Inspection method for high-pressure tank

Abstract

To provide a technique capable of detecting internal damage even when a fiber-reinforced resin layer is thick.SOLUTION: A method for inspecting a high pressure tank in which a reinforcement layer formed by laminating a plurality of members is formed on an outer periphery of a tank container includes a wave transmission step of transmitting an ultrasonic wave of a Lamb wave to the reinforcement layer, a wave reception step of receiving a reflected wave of the ultrasonic wave, and a determination step of determining that damage has occurred inside the reinforcement layer when an intensity of the reflected wave after a lapse of a predetermined threshold time from the transmission of the ultrasonic wave is equal to or less than a predetermined threshold intensity.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a method for inspecting a high-pressure tank. [Background technology]

[0002] A high-pressure tank is known in which a fiber-reinforced resin layer is formed on the outer periphery of the tank container. Patent Document 1 describes a technology for detecting damage inside the fiber-reinforced resin layer based on the presence or absence of a phase shift in the reflected waves of ultrasonic waves transmitted to the tank. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 6133707 Summary of the Invention [Problem to be solved by the invention]

[0004] When the fiber-reinforced resin layer is thick, increasing the amplitude of the transmitted ultrasonic waves to reach a deeper position from the surface of the fiber-reinforced resin layer can cause a phase shift even when there is no internal damage. Therefore, there has been a demand for a technology that can detect internal damage even when the fiber-reinforced resin layer is thick. [Means for solving the problem]

[0005] The present disclosure has been made to solve the above-mentioned problems, and can be realized in the following forms.

[0006] (1) According to an embodiment of the present disclosure, there is provided a method for inspecting a high-pressure tank having a reinforcing layer formed on the outer periphery of a tank container, the method including: a wave transmitting step of transmitting ultrasonic Lamb waves to the reinforcing layer; a wave receiving step of receiving reflected waves of the ultrasonic waves; and a determination step of determining that damage has occurred inside the reinforcing layer if the intensity of the reflected waves is equal to or less than a predetermined threshold intensity after a predetermined threshold time has elapsed since the ultrasonic waves were transmitted. If no damage occurs inside the reinforcing layer, the Lamb waves applied in the wave-transmitting process disperse, and an A0 mode wave generated shallow from the surface of the reinforcing layer appears, followed by an A1 mode wave generated deep from the surface of the reinforcing layer. On the other hand, if damage occurs inside the reinforcing layer, the A1 mode wave is reflected at the interface of the internal damage and dissipates as thermal energy into the space of the internal damage. According to this type of inspection method, internal damage is determined to have occurred if the intensity of the reflected wave is below the threshold intensity after a threshold time has elapsed since the ultrasonic waves were transmitted. Therefore, internal damage in the reinforcing layer of a high-pressure tank can be detected. (2) In the inspection method of the above aspect, the reinforcing layer may be formed by winding fibers around the tank container. According to this type of inspection method, for example, internal damage to a high-pressure tank in which a reinforcing layer is formed by a filament winding method can be detected. (3) In the inspection method of the above aspect, the determining step may determine the intensity of the reflected wave in a frequency band of 100 kHz or more and 500 kHz or less. The peak intensity of the reflected wave can be detected more easily in an analysis using the reflected wave in a frequency band that includes the natural frequency of the reinforcing layer than in an analysis using the reflected wave in any frequency band. Therefore, this type of inspection method can accurately determine whether the intensity of the reflected wave is equal to or less than a predetermined threshold intensity. (4) In the inspection method of the above aspect, the determination step may not use the reflected wave that continues for a period longer than the disappearance time, which is the time it takes for the ultrasonic wave to disappear. According to the inspection method of this embodiment, for example, it is possible to prevent the determination step from being performed using continuous waves generated by friction, thereby improving the accuracy of the determination. (5) In the inspection method of the above form, the method may include a positioning step of positioning the transmitter and the receiver so that the distance L between the transmitter that emits the ultrasonic waves and the receiver that receives the reflected waves, the diameter D1 of the transmitter, and the diameter D2 of the receiver satisfy the relationship of the following formula (1). (D1+D2) / 2 < L < (D1+D2) / 0.2…(1) The inventors discovered that the peak of the reflected wave intensity can be detected more easily when the diameters D1, D2, and the distance L satisfy the relationship of the above-mentioned formula (1) than when the diameters D1, D2, and the distance L do not satisfy the relationship of the above-mentioned formula (1). Therefore, according to the inspection method of this embodiment, it is possible to accurately determine whether the intensity of the reflected wave is equal to or less than the threshold intensity.

[0007] The present disclosure can be realized in various forms, for example, in the form of an inspection system or the like. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is an explanatory diagram illustrating a configuration of an inspection system. [Figure 2] 10 is a flowchart illustrating an example of an inspection process. [Figure 3] 1 is a graph showing an example of a dispersion curve of a Lamb wave. [Figure 4] 10 is a graph showing an example of a change in intensity of a reflected wave. [Figure 5] 11 is a flowchart showing an example of an inspection process in the third embodiment. [Figure 6] 10 is a graph showing another example of changes in the intensities of reflected waves and continuous wave noise. DETAILED DESCRIPTION OF THE INVENTION

[0009] A. First embodiment: 1 is an explanatory diagram showing the configuration of an inspection system 100 in this embodiment. The inspection system 100 inspects a high-pressure tank 10 for abnormalities. The inspection system 100 includes the high-pressure tank 10, a wave transmitter 20, a wave receiver 30, and an inspection device 40.

[0010] The high-pressure tank 10 contains high-pressure hydrogen of, for example, 10 to 70 MPa, and is mounted on a fuel cell vehicle. The high-pressure tank 10 includes a tank container 11, a reinforcing layer 12, and a mouthpiece 13.

[0011] The tank container 11 is a gas-impermeable material. The tank container 11 is formed of a resin having gas barrier properties against hydrogen gas, such as polyethylene, nylon, or polypropylene. In this embodiment, the tank container 11 is made of resin, but it may also be made of metal, or may be formed by mixing a gas-impermeable material such as a hydrogen storage alloy into the above-mentioned resin. The tank container 11 has a cylindrical portion 14 and two dome portions 15 provided on both ends of the cylindrical portion 14. The dome portions 15 have a substantially hemispherical shape. The central axis of the cylindrical portion 14 and the central axis of the dome portions 15 both coincide with the central axis of the high-pressure tank 10.

[0012] The reinforcing layer 12 is formed on the outer periphery of the tank container 11. The reinforcing layer 12 is formed by bundling approximately 10,000 to 40,000 strands of fiber reinforced plastic (CFRP) such as glass fiber or carbon fiber, impregnating the bundle with a thermosetting resin such as epoxy, and then winding the resulting fiber bundle around the tank container 11 and thermally curing it. In this embodiment, the reinforcing layer 12 has a thickness of 20 mm.

[0013] The nozzle 13 is a metal member that connects the inside and outside of the tank container 11. In this embodiment, the nozzle 13 is provided at one end of the tank container 11 in the longitudinal direction, but may be provided at both ends.

[0014] The wave transmitter 20 is a device that transmits ultrasonic Lamb waves toward the reinforcing layer 12. The wave receiver 30 is a device that receives reflected waves that are composite waves formed by combining the ultrasonic waves transmitted by the wave transmitter 20 and the reflected waves that are reflected by each layer of the reinforcing layer 12. In this embodiment, the wave transmitter 20 and the wave receiver 30 are arranged so that the distance L between the wave transmitter 20 and the wave receiver 30, the diameter D1 of the wave transmitter 20, and the diameter D2 of the wave receiver 30 satisfy the relationship of the following formula (1).

[0015] (D1+D2) / 2 < L < (D1+D2) / 0.2…(1)

[0016] In this embodiment, the diameter D1 and the diameter D2 are both 8 mm, and the distance L is 72 mm.

[0017] The inspection device 40 is a device that inspects the high-pressure tank 10 for abnormalities using the reflected waves received by the receiver 30. The inspection device 40 is composed of a computer equipped with an input / output interface 41, a storage unit 42, and a CPU 43. The input / output interface 41, the storage unit 42, and the CPU 43 are connected to enable bidirectional communication. The storage unit 42 is composed of ROM and RAM.

[0018] The CPU 43 executes a program pre-installed in the storage unit 42, and uses the reflected waves received by the receiver 30 to determine whether or not damage has occurred inside the reinforcing layer 12. However, some or all of the functions of these units may be realized by a hardware circuit.

[0019] 2 is a flowchart showing an example of the inspection process. The inspection process is a process for inspecting whether or not damage has occurred inside the reinforcing layer 12. This process is performed, for example, on the cylindrical portion 14 and the tank shoulder portion extending from the boundary between the cylindrical portion 14 and the dome portion 15 toward the tip of the dome portion 15, and is performed at predetermined intervals.

[0020] In step S100, an "arrangement step" is performed in which the wave transmitter 20 and the wave receiver 30 are placed on the surface of the reinforcing layer 12. In this embodiment, the wave transmitter 20 and the wave receiver 30 are arranged on the outer peripheral surface of the reinforcing layer 12 so as to satisfy the relationship of the above-mentioned formula (1).

[0021] In step S110, the wave transmitter 20 executes a "wave transmission step" of transmitting ultrasonic waves to the reinforcing layer 12. The ultrasonic waves are, for example, Lamb waves consisting of five pulse waves with a pulse width of 50 μs. The transmission interval of the Lamb waves is 1000 μs.

[0022] In step S120, the wave receiver 30 executes a "wave receiving step" of receiving reflected waves that are the ultrasonic waves transmitted by the wave transmitter 20 in step S110 and propagated to each position in the thickness direction of the reinforcing layer 12.

[0023] FIG. 3 is a graph showing an example of a dispersion curve of a reflected wave. In the graph shown in FIG. 3, the horizontal axis represents the value obtained by multiplying the frequency of the Lamb wave by the thickness of the reinforcing layer 12, which is a value corresponding to the distance from the surface of the reinforcing layer 12. The vertical axis represents the phase velocity of the Lamb wave. Dispersion curve G1 is a dispersion curve representing the A0 mode wave. Dispersion curve G2 is a dispersion curve representing the A1 mode wave. As shown in FIG. 3, the A1 mode wave does not occur when the value obtained by multiplying the frequency of the Lamb wave by the thickness of the reinforcing layer 12 is small, that is, in a shallow portion of the reinforcing layer 12 from the surface. Therefore, an A0 mode wave generated in a shallow portion of the reinforcing layer 12 from the surface appears, and then an A1 mode wave generated in a deep portion of the reinforcing layer 12 from the surface appears.

[0024] FIG. 4 is a graph showing an example of changes in the intensity of reflected waves. In the graph shown in FIG. 4, the horizontal axis represents time, and the vertical axis represents intensity. Characteristic line Gr1 is a characteristic line that shows the intensity when no damage occurs inside the reinforcing layer 12. Characteristic line Gr2 is a characteristic line that shows the intensity when damage occurs inside the reinforcing layer 12. When no damage occurs inside the reinforcing layer 12, the Lamb waves applied in the wave transmitting process are dispersed, and S0 mode waves and A0 mode waves generated in a shallow portion from the surface of the reinforcing layer 12 appear as early waves, followed by A1 mode waves generated in a deep portion from the surface of the reinforcing layer 12 as late waves. On the other hand, when damage occurs inside the reinforcing layer 12, the A1 mode waves are reflected at the interface of the internal damage and dissipate as thermal energy into the space surrounding the internal damage. Therefore, as shown in FIG. 4, the intensity of the late waves when damage occurs inside the reinforcing layer 12 is significantly reduced compared to the intensity of the late waves when no damage occurs inside the reinforcing layer 12. Hereinafter, the reflected wave that appears after the threshold time Tth at which the A1 mode wave appears is also referred to as a delayed wave.

[0025] In step S130 (see FIG. 2), the CPU 43 executes a "determination step" in which, using the reflected wave received in step S120, the CPU 43 determines whether the intensity of the reflected wave after a predetermined threshold time Tth has elapsed since the wave transmitter 20 emitted ultrasonic waves in step S110 is equal to or less than a predetermined threshold intensity. That is, the CPU 43 determines whether the intensity of the subsequent wave is equal to or less than a threshold intensity. The threshold time Tth is, for example, 60 μs. The threshold time Tth may also be a value determined experimentally or empirically in advance. The intensity of the subsequent wave is, for example, the average value of the intensity of the subsequent wave in a frequency band from 100 kHz to 500 kHz calculated using a fast Fourier transform (FFT). The intensity of the subsequent wave may also be the effective value of the subsequent wave. The threshold intensity is a value indicating that damage has occurred inside the reinforcing layer 12. The threshold intensity is, for example, a value equal to or less than 70% of the intensity of the advance wave. The threshold intensity may also be a value determined experimentally or empirically in advance. If the intensity of the subsequent wave is equal to or less than the threshold intensity, the CPU 43 proceeds to the process of step S 140. On the other hand, if the intensity of the subsequent wave is greater than the threshold intensity, the CPU 43 ends the inspection process.

[0026] In step S140, the CPU 43 executes a "notification step" of notifying, via a notifying device (not shown), that damage has occurred inside the reinforcing layer 12. Note that step S140 may be omitted.

[0027] According to the inspection method of the present embodiment described above, ultrasonic Lamb waves are transmitted to the reinforcing layer 12, and internal damage is determined to have occurred if the intensity of the reflected waves is equal to or less than the threshold intensity after the threshold time Tth has elapsed since the ultrasonic waves were transmitted. If damage occurs inside the reinforcing layer 12 having a multilayer structure, causing delamination, most of the A1 mode Lamb waves are reflected at the damaged interface and dissipate as thermal energy into the space created by the damage, preventing them from reaching a location deeper than the damage in the reinforcing layer 12. Furthermore, because Lamb waves are used instead of single-pulse waves, ultrasonic waves can reach deep positions in the reinforcing layer 12 without increasing the output amplitude. Therefore, internal damage in the reinforcing layer 12 of the high-pressure tank 10 can be detected even if the fiber-reinforced resin layer is thick.

[0028] Furthermore, the wave transmitter 20 and the wave receiver 30 are arranged so that the diameters D1, D2, and the distance L satisfy the relationship of the above-mentioned formula (1). The inventors discovered that the peak of the intensity of the subsequent wave can be detected more easily when the diameters D1, D2, and the distance L satisfy the relationship of the above-mentioned formula (1) than when the diameters D1, D2, and the distance L do not satisfy the relationship of the above-mentioned formula (1). Therefore, in this embodiment, the CPU 43 can accurately determine whether the intensity of the subsequent wave is equal to or less than a predetermined threshold intensity in the determination step (step S130 in FIG. 2).

[0029] B. Second embodiment: The inspection method in the second embodiment differs from the inspection method in the first embodiment in that a reflected wave in a frequency band of 200 kHz or more and 300 kHz or less is used in the determination step (step S130 in FIG. 2), but the other steps are the same as those in the first embodiment. The configuration of the inspection system 100 in the second embodiment is the same as the configuration of the inspection system 100 in the first embodiment, so a description of the configuration of the inspection system 100 will be omitted.

[0030] In this embodiment, the natural frequency of the CFRP forming the reinforcing layer 12 is about 250 kHz. For example, the intensity of the delayed wave at 100 kHz when no damage occurs inside the reinforcing layer 12 is about 2 dB higher than the intensity of the delayed wave at 100 kHz when damage occurs inside the reinforcing layer 12. On the other hand, the intensity of the delayed wave at 300 kHz when no damage occurs inside the reinforcing layer 12 is about 11 dB higher than the intensity of the delayed wave at 300 kHz when damage occurs inside the reinforcing layer 12. In other words, the intensity of the delayed wave can be more easily detected by analysis using reflected waves in a frequency band that includes the natural frequency of the CFRP forming the reinforcing layer 12 than by analysis using reflected waves that do not limit the frequency band.

[0031] According to the inspection method of the second embodiment described above, the judgment process is performed using reflected waves in a frequency band ranging from 200 kHz or more to 300 kHz or less, which includes the natural frequency of the reinforcing layer 12, so that the CPU 43 can accurately determine whether the intensity of the subsequent wave is below a predetermined threshold intensity.

[0032] C. Third embodiment: FIG. 5 is a flowchart showing an example of the inspection process in the third embodiment. FIG. 6 is a graph showing another example of the changes in the intensity of the reflected wave and continuous wave noise. In the graph shown in FIG. 6, the horizontal axis represents time, and the vertical axis represents intensity. Characteristic line Gr3 represents the intensity of continuous wave noise caused by friction, etc. The inspection process method in the third embodiment differs from the inspection method in the first embodiment in that the judgment process is not performed using a reflected wave that has continued for more than a predetermined decay time, but the other processes are the same as those in the first embodiment. The configuration of the inspection system 100 in the third embodiment is the same as the configuration of the inspection system 100 in the first embodiment, so a description of the configuration of the inspection system 100 will be omitted.

[0033] In step S125 (see FIG. 5), the CPU 43 determines whether the duration of the reflected wave acquired in step S120 is equal to or longer than the disappearance time. If the reflected wave disappears before the disappearance time, the CPU 43 proceeds to the process of step S130. On the other hand, if the reflected wave continues for equal to or longer than the disappearance time, the CPU 43 returns to the process of step S110. In other words, the CPU 43 repeats the processes of steps S110 to S125 until it acquires a reflected wave that disappears before the disappearance time.

[0034] The disappearance time Tva is the time it takes for the ultrasonic waves transmitted by the wave transmitter 20 in step S110 to disappear when no damage has occurred inside the reinforcing layer 12. As shown in Fig. 6, the characteristic line Gr3 indicating the intensity of the continuous wave noise continues longer than the disappearance time Tva, which is the time it takes for the characteristic line Gr1 to disappear when no damage has occurred inside the reinforcing layer 12. The disappearance time Tva is, for example, 200 µs.

[0035] According to the inspection method of the third embodiment described above, the determination step is performed using the reflected wave that has disappeared within the decay time, so it is possible to prevent the determination step from being performed using, for example, a continuous wave generated by friction when the wave transmitter 20 and the wave receiver 30 are installed in the high-pressure tank 10. This improves the accuracy of the determination.

[0036] D. Other Embodiments: (D1) In the above-described embodiment, the reinforcing layer 12 is formed by winding fibers around the tank container 11. However, the reinforcing layer 12 may be formed by laminating a plurality of members. For example, the reinforcing layer 12 may be formed by laminating a plurality of sheet-shaped resins on the tank container 11.

[0037] (D2) In the above-described embodiment, the wave transmitter 20 and the wave receiver 30 are arranged on the outer peripheral surface of the reinforcing layer 12 so as to satisfy the relationship of the above-described formula (1). However, the present invention is not limited to this, and the wave transmitter 20 and the wave receiver 30 may be arranged on the inner peripheral surface of the reinforcing layer 12. Furthermore, the wave transmitter 20 and the wave receiver 30 may be arranged on the surface of the reinforcing layer 12 in any positional relationship.

[0038] (D3) The inspection process in the above-described embodiment may be performed periodically, for example, when a fuel cell vehicle equipped with the high-pressure tank 10 comes into contact with a road surface and an impact is applied to the high-pressure tank 10. The inspection process may be performed on the entire reinforcing layer 12, or may be performed only on a portion of the reinforcing layer 12 that is estimated to have internal damage. For example, if it is estimated that there is internal damage of about 5 mm, it is preferable to perform the inspection process on an area of ​​about 20 mm that includes the portion estimated to be the center of the internal damage.

[0039] (D4) In the determination step (step S130 in FIG. 2) in the above-described embodiment, a reflected wave that has been subjected to known noise removal processing may be used. The natural frequency f of the A1 mode wave, which is a frequency suitable for ultrasonic waves to propagate inside the reinforcing layer 12, can be expressed by the following equation (2):

[0040]

number

[0041] Here, h is the thickness of one reinforcing layer 12, E is the modulus of longitudinal elasticity of the reinforcing layer 12, e.g., 383 Gpa, and ρ is the density of the reinforcing layer 12, e.g., 1.7×10 3 kg / m 3 is.

[0042] The larger the diameter D1 of the wave transmitter 20, the greater the energy of the transmitted ultrasonic waves, allowing the ultrasonic waves to reach deeper positions from the surface of the reinforcing layer 12; however, as shown in the above-mentioned formula (2), the natural frequency f becomes lower. The lower the natural frequency f, the greater the possibility that the reflected waves received by the wave receiver 30 will contain a lot of noise. Therefore, by performing noise removal processing, the accuracy of the determination can be improved.

[0043] E. Application example: In the above-described embodiment, the inspection system 100 detects internal damage to the reinforcing layer 12 of the high-pressure tank 10. Alternatively, the inspection system 100 may detect internal damage to the reinforcing layer 12 of an inspection object having the reinforcing layer 12. The inspection system 100 can inspect the quality of, for example, a cylindrical member having the reinforcing layer 12.

[0044] The present disclosure is not limited to the above-described embodiments and can be realized in various configurations without departing from the spirit thereof. For example, the technical features in the embodiments corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be appropriately deleted. [Explanation of symbols]

[0045] 10...High-pressure tank, 11...Tank container, 12...Reinforcing layer, 13...Nozzle, 14...Cylindrical portion, 15...Dome portion, 20...Transmitter, 30...Receiver, 40...Inspection device, 41...Input / output interface, 42...Memory unit, 43...CPU, 100...Inspection system

Claims

1. 1. A method for inspecting a high-pressure tank in which a reinforcing layer formed by laminating a plurality of members is formed on the outer periphery of a tank container, comprising: a wave transmitting step of transmitting ultrasonic waves of Lamb waves to the reinforcing layer; a wave receiving step of receiving a reflected wave of the ultrasonic wave; and a determination step of determining that damage has occurred inside the reinforcing layer if the intensity of the reflected wave after a predetermined threshold time has elapsed since the ultrasonic wave was transmitted is equal to or less than a predetermined threshold intensity.

2. The inspection method according to claim 1, The reinforcing layer is formed by wrapping fibers around the tank container.

3. The inspection method according to claim 1 or 2, In the determining step, the determination is made using the intensity of the reflected wave in a frequency band of 200 kHz or more and 300 kHz or less.

4. The inspection method according to claim 1 or 2, In the determination step, the reflected wave that continues for a period longer than the disappearance time, which is the time it takes for the ultrasonic wave to disappear, is not used.

5. The inspection method according to claim 1 or 2, further comprising: An inspection method including an arrangement step of arranging the transmitter and the receiver so that the distance L between the transmitter that emits the ultrasonic waves and the receiver that receives the reflected waves, the diameter D1 of the transmitter, and the diameter D2 of the receiver satisfy the relationship of the following formula (1). (D1+D2) / 2 < L < (D1+D2) / 0.2...(1)

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