Method and apparatus for evaluating the adhesive condition of adhesive joints in 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 apparatus for evaluating the adhesive condition of adhesive joints in impermeable graphite using ultrasonic waves, and more particularly to a method and apparatus for evaluating the adhesive condition of adhesive joints in impermeable graphite using ultrasonic waves, which transmit ultrasonic waves from an ultrasonic probe toward an adhesive joint between an end of a heat exchange tube fixed in a through-hole drilled in a tube sheet in a heat exchanger and the through-hole, receive reflected waves, and evaluate the adhesive condition of the adhesive joint based on the reflection signal of the received reflected waves. [Background technology]

[0002] Conventionally, methods have been known for inspecting the wall thickness and cracks of heat transfer tubes of heat exchangers by using an immersion ultrasonic method to transmit and receive ultrasonic waves from a probe inside the tube, as described in Patent Documents 1 and 2. However, these methods are intended to detect thinning and cracks in the heat transfer tube itself, and are not intended to inspect or evaluate the bonding condition of the components at the joints between the tube sheet and the heat transfer tube of the heat exchanger.

[0003] Furthermore, the connection (bonded portion) may be tapered, or the heat transfer tube may be made of an attenuating material that makes it difficult for ultrasonic waves to propagate. Therefore, even if the above-mentioned method is applied, it may not be possible to obtain the reflected waves necessary to inspect and evaluate the bonding condition, making it difficult to evaluate the bonding condition using normal ultrasonic inspection. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-3344 [Patent Document 2] International Publication No. WO2012 / 124731 Summary of the Invention [Problem to be solved by the invention]

[0005] In view of the above-described conventional situation, the present invention aims to provide a method and apparatus for evaluating the adhesive condition of an impermeable graphite bond using ultrasonic waves, which can accurately evaluate the adhesive condition of even bonded joints that are difficult to inspect with ultrasonic waves. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, the method for evaluating the adhesive condition of adhesive joints of impermeable graphite using ultrasound according to the present invention is characterized in that it transmits ultrasonic waves from an ultrasonic probe toward the adhesive joint between the end of a heat exchange tube fixed in a through hole drilled in a tube sheet of a heat exchanger and the through hole, receives reflected waves, and evaluates the adhesive condition of the adhesive joint based on the reflected signal of the received reflected waves, in which the heat exchange tube is made of impermeable graphite material with a wall thickness of 5 mm or less, a tapered portion is formed in the adhesive joint 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 at the tapered portion is 3° to 8°, the ultrasonic waves are low-frequency ultrasonic waves with a nominal frequency of 2.25 MHz to 3 MHz, the ultrasonic probe is inserted inside the heat exchange tube which is immersed in water, 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, and the adhesive condition of the adhesive joint is evaluated based on the reflected signal of the received reflected waves.

[0007] The object of inspection in the present invention is the adhesive joint between the end of a heat exchange tube fixed in a through hole drilled in a tube sheet of 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 joint by the inner surface of the through hole and the outer surface of the heat exchange tube. Therefore, when ultrasonic waves are transmitted from inside the tube, the ultrasonic waves are reflected and scattered by the tapered portion (surface), and it may be impossible to obtain the reflected waves required for inspection. Moreover, because the impermeable graphite material is an attenuating material that does not easily transmit ultrasonic waves, the reflected waves that can be received are few (weak) in the first place.

[0008] According to the above configuration, the taper angle of the outer surface of the heat exchanger tube at the tapered portion is 3° to 8°, and the ultrasonic waves are low-frequency ultrasonic waves with a nominal frequency of 2.25 MHz to 3 MHz. Experiments by the inventors have found that, within this taper angle and nominal frequency range, it is possible to evaluate the adhesive condition of the adhesive joint, which is difficult to inspect by ultrasonic testing as described above. Therefore, by inserting the ultrasonic probe into the heat exchanger tube immersed in water and transmitting the low-frequency ultrasonic waves from the inside of the heat exchanger tube toward the tapered portion in a direction perpendicular to the tube axis and receiving the reflected waves, it is possible to accurately evaluate the adhesive condition of the adhesive joint based on the reflected signals of the received reflected waves.

[0009] In the above configuration, it is preferable to generate a C-scan image based on the reflected signals received by scanning the ultrasonic probe along the circumferential direction and the axial direction of the heat exchanger tube, thereby making it possible to easily grasp the overall bonding condition of the bonding portion.

[0010] Furthermore, in this configuration, the C-scan image may display only those reflected signals of the received reflected waves whose signal strength is equal to or greater than a predetermined value. Since only reflected signals from areas where the adhesion is insufficient (poorly adhered areas) are displayed, the adhesion status can be more easily determined and inspection accuracy can be improved.

[0011] In the above configuration, the ultrasonic probe may be scanned along the circumferential direction of the heat exchange tube, and a B-scan image may be generated based on the received reflected signal.

[0012] In any of the above configurations, a signal of a reflected wave from the outer surface of the main body of the heat exchanger tube located outside the bonded portion may be used as a reference signal, and the bonded state may be evaluated based on a signal obtained by standardizing the reflected signal of the received reflected wave using the reference signal. This makes it possible to standardize the relative echo height of the bonded portion, reduce errors due to individual differences in the heat exchanger tube, and improve inspection accuracy. In the above configuration, the ultrasonic probe may be inserted into the through hole from outside the tube sheet.

[0013] Furthermore, a sleeve may be provided in the through hole, and the inner surface of the end of the sleeve may be inclined toward the outer surface of the heat exchanger tube, so that the tapered portion is formed by the inner surface of the end of the sleeve and the outer surface of the heat exchanger tube. Even with such a configuration, the adhesive condition can be evaluated with the same accuracy as described above.

[0014] Furthermore, in the above configuration, the thickness of the tapered portion is, for example, 2 mm or more and 5 mm or less.

[0015] In order to achieve the above-mentioned object, the device for evaluating the adhesive condition of adhesive joints of impermeable graphite using ultrasound according to the present invention is characterized in that it is configured to include an ultrasonic probe that transmits ultrasonic waves toward the adhesive joint between the end of a heat exchange tube fixed in a through hole drilled in a tube sheet of a heat exchanger and the through hole and receives reflected waves, and a signal processing device that processes reflected signals of the received reflected waves, wherein the heat exchange tube is made of impermeable graphite material with a wall thickness of 5 mm or less, a tapered portion is formed in the adhesive joint by the inner surface of the through hole and the outer surface of the heat exchange tube, and the taper angle of the outer surface of the heat exchange tube at the tapered portion is 3° to 8°, the ultrasonic waves are low-frequency ultrasonic waves with a nominal frequency of 2.25 MHz to 3 MHz, and the device further includes a moving means for inserting and moving the ultrasonic probe inside the heat exchange tube that is immersed in water, the ultrasonic probe transmits the low-frequency ultrasonic waves from the inside of the heat exchange tube toward the tapered portion in a direction perpendicular to the tube axial direction and receives the reflected waves, and the signal processing device evaluates the adhesive condition of the adhesive joint based on the reflected signals of the received reflected waves.

[0016] In the above configuration, the ultrasonic probe may have a rotating means for rotating the heat exchange tube in a circumferential direction, the moving means and the rotating means may cause the ultrasonic probe to scan in the circumferential direction and the axial direction, and the signal processing device may have a C-scan image generating unit that generates a C-scan image based on the reflected signal received by scanning in the circumferential direction and the axial direction.

[0017] In addition, in the above configuration, the rotating means may cause the ultrasonic probe to scan along the circumferential direction of the heat exchanger tube, and the signal processing device may have a B-scan image generating unit that generates a B-scan image based on the reflected signal received by scanning along the circumferential direction of the tube.

[0018] In addition, in any of the above configurations, the heat exchanger may be 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 displays the bonding status of the plurality of bonding portions on a front view of the tube sheet. [Effects of the Invention]

[0019] According to the features of the method and apparatus for evaluating the adhesive condition of adhesive joints of impermeable graphite using ultrasonic waves according to the present invention, it is now possible to accurately evaluate the adhesive condition of adhesive joints even in adhesive joints that are difficult to inspect with ultrasonic waves.

[0020] Other objects, configurations and effects of the present invention will become apparent from the following detailed description of the preferred embodiments of the present invention. [Brief explanation of the drawings]

[0021] [Figure 1] 1A and 1B are diagrams showing an adhesive state evaluation device according to the present invention, in which FIG. 1A is a schematic diagram of the entire device, and FIG. 1B is a block diagram of a signal processing device. [Figure 2] FIG. 1 is a schematic diagram illustrating the behavior of ultrasonic waves. [Figure 3] FIG. 2 is a schematic diagram showing an adhesive portion and a probe. [Figure 4] 4(a) and 4(c) are schematic diagrams showing the heat exchanger to be inspected, where (a) is a partial schematic diagram, (b) is a partial enlarged view of part A in FIG. 4(a), and (c) is a partial enlarged view of part B in FIG. 4(b). [Figure 5] This is a graph showing an example of a signal waveform obtained by irradiating an ultrasonic wave into a 5 mm thick impermeable graphite tube and receiving the reflected wave. (a) is a schematic diagram of ultrasonic flaw detection, (b) is the actual waveform at 2.25 MHz, (c) is the simulated waveform at 2.25 MHz, (d) is the actual waveform at 5 MHz, (e) is the simulated waveform at 5 MHz, (f) is the actual waveform at 10 MHz, and (g) is the simulated waveform at 10 MHz. [Figure 6]This is a graph showing an example of a simulated waveform obtained by irradiating an ultrasonic wave into a 3 mm thick tube made of impermeable graphite material and receiving the reflected wave. (a) is a schematic diagram of ultrasonic flaw detection in a straight pipe section, (b) is a simulated waveform at 2.25 MHz in a straight pipe section, (c) is a simulated waveform at 5 MHz in the same section, (d) is a simulated waveform at 10 MHz in the same section, (e) is a schematic diagram of ultrasonic flaw detection in a tapered section, (f) is a simulated waveform at 2.25 MHz in a tapered section, (g) is a simulated waveform at 5 MHz in the same section, and (h) is a simulated waveform at 10 MHz in the same section. [Figure 7] (a) is a schematic diagram of ultrasonic flaw detection, and (b) is a diagram showing an ultrasonic waveform. [Figure 8] This is a graph showing an example of a simulated waveform obtained by irradiating an ultrasonic wave onto a test specimen made of an impermeable graphite tube with a taper angle of 0° and a wall thickness of 3 mm, and receiving the reflected wave. (a) is a schematic diagram of ultrasonic flaw detection, (b) is a simulated waveform at 0.5 MHz, (c) is a simulated waveform at 1 MHz, (d) is a simulated waveform at 2.25 MHz, (e) is a simulated waveform at 3 MHz, (f) is a simulated waveform at 5 MHz, and (g) is a simulated waveform at 10 MHz. [Figure 9] This is a view equivalent to Figure 8 of a test specimen made of an impermeable graphite tube with a taper angle of 2.69°. [Figure 10] This is a view equivalent to Figure 8 of a test specimen made of an impermeable graphite tube with a taper angle of 3°. [Figure 11] This is a view equivalent to Figure 8 of a test specimen made of an impermeable graphite tube with a taper angle of 5.38°. [Figure 12] This is a view equivalent to Figure 8 of a test specimen made of an impermeable graphite tube with a taper angle of 8°. [Figure 13] This is a view equivalent to Figure 8 of a test specimen made of an impermeable graphite tube with a taper angle of 10.76°. [Figure 14] 1 shows an example of test results for a simulated specimen, where (a) is a C-scan image, and (b) and (c) are B-scan images. [Figure 15]The figures show the echo height display of C-scan images of an example of test results for a simulated test specimen, where (a) is the case when the adhesive filling amount is 50%, (b) is the case when the adhesive filling amount is 70%, and (c) is the case when the adhesive filling amount is 100%. [Figure 16] FIG. 16 is a diagram showing the C-scan image of FIG. 15 in thickness. [Figure 17] FIG. 10 is a diagram showing a tube sheet diagram of an example of test results. [Figure 18] FIG. 10 is a schematic diagram showing a connection portion in which a sleeve is attached to a through hole in a tube sheet. [Figure 19] This is a C-scan image of a simulated test specimen in which a sleeve is attached to a through-hole in a tube sheet, with the wall thickness displayed. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention will now be described in more detail with reference to the accompanying drawings where appropriate. (Evaluation device 1 overview) As shown in FIG. 1(a), the bonding status evaluation device 1 according to the present invention mainly comprises an ultrasonic probe 2 (hereinafter abbreviated as "probe 2") that transmits ultrasonic waves toward the bonding portion 101 of the heat exchanger 100 and receives reflected waves, a signal processing device 3 that processes the reflected signals of the received reflected waves, a probe pulling device as a moving means 4 that moves the probe 2 through the heat exchange tube 120 (hereinafter abbreviated as "tube 120") in the tube axis direction X along the tube axis Ax, and a water supply means 5 that includes a tank 5a that supplies water W to the tube 120, a high-pressure pump 5b, and a filter 5c.

[0023] (Ultrasonic behavior) In the bonding condition evaluation method according to the present invention, ultrasonic waves are transmitted and received from within the tube 120 toward the bonded portion 101 using a water immersion method, and the bonding condition of the bonded portion 101 is evaluated based on the reflected signal of the received reflected wave. As shown in FIG. 2 , when the tube sheet 110 and the tube 120 are properly bonded with adhesive G (healthy portion), most of the incident wave Iw propagating within the tube 120 propagates (passes) through the adhesive G and propagates to the tube sheet 110 as a transmitted wave Tw, while a portion is reflected at the bonding interface and propagates through the tube 120 as a reflected wave Rw. On the other hand, when the adhesive G is insufficient and the tube sheet 110 and the tube 120 are not bonded (poorly bonded portion), a gap K is generated between the tube sheet 110 and the tube 120. Therefore, the incident wave Iw propagating within the tube 120 does not generate a transmitted wave Tw due to the air in the gap K, and almost all of it is reflected and propagates through the tube 120 as a reflected wave Rw. In this way, the difference in the behavior of the ultrasonic waves makes it possible to evaluate the bonding condition (situation).

[0024] (Signal Processing Device 3) The signal processing device 3 is configured by, for example, a personal computer, and as shown in FIG. 1(b), it controls a pulser 31 via a control unit 30a to generate an ultrasonic pulse from the probe 21 of the probe 2. The transmitted ultrasonic pulse is reflected by the adhesive part 101, and the reflected wave is received by the probe 21. The received reflected signal (reflected wave) is amplified by a preamplifier 32 and received by a receiver 33, and converted into a digital signal by an A / D converter 35 after noise has been removed by a filter 34. The signal is then processed by the signal processing device 3 and displayed on a display 6.

[0025] As shown in FIG. 1(b), the signal processing device 3 generally includes a control unit 30a that controls the generation of ultrasonic pulses from the probe 21, and an image generation unit 30b that processes reflected signals received along with scanning position data from a counter 7 that detects signals indicating the scanning position and rotational position (orientation) of the probe 21, and generates various images. The image generation unit 30b includes a B-scan image generation unit 30b1 that generates B-scan images such as those shown in FIGS. 14(b) and 14(c), a C-scan image generation unit 30b2 that generates C-scan images such as those shown in FIGS. 14(a), 14(a), 14(b), and 14(c), and a tubesheet diagram generation unit 30b3 that displays the bonding state of the bonding portion 101 on a front view of the tubesheet 110, as shown in FIG. 17. The scanned images generated by the image generation unit 30b are displayed on a display 6. Although this signal processing device 3 is configured using a personal computer, it is also possible to use a flaw detection device 10 having a signal processing unit with similar functions, a pulser 31, a preamplifier 32, a receiver 33, a filter 34, an A / D converter 35, a display 6, and a counter 7.

[0026] (Ultrasound probe 2) 3, the probe 2 generally includes a probe 21 housed in a housing 20 and configured to transmit and receive ultrasonic waves, a reflecting mirror 22 that reflects the ultrasonic waves transmitted from the probe 21 in a direction (pipe diameter direction Y) perpendicular to the pipe axis direction X, and a rotary turbine 23 that rotates the reflecting mirror 22 along the pipe circumferential direction C. The rotary turbine 23 is rotatably mounted relative to the housing 20 via a bearing or the like (not shown).

[0027] (Summary of adhesive part 101) The heat exchanger 100 to be inspected in the present invention is a multi-tube heat exchanger as shown in Figures 4(a) and 4(b), in which end portions 122 of heat exchange tubes 120 are inserted and fixed into a plurality of through-holes 111 drilled in a tube sheet 110, thereby forming a bonding portion 101. As shown in Figure 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. An adhesive G is applied to these tapered surfaces 113, 123, and a tapered portion 102 is formed in the bonding portion 101 by adhering them together.

[0028] (Tapered part 102) As described above, the tapered portion 102 has a tapered shape with the tapered surfaces 113 and 123 facing each other. However, due to an insufficient amount of adhesive G applied or the inclusion of air bubbles, the adhesive G may be locally insufficient on the bonding surface (tapered portion 102), resulting in a poorly bonded area. This poor bonding may lead to a risk of fluid leakage. The present invention evaluates the bonding condition of the tapered surfaces 113 and 123 in the tapered portion 102 using immersion ultrasonic testing. As will be described in detail later, the taper angle θ of the outer surface (tapered surface 123) of the tube 120 in the bonding portion 101 (tapered portion 102), which is the subject of testing in the present invention, is between 3° and 8°. This taper angle θ refers to the angle between the tube axis direction X of the tube 120 and the tapered surface 123 of the tube 120. Furthermore, the wall thickness of the heat exchanger tube 120 in the tapered portion 102 is a maximum of 5 mm and a minimum of 2 mm.

[0029] (Heat exchange tube 120) The tube sheet 110 and the heat exchanger tubes 120 are made of impermeable graphite. This material has high corrosion resistance and thermal conductivity, and is therefore used in heat exchangers in, for example, pharmaceutical manufacturing processes. However, impermeable graphite is a highly attenuating material that attenuates ultrasonic waves more than general steel materials. In particular, the effect of attenuation increases as the frequency increases, limiting the ultrasonic frequencies that can be used for inspection.

[0030] (ultrasonic frequency) Here, ultrasonic waves of 2.25 MHz, 5 MHz, and 10 MHz were incident on a test tube made of impermeable graphite material with a wall thickness of 5 mm in the direction Y perpendicular to the tube axis direction X. The signal waveforms of the reflected waves are shown in Figure 5(b), (d), and (f), and the simulation results corresponding to these actual waveforms are shown in Figure 5(c), (e), and (g). According to experiments conducted by the inventors, the results shown in Figure 5 indicate that at frequencies above 5 MHz, multiple reflected waves (echoes) after the second bottom echo fall below the noise level, making signal detection difficult. The dotted lines in the figures indicate the approximate noise levels measured at each frequency, and this also applies to the figures described below.

[0031] Moreover, as described above, the adhesive bond 101 has a tapered shape. Here, Fig. 6(b)-(d) show 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 pipe section of the test tube made of impermeable graphite material with a wall thickness of 3 mm, as shown in Fig. 6(a). Fig. 6(f)-(h) show the simulation results for the tapered section of the same test tube with a wall thickness of 3 mm. The results shown in Fig. 6(e) reveal that, because the incident wave is not perpendicular to the adhesive interface (tapered surface) at the tapered section (inclined section), the reflected signal of the reflected wave received is weaker than that at a straight pipe section (taper angle 0°). Furthermore, at the tapered section, at frequencies above 5 MHz, the reflected wave itself falls below the noise level, making it difficult to detect the reflected signal.

[0032] As such, it is clear that there is an upper limit to the usable frequency for evaluating the adhesive condition of the adhesive joint 101, which is the subject of inspection in the present invention, and that it is difficult to evaluate the adhesive condition using conventional ultrasonic flaw detection.

[0033] Furthermore, as mentioned above, the wall thickness of the heat exchanger tube 120 at the tapered portion 102 is a maximum of 5 mm and a minimum of 2 mm. In order to evaluate the adhesive condition of the adhesive interface using ultrasound, it is necessary to separate the reflected signal (S) from the surface and the reflected signal (B1) from the adhesive interface in terms of time. As shown in Figure 7, the time interval between the reflected signal (S) of the ultrasound and the reflected signal (B1) from the adhesive interface is 2T / C, which is 1.46 μs for a plate thickness of 2 mm and a sound speed of 2740 m / s.

[0034] [Table 1]

[0035] As shown in Table 1, for the same wavenumber, the lower the frequency, the longer the duration of the ultrasonic signal. At 2.25 MHz, 5 MHz, and 10 MHz, the duration of the ultrasonic signal is relatively long, so even if a narrowband probe with poor time resolution is used and the wavenumber is three waves, the time interval between the reflected signal (S) and the reflected signal (B1) will not be exceeded. On the other hand, at 1 MHz, the time interval between the reflected signal (S) and the reflected signal (B1) will be exceeded, and these signals cannot be separated, not only when a narrowband probe with a wavenumber of about three waves is used, but also when a wideband probe with a wavenumber of 1.5 waves is used.

[0036] As described above, in order to evaluate the adhesive condition of the adhesive joint 101, which is the target of inspection in the present invention and has a thin plate thickness, there is a lower limit to the usable frequency, and it is clear that it is difficult to evaluate the adhesive condition using 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 transducer of the probe 21. Normally, the element size is increased to lower the frequency, but size restrictions also pose a lower limit to the frequency.

[0037] Therefore, the inventors simulated the reflected signals of the reflected waves by irradiating low-frequency ultrasonic waves with nominal frequencies of 0.5 MHz, 1 MHz, 2.25 MHz, 3 MHz, 5 MHz, and 10 MHz onto each test specimen in tube 120 made of impermeable graphite material, with taper angles θ of tapered surface 123 of tube 120 in tapered portion 102 (bonded portion 101) of 0°, 2.69°, 3°, 5.38°, 8°, and 10.76°. The simulation results are shown in Figures 8 to 13.

[0038] In the case of a taper angle of 0° shown in Figure 8, when the nominal frequency was 2.25 MHz or higher, the reflected signal from the interface (bottom surface of the test piece) was above the noise level and could be distinguished (separated) from the incident wave (reflected signal from the surface). On the other hand, when the nominal frequency was 0.5 MHz, it was impossible to distinguish (separate) the reflected and incident wave signals. Furthermore, when the nominal frequency was 1 MHz, the first reflected echo from the interface rose before the incident wave (transmitted pulse) dropped below the noise level, making it difficult to distinguish between the incident and reflected waves. Note that the results for the nominal frequency of 0.5 MHz were similar for all other test pieces. The results for the nominal frequency of 1 MHz were also similar for the test pieces with nominal frequencies of 2.69°, 3°, and 5.38°.

[0039] In the case of the taper angle of 2.69° shown in Figure 9, when the nominal frequency was between 2.25 MHz (1 MHz) and 5 MHz, the reflected signal from the interface (bottom surface of the test piece) was greater than the noise level and could be distinguished (separated) from the incident wave. However, when the nominal frequency was 10 MHz, the reflected signal from the interface became smaller than the noise level. The results for a nominal frequency of 10 MHz were similar for test pieces with a nominal frequency of 3°, 5.38°, 8°, and 10.76°.

[0040] For the taper angles of 3° and 5.38° shown in Figures 10 and 11, at nominal frequencies of 2.25 MHz (1 MHz) and 3 MHz, the reflected signal from the interface (bottom surface of the test specimen) was greater than the noise level and could be distinguished (separated) from the incident wave. However, at nominal frequencies of 5 MHz or higher, the reflected signal from the interface became smaller than the noise level. The results for nominal frequencies of 5 MHz or higher were similar for test specimens of 5.38°, 8°, and 10.76°.

[0041] In the case of a taper angle of 8° shown in Figure 12, when the nominal frequency was 2.25 MHz and 3 MHz, the reflected signal from the interface (bottom surface of the test piece) was greater than the noise level, making it possible to distinguish (separate) it from the incident wave. On the other hand, when the nominal frequency was 1 MHz or less, the strength of the reflected signal of the reflected wave was smaller than that of the above test piece, making it impossible to distinguish (separate) it from the incident wave. Furthermore, when the nominal frequency was 5 MHz or more, the reflected signal from the interface became smaller than the noise level.

[0042] Furthermore, in the case of a taper angle of 10.76° shown in Figure 13, only when the nominal frequency was 2.25 MHz, the reflected signal from the interface (bottom surface of the test piece) was greater than the noise level, making it possible to distinguish (separate) it from the incident wave.

[0043] In this way, it was found that by using low-frequency ultrasound with a nominal frequency of 2.25 MHz or more and 3 MHz or less, it is possible to evaluate the adhesive state based on the reflected signal of the received reflected wave at adhesive joint 101 of tube 120 made of impermeable graphite material, in which the taper angle of tapered surface 123 in tapered portion 102 is 3° or more and 8° or less.

[0044] (Adhesion status evaluation procedure) Next, the procedure for evaluating the adhesion state according to the present invention will be described. First, the probe 2 is inserted into the through-hole 111 from outside the tube sheet 110, and then moved within the tube sheet 110 by the probe pulling device 4, passing the bonded portion 101 (the tapered portion 102) and reaching the straight pipe portion 124 of the tube 120 located outside the bonded portion 101 (inside the tube sheet 110). Then, in the straight pipe portion 124, ultrasonic waves are transmitted from within the tube 120 in a direction Y (diameter direction) perpendicular to the tube axis direction X, and the reflected waves from the tube 120 are received and used as a reference signal. This standardizes the relative echo height of the bonded portion 101, reducing errors due to individual differences in the tube 120 and improving inspection accuracy. The gate level during inspection is determined based on the echo height of this reference signal.

[0045] Next, the probe 2 is moved to the vicinity of the bonded portion 101, and the probe 2 is rotated in the circumferential direction C of the tube 120 and moved in the axial direction X by the probe pulling device 4 and water supply means 5 to scan the bonded portion 101. The signal processing device 3 then processes the received reflected signal together with the scanning position data of the counter 7 that detected the scanning position and rotational position (orientation) of the probe 21, and the image generating unit 30b generates an image and displays it on the display 6.

[0046] For example, the C-scan image generator 30b2 generates a C-scan image as shown in FIG. 14(a) and displays it on the display 6. The C-scan image is expanded along the tube axis direction X and the tube circumferential direction C, with the inner surface 110x of the tube sheet 110 as the reference (0 mm). FIG. 14(a) shows an image generated using the thickness value display. The thickness value display is a display obtained by signal processing with the gate level for detecting the reflected signal set to, for example, 50% of the healthy portion. As described above, in the poorly bonded area, the incident wave is almost entirely reflected by the air at the interface (gap K), resulting in a strong reflected signal. As shown in FIG. 15, by displaying a reflected signal with a certain intensity or higher (thickness value display), the range (portion) of the poorly bonded area can be easily identified and easily distinguished from noise. Furthermore, as shown in FIG. 14(a), the position of the tapered portion 102 can also be easily determined. In this way, the adhesive condition of the adhesive joint 101 can be accurately evaluated based on the reflected signal.

[0047] Since multiple tubes 120 are bonded to the tube sheet 110, the above-described process is repeated for each tube 120. When the process is completed, the tube sheet diagram generating unit 30b3 generates and displays a front view of the tube sheet 120 as shown in Fig. 17 based on the reflected signals of each tube 120. This makes it easy to grasp the extent and range of poor bonding of the tubes 120 across the entire tube sheet 110 (heat exchanger 100).

[0048] Finally, the possibility of further embodiments of the present invention will be described. Note that the same reference numerals are used to designate the same components as those in the above-described embodiment. In the above embodiment, the C-scan image generating unit 30b2 generates and displays a C-scan image with a thickness value display as shown in Fig. 15. However, the display of the C-scan image is not limited to this, and it may be an echo height display with a lower gate level (for example, 0% of a healthy area) and signal processing, as shown in Fig. 16. However, the thickness value display of the above embodiment is superior in terms of visibility.

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

[0050] In the above embodiment, the tube 120 was bonded to the through-hole 111 of the tube sheet 110. However, even when a sleeve 130 is provided, as shown in Fig. 18, it is possible to evaluate the bonding condition of the bonded portion 101' between the tube 120 and the sleeve 130 (the tapered portion 102 consisting of the tapered surface 123 of the tube 120 and the tapered surface 133 of the sleeve 130). It is also possible to inspect the bonded portion between the straight pipe portion 135 of the sleeve 130 and the through-hole 111 as well as the tapered bonded portion 101', and generate and display the results as a C-scan image with a wall thickness value display, as shown in Fig. 19, for example. [Explanation of symbols]

[0051] 1: Adhesion status evaluation device, 2: Ultrasonic probe (probe), 3: Signal processing device, 4: Moving means (probe tension device), 5: Water supply means, 5a: Tank, 5b: High-pressure pump, 5c: Filter, 6: Display, 7: Counter, 10: Flaw detection device, 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, 1 01, 101': adhesive part, 102: tapered part (adhesive surface), 110: tube sheet, 110x: inner surface, 111: through hole, 112: inner surface, 113: tapered surface, 120: heat exchange tube (tube, heat transfer tube), 120a: inside of tube, 121: outer surface, 122: end, 123: tapered surface, 124: straight tube section, 130: sleeve, 133: tapered surface, 135: straight tube section, Ax: tube axis, B1: reflected signal at adhesive surface, C: tube circumferential direction, G: adhesive, Iw: incident wave, K: air gap, P: ultrasonic wave, S: reflected signal at surface, Rw: reflected wave, Tw: transmitted wave, W: water, X: tube axial direction, Y: tube radial direction, θ: taper angle

Claims

1. A method for evaluating the adhesive condition of an adhesive joint of impermeable graphite using ultrasonic waves, the method comprising transmitting ultrasonic waves from an ultrasonic probe toward an adhesive joint between an end of a heat exchange tube fixed in a through-hole drilled in a tube sheet of a heat exchanger and the through-hole, receiving reflected waves, and evaluating the adhesive condition of the adhesive joint based on a reflection signal of the received reflected waves, The heat exchange tube is made of an impermeable graphite material having a wall thickness of 5 mm or less, a tapered portion is formed in the adhesive 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 at the tapered portion is equal to or greater than 3° and equal to or less than 8°; The ultrasonic waves are low-frequency ultrasonic waves having a nominal frequency of 2.25 MHz or more and 3 MHz or less, Inserting the ultrasonic probe into the heat exchange tube immersed in water; The low-frequency ultrasonic wave is transmitted from the inside of the heat exchange tube toward the tapered portion in a direction perpendicular to the tube axis direction, and a reflected wave is received. A method for evaluating the adhesive condition of an adhesive joint of impermeable graphite using ultrasound, which evaluates the adhesive condition of the adhesive joint based on the reflected signal of the received reflected wave.

2. 2. A method for evaluating the adhesive condition of adhesive joints of impermeable graphite using ultrasound according to claim 1, wherein the ultrasonic probe is scanned along the circumferential direction and the axial direction of the heat exchange tube, and a C-scan image is generated based on the received reflected signals.

3. 3. A method for evaluating the adhesive condition of adhesive joints in impermeable graphite using ultrasound as described in claim 2, wherein the C-scan image displays only the reflected signals of the received reflected waves whose signal strength is equal to or greater than a predetermined value.

4. 2. A method for evaluating the adhesive condition of adhesive joints of impermeable graphite using ultrasound according to claim 1, wherein the ultrasonic probe is scanned along the circumferential direction of the heat exchange tube, and a B-scan image is generated based on the received reflected signal.

5. 5. A method for evaluating the adhesive condition of an adhesive joint of impermeable graphite using ultrasound according to any one of claims 1 to 4, wherein a signal of a reflected wave from the outer surface of the main body of the heat exchanger tube located outside the adhesive joint is used as a reference signal, and the adhesive condition is evaluated based on a signal obtained by standardizing the reflected signal of the received reflected wave using the reference signal.

6. 2. The method for evaluating the adhesive state of adhesive joints of impermeable graphite using ultrasonic waves according to claim 1, wherein the ultrasonic probe is inserted into the through-hole from outside the tube sheet.

7. A method for evaluating the adhesive condition of adhesive joints of impermeable graphite using ultrasound, as described in claim 1, wherein a sleeve is provided in the through hole, the inner surface of the end of the sleeve is inclined toward 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.

8. An ultrasonic probe for transmitting ultrasonic waves to a bonding portion between an end of a heat exchange tube fixed in a through hole drilled in a tube sheet of a heat exchanger and the through hole and for receiving reflected waves, and a signal processing device for processing a reflected signal of the received reflected waves, The heat exchange tube is made of an impermeable graphite material having a wall thickness of 5 mm or less, a tapered portion is formed in the adhesive 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 at the tapered portion is equal to or greater than 3° and equal to or less than 8°; The ultrasonic waves are low-frequency ultrasonic waves having a nominal frequency of 2.25 MHz or more and 3 MHz or less, a moving means for inserting and moving the ultrasonic probe into the heat exchange tube immersed in water; the ultrasonic probe transmits the low-frequency ultrasonic waves from inside the heat exchange tube toward the tapered portion in a direction perpendicular to the tube axis direction and receives reflected waves; The signal processing device is an ultrasonic bonding condition evaluation device for evaluating the bonding condition of the adhesive joint of impermeable graphite based on the reflected signal of the received reflected wave.

9. 9. The device for evaluating the bonding status of adhesive joints of impermeable graphite using ultrasound as set forth in claim 8, wherein the ultrasonic probe has a rotating means for rotating the ultrasonic probe in the circumferential direction of the heat exchange tube, the moving means and the rotating means cause the ultrasonic probe to scan in the circumferential direction and the axial direction of the tube, and the signal processing device has a C-scan image generating unit that generates a C-scan image based on the reflected signal received by scanning in the circumferential direction and the axial direction of the tube.

10. 10. The device for evaluating the adhesive condition of adhesive joints of impermeable graphite using ultrasound as described in claim 9, wherein the rotating means causes the ultrasonic probe to scan along the circumferential direction of the heat exchange tube, and the signal processing device has a B-scan image generating unit that generates a B-scan image based on the reflected signal received by scanning along the circumferential direction of the tube.

11. The device for evaluating the adhesive status of adhesive joints of impermeable graphite using ultrasound according to any one of claims 8 to 10, wherein the heat exchanger is provided with a plurality of the through holes and the heat exchange tubes, and the signal processing device has a tube sheet diagram generation unit that displays the adhesive status of the plurality of adhesive joints on a front view of the tube sheet.

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