A method for detecting eddy currents in pipes based on cross-excitation

Abstract

This invention discloses a pipe eddy current internal detection method based on cross-excitation, comprising: placing an internal detector inside the pipe to be inspected; the internal detector comprising: a first excitation coil generating a magnetic field propagating along the pipe wall direction; a second excitation coil generating a magnetic field perpendicular to the pipe wall, the first excitation coil being a certain distance from the second excitation coil; a receiving coil disposed between the second excitation coil and the pipe wall; a shielding sheet disposed between the first and second excitation coils; driving the first and second excitation coils to form a cross-magnetic field between the receiving coil and the pipe wall; controlling the internal detector according to a preset lift-off speed and moving speed, using the cross-magnetic field signal received by the receiving coil as the detection signal for the pipe to be inspected; and analyzing the detection signal to obtain the inner and outer wall defects of the pipe to be inspected. This invention enables the internal detector to detect outer wall defects of pipes without sacrificing the near-field eddy current's ability to detect minute defects such as cracks.

Description

Technical Field

[0001] This invention relates to the field of pipeline inspection, and more particularly to a pipeline eddy current inspection method based on cross-excitation. Background Technology

[0002] Non-destructive testing (NDT) is an important pipeline inspection technique. It involves using a range of physical and chemical phenomena, including light, electricity, sound, heat, and magnetism, to detect internal and external defects in engineering materials, components, and structures without damaging the material. This allows for the determination of the location, size, shape, and number of surface and internal defects, thereby assessing the degree of damage. After years of scientific research, NDT has developed a complete technical system, with various new technologies constantly emerging. Computer technology, pattern recognition, artificial intelligence, and various data processing techniques are all widely used in NDT.

[0003] Currently, the main technologies for detecting defects on the inner and outer walls of pipelines include magnetic flux leakage (MFL) testing, ultrasonic testing, and eddy current testing. MFL testing is relatively mature for large-diameter pipelines, but its cost is too high for small-diameter pipelines, the equipment is too large, and its throughput is poor. Ultrasonic testing has a large penetration depth and is suitable for detecting internal pipeline defects, but it requires a coupling agent to fill the gap between the ultrasonic probe and the test piece to ensure sufficient acoustic coupling, making the testing more difficult and difficult to automate.

[0004] Eddy current testing is a non-destructive testing method that utilizes the principle of electromagnetic induction to non-destructively evaluate certain properties of conductive materials and workpieces, or to detect defects, by measuring changes in induced eddy currents within the workpiece. In industrial production, eddy current testing is one of the main means of controlling the quality of various metallic materials and a few non-metallic conductive materials such as graphite and carbon fiber composites, and it holds an important position in the field of non-destructive testing technology. Eddy current testing is a non-destructive testing method based on the principle of electromagnetic induction, and it is applicable to conductive materials. When a conductor is placed in an alternating magnetic field, an induced current exists within the conductor, i.e., eddy currents are generated. Due to changes in various factors of the conductor itself (such as conductivity, permeability, shape, size, and defects), changes in eddy currents will occur. The testing method that uses this phenomenon to determine the properties and state of the conductor is called eddy current testing. Because there is a certain phase difference between the excitation current and the reaction current, and this phase difference changes with the properties of the test piece, information about the test piece is often detected by measuring the phase change. This phase change is closely related to the change in coil impedance. Most eddy current testing instruments are based on impedance analysis to identify various factors that cause changes in eddy currents. Because eddy currents exhibit the skin effect, eddy current testing can only detect surface and near-surface defects. Due to variations in specimen shape and testing location, the shape of the detection coil and its approach to the specimen also differ. To meet diverse testing needs, various detection coils and eddy current testing instruments have been designed.

[0005] Existing technologies for internal detectors that employ near-field eddy current detection can only generate eddy currents on the pipe surface to intelligently detect defects on the inner surface of the pipe. In other words, without sacrificing the ability of near-field eddy currents to detect minute defects such as cracks, these internal detectors cannot simultaneously detect defects on the outer wall of the pipe.

[0006] Therefore, providing a method for detecting eddy currents in pipes based on cross-excitation is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for detecting eddy currents in pipes based on cross-excitation.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] A first aspect of the present invention provides a method for detecting eddy currents in a pipe based on cross-excitation, comprising the following steps:

[0010] An internal detector is placed inside the pipe to be inspected. The internal detector includes: a first excitation coil that generates a magnetic field propagating along the pipe wall; a second excitation coil that generates a magnetic field perpendicular to the pipe wall, wherein the first excitation coil is a certain distance away from the second excitation coil; a receiving coil disposed between the second excitation coil and the pipe wall, and coaxially coupled to the second excitation coil; and a shielding sheet disposed between the first excitation coil and the second excitation coil.

[0011] The first excitation coil and the second excitation coil are driven to form a cross magnetic field between the receiving coil and the tube wall;

[0012] The internal detector is controlled according to the preset lift-off speed and moving speed, and the cross magnetic field signal received by the receiving coil is used as the detection signal of the pipeline to be detected.

[0013] By analyzing the detection signal, the defects on the inner and outer walls of the pipeline to be inspected are obtained.

[0014] Furthermore, the first excitation coil is a wound excitation coil, and the second excitation coil is a planar PCB excitation coil.

[0015] Furthermore, the receiving coil includes four layers of PCB rectangular differential coils, each layer of the sub-coil is provided with a via, and the upper and lower layers of the sub-coil are connected in series by copper wire passing through the via.

[0016] Furthermore, a resonant capacitor is connected in parallel between the input and output terminals of the receiving coil.

[0017] Furthermore, the specified distance is 2-3 times the pipe diameter.

[0018] Furthermore, the shielding sheet is a permalloy shielding sheet.

[0019] Furthermore, the first excitation coil and the second excitation coil are excited by a medium-frequency sine wave.

[0020] Furthermore, the planar PCB excitation coil is a planar PCB rectangular differential excitation coil.

[0021] Furthermore, the internal detector also includes: a signal generator for driving the first excitation coil and the second excitation coil; and a signal acquisition module for processing the signal from the receiving coil.

[0022] Further, the analysis of the detection signal to obtain the inner and outer wall defects of the pipeline to be detected includes:

[0023] The amplitude and phase of the detection signal are obtained, and defects on the inner and outer walls are judged based on historical experience; among them, the amplitude and phase of the internal defects are much larger than those of the external defects.

[0024] The beneficial effects of this invention are:

[0025] (1) In an exemplary embodiment of the present invention, the eddy current coil is excited by cross-excitation. The two magnetic fields cross below the second excitation coil to form a cross magnetic field that is detected by the receiving coil. This allows the receiving coil to detect not only defects on the inner wall of the pipe but also defects on the outer wall of the pipe. For defects inside the pipe, high-precision near-field eddy current detection is used. For defects outside the pipe, the traditional method of directly detecting the magnetic field is not used. Instead, the influence of the magnetic field penetrating the pipe wall on the near-field eddy current is detected indirectly, which improves the sensitivity to external defects.

[0026] The cross-excitation generated cross magnetic field can obtain the depth information of the pipeline, overcoming the shortcomings of near-field eddy currents which can only generate eddy currents on the pipeline surface to detect defects on the inner surface of the pipeline. This allows the internal detector to obtain the ability to detect defects on the outer wall of the pipeline without losing the ability of near-field eddy currents to detect small defects such as cracks.

[0027] (2) In another exemplary embodiment of the present invention, the second excitation coil uses a PCB planar coil, which has the advantages of small size, high sensitivity to surface defects, broad prospects in eddy current detection, and high sensitivity to cracks due to its small effective lift-off amount. It is directly manufactured using printed circuit board (PCB) technology, making it easy to permanently fix to the part to be inspected. Furthermore, the PCB has sufficient flexibility to allow the coil to conform to the surface, thus offering broad prospects for inspecting complex surface geometries. Simultaneously, the planar PCB excitation coil employs a differential rectangular structure, which facilitates the differentiation of defect portions, and the rectangular structure makes it easier to distinguish defects of different shapes compared to a circular structure.

[0028] (3) In another exemplary embodiment of the present invention, the receiving coil is a four-layer array, which makes it easy to print multiple coils on the same board to create a multi-coil array, thereby increasing the inspection range and reducing the inspection time; in addition, using rectangular coils makes it easier to splice and combine them when laid out in an array, and it is less sensitive to edge effects. The multi-layer structure of the receiving coil can improve the detection sensitivity on the one hand, and at the same time reduce the optimal detection frequency, effectively reducing the requirements for the excitation signal.

[0029] (4) In another exemplary embodiment of the present invention, a resonant capacitor is connected in parallel between the input and output terminals of the receiving coil; specifically, the added resonant capacitor can make the excitation circuit and the detection circuit reach a resonant state, increasing the coil voltage when a defect is detected, making the signal of the external defect of the pipeline more obvious and improving the detection capability of the detection device for defects on the inner and outer walls of the pipeline. The capacitor can be integrated with the receiving coil, improving the defect detection performance and being easy to implement.

[0030] (5) In another exemplary embodiment of the present invention, the first excitation coil and the second excitation coil are excited by a medium-frequency sine wave. Since the eddy current effect is affected by the skin depth, although high-frequency excitation has high detection sensitivity, the eddy current is only generated on the surface of the pipe wall. Low-frequency excitation has a high eddy current penetration depth but the signal is weak. In order to balance detection sensitivity and detection depth, this device uses a medium-frequency sine wave excitation coil, generally around 600KHZ. The receiving coil collects the signal of the cross magnetic field below the coil. The signal contains both the surface defect information of the pipe wall and the external and deep defect information of the pipe wall.

[0031] (6) In another exemplary embodiment of the present invention, the internal defect signal and the external defect signal of the cross-excited pipe eddy current detection device have a significant difference, which can distinguish between internal and external defects. Attached Figure Description

[0032] Figure 1 A flowchart of a pipe eddy current detection method based on cross-excitation provided as an exemplary embodiment of the present invention;

[0033] Figure 2 A schematic diagram of the structure of a cross-excitation-based eddy current detector in a pipeline, provided as an exemplary embodiment of the present invention;

[0034] Figure 3 A schematic diagram of the structure of a wound excitation coil provided for an exemplary embodiment of the present invention;

[0035] Figure 4 A schematic diagram of the structure of a PCB rectangular differential excitation coil provided as an exemplary embodiment of the present invention;

[0036] Figure 5 A schematic diagram of the structure of a receiving coil provided in an exemplary embodiment of the present invention;

[0037] Figure 6 A schematic diagram of the structure of a first-layer PCB rectangular differential coil provided as an exemplary embodiment of the present invention;

[0038] Figure 7 A schematic diagram of the structure of a second-layer PCB rectangular differential coil provided as an exemplary embodiment of the present invention;

[0039] Figure 8 A schematic diagram of the structure of a third-layer PCB rectangular differential coil provided as an exemplary embodiment of the present invention;

[0040] Figure 9 A schematic diagram of the structure of a fourth-layer PCB rectangular differential coil provided in an exemplary embodiment of the present invention;

[0041] Figure 10This is a schematic diagram of a ferromagnetic pipe with internal and external artificial defects provided in an exemplary embodiment of the present invention;

[0042] Figure 11 This is a schematic diagram illustrating the results of external defect detection of a ferromagnetic pipe without the introduction of a pipe eddy current detector based on cross-excitation in an exemplary embodiment of the present invention.

[0043] Figure 12 This is a schematic diagram showing the result of external defect detection in a ferromagnetic pipe using a pipe eddy current detector based on cross-excitation, provided in an exemplary embodiment of the present invention.

[0044] Figure 13 This is a schematic diagram illustrating the results of internal defect detection in a ferromagnetic pipe using a pipe eddy current detector based on cross-excitation, provided in an exemplary embodiment of the present invention.

[0045] Figure 14 This is a schematic diagram illustrating the results of external defect detection in a ferromagnetic pipe using a pipe eddy current detector based on cross-excitation, provided in an exemplary embodiment of the present invention.

[0046] In the figure, 1-first excitation coil, 101-directly coupled magnetic field, 102-indirectly coupled magnetic field, 2-second excitation coil, 3-receiving coil, 301-first layer PCB rectangular differential coil, 302-second layer PCB rectangular differential coil, 303-third layer PCB rectangular differential coil, 304-fourth layer PCB rectangular differential coil, 4-shielding sheet, 5-tube wall. Detailed Implementation

[0047] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] In the description of this invention, it should be noted that the directions or positional relationships indicated by terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of describing this 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 this invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0049] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0050] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0051] Eddy current testing is a non-destructive testing method that utilizes the principle of electromagnetic induction to non-destructively evaluate certain properties of conductive materials and workpieces, or to detect defects, by measuring changes in induced eddy currents within the inspected workpiece. In industrial production, eddy current testing is one of the main means of controlling the quality of various metallic materials and a few non-metallic conductive materials such as graphite and carbon fiber composites, and it holds an important position in the field of non-destructive testing technology. Eddy current testing is a non-destructive testing method based on the principle of electromagnetic induction, and it is applicable to conductive materials. When a conductor is placed in an alternating magnetic field, an induced current exists within the conductor, i.e., eddy currents are generated. Due to changes in various factors of the conductor itself (such as conductivity, permeability, shape, size, and defects), changes in eddy currents occur. The testing method that uses this phenomenon to determine the properties and state of the conductor is called eddy current testing. Because eddy currents have a skin effect, eddy current testing can only detect surface and near-surface defects. Due to differences in the shape of the specimen and the location of the test, the shape of the detection coil and the way it approaches the specimen also vary. To meet various testing needs, various detection coils and eddy current testing instruments have been designed.

[0052] Existing technologies for internal detectors that employ near-field eddy current detection can only generate eddy currents on the pipe surface to intelligently detect defects on the inner surface. This means that while maintaining the ability of near-field eddy currents to detect minute defects such as cracks, these detectors cannot simultaneously detect defects on the outer wall of the pipe. The following exemplary embodiments will illustrate this point:

[0053] See Figure 1 , Figure 1 An exemplary embodiment of the present invention provides a method for detecting eddy currents in a pipe based on cross-excitation, comprising the following steps:

[0054] The internal detector is placed inside the pipe to be inspected, such as... Figure 2As shown, the internal detector includes: a first excitation coil 1 that generates a magnetic field propagating along the pipe wall 5; a second excitation coil 2 that generates a magnetic field perpendicular to the pipe wall 5, wherein the first excitation coil 1 is a certain distance away from the second excitation coil 2; a receiving coil 3 disposed between the second excitation coil 2 and the pipe wall 5, and coaxially coupled to the second excitation coil 2; and a shielding sheet 4 disposed between the first excitation coil 1 and the second excitation coil 2.

[0055] The first excitation coil 1 and the second excitation coil 2 are driven to form a cross magnetic field between the receiving coil 3 and the tube wall 5;

[0056] The internal detector is controlled according to the preset lift-off speed and moving speed, and the cross magnetic field signal received by the receiving coil 3 is used as the detection signal of the pipeline to be detected.

[0057] By analyzing the detection signal, the defects on the inner and outer walls of the pipeline to be inspected are obtained.

[0058] Specifically, in this exemplary embodiment, when the second excitation coil 2 is energized, it generates a magnetic field perpendicular to the pipe wall 5 and generates a near-field eddy current region on the inner wall of the pipe wall 5. At this time, the near-field eddy current detection device composed of the second excitation coil 2 and the receiving coil 3 has a high sensitivity to defects on the inner wall surface of the pipe.

[0059] Simultaneously, when the first excitation coil 1 is energized, it generates a magnetic field propagating along the pipe wall 5. This includes a direct coupled magnetic field 101 generated by the first excitation coil 1 within the pipe, and an indirect coupled magnetic field 102 that penetrates the pipe wall 5 and intersects with the magnetic field generated by the second excitation coil 2 below the receiving coil 3 at the rear end of the device, forming a cross magnetic field. Since the direct coupled magnetic field 101 does not contain pipe defect information, it is shielded by a shielding plate 4 placed between the first and second excitation coils 1 and 2. If the receiving coil 3 receives this signal, its sensitivity to defects will decrease, potentially leading to misjudgment of defects. As for the indirect coupled magnetic field 102, according to the eddy current detection principle, its energy rapidly decays after penetrating the pipe wall 5 a second time. Generally, the signal directly acquired by the receiving coil 3 is relatively weak. Although it contains information about external defects in the pipe, it is difficult to directly identify the defect information. However, in this exemplary embodiment, the indirect coupling magnetic field 102 affects the magnetic field generated by the second excitation coil 2 and further affects the near-field eddy current region generated on the inner wall of the pipe wall 5. The eddy current flows in a uniform band shape. The eddy current changes direction at the defect. Because the eddy current changes, the secondary magnetic field generated by the eddy current changes, and thus the amplitude and phase of the receiving coil 3 change. Since the receiving coil 3 acquires the signal obtained by the influence of the indirect coupling magnetic field 102 penetrating the pipe wall 5 on the near-field eddy current generated by the second excitation coil 2, it also has good sensitivity to external defects in the pipe, thereby accurately detecting defect information (including inner wall defects and external field defects).

[0060] An internal detector is used to detect internal and external defects in ferromagnetic structures at a lift of 5 mm and a moving speed of 1 m / s. The detection results are then processed to obtain a detection signal diagram of the cross magnetic field signal. When the sensor passes through a defect-free position, the detection signal amplitude remains unchanged, while when the sensor passes through a defective position, the detection signal amplitude changes.

[0061] Traditional pipeline eddy current internal detection technology requires the use of far-field eddy currents with frequencies below 1 kHz to detect external pipeline defects. Although these technologies can generate magnetic fields that penetrate the pipe wall, the defect signals are relatively weak, typically only a few millivolts to tens of millivolts. In contrast, this invention employs a pipeline eddy current internal detector based on cross-excitation, which detects signal changes of hundreds of millivolts for internal pipe wall defects and tens to hundreds of millivolts for external defects. This allows the internal detector to detect external pipeline wall defects without sacrificing the ability of near-field eddy currents to detect minute defects such as cracks.

[0062] In summary, in this exemplary embodiment, a cross-excitation method is used to excite the eddy current coil. The two magnetic fields cross below the second excitation coil 2 to form a cross magnetic field, which is detected by the receiving coil 3. This allows the receiving coil 3 to detect defects not only inside the pipe wall but also outside the pipe wall. For internal pipe defects, high-precision near-field eddy current detection is used. For external pipe defects, instead of the traditional method of directly detecting the magnetic field, the traditional method of directly detecting the magnetic field is used. Instead, the influence of the magnetic field penetrating the pipe wall 5 on the near-field eddy current is detected indirectly, thus improving the sensitivity to external defects. More specifically, the first excitation coil 1 can generate a strong magnetic field inside the pipe wall, and part of the magnetic field can penetrate the pipe wall 5, thereby affecting the near-field eddy current generated by the second excitation coil 2 on the inner wall of the pipe. This allows the signal collected by the receiving coil 3 to simultaneously include both internal and external pipe defects, and both have high sensitivity.

[0063] The cross-excitation generated cross magnetic field can obtain the depth information of the pipeline, overcoming the shortcomings of near-field eddy currents which can only generate eddy currents on the pipeline surface to detect defects on the inner surface of the pipeline. This allows the internal detector to obtain the ability to detect defects on the outer wall of the pipeline without losing the ability of near-field eddy currents to detect small defects such as cracks.

[0064] More preferably, in an exemplary embodiment, the first excitation coil 1 is a wound excitation coil, and the second excitation coil 2 is a planar PCB excitation coil. More preferably, in an exemplary embodiment, the planar PCB excitation coil is a planar PCB rectangular differential excitation coil.

[0065] Specifically, such as Figure 3 As shown, the winding excitation coil is a cylindrical coil with a magnetic focusing device, and it is provided with an input interface and an output interface. The coil radius is r1, the wire diameter is d1, the number of turns is n1, and the thickness of the entire coil is w1. In another specific exemplary embodiment, the winding excitation coil is made of enameled wire with a wire diameter of 0.03mm, the coil diameter is 190mm, the number of turns is 800, and the coil width is 20mm.

[0066] like Figure 4 As shown, when the second excitation coil 2 is a planar PCB excitation coil, specifically a single-layer PCB rectangular differential excitation coil, it is equipped with an input interface input1 and an output interface output1; the length of the PCB rectangular differential excitation coil is a. 1 The width is b1, and the line diameter of the intermediate difference region is d. 21 The diameter of the remaining lines is d. 22 The line spacing is d 23 , and d 21 >d 22 .

[0067] The PCB planar coil used has advantages such as small size, high sensitivity to surface defects, and broad prospects in eddy current testing. Furthermore, due to its small effective lift-off amount, it is highly sensitive to cracks. Direct manufacturing using printed circuit board (PCB) technology allows for easy and permanent mounting to the parts to be inspected. In addition, the PCB has sufficient flexibility to allow the coil to conform to the surface, making it suitable for inspecting complex surface geometries. Moreover, the planar PCB excitation coil employs a differential rectangular structure, which facilitates the differentiation of defect portions, and the rectangular structure makes it easier to distinguish defects of different shapes compared to a circular structure.

[0068] More preferably, in an exemplary embodiment, the receiving coil 3 includes four layers of PCB rectangular differential coils, each layer of the sub-coil is provided with a via, and the upper and lower layers of the sub-coil are connected in series by copper wire passing through the via.

[0069] Specifically, such as Figure 5 The diagram shown is a schematic of the receiving coil 3 of the present invention. The receiving coil 3 includes a four-layer PCB rectangular differential coil, which has a rectangular structure with a length of a2, a width of b2, and a copper wire diameter of d. 21 The line spacing is d 23 Through holes are provided between different layers of coils, and sub-coils between different layers are connected in series by copper wire; an input interface (input2) and an output interface (output2) are provided.

[0070] In one specific exemplary embodiment, the wire diameter of the PCB rectangular differential coil in each layer ranges from 0.0665 to 0.1016 mm, the wire spacing ranges from 0.0665 to 0.1016 mm, the length ranges from 26.005 to 32.516 mm, and the width ranges from 12.520 to 19.620 mm.

[0071] The receiving coil 3 is equipped with three vias (via1, via2, and via3) for connecting the four layers of coils, and two interfaces (input2 and output2). Figure 6 As shown, one end of the rectangular differential coil 301 on the first layer PCB is connected to interface input2, and the other end is connected to via2; Figure 7 As shown, one end of the second-layer PCB rectangular differential coil 302 is connected to the first-layer PCB rectangular differential coil 301 through via 2, and the other end is connected to via 3; Figure 8 As shown, one end of the third-layer PCB rectangular differential coil 303 is connected to the second-layer PCB rectangular differential coil 302 through via 3, and the other end is connected to via 1; Figure 9As shown, one end of the fourth layer PCB rectangular differential coil 304 is connected to the third layer PCB rectangular differential coil 303 through via via1, and the other end is connected to interface output2.

[0072] In this exemplary embodiment, multiple coils can be easily printed on the same board to create a multi-coil array, thereby increasing the inspection range and reducing inspection time. Furthermore, using rectangular coils makes them easier to assemble when laid out in an array, and reduces sensitivity to edge effects. The receiving coil 3, with its multi-layer structure, can improve detection sensitivity while simultaneously lowering the optimal detection frequency, effectively reducing the requirements for the excitation signal.

[0073] More preferably, in an exemplary embodiment, a resonant capacitor is connected in parallel between the input and output terminals of the receiving coil 3.

[0074] Specifically, in this exemplary embodiment, it can be connected to, such as Figure 4 The added resonant capacitor between input2 and output2 can make the excitation circuit and the detection circuit reach a resonant state, increasing the coil voltage when a defect is detected, making the signal of external defects in the pipeline more obvious and improving the detection device's ability to detect defects on the inner and outer walls of the pipeline.

[0075] More specifically, the resonant capacitor is used to couple the receiving coil 3 with the first excitation coil 1, thereby enhancing the signal of the first excitation coil 1 and improving the identification of external defects. The magnetic field of the first excitation coil 1 at the front end is very weak when it is transmitted to the receiving coil 3 along the tube wall 5, and a resonant capacitor is needed to enhance signal coupling and improve sensitivity.

[0076] In addition, the capacitors can be integrated with the receiving coil 3, which improves the defect detection performance and is easy to implement.

[0077] In one specific exemplary embodiment, the resonant capacitor has a capacitance of 680pF.

[0078] More preferably, in an exemplary embodiment, the distance is 2-3 times the pipe diameter.

[0079] More preferably, in one exemplary embodiment, the shielding sheet 4 is a permalloy shielding sheet. In a more specific exemplary embodiment, the shielding sheet 4 is a circular sheet made of permalloy with a diameter of 190 mm and a thickness of 1 mm.

[0080] More preferably, in an exemplary embodiment, the first excitation coil 1 and the second excitation coil 2 are excited by a mid-frequency sine wave.

[0081] Specifically, in this exemplary embodiment, the defects on the inner and outer walls of the pipe are detected using the same method, eddy current detection, but the magnetic fields detected are different. The receiving coil 3 simultaneously receives magnetic fields from two directions. Since the eddy current effect is affected by the skin depth, although high-frequency excitation has high detection sensitivity, the eddy current is only generated on the surface of the pipe wall 5. Low-frequency excitation has a high eddy current penetration depth but the signal is weak. In order to balance detection sensitivity and detection depth, this device uses a medium-frequency sine wave excitation coil, generally around 600KHZ. The receiving coil 3 collects the signal of the cross magnetic field below the coil. The signal simultaneously contains information on surface defects of the pipe wall 5 and information on external and deep defects of the pipe wall 5.

[0082] More preferably, in an exemplary embodiment, the internal detector further includes:

[0083] A signal generator that drives the first excitation coil 1 and the second excitation coil 2.

[0084] Specifically, in this exemplary embodiment, the signal generator generates a sinusoidal signal of a certain frequency and amplifies its power to drive the first excitation coil 1 at the front end of the drive device and the second excitation coil 2 at the rear end.

[0085] More preferably, in an exemplary embodiment, the internal detector further includes:

[0086] A signal acquisition module that processes the signal from receiving coil 3.

[0087] In one specific exemplary embodiment, the subsequent signal acquisition module may include a signal processing module and a host computer. The signal processing module may be an FPGA. The FPGA processes the acquired data and uploads it to the host computer, which then analyzes and displays the data. This content is a technical means commonly used in this field and will not be elaborated upon here.

[0088] Based on the above exemplary embodiments, it can be seen that the input and output interfaces of the wound excitation coil (preferred exemplary embodiment of the first excitation coil 1) are connected to the signal generator (excitation signal source). Then, the input2 and output2 of the planar PCB rectangular differential excitation coil (preferred exemplary embodiment of the second excitation coil 2) are connected to the signal generator (excitation signal source). The input3 and output3 of the receiving coil 3 are connected to the resonant capacitor and then to the signal acquisition module. The wound excitation coil is placed 2-3 times the pipe diameter in front of the receiving coil 3, and the assembly is placed together with the device into the pipe under test (this can be achieved using a specially designed fixing device). The signal generator generates a sinusoidal signal of a certain frequency and amplifies its power. The driving excitation coil and the planar PCB rectangular differential excitation coil (first excitation coil 1 and second excitation coil) are driven. Due to the change in the magnetic flux generated by the excitation coil, according to Maxwell's equations, the winding excitation coil forms a magnetic field that propagates along the pipe wall and affects the planar PCB rectangular differential excitation coil to form eddy currents on the pipe. The eddy currents flow in a uniform band. The flow direction of the eddy currents changes at the defect. Because the eddy currents change, the secondary magnetic field generated by the eddy currents changes, which in turn changes the amplitude and phase of the receiving coil 3, thereby accurately detecting the defect information. The two magnetic fields cross below the excitation coil to form a cross magnetic field, which is detected by the receiving coil 3. Thus, the receiving coil 3 can detect not only defects on the inner wall of the pipe but also defects on the outer wall of the pipe.

[0089] More preferably, in an exemplary embodiment, analyzing the detection signal to obtain the inner and outer wall defects of the pipe to be detected includes:

[0090] The amplitude and phase of the detection signal are obtained, and defects on the inner and outer walls are judged based on historical experience; among them, the amplitude and phase of the internal defects are much larger than those of the external defects.

[0091] Figure 10 This is a ferromagnetic conduit with internal and external artificial defects provided in an exemplary embodiment of the present invention, wherein... Figure 10 The three internal defects on the left have dimensions of 10mm*10mm*5mm, 10mm*10mm*3mm, and 10mm*5mm*3mm. Figure 10 The right side shows two external defects, with dimensions of 10mm*10mm*3mm and 10mm*5mm*3mm.

[0092] Figure 11 and Figure 12The diagrams show the results of external defect detection of the ferromagnetic pipe using a pipe eddy current detector based on cross-excitation provided in the exemplary embodiments described above, and the results of external defect detection of the ferromagnetic pipe using a pipe eddy current detector based on cross-excitation provided in the exemplary embodiments described above.

[0093] Specifically, in this exemplary embodiment, an internal detector is used to detect defects of different sizes in a ferromagnetic pipe. The detection is performed with a lift of 5mm and a moving speed of 1m / s. The detection results are then processed to obtain... Figure 11 and Figure 12 The detection signal diagram shown illustrates that when the sensor passes through a defect-free location, the detection signal amplitude remains constant. However, when the sensor passes through a defective location, the detection signal amplitude changes, and the magnitude of this change is related to the size of the defect. In this experiment, Figure 11 The image shows the detection signal of a conventional planar probe used to detect external defects in a pipeline without a cross-excitation probe. It can be seen that the conventional eddy current probe does not have obvious defect signals. Figure 12 The cross-excitation method is used to detect external defects in the pipeline using an in-pipe detector. It can be seen that the cross-excitation detection probe can obtain defect information and can identify defects relatively clearly.

[0094] Figure 13 and Figure 14 The diagrams show the results of internal defect detection in the ferromagnetic pipe using the cross-excitation-based pipe eddy current detector provided in the above exemplary embodiments, and the results of external defect detection in the ferromagnetic pipe using the cross-excitation-based pipe eddy current detector provided in the above exemplary embodiments. The upper diagram shows the signal amplitude change, and the lower diagram shows the phase change.

[0095] Specifically, in this exemplary embodiment, an internal detector is used to detect internal and external defects in the ferromagnetic core at a lifting distance of 5 mm and a moving speed of 1 m / s. The detection results are then processed to obtain... Figure 13 and Figure 14 The detection signal diagram shown indicates that the detection signal amplitude remains unchanged when the sensor passes through a defect-free location, but changes when the sensor passes through a defective location. Figure 13 The signal diagram for detecting internal defects in a pipe using a cross-excited eddy current detector shows that both the amplitude and phase of the signal change significantly. Figure 14 The signal diagram for detecting external defects in a pipeline using a cross-excited eddy current detector shows that the amplitude and phase of the signal also change significantly, which can identify external defects. Furthermore, the phase signals of external defects differ from those of internal defects, which can be used as a basis for differentiation.

[0096] More specifically, comparing the signals of the two types of defects reveals that the signal of the internal defect is significantly larger than that of the external defect in both amplitude and phase. Furthermore, the detector is highly sensitive to the phase of the internal defect, far exceeding the phase of the external signal. This difference serves as the basis for determining whether the defect is on the inner or outer wall. Therefore, the significant difference between the internal and external defect signals in the cross-excited pipe eddy current detection device allows for the differentiation between internal and external defects.

[0097] in, Figures 11-14 The upper part represents the signal amplitude change, with the horizontal axis representing the number of sampling points (in units) and the vertical axis representing the signal amplitude (in millivolts, mV). The lower part represents the phase change, with the horizontal axis representing the number of sampling points (which can correspond to distance and time) (in units) and the vertical axis representing the signal phase difference (in radians).

[0098] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method of in-pipe eddy current internal inspection based on cross excitation, characterized in that: Includes the following steps: An internal detector is placed inside the pipe to be inspected. The internal detector includes: a first excitation coil that generates a magnetic field propagating along the pipe wall; a second excitation coil that generates a magnetic field perpendicular to the pipe wall, wherein the first excitation coil is at a certain distance from the second excitation coil, the certain distance being 2-3 times the pipe diameter, and the first and second excitation coils are excited by a medium-frequency sine wave; a receiving coil disposed between the second excitation coil and the pipe wall, and coaxially coupled to the second excitation coil; and a shielding sheet disposed between the first and second excitation coils. The first excitation coil and the second excitation coil are driven to form a cross magnetic field between the receiving coil and the tube wall; The internal detector is controlled according to the preset lift-off speed and moving speed, and the cross magnetic field signal received by the receiving coil is used as the detection signal of the pipeline to be detected. By analyzing the detection signal, the defects on the inner and outer walls of the pipeline to be inspected are obtained.

2. The method for detecting eddy currents in a pipe based on cross-excitation according to claim 1, characterized in that: The first excitation coil is a wound excitation coil, and the second excitation coil is a planar PCB excitation coil.

3. The method for detecting eddy currents in a pipe based on cross-excitation according to claim 1, characterized in that: The receiving coil includes four layers of PCB rectangular differential coils. Each layer of the sub-coil is provided with a via, and the upper and lower layers of the sub-coil are connected in series by copper wire passing through the via.

4. The method for detecting eddy currents in a pipe based on cross-excitation according to claim 1, characterized in that: A resonant capacitor is connected in parallel between the input and output terminals of the receiving coil.

5. The method for detecting eddy currents in a pipe based on cross-excitation according to claim 1, characterized in that: The shielding sheet is a permalloy shielding sheet.

6. The method for detecting eddy currents in a pipe based on cross-excitation according to claim 2, characterized in that: The planar PCB excitation coil is a planar PCB rectangular differential excitation coil.

7. The method for detecting eddy currents in a pipe based on cross-excitation according to claim 1, characterized in that: The internal detector further includes: a signal generator for driving the first excitation coil and the second excitation coil; and a signal acquisition module for processing the signal from the receiving coil.

8. The method for detecting eddy currents in a pipe based on cross-excitation according to claim 1, characterized in that: The analysis of the detection signal yields the defects on the inner and outer walls of the pipe to be inspected, including: The amplitude and phase of the detection signal are obtained, and defects on the inner and outer walls are judged based on historical experience; among them, the amplitude and phase of the internal defects are much larger than those of the external defects.

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