A pulsed eddy current detection device and method for pipes with insulation layer

Abstract

This invention provides a pulsed eddy current testing device and method for pipelines with insulation layers, belonging to the field of non-destructive testing technology for pipelines. It can at least partially solve the problems of existing pulsed eddy current testing methods, such as lift-off fluctuations and electromagnetic shielding interference caused by the outer metal protective layer, low testing reliability, and the need to remove the insulation layer. This invention includes: a flexible sensing strip and a control module. The flexible sensing strip is composed of multiple sensing strip segments assembled by a connecting mechanism and fitted onto the outside of the pipeline to be tested. From the inside out, it includes a lift-off compensation layer, an electromagnetic sensing layer, and a magnetic shielding layer. The lift-off compensation layer includes an airbag unit to adaptively conform to the surface of the outer protective layer to eliminate lift-off fluctuations. The electromagnetic sensing layer includes an excitation unit and a differential receiving unit to cancel common-mode interference from the outer protective layer at the hardware level. The magnetic shielding layer includes a magnetic unit array to concentrate the magnetic field and enhance penetration. This invention achieves in-service testing without removing the insulation layer through three-layer synergy.

Description

Technical Field

[0001] This invention belongs to the field of pipeline non-destructive testing technology, specifically relating to a pulse eddy current testing device and method for pipelines with insulation layers. Background Technology

[0002] Large-diameter pipelines, such as the main steam pipelines, feedwater pipelines, reheat hot section pipelines, reheat cold section pipelines, and header connecting pipes in power plant boiler heating network systems, are typically covered with insulation layers such as aluminum silicate fiber, and the outside of the insulation layer is wrapped with galvanized iron, aluminum, or stainless steel sheet as a protective layer. These pipelines can reach lengths of several kilometers and contain numerous welds, elbows, and tees. These areas are considered weak points in the pipeline system due to welding stress and media impact. During long-term service, these pipelines suffer from problems such as corrosion under the insulation layer, erosion thinning, mechanical damage, and structural deterioration, making them key areas for maintenance.

[0003] However, the actual inspection of the aforementioned pipelines requires the complete removal of the outer protective layer and insulation layer, as well as grinding of the area to be inspected. This process necessitates the erection of a large amount of scaffolding, and the removal and restoration of the insulation layer, along with the pipeline grinding, is costly and time-consuming, severely impacting the power plant's maintenance schedule. Furthermore, prolonged work at height increases labor intensity and safety risks.

[0004] While conventional pulsed eddy current testing theoretically possesses the capability to perform testing without removing the insulation layer, it faces two major technical bottlenecks in field operations: First, the outer metal protective layer usually has overlapping seams and dents, which causes the lift-off value between the probe and the underlying pipe to fluctuate drastically during the scanning process, seriously interfering with the thickness measurement accuracy.

[0005] Secondly, the metal protective layer such as galvanized iron sheet has electromagnetic shielding and skin effect, which makes it difficult for low-frequency pulse magnetic fields to penetrate effectively. The secondary eddy current signal generated by the bottom pipe wall is extremely weak and has a low signal-to-noise ratio, making it easy to misjudge the change in the thickness of the outer skin as corrosion of the pipe wall.

[0006] Currently, there is a lack of a device that can effectively overcome the dual interference of lift-off fluctuations and metal outer shielding, and achieve in-service testing of the insulation layer without disassembly. Summary of the Invention

[0007] The present invention aims to solve at least one of the technical problems existing in the prior art, and provides a pulse eddy current detection device and method for pipes with insulation layer.

[0008] This invention provides a pulsed eddy current detection device for pipes with insulation layers, comprising: A flexible sensing strip includes multiple sensing strip segments assembled by a connecting mechanism and fitted onto the outside of the pipe to be tested. The flexible sensing strip, from the inside out, includes a lift-off compensation layer, an electromagnetic sensing layer, and a magnetic shielding layer. A control module is used to be electrically connected to the flexible sensor; The lift-off compensation layer includes an airbag unit for adjusting the adhesion between the electromagnetic sensing layer and the outer protective layer surface of the pipeline under test by inflating and deflating the airbag; the electromagnetic sensing layer includes an excitation unit and a differential receiving unit disposed on a flexible substrate, the differential receiving unit being used to synchronously acquire eddy current signals and cancel common-mode interference generated by the outer protective layer; the magnetic shielding layer includes a magnetic unit array and a shielding shell.

[0009] Furthermore, the airbag unit adopts a multi-chamber independently divided structure, and each chamber is equipped with a pressure sensing unit; the control module includes an air source component and a multi-way proportional solenoid valve group. The air source component is connected to each chamber through the multi-way proportional solenoid valve group to independently adjust the pressure of each chamber according to the feedback signal of each pressure sensing unit and maintain it within a preset pressure range.

[0010] Furthermore, the excitation unit is an excitation coil disposed on the flexible substrate; the differential receiving unit includes a first receiving coil and a second receiving coil disposed on both sides of the excitation coil, and the output terminals of the first receiving coil and the second receiving coil are connected to a differential amplifier so as to use the common-mode rejection characteristics of the differential amplifier to subtract and cancel the in-phase interference signal generated by the outer protective layer.

[0011] Furthermore, the magnetic focusing unit array includes multiple magnetic focusing covers arranged in an array on the back side of the excitation unit. The magnetic focusing covers are in the shape of an inverted trapezoidal funnel, and the inner wall of the magnetic focusing covers has an inclination angle of 35° to 55°, so as to concentrate the magnetic field generated by the excitation unit into a vertical magnetic flux beam that penetrates the insulation layer and the outer protective layer of the pipe under test.

[0012] Furthermore, the connecting mechanism is a hydraulic pin quick-lock mechanism, used to assemble or disassemble multiple segments of the sensing strip along the circumference of the pipe to be tested.

[0013] Furthermore, the flexible sensing strip also includes a wear-resistant layer disposed inside the lift-off compensation layer; the control module includes a remote control terminal, which is wirelessly connected to the flexible sensing strip, and the remote control terminal is equipped with a detection process parameter setting unit and a result display unit.

[0014] Another aspect of the present invention provides a pulsed eddy current detection method for pipes with insulation layers, implemented using the aforementioned pulsed eddy current detection device for pipes with insulation layers, comprising: Multiple segments of the sensor strip are fitted over the outside of the pipe to be tested and assembled by the connecting mechanism, so that the flexible sensor strip surrounds the outer protective layer surface of the pipe to be tested, and the flexible sensor strip is connected to the control module by a composite cable. Inflate the airbag unit to cause the electromagnetic sensing layer and the magnetic shielding layer to deform inward and adhere to the surface of the outer protective layer, and maintain the pressure inside the airbag unit within a preset pressure range. The excitation unit is driven to emit a pulse signal. The pulse signal is converged by the magnetic focusing unit array and penetrates the outer protective layer to reach the bottom pipe wall. The differential receiving unit synchronously collects the eddy current attenuation signal fed back by the bottom pipe wall and the interference signal generated by the outer protective layer, and performs differential processing to cancel the common mode interference to obtain the detection signal of the bottom pipe wall.

[0015] Furthermore, in the step of inflating the airbag unit, pressure data is collected in real time by the pressure sensing unit in each of the chambers and fed back to the control module. The control module dynamically adjusts the air intake and exhaust volume of each chamber according to the pressure data through the multi-way proportional solenoid valve group to maintain the pressure of each chamber between 0.2MPa and 0.4MPa.

[0016] Furthermore, the detection signal is characterized by features extracted by the control module and transmitted to the remote control terminal via wireless communication, and the remote control terminal generates a wall thinning distribution map of the pipe under test.

[0017] Furthermore, during the axial drag scanning process, the pressure sensing unit within the airbag unit monitors the changes in the bonding pressure between each chamber and the outer protective layer in real time. The control module dynamically fine-tunes the air intake and exhaust volume of each chamber according to the changes in bonding pressure to maintain constant force contact between the electromagnetic sensing layer and the surface of the outer protective layer. After the detection is completed, the control module issues an exhaust command to depressurize and contract the airbag unit, disconnect the composite cable, and remove the flexible sensing strip.

[0018] The beneficial effects of this invention are as follows: This invention uses a flexible sensing strip to form a three-layer composite structure consisting of a lift-off compensation layer, an electromagnetic sensing layer, and a magnetic shielding layer, arranged sequentially from the inside out. Multiple segments of the sensing strip are assembled and fitted onto the outside of the pipeline under test through a connecting mechanism, enabling pulsed eddy current detection of the pipeline without removing the insulation layer.

[0019] The airbag unit in the lift-off compensation layer fills the physical gaps in the overlapping seams and recessed areas of the outer protective layer through adaptive deformation during inflation and deflation. This ensures that the electromagnetic sensing layer always maintains a constant fit with the surface of the outer protective layer, thereby eliminating signal distortion caused by lift-off value fluctuations during dynamic detection.

[0020] The differential receiving unit in the electromagnetic sensing layer adopts a dual-coil symmetrical structure to synchronously acquire signals and perform differential amplification. By utilizing the common-mode rejection characteristic, the in-phase interference signal generated by the outer protective layer is directly subtracted and canceled at the hardware level. The eddy current attenuation signal of the bottom pipe wall is extracted at the signal front end, reducing the computational dependence on the subsequent algorithm.

[0021] The magnetic unit array in the magnetic shielding layer utilizes the spatial compression effect of high permeability material and funnel geometry to force the originally divergent magnetic field generated by the excitation unit into a high-density vertical magnetic flux bundle. This allows the pulsed magnetic field to penetrate the insulation layer and outer protective layer with concentrated energy and reach the bottom tube wall, significantly improving the signal penetration depth and signal-to-noise ratio.

[0022] In addition, the modular design of the multi-segment sensing belt, assembled through a connecting mechanism, eliminates the costly process of peeling and restoring the insulation layer, reducing labor intensity and shortening the time spent working at heights. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the overall structure and testing of a pulse eddy current testing device for a pipe with insulation layer according to a specific embodiment of the present invention. Figure 2 This is a schematic diagram illustrating the connection method of multiple sensing band segments in a pulse eddy current detection device for a pipe with insulation layer, according to a specific embodiment of the present invention. Figure 3 This is a schematic diagram comparing the magnetic field distribution of a magnetic focusing unit array according to a specific embodiment of the present invention with that of a traditional eddy current detection method; Figure 4 This is a schematic diagram illustrating the hardware noise reduction principle of a differential receiving unit according to a specific embodiment of the present invention.

[0024] The components include: 1. Shielding shell, 2. Magnetizing cover, 3. Excitation coil, 4. Differential receiving coil, 5. Airbag unit, 6. Wear-resistant layer, 7. Flexible circuit board layer, 8. Wire, 9. Composite cable, 10. Battery compartment, 11. Pneumatic-electric quick-connect port, 12. Controller data connection port, 13. Controller housing, 14. Air extraction port, 15. Main control and signal processing board, 16. Bamboo-shaped antenna, 17. Air source assembly, 18. Airbag inflation and deflation control module, 19. Signal transceiver module, 20. Pressure sensing unit, 21. Hydraulic pin quick-lock mechanism, 22. Remote control housing, 23. Controller control module, 24. Detection process parameter setting unit, 25. Result display unit, 26. Signal antenna, and 27. Multi-channel proportional solenoid valve group. Detailed Implementation

[0025] To make the objectives, technical solutions, and beneficial effects of this application clearer, the following detailed description, in conjunction with the accompanying drawings and specific embodiments, further illustrates this application. It should be understood that the specific embodiments described in this specification are merely for explaining this application and are not intended to limit it.

[0026] In the description of this invention, it should be understood that the terms "inner," "outer," "upper," "lower," "axial," "circumferential," and "radial," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0027] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly, and can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections, direct connections, or indirect connections through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0028] See Figure 1 and Figure 2 The present invention provides a pulsed eddy current detection device for pipes with insulation layers, comprising a flexible sensing belt and a control module, wherein: The flexible sensing strip is assembled from four segments via a hydraulic pin quick-locking mechanism 21. The outer diameter of each segment is slightly larger than the outer diameter of the pipe being tested. During testing, the four segments are fitted onto the outside of the pipe and circumferentially closed using the hydraulic pin quick-locking mechanism 21. From the inside out, the flexible sensing strip includes a lift-off compensation layer, an electromagnetic sensing layer, and a magnetic shielding layer.

[0029] The control module is connected to the flexible sensing strip via composite cable 9. Composite cable 9 is an integrated pneumatic and electrical composite cable, which integrates both pneumatic piping and electrical signal transmission wires within the same outer sheath, enabling synchronous control of pneumatic charging / discharging and electrical signal transmission. One end of composite cable 9 is connected to the flexible sensing strip via pneumatic-electric quick-connect port 11, and the other end is connected to the controller data connection port 12 on the controller housing 13 of the control module.

[0030] Specifically, the airbag unit 5 in the lift-off compensation layer is made of high-strength, wear-resistant polyurethane. The airbag unit 5 adopts a multi-chamber independently divided structure, with a pressure sensing unit 20 in each chamber. The air source component 17 in the control module is a small air compressor, which is connected to each chamber via a multi-way proportional solenoid valve group 27. The multi-way proportional solenoid valve group 27 consists of multiple miniature proportional solenoid valves, each controlling the intake and exhaust of an independent chamber. The airbag inflation / deflation control module 18 in the control module independently adjusts the pressure of each chamber based on the feedback signals from each pressure sensing unit 20, maintaining it between 0.2 MPa and 0.4 MPa. In the tightened state, the airbag unit 5 adaptively deforms and fills the physical gaps in the overlapping seams and localized depressions on the outer protective layer, thereby eliminating lift-off fluctuations during dynamic detection.

[0031] Furthermore, the flexible substrate of the electromagnetic sensing layer is made of polyimide material with a thickness of 0.1 mm to 0.3 mm, combining lightweight and flexibility. The excitation unit is an excitation coil 3 disposed on the flexible substrate. The differential receiving unit includes a first receiving coil and a second receiving coil symmetrically disposed on both sides of the excitation coil 3, which together constitute a differential receiving coil 4. The output terminals of the first receiving coil and the second receiving coil are connected to a differential amplifier. The common-mode rejection characteristic of the differential amplifier is used to subtract and cancel the strong, in-phase electromagnetic interference signal generated by the outer protective layer, thereby extracting the weak eddy current attenuation signal of the bottom tube wall at the hardware bottom layer.

[0032] Furthermore, the magnetic focusing shielding layer consists of two parts: a magnetic focusing unit array and a shielding shell. The magnetic focusing unit array includes multiple magnetic focusing covers 2, which are made of permalloy material with extremely high initial permeability, greater than 50,000. The magnetic focusing covers 2 are in the shape of an inverted trapezoidal funnel and are arrayed and attached to the back side of the excitation coil 3. The inner wall inclination angle of the magnetic focusing covers 2... The setting is within the range of 35° to 55°. The magnetic focusing shield 2 acts as a physical magnetic lens, utilizing the low magnetic resistance characteristics of permalloy and the spatial compression effect of funnel geometry to forcibly converge the originally diverging magnetic field lines, transforming them into a high-density vertical magnetic flux beam. This allows the concentrated energy to penetrate the insulation layer and outer protective layer, directly reaching the target detection pipeline. The shielding shell 1 is located on the outermost side of the magnetic focusing shielding layer and is made of flexible conductive fabric to block external power frequency and electromagnetic interference.

[0033] Based on the above basic implementation method, the flexible sensing strip also includes a wear-resistant layer 6 disposed inside the lift-off compensation layer. The wear-resistant layer 6 is the innermost layer that is closely attached to the surface of the outer protective layer. During the process of dragging and scanning the flexible sensing strip along the pipeline axis, the wear-resistant layer 6 protects the airbag unit 5 from being scratched by the sharp edges and burrs on the surface of the outer protective layer.

[0034] In one specific embodiment, a hydraulic pin quick-lock mechanism 21 is disposed at the mating end face of two adjacent sensor strip segments. The hydraulic pin quick-lock mechanism 21, driven by hydraulic pressure, pushes a locking pin into a locking groove on the end face of the opposite sensor strip segment, causing the locking pin to form surface contact with the groove wall and generating sufficient friction to maintain the locked state. The locking time of a single hydraulic pin quick-lock mechanism 21 does not exceed 10 seconds, enabling the segmented assembly and disassembly of sensor strip segments without additional tools.

[0035] In another specific embodiment, the control module further includes a remote control terminal. The remote control terminal includes a remote control housing 22, a controller control module 23, a detection process parameter setting unit 24, a result display unit 25, and a signal antenna 26. The remote control terminal and the signal transceiver module 19 within the controller housing 13 establish a wireless communication link via the bamboo-shaped antenna 16. The detection process parameter setting unit 24 is used to set detection process parameters such as pulse frequency, number of repetitions, and scanning speed. The result display unit 25 is used to display a real-time distribution map of the thinning of the pipe wall under the insulation layer for inspection personnel to interpret.

[0036] In another embodiment of the invention, the controller housing 13 further includes a main control and signal processing board 15, a battery compartment 10, and an exhaust port 14. The main control and signal processing board 15 is used to control the transmission timing of the pulse power drive module, acquire the differentially amplified eddy current attenuation signal, and extract features. The battery compartment 10 provides a portable power supply for the control module. The exhaust port 14 is used to vent the air circuit system after detection is completed.

[0037] Specifically, the pneumatic pipeline section within the composite cable 9 is connected to the multi-way proportional solenoid valve group 27, while the electrical signal transmission wire section is connected to the main control and signal processing board 15. Both ends of the composite cable 9 are equipped with quick-connect pneumatic and electrical ports 11, enabling simultaneous connection and disconnection of the pneumatic and electrical circuits.

[0038] In one specific embodiment, the airbag unit 5 is made of flexible reinforced silicone, and has 6 to 12 chambers arranged sequentially along the circumferential direction of the flexible sensing strip. Pressure sensing units 20 are embedded inside the walls of each chamber, with a range of 0 to 0.6 MPa and a resolution of 0.005 MPa. The response time of each solenoid valve in the multi-channel proportional solenoid valve group 27 does not exceed 150 ms, ensuring that the pressure in each chamber can be adjusted in real time to follow the changes in the surface contour of the outer protective layer during drag-and-drop scanning.

[0039] In another specific embodiment, an array of excitation coils 3 and differential receiving coils 4 is integrated on the flexible substrate. The number of excitation coils 3 is 8 to 16, arranged at equal intervals along the circumferential direction of the flexible sensing strip. Each excitation coil 3 has a receiving coil on each side, forming a group of differential receiving units. Multiple groups of differential receiving units are arranged sequentially along the circumferential direction, forming an array probe covering the complete circumferential cross-section of the pipe under test. A differential amplifier is disposed on the flexible circuit board layer 7 and connected to each group of differential receiving units. A wire 8 collects and transmits the electrical signals on the flexible circuit board layer 7 to the composite cable 9.

[0040] In one specific embodiment, the number of magnetic condensing covers 2 corresponds one-to-one with the number of excitation coils 3, with each magnetic condensing cover 2 covering one excitation coil 3. The upper opening width of the magnetic condensing cover 2 is larger than the outer diameter of the excitation coil 3, and the lower opening width is smaller than the upper opening width, forming a funnel-shaped channel that gradually narrows from the outside to the inside. After the magnetic lines of force are emitted from the excitation coil 3, they enter the upper opening of the magnetic condensing cover 2, are gradually compressed along the inclined inner wall, and finally exit from the lower opening as a high-density vertical magnetic flux beam, penetrating the insulation layer and outer protective layer of the pipe under test.

[0041] In another specific embodiment, the shielding shell 1 is made of a flexible conductive fabric woven from silver-plated fibers, with a thickness of 0.2 mm to 0.5 mm, which provides shielding attenuation against 50 Hz power frequency interference and surrounding electromagnetic radiation while maintaining flexibility.

[0042] In another specific embodiment, see Figure 3 The permalloy funnel-shaped magnetic shield 2 exhibits a significant difference in magnetic field distribution compared to traditional eddy current detection methods. In traditional eddy current detection, the magnetic flux generated by the excitation coil expands and diverges, with only a small portion reaching the surface of the pipe under test, resulting in insufficient penetration due to energy dispersion. However, with the magnetic shield 2, the divergent magnetic lines of force are forcibly converged by the funnel structure of the shield 2, significantly increasing the magnetic flux density and forming a highly concentrated vertical magnetic field beam. This allows the pulsed magnetic field to penetrate the insulation layer and outer protective layer with sufficient energy, inducing a stronger eddy current signal in the bottom pipe wall, providing a higher signal-to-noise ratio for subsequent signal processing.

[0043] In another specific embodiment, see Figure 4The hardware noise reduction principle of the differential receiving unit is as follows: The first receiving coil (differential receiving coil A) and the second receiving coil (differential receiving coil B) are symmetrically distributed on both sides of the excitation coil 3, and they synchronously acquire signals. Because the outer protective layer (galvanized iron sheet) is close to the two receiving coils, the amplitude and phase of the interference signals generated by it are basically the same, constituting common-mode interference. Due to the slight difference in the positions of the two receiving coils and the asymmetry of the magnetic field distribution, the eddy current attenuation signal from the bottom pipe wall generates a differential-mode component in the two receiving coils. The signals from both receiving coils are simultaneously input to the differential amplifier, which subtracts the two signals, canceling out the common-mode interference. The differential-mode signal (i.e., the actual eddy current attenuation signal from the bottom pipe wall) is retained and amplified. Subsequently, the amplified signal enters the subsequent signal processing circuit for further filtering and feature extraction.

[0044] In one specific embodiment, based on the above-described apparatus, the detection method includes the following steps: Step 1: The staff brings the device to the site and selects four suitable sensor strip segments based on the diameter of the pipe to be tested. The four sensor strip segments are then sequentially fitted onto the outside of the pipe to be tested, with the end of each sensor strip segment aligned with the end of the adjacent sensor strip segment. The sensor strip segments are then connected and fixed using the hydraulic pin quick-locking mechanism 21, so that the flexible sensor strip surrounds the outer protective layer surface of the pipe to be tested to form a complete circumferential ring.

[0045] Step 2: Connect the flexible sensing strip to the control module via composite cable 9. Insert the pneumatic quick-connect port 11 at one end of composite cable 9 into the pneumatic quick-connect port 11 at the end of the flexible sensing strip, and connect the other end to the controller data connection port 12 on the controller housing 13 to establish a pneumatic and data transmission channel.

[0046] Step 3: Turn on the power to the control module. The main control and signal processing board 15 completes initialization, and the air source component 17 starts.

[0047] Step 4: The airbag inflation / deflation control module 18 controls the multi-way proportional solenoid valve group 27 to inflate each chamber. As the pressure in each chamber gradually increases, the airbag unit 5 expands inward, pushing the outer electromagnetic sensing layer and magnetic shielding layer to deform inward. After the airbag inflates, under the circumferential closure constraint of the flexible sensing band, each chamber independently inflates and adaptively fills the overlap seams and pit gaps on the surface of the outer protective layer, making the electromagnetic sensing layer and magnetic shielding layer tightly adhere to the surface of the outer protective layer. In areas where there are overlap seams and pits in the outer protective layer, the local chambers of the airbag unit 5 independently inflate and adaptively fill the physical gaps. The pressure sensing unit 20 in each chamber collects pressure data in real time and feeds it back to the airbag inflation / deflation control module 18. The airbag inflation / deflation control module 18 dynamically adjusts the air intake and exhaust volume of each chamber through the multi-way proportional solenoid valve group 27, so that the pressure of each chamber is stably maintained within the preset pressure range of 0.2MPa to 0.4MPa.

[0048] Step 5: In the above-mentioned bonding state, the main control and signal processing board 15 triggers the pulse power drive module to sequentially or synchronously transmit high-energy square wave pulse signals to each excitation coil 3 in the array. The magnetic field generated by the pulse signal is compressed and focused by the corresponding magnetic shield 2, and then penetrates the outer protective layer to reach the bottom tube wall as a high-density vertical magnetic flux bundle.

[0049] Step Six: The secondary eddy current signal generated in the bottom pipe wall and the interference signal generated in the outer protective layer are synchronously captured by the first and second receiving coils in each differential receiving unit. The two signals are subtracted at the hardware level by a differential amplifier, canceling the common-mode interference generated by the outer protective layer, while retaining and amplifying the eddy current attenuation signal from the bottom pipe wall. The hardware-denoised signal is then used by the main control and signal processing board 15 to extract features.

[0050] Step 7: The main control and signal processing board 15 wirelessly transmits the feature data to the remote control terminal via the signal transceiver module 19 and the bamboo antenna 16. The controller module 23 of the remote control terminal receives the data and generates a real-time distribution map of the pipe wall thinning of the pipeline under test on the result display unit 25 for analysis and identification by the testing personnel.

[0051] Step 8: During the axial dragging scan or crossing uneven sections, the pressure sensing unit 20 in each chamber monitors the changes in the contact pressure in real time. When the pressure sensing unit 20 detects that the pressure in a certain chamber deviates from the preset pressure range, it feeds back the deviation signal to the airbag inflation / deflation control module 18. The airbag inflation / deflation control module 18 dynamically fine-tunes the air intake and exhaust volume of the chamber through the proportional solenoid valve of the corresponding path, thereby ensuring that the electromagnetic sensing layer always maintains constant contact with the outer protective layer surface during the scan, eliminating dynamic lift-off fluctuations.

[0052] Step 9: After the current pipe section is inspected, turn off the pulse excitation power supply and stop signal transmission and reception.

[0053] Step 10: The airbag inflation / deflation control module 18 issues an exhaust command, the multi-way proportional solenoid valve group 27 is fully opened to perform pressure relief, the airbag unit 5 contracts, and the electromagnetic sensing layer and the magnetic shielding layer are separated from the outer protective layer and are in a tightly fitted state.

[0054] Step 11: Disconnect the pneumatic quick-connect ports 11 at both ends of the composite cable 9 to separate the connection between the flexible sensing strip and the control module.

[0055] Step 12: Release the hydraulic pin quick-lock mechanism 21, and remove the four sensor belt sections in sequence to complete the test.

[0056] To aid in a better understanding of the present invention, a more comprehensive and specific embodiment is described, in which the present invention provides a pulsed eddy current detection device for pipes with insulation layers, comprising: The flexible sensing belt is assembled from six sensing belt segments via a hydraulic pin quick-locking mechanism 21. The six sensing belt segments are fitted onto the outside of the main steam pipe with a diameter of 600mm. From the inside out, the flexible sensing belt includes a lift-off compensation layer, an electromagnetic sensing layer, and a magnetic shielding layer. The inner side of the lift-off compensation layer is also provided with a wear-resistant layer 6.

[0057] The airbag unit 5 in the lift-off compensation layer is made of high-strength, wear-resistant polyurethane material and has 10 independent chambers arranged sequentially along the circumferential direction. Each chamber contains a pressure sensing unit 20 with a range of 0 to 0.6 MPa and a resolution of 0.005 MPa. The air source component 17 in the control module is a small air compressor with a rated output pressure of 0.6 MPa. The air source component 17 is connected to the 10 independent chambers via 10 miniature proportional solenoid valves in the multi-channel proportional solenoid valve group 27. The airbag inflation / deflation control module 18 collects pressure data from each pressure sensing unit 20 with a control cycle of 50 ms, calculates the target intake and exhaust volume for each chamber using a PID control algorithm, and drives the corresponding proportional solenoid valves to perform inflation / deflation operations, stabilizing the pressure in each chamber at a preset operating point of 0.3 MPa.

[0058] The flexible substrate of the electromagnetic sensing layer is made of 0.15mm thick polyimide material. Twelve sets of excitation coils 3 are arranged at equal intervals along the circumferential direction on the flexible substrate. Each set of excitation coils 3 has a receiving coil on each side, forming 12 differential receiving units. Differential amplifiers are mounted on the flexible circuit board layer 7, with a total of 12 differential amplifier channels, each corresponding to one of the 12 differential receiving units. The common-mode rejection ratio of each differential amplifier channel is greater than 80dB. Wires 8 collect the 12 differential output signals from the flexible circuit board layer 7 and transmit them to the main control and signal processing board 15 via composite cables 9.

[0059] The magnetic focusing unit array in the magnetic focusing shielding layer includes 12 magnetic focusing covers 2, each corresponding to one of 12 sets of excitation coils 3. The magnetic focusing covers 2 are made of permalloy material with an initial magnetic permeability greater than 80,000, and are formed after vacuum annealing. The magnetic focusing covers 2 are in the shape of an inverted trapezoidal funnel, with an upper opening width of 30mm, a lower opening width of 15mm, a height of 20mm, and an inner wall inclination angle. The angle is 45°. The shielding shell 1 is made of silver-plated fiber woven flexible conductive fabric with a thickness of 0.3mm, and the shielding attenuation for 50Hz power frequency interference is greater than 40dB.

[0060] The control module includes a controller housing 13, which houses a main control and signal processing board 15, an airbag inflation / deflation control module 18, a signal transceiver module 19, and a battery compartment 10. The main control and signal processing board 15 uses an ARM processor with a 1GHz clock speed and 16-channel synchronous acquisition capability. The signal transceiver module 19 establishes a wireless communication link with the remote control terminal via a bamboo-shaped antenna 16. The remote control terminal includes a remote control housing 22, a controller control module 23, a detection process parameter setting unit 24, a result display unit 25, and a signal antenna 26. The result display unit 25 is a 1280×720 resolution LCD screen.

[0061] The wear-resistant layer 6 is made of polytetrafluoroethylene and has a thickness of 0.5 mm. It is set on the inner surface of the airbag unit 5.

[0062] Based on the above-described apparatus, the detection method of this embodiment includes the following steps: Step 1: The staff brings the device to the site and selects six suitable sensor strip segments. The six sensor strip segments are then sequentially fitted onto the outside of the main steam pipeline to be tested, with the end of each sensor strip segment aligned with the end of the adjacent sensor strip segment. The sensor strip segments are then connected and fixed using the hydraulic pin quick-locking mechanism 21, so that the flexible sensor strip surrounds the outer protective layer surface of the pipeline to be tested, forming a complete circumferential ring.

[0063] Step 2: Connect the flexible sensing strip to the control module via composite cable 9. Insert the pneumatic quick-connect port 11 at one end of composite cable 9 into the pneumatic quick-connect port 11 at the end of the flexible sensing strip, and connect the other end to the controller data connection port 12 on the controller housing 13 to establish a pneumatic and data transmission channel.

[0064] Step 3: Power on the control module; the main control and signal processing board 15 completes initialization. On the remote terminal, set the pulse frequency to 100Hz, the number of repetitions to 32, and the scanning speed to 50mm / s via the detection process parameter setting unit 24. The air supply component 17 starts.

[0065] Step 4: The airbag inflation / deflation control module 18 controls the 10 proportional solenoid valves in the multi-channel proportional solenoid valve group 27 to simultaneously inflate the 10 independent chambers. As the pressure in each chamber gradually increases, the airbag unit 5 expands inward, pushing the electromagnetic sensing layer and the magnetic shielding layer to deform inward, making them tightly adhere to the surface of the outer protective layer. In areas where there are overlaps and pits in the outer protective layer, the corresponding chambers adaptively fill the physical gaps through independent inflation. The 10 pressure sensing units 20 collect pressure data in real time at a 50ms cycle and feed it back to the airbag inflation / deflation control module 18. The airbag inflation / deflation control module 18 calculates the target intake and exhaust volume of each chamber through a PID control algorithm, drives the corresponding proportional solenoid valves to perform operations, and keeps the pressure in each chamber stable at 0.3MPa.

[0066] Step 5: Under the above-mentioned bonding state, the main control and signal processing board 15 triggers the pulse power drive module to sequentially transmit square wave pulse signals to the 12 sets of excitation coils 3. The magnetic field generated by each set of excitation coils 3 is compressed and gathered by the corresponding magnetic shield 2, and then penetrates the outer protective layer and the insulation layer with a high-density vertical magnetic flux bundle to reach the bottom tube wall.

[0067] Step Six: The secondary eddy current signal generated in the bottom pipe wall and the interference signal generated in the outer protective layer are synchronously captured by the first and second receiving coils in the 12 sets of differential receiving units. The two signals are subtracted at the hardware level through 12 differential amplifier channels, canceling the common-mode interference generated by the outer protective layer, and retaining and amplifying the eddy current attenuation signal from the bottom pipe wall. The 12 signals after hardware denoising are acquired by the 16-channel synchronous acquisition system of the main control and signal processing board 15, and the eddy current attenuation time constant and peak amplitude characteristics are extracted.

[0068] Step 7: The main control and signal processing board 15 wirelessly transmits the 12 characteristic data channels to the remote control terminal via the signal transceiver module 19 and the bamboo antenna 16. The controller module 23 of the remote control terminal receives the data and generates a real-time distribution map of the pipe wall thinning of the pipeline under test on the result display unit 25, so that the testing personnel can analyze the distribution of pipe wall corrosion and erosion thinning.

[0069] Step 8: While observing the thinning distribution map using a handheld remote terminal, the inspector drags the flexible sensing strip at a constant speed along the axial direction. During the dragging and scanning process, when the flexible sensing strip crosses the overlap seam or uneven section of the outer protective layer surface, the pressure sensing unit 20 of the corresponding chamber detects a pressure deviation from the preset operating point of 0.3 MPa and feeds back the deviation signal to the airbag inflation / deflation control module 18. The airbag inflation / deflation control module 18 dynamically fine-tunes the air intake and exhaust volume of the chamber through the corresponding proportional solenoid valve, restoring the pressure of the chamber to 0.3 MPa within 150 ms, thereby ensuring that the 12 sets of differential receiving units maintain constant contact with the outer protective layer surface during the scanning process and eliminating dynamic lift-off fluctuations.

[0070] Step 9: After the current pipe section is inspected, turn off the pulse excitation power supply via the remote control terminal to stop signal transmission and reception.

[0071] Step 10: The airbag inflation / deflation control module 18 issues an exhaust command, all 10 proportional solenoid valves open to release pressure, the 10 independent chambers complete the exhaust within 3 seconds, the airbag unit 5 contracts, and the electromagnetic sensing layer and magnetic shielding layer separate from the outer protective layer and are in a tightly fitted state.

[0072] Step 11: Disconnect the pneumatic quick-connect ports 11 at both ends of the composite cable 9 to separate the connection between the flexible sensing strip and the control module.

[0073] Step 12: Release the locking of the six hydraulic pin quick-lock mechanisms 21 one by one, and remove the six sensor belt segments in sequence to complete the test.

[0074] In summary, the embodiments disclosed herein have at least the following technical effects: This invention constructs a flexible adaptive anti-interference architecture with multi-field coupling of "air-magnetic-electric" by setting the flexible sensing strip into a three-layer composite structure from the inside out: a lift-off compensation layer, an electromagnetic sensing layer, and a magnetic shielding layer. The airbag unit in the lift-off compensation layer is controlled by multi-chamber independent pressure closed-loop control, enabling each chamber to independently adapt to deformation and fill the physical gaps in the overlapping seams and local depressions on the outer protective layer. This ensures that the electromagnetic sensing layer maintains constant contact with the surface of the outer protective layer during both static bonding and dynamic scanning, thereby completely eliminating signal distortion and thickness measurement errors caused by lift-off value fluctuations in traditional pulsed eddy current detection.

[0075] The differential receiving unit in the electromagnetic sensing layer adopts a dual-coil symmetrical distribution structure. The two receiving coils synchronously acquire signals and then subtract them directly at the hardware level via a differential amplifier. Since the electromagnetic interference signals generated by the outer protective layer on the two receiving coils have basically the same amplitude and phase and belong to common-mode interference, they are canceled out after subtraction. However, the eddy current attenuation signal from the bottom tube wall generates differential-mode components in the two receiving coils due to the difference in magnetic field distribution. These components are retained and amplified after subtraction. This hardware-level noise reduction method moves the signal purification work to the front end of the acquisition process, reducing the computational power dependence and latency of subsequent digital signal processing algorithms.

[0076] The magnetic shielding layer uses a permalloy material with an initial magnetic permeability greater than 50,000 and is shaped like an inverted trapezoidal funnel. Utilizing the low magnetic reluctance of permalloy and the spatial compression effect of the funnel geometry, the magnetic field lines originally diverging outwards from the excitation coil are forcibly concentrated into a high-density vertical magnetic flux bundle. This allows the pulsed magnetic field to penetrate the thick insulation layer and metal protective shell with concentrated energy, inducing eddy current signals in the bottom tube wall with significantly higher intensity than traditional detection methods, greatly improving the penetration depth and signal-to-noise ratio.

[0077] In addition, the flexible sensing belt adopts a modular design with multiple sensing belt segments assembled by a hydraulic pin quick-locking mechanism. It can be installed on the outside of the pipeline for detection without removing the pipeline insulation layer and outer protective layer. This eliminates the high-cost preliminary procedures such as insulation layer peeling and restoration and pipeline grinding in traditional detection methods, greatly reducing the maintenance cycle and labor intensity, while also reducing the time spent working at height and personnel safety risks.

[0078] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A pulsed eddy current testing apparatus for a pipe with an insulating layer, characterized in that, include: The flexible sensing strip includes multiple sensing strip segments for assembly by a connecting mechanism and sleeved on the outside of the pipe to be tested. The flexible sensing strip includes, from the inside to the outside, a lift-off compensation layer, an electromagnetic sensing layer and a magnetic shielding layer. as well as A control module is used to be electrically connected to the flexible sensor; The lift-off compensation layer includes an airbag unit for adjusting the adhesion between the electromagnetic sensing layer and the outer protective layer surface of the pipeline under test by inflating and deflating the airbag; the electromagnetic sensing layer includes an excitation unit and a differential receiving unit disposed on a flexible substrate, the differential receiving unit being used to synchronously acquire eddy current signals and cancel common-mode interference generated by the outer protective layer; the magnetic shielding layer includes a magnetic unit array and a shielding shell.

2. A pulsed eddy current testing apparatus for a pipe with an insulating layer according to claim 1, characterized in that The airbag unit adopts a multi-chamber independently divided structure, and each chamber is equipped with a pressure sensing unit; the control module includes an air source component and a multi-way proportional solenoid valve group. The air source component is connected to each chamber through the multi-way proportional solenoid valve group to independently adjust the pressure of each chamber according to the feedback signal of each pressure sensing unit and maintain it within a preset pressure range.

3. The pulse eddy current detection device for pipes with insulation layer according to claim 1, characterized in that, The excitation unit is an excitation coil disposed on the flexible substrate; the differential receiving unit includes a first receiving coil and a second receiving coil disposed on both sides of the excitation coil, and the output terminals of the first receiving coil and the second receiving coil are connected to a differential amplifier so as to use the common-mode rejection characteristics of the differential amplifier to subtract and cancel the in-phase interference signal generated by the outer protective layer.

4. The pulse eddy current detection device for pipes with insulation layer according to claim 1, characterized in that, The magnetic focusing unit array includes multiple magnetic focusing covers arranged in an array on the back side of the excitation unit. The magnetic focusing covers are in the shape of an inverted trapezoidal funnel, and the inner wall of the magnetic focusing covers has an inclination angle of 35° to 55°, so as to concentrate the magnetic field generated by the excitation unit into a vertical magnetic flux beam that penetrates the insulation layer and the outer protective layer of the pipe under test.

5. The pulse eddy current detection device for pipes with insulation layer according to claim 1, characterized in that, The connecting mechanism is a hydraulic pin quick-lock mechanism, used to assemble or disassemble multiple segments of the sensing strip along the circumference of the pipe to be tested.

6. The pulse eddy current detection device for pipes with insulation layer according to claim 1, characterized in that, The flexible sensing strip also includes a wear-resistant layer disposed inside the lift-off compensation layer; the control module includes a remote control terminal, which is wirelessly connected to the flexible sensing strip, and the remote control terminal is equipped with a detection process parameter setting unit and a result display unit.

7. A pulsed eddy current detection method for pipes with insulation layer, characterized in that, The pulse eddy current detection device for pipes with insulation layer as described in any one of claims 1 to 6 is used, comprising: Multiple segments of the sensor strip are fitted over the outside of the pipe to be tested and assembled by the connecting mechanism, so that the flexible sensor strip surrounds the outer protective layer surface of the pipe to be tested, and the flexible sensor strip is connected to the control module by a composite cable. Inflate the airbag unit to cause the electromagnetic sensing layer and the magnetic shielding layer to deform inward and adhere to the surface of the outer protective layer, and maintain the pressure inside the airbag unit within a preset pressure range. The excitation unit is driven to emit a pulse signal. The pulse signal is converged by the magnetic focusing unit array and penetrates the outer protective layer to reach the bottom pipe wall. The differential receiving unit synchronously collects the eddy current attenuation signal fed back by the bottom pipe wall and the interference signal generated by the outer protective layer, and performs differential processing to cancel the common mode interference to obtain the detection signal of the bottom pipe wall.

8. The pulse eddy current detection method for pipes with insulation layer according to claim 7, characterized in that, The airbag unit adopts a multi-chamber independently divided structure, and each chamber is equipped with a pressure sensing unit. The control module includes a multi-way proportional solenoid valve group. In the step of inflating the airbag unit, the pressure sensing unit in each chamber collects pressure data in real time and feeds it back to the control module. The control module dynamically adjusts the air intake and exhaust volume of each chamber according to the pressure data through the multi-way proportional solenoid valve group to maintain the pressure of each chamber between 0.2MPa and 0.4MPa.

9. The pulse eddy current detection method for pipes with insulation layer according to claim 7, characterized in that, The detection signal is characterized by features extracted by the control module and transmitted to the remote control terminal via wireless communication. The remote control terminal then generates a wall thinning distribution map of the pipe under test.

10. The pulse eddy current detection method for pipes with insulation layer according to claim 7, characterized in that, The airbag unit adopts a multi-chamber independently divided structure, and each chamber is equipped with a pressure sensing unit. The control module includes a multi-way proportional solenoid valve group. During the axial drag scanning process, the pressure sensing unit in the airbag unit monitors the change in the bonding pressure between each chamber and the outer protective layer in real time. The control module dynamically fine-tunes the air intake and exhaust volume of each chamber according to the change in bonding pressure to maintain constant force contact between the electromagnetic sensing layer and the surface of the outer protective layer. After the test is completed, the control module issues an exhaust command to depressurize and contract the airbag unit, disconnect the composite cable, and remove the flexible sensing strip.

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