JP6798800B2 - Pressure tank inspection method, inspection system and inspection program - Google Patents

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 detecting an acoustic emission wave generated from a pressure tank and inspecting fatigue damage.

In recent years, in response to issues such as global warming and fossil fuel depletion, it has been required to drastically strengthen energy saving, improve energy security, and reduce environmental load. Technology related to fuel cell vehicles (FCV) and technology related to hydrogen production, hydrogen transportation, and hydrogen storage are positioned as important technologies in Japan's policy, and their widespread use is expected at an early stage. In order to improve the competitiveness of FCV-related industries, it is indispensable to further enhance the safety and reliability of hydrogen stations, to secure social acceptance, and to promote the installation of hydrogen stations.

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

The structures of the four main types of pressure tanks are shown in FIGS. 1A to 1D. 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. Further, FIG. 1B is a composite container (pressure tank) having a metal liner 21 such as chromolybdenum steel and a hoop layer 22 made of carbon fiber reinforced resin (CFRP) in which a hoop is wound around the body of the liner 21. Shows type 2 container 20.

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

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

Visual inspection, penetrant inspection, ultrasonic flaw detection inspection, and radiation transmission inspection are being studied as methods for inspecting fatigue damage in pressure tanks. Fatigue damage occurs from the inner surface of the liner during use of the pressure tank, and the fatigue damage progresses and penetrates the liner, causing hydrogen to leak. Therefore, in order to prevent leakage, an inspection technique for inspecting the progress of fatigue damage is required. However, all of the above inspection methods under consideration are insufficient as security inspections as shown below.

Visual inspection from the outside does not allow the inspector to detect fatigue damage on the inside 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 cannot be detected visually because it is an extremely fine crack. In addition, the work of opening the pressure tank requires stopping the operation of the hydrogen station, which cannot be inspected during operation, which may affect the suspension of business.

In the penetrant inspection, it is possible to stop the use of the pressure tank, open the inside of the pressure tank, and detect minute cracks due to fatigue damage from the inner surface of the liner. However, in the penetrant inspection, the penetrant is applied to the inner surface of the metal liner, so it is difficult to completely remove the penetrant after the inspection. Therefore, the inside of the pressure tank may be contaminated with the penetrant, and it may not be possible to store the FCV fuel that requires a hydrogen purity of 99.99% or more. In addition, the work of opening the pressure tank requires stopping the operation of the hydrogen station, which cannot be inspected during operation, which may affect the suspension of business.

In ultrasonic flaw detection inspection, an inspector inspects the progress of fatigue damage by injecting ultrasonic waves from the outer surface of the pressure tank to detect and analyze the reflected wave from the fatigue damage without opening the pressure tank. For example, the mirror portion of the type 2 container 20 can detect fatigue damage by ultrasonic waves. However, in the body of the type 2 container 20, it is difficult to detect fatigue damage by ultrasonic waves due to the hoop layer 22 made of CFRP. Further, since the body of the pressure tank having a capacity of 300 L has a wide flaw detection range of about 0.5 m in diameter and about 3 to 6 m in length, it takes time to inspect. Furthermore, in ultrasonic flaw detection inspection, it is necessary to discharge hydrogen in the pressure tank, which cannot be inspected during operation, which may affect the suspension of work.

Further, in a hydrogen station, a plurality of pressure tanks are stacked and mounted on a curdle. Therefore, some pressure tanks cannot receive ultrasonic waves because the surface of the pressure tank cannot be accessed. If the pressure tank is taken out from the curdle, 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, and it cannot be inspected during operation, which affects the suspension of work. Further, in order to reload the removed pressure tank on the curdle, it takes about one week including the inspection time after mounting. The entire surface of the metal liner 31 of the type 3 container 30 is covered with a thick CFRP hoop layer 32. Since CFRP has a large ultrasonic attenuation, it is difficult to detect fatigue damage by ultrasonic flaw detection inspection.

In the radiation transmission test, it is necessary to remove the pressure tank mounted on the curdle of the hydrogen station. The work of taking out the pressure tank requires the operation of the hydrogen station to be stopped, and it cannot be inspected during operation, which may affect the suspension of business. Further, in order to reload the removed pressure tank on the curdle, it takes about one week including the inspection time after mounting.

Therefore, there is a need for a practical inspection method for fatigue damage to pressure tanks 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 hoop layers 22 and 32 made of CFRP. As a result, very fine cracks on the inner surface of the liners 21 and 31 thickly wrapped in the hoop layers 22 and 32 grow in the thickness direction of the liners 21 and 31. And there is no practical inspection method for such fatigue damage.

In this regard, there are many cases in which the progress of fatigue damage of metallic materials is inspected using the acoustic emission (AE) method, which is a kind of non-destructive inspection technology. In the AE method, an AE sensor is installed in the inspection target, and elastic waves (AE waves) generated by the growth of cracks inside the inspection target are passively detected to detect damage to the inspection target. For example, Patent Document 1 discloses a bearing diagnosis method for diagnosing the life of a bearing in a rotating machine by using the AE method.

Japanese Unexamined Patent Publication No. 2012-242336

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

In order to solve the above problems, the 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 obtains an acoustic emission parameter. It is characterized in that damage to the pressure tank is determined based on the acoustic emission parameters.

Further, in the pressure tank inspection system as another example of the present invention, a sensor that detects an acoustic emission wave generated from the pressure tank and a parameter acquisition that acquires an acoustic emission parameter based on the detected acoustic emission wave. Amplitude, which is the ratio of the representative value of the amplitude value in the second frequency band different from the first frequency band of the acoustic emission wave to the representative value in the amplitude value of the first frequency band of the acoustic emission wave. It is characterized by including a parameter acquisition unit that acquires the value of the ratio as the acoustic emission parameter.

Further, in the pressure tank inspection program as another example of the present invention, the computer functions as a parameter acquisition unit for acquiring acoustic emission parameters based on the acoustic emission wave generated from the pressure tank, and the parameter acquisition unit may be used. The value of the amplitude ratio, which is the ratio of the representative value of the amplitude value in the second frequency band different from the first frequency band of the acoustic emission wave, to the representative value in the amplitude value of the first frequency band of the acoustic emission wave. It is characterized in that it is acquired as the acoustic emission parameter.

As a result, fatigue damage of the pressure tank can be inspected during the operation of the pressure tank.

Further features of the present invention will become apparent from the description of the following examples exemplified by reference to the accompanying drawings.

A schematic side view of the outside of the container and a schematic cross-sectional view of the center of the container cut along the longitudinal direction are shown, where A indicates a type 1 container, B indicates a type 2 container, C indicates a type 3 container, and D. Indicates a type 4 container. It is a schematic perspective view around the end of a pressure tank. It is a graph which shows the relationship between the AE amplitude value of the frequency band of 200kHz to 300kHz, 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 the AE amplitude ratio and the number of cycles until leakage. It is a graph which shows the relationship between the AE amplitude ratio and the stress amplitude. It is a schematic block diagram which shows the inspection system which concerns on 1st 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, the dimensions, materials, shapes, relative positions of the components, etc. described in the following embodiments are arbitrary and can be changed according to the configuration of the device to which the present invention is applied or various conditions. Further, 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 signal processing the AE wave detected by the AE sensor. Specifically, the AE parameters include the number of AEs generated, the AE amplitude, the AE energy, the AE waveform (maximum amplitude value, rise time, duration, etc.), AE frequency, AE mean value, AE effective value, AE count rate, and. Includes the total number of AE counts. When the AE method is used when inspecting the progress of fatigue damage, AE parameters such as the number of AE occurrences, AE amplitude, and absolute value of AE energy generally increase with the progress of fatigue damage. The inventors confirmed in a fatigue test using a test piece that among the AE parameters, in particular, the amplitude value of AE increased upward with the progress of fatigue damage. Therefore, if this parameter is used as an inspection index, it is possible to grasp the progress state of fatigue damage in the pressure tank.

[Installation location of AE sensor]
When the AE sensor is installed in the pressure tank, in particular, when the AE sensor is installed in the type 2 container 20 of FIG. 1B and the type 3 container 30 of FIG. 1C, some ingenuity is required. 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. Therefore, the AE sensor cannot be directly installed on the liner 21, and the AE cannot be detected with high sensitivity. Further, although the AE sensor can be installed on the hoop layer 22, it is not realistic because the CFRP has a large attenuation and the AE detection sensitivity becomes low. Similarly, the AE detection sensitivity of the type 3 container 30 is lowered.

Therefore, the installation location of the AE sensor for measuring the AE wave with high sensitivity will be described with reference to FIG. 2, which shows an enlarged view of the periphery of the end of the pressure tank 50. Since both ends of the pressure tank 50 have the same configuration, only one end thereof will be described and the other end will be 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 surface portion 53 for contacting the pressure tank 50 with a tool (wrench) for fixing the valve 51. Therefore, the AE sensor 54 is adhered to the flat surface portion 53 of the valve 51. As a result, 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 surface 53 of the valve 51, the AE sensor 54 can be installed without opening the pressure tank 50 during service at the hydrogen station. Further, since the valve 51 is generally provided with a flat surface portion 53, it is not necessary to form a separate flat surface in order to attach 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, a jig (not shown) is first fixed to the flat surface portion 53 of the container valve 51. Then, the AE sensor 54 is inserted into the fixed jig, and the AE sensor 54 is fixed from behind the AE sensor 54 with a screw or the like via an elastic body. Further, an insulating tape for noise suppression may be wrapped around the case of the AE sensor 54. Further, a contact medium such as petrolatum may be applied to the receiving surface of the AE sensor 54.

[Amplitude ratio]
The absolute value of the number of AEs generated, the AE amplitude, and the AE energy is greatly affected by the inspection conditions (the installation location of the AE sensor, the evaluation target, the range of pressure fluctuation, etc.). Therefore, fatigue damage can be inspected by monitoring with an AE sensor always attached to the pressure tank, but it is not suitable for in-service inspection, which is a regular inspection. On the other hand, there is an AE frequency as an AE parameter that is not affected by the inspection conditions. Then, as a result of the fatigue test conducted by the inventors with the test piece, it became clear that the AE of the pressure tank accompanying the progress of fatigue damage has 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 AE of the pressure tank accompanying the progress of fatigue damage. It became clear that it was AE. Since the pressure tank is subjected to autofrettage treatment at a pressure higher than the normal pressure, the CFRP hoop layer, which has a particularly remarkable Kaiser effect, is not destroyed if it is used at the normal pressure. This Kaiser effect is an irreversible phenomenon peculiar to AE that AE is generated when a load is applied to a material, but AE is not generated until the previous maximum load is exceeded when the load is once removed and the load is applied again. Therefore, when evaluating the fatigue damage of the pressure tank, it is possible not to consider the fracture of the hoop layer made of CFRP.

However, it is also conceivable that the hoop layer is destroyed due to the surface damage of the hoop layer generated during the transportation of the pressure tank, and AE is generated along with the destruction. Therefore, it is desirable to distinguish the AE wave associated with the fracture of the hoop layer from the AE wave associated with fatigue damage of the metal liner. Specifically, the inventors have confirmed from the 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 contains a large amount of a component of 70 kHz.

However, as a result of the accelerated fatigue test using the type 3 container 30, the inventors may not observe a significant correlation between the progress of fatigue damage and the high frequency AE amplitude value. 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 shows the absolute value of the maximum AE amplitude value in each cycle, and the horizontal axis shows the number of fatigue test cycles. 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 (burst safety factor 3 or more), content capacity: 30 L, aluminum liner material: A6061-T6, hoop layer material: PAN type. Further, at the time of manufacturing this composite container, a residual compressive stress of 253 MPa was applied by the autofrettage treatment.

The test conditions for the fatigue test are: 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, VS150-RIC sensors (manufactured by Vallen) as AE sensors were attached to the flat surfaces of the valves at both ends of the composite container. Further, as an AE sensor, an AE-144A sensor (manufactured by Fuji Ceramic) was attached to the flat surfaces of the valves at both ends of the composite container. Moreover, AMSY-5 (manufactured by Vallen) was used as the AE measuring device.

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 with a shear type. At this time, even when observing the time course of the AE amplitude value from 200 kHz to 300 kHz, as shown in the graph of FIG. 3, the pattern did not increase with the number of cycles and became the maximum immediately before fatigue fracture.

The composite vessel is autofrettage-treated to cause plastic deformation of the metal liner and shift the average stress of the liner to the compression side (a large residual compressive stress is applied to the liner during manufacturing) to extend the fatigue life. Has been done. Therefore, the inventors considered that the reason why no significant correlation was observed between the progress of fatigue damage and the high frequency AE amplitude value was the following three effects due to the autofrettage treatment.

First, the self-tightening process causes slip lines on the metal liner, but the AE of fatigue damage along the slip lines has a small amplitude value and a small number of occurrences. Secondly, AE is generated from a stress concentration portion by autofrettage treatment or a minute scratch when processing a metal liner at an early stage of fatigue damage. Thirdly, since the phenomenon that the crack grows in the shearing method due to the autofrettage treatment is observed, when the crack grows in the shearing direction, the stress applied to the crack tip is halved due to the influence of the AE radiation direction. Then, the AE amplitude value becomes smaller.

Due to these three effects, unlike the test piece, during the fatigue test of the composite container, in addition to the AE associated with the progress of fatigue damage with a low amplitude value of 200 kHz to 300 kHz, the cause is the local stress concentration part or the initial crack. It is considered that a large number of AEs with high amplitude values are measured. Therefore, the AE of fatigue damage is mixed with other AEs, and it is considered difficult to observe the progress of fatigue damage only by the time course 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 a 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, and the AE amplitude value in all the detected frequency bands. The "amplitude ratio" was calculated by dividing by. Then, as a result of verifying the amplitude ratio during the accelerated fatigue test, the inventors confirmed that the amplitude ratio increases upward as the fatigue damage progresses.

Specifically, FIG. 4 is a graph showing AE amplitude values in all detected frequency bands. Similar to FIG. 3, in FIG. 4, the vertical axis shows the AE amplitude value, and the horizontal axis shows the number of fatigue test cycles. 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 the entire frequency band is shown in the graph of FIG. The absolute value of the maximum AE amplitude value in each cycle was used as a representative value for calculating the amplitude ratio in FIG.

As shown in FIG. 5, it can be seen that the amplitude ratio increases from about 0.2 to the right as the fatigue damage progresses. From this, it is possible to operate a rational pressure tank while ensuring safety by performing maintenance inspections that regularly measure AE during operation of the pressure tank of the hydrogen station and record and manage changes in the amplitude ratio. 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 by an experiment using a flat plate test piece. The conditions of this flat plate test piece are: shape of test piece: rectangular, length of test piece: 250 ± 0.15 mm, width of test piece: 30 ± 0.15 mm, thickness of test piece: 12 ± 0.15 mm. It was. The test conditions for the flat plate test are load fluctuation: 0.8 MPa to 336 MP, number of repetitions (number of cycles): about 50,000 cycles (including test pieces that do not break), and the maximum load is aluminum alloy in all test conditions. Under plastic stress equal to or greater than the proof stress of.

Further, in the flat plate test, a single swing four-point bending fatigue test apparatus including an upper jig for pressurizing four points on the upper surface of the flat plate test piece and a lower jig for supporting four points on the lower surface of 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 narrower than the distance between the pressure points of the upper jig (210 mm). As a result, when the load is increased, the upper side is convex and the flat plate test piece is bent so that the substantially central portion of the flat plate test piece located between the support points of the lower jig is pushed up from below. Tensile force acts on the upper surface side. As a result, fatigue cracks are generated in the substantially central portion of the flat plate test piece.

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

The results of the fatigue tests performed multiple times are summarized in FIG. 6 by stress amplitude and amplitude ratio. In FIG. 6, the average amplitude ratio of the initial 0 to 10% of the stress amplitude fatigue life (test period if unbroken) is indicated by a circle mark, and the average amplitude ratio of the late 80% to 100% of the fatigue life is squared. It is indicated by a mark. Further, in the stress amplitude test under the condition 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 maintained at less than 0.3 and fracture does not occur. 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 test piece breaks when the average amplitude ratio reaches 0.5 to 0.6 in the latter half of 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 upward with the progress of fatigue damage, 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 a hydrogen station. On the other hand, when the stress amplitude was small, the amplitude ratio was small, and even if 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, an internal pressure of 0 to 150% of the design pressure of the pressure tank is repeatedly applied to the pressure tank in order to shorten the test time, and the test is performed in a very severe environment (with a large stress amplitude). On the other hand, the working pressure of the pressure tank in the actual hydrogen station is 60% to 100% of the design pressure even under the harshest conditions, and the stress amplitude applied is smaller than that in the accelerated fatigue test.

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

[Inspection system]
Subsequently, with reference to FIGS. 7 and 8, a safety inspection in service using the AE wave of the pressure tank at the hydrogen station will be described. Note that FIG. 7 is a schematic block diagram showing an inspection system 100 for a pressure tank in a hydrogen station, and FIG. 8 is a flowchart illustrating an 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 fixedly installed on a curdle 140 installed in a hydrogen station. Then, hydrogen boosted by the high-pressure compressor 141 is temporarily stored in the first pressure tank 110, the second pressure tank 120, and the third pressure tank 130. The curdle 140 to which the pressure tank is fixed is installed behind the office of the hydrogen station or on the roof of the hydrogen station. The curdle 140 may be equipped with more than three (for example, 16) pressure tanks.

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. Repeated stress is applied to the liner of each pressure tank as hydrogen is taken in and out. The number of load cycles to each pressure tank is recorded in a recording device (not shown) using a pressure gauge or the like. In addition, 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 is an explosion-proof AE sensor 150 (FBG type, Doppler type) as a sensor for detecting AE waves generated from the first pressure tank 110, the second pressure tank 120, and the third pressure tank 130. Or it is equipped with an optical fiber type AE sensor such as Michaelson type). The AE sensor 150 detects an AE wave generated under pressure in which a pressure tank is filled with a fluid, and valves 51 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 of. Further, the inspection system 100 includes a personal computer (PC) 160 functioning as an AE analyzer and an AE measuring device 170 connected to the AE analyzer 160. What are the AE analyzer 160 and the AE measuring device 170? It is installed in the AE measurement vehicle 180.

The AE analyzer 160 has a CPU (not shown) and a storage unit 161 that stores a control program and the like. Then, the CPU controls the entire AE analyzer 160 based on the program or the like stored in the storage unit 161 and also comprehensively controls various processes. Further, the storage unit 161 has a RAM, which is a system work memory for operating the CPU, a ROM for storing a program, system software, and the like, and / or a hard disk drive and the like. 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 the ROM or the hard disk drive. Further, the AE analyzer 160 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, etc. 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 implemented in the storage unit 161. Then, when the CPU executes various processes in response to the inspection program, 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 the 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 that has been signal-processed via the AE measuring device 170. Then, the parameter acquisition unit 162 processes 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 processes 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. As a result, the parameter acquisition unit 162 acquires the value of the amplitude ratio as the AE parameter. Further, the parameter acquisition unit 162 sends the value of the amplitude ratio to the storage unit 161 as the measurement result of the AE, 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, and is, 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, and is, 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, they are not limited to the above-exemplified range. The second frequency band is preferably a frequency band narrower 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 value of the amplitude ratio acquired by the parameter acquisition unit 162 with a predetermined control value, and determines that each pressure tank is normal when the value of the amplitude ratio is less than the control value. Further, 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 control 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.

Further, 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. 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 by wire or wirelessly as an external device. Further, 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 a security inspection, the inspector first parks the AE measuring vehicle 180 during the operation of the hydrogen station, and then parks the AE analyzer 160 and the AE measuring device in the non-explosion-proof area of the hydrogen station. 170 is installed (S101). The non-explosion-proof area is, for example, the internal area of the management office of the hydrogen station or the internal area of the AE measuring vehicle 180 parked at the hydrogen station.

Then, the inspector attaches an 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 surface portion 53 of the valve 51 at one end of each pressure tank or the flat surface portion 53 of the valve 51 at both ends of each pressure tank with an instant adhesive. After that, the inspector connects the attached AE sensor 150 and the AE measuring device 170 with a signal cable (S103). When the connection is completed, the initial setting of the AE measuring device 170 and the condition setting such as environmental noise are performed (S104), and the preparation for the AE measurement is completed.

It is desirable that the AE is measured while the internal pressure of the pressure tank is being boosted at a constant boosting speed. Therefore, under pressure filled with fluid, the AE sensor 150 attached to each pressure tank detects the AE wave generated from each pressure tank (S105). That is, hydrogen is supplied to the FCV 143 at the hydrogen station, and the AE when each pressure tank is filled with hydrogen by the high pressure compressor 141 is measured from the state of the minimum working pressure of each pressure tank. At this time, the boosting speed due to hydrogen filling is constant, and the AE wave is measured during a predetermined measurement period (for example, during a pressure fluctuation of about 10 cycles). Then, the same measurement is performed for each of the plurality of pressure tanks. In addition, it is preferable to carry out AE measurement at the time of boosting 2-3 times in one security inspection. However, since it depends on the supply timing to the FCV 143, the AE measurement in one security inspection may be one time. Further, if the boost timing is matched, the AEs of a plurality of pressure tanks can be measured at one time.

The AE amplitude value or the like measured by performing the measurement a plurality of times is recorded in the storage unit 161 in the AE analyzer 160 via the AE measuring device 170. Further, the AE measuring device 170 processes the detected AE wave into a signal to generate an AE signal, and the parameter acquisition unit 162 of the AE analyzer 160 obtains the AE parameter based on the AE signal acquired via the AE measuring device 170. Acquire (S106). Specifically, the parameter acquisition unit 162 acquires, as an AE parameter, a value of the amplitude ratio, which is the 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. Then, the acquired AE parameters are recorded in the storage unit 161 in the AE analyzer 160.

After that, the determination unit 163 in the AE analyzer 160 determines the fatigue damage of the pressure tank based on the AE parameters (S107). Specifically, the determination unit 163 compares the value of the amplitude ratio stored in the storage unit 161 with the preset control value. Then, 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 stores the inspection result that the pressure tank is normal in the storage unit 161. On the other hand, when the value of the amplitude ratio is equal to or larger than the control value, the determination unit 163 determines that the pressure tank is abnormal, and stores the inspection result that the pressure tank is abnormal in the storage unit 161. The control value is set within a range that does not reach the value of the amplitude ratio when hydrogen leaks, and can be obtained by experiment.

Further, the determination unit 163 can calculate the increase amount by subtracting the initial value of the amplitude ratio measured in advance from the acquired amplitude ratio value, and determine the damage of the pressure tank based on the increase amount. In this case, the determination unit 163 determines that the increase amount is normal when it is less than the control value, and determines that it is abnormal when the increase amount is greater than or equal to the control value. By inspecting whether the amount of increase exceeds the control value, the initial value of the amplitude ratio is significantly different for multiple pressure tanks that have undergone different autofrettage treatments due to the difference in autofrettage treatment. However, the pressure tank can be managed based on the amount of increase in the amplitude ratio.

Further, the determination unit 163 can also predict the fluctuation of the amplitude ratio value 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 the AE wave generated from each pressure tank in the initial state and acquires the initial value of the amplitude ratio in advance. Then, the determination unit 163 predicts the value of the future amplitude ratio from the initial value in the past, and determines whether or not the predicted value of the amplitude ratio exceeds the preset control value (threshold value). As a result, if it is regularly confirmed that the predicted value of the amplitude ratio is smaller than the control value, the pressure tank can be continuously operated while ensuring the soundness. 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 the AE frequency spectra obtained by measuring a plurality of times and store them in the storage unit 161. By comparing the superimposed AE frequency spectra, for example, an increase or decrease in the AE amplitude value in the 200 kHz to 300 kHz band can be recorded in the storage unit 161. Depending on the specifications of the pressure tank, there is a possibility that a frequency shift showing a remarkable increase / decrease may occur in addition to the 200 kHz to 300 kHz band. Therefore, the AE amplitude value of the frequency band showing a remarkable increase / decrease is also stored in the storage unit 161.

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

For the spread and operation of hydrogen stations, safety inspections in service are indispensable for confirming the pressure resistance performance and strength of pressure tanks, but there has been no practical and effective safety inspection. In this regard, according to the first embodiment, fatigue damage of the pressure tank can be inspected during the operation of the pressure tank. In addition, the progress of fatigue damage of the metal liner of the pressure tank can be emphasized by the amplitude ratio and inspected. Therefore, according to the present invention, it is possible to inspect the progress of fatigue damage in the pressure tank, particularly the type 1 container, the type 2 container, and the type 3 container provided with the metal liner.

The number of times the pressure tank can be used is defined as the number of times the design pressure cycle is divided by the fatigue design safety factor Kn. For example, in the case of a pressure tank having a design pressure cycle 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 design pressure cycle number of the pressure tank. In this regard, according to the first embodiment, the use can be extended if no sign of the progress of fatigue damage (increase in the amplitude ratio) is observed even if the number of times of use is exceeded. As a result, the pressure tank can be operated while confirming safety up to the number of times it can be used, and the use of the pressure tank can be continued while confirming safety even after the number of times it can be used. Therefore, it can contribute to the spread of safe and secure hydrogen stations.

Further, the composite container that exceeds the usable number of times is disposed of, but it is not easy to dispose of the composite container that uses a large amount of carbon fiber. Therefore, as hydrogen stations become more widespread, the number of disposals may become a social issue in the future. In this respect, if the number of times the composite container is used increases according to the first embodiment, it can contribute to reducing the number of times of disposal.

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

[Second Embodiment]
In the differential pressure filling type hydrogen station which is 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 3-bank switching method in 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 a 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 also different for each pressure bank.

Therefore, in the second embodiment, a different control 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, the differences from the first embodiment will be described, and the description of the components described in the first embodiment will be omitted. Unless otherwise specified, the components with the same reference numerals perform substantially the same operations and functions, and the effects thereof are also substantially the same.

In the second embodiment, the acoustic emission wave generated from the first pressure tank (low pressure tank) 210 having a wider fluctuation range of the internal pressure than the second pressure tank (medium pressure tank) 220 is further detected, and the second pressure is further detected. Further, 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 control values are set in advance for each of the second pressure tank 220, the first pressure tank 210, and the third pressure tank 230.

Further, the first pressure tank 210, the second pressure tank 220, and the third pressure tank 230 are provided with a first valve 291 and a second valve 292 and a third valve 293, respectively. Then, by opening and closing the first valve 291 and the second valve 292 and the third valve 293, the pressure tank for performing differential pressure filling with the FCV 143 is appropriately switched. A total of nine pressure tanks consisting of more than three pressure tanks, for example, three pressure tanks per bank, may be installed in the cardle 140.

When filling FCV 143, first, the second valve 292 and the third valve 293 are closed, and only the first valve 291 is opened to perform differential pressure filling from the first pressure tank 210 to the FCV 143 via the dispenser 142. .. After that, the flow path from the first pressure tank (low pressure bank) 210 is the second pressure tank (for example, 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. Therefore, the first valve 291 and the third valve 293 are closed, and only the second valve 292 is opened to perform differential pressure filling from the second pressure tank 220 to the FCV 143 via the dispenser 142.

After that, the flow path from the second pressure tank (medium pressure bank) 220 is 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). (High pressure bank) Switch to the flow path from 230. Therefore, the first valve 291 and the second valve 292 are closed, and only the third valve 293 is opened to perform differential pressure filling 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).

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

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 also different for each pressure bank. Therefore, in the second embodiment, the control value of the second pressure tank 220, the control value of the first pressure tank 210, and the control value of the third pressure tank 230 are set to be different from each other, and the AE analysis is performed. The determination unit 163 of the device 160 compares the value of each amplitude ratio with each control value.

According to the second embodiment described above, fatigue damage of the pressure tank can be inspected during the operation of the pressure tank. In addition, the pressure tank can be operated while checking the safety up to the number of times it can be used, and the use of the pressure tank can be extended while checking the safety even if the number of times it can be used is exceeded. Further, according to the second embodiment, even when the three-bank switching method is adopted, the fatigue damage of the pressure tank can be accurately inspected according to the pressure fluctuation.

Although the present invention has been described above with reference to each embodiment, the present invention is not limited to the above embodiments. The present invention also includes inventions modified to the extent not contrary to the present invention, and inventions equivalent to the present invention. In addition, each embodiment and each modification can be appropriately combined within a range not contrary to the present invention.

For example, the present invention can also be applied to a pressure tank installed at a place other than a 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 to constantly measure the AE. The present invention may also be applied to an empty pressure tank before it is filled with fluid.

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

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

Some or all of the above embodiments may also be described, but not limited to:

(Appendix 1)
It ’s a pressure tank inspection method.
Detects the acoustic emission wave generated from the pressure tank and
Calculate the value of the amplitude ratio, which is the ratio of the representative value of the amplitude value in the second frequency band different from the first frequency band of the acoustic emission wave to the representative value of the amplitude value in the first frequency band of the acoustic emission wave. And
The value of the amplitude ratio is compared with a predetermined control value, and when the value of the amplitude ratio is less than the control value, it is determined that the pressure tank is normal, and the value of the amplitude ratio is equal to or more than the control value. In this case, an inspection method for determining that the pressure tank is abnormal.

(Appendix 2)
The inspection method according to Appendix 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 has a metal liner and a CFRP hoop layer.

(Appendix 5)
The inspection method according to Appendix 1, wherein an optical fiber type sensor for detecting an 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 the maximum amplitude value within a predetermined measurement period.

(Appendix 7)
It ’s a pressure tank inspection method.
Detects the acoustic emission wave generated from the pressure tank and
At the initial time point, the amplitude ratio which is the ratio of the representative value of the amplitude value in the second frequency band different from the first frequency band of the acoustic emission wave to the representative value of the amplitude value in the first frequency band of the acoustic emission wave. Calculate the initial value of
After the initial time point, the value of the amplitude ratio is calculated again.
The difference between the recalculated amplitude ratio value and the initial value is compared with a predetermined control value, and if the difference is less than the control value, it is determined that the pressure tank is normal, and the difference is said. An inspection method for determining that the pressure tank is abnormal when the value is equal to or higher than the control value.

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 (7)

Detecting the acoustic emission wave generated from pressure tank,
Acquire the acoustic emission parameter based on the detected acoustic emission wave, and
In the pressure tank inspection method for determining damage to the pressure tank based on the acoustic emission parameters ,
The medium pressure tank includes a medium pressure tank, a low pressure tank having a wider internal pressure fluctuation range than the medium pressure tank, and a high pressure tank having a narrower internal pressure fluctuation range than the medium pressure tank. Detecting acoustic emission waves generated from each of the low pressure tank and the high pressure tank,
For each of the medium pressure tank, the low pressure tank, and the high pressure tank, the acoustic emission is a representative value of the amplitude value in the second frequency band caused by the progress of fatigue damage of the pressure tank in the acoustic emission wave. The value of the amplitude ratio, which is the ratio of the amplitude value in the first frequency band different from the second frequency band of the wave to the representative value, is acquired as the acoustic emission parameter.
For each of the medium pressure tank, the low pressure tank, and the high pressure tank, the values of the amplitude ratios are individually compared with predetermined control values, and when all the values of each amplitude ratio are less than the control values, It is a method of determining that the pressure tank is normal, and when any of the values of each amplitude ratio is equal to or greater than the control value, it is determined that the pressure tank is abnormal.
A method characterized in that the control value of the medium pressure tank, the control value of the low pressure tank, and the control value of the high pressure tank are set to be different from each other. For each of the high pressure tank and the low-pressure tank and the in pressure tank, the second frequency band, the inspection method according to claim 1 is a narrow frequency band than the first frequency band. For each of the high pressure tank and the low-pressure tank and the in pressure tank, the inspection method according to claim 1 or 2 mounting a sensor for detecting the acoustic emission wave to the valve of the pressure tank. For each of the medium pressure tank, the low pressure tank, and the high pressure tank, the acoustic emission wave generated from the pressure tank at the initial time point is detected and the initial value of the amplitude ratio is acquired in advance.
The inspection method according to any one of claims 1 to 3 , which predicts fluctuations in the amplitude ratio value based on a comparison result between the amplitude ratio value and the initial value. A pressure tank inspection system for carrying out the pressure tank inspection method according to claim 1 .
Sensors that detect acoustic emission waves generated from the medium pressure tank , the low pressure tank, and the high pressure tank , respectively .
Respectively based on each acoustic emission wave sensed a parameter acquisition unit for acquiring acoustic emission parameters, the representative value of the amplitude value of the first frequency band of the acoustic emission wave, said first frequency of said acoustic emission wave A parameter acquisition unit that acquires an amplitude ratio value, which is a ratio of representative values of amplitude values in a second frequency band different from the band, as the acoustic emission parameter of the pressure tank .
The acquired values of each amplitude ratio are individually compared with the predetermined control values, and if all the values of each amplitude ratio are less than the predetermined control values for the pressure tank, it is determined that the pressure tank is normal. An inspection system including a determination unit for determining that the pressure tank is abnormal when any of the values of each amplitude ratio is equal to or greater than the predetermined control value for the pressure tank . The inspection system according to claim 5 , further comprising an output unit that outputs the value of each amplitude ratio acquired by the parameter acquisition unit. An inspection program used in the pressure tank inspection system according to claim 5 .
By being mounted on a computer that functions as a parameter acquisition unit that acquires acoustic emission parameters based on the acoustic emission waves generated from the medium pressure tank , the low pressure tank, and the high pressure tank , respectively .
The computer, as the parameter acquiring unit, the representative value of the amplitude value of the first frequency band of the acoustic emission wave, the representative value of the amplitude value in a different second frequency band than the first frequency band of the acoustic emission wave The value of the amplitude ratio, which is a ratio, is acquired as the acoustic emission parameter of the pressure tank, and is also obtained .
The acquired values of each amplitude ratio are individually compared with the predetermined control values, and if all the values of each amplitude ratio are less than the predetermined control values for the pressure tank, it is determined that the pressure tank is normal. Then, when any of the values of each amplitude ratio is equal to or higher than the predetermined control value for the pressure tank, the computer is operated so as to further function as a determination unit for determining that the pressure tank is abnormal. Inspection program.

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