Visualized Defect Detection Method for Ferromagnetic Materials Based on AC / DC Composite Excitation

Abstract

This invention belongs to the field of nondestructive testing technology, and particularly relates to a visual detection method for ferromagnetic material defects based on AC / DC composite excitation. This method overcomes the problem of existing AC electromagnetic field detection methods failing to obtain complete visualization of complex defect morphologies in ferromagnetic materials due to mutual interference between current disturbances and leakage magnetic field disturbances, thus providing more detailed and reliable data support for structural safety assessments of offshore oil platforms and offshore wind power platforms. The visual detection method for ferromagnetic material defects based on AC / DC composite excitation includes the following steps: scanning to obtain a magnetic field signal SBz; extracting the DC component SBz from the magnetic field signal SBz. z and communication component SBz j And form a surface matrix; calculate matrix Bz z Matrix Bz j The difference is used to obtain matrix Bz. By performing operations such as curl calculation, gradient calculation, grayscale conversion and binarization on the array of matrix Bz and the image, the defect contour, disturbance current density and disturbance current line image are obtained.

Description

Technical Field

[0001] This invention belongs to the field of nondestructive testing technology, and particularly relates to a visual testing method for defects in ferromagnetic materials based on AC / DC composite excitation. Background Technology

[0002] Ferromagnetic materials are widely used in the support systems of offshore oil platforms and offshore wind power platforms due to their excellent mechanical properties, corrosion resistance, and superior magnetic characteristics. However, in complex underwater environments, ferromagnetic materials are prone to defects such as cracks, pores, and folds due to the effects of low temperature, high salinity, wave impact, and complex alternating stress. Furthermore, because the direction of stress varies, the location and direction of defect formation are often uncertain.

[0003] Therefore, to effectively assess the surface or internal defects of underwater ferromagnetic materials, timely and accurate defect detection is crucial. One common method for detecting underwater structural defects is alternating current field measurement (ACFM), which detects the magnetic field disturbance caused by surface or near-surface defects, thereby enabling effective identification and detection of surface or internal defects in ferromagnetic materials.

[0004] However, after further research, the inventors discovered that for ferromagnetic materials, when detecting cracks and corrosion defects with complex orientations, the combined effects of current disturbance and magnetic leakage lead to a decrease in the quality of the acquired signals. This ultimately results in incomplete and inaccurate visualization assessment results of defects in ferromagnetic materials, which in turn affects the accurate judgment and quantitative analysis of defects in ferromagnetic materials. Summary of the Invention

[0005] This invention provides a visual detection method for defects in ferromagnetic materials based on AC / DC composite excitation. This method overcomes the problem that existing AC electromagnetic field detection methods cannot obtain complete visualization of complex defect morphologies in ferromagnetic materials due to mutual interference between current disturbances and leakage magnetic disturbances. It provides more detailed and reliable data support for the structural safety assessment of offshore oil platforms and offshore wind power platforms.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A visual detection method for defects in ferromagnetic materials based on AC / DC composite excitation includes the following steps:

[0008] Step 1: Use an AC / DC composite excitation signal to scan the ferromagnetic material under test to obtain the leakage magnetic field signal SBz;

[0009] Step 2: Perform AC / DC filtering on the leakage magnetic field signal SBz and extract its DC component SBz. z and communication component SBz j The DC component SBz was constructed. z The matrix Bz z and communication component SBz j The matrix Bz j ;

[0010] Wherein, matrix Bz z Sum matrix Bz j They respectively satisfy:

[0011] ; ;

[0012] Step 3: For matrix Bz respectively z Matrix Bz j Perform normalization and calculate matrix Bz. z Matrix Bz j The difference is used to obtain matrix Bz;

[0013] Where the matrix Bz satisfies:

[0014] ;

[0015] Step 4: Calculate the curl field matrix Jx in the Y direction and the curl field matrix Jy in the X direction of matrix Bz;

[0016] Step 5: Perform minimum value removal on matrices Jx and Jy to obtain matrices Jx' and Jy';

[0017] Among them, matrices Jx' and Jy' satisfy the following:

[0018] ; ;

[0019] Step 6: Calculate the disturbance current density matrix J based on matrices Jx' and Jy';

[0020] The disturbance current density matrix J satisfies:

[0021] ;

[0022] Step 7: Calculate the gradient field matrix Gy in the Y direction of matrix Jx and the gradient field matrix Gx in the X direction of matrix Jy;

[0023] Where matrices Gx and Gy satisfy the following conditions:

[0024] ;

[0025] ;

[0026] Step 8: Set the values ​​of negative numbers in matrices Jx and Jy to 0, and then obtain matrices Jx'' and Jy''.

[0027] Among them, matrices Jx'' and Jy'' satisfy the following:

[0028] ; ;

[0029] Step 9: Perform grayscale processing on the RGB image obtained by adding the absolute values ​​of matrices Jx'', Jy'' and Gx, and Gy to obtain grayscale image A;

[0030] Binarize the grayscale image A to obtain the defect contour.

[0031] Furthermore, it also includes the following steps:

[0032] Step 10: Convert the RGB image of matrix Bz to grayscale to obtain grayscale image B;

[0033] The gradient matrix ZGx in the X direction and the gradient matrix ZGy in the Y direction of the grayscale image B are constructed. The root mean square of the sum of squares of matrices ZGx and ZGy is solved to obtain the image of the perturbation current line.

[0034] Preferably, in the AC / DC composite excitation signal used in step one, the AC excitation magnetic field and the DC excitation magnetic field are set in the same direction.

[0035] Preferably, the matrix Jx in step four is the X-direction component of the current density, satisfying: ;

[0036] In step four, the matrix Jy represents the Y-direction component of the current density, satisfying:

[0037] .

[0038] This invention provides a visual detection method for defects in ferromagnetic materials based on AC / DC composite excitation. The method includes the following steps: scanning to obtain a magnetic field signal SBz; extracting the DC component SBz from the magnetic field signal SBz. z and communication component SBz j And form a surface matrix; calculate matrix Bz z Matrix Bz jThe difference is used to obtain matrix Bz. By performing operations such as curl calculation, gradient calculation, grayscale conversion and binarization on the array of matrix Bz and the image, the defect contour, disturbance current density and disturbance current line image are obtained.

[0039] The visual detection method for defects in ferromagnetic materials based on AC / DC composite excitation, which has the above-described steps, has at least the following technical advantages compared to existing technologies:

[0040] (1) The present invention provides a visual detection method for ferromagnetic material defects based on AC / DC composite excitation, which calculates matrix Bz. z Matrix Bz j The difference in the values ​​unifies the current disturbance effect and leakage magnetic disturbance effect in electromagnetic composite excitation, and overcomes the technical problems that existing technologies cannot solve the mutual interference between current disturbance and leakage magnetic disturbance and cannot fully visualize the complex defect morphology of ferromagnetic materials.

[0041] (2) The visual detection method for ferromagnetic material defects based on AC-DC composite excitation provided by the present invention provides more detailed and reliable data support for the visual detection of ferromagnetic material defects; its detection process effectively improves the signal-to-noise ratio of AC detection signals, makes full use of the signal characteristics of micro-defects, and has a higher micro-defect detection rate. Attached Figure Description

[0042] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the following drawings:

[0043] Figure 1 A flowchart illustrating a visual detection method for defects in ferromagnetic materials based on AC / DC composite excitation provided by this invention;

[0044] Figure 2 DC component SBz z The matrix Bz z A schematic diagram of the image;

[0045] Figure 3 For the AC component SBz j The matrix Bz j A schematic diagram of the image;

[0046] Figure 4 This is a schematic diagram of the calculated matrix Bz;

[0047] Figure 5 A schematic diagram of the calculated disturbance current density matrix J;

[0048] Figure 6 This is a schematic diagram of the defect contour image obtained after binarization.

[0049] Figure 7 This is a schematic diagram of the calculated disturbance current line image. Detailed Implementation

[0050] This invention provides a visual detection method for defects in ferromagnetic materials based on AC / DC composite excitation. This method overcomes the problem that existing AC electromagnetic field detection methods cannot obtain complete visualization of complex defect morphologies in ferromagnetic materials due to mutual interference between current disturbances and leakage magnetic disturbances. It provides more detailed and reliable data support for the structural safety assessment of offshore oil platforms and offshore wind power platforms.

[0051] This invention provides a method for visually detecting defects in ferromagnetic materials based on AC / DC composite excitation, such as... Figure 1 As shown, it includes the following steps:

[0052] Step 1: Use an AC / DC composite excitation signal to scan the ferromagnetic material under test to obtain the leakage magnetic field signal SBz.

[0053] It is worth noting that during the scanning of the ferromagnetic material under test using a composite AC / DC excitation signal, the direction of the AC / DC magnetic field at the location of the magnetic field sensor is set as the X direction, the direction parallel to the surface of the ferromagnetic material under test and perpendicular to the X direction is set as the Y direction, and the direction perpendicular to the surface of the ferromagnetic material under test is set as the Z direction. In a preferred embodiment of the present invention, the AC excitation magnetic field and the DC excitation magnetic field in the composite AC / DC excitation signal used in step one are preferably set in the same direction.

[0054] Step 2: Perform AC / DC filtering on the leakage magnetic field signal SBz and extract its DC component SBz. z and communication component SBz j The DC component SBz was constructed. z The matrix Bz z and communication component SBz j The matrix Bz j .

[0055] After completing step one, proceed to step two. (See reference below.) Figure 2 ,like Figure 3 As shown, Figure 2 DC component SBz z The matrix Bz z A schematic diagram of the image; Figure 3 For the AC component SBz j The matrix Bz j A diagram illustrating this. Specifically, the matrix Bz... z Sum matrix Bz j They respectively satisfy the following:

[0056] ; .

[0057] Step 3: Calculate matrix Bz z Matrix Bz j The difference is used to obtain the matrix Bz.

[0058] Where the matrix Bz satisfies:

[0059] . The image of matrix Bz can be found as follows: Figure 4 As shown.

[0060] Step 4: Calculate the Y-direction curl field matrix Jx and the X-direction curl field matrix Jy of matrix Bz.

[0061] Wherein, matrices Jx and Jy satisfy:

[0062] ;

[0063] .

[0064] Step 5: Perform minimum value removal on matrices Jx and Jy to obtain matrices Jx' and Jy'.

[0065] Among them, matrices Jx' and Jy' satisfy the following:

[0066] ; .

[0067] Step 6: Calculate the disturbance current density matrix J based on matrix Jx' and matrix Jy'.

[0068] Based on completing step five, step six is ​​further implemented. In a preferred embodiment of the present invention, the disturbance current density matrix J in step six satisfies:

[0069] .

[0070] The image of the disturbance current density matrix J can be found in the following figure. Figure 5 As shown.

[0071] Step 7: Calculate the gradient field matrix Gy in the Y direction of matrix Jx and the gradient field matrix Gx in the X direction of matrix Jy.

[0072] Where matrices Gx and Gy satisfy the following conditions:

[0073] ;

[0074] .

[0075] Step 8: Set the values ​​of negative numbers in matrices Jx and Jy to 0, and then obtain matrices Jx'' and Jy''.

[0076] Among them, matrices Jx'' and Jy'' satisfy the following:

[0077] ; .

[0078] Step 9: Perform grayscale processing on the RGB image obtained by adding the absolute values ​​of matrices Jx'', Jy'' and Gx, and Gy to obtain grayscale image A; perform binarization processing on grayscale image A to obtain the defect contour.

[0079] Building upon step eight, step nine is then implemented. Specifically, the RGB image obtained by adding the absolute values ​​of matrices Jx'', Jy'', Gx, and Gy is converted to grayscale, resulting in grayscale image A. Based on grayscale image A, it is further binarized. The defect contour obtained from the binarization process can be referenced as follows... Figure 6 As shown.

[0080] Furthermore, as a preferred embodiment of the present invention, the visual detection method for ferromagnetic material defects based on AC / DC composite excitation provided by the present invention further includes the following steps:

[0081] Step 10: Convert the RGB image of matrix Bz to grayscale to obtain grayscale image B; construct the X-direction gradient matrix ZGx and Y-direction gradient matrix ZGy of grayscale image B, and solve for the root mean square of the sum of squares of matrices ZGx and ZGy to obtain the image of the disturbance current line.

[0082] Specifically, the RGB image of matrix Bz is converted to grayscale to obtain grayscale image B; then, the perturbation current line image can be obtained by using the X-direction gradient matrix ZGx and the Y-direction gradient matrix ZGy of grayscale image B. This perturbation current line image can be referenced as follows: Figure 7 As shown.

[0083] Thus, the present invention provides a visual detection method for defects in ferromagnetic materials based on AC / DC composite excitation, which obtains the magnetic field signal SBz by scanning and extracts the DC component SBz from the magnetic field signal SBz. z and communication component SBz jA surface matrix was formed. Then, through a series of operations such as curl calculation, gradient calculation, grayscale conversion, and binarization of the array of matrix Bz and the image, the defect contour map, perturbation current density map, and perturbation current line map were calculated. Furthermore, using the defect contour map, perturbation current density map, and perturbation current line map, complete visual detection of defects in ferromagnetic materials can be achieved.

[0084] Finally, to facilitate understanding by those skilled in the art of the present invention regarding the visual detection method for ferromagnetic material defects based on AC / DC composite excitation, an enhanced detection probe structure based on AC / DC composite excitation and a DC excitation device structure are provided here as examples.

[0085] The enhanced detection probe based on AC / DC composite excitation typically includes the following components: a probe housing, a DC excitation device, an AC excitation device, a signal conditioning circuit, a sensor array, signal lines, and wheels. The DC excitation device, AC excitation device, signal conditioning circuit, and sensor array can be optionally installed inside the probe housing. The signal lines can be optionally installed on one side of the probe housing for signal transmission. The wheels are installed on both sides of the signal lines to ensure stable scanning operation of the enhanced detection probe.

[0086] Furthermore, the specific structure of the DC excitation device includes a magnet and a yoke. The magnets are located on both sides of the yoke and are used to generate a static magnetization field on the surface of the ferromagnetic material. The AC excitation device includes an excitation coil and a magnetic core. The excitation coil is wound around the magnetic core and is used to generate an AC magnetic field on the surface of the ferromagnetic material. The AC excitation device is installed below the DC excitation device, and the corresponding sensor array is installed at the bottom of the probe housing directly below the AC excitation device (the number of sensors in the sensor array is set to 101). The sensor array can acquire the magnetic field signal SBz perpendicular to the surface of the ferromagnetic material in space. It should be added that the signal conditioning circuit is installed above the DC excitation device and is used for AC / DC filtering of the magnetic field signal SBz.

[0087] This invention provides a visual detection method for defects in ferromagnetic materials based on AC / DC composite excitation. The method includes the following steps: scanning to obtain a magnetic field signal SBz; extracting the DC component SBz from the magnetic field signal SBz. z and communication component SBz j And form a surface matrix; calculate matrix Bz z Matrix Bz j The difference is used to obtain matrix Bz. By performing operations such as curl calculation, gradient calculation, grayscale conversion and binarization on the array of matrix Bz and the image, the defect contour, disturbance current density and disturbance current line image are obtained.

[0088] The visual detection method for defects in ferromagnetic materials based on AC / DC composite excitation, which has the above-described steps, has at least the following technical advantages compared to existing technologies:

[0089] (1) The present invention provides a visual detection method for ferromagnetic material defects based on AC / DC composite excitation, which calculates matrix Bz. z Matrix Bz j The difference in the values ​​unifies the current disturbance effect and leakage magnetic disturbance effect in electromagnetic composite excitation, and overcomes the technical problems that existing technologies cannot solve the mutual interference between current disturbance and leakage magnetic disturbance and cannot fully visualize the complex defect morphology of ferromagnetic materials.

[0090] (2) The visual detection method for ferromagnetic material defects based on AC-DC composite excitation provided by the present invention provides more detailed and reliable data support for the visual detection of ferromagnetic material defects; its detection process effectively improves the signal-to-noise ratio of AC detection signals, makes full use of the signal characteristics of micro-defects, and has a higher micro-defect detection rate.

[0091] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A visual detection method for defects in ferromagnetic materials based on AC / DC composite excitation, characterized in that, The steps include the following: Step 1: Use an AC / DC composite excitation signal to scan the ferromagnetic material under test to obtain the leakage magnetic field signal SBz; Step 2: Perform AC / DC filtering on the leakage magnetic field signal SBz and extract its DC component SBz. z and communication component SBz j The DC component SBz was constructed. z The matrix Bz z and communication component SBz j The matrix Bz j ; Wherein, matrix Bz z Sum matrix Bz j They respectively satisfy: ； ； Step 3: For matrix Bz respectively z Matrix Bz j Perform normalization and calculate matrix Bz. z Matrix Bz j The difference is used to obtain matrix Bz; Where the matrix Bz satisfies: ； Step 4: Calculate the curl field matrix Jx in the Y direction and the curl field matrix Jy in the X direction of matrix Bz; Step 5: Perform minimum value removal on matrices Jx and Jy to obtain matrices Jx' and Jy'; Among them, matrices Jx' and Jy' satisfy the following: ； ； Step 6: Calculate the disturbance current density matrix J based on matrices Jx' and Jy'; The disturbance current density matrix J satisfies: ； Step 7: Calculate the gradient field matrix Gy in the Y direction of matrix Jx and the gradient field matrix Gx in the X direction of matrix Jy; Where matrices Gx and Gy satisfy the following conditions: ； ； Step 8: Set the values ​​of negative numbers in matrices Jx and Jy to 0, and then obtain matrices Jx'' and Jy''. Among them, matrices Jx'' and Jy'' satisfy the following: ； ； Step 9: Perform grayscale processing on the RGB image obtained by adding the absolute values ​​of matrices Jx'', Jy'' and Gx, and Gy to obtain grayscale image A; Binarize the grayscale image A to obtain the defect contour.

2. The visual detection method for ferromagnetic material defects based on AC / DC composite excitation according to claim 1, characterized in that, It also includes the following steps: Step 10: Convert the RGB image of matrix Bz to grayscale to obtain grayscale image B; The gradient matrix ZGx in the X direction and the gradient matrix ZGy in the Y direction of the grayscale image B are constructed. The root mean square of the sum of squares of matrices ZGx and ZGy is solved to obtain the image of the perturbation current line.

3. The visual detection method for ferromagnetic material defects based on AC / DC composite excitation according to claim 1, characterized in that, In the AC / DC composite excitation signal used in step one, the AC excitation magnetic field and the DC excitation magnetic field are set in the same direction.

4. The visual detection method for ferromagnetic material defects based on AC / DC composite excitation according to claim 1, characterized in that, In step four, the matrix Jx represents the X-direction component of the current density, satisfying: ； In step four, the matrix Jy represents the Y-direction component of the current density, satisfying: 。

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