A method and system for detecting defects in a metal pipe based on eddy current induction

Abstract

This invention discloses a method and system for detecting defects in metal pipes based on eddy current induction. It solves the problems of poor detection accuracy, inability to locate defects, and inability to measure defect dimensions in existing metal pipe defect detection methods. The method includes the following steps: establishing a two-dimensional axisymmetric model of the metal pipe with an external circumferential defect using a CFD algorithm, and fitting a linear function of the magnetic field amplitude and defect geometric parameters; applying an alternating excitation magnetic field to the metal pipe to obtain the induced magnetic field generated on the pipe surface; obtaining the resultant magnetic field amplitude and acquiring a scanning curve showing the change of the resultant magnetic field amplitude with the scanning position through axial scanning; determining whether a defect exists on the metal pipe surface based on the scanning curve, and if a defect exists, locating the defect center based on the scanning curve, and obtaining the defect depth and width using an inversion algorithm. This achieves simultaneous quantitative measurement of defect depth and width, as well as precise location of metal pipe defects.

Description

Technical Field

[0001] This invention relates to the field of nondestructive testing technology for metal pipes, and in particular to a method and system for detecting defects in metal pipes based on eddy current induction. Background Technology

[0002] Metal pipelines are critical infrastructure in oil and gas transportation, chemical production, and marine engineering, and their structural integrity directly affects the operational safety of industrial systems. During pipeline manufacturing and installation, fluctuations in welding processes can easily lead to circumferential defects such as cracks, lack of fusion, and incomplete penetration in the circumferential weld area. During long-term service, environmental factors such as corrosion and fatigue can exacerbate these defects. Statistics show that over 70% of leaks during pipeline pressure testing and initial operation are caused by circumferential weld quality issues, seriously threatening personnel and equipment safety. Therefore, conducting regular and accurate non-destructive testing of pipeline circumferential defects is crucial to ensuring the long-term reliable operation of pipelines.

[0003] Patent CN118731150A describes a device and method for detecting defects in pipe circumferential welds that resist lifting. It sends AC sinusoidal signals to a first orthogonal excitation unit and a second orthogonal excitation unit via an excitation signal generator. This causes the first and second excitation coils, orthogonally arranged in the first orthogonal excitation unit, and the third and fourth excitation coils, orthogonally arranged in the second orthogonal excitation unit, to generate a composite alternating magnetic field. By detecting the amplitude of the induced voltage generated by vertical cutting, it can achieve rapid and accurate detection of defects in pipe circumferential welds at different positions and angles, thereby improving detection efficiency and reducing detection costs. However, it only utilizes a single magnetic field generated by the excitation unit and does not consider the magnetic field of the excitation unit itself, resulting in poor detection accuracy. Furthermore, it only achieves qualitative detection of defects and cannot locate or measure the size of defects. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of poor detection accuracy, inability to locate defects, and inability to measure the size of defects in metal pipes based on eddy current induction in the prior art. It provides a method and system for detecting defects in metal pipes based on eddy current induction, which realizes quantitative measurement of defect depth and width, and achieves accurate measurement of metal pipe defects.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for detecting defects in metal pipes based on eddy current induction includes the following steps: S1: A two-dimensional axisymmetric model for detecting metal pipes with external circumferential defects is established using CFD algorithms. A linear function of the resultant magnetic field amplitude and defect geometric parameters is fitted to establish a resultant magnetic field amplitude-defect fitting model. S2: Apply an alternating excitation magnetic field to the metal pipe to obtain the induced magnetic field generated on the surface of the metal pipe; S3: Obtain the amplitude of the resultant magnetic field by obtaining the scanning curve of the amplitude of the resultant magnetic field as a function of the scanning position through axial scanning; S4: Determine whether there are defects on the surface of the metal pipe based on the scanning curve. If there are defects, locate the center of the defect based on the scanning curve and use the inversion algorithm to obtain the depth and width of the defect.

[0006] The present invention provides a method for detecting defects in metal pipes based on eddy current induction. An alternating excitation magnetic field is applied to the metal pipe by an excitation coil, causing induced eddy currents and induced magnetic fields to be generated on the pipe surface. The resultant magnetic field of the excitation magnetic field and the induced magnetic field is measured, and the magnetic field amplitude curve is obtained by axial scanning. The defect center is located by using the minimum value of the curve. The sensor is fixed at the defect center, and the linear relationship between the resultant magnetic field amplitude and the defect depth and width within a specific range is used to combine with an inversion algorithm to achieve quantitative measurement of the defect depth and width.

[0007] As a preferred method, it is determined whether the difference between the amplitude of the combined magnetic field at the highest and lowest points of the scanning curve over the entire length of the metal pipe is less than a preset amplitude threshold. If so, the surface of the metal pipe is free of defects; otherwise, the surface of the metal pipe is defective, and the lowest point of the combined magnetic field amplitude is taken as the defect center.

[0008] As a preferred method, multiple sets of excitation current frequencies are set sequentially, and an axial scan is performed on a metal pipe with only one defect. The scan curve is normalized. The normalized magnetic field value at the center of the defect in the metal pipe is extracted at each excitation current frequency, and the relationship curve between the excitation current frequency and the normalized magnetic field is obtained. The excitation current frequency corresponding to the lowest normalized magnetic field value is selected as the optimal excitation current frequency.

[0009] By optimizing the excitation frequency to 310 Hz, it is possible to locate and measure the geometric parameters of circumferential defects within the range of width 5-20 mm and depth 0.5-1.5 mm.

[0010] Preferably, S4 includes: using the linear fitting curves of the defect depth and the magnitude of the resultant magnetic field at the defect center established by the finite element simulation in S1, and the linear fitting curves of the defect width and the magnitude of the resultant magnetic field; and solving the two sets of linear fitting curves based on the magnitude of the resultant magnetic field at the current defect center to obtain the defect depth and the defect width.

[0011] Preferably, the two-dimensional axisymmetric model for metal pipe detection is established based on the axisymmetric structure of the excitation coil and the metal pipe, and a moving reference point is set at the center of the line connecting the excitation coil and the metal pipe. During axial scanning simulation, the excitation coil and the moving reference point move synchronously and uniformly along the axial direction of the metal pipe.

[0012] Preferably, the scanning range is Z = -80mm to Z = 80mm, and the scanning range is more than 70mm away from both ends of the metal pipe. A defect detection system for metal pipes based on eddy current induction, comprising: The excitation coil applies an alternating excitation magnetic field to the metal pipe under the action of an alternating current source; A magnetic field detection device is installed between the metal pipe to be tested and the excitation coil to detect the combined magnetic field of the excitation magnetic field and the induced magnetic field. The dynamic signal analyzer has a built-in two-dimensional axisymmetric model for metal pipe detection. Based on the detection results of the magnetic field detection device, it locates the defect center and inverts the defect geometric parameters.

[0013] The magnetic field detection device can be an ME sensor, a TMR sensor, or an AMR sensor, but the magnetic field detection device is not limited to the aforementioned types of sensors, as long as it can detect the magnetic field strength.

[0014] Preferably, the magnitude of the resultant magnetic field at the defect center is the product of the first fitting coefficient and the logarithm of the defect depth plus the second fitting coefficient; the magnitude of the resultant magnetic field at the defect center is the product of the third fitting coefficient and the logarithm of the defect width plus the fourth fitting coefficient.

[0015] Preferably, the magnetic field detection device is a magnetoelectric sensor, which has a multi-push-pull composite structure, including a magnetostrictive layer and a piezoelectric layer, wherein the magnetostrictive layer and the piezoelectric layer are alternately stacked.

[0016] Preferably, a charge amplifier is provided between the magnetic field detection device and the dynamic signal analyzer; the center of the magnetoelectric sensor, the center of the metal pipe, and the center of the excitation coil are located on the same horizontal line.

[0017] Therefore, the present invention has the following beneficial effects: 1. By axial scanning to locate the defect center and utilizing the linear relationship between the magnetic field amplitude at the defect center and the defect depth and width within a specific range, the precise location and geometric parameter measurement of circumferential defects in metal pipes with widths of 5-20 mm and depths of 0.5-1.5 mm were achieved.

[0018] 2. By using finite element simulation, the optimal excitation current frequency was determined, providing the best detection conditions for eddy current induction-based metal pipe defect detection and improving the accuracy of eddy current induction-based metal pipe defect detection. Attached Figure Description

[0019] Figure 1 This is a flowchart of the steps in the metal pipe defect detection method based on eddy current induction in this invention.

[0020] Figure 2This is a graph showing the relationship between different scanning positions and the normalized magnetic field at different excitation frequencies in this invention.

[0021] Figure 3 This is a graph showing the relationship between the excitation frequency and the normalized magnetic field at z=0 in this invention.

[0022] Figure 4 This is a graph showing the relationship between the probe scanning coordinates and the magnetic field signal amplitude in this invention.

[0023] Figure 5 This is a linear fitting curve of the logarithm of the defect depth and the magnitude of the resultant magnetic field in this invention.

[0024] Figure 6 This is a graph showing the slope of the linear fitting curve versus the logarithm of the defect width in this invention.

[0025] Figure 7 This is a linear fitting curve of the logarithm of the defect width and the magnitude of the resultant magnetic field in this invention.

[0026] Figure 8 This is a graph showing the slope of the linear fitting curve versus the logarithm of the defect depth in this invention.

[0027] Figure 9 This is a schematic diagram of the architecture of the metal pipe defect detection system based on eddy current induction in this invention.

[0028] Figure 10 This is a schematic diagram of the experimental results of a scanning pipeline with a fixed defect width but a variable defect depth in this invention.

[0029] Figure 11 This is a schematic diagram of the experimental results of a scanning pipeline with a fixed defect depth but a variable defect width in this invention.

[0030] Figure 12 This is a schematic diagram of the curves of defect depth versus resultant magnetic field amplitude when the probe is located at z=0 and the defect width is 10 mm in this invention.

[0031] Figure 13 This is a schematic diagram of the curves of defect width versus resultant magnetic field amplitude when the probe is located at z=0 and the defect depth is 1mm in this invention.

[0032] In the diagram: 1. AC current source; 2. Excitation coil; 3. Metal pipe under test; 4. Magnetoelectric sensor; 5. Charge amplifier; 6. Dynamic signal analyzer. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this application will be further described in detail below through embodiments and in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only one preferred embodiment of this application and are only used to explain this application. They do not limit the scope of protection of this application. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0034] Eddy current testing is a commonly used technique in pipeline non-destructive testing. Based on the principle of electromagnetic induction, it offers advantages such as non-contact, non-destructive operation, no need for coupling agents, high testing efficiency, and low cost. When an excitation magnetic field is applied to the metal pipeline under test, induced eddy currents are generated inside the conductor, exciting a secondary magnetic field. The presence of defects disturbs the eddy current path, causing the amplitude and phase of the induced magnetic field to change according to the defect characteristics. By acquiring and analyzing this changing signal through sensors, the pipeline defect can be located and its parameters quantified.

[0035] However, current methods for detecting circumferential defects in pipelines largely remain at the stage of location and qualitative identification. While some studies have attempted parameter quantification, they are still limited to a single dimension. For example, some studies have used differential surface coil probes to identify minute circumferential defects on stainless steel pipes, but failed to quantify their size; other studies, based on the principle of long-range eddy currents or tilting coil probes, have identified defects on ferromagnetic or nickel-based alloy pipes, but these remain at the qualitative stage. A few studies have achieved quantitative measurements of defect depth or length, but these are all limited to single geometric parameters, making it difficult to comprehensively obtain dimensional information about the defects. The main reason for this limitation is that the eddy currents induced by traditional through-type coil probes are circumferentially distributed, resulting in a weak response to circumferential defects parallel to the eddy current direction. Furthermore, their limited sensitivity makes it difficult to capture subtle changes in weak magnetic field signals. Therefore, there is an urgent need for a technical solution that can accurately detect defects in metal pipelines and precisely calculate defect depth and width.

[0036] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0037] Example 1: This embodiment provides a method for detecting defects in metal pipes based on eddy current induction, such as... Figure 1As shown, the operation process is as follows: Step 1, a two-dimensional axisymmetric model of a metal pipe with an external circumferential defect is established using a CFD algorithm, and a linear function of the magnetic field amplitude and defect geometric parameters is fitted to establish a magnetic field amplitude-defect fitting model; Step 2, an alternating excitation magnetic field is applied to the metal pipe to obtain the induced magnetic field generated on the surface of the metal pipe; Step 3, the magnetic field amplitude is obtained, and a scanning curve showing the change of the magnetic field amplitude with the scanning position is obtained through axial scanning; Step 4, the presence of a defect on the surface of the metal pipe is determined based on the scanning curve, and if a defect exists, the defect center is located based on the scanning curve, and the defect depth and defect width are obtained using an inversion algorithm.

[0038] The eddy current induction-based metal pipe defect detection method provided in this embodiment is mainly used to address the problem that while existing pipe defect detection methods can identify and locate cracks in copper, aluminum, and stainless steel pipes based on the eddy current detection principle, they mostly remain at the identification stage and cannot quantify geometric parameters, making it difficult to comprehensively obtain the size information of the defect. By axially scanning to locate the defect center, and utilizing the linear relationship between the magnetic field amplitude at the defect center and the defect depth and width within a specific range, quantitative measurement of the defect depth and width can be achieved, thus realizing accurate detection of metal pipe defects.

[0039] The following examples and specific application scenarios further illustrate the technical solution and effects of the present invention. The following examples are explanations of the present invention, but the present invention is not limited to the following examples.

[0040] This embodiment provides a method for detecting defects in metal pipes based on eddy current induction, specifically including the following steps: Step 1: Use CFD algorithm to establish a two-dimensional axisymmetric model for metal pipe inspection with external circumferential defects, fit a linear function of the resultant magnetic field amplitude and defect geometric parameters, and establish a resultant magnetic field amplitude-defect fitting model.

[0041] By establishing a two-dimensional axisymmetric model of a metal pipe with an external circumferential defect, employing a moving reference point equivalent magnetic field sensor, and utilizing parametric scanning functionality to achieve axial scanning simulation analysis of the probe, the linear relationship between the resultant magnetic field amplitude and the defect depth and width within a specific interval was revealed. The linear interval and the fitting relationship were verified and determined through both finite element simulation and experimental data. Based on this, the correlation between the slope of the linear fitting function and the defect size was clarified, and the mechanism for quantitatively measuring the defect depth and width by extracting the magnetic field amplitude at the defect center was elucidated.

[0042] In this embodiment, the two-dimensional axisymmetric model for metal pipe detection is based on the axisymmetric structure of the metal pipe and the excitation coil and is established in the finite element simulation software. The moving reference point is located at the center of the line connecting the excitation coil and the metal pipe to be tested. In the axial scanning simulation, the coil and the reference point are moved synchronously along the pipe axis through the parameterized scanning function. The scanning range is from z=-80 mm to z=80 mm.

[0043] Theoretically, the metal pipe defect detection method provided in this embodiment is suitable for defect detection in long pipes. However, the actual pipe length is limited, and when the detection position is close to the pipe end, abrupt boundary changes can disrupt the eddy current distribution and produce edge effects, thus affecting the measurement accuracy. To avoid edge effect interference, this embodiment selects the middle region of the pipe for scanning, with the scanning range set from z=-80 mm to z=80 mm. This region is more than 70 mm away from both ends of the pipe, effectively ignoring end effects and satisfying the approximate detection conditions for long pipes.

[0044] In this embodiment, the established magnetic field amplitude-defect fitting model includes linear fitting curves of defect depth and magnetic field amplitude at the defect center, as well as linear fitting curves of defect width and magnetic field amplitude. Specifically, the linear fitting curve of defect depth and magnetic field amplitude at the defect center shows a linear relationship between the magnetic field amplitude at the defect center and the logarithm of the defect depth when the defect depth is between 0.8 mm and 1.9 mm. That is, the magnetic field amplitude at the defect center is the product of the first fitting coefficient and the logarithm of the defect depth, plus the second fitting coefficient.

[0045] The linear fitting curve of the defect width and the magnitude of the resultant magnetic field at the defect center is as follows: when the defect width is between 8 mm and 30 mm, the magnitude of the resultant magnetic field at the defect center is linearly related to the logarithm of the defect width. That is, the magnitude of the resultant magnetic field at the defect center is the product of the third fitting coefficient and the logarithm of the defect width, plus the fourth fitting coefficient. The first, second, third, and fourth fitting coefficients are all obtained by fitting the two-dimensional axisymmetric model of the metal pipe inspection for external circumferential defects or determined based on calibration experiments.

[0046] Step 2: Apply an alternating excitation magnetic field to the metal pipe to obtain the induced magnetic field generated on the surface of the metal pipe.

[0047] An alternating excitation magnetic field is applied to a metal pipe to induce eddy currents and a magnetic field. In this embodiment, the alternating excitation magnetic field is generated by an excitation current.

[0048] To determine the optimal excitation current frequency, multiple sets of excitation current frequencies were sequentially set, and an axial scan was performed on a metal pipe with only one defect. The scan curve was normalized. The normalized magnetic field value at the center of the defect in the metal pipe was extracted at each excitation current frequency, and the relationship curve between the excitation current frequency and the normalized magnetic field was obtained. The excitation current frequency corresponding to the lowest normalized magnetic field value was selected as the optimal excitation current frequency.

[0049] Specifically, in this embodiment, the conductivity of the metal pipe under test is 5.998 × 10⁻⁶. 7 Taking a sample with S / m, relative permeability of 1, thickness of 2 mm, and length of 300 mm as an example, the defect center is located at z=0.

[0050] To determine the optimal excitation frequency, multiple sets of excitation current frequencies were sequentially set in the simulation: 60 Hz, 110 Hz, 160 Hz, 310 Hz, 610 Hz, 1 kHz, 5 kHz, and 40 kHz. An axial scan was performed on a metal pipe with an external circumferential defect of 10 mm width and 1 mm depth. To visually compare the differences in probe sensitivity to the defect at different frequencies, the scan curves were normalized.

[0051] like Figure 3 As shown, when the probe sweeps across the defect area, the normalized magnetic field decreases. When the probe is located at the defect center z=0, the normalized magnetic field reaches its minimum value, thereby enabling the location of the defect center.

[0052] Extract the normalized magnetic field value at z=0 at each excitation current frequency to obtain, as follows: Figure 3 The curve showing the relationship between the excitation frequency and the normalized magnetic field is shown. According to... Figure 3 It can be seen that when the excitation frequency is close to 310 Hz, the normalized magnetic field value at z=0 reaches a relatively low level, at which point the probe has the optimal sensitivity for defect detection. Therefore, 310 Hz was selected as the excitation frequency for both subsequent simulations and experiments.

[0053] Finite element simulation was used to sequentially set multiple excitation current frequencies (60 Hz, 110 Hz, 160 Hz, 310 Hz, 610 Hz, 1 kHz, 5 kHz, and 40 kHz) to perform axial scanning on a metal pipe with an external circumferential defect of 10 mm width and 1 mm depth. The normalized magnetic field value at the defect center was extracted at each frequency. The results show that the normalized magnetic field value at the defect center is lowest when the excitation frequency is 310 Hz, resulting in optimal probe sensitivity for defect detection. At lower frequencies, the magnetic field change caused by the defect is smaller; at higher frequencies, due to the skin effect, eddy currents concentrate on the pipe surface, making it difficult to penetrate the pipe wall for effective defect detection. Therefore, 310 Hz was determined to be the optimal excitation frequency, providing the best detection conditions for defect detection.

[0054] Step 3: Obtain the resultant magnetic field of the excitation magnetic field and the induced magnetic field, and obtain the scanning curve of the resultant magnetic field amplitude as a function of the scanning position through axial scanning.

[0055] like Figure 4 As shown, this is the curve relating the probe scanning coordinate z to the amplitude B of the resultant magnetic field signal. Figure 4 The black dots in the middle represent the intersections of the scanning curves. When the detection probe is located at z=0, i.e., the center of the defect, the amplitude B of the resultant magnetic field signal reaches its minimum value, thus achieving the location of the defect center.

[0056] Step 4: Determine whether there are defects on the surface of the metal pipe based on the scanning curve, and if defects are present, locate the center of the defect based on the scanning curve.

[0057] During the scanning process, if the scanning curve remains flat and does not show a significant decrease in amplitude over the entire length of the pipeline, the pipeline is determined to be without defects; if the scanning curve shows a significant decrease in amplitude in a certain local area and there is a minimum amplitude value in that area, the area is determined to have a defect, and the defect center is located at the location of the minimum value.

[0058] Specifically: if the scanning curve remains flat along the entire length of the pipeline without a significant decrease in amplitude, the pipeline is determined to be defect-free; if the scanning curve shows a significant decrease in amplitude in a certain local area, and there is a minimum amplitude value in that area, the area is determined to be defective, and the defect center is located at the location of the minimum value.

[0059] Step 5: Obtain the magnitude of the combined magnetic field at the defect center. Based on the combined magnetic field magnitude-defect fitting model, use the inversion algorithm to obtain the defect depth and defect width.

[0060] The magnetic field detection device is fixed at the center of the defect. Based on the linear relationship between the combined magnetic field amplitude and the depth and width of the defect within a specific range, the depth and width of the defect are calculated using an inversion algorithm.

[0061] The inversion algorithm is as follows: If both the defect width and the defect depth are unknown, then based on the resultant magnetic field amplitude-defect fitting model obtained in step one, combined with the real-time resultant magnetic field amplitude at the currently detected defect center position, the linear fitting curves of the defect depth and resultant magnetic field amplitude at the defect center and the linear fitting curves of the defect width and resultant magnetic field amplitude are obtained by linear iteration.

[0062] If the defect width is known, the defect depth can be deduced by using the measured amplitude of the resultant magnetic field at the defect center, combined with the linear fitting curve of the defect depth and the resultant magnetic field amplitude at the defect center. Conversely, if the defect depth is known, the defect width can be deduced by using the measured amplitude of the resultant magnetic field at the defect center, combined with the linear fitting curve of the defect width and the resultant magnetic field amplitude at the defect center.

[0063] Specifically, after locating the defect center through axial scanning with the probe, the detection probe is fixed at the defect center to conduct quantitative research on the defect's geometric parameters. For example... Figure 5 The figure shows the relationship between defect depth and magnetic field amplitude B for different defect widths. When the defect depth is in the range of 0.8-1.9 mm, the magnetic field amplitude shows a good linear relationship with the logarithm of the depth; the black curve in the figure is the linear fitting curve. Figure 6 As shown, the relationship between the slope k of the linear fitting curve and the logarithm of the defect width is illustrated. Within the defect width range of 5-40 mm, the slope k decreases linearly with increasing logarithm of the width. Therefore, the linear relationship between the magnetic field amplitude and the defect depth can be used to quantitatively invert the defect depth.

[0064] like Figure 7 The figure shows the relationship between the defect width and the magnetic field amplitude B when the probe is fixed at z=0. When the defect width is in the range of 8-30 mm, the magnetic field amplitude and the logarithm of the width show a good linear relationship. The black curve in the figure is the corresponding linear fitting curve. Figure 8 As shown, the slope k of the linear fitting curve is related to the defect depth. Within the defect depth range of 0.1-1.5 mm, the slope k decreases linearly with the increase of the logarithm of the defect width. Therefore, the linear relationship between the magnetic field amplitude and the defect width can be used to achieve quantitative inversion of the defect width.

[0065] This embodiment also provides a metal pipe defect detection system based on eddy current induction using a magnetoelectric sensor, such as... Figure 9 As shown, the system includes an AC current source 1, an excitation coil 2, a metal pipe under test 3, a magnetic field sensor 4, a charge amplifier 5, and a dynamic signal analyzer 6. The AC current source provides the excitation current, which generates an excitation magnetic field through an excitation coil with an inner diameter of 10 cm, an outer diameter of 10.1 cm, and 23 turns. The magnetoelectric sensor is placed between the pipe and the coil, aligned horizontally with the centers of both components. A displacement device drives the pipe to move axially at a uniform speed, enabling the probe to scan the pipe axially. The output of the charge amplifier is connected to the dynamic signal analyzer for signal processing and analysis, acquiring magnetic field amplitude information to locate the defect center and invert the defect's geometric parameters.

[0066] To verify the effectiveness of the eddy current induction-based metal pipe defect detection method and system based on magnetoelectric sensors provided in this embodiment, a copper pipe was selected as the research object. Defects were machined onto the outer surface of the copper pipe using a precision CNC milling machine, and all defects were located at the center of the pipe's length. Defect specifications were defined by "width × depth (unit: mm)," and were successively 5 mm × 1 mm, 10 mm × 0.5 mm, 10 mm × 0.8 mm, 10 mm × 1 mm, 10 mm × 1.5 mm, 15 mm × 1 mm, and 20 mm × 1 mm.

[0067] It should be noted that this embodiment selects copper pipes as the research object, which does not mean that the metal pipe defect detection provided in this application can only be used to detect copper pipes. Metal pipes made of aluminum, iron, copper and other metals can also be defect detected by the method provided in this application.

[0068] like Figure 10 The image shows the results of pipe scanning experiments for defects with widths of 10 mm and depths of 0.5 mm, 0.8 mm, 1 mm, and 1.5 mm, respectively. Figure 11 The figure shows the results of pipe scanning experiments with a defect depth of 1 mm and widths of 5 mm, 10 mm, 15 mm, and 20 mm.

[0069] In the initial stage of the experiment, the defect was located far from the probe, and the measured magnetic field amplitude was stable at 17.21 μT. As the detection probe gradually approached the pipe defect, the defect disturbed the eddy current distribution, causing the magnetic field amplitude to decrease significantly and reach its minimum value at the center of the defect (z=0), thus achieving accurate location of the defect.

[0070] like Figure 12 The image shows the detection results of a pipe with defects 10 mm wide and 0.5 mm, 0.8 mm, 1 mm, and 1.5 mm deep, with the probe fixed at z=0. The magnetic field value of the experimental signal decreases linearly with increasing defect depth. Figure 13 The figure shows the detection results of pipes with defects of 1 mm depth and widths of 5 mm, 10 mm, 15 mm, and 20 mm, respectively, when the probe is at the same z=0 position. As the defect width increases, the magnetic field value of the experimental signal decreases linearly.

[0071] Experimental results show that, within a specific range, the magnetic field amplitude B at the defect center is linearly related to both the defect depth and width. The experimental signal characteristics are highly consistent with the simulation results, verifying the effectiveness of the eddy current induction-based metal pipe defect detection method proposed in this embodiment.

[0072] The eddy current induction-based defect detection method for metal pipes provided in this embodiment has the following beneficial effects: 1. A method for locating defects and measuring geometric parameters in metal pipes is proposed. It reveals the linear relationship between the amplitude of the combined magnetic field and the depth and width of the defect within a specific range. It clarifies the mechanism for quantitatively measuring the depth and width of defects by extracting the magnetic field amplitude at the center of the defect. It also discovers the correlation between the slope of the linear fitting function and the defect size. It can achieve accurate location and geometric parameter measurement of circumferential defects with a width of 5-20 mm and a depth of 0.5-1.5 mm.

[0073] 2. Through finite element simulation, multiple sets of excitation current frequencies were set sequentially to determine the optimal excitation current frequency, providing the best detection conditions for defect detection.

[0074] Example 2: This embodiment provides a metal pipe defect detection system based on eddy current induction, which is used to implement the metal pipe defect detection method based on eddy current induction in Embodiment 1.

[0075] Specifically, such as Figure 7 As shown, a metal pipe defect detection system based on eddy current induction includes: an AC current source 1, an excitation coil 2, a magnetoelectric sensor 4, a charge amplifier 5, and a dynamic signal analyzer 6. The AC current source is connected to the excitation coil. The metal pipe 3 to be tested is placed between the excitation coil and the magnetoelectric sensor. The magnetoelectric sensor is connected to the input terminal of the charge amplifier, and the output terminal of the charge amplifier is connected to the dynamic signal analyzer. The magnetoelectric sensor, the center of the metal pipe to be tested, and the center of the excitation coil are all located on the same horizontal line.

[0076] In this embodiment, an alternating current source provides excitation current to the excitation coil; the excitation coil, under the action of the alternating current source, applies an alternating excitation magnetic field to the metal pipe under test, thereby inducing a magnetic field in the metal pipe. In this embodiment, the excitation coil has 10 turns, and the excitation current is 0.1 A; the conductivity of the metal pipe under test is 5.998 × 10⁻⁶. 7 It has a permeability of 1 S / m, a thickness of 2 mm, and a length of 300 mm.

[0077] A magnetic field detection device is installed between the metal pipe to be tested and the excitation coil to detect the combined magnetic field of the excitation magnetic field and the induced magnetic field.

[0078] In this embodiment, the magnetic field detection device is a magnetoelectric sensor, which is a magnetic field sensor based on the magnetoelectric effect. Magnetoelectric sensors exhibit extremely high magnetic field detection sensitivity at their resonant frequency, with a minimum magnetic field detection limit reaching the femtotes level, far exceeding traditional magnetic induction coils, Hall sensors, and magnetoresistive sensors, giving them a significant advantage in the detection of weak magnetic field signals.

[0079] In this embodiment, the magnetoelectric sensor employs a multi-push-pull composite structure, comprising a magnetostrictive layer and a piezoelectric layer, which are alternately stacked. The magnetostrictive layer is made of Metglas amorphous ribbon based on the FeSiBC system, and the piezoelectric layer is made of PZT piezoelectric material. This magnetoelectric sensor exhibits an equivalent magnetic noise of 33.9 pT / √Hz at 310 Hz and a detection limit of 26.6 pT / √Hz, effectively detecting weak magnetic field changes caused by defects.

[0080] The charge amplifier amplifies the resultant magnetic field detected by the magnetic field detection device and outputs it to the dynamic signal analyzer. In this embodiment, the feedback capacitor Cf of the charge amplifier is 100 pF, and a feedback resistor Rf is connected in parallel with a resistance of 500 MΩ. The dynamic signal analyzer incorporates a two-dimensional axisymmetric model for metal pipe inspection, used for signal processing and analysis to acquire magnetic field amplitude information, locate the defect center, and invert the defect's geometric parameters. The two-dimensional axisymmetric model for metal pipe inspection is based on the axisymmetric structure of the excitation coil and the metal pipe, with a moving reference point set at the center of the line connecting the excitation coil and the metal pipe. During axial scan simulation, the excitation coil and the moving reference point move synchronously and uniformly along the axial direction of the metal pipe.

[0081] In this embodiment, a displacement device is also included. This device drives the metal pipe under test to move at a constant speed along the axial direction, thereby enabling the probe to scan the metal pipe axially. The displacement device can be implemented using a robotic arm fixed to the surface of the metal pipe under test, which moves the pipe axially at a constant speed. Alternatively, the metal pipe under test can be placed on a conveying mechanism, which then moves the pipe axially at a constant speed.

[0082] The eddy current induction-based metal pipe defect detection system provided in this embodiment utilizes a designed and fabricated magnetoelectric sensor to construct the system. It locates the defect center through axial scanning and leverages the linear relationship between the magnetic field amplitude at the defect center and the defect depth and width within a specific range to achieve simultaneous quantitative measurement of the defect depth and width. This system can accurately locate and measure the geometric parameters of circumferential defects with widths of 5-20 mm and depths of 0.5-1.5 mm. Compared with existing technologies, this invention, in addition to defect location, achieves quantitative measurement of the depth and width of circumferential defects, overcoming the limitations of traditional methods that can only identify the presence of defects.

[0083] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Other variations and modifications are possible without departing from the technical solutions described in the claims.

Claims

1. A method for detecting defects in metal pipes based on eddy current induction, characterized in that, include: S1: A two-dimensional axisymmetric model for detecting metal pipes with external circumferential defects is established using CFD algorithms. A linear function of the resultant magnetic field amplitude and defect geometric parameters is fitted to establish a resultant magnetic field amplitude-defect fitting model. S2: Apply an alternating excitation magnetic field to the metal pipe to obtain the induced magnetic field generated on the surface of the metal pipe; S3: Obtain the amplitude of the resultant magnetic field by obtaining the scanning curve of the amplitude of the resultant magnetic field as a function of the scanning position through axial scanning; S4: Determine whether there are defects on the surface of the metal pipe based on the scanning curve, and if there are defects, locate the center of the defect based on the scanning curve, and use the inversion algorithm to obtain the depth and width of the defect.

2. The method for detecting defects in metal pipes based on eddy current induction according to claim 1, characterized in that, Determine whether the difference between the amplitude of the combined magnetic field at the highest and lowest points of the scanning curve over the entire length of the metal pipe is less than a preset amplitude threshold. If so, the surface of the metal pipe is free of defects; otherwise, the surface of the metal pipe is defective, and the lowest point of the combined magnetic field amplitude is taken as the defect center.

3. The method for detecting defects in metal pipes based on eddy current induction according to claim 1, characterized in that, Multiple sets of excitation current frequencies were set sequentially, and an axial scan was performed on a metal pipe with only one defect. The scan curve was normalized. The normalized magnetic field value at the center of the defect in the metal pipe was extracted at each excitation current frequency, and the relationship curve between the excitation current frequency and the normalized magnetic field was obtained. The excitation current frequency corresponding to the lowest normalized magnetic field value is selected as the optimal excitation current frequency.

4. A method for detecting defects in metal pipes based on eddy current induction according to claim 1, 2, or 3, characterized in that, S4 includes: using the linear fitting curves of the defect depth and the magnitude of the resultant magnetic field at the defect center established by the finite element simulation in S1, and the linear fitting curves of the defect width and the magnitude of the resultant magnetic field; based on the magnitude of the resultant magnetic field at the current defect center, solving the two sets of linear fitting curves to obtain the defect depth and defect width.

5. The method for detecting defects in metal pipes based on eddy current induction according to claim 4, wherein the amplitude of the resultant magnetic field at the defect center is the product of the first fitting coefficient and the logarithm of the defect depth plus the second fitting coefficient; the amplitude of the resultant magnetic field at the defect center is the product of the third fitting coefficient and the logarithm of the defect width plus the fourth fitting coefficient.

6. A method for detecting defects in metal pipes based on eddy current induction according to claim 1, 2, or 3, characterized in that, The scanning range is from Z = -80mm to Z = 80mm, and the distance between the scanning range and both ends of the metal pipe is greater than 70mm.

7. A metal pipe defect detection system based on eddy current induction, employing the metal pipe defect detection method based on eddy current induction as described in any one of claims 1-6, characterized in that, include: The excitation coil applies an alternating excitation magnetic field to the metal pipe under the action of an alternating current source; A magnetic field detection device is installed between the metal pipe to be tested and the excitation coil to detect the combined magnetic field of the excitation magnetic field and the induced magnetic field. The dynamic signal analyzer has a built-in two-dimensional axisymmetric model for metal pipe detection. Based on the detection results of the magnetic field detection device, it locates the defect center and inverts the defect geometric parameters.

8. A metal pipe defect detection system based on eddy current induction according to claim 7, characterized in that, The two-dimensional axisymmetric model for metal pipe detection is established based on the axisymmetric structure of the excitation coil and the metal pipe. A moving reference point is set at the center of the line connecting the excitation coil and the metal pipe. During axial scanning simulation, the excitation coil and the moving reference point move synchronously and uniformly along the axial direction of the metal pipe.

9. A metal pipe defect detection system based on eddy current induction according to claim 7 or 8, characterized in that, The magnetic field detection device is a magnetoelectric sensor, which has a multi-push-pull composite structure, including a magnetostrictive layer and a piezoelectric layer, which are alternately stacked.

10. A metal pipe defect detection system based on eddy current induction according to claim 7 or 8, characterized in that, A charge amplifier is provided between the magnetic field detection device and the dynamic signal analyzer; the center of the magnetic field detection device, the center of the metal pipe under test, and the center of the excitation coil are located on the same horizontal line.

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