Nuclear-grade externally-clamped time-difference-method ultrasonic transducer

Abstract

The invention discloses a nuclear-grade external clamping type time-difference method ultrasonic transducer which comprises a shell, an acoustic wedge is arranged at one end of the shell, a cavity is defined by the shell and the acoustic wedge, a piezoelectric ceramic piece and a pressing mechanism are arranged in the cavity, the piezoelectric ceramic piece is arranged on the acoustic wedge, and the pressing mechanism acts on the piezoelectric ceramic piece and the acoustic wedge. Therefore, the piezoelectric ceramic piece and the acoustic wedge are tightly attached together. Wherein the piezoelectric ceramic piece is Ti-rich PZT-5 piezoelectric ceramic, and the Ti-rich PZT-5 piezoelectric ceramic is obtained by compounding, doping and optimizing a continuous solid solution composed of a ferroelectric PbTiO3 and an antiferroelectric PbZrO3 with an Nb donor and a trace amount of Mn element. According to the nuclear-grade external clamping type time-difference method ultrasonic transducer provided by the invention, material selection and structural design are all carried out around improvement of high-temperature irradiation adaptability and acoustic coupling stability, and the nuclear-grade external clamping type time-difference method ultrasonic transducer can reliably work in a harsh environment of a nuclear island for a long time and maintain excellent ultrasonic signal transmission performance at the same time.

Description

[0001] Glossary PZT (Lead Zirconate Titanate): Lead zirconate titanate piezoelectric ceramic.

[0002] PbTiO3 / PbZrO3 (Lead Titanate / Lead Zirconate): Lead titanate / lead zirconate (constituting the continuous solid solution end members of PZT).

[0003] T c (Curie Temperature): The phase transition temperature at which piezoelectric properties disappear.

[0004] SNR (Signal-to-Noise Ratio): One of the acceptance thresholds for ultrasonic transducers.

[0005] K3ad (Equipment Qualification Class K3ad): Equipment qualification class. K3ad class equipment refers to equipment installed outside the containment and required to perform its functions under normal operation, accident and / or post-accident environmental conditions, and seismic loads.

[0006] Inconel X-750 (Inconel X-750 Nickel-Chromium Alloy): Inconel X-750 is a nickel-chromium high-temperature alloy. Technical Field

[0007] This invention relates to the field of nuclear power measurement instruments, and in particular to an external clamp-on time-difference ultrasonic transducer suitable for high temperature, strong radiation, seismic and fire conditions in the nuclear island of a nuclear power plant. Background Technology

[0008] Currently, flow measurement within the nuclear island of nuclear power plants mostly employs throttling devices such as Venturi or orifice plates paired with differential pressure transmitters. However, these devices are invasive, resulting in significant pressure loss, complex modification and installation, and long-term accuracy degradation. To avoid altering the flow state within the pipe and introducing permanent pressure loss, clamp-on ultrasonic flow meters are the preferred choice for flow measurement. The core advantages of clamp-on ultrasonic flow meters are their non-invasive nature and ability to be installed online, requiring no pipe cutting / drilling, and they are particularly suitable for high-pressure, high-purity, or sensitive media. Over the past decade, clamp-on ultrasonic flow meters have been widely adopted in industries such as chemical, energy, municipal water, and oil and gas storage and transportation. Typical application temperature ranges are mostly between ambient and 150°C, with a few high-temperature versions capable of continuous operation at around 200°C.

[0009] However, in harsh environments (high temperature, high radiation, fire / earthquake accident conditions), traditional clamp-on ultrasonic flowmeter solutions suffer from insufficient reliability due to limitations in materials and interface coupling. While clamp-on ultrasonic flowmeters are used in conventional industrial applications for high-temperature conditions, their application environments are typically limited to low-to-medium radiation environments. Existing transducer designs generally consist of piezoelectric ceramic plates, acoustic wedges, coupling layers, and housings. Conventional products often utilize PZT piezoelectric ceramics with moderate Curie temperatures, plastic or resin acoustic wedges, and viscoelastic coupling materials to operate within a temperature range of approximately 180°C. Some improved products use metal waveguides or high-temperature coupling agents, extending the operating temperature to approximately 300-400°C. These transducers are fixed to the pipe wall with bolts or clamps, and coupling agents (such as silicone grease or thermal paste) are used to improve ultrasonic energy transmission efficiency. However, their application environments are typically limited to low-to-medium radiation environments, making them unsuitable for nuclear power plant accident conditions and fire conditions. Summary of the Invention

[0010] To address one of the technical problems existing in the prior art, the present invention provides a nuclear-grade external clamp-on time-difference ultrasonic transducer.

[0011] According to a first aspect of the present invention, a nuclear-grade external clamp-on time-of-flight ultrasonic transducer includes a housing, one end of which is provided with an acoustic wedge. The housing and the acoustic wedge define a cavity. A piezoelectric ceramic sheet and a clamping mechanism are disposed within the cavity. The piezoelectric ceramic sheet is disposed on the acoustic wedge, and the clamping mechanism acts on the piezoelectric ceramic sheet and the acoustic wedge to make the piezoelectric ceramic sheet and the acoustic wedge tightly adhered together. The piezoelectric ceramic sheet is a Ti-rich PZT-5 piezoelectric ceramic, which is a continuous solid solution composed of ferroelectric PbTiO3 and antiferroelectric PbZrO3, optimized by composite doping with Nb donors and trace amounts of Mn elements.

[0012] According to the first aspect of the present invention, the nuclear-grade external clamp-on time-difference ultrasonic transducer is provided in which the acoustic wedge is made of high-purity copper material.

[0013] According to the first aspect of the present invention, the nuclear-grade external clamp-on time-of-flight ultrasonic transducer has an anti-oxidation layer on the outer surface of the acoustic wedge, and the anti-oxidation layer is a low-stress nickel plating layer.

[0014] According to the first aspect of the present invention, the thickness of the anti-oxidation layer in the nuclear-grade external clamp-on time-of-flight ultrasonic transducer is 5–20 µm.

[0015] According to the first aspect of the present invention, a nuclear-grade external clamp-on time-difference ultrasonic transducer is provided with a coupling layer on the side of the acoustic wedge facing away from the cavity, and the coupling layer is made of a high-purity gold sheet.

[0016] According to the first aspect of the present invention, in the nuclear-grade external clamp-on time-of-flight ultrasonic transducer, the housing and the acoustic wedge, as well as the piezoelectric ceramic plate and the acoustic wedge, are all fixedly connected by bolts.

[0017] According to the first aspect of the present invention, a nuclear-grade external clamp-on time-of-flight ultrasonic transducer is provided at the connection between the housing and the acoustic wedge, and the sealing element is a copper sealing gasket.

[0018] According to the first aspect of the present invention, a nuclear-grade external clamp-on time-of-flight ultrasonic transducer is provided with a backing block on the side of the piezoelectric ceramic sheet facing away from the acoustic wedge, and the backing block is alumina ceramic.

[0019] According to the first aspect of the present invention, in the nuclear-grade external clamp-on time-of-flight ultrasonic transducer, the backing block and the piezoelectric ceramic sheet are fixedly connected by bolts.

[0020] According to the first aspect of the present invention, the nuclear-grade external clamping time-difference ultrasonic transducer includes a clamping mechanism comprising a disc spring made of a high-temperature resistant alloy.

[0021] According to the first aspect of the present invention, the nuclear-grade external clamp-on time-difference ultrasonic transducer is provided in which the disc spring is made of Inconel X-750 high-temperature alloy.

[0022] According to the first aspect of the present invention, the nuclear-grade external clamp-on time-of-flight ultrasonic transducer is wherein the housing is made of stainless steel.

[0023] According to the first aspect of the present invention, a nuclear-grade external clamp-on time-of-flight ultrasonic transducer is provided inside the cavity, wherein a lead wire is provided inside the cavity, one end of the lead wire is connected to the piezoelectric ceramic sheet, and the other end of the lead wire extends out of the housing to be connected to an external power source.

[0024] According to the first aspect of the present invention, the nuclear-grade external clamp-on time-of-flight ultrasonic transducer has a lead wire that is a mica-insulated nickel wire.

[0025] According to the first aspect of the present invention, in the nuclear-grade external clamp-on time-difference ultrasonic transducer, the lead wire is led out to the outside of the housing through a high-temperature sealed connector.

[0026] According to the first aspect of the present invention, a nuclear-grade external clamp-on time-of-flight ultrasonic transducer is provided inside the cavity, wherein a wire clamp is provided to clamp the lead wire inside the cavity.

[0027] The present invention has the following beneficial effects: The nuclear-grade external clamp-on time-of-flight ultrasonic transducer provided by this invention focuses on improving high-temperature irradiation adaptability and acoustic coupling stability, from material selection to structural design. Furthermore, the entire nuclear-grade external clamp-on time-of-flight ultrasonic transducer adopts a modular and detachable design, enabling rapid positioning, installation, and replacement with dedicated mounting clamps, significantly improving on-site maintenance convenience. The synergistic effect of these factors allows the nuclear-grade external clamp-on time-of-flight ultrasonic transducer to operate reliably in the harsh environment of a nuclear island for extended periods. It can withstand a gamma radiation dose of 250 kGy / 60 years, achieving the K3ad qualification level. It can cope with containment accident environmental conditions, adapting to long-term operating temperatures of 240°C and fire conditions of 400°C × 2 hours. After a fire, the core components of the nuclear-grade external clamp-on time-of-flight ultrasonic transducer maintain structural and functional integrity while preserving excellent ultrasonic signal transmission performance.

[0028] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the description, claims, and drawings. Attached Figure Description

[0029] To more clearly illustrate the technical solution of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and embodiments. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort. In the drawings: Figure 1 This is a schematic diagram of the structure of the nuclear-grade external clamp-on time-of-flight ultrasonic transducer provided by the present invention; Figure 2 yes Figure 1 A schematic diagram of the decomposition process; Figure 3 yes Figure 2 Enlarged view of point A in the middle; Figure 4 This is a schematic diagram of the nuclear-grade external clamp-on time-difference ultrasonic transducer of the present invention applied to a pipeline.

[0030] Explanation of icon numbers: Housing 10, cavity 11, acoustic wedge 20, anti-oxidation layer 21, coupling layer 22, piezoelectric ceramic sheet 30, backing block 31, clamping mechanism 40, sealing element 50, lead wire 60, wire clamping device 70. Detailed Implementation

[0031] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings. Similar elements in different embodiments are referred to by associated similar element reference numerals. In the following embodiments, many details are described to facilitate a better understanding of the invention. However, those skilled in the art will readily recognize that some features may be omitted in different situations, or may be replaced by other elements, materials, or methods. In some cases, certain operations related to the present invention are not shown or described in the specification. This is to avoid obscuring the core parts of the invention with excessive description. For those skilled in the art, detailed description of these related operations is not necessary; they can fully understand the related operations based on the description in the specification and general technical knowledge in the art.

[0032] Furthermore, the features, operations, or characteristics described in the specification can be combined in any suitable manner to form various embodiments. At the same time, the order of the steps or actions in the method description can be changed or adjusted in a manner obvious to those skilled in the art. Therefore, the various orders in the specification and drawings are only for the clear description of a particular embodiment and do not imply a necessary order, unless otherwise stated that a particular order must be followed.

[0033] The serial numbers assigned to components in this document, such as "first" and "second," are used only to distinguish the described objects and have no sequential or technical meaning. The terms "connection" and "linkage" used in this invention, unless otherwise specified, include both direct and indirect connections (linkages).

[0034] Conventional clamp-on ultrasonic flow meters typically use PZT piezoelectric ceramics, plastic or resin acoustic wedges, and viscoelastic coupling materials with moderate Curie temperatures to operate within a range of room temperature to approximately 180°C. Therefore, conventional clamp-on ultrasonic flow meters exhibit significant shortcomings in the harsh environment of a nuclear island: First, they lack sufficient resistance to high radiation. The sensitivity of conventional PZT piezoelectric ceramics decreases significantly above 200°C, and their polarization intensity may degrade under long-term irradiation. Plastic or resin wedges soften or even decompose at high temperatures, making it difficult to withstand long-term operating temperatures ≥240°C, let alone short-term fire temperatures of 400°C. Commonly used coupling agents, such as silicone greases, are prone to drying and cracking at high temperatures, losing their coupling effect. The irradiation aging problem of materials is also prominent; ordinary organic materials age and crack under cumulative radiation, resulting in performance degradation. Secondly, coupling stability is poor. Traditional transducers often use rigid fixing and soft coupling agents. In high-temperature environments, the different thermal expansion of the pipe and the transducer can lead to changes in contact pressure. The coupling layer may develop gaps due to thermal expansion and contraction, resulting in a decrease in acoustic energy transmission efficiency. Under impact and vibration environments, the fixed structure, lacking elastic compensation, is prone to loosening and displacement, making it impossible to ensure long-term stable contact between the transducer and the pipe wall. Thirdly, adaptability to accident conditions is weak. In nuclear power accident scenarios (such as transient overheating, steam release, etc.), conventional clamp-on transducers cannot maintain structural integrity and normal function. Instantaneous temperature rise or radioactive leakage can cause conventional seals and structural components to fail, and internal components of the transducer may be damaged, failing to meet nuclear safety requirements. Therefore, high-temperature clamp-on ultrasonic flowmeters used in conventional industrial fields cannot be directly used in the high-temperature, high-radiation, and accident environments of nuclear islands, requiring targeted improvements and innovations in materials and structures.

[0035] The following is in conjunction with the appendix Figures 1 to 4 The provided embodiments further illustrate the nuclear-grade external clamp-on time-difference ultrasonic transducer proposed in this invention.

[0036] Reference Figures 1 to 4 An embodiment of the present invention provides a nuclear-grade external clamping time-of-flight ultrasonic transducer, including a housing 10, an acoustic wedge 20 disposed at one end of the housing 10, the housing 10 and the acoustic wedge 20 defining a cavity 11, a piezoelectric ceramic sheet 30 and a pressing mechanism 40 disposed in the cavity 11, the piezoelectric ceramic sheet 30 being disposed on the acoustic wedge 20, and the pressing mechanism 40 acting on the piezoelectric ceramic sheet 30 and the acoustic wedge 20 to make the piezoelectric ceramic sheet 30 and the acoustic wedge 20 tightly adhered together.

[0037] Among them, the piezoelectric ceramic sheet 30 is a Ti-rich PZT-5 piezoelectric ceramic with a high Curie temperature. The Ti-rich PZT-5 piezoelectric ceramic is a continuous solid solution composed of ferroelectric PbTiO3 and antiferroelectric PbZrO3, which is optimized by composite doping with Nb donors and trace amounts of Mn elements. The Curie temperature T of the piezoelectric ceramic sheet 30 is the highest. cThe temperature is >430℃, and the room temperature piezoelectric constant d33 >150 pC / N. Preferably, in some embodiments of the present invention, the piezoelectric ceramic sheet 30 is made of ceramic with a Curie point as high as approximately 470℃, selected through experimental screening, to ensure that it does not fail under operating conditions up to 240℃ and in case of accidental transients. This piezoelectric ceramic sheet 30 can operate stably for a long time within a range of ±10% capacitance and ±5% resonant frequency variation, ensuring the strength and quality of the ultrasonic transducer's signal transmission and reception.

[0038] Furthermore, to ensure the stable operation of the ultrasonic probe within a certain range of sound velocity variation, and to ensure that the dimensions of the piezoelectric ceramic plate 30 and the matching acoustic wedge 20 can cover the changes in installation distance caused by variations in the water sound velocity, the refraction angle of the sound wave within the pipe wall and the refraction angle of the sound wave in the water can be calculated sequentially using the law of refraction. For example, in some embodiments of the present invention, the incident angle of the acoustic wedge 20 can be designed to be 60°. For measuring points with small pipe diameters of DN15-DN100 and large pipe diameters of DN100-DN300, the size of the piezoelectric ceramic plate 30 used in the ultrasonic transducer is designed to be 20°. 20 2mm and 40 20 The 4mm diameter can cover variations at the acoustic receiver end, ensuring signal strength, as shown in Table 1 below. Regarding the selection of the ultrasonic transducer's operating frequency, the typical frequency range for liquid flow measurement is 0.5MHz to 2MHz. Higher ultrasonic frequencies result in smaller beam spread angles, more concentrated energy, better directionality, and higher resolution. Considering the acoustic attenuation of the ultrasonic transducer in high-temperature environments, within the DN300 and smaller measurement diameter range, at lower medium temperatures (20-100℃), attenuation is dominated by viscous losses, with higher frequencies leading to greater attenuation. At temperatures of 100-300℃ (especially above 200℃), dissolved gases in water precipitate to form microbubbles, enhancing scattering and drastically increasing high-frequency acoustic attenuation. Therefore, appropriately reducing the ultrasonic frequency is a key strategy to reduce attenuation. In some embodiments of this invention, to ensure sufficient signal strength, the resonant frequency for small diameters (DN15-DN100) is determined to be 1MHz, and for large diameters (DN100-DN300), the resonant frequency is 500kHz, based on the length of the ultrasonic propagation path.

[0039] Table 1 Key parameters of high-temperature piezoelectric ceramic sheets like Figure 2As shown, in some embodiments of the present invention, in the nuclear-grade externally clamped time-of-flight ultrasonic transducer, the acoustic wedge 20 serves both as the directionality and incident geometry of the sound beam and determines the energy coupling efficiency across the "piezoelectric ceramic-solid-tube wall-fluid" interface. Considering that the nuclear-grade externally clamped time-of-flight ultrasonic transducer of the present invention needs to operate in high-temperature and high-irradiation environments for extended periods, while traditional polymer-based matching / wedge blocks have certain sound transmission advantages, they will irreversibly age under high temperature, flame, irradiation, and long-term humid heat coupling. Therefore, the present invention integrates the acoustic wedge 20 and the matching layer into a single metal material, achieving both directional oblique incidence and acoustic impedance transition with a single metal block, avoiding drift and failure caused by multi-layer interfaces and organic materials. Furthermore, as... Figure 4 As shown, based on the refraction conditions measured by the time-of-flight method, the sound beam needs to achieve reasonable mode conversion within the steel pipe wall and ultimately be incident on the liquid. Therefore, the material selection should ensure that the sound velocity is between that of water and stainless steel (to facilitate control of the refraction angle and energy distribution in the water), while also possessing high sound conduction, low internal loss, excellent thermal stability, and radiation resistance. Through scheme screening and comparative experiments, this invention preferentially selects high-purity copper as the body of the acoustic wedge 20. Its longitudinal wave velocity is between that of water (approximately 1.48 km / s) and austenitic stainless steel (5.8–6.0 km / s), meeting the requirements for refraction and mode control. Copper has low intrinsic acoustic loss and high sound transmission efficiency, and can obtain higher first-echo amplitude and better signal-to-noise ratio under the same incident geometry. It can still maintain good geometric stability and acoustic consistency after long-term operation at 240℃ and high-temperature impact of a fire at 400℃ for 2 hours. Furthermore, the metallic material is not sensitive to γ-radiation, making it suitable for the life cycle conditions of nuclear islands. It should be noted that, in some embodiments of the present invention, in order to achieve the function of the acoustic wedge 20 without introducing an additional interface, according to acoustic theory, when the thickness of the acoustic wedge 20 is an odd multiple of a quarter wavelength [(2n+1)×λ / 4, which can destructively interfere (minimize reflection energy)], the best transmission effect can be achieved, thus eliminating the need to superimpose an independent matching layer; at the same time, a wedge geometry with an incident angle of 60° (relative to the normal) is designed to take into account both the excitation of the target waveform inside the steel pipe and the suppression of false echoes.

[0040] Furthermore, such as Figure 3As shown, in some embodiments of the present invention, considering the surface oxidation of copper under high temperature and humidity conditions and the possible interdiffusion of elements with the coupling layer 22 (Au foil in this invention), an anti-oxidation layer 21 is provided on the outer surface of the acoustic wedge 20. The anti-oxidation layer 21 is a low-stress nickel plating layer. The thickness of the anti-oxidation layer 21 is preferably 5–20 µm. The nickel layer, as an anti-oxidation barrier, can effectively suppress the high-temperature discoloration and surface degradation of the acoustic wedge 20. As a diffusion barrier layer, it avoids acoustic impedance drift caused by the interdiffusion of Au in the coupling layer 22 and Cu in the acoustic wedge 20. At the same time, it significantly improves the surface hardness and resistance to scratches, fretting wear, and thermal creep, so that the acoustic wedge 20 body maintains the stability of the incident angle and bonding geometry under long-term surface pressure and thermal cycling. Combined with equipotential grounding and a unified metal system, it can reduce the risk of electrochemical corrosion caused by multi-metal contact and further enhance the full-lifetime reliability in a nuclear-grade environment. In summary, by using a copper-based acoustic wedge 20 and a low-stress nickel plating layer 21 on the surface of the acoustic wedge 20 as an anti-oxidation layer, the acoustic wedge 20 of the present invention achieves shorter acoustic links, fewer interfaces, and higher transmission efficiency while meeting the requirements of temperature resistance, radiation resistance, and fire survivability. This provides a core component solution for nuclear-grade external clamp-on time-of-flight ultrasonic transducers that features high SNR, low drift, and easy standardization of manufacturing.

[0041] like Figure 3As shown, in some embodiments of the present invention, a coupling layer 22 is provided on the side of the acoustic wedge 20 facing away from the cavity 11. The coupling layer 22 is a transition layer between the acoustic wedge 20 and the test tube wall. To cope with the requirements of long-term operating temperature of 240℃ and fire conditions of 400℃×2h and high-radiation nuclear-grade environment, the failure risk of organic coupling materials such as grease and adhesives after high-temperature volatilization, cracking and aging is generally eliminated. Therefore, the present invention explicitly uses a metal coupling agent to make the coupling layer 22 to ensure acoustic and dimensional stability. Furthermore, in some embodiments of the present invention, the coupling layer 22 is made of high-purity gold (≥99.99%) sheet. Gold is soft at room temperature and has excellent plasticity. It can fully "flow" into the micro-rough peaks and valleys under the action of assembly pre-tightening force to achieve large-area, air-gap-free bonding. After heating, gold has good wettability to the metal interface and does not volatilize, carbonize or lose water, maintaining stable acoustic impedance and contact state throughout the entire life temperature spectrum. Thanks to the inherent low internal friction, high density, and elastic modulus of metals, the additional attenuation of gold foil at ultra-thin scales is negligible. It can efficiently transfer acoustic energy from the acoustic wedge to the tube wall and improve first echo and SNR. Simultaneously, its chemical inertness and high purity avoid adverse electrochemical effects on the stainless steel tube wall, and it is insensitive to γ-irradiation, with its mechanical and acoustic properties remaining essentially unchanged after long-term irradiation. Compared with other metals, the coupling layer 22 made of pure gold is significantly superior to organic coupling agents in terms of high-temperature stability, irradiation tolerance, acoustic efficiency, and assembly repeatability. It can work synergistically with the acoustic wedge 20 of this invention to form a reliable and reproducible acoustic interface for the nuclear-grade external clamp-on time-of-flight ultrasonic transducer.

[0042] Furthermore, this invention avoids the use of organic adhesives as much as possible. Therefore, in some embodiments of this invention, the housing 10 and the acoustic wedge 20, and the piezoelectric ceramic sheet 30 and the acoustic wedge 20 are all fixedly connected by bolts. This eliminates the potential hazards of organic adhesives generating gas and causing material migration under irradiation, fundamentally improving the long-term reliability of the nuclear-grade external clamp-on time-of-flight ultrasonic transducer. In addition, it is readily understood that in other embodiments of this invention, mechanical pre-tightening connections using other metal parts besides bolted connections can also be used to achieve the same effect.

[0043] Furthermore, such as Figure 1 and Figure 2 As shown, in some embodiments of the present invention, a sealing element 50 is provided at the connection between the housing 10 and the acoustic wedge 20 to ensure the airtightness and waterproof and moisture-proof performance of the cavity 11. The sealing element 50 is preferably a copper sealing gasket. Copper is soft and resistant to high temperature. Unlike organic sealing elements, it will not age and fail under irradiation or high temperature. It can keep the inside of the housing clean and dry for a long time and protect the piezoelectric element from environmental influences.

[0044] Furthermore, such as Figure 1 and Figure 2As shown, in some embodiments of the present invention, a backing block 31 is provided on the side of the piezoelectric ceramic sheet 30 facing away from the acoustic wedge 20. The backing block 31 is preferably alumina ceramic. The backing block 31 serves as a mechanical support for the piezoelectric ceramic sheet 30, protecting the piezoelectric ceramic sheet 30 and improving the directionality of sound energy transmission. On the other hand, alumina material is also resistant to high temperatures and radiation, and will not suffer from the aging and performance drift problems common to organic backing materials. It is easy to understand that the backing block 31 and the piezoelectric ceramic sheet 30 are also fixedly connected by bolts, making the connection simple and convenient.

[0045] Furthermore, such as Figure 1 As shown, in some embodiments of the present invention, the clamping mechanism 40 includes a disc spring made of a high-temperature resistant alloy. The present invention regards the clamping mechanism 40 as a "fundamental component" for the reliability of nuclear-grade external clamping time-of-flight ultrasonic transducers: its function is to continuously ensure stable surface pressure and zero-gap contact between the piezoelectric ceramic sheet 30, the acoustic wedge 20, and the electrode under high temperature, irradiation, and vibration / seismic loads throughout its entire lifespan, thereby obtaining repeatable, low-drift acoustic coupling. Therefore, in some embodiments of the present invention, disc springs made of Inconel X-750 high-temperature alloy are stacked as the core elastic element of the clamping mechanism 40. The disc springs made of Inconel X-750 high-temperature alloy maintain elasticity and creep resistance in high-temperature and irradiation environments. The characteristics of the disc springs can automatically compensate for thickness changes caused by thermal expansion and contraction, and prevent the rigid clamping from becoming loose or stress concentrated under temperature changes and impacts. This can provide a sufficiently large preload force, which is significantly higher than the inertial force caused by vibration acceleration during operation, to prevent loosening of the fit and false echoes. In addition, the preload force should not be too large to avoid damaging or cracking the piezoelectric ceramic sheet 30. In some embodiments of the present invention, by combining assembly-flow-thermal cycling tests, the equivalent preload torque can be set to 1 N·m (tolerance 0.6–1.4 N·m). Within this window, the field acceptance thresholds of first echo amplitude >100mV and SNR >10 can be stably obtained. After thermal cycling and seismic conditions, the contact pressure and signal indicators are maintained, achieving "constant pressure coupling under all operating conditions," which provides a mechanical prerequisite for subsequent measurement accuracy and post-accident recoverability.

[0046] Furthermore, such as Figure 1 and Figure 2 As shown, in some embodiments of the present invention, the housing 10 is made of high-temperature resistant and corrosion-resistant stainless steel, such as 304 stainless steel, which can shield electromagnetic interference and resist radiation.

[0047] Furthermore, such as Figure 1As shown, in some embodiments of the present invention, a lead wire 60 and a wire clamp 70 are also provided inside the cavity 11. The lead wire 60 is used to connect the piezoelectric ceramic plate 30 to an external power source, and the wire clamp 70 clamps the lead wire 60 inside the cavity 11 to prevent the end of the lead wire 60 connected to the piezoelectric ceramic plate 30 from moving and causing poor contact. In some embodiments of the present invention, the lead wire 60 is preferably made of mica-insulated nickel wire, which is led out to the outside of the housing 10 through a high-temperature sealed connector, ensuring the stability of the electrical connection and facilitating connection with an external low-temperature cable.

[0048] like Figure 4 As shown, the nuclear-grade external clamp-on time-of-flight ultrasonic transducer of this invention is installed on a pipeline via an installation accessory to achieve the transmission and reception of ultrasonic signals. The nuclear-grade external clamp-on time-of-flight ultrasonic transducer provided by this invention has the following advantages: First, its environmental adaptability is significantly improved. The nuclear-grade external clamp-on time-of-flight ultrasonic transducer can operate continuously under a medium temperature of 240°C, and its structure and function remain intact under a fire condition of 400°C × 2h, meeting the requirements of nuclear power plant accident environments. All constituent materials are not sensitive to cumulative irradiation of 250kGy / 60 years, and its performance shows no significant degradation after long-term irradiation. Environmental test results conducted by authoritative institutions show that the nuclear-grade external clamp-on time-of-flight ultrasonic transducer of this invention successfully passed environmental adaptability tests such as high and low temperature cycling, temperature shock, and damp heat aging, as well as irradiation aging tests (dose level conforming to 60 years 250kGy), all of which were deemed qualified. The nuclear-grade external clamp-on time-of-flight ultrasonic transducer maintained its structural seal and electrical performance well during the comprehensive test simulating the qualification environment of nuclear power C+F category equipment, meeting the qualification requirements of nuclear safety grade K3ad equipment. These results demonstrate that the present invention possesses excellent survivability and reliability under high temperature, irradiation, and accident conditions. Secondly, the acoustic coupling is stable and reliable, with excellent signal quality. Thanks to the application of the metal coupling layer 22 and the clamping mechanism 40, the acoustic wave transmission between the nuclear-grade external clamp-on time-of-flight ultrasonic transducer and the pipeline remains stable and efficient. Actual measurements show that within the range from room temperature to high operating temperature, the received signal strength changes very little, and the signal-to-noise ratio remains consistently above 10. The nuclear-grade external clamp-on time-of-flight ultrasonic transducer is insensitive to vibration and seismic shocks, with no structural loosening or displacement, and negligible zero-point drift and gain changes. Compared to traditional designs without elastic compensation, the nuclear-grade external clamp-on time-of-flight ultrasonic transducer of this invention does not require readjustment after sudden temperature changes, the coupling layer shows no cracking or voids, and the measurement results are highly consistent after repeated installation tests. This demonstrates that the present invention significantly improves the long-term stability of acoustic coupling and enhances the repeatability and reliability of measurement results. Based on a comprehensive evaluation of the test report and the qualification test outline, the nuclear-grade external clamp-on time-of-flight ultrasonic transducer proposed in this invention meets the technical requirements for nuclear-grade flow measurement in nuclear islands in terms of key technical indicators. It combines high performance and high availability, making it highly suitable for applications such as nuclear power plants where reliability and safety requirements are extremely high.

[0049] It is understood that the above embodiments only illustrate preferred embodiments of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can freely combine the above technical features without departing from the concept of the present invention, and can also make several modifications and improvements, all of which fall within the protection scope of the present invention. Therefore, all equivalent transformations and modifications made with respect to the scope of the claims of the present invention should fall within the scope of the claims of the present invention.

Claims

1. A nuclear-grade external clamp-on time-of-flight ultrasonic transducer, characterized in that, Includes a housing (10), one end of which is provided with an acoustic wedge (20). The housing (10) and the acoustic wedge (20) define a cavity (11). A piezoelectric ceramic sheet (30) and a clamping mechanism (40) are provided inside the cavity (11). The piezoelectric ceramic sheet (30) is disposed on the acoustic wedge (20). The clamping mechanism (40) acts on the piezoelectric ceramic sheet (30) and the acoustic wedge (20) to make the piezoelectric ceramic sheet (30) and the acoustic wedge (20) fit tightly together. The piezoelectric ceramic sheet (30) is a Ti-rich PZT-5 piezoelectric ceramic, which is a continuous solid solution composed of ferroelectric PbTiO3 and antiferroelectric PbZrO3, and is optimized by Nb donor and trace Mn element composite doping.

2. The nuclear-grade external clamp-on time-of-flight ultrasonic transducer as described in claim 1, characterized in that, The acoustic wedge (20) is made of high-purity copper.

3. The nuclear-grade external clamp-on time-of-flight ultrasonic transducer as described in claim 2, characterized in that, The outer surface of the acoustic wedge (20) is provided with an anti-oxidation layer (21), which is a low-stress nickel plating layer.

4. The nuclear-grade external clamp-on time-of-flight ultrasonic transducer as described in claim 3, characterized in that, The thickness of the antioxidant layer (21) is 5–20 µm.

5. The nuclear-grade external clamp-on time-of-flight ultrasonic transducer as described in claim 1, characterized in that, The acoustic wedge (20) has a coupling layer (22) on the side facing away from the cavity (11), and the coupling layer (22) is made of high-purity gold sheet.

6. The nuclear-grade external clamp-on time-of-flight ultrasonic transducer as described in claim 1, characterized in that, The housing (10) and the acoustic wedge (20), as well as the piezoelectric ceramic sheet (30) and the acoustic wedge (20), are all fixedly connected by bolts.

7. The nuclear-grade external clamp-on time-of-flight ultrasonic transducer as described in claim 6, characterized in that, A sealing element (50) is provided at the connection between the housing (10) and the acoustic wedge (20), and the sealing element (50) is a copper sealing gasket.

8. The nuclear-grade external clamp-on time-of-flight ultrasonic transducer as described in claim 6, characterized in that, The piezoelectric ceramic sheet (30) has a backing block (31) on the side facing away from the acoustic wedge (20), and the backing block (31) is made of alumina ceramic.

9. The nuclear-grade external clamp-on time-of-flight ultrasonic transducer as described in claim 8, characterized in that, The backing block (31) and the piezoelectric ceramic sheet (30) are fixedly connected by bolts.

10. The nuclear-grade external clamp-on time-of-flight ultrasonic transducer as described in claim 1, characterized in that, The clamping mechanism (40) includes a disc spring made of high-temperature resistant alloy.

11. The nuclear-grade external clamp-on time-of-flight ultrasonic transducer as described in claim 10, characterized in that, The disc spring is made of Inconel X-750 high-temperature alloy.

12. The nuclear-grade external clamp-on time-of-flight ultrasonic transducer as described in claim 1, characterized in that, The housing (10) is made of stainless steel.

13. The nuclear-grade external clamp-on time-of-flight ultrasonic transducer as described in claim 1, characterized in that, The cavity (11) is provided with a lead wire (60), one end of which is connected to the piezoelectric ceramic sheet (30), and the other end of which passes through the housing (10) to connect to an external power source.

14. The nuclear-grade external clamp-on time-of-flight ultrasonic transducer as described in claim 13, characterized in that, The lead (60) is a mica-insulated nickel wire.

15. The nuclear-grade external clamp-on time-of-flight ultrasonic transducer as described in claim 13, characterized in that, The lead wire (60) is led out to the outside of the housing (10) through a high-temperature sealing connector.

16. The nuclear-grade external clamp-on time-of-flight ultrasonic transducer as described in claim 13, characterized in that, The cavity (11) is provided with a wire clamp (70) to clamp the lead wire (60) inside the cavity (11).

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