shape echoes remain in the differential signal, causing a problem that the S / N ratio cannot be improved reliably.

In order to reduce the influence of the difference in height between the shape echoes, a flaw detection signal output from the one ultrasonic probe when the material to be flawed is an internally finned tube in which the defect does not occur. And the other of the flaw detection signal output from the one ultrasonic probe and / or the other of the flaw detection signal so that the amplitude of the flaw detection signal is substantially equal to the amplitude of the flaw detection signal output from the other ultrasonic probe. It is preferable to adjust the amplitude of the flaw detection signal output from the ultrasonic probe.

According to such a preferable aspect, when the material to be inspected is an internally finned tube having no defect, the amplitude of the flaw detection signal output from one ultrasonic probe and the other ultrasonic probe. So that the amplitude of the signal of the flaw detection signal output from the probe is substantially the same (in other words, the amplitude of the shape echo included in the flaw detection signal output from each ultrasonic probe is substantially the same). In order to adjust the amplitude of the flaw detection signal output from one ultrasonic probe and / or the flaw detection signal output from the other ultrasonic probe, the influence of the difference in the height of the shape echo is reduced, It is possible to improve the S / N ratio more reliably.

In order to solve the above-mentioned problem, the present invention provides an ultrasonic probe installed on the outer surface side of a tube with an inner surface fin formed by ridges and valleys whose inner surfaces are alternately provided in the circumferential direction. An ultrasonic flaw detector that detects a defect extending in the tube axis direction at a valley bottom of the inner surface of the tube by performing oblique angle ultrasonic flaw detection while relatively moving in the tube circumferential direction of the tube. Two ultrasonic probes arranged along the tube axis direction and at a distance larger than the length of the defect to be detected in the tube axis direction, and output from each of the ultrasonic probes Signal processing means for detecting the defect based on the detected flaw detection signal, and the signal processing means includes a flaw detection signal output from one of the two ultrasonic probes, and Differential operation with the flaw detection signal output from the other ultrasonic probe , It is also provided as an ultrasonic flaw detector with the inner surface fin tube and detects the defect based on a differential signal obtained by the differential operation.

  Preferably, the signal processing means includes a delay control unit for delaying a time of a flaw detection signal output from the one ultrasonic probe or a flaw detection signal output from the other ultrasonic probe. Composed.

  Preferably, the signal processing means adjusts an amplitude of a flaw detection signal output from the one ultrasonic probe and / or an amplitude of a flaw detection signal output from the other ultrasonic probe. It is comprised so that it may comprise.

  Further, when the signal processing means includes two ultrasonic flaw detectors for controlling transmission and reception of ultrasonic beams by the two ultrasonic probes, the two ultrasonic flaw detectors have frequency characteristics relative to each other. Are preferably the same.

  According to the ultrasonic flaw detection method and apparatus for an internally deformed tube according to the present invention, even if the inner surface shape of the tube is not uniform in the tube circumferential direction, a minute defect (cracked minute defect) extending in the tube axis direction. Can be reliably detected.

  Hereinafter, an embodiment in the case of applying an ultrasonic flaw detection method according to the present invention to an internally finned tube as an internally deformed tube will be described with reference to the accompanying drawings as appropriate.

FIG. 6 is a diagram showing a schematic configuration of an ultrasonic flaw detection apparatus for carrying out the ultrasonic flaw detection method according to the present embodiment, and FIG. 6 (a) is a schematic diagram showing an installation mode of each ultrasonic probe. FIG. 6B is a schematic view for explaining the appearance of reflected echoes from one ultrasonic probe 1B, and FIG. 6C is a schematic view from the other ultrasonic probe 1A. FIG. 6D is a schematic diagram for explaining the appearance of the reflected echo, and FIG. 6D is a block diagram showing the device configuration of the ultrasonic flaw detector.
As shown in FIG. 6, the ultrasonic flaw detector 10 according to the present embodiment includes a defect (valley bottom of the inner surface of the tube P) along the tube axis direction with each other on the outer surface side of the inner surface finned tube P. A defect extending in the tube axis direction at Rs) is output from the two ultrasonic probes 1A and 1B arranged at a distance larger than the length in the tube axis direction of K and the respective ultrasonic probes 1A and 1B. Signal processing means 2 for detecting the defect K based on the flaw detection signal. Then, oblique ultrasonic flaw detection is performed while relatively moving the ultrasonic probes 1A and 1B in the tube circumferential direction of the tube P (in this embodiment, the tube P is rotated in the tube circumferential direction).

  The ultrasonic probes 1A and 1B have an incident angle (incident angle with respect to the valley bottom portion Rs) θ of the transmitted ultrasonic beam U within a range of 35 to 55 °, as in a general oblique ultrasonic flaw detection. It is set to an angle.

  As a preferred mode, the signal processing means 2 according to the present embodiment preferably includes an ultrasonic flaw detector 21A for controlling transmission / reception of an ultrasonic beam by the ultrasonic probe 1A and an ultrasonic beam by the ultrasonic probe 1B. And an ultrasonic flaw detector 21B for controlling transmission and reception. As a preferred mode, the ultrasonic flaw detector 21A and the ultrasonic flaw detector 21B have the same frequency characteristics of a pulse signal and an amplifier which will be described later (in this embodiment, the same known ultrasonic wave). Using a flaw detector). The ultrasonic flaw detectors 21A and 21B include an oscillator (not shown) that supplies a pulse signal for transmitting an ultrasonic beam from each of the ultrasonic probes 1A and 1B at a predetermined timing, and an ultrasonic probe. Since this is a general known ultrasonic flaw detector provided with an amplifier (not shown) for amplifying flaw detection signals output from the touch elements 1A and 1B, description of the specific configuration is omitted. .

  Moreover, the signal processing means 2 is equipped with the amplitude adjustment part which adjusts the amplitude of the flaw detection signal output from the ultrasonic probe 1A and / or the flaw detection signal output from the ultrasonic probe 1B as a preferable aspect. . In the present embodiment, the amplitude adjusting unit 22A that adjusts the amplitude of the flaw detection signal (more specifically, the amplified flaw detection signal output from the ultrasonic flaw detector 21A) output from the ultrasonic probe 1A and the super It is configured to include both an amplitude adjustment unit 22B that adjusts the amplitude of the flaw detection signal output from the acoustic probe 1B (more specifically, the amplified flaw detection signal output from the ultrasonic flaw detector 21B). ing. Note that the amplitude adjusting units 22A and 22B according to the present embodiment are amplifier circuits.

  Further, the signal processing means 2 includes a flaw detection signal output from the ultrasonic probe 1A (more specifically, a flaw detection signal after amplitude adjustment output from the amplitude adjustment unit 22A) and the ultrasonic probe 1B. A differential operation unit 23 is provided for performing a differential operation on the flaw detection signal output from the signal (more specifically, the flaw detection signal after amplitude adjustment output from the amplitude adjustment unit 22B) and outputting the differential signal. The differential operation unit 23 according to the present embodiment is a differential amplifier circuit.

  Moreover, the signal processing means 2 is provided with the delay control part 24 which delays the flaw detection signal output from the ultrasonic probe 1A or the flaw detection signal output from the ultrasonic probe 1B as a preferable aspect. The delay control unit 24 according to the present embodiment delays one of the pulse signal supply timings to the ultrasonic probes 1A and 1B by the oscillators included in the ultrasonic flaw detectors 21A and 21B by a predetermined time. It is configured.

  Further, the signal processing means 2 sets a flaw detection gate for detecting a reflection echo (defect echo) from the defect K with respect to the differential signal output from the differential operation unit 23, A defect detection unit 25 is provided that compares the differential signal with a predetermined threshold and detects a differential signal having a height equal to or higher than the threshold as a defect echo.

  According to the ultrasonic flaw detector 10 having the above-described configuration, the two ultrasonic probes 1A and 1B are arranged on the outer surface side of the tube P at intervals along the tube axis direction. Each ultrasonic probe at a flaw detection position (position in the tube circumferential direction of the tube P) where the ultrasonic beam transmitted from the sound probes 1A and 1B reaches the fin of the tube P to generate a reflected echo (shape echo). Both flaw detection signals output from the children 1A and 1B include equivalent shape echoes from the fins of the tube P (see FIGS. 6B and 6C). Further, since the arrangement interval between the two ultrasonic probes 1A and 1B is larger than the length of the defect K to be detected in the tube axis direction, the ultrasonic probe 1A or the ultrasonic probe 1B. A defect is included only in the flaw detection signal output from either one (see FIG. 6C). Accordingly, the differential signal obtained by differentially calculating the flaw detection signal output from the ultrasonic probe 1A and the flaw detection signal output from the ultrasonic probe 1B in the differential calculation unit 23 includes a defect echo. And the shape echo is subtracted to reduce its height. As a result, the S / N ratio (height of defect echo / height of shape echo) of the differential signal is improved.

  In addition, even if the appearance of the shape echo is not uniform in the pipe circumferential direction due to the inner surface shape of the pipe P being non-uniform in the pipe circumferential direction, Since the flaw detection signals output from the ultrasonic probes 1A and 1B include non-uniform shape echoes in the equivalent tube circumferential direction, the height of the shape echoes included in the differential signal is also reduced. Become. Therefore, even if the inner surface shape of the tube P is not uniform in the tube circumferential direction, the S / N ratio of the differential signal is improved.

  And since the defect detection part 25 detects a defect based on such a differential signal, even if it is a case where the inner surface shape of the pipe P is non-uniform | heterogenous in a pipe circumferential direction, the minute defect K extended in a pipe axial direction Can be reliably detected.

  It should be noted that the delay control unit 24 outputs the differential signal obtained from the ultrasonic probe 1A so that the amplitude of the differential signal obtained when the material to be inspected is the tube P having no defect. It is preferable to delay the flaw detection signal or the flaw detection signal output from the ultrasonic probe 1B. In other words, after the delay time is adjusted in advance so that the amplitude of the differential signal becomes smaller than a predetermined value using the tube P that is known to have no defect, the tube that is the actual flawed material It is preferable to detect P.

  According to such a preferable aspect, the amplitude of the differential signal obtained when the material to be inspected is the tube P in which no defect is generated is reduced to a predetermined value or less (in other words, each ultrasonic probe). Flaw detection signals output from the ultrasonic probe 1A so that the amplitude of the differential signal when the flaw detection signals output from 1A and 1B do not include defect echoes and only shape echoes are smaller than a predetermined value) Due to the time delay of the signal or the flaw detection signal output from the ultrasonic probe 1B, it is caused by the error in the mounting position of each ultrasonic probe 1A, 1B, the shape of the tube P being different in the tube axis direction, etc. Thus, it is possible to reduce the influence of the positional deviation of the shape echo that can occur and to improve the S / N ratio more reliably.

  Further, when the flaw detection material is a tube P in which no defect is generated, the amplitude of the flaw detection signal output from the ultrasonic probe 1A and the amplitude of the flaw detection signal signal output from the ultrasonic probe 1B. Are adjusted by the amplitude adjusters 22A and 22B so that the amplitude of the flaw detection signal output from the ultrasonic probe 1A and / or the flaw detection signal output from the ultrasonic probe 1B is adjusted. Is preferred. In other words, the amplitude of the flaw detection signal output from the ultrasonic probe 1A and the signal of the flaw detection signal output from the ultrasonic probe 1B using the tube P that is known to have no defect. After adjusting the amplification factors of the amplitude adjusters 22A and 22B in advance so that the amplitude of the tube P is substantially equal, it is preferable to detect the tube P that is an actual flaw detection material.

  According to such a preferable aspect, when the material to be inspected is the tube P having no defect, the amplitude of the flaw detection signal output from the ultrasonic probe 1A and the output from the ultrasonic probe 1B. The amplitude of the signal of the flaw detection signal is substantially equal (in other words, the amplitude of the shape echo included in the flaw detection signal output from each of the ultrasonic probes 1A and 1B is substantially equal). In order to adjust the amplitude of the flaw detection signal output from the ultrasonic probe 1A and / or the flaw detection signal output from the ultrasonic probe 1B, the difference in sensitivity of each of the ultrasonic probes 1A and 1B, and the attachment It is possible to reduce the influence of the difference in the height of the shape echo, which can be caused by the position error, the shape of the tube P being different in the tube axis direction, etc., and improve the S / N ratio more reliably. is there.

  FIG. 7 shows a 5% notch (depth) at one valley bottom of an internally finned tube (valley wall thickness: 6 mm, peak height: 6 mm) with an outer diameter of 60.3 mmφ and 10 fins formed. 0.3 mm), and an example of the result of flaw detection of this tube by the ultrasonic flaw detection method according to the present embodiment will be shown. More specifically, FIG. 7A shows an ultrasonic probe at a predetermined flaw detection position (position in the tube circumferential direction) where there is no 5% notch (the ultrasonic beam does not reach the 5% notch). It is an example of a flaw detection signal (more specifically, an output signal of the amplitude adjusting unit 22A) output from the toucher 1A. FIG. 7B is an example of a flaw detection signal (more specifically, an output signal of the amplitude adjustment unit 22B) output from the ultrasonic probe 1B at the same predetermined flaw detection position as described above. FIG. 7C shows a differential signal obtained by differentially calculating the flaw detection signal shown in FIG. 7A and the flaw detection signal shown in FIG. It is. FIG. 7D shows a chart output that displays differential signals output at each predetermined flaw detection position (predetermined pipe circumferential direction position) by rotating the pipe P in the pipe circumferential direction (the horizontal axis indicates the pipe circumference of the pipe). Direction position).

  As shown in FIG. 7C, the shape echo (FIG. 7A) included in the flaw detection signal of the ultrasonic probe 1A and the shape echo (FIG. 7C) included in the flaw detection signal of the ultrasonic probe 1B. It is understood that the shape echo has disappeared from the differential signal at the flaw detection position by performing a differential operation with b)). As shown in FIG. 7D, the differential signal output by rotating the tube P in the circumferential direction of the tube has a small shape echo, but the S / N ratio (of the defect echo). It was possible to obtain height / height of shape echo) = about 4.

FIG. 1 is a schematic cross-sectional view showing an example of an internally finned tube. FIG. 2 is a schematic cross-sectional view showing an installation mode of a general ultrasonic probe. FIG. 3 is a schematic cross-sectional view showing flaw detection conditions for a flaw detection test conducted by the inventors of the present invention. FIG. 4 is a diagram showing the results of the flaw detection test shown in FIG. FIG. 5 is a schematic cross-sectional view showing an installation mode of an ultrasonic probe described in a prior art document. FIG. 6 is a diagram showing a schematic configuration of an ultrasonic flaw detection apparatus for carrying out the ultrasonic flaw detection method according to the present invention. FIG. 7 shows an example of a result of flaw detection performed by the ultrasonic flaw detector shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1A, 1B ... Ultrasonic probe 2 ... Signal processing means 10 ... Ultrasonic flaw detector 21A, 21B ... Ultrasonic flaw detector 22A, 22B ... Amplitude adjustment part 23 ... Difference Dynamic calculation unit 24 ... Delay control unit 25 ... Defect detection unit P ... Tube K ... Defect Rs ... Valley bottom

Claims (7)

While the ultrasonic probe installed on the outer surface side of the inner finned tube formed by the crests and troughs whose inner surfaces are alternately provided in the circumferential direction, the oblique angle is moved while relatively moving in the tube circumferential direction of the tube. An ultrasonic flaw detection method for detecting defects extending in the tube axis direction at the valley bottom of the inner surface of the tube by performing ultrasonic flaw detection,
Two ultrasonic probes are arranged on the outer surface side of the tube along the tube axis direction with a gap larger than the length of the defect to be detected in the tube axis direction,
Of the two ultrasonic probes, the flaw detection signal output from one ultrasonic probe and the flaw detection signal output from the other ultrasonic probe are differentially calculated,
An ultrasonic flaw detection method for an internally finned tube , wherein the defect is detected based on a differential signal obtained by the differential operation. The flaw detection signal output from the one ultrasonic probe so that the amplitude of the differential signal obtained when the flaw detection material is an internally finned tube without the defect is reduced to a predetermined value or less. 2. The ultrasonic flaw detection method for an internally finned tube according to claim 1, wherein the flaw detection signal output from the other ultrasonic probe is time-delayed. When the flaw detection material is an internally finned tube in which no defect occurs, the amplitude of a flaw detection signal output from the one ultrasonic probe and the flaw detection output from the other ultrasonic probe The amplitude of the flaw detection signal output from the one ultrasonic probe and / or the flaw detection signal output from the other ultrasonic probe is adjusted so that the amplitude of the signal is substantially equal. The ultrasonic flaw detection method for an internally finned tube according to claim 1 or 2. The ultrasonic probe installed on the outer surface side of the inner finned tube formed by the crests and troughs whose inner surfaces are alternately provided in the circumferential direction is obliquely moved while relatively moving in the tube circumferential direction of the tube. By performing ultrasonic flaw detection, an ultrasonic flaw detection device that detects a defect extending in the tube axis direction at the valley bottom of the inner surface of the tube,
Two ultrasonic probes arranged on the outer surface side of the tube along the tube axis direction with a larger interval than the length of the defect to be detected in the tube axis direction;
Signal processing means for detecting the defect based on a flaw detection signal output from each of the ultrasonic probes,
The signal processing means includes
Of the two ultrasonic probes, differentially calculates a flaw detection signal output from one ultrasonic probe and a flaw detection signal output from the other ultrasonic probe,
An ultrasonic flaw detector for an internally finned tube , wherein the defect is detected based on a differential signal obtained by the differential operation. The signal processing means includes a delay control unit that delays a time of a flaw detection signal output from the one ultrasonic probe or a flaw detection signal output from the other ultrasonic probe. The ultrasonic flaw detector for an internally finned tube according to claim 4 . The signal processing means includes an amplitude adjustment unit that adjusts the amplitude of the flaw detection signal output from the one ultrasonic probe and / or the flaw detection signal output from the other ultrasonic probe. The ultrasonic flaw detector for an internally finned tube according to claim 4 or 5 . The signal processing means includes two ultrasonic flaw detectors for controlling transmission and reception of ultrasonic beams by the two ultrasonic probes,
The two ultrasonic flaw detector ultrasonic flaw detector with the inner surface fin tube according to claim 4 to 6, characterized in that the frequency characteristics match each other.

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