Ultrasonic inspection method and device

Abstract

To provide an ultrasonic inspection method and device capable of measuring the plate thickness of an inner tank of a double-structure container even when the plate thickness of the inner tank varies, and also capable of shortening working time.SOLUTION: In an ultrasonic inspection method using an ultrasonic probe 11 disposed on an outer surface of an outer tank 5 of a double-structure container 2, a time interval ΔT of a plurality of ultrasonic pulses received before a predetermined time elapses is acquired, and first, second, and third ultrasonic pulses received after the predetermined time elapses and having intensities greater than a predetermined value are selected. When a time interval ΔTa between the first and second ultrasonic pulses is smaller than ΔT, ΔT'=ΔTa is set. When the time interval ΔTa is equal to ΔT and a time interval ΔTb between the second and third ultrasonic pulses is smaller than ΔT, ΔT'=ΔTa+ΔTb is set. When the time interval ΔTa is equal to ΔT and the time interval ΔTb is equal to ΔT, ΔT'=ΔTa or ΔTb is set. A plate thickness of an inner tank 3 is calculated on the basis of the time interval ΔT'.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to an ultrasonic inspection method and device for measuring the wall thickness of an inner vessel of a double-structure container using an ultrasonic probe placed on the outer surface of the outer vessel, with an ultrasonic transmitting material filled between the outer vessel and the inner vessel. [Background technology]

[0002] In various industrial fields, inspections are performed to measure the thickness of structures to evaluate their integrity. Among large structures, there are those called double-structure vessels. A double-structure vessel has an inner vessel that contains a substance and an outer vessel that covers the outside of the inner vessel at a distance. The outer vessel is intended, for example, to keep the substance contained in the inner vessel warm or to prevent the substance from being released if the inner vessel is damaged. One ultrasonic inspection method for measuring the thickness of the inner vessel of a double-structure vessel uses an ultrasonic probe placed on the inner surface of the inner vessel. This method requires the removal of the substance contained in the inner vessel, which increases the work time.

[0003] Patent Document 1 discloses an ultrasonic inspection method for measuring the wall thickness of the inner vessel of a double-structured container, in which an ultrasonic probe is placed on the outer surface of the outer vessel while an ultrasonic transmitting material (e.g., water) is filled between the outer and inner vessels of the double-structured container. In this method, since an ultrasonic transmitting material is filled between the outer and inner vessels of the double-structured container, ultrasonic pulses transmitted from the ultrasonic probe are transmitted not only to the outer vessel but also to the inner vessel. Furthermore, unlike when the ultrasonic probe is placed on the inner surface of the inner vessel, there is no need to remove the material contained in the inner vessel, which reduces the work time.

[0004] The ultrasonic probe in Patent Document 1 transmits ultrasonic pulses toward the outer and inner tanks, and then receives multiple ultrasonic pulses that travel along different propagation paths. The multiple ultrasonic pulses received by the ultrasonic probe include multiple ultrasonic pulses that have been reflected once or multiple times from the inner surface of the outer tank (in other words, multiple ultrasonic pulses that have traveled back and forth within the plate of the outer tank once or multiple times), an ultrasonic pulse that has been reflected once from the outer surface of the inner tank (in other words, an ultrasonic pulse that has traveled back and forth once within the plate of the outer tank and between the outer and inner tanks), and an ultrasonic pulse that has been reflected once from the outer surface of the inner tank (in other words, an ultrasonic pulse that has traveled back and forth once within the plate of the outer tank, between the outer and inner tanks, and within the plate of the inner tank).

[0005] In the method of Patent Document 1, for example, an ultrasonic pulse reflected once from the outer surface of the inner tank and an ultrasonic pulse reflected once from the inner surface of the inner tank are selected from among multiple ultrasonic pulses received by an ultrasonic probe, and the time interval ΔT' between them is obtained. More specifically, for example, the outer and inner tanks are made of the same material, but the thicknesses of the outer and inner tanks are different. Therefore, it is assumed that the time interval ΔT between multiple ultrasonic pulses reflected once or multiple times from the inner surface of the outer tank is different from the time interval ΔT' described above. Then, multiple ultrasonic pulses reflected once or multiple times from the inner surface of the outer tank are selected, and the time interval ΔT between them is obtained. Then, an ultrasonic pulse reflected once from the outer surface of the inner tank and an ultrasonic pulse reflected once from the inner surface of the inner tank are selected because they do not belong to the multiple ultrasonic pulses received within the time interval ΔT, and the time interval ΔT' between them is obtained. The thickness of the inner tank is then calculated based on the time interval ΔT' described above. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-300521 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the method of Patent Document 1 has the following problem. For example, if the thickness of the inner tank changes due to corrosion of the inner tank, and the time interval ΔT and the time interval ΔT' become the same, it is not possible to select the ultrasonic pulse reflected once by the outer surface of the inner tank and the ultrasonic pulse reflected once by the inner surface of the inner tank, and it is not possible to obtain the time interval ΔT' between them. Therefore, it is not possible to measure the thickness of the inner tank.

[0008] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide an ultrasonic inspection method and apparatus that can measure the thickness of the inner tank of a double-structure container even if the thickness of the inner tank varies, and that can shorten the operation time. [Means for solving the problem]

[0009] In order to achieve the above object, a representative aspect of the present invention is an ultrasonic inspection method for measuring the thickness of an inner tank using an ultrasonic probe placed on the outer surface of an outer tank in a state in which an ultrasonic transmitting material is filled between the outer and inner tanks of a double-structure container, the method comprising: transmitting ultrasonic pulses toward the outer and inner tanks using the ultrasonic probe; receiving a plurality of ultrasonic pulses having different propagation paths using the ultrasonic probe; acquiring a time interval ΔT between the plurality of ultrasonic pulses received by the ultrasonic probe before a predetermined time has elapsed since the transmission timing of the ultrasonic probe; selecting first, second, and third ultrasonic pulses received by the ultrasonic probe after the predetermined time has elapsed since the transmission timing of the ultrasonic probe and having intensities greater than a predetermined value; and determining the time interval ΔTa between the first ultrasonic pulse and the second ultrasonic pulse as The time interval ΔTa is compared with the time interval ΔT, and if the time interval ΔTa is smaller than the time interval ΔT, the time interval ΔTa is obtained as the time interval ΔT' corresponding to the thickness of the inner tank. If the time interval ΔTa is the same as the time interval ΔT, the time interval ΔTb between the second ultrasonic pulse and the third ultrasonic pulse is compared with the time interval ΔT. If the time interval ΔTa is the same as the time interval ΔT and the time interval ΔTb is smaller than the time interval ΔT, the sum of the time intervals ΔTa and ΔTb is obtained as the time interval ΔT'. If the time interval ΔTa is the same as the time interval ΔT and the time interval ΔTb is the same as the time interval ΔT, the time interval ΔTa or ΔTb is obtained as the time interval ΔT', and the thickness of the inner tank is calculated based on the obtained time interval ΔT'. [Effects of the Invention]

[0010] According to the present invention, the thickness of the inner tank of a double-structure container can be measured even if the thickness of the inner tank varies, and the working time can be reduced. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram illustrating an overview of an ultrasonic inspection method according to an embodiment of the present invention. [Figure 2]1 is a block diagram showing the configuration of an ultrasonic inspection device according to an embodiment of the present invention. [Figure 3] 1 is a diagram showing a specific example of a propagation path of an ultrasonic pulse in one embodiment of the present invention. [Figure 4] FIG. 10 is a diagram showing a specific example of data according to an embodiment of the present invention. [Figure 5] FIG. 10 is a diagram showing a specific example of data after a predetermined time has elapsed in one embodiment of the present invention, showing a case where the plate thickness of the inner tank is greater than the plate thickness of the outer tank. [Figure 6] FIG. 10 is a diagram showing a portion of a double-structure container according to an embodiment of the present invention, and also showing a specific example of data after a predetermined time has elapsed, in which the plate thickness of the inner tank is the same as the plate thickness of the outer tank. [Figure 7] FIG. 10 is a diagram showing a portion of a double-structure container according to an embodiment of the present invention, and also showing a specific example of data after a predetermined time has elapsed, in which the plate thickness of the inner tank is smaller than the plate thickness of the outer tank. [Figure 8] 1 is a flowchart showing the procedure of an ultrasonic inspection method according to an embodiment of the present invention. [Figure 9] FIG. 10 is a block diagram showing the configuration of an ultrasonic inspection device according to a modified example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] An embodiment of the present invention will be described with reference to the drawings.

[0013] FIG. 1 is a diagram showing an overview of the ultrasonic inspection method according to this embodiment.

[0014] The object to be inspected in this embodiment is a double-structure vessel 2 installed inside a concrete bulkhead 1 of a reprocessing facility. The double-structure vessel 2 has an inner tank 3 that contains a nitric acid solution (substance), a heating coil 4 that is placed inside the inner tank 3 and heats the nitric acid solution, and an outer tank 5 that covers the outside of the inner tank 3 at a distance to keep the acetic acid solution heated by the heating coil 4 warm. The inner tank 3 and the outer tank 5 are made of the same material, such as metal. Because the inner tank 3 (particularly the portion close to the heating coil 4) is prone to corrosion, an ultrasonic inspection method is performed to measure the plate thickness of the inner tank 3.

[0015] The ultrasonic inspection method of this embodiment uses an ultrasonic probe 11 placed on the outer surface of the outer tank 5, with the space between the outer tank 5 and the inner tank 3 filled with an ultrasonic transmitter 6 (specifically, a liquid such as water). In this method, since the space between the outer tank 5 and the inner tank 3 is filled with the ultrasonic transmitter 6, ultrasonic pulses transmitted from the ultrasonic probe 11 are transmitted not only to the outer tank 5 but also to the inner tank 3. Furthermore, unlike when the ultrasonic probe 11 is placed on the inner surface of the inner tank 3, there is no need to remove the nitric acid solution contained in the inner tank 3, which reduces the operation time. The ultrasonic probe 11 can be placed at any position on the outer surface of the outer tank 5, as long as there is no piping 7 connected to the outer tank 5. The ultrasonic transmitter 6 may be filled in all the time, not just during inspection.

[0016] Next, the configuration of an ultrasonic inspection device used in the above-described ultrasonic inspection method will be described with reference to Fig. 2. Fig. 2 is a block diagram showing the configuration of an ultrasonic inspection device in this embodiment.

[0017] The ultrasonic inspection device of this embodiment includes an ultrasonic probe 11 arranged on the outer surface of the outer tank 5 of the double-structure container 2 as described above, a control device 12 that controls the ultrasonic probe 11, a computer 13 connected to the control device 12, and a display device 14 and an input device 15 connected to the computer 13. The control device 12 has a pulser 16, a receiver 17, an amplifier 18, a filter 19, and a data recording unit 20, and the data recording unit 20 is composed of a memory or the like. The computer 13 is composed of a computer or the like, the display device 14 is composed of a display or the like, and the input device 15 is composed of a mouse, keyboard, touch panel, or the like.

[0018] The computer 13 outputs a command to the control device 12 in response to an input from the input device 15. The pulser 16 of the control device 12 outputs a pulse signal (voltage signal) to the ultrasonic probe 11 in response to the command. The ultrasonic probe 11 is, for example, a vertical probe having one piezoelectric element. The piezoelectric element of the ultrasonic probe 11 oscillates in response to the pulse signal and transmits ultrasonic pulses toward the outer tank 5 and the inner tank 3. The piezoelectric element of the ultrasonic probe 11 also receives multiple ultrasonic pulses with different propagation paths, converts them into multiple pulse signals, and outputs them to a receiver 17 of the control device 12.

[0019] The pulse signal input to the receiver 17 of the control device 12 is amplified in intensity by the amplifier 18, noise is removed by the filter 19, and the signal is converted into a digital signal. The data generated in this manner includes the reception times of a plurality of ultrasonic pulses (more specifically, the elapsed time from the transmission timing of the ultrasonic probe 11) and intensities, and is recorded by the data recording unit 20.

[0020] The computer 13 displays the data recorded by the data recording unit 20 of the control device 12 on the display device 14. The computer 13 also processes the data recorded by the data recording unit 20 of the control device 12 to calculate the thickness of the inner tank 3, and displays the calculated thickness of the inner tank 3 on the display device 14.

[0021] Next, the data recorded by the data recording unit 20 of the control device 12 will be described with reference to Figures 3(a), 3(b), 4, and 5. Figures 3(a) and 3(b) are diagrams showing specific examples of propagation paths of ultrasonic pulses in this embodiment. Figure 4 is a diagram showing specific examples of data in this embodiment. Figure 5 is a diagram showing specific examples of data after a predetermined time has elapsed in this embodiment. In Figures 4 and 5, the horizontal axis shows the reception time of the ultrasonic pulse, and the vertical axis shows the intensity of the ultrasonic pulse.

[0022] As shown in Figure 3(a), the ultrasonic probe 11 receives an ultrasonic pulse F100 reflected once by the inner surface of the outer tank 5 (in other words, an ultrasonic pulse that has made one round trip inside the outer tank 5), an ultrasonic pulse F200 reflected twice by the inner surface of the outer tank 5 (in other words, an ultrasonic pulse that has made two round trips inside the outer tank 5), and an ultrasonic pulse F300 reflected three times by the inner surface of the outer tank 5 (in other words, an ultrasonic pulse that has made three round trips inside the outer tank 5). That is, the data recorded by the data recording unit 20 of the control device 12 includes the reception times and intensities of the ultrasonic pulses F100, F200, and F300, as shown in Figure 4. The time interval between the ultrasonic pulses F100, F200, and F300 corresponds to the thickness t2 of the outer tank 5 and is ΔT (= thickness t2 of the outer tank 5 × 2 / speed of sound V).

[0023] As shown in FIG. 3(a), the ultrasonic probe 11 receives an ultrasonic pulse F110 that has been reflected once from the outer surface of the inner vessel 3 (in other words, an ultrasonic pulse that has made one round trip inside the plate of the outer vessel 5 and between the outer vessel 5 and the inner vessel 3); as shown in FIG. 3(a), a pulse F210 that has been reflected once from the outer surface of the inner vessel 3 and once from the inner surface of the outer vessel 5 (in other words, an ultrasonic pulse that has made two round trips inside the plate of the outer vessel 5 and one round trip between the outer vessel 5 and the inner vessel 3); and as shown in FIG. 3(b), a pulse F310 that has been reflected once from the outer surface of the inner vessel 3 and twice from the inner surface of the outer vessel 5 (in other words, an ultrasonic pulse that has made three round trips inside the plate of the outer vessel 5 and one round trip between the outer vessel 5 and the inner vessel 3). That is, the data recorded by the data recording unit 20 of the control device 12 includes the reception times and intensities of the ultrasonic pulses F110, F210, and F310, as shown in Figures 4 and 5. The time interval between the ultrasonic pulses F110, F210, and F310 is the above-mentioned ΔT.

[0024] The ultrasonic probe 11 receives an ultrasonic pulse F111 that has been reflected once from the inner surface of the inner vessel 3 as shown in FIG. 3(a) (in other words, an ultrasonic pulse that has made one round trip inside the plate of the outer vessel 5, between the outer vessel 5 and the inner vessel 3, and inside the plate of the inner vessel 3); F211 that has been reflected once from the inner surface of the inner vessel 3 and once from the inner surface of the outer vessel 5 as shown in FIG. 3(b) (in other words, an ultrasonic pulse that has made two round trips inside the plate of the outer vessel 5, and one round trip between the outer vessel 5 and the inner vessel 3, and inside the plate of the inner vessel 3); and F112 that has been reflected twice from the inner surface of the inner vessel 3 as shown in FIG. 3(b) (in other words, an ultrasonic pulse that has made one round trip inside the plate of the outer vessel 5, between the outer vessel 5 and the inner vessel 3, and inside the plate of the inner vessel 3 twice). That is, the data recorded by the data recording unit 20 of the control device 12 includes the reception times and intensities of the ultrasonic pulses F111, F211, and F112, as shown in Fig. 5. The time interval between the ultrasonic pulses F111 and F211 is the above-mentioned ΔT.

[0025] The time interval between ultrasonic pulses F110, F111, and F112 corresponds to the thickness t1 of the inner tank 3 and is ΔT' (= thickness t1 of inner tank 3 × 2 / speed of sound V). If the computer 13 selects the ultrasonic pulses F110 and F111 from the data recorded by the data recording unit 20 of the control device 12 and obtains the time interval ΔT' between them, it is possible to calculate the thickness t1 of the inner tank 3 based on the time interval ΔT'. However, if the thickness t1 of the inner tank 3 changes due to corrosion of the inner tank 3, the time interval ΔT' will also change, making it difficult to select the ultrasonic pulses F110 and F111.

[0026] More specifically, if the thickness t1 of the inner tank 3 is greater than the thickness t2 of the outer tank 5, then the time interval ΔT' is greater than the time interval ΔT, and therefore the relationship is: reception time of ultrasonic pulse F110 < reception time of ultrasonic pulse F210 < reception time of ultrasonic pulse F111, as shown in Figure 5. However, as shown in Figure 6(a), if the corrosion of the inner tank 3 progresses and the thickness t1 of the inner tank 3 becomes equal to the thickness t2 of the outer tank 5, then the time interval ΔT' = time interval ΔT, and therefore the relationship is: reception time of ultrasonic pulse F110 < reception time of ultrasonic pulse F210 = reception time of ultrasonic pulse F111, as shown in Figure 6(b). As shown in Figure 7(a), if the corrosion of the inner tank 3 progresses further and the thickness t1 of the inner tank 3 becomes smaller than the thickness t2 of the outer tank 5, the time interval ΔT' becomes smaller than the time interval ΔT, and as shown in Figure 7(b), the relationship becomes: reception time of ultrasonic pulse F110 < reception time of ultrasonic pulse F111 < reception time of ultrasonic pulse F210.

[0027] Therefore, the computer 13 selects ultrasonic pulses F110 and F111 by determining the time intervals between the three ultrasonic pulses, and obtains their time interval ΔT'. An ultrasonic inspection method having such characteristics will be described with reference to Fig. 8. Fig. 8 is a flowchart showing the procedure of the ultrasonic inspection method in this embodiment.

[0028] First, in step S1, the ultrasonic probe 11 transmits ultrasonic pulses toward the outer tank 5 and the inner tank 3. The ultrasonic probe 11 also receives a plurality of ultrasonic pulses having different propagation paths, converts them into a plurality of pulse signals, and outputs them to the control device 12.

[0029] Proceeding to step S2, the control device 12 processes the plurality of pulse signals to create and record data indicating the reception times and intensities of the plurality of ultrasonic pulses.

[0030] Proceeding to step S3, the computer 13 processes the data recorded by the data recording unit 20 of the control device 12, selects multiple ultrasonic pulses F100, F200, and F300 received by the ultrasonic probe 11 before a predetermined time (e.g., 100 μs) has elapsed since the transmission timing of the ultrasonic probe 11, and obtains the time interval ΔT between them.

[0031] Proceeding to step S4, the computer 13 processes the data recorded by the data recording unit 20 of the control device 12 and selects the first, second, and third ultrasonic pulses that are received by the ultrasonic probe 11 after a predetermined time (e.g., 100 μs) has elapsed since the transmission timing of the ultrasonic probe 11 and have intensities greater than a predetermined value (e.g., relative value 0.05). Note that the first, second, and third ultrasonic pulses are ultrasonic pulses F110, F210, and F111 as shown in Fig. 5, ultrasonic pulses F110, F210, and F111 as shown in Fig. 6(b), or ultrasonic pulses F110, F111, and F210 as shown in Fig. 7(b).

[0032] Proceeding to step S5, the computer 13 compares the time interval ΔTa between the first ultrasonic pulse and the second ultrasonic pulse with the time interval ΔT, and determines whether the time interval ΔTa is smaller than the time interval ΔT. If the time interval ΔTa is smaller than the time interval ΔT (in other words, as shown in FIG. 7(b), the second ultrasonic pulse is ultrasonic pulse F111), proceed to step S6, and acquire the time interval ΔTa as the time interval ΔT'. On the other hand, if the time interval ΔTa is the same as the time interval ΔT (in other words, as shown in FIG. 5 or FIG. 6(b), the second ultrasonic pulse is ultrasonic pulse F210), proceed to step S7.

[0033] In step S7, the computer 13 compares the time interval ΔTb between the second and third ultrasonic pulses with the time interval ΔT, and determines whether the time interval ΔTb is smaller than the time interval ΔT. If the time interval ΔTb is smaller than the time interval ΔT (in other words, as shown in FIG. 5, the third ultrasonic pulse is ultrasonic pulse F111), the process proceeds to step S8, where the sum of the time interval ΔTa and the time interval ΔTb is obtained as the time interval ΔT'. On the other hand, if the time interval ΔTb is the same as the time interval ΔT (in other words, as shown in FIG. 6(b), the third ultrasonic pulse is ultrasonic pulse F310), the process proceeds to step S9, where the time interval ΔTa or ΔTb is obtained as the time interval ΔT'.

[0034] After step S6, S8, or S9, the process proceeds to step S10. In step S10, the calculator 13 calculates the thickness of the inner tank 3 based on the acquired time interval ΔT'. To explain in more detail, the thickness of the inner tank 3 is calculated using, for example, the sound speed V and the time interval ΔT' stored in advance.

[0035] As described above, in this embodiment, even if the thickness of the inner tank 3 of the double-structure container 2 changes, the thickness of the inner tank 3 can be measured.

[0036] In the above embodiment, the calculator 13 calculates the thickness of the inner tank 3 using the pre-stored sound speed in the inner tank 3 and the time interval ΔT'. However, this is not limiting. If the sound speed in the inner tank 3 is the same as the sound speed in the outer tank 5, it can be calculated using the thickness of the outer tank 5 and the time interval ΔT. Therefore, the calculator 13 may calculate the thickness of the inner tank 3 using the pre-stored sound speed in the outer tank 5 and the time interval ΔT and the time interval ΔT'. In this case, sound speed errors due to the influence of temperature can be reduced, and the calculation accuracy of the thickness of the inner tank 3 can be improved.

[0037] In the above embodiment, the case where the calculator 13 obtains the time interval ΔT, selects the first, second, and third ultrasonic pulses, obtains the time interval ΔT', and calculates the thickness of the inner tank 3 based on the data recorded by the control device 12 has been described as an example, but the present invention is not limited to this. An operator may obtain the time interval ΔT, select the first, second, and third ultrasonic pulses, obtain the time interval ΔT', and calculate the thickness of the inner tank 3 based on the data recorded by the control device 12 and displayed on the display device 14.

[0038] In the above embodiment, the ultrasonic probe 11 is a vertical probe having one piezoelectric element and a fixed transmission / reception direction, but the present invention is not limited to this. For example, as in a modified example shown in Fig. 9, the ultrasonic probe 11A may be an array probe having a plurality of piezoelectric elements 21 and a variable transmission / reception direction.

[0039] The control device 12 controls the transmission and reception timing of ultrasonic pulses in each of the plurality of piezoelectric elements 21 to vary the transmission and reception direction of the composite ultrasonic pulse (in other words, the transmission and reception direction of the ultrasonic probe 11A), and creates and records corresponding data (phased array method). Alternatively, the control device 12 controls to change the combination of the piezoelectric elements 21 that transmit ultrasonic pulses and the piezoelectric elements 21 that receive ultrasonic pulses, and records corresponding data. The computer 13 creates data corresponding to the virtual transmission and reception direction of the ultrasonic probe 11A based on the data recorded by the control device 12 (full matrix capture).

[0040] The calculator 13 processes the data corresponding to the transmission and reception direction of the ultrasonic probe 11A described above, and selects the first ultrasonic pulse F110 that is received by the ultrasonic probe 11 after a predetermined time has elapsed since the transmission timing of the ultrasonic probe 11A and has an intensity greater than a predetermined value. This acquires the relationship between the transmission and reception direction of the ultrasonic probe 11A and the intensity of the ultrasonic pulse F110. Based on the relationship described above, the calculator 13 sets the transmission and reception direction (transmission and reception angle θ) of the ultrasonic probe 11A at which the intensity of the ultrasonic pulse F110 is maximized, and calculates the thickness of the inner tank 3 using data corresponding to this. Alternatively, the calculator 13 displays the relationship between the transmission and reception direction of the ultrasonic probe 11A and the intensity of the ultrasonic pulse F110 on the display device 14. Based on the relationship displayed on the display device 14, the operator sets the transmission and reception direction (transmission and reception angle θ) of the ultrasonic probe 11A at which the intensity of the ultrasonic pulse F110 is maximized using the input device 15. The calculator 13 calculates the thickness of the inner tank 3 using data corresponding to the transmission and reception direction of the ultrasonic probe 11A set by the input device 15.

[0041] In this modification, ultrasonic pulses F110, F111, etc. can be detected with sufficient sensitivity even when the outer tank 5 and inner tank 3 are not parallel, as shown in Fig. 9. More specifically, when the transmission and reception direction of the ultrasonic probe 11A is perpendicular to the outer surface of the outer tank 5, the propagation path of the ultrasonic pulse F111 is as shown by the dotted arrow in Fig. 9, and therefore the ultrasonic pulse F111 is not detected with sufficient sensitivity. On the other hand, when the transmission and reception direction of the ultrasonic probe 11A is oblique to the outer surface of the outer tank 5, the propagation path of the ultrasonic pulse F111 is as shown by the solid arrow in Fig. 9, and therefore the ultrasonic pulse F111 is detected with sufficient sensitivity. Therefore, even when the outer tank 5 and inner tank 3 are not parallel, the thickness of the inner tank 3 can be measured.

[0042] In the above, the object to be inspected has been described as a double-structure vessel 2 installed inside the concrete bulkhead 1 of a reprocessing facility, but the present invention is not limited to this and may be other double-structure vessels. Also, although the case where the inner vessel 3 and outer vessel 5 of the double-structure vessel 2 are made of the same material has been described as an example, they may be made of different materials. [Explanation of symbols]

[0043] 2 Double-walled container 3 Inner tank 5 Outer tank 6 Ultrasound transmitters 11,11A ultrasonic probe 12 Control device 13 Calculator

Claims

1. 1. An ultrasonic inspection method for measuring a wall thickness of an inner shell of a double-structure container using an ultrasonic probe disposed on an outer surface of the outer shell, with an ultrasonic transmitting material filled between the outer shell and the inner shell, comprising: transmitting ultrasonic pulses toward the outer tank and the inner tank using the ultrasonic probe; The ultrasonic probe receives a plurality of ultrasonic pulses having different propagation paths; acquiring a time interval ΔT between a plurality of ultrasonic pulses received by the ultrasonic probe before a predetermined time has elapsed from a transmission timing of the ultrasonic probe; selecting first, second, and third ultrasonic pulses that are received by the ultrasonic probe after the predetermined time has elapsed from the transmission timing of the ultrasonic probe and have intensities greater than a predetermined value; Comparing the time interval ΔTa between the first ultrasonic pulse and the second ultrasonic pulse with the time interval ΔT; When the time interval ΔTa is smaller than the time interval ΔT, the time interval ΔTa is acquired as the time interval ΔT′ corresponding to the wall thickness of the inner tank; When the time interval ΔTa is the same as the time interval ΔT, the time interval ΔTb between the second ultrasonic pulse and the third ultrasonic pulse is compared with the time interval ΔT; When the time interval ΔTa is equal to the time interval ΔT and the time interval ΔTb is smaller than the time interval ΔT, the sum of the time interval ΔTa and the time interval ΔTb is obtained as the time interval ΔT′; When the time interval ΔTa is the same as the time interval ΔT and the time interval ΔTb is the same as the time interval ΔT, the time interval ΔTa or ΔTb is acquired as the time interval ΔT′; and calculating a wall thickness of the inner tank based on the acquired time interval ΔT'.

2. The ultrasonic inspection method according to claim 1, A plurality of piezoelectric elements constituting the ultrasonic probe are controlled to vary the transmission and reception direction of the ultrasonic probe, and the intensity of the corresponding first ultrasonic pulse is acquired; an ultrasonic inspection method, characterized in that a transmission / reception direction of the ultrasonic probe is set so that the intensity of the first ultrasonic pulse is maximized;

3. The ultrasonic inspection method according to claim 1, an ultrasonic inspection method, characterized in that, when the material of the outer tank and the material of the inner tank are the same, the thickness of the inner tank is calculated using the thickness of the outer tank, the time interval ΔT, and the time interval ΔT'.

4. 1. An ultrasonic inspection device for measuring the thickness of an inner shell of a double-structure container using an ultrasonic probe disposed on the outer surface of the outer shell, with an ultrasonic transmitting material filled between the outer shell and the inner shell, a control device that controls the ultrasonic probe to transmit ultrasonic pulses toward the outer tank and the inner tank, processes signals converted from a plurality of ultrasonic pulses received by the ultrasonic probe along different propagation paths, and records data indicating the reception times and intensities of the plurality of ultrasonic pulses; a computer that calculates the thickness of the inner tank using data recorded by the control device, The computer acquiring a time interval ΔT between a plurality of ultrasonic pulses received by the ultrasonic probe before a predetermined time has elapsed from a transmission timing of the ultrasonic probe; selecting first, second, and third ultrasonic pulses that are received by the ultrasonic probe after the predetermined time has elapsed from the transmission timing of the ultrasonic probe and have intensities greater than a predetermined value; Comparing the time interval ΔTa between the first ultrasonic pulse and the second ultrasonic pulse with the time interval ΔT; When the time interval ΔTa is smaller than the time interval ΔT, the time interval ΔTa is acquired as the time interval ΔT′ corresponding to the wall thickness of the inner tank; When the time interval ΔTa is the same as the time interval ΔT, the time interval ΔTb between the second ultrasonic pulse and the third ultrasonic pulse is compared with the time interval ΔT; When the time interval ΔTa is equal to the time interval ΔT and the time interval ΔTb is smaller than the time interval ΔT, the sum of the time interval ΔTa and the time interval ΔTb is obtained as the time interval ΔT′; When the time interval ΔTa is the same as the time interval ΔT and the time interval ΔTb is the same as the time interval ΔT, the time interval ΔTa or ΔTb is acquired as the time interval ΔT′; The ultrasonic inspection device calculates the wall thickness of the inner tank based on the acquired time interval ΔT'.

5. 5. The ultrasonic inspection device according to claim 4, the ultrasonic probe has a plurality of piezoelectric elements; the control device controls the plurality of piezoelectric elements to vary the transmission and reception direction of the ultrasonic probe; The ultrasonic inspection device is characterized in that the computer acquires the intensity of the first ultrasonic pulse corresponding to the transmission and reception direction of the ultrasonic probe, and sets the transmission and reception direction of the ultrasonic probe in which the intensity of the first ultrasonic pulse is maximum.

6. 5. The ultrasonic inspection device according to claim 4, The ultrasonic inspection device is characterized in that, when the material of the outer tank and the material of the inner tank are the same, the computer calculates the thickness of the inner tank using the thickness of the outer tank, the time interval ΔT, and the time interval ΔT'.

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