An electromagnetic ultrasonic transducer, monitoring system and method for in-situ inspection of high temperature welds

Abstract

The application discloses an electromagnetic ultrasonic transducer, a monitoring system and a method for in-situ detection of high-temperature welds, comprising an adjustable magnetic circuit mechanism and a multi-channel coil assembly; the adjustable magnetic circuit mechanism can flexibly adjust the distance between the magnetic field generating part and the surface coating of the high-temperature weld of the detected object to adapt to the optimal working magnetic field of the coating; the multi-channel coil assembly comprises at least two independent coils insulated from each other, each independent coil constitutes an independent detection channel, and the size of the independent coil is matched with the size of the bottom surface of the magnetic field generating part to realize local concentrated detection. The application can solve the technical problems that the existing electromagnetic ultrasonic transducer is limited in transduction efficiency due to the mismatch between the magnetic field strength and the optimal working magnetic field required by the magnetostrictive coating, and the sensitivity of micro defect detection is insufficient due to the excessively large sound field action area of the single coil structure, improves the stability and reliability of the transducer in a high-temperature environment, and realizes efficient and accurate in-situ detection of high-temperature welds.

Description

Technical Field

[0001] This invention belongs to the field of nondestructive testing technology, and particularly relates to an electromagnetic ultrasonic transducer, monitoring system and method for in-situ flaw detection of high-temperature welds. Background Technology

[0002] Welds are critical connection points in pressure-bearing equipment and high-temperature pipelines. Operating under prolonged high temperature, high pressure, and complex stress environments, they are prone to creep, fatigue cracking, and other damage. Online monitoring and in-situ flaw detection are crucial for ensuring the structural integrity of equipment. Electromagnetic acoustic transducers (EMATs) have shown promise in high-temperature weld inspection due to their non-contact nature, lack of acoustic coupling agent requirements, and suitability for high temperatures and rough surfaces. However, existing EMATs still have significant limitations in their adaptability to the magnetostrictive detection mechanism for high-temperature welds and their sensitivity in detecting minute defects.

[0003] First, there is a significant contradiction between the magnetic field design of existing electromagnetic ultrasonic transducers and the inspection requirements of magnetostrictive coatings. Traditional electromagnetic ultrasonic transducers generally follow the design principle of maximizing magnetic field strength, typically employing high-remanence permanent magnets (0.5T or higher) to enhance the Lorentz force or magnetostrictive effect, thereby obtaining stronger excitation and reception signals. However, in the inspection of high-temperature welds, to achieve signal enhancement at high temperatures, it is often necessary to pre-apply or spray a magnetostrictive coating on the surface of the inspected workpiece. Studies have shown that the bias magnetic field strength required for such coatings to achieve optimal electromagnetic ultrasonic transduction efficiency is usually low, generally below 0.3T. If conventional high-field-strength permanent magnets are used, the coating will operate in an oversaturated magnetization state, which not only fails to improve transduction efficiency but also reduces signal amplitude due to changes in the magnetic domain motion mechanism. Furthermore, permanent magnets face the risk of thermal demagnetization and changes in coating characteristics at high temperatures, and the fixed magnetic circuit structure cannot adaptively adjust the magnetic field strength according to temperature changes. Although existing research has explored the use of pulsed electromagnets (EMAT) to achieve continuously adjustable bias magnetic fields, such structures are often complex and bulky, and there is still a lack of an engineering solution that can conveniently adjust the actual magnetic field acting on the workpiece surface.

[0004] Secondly, the existing coil structure of electromagnetic ultrasonic transducers has limitations in terms of defect detection sensitivity. Conventional electromagnetic ultrasonic transducers typically use a single integral coil with a large effective aperture, resulting in a dispersed sound field area and unconcentrated energy. When detecting small defects that have formed early in high-temperature welds, the sound beam coverage area is much larger than the defect size, leading to weak defect echo signals, low signal-to-noise ratios, and a high risk of missed detections. Although some studies have proposed using multi-layered coils or focusing coil structures to improve sound field characteristics, these solutions focus on focusing the sound beam to increase energy density, rather than addressing the issue of dividing a single detection area into multiple independent detection channels to improve the spatial resolution of small defects. In existing technologies, designing the receiving coil as a separate multi-channel configuration is mainly for the needs of phased array imaging algorithms, rather than aiming to improve the detection sensitivity of localized small defects by reducing the effective aperture of a single channel and making the sound field area more concentrated.

[0005] In summary, existing electromagnetic ultrasonic transducers, when used for in-situ flaw detection of high-temperature welds, lack, on the one hand, a magnetic circuit structure capable of flexibly adjusting the actual magnetic field strength on the workpiece surface based on the optimal working magnetic field of the magnetostrictive coating; and on the other hand, their traditional single-coil configuration struggles to simultaneously meet the demands of large-area scanning and high-sensitivity detection of minute defects. Therefore, there is an urgent need for an electromagnetic ultrasonic transducer, monitoring system, and method that can match the magnetic field strength to the characteristics of the inspected coating and possess higher resolution for detecting local defects. Summary of the Invention

[0006] Purpose of the invention: This invention proposes an electromagnetic ultrasonic transducer, monitoring system, and method for in-situ flaw detection of high-temperature welds. It solves the technical problems of existing electromagnetic ultrasonic transducers, such as limited transduction efficiency due to the mismatch between the magnetic field strength and the optimal working magnetic field required by the magnetostrictive coating, and insufficient sensitivity for detecting minute defects due to the excessively large acoustic field area of ​​the single coil structure. It improves the stability and reliability of the transducer in high-temperature environments, and realizes efficient and accurate in-situ flaw detection of high-temperature welds.

[0007] Technical Solution: This invention includes an adjustable magnetic circuit mechanism and a multi-channel coil assembly. The adjustable magnetic circuit mechanism can adjust the distance between the magnetic field generator and the coating on the surface of the high-temperature weld of the inspected object, so as to control the magnetic flux density on the coating surface within the optimal working magnetic field range. The adjustable magnetic circuit mechanism includes an elastic telescopic component and a magnet housing. The magnetic field generator is disposed inside the magnet housing. The elastic telescopic component drives the magnet housing to move the magnet generator synchronously, thereby realizing stepless adjustment of the distance between the magnetic field generator and the coating. The multi-channel coil assembly includes at least two mutually insulated independent coils. Each independent coil constitutes an independent detection channel. The size of the independent coil located on the inner side is smaller than the radial dimension of the bottom surface of the magnetic field generator, and the size of the independent coil located on the outer side is smaller than or equal to the radial dimension of the bottom surface of the magnetic field generator, thereby realizing localized centralized detection.

[0008] The independent coils are arranged in a concentric array on the same plane directly below the magnetic field generator. The diameter of each independent coil increases from the inside to the outside, and each independent coil adopts a single-layer or multi-layer tightly wound structure.

[0009] The optimal working magnetic field is less than 0.3T.

[0010] The magnet housing is made of non-ferromagnetic high-temperature resistant material, the magnetic field generator is a permanent magnet, and the elastic telescopic component can realize stepless adjustment of the distance between the magnetic field generator and the coating.

[0011] A high-temperature weld in-situ flaw detection and monitoring system based on the aforementioned transducer includes a multi-channel excitation circuit, a multi-channel receiving circuit, and a main control unit. The multi-channel excitation circuit and the multi-channel receiving circuit are respectively connected to each independent coil. The main control unit controls the excitation timing and parameters and processes digital signals to generate detection results.

[0012] The multi-channel receiving circuit includes a low-noise amplifier, a bandpass filter, a controllable gain amplifier, and a high-pass filter connected in sequence.

[0013] A method for in-situ flaw detection and monitoring of high-temperature welds based on the aforementioned transducer includes the following steps: S1, a magnetostrictive coating is pre-applied to the surface of the high-temperature weld area of ​​the object under inspection, and the transducer is placed close to the coating; S2, the distance between the magnetic field generator and the coating is adjusted by an adjustable magnetic circuit mechanism to make the magnetic field strength on the coating surface match the optimal working magnetic field; S3, a high-voltage pulse signal is applied to each independent coil through a multi-channel excitation circuit to excite ultrasonic waves and propagate inside the object under inspection; S4, the echo signal is received and conditioned by a multi-channel receiving circuit and transmitted to the main control unit; S5, the main control unit processes the multi-channel signals, identifies defect parameters, and generates detection results.

[0014] In step S2, while adjusting the distance between the magnetic field generator and the coating, the magnetic flux density on the coating surface is detected in real time until the magnetic flux density reaches the optimal range of less than 0.3T.

[0015] In step S5, the main control unit uses a time-delay superposition algorithm to fuse data, combines the detection signals of each independent coil, performs spatial registration of the defect based on the arrival time difference of the ultrasonic signals of each channel, locates the defect position and determines the defect size, and generates two-dimensional or three-dimensional imaging results.

[0016] A high-temperature weld in-situ flaw detection terminal device integrates an electromagnetic ultrasonic transducer and a monitoring system to realize independent on-site detection and data processing of high-temperature welds.

[0017] Beneficial effects: This invention has the following advantages:

[0018] (1) The present invention achieves flexible adjustment of the distance between the magnetic field generator and the magnetostrictive coating through an adjustable magnetic circuit mechanism, thereby controlling the magnetic field strength on the coating surface within the optimal working range and improving the energy conversion efficiency of electromagnetic ultrasound.

[0019] (2) The present invention adopts a multi-independent coil array design, which not only realizes the large-scale scanning of the weld area, but also concentrates the sound field area through single-channel local concentrated detection, improves the sensitivity of small defect detection, and solves the contradiction that traditional transducers cannot take into account both large-scale scanning and small defect detection. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall structure of the electromagnetic ultrasonic transducer of the present invention;

[0021] Figure 2 A structural example of a single integral coil for comparison;

[0022] Figure 3 Here is an example of a structure with three independent coil groups;

[0023] Figure 4 This is a block diagram of an electromagnetic ultrasonic monitoring system.

[0024] Figure 5 This is a schematic diagram of the receiving section of an electromagnetic ultrasound receiving circuit.

[0025] Figure 6 This is a schematic diagram of the terminal device;

[0026] Figure 7 The received signal diagrams for the comparative examples are as follows: (a) the specimen is defect-free, and (b) the specimen contains defects.

[0027] Figure 8 The received signal diagrams for the first coil group in the three independent coil groups are as follows: (a) the specimen is defect-free, and (b) the specimen contains defects.

[0028] Figure 9 Experimental results of coated specimens at different permanent magnet lift-off distances: (a) A-scan waveform, (b) peak-to-peak value of the first bottom transverse wave echo in the received signal, and vertical magnetic flux density on the specimen surface. Detailed Implementation

[0029] The invention will now be further described with reference to the accompanying drawings.

[0030] Example 1

[0031] like Figure 1 As shown, the electromagnetic ultrasonic transducer for in-situ flaw detection of high-temperature welds in this embodiment includes an adjustable magnetic circuit mechanism 2, a multi-channel coil assembly 3, a housing assembly 1, a ceramic sheet 4, a heat insulation material 5, and a magnetostrictive coating 6. The components work together to achieve high-sensitivity flaw detection of high-temperature welds. The adjustable magnetic circuit mechanism 2 is used to adjust the distance between the magnetic field generator and the coating on the surface of the high-temperature weld of the object being inspected, and to adapt to the optimal working magnetic field of the coating. The multi-channel coil assembly 3 enables localized centralized detection. The ceramic sheet 4 and the heat insulation material 5 ensure the stability of the components under high-temperature conditions. The magnetostrictive coating 6 improves the efficiency of ultrasonic excitation and reception.

[0032] The adjustable magnetic circuit mechanism 2 is used to adjust the distance between the magnetic field generator and the magnetostrictive coating, thereby changing the actual magnetic field strength acting on the magnetostrictive coating 6. This makes the actual magnetic field strength approach the optimal working magnetic field required for the magnetostrictive coating to achieve the best electromagnetic ultrasonic transduction efficiency, which is less than 0.3T. The adjustable magnetic circuit mechanism 2 includes an elastic telescopic component and a magnet housing. The magnetic field generator is placed inside the magnet housing. The elastic telescopic component is a telescopic spring mechanism located inside the housing, which can drive the magnet housing to synchronously displace the magnetic field generator. This allows for flexible adjustment of the distance between the magnetic field generator and the magnetostrictive coating 6 on the inspected workpiece 71. The structure is simple and highly feasible for engineering. The elastic telescopic component 2 enables stepless adjustment of the distance between the magnetic field generator and the magnetostrictive coating 6, ensuring that the magnetic field strength is at the optimal electromagnetic ultrasonic transduction operating point required by the coating.

[0033] The telescopic spring mechanism includes a bolt 201, a connector 202, a spring top plate 203, a spring cavity 204, a telescopic spring 205, a moving column 206, a screw 207, a limiting ring 208, a magnet housing 209, and a support spring 211. The connector 202 is vertically fixed to the corresponding position on the top cover 11 of the housing, with its top end located below the top cover 11 and its bottom end located above the spring top plate 203. The connector 202 has an internal threaded hole that matches the bolt 201, which is threaded into the internal threaded hole on the connector 202. The top end of the bolt 201 extends above the top cover 11 for easy external adjustment. The connector 202 has an external thread that matches the top of the spring cavity 204, and the top of the spring cavity 204 is fitted onto the bottom end of the connector 202. A spring top plate 203 is vertically fixed to the top of the movable column 206. Both the movable column 206 and the spring top plate 203 are located inside the spring cavity 204, with the spring top plate 203 positioned below the connector 202. The bottom end of the movable column 206 protrudes from the bottom of the spring cavity 204, and a limiting ring 208 is coaxially fixed to the inner wall of the bottom end of the movable column 206. A telescopic spring 205 slides up and down on the movable column 206, located between the lower surface of the spring cavity 204 and the spring top plate 203, providing elastic support and restoring force for the movable column. The limiting ring 208 has an internal threaded hole that matches the screw 207, which is threaded into the internal threaded hole of the limiting ring 208. The magnet housing 209 is made of a non-ferromagnetic metal material (such as stainless steel or high-temperature alloy). Its top has an internally threaded hole coaxial with the screw 207. The lower end of the screw 207 is threaded into the internally threaded hole on the top of the magnet housing 209, thus achieving a fixed connection between the moving column 206 and the magnet housing 209. A permanent magnet 210 is placed inside the magnet housing 209. The lower part of the magnet housing 209 contacts a support spring 211, and the lower end of the support spring 211 abuts against the upper surface of the housing base plate 13. The support spring 211 provides auxiliary support for the permanent magnet 210 and acts as a buffer during movement.

[0034] When the operator rotates bolt 201, the rotational motion of bolt 201 is converted into the axial movement of moving column 206, which in turn drives the magnet housing 209 and the permanent magnet 210 inside to move up and down synchronously, thereby controllably adjusting the distance between permanent magnet 210 and magnetostrictive coating 6 on the workpiece 71 being inspected. The telescopic spring 205 and the support spring 211 work together to provide buffering and restoring force during the movement process and maintain the positional stability of permanent magnet 210 in the working state.

[0035] The multi-channel coil assembly 3 includes at least two mutually insulated independent coils, each forming an independent detection channel. The dimensions of each independent coil are adapted to the bottom surface dimensions of the magnetic field generator, enabling localized concentrated detection and improving the sensitivity for detecting minute defects. The independent coils are arranged in an array on the same plane directly below the magnetic field generator. Each independent coil employs a single-layer or multi-layer tightly wound structure, wound with high-temperature resistant wire to prevent electrical performance failure due to high temperatures. Each independent coil is mutually insulated and arranged side-by-side between the permanent magnet and the object under inspection, forming an independent detection channel. The size of the inner independent coil 31 is smaller than the bottom surface dimensions of the permanent magnet, while the size of the outer independent coil 32 is smaller than, equal to, or slightly larger than the bottom surface dimensions of the permanent magnet, concentrating the area of ​​the generated sound field and improving the sensitivity for detecting localized minute defects. The multi-channel coil assembly 3 enables simultaneous excitation and reception of multi-channel electromagnetic ultrasound, accommodating both large-area scanning and localized minute defect detection, solving the problems of dispersed sound fields and missed detection of small defects associated with traditional single-coil systems.

[0036] The coil assembly in this embodiment includes a first coil group 31, a second coil group 32, coil leads 33, and a cable connector 34. The first coil group 31 and the second coil group 32 are two independent coils, insulated from each other and arranged side-by-side between the permanent magnet 210 and the workpiece 71 under inspection. The workpiece 71 is a high-temperature pipe or pressure vessel to be inspected, with a high-temperature weld 72 on it. The two independent coils are distributed in an array on the same plane directly below the permanent magnet 210. The diameter of the first coil group 31, located on the inner side, is smaller than the radial dimension of the bottom surface of the permanent magnet 210, and the diameter of the second coil group 32, located on the outer side, is smaller than, equal to, or slightly larger than the radial dimension of the bottom surface of the permanent magnet 210. Each independent coil adopts a multi-layer tightly wound structure, made of high-temperature resistant wire, to adapt to high-temperature working environments. The first coil group 31 and the second coil group 32 are respectively connected to the cable connector 34 via coil leads 33. The cable connector 34 is fixed to the top cover 11 of the outer casing for electrical connection with an external multi-channel excitation receiving unit. Each independent coil constitutes an independent detection channel, which can independently excite and receive electromagnetic ultrasonic waves.

[0037] The magnet housing is made of non-ferromagnetic, high-temperature resistant material to avoid interfering with the magnetic field distribution of the permanent magnet 210. The magnetic field generator is the permanent magnet 210, which can maintain relatively stable magnetic properties in a high-temperature environment and provide the bias magnetic field required for the electromagnetic ultrasonic transduction process of the magnetostrictive coating. The permanent magnet 210 is located inside the magnet housing and installed at the telescopic end of the telescopic spring mechanism. It is driven by the telescopic spring mechanism to move synchronously and ensure the stability of the magnetic field adjustment.

[0038] The housing assembly provides physical protection and mounting support for the internal components. It can be made of stainless steel or high-temperature alloy materials, and its overall size can be designed according to the actual testing scenario. The housing assembly includes a top cover 11, a side cover 12, and a bottom cover 13, which together form a closed cavity. The top cover 11 is located at the top of the overall structure. The side cover 12 is vertically connected between the top cover 11 and the bottom cover 13. The bottom cover 13 is located at the bottom, and its central area has a hollow structure to accommodate the ceramic plate 4 and the coil assembly. All components of the housing are made of high-temperature resistant metal materials to ensure structural stability in high-temperature environments. Each independent coil in the coil assembly is positioned above the ceramic plate 4, which provides physical support, electrical insulation, and thermal isolation for the coil assembly.

[0039] The thermal insulation material 5, made of aerogel insulation felt, ceramic fiber cotton, or high-temperature glass wool, is filled between the top cover 11, the sides 12, the bottom plate 13 of the outer shell, and the internal components, as well as between the components of the telescopic spring mechanism. This is used to block the heat transferred from the high-temperature workpiece 71 to the permanent magnet 210, thus slowing down the high-temperature demagnetization of the permanent magnet 210. The magnetostrictive coating 6 is pre-formed or sprayed onto the surface of the high-temperature weld area of ​​the inspected object. The material can be selected from iron oxide coating, nickel coating, iron-cobalt alloy coating, iron-gallium alloy coating, iron-based alloy coating, or cobalt-based alloy coating, with a thickness of 50μm-500μm. It is used to generate a magnetostrictive effect under the combined action of the bias magnetic field provided by the permanent magnet 210 and the alternating magnetic field excited by the coil assembly, thereby exciting electromagnetic ultrasound and receiving echo signals.

[0040] Before actual testing, the target magnetic field strength required to achieve optimal electromagnetic ultrasonic transduction efficiency is determined based on the material properties of the magnetostrictive coating 6. The distance between the permanent magnet 210 and the magnetostrictive coating 6 is adjusted by rotating bolt 201 to bring the actual magnetic field strength acting on the coating surface close to the target value. During testing, the transducer is placed above the high-temperature weld seam 72 area of ​​the workpiece 71 under inspection, with the base plate 13 of the outer casing close to or in contact with the workpiece surface. The external multi-channel electromagnetic ultrasonic excitation / receiving unit applies high-voltage pulse signals to the first coil group 31 and the second coil group 32 via cable connector 34 and coil leads 33, respectively. Under the bias magnetic field provided by the permanent magnet 210, the coil groups excite electromagnetic ultrasonic waves in the magnetostrictive coating 6. The electromagnetic ultrasonic waves propagate inside the workpiece, generating reflected echoes when encountering defects. These echo signals are received by the first coil group 31 and the second coil group 32 and converted into electrical signals, which are then transmitted via coil leads 33 and cable connector 34 to the external multi-channel excitation and receiving unit for further processing.

[0041] This embodiment achieves controllable adjustment of the distance between the permanent magnet 210 and the magnetostrictive coating 6 through a retractable spring mechanism, which can control the actual magnetic field strength on the coating surface near the optimal operating point and improve the transduction efficiency. At the same time, the design of two independent coils makes the sound field action area more concentrated and improves the detection sensitivity of small defects. The setting of heat insulation material 5 and ceramic sheet 4 effectively ensures the reliable operation of the transducer in high-temperature environments.

[0042] Example 2

[0043] This embodiment is for an in-situ flaw detection and monitoring system for high-temperature welds, such as... Figure 4 As shown, it includes an electromagnetic ultrasonic transducer 100, a multi-channel electromagnetic ultrasonic excitation circuit 200, a multi-channel electromagnetic ultrasonic receiving circuit 300, and a main control unit 400. A communication module 500 and a display module 600 can also be added as needed. All components work together to achieve multi-channel electromagnetic ultrasonic excitation, signal reception, data processing, and result display. Specific details are as follows:

[0044] The electromagnetic ultrasonic transducer 100 comprises multiple independent coils. In this embodiment, it includes a first coil group 31, a second coil group 32, and a third coil group 33. Each coil group is led out through coil leads and cable connectors and connected to an external circuit. Each coil group has two terminals: a common ground terminal and a signal terminal. Specifically, the common ground terminal of the first coil group 31 is grounded, and its signal terminal is defined as NQ1; the common ground terminal of the second coil group 32 is grounded, and its signal terminal is defined as NQ2; the common ground terminal of the third coil group 33 is grounded, and its signal terminal is defined as NQ3. Each signal terminal is connected to the corresponding excitation and receiving circuits. As the core detection component of the monitoring system, the electromagnetic ultrasonic transducer 100 is used to attach to or approach the surface of a high-temperature weld to excite and receive electromagnetic ultrasonic signals. Its multiple independent coils are respectively connected to the excitation and receiving channels of the monitoring system to achieve multi-channel synchronous detection, converting ultrasonic signals into electrical signals and transmitting them to the receiving circuit.

[0045] Multi-channel electromagnetic ultrasonic excitation circuit 200: It includes an excitation channel equal to the number of independent coils, which are connected one-to-one to each independent coil. Under the control of the main control unit, a high-voltage pulse signal is applied to the excitation coil to generate ultrasonic waves and receive the electrical signals converted by each independent coil after being reflected by the defect.

[0046] The multi-channel electromagnetic ultrasonic excitation circuit 200 of this embodiment includes three independent excitation channels TX1, TX2, and TX3. The output terminal of each excitation channel is connected to the signal terminal of the corresponding coil group: TX1 is connected to NQ1, TX2 is connected to NQ2, and TX3 is connected to NQ3. Under the control of the main control unit 400, the excitation circuit applies a high-voltage pulse signal to each coil group to excite electromagnetic ultrasonic waves.

[0047] The multi-channel electromagnetic ultrasound receiving circuit 300 includes a corresponding number of receiving channels. The input terminal of each receiving channel is connected to the signal terminal of the corresponding coil group to receive the echo signal induced by the coil and perform amplification and filtering preprocessing. A high-voltage protection circuit is provided at the front end of the receiving channel to protect the downstream circuitry during the excitation pulse. The high-voltage protection circuit includes two diodes connected in anti-parallel to clamp the input voltage within ±0.7V, thus protecting the low-noise amplifier. The receiving section of the receiving channel also includes a low-noise amplifier, a bandpass filter, a controllable gain amplifier, and a high-pass filter connected in sequence.

[0048] like Figure 5 As shown, the input port IN of the receiver is connected to the coil of the electromagnetic ultrasonic transducer. To protect the downstream low-noise amplifier from damage caused by high-voltage excitation pulses, two reverse-connected diodes D1 and D2 are connected in parallel at the input. When the high-voltage excitation arrives, the diodes conduct, clamping the input voltage within ±0.7V, thus effectively isolating the high voltage. After passing through the diodes, the signal enters the low-noise amplifier LNA for pre-amplification, then passes through the bandpass filter BPF to filter out out-of-band noise, then through the controllable gain amplifier VGA for amplitude adjustment, and finally through the high-pass filter HFP to be output to the analog-to-digital converter, converting the analog signal into a digital signal for processing by the main control unit.

[0049] The multi-channel electromagnetic ultrasound receiving circuit 300 of this embodiment includes three independent receiving channels RX1, RX2, and RX3. The input terminal of each receiving channel is connected to the signal terminal of the corresponding coil group: RX1 is connected to NQ1, RX2 is connected to NQ2, and RX3 is connected to NQ3.

[0050] The main control unit 400 is connected to both the multi-channel electromagnetic ultrasonic excitation circuit 200 and the multi-channel electromagnetic ultrasonic receiving circuit 300. The main control unit controls the transmission timing and pulse parameters of the excitation channels and receives digital signals from each receiving channel. The main control unit processes the multi-channel received signals (e.g., filtering, averaging, defect identification, data fusion) to generate detection results.

[0051] The communication module 500 is connected to the main control unit 400 and supports wired (Ethernet, RS485, etc.) and wireless (Wi-Fi, 4G / 5G, etc.) communication methods. It is used for the transmission of detection data and imaging results and the reception of remote control commands.

[0052] The display module 600 is connected to the communication module 500 or the main control unit 400 to display the waveforms, detection results and system status of each channel in real time, so that operators can view and operate it on site.

[0053] The system workflow is as follows:

[0054] Initialization: The main control unit 400 sets the excitation parameters (pulse voltage, frequency, repetition frequency, etc.) and the receiving parameters (gain, filter bandwidth, etc.), and sends the parameters to each channel.

[0055] Excitation: The main control unit triggers excitation channels TX1, TX2, and TX3, and each channel applies high-voltage pulses to the corresponding coil group (through NQ1, NQ2, and NQ3) according to the set timing. Under the action of the bias magnetic field provided by the permanent magnet, the coil group excites ultrasonic waves in the workpiece being inspected.

[0056] Reception: Ultrasonic waves propagate within the workpiece and generate echoes when they encounter defects or boundaries. The echo signals are sensed by each coil group, amplified and filtered by the front-end circuits of the corresponding receiving channels RX1, RX2, and RX3, and then sent to the analog-to-digital converter for digitization.

[0057] Data processing: The main control unit 400 acquires digital signals from each channel, performs filtering, averaging, feature extraction and other processing to generate two-dimensional or three-dimensional imaging results of internal defects in the weld.

[0058] Display and transmission: Imaging results and raw waveforms are displayed in real time through display module 600, and simultaneously uploaded to a remote monitoring center or cloud server through communication module 500 to achieve data sharing and remote diagnosis.

[0059] Example 3

[0060] This embodiment of the in-situ flaw detection and monitoring method for high-temperature welds, combined with the structural characteristics of the transducer and monitoring system, enables in-situ detection of minute defects in high-temperature welds, specifically including the following steps:

[0061] Step S1: Test Preparation

[0062] On the surface of the high-temperature weld area of ​​the inspected object (high-temperature pipeline, pressure vessel, etc.), a magnetostrictive coating is pre-applied using thermal spraying or coating methods. The coating material is selected as iron oxide or iron-cobalt alloy, and the thickness is controlled at 100μm to ensure that the coating is flat, undamaged, and free of bubbles. The electromagnetic ultrasonic transducer is placed close to the coating, with the multi-channel coil assembly aligned directly with the coating. The base plate of the transducer housing is tightly attached to the surface of the inspected object to prevent high-temperature gas from entering the transducer and interfering with the operation of the components. At the same time, the high-temperature weld in-situ flaw detection terminal equipment is activated to check the working status of each component, such as the transducer, multi-channel excitation circuit, multi-channel receiving circuit, and main control unit, to ensure that the equipment is fault-free and the wiring connections are normal.

[0063] Step S2: Magnetic field adjustment

[0064] The elastic telescopic component of the adjustable magnetic circuit mechanism is activated. The elastic telescopic component (telescopic spring, moving column, etc.) drives the magnet housing to slowly move the permanent magnet along a direction perpendicular to the magnetostrictive coating, adjusting the distance between the permanent magnet and the coating. During the adjustment process, a gaussmeter is used to measure the vertical magnetic flux density on the coating surface in real time. Based on the characteristics of the magnetostrictive coating, the magnetic flux density is adjusted to the optimal working range of less than 0.3T. After the adjustment is completed, the position of the permanent magnet is fixed by the limiting component of the adjustable magnetic circuit mechanism to avoid changes in magnetic field strength caused by displacement deviation, ensuring efficient excitation of the magnetostrictive effect.

[0065] Step S3: Electromagnetic ultrasonic excitation

[0066] The excitation parameters are set through the human-machine interaction module of the terminal device. The main control unit generates an excitation timing signal according to the set parameters, controls the operation of the multi-channel electromagnetic ultrasonic excitation circuit, and applies a high-voltage pulse signal to each independent coil of the transducer. Each independent coil generates an alternating magnetic field, and under the action of the bias magnetic field provided by the permanent magnet, it excites the coating to generate mechanical vibration, thereby forming electromagnetic ultrasonic waves. The ultrasonic waves propagate along the inside of the inspected workpiece (high-temperature pipe, pressure vessel).

[0067] Step S4: Echo signal reception and conditioning

[0068] When ultrasonic waves encounter defects (such as cracks, pores, inclusions, etc.) while propagating inside the inspected object, they generate reflected echoes. These echoes propagate to the magnetostrictive coating, causing it to vibrate slightly. This vibration causes the individual coils of the transducer to cut magnetic field lines, converting the mechanical vibrations into echo electrical signals. The echo signals received by each individual coil are transmitted to a multi-channel receiving circuit. First, the signal passes through a high-voltage protection circuit at the front end of the receiving channel to prevent high-voltage pulses from interfering with the echo signal. Then, the signal is amplified and filtered for interference by passing through a low-noise amplifier, a bandpass filter, a controllable gain amplifier, and a high-pass filter. The conditioned analog signal is then converted into a digital signal by an ADC and transmitted to the main control unit.

[0069] Step S5: Signal Processing and Defect Identification

[0070] The main control unit adopts an FPGA+MCU architecture to further process the digital signals transmitted through multiple channels: First, filtering and averaging are performed to remove residual interference signals and improve the signal-to-noise ratio; then, key characteristic parameters such as the amplitude and transit time of the defect echo are extracted; next, a data fusion algorithm is used to combine the detection signals of each independent coil (different independent coils correspond to different local areas of the weld), and a delay superposition algorithm is used to perform data fusion. Based on the arrival time difference of the ultrasonic signals from each channel, the defects are spatially registered to achieve accurate location of the defects, determination of the defect size, and identification of the defect type; finally, a computer imaging algorithm program is executed to convert the processed signals into two-dimensional or three-dimensional imaging results, clearly showing the specific location, shape, and size of the defects.

[0071] Step S6: Results Display and Data Retention

[0072] The test results (including waveforms of each channel, defect imaging images, defect parameters, etc.) are displayed in real time through the display module of the terminal device. Operators can view detailed information and confirm the defect status through the touch screen. At the same time, the main control unit stores the test data, imaging results, test parameters, etc. in the memory of the terminal device for easy subsequent query and analysis. Data can also be uploaded to the cloud server or local computer through the communication module (wired or wireless) to achieve data sharing, remote diagnosis, and historical data traceability. After the test is completed, the terminal device is turned off, the transducer and related test tools are tidied up, and the entire high-temperature weld in-situ flaw detection process is completed.

[0073] Example 4

[0074] like Figure 6 As shown, this embodiment provides a high-temperature weld in-situ flaw detection terminal device, integrating the aforementioned electromagnetic ultrasonic transducer and monitoring system, to achieve independent on-site detection, data processing, and result display without the need for external equipment. It is suitable for on-site in-situ flaw detection scenarios, specifically including:

[0075] Electromagnetic ultrasonic transducer 1001: Internally contains multiple independent coils, specifically a first coil group 31, a second coil group 32, and a third coil group 33. Each coil group is connected to the transmitting circuit and the receiving circuit 1002 via internal leads, and is used to excite electromagnetic ultrasonic waves in the high-temperature weld area and receive echo signals.

[0076] Transmitting and receiving circuits 1002: Integrated within the terminal device, these circuits include a multi-channel electromagnetic ultrasonic excitation circuit and a multi-channel electromagnetic ultrasonic receiving circuit. The transmitting circuit comprises three independent excitation channels, respectively connected to the first coil group 31, the second coil group 32, and the third coil group 33; the receiving circuit comprises three independent receiving channels, also respectively connected to each coil group. Both the transmitting and receiving circuits are bidirectionally connected to the main control circuit 1003, receiving main control commands for parameter setting and trigger control, and transmitting the received digital signals to the main control circuit.

[0077] Main control circuit 1003: As the core processing unit of the terminal device, it is connected to the transmitting circuit and receiving circuit 1002. It is used to control the transmission timing, excitation parameters, and receiving parameters, and to acquire multi-channel electromagnetic ultrasonic echo data. The main control circuit integrates a microprocessor, FPGA, or DSP chip to run a pre-programmed or loaded algorithm.

[0078] Communication module 1004: bidirectionally connected to the main control circuit 1003, supporting wired (such as Ethernet, USB) or wireless (such as Wi-Fi, Bluetooth, 4G / 5G) communication methods, used to upload detection data and imaging results to a remote monitoring center or cloud server, and can also receive remote commands for firmware upgrades or parameter adjustments.

[0079] Display module 1005: Unidirectionally connected to the main control circuit 1003, used to receive image and text information output by the main control circuit, and to display the A-scan waveforms of each channel, defect imaging results, system status, and operation interface in real time. The display module can use a touch screen to realize human-computer interaction.

[0080] Memory 1006: Connected to the main control circuit 1003, it is used to store computer programs, detection parameters, raw data, and imaging results. In particular, the memory stores computer algorithm programs, which, when executed by the main control circuit, can perform data fusion and imaging processing on multi-channel electromagnetic ultrasonic signals to generate two-dimensional or three-dimensional images of internal defects in high-temperature welds.

[0081] The terminal device's workflow is as follows:

[0082] Initialization and parameter setting: The user sets the detection parameters, including excitation voltage, frequency, repetition frequency, receiving gain, and filter bandwidth, through the touch interface of the display module 1005. The main control circuit 1003 stores these parameters in the memory 1006 and sends them to the transmitting circuit and the receiving circuit 1002.

[0083] Electromagnetic ultrasonic excitation and signal acquisition: The main control circuit 1003 triggers the transmitting circuit and the receiving circuit 1002, causing each excitation channel to apply high-voltage pulses to the corresponding coil group according to a set timing sequence. Under the action of the bias magnetic field provided by the permanent magnet, the coil group excites ultrasonic waves through the magnetostrictive coating on the surface of the workpiece being inspected. The echo signal is sensed by each coil group, amplified, filtered, and digitized by the receiving circuit, and then transmitted back to the main control circuit 1003.

[0084] Data processing and imaging: The main control circuit 1003 calls the computer algorithm program in the memory 1006 to process the multi-channel digital signals. The processing steps include: filtering, averaging and feature extraction of each channel signal; identifying the local defect features of the corresponding sound field area of ​​each channel; performing data fusion based on the time-delay superposition algorithm and spatially registering the features of each channel; and generating two-dimensional or three-dimensional imaging results of internal defects in high-temperature welds.

[0085] Results display and storage: The main control circuit 1003 sends the imaging results and raw waveform data to the display module 1005 for real-time display, and at the same time stores the data in the memory 1006 for later review.

[0086] Remote data transmission: Users can choose to upload test data to a remote server via the communication module 1004 to achieve data sharing and remote diagnostics. The communication module can also receive remote commands for device control or program updates.

[0087] Example 5

[0088] This embodiment verifies, through comparative testing, the significant improvement in sensitivity for detecting minute defects achieved by the multi-independent coil structure of the present invention compared to the traditional single coil structure.

[0089] like Figure 8 As shown, the test specimen is made of carbon steel, with a diameter of 50 mm and a thickness of 10 mm. A flat-bottomed hole defect with a diameter of 2 mm and a depth of 3.33 mm is pre-drilled at the center of the specimen to simulate a small defect in the weld.

[0090] The comparative example electromagnetic ultrasonic transducer uses a traditional single-coil structure, and its coil is as follows: Figure 2 As shown. The permanent magnet has a diameter of 25mm and a height of 30mm, and the diameter of a single integral coil is 15mm.

[0091] The transducer of this invention adopts a three-independent coil structure, and its coil layout is as follows: Figure 3As shown. The diameters of the three independent coils are as follows: the inner first coil group 31 is 8mm, the middle second coil group 32 is 12mm, and the outer third coil group 33 is 15mm. Each coil adopts a multi-layered, tightly wound structure, insulated from each other, forming three independent detection channels. The remaining structure of the transducer (permanent magnet, retractable spring mechanism, heat insulation material, etc.) is the same as in Example 1.

[0092] The testing system adopts Figure 4 The diagram shows the architecture of an electromagnetic ultrasonic monitoring system. Each coil group of the electromagnetic ultrasonic transducer is connected to the corresponding channel of the multi-channel excitation and receiving unit 100. The excitation parameters are set as follows: pulse voltage 1000V, center frequency 4MHz. The received signal is amplified, filtered, and then processed by the main control unit 400.

[0093] Test Results and Analysis

[0094] (1) Comparative test results

[0095] Figure 7 The waveforms of the received signal, measured on a defect-free specimen and a defective specimen, are shown for a comparative example (a single integral coil). Wherein: Figure 7 (a) shows the waveform of the defect-free specimen, which clearly shows the mode conversion wave 82, the primary bottom surface transverse wave echo 83, and the secondary bottom surface transverse wave echo 84. Figure 7 (b) shows the waveform of the defective specimen, where a defect echo 81 appears at the defect location. The amplitude of this defect echo is low and not prominent enough compared to the mode conversion wave and the bottom surface echo, posing a risk of missed detection.

[0096] Figure 8 This is a waveform diagram of the received signal measured under the same test conditions for the first coil group 31 (innermost coil, 8mm in diameter) in the transducer of the present invention. Wherein: Figure 8 (a) shows the waveform of the defect-free specimen, and the mode conversion wave 82, the primary bottom surface shear wave echo 83, and the secondary bottom surface shear wave echo 84 are also visible. Figure 8 (b) shows the waveform of the defective specimen. The amplitude of the defect echo 81 is significantly enhanced, much higher than that of the mode conversion wave 82. The waveform is sharp and the characteristics are very clear.

[0097] contrast Figure 7 (b) and Figure 8As can be seen from (b), the small-diameter independent coil (8mm) used in this invention makes the ultrasonic field action area more concentrated, significantly improving the sensitivity to flat-bottomed hole defects. The defect echo amplitude is improved compared to the traditional single coil (15mm in diameter), and the signal-to-noise ratio is significantly improved. This verifies that by dividing the traditional single coil into multiple independent coils with smaller diameters, this invention achieves coverage of the detection area while retaining high spatial resolution, overcoming the shortcomings of traditional large-aperture coils that have weak response to small defects and are prone to missed detection.

[0098] Example 6

[0099] This embodiment experimentally verifies the effect of adjusting the permanent magnet lift-off distance using a retractable spring mechanism on the electromagnetic ultrasonic transduction efficiency, and determines the optimal working magnetic field for the magnetostrictive coating.

[0100] The electromagnetic ultrasonic transducer of this invention (equipped with a retractable spring mechanism for controllable adjustment of the distance between the permanent magnet and the coating surface) is used. The workpiece under test is a specimen with a 100 μm thick magnetostrictive coating of iron oxide. The vertical magnetic flux density on the coating surface is measured using a gaussmeter. The lifting distance of the permanent magnet is changed by rotating the bolt, and the waveform and amplitude of the received signal at different lifting distances are recorded.

[0101] Figure 9 The test results are shown at different permanent magnet lift-off distances. Figure 9 (a) shows the A-scan waveforms measured at lift-off distances of 1 mm, 5 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, and 40 mm. The waveforms mainly contain the following characteristic waves: primary bottom longitudinal wave echo 91; mode conversion wave 92; primary bottom transverse wave echo 93; and secondary bottom transverse wave echo 94.

[0102] As can be seen from the waveform diagram, the amplitude of each echo first increases and then decreases as the lift-off distance increases. Figure 9 (b) Quantitatively plots the peak-to-peak value (normalized amplitude) of the first bottom shear wave echo 93 and the curves showing the change of vertical magnetic flux density on the sample surface with the lift-off distance. It can be seen that when the lift-off distance is 1 mm, the surface magnetic flux density is as high as about 0.52 T, but the signal amplitude is low; as the lift-off distance increases, the magnetic flux density gradually decreases, and the signal amplitude gradually increases; when the lift-off distance is 20 mm, the surface magnetic flux density is about 0.12 T, at which point the amplitude of the first bottom shear wave echo reaches its maximum; with further increases in the lift-off distance, the magnetic flux density further decreases, and the signal amplitude also decreases accordingly.

[0103] Experimental results show that for magnetostrictive coatings of iron oxide, the target magnetic field strength required to obtain the optimal electromagnetic ultrasonic transduction efficiency is approximately 0.12 T, which is far lower than the magnetic field strength provided by traditional high-remanence permanent magnets (above 0.5 T). By controllably adjusting the lifting distance of the permanent magnet through a retractable spring mechanism, the actual magnetic field on the coating surface can be controlled near the optimal operating point, thereby significantly improving the electromagnetic ultrasonic transduction efficiency and the amplitude of the received signal.

Claims

1. An electromagnetic ultrasonic transducer for in-situ flaw detection of high-temperature welds, characterized in that, The device includes an adjustable magnetic circuit mechanism and a multi-channel coil assembly. The adjustable magnetic circuit mechanism can adjust the distance between the magnetic field generator and the coating on the surface of the high-temperature weld of the inspected object to control the magnetic flux density on the coating surface within the optimal working magnetic field range. The adjustable magnetic circuit mechanism includes an elastic telescopic component and a magnet housing. The magnetic field generator is disposed inside the magnet housing. The elastic telescopic component drives the magnet housing to synchronously displace the magnetic field generator, thereby achieving stepless adjustment of the distance between the magnetic field generator and the coating. The multi-channel coil assembly includes at least two mutually insulated independent coils, each of which constitutes an independent detection channel, enabling localized centralized detection. The elastic telescopic component is a telescopic spring mechanism, which includes a bolt, a connector, a spring top plate, a spring cavity, a telescopic spring, a moving column, a screw, a limiting ring, a magnet housing, and a supporting spring. The connector is vertically fixed to the corresponding position on the top cover of the housing, with the top end of the connector located below the top cover and the bottom end of the connector located above the spring top plate. The connector has an internal threaded hole that matches the bolt, and the bolt is threaded into the internal threaded hole on the connector, with the top end of the bolt extending above the top cover of the housing. The connector has an external thread that matches the top of the spring cavity, and the top of the spring cavity is fitted onto the bottom end of the connector. The spring top plate is vertically fixed to the top of the moving column, and the moving column and... All spring top plates are placed inside the spring cavity, located below the connector. The bottom end of the moving column protrudes from the bottom of the spring cavity, and a limiting ring is coaxially fixed on the inner wall of the bottom end of the moving column. The telescopic spring slides up and down on the moving column and is located between the lower surface of the spring cavity and the spring top plate. The limiting ring has an internal threaded hole that matches the screw, and the screw is threaded into the internal threaded hole of the limiting ring. The magnet shell is made of non-ferromagnetic metal material, and its top has an internal threaded hole that is coaxial with the screw. The lower end of the screw is threaded into the internal threaded hole on the top of the magnet shell. A permanent magnet is placed inside the magnet shell, and the lower part of the magnet shell is in contact with the support spring. The lower end of the support spring abuts against the upper surface of the shell bottom plate.

2. The electromagnetic ultrasonic transducer according to claim 1, characterized in that, The independent coils are arranged in a concentric array on the same plane directly below the magnetic field generator. The diameter of each independent coil increases from the inside to the outside. The size of the independent coil on the inside is smaller than the radial dimension of the bottom surface of the magnetic field generator, and the size of the independent coil on the outside is smaller than or equal to the radial dimension of the bottom surface of the magnetic field generator. Each independent coil adopts a single-layer or multi-layer tightly wound structure.

3. The electromagnetic ultrasonic transducer according to claim 1, characterized in that, The optimal working magnetic field is less than 0.3T.

4. The electromagnetic ultrasonic transducer according to claim 1, characterized in that, The magnet housing is made of non-ferromagnetic material, the magnetic field generator is a permanent magnet, and the elastic telescopic component enables stepless adjustment of the distance between the magnetic field generator and the coating.

5. A high-temperature weld in-situ flaw detection and monitoring system comprising the electromagnetic ultrasonic transducer according to any one of claims 1-4, characterized in that, It includes a multi-channel excitation circuit, a multi-channel receiving circuit, and a main control unit. The multi-channel excitation circuit and the multi-channel receiving circuit are respectively connected to each independent coil. The main control unit controls the excitation timing and parameters and processes the digital signal to generate the detection result.

6. The high-temperature weld in-situ flaw detection and monitoring system according to claim 5, characterized in that, The multi-channel receiving circuit includes a low-noise amplifier, a bandpass filter, a controllable gain amplifier, and a high-pass filter connected in sequence.

7. A method for in-situ flaw detection and monitoring of high-temperature welds based on the electromagnetic ultrasonic transducer according to any one of claims 1-4, characterized in that, Includes the following steps: S1. A magnetostrictive coating is pre-applied to the surface of the high-temperature weld area of ​​the inspected object, and the transducer is placed close to the coating. S2. The distance between the magnetic field generator and the coating is adjusted using an adjustable magnetic circuit mechanism to ensure the magnetic field strength on the coating surface matches the optimal working magnetic field. S3. A high-voltage pulse signal is applied to each independent coil through a multi-channel excitation circuit to generate ultrasonic waves that propagate inside the inspected object. S4. The echo signal is received and conditioned by a multi-channel receiving circuit and transmitted to the main control unit. S5. The main control unit processes the multi-channel signals, identifies defect parameters, and generates inspection results.

8. The in-situ flaw detection and monitoring method for high-temperature welds according to claim 7, characterized in that, In step S2, while adjusting the distance between the magnetic field generator and the coating, the magnetic flux density on the coating surface is detected in real time until the magnetic flux density reaches the optimal range of less than 0.3T.

9. The in-situ flaw detection and monitoring method for high-temperature welds according to claim 7, characterized in that, In step S5, the main control unit uses a time-delay superposition algorithm to fuse data, combines the detection signals of each independent coil, performs spatial registration of the defect based on the arrival time difference of the ultrasonic signals of each channel, locates the defect position and determines the defect size, and generates two-dimensional or three-dimensional imaging results.

10. A high-temperature weld in-situ flaw detection terminal device, characterized in that, The terminal device integrates the electromagnetic ultrasonic transducer as described in any one of claims 1-4, enabling independent on-site detection and data processing of high-temperature welds.

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