Multilayer casing conductivity and magnetic conductivity inversion method

Abstract

The invention discloses a multi-layer casing conductivity and magnetic conductivity inversion method, which belongs to the field of electromagnetic nondestructive testing, and comprises the following steps: determining a transient response expression of a multi-layer ferromagnetic casing under pulsed eddy current excitation by adopting a pulsed eddy current testing rapid analysis model; converting an electromagnetic parameter measurement problem of the multilayer ferromagnetic sleeve into an optimization problem, wherein the optimization problem aims at minimizing an error between an actually measured transient response and a theoretical transient response calculated by a transient response expression; solving the optimization problem by adopting a Gaussian-Newton method to obtain coupling parameters related to the conductivity, the relative permeability and the wall thickness of the sleeve; based on the known wall thickness of each layer of the multi-layer ferromagnetic sleeve, the coupling parameters and the wall thickness of the corresponding layer are calculated, and the conductivity and the relative permeability of each layer of sleeve are obtained; according to the sequence from the bottom of the well to the ground, operation is carried out on different levels in the multi-layer ferromagnetic casing in sequence, and inversion of the conductivity and the relative permeability of the casing of all the levels is completed.

Description

Technical Field

[0001] This invention belongs to the field of electromagnetic nondestructive testing technology, and in particular relates to a method for inverting the conductivity and permeability of multilayer sleeves. Background Technology

[0002] In the field of electromagnetic nondestructive testing (EMT) technology, the health status assessment of metal pipelines (especially multi-layer ferromagnetic sleeves) is crucial for industrial production safety (such as the maintenance of downhole casings in oil wells). The electrical conductivity and magnetic permeability of metal sleeves, as core electromagnetic parameters, are not only important bases for distinguishing pipelines of different materials, but also allow for quantitative assessment of structural parameters such as pipe wall thickness using mathematical models, thus becoming core detection targets for EMT. Currently, Pulsed Eddy Current Testing (PECT) technology, due to its advantages such as non-contact operation, no need for coupling agents, and sensitivity to deep defects, has been widely applied to the electromagnetic parameter testing of metal sleeves. In practice, existing technologies mostly construct PECT analytical models based on the Residue Theorem (RT) or Fourier Transform (FT). By calculating the response signal of the sleeve under pulsed eddy current excitation, a preliminary inversion analysis of electromagnetic parameters is achieved, providing fundamental technical support for the testing of multi-layer sleeves.

[0003] However, existing PECT (Positive Electron Conversion) technology for multi-layer casing still has significant shortcomings, making it difficult to meet the comprehensive requirements of detection efficiency, inversion accuracy, and scenario adaptability in practical applications. On the one hand, traditional models based on the residue theorem or Fourier transform have high computational complexity. When faced with the large number of iterative calculations required for multi-layer casing detection, excessive computation time can easily occur, leading to low detection efficiency and making it unsuitable for scenarios with high requirements for detection timeliness, such as downhole drilling. On the other hand, existing technologies lack adaptability to multi-layer structures. Most models are designed only for single-layer casing, failing to consider the electromagnetic coupling effect between multiple layers of casing, and lack precise analysis of parameter sensitivity during the inversion process. This makes it difficult to determine the optimal detection time window, resulting in large errors in the inversion results of conductivity and permeability, and even failing to accurately distinguish the differences in electromagnetic parameters between different layers of casing. In addition, some technologies fail to balance computational efficiency and inversion accuracy. Pursuing accuracy further increases computational costs, while simplifying calculations sacrifices accuracy, ultimately affecting the accuracy and reliability of downhole multi-layer casing health status assessment. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes a method for inverting the conductivity and permeability of multilayer bushings, thereby resolving the issues present in the prior art.

[0005] To achieve the above objectives, the present invention provides a method for inverting the conductivity and permeability of multilayer bushings, comprising: Step 1: Using a pulsed eddy current detection fast analytical model, determine the transient response expression of the multilayer ferromagnetic sleeve under pulsed eddy current excitation. The transient response expression is transformed from the complex frequency domain to the time domain through the inverse Laplace transform, and the inverse Laplace transform is solved by the Fixed-Talbot algorithm. Step 2: The electromagnetic parameter measurement problem of the multilayer ferromagnetic bushing is transformed into an optimization problem. The optimization problem aims to minimize the error between the actual measured transient response and the theoretical transient response calculated from the transient response expression in Step 1. Step 3: Solve the optimization problem in Step 2 using the Gauss-Newton method to obtain the coupling parameters related to the bushing conductivity, relative permeability and wall thickness; Step 4: Based on the known wall thickness of each layer of the multilayer ferromagnetic bushing, calculate the coupling parameters obtained in Step 3 with the corresponding layer wall thickness to obtain the conductivity and relative permeability of each layer of the bushing. Step 5: Following the order from the bottom of the well to the surface, perform steps 1 to 4 sequentially on different levels of the multi-layer ferromagnetic casing to complete the inversion of the electrical conductivity and relative magnetic permeability of all levels of casing.

[0006] Preferably, in step 1, the process of determining the transient response expression of the multilayer ferromagnetic sleeve under pulsed eddy current excitation includes: Determine the structural correlation parameters between the excitation coil and the receiving coil, and derive the complex frequency domain expression of the transient response of the multilayer ferromagnetic sleeve pulse eddy current detection based on the structural correlation parameters; The transient response expression in the time domain is obtained by performing an inverse Laplace transform on the complex frequency domain expression of the transient response using the Fixed-Talbot algorithm.

[0007] Preferably, the structural correlation parameters include the turns density of the excitation coil, the turns density of the receiving coil, the start and end positions of the excitation coil on the z-axis, the start and end positions of the receiving coil on the z-axis, the inner and outer radii of the excitation coil, and the inner and outer radii of the receiving coil.

[0008] Preferably, in step 1, when performing the inverse Laplace transform on the complex frequency domain expression of the transient response using the Fixed-Talbot algorithm, free parameters are set, transformation-related parameters in the Fixed-Talbot algorithm are determined based on the free parameters, and the inverse Laplace transform result is calculated using the transformation-related parameters.

[0009] Preferably, in step 2, the constraint condition of the optimization problem is that the coupling parameters characterizing the coupling relationship between electromagnetic parameters and wall thickness are all greater than zero.

[0010] Preferably, in step 2, the actual measured transient response is obtained by detecting the multilayer ferromagnetic bushing using a pulsed eddy current detection device. The pulsed eddy current detection device includes an excitation coil and a receiving coil. The excitation coil is used to apply a pulsed excitation current to the multilayer ferromagnetic bushing, and the receiving coil is used to collect the response signal generated by the multilayer ferromagnetic bushing under the action of the pulsed excitation current. The response signal is processed to obtain the actual measured transient response.

[0011] Preferably, in step 3, the process of solving the optimization problem using the Gauss-Newton method includes: Initialize the initial values ​​of the coupling parameters for iteration, and calculate the theoretical transient response based on the initial values ​​of the iteration and the transient response expression in step 1; The error is obtained by comparing the theoretical transient response with the actual measured transient response; The coupling parameters are adjusted based on the error, and the iteration process is repeated until the error meets the preset conditions to obtain the final coupling parameters.

[0012] Preferably, the preset condition is that the error is less than a preset threshold, or the number of iterations reaches a preset number.

[0013] Preferably, in step 4, the coupling parameters include the product of conductivity and wall thickness, and the product of relative permeability and wall thickness. The coupling parameters are divided by the wall thickness of the corresponding layer to obtain the conductivity and relative permeability of each layer of the sleeve.

[0014] Preferably, in step 5, when performing steps 1 to 4 sequentially on different levels of bushings, for each level of bushing, based on the structural positional relationship between the bushing of that level and other levels of bushings, the hierarchical correlation parameters in the pulse eddy current detection rapid analysis model are adjusted, and then subsequent steps are performed based on the adjusted model.

[0015] Compared with the prior art, the present invention has the following advantages and technical effects: This invention solves the inverse Laplace transform using the Fixed-Talbot algorithm, which significantly reduces the computation time of the transient response expression of multilayer bushings compared to traditional models based on the residue theorem or Fourier transform. It also meets the need for a large number of iterative calculations during the inversion process and solves the problem of low computational efficiency in existing technologies.

[0016] This invention constructs an optimization problem with the goal of minimizing the error between the actual measured transient response and the theoretical transient response, and accurately solves the coupling parameters using the Gauss-Newton method. It also calculates the conductivity and relative permeability using the known wall thickness, thereby reducing parameter inversion errors and solving the problem of insufficient accuracy in the electromagnetic parameter inversion of multilayer sleeves in existing technologies.

[0017] This invention performs the inversion process on different levels of multi-layer casing sequentially from the bottom of the well to the surface. It can specifically handle the electromagnetic coupling effect between multi-layer casings and realize the separate inversion of electromagnetic parameters of each level of multi-layer ferromagnetic casing. This solves the problem that existing technologies are mostly adapted to single-layer casings and cannot meet the detection requirements of multi-layer structures.

[0018] This invention provides reliable parameters for subsequent differentiation of casing materials and quantitative assessment of key health indicators such as casing wall thickness by efficiently and accurately inverting the conductivity and relative permeability of multi-layer casing, thereby improving the accuracy and reliability of downhole multi-layer casing health status assessment. Attached Figure Description

[0019] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a schematic diagram of a multi-layer ferromagnetic sleeve under an offshore oil production platform according to an embodiment of the present invention; Figure 2 This is a three-dimensional schematic diagram of pulsed eddy current detection (PECT) on a multilayer ferromagnetic sleeve according to an embodiment of the present invention. Figure 3 The partial derivatives related to the ferromagnetic bushing in the embodiments of the present invention are as follows: (a) is the partial derivative of bushing 1; (b)-(c) are the partial derivatives of bushing 1 and bushing 2 in the double-layer structure; (d)-(f) are the partial derivatives of bushing 1, bushing 2 and bushing 3 in the triple-layer structure. Detailed Implementation

[0020] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0021] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0022] Example 1 This embodiment provides a method for inverting the conductivity and permeability of multilayer bushings. A fast pulsed eddy current testing (PECT) analytical model is used to calculate the theoretical response. Then, an optimization algorithm (such as the Gauss-Newton method) is used to match the theoretical response with actual measurement data, thereby inverting the bushing's conductivity (σ) and relative permeability (μ). rCompared to traditional models based on the residue theorem (RT) or Fourier transform (FT), the FTA algorithm significantly reduces computation time, making it more suitable for inversion problems requiring numerous iterative calculations. The specific steps include: Step 1: Using a pulsed eddy current detection fast analytical model, determine the transient response expression of the multilayer ferromagnetic sleeve under pulsed eddy current excitation. The transient response expression is transformed from the complex frequency domain to the time domain through the inverse Laplace transform, and the inverse Laplace transform is solved by the Fixed-Talbot algorithm. Furthermore, in step 1, the process of determining the transient response expression of the multilayer ferromagnetic sleeve under pulsed eddy current excitation includes: Determine the structural correlation parameters between the excitation coil and the receiving coil, and derive the complex frequency domain expression of the transient response of the multilayer ferromagnetic sleeve pulse eddy current detection based on the structural correlation parameters; The transient response expression in the time domain is obtained by performing an inverse Laplace transform on the complex frequency domain expression of the transient response using the Fixed-Talbot algorithm.

[0023] Furthermore, the structural correlation parameters include the turns density of the excitation coil, the turns density of the receiving coil, the start and end positions of the excitation coil on the z-axis, the start and end positions of the receiving coil on the z-axis, the inner and outer radii of the excitation coil, and the inner and outer radii of the receiving coil.

[0024] Further, in step 1, when performing the inverse Laplace transform on the complex frequency domain expression of the transient response using the Fixed-Talbot algorithm, free parameters are set, and the transform-related parameters in the Fixed-Talbot algorithm are determined based on the free parameters. Then, the inverse Laplace transform result is calculated using the transform-related parameters.

[0025] Specifically, a schematic diagram of a multi-layer ferromagnetic casing under an offshore oil production platform, such as... Figure 1 As shown. To measure the conductivity and relative permeability of the bushing, this embodiment employs a fast analytical model of pulsed eddy current detection (PECT), as this model significantly reduces computation time during the measurement process. Based on previous research, the complex frequency domain expression U(s) of the transient response of pulsed eddy current detection for multilayer ferromagnetic bushings can be expressed as: (1) in, and These are the turns density of the excitation coil and the receiving coil, respectively; The vacuum permeability; The amplitude of the pulse excitation current; and These represent the start and end positions of the receiving coil on the z-axis, respectively. and These are the inner and outer radii of the receiving coil, respectively. and For first-order modified Bessel function Let be the integral variable, and Ξ(s) / Λ(s) be the system's transfer function in the complex frequency domain. intermediate variables in, and These represent the start and end positions of the drive coil on the z-axis, respectively. and Let be the inner and outer radii of the driving coil, respectively; Ξ(s) and Λ(s) can be calculated using the following formulas: in, , For complex frequency domain magnetic vector potential Unknown parameters, All are coefficients of the magnetic vector potential in the air layer outside the outermost sleeve and =0, Let n be the transformation matrix between region n+1 and region n.

[0026] (6) (7) (8) (9) (10) in, , , , These are the field transmission / connection coefficients between two adjacent layers (layer n and layer n-1) in a multilayer cylindrical layered medium. It is a transformation matrix. , and They are 2 Components of the transformation matrix. Let n be the transformation matrix between region n and region n-1. = , , These are the magnetic permeability and electrical conductivity of the nth layer, respectively. , , , These are modified Bessel functions of the first and second kind. It is the outer radius of the (n-1)th layer of medium. The integral variable with respect to the coil radius, It is a point in the complex frequency domain magnetic vector potential, It is the expression for the current density of the excitation coil in the complex frequency domain; It is the Green's function in multilayer media. It is the integral variable of the coil's length along the z-axis.

[0027] Substituting equations (1) to (11) into equation (12), and comparing equation (12) with equation (1), we can obtain: (13) (14) Based on the inverse Laplace transform, the time-domain expression of equation (1) can be simplified to: in, This represents the inverse Laplace transform of Ξ(s) / Λ(s), a function that can be quickly solved using the Fixed-Talbot algorithm. Its expression is: In equation (16), M represents the free parameter. It is an intermediate variable about time, and its expression is as shown in equation (17). When the independent variable is s=Y (t) Complex frequency domain expression, The intermediate variables M and k are expressed as in equation (18). about And the exponential term of time t, The expression is as shown in equation (19); j= ; It is about The expression for is as shown in (20).

[0028] When the free parameter M is set to 7, appropriate accuracy of the inverse Laplace transform can be achieved; F(s) represents the time-domain function. The complex frequency domain expression of (t). Furthermore, the remaining parameters are defined as follows: (17) (18) (19) (20) Step 2: The electromagnetic parameter measurement problem of the multilayer ferromagnetic bushing is transformed into an optimization problem. The optimization problem aims to minimize the error between the actual measured transient response and the theoretical transient response calculated from the transient response expression in Step 1. Furthermore, in step 2, the constraint condition of the optimization problem is that the coupling parameters characterizing the coupling relationship between electromagnetic parameters and wall thickness are all greater than zero.

[0029] Further, in step 2, the actual measured transient response is obtained by detecting the multilayer ferromagnetic bushing using a pulsed eddy current detection device. The pulsed eddy current detection device includes an excitation coil and a receiving coil. The excitation coil is used to apply a pulsed excitation current to the multilayer ferromagnetic bushing, and the receiving coil is used to collect the response signal generated by the multilayer ferromagnetic bushing under the action of the pulsed excitation current. The response signal is processed to obtain the actual measured transient response.

[0030] like Figure 2 The figure shows a three-dimensional schematic diagram of pulsed eddy current detection (PECT) on a multilayer ferromagnetic sleeve.

[0031] Specifically, the electromagnetic parameter inversion method is a method that derives the inherent electromagnetic properties of the material under test (such as electrical conductivity σ and relative permeability μ) by analyzing electromagnetic detection response signals (such as pulsed eddy current PECT response). r ) computing technology.

[0032] To obtain the electromagnetic parameters of the conductive material under test, the inversion method is based on the Gauss-Newton method and the pulsed eddy current detection (PECT) fast analytical model technology.

[0033] The problem of measuring the electromagnetic parameters of a ferromagnetic bushing can be formulated as an optimization problem, with the following mathematical form: (twenty one) in, Indicates at a certain point in time. The amplitude of the actual transient response, Represents a point in time The amplitude of the theoretical response is processed, which is calculated using a fast analytical model of pulsed eddy current detection (PECT); m It refers to the number of data points used in the inversion. x It is the unknown parameter vector of the bushing.

[0034] Step 3: Solve the optimization problem in Step 2 using the Gauss-Newton method to obtain the coupling parameters related to the bushing conductivity, relative permeability and wall thickness; Furthermore, in step 3, the process of solving the optimization problem using the Gauss-Newton method includes: Initialize the initial values ​​of the coupling parameters for iteration, and calculate the theoretical transient response based on the initial values ​​of the iteration and the transient response expression in step 1; The error is obtained by comparing the theoretical transient response with the actual measured transient response; The coupling parameters are adjusted based on the error, and the iteration process is repeated until the error meets the preset conditions to obtain the final coupling parameters.

[0035] Furthermore, the preset condition is that the error is less than a preset threshold, or the number of iterations reaches a preset number.

[0036] Step 4: Based on the known wall thickness of each layer of the multilayer ferromagnetic bushing, calculate the coupling parameters obtained in Step 3 with the corresponding layer wall thickness to obtain the conductivity and relative permeability of each layer of the bushing. Further, in step 4, the coupling parameters include the product of conductivity and wall thickness, and the product of relative permeability and wall thickness. The coupling parameters are divided by the wall thickness of the corresponding layer to obtain the conductivity and relative permeability of each layer of the sleeve.

[0037] Specifically, since the dimensional information (such as wall thickness, radius, etc.) of similar sleeves used to measure electromagnetic parameters can be determined in advance before testing, the unknown parameters... x It can be represented as (i.e., electrical conductivity and relative permeability). Because when the partial derivatives of the transient response satisfy equation (22), the electrical conductivity... With permeability They will be coupled with the wall thickness in a product form.

[0038] in, It is a time-domain induced voltage signal. It refers to the wall thickness of the casing.

[0039] Therefore, the unknown parameters x It can be written as ,and The solution can be found by optimizing the equations.

[0040] (twenty three) in, It is the product of electrical conductivity and wall thickness. It is the product of magnetic permeability and wall thickness.

[0041] Therefore, the conductivity and permeability of a single bushing can be determined by... get.

[0042] Step 5: Following the order from the bottom of the well to the surface, perform steps 1 to 4 sequentially on different levels of the multi-layer ferromagnetic casing to complete the inversion of the electrical conductivity and relative magnetic permeability of all levels of casing.

[0043] Furthermore, in step 5, when performing steps 1 to 4 sequentially on different levels of bushings, for each level of bushing, based on the structural positional relationship between the bushing of that level and other levels of bushings, the hierarchical correlation parameters in the pulse eddy current detection rapid analysis model are adjusted, and then subsequent steps are performed based on the adjusted model.

[0044] Specifically, according to Figure 1 The casing structure shown gradually increases in the number of casing layers from 1 to 3, and the actual test involved uniformly dragging the casing from the bottom of the well to the surface. Therefore, the casing 1, casing 2, and casing 3 are related to... The process can be reversed sequentially.

[0045] In this embodiment, to verify the effectiveness of the proposed electromagnetic parameter inversion method, simulation experiments were conducted using the numerical software COMSOL and MATLAB. The pulsed eddy current detection (PECT) response in the simulation was obtained using the finite element software COMSOL, and the theoretical data of the response and the Gauss-Newton inversion operation were calculated using MATLAB. In the simulation, the pulse excitation current amplitude was 1A, and the parameters of the excitation coil and receiving coil are shown in Table 1, with wire diameters of 0.8mm and 0.06mm, respectively. The parameters of the bushing are listed in Table 2. Therefore, the partial derivative relationships corresponding to single-layer, double-layer, and triple-layer bushing structures can be obtained, such as... Figure 3 As shown.

[0046] Table 1 Table 2 Figure 3 In the middle, partial derivatives and functions subscript Indicates in The first layer in the layer structure Layered sleeve. According to... Figure 3 The results show that, Figure 3 The values ​​of (a), (b), and (d) gradually converge to zero, but their convergence time varies with the number of casing layers. It varies depending on the situation. Figure 3 As shown in (a), (b), and (d) in the figure, the first layer of sleeve corresponds to It approaches zero after 20 milliseconds, and at this point, it is related to the conductivity. Relative permeability The partial derivatives related to thickness d show good sensitivity around 20 milliseconds. According to... Figure 3In (c) and (e), the convergence time corresponding to the second layer of sleeve is approximately 60 milliseconds; while according to Figure 3 f in the context of the third-layer casing It begins to approach zero after 20 milliseconds, but its value first decreases before 85 milliseconds, and then gradually converges to zero.

[0047] Furthermore, due to the decay of the PECT transient response, the sensitivity of the partial derivatives increases with the number of layers. The increase in [something] leads to a decrease, and this decay also leads to... It rapidly approaches zero after 20 milliseconds. Figure 3 The results further show that equation (11) is applicable to single-layer, double-layer, and triple-layer sleeve structures. The final inversion results are shown in Table 3.

[0048] Table 3 The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A multi-layered sleeve conductivity and permeability inversion method characterized by, The method comprises the following steps: Step 1: a fast analytical model of pulsed eddy current detection is used to determine the transient response expression of the multi-layer ferromagnetic casing under pulsed eddy current excitation, the transient response expression is converted from the complex frequency domain to the time domain through inverse Laplace transform, and the inverse Laplace transform is solved through the Fixed-Talbot algorithm; Step 2: the electromagnetic parameter measurement problem of the multi-layer ferromagnetic casing is converted into an optimization problem, the optimization problem aims to minimize the error between the actual measured transient response and the theoretical transient response calculated by the transient response expression in step 1; Step 3: the optimization problem in step 2 is solved by using the Gauss-Newton method to obtain the coupling parameters related to the casing conductivity, relative permeability and wall thickness; Step 4: based on the known wall thickness of each layer of the multi-layer ferromagnetic casing, the coupling parameters obtained in step 3 are operated with the corresponding layer wall thickness to obtain the conductivity and relative permeability of each layer of the casing; Step 5: according to the order from the bottom to the ground, steps 1 to 4 are sequentially performed on different levels of the multi-layer ferromagnetic casing to complete the inversion of the conductivity and relative permeability of all levels of the casing.

2. The method of claim 1, wherein, In step 1, the process of determining the transient response expression of the multi-layer ferromagnetic casing under pulsed eddy current excitation comprises: determining the structure-related parameters of the excitation coil and the receiving coil, and deriving the transient response complex frequency domain expression of the multi-layer ferromagnetic casing pulsed eddy current detection based on the structure-related parameters; the inverse Laplace transform of the transient response complex frequency domain expression is performed through the Fixed-Talbot algorithm to obtain the transient response expression in the time domain.

3. The method of claim 2, wherein, The structure-related parameters include the number of turns density of the excitation coil, the number of turns density of the receiving coil, the starting and ending positions of the excitation coil on the z-axis, the starting and ending positions of the receiving coil on the z-axis, the inner and outer radii of the excitation coil, and the inner and outer radii of the receiving coil.

4. The method of claim 1, wherein, In step 1, when the inverse Laplace transform of the transient response complex frequency domain expression is performed through the Fixed-Talbot algorithm, a free parameter is set, the transformation-related parameters in the Fixed-Talbot algorithm are determined based on the free parameter, and the inverse Laplace transform result is calculated through the transformation-related parameters.

5. The method of claim 1, wherein, In step 2, the constraint condition of the optimization problem is that the coupling parameters representing the coupling relationship between the electromagnetic parameters and the wall thickness are greater than zero.

6. The method of claim 1, wherein, In step 2, the actual measured transient response is obtained by detecting the multi-layer ferromagnetic casing through a pulsed eddy current detection device, the pulsed eddy current detection device comprises an excitation coil and a receiving coil, the excitation coil is used to apply a pulsed excitation current to the multi-layer ferromagnetic casing, and the receiving coil is used to collect the response signal generated by the multi-layer ferromagnetic casing under the action of the pulsed excitation current, the response signal is processed to obtain the actual measured transient response.

7. The method of claim 1, wherein, In step 3, the process of solving the optimization problem by using the Gauss-Newton method comprises: initialize the iteration initial value of the coupling parameters, calculate the theoretical transient response based on the iteration initial value and the transient response expression in step 1; compare the theoretical transient response with the actual measured transient response to obtain the error; The coupling parameters are adjusted according to the error, and the iteration process is repeated until the error meets a preset condition, so as to obtain final coupling parameters.

8. The method of claim 7, wherein, The preset condition is that the error is less than a preset threshold, or the number of iterations reaches a preset number.

9. The method of claim 1, wherein, In step 4, the coupling parameters include the product of the conductivity and the wall thickness, and the product of the relative magnetic permeability and the wall thickness, and the coupling parameters are divided by the wall thickness of the corresponding layer to obtain the conductivity and the relative magnetic permeability of each layer of the sleeve.

10. The method of claim 1, wherein, In step 5, when steps 1 to 4 are sequentially performed on different layers of the sleeve, for each layer of the sleeve, the hierarchical correlation parameters in the pulse eddy current detection fast analysis model are adjusted based on the structural positional relationship between the layer of the sleeve and other layers of the sleeve, and the subsequent steps are performed based on the adjusted model.

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