In-pipe non-contact electromagnetic acoustic torsional mode guided wave transducer system and testing method

Abstract

This invention discloses a non-contact electromagnetic acoustic torsional mode guided wave transducer system and testing method for pipes. The system includes several sets of pulse electromagnets and excitation coils located at one end of the pipe under test. The pulse electromagnets generate an instantaneous static magnetic field along the radial direction of the pipe under test. The excitation coil is placed along the inner wall of the pipe under test through a mold. After being energized, the current passes through the excitation coil, inducing an alternating eddy current field on the inner surface of the pipe at the skin depth. Simultaneously, under the action of the static magnetic field of the pulse electromagnets, a Lorentz force is generated in the pipe under test along the tangential direction, which then propagates within the pipe and excites a torsional mode guided wave. When the torsional mode guided wave encounters a defect in the pipe wall, it is reflected. When the reflected echo passes through the excitation coil, it causes a change in the induced voltage of the sensing coil. By observing the change in induced voltage over time, the presence of a defect in the pipe under test can be determined, and the defect can be located and evaluated.

Description

Technical Field

[0001] This invention belongs to the field of pipeline ultrasonic guided wave nondestructive testing technology, and more specifically, relates to a non-contact electromagnetic acoustic torsional mode guided wave transducer system and testing method for pipelines. Background Technology

[0002] Heat exchangers are widely used in large factories such as chemical plants and nuclear power plants. Operating in harsh environments for extended periods, heat exchanger tube bundles are highly susceptible to various types of corrosion and defects, leading to leaks. This is especially true for critical heat exchangers, such as evaporators in nuclear power plants, where leaks could cause nuclear contamination. Therefore, structural health inspections of the slender tube bundles in these critical heat exchangers are essential. However, because the heat exchanger tubes do not extend outside the heat exchanger and are located in a high-temperature, high-radiation environment, access is difficult for inspection personnel. Currently, the primary method for inspecting slender heat exchanger tubes is eddy current testing. While eddy current testing offers high sensitivity, it requires point-to-point inspection, resulting in low efficiency and installation difficulties.

[0003] In addition, ultrasonic guided wave transducers used for pipeline inspection mainly include piezoelectric transducers and electromagnetic ultrasonic transducers. Piezoelectric transducers generally require coupling agents, and the materials are generally expensive and relatively complex to manufacture. They also generally have weak performance due to the magnetostrictive effect of the specimen itself, and it is difficult to excite torsional guided waves. Furthermore, although existing pipeline inspection transducer technology has successfully excited circumferential torsional guided wave modes of T(0,2) using an in-pipe electromagnetic acoustic sensor with an array of periodic permanent magnets (PPM), and used periodic permanent magnets to enhance the conversion efficiency of in-pipe EMAT, permanent magnets have problems such as large size, fixed residual magnetic flux density, and monotonous shape, which are not conducive to the inspection of slender pipelines and the installation of sensors, posing certain difficulties in engineering applications.

[0004] Therefore, there is an urgent need for an electromagnetic acoustic torsional modal testing device that can be applied to non-ferromagnetic slender pipes such as heat exchanger tube bundles, and that is simple in structure, small in size, easy to install, and capable of performing non-destructive testing on the entire slender pipe. Summary of the Invention

[0005] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides an in-pipe non-contact electromagnetic acoustic torsional mode guided wave transducer system and testing method. The system involves inserting a pulsed electromagnet and an excitation coil into one end of the pipe under test, with the excitation coil conforming to the curvature of the pipe's inner wall. A power amplifier and a signal preprocessing device are communicatively connected to the excitation coil. A signal generator is communicatively connected to the power amplifier, and a signal receiver is communicatively connected to the signal preprocessing device. A sinusoidal signal is emitted by the signal generator, amplified by the power amplifier, and sent to the excitation coil. This induces an alternating eddy current field at the skin depth surface within the pipe under test. Under the static magnetic field of the pulsed electromagnet, a Lorentz force is generated tangentially within the pipe under test. Based on the Lorentz... Based on the principle of force, strain is generated along the tangential direction of the tested pipe, which is then transmitted within the pipe, thereby exciting a torsional mode guided wave. This torsional mode guided wave propagates along the pipe axis and is reflected upon encountering a defect. When the reflected echo passes through the excitation coil, it causes a change in the induced voltage of the sensing coil. By observing the change of this induced voltage over time, it is possible to determine whether a defect exists in the pipe and to locate and evaluate the defect. This invention enables non-destructive testing of the entire slender pipe, with advantages such as non-contact operation, low requirements for pipe surface, and high testing efficiency. This invention uses torsional mode guided waves excited inside the pipe, avoiding the testing problems caused by the heat exchanger pipes not being exposed, the difficulty of human access, and the presence of liquid load inside the pipe.

[0006] To achieve the above objectives, one aspect of the present invention provides an in-pipe non-contact electromagnetic-acoustic torsional mode guided wave transducer system, comprising a plurality of pulse electromagnets and excitation coils disposed at one end of the pipe under test, a power amplifier and a signal preprocessing device communicatively connected to the excitation coils, a signal generator connected to the power amplifier, and a signal receiver communicatively connected to the signal preprocessing device; wherein...

[0007] The pulse electromagnet is wound using a special mold and can generate an instantaneous static magnetic field along the radial direction of the pipe under test. The excitation coil is racetrack-shaped and placed along the inner wall of the pipe under test using the mold, with a lift-off distance of 0.3 mm from the inner wall. The pulse electromagnets are arranged in an array periodically. The pulse coil of each group of pulse electromagnets is wound inside the pipe under test in four corresponding radial directions, and the included angle between the pulse coils of two adjacent groups of pulse electromagnets is 90 degrees, forming four mutually perpendicular static magnetic fields in the circumferential direction. A periodic sinusoidal signal is emitted by the signal generator, amplified by the power amplifier, and sent to the excitation coil. An alternating eddy current field is induced on the inner surface of the tested pipe at its skin depth. Simultaneously, under the action of the static magnetic field of the pulsed electromagnet, a Lorentz force is generated tangentially within the tested pipe, thereby generating a tangential shear force that propagates within the pipe and excites a torsional mode guided wave. The torsional mode guided wave propagates along the axial direction of the tested pipe and is reflected upon encountering a defect in the pipe wall. When the reflected echo passes through the excitation coil, it causes a change in the induced voltage of the sensing coil. By observing the change in the induced voltage over time, the presence of a defect in the tested pipe can be determined, and the defect can be located and evaluated.

[0008] Furthermore, the excitation of the torsional mode guided wave also includes the guided wave signal caused by the induced current change in the excitation coil due to the echo flowing into the signal preprocessing device and then inputting it into the signal receiver for signal post-processing and mode extraction.

[0009] Furthermore, the excitation coil includes a straight portion and an arc-shaped portion, the straight portion being arranged along the axial direction of the pipe under test and perpendicular to the magnetic field direction of the pulse electromagnet.

[0010] Furthermore, the pulsed electromagnet forms a periodic alternating magnetic field along the axial direction of the pipe under test, and is placed alternately according to the half wavelength calculated based on the selected excitation frequency and its dispersion curve.

[0011] Furthermore, the number of arrays of pulse electromagnets is related to the circumferential size of the pipe being tested. The number of arrays and their dimensions differ for pipes of different sizes. Moreover, changes in the circumferential size of the pipe being tested will cause changes in the size of each array, as well as changes in the number and size of the excitation coils.

[0012] Furthermore, given a fixed number of pulse electromagnets arranged axially along the tested pipe, the spacing between the pulse electromagnets in opposite magnetic field directions along the same axial direction of the tested pipe is... λ is the wavelength; by changing the direction of the current flow in the pulse electromagnet, the distance between the two pulse electromagnets with different magnetic field directions is changed.

[0013] Furthermore, the waveguide group velocity dispersion curve, phase velocity dispersion curve, and structure of each mode of guided wave of the tested pipeline at different frequencies are obtained by semi-analytical finite element calculation based on the dimensions of the tested pipeline, the Poisson's ratio of the material, and the Young's modulus parameters.

[0014] Another aspect of the present invention provides a testing method for an in-tube non-contact electromagnetic acoustic torsional mode guided wave transducer system, comprising the following steps:

[0015] S1: Insert the pulse electromagnet and excitation coil into one end of the pipe under test, so that the excitation coil fits the curvature of the inner wall of the pipe under test;

[0016] S2: Connect the power amplifier and the signal preprocessing device to the excitation coil for communication, connect the signal generator to the power amplifier for communication, and connect the signal receiver to the signal preprocessing device for communication.

[0017] S3: The signal generator emits a periodic sinusoidal signal, which is amplified by the power amplifier and sent to the excitation coil. An alternating eddy current field is induced on the skin depth surface inside the tube under test. Under the action of the static magnetic field of the pulse electromagnet, a Lorentz force is generated in the tube under test along the tangential direction of the tube under test, which in turn causes strain in the tube under test along the tangential direction of the tube. This deformation is then transmitted in the tube under test, thereby exciting ultrasonic guided waves.

[0018] S4: After the ultrasonic guided wave is excited, the excitation coil acts as the receiving coil. The echo of the ultrasonic guided wave will generate an induced current in the receiving coil and be received by the signal receiver. The time domain diagram of the circumferential displacement signal of the ultrasonic guided wave is obtained. By calculating the time interval between two adjacent signal echoes and the distance between the first time the guided wave passes through the signal receiver and the second time it arrives at the signal receiver, the ultrasonic guided wave group velocity is obtained.

[0019] S5: Based on the dimensions of the tested pipeline, the Poisson's ratio of the material, and Young's modulus, the waveguide group velocity dispersion curve and phase velocity dispersion curve of the tested pipeline at different frequencies are obtained by semi-analytical finite element calculation.

[0020] S6: Compare the time interval between two adjacent signal echoes obtained in step S4, the distance between the first and second arrival of the guided wave at the signal receiver, and the ultrasonic guided wave group velocity with the guided wave group velocity dispersion curve obtained in step S5 to obtain the torsional mode of the ultrasonic guided wave.

[0021] S7: The torsional mode guided wave propagates along the axis of the pipe under test and is reflected after encountering a defect. When the reflected echo passes through the excitation coil, it causes a change in the induced voltage of the sensing coil. By observing the change of this induced voltage over time, it is possible to determine whether there is a defect in the pipe and to locate and evaluate the defect.

[0022] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0023] (1) The non-contact electromagnetic acoustic torsional mode guided wave transducer system in the tube of the present invention uses torsional mode ultrasonic guided waves. Ultrasonic guided wave detection technology is a new type of non-destructive testing method. The ultrasonic guided wave only needs to be excited at a single point and can propagate along the axial direction. The propagation loss is low and the propagation distance is long. Therefore, for heat exchanger pipelines, only one end of the tube needs to be excited to detect the entire tube, which has high detection efficiency. The torsional mode ultrasonic guided wave of the present invention is a circumferential displacement guided wave. It has higher sensitivity to the detection of longitudinal cracks in the pipe compared with other modes of guided waves. Moreover, the torsional wave is not sensitive to the liquid inside the tube and the load outside the tube, making it more suitable for the defect detection of heat exchanger pipelines.

[0024] (2) The tube-mounted non-contact electromagnetic acoustic torsional mode guided wave transducer system of the present invention employs an electromagnetic acoustic transducer. Electromagnetic ultrasonic transducers (EMATs) do not require physical constraints from coupling agents and pipes. Instead, they utilize the principle of electromagnetic induction. A high-frequency current is passed through a coil near the surface of the metal being tested. Due to the skin effect, eddy currents of the same frequency are induced in the metal. Under the influence of an external magnetic field, these induced eddy currents generate Lorentz forces of the same frequency, acting on the metal lattice and causing it to vibrate periodically, thereby exciting ultrasonic guided waves. EMATs have low requirements for the surface of the object being tested and can directly detect high-temperature objects and objects with coatings. EMATs use the test piece in the electromagnetic field as the medium for transmitting and receiving sound waves, thus eliminating the need for coupling agents such as oil or water and avoiding contact pressure variations, resulting in stable flaw detection sensitivity. Therefore, compared to traditional piezoelectric transducers, electromagnetic ultrasonic transducers have the advantages of being non-contact, having low requirements for pipe surfaces, and high detection efficiency. This invention uses in-pipe excitation and torsional mode guided waves, avoiding detection problems caused by exposed heat exchanger pipes, difficulty in human access, and liquid loads inside the pipes.

[0025] (3) The non-contact electromagnetic-acoustic torsional mode guided wave transducer system in the pipe of the present invention, compared with other electromagnetic-acoustic guided wave transducers, can excite two frequencies of T(0,m) torsional mode guided waves in the same pipe, and their frequencies are twice that of each other. It is simple in structure, easy to install, and low in cost. Since a long pulse electromagnet is used instead of a traditional permanent magnet, it is easier to adjust the static magnetic field strength, thereby better matching with the dynamic magnetic field, making the transducer highly efficient and less prone to burnout. In addition, since the present invention is installed in the pipe and does not require coupling agent to connect to the pipe, it is suitable for detecting various pipeline systems in areas that are inaccessible to human personnel.

[0026] (4) The tube-based non-contact electromagnetic acoustic torsional mode guided wave transducer system of the present invention adopts an electromagnetic acoustic transducer and uses an array of periodic pulse electromagnets instead of permanent magnets in the traditional EMAT transducer. The pulse electromagnets have a larger current amplitude, can provide a magnetic field with a higher magnetic flux density than traditional permanent magnets and DC electromagnets, and have low energy consumption, thus avoiding the problem of overheating of ordinary DC electromagnets. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the overall structure of the tube-mounted non-contact electromagnetic acoustic torsional mode waveguide transducer system according to an embodiment of the present invention.

[0028] Figure 2 This is a three-dimensional structural schematic diagram of the tube-mounted non-contact electromagnetic acoustic torsional mode waveguide transducer system according to an embodiment of the present invention.

[0029] Figure 3 This is a schematic diagram of the arrangement of pulse electromagnets in the tube-mounted non-contact electromagnetic acoustic torsional mode waveguide transducer system according to an embodiment of the present invention.

[0030] Figure 4 This is a schematic diagram of the excitation coil of the tube-mounted non-contact electromagnetic acoustic torsional mode waveguide transducer system according to an embodiment of the present invention.

[0031] Figure 5 This is a schematic diagram of the arrangement of the excitation coil in the pipe of the non-contact electromagnetic acoustic torsional mode guided wave transducer system in an embodiment of the present invention.

[0032] Figure 6 This is a schematic diagram of the phase velocity dispersion curve of the pipeline according to an embodiment of the present invention;

[0033] Figure 7 This is a schematic diagram of the velocity dispersion curve of the pipeline group according to an embodiment of the present invention;

[0034] Figure 8 This is a time-domain schematic diagram of the circumferential displacement signal received by the guided wave signal receiver according to an embodiment of the present invention;

[0035] Figure 9This is a schematic flowchart of the testing method for the non-contact electromagnetic acoustic torsional mode guided wave transducer system inside a tube, according to an embodiment of the present invention.

[0036] In all the accompanying drawings, the same reference numerals denote the same technical features, specifically: 1-the pipe under test, 2-pulse electromagnet, 3-excitation coil, 4-power amplifier, 5-signal generator, 6-signal preprocessing device, 7-signal receiver. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0038] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, when an element is referred to as "fixed to," "set on," or "provided on" another element, it can be directly on or indirectly on the other element. When an element is referred to as "connected to" another element, it can be directly connected to or indirectly connected to the other element. The terms "mounted," "connected," "linked," and "provided with" should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral connection; it can refer to a mechanical connection or an electrical connection; it can refer to a direct connection or an indirect connection through an intermediate medium; it can refer to the internal communication of two elements or the interaction between two elements. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0039] like Figures 1-8As shown, this invention provides a non-contact electromagnetic-acoustic torsional mode guided wave transducer system for pipes, including several sets of pulse electromagnets 2 and excitation coils 3 located at one end of the pipe 1 under test, a power amplifier 4 and a signal preprocessing device 6 communicatively connected to the excitation coils 3, a signal generator 5 connected to the power amplifier 4, and a signal receiver 7 communicatively connected to the signal preprocessing device 6. This invention inputs a sinusoidal AC signal into the excitation coils 3 via the signal generator 5 connected to the power amplifier 4. The induced current in the excitation coils 3 caused by the echo flows through a wire into the signal preprocessing device 6 and is then input to the signal receiver 7. The electromagnetic-acoustic torsional mode guided wave transducer of this invention also serves as a signal acquisition device, collecting guided wave signals by the changes in the coil induced current caused by the echo and transmitting them to the signal receiver 7. The invention performs post-processing and mode extraction of the signal; by observing the change of induced voltage over time, it can determine whether there are defects in the pipeline and locate and evaluate the defects; the invention can excite two frequencies of T(0,m) torsional mode guided waves in the same pipeline, and their frequencies are twice that of each other, and the structure is simple, easy to install, and low in cost; it has higher sensitivity to the detection of longitudinal cracks in pipelines compared with other modes of guided waves, and the torsional wave is not sensitive to the liquid inside the pipe and the load outside the pipe, making it more suitable for defect detection of heat exchanger pipelines compared with the longitudinal wave of the prior art; the invention has the advantages of non-contact, low requirements for the pipe surface, and high detection efficiency; the invention uses torsional mode guided waves to be excited inside the pipe and uses them, avoiding the detection problems caused by the heat exchanger pipeline not being exposed, the difficulty of human access, and the presence of liquid load inside the pipe.

[0040] Furthermore, such as Figures 1-8 As shown, the pulse electromagnet 2 is wound using a special mold and can generate an instantaneous static magnetic field along the radial direction of the pipe under test 1; the excitation coil 3 is racetrack-shaped, including a straight section and an arc section; the straight section of the excitation coil 3 is placed along the axial direction of the pipe under test 1 and close to the inner wall of the pipe under test 1. After passing an alternating current through it, due to the skin effect, an alternating eddy current field can be induced on the inner surface of the pipe under test 1 at the skin depth under the action of the alternating current; the induced alternating eddy current field in the pipe under test 1, under the action of the static magnetic field of the pulse electromagnet, can cause the... A Lorentz force is generated tangentially within the tested pipe 1. Based on the Lorentz force principle, a tangential shear force can be generated within the tested pipe 1, and this tangential shear stress propagates within the tested pipe 1, thereby exciting a torsional mode guided wave in the tested pipe 1. This torsional mode guided wave propagates along the pipe axis and is reflected after encountering a defect. When the reflected echo passes through the excitation coil, it causes a change in the induced voltage of the sensing coil. By observing the change of this induced voltage over time, it is possible to determine whether a defect exists in the pipe and to locate and evaluate the defect.

[0041] Furthermore, such as Figures 1-8 As shown, the pulse electromagnets 2 are arranged in an array-like, periodic configuration. The number of pulse electromagnets 2 in the array is related to the circumferential dimension of the pipe 1 under test; the number and size of the arrays differ for pipes of different sizes. Furthermore, changes in the circumferential dimension of the pipe 1 under test will cause changes in the size of each array, as well as changes in the number and size of the excitation coils 3. Given a fixed number of pulse electromagnets 2 arranged along the axial direction of the pipe 1 under test, since the interval between pulse electromagnets with opposite magnetic field directions in the same axial direction is... By changing the direction of current flow within the pulse electromagnet and altering the spacing between two pulse electromagnets with different magnetic field directions, the non-contact electromagnetic-acoustic torsional mode waveguide transducer system in the pipe of this invention can excite two frequencies of T(0,m) torsional mode waveguides in the same pipe, with their frequencies being twice that of each other.

[0042] Furthermore, such as Figures 1-5 As shown, in this embodiment, the outer diameter of the tested pipe 1 is 20mm, the wall thickness is 2mm, and the length is 0.5m. The 20mm outer diameter heat exchanger pipe can accommodate four sets of pulse electromagnets 2 and two sets of excitation coils 3. The pulse coil of each set of pulse electromagnets 2 is wound inside the tested pipe 1 in four radial directions, with the included angle between the pulse coils of adjacent sets of pulse electromagnets 2 being 90 degrees, thus forming four mutually perpendicular static magnetic fields in the circumferential direction. The two sets of excitation coils 3 are placed along the inner wall of the tested pipe 1 using a mold, with a lift-off distance of 0.3mm, and do not contact the inner wall of the pipe. The two sets of excitation coils 3 are fitted together, and the four straight sections of each set of excitation coils 3 are along the axial direction of the pipe and perpendicular to the magnetic field direction of the pulse electromagnet 2. Since the excitation coils 3 have two currents in opposite directions, the clockwise static magnetic field generated by the pulse electromagnet 2 on the two straight sections of each excitation coil 3 is also in opposite directions. The magnetic field direction of the pulse electromagnet 2 matches the current direction of the alternating eddy current field induced on the inner wall of the pipe under test 1, thereby ensuring that the circumferential Lorentz force is in the same direction, so that the tangential stress in the same circumferential direction is generated in the pipe under test 1, which enhances the circumferential vibration and generates torsional waves that propagate along the pipe.

[0043] Furthermore, according to Maxwell's equations, the Lorentz force of the electromagnetic acoustic transducer (EMAT) is calculated using equations (1) to (6):

[0044]

[0045] B d =μ m H d (2)

[0046]

[0047] J e =γE E (4)

[0048] f L =J e ×(B d +B s (5)

[0049] F L =∫∫∫ V f L dV (6)

[0050] in, It is the gradient operator; H d J0 is the dynamic magnetic field strength of the excitation coil, J0 is the excitation current density, and B is the excitation current density. d It is the dynamic magnetic flux density of the pulse electromagnet; μ m It is the relative permeability of the pipe being tested, E E J is the electric field strength of the induced eddy current field, γ is the conductivity of the tested pipe, and J is the electric field strength of the induced eddy current field. e It is the eddy current density, B s It is the static magnetic flux density of the pulse electromagnet, f L It is the Lorentz force per unit volume, F L It is the Lorentz force.

[0051] According to formula (5), the Lorentz force is determined by the magnetic field and the eddy current field; when the excitation current is not high, the dynamic magnetic field of the pulse electromagnet is much weaker than the static magnetic field; therefore, formula (5) can also be expressed as:

[0052] f L =J e ×B s (7)(7)

[0053] As can be seen from the above, by controlling the direction of the static magnetic field of the pulse electromagnet and the direction of the excitation current of the excitation coil, a Lorentz force F in a specific direction can be generated in the pipe under test. L According to formulas (1) to (4) and (7), the Lorentz force F is known. L The excitation frequency is determined by the excitation current density J0;

[0054] For a periodic pulsed electromagnet that excites torsional mode guided waves, the radial magnetic field and axial current are designed to be placed inside the pipe under test and to generate a Lorentz force along the tangential direction of the pipe under test, thereby exciting torsional waves; the periodic pulsed electromagnet provides a periodic alternating magnetization effect in the axial direction and is placed alternately according to the half wavelength calculated based on the selected excitation frequency and its dispersion curve, which amplifies its circumferential vibration.

[0055] Furthermore, such as Figures 1-8 As shown, an electromagnetic acoustic torsional mode guided wave transducer with an array of four periodic pulsed electromagnets is installed at the left end of the pipe under test 1. In this embodiment, the outer diameter of the pipe under test 1 is 20 mm, the length is 0.5 m, and the wall thickness is 2 mm. The signal generator 5 is connected to the power amplifier 4 to input a sinusoidal AC signal into the excitation coil 3. The induced current in the excitation coil 3 caused by the echo flows through the wire into the signal preprocessing device 6 and then into the signal receiver 7. The electromagnetic acoustic torsional mode guided wave transducer of this invention also serves as a signal acquisition device. It collects the guided wave signal by the change in the coil induced current caused by the echo and transmits it to the signal receiver 7 for signal post-processing and mode extraction. Based on the dimensions of the pipe under test 1, the Poisson's ratio and Young's modulus of the material, and other parameters, the guided wave group velocity dispersion curve of the pipe under test 1 is obtained by semi-analytical finite element calculation (e.g., Figure 7 (as shown), phase velocity dispersion curve (as shown) Figure 6 (As shown) and the structure of each modal waveguide; where L(0,1) and L(0,2) are longitudinal waveguides, T(0,1) is a circumferential torsional wave, and F(1,1) and F(1,2) are non-axisymmetric bending waves; the final excitation frequency selected in the embodiment is 80kHz, and its corresponding target torsional mode is T(0,1), and its dispersion curve is shown in the figure. Figure 7 and Figure 6 The theoretical group velocity indicated by the markings is 3194 m / s;

[0056] like Figure 9 As shown, another aspect of the present invention provides a non-contact electromagnetic acoustic torsional mode guided wave transducer method in a tube, comprising the following steps:

[0057] S1: Insert the pulse electromagnet and excitation coil into one end of the pipe under test, so that the excitation coil fits the curvature of the inner wall of the pipe under test;

[0058] S2: Connect the power amplifier and the signal preprocessing device to the excitation coil for communication, connect the signal generator to the power amplifier for communication, and connect the signal receiver to the signal preprocessing device for communication.

[0059] S3: The signal generator emits a 5-cycle sinusoidal signal modulated by a Hanning window, which is amplified by a power amplifier and sent to the excitation coil. An alternating eddy current field is induced on the skin depth surface inside the tube under test. Under the action of the static magnetic field of the pulse electromagnet, a Lorentz force along the tangential direction of the tube under test is generated in the tube under test 1. According to the Lorentz force principle, strain along the tangential direction of the tube is generated in the tube under test, thereby transmitting this deformation in the tube under test and exciting ultrasonic guided waves.

[0060] S4: After the ultrasonic guided wave is excited, the excitation coil 3 acts as a receiving coil. The echo of the ultrasonic guided wave will induce a current in the receiving coil and be received by the signal receiver, obtaining a time-domain diagram of the circumferential displacement signal of the ultrasonic guided wave. By calculating the time interval between two adjacent signal echoes and the distance between the first and second arrivals of the guided wave at the signal receiver, the group velocity of the ultrasonic guided wave packet is obtained. Specifically, the signal receiver receives the ultrasonic guided wave signal obtained in step S2 and obtains a time-domain diagram of the circumferential displacement signal of the ultrasonic guided wave (e.g., ...). Figure 8 As shown), calculate the time interval between two adjacent signal echoes, the distance between the first and second arrivals of the guided wave at the signal receiver, and the ultrasonic guided wave group velocity; wherein, in this embodiment, the time interval between two adjacent signal echoes Δt = 0.32 [ms]; the distance between the first and second arrivals of the guided wave at the signal receiver Δs = 1000 [mm]; and the ultrasonic guided wave group velocity c g =3125 [m / s];

[0061] S5: Based on the dimensions of the tested pipe, the Poisson's ratio of the material, and Young's modulus, the waveguide group velocity dispersion curves of the tested pipe at different frequencies are obtained using semi-analytical finite element analysis (e.g., Figure 7 (as shown), phase velocity dispersion curve (as shown) Figure 6 (as shown); where L(0,1) and L(0,2) are longitudinal guided waves, T(0,1) is a circumferential torsional wave, and F(1,1) and F(1,2) are non-axisymmetric bending waves;

[0062] S6: Compare the time interval between two adjacent signal echoes obtained in step S4, the distance between the first and second arrival of the guided wave at the signal receiver, and the ultrasonic guided wave group velocity with the guided wave group velocity dispersion curve obtained in step S5 to obtain the torsional mode of the ultrasonic guided wave, i.e., the torsional mode guided wave; the guided wave excited by the tube-mounted non-contact electromagnetic acoustic torsional mode guided wave transducer system of the present invention is a circumferential axisymmetric torsional wave T(0,1); if the guided wave group velocity measured in the experiment is the same as the group velocity at the corresponding frequency in the group velocity dispersion curve, then the present invention can excite a pure torsional wave T(0,1);

[0063] S7: The torsional mode guided wave propagates along the axis of the pipe under test and is reflected after encountering a defect. When the reflected echo passes through the excitation coil, it causes a change in the induced voltage of the sensing coil. By observing the change of this induced voltage over time, it is possible to determine whether there is a defect in the pipe and to locate and evaluate the defect.

[0064] The working principle of the non-contact electromagnetic acoustic torsional mode guided wave transducer system and method for pipes provided by this invention is as follows: A pulse electromagnet and an excitation coil are inserted into one end of the pipe under test, so that the excitation coil conforms to the curvature of the inner wall of the pipe under test; a power amplifier and a signal preprocessing device are respectively connected to the excitation coil for communication; a signal generator is connected to the power amplifier for communication, and a signal receiver is connected to the signal preprocessing device for communication; a sinusoidal signal is emitted by the signal generator, amplified by the power amplifier, and sent to the excitation coil, inducing an alternating eddy current field on the skin depth surface inside the pipe under test. Under the action of the static magnetic field of the pulse electromagnet, a Lorentz force along the tangential direction of the pipe under test can be generated inside the pipe under test; based on the Lorentz force... The principle is that strain is generated tangentially within the tested pipe, which is then transmitted within the pipe, thereby exciting torsional mode guided waves. Compared to other electromagnetic waveguide transducers, this invention can excite torsional mode guided waves in the tested pipe 1, and it has a simple structure, is easy to install, and has a low cost. Because a long-pulse electromagnet is used instead of a traditional permanent magnet, the static magnetic field strength is easier to adjust, thus better matching with the dynamic magnetic field, resulting in high excitation efficiency and less risk of burnout. In addition, since this invention is installed inside the pipe and uses an excitation coil to generate an alternating eddy current field along the axial direction of the pipe, and no coupling agent is required between the coil and the pipe, installation is simple and suitable for testing pipeline systems in areas inaccessible to human personnel.

[0065] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A non-contact electromagnetic acoustic torsional mode guided wave transducer system inside a tube, characterized in that: It includes several sets of pulse electromagnets (2) and excitation coils (3) located at one end of the pipe (1) under test, a power amplifier (4) and a signal preprocessing device (6) communicatively connected to the excitation coils (3), a signal generator (5) connected to the power amplifier (4), and a signal receiver (7) communicatively connected to the signal preprocessing device (6); wherein, The pulse electromagnet (2) is wound using a special mold and can generate an instantaneous static magnetic field along the radial direction of the pipe under test (1); the excitation coil (3) is racetrack-shaped and is placed along the inner wall of the pipe under test (1) using a mold, with a lift-off distance of 0.3 mm from the inner wall of the pipe under test (1); the excitation coil (3) includes a straight section and an arc section, the straight section is arranged along the axial direction of the pipe under test (1) and is perpendicular to the magnetic field direction of the pulse electromagnet (2); the pulse electromagnets (2) are arranged in an array-like periodic configuration; the pulse coils of each group of pulse electromagnets (2) are wound inside the pipe under test (1) in four radial directions, and the included angle between the pulse coils of two adjacent groups of pulse electromagnets (2) is 90 degrees, which can form four mutually perpendicular static magnetic fields in the circumferential direction; through the signal generator (5) A periodic sinusoidal signal is emitted, amplified by the power amplifier (4), and sent to the excitation coil (3). An alternating eddy current field is induced on the inner surface of the skin depth of the pipe under test (1). At the same time, under the action of the static magnetic field of the pulse electromagnet (2), a Lorentz force is generated in the pipe under test (1) along the tangential direction, which in turn generates a shear force in the pipe under test (1) and propagates in the pipe under test (1), thereby exciting a torsional mode guided wave. The torsional mode guided wave propagates along the axial direction of the pipe under test (1) and is reflected after encountering a defect in the pipe wall. When the reflected echo passes through the excitation coil (3), it can cause a change in the induced voltage of the sensing coil. By observing the change of the induced voltage over time, it is determined whether there is a defect in the pipe under test (1) and the defect is located and evaluated.

2. The in-tube non-contact electromagnetic acoustic torsional mode guided wave transducer system according to claim 1, characterized in that: The excitation of the torsional mode guided wave also includes the current change signal induced by the echo in the excitation coil (3) flowing into the signal preprocessing device (6) and then inputting it into the signal receiver (7) for signal post-processing and mode extraction.

3. The in-tube non-contact electromagnetic acoustic torsional mode guided wave transducer system according to claim 2, characterized in that: The pulse electromagnet (2) forms a periodic alternating magnetic field in the axial direction of the pipe (1) under test, and is placed alternately according to the half wavelength calculated based on the selected excitation frequency and its dispersion curve.

4. The in-tube non-contact electromagnetic acoustic torsional mode guided wave transducer system according to claim 3, characterized in that: The number of arrays of the pulse electromagnets (2) is related to the circumferential size of the pipe (1) under test. The number of arrays and the size are different for pipes of different sizes. Furthermore, the change in the circumferential size of the pipe (1) under test will cause a change in the size of each array, as well as a change in the number and size of the excitation coils (3).

5. The in-tube non-contact electromagnetic acoustic torsional mode guided wave transducer system according to claim 4, characterized in that: Given a fixed number of pulse electromagnets (2) arranged axially along the pipe (1) under test, the spacing between the pulse electromagnets (2) in opposite magnetic field directions along the same axial direction of the pipe (1) under test is... , The wavelength is denoted by λ. By changing the direction of the current flow inside the pulse electromagnet, the distance between the two pulse electromagnets with different magnetic field directions is changed.

6. The in-tube non-contact electromagnetic acoustic torsional mode guided wave transducer system according to claim 5, characterized in that: The waveguide group velocity dispersion curve, phase velocity dispersion curve, and structure of each mode of the tested pipeline (1) at different frequencies were obtained by semi-analytical finite element calculation based on the dimensions of the tested pipeline (1), the Poisson's ratio of the material, and the Young's modulus parameters.

7. A testing method for an in-tube non-contact electromagnetic-acoustic torsional mode guided wave transducer system, implemented using the in-tube non-contact electromagnetic-acoustic torsional mode guided wave transducer system as described in any one of claims 1-6, comprising the following steps: S1: Insert the pulse electromagnet and excitation coil into one end of the pipe under test, so that the excitation coil fits the curvature of the inner wall of the pipe under test; S2: Connect the power amplifier and the signal preprocessing device to the excitation coil for communication, connect the signal generator to the power amplifier for communication, and connect the signal receiver to the signal preprocessing device for communication. S3: The signal generator emits a periodic sinusoidal signal, which is amplified by the power amplifier and sent to the excitation coil. An alternating eddy current field is induced on the skin depth surface inside the tube under test. Under the action of the static magnetic field of the pulse electromagnet, a Lorentz force is generated in the tube under test along the tangential direction of the tube under test, which in turn causes strain in the tube under test along the tangential direction of the tube. This deformation is then transmitted in the tube under test, thereby exciting ultrasonic guided waves. S4: After the ultrasonic guided wave is excited, the excitation coil acts as the receiving coil. The echo of the ultrasonic guided wave will generate an induced current in the receiving coil and be received by the signal receiver. The time domain diagram of the circumferential displacement signal of the ultrasonic guided wave is obtained. By calculating the time interval between two adjacent signal echoes and the distance between the first time the guided wave passes through the signal receiver and the second time it arrives at the signal receiver, the ultrasonic guided wave group velocity is obtained. S5: Based on the dimensions of the tested pipeline, the Poisson's ratio of the material, and Young's modulus, the waveguide group velocity dispersion curve and phase velocity dispersion curve of the tested pipeline at different frequencies are obtained by semi-analytical finite element calculation. S6: Compare the ultrasonic guided wave group velocity obtained in step S4 with the guided wave group velocity dispersion curve and phase velocity dispersion curve obtained in step S5 to obtain the torsional mode ultrasonic guided wave. S7: The torsional mode guided wave propagates along the axis of the pipe under test and is reflected after encountering a defect. When the reflected echo passes through the excitation coil, it causes a change in the induced voltage of the sensing coil. By observing the change of this induced voltage over time, it is possible to determine whether there is a defect in the pipe and to locate and evaluate the defect.

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