Tank evaluation method and tank evaluation device

Abstract

To provide a tank evaluation method capable of accurately detecting a rupture of a high-pressure tank before it ruptures.SOLUTION: The tank evaluation method includes: a step of measuring acoustic emission while pressurizing the tank; and a step of calculating cumulative acoustic emission energy using the measured acoustic emission. The pressure at which the rate of increase in the cumulative acoustic emission energy exceeds a threshold is defined as the pressure immediately before bursting. The tank evaluation method also has a step of calculating the waveform duration based on the measured acoustic emission. The pressure at which the rate of increase in the waveform duration exceeds a threshold is defined as the pressure just before bursting.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to tank evaluation. [Background technology]

[0002] High-pressure tanks that store hydrogen, the fuel for fuel cell vehicles, have a liner that forms the internal space of the high-pressure tank, and a reinforcing layer is formed around the periphery of this liner by providing a fiber layer impregnated with resin, thereby achieving high strength.

[0003] Patent Document 1 discloses a method for evaluating high-pressure tanks, in which acoustic emission (AE) signals are measured and signs of tank rupture are detected based on the hit rate, which indicates the time change in the number of these signals. Here, the point at which the hit rate stops increasing and reaches saturation is determined to be a sign of tank rupture. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication WO2009 / 008515 Summary of the Invention [Problem to be solved by the invention]

[0005] The method of Patent Document 1 can also detect signs of rupture in a high-pressure tank, but depending on the high-pressure tank (e.g., size), it is difficult for the occurrence of microcracks to saturate, and there are many cases where the increase in hit rate does not saturate. Therefore, it is necessary to be able to determine signs of rupture with greater accuracy.

[0006] The present disclosure has been made in consideration of these circumstances, and aims to provide an evaluation method that can accurately detect the rupture of a high-pressure tank before the rupture occurs, and also to provide an evaluation device for that purpose. [Means for solving the problem]

[0007] The present application discloses a method for evaluating a tank, which includes a step of measuring acoustic emissions while pressurizing the tank, and a step of calculating cumulative acoustic emission energy based on the measured acoustic emissions, and the pressure at which the rate of increase in cumulative acoustic emission energy reaches or exceeds a certain level is defined as the pre-burst pressure.

[0008] The present application also discloses a method for evaluating a tank, which includes a step of measuring acoustic emissions while pressurizing the tank, and a step of calculating a waveform duration due to the measured acoustic emissions, and the pressure at which the rate of increase in the waveform duration reaches or exceeds a certain level is determined to be the pre-rupture pressure.

[0009] The present application also discloses a method for evaluating a tank, which includes a step of measuring acoustic emissions while pressurizing the tank, and a step of calculating acoustic emission energy of a single waveform based on the measured acoustic emissions, and the pressure at which the acoustic emission energy of the single waveform becomes equal to or exceeds a threshold value is defined as the pre-burst pressure. 8 (eU)~10×10 8 (eU) may also be used.

[0010] The present application also discloses a method for evaluating a tank, which includes a step of measuring sound while pressurizing the tank, and defines the pressure at which at least one of the amplitude and frequency of the sound exceeds a threshold as the pressure just before rupture.

[0011] Furthermore, in the above tank evaluation method, the estimated burst pressure may be the pressure just before bursting plus a predetermined value.

[0012] The present application also discloses a tank evaluation device that includes an acoustic emission sensor disposed in the tank and a calculation device that acquires acoustic emission data from the acoustic emission sensor and performs calculations, wherein the calculation device calculates cumulative acoustic emission energy from the acoustic emission data and calculates the pressure at which the rate of increase of the cumulative acoustic emission energy reaches or exceeds a certain level as the pressure immediately before rupture.

[0013] The present application also discloses a tank evaluation device that includes an acoustic emission sensor placed in the tank and a calculation device that acquires acoustic emission data from the acoustic emission sensor and performs calculations, wherein the calculation device calculates a waveform duration based on the acoustic emission data and calculates the pressure at which the rate of increase in the waveform duration reaches or exceeds a certain level as the pressure immediately before rupture.

[0014] The present application also discloses a tank evaluation device that includes an acoustic emission sensor disposed in the tank and a calculation device that acquires acoustic emission data from the acoustic emission sensor and performs calculations, where the calculation device calculates acoustic emission energy of a single waveform from the acoustic emission data and calculates the pressure at which the acoustic emission energy of the single waveform becomes equal to or greater than a threshold value as the pressure immediately before rupture. Here, the threshold value is 1×10 8 (eU)~10×10 8 (eU) may also be used.

[0015] The present application also discloses a tank evaluation device that includes a sound collector placed in the tank and a calculation device that acquires sound data from the sound collector and performs calculations, and the calculation device performs calculations based on the sound data to determine that the pressure at which at least one of the amplitude and frequency of the sound exceeds a threshold value is the pressure just before rupture.

[0016] In the tank evaluation device, the calculation device can estimate the burst pressure by adding a predetermined value to the pressure just before burst. [Effects of the Invention]

[0017] According to the present disclosure, tank rupture can be detected with high accuracy before the rupture occurs. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram showing a schematic external view of a high-pressure tank 10. As shown in FIG. [Figure 2] FIG. 2 is a schematic cross-sectional view of the high-pressure tank 10. As shown in FIG. [Figure 3] FIG. 3 is a diagram illustrating the configuration of the evaluation device 20. [Figure 4] FIG. 4 is a diagram illustrating the configuration of the arithmetic unit 22. [Figure 5] FIG. 5 is a diagram illustrating the evaluation method S10. [Figure 6] FIG. 6 is a diagram illustrating the cumulative AE energy increase rate. [Figure 7] FIG. 7 is a diagram showing the relationship between the applied pressure and the accumulated AE energy in an actual example. [Figure 8] FIG. 8 is a diagram illustrating the evaluation method S20. [Figure 9] FIG. 9 is a diagram illustrating the waveform duration increase rate. [Figure 10] FIG. 10 is a diagram illustrating the evaluation method S30. [Figure 11] FIG. 11 is a diagram illustrating the relationship between the AE energy of a single waveform and rupture. [Figure 12] FIG. 12(a) is a diagram showing an example of an AE waveform before the threshold value, and FIG. 12(b) is a diagram showing an example of an AE waveform after the threshold value. [Figure 13] FIG. 13 is a diagram illustrating the configuration of the evaluation device 30. [Figure 14] FIG. 14 is a diagram for explaining the evaluation method S40. [Figure 15] FIG. 15 is a diagram showing the amplitude of the detected sound over time. DETAILED DESCRIPTION OF THE INVENTION

[0019] 1. High-pressure tank structure Fig. 1 shows a schematic view of the appearance of a high-pressure tank 10 according to one embodiment, and Fig. 2 shows a schematic cross section along the axis of the high-pressure tank 10. As can be seen from these figures, in this embodiment, the high-pressure tank 10 has a liner 11, a reinforcing layer 12, a protective layer 13, and a nozzle 14. Each component will be described below.

[0020] 1.1. Liner The liner 11 is a hollow member that defines the internal space of the high-pressure tank 10. The liner 11 may be made of any material that can hold the contents (e.g., hydrogen) contained in the internal space without leaking, and any known material can be used. Specifically, the liner 11 may be made of, for example, nylon resin, polyethylene-based synthetic resin, or metal such as stainless steel or aluminum. The thickness of the liner 11 is not particularly limited, but is preferably 0.5 mm to 1.0 mm.

[0021] 1.2.Reinforcing layer The reinforcing layer 12 is made up of multiple layers of fibers and contains a hardened resin that has been impregnated into the fibers. The fiber layer is formed by wrapping fiber bundles around the outer surface of the liner 11 in multiple layers to a predetermined thickness. The thickness of the reinforcing layer 12 is determined depending on the required strength and is not particularly limited, but is about 10 mm to 30 mm.

[0022] Carbon fibers are used for the fiber bundles of the reinforcing layer 12, and the fiber bundles are band-shaped bundles of carbon fibers having a predetermined cross-sectional shape (for example, a rectangular cross-section). Specific examples include, but are not limited to, a rectangular cross-sectional shape with a width of about 6 mm to 10 mm and a thickness of about 0.1 mm to 0.15 mm. The amount of carbon fibers contained in the fiber bundle is also not particularly limited, but may be, for example, about 36,000 carbon fibers.

[0023] The resin impregnated into the fibers in the reinforcing layer 12 and cured is not particularly limited as long as it can increase the strength of the fibers. Examples of such resins include thermosetting resins that are cured by heat, such as epoxy resins and unsaturated polyester resins that contain an amine- or anhydride-based curing accelerator and a rubber-based toughening agent. Other examples include resin compositions that use an epoxy resin as the base agent and are cured by mixing a curing agent into it. In this case, the resin composition, which is a mixture of the base agent and the curing agent, reaches and penetrates the fiber layer between the time of mixing and the time of curing, and then automatically hardens.

[0024] 1.3.Protective layer The protective layer 13 is a layer that is arranged on the outer periphery of the reinforcing layer 12 as needed, and when provided, is made by wrapping, for example, glass fiber and impregnating it with resin. The impregnated resin can be considered to be the same as the reinforcing layer 12. This makes it possible to impart impact resistance to the high-pressure tank 10. The thickness of the protective layer 13 is not particularly limited, but can be about 1.0 mm to 2.0 mm.

[0025] 1.4.Socket The nozzles 14 are components attached to the two opening ends of the liner 11, one of which functions as an opening that connects the inside and outside of the high-pressure tank 10, and also functions as an attachment part for attaching piping and valves to the high-pressure tank 10. If the liner 11 is made of metal, there is no need to provide a separate mouthpiece, and it is sufficient if a shape similar to that of the mouthpiece is formed continuously from the liner 11.

[0026] 2. Acoustic Emission Evaluation 2.1.Evaluation equipment An example of an evaluation device 20 will be described with reference to the drawings. FIG. 3 is a conceptual diagram illustrating the configuration of the evaluation device 20 together with the high-pressure tank 10 being evaluated. The evaluation device 20 is a device that detects and notifies the rupture of the high-pressure tank 10 due to an increase in the internal pressure of the high-pressure tank 10 before the rupture occurs. The evaluation device is required to detect the rupture at a pre-rupture pressure that is as close as possible to the pressure that will cause the rupture. When detecting signs of rupture before the rupture, it is relatively easy to make a safe judgment. However, if the rupture is judged too cautiously, it becomes impossible to properly grasp the relationship between the internal pressure of the high-pressure tank and the rupture, such as estimating the rupture mode or the burst pressure without causing the rupture. According to this embodiment, signs of rupture can be detected at a pre-rupture pressure that is close to the pressure that will cause the rupture (within a few MPa of the burst pressure).

[0027] The evaluation device 20 detects signs of rupture associated with filling of the high-pressure tank 10 with a fluid (e.g., hydrogen) by acoustic emission (AE). AE is a phenomenon in which strain energy stored in a material is released as elastic waves when force is applied to the material, resulting in deformation, and these elastic waves are called AE waves. In other words, when filling the high-pressure tank 10 with a fluid, deformation occurs in the high-pressure tank 10 during this process, and AE waves are generated in association with this deformation. The evaluation device 20 detects and processes these AE waves to obtain signs of rupture of the high-pressure tank 10. For this reason, the evaluation device 20 includes an acoustic emission sensor (AE sensor) 21 that detects acoustic emissions (AE) generated from the high-pressure tank 10 being evaluated, and a calculation device 22 that acquires information (digital signals) obtained by the AE sensor 21 and determines whether or not the tank will explode.

[0028] 2.1.1.AE Sensor The AE sensor 21 is a sensor that is attached to the surface of the high-pressure tank 10 and detects AE waves generated in the high-pressure tank 10. A known sensor can be used as the AE sensor 21, and is configured to include, for example, a piezoelectric element or the like. The placement of the AE sensors 21 on the high-pressure tank 10 is not particularly limited as long as they can effectively detect the AE waves generated in the high-pressure tank 10, and the necessary positions and number of AE sensors are applied for that purpose. For example, if detection is possible with one AE sensor 21, the AE sensor 21 may be placed in the center of the surface of the high-pressure tank 10, and if the length of the high-pressure tank 10 (the distance between the two nozzles 14) is greater than 1.5 m, multiple AE sensors 21 may be applied depending on the size.

[0029] 2.1.2. Arithmetic device The arithmetic unit 22 performs calculations on the digital data of the AE waves detected by the AE sensor 21 and determines whether there is a sign of a rupture. As conceptually shown in Fig. 4, the arithmetic unit 22 includes a CPU (Central Processing Unit) 22a which is a processor and performs calculations, a RAM (Random Access Memory) 22b which functions as a work area, a ROM (Read-Only Memory) 22c which functions as a recording medium, a receiving unit 22d which is an interface that receives information into the arithmetic unit 22 whether wired or wireless, and a transmitting unit 22e which is an interface that sends information from the arithmetic unit 22 to the outside whether wired or wireless. Therefore, the arithmetic unit 22 is connected to the AE sensor 21 and other devices via a receiving unit 22d and a transmitting unit 22e, and is configured to be able to transmit and receive signals.

[0030] The arithmetic device 22 stores a program that processes AE wave data (signals) from the AE sensor 21 and determines whether there is a sign of rupture. In the evaluation device 20, the CPU 22a, RAM 22b, and ROM 22c, which serve as hardware resources, work together with the program. Specifically, the CPU 22a executes the computer program recorded in the ROM 22c in the RAM 22b, which functions as a work area, thereby realizing various functions including the determination of a sign of rupture. Information acquired or generated by the CPU 22a is stored in the RAM 22b. Alternatively, a separate recording medium may be provided inside or outside the arithmetic device 22, and the program and various data may be recorded thereon.

[0031] In this embodiment, the arithmetic unit 22 acquires AE wave data from the AE sensor 21 via the receiver 22d. Then, based on the acquired digital data, the arithmetic unit 20 executes a computer program stored in the ROM 22c or another recording medium, while using a database stored in the ROM 22c or another recording medium, to perform arithmetic processing to determine whether or not a rupture has occurred, and records the determination in the RAM 22b or another recording medium. Specific details of the rupture determination will be described later. Necessary information regarding the result of the rupture determination is output from the transmitter 22e to the monitor 24 or the like.

[0032] Such an arithmetic unit 22 can typically be configured by a computer. Therefore, the arithmetic unit 22 has input means (keyboard, mouse, etc.) 23 for operating the arithmetic unit 22 connected to a receiving unit 22d.

[0033] 2.2.Rupture determination Next, a specific method for determining whether a product has burst will be described. In the following embodiments, the determination of whether a product has burst is performed by processing the AE wave data obtained by the AE sensor 21 with the arithmetic device 22, as described above. Here, the method for determining whether a product has burst will be described. To specifically execute this method, a computer program having steps corresponding to each process of the method is created, recorded in the ROM 22c of the arithmetic device 22 or a recording medium, and executed to determine whether a product has burst. The methods for determining whether a product has burst according to embodiments 1 to 3 will be described below. As described above, the computer program based on this method is recorded in the ROM 22c of the arithmetic device 22 or a recording medium, and functions as one component of the evaluation device 20.

[0034] 2.2.1. Example 1 Fig. 5 shows the flow of the burst determination method S10 according to embodiment 1. As can be seen from Fig. 5, the burst determination method S10 of this embodiment includes a pressurization start step S11, an AE wave data acquisition step S12, a cumulative AE energy calculation step S13, a cumulative AE energy sudden increase determination step S14, a pressurization stop step S15, and a burst pressure estimation step S16. Each step will be described below.

[0035] 2.2.1a. Pressurization process The pressurization start process S11 (sometimes referred to as "process S11") is a process in which pressurization of the inside of the high-pressure tank is started. The pressurization means and pressurization speed can be set appropriately depending on the high-pressure tank to be evaluated. For example, in the case of a hydrogen tank for a fuel cell, pressurization can be achieved by filling the high-pressure tank with hydrogen (or filling with a fluid other than hydrogen). The pressurization (pressurization) speed can be, for example, the pressure increase speed for normal hydrogen filling (0.15 MPa / sec to 0.35 MPa / sec). After pressurization is started in step S11, pressurization is continuously performed until pressurization is stopped in step S15, which will be described later.

[0036] 2.2.1b. AE wave data acquisition process In the AE wave data acquisition process S12 (sometimes referred to as "process S12"), AE wave data is acquired from the high-pressure tank. Specifically, when the above-mentioned evaluation device 20 is used, the calculation device 22 acquires the AE wave data from the AE sensor 21 installed in the high-pressure tank 10. Here, the interval at which the AE waves are acquired is not particularly limited, but can be acquired at a sampling rate of about 40 MHz, for example.

[0037] 2.2.1c. Accumulated AE energy calculation process In step S13 of calculating the accumulated AE energy (sometimes referred to as "step S13"), calculation is performed to obtain the accumulated AE energy. The accumulated AE energy has the following value. The obtained AE wave data has an AE waveform, which forms a waveform with an amplitude (not constant) (repeating a non-constant cycle) on either side of a reference line. In the AE waveform, one wave is counted from the point where it exceeds a certain set value to the point where it falls below the set waveform separation time value, and the AE energy is obtained by the area enclosed by the waveform of this one wave and the reference line. The cumulative AE energy is the accumulated value of all AE energy values generated per 0.1 MPa. In this embodiment, calculations are performed using Vallen's Vakken Acquisition.

[0038] 2.2.1d. Process for determining sudden increase in cumulative AE energy In step S14 of determining whether the accumulated AE energy has suddenly increased (sometimes referred to as "step S14"), it is determined whether the accumulated AE energy obtained in step S13 has suddenly increased. If it is determined in step S14 that the accumulated AE energy has suddenly increased, Yes is selected and the process proceeds to step S15, where pressurization is stopped. On the other hand, if it is determined in step S14 that the accumulated energy has not suddenly increased, the process returns to step S12 and continues acquiring AE wave data.

[0039] Whether or not the cumulative AE energy has increased sharply can be determined by whether or not the cumulative AE energy increase rate (ΔE / Δp), which is the ratio of the cumulative AE energy increase amount ΔE to the pressure increase amount Δp inside the high-pressure tank, exceeds a threshold, as shown schematically in Figure 6. The specific threshold can be set appropriately depending on the configuration of the high-pressure tank, etc., but for example, if the cumulative AE energy increase per 0.1 MPa is 50 × 10 7 (eU), i.e., the cumulative AE energy increase rate is 5×10 9 (eU / MPa), where 1 (eU) = 10 -14 (V 2 s).

[0040] Figure 7 shows a graph based on actual measurement results. In Figure 7, the horizontal axis shows the pressure (MPa) inside the high-pressure tank, and the vertical axis shows the accumulated AE energy (eU). As can be seen from this graph, the accumulated AE energy (eU) increases sharply at pressure P1, and it is at this point that the rate of increase in the accumulated AE energy exceeds the threshold value for the first time. This P1 is then taken as the pressure immediately before rupture.

[0041] 2.2.1e. Depressurization process In step S15 of stopping pressurization (sometimes referred to as "step S15"), when step S14 returns "Yes," the pressurization in the high-pressure tank is stopped. After the pressurization is stopped, the pressure in the high-pressure tank may be gradually reduced, or the pressure in the high-pressure tank may be maintained. However, at the time of step S15, damage to the high-pressure tank is considered to have progressed to a certain extent, and maintaining the pressure is likely to lead to rupture, so it is preferable to reduce the pressure.

[0042] 2.2.1f. Burst pressure estimation process In the burst pressure estimation step S16 (sometimes referred to as "step S16"), the burst pressure of the high-pressure tank is estimated and notified. The estimated burst pressure of the high-pressure tank is based on AE data obtained when a burst test of the high-pressure tank is conducted in advance. Therefore, the estimated burst pressure is calculated by adding a predetermined value based on AE data obtained when the burst test is conducted to the pressure just before rupture. According to this embodiment, the difference between the pressure just before rupture and the estimated burst pressure can be reduced. For example, the difference between the estimated burst pressure and the pressure just before rupture can be kept within 10 MPa. In the example shown in Figure 7, the high-pressure tank actually ruptured when 5 MPa was applied from the just before rupture pressure P1. The notification is made by displaying on a monitor or the like.

[0043] 2.2.2. Example 2 Fig. 8 shows the flow of the burst determination method S20 according to embodiment 2. As can be seen from Fig. 8, the burst determination method S20 of this embodiment includes a pressurization start step S21, an AE wave data acquisition step S22, a waveform duration calculation step S23, a waveform duration sudden increase determination step S24, a pressurization stop step S25, and a burst pressure estimation step S26. Each step will be described below.

[0044] 2.2.2a. Pressurization start process The pressurization start process S21 (sometimes referred to as "process S21") is a process in which pressurization inside the high-pressure tank is started. Process S21 can be considered to be the same as the above-mentioned process S11.

[0045] 2.2.2b. AE wave data acquisition process In the AE wave data acquisition step S22 (sometimes referred to as "step S22"), AE wave data is acquired from the high-pressure tank. Step S22 can be considered to be the same as step S12 above.

[0046] 2.2.2c. Waveform duration calculation process In the waveform duration calculation process S23 (sometimes referred to as "process S23"), the waveform duration is calculated. The waveform duration is well known. AE waves occur intermittently as the pressure in the high-pressure tank increases, and the waveform duration is the time during which a wave with an amplitude exceeding a certain set value persists. This set value can be determined as needed. In other words, as described above, the period from when the AE wave exceeds the set value to when it falls below the set waveform separation time value is counted as one wave, and the waveform duration is the time from when this wave exceeds the set value to when it falls below the set value by the waveform separation time.

[0047] 2.2.2d. Waveform Duration Sudden Increase Judgment Process In step S24 of determining whether the waveform duration has suddenly increased (sometimes referred to as "step S24"), it is determined whether the waveform duration obtained in step S23 has suddenly increased. If it is determined in step S24 that the waveform duration has suddenly increased, Yes is selected and the process proceeds to step S25, where pressure is stopped. On the other hand, if it is determined in step S24 that the waveform duration has not suddenly increased, the process returns to step S22 and continues acquiring AE wave data.

[0048] Whether or not the waveform duration has increased suddenly can be determined by whether or not the waveform duration increase rate (ΔT / Δp), which is the ratio of the increase in waveform duration ΔT to the increase in pressure Δp in the high-pressure tank, exceeds a threshold, as shown schematically in Figure 9. The specific threshold can be set appropriately depending on the configuration of the high-pressure tank, etc. The pressure when the threshold value is exceeded for the first time is defined as the pre-breakdown pressure.

[0049] 2.2.2e. Depressurization process In step S25 of stopping pressurization (sometimes referred to as "step S25"), when step S24 returns "Yes," the pressurization in the high-pressure tank is stopped. After the pressurization is stopped, the pressure in the high-pressure tank may be gradually reduced, or the pressure in the high-pressure tank may be maintained. However, at the time of step S25, damage to the high-pressure tank is considered to have progressed to a certain extent, and maintaining the pressure is likely to lead to rupture, so it is preferable to reduce the pressure.

[0050] 2.2.2f. Burst pressure estimation process In the burst pressure estimation step S26, the burst pressure of the high-pressure tank is estimated and notified. The estimated burst pressure of the high-pressure tank is based on AE data obtained when a burst test of the high-pressure tank is conducted in advance. Therefore, the estimated burst pressure is calculated by adding a predetermined value based on AE data obtained when the burst test is conducted to the pressure just before burst. According to this embodiment, the difference between the pressure just before burst and the estimated burst pressure can be reduced. For example, the difference between the estimated burst pressure and the pressure just before burst can be reduced to within 10 MPa. The notification is made by displaying on a monitor or the like.

[0051] 2.2.3. Example 3 Fig. 10 shows the flow of the burst determination method S30 according to embodiment 3. As can be seen from Fig. 10, the burst determination method S30 of this embodiment includes a pressurization start step S31, an AE wave data acquisition step S32, a single waveform AE energy calculation step S33, a determination step S34 as to whether the AE energy is equal to or greater than a threshold value, a pressurization stop step S35, and a burst pressure estimation step S36. Each step will be described below.

[0052] 2.2.3a. Pressurization process The pressurization start process S31 (sometimes referred to as "process S31") is a process in which pressurization inside the high-pressure tank is started. Process S31 can be considered to be the same as process S11 described above.

[0053] 2.2.3b. AE wave data acquisition process In the AE wave data acquisition step S32 (sometimes referred to as "step S32"), AE wave data (signals) are acquired from the high-pressure tank. Step S32 can be considered to be the same as step S12 above.

[0054] 2.2.3c. AE energy calculation process for single waveform In the step S33 of calculating the AE energy of a single waveform (sometimes referred to as "step S33"), the AE energy is calculated for each single waveform of the AE wave. Here, the AE energy of a single waveform is the time integral value of the square of the AE wave signal, which roughly corresponds to the square of the voltage value at each point of the AE wave signal multiplied by the sampling interval, and is expressed as 1(eU)=10 -14 (V 2 s).

[0055] 2.2.3d. Process for determining whether the threshold is exceeded In step S34 of determining whether the AE energy of the single waveform obtained in step S33 is equal to or greater than the threshold (sometimes referred to as "step S34"), it is determined whether the AE energy of the single waveform obtained in step S33 is equal to or greater than the threshold. If it is determined in step S34 that the AE energy of the single waveform is equal to or greater than the threshold, Yes is selected and the process proceeds to step S35, where pressure application is stopped. On the other hand, if it is determined in step S34 that the AE energy of the single waveform is lower than the threshold, the process returns to step S32 and continues acquiring AE wave data. The pressure when it first exceeds the threshold is then determined to be the pre-breakdown pressure.

[0056] The inventors have discovered that the AE energy of a single waveform increases immediately before rupture, as shown in Figure 11. Figure 11, with time on the horizontal axis, shows the change in the AE energy of a single waveform as the internal pressure of the high-pressure tank is increased. As can be seen from Figure 11, the AE energy of a single waveform rises sharply immediately before the high-pressure tank ruptures. Figure 12 shows a portion of the AE waveform. Figure 12(a) shows the waveform before the threshold, and Figure 12(b) shows the waveform after the threshold. As can be seen, the AE waveform changes significantly before and after the threshold, with the amplitude increasing.

[0057] The threshold value for determining the AE energy of a single waveform differs depending on the size, structure, and type of the high-pressure tank, and it is advisable to obtain a threshold value in advance for each type of tank, and there are no particular limitations. However, as a result of the inventors' investigations, it was decided that the threshold value should be 1×10 regardless of the size, structure, and type of these tanks. 8 (eU)~10×10 8 (eU), preferably 5 × 10 8 (eU). This produces the effects described below. The AE energy of a single waveform obtained when the pressure inside the tank is low (before the threshold) is 1 x 10 5 (eU) or less.

[0058] 2.2.3e. Depressurization process In step S35 of stopping pressurization (sometimes referred to as "step S35"), when step S34 returns "Yes," the pressurization in the high-pressure tank is stopped. After the pressurization is stopped, the pressure in the high-pressure tank may be gradually reduced, or the pressure in the high-pressure tank may be maintained. However, at the time of step S35, damage to the high-pressure tank is considered to have progressed to a certain extent, and maintaining the pressure is likely to lead to rupture, so it is preferable to reduce the pressure.

[0059] 2.2.3f. Burst pressure estimation process In the burst pressure estimation step S36, the burst pressure of the high-pressure tank is estimated and notified. The estimated burst pressure of the high-pressure tank is based on AE data obtained when a burst test of the high-pressure tank is conducted in advance. Therefore, the estimated burst pressure is calculated by adding a predetermined value based on AE data obtained when the burst test is conducted to the pressure just before burst. According to this embodiment, the difference between the pressure just before burst and the estimated burst pressure can be reduced. For example, the difference between the estimated burst pressure and the pressure just before burst can be reduced to within 10 MPa. The notification is made by displaying on a monitor or the like.

[0060] 2.3. Effects etc. The device and method of this embodiment make it possible to estimate the burst pressure of a high-pressure tank with high accuracy without causing the tank to burst. According to the inventors' studies, other characteristic values of AE waves (AE count number, maximum amplitude value, etc.) have large fluctuations in magnitude and differ greatly between high-pressure tanks, making it difficult to improve the accuracy of burst pressure estimation. In contrast, this embodiment makes it possible to estimate the burst pressure of a high-pressure tank with high accuracy without causing the high-pressure tank to burst, making it easier to observe the cross-section of a high-pressure tank just before it bursts and to conduct development evaluations while preventing damage to equipment.

[0061] Furthermore, in Form 3, the judgment is made based on the AE energy of a single waveform, so the time required for judgment can be shortened compared to judgment after obtaining the cumulative value as in Form 1 or the duration as in Form 2, and a more accurate state immediately before rupture can be obtained.

[0062] 3. Evaluation by sound 3.1.Evaluation equipment An example of an evaluation device 30 will be described with reference to the drawings. FIG. 13 is a conceptual diagram illustrating the configuration of the evaluation device 30 together with the high-pressure tank 10 being evaluated. The evaluation device 30 is a device that detects and notifies the rupture of the high-pressure tank 10 due to an increase in the internal pressure of the high-pressure tank 10 before the rupture occurs. The evaluation device is required to detect the rupture at a pre-rupture pressure that is as close as possible to the pressure that will cause the rupture. When detecting signs of rupture before the rupture, it is relatively easy to make a safe judgment. However, if the rupture is judged too cautiously, it becomes impossible to properly grasp the relationship between the internal pressure of the high-pressure tank and the rupture, such as estimating the rupture mode or the burst pressure without causing the rupture. According to this embodiment, signs of rupture can be detected at a pre-rupture pressure that is close to the pressure that will cause the rupture (within a few MPa of the burst pressure).

[0063] The evaluation device 30 detects signs of rupture by sound when the high-pressure tank 10 is filled with a fluid (e.g., hydrogen). The inventors discovered that as the internal pressure of the high-pressure tank 10 increases, a characteristic sound is generated just before the tank ruptures. This fact is utilized to detect signs of rupture. Therefore, the evaluation device 30 is equipped with a sound collector 31 that detects the sound generated from the high-pressure tank 10 being evaluated, and a calculation device 32 that acquires the information (digital signal) obtained by the sound collector 31 and determines whether or not the tank will burst.

[0064] 3.1.1. Sound collector The sound collector 31 is a sensor that collects sounds emitted from the high-pressure tank 10. A known sound collector can be used as the sound collector 31, and for example, a sound collecting microphone can be mentioned. The number and arrangement of the sound collectors 31 are not particularly limited as long as they can effectively detect sounds generated in the high-pressure tank 10, and any position necessary for that purpose can be used. For example, when the axial size of the high-pressure tank 10 is the overall length, one sound collector can be placed at a position 200 mm away from the tank surface in the center. However, as mentioned above, the number and arrangement are not limited to this and can be set appropriately depending on the conditions.

[0065] 3.1.2. Arithmetic device The arithmetic unit 32 performs calculations on the digital data of the sound detected by the sound collector 31 and determines whether there is a sign of an explosion. The specific embodiment can be considered to be similar to that of the arithmetic unit 22 described above, with the sound collector 31 instead of the AE sensor 21 being communicably connected to the receiving unit 22d, and the obtained sound is evaluated as will be described later.

[0066] 3.2.Rupture determination Next, a specific method for determining whether a sound has burst will be described. In the following embodiment, the determination of whether a sound has burst is performed by processing sound data obtained by the sound collector 31 with the arithmetic device 32, as described above. Here, the method for determining whether a sound has burst will be described. To specifically execute this method, a computer program having steps corresponding to each process of the method is created, recorded in the ROM 22c of the arithmetic device 32 or a recording medium, and executed to perform the determination of whether a sound has burst. A method for determining whether a sound has burst according to embodiment 4 will be described below. As described above, a computer program based on this method is recorded in the ROM 22c of the arithmetic device 32 or a recording medium, and functions as one component of the evaluation device 30.

[0067] Fig. 14 shows the flow of the burst determination method S40 according to embodiment 4. As can be seen from Fig. 14, the burst determination method S40 of this embodiment includes a pressurization start step S41, a sound data acquisition step S42, a determination step S43 as to whether the sound data is equal to or greater than a threshold value, a pressurization stop step S44, and a burst pressure estimation step S45. Each step will be described below.

[0068] 3.2.1.Pressure Start Process The pressurization start process S41 (sometimes referred to as "process S41") is a process in which pressurization inside the high-pressure tank is started, and can be considered to be the same as the pressurization start process S11 described above.

[0069] 3.2.2. Sound data acquisition process In the sound data acquisition process S42 (sometimes referred to as "process S42"), data on the sound emitted from the high-pressure tank is acquired. Specifically, when the evaluation device 30 described above is used, the calculation device 32 acquires the sound data from the sound collector 31 installed in the high-pressure tank 10. The interval at which the sound is acquired here is not particularly limited, but it can be acquired at a sampling rate of about 40 MHz, for example.

[0070] 3.2.3. Process for determining whether the threshold is exceeded In step S43 (sometimes referred to as "step S43") of determining whether the sound is above the threshold, it is determined whether the sound obtained in step S42 is above the threshold. If it is determined in step S43 that the sound is above the threshold, Yes is selected and the process proceeds to step S44, where pressurization is stopped. On the other hand, if it is determined in step S43 that the sound is lower than the threshold, the process returns to step S42 and continues acquiring sound data. The pressure when the threshold is exceeded for the first time is set as the pre-breakdown pressure.

[0071] The inventors have discovered that the AE energy of a single waveform increases immediately before the explosion, as explained in the third embodiment above, and have also discovered that a distinctive sound occurs at the same time. This sound is a high-pitched sound (similar to a "bang") that can be detected by the human ear. As a result of extensive research, it has been discovered that a sound with a different frequency and / or amplitude occurs immediately before the explosion. Figure 15 shows the waveform of the sound, with the horizontal axis representing time (seconds). As can be seen from Figure 15, the amplitude of the sound increases immediately before the explosion. It has also been discovered that the frequency immediately before the explosion increases.

[0072] The sound threshold varies depending on the size, structure, and type of the high-pressure tank and the placement of the sound collector, and it is advisable to determine the threshold in advance depending on the conditions, and there are no particular limitations. However, as a result of the inventors' investigation, it was decided that the threshold is not limited to these conditions and that the amplitude is 3 × 10 4 The frequency band can be 15 kHz. When the pressure inside the high-pressure tank is low, the amplitude obtained is 3 x 10 2 , the frequency band is lower than 15kHz.

[0073] 3.2.4. Pressure Stop Process In step S44 of stopping pressurization (sometimes referred to as "step S44"), when step S43 returns "Yes," the pressurization in the high-pressure tank is stopped. After the pressurization is stopped, the pressure in the high-pressure tank may be gradually reduced, or the pressure in the high-pressure tank may be maintained. However, at the time of step S44, damage to the high-pressure tank is considered to have progressed to a certain extent, and maintaining the pressure is likely to lead to rupture, so it is preferable to reduce the pressure.

[0074] 3.2.5. Burst pressure estimation process In the burst pressure estimation step S45, the burst pressure of the high-pressure tank is estimated and notified. The estimated burst pressure of the high-pressure tank is based on sound data obtained when a burst test of the high-pressure tank is conducted in advance. Therefore, the estimated burst pressure is calculated by adding a predetermined value based on sound data obtained when the burst test is conducted to the pressure just before burst. According to this embodiment, the difference between the pressure just before burst and the estimated burst pressure can be reduced. For example, the difference between the estimated burst pressure and the pressure just before burst can be reduced to within 10 MPa. The notification is made by displaying on a monitor or the like.

[0075] 3.3. Effects etc. The device and method of this embodiment make it possible to estimate the burst pressure of a high-pressure tank with high accuracy without causing the tank to burst. According to the inventors' studies, other characteristic values of AE waves (AE count number, maximum amplitude value, etc.) have large fluctuations in magnitude and differ greatly between high-pressure tanks, making it difficult to improve the accuracy of burst pressure estimation. In contrast, this embodiment makes it possible to estimate the burst pressure of a high-pressure tank with high accuracy without causing the high-pressure tank to burst, making it easier to observe the cross-section of a high-pressure tank just before it bursts and to conduct development evaluations while preventing damage to equipment.

[0076] Furthermore, this embodiment is also useful when it is desired to simply detect signs of explosion, such as when measurement equipment using AE is not available. [Explanation of symbols]

[0077] 10...High-pressure tank, 11...Liner, 12...Reinforcing layer, 13...Protective layer, 14...Mouth cap, 20...Evaluation device, 21...AE sensor, 22...Calculation device, 30...Evaluation device, 31...Sound collector, 32...Calculation device

Claims

1. 1. A method for evaluating a tank, comprising: measuring acoustic emissions while pressurizing the tank; and calculating a waveform duration due to the measured acoustic emission, The pressure at which the increase rate of the waveform duration is equal to or greater than a threshold is defined as the pre-burst pressure. How to evaluate tanks.

2. 2. The tank evaluation method according to claim 1, further comprising the step of adding a predetermined value to the pressure immediately before rupture to obtain an estimated rupture pressure.

3. A tank evaluation device, comprising: an acoustic emission sensor disposed in the tank; a calculation device that acquires acoustic emission data from the acoustic emission sensor and performs calculations; The calculation device calculates a waveform duration based on the acoustic emission data, and determines the pressure at which the rate of increase of the waveform duration reaches a certain level or more as the pre-burst pressure. Tank evaluation device.

4. 4. The tank evaluation device according to claim 3, wherein the calculation device estimates the burst pressure by adding a predetermined value to the immediately preceding burst pressure.

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