JP2021183915A - Piezoelectric element fixing device and fixing method - Google Patents

Abstract

To provide a piezoelectric element fixing device and a fixing method which can reduce weight of the piezoelectric element fixing device so as not to affect seismic design of an inspection object, and can improve an acoustic coupling between a piezoelectric element and a surface of the inspection object.SOLUTION: A fixing device which fixes a piezoelectric element 20 which transmits and receives ultrasonic waves to an outer surface of a pipe 10 has an alumina tape 26 which is non-metal and is formed into a strip shape so as to extend over the entire circumferential direction of the pipe 10, and urges pressing force to the piezoelectric element 20 so that the piezoelectric element 20 is fixed on the surface of the pipe 10. The alumina tape 26 has a smaller linear expansion coefficient than the pipe 10.SELECTED DRAWING: Figure 1

Description

The present invention relates to a fixing device and a fixing method for a piezoelectric element.

In the ultrasonic inspection, an ultrasonic sensor (specifically, a piezoelectric element) that transmits and receives ultrasonic waves is used to inspect the inspection object for deterioration (specifically, for example, cracking or thinning). This ultrasonic inspection is used in a wide range of fields because it can inspect the inspection object as it is, the cost required for the inspection is low, and it is easy to apply. In nuclear power plants, thermal power plants, etc., ultrasonic inspections are carried out to confirm the soundness of pipes, containers, etc.

Patent Document 1 discloses that a plurality of ultrasonic sensors are fixed to the outer surface of a pipe by using a band-shaped member. The band-shaped member is made of metal and is formed so as to extend over the entire circumferential direction of the pipe.

Patent No. 6108523

There is room for improvement in the above-mentioned prior art as follows. The band-shaped member of Patent Document 1 is made of metal, and its weight is increased as compared with the case of being made of non-metal. Therefore, in particular, when the piezoelectric element is permanently installed on the surface of the inspection target, it becomes necessary to review the seismic design of the inspection target. Therefore, it is desired to reduce the weight of the fixing device for the piezoelectric element. It is also desired to enhance the acoustic coupling between the piezoelectric element and the surface of the inspection object.

An object of the present invention is to reduce the weight of the piezoelectric element fixing device so as not to affect the seismic design of the inspection object, and to improve the acoustic coupling between the piezoelectric element and the surface of the inspection object. It is an object of the present invention to provide a fixing device and a fixing method of a piezoelectric element which can be performed.

In order to achieve the above object, the present invention is a fixing device for fixing a piezoelectric element that transmits and receives ultrasonic waves to the surface of an inspection object, which is non-metal and extends over the entire circumferential direction of the inspection object. It is formed in a strip shape so as to exist, and has a fixing member that applies a pressing force to the piezoelectric element to fix the piezoelectric element to the surface of the inspection object, and the fixing member linearly expands from the inspection object. The coefficient is small.

According to the present invention, it is possible to reduce the weight of the fixing device for the piezoelectric element so as not to affect the seismic design of the inspection object, and to improve the acoustic coupling between the piezoelectric element and the surface of the inspection object. can.

It is sectional drawing of the part in the circumferential direction of a pipe which shows the fixing device of a piezoelectric element in 1st Embodiment of this invention together with a transmission / reception coil and a probe which are other parts other than a piezoelectric element constituting an ultrasonic inspection system. It is a developed view of the pipe surface which shows the fixing device of the piezoelectric element in 1st Embodiment of this invention. It is a developed view of the metal exterior plate which shows the transmission / reception coil in 1st Embodiment of this invention. It is a perspective view which shows the fixing device of the piezoelectric element in 1st Embodiment of this invention. It is a developed view of the pipe surface which shows the fixing device of the piezoelectric element in the 1st modification of this invention. It is a developed view of the pipe surface which shows the fixing device of the piezoelectric element in the 2nd modification of this invention. It is a developed view of the pipe surface which shows the fixing device of the piezoelectric element in the 3rd modification of this invention. It is a developed view of the pipe surface which shows the fixing device of the piezoelectric element in the 4th modification of this invention. It is sectional drawing of the part of the pipe circumferential direction which shows the fixing device of the piezoelectric element in the 2nd Embodiment of this invention. It is sectional drawing of the part of the pipe circumferential direction which shows the fixing device of the piezoelectric element in 3rd Embodiment of this invention.

The first embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional view of a part of the pipe circumferential direction showing the piezoelectric element fixing device in the present embodiment together with a transmission / reception coil and a probe which are other parts other than the piezoelectric element constituting the ultrasonic inspection system. FIG. 2 is a developed view of a pipe surface showing a fixing device for a piezoelectric element in the present embodiment. FIG. 3 is a developed view of a metal exterior plate showing a transmission / reception coil in the present embodiment. FIG. 4 is a perspective view showing the fixing device of the piezoelectric element in the present embodiment. In FIGS. 2 and 4, for convenience, the heat insulating material, the metal exterior plate, the transmission / reception coil, and the like are not shown.

The pipe 10 which is the inspection target of the present embodiment is made of a metal such as carbon steel or stainless steel, and a liquid or gas flows during plant operation to cause a high temperature. Therefore, the outside of the pipe 10 is covered with a heat insulating material 11 such as rock wool or glass wool, and the outside of the heat insulating material 11 is covered with a metal exterior plate 12 such as aluminum or galvanized steel plate.

The ultrasonic inspection system is for inspecting, for example, whether or not the thickness of the pipe 10 is thinned. The plurality of piezoelectric elements 20 fixed to the surface of the pipe 10 and a plurality of piezoelectric elements 20 arranged outside the metal exterior plate 12 are provided. A probe that selectively faces one of a plurality of transmission / reception coils 21 connected to each of the piezoelectric elements 20 and one of the plurality of transmission / reception coils 21 and transmits / receives a signal by electromagnetic induction between the facing transmission / reception coils 21. 22 is provided with a control device (not shown) connected to the probe 22. The plurality of piezoelectric elements 20 correspond to a plurality of measurement points in the pipe 10, and are arranged so as to be separated from each other in the circumferential direction and the axial direction of the pipe 10, for example.

For the piezoelectric element 20, for example, a material such as lead Zirconate titanate PZT, which has a large piezoelectric effect, is used. Further, for example, in consideration of the case where the temperature of the pipe 10 exceeds 200 ° C., a material such as lithium niobate having heat resistance is used.

The piezoelectric element 20 has two electrodes (positive electrode and negative electrode). The surface of the piezoelectric element 20 facing the pipe 10 is a negative electrode, and this negative electrode is electrically connected to the pipe 10 via a silver sheet described later.

The surface of the piezoelectric element 20 on the opposite side of the pipe 10 is a positive electrode, and this positive electrode is connected to one end of the signal line 24A via a silver paste 23. The signal line 24A penetrates the heat insulating material 11 and the metal exterior plate 12, and the other ends are connected to the transmission / reception coil 21. An insulating tube 25A for avoiding contact with a silver sheet or the like, which will be described later, is provided on one end side of the signal line 24A, and contact with the metal exterior plate 12 is avoided on the other end side of the signal line 24A. Insulation tube 25B is provided. The insulating tubes 25A and 25B are, for example, ceramic beads or the like, and are adapted to maintain the insulating property even in a high temperature environment.

The transmission / reception coil 21 is a flat coil composed of a spiral copper wire, and one end thereof is connected to the positive electrode of the piezoelectric element 20 via the signal line 24A described above. The other end of the transmission / reception coil 21 is connected to the metal exterior plate 12 via the signal line 24B. The metal exterior plate 12 and the pipe 10 are electrically connected at at least one place. Therefore, the other end of the transmission / reception coil 21 is connected to the negative electrode of the piezoelectric element 20.

The control device transmits a pulse signal to the piezoelectric element 20 via the probe 22 and the transmission / reception coil 21. As a result, the piezoelectric element 20 transmits ultrasonic waves toward the inside of the pipe 10, receives the ultrasonic waves reflected by the inner surface of the pipe 10, and converts the received ultrasonic waves into a waveform signal. The control device receives the waveform signal from the piezoelectric element 20 via the probe 22 and the transmission / reception coil 21. The control device calculates the thickness of the pipe 10 based on the waveform signal, and stores or displays it in association with the position information of the corresponding piezoelectric element 20.

The plurality of piezoelectric elements 20 are fixed to the surface of the pipe 10 by a fixing device. The fixing device of this embodiment has a plurality of alumina tapes 26 (fixing members). The fixing device of the present embodiment further includes a silver sheet 27 (soft metal) that is arranged between each piezoelectric element 20 and the outer surface of the pipe 10 and acoustically couples them.

The alumina tape 26 is made of alumina (ceramic) and is formed in a strip shape so as to extend over the entire circumferential direction of the pipe 10. The alumina tape 26 has a smaller coefficient of linear expansion than that of the pipe 10.

A fastener 28 is provided on one end side of the alumina tape 26. The fastener 28 inserts the other end side portion of the alumina tape 26 and is locked to the other end side portion of the alumina tape 26 at an arbitrary position. As a result, the alumina tape 26 is pulled and tightened in the circumferential direction of the pipe 10 to apply a pressing force to the piezoelectric element 20. Then, in a state where the silver sheet 27 is arranged between the piezoelectric element 20 and the outer surface of the pipe 10, a pressing force is applied from the alumina tape 26 to the piezoelectric element 20, so that the pipe 10, the silver sheet 27, and the piezoelectric element are applied. The piezoelectric element 20 is fixed while the 20s are in close contact with each other.

The piezoelectric element 20 has, for example, a rectangular shape when viewed from the outside in the radial direction of the pipe 10, and its short side is arranged in the circumferential direction of the pipe 10. This prevents the piezoelectric element 20 from being damaged by the pressing force from the alumina tape 26. However, the piezoelectric element 20 may have a square shape or a circular shape when viewed from the outside in the radial direction of the pipe 10, for example.

In this embodiment, a plurality of piezoelectric elements 20 and fixing devices are permanently installed on the surface of the pipe 10. Therefore, it is not necessary to disassemble the heat insulating material 11 and the metal outer plate 12 before the start of the ultrasonic inspection, and to reconstruct the heat insulating material 11 and the metal outer plate 12 after the ultrasonic inspection is completed.

As described above, in the fixing device of the present embodiment, the piezoelectric element 20 is fixed by using the alumina tape 26, and the weight of the fixing device is heavier than that in the case of using a metal band-shaped member as in the prior art. Decrease. That is, the weight of the fixing device can be reduced. Therefore, even when the piezoelectric element 20 is permanently installed on the outer surface of the pipe 10, it is not necessary to review the seismic design of the pipe 10. Not only the fixing device but also the piezoelectric element 20 and the transmission / reception coil 21 are lightweight.

Further, the alumina tape 26 has a smaller coefficient of linear expansion than that of the pipe 10. Therefore, if the pipe 10 becomes a high temperature state during the plant operation and the pipe 10 and the alumina tape 26 expand, the pressing force applied to the piezoelectric element 20 can be increased by the difference in the amount of expansion thereof. Therefore, the adhesion between the outer surfaces of the piezoelectric element 20, the silver sheet 27, and the pipe 10 can be improved, and the acoustic coupling between the piezoelectric element 20 and the outer surface of the pipe 10 can be improved.

A specific numerical example will be described. For example, the outer diameter of the pipe 10 is 165.2 mm, the thickness of the pipe 10 is 7.1 mm, and the thickness of the alumina tape 26 is 0.3 mm. Further, the material of the pipe 10 is carbon steel, the coefficient of linear expansion of the pipe 10 is 11.7 × 10 ^-6 / K, and the coefficient of linear expansion of the alumina tape 26 is 7.2 × 10 ^-6 / K. be. That is, the difference between the linear expansion coefficient of the pipe 10 and the linear expansion coefficient of the alumina tape 26 is 2 × 10 ^-6 / K or more. Then, for example, when the temperature of the pipe 10 rises from 20 ° C. to 320 ° C., the pressing force applied to the piezoelectric element 20 becomes about 2 MPa.

In the first embodiment, the case where the piezoelectric element fixing device has a silver sheet 27 arranged between the piezoelectric element 20 and the outer surface of the pipe 10 has been described as an example, but the present invention is not limited to silver. It may have a soft metal other than the sheet (specifically, for example, gold). Further, as in the first modification shown in FIG. 5, for example, a contact medium 29 arranged between the silver sheet 27 and the outer surface of the pipe 10 and available at 200 ° C. or higher may be further provided. That is, the silver sheet 27 and the contact medium 29 may enhance the acoustic coupling between the piezoelectric element 20 and the outer surface of the pipe 10.

Further, for example, as in the second modification shown in FIG. 6, the piezoelectric element fixing device is arranged between the piezoelectric element 20 and the outer surface of the pipe 10, and has a contact medium 29 that can be used at 200 ° C. or higher. You may. Further, for example, as in the third modification shown in FIG. 7, the piezoelectric element fixing device is arranged between the piezoelectric element 20 and the outer surface of the pipe 10, and the ionic liquid 30 that maintains a liquid state even at 200 ° C. or higher is provided. You may have. Further, for example, as in the fourth modification shown in FIG. 8, the piezoelectric element fixing device may be arranged between the piezoelectric element 20 and the outer surface of the pipe 10 and may have a silver paste 23 having an adhesive force. good. Even in these modifications, it is possible to secure an acoustic bond between the piezoelectric element 20 and the outer surface of the pipe 10.

A second embodiment of the present invention will be described with reference to FIG. FIG. 9 is a cross-sectional view of a part of the pipe circumferential direction showing the fixing device of the piezoelectric element in the present embodiment. In FIG. 9, unlike FIG. 1 described above, the heat insulating material, the metal exterior plate, and the transmission / reception coil are not shown. In the present embodiment, the same parts as those in the above embodiment are designated by the same reference numerals, and the description thereof will be omitted as appropriate.

When the pipe 10 and the alumina tape 26 become hot during the operation of the plant, the difference between the expansion amount of the pipe 10 and the expansion amount of the alumina tape 26 becomes larger than that in the normal temperature state, and the pressing force applied to the piezoelectric element 20 becomes large. Become. However, in the normal temperature state, the pressing force applied to the piezoelectric element 20 becomes small.

Therefore, the fixing device of the present embodiment has a thermal deformation member 31 which is arranged between each piezoelectric element 20 and the alumina tape 26 and whose thickness increases as the temperature drops. In the normal temperature state, the thickness of the heat deforming member 31 is increased, so that it is possible to suppress a decrease in the pressing force applied to the piezoelectric element 20.

A third embodiment of the present invention will be described with reference to FIG. FIG. 10 is a cross-sectional view of a part of the pipe circumferential direction showing the fixing device of the piezoelectric element in the present embodiment. In FIG. 10, as in FIG. 9 described above, the heat insulating material, the metal exterior plate, and the transmission / reception coil are not shown. In the present embodiment, the same parts as those in the above embodiment are designated by the same reference numerals, and the description thereof will be omitted as appropriate.

The fixing device of the present embodiment has a magnet member 32 adsorbed on the outer surface of each piezoelectric element 20 (specifically, the surface on the side opposite to the inspection object). The magnetic force of the magnet member 32 makes it possible to easily position the piezoelectric element 20 with respect to the outer surface of the pipe 10. Further, it is possible to prevent the position shift of the piezoelectric element 20 from the positioning of the piezoelectric element 20 to the winding of the alumina tape 26. The corners of the magnet member 32 have a rounded shape. This prevents the alumina tape 26 from being damaged when the alumina tape 26 is tightened.

In the above-described embodiment and modification, the case where the piezoelectric element fixing device has a plurality of alumina tapes 26 has been described as an example, but the present invention is not limited to this, and at least one alumina tape 26 may be provided. Further, in the above-described embodiment and modification, the case where a plurality of piezoelectric elements 20 are fixed to each alumina tape 26 has been described as an example, but the present invention is not limited to this, and at least one piezoelectric element 20 may be fixed.

Further, in the above-described embodiment and modification, the case where the non-metal fixing member is the alumina tape 26, which is one of the ceramic tapes, has been described as an example, but the present invention is not limited to this. The non-metal fixing member may be a ceramic tape other than the alumina tape. Further, the fixing member made of non-metal may be a glass cloth tape. In these cases as well, the same effect as described above can be obtained.

Further, in the above-described embodiment and modification, the case where the fastener 28 is used as the fixing method of the alumina tape 26 has been described as an example, but the present invention is not limited to this. For example, the one end side portion and the other end side portion of the alumina tape 26 may be deformed into a string shape and tied together.

Further, in the above-described embodiment and modification, the case where the transmission / reception coil 21 and the probe 22 are interposed between the piezoelectric element 20 and the control device has been described as an example, but the present invention is not limited to this. For example, a signal cable may be interposed instead of the transmission / reception coil 21 and the probe 22.

Further, in the above-described embodiment and modification, the case where the inspection object is a pipe 10 through which a liquid or gas flows has been described as an example, but the present invention is not limited to this, and for example, a container for storing liquid or gas may be used. ..

10 Piping (object to be inspected)
20 Piezoelectric element 23 Silver paste 26 Alumina tape (fixing member)
27 Silver sheet (soft metal)
29 Contact medium 30 Ionic liquid 31 Thermal deformation member 32 Magnet member

Claims (11)

In a fixing device that fixes a piezoelectric element that transmits and receives ultrasonic waves to the surface of an object to be inspected.
It is a non-metal and is formed in a band shape so as to extend over the entire circumferential direction of the inspection object, and a pressing force is applied to the piezoelectric element to fix the piezoelectric element to the surface of the inspection object. Has a fixing member,
The fixing member is a device for fixing a piezoelectric element, characterized in that the coefficient of linear expansion is smaller than that of the object to be inspected. In the piezoelectric element fixing device according to claim 1,
A piezoelectric element fixing device characterized in that the difference between the linear expansion coefficient of the inspection object and the linear expansion coefficient of the fixing member is 2 × 10 ^{-6 / K or more.} In the piezoelectric element fixing device according to claim 1,
The fixing member is a piezoelectric element fixing device, characterized in that it is a ceramic tape or a glass cloth tape. In the piezoelectric element fixing device according to claim 1,
A device for fixing a piezoelectric element, which further comprises a soft metal arranged between the piezoelectric element and the surface of the inspection object. In the piezoelectric element fixing device according to claim 4,
A device for fixing a piezoelectric element, which is arranged between the soft metal and the surface of the object to be inspected and further has a contact medium that can be used at 200 ° C. or higher. In the piezoelectric element fixing device according to claim 1,
A device for fixing a piezoelectric element, which is arranged between the piezoelectric element and the surface of the inspection object and further has a contact medium that can be used at 200 ° C. or higher. In the piezoelectric element fixing device according to claim 1,
A device for fixing a piezoelectric element, which is arranged between the piezoelectric element and the surface of the inspection object and further has an ionic liquid that maintains a liquid state even at 200 ° C. or higher. In the piezoelectric element fixing device according to claim 1,
A device for fixing a piezoelectric element, which is arranged between the piezoelectric element and the surface of the object to be inspected and further has a silver paste having an adhesive force. In the piezoelectric element fixing device according to claim 1,
A device for fixing a piezoelectric element, which is arranged between the piezoelectric element and the fixing member and further has a heat-deforming member whose thickness increases as the temperature drops. In the piezoelectric element fixing device according to claim 1,
A device for fixing a piezoelectric element, which further has a magnet member adsorbed on the surface of the piezoelectric element on the side opposite to the object to be inspected. In the fixing method of fixing the piezoelectric element that transmits and receives ultrasonic waves to the surface of the inspection object,
Using a fixing member that is non-metal and is formed in a band shape so as to extend over the entire circumferential direction of the inspection object, a pressing force is applied to the piezoelectric element to make the piezoelectric element the inspection object. It is fixed to the surface of
The fixing member is a method for fixing a piezoelectric element, characterized in that the coefficient of linear expansion is smaller than that of the object to be inspected.

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