In-pipe nondestructive inspection device and method based on Lorentz force

Abstract

The invention discloses a lorentz force-based in-pipe nondestructive inspection device and method, the lorentz force-based in-pipe nondestructive inspection device comprises a plurality of connecting rings, a plurality of connecting strips, a plurality of permanent magnet groups and a plurality of coils, the plurality of permanent magnet groups taking the connecting rings and the connecting strips as carriers can be conveniently adjusted so as to adapt to pipelines of different materials and specifications, and when in use, the permanent magnet groups can be conveniently adjusted so as to adapt to the pipelines of different materials and specifications. After the coil is electrified with alternating current through the signal output module, an alternating vortex field is conveniently induced on the skin depth inner surface of the to-be-detected pipeline, so that shear force along the tangential direction can be generated in the to-be-detected pipeline and is spread in the to-be-detected pipeline, and then torsional mode guided waves are stimulated; the torsional mode guided wave is propagated along the axis direction of the to-be-detected pipeline and is reflected after encountering a pipe wall defect, the reflected echo enters the signal detection module through the coil, and through the arrangement, an array type periodic permanent magnet technology can be formed in a high-adaptability mode, so that the defects in the prior art are overcome, and the detection accuracy is improved. And the detection precision is improved on the premise of not depending on pipe wall conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of nondestructive testing of pipelines using ultrasonic guided waves, and in particular to a nondestructive flaw detection device and method for pipelines based on Lorentz force. Background Art

[0002] In the field of pipeline flaw detection, it is difficult to arrange inspection devices on the outer surface of some types of pipelines, such as heat exchange pipelines in ships, power plants, chemical plants, and dense heat exchanger tube bundles. The pipelines are slender and located in a narrow space, making it difficult to perform flaw detection from the outside of the pipeline. Therefore, some existing technologies have emerged that can perform flaw detection inside the pipeline, thereby performing full-pipeline flaw detection on slender pipelines.

[0003] Current non-destructive pipeline inspection technologies primarily utilize ultrasonic guided wave transducers based on the magnetostrictive principle and eddy current testing. The magnetostrictive ultrasonic guided wave transducer relies on the magnetic field generated by the pipeline to achieve magnetostriction, generating high-frequency expansion and contraction deformation in the pipeline material, which in turn generates ultrasonic detection waves. While capable of non-destructive inspection within pipelines, it requires ferromagnetic metal pipes to produce magnetostriction and is unsuitable for metal pipes made of other materials. Eddy current testing, while not specific to the pipe material, requires point-by-point inspection of the pipeline in practice. This point-to-point testing technology does not effectively address the inspection challenges of complex, long, and slender pipelines, and can be difficult to detect, miss, or misdetect.

[0004] Therefore, when performing non-destructive in-pipe flaw detection on slender and complex metal pipelines, the existing technology has the defect of being difficult to achieve both adaptability and detection effect. If good flaw detection results are to be achieved, magnetostrictive flaw detection technology that relies on specific pipe wall conditions must be used. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problems in the prior art and to provide a device and method for achieving good non-destructive flaw detection inside a pipe without relying on the ferromagnetic conditions of the metal pipe wall.

[0006] In one aspect, the present invention provides a Lorentz force-based in-pipe nondestructive testing device for performing nondestructive testing on a pipeline to be tested, comprising a signal output module, a signal detection module, and a transducer component disposed in the pipeline to be tested, wherein the transducer component is connected between the signal output module and the signal detection module, and comprises:

[0007] A plurality of connecting rings are arranged side by side with their center lines coinciding, thereby having a leading connecting ring and a trailing connecting ring;

[0008] A plurality of connecting bars, wherein the length direction of the connecting bars is parallel to the center line of the connecting ring, and two adjacent connecting rings are detachably connected through the plurality of connecting bars;

[0009] A permanent magnet group is located between two adjacent connecting rings. Each permanent magnet group includes at least one radial permanent magnet. The radial permanent magnet has a ring structure and its centerline coincides with the centerline of the connecting ring. The radial permanent magnet is sleeved on the outside of a plurality of connecting strips and abuts against the connecting strips. The number of permanent magnet groups is n, the number of connecting rings is n+1, and n is a minimum of 1.

[0010] Several coils are wound between the head connecting ring and the tail connecting ring, so that each radial permanent magnet between the two is enclosed in the coil. Multiple coils are distributed in the circumferential direction of the connecting ring. The input end of the coil is connected to the signal output module, and the output end of the coil is connected to the signal detection module.

[0011] Furthermore, the signal output module includes a signal generator and a power amplifier. The signal generator is connected to the input end of the coil through the power amplifier. The signal generator is used to emit an AC excitation signal, which is amplified by the power amplifier and sent to the coil through the input end. The current inside the coil and the static magnetic field of the permanent magnet group will form a torsional mode guided wave that propagates axially along the pipeline to be tested. When the torsional mode guided wave encounters a defect in the pipe wall, the torsional mode guided wave will be reflected and react to the current in the coil.

[0012] Furthermore, the signal detection module includes a signal preprocessing device and a signal receiver. The signal receiver is connected to the output end of the coil through the signal preprocessing device. The signal preprocessing device preprocesses the current in the coil affected by the torsional mode waveguide to form a feedback signal, and then transmits the feedback signal to the signal receiver for detection and processing.

[0013] Furthermore, there is a gap of no more than 2 mm between the side of the coil away from the center line of the connecting ring and the inner wall of the pipeline to be measured.

[0014] Furthermore, a plurality of wire grooves are provided on the outer surface of the connecting ring, and parts of the coils wound around the connecting ring are correspondingly embedded in the wire grooves.

[0015] Furthermore, one end of the connecting strip is fixedly connected to the connecting ring on one side thereof, and the other end of the connecting strip is detachably connected to the connecting ring on the other side thereof.

[0016] Furthermore, a groove is provided on the side surface where the connecting ring and the connecting strip are detachably connected, the connecting strip can be embedded in the groove, and the groove has an opening on the arc surface of the connecting ring, a pin hole is provided on the bottom surface of the groove close to the central axis of the connecting ring, a through hole is provided on the end portion where the connecting strip can be embedded in the groove, and pins are placed in the through hole and the pin hole to realize a detachable connection between the connecting ring and the connecting strip.

[0017] In another aspect, the present invention provides a method for non-destructive flaw detection in pipes based on Lorentz force, applicable to any of the above-mentioned non-destructive flaw detection devices in pipes based on Lorentz force, comprising:

[0018] S1, calculating a dispersion curve based on the material parameters of the pipeline to be tested, and determining the spacing between the centers of adjacent permanent magnet groups through the dispersion curve and the wavelength of the guided wave frequency of the torsional mode excited by the coil, thereby determining the number of radial permanent magnets contained in each permanent magnet group;

[0019] S2. Determine the number of connecting rings and permanent magnet groups based on the diameter, length, and signal-to-noise ratio of the pipeline to be tested, so that the signal strength and field range are adapted to the detection conditions of the pipeline to be tested. Connect the connecting rings using connecting bars, and place the radial permanent magnets of each permanent magnet group outside the connecting bars, thereby arranging the permanent magnet groups between adjacent connecting rings.

[0020] S3, set up coils, wind several coils between the head connecting ring and the tail connecting ring, and put each connecting ring and each radial permanent magnet into the coils, so that each coil is evenly distributed around the circumference of the connecting ring, and connect the coils between the signal output module and the signal detection module;

[0021] S4, place the transducer assembly into the pipe to be tested, and use the signal output module to input the processed AC excitation signal into the coil. The current in the coil, combined with the static magnetic field of the permanent magnet group, will form a torsional mode guided wave that propagates along the axial direction of the pipe to be tested. When the torsional mode guided wave encounters a defect in the pipe wall, it will be reflected and react to the current in the coil. The signal detection module then detects and processes the affected current in the coil.

[0022] Furthermore, when the detection signal received by the signal detection module is weak, the number of permanent magnet groups and connecting rings is increased; when the near field area is large, the number of permanent magnet groups and connecting rings is reduced.

[0023] Furthermore, the spacing between the centers of adjacent permanent magnet groups is half the wavelength of the torsional mode guided wave at a certain frequency.

[0024] Compared with the prior art, the beneficial effect of the present invention is that: when in use, after the coil is passed through the signal output module with an alternating current, an alternating eddy current field is induced on the inner surface of the skin depth of the pipeline to be tested. The eddy current field generates a Lorentz force along the tangential direction of the pipeline to be tested in the pipeline to be tested, thereby generating a shear force along the tangential direction in the pipeline to be tested and propagating in the pipeline to be tested, thereby stimulating a torsional mode guided wave. The torsional mode guided wave propagates along the axial direction of the pipeline to be tested and is reflected after encountering a wall defect. The reflected echo passes through the coil and enters the signal detection module for subsequent processing and mode extraction. This Lorentz force The force-type transducer principle does not require the pipeline to be ferromagnetic, because the generation of the Lorentz force only requires the generation of induced eddy currents and magnetic fields. Therefore, the only requirement for the pipeline is that the pipe wall material is metal. Therefore, through the above-mentioned setting, multiple groups of permanent magnets with connecting rings and connecting bars as carriers can be conveniently adjusted to adapt to pipelines of different materials and specifications. Arrayed periodic permanent magnet technology is formed in a highly adaptable manner, which improves the signal strength of the torsional mode guided wave it excites, thereby overcoming the defects in the existing technology and improving the detection accuracy without relying on ferromagnetic pipe wall conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the overall structure of one embodiment;

[0026] Figure 2 A schematic diagram of a portion of a transducer assembly according to one embodiment;

[0027] Figure 3 is a cross-sectional view of a connecting ring and a connecting strip according to one embodiment;

[0028] Figure 4 A radial permanent magnet magnetic field direction diagram of one embodiment;

[0029] Figure 5 A schematic diagram of the installation in the pipeline to be tested of one embodiment

[0030] Figure 6 A schematic diagram of a pipeline phase velocity dispersion curve according to one embodiment;

[0031] Figure 7 Schematic diagram of a pipeline group velocity dispersion curve according to one embodiment.

[0032] Description of reference numerals:

[0033] 11. Connecting ring; 111. Pin; 12. Connecting bar; 2. Radial permanent magnet; 3. Coil; 41. Signal generator; 42. Power amplifier; 51. Signal preprocessing device; 52. Signal receiver. DETAILED DESCRIPTION

[0034] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited by the specific embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0035] On the one hand, the present invention provides an in-pipe non-destructive testing device based on Lorentz force, which is used for performing non-destructive testing on a pipeline to be tested, comprising a signal output module, a signal detection module and a transducer assembly placed in the pipeline to be tested, wherein the transducer assembly is connected between the signal output module and the signal detection module, and the transducer assembly comprises: a plurality of connecting rings 11, a plurality of connecting bars 12, a permanent magnet group and a plurality of coils 3, wherein each connecting ring 11 is arranged side by side in the form of overlapping center lines, thereby having a head connecting ring 11 and a tail connecting ring 11; the length direction of the connecting bar 12 is parallel to the center line of the connecting ring 11, and two adjacent connecting rings 11 are detachably connected by a plurality of connecting bars 12; the permanent magnet group 3 is connected to the pipeline to be tested, wherein the connecting ring 11 is connected to the pipeline to be tested, wherein the connecting bar 12 ... The magnet group is located between two adjacent connecting rings 11. A permanent magnet group includes at least one radial permanent magnet 2. The radial permanent magnet 2 has a ring structure and its center line coincides with the center line of the connecting ring 11. The radial permanent magnet 2 is sleeved on the outside of multiple connecting bars 12 and is against the connecting bars 12. The number of permanent magnet groups is n, and the number of connecting rings 11 is n+1, where n is a minimum of 1. The coil 3 is wound between the head connecting ring 11 and the tail connecting ring 11, so that each radial permanent magnet 2 between the two is sleeved in the coil 3. Multiple coils 3 are distributed circumferentially in the connecting ring 11. The input end of the coil 3 is connected to the signal output module, and the output end of the coil 3 is connected to the signal detection module.

[0036] Specifically, please refer to Figures 1 to 7 During use, the transducer assembly is inserted into the pipe to be tested and connected to the corresponding signal output module and signal detection module. Since the radial permanent magnet 2 excites a radial static magnetic field in the entire circumferential direction, when the coil 3 wound along the side of the radial permanent magnet 2 is supplied with an alternating current through the signal output module, an alternating eddy current field is induced on the inner surface of the skin depth of the pipe to be tested. This eddy current field generates a Lorentz force along the tangential direction of the pipe to be tested, which in turn generates a shear force along the tangential direction of the pipe to be tested. This force propagates within the pipe to be tested, thereby stimulating a torsional modal waveguide. The torsional modal waveguide propagates along the axis of the pipe to be tested and is reflected after encountering a wall defect. The reflected echo passes through the coil 3 and enters the signal detection module for subsequent processing and modal extraction. This Lorentz force-based transducer principle does not require the pipe to be ferromagnetic, because the generation of the Lorentz force only requires the generation of induced eddy currents and magnetic fields. Therefore, the only requirement for the pipe wall is that the pipe be made of metal.

[0037] Due to the flaw detection principle of the transducer assembly, the material, diameter, length and signal-to-noise ratio of the pipeline to be tested must be considered, and the coil and the permanent magnet group need to be adjusted. Different situations require different numbers of permanent magnet groups, and the number of radial permanent magnets 2 in the permanent magnet group must be adjusted. Therefore, a detachable connection between the connecting ring 11 and the connecting bar 12 is specially provided. The connecting ring 11 is used as a bearing base structure that is convenient for extending into the pipeline to be tested and separating the permanent magnet groups. The connecting bar 12 is then laid between the connecting rings 11 as a sleeve support structure for the radial permanent magnets 2. The detachable connection between the connecting ring 11 and the connecting bar 12 facilitates adjustment of the number of permanent magnet groups and the number of radial permanent magnets 2 in each permanent magnet group.

[0038] Through the above arrangement, multiple permanent magnet groups, supported by connecting rings 11 and connecting bars 12, can be easily adjusted to accommodate pipes of varying materials and specifications. This provides a highly adaptable array of periodic permanent magnet (PPM) technology, enhancing the signal strength of the excited torsional mode guided waves and thus improving detection accuracy. This solves the problems mentioned in the prior art.

[0039] In this embodiment, the radial permanent magnet 2 is a radially magnetized annular magnet. This type of permanent magnet has not yet been used in the fields of ultrasonic guided waves and non-destructive testing. Its existing applications are for motor driving, generating a rotating magnetic field, magnetic bearings, and reducing friction. Therefore, in this embodiment, this technology is actually transferred. In order to adapt to the diameter of the slender pipe to be tested, a manufacturer-customized method is adopted to reduce its volume while maintaining its structure and function.

[0040] Furthermore, the signal output module includes a signal generator 41 and a power amplifier 42. The signal generator 41 is connected to the input end of the coil 3 through the power amplifier 42. The signal generator 41 is used to emit an AC excitation signal, which is amplified by the power amplifier 42 and sent to the coil 3 through the input end. The current inside the coil 3 cooperates with the static magnetic field of the permanent magnet group to form a torsional mode guided wave that propagates axially along the pipeline to be tested. When the torsional mode guided wave encounters a defect in the pipe wall, the torsional mode guided wave will be reflected and react to the current in the coil 3.

[0041] Furthermore, the signal detection module includes a signal preprocessing device 51 and a signal receiver 52. The signal receiver is connected to the output end of the coil 3 through the signal preprocessing device 51. The signal preprocessing device 51 preprocesses the current in the coil 3 affected by the torsional mode waveguide to form a feedback signal, and then transmits the feedback signal to the signal receiver 52 for detection and processing.

[0042] In this embodiment, the torsional mode guided wave formed by the permanent magnet group of coil 3 in the pipeline to be tested will propagate along the pipeline axis and be reflected when encountering a defect. When the reflected echo passes through coil 3, it will cause the induced voltage in coil 3 to change. By observing the change of this induced voltage over time through the signal detection module, it can be determined whether there is a defect in the pipeline and the defect can be located and evaluated.

[0043] Furthermore, there is a gap of no more than 2 mm between the side of the coil 3 away from the center line of the connecting ring 11 and the inner wall of the pipeline to be measured, thereby avoiding contact between the coil 3 and the pipeline to be measured, thereby affecting the transmission of the guided wave.

[0044] Furthermore, a plurality of wire grooves are provided on the outer surface of the connecting ring 11 , and portions of the coils 3 wound around the connecting ring 11 are correspondingly embedded in the wire grooves.

[0045] Furthermore, one end of the connecting bar 12 is fixedly connected to the connecting ring 11 on one side thereof, and the other end of the connecting bar 12 is detachably connected to the connecting ring 11 on the other side thereof.

[0046] Furthermore, a groove is provided on the side surface of the connecting ring 11 and the connecting strip 12 for detachable connection, the connecting strip 12 can be embedded in the groove, and the groove has an opening on the arc surface of the connecting ring 11, and a pin hole is provided on the bottom surface of the groove close to the central axis of the connecting ring 11, and a through hole is provided on the end portion of the groove in which the connecting strip 12 can be embedded, and a pin 111 is placed in the through hole and the pin hole to realize a detachable connection between the connecting ring 11 and the connecting strip 12.

[0047] In another aspect, the present invention provides a method for non-destructive flaw detection in pipes based on Lorentz force, applicable to any of the above-mentioned non-destructive flaw detection devices in pipes based on Lorentz force, comprising:

[0048] S1, calculating a dispersion curve based on the material parameters of the pipeline to be tested, and determining the spacing between the centers of adjacent permanent magnet groups through the dispersion curve and the wavelength of the guided wave frequency of the torsional mode excited by the coil 3, thereby determining the number of radial permanent magnets 2 included in each permanent magnet group;

[0049] S2. Determine the number of connecting rings 11 and permanent magnet groups based on the diameter, length, and signal-to-noise ratio of the pipeline to be tested, so that the signal strength and field range are adapted to the detection conditions of the pipeline to be tested. Connect the connecting rings 11 using connecting bars 12, and place the radial permanent magnets 2 of each permanent magnet group outside the connecting bars 12, thereby arranging the permanent magnet groups between adjacent connecting rings 11.

[0050] S3, set up coils 3, wind several coils 3 between the head connecting ring 11 and the tail connecting ring 11, and put each connecting ring 11 and each radial permanent magnet 2 into the coil 3, so that each coil 3 is evenly distributed around the circumference of the connecting ring 11, and connect the coils 3 between the signal output module and the signal detection module;

[0051] S4, place the transducer assembly into the pipe to be tested, and use the signal output module to input the processed AC excitation signal into the coil 3. The current in the coil 3 and the static magnetic field of the permanent magnet group will form a torsional mode guided wave that propagates along the axial direction of the pipe to be tested. When the torsional mode guided wave encounters a pipe wall defect, the torsional mode guided wave will be reflected and react to the current in the coil 3. The signal detection module then detects and processes the affected current in the coil 3.

[0052] In this embodiment, the guided wave group velocity dispersion curve, phase velocity dispersion curve and the structure of each mode of guided wave of the pipeline to be tested at different frequencies are obtained by semi-analytical finite element calculation based on the size of the pipeline to be tested, the Poisson's ratio and Young's modulus parameters of the material, which belongs to the existing technical means.

[0053] In this embodiment, the signal detection module collects the guided wave signal and performs signal post-processing and mode extraction. According to the parameters such as the size of the tested pipeline, the Poisson's ratio and Young's modulus of the material, the guided wave group velocity dispersion curve of the tested pipeline is obtained by semi-analytical finite element calculation (such as Figure 7 As shown in ), phase velocity dispersion curve (as shown in Figure 6 As shown in the figure) and the structure of each mode guided wave; in the figure, L(0,1) and L(0,2) are longitudinal guided waves, T(0,1) is the circumferential torsional wave, and F(1,1) and F(1,2) are non-axisymmetric bending waves.

[0054] Furthermore, when the detection signal received by the signal detection module is weak, the number of permanent magnet groups and connecting rings 11 is increased; when the near-field area is large, the number of permanent magnet groups and connecting rings 11 is reduced.

[0055] Furthermore, the spacing between the centers of adjacent permanent magnet groups is half the wavelength of the torsional mode guided wave at a certain frequency.

Claims

1. A nondestructive flaw detection device in a pipe based on Lorentz force, used for nondestructive flaw detection of a pipe to be tested, comprising a signal output module, a signal detection module and a transducer component placed in the pipe to be tested, wherein the transducer component is connected between the signal output module and the signal detection module, and is characterized in that: The transducer components include: A plurality of connecting rings (11), each connecting ring (11) being arranged side by side in a form where the center lines overlap, thereby comprising a connecting ring (11) at the head and a connecting ring (11) at the tail; A plurality of connecting strips (12), wherein the length direction of the connecting strips (12) is parallel to the center line of the connecting ring (11), and adjacent connecting rings (11) are detachably connected via the plurality of connecting strips (12); At least one permanent magnet group, one permanent magnet group between every two adjacent connecting rings (11), one permanent magnet group comprising at least one radial permanent magnet (2), the radial permanent magnet (2) being a ring body and having a center line that coincides with the center line of the connecting ring (11), the radial permanent magnet (2) being sleeved on the outside of a plurality of connecting strips (12) and abutting against the connecting strips (12); A plurality of coils (3) are wound between a head connecting ring (11) and a tail connecting ring (11), so that each radial permanent magnet (2) between the two is enclosed in the coil (3), and the plurality of coils (3) are distributed in the circumferential direction of the connecting ring (11), the input end of the coil (3) is connected to a signal output module, and the output end of the coil (3) is connected to a signal detection module.

2. The Lorentz force-based nondestructive flaw detection device in a pipe according to claim 1, characterized in that: The signal output module comprises a signal generator (41) and a power amplifier (42); the signal generator (41) is connected to an input end of the coil (3) via the power amplifier (42); the signal generator (41) is used to send an AC excitation signal, which is amplified by the power amplifier (42) and sent to the coil (3) via the input end in the form of current.

3. The Lorentz force-based nondestructive flaw detection device in a pipe according to claim 1, characterized in that: There is a gap of less than or equal to 2 mm between the side of the coil (3) away from the center line of the connecting ring (11) and the inner wall of the pipeline to be tested.

4. The non-destructive flaw detection device in a pipe based on Lorentz force according to claim 1, characterized in that: A plurality of wire grooves are provided on the outer surface of the connecting ring (11), and parts of the coils (3) wound around the connecting ring (11) are correspondingly embedded in the wire grooves.

5. The non-destructive flaw detection device in a pipe based on Lorentz force according to claim 1, characterized in that: One end of the connecting strip (12) is fixedly connected to the connecting ring (11) on one side thereof, and the other end of the connecting strip (12) is detachably connected to the connecting ring (11) on the other side thereof.

6. The Lorentz force-based nondestructive flaw detection device in a pipe according to claim 1, characterized in that: A groove is provided on the side surface of the connecting ring (11) and the connecting strip (12) for detachable connection, the connecting strip (12) can be embedded in the groove, and the groove is provided with an opening on the annular arc surface of the connecting ring (11), a pin hole is provided on the bottom surface of the groove close to the central axis of the connecting ring (11), a through hole is provided on the end of the groove for the connecting strip (12) to be embedded, and a pin (111) is arranged in the through hole and the pin hole to realize the detachable connection between the connecting ring (11) and the connecting strip (12).

7. A non-destructive flaw detection method in a pipe based on Lorentz force, applicable to the non-destructive flaw detection device in a pipe based on Lorentz force according to any one of claims 1 to 7, characterized in that: include: S1, calculating a dispersion curve according to the material parameters of the pipeline to be tested, and determining the spacing between the centers of adjacent permanent magnet groups through the dispersion curve and the waveguide wavelength of the torsional mode waveguide frequency excited by the coil (3), thereby determining the number of radial permanent magnets (2) contained in each permanent magnet group; S2, according to the pipe diameter, pipe length and signal-to-noise ratio of the pipeline to be tested, the number of connecting rings (11) and the number of permanent magnet groups are determined so that the signal strength and the field range are adapted to the detection conditions of the pipeline to be tested, and the connecting strips (12) are used to connect the connecting rings (11), and the radial permanent magnets (2) of each permanent magnet group are placed outside the connecting strips (12), so that the permanent magnet groups are arranged between adjacent connecting rings (11); S3, setting coils (3), winding a plurality of coils (3) between a head connecting ring (11) and a tail connecting ring (11), and sleeve each connecting ring (11) and each radial permanent magnet (2) in the coils (3), each coil (3) being evenly distributed in the circumferential direction of the connecting ring (11), and connecting the coils (3) between a signal output module and a signal detection module; S4, placing the energy conversion component in the pipeline to be tested, using the signal output module to input the processed AC excitation signal into the coil (3), the current in the coil (3) cooperates with the static magnetic field of the permanent magnet group to form a torsional mode guided wave in the pipeline to be tested that propagates along the axial direction of the pipeline to be tested, and when the torsional mode guided wave encounters a pipe wall defect, the torsional mode guided wave will be reflected and react to the current in the coil (3), and then the signal detection module detects and processes the affected current in the coil (3).

8. The method for nondestructive flaw detection in a pipe based on Lorentz force according to claim 7, characterized in that: When the detection signal received by the signal detection module is weak, the number of permanent magnet groups and connecting rings (11) is increased, and when the near field area is large, the number of permanent magnet groups and connecting rings (11) is reduced.

9. The method for nondestructive flaw detection in a pipe based on Lorentz force according to claim 7, characterized in that: The spacing between the centers of adjacent permanent magnet groups is half the wavelength of the torsional mode guided wave at a certain frequency.

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