A method for improving detection sensitivity by adjusting magnetic shielding effect based on actual magnetic leakage conditions

Abstract

A method for improving detection sensitivity that can adjust the magnetic shielding effect based on actual magnetic leakage working conditions, step 1: construct a finite element model for magnetic field analysis; step 2: establish a finite element model for magnetic signal detection that considers parameter information of an adjustable magnetic shielding sensor; step 3: obtain the magnetic leakage detection effect of the adjustable magnetic shielding sensor under different parameters; step 4: carry out optimization analysis of the magnetic leakage detection effect under different parameters, and obtain the magnetic shielding parameters corresponding to the optimal detection sensitivity based on the intelligent algorithm according to the magnetic leakage detection effect of different magnetic shielding parameters; step 5: achieve high sensitivity and accuracy detection of defects; step 6: carry out detection applications for defect types, defect sizes and detection objects in actual working conditions. The present invention has the characteristics of improving signal strength and resisting environmental interference, and improves the detection capability of small-sized defects to improve the accuracy and reliability of magnetic leakage detection.

Description

Technical Field

[0001] The present invention belongs to the technical field of nondestructive testing of mechanical engineering, and in particular relates to a method for improving detection sensitivity by adjusting a magnetic shielding effect based on actual magnetic leakage conditions. Background Art

[0002] Magnetic flux leakage detection technology has the advantages of no need for coupling agents, easy operation, low detection cost and easy automation. It is effective in detecting defects such as cracks and holes on the surface and inside of ferromagnetic workpieces. It is widely used in the detection of ferromagnetic structural parts such as steel pipes, drill pipes, storage tanks, pipelines, and rails.

[0003] The working principle of magnetic flux leakage detection technology is to magnetize the ferromagnetic material to be tested through a magnetizing device. When there are defects such as cracks or corrosion on the surface of the magnetized ferromagnetic material, the leakage of magnetic flux lines will cause the path of the magnetic flux lines to change, and some magnetic flux lines will leak out of the material to be tested, forming a leakage magnetic field. Therefore, the magnetic field changes near the material to be tested can be collected by sensors to determine whether there are defects. Since infrastructure such as oil storage tanks and natural gas pipelines have been serving in harsh and demanding operating environments for a long time, higher requirements are placed on the accuracy and reliability of their magnetic flux leakage detection to reduce missed and misjudgment of defects.

[0004] Existing magnetic flux leakage detection methods are easily affected by the interference magnetic field in the surrounding environment. For oil and gas pipelines that have been in service for a long time in harsh environments, the existing magnetic flux leakage detection methods, when using magnetic sensors as probes, are affected by the interference magnetic fields introduced by ferromagnetic branch auxiliary structures and running motors in the detection environment, which directly affects the quality of defect detection signals, resulting in a decrease in the accuracy and reliability of the detection results. Summary of the invention

[0005] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a method for improving detection sensitivity by adjusting the magnetic shielding effect based on actual magnetic leakage conditions. This method has the characteristics of improving signal strength and resisting environmental interference, improving the detection capability of small-size defects, and improving the accuracy and reliability of magnetic leakage detection.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for improving detection sensitivity by adjusting magnetic shielding effect based on actual magnetic leakage working conditions, comprising the following steps;

[0008] Step 1: According to the actual test conditions, a magnetic field analysis finite element model is constructed that takes into account the specimen size and material properties, the magnetization device size and material property parameter information;

[0009] Step 2: Based on the finite element model of magnetic field analysis, according to the actual detection needs, referring to the structural parts to be tested and the defect size information, a magnetic signal detection finite element model considering the parameter information of the adjustable magnetic shielding sensor is established; the parameters include the length, width, height and thickness of magnetic shielding of different geometric types;

[0010] Step 3: For the adjustable magnetic shielding sensor, take different parameters to carry out finite element model analysis to obtain the leakage magnetic field detection effect under different parameters of the adjustable magnetic shielding sensor;

[0011] Step 4: Carry out optimization analysis of the leakage magnetic field detection effect under different parameters, and obtain the magnetic shielding parameters corresponding to the optimal detection sensitivity based on the intelligent algorithm according to the leakage magnetic field detection effect of different magnetic shielding parameters;

[0012] Step 5: adjusting the parameters of the magnetic shielding sensor according to the optimal parameters, and realizing high sensitivity and accuracy detection of defects through the magnetic flux leakage detection system of the adjustable magnetic shielding sensor;

[0013] Step 6: Carry out detection application based on the defect type, defect size and detection object in actual working conditions.

[0014] Furthermore, in step 1, the finite element model for magnetic field analysis includes a powered coil, a magnetic yoke, a test piece, and an air domain; the copper coil is wound around the magnetic yoke to magnetize the test piece; and the air domain is wrapped around the powered coil, the magnetic yoke, and the test piece.

[0015] The finite element model constructed based on the actual detection problem takes into account the geometry of the test piece, the size of the test piece, the material properties of the test piece (including conductivity, magnetic permeability and relative dielectric constant), the geometry of the yoke in the magnetization system, the size of the yoke, the material properties of the yoke (including conductivity, magnetic permeability and relative dielectric constant), the number of turns of the coil in the magnetization system and the parameter information of the magnetization current, the size parameters of the air domain and the material properties. The Maxwell equations are used to solve the leakage magnetic finite element model, analyze and simulate the distribution and changes of the defect leakage magnetic field. The specific technical solution steps are as follows:

[0016] a) Establishing a geometric model; creating a geometric model based on the actual size and shape of the object to be detected, the geometric shape and size of the yoke in the magnetization system, the size and type of the coil, and the size of the air domain;

[0017] b) Define material properties and specify the correct material properties for each geometric part in the geometric model, including the electrical conductivity, magnetic permeability and relative permittivity of each geometric model;

[0018] c) Set boundary conditions and excitation sources for the finite element model for magnetic field analysis; the theoretical equations used in the yoke and air domain are: J = σE and B = μ0μr H, where H is the magnetic field intensity (A / m), J is the current density (A / m 2 ), B is magnetic induction intensity (T), A is magnetic vector potential, E is electric field intensity (V / m), σ is conductivity (S / m), μ0=4π×10 -7 H / m is the vacuum magnetic permeability, μ r is the relative magnetic permeability, and the theoretical equation used for the ferromagnetic material to be tested is J = σE, B = f(|H|)H / |H|, where |H| is the magnetic field intensity vector, and f(|H|) is a nonlinear function related to the magnetic field vector intensity. This functional relationship needs to be obtained using the magnetic property measurement method; the theoretical equation used by the coil is J = (NV / A coil R)e and B=μ0μ r H, where N is the number of turns of the coil, e is the unit vector, and A coil is the cross-sectional area of ​​the coil (m 2 ), V is the coil input voltage (V) and R is the coil resistance (Ω);

[0019] d) Meshing, which divides the geometric model into smaller units, usually triangular or tetrahedral meshes with side lengths less than 0.1 mm;

[0020] e) Model solution: choose steady-state, transient or frequency domain solution according to actual detection requirements. The steady-state solution is when the magnetic field does not change with time, the transient solution is when the magnetic field changes arbitrarily with time, and the frequency domain solution is when the periodic field changes with time.

[0021] Furthermore, in step 2, based on the established magnetic field analysis model, the adjustable magnetic shielding sensor geometry is considered in the magnetic signal detection finite element model, wherein the adjustable magnetic shielding sensor is used to collect detection signals, and the detection signal enhancement can be achieved by adjusting the magnetic shielding geometry parameters;

[0022] Based on the finite element model constructed in step 1, a magnetic shielding sensor geometric model is first established to determine the size of the geometric model, and then material property parameter information is defined for the geometric model, and the solution equation of magnetic shielding in the finite element model is set, and finally the finite element model is solved;

[0023] Among them, the theoretical equation used in the finite element model for magnetic shielding analysis is: J = σE and B = μ0μ r H, where H is the magnetic field intensity (A / m), J is the current density (A / m 2 ), B is magnetic induction intensity (T), A is magnetic vector potential, E is electric field intensity (V / m), σ is conductivity (S / m), μ0=4π×10 -7 H / m is the vacuum magnetic permeability, μr is the relative magnetic permeability.

[0024] Furthermore, in step 3, finite element analysis is carried out by inputting different adjustable magnetic shielding sensor size parameters into the model established in step 2 to obtain the leakage magnetic detection effect under different parameters of the adjustable magnetic shielding sensor, including the detection signal results corresponding to the magnetic shielding under different lengths, widths and thicknesses.

[0025] Further, based on the leakage magnetic detection effect of the adjustable magnetic shielding sensor under different parameters obtained in step 3, step 4 performs optimization analysis of the detection effect of the adjustable magnetic shielding sensor through an optimal gradient algorithm or an intelligent algorithm of a neural network or particle swarm optimization; determines the optimal sensitivity, including the optimal magnetic shielding geometry and size, and the detailed operation steps are as follows:

[0026] a) Data preparation: Based on the finite element model established in step 2, the leakage magnetic signal of the adjustable magnetic shielding sensor under different parameters is obtained;

[0027] b) Define the optimization problem: determine the parameters to be optimized, the geometric structure and size of the magnetic shield; the optimization conditions, the number of turns of the known coil and the magnetizing current; determine the constraints: the size of the magnetic shield is smaller than the size of the yoke;

[0028] c) Evaluate the objective function based on intelligent algorithm: The objective function is in To obtain different magnetic shielding lengths l, different magnetic shielding widths w, different magnetic shielding heights h, different magnetic shielding thicknesses t and different magnetic shielding geometries lx based on the finite element model of the adjustable magnetic shielding sensor i Magnetic leakage signal under different types (i=1, 2, 3, 4 represent different magnetic shielding geometry types); H s is the desired target signal, which can reflect the sensor's ability to respond to small magnetic field changes; j represents the jth sample; k represents the total number of data samples;

[0029] d) Determine whether the objective function meets the termination condition: the termination condition is that the objective function J < 0.001. If it meets the condition, the optimal magnetic shielding combination type and size parameters are output; if it does not meet the condition, recalculate.

[0030] Furthermore, in step 5, according to the optimal parameters of the adjustable magnetic shielding sensor determined in step 4, a leakage magnetic field detection system including an adjustable magnetic shielding sensor is designed and developed, and the detection system includes an adjustable magnetic shielding sensor for enhancing the leakage magnetic field detection signal and a control panel (including a signal generator, an oscilloscope and a power amplifier function, etc.), wherein the adjustable magnetic shielding sensor for enhancing the leakage magnetic field detection signal is packaged using the pin principle.

[0031] Furthermore, in the step 5, in the magnetic flux leakage detection system, the adjustable magnetic shielding sensor is connected to an oscilloscope in the control panel, and the defect signal information collected by the adjustable magnetic shielding sensor is displayed in real time by the oscilloscope;

[0032] The adjustable magnetic shielding sensor comprises a detachable packaging box 1, a detachable packaging box 2 and an adjustable magnetic shielding box with a pulley. The detachable packaging box 1 is a rectangular structure without a side cover plate. The detachable packaging box 2 is a thin rectangular cover plate structure corresponding to the detachable packaging box 1. The detachable packaging box 1 and the detachable packaging box 2 are assembled by inserting pins. The adjustable magnetic shielding box with a pulley is a pair of thin rectangular structures with hollow interiors. The pulley and the adjustable magnetic shielding box are horizontally moved by a pulley track. The adjustable magnetic shielding box with a pulley is used to place magnetic shielding plates of different widths, heights and thicknesses. The pulley is used to control the magnetic shielding length arbitrarily. The coil yoke and the magnetic sensitive element are encapsulated in the detachable packaging box 1. Here, the adjustable function of the adjustable magnetic shielding box is used to adjust the geometric parameters of the magnetic shielding, so as to improve the detection signal strength and defect detection capability.

[0033] Furthermore, step 6 is used to test the magnetic flux leakage detection system constructed in step 5, select test pieces with geometric defects or corrosion defects of different defect sizes, perform magnetic flux leakage detection and defect evaluation on them, and test the application capability of the proposed method in actual detection.

[0034] In addition, the present invention provides a method for improving detection sensitivity by adjusting the magnetic shielding effect based on actual magnetic leakage conditions. The detection system includes: an adjustable magnetic shielding magnetic sensor and a control panel including a signal generator, an oscilloscope and a power amplifier;

[0035] The adjustable magnetic shielding magnetic sensor is used to improve the sensitivity of the defect signal during the process of collecting the defect signal;

[0036] The signal generator is used to provide an excitation signal of a specific waveform and frequency;

[0037] The power amplifier is used to amplify the excitation signal in the signal generator. The power amplifier is connected to the magnetization device. The oscilloscope is connected to the magnetization device and the sensor respectively, and is used to display the excitation signal and the signal collected by the sensor in real time.

[0038] Beneficial effects of the present invention:

[0039] The present invention provides a method for improving detection sensitivity by adjusting the magnetic shielding effect based on actual magnetic leakage conditions. An adjustable magnetic shielding box with a pulley in an adjustable magnetic shielding sensor is used to realize magnetic shielding packaging with arbitrary width, height and thickness and control of the horizontal distance between two magnetic shielding boxes.

[0040] The present invention provides a method for improving detection sensitivity by adjusting the magnetic shielding effect based on actual magnetic leakage conditions. The defect-induced magnetic leakage detection signal is enhanced by the proposed adjustable magnetic shielding magnetic sensor, thereby improving the detection capability of small defects and defects in harsh environments.

[0041] The present invention can calculate the optimal adjustable magnetic shielding sensor type and size parameters under different detection conditions through finite element models and intelligent optimization algorithms, and can adapt to the detection signal enhancement requirements under different conditions by adjusting the magnetic shielding parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 Schematic diagram of the process of the present invention.

[0043] Figure 2 Magnetic flux leakage finite element model.

[0044] Figure 3 Finite element model of magnetic flux leakage based on adjustable magnetic shielding.

[0045] Figure 4 The magnetic flux leakage detection data acquisition under different parameters of the adjustable magnetic shielding sensor.

[0046] Figure 5 Optimization analysis of detection effect of adjustable magnetic shielding sensor parameters.

[0047] Figure 6 Schematic diagram of the detection system of the present invention.

[0048] Figure 7 Schematic diagram of a typical geometric configuration of the magnetic shielding material of the present invention.

[0049] Figure 8 It is a schematic diagram of the adjustable magnetic shielding sensor of the present invention.

[0050] Fig. 9 Schematic diagram of the magnetic flux leakage signal enhancement effect of the present invention. DETAILED DESCRIPTION

[0051] The present invention is further described in detail below in conjunction with embodiments.

[0052] Example:

[0053] Based on the magnetic flux leakage detection of oil and gas pipelines as an embodiment, the present invention is further described in detail below with reference to the accompanying drawings.

[0054] As attached Figure 1As shown, the present invention provides a method for improving detection sensitivity by adjusting the magnetic shielding effect based on actual magnetic leakage working conditions. The method includes: constructing a magnetic field analysis finite element model that takes into account parameter information such as the size and material properties of oil and gas pipelines, the size and material properties of magnetization devices, and establishing a magnetic signal detection finite element model that takes into account the parameter information of adjustable magnetic shielding sensors, performing an optimization analysis of parameter detection effects, and then designing and developing a magnetic leakage detection system including an adjustable magnetic shielding sensor based on the optimal parameters of the adjustable magnetic shielding sensor to improve the detection sensitivity of the detection system. The specific implementation methods are as follows:

[0055] Step 1: Construct a finite element model for magnetic flux leakage detection based on the actual detection problem. The finite element model takes into account the geometry, size, material properties (including conductivity, magnetic permeability and relative dielectric constant) of the pipeline to be tested, the geometry, size, material properties (including conductivity, magnetic permeability and relative dielectric constant) of the yoke in the magnetization system, the number of turns of the coil in the magnetization system, and the magnitude of the magnetization current. Figure 2 Maxwell equations are used to solve the leakage magnetic field finite element model, analyze and simulate the distribution and changes of the defect leakage magnetic field. The specific steps are:

[0056] Create a geometric model. Create a geometric model based on the size and shape of the oil and gas pipeline (according to the "GB / T 34275-2017 Pressure Pipeline Long-distance Pipeline" specification, the pipeline material is determined to be carbon steel and low alloy steel, the pipe diameter is 508mm, the maximum wall thickness is 20mm, and the pipe length is 12000mm), the geometric shape and size of the yoke in the magnetization system, the size and type of the coil, and the size of the air domain.

[0057] Define material properties. Assign the correct material properties to each geometric part of the model, including electrical conductivity, magnetic permeability, and relative permittivity for each geometric model.

[0058] Set the boundary conditions and excitation sources. The theoretical equations used for the yoke and air domains are J = σE and B = μ0μ r H, where H is the magnetic field intensity (A / m), J is the current density (A / m 2 ), B is magnetic induction intensity (T), A is magnetic vector potential, E is electric field intensity (V / m), σ is conductivity (S / m), μ0=4π×10 -7 H / m is the vacuum magnetic permeability, μ r is the relative magnetic permeability. The theoretical equation used for the pipeline to be tested is J = σE, B = f(|H|)H / |H|, where |H| is the magnetic field intensity vector, and f(|H|) is a nonlinear function related to the magnetic field vector intensity. This functional relationship is obtained through the magnetic property measurement method. The theoretical equation used by the coil is J = (NV / Acoil R)e and B=μ0μ r H, where N is the number of turns of the coil, e is the unit vector, and A coil is the cross-sectional area of ​​the coil (m 2 ), V is the coil input voltage (V) and R is the coil resistance (Ω).

[0059] Meshing. Dividing the geometry into smaller elements, usually triangles or tetrahedrons.

[0060] Model solving: Choose steady-state, transient or frequency domain solutions according to actual testing requirements.

[0061] Step 2: Establish a finite element model for magnetic signal detection considering the parameter information of the adjustable magnetic shielding sensor, as shown in the attached figure. Figure 3 Based on the finite element model established in step 1, the magnetic signal detection finite element model containing the parameter information of the adjustable magnetic shielding sensor established in step 2 takes into account the additional Figure 7 The four types of magnetic shielding geometries in the diagram are as follows:

[0062] Create a geometric model. Create a geometric model based on the actual size and shape of the pipe being inspected, the geometry and size of the yoke in the magnetizing system, the adjustable magnetic shielding sensor, the size and type of the coil, and the size of the air domain.

[0063] Define material properties. Assign the correct material properties to each geometric part of the model, including electrical conductivity, magnetic permeability, and relative permittivity for each geometric model.

[0064] Set the boundary conditions and excitation sources. The theoretical equations used for the adjustable magnetic shield, yoke, and air domain are: J = σE and B = μ0μ r H, where H is the magnetic field intensity (A / m), J is the current density (A / m 2 ), B is magnetic induction intensity (T), A is magnetic vector potential, E is electric field intensity (V / m), σ is conductivity (S / m), μ0=4π×10 -7 H / m is the vacuum magnetic permeability, μ r is the relative magnetic permeability. The theoretical equation used for the pipeline to be tested is J = σE, B = f(|H|)H / |H|, where |H| is the magnetic field intensity vector, and f(|H|) is a nonlinear function related to the magnetic field vector intensity. This functional relationship is obtained through the magnetic property measurement method. The theoretical equation used by the coil is J = (NV / A coil R)e and B=μ0μ r H, where N is the number of turns of the coil, e is the unit vector, and A coil is the cross-sectional area of ​​the coil (m 2), V is the coil input voltage (V) and R is the coil resistance (Ω).

[0065] Meshing. Dividing the geometry into smaller elements, usually triangles or quadrilaterals.

[0066] Model solution. Choose steady-state, transient or frequency domain solution according to actual needs.

[0067] Step 3: Take different adjustable magnetic shielding sensor parameters to carry out finite element analysis. The parameters include the four magnetic shielding types described in step 2 above, different magnetic shielding lengths, widths, thicknesses and other dimensional parameters. According to the different adjustable magnetic shielding sensor parameters traversed, the finite element model is solved to obtain the leakage magnetic detection signal data of the adjustable magnetic shielding sensor under different parameters. The specific steps are as shown in the attached figure. Figure 4 shown.

[0068] Step 4: Conduct optimization analysis of parameter detection effects. Based on the optimal gradient algorithm or neural network, particle swarm optimization intelligent algorithm, determine the optimal sensitivity, including the optimal magnetic shielding geometry, size and material properties. Figure 5 The detailed operation steps are as follows:

[0069] Data preparation: Based on the finite element model established in step 2, obtain the magnetic flux leakage signal under different parameters of the adjustable magnetic shielding sensor;

[0070] Define the optimization problem: determine the parameters to be optimized (magnetic shield geometry and size); determine the constraints: the size of the magnetic shield must be smaller than the size of the yoke;

[0071] Evaluate the objective function based on the intelligent algorithm: The objective function is in To obtain different magnetic shielding lengths l, different magnetic shielding widths w, different magnetic shielding heights h, different magnetic shielding thicknesses t and different magnetic shielding geometries lx based on the finite element model of the adjustable magnetic shielding sensor i The leakage magnetic signal under the type (i = 1, 2, 3. 4 represents different magnetic shielding geometry types, such as the attached Figure 7 H s is the desired target signal, which can better reflect the sensor's ability to respond to tiny magnetic field changes; j represents the jth sample; k represents the total number of data samples.

[0072] Determine whether the objective function meets the termination conditions: if so, output the optimal magnetic shielding combination type and size parameters; if not, recalculate.

[0073] Step 4: Based on the optimal parameters of the adjustable magnetic shielding sensor, design and develop a magnetic flux leakage detection system including an adjustable magnetic shielding sensor, as shown in the attached Figure 6As shown, the detection system includes an adjustable magnetic shielding sensor for enhancing the leakage magnetic detection signal and a control panel (including a signal generator, an oscilloscope and a power amplifier function, etc.), wherein an adjustable magnetic shielding sensor for enhancing the leakage magnetic detection signal is packaged using a pin principle, including a detachable packaging box 1, a detachable packaging box 2 and an adjustable magnetic shielding box with a pulley, as shown in the attached Figure 8 Attached Figure 8 The adjustable magnetic shielding box with a pulley in the middle is used to place magnetic shields of different widths, heights and thicknesses, and the pulley is used to arbitrarily control the length of the magnetic shielding. The magnetic yoke with coil and the magnetic sensitive element are packaged in a detachable packaging box 1. The adjustable function of the adjustable magnetic shielding box is used here to adjust the geometric parameters of the magnetic shielding material, thereby improving the detection signal strength and defect detection capability.

[0074] Step 5: Test the applicability of the proposed method in actual testing. Select the material to be tested with geometric defects or corrosion defects, conduct magnetic flux leakage detection and defect evaluation on it, and test the applicability of the proposed method in actual testing. Fig. 9 As shown, compared with the traditional magnetic flux leakage detection method, the defect signal detected by the signal enhancement method proposed in this patent is more obvious.

[0075] Thus, the present invention provides a method for improving detection sensitivity by adjusting the magnetic shielding effect based on actual magnetic flux leakage conditions, so as to improve the accuracy and reliability of magnetic flux leakage detection.

Claims

1. A method for improving detection sensitivity by adjusting the magnetic shielding effect based on actual magnetic leakage conditions, characterized in that: The steps include: Step 1: Construct a finite element model for magnetic field analysis based on actual testing conditions; Step 2: Based on the magnetic field analysis finite element model, a magnetic signal detection finite element model considering the parameter information of the adjustable magnetic shielding sensor is established; Step 3: For the adjustable magnetic shielding sensor, take different parameters to carry out finite element model analysis to obtain the leakage magnetic field detection effect under different parameters of the adjustable magnetic shielding sensor; Step 4: Carry out optimization analysis of the leakage magnetic field detection effect under different parameters, and obtain the magnetic shielding parameters corresponding to the optimal detection sensitivity based on the intelligent algorithm according to the leakage magnetic field detection effect of different magnetic shielding parameters; Step 5: Based on the magnetic shielding parameters corresponding to the optimal detection sensitivity, a magnetic flux leakage detection system of an adjustable magnetic shielding sensor is used to achieve high sensitivity and accuracy detection of defects; Step 6: Carry out detection application according to the defect type, defect size and detection object in actual working conditions; Based on the leakage magnetic detection effect of the adjustable magnetic shielding sensor under different parameters obtained in step 3, step 4 performs optimization analysis of the detection effect of the adjustable magnetic shielding sensor through an optimal gradient algorithm or an intelligent algorithm of a neural network or particle swarm optimization; determines the optimal sensitivity, including the optimal magnetic shielding geometry and size. The detailed operation steps are as follows: a) Data preparation: Based on the finite element model established in step 2, the leakage magnetic signal of the adjustable magnetic shielding sensor under different parameters is obtained; b) Define the optimization problem: determine the parameters to be optimized, the magnetic shield geometry and size; optimization conditions, the number of turns of the known coil and the magnetizing current; Determine the constraints: the size of the magnetic shield is smaller than the size of the magnetic yoke; c) Evaluate the objective function based on intelligent algorithm: The objective function is in To obtain different magnetic shielding lengths l, different magnetic shielding widths w, different magnetic shielding heights h, different magnetic shielding thicknesses t and different magnetic shielding geometries lx based on the finite element model of the adjustable magnetic shielding sensor i The leakage magnetic signal under the type, i = 1, 2, 3, 4 represents different magnetic shielding geometry types; H s is the desired target signal, which can reflect the sensor's ability to respond to small magnetic field changes; j represents the jth sample; k represents the total number of data samples; d) Determine whether the objective function meets the termination conditions: if so, output the optimal magnetic shielding combination type and size parameters; if not, recalculate.

2. A method for improving detection sensitivity that can adjust the magnetic shielding effect based on actual magnetic leakage conditions according to claim 1, characterized in that: In step 1, the finite element model for magnetic field analysis includes a powered coil, a magnetic yoke, a test piece, and an air domain; the copper coil is wound around the magnetic yoke to magnetize the test piece, and the air domain is wrapped around the powered coil, the magnetic yoke, and the test piece.

3. A method for improving detection sensitivity that can adjust the magnetic shielding effect based on actual magnetic leakage conditions according to claim 2, characterized in that: The finite element model constructed based on the actual detection problem takes into account the geometry of the test piece, the size of the test piece, the material properties of the test piece, the geometry of the yoke in the magnetization system, the size of the yoke, the material properties of the yoke, the number of turns of the coil in the magnetization system, the parameter information of the magnetization current, the size parameters and material properties of the air domain, and uses the Maxwell equations to solve the leakage magnetic field finite element model to analyze and simulate the distribution and changes of the defect leakage magnetic field. The specific technical solution steps are as follows: a) Establishing a geometric model; creating a geometric model based on the actual size and shape of the object to be detected, the geometric shape and size of the yoke in the magnetization system, the size and type of the coil, and the size of the air domain; b) Define material properties and specify the correct material properties for each geometric part in the geometric model, including the electrical conductivity, magnetic permeability and relative permittivity of each geometric model; c) Set boundary conditions and excitation sources for the finite element model for magnetic field analysis; the theoretical equations used in the yoke and air domain are: J = σE and B = μ0μ r H, where H is the magnetic field intensity, J is the current density, B is the magnetic induction intensity, A is the magnetic vector potential, E is the electric field intensity, σ is the conductivity, μ0=4π×10 -7 H / m is the vacuum magnetic permeability, μ r is the relative magnetic permeability, and the theoretical equation used for the ferromagnetic material to be tested is J = σE, B = f(|H|)H / |H|, where |H| is the magnetic field intensity vector, and f(|H|) is a nonlinear function related to the magnetic field vector intensity. This functional relationship needs to be obtained using the magnetic property measurement method; the theoretical equation used by the coil is J = (NV / A coil R)e and B=μ0μ r H, where N is the number of turns of the coil, e is the unit vector, and A coil is the cross-sectional area of ​​the coil, V is the coil input voltage and R is the coil resistance; d) Meshing, dividing the geometric model into smaller units; e) Model solution: choose steady-state, transient or frequency domain solution according to actual detection requirements.

4. A method for improving detection sensitivity that can adjust the magnetic shielding effect based on actual magnetic leakage conditions according to claim 3, characterized in that: In the step 2, Based on the finite element model constructed in step 1, a magnetic shielding sensor geometric model is first established to determine the size of the geometric model, and then material property parameter information is defined for the geometric model, and the solution equation of magnetic shielding in the finite element model is set, and finally the finite element model is solved; Among them, the theoretical equation used in the finite element model for magnetic shielding analysis is: J = σE and B = μ0μ r H, where H is the magnetic field intensity, J is the current density, B is the magnetic induction intensity, A is the magnetic vector potential, E is the electric field intensity, σ is the conductivity, μ0=4π×10 -7 H / m is the vacuum magnetic permeability, μ r is the relative magnetic permeability.

5. A method for improving detection sensitivity that can adjust the magnetic shielding effect based on actual magnetic leakage conditions according to claim 4, characterized in that: In step 3, finite element analysis is performed by inputting different dimensional parameters of the adjustable magnetic shielding sensor into the model established in step 2 to obtain the leakage magnetic detection effect under different parameters of the adjustable magnetic shielding sensor, including the detection signal results corresponding to the magnetic shielding under different lengths, widths and thicknesses.

6. The method for improving detection sensitivity by adjusting the magnetic shielding effect based on actual magnetic leakage conditions according to claim 1, characterized in that: In the step 5, according to the optimal parameters of the adjustable magnetic shielding sensor determined in step 4, a magnetic flux leakage detection system including the adjustable magnetic shielding sensor is designed and developed, the detection system includes an adjustable magnetic shielding sensor for enhancing the magnetic flux leakage detection signal and a control panel, wherein the adjustable magnetic shielding sensor for enhancing the magnetic flux leakage detection signal is packaged using the pin principle.

7. A method for improving detection sensitivity by adjusting the magnetic shielding effect based on actual magnetic leakage conditions according to claim 6, characterized in that: In the step 5, in the magnetic flux leakage detection system, the adjustable magnetic shielding sensor is connected to an oscilloscope in the control panel, and the defect signal information collected by the adjustable magnetic shielding sensor is displayed in real time through the oscilloscope; The adjustable magnetic shielding sensor comprises a detachable packaging box one (1), a detachable packaging box two (2) and an adjustable magnetic shielding box with a pulley. The detachable packaging box one (1) is a rectangular structure without a side cover plate. The detachable packaging box two (2) is a thin rectangular cover plate structure corresponding to the detachable packaging box one (1). The detachable packaging box one (1) and the detachable packaging box two (2) are assembled by inserting pins. The adjustable magnetic shielding box with a pulley is a pair of thin rectangular structures with hollow interiors. The pulley and the adjustable magnetic shielding box are horizontally moved by a pulley track. The adjustable magnetic shielding box with a pulley is used to place magnetic shields of different widths, heights and thicknesses. The magnetic shielding length can be arbitrarily controlled by the pulley. A magnetic yoke with a coil and a magnetic sensitive element are encapsulated in the detachable packaging box one (1).

8. A method for improving detection sensitivity that can adjust the magnetic shielding effect based on actual magnetic leakage conditions according to claim 7, characterized in that: The step 6 is used to test the magnetic flux leakage detection system built in step 5, select test pieces with geometric defects or corrosion defects of different defect sizes, perform magnetic flux leakage detection and defect evaluation on them, and test the application capability of the proposed method in actual detection.

9. A detection system for implementing the method according to any one of claims 1 to 8 comprising: Adjustable magnetically shielded magnetic sensor and control panel including signal generator, oscilloscope and power amplifier functions; The adjustable magnetic shielding magnetic sensor is used to improve the sensitivity of the defect signal during the process of collecting the defect signal; The signal generator is used to provide an excitation signal of a specific waveform and frequency; The power amplifier is used to amplify the excitation signal in the signal generator. The power amplifier is connected to the magnetization device. The oscilloscope is connected to the magnetization device and the sensor respectively, and is used to display the excitation signal and the signal collected by the sensor in real time.

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