JP2017223564A - Pressure tank inspection method, inspection system and inspection program - Google Patents

Abstract

An object of the present invention is to inspect a pressure tank for fatigue damage while the pressure tank is in service. [Solution] In a pressure tank inspection method, acoustic emission waves generated from the pressure tank are detected, acoustic emission parameters are acquired based on the detected acoustic emission waves, and damage to the pressure tank is detected based on the acoustic emission parameters. to decide. [Selection diagram] Figure 9

Description

  The present invention relates to a pressure tank inspection method, an inspection system, and an inspection program, and more particularly to an inspection method for inspecting fatigue damage by detecting an acoustic emission wave generated from a pressure tank.

  In recent years, with respect to issues such as global warming and depletion of fossil fuels, drastic enhancement of energy saving, improvement of energy security, and reduction of environmental load are required. Technologies related to fuel cell vehicles (FCV) and technologies related to hydrogen production, hydrogen transport and hydrogen storage are positioned as important technologies in Japan's policy, and are expected to spread quickly. In order to improve the competitiveness of FCV-related industries, it is indispensable to increase the safety and reliability of hydrogen stations, thereby ensuring social acceptance and promoting the installation of hydrogen stations.

  This hydrogen station has a high pressure compressor connected to a hydrogen supply source, a plurality of pressure accumulators (pressure tanks) connected to the high pressure compressor, and a dispenser connected to the pressure accumulator and supplying hydrogen to the FCV. It has a configuration. In the past, the accumulator was limited to a steel pressure tank, resulting in a thick wall and a significant increase in cost for installing the hydrogen station. Therefore, technical standards are being developed so that a pressure tank made of a composite container that is lighter than a steel pressure tank and is expected to reduce costs can be used.

  The structure of four main types of pressure tanks is shown in FIGS. 1A to 1D, the left side portion of each pressure tank is a schematic side view showing the outside of the container, and the right side portion of each pressure tank is a schematic cross-sectional view showing the inside of the container. FIG. 1A shows a type 1 container 10 which is a metal pressure tank. FIG. 1B is a composite container (pressure tank) having a liner 21 made of metal such as chromomolybdenum steel and a hoop layer 22 made of carbon fiber reinforced resin (CFRP) wound around the body of the liner 21. A type 2 container 20 is shown.

  FIG. 1C shows a metal liner 31 such as an aluminum alloy, a CFRP hoop layer 32 wound around the body of the liner 31, and a CFRP helical layer 33 helically wound around the mirror portion of the liner 31. A type 3 container 30 is shown which is a composite container. 1D shows a liner 41 made of thermoplastic resin, a hoop layer 42 made of CFRP wound around the body of the liner 41, a helical layer 43 made of CFRP helically wound around the mirror part of the liner 41, 1 shows a type 4 container 40 which is a composite container having a base 44 provided on a liner 41.

  The main deterioration phenomenon of the pressure tank at the hydrogen station is liner fatigue damage due to repeated pressurization by supplying hydrogen to the pressure tank and depressurization by releasing hydrogen to FCV. Fatigue damage occurs on the inner surface of the liner, progresses from the inner surface, penetrates the liner, and hydrogen leaks. What is required of the safety inspection to prevent hydrogen leakage is to grasp the progress of fatigue damage during the operation of the pressure tank without greatly hindering the operation of the hydrogen station.

  As inspection methods for fatigue damage of pressure tanks, visual inspection, penetration inspection, ultrasonic inspection, and radiographic inspection are being studied. Fatigue damage occurs from the inner surface of the liner during use of the pressure tank, fatigue damage develops, and hydrogen leaks through the liner. Therefore, an inspection technique for inspecting the progress of fatigue damage is required in order to prevent leakage. However, any of the above-described inspection methods being considered is insufficient as a security inspection as shown below.

  Visual inspection from the outside does not allow the inspector to find fatigue damage that has occurred on the inside surface of the liner. The inspector can also stop using the pressure tank, open the inside of the pressure tank, and visually inspect the inner surface of the liner with a fiberscope. However, fatigue damage is an extremely fine crack and cannot be detected visually. In addition, the operation of opening the pressure tank needs to stop the operation of the hydrogen station, and since it cannot be inspected during operation, it has the effect of a loss of work.

  In the penetrant inspection, the use of the pressure tank is stopped, the inside of the pressure tank is opened, and a fine crack due to fatigue damage can be detected from the inner surface of the liner. However, in the penetrant inspection, since the penetrant is applied to the inner surface of the metal liner, it is difficult to completely remove the penetrant after the inspection. Therefore, the inside of the pressure tank is contaminated with the permeate, and there is a possibility that the fuel for FCV that requires a hydrogen purity of 99.99% or more cannot be stored. In addition, the operation of opening the pressure tank needs to stop the operation of the hydrogen station, and since it cannot be inspected during operation, it has the effect of a loss of work.

  In the ultrasonic flaw detection inspection, the inspector enters the ultrasonic wave from the outer surface of the pressure tank without opening the pressure tank, and detects and analyzes the reflected wave from the fatigue damage to inspect the progress of the fatigue damage. For example, the mirror part of the type 2 container 20 can detect fatigue damage by ultrasonic waves. However, due to the CFRP hoop layer 22, it is difficult to detect fatigue damage by ultrasonic waves in the body portion of the type 2 container 20. In addition, since the body of the 300 L pressure tank has a wide flaw detection range of about 0.5 m in diameter and about 3 to 6 m in length, inspection takes time. Furthermore, in the ultrasonic flaw detection, it is necessary to discharge the hydrogen in the pressure tank, and since it cannot be inspected during operation, it has the effect of being closed.

  In the hydrogen station, a plurality of pressure tanks are stacked and mounted on the curdle. For this reason, there is a pressure tank in which ultrasonic waves cannot be incident because the surface of the pressure tank cannot be accessed. If the pressure tank is taken out from the cardle, ultrasonic waves can be incident, but it is necessary to stop the operation of the hydrogen station in order to take out the pressure tank. Furthermore, it takes about one week including the inspection time after mounting to remount the removed pressure tank on the curdle. The metal liner 31 of the type 3 container 30 is covered with a thick CFRP hoop layer 32 on the entire surface. Since CFRP has a large attenuation of ultrasonic waves, it is difficult to detect fatigue damage by ultrasonic flaw detection.

  In the radiation transmission test, it is necessary to remove the pressure tank mounted on the curdle of the hydrogen station. The work to take out the pressure tank needs to stop the operation of the hydrogen station, and because it cannot be inspected during operation, it will have an impact on business hours off. Furthermore, it takes about one week including the inspection time after mounting to remount the removed pressure tank on the curdle.

  Therefore, there is a need for a practical inspection method for fatigue damage of a pressure tank in service. In particular, in the type 2 container 20 shown in FIG. 1B and the type 3 container 30 shown in FIG. 1C, the metal liners 21 and 31 are reinforced by the CFRP hoop layers 22 and 32. Thereby, very fine cracks on the inner surfaces of the liners 21 and 31 wrapped thickly in the hoop layers 22 and 32 propagate in the thickness direction of the liners 21 and 31. There is no practical inspection method for such fatigue damage.

  In this regard, there are many examples of inspecting the progress of fatigue damage of a metal material using an acoustic emission (AE) method which is a kind of nondestructive inspection technology. In the AE method, an AE sensor is installed on an inspection target, and elastic waves (AE waves) generated with the progress of a crack inside the test target are passively detected to detect damage on the inspection target. For example, Patent Document 1 discloses a bearing diagnosis method for diagnosing the life of a bearing in a rotating machine using the AE method.

JP 2012-242336 A

  However, since the AE parameter is greatly affected by the inspection target, the bearing life diagnosis method cannot be directly used as the pressure tank inspection method.

  In order to solve the above-described problem, a pressure tank inspection method as an example of the present invention detects an acoustic emission wave generated from the pressure tank, acquires an acoustic emission parameter based on the detected acoustic emission wave, and The damage of the pressure tank is determined based on the acoustic emission parameter.

  According to another embodiment of the present invention, a pressure tank inspection system includes a sensor for detecting an acoustic emission wave generated from the pressure tank, and a parameter acquisition for acquiring an acoustic emission parameter based on the detected acoustic emission wave. An amplitude that is a ratio of a representative value of an amplitude value in a second frequency band different from the first frequency band of the acoustic emission wave to a representative value in an amplitude value of the first frequency band of the acoustic emission wave And a parameter acquisition unit that acquires a value of the ratio as the acoustic emission parameter.

  Further, the pressure tank inspection program as another example of the present invention causes a computer to function as a parameter acquisition unit that acquires an acoustic emission parameter based on an acoustic emission wave generated from the pressure tank, and the parameter acquisition unit includes: A value of an amplitude ratio that is a ratio of a representative value of an amplitude value in a second frequency band different from the first frequency band of the acoustic emission wave to a representative value in an amplitude value of the first frequency band of the acoustic emission wave, Obtained as the acoustic emission parameter.

  Thereby, fatigue damage of the pressure tank can be inspected while the pressure tank is in service.

  Further features of the present invention will become apparent from the following description of embodiments, given by way of example with reference to the accompanying drawings.

A schematic side view of the outside of the container and a schematic cross-sectional view of the container center cut along the longitudinal direction are shown. A shows a type 1 container, B shows a type 2 container, C shows a type 3 container, D Indicates a type 4 container. It is a schematic perspective view around the edge part of a pressure tank. It is a graph which shows the relationship between the AE amplitude value of the frequency band of 200 kHz-300 kHz, and the number of cycles until leakage. It is a graph which shows the relationship between the AE amplitude value of all frequency bands, and the number of cycles until leakage. It is a graph which shows the relationship between AE amplitude ratio and the cycle number until a leak. It is a graph which shows the relationship between AE amplitude ratio and stress amplitude. 1 is a schematic block diagram illustrating an inspection system according to a first embodiment. It is a flowchart explaining an inspection procedure. It is a schematic block diagram which shows the inspection system which concerns on 2nd Embodiment.

  Hereinafter, exemplary embodiments for carrying out the present invention will be described in detail with reference to the drawings. However, dimensions, materials, shapes, and relative positions of components described in the following embodiments are arbitrary, and can be changed according to the configuration of the apparatus to which the present invention is applied or various conditions. In addition, unless otherwise specified, the scope of the present invention is not limited to the embodiments specifically described below.

[First Embodiment]
The acoustic emission parameter (AE parameter) to be inspected is acquired by performing signal processing on the AE wave detected by the AE sensor. Specifically, the AE parameters include the number of AE occurrences, AE amplitude, AE energy, AE waveform (maximum amplitude value, rise time, duration, etc.), AE frequency, AE average value, AE effective value, AE count rate, and Includes the total number of AE counts. When the AE method is used when examining the progress of fatigue damage, the AE parameters such as the number of AEs generated, the AE amplitude, and the absolute value of the AE energy generally increase as the fatigue damage progresses. The inventors confirmed in the fatigue test using the test piece that the amplitude value of AE among the AE parameters, in particular, increased to the right as the fatigue damage progressed. Therefore, if this parameter is used as an inspection index, the progress of fatigue damage of the pressure tank can be grasped.

[Installation location of AE sensor]
When installing the AE sensor in the pressure tank, in particular, when installing the AE sensor in the type 2 container 20 of FIG. 1B and the type 3 container 30 of FIG. This is because, for example, the surface of the metal liner 21 of the type 2 container 20 is covered with the hoop layer 22 made of CFRP, and there is almost no exposed portion of the liner 21 to the outside. For this reason, the AE sensor cannot be installed directly on the liner 21 and AE cannot be detected with high sensitivity. Although an AE sensor can be installed on the hoop layer 22, CFRP has a large attenuation, so that the detection sensitivity of AE is lowered, which is not realistic. Similarly, the type 3 container 30 also has low AE detection sensitivity.

  Therefore, the installation location of the AE sensor for measuring the AE wave with high sensitivity will be described with reference to FIG. In addition, since the both ends of the pressure tank 50 are equipped with the same structure, only the one end is demonstrated and description of the other end is abbreviate | omitted.

  Generally, a container valve 51 is provided at the end of the pressure tank 50, and a hydrogen pipe 52 can be attached to the valve 51. The valve 51 is provided with a flat portion 53 for coming into contact with a tool (wrench) for fixing the valve 51 to the pressure tank 50. Therefore, the AE sensor 54 is bonded to the flat portion 53 of the valve 51. Thereby, since the container valve 51 is firmly fixed to the metal liner with the metal screw, the AE sensor 54 can measure the AE wave with high sensitivity.

  When installed on the flat portion 53 of the valve 51, the AE sensor 54 can be installed without opening the pressure tank 50 during operation at the hydrogen station. Furthermore, since the valve 51 is generally provided with a flat portion 53, it is not necessary to form a separate flat surface for attaching the AE sensor 54. The AE sensor 54 is attached by a general method. For example, when the AE sensor 54 is a piezoelectric element type, first, a jig (not shown) is fixed to the flat portion 53 of the container valve 51. Then, the AE sensor 54 is inserted into the fixed jig, and is fixed from behind the AE sensor 54 with a screw or the like via an elastic body. Furthermore, an insulating tape for noise suppression may be wound around the case of the AE sensor 54. Further, a contact medium such as petrolatum may be applied to the wave receiving surface of the AE sensor 54.

[Amplitude ratio]
The absolute value of the number of AE occurrences, the AE amplitude, and the AE energy is greatly affected by inspection conditions (AE sensor installation location, evaluation target, pressure fluctuation range, and the like). Therefore, fatigue damage can be inspected by monitoring with an AE sensor that is always attached to the pressure tank, but it is not suitable for in-service inspections, which are regular inspections. On the other hand, there is an AE frequency as an AE parameter which is not affected by the inspection condition. As a result of the inventors conducting a fatigue test with the test piece, it was revealed that the AE of the pressure tank accompanying the progress of fatigue damage is a high frequency (for example, 200 kHz to 300 kHz).

  That is, the AE in the high frequency band obtained by removing the low frequency (for example, 100 kHz or less) AE with a frequency filter in order to remove the AE from the hoop layer is the pressure tank accompanying the progress of fatigue damage. It became clear that it was AE. Since the pressure tank is subjected to self-tightening treatment at a pressure higher than the normal pressure, the CFRP hoop layer having a particularly remarkable Kaiser effect is not destroyed if the pressure tank is used at the normal pressure. The Kaiser effect is an irreversible phenomenon peculiar to AE in which AE is generated when a load is applied to the material, but AE is not generated until the previous maximum load is exceeded when the load is unloaded once and the load is applied again. Therefore, when evaluating the fatigue damage of the pressure tank, it is possible not to consider the destruction of the CFRP hoop layer.

  However, it is also conceivable that the hoop layer is damaged due to the surface damage of the hoop layer that occurs during the transportation of the pressure tank, and the hoop layer is destroyed, and AE is generated along with the destruction. Therefore, it is desirable to distinguish the AE wave accompanying the destruction of the hoop layer from the AE wave accompanying the fatigue damage of the metal liner. Specifically, the inventors have confirmed from experimental results that the AE wave accompanying the destruction of the hoop layer is composed of a frequency component of less than 200 kHz, and particularly includes a large amount of a component of 70 kHz.

  However, as a result of the accelerated fatigue test using the type 3 container 30 by the inventors, a significant correlation may not be observed between the progress of fatigue damage and the AE amplitude value at a high frequency. This will be described with reference to the graph of the AE amplitude value in the frequency band of 200 kHz to 300 kHz shown in FIG. In FIG. 3, the vertical axis indicates the absolute value of the maximum AE amplitude value in each cycle, and the horizontal axis indicates the number of cycles in the fatigue test. In this fatigue test, the AE generation behavior of the composite container as a pressure tank was investigated. The specifications of this composite container were: design pressure: 45 MPa, minimum burst pressure: 135 MPa (rupture safety factor of 3 or more), internal volume: 30 L, aluminum liner material: A6061-T6, hoop layer material: PAN system. Further, at the time of manufacturing the composite container, a residual compressive stress of 253 MPa was applied by the self-tightening process.

  The test conditions of the fatigue test were: pressure medium: ion-exchanged water, pressure range: 1 to 75 MPa, repetition frequency: 0.05 Hz, circumferential stress range: −253 to 5 MPa, number of repetitions until leakage (number of cycles): 24, It was 925 times. Further, a VS150-RIC sensor (manufactured by Vallen) as an AE sensor was attached to the flat portions of the valves at both ends of the composite container. Furthermore, an AE-144A sensor (manufactured by Fuji Ceramics) was attached as an AE sensor to the flat portions of the valves at both ends of the composite container. Moreover, AMSY-5 (made by Vallen) was used for the AE measuring apparatus.

  When an internal pressure of 75 MPa was applied to the composite container having a design pressure of 45 MPa, leakage was confirmed in about 25,000 cycles, and the crack penetrated from the body of the liner in a shearing manner. At this time, even if the time-dependent change in the AE amplitude value of 200 kHz to 300 kHz was observed, as shown in the graph of FIG.

  The composite container is self-adhesive and causes plastic deformation in the metal liner, shifting the average stress of the liner to the compression side (loading the liner with a large residual compressive stress during manufacturing) and extending the fatigue life. Has been. Therefore, the inventors considered that the following three influences due to the self-tightening treatment were due to the fact that no significant correlation was observed between the progress of fatigue damage and the high-frequency AE amplitude value.

  First, slip lines are generated in a metal liner by self-tightening treatment, but the AE of fatigue damage along the slip lines has a small amplitude value and a small number of occurrences. Secondly, AE occurs from a stress-concentrated portion due to self-adhesive processing or a micro-scratch when processing a metal liner at an early stage of fatigue damage. Third, since the phenomenon that the crack progresses to the shearing method by self-tightening treatment is observed, when the crack propagates in the shear direction, the stress applied to the crack tip is reduced by half due to the influence of the radial direction of AE. As a result, the AE amplitude value decreases.

  Due to these three effects, in contrast to specimens, during fatigue testing of composite containers, in addition to AE associated with the progress of fatigue damage with a low amplitude value of 200 kHz to 300 kHz, it is caused by localized stress concentration or initial cracks. It is thought that many AEs with high amplitude values are measured. For this reason, the AE of fatigue damage is mixed with other AEs, and it is considered difficult to observe the progress of fatigue damage only by a change with time of the AE amplitude value.

  However, even if the amplitude value is small, it is clear that the frequency of AE accompanying the progress of fatigue damage is 200 kHz to 300 kHz. Therefore, the inventors considered observing the progress of fatigue damage by emphasizing the frequency. That is, in order to emphasize the AE amplitude value in the specific frequency band, the inventors set the AE amplitude value in the frequency band caused by fatigue damage among the AEs of the pressure tank to the AE amplitude value in all detected frequency bands. The “amplitude ratio” was calculated by dividing by. As a result of verifying the amplitude ratio during the accelerated fatigue test, the inventors have confirmed that the amplitude ratio increases upward as fatigue damage progresses.

  Specifically, FIG. 4 is a graph showing AE amplitude values in all detected frequency bands. As in FIG. 3, in FIG. 4, the vertical axis indicates the AE amplitude value, and the horizontal axis indicates the number of cycles of the fatigue test. Further, in each cycle, the amplitude ratio (absolute value) calculated by dividing the representative value of the AE amplitude value in the frequency band of 200 kHz to 300 kHz by the representative value of the AE amplitude value in all frequency bands is shown in the graph of FIG. In the calculation of the amplitude ratio in FIG. 5, the absolute value of the maximum AE amplitude value in each cycle was used as a representative value.

  As shown in FIG. 5, it can be seen that the amplitude ratio rises from about 0.2 to the right shoulder with the progress of fatigue damage. From this, it is possible to operate a reasonable pressure tank while ensuring safety through maintenance inspections in which the AE is periodically measured during operation of the pressure tank of the hydrogen station, and changes in the amplitude ratio are recorded and managed. all right.

[Stress amplitude and amplitude ratio]
Next, the inventors examined the relationship between the stress amplitude and the amplitude ratio in an actual hydrogen station through an experiment using a flat specimen. The conditions of the flat plate test piece were: test piece shape: rectangular, test piece length: 250 ± 0.15 mm, test piece width: 30 ± 0.15 mm, test piece thickness: 12 ± 0.15 mm. It was. Moreover, the test conditions of the flat plate test are load fluctuation: 0.8 MPa to 336 MP, repetition rate (number of cycles): about 50,000 cycles (including test pieces that do not break), and the maximum load is aluminum alloy in any test conditions It was under a plastic stress exceeding the proof stress.

  In the flat plate test, a single swing four-point bending fatigue test apparatus including an upper jig that pressurizes four points on the upper surface of the flat plate test piece and a lower jig that supports the lower four points on the flat plate test piece was used. In the length direction of the flat plate test piece, the distance between the support points of the lower jig (70 mm) was made narrower than the distance between the pressure points of the upper jig (210 mm). As a result, when the load increases, the flat test piece is bent upward so that the substantially central portion of the flat test piece located between the support points of the lower jig is pushed up from below, and the flat test piece is bent. A tensile force acts on the upper surface side. As a result, a fatigue crack was generated at the substantially central portion of the flat plate test piece.

  Two AE sensors were installed on the upper surface of the flat test piece in order to detect fatigue cracks. The two AE sensors were installed on the bisectors along the length direction of the flat plate test piece at positions separated by 50 mm from the bisectors along the width direction of the flat plate test piece. Further, in order to detect disturbance factors such as noise caused by contact friction between the indenter and the flat plate test piece, one AE sensor for reference is installed in each of the upper jig and the lower jig. Then, by using the arrival time difference of the AE wave for each AE sensor, the AE wave only in the fatigue crack generation area was selectively extracted and distinguished from the noise signal on the contact surface of the four indenters of the four-point bending. The AE sensor used was AE-144A (manufactured by Fuji Ceramics), and the AE measuring device used was AMSY-5 (manufactured by Vallen).

  The results of the fatigue test conducted several times are arranged in FIG. 6 by the stress amplitude and the amplitude ratio. In FIG. 6, the average amplitude ratio of the initial 0 to 10% of the fatigue life of the stress amplitude (the test period in the case of unbreakage) is indicated by a circle mark, and the average amplitude ratio of the latter 80% to 100% of the fatigue life is represented by a square. Shown with a mark. Furthermore, in the test of stress amplitude under the conditions surrounded by the dotted line in FIG. 6, the test was stopped because it was not broken even after reaching 20 million cycles. As shown in FIG. 6, when the stress amplitude is small, the average amplitude ratio is kept below 0.3 and does not break. However, when the stress amplitude is large, the average amplitude ratio is large immediately after the start of the test (for example, 0.3 or more), and the specimen breaks when the average amplitude ratio reaches 0.5 to 0.6 later in the fatigue life. .

  As a result, it was found that when the stress amplitude was large as in the accelerated fatigue test, the amplitude ratio increased to the right as the fatigue damage progressed, and the amplitude ratio was large from the beginning of the fatigue life. Furthermore, it was found that when the stress amplitude is large, the amplitude ratio is large as compared with the case where the stress amplitude is small as in the usage environment at the hydrogen station. On the other hand, when the stress amplitude was small, the amplitude ratio was small, and even when the load was repeatedly applied 20 million times or more, the crack due to fatigue damage did not penetrate the test piece.

  In the accelerated fatigue test, in order to shorten the test time, an internal pressure of 0 to 150% of the design pressure of the pressure tank is repeatedly applied to the pressure tank, and the test is performed in a very severe environment (large stress amplitude). On the other hand, the working pressure of the pressure tank at the actual hydrogen station is 60% to 100% of the design pressure even under the strictest conditions, and the stress amplitude to be applied is small compared to the accelerated fatigue test.

  As shown in FIG. 6, when the stress amplitude is small, the amplitude ratio is small, and a crack due to fatigue damage does not penetrate the test piece even when a load is repeatedly applied 20 million times or more. That is, when the amplitude ratio is used for the maintenance inspection of the pressure tank, it can be said that the amplitude ratio of a normal pressure tank normally used at the hydrogen station (small stress amplitude) is small (for example, less than 0.3). Therefore, if it is regularly confirmed that the amplitude ratio is smaller than the control value (for example, 0.3), the pressure tank can be continuously used while ensuring soundness.

[Inspection system]
Subsequently, with reference to FIG. 7 and FIG. 8, a security check during operation using the AE wave of the pressure tank in the hydrogen station will be described. FIG. 7 is a schematic block diagram showing a pressure tank inspection system 100 in the hydrogen station, and FIG. 8 is a flowchart for explaining the inspection procedure.

  As shown in FIG. 7, a plurality of pressure tanks (first pressure tank 110, second pressure tank 120, and third pressure tank 130) are secured to a curl 140 installed in the hydrogen station. The first pressure tank 110, the second pressure tank 120, and the third pressure tank 130 temporarily store hydrogen that has been pressurized by the high-pressure compressor 141. The curl 140 to which the pressure tank is fixed is installed behind the hydrogen station office or on the roof of the hydrogen station. In addition, more than three (for example, 16) pressure tanks may be installed in the curl 140.

  The hydrogen stored in the first pressure tank 110, the second pressure tank 120, and the third pressure tank 130 is supplied to the FCV 143 by the dispenser 142. As the hydrogen is taken in and out, stress is repeatedly applied to the liner of each pressure tank. The number of duty cycles for each pressure tank is recorded in a recording device (not shown) using a pressure gauge or the like. Specifications such as the dimensions of each pressure tank, the number of design pressure cycles, and the number of usable cycles are also recorded in a recording device (not shown).

  The inspection system 100 according to the first embodiment includes an explosion-proof AE sensor 150 (FBG type, Doppler type) as a sensor that detects AE waves generated from the first pressure tank 110, the second pressure tank 120, and the third pressure tank 130. Or an optical fiber type AE sensor such as a Michelson type). The AE sensor 150 detects an AE wave generated particularly under pressure in which the pressure tank is filled with fluid, and the valves 51 are provided at both ends of the first pressure tank 110, the second pressure tank 120, and the third pressure tank 130, respectively. It is adhered to the flat surface portion 53. Furthermore, the inspection system 100 includes a personal computer (PC) 160 that functions as an AE analyzer, and an AE measurement device 170 connected to the AE analyzer 160. The AE analyzer 160 and the AE measurement device 170 are It is installed in the AE measuring wheel 180.

  The AE analyzer 160 includes a CPU (not shown) and a storage unit 161 that stores a control program and the like. The CPU controls the entire AE analyzer 160 based on a program stored in the storage unit 161 and also performs overall control of various processes. The storage unit 161 includes a RAM that is a system work memory for operating the CPU, a ROM that stores a program or system software, and / or a hard disk drive. The AE analyzer 160 and the AE measuring device 170 further include other means such as an A / D conversion means for a piezoelectric element type AE sensor, an optical signal processing means for an optical fiber type AE sensor, and an A / D conversion means. be able to.

  In the first embodiment, the CPU can execute various processing operations such as calculation, control, and determination according to a control program stored in a ROM or a hard disk drive. The AE analyzer 160 also includes an operation unit including a keyboard or various switches for inputting predetermined commands or data, a display unit for displaying the input state, setting state, measurement result, various information, and the like of the device. The external device is wired or wirelessly connected. The CPU can also be controlled according to a program stored in an external storage medium such as a CD (Compact Disc) or a server on the Internet.

  An inspection program is installed in the storage unit 161. Then, the CPU executes various processes corresponding to the inspection program, so that each unit such as the parameter acquisition unit 162, the determination unit 163, and the output unit 164 of the computer is logically realized as various functions. That is, the inspection program causes the AE analyzer 160 as a computer to function as the parameter acquisition unit 162, the determination unit 163, and the output unit 164, and executes a pressure tank inspection method described later. The inspection program is recorded on a computer-readable internal or external recording medium.

  The AE analyzer 160 includes a parameter acquisition unit 162 that acquires AE parameters based on the detected AE wave. The parameter acquisition unit 162 acquires the AE wave detected by the AE sensor 150 as an AE signal subjected to signal processing via the AE measurement device 170. Then, the parameter acquisition unit 162 performs signal processing on the AE signal, and acquires, for example, the absolute value of the maximum AE amplitude value as a representative value in the amplitude value of the first frequency band (reference frequency band) of the AE wave. Similarly, the parameter acquisition unit 162 performs signal processing on the AE signal, and acquires, for example, the absolute value of the maximum AE amplitude value as a representative value of the amplitude value in the second frequency band (target frequency band) of the AE wave.

  The parameter acquisition unit 162 calculates the ratio of the representative value of the amplitude value in the second frequency band to the representative value in the amplitude value of the first frequency band. Thereby, the parameter acquisition unit 162 acquires the value of the amplitude ratio as the AE parameter. In addition, the parameter acquisition unit 162 sends the amplitude ratio value to the storage unit 161 as the AE measurement result, and the storage unit 161 stores the received measurement result. The second frequency band is an AE frequency generated due to the progress of fatigue damage, for example, a frequency band of 200 kHz to 300 kHz. Further, the first frequency band is a frequency band different from the second frequency band, for example, the entire frequency band including the second frequency band. However, since the first frequency band and the second frequency band differ depending on the inspection target, the first frequency band and the second frequency band are not limited to the above exemplary ranges. The second frequency band is preferably a narrower frequency band than the first frequency band.

  The AE analyzer 160 includes a determination unit 163 that determines whether each pressure tank is normal or abnormal. The determination unit 163 compares the amplitude ratio value acquired by the parameter acquisition unit 162 with a predetermined management value, and determines that each pressure tank is normal when the amplitude ratio value is less than the management value. The determination unit 163 determines that each pressure tank is abnormal when the value of the amplitude ratio is equal to or greater than the management value. Then, the determination unit 163 sends information indicating that each pressure tank is normal or abnormal to the storage unit 161 as an inspection result, and the storage unit 161 stores the received inspection result.

  In addition, the AE analyzer 160 includes an output unit 164 that outputs the value of the amplitude ratio acquired by the parameter acquisition unit 162. The output unit 164 outputs the measurement result and the inspection result stored in the storage unit 161. That is, the output unit 164 outputs the value of the amplitude ratio acquired by the parameter acquisition unit 162 and stored in the storage unit 161 to an external device (not shown) connected to the AE analyzer 160. Note that an external storage device, an external server, a display, a printing device, a communication device, or the like is connected to the AE analyzer 160 as an external device by wired connection or wireless connection. The output unit 164 outputs various information in a form adapted to the data format of the external device.

[Inspection method]
As shown in the flowchart of FIG. 8, when performing the security inspection, the inspector first parks the AE measurement vehicle 180 during the operation of the hydrogen station, and the AE analyzer 160 and the AE measurement device in the non-explosion-proof area of the hydrogen station. 170 is installed (S101). The non-explosion-proof area is, for example, an internal area of the hydrogen station management office or an internal area of the AE measuring vehicle 180 parked at the hydrogen station.

  Then, the inspector attaches the explosion-proof AE sensor 150 to the valve 51 of each pressure tank as a sensor for detecting the AE wave (S102). At this time, the AE sensor 150 is attached to the flat portion 53 of the valve 51 at one end of each pressure tank or the flat portion 53 of the valve 51 at both ends of each pressure tank with an instantaneous adhesive. Thereafter, the inspector connects the attached AE sensor 150 and the AE measuring device 170 with a signal cable (S103). When the connection is completed, initial setting of the AE measuring device 170 and setting of conditions such as environmental noise are performed (S104), and preparation for AE measurement is completed.

  The AE is desirably measured while the internal pressure of the pressure tank is increased at a constant pressure increase rate. In view of this, AE waves generated from each pressure tank are detected by the AE sensor 150 attached to each pressure tank under pressure filled with fluid (S105). That is, hydrogen is supplied to the FCV 143 at the hydrogen station, and AE when the pressure tanks are filled with hydrogen by the high-pressure compressor 141 is measured from the state of the lowest use pressure of each pressure tank. At this time, the pressure increase rate due to hydrogen filling is constant, and the AE wave during a predetermined measurement period (for example, during pressure fluctuation of about 10 cycles) is measured. And the same measurement is each implemented with respect to a some pressure tank. In addition, it is preferable to perform AE measurement at the time of pressure | voltage rise 2 to 3 times by one security inspection. However, since it depends on the supply timing to the FCV 143, the AE measurement in one security check may be performed once. In addition, if the boost timing is met, the AEs of a plurality of pressure tanks can be measured at a time.

  The AE amplitude value and the like measured by performing measurement a plurality of times are recorded in the storage unit 161 in the AE analyzer 160 via the AE measuring device 170. The AE measurement device 170 processes the detected AE wave to generate an AE signal, and the parameter acquisition unit 162 of the AE analysis device 160 calculates the AE parameter based on the AE signal acquired via the AE measurement device 170. Obtain (S106). Specifically, the parameter acquisition unit 162 acquires, as an AE parameter, an amplitude ratio value that is a ratio of the representative value of the amplitude value in the second frequency band of the AE wave to the representative value of the amplitude value in the first frequency band of the AE wave. To do. The acquired AE parameters are recorded in the storage unit 161 in the AE analyzer 160.

  Thereafter, the determination unit 163 in the AE analyzer 160 determines fatigue damage of the pressure tank based on the AE parameter (S107). Specifically, the determination unit 163 compares the amplitude ratio value stored in the storage unit 161 with a preset management value. When the value of the amplitude ratio is less than the control value, the determination unit 163 determines that the pressure tank is normal, and causes the storage unit 161 to store the inspection result indicating that the pressure tank is normal. On the other hand, when the value of the amplitude ratio is equal to or greater than the management value, the determination unit 163 determines that the pressure tank is abnormal and causes the storage unit 161 to store the inspection result indicating that the pressure tank is abnormal. The control value is set in a range that does not reach the value of the amplitude ratio when hydrogen leakage occurs, and can be obtained by experiment.

  The determination unit 163 can also calculate an increase amount by subtracting an initial value of the amplitude ratio measured in advance from the acquired amplitude ratio value, and can determine whether the pressure tank is damaged based on the increase amount. In this case, the determination unit 163 determines that it is normal when the increase amount is less than the management value, and determines that it is abnormal when the increase amount is equal to or greater than the management value. By inspecting whether the increase amount exceeds the control value, the initial value of the amplitude ratio is greatly different due to the difference in self-tightening processing for multiple pressure tanks that have been subjected to different self-tightening processing. However, the pressure tank can be managed based on the increase amount of the amplitude ratio.

  The determination unit 163 can also predict fluctuations in the value of the amplitude ratio based on the comparison result between the acquired amplitude ratio value and the initial value of the amplitude ratio. In this case, the parameter acquisition unit 162 detects an AE wave generated from each pressure tank in the initial state and acquires an initial value of the amplitude ratio in advance. Then, the determination unit 163 predicts the value of the future amplitude ratio from the past initial value, and determines whether or not the predicted value of the amplitude ratio exceeds a preset management value (threshold value). Thereby, if it regularly confirms that the predicted value of the amplitude ratio is smaller than the management value, the pressure tank can be continuously operated while ensuring soundness. Note that the predicted value of the amplitude ratio when the next number of measurement cycles (for example, 5000 cycles) is reached can be calculated based on, for example, an approximate straight line obtained from a plurality of amplitude ratio values acquired in the past. Here, the number of measurement cycles is equal to the number of times the FCV 143 is filled.

  Further, the AE analyzer 160 may superimpose and store the AE frequency spectrum obtained by measuring a plurality of times in the storage unit 161. By comparing the overlapped AE frequency spectra, for example, the increase / decrease of the AE amplitude value in the 200 kHz to 300 kHz band can be recorded in the storage unit 161. In addition, depending on the specifications of the pressure tank, there is a possibility that a frequency shift showing a significant increase or decrease other than the 200 kHz to 300 kHz band may occur. Therefore, the storage unit 161 also stores an AE amplitude value in a frequency band that shows a significant increase or decrease.

  Thereafter, the inspector outputs the measurement result and the inspection result by the output unit 164 of the AE analyzer 160 (S108), and reports it to the administrator of the hydrogen station. When the report is completed, the inspector withdraws the inspection system 100 from the hydrogen station, and the security inspection ends. This security check can be carried out periodically once to several times a year, and the amplitude ratio and AE frequency band are recorded. Also, when installing a new pressure tank in the hydrogen station (initial time) and when a predetermined period (for example, one year) has elapsed since installation, the value of the amplitude ratio is measured and recorded, and the value is below the control value. It is desirable to confirm that there is. Further, the security inspection may be performed when the number of times the pressure tank can be used is exceeded.

  For the spread and operation of hydrogen stations, in-service security inspections are indispensable to confirm the pressure performance and strength of pressure tanks, but no practical and effective security inspections existed. In this regard, according to the first embodiment, fatigue damage of the pressure tank can be inspected during use of the pressure tank. In addition, the progress of fatigue damage of the metal liner of the pressure tank can be inspected with an amplitude ratio emphasized. Therefore, according to the present invention, it is possible to inspect the progress of fatigue damage of a pressure tank, particularly a type 1 container, a type 2 container, and a type 3 container having a metal liner.

  The number of times the pressure tank can be used is defined as the number of times the design pressure cycle number is divided by the fatigue design safety factor Kn. For example, in the case of a pressure tank having a design pressure cycle number of 100,000 times, when the fatigue design safety factor Kn = 4.0, about 25,000 times can be used. Therefore, the number of times the current pressure tank can be used does not reach 50% of the number of pressure tank design pressure cycles. In this regard, according to the first embodiment, the use can be extended if the signs of fatigue damage progress (increase in the amplitude ratio) are not observed even after the usable number of times is exceeded. Thus, the pressure tank can be operated while confirming safety up to the number of usable times, and the use of the pressure tank can be continued while confirming safety even when the number of usable times is exceeded. Therefore, it can contribute to the spread of safe and secure hydrogen stations.

  Furthermore, composite containers that exceed the number of times that they can be used are disposed of, but disposal of composite containers that use a large amount of carbon fiber is not easy. For this reason, as the hydrogen stations become widespread, the number of disposals may become a future social problem. In this regard, if the number of times of use of the composite container is increased according to the first embodiment, it can also contribute to a reduction in the number of times of disposal.

  Although the optical fiber type AE sensor has been described in the first embodiment, a piezoelectric element type AE sensor can also be used. However, if it is an optical fiber type AE sensor, the AE wave of the pressure tank installed in the explosion-proof area can be measured. Further, the representative value of the AE amplitude value serving as a reference for calculating the amplitude ratio is not limited to the maximum AE amplitude value. For example, it may be an average value of maximum AE amplitude values in a plurality of frequency bands, or a median value of AE amplitude values in frequency bands.

[Second Embodiment]
In the differential pressure filling type hydrogen station that is generally expected to be widely used, a high pressure bank (high pressure tank: for example, 82 to 80 MPa), a medium pressure bank (medium pressure tank: for example, 82 to 70 MPa), and a low pressure bank A three-bank switching system by combination with (low pressure tank: for example, 82 to 50 MPa) is efficient. In this three-bank switching method, it is assumed that filling with small pressure fluctuation is repeatedly performed between the pressure banks. Therefore, as a result of the pressure fluctuation of each pressure bank being different, the stress amplitude is different, so that the value of the amplitude ratio is different for each pressure bank.

  Therefore, in the second embodiment, a different management value is set for each pressure bank and compared with the measured amplitude ratio value. Specifically, the second embodiment will be described with reference to the inspection system 200 shown in FIG. In the description of the second embodiment, differences from the first embodiment will be described, and description of the components described in the first embodiment will be omitted. Except where specifically described, the constituent elements having the same reference numerals perform substantially the same operations and functions, and the effects thereof are also substantially the same.

  In the second embodiment, an acoustic emission wave generated from the first pressure tank (low pressure tank) 210 having a wider range of internal pressure than the second pressure tank (medium pressure tank) 220 is further detected, and the second pressure The acoustic emission wave generated from the third pressure tank (high pressure tank) 230 whose internal pressure fluctuation range is narrower than that of the tank 220 is further detected. Then, different management values are set in advance for each of the second pressure tank 220, the first pressure tank 210, and the third pressure tank 230.

  The first pressure tank 210, the second pressure tank 220, and the third pressure tank 230 are respectively provided with a first valve 291, a second valve 292, and a third valve 293. And the pressure tank which performs differential pressure filling with respect to FCV143 is switched suitably by opening and closing the 1st valve | bulb 291, the 2nd valve | bulb 292, and the 3rd valve | bulb 293. Note that more than three pressure tanks, for example, a total of nine pressure tanks including three pressure tanks per bank may be installed in the curl 140.

  When filling the FCV 143, first, the second valve 292 and the third valve 293 are closed and only the first valve 291 is opened, so that the differential pressure filling is performed from the first pressure tank 210 to the FCV 143 via the dispenser 142. . Thereafter, the flow path from the first pressure tank (low pressure bank) 210 is connected to the second pressure tank (low pressure bank) so that the internal pressure of the first pressure tank 210 is maintained within a predetermined fluctuation range (for example, a fluctuation range of 82 MPa to 50 MPa). It is switched to the flow path from the medium pressure bank) 220. For this purpose, the first valve 291 and the third valve 293 are closed and only the second valve 292 is opened, so that the differential pressure filling is performed from the second pressure tank 220 to the FCV 143 via the dispenser 142.

  Thereafter, the flow path from the second pressure tank (intermediate pressure bank) 220 becomes the third pressure tank so that the internal pressure of the second pressure tank 220 is maintained within a predetermined fluctuation range (for example, a fluctuation range of 82 MPa to 70 MPa). The flow path is switched from the (high pressure bank) 230. For this purpose, the first valve 291 and the second valve 292 are closed and only the third valve 293 is opened, so that the differential pressure filling is performed from the third pressure tank 230 to the FCV 143 via the dispenser 142. Then, differential pressure filling is performed so that the internal pressure of the third pressure tank 230 is maintained within a predetermined fluctuation range (for example, a fluctuation range of 82 MPa to 80 MPa).

  Accordingly, when the differential pressure filling is performed on the FCV 143 only from the first pressure tank 210, the stress amplitude of the first pressure tank 210 is further reduced (for example, 32 MPa) when the internal pressure is reduced from 82 MPa to 40 MPa, for example. Can do. Similarly, the stress amplitude of the second pressure tank 220 can be reduced (for example, 12 MPa), and the stress amplitude of the third pressure tank 230 can be suppressed (for example, 2 MPa).

  As a result of the pressure fluctuation of each pressure bank being different in this manner, the amplitude of the amplitude is different for each pressure bank because the stress amplitude is different. Therefore, in the second embodiment, the management value of the second pressure tank 220, the management value of the first pressure tank 210, and the management value of the third pressure tank 230 are set to be different from each other, and AE analysis is performed. The determination unit 163 of the device 160 compares the value of each amplitude ratio with each management value.

  According to the second embodiment described above, fatigue damage of the pressure tank can be inspected during use of the pressure tank. In addition, the pressure tank can be operated while confirming safety up to the number of usable times, and the use of the pressure tank can be extended while confirming safety even when the number of usable times is exceeded. Furthermore, according to the second embodiment, even when the three-bank switching method is employed, the fatigue damage of the pressure tank can be accurately inspected according to the pressure fluctuation.

  The present invention has been described above with reference to each embodiment. However, the present invention is not limited to the above embodiment. Inventions modified within the scope not departing from the present invention and inventions equivalent to the present invention are also included in the present invention. Moreover, each embodiment and each modification can be combined suitably in the range which is not contrary to this invention.

  For example, the present invention can also be applied to a pressure tank installed at a place other than the hydrogen station, for example, a pressure tank mounted on a vehicle. In this case, for example, the AE of the pressure tank is measured at the time of vehicle inspection, or the AE measuring device 170 and the AE analyzer 160 are mounted on the vehicle and the AE is constantly measured. The present invention may also be applied to an empty pressure tank before being filled with fluid.

  Further, the AE measurement result and the inspection result may be stored in an external storage device instead of or in addition to the storage unit 161 in the AE analyzer 160. For example, the AE analyzer 160 may include a communication unit that transmits and receives data to and from an external storage device, and may transmit AE measurement results and test results to the external storage device via the communication unit.

  Further, the first frequency band (reference frequency band) may not be the entire frequency band. For example, the first frequency band may be the remaining frequency band obtained by removing unnecessary frequency bands from the entire frequency band by a noise filter. Further, the first frequency band may not include the second frequency band (target frequency band).

  A part or all of the above-described embodiment can be described as in the following supplementary notes, but is not limited thereto.

(Appendix 1)
A pressure tank inspection method,
Detecting acoustic emission waves generated from the pressure tank,
A value of an amplitude ratio that is a ratio of a representative value of an amplitude value in a second frequency band different from the first frequency band of the acoustic emission wave to a representative value of an amplitude value in the first frequency band of the acoustic emission wave is calculated. And
The value of the amplitude ratio is compared with a predetermined management value, and if the value of the amplitude ratio is less than the management value, it is determined that the pressure tank is normal, and the value of the amplitude ratio is greater than or equal to the management value An inspection method for determining that the pressure tank is abnormal in some cases.

(Appendix 2)
The inspection method according to attachment 1, wherein the second frequency band is 200 kHz to 300 kHz.

(Appendix 3)
The inspection method according to appendix 1, wherein the first frequency band is the entire frequency band of the acoustic emission wave.

(Appendix 4)
The inspection method according to appendix 1, wherein the pressure tank includes a metal liner and a CFRP hoop layer.

(Appendix 5)
The inspection method according to appendix 1, wherein an optical fiber type sensor that detects the acoustic emission wave is attached to a valve of the pressure tank.

(Appendix 6)
The inspection method according to appendix 1, wherein the representative value is a maximum amplitude value within a predetermined measurement period.

(Appendix 7)
A pressure tank inspection method,
Detecting acoustic emission waves generated from the pressure tank,
An amplitude ratio that is a ratio of a representative value of an amplitude value in a second frequency band different from the first frequency band of the acoustic emission wave to a representative value of an amplitude value in the first frequency band of the acoustic emission wave at an initial time point Calculate the initial value of
Calculate the amplitude ratio value again after the initial time point,
The difference between the value of the amplitude ratio calculated again and the initial value is compared with a predetermined management value, and when the difference is less than the management value, it is determined that the pressure tank is normal, and the difference is An inspection method for determining that the pressure tank is abnormal when the control value is exceeded.

  50: Pressure tank, 51: Valve, 54: Sensor, 100: Inspection system, 162: Parameter acquisition unit, 163: Judgment unit, 164: Output unit, 210: Low pressure tank, 220: Medium pressure tank, 230: High pressure tank

Claims (11)

A pressure tank inspection method,
Detecting acoustic emission waves generated from the pressure tank,
Obtaining an acoustic emission parameter based on the detected acoustic emission wave;
An inspection method for judging damage of the pressure tank based on the acoustic emission parameter. A value of an amplitude ratio that is a ratio of a representative value of an amplitude value in a second frequency band different from the first frequency band of the acoustic emission wave to a representative value of an amplitude value in the first frequency band of the acoustic emission wave; Acquired as the acoustic emission parameter,
The value of the amplitude ratio is compared with a predetermined management value, and if the value of the amplitude ratio is less than the management value, it is determined that the pressure tank is normal, and the value of the amplitude ratio is greater than or equal to the management value The inspection method according to claim 1, wherein in this case, it is determined that the pressure tank is abnormal.   The inspection method according to claim 2, wherein the second frequency band is a frequency band narrower than the first frequency band.   The inspection method according to any one of claims 1 to 3, wherein a sensor that detects the acoustic emission wave is attached to a valve of the pressure tank. Further detecting acoustic emission waves generated from a low pressure tank having a wider internal pressure fluctuation range than the pressure tank, and further detecting acoustic emission waves generated from a high pressure tank having a narrower internal pressure fluctuation range than the pressure tank. ,
Obtaining a value of the amplitude ratio for each of the low pressure tank and the high pressure tank;
The management value of the pressure tank, the management value of the low pressure tank, and the management value of the high pressure tank are set to be different from each other, and when comparing the value of the amplitude ratio with the management value 5. The inspection method according to claim 2, wherein each amplitude ratio value is compared with each control value. An acoustic emission wave generated from the pressure tank at the initial time point is detected to obtain an initial value of the amplitude ratio in advance,
The inspection method according to any one of claims 2 to 5, wherein a fluctuation in the value of the amplitude ratio is predicted based on a comparison result between the value of the amplitude ratio and the initial value. A pressure tank inspection system,
A sensor for detecting an acoustic emission wave generated from the pressure tank;
A parameter acquisition unit that acquires an acoustic emission parameter based on the detected acoustic emission wave, the first frequency band of the acoustic emission wave with respect to a representative value in an amplitude value of the first frequency band of the acoustic emission wave And a parameter acquisition unit that acquires, as the acoustic emission parameter, an amplitude ratio value that is a ratio of representative values of amplitude values in a second frequency band different from the above.   The value of the amplitude ratio is compared with a predetermined management value, and if the value of the amplitude ratio is less than the management value, it is determined that the pressure tank is normal, and the value of the amplitude ratio is greater than or equal to the management value The inspection system according to claim 7, further comprising a determination unit that determines that the pressure tank is abnormal.   The inspection system according to claim 7, further comprising an output unit that outputs the value of the amplitude ratio acquired by the parameter acquisition unit. A pressure tank inspection program,
The computer functions as a parameter acquisition unit that acquires an acoustic emission parameter based on an acoustic emission wave generated from the pressure tank,
The parameter acquisition unit is a ratio of a representative value of an amplitude value in a second frequency band different from the first frequency band of the acoustic emission wave to a representative value in an amplitude value of the first frequency band of the acoustic emission wave. An inspection program for acquiring an amplitude ratio value as the acoustic emission parameter.   The value of the amplitude ratio is compared with a predetermined management value, and if the value of the amplitude ratio is less than the management value, it is determined that the pressure tank is normal, and the value of the amplitude ratio is greater than or equal to the management value The inspection program according to claim 10, further causing the computer to function as a determination unit that determines that the pressure tank is abnormal.

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