Method and apparatus for evaluating adhesion state of bonded parts of impermeable graphite using ultrasonic waves

Abstract

To provide a method and an apparatus for evaluating the adhesion state of bonded parts of impermeable graphite using ultrasonic waves that can accurately evaluate the adhesion state of bonded parts, even in a case where an ultrasonic inspection is difficult in the bonded parts.SOLUTION: A heat exchange tube 120 is made of impermeable graphite material. A bonded part 101 is formed with a tapered part 102 by the inner surface of a through-hole 111 and the outer surface of the heat exchange tube 120. The taper angle θ of the outer surface of the heat exchange tube 120 in the tapered part 102 is between 3° and 8°. The ultrasonic wave is the low-frequency ultrasonic wave with a nominal frequency of 2.25 MHz to 3 MHz. The low-frequency ultrasonic waves are transmitted in a direction Y perpendicular to the tube axis direction X from the inside of the heat exchange tube 120 toward the tapered part 102, reflected waves are received, and the adhesion state of the bonded part 101 is evaluated on the basis of the reflection signals of the received reflected waves.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method and an apparatus for evaluating the bonding state of an impermeable graphite bonding portion using ultrasonic waves. More specifically, ultrasonic waves are transmitted from an ultrasonic probe toward a bonding portion between an end portion of a heat exchange tube fixed to a through hole drilled in a tube sheet of a heat exchanger and the through hole, and reflected waves are received, and based on the reflection signals of the received reflected waves, the present invention relates to a method and an apparatus for evaluating the bonding state of an impermeable graphite bonding portion using ultrasonic waves for evaluating the bonding state of the bonding portion.

Background Art

[0002] Conventionally, with regard to heat exchange tubes (tubes) of a heat exchanger, for example, as described in Patent Documents 1 and 2, a method of transmitting and receiving ultrasonic waves from a probe inside the tube by the immersion ultrasonic method to inspect the tube wall thickness and cracks is known. However, these methods are for detecting wall thickness reduction and cracks in the heat exchange tubes themselves, and do not inspect and evaluate the bonding state of these members at the connection portion between the tube sheet of the heat exchanger and the heat exchange tubes.

[0003] In addition, the shape of this connection portion (bonding portion) may be tapered, or the heat exchange tube may be a damping material through which ultrasonic waves are difficult to propagate. Therefore, even if the above-described method is applied, it may not be possible to obtain the reflected waves necessary for inspecting and evaluating the bonding state, and it is difficult to evaluate the bonding state by ordinary ultrasonic inspection.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In view of such a conventional situation, an object of the present invention is to provide a method and an apparatus for evaluating the adhesion state of an impermeable graphite adhesive part using ultrasonic waves, which can accurately evaluate the adhesion state of the adhesive part even in an adhesive part where ultrasonic inspection is difficult.

Means for Solving the Problems

[0006] To achieve the above object, the method for evaluating the adhesion state of an impermeable graphite adhesive part using ultrasonic waves according to the present invention is characterized in that ultrasonic waves are transmitted from an ultrasonic probe toward an adhesive part between an end portion of a heat exchange tube fixed to a through hole drilled in a tube sheet in a heat exchanger and the through hole, and a reflected wave is received, and in a method for evaluating the adhesion state of the adhesive part based on the reflection signal of the received reflected wave, the heat exchange tube is made of an impermeable graphite material, a tapered portion is formed at the adhesive part by the inner surface of the through hole and the outer surface of the heat exchange tube, the taper angle of the outer surface of the heat exchange tube in the tapered portion is 3° or more and 8° or less, the ultrasonic waves are low-frequency ultrasonic waves with a nominal frequency of 2.25 MHz or more and 3 MHz or less, the ultrasonic probe is inserted into the inside of the water-immersed heat exchange tube, and the low-frequency ultrasonic waves are transmitted from the inside of the heat exchange tube toward the tapered portion in a direction orthogonal to the tube axis direction, and a reflected wave is received, and the adhesion state of the adhesive part is evaluated based on the reflection signal of the received reflected wave.

[0007] Here, the inspection object of the present invention is an adhesive part between an end portion of a heat exchange tube fixed to a through hole drilled in a tube sheet in a heat exchanger and the through hole. The heat exchange tube is made of an impermeable graphite material, and a tapered portion is formed at the adhesive part by the inner surface of the through hole and the outer surface of the heat exchange tube. Therefore, when ultrasonic waves are transmitted from the inside of the tube, the ultrasonic waves are reflected and scattered at the tapered portion (surface), and it may be impossible to obtain the reflected waves necessary for inspection. Moreover, since the impermeable graphite material is a damping material in which ultrasonic waves are difficult to propagate, there are few (weak) receivable reflected waves in the first place.

[0008] According to the above configuration, the taper angle of the outer surface of the heat exchange tube in the tapered portion is 3° or more and 8° or less, and the ultrasonic wave is a low-frequency ultrasonic wave with a nominal frequency of 2.25 MHz or more and 3 MHz or less. According to the experiments of the inventors, it has been found that within this range of the taper angle and the nominal frequency, it is possible to evaluate the adhesion state of the adhesive portion where ultrasonic inspection is difficult as described above. Therefore, the ultrasonic probe is inserted into the interior of the water-immersed heat exchange tube, and the low-frequency ultrasonic wave is transmitted in a direction perpendicular to the tube axis direction from the inside of the heat exchange tube toward the tapered portion while receiving the reflected wave, so that the adhesion state of the adhesive portion can be accurately evaluated based on the reflection signal of the received reflected wave.

[0009] In the above configuration, it is preferable to generate a C-scan image based on the reflection signal received by scanning the ultrasonic probe along the circumferential direction and the axial direction of the heat exchange tube. Thereby, the overall adhesion state of the adhesive portion can be easily grasped.

[0010] Furthermore, in such a configuration, the C-scan image is preferably one in which only signals having a signal intensity equal to or higher than a predetermined value among the reflection signals of the received reflected waves are displayed. Since only the reflection signals from the portions where the adhesion is not sufficient (adhesion defective portions) are displayed, the adhesion state is easier to discriminate and the inspection accuracy is also improved.

[0011] Also, in the above configuration, a B-scan image may be generated based on the reflection signal received by scanning the ultrasonic probe along the circumferential direction of the heat exchange tube.

[0012] In any of the above configurations, it is preferable to use the signal of the reflected wave from the outer surface of the main body portion of the heat exchange tube located outside the adhesive portion as a reference signal. Thereby, the relative echo height of the adhesive portion can be standardized, the error due to individual differences in the heat exchange tube can be reduced, and the inspection accuracy can be improved. In the above configuration, the ultrasonic probe is preferably inserted into the through hole from the outside of the tube sheet.

[0013] Further, a sleeve is provided in the through hole, and the inner surface of the end portion of the sleeve is inclined to face the outer surface of the heat exchange tube, and the taper portion may be formed by the inner surface of the end portion of the sleeve and the outer surface of the heat exchange tube. Also in the adhesive portion having such a configuration, the adhesive situation can be evaluated with the same accuracy as above.

[0014] Furthermore, in the above configuration, the wall thickness of the heat exchange tube is, for example, 5 mm or less, and the wall thickness in the taper portion is, for example, 2 mm or more and 5 mm or less.

[0015] To achieve the above object, an apparatus for evaluating the adhesion situation of an adhesive portion of impervious graphite using ultrasonic waves according to the present invention is characterized in that an ultrasonic probe that transmits ultrasonic waves toward an adhesive portion between an end portion of a heat exchange tube fixed to a through hole drilled in a tube sheet in a heat exchanger and the through hole and receives a reflected wave, and a signal processing device that processes a reflection signal of the received reflected wave. In the configuration, the heat exchange tube is made of an impervious graphite material, a taper portion is formed by the inner surface of the through hole and the outer surface of the heat exchange tube in the adhesive portion, the taper angle of the outer surface of the heat exchange tube in the taper portion is 3° or more and 8° or less, the ultrasonic wave is a low-frequency ultrasonic wave having a nominal frequency of 2.25 MHz or more and 3 MHz or less, and further has moving means for inserting and moving the ultrasonic probe into the water-immersed heat exchange tube. The ultrasonic probe transmits the low-frequency ultrasonic wave in a direction perpendicular to the tube axis direction from the inside of the heat exchange tube toward the taper portion and receives a reflected wave, and the signal processing device evaluates the adhesion situation of the adhesive portion based on the reflection signal of the received reflected wave.

[0016] In the above configuration, the ultrasonic probe has rotating means for rotating along the circumferential direction of the heat exchange tube, and the moving means and the rotating means scan the ultrasonic probe along the circumferential direction and the axial direction of the tube. The signal processing device may have a C-scan image generation unit that generates a C-scan image based on the reflection signals received by scanning along the circumferential direction and the axial direction of the tube.

[0017] Further, in the above configuration, the rotating means scans the ultrasonic probe along the circumferential direction of the heat exchange tube, and the signal processing device may have a B-scan image generation unit that generates a B-scan image based on the reflection signals received by scanning along the circumferential direction of the tube.

[0018] Also, in any of the above configurations, the heat exchanger is provided with a plurality of the through holes and the heat exchange tubes, and the signal processing device may have a tube sheet diagram generation unit that indicates the adhesion status of the plurality of the adhesion portions in a front view of the tube sheet.

Advantages of the Invention

[0019] According to the features of the method and apparatus for evaluating the adhesion status of the adhesion portion of impermeable graphite using ultrasonic waves according to the present invention, it is possible to accurately evaluate the adhesion status of the adhesion portion even in an adhesion portion where ultrasonic inspection is difficult.

[0020] Other objects, configurations, and effects of the present invention will become apparent from the following sections of the embodiments of the invention.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Figure 4

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Figure 8

Figure 9

Figure 10

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Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Figure 18

Figure 19

Embodiments for Carrying Out the Invention

[0022] Next, the present invention will be described in more detail with appropriate reference to the accompanying drawings. (Overview of Evaluation Device 1) As shown in Fig. 1(a), the adhesion state evaluation apparatus 1 according to the present invention generally includes an ultrasonic probe 2 (hereinafter abbreviated as "probe 2") that transmits ultrasonic waves toward the adhesion part 101 of the heat exchanger 100 and receives reflected waves, a signal processing device 3 that processes the reflection signals of the received reflected waves, a probe pulling device as moving means 4 for moving the probe 2 in the heat exchange tube 120 (hereinafter abbreviated as "tube 120") in the tube axis direction X along its tube axis Ax, and a water supply means 5 including a tank 5a for supplying water W to the tube 120, a high-pressure pump 5b, and a filter 5c.

[0023] (Ultrasonic behavior) In the adhesion state evaluation method according to the present invention, ultrasonic waves are transmitted and received from inside the tube 120 toward the adhesion part 101 by the immersion method, and the adhesion state of the adhesion part 101 is evaluated based on the reflection signals of the received reflected waves. As shown in Fig. 2, when the tube sheet 110 and the tube 120 are normally adhered by the adhesive G (healthy part), most of the incident wave Iw propagating in the tube 120 propagates (transmits) through the adhesive G and propagates to the tube sheet 110 as the transmitted wave Tw, and a part is reflected at the adhesion interface and propagates through the tube 120 as the reflected wave Rw. On the other hand, when the adhesive G is insufficient and the tube sheet 110 and the tube 120 are not adhered (adhesion failure part), a gap K is generated between the tube sheet 110 and the tube 120. Therefore, the incident wave Iw propagating in the tube 120 is almost entirely reflected by the air in the gap K and propagates through the tube 120 as the reflected wave Rw without generating the transmitted wave Tw. Thus, the adhesion state (condition) can be evaluated based on the difference in the behavior of ultrasonic waves.

[0024] (Signal processing device 3) The signal processing device 3 is constituted by, for example, a personal computer. As shown in Fig. 1(b), it controls the pulsar 31 via the control unit 30a to generate ultrasonic pulses from the probe 21 of the probe 2. The transmitted ultrasonic pulses are reflected by the bonding part 101, and the reflected waves are received by the probe 21. The received reflected signal (reflected wave) is amplified by the preamplifier 32 and received by the receiver 33, and is converted into a digital signal by the A / D converter 35 with noise removed by the filter 34. Then, signal processing is performed by the signal processing device 3 and displayed on the display 6.

[0025] As shown in Fig. 1(b), the signal processing device 3 generally has a control unit 30a that controls the generation of ultrasonic pulses from the probe 21, etc., and an image generation unit 30b that processes the reflected signal received together with the scanning position data of the counter 7 that detects the signals indicating the scanning position and rotational position (orientation) of the probe 21 to generate various images. The image generation unit 30b has a B-scan image generation unit 30b1 that generates B-scan images such as those in Figs. 14(b) and (c), a C-scan image generation unit 30b2 that generates C-scan images such as those in Figs. 14(a), 15, and 16, and a tube sheet diagram generation unit 30b3 that represents the bonding state of the bonding part 101 in a front view of the tube sheet 110 as shown in Fig. 17. The scanning images, etc. generated by the image generation unit 30b are displayed on the display 6. Although this signal processing device 3 is constituted by a personal computer, it is also possible to use a flaw detector 10 having a signal processing unit with the same function, and a pulsar 31, a preamplifier 32, a receiver 33, a filter 34, an A / D converter 35, a display 6, and a counter 7.

[0026] (Ultrasonic probe 2) As shown in Fig. 3, the probe 2 generally includes a probe 21 housed in a housing 20 for transmitting and receiving ultrasonic waves, a reflection mirror 22 that reflects the ultrasonic waves transmitted from the probe 21 in a direction (diameter direction Y) orthogonal to the tube axis direction X, and a rotary turbine 23 that rotates the reflection mirror 22 along the circumferential direction C of the tube. The rotary turbine 23 is rotatably provided with respect to the housing 20 via bearings, etc. (not shown).

[0027] (Outline of the joint part 101) The heat exchanger 100 to be inspected according to the present invention is a multi-tube heat exchanger as shown in FIGS. 4(a) and 4(b). The end portion 122 of each of the plurality of through holes 111 drilled in the tube sheet 110 is inserted and fixed with the heat exchange tube 120, and the joint part 101 is formed. Further, as shown in FIG. 4(c), a tapered surface 113 is formed on the inner surface 112 near the outside of the through hole 111, and a tapered surface 123 is also formed on the outer surface of the end portion 122 of the tube 120. Then, an adhesive G is applied to these tapered surfaces 113 and 123, and by adhering them, a tapered portion 102 is formed in the joint part 101.

[0028] (Tapered portion 102) As described above, the tapered portion 102 has a tapered shape in which the tapered surfaces 113 and 123 face each other. However, due to insufficient application amount of the adhesive G or mixing of air bubbles, etc., the adhesive G may be locally insufficient on the adhesive surface (tapered portion 102), and an adhesion failure portion may occur. This adhesion failure may lead to a risk of fluid leakage in some cases. The present invention evaluates the adhesion status of the tapered surfaces 113 and 123 in the tapered portion 102 by immersion ultrasonic flaw detection. Although details will be described later, the taper angle θ of the outer surface (tapered surface 123) of the tube 120 in the joint part 101 (tapered portion 102) to be inspected according to the present invention is 3° or more and 8° or less. This taper angle θ refers to the angle formed by the tube axis direction X of the tube 120 and the tapered surface 123 of the tube 120. Further, the wall thickness of the heat exchange tube 120 in the tapered portion 102 is at most 5 mm and at least 2 mm.

[0029] (Heat exchange tube 120) In addition, this tube sheet 110 and the heat exchange tubes 120 are made of an impermeable graphite material. Since this material has high corrosion resistance and high thermal conductivity, it is used in heat exchangers such as in the manufacturing process of chemicals, for example. However, the impermeable graphite material is a high-attenuation material with a large ultrasonic attenuation compared to general steel materials. In particular, as the frequency increases, the influence of attenuation becomes greater, so the ultrasonic frequency available for inspection is limited.

[0030] (Ultrasonic frequency) Here, the signal waveforms of the reflected waves received when ultrasonic waves of 2.25 MHz, 5 MHz, and 10 MHz are incident in the direction Y perpendicular to the tube axis direction X on a test tube made of an impermeable graphite material with a wall thickness of 5 mm are shown in FIGS. 5(b), (d), and (f), and the simulation results corresponding to these actual waveforms are shown in FIGS. 5(c), (e), and (g). According to the experiments of the inventors, from the results shown in the figure, it can be seen that when the frequency is 5 MHz or more, the multiple reflected waves (echoes) after the second bottom surface echo become below the noise level, and it is difficult to detect the signal. The dotted lines shown in the figure indicate the approximate noise levels measured at each frequency, and the same applies to the figures described below.

[0031] Moreover, as described above, the adhesive portion 101 has a tapered shape. Here, the simulation results of the signal waveforms of the reflected waves when ultrasonic waves of 2.25 MHz, 5 MHz, and 10 MHz are incident on the straight tube portion of a test tube made of an impermeable graphite material with a wall thickness of 3 mm shown in FIG. 6(a) are shown in FIGS. 6(b) to (d), and the same simulation results in the portion with a wall thickness of 3 mm in the tapered portion of the same test tube shown in FIG. 6(e) are shown in FIGS. 6(f) to (h). From the results shown in the figure, it can be seen that in the tapered portion (inclined portion), since the incident wave is not perpendicular to the adhesive interface (tapered surface), the reflected signal of the reflected wave received is weaker than that in the straight tube portion (taper angle 0°). Moreover, in the tapered portion, when the frequency is 5 MHz or more, the reflected wave itself becomes below the noise level, and it is difficult to detect the reflected signal.

[0032] Thus, in order to evaluate the adhesion state of the adhesion part 101 to be inspected according to the present invention, there is an upper limit to the available frequency, and it can be seen that it is difficult to evaluate the adhesion state by ordinary ultrasonic flaw detection.

[0033] Furthermore, as described above, the wall thickness of the heat exchange tube 120 in the tapered part 102 is maximum 5 mm and minimum 2 mm. In order to evaluate the adhesion state of the adhesion interface by ultrasonic waves, it is necessary to temporally separate the reflection signal (S) on the surface and the reflection signal (B1) on the adhesion interface. As shown in FIG. 7, the time interval between the ultrasonic reflection signal (S) and the reflection signal (B1) on the adhesion interface is 2T / C. When the plate thickness is 2 mm and the sound velocity is 2740 m / s, the time interval is 1.46 μs.

[0034]

Table 1

[0035] And, as shown in Table 1, when the frequency is the same, the lower the frequency, the longer the duration of the ultrasonic signal. In the cases of 2.25 MHz, 5 MHz, and 10 MHz, since the duration of the ultrasonic signal is relatively long, even when a narrow-band probe with poor time resolution is used and the number of waves is 3, the time interval between the reflection signal (S) and the reflection signal (B1) is not exceeded. On the other hand, in the case of 1 MHz, not only in the case of a narrow-band probe with about 3 waves of frequency, but also when a wide-band probe with 1.5 waves of frequency is used, the time interval between the reflection signal (S) and the reflection signal (B1) is exceeded, and these signals cannot be separated.

[0036] Thus, in order to evaluate the adhesion state of the adhesion part 101 to be inspected according to the present invention with a thin plate thickness, there is also a lower limit to the available frequency, and it can be seen that it is difficult to evaluate the adhesion state by ordinary ultrasonic flaw detection. Moreover, in the present invention, since ultrasonic waves are transmitted and received from inside the tube 120, there is an upper limit to the size of the vibrator of the probe 21. Usually, the element size is increased to lower the frequency, but due to the size limitation, there is also a lower limit to the frequency.

[0037] Therefore, the inventors made the taper angle θ of the taper surface 123 of the tube 120 in the taper portion 102 (adhesive portion 101) 0°, 2.69°, 3°, 5.38°, 8°, and 10.76°. In the impermeable graphite tube 120, low-frequency ultrasonic waves with nominal frequencies of 0.5 MHz, 1 MHz, 2.25 MHz, 3 MHz, 5 MHz, and 10 MHz were incident on each test body to simulate the reflection signals of the reflected waves. The simulation results are shown in FIGS. 8 to 13.

[0038] In the case of the taper angle of 0° shown in FIG. 8, when the nominal frequency is 2.25 MHz or higher, the reflection signal from the interface (bottom surface of the test body) is larger than the noise level and can be distinguished (separated) from the incident wave (reflection signal on the surface). On the other hand, when the nominal frequency is 0.5 MHz, the distinction (separation) between the reflected wave and the incident wave becomes impossible. Also, when the nominal frequency is 1 MHz, since the first reflection echo at the interface rises before the incident wave (transmission pulse) falls below the noise level, the distinction between the incident wave and the reflected wave becomes unclear. The result for the nominal frequency of 0.5 MHz was the same for all other test bodies. Also, the result for the nominal frequency of 1 MHz was the same for the test bodies with taper angles of 2.69°, 3°, and 5.38°.

[0039] In the case of the taper angle of 2.69° shown in FIG. 9, when the nominal frequency is 2.25 MHz (1 MHz) or higher and 5 MHz or lower, the reflection signal from the interface (bottom surface of the test body) is larger than the noise level and can be distinguished (separated) from the incident wave. However, when the nominal frequency is 10 MHz, the reflection signal from the interface becomes smaller than the noise level. The result for the nominal frequency of 10 MHz was the same for the test bodies with taper angles of 3°, 5.38°, 8°, and 10.76°.

[0040] In the cases of the taper angles of 3° and 5.38° shown in FIGS. 10 and 11, when the nominal frequencies were 2.25 MHz (1 MHz) and 3 MHz, the reflection signals from the interface (the bottom surface of the specimen) were larger than the noise level and could be distinguished (separated) from the incident wave. However, when the nominal frequency was 5 MHz or higher, the reflection signals from the interface became smaller than the noise level. Note that the results for the nominal frequency of 5 MHz or higher were the same for each of the specimens with the taper angles of 5.38°, 8°, and 10.76°.

[0041] In the case of the taper angle of 8° shown in FIG. 12, when the nominal frequencies were 2.25 MHz and 3 MHz, the reflection signals from the interface (the bottom surface of the specimen) were larger than the noise level and could be distinguished (separated) from the incident wave. On the other hand, when the nominal frequency was 1 MHz or lower, since the intensity of the reflection signal of the reflected wave was smaller than that of the above specimen, it was considered that the distinction (separation) from the incident wave became impossible. Also, when the nominal frequency was 5 MHz or higher, the reflection signals from the interface became smaller than the noise level.

[0042] Furthermore, in the case of the taper angle of 10.76° shown in FIG. 13, only when the nominal frequency was 2.25 MHz, the reflection signals from the interface (the bottom surface of the specimen) were larger than the noise level and could be distinguished (separated) from the incident wave.

[0043] Thus, by using low-frequency ultrasonic waves with a nominal frequency of 2.25 MHz or higher and 3 MHz or lower, it was led that it was possible to evaluate the adhesion state based on the reflection signals of the received reflected waves in the adhesion part 101 of the tube 120 made of an impermeable graphite material where the taper angle of the taper surface 123 in the taper part 102 was 3° or more and 8° or less.

[0044] (Adhesion state evaluation procedure) Next, the procedure for evaluating the adhesion state according to the present invention will be described. First, insert the probe 2 into the through-hole 111 from the outside of the tube sheet 110, move it inside the tube sheet 110 by the probe pulling device 4, pass through the bonding portion 101 (tapered portion 102), and move it to the straight tube portion 124 of the tube 120 located outside the bonding portion 101 (inside the tube sheet 110). Then, in the straight tube portion 124, transmit ultrasonic waves in the direction Y (diameter direction) orthogonal to the tube axis direction X from inside the tube 120 and receive the reflected waves from the tube 120, and use it as the reference signal of the reflected signal. Thereby, the relative echo height of the bonding portion 101 can be standardized, the error due to individual differences of the tube 120 can be reduced, and the inspection accuracy can be improved. Note that the gate level during inspection is determined according to the echo height of this reference signal.

[0045] Next, move the probe 2 to the vicinity of the bonding portion 101, and scan the bonding portion 101 while rotating the probe 2 in the circumferential direction C of the tube 120 and moving it in the tube axis direction X by the probe pulling device 4 and the water supply means 5. Then, the signal processing device 3 processes the received reflected signal together with the scanning position data of the counter 7 that detected the scanning position and the rotational position (orientation) of the probe 21, and the image generation unit 30b generates an image and displays it on the display 6.

[0046] For example, the C-scan image generation unit 30b2 generates a C-scan image as shown in FIG. 14(a) and displays it on the display 6. The C-scan image is developed with the tube axis direction X and the circumferential direction C as axes, and the inner surface 110x of the tube sheet 110 is used as a reference (0 mm). FIG. 14(a) is an image generated by thickness value display. The thickness value display is a display obtained by setting the gate level for detecting the reflected signal to, for example, 50% of the healthy portion and performing signal processing. As described above, in the bonding defect portion, the incident wave is almost reflected by the air at the interface (void K), so the reflected signal becomes strong. As shown in FIG. 15, by displaying the reflected signal having a certain intensity or more (thickness value display), the range (portion) of the bonding defect portion can be easily identified, and it is also easy to distinguish from noise. Also, as shown in FIG. 14(a), the position of the tapered portion 102 can be easily grasped. In this way, the bonding state of the bonding portion 101 can be accurately evaluated based on the reflected signal.

[0047] Since a plurality of tubes 120 are adhered to the tube sheet 110, the above operation is repeated for each tube 120. When the operation is completed, the tube sheet drawing generation unit 30b3 generates and displays a front view of the tube sheet 120 as shown in FIG. 17 based on the reflection signals of the respective tubes 120. Thereby, in the entire tube sheet 110 (heat exchanger 100), the degree and range of poor adhesion of the tubes 120 can be easily grasped.

[0048] Finally, the possibility of still another embodiment of the present invention will be described. Note that the same reference numerals are given to members similar to those in the above-described embodiment. In the above embodiment, the C-scan image generation unit 30b2 generates and displays a C-scan image with a wall thickness value display as shown in FIG. 15. However, the display of the C-scan image is not limited to this, and as shown in FIG. 16, an echo height display in which the gate level is set lower (for example, 0% of the sound portion) and signal processing is performed may be used. However, the wall thickness value display in the above embodiment is excellent in terms of visibility.

[0049] Also, the generated image is not limited to the C-scan image. For example, the B-scan image generation unit 30b1 may generate and display a B-scan image as shown in FIGS. 14(b) and (c). Of course, it is also possible to switch between the display of the B-scan image and the C-scan image, and an A-scan image may be displayed.

[0050] In the above embodiment, the tube 120 was adhered to the through hole 111 of the tube sheet 110. However, for example, as shown in FIG. 18, even when the sleeve 130 is provided, it is possible to evaluate the adhesion state of the adhesion portion 101' between the tube 120 and the sleeve 130 (the tapered portion 102 formed by the tapered surface 123 of the tube 120 and the tapered surface 133 of the sleeve 130). Note that the adhesion portion between the straight tube portion 135 of the sleeve 130 and the through hole 111 is also inspected together with the tapered adhesion portion 101', and as a result, a C-scan image may be generated and displayed with a wall thickness value display as shown in FIG. 19, for example.

Explanation of Reference Numerals

[0051] 1: Adhesion condition evaluation device, 2: Ultrasonic probe (probe), 3: Signal processing device, 4: Moving means (probe tensioning device), 5: Water supply means, 5a: Tank, 5b: High-pressure pump, 5c: Filter, 6: Display, 7: Counter, 10: Flaw detector, 20: Housing, 21: Probe, 22: Reflecting mirror, 23: Rotating turbine, 30a: Control unit, 30b: Image generation unit, 30b1: B-scan image generation unit, 30b2: C-scan image generation unit, 30b3: Tube sheet diagram generation unit, 31: Pulser, 32: Preamplifier, 33: Receiver, 34: Filter, 35: A / D converter, 100: Heat exchanger, 101, 101’: Adhesion part, 102: Taper part (adhesion surface), 110: Tube sheet, 110x: Inner surface, 111: Through hole, 112: Inner surface, 113: Taper surface, 120: Heat exchange tube (tube, heat transfer tube), 120a: Inside of the tube, 121: Outer surface, 122: End, 123: Taper surface, 124: Straight tube part, 130: Sleeve, 133: Taper surface, 135: Straight tube portion, Ax: Tube axis, B1: Reflection signal at the adhesion surface, C: Tube circumferential direction, G: Adhesive, Iw: Incident wave, K: Gap, P: Ultrasonic wave, S: Reflection signal at the surface, Rw: Reflection wave, Tw: Transmission wave, W: Water, X: Tube axis direction, Y: Tube diameter direction, θ: Taper angle

Claims

1. An ultrasonic method for evaluating the adhesion status of an impermeable graphite adhesive joint, which transmits ultrasonic waves from an ultrasonic probe toward the adhesive joint between the end of a heat exchange tube fixed to a through hole drilled in a tube sheet of a heat exchanger and the through hole, receives the reflected waves, and evaluates the adhesion status of the adhesive joint based on the reflection signals of the received reflected waves, wherein: the heat exchange tube is made of an impermeable graphite material; a tapered portion is formed on the inner surface of the through hole and the outer surface of the heat exchange tube at the adhesive joint; the taper angle of the outer surface of the heat exchange tube in the tapered portion is 3° or more and 8° or less; the ultrasonic waves are low-frequency ultrasonic waves with a nominal frequency of 2.25 MHz or more and 3 MHz or less; the ultrasonic probe is inserted into the water-soaked heat exchange tube; the low-frequency ultrasonic waves are transmitted from the inside of the heat exchange tube toward the tapered portion in a direction perpendicular to the tube axis direction, and the reflected waves are received; An ultrasonic method for evaluating the adhesion status of an impermeable graphite adhesive joint, which evaluates the adhesion status of the adhesive joint based on the reflection signals of the received reflected waves.

2. The ultrasonic method for evaluating the adhesion status of an impermeable graphite adhesive joint according to claim 1, wherein a C-scan image is generated based on the reflection signals received by scanning the ultrasonic probe along the circumferential direction and the axial direction of the heat exchange tube.

3. The ultrasonic method for evaluating the adhesion status of an impermeable graphite adhesive joint according to claim 2, wherein the C-scan image displays only the signals with a signal intensity equal to or higher than a predetermined value among the reflection signals of the received reflected waves.

4. The ultrasonic method for evaluating the adhesion status of an impermeable graphite adhesive joint according to claim 1, wherein a B-scan image is generated based on the reflection signals received by scanning the ultrasonic probe along the circumferential direction of the heat exchange tube.

5. The ultrasonic method for evaluating the adhesion status of an impermeable graphite adhesive joint according to any one of claims 1 to 4, wherein the signal of the reflected wave from the outer surface of the main body portion of the heat exchange tube located outside the adhesive joint is used as a reference signal.

6. The ultrasonic method for evaluating the adhesion status of an impermeable graphite adhesive joint according to claim 1, wherein the ultrasonic probe is inserted into the through hole from outside the tube sheet.

7. A sleeve is provided in the through hole, the inner surface of the end of the sleeve is inclined so as to face the outer surface of the heat exchange tube, and the tapered portion is formed by the inner surface of the end of the sleeve and the outer surface of the heat exchange tube. The method for evaluating the adhesion status of the bonded portion of impermeable graphite using ultrasonic waves according to claim 1.

8. The method for evaluating the adhesion status of the bonded portion of impermeable graphite using ultrasonic waves according to claim 1, wherein the wall thickness of the heat exchange tube is 5 mm or less.

9. An ultrasonic wave probe that transmits ultrasonic waves toward the bonded portion between the end of the heat exchange tube fixed to the through hole drilled in the tube sheet of the heat exchanger and the through hole and receives the reflected wave, and a signal processing device that processes the reflected signal of the received reflected wave. An apparatus for evaluating the adhesion status of the bonded portion of impermeable graphite using ultrasonic waves, comprising: The heat exchange tube is made of an impermeable graphite material. A tapered portion is formed at the bonded portion by the inner surface of the through hole and the outer surface of the heat exchange tube. The taper angle of the outer surface of the heat exchange tube in the tapered portion is 3° or more and 8° or less. The ultrasonic wave is a low-frequency ultrasonic wave having a nominal frequency of 2.25 MHz or more and 3 MHz or less. Further comprising moving means for inserting and moving the ultrasonic wave probe into the water-immersed heat exchange tube. The ultrasonic wave probe transmits the low-frequency ultrasonic wave in a direction perpendicular to the tube axis direction from the inside of the heat exchange tube toward the tapered portion and receives the reflected wave. The signal processing device is an apparatus for evaluating the adhesion status of the bonded portion of impermeable graphite using ultrasonic waves, which evaluates the adhesion status of the bonded portion based on the reflected signal of the received reflected wave.

10. The ultrasonic wave probe has rotating means for rotating along the circumferential direction of the heat exchange tube. The moving means and the rotating means scan the ultrasonic wave probe along the circumferential direction and the tube axis direction of the tube. The signal processing device is based on the reflected signal received by scanning along the circumferential direction and the tube axis direction of the tube. The apparatus for evaluating the adhesion status of the bonded portion of impermeable graphite using ultrasonic waves according to claim 9, which has a C-scan image generation unit for generating a C-scan image.

11. The rotation means scans the ultrasonic probe along the circumferential direction of the heat exchange tube, and the signal processing device has a B-scan image generation unit that generates a B-scan image based on the reflection signal received by scanning along the circumferential direction of the tube. The apparatus for evaluating the adhesion state of the impermeable graphite adhesive part using ultrasonic waves according to claim 9.

12. A plurality of the through holes and the heat exchange tubes are provided in the heat exchanger, and the signal processing device has a tube sheet diagram generation unit that indicates the adhesion states of the plurality of adhesive parts in a front view of the tube sheet. The apparatus for evaluating the adhesion state of the impermeable graphite adhesive part using ultrasonic waves according to any one of claims 9 to 11.

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