Non-destructive testing methods and non-destructive testing apparatus for structures

Abstract

In non-destructive testing, which involves exciting vibrations in a structure through impact from a liquid mass, attempting to inject a liquid mass with a large impact force by intermittently using a pressurized liquid flow not only requires large and expensive on / off valves, but also makes it difficult to give the impact force a wide bandwidth of frequency components, and increases the amount of liquid required for each impact. [Solution] A liquid mass injection mechanism is used, in which multiple flow paths, each equipped with an on / off valve, are connected in parallel. By connecting n flow paths in parallel, a liquid mass with the same impact force can be injected by intermittently injecting a flow rate of 1 / n. The individual on / off valves become smaller, their pressure resistance increases, and they can be opened and closed at high speeds, so it is possible to inject pulsed liquid masses that provide a larger and broader impact force.

Description

Technical Field

[0001] The present invention relates to a non-destructive inspection method and a non-destructive inspection device for inspecting the soundness of a structure.

Background Art

[0002] Infrastructure structures such as tunnels and bridges, and building outer walls, if their soundness is lost due to aging or disasters, may lead to serious accidents such as wall peeling, so regular inspections are essential. And a typical method for non-destructively inspecting the object is impact echo testing.

[0003] As a method for remotely and efficiently performing impact echo testing, a method using water hammer has been proposed. In Patent Document 1, a non-destructive inspection method for remotely hitting a test surface by injecting water is described. In Patent Document 2, an inspection method for periodically hitting a test surface by utilizing the formation of water droplets by a water flow jet in air is described. Also, in Non-Patent Document 1, the practical application of the pulsed water jet method, in which a water flow pressurized by high-pressure air is interrupted by a valve to inject water masses and hit the inspection object, is being studied.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Regardless of the method used to detect vibrations excited in the target structure, in order to detect vibrations remotely, unaffected by the surrounding environment, and with a sufficient signal-to-noise ratio, the impact of the liquid mass on the target must be of sufficient magnitude. In other words, the injected liquid mass must have a sufficiently large flow rate and velocity. This condition is also necessary to minimize the effect of wind on the injected liquid mass and maintain accuracy in determining the impact location.

[0007] On the other hand, the frequency of vibrations excited on the surface of a target structure by impact varies depending on the structure and the defect conditions. In order to detect unknown defects without overlooking them, impacts containing a wide range of frequency components are necessary. In other words, the impact force generated by the collision of a liquid mass must contain a wide bandwidth of frequency components.

[0008] To impart an impact force containing broadband frequency components, it is necessary to create a pulsed impact by rapidly and intermittently injecting a liquid flow. However, generally, increasing the liquid flow rate / velocity and rapidly intermittently injecting the liquid flow are conflicting requirements. In the case of electromagnetic valves, which are most commonly used for intermittently injecting liquid flow, a large opening (orifice) area is required to allow a large flow rate. However, generally, the larger the opening area, the lower the pressure resistance of the valve. Therefore, the pressure used to push out the liquid must be kept low, and the flow velocity cannot be increased. In addition, the valve becomes large and expensive, and the power required to operate it also increases.

[0009] Furthermore, a larger opening area results in a larger valve body (plunger), increasing its mass and the displacement of the valve body during opening and closing, making high-speed intermittent operation difficult. The valve opening changes slowly, and the period in the intermediate state between fully open and fully closed becomes longer. As a result, the flow rate of the liquid mass also changes slowly, making it impossible to spray a liquid mass with pulsed impact force. Moreover, because liquid flows out during the intermediate state, the amount of liquid required for a single impact increases. This increase in required liquid volume directly leads to a reduction in the total inspection time in inspections where the liquid used for impact is held in a tank.

[0010] The present invention has been made in view of the above problems, and aims to provide a non-destructive testing method and non-destructive testing apparatus that enables low-cost and efficient impact sound testing by realizing pulse-like impacts with broadband frequency components and sufficient magnitude. [Means for solving the problem]

[0011] To solve the above problems, the present invention provides a non-destructive testing method for inspecting the structural integrity of a structure by injecting a liquid mass and causing it to collide with the structure, and then performing frequency analysis on the excited vibrations. In this method, multiple flow paths equipped with flow path on / off valves are connected in parallel, and the intermittent liquid flows caused by the on / off valves are merged to inject the liquid mass.

[0012] In the invention described in claim 2, in the non-destructive testing method of claim 1, the multiple flow paths are designed such that the acoustic impedance from the liquid supply source to the liquid mass injection port is equal in all flow paths when the flow path opening valve is opened.

[0013] In the invention described in claim 3, a liquid mass that delivers an impact force of a desired waveform is injected by controlling the opening and closing timing of each flow path valve.

[0014] The invention described in claim 4 involves scanning the impact position of the sprayed liquid mass to inspect the integrity of an object having a linear or planar spread. [Effects of the Invention]

[0015] In this invention, by rapidly intermittently interrupting the liquid flow in multiple flow paths using flow path valves with high pressure resistance and small opening area, and by adding these multiple intermittent liquid flows in parallel, it becomes possible to inject pulsed liquid masses that have sufficient flow rate / flow velocity and provide broadband impact. The time that the valves are in an intermediate state between fully open and fully closed is shortened, and the amount of liquid required for a single impact is reduced. Since the individual valves used are small, costs are lowered and the energy required to drive them is also reduced.

[0016] In the invention according to claim 2, by designing such that the acoustic impedance from the liquid supply source to the injection port is equal in each flow path, the dynamic conditions of the liquid in each flow path are made the same. As a result, it is possible to prevent the "sagging" of the liquid mass shape due to variations between multiple flow paths of fluid motion and inject a pulsed liquid mass that gives a broadband impact.

[0017] In the invention according to claim 3, by controlling the opening and closing timing of the flow path opening and closing valve for each opening and closing valve, it is possible to adjust the shape of the injected liquid mass according to the inspection target. When there are variations in the acoustic impedance between multiple flow paths or the dynamic characteristics of the opening and closing valve, they can be corrected and adjusted to inject a pulsed liquid mass, or a liquid mass with an intentionally sagging shape can be injected to optimize the frequency spectrum of the impact according to the inspection target and improve the S / N ratio during inspection.

[0018] In the invention according to claim 4, by scanning the collision position of the injected liquid mass, it is possible to obtain information regarding the soundness of a linear or planar spreading object.

Brief Description of the Drawings

[0019] [Figure 1] It is a diagram showing the configuration of an inspection device 1 which is an embodiment of the present invention. [Figure 2] It is a diagram showing the liquid mass injection part of the inspection device 1. [Figure 3] It is a structural diagram of an electromagnetic valve used in a prototype device. [Figure 4] It is a schematic diagram of a liquid mass injected using a single electromagnetic valve. [Figure 5] It is a schematic diagram of a liquid mass injected from the liquid mass injection mechanism of the present invention. [Figure 6] It is the impact force and spectrum of a liquid mass injected using a prototype device (single electromagnetic valve). [Figure 7] It is the impact force and spectrum of a liquid mass injected using a prototype device (three parallel valves). [Figure 8] It is an example of the tile floating inspection result by a prototype device (three parallel valves). [Figure 9] This figure shows the configuration and application examples of inspection device 2. [Figure 10] This is a diagram showing the liquid mass injection section of the inspection device 3. [Modes for carrying out the invention]

[0020] The embodiments of the present invention will be described below based on examples. [Examples]

[0021] (Configuration of inspection device 1) Figure 1 shows the configuration of Embodiment 1 (Inspection Device 1) of the present invention. In Figure 1, 1 is the structure to be inspected, and 2 is a cavity in the structure. 11 is a nozzle for spraying liquid mass, 12 is an electromagnetic valve, 13 is a liquid supply port, 14 is an accumulator installed immediately next to the liquid mass spraying section, and 15 represents the sprayed liquid mass.

[0022] 21 is a liquid pumped from a high-pressure pump (not shown) and stored in a high-pressure tank 22. The high-pressure tank is filled with high-pressure gas 23 along with the liquid. The liquid in the high-pressure tank 22 is sent through a hose 25 to the liquid supply port 13 of the liquid injection unit. 24 is a valve drive circuit that controls the operation of the electromagnetic valve 12.

[0023] When the ejected liquid mass 15 collides with the structure 1, vibrations are excited by the impact force. 31 is the impact sound radiated by the vibrations on the surface of the structure. The impact sound 31 is recorded by a unidirectional microphone 32 and frequency-analyzed. 33 is a video camera that records the structure under inspection and the state of the liquid mass.

[0024] Figure 2 is an enlarged view of the liquid mass injection section of the inspection device 1. In this inspection device, eight electromagnetic valves 12 are arranged in a star shape with rotational symmetry. The liquid supply port 13 of the liquid mass injection section is connected to a high-pressure tank 22 via a hose. The liquid flowing in from the liquid supply port 13 fills the input side flow path 16 of the electromagnetic valve 12 and is also stored in the accumulator 14. The output side flow paths 17 of the electromagnetic valves are joined in parallel and connected to the nozzle 11.

[0025] (Operation and function of inspection device 1) In the inspection device 1, the electromagnetic valve 12 is rapidly opened and closed by a pulsed current supplied from the drive circuit 24. The liquid in the input-side flow path 16, which is pressurized to a high pressure, is sent to the output-side flow path 17 the moment the electromagnetic valve opens, where they merge and are ejected from the nozzle 11 as a liquid mass 15. The liquid ejected at the moment of ejection is mainly supplied from the accumulator 14, with only a small amount supplied from the liquid supply port 13. Immediately after ejection, the liquid in the accumulator decreases, but during the period until the next ejection, it is slowly replenished from the high-pressure tank 22 via the hose 25 and the liquid supply port 13.

[0026] The ejected liquid mass 15 collides with structure 1, applying a pulsed impact force to the structure's surface. In a sound structure, the surface is rigid and heavy, so even when an impact force is applied, little vibration occurs. However, if defects such as internal cavities or delamination of the outer wall exist, the impact force excites flexural vibrations in the surface layer above the defects. These flexural vibrations typically have a resonant frequency determined by the structure's structure and materials, as well as the depth, size, and shape of the defects. When struck at a frequency equal to the resonant frequency, a large vibration occurs. The sound radiated from the vibration of the structure's surface is what is known as percussive noise.

[0027] The impact sound 31 emitted from structure 1 is detected by a unidirectional microphone 32 and frequency-analyzed by a signal processing device (not shown). Based on this result, the presence, size, and depth of defects are determined. The microphone's unidirectional directivity is chosen to avoid interference from noise arriving from directions other than the point of impact. A video camera 33 is used to film the collision between the structure under inspection and the liquid mass, and to confirm and record the inspection location and inspection status.

[0028] (Effects of inspection device 1) Figure 3 shows the structure of a typical solenoid valve. The prototype device used in the experiment described later also used a solenoid valve with a similar structure. In the figure, 121 is the coil, 122 is the plunger, 123 is the spring, 124 is the seal, and 125 is the valve seat. In the normal state when no current flows through the coil, the plunger 122 is pressed against the valve seat 125 by the spring 123, and the opening of the valve seat is closed by the seal 124. When current flows through the coil, the plunger is pulled upward, and the opening of the valve seat opens, allowing fluid to flow from the input side passage 16 to the output side passage 17.

[0029] To increase the flow rate through a solenoid valve, it is necessary to increase both the opening area of ​​the valve seat and the travel distance of the plunger. However, increasing the opening area reduces the pressure resistance of the solenoid valve. Furthermore, a larger valve seat opening area increases the mass of the plunger and the travel distance of the plunger, making high-speed intermittent operation difficult. Even with solenoid valves of different shapes and structures than those shown in Figure 3, it is generally true that the operating speed of the solenoid valve slows down as the flow rate increases. Increasing the allowable flow rate while maintaining high-speed operation becomes unrealistic from a cost perspective.

[0030] Figure 4 schematically shows a liquid mass injection unit using a single large electromagnetic valve 42 for high flow rates, and the injected liquid mass 45. 41 is the nozzle, 43 is the liquid supply port, and 44 is the accumulator. With a large electromagnetic valve, the valve opening cannot be changed in a pulsed manner, resulting in a longer period of time in an intermediate state between fully open and fully closed. As a result, the flow rate gradually increases to a certain amount, then gradually decreases to zero. Consequently, the injected liquid mass 45 extends far in the direction of injection, and the time waveform of the impact force upon collision with a structure also exhibits a long duration and gradual time change.

[0031] Figure 5 is a schematic diagram of the liquid mass injection section and the liquid mass 15 to be injected in the inspection device 1 according to the present invention. In this liquid mass injection section, small electromagnetic valves are used in parallel, so the flow path can be opened and closed at high speed. The liquid mass injected from the nozzle is a liquid mass with a short length in the injection direction. When the short liquid mass collides with a structure, the impact force acting on the surface of the structure is a pulse-like impact force with a short duration. The accumulator 14 installed immediately next to the valve is an essential component for injecting short, sharp liquid masses. If an accumulator is not installed, the liquid injected from the nozzle will be supplied from a high-pressure pump via a hose, and this long flow path will have a large inertance, preventing a rapid change in flow velocity.

[0032] The pulsed impact force contains a wide range of frequency components. Because it can excite deflection vibrations from defects with low-frequency resonant frequencies to those with high-frequency resonant frequencies, it becomes possible to detect defects under a wide range of conditions. Furthermore, the amount of liquid required for a single impact is significantly less compared to using large valves, and the overall cost of the solenoid valve and its drive mechanism can also be drastically reduced.

[0033] In the inspection device 1, the eight electromagnetic valves, input flow path, and output flow path are arranged in a star shape, resulting in a configuration that is rotationally symmetrical with respect to the central axis of the nozzle 11. When the valves are open, the acoustic impedance of the flow path from the accumulator to the nozzle is equal in all flow paths, and if the electromagnetic valves open and close at the same time, the flow velocity in all flow paths will be equal. This configuration minimizes the distortion of the shape of the ejected liquid mass and the narrowing of the frequency band of the impact force that can occur due to differences in the rise / fall of the flow velocity between parallel flow paths.

[0034] (Example of experiment) Figures 6 and 7 show the impact force and its spectrum when a water mass was actually impacted onto a test specimen using the prototype experimental apparatus. Figure 6 shows the impact force waveform and spectrum when a water mass was ejected using a single electromagnetic valve. The impact force was measured by a pressure sensor embedded in the test specimen. Figure 7 shows the impact force and spectrum when three electromagnetic valves were used in parallel. The valve opening areas in Figures 6 and 7 were set to be approximately the same. In Figure 6, the discharge pressure was 1.0 MPa and the water mass ejection velocity was approximately 22 m / s, while in Figure 7, the discharge pressure was 2.0 MPa and the water mass ejection velocity was approximately 50 m / s.

[0035] Comparing Figures 6 and 7, it can be seen that parallelizing the valves improves the impact force, making it sharper and more pulse-like. Comparing the spectra, the effect is clear, as parallelizing the valves homogenizes the components up to 10 kHz. Furthermore, the amount of water consumed per impact is also significantly reduced, as can be seen from the impact force waveform. The amount of water required per impact was 6 milliliters for the single valve in Figure 6 and 0.6 milliliters for the three parallel valves in Figure 7.

[0036] A prototype device using three electromagnetic valves was used to inspect a tiled wall surface. Exterior wall tiles were attached to concrete, and one of the tiles had been artificially delaminated (lifted) to create a test specimen. Figure 8 shows the results of frequency analysis of the sound produced when the tile surface was struck with a water swabs. The left shows the result when a sound, undamaged area was struck, and the right shows the result when a delaminated tile was struck. The sound from the sounded area shows only a broad spectrum due to noise, with no peaks observed. In contrast, a large peak around 1.1 kHz is observed in the spectrum of the sound produced above the defect. [Examples]

[0037] (Inspection device 2) Figure 9 shows the configuration and application example of a second embodiment (inspection device 2) of the present invention. In the figure, 91 is the tunnel to be inspected, and 92 is the inspection vehicle that travels inside the tunnel carrying the implementation device 2. 93 is a movable stand on which the liquid mass injection unit is mounted, 22 is a high-pressure tank, and 94 is a tank for storing the inspection liquid. In the implementation device 2, the injection direction can be controlled by moving the movable stand 93 on which the liquid mass injection unit is mounted, and the position on the target that the injected liquid mass strikes can be scanned linearly or in a surface manner. By scanning the liquid mass injection unit linearly while the inspection vehicle travels inside the tunnel and performs continuous inspections, the inside of the tunnel is inspected in a surface manner. [Examples]

[0038] (Implementation device 3) Figure 10 shows the liquid mass injection section of the third embodiment (inspection device 3) of the present invention. The basic configuration of the liquid mass injection mechanism is the same as that of the implementation device 1 (Figure 2). However, in this implementation device, three electromagnetic valves 12 are connected in parallel. 241 is a valve drive device, and 242 is a power supply circuit for driving the electromagnetic valves. In this valve drive device, the on / off timing of the switching circuit 243 connected to each electromagnetic valve can be individually controlled by the timing control circuit 244. By using such a valve drive device, the shape of the injected liquid mass can be controlled to obtain a desired impact force waveform.

[0039] (Operation and effects of inspection device 3) If there are variations in the acoustic impedance from the liquid supply source (accumulator 14) to the nozzle among multiple flow paths, or if there are variations in the dynamic characteristics of multiple electromagnetic valves, the flow velocities in each flow path will not rise simultaneously. As a result, the shape of the liquid mass that is ejected after merging will be distorted, and the frequency band of the impact force generated at the time of collision will be narrowed. In the implementation device 3, by adjusting the opening and closing timing of the electromagnetic valves so that the flow velocities in each flow path rise at the same time, it becomes possible to eject a liquid mass with a pulsed impact force.

[0040] Furthermore, depending on the conditions of the object being inspected, it may be acceptable for the deflection vibration originating from the defect to be low-frequency, and for the impact force caused by the liquid mass collision not to contain a very wide frequency range. In such cases, it is possible to intentionally smooth the impact force waveform while ensuring the necessary impact force (impulse) for inspection. This reduces noise associated with liquid mass ejection and collision, making it possible to detect even small deflection vibrations.

[0041] It is also possible to spray a long, continuous mass of liquid to strike the target structure. In this case, the impact force applied to the structure will have a step-like waveform rather than a pulse-like one. For example, by adjusting the valve timing to gradually increase the flow velocity of the jet until it reaches a steady value, and then rapidly stopping the jet, a negative step-like impact force will be applied to the surface of the structure. The impact sound radiated from the deflection vibration occurs and is detected after the jet has stopped, making it possible to perform inspections without being affected by noise from the jet impact.

[0042] Here, the valve that stops the continuous jet in a stepwise manner needs to operate at a sufficiently high speed. A stepwise impact force, if the intermittence is performed at high speed, contains a wide frequency range, though not as wide as a pulsed impact force. However, if the intermittence is gradual, the frequency range becomes narrow. The ability to achieve a wide-bandwidth impact force while using a continuous jet is a unique feature of the present invention, which involves connecting small valves in parallel.

[0043] (supplementary explanation) While water is commonly used as the liquid sprayed for inspection, in some cases seawater, water mixed with detergent or surfactant, or an aqueous solution of some kind of chemical may be used. Furthermore, in special applications, liquids other than water may be used. In these cases as well, the parallel connection of multiple valves according to the present invention has exactly the same effect.

[0044] In all of the embodiments described above, a microphone is used to detect the impact sound emitted from the vibration in order to perform frequency analysis of the vibration of the target structure. However, the means for detecting vibrations of the target surface are not limited to microphones. Depending on the conditions of the target surface, vibration detection means such as a laser Doppler velocometer or a laser displacement meter can be used, or if it is possible to easily bring the device close to the target structure, an acceleration pickup can be used. In short, the essence of the present invention lies in rapidly intermittently switching multiple parallel-connected channels to achieve impacts with desired characteristics, and various known means can be used for detecting and frequency analysis of the excited vibrations. [Explanation of symbols]

[0045] 1 structure 2 cavities 11 nozzles 12 Solenoid valves 13 Liquid supply port 14 Accumulator 15 Liquid mass 16 Input channel 17 Output side flow path 21 liquid 22 High-pressure tank 23. High-pressure gas 24 Valve drive circuit 25 hoses 26 High-pressure pump 31. Percussion 32 Unidirectional Microphone 33 video cameras 41. Nozzle (of the liquid mass injection section using a large electromagnetic valve) 42 Large Solenoid Valves 43. Liquid supply port (of the liquid mass injection section using a large electromagnetic valve) 44. Accumulator (of the liquid mass injection section using a large electromagnetic valve) 45. Liquid mass (of the liquid mass injection section using a large electromagnetic valve) 91 Tunnel 92 Inspection Vehicles 93 Movable stand 94 tanks 121 coil 122 Plunger 123 Spring 124 stickers 125 valve seat 241 Valve drive unit (with timing control function) 242 Power supply circuit 243 Switching Circuits 244 Timing control circuit

Claims

1. A non-destructive testing method for inspecting the structural integrity of a structure by injecting a liquid mass toward the structure to be inspected, causing the liquid mass to collide with the surface of the structure to excite vibrations in the structure, and then performing frequency analysis on the vibrations, characterized in that a plurality of flow paths equipped with flow path on / off valves are connected in parallel, and the liquid flows from each of the intermittently connected flow paths are merged by the on / off valves to inject a liquid mass.

2. The non-destructive testing method according to claim 1, wherein each flow path is designed such that the acoustic impedance from the liquid supply source to the liquid mass injection port is equal in all flow paths when the flow path opening valve is opened.

3. A non-destructive testing method according to claim 1 or 2, wherein a liquid mass is injected onto a target structure to impart an impact force of a desired waveform by controlling the opening and closing timing of each flow path valve.

4. A non-destructive testing method according to claims 1 to 3, wherein the impact position of a sprayed liquid mass is scanned to inspect the integrity of an object that has a linear or planar spread.

5. A non-destructive testing apparatus that injects a liquid mass toward a structure to be inspected, causing the liquid mass to collide with the surface of the structure to excite vibrations in the structure, and performs frequency analysis of the vibrations to inspect the soundness of the structure, comprising a liquid mass injection means that connects a plurality of flow paths, each equipped with an on / off valve, in parallel and merges the liquid flows of each flow path, and using the non-destructive testing method described in claims 1 to 4.

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