Quantitative ultrasonic detection and evaluation method for corrosion defects of inner surface of structural part

Abstract

The invention relates to a quantitative ultrasonic detection and evaluation method for corrosion defects on the inner surface of a structural part, and belongs to the technical field of ultrasonic detection. The method mainly comprises the following steps: carrying out positioning ultrasonic C scanning detection on a non-corrosion surface on a structural member, carrying out parameterized quantitative analysis on the corrosion state of the inner surface of the structure based on ultrasonic detection signal characteristics, and carrying out imaging characterization on the corrosion state degree to realize quantitative detection. Then, a physical model of typical corrosion defects is established, results of positioning ultrasonic C scanning detection and high-precision laser sensing 3D digital detection are compared, and an ultrasonic analysis and characterization algorithm is corrected to achieve detection and evaluation. The method can quantitatively detect the corrosion defect of the inner surface of the metal structural member and evaluate the detection precision, provides accurate reference for corrosion detection of the metal structural member in actual production, improves the detection efficiency, greatly reduces the detection cost, and has important significance for actual production.

Description

Technical Field

[0001] The present invention relates to the field of ultrasonic detection technology, and in particular to a quantitative ultrasonic detection and evaluation method for corrosion defects on the inner surface of a structural part, which is mainly applicable to the imaging and quantitative detection and identification of corrosion defects on the inner surface of a metal structural part. Background Art

[0002] In industrial production, metal structural parts are used in all aspects of the production process. After the outer surface of some metal structural parts rusts, it is very easy to be discovered, so that they can be repaired or replaced in time. However, after the inner surface of the metal structural parts corrodes, it is difficult to determine whether there is a corrosion defect by observation. Once the structural parts are damaged due to corrosion defects, the normal production process will be affected, which will bring huge losses.

[0003] Commonly used non-destructive testing technologies include eddy current monitoring, magnetic flux leakage testing, X-ray testing, ultrasonic testing, etc. Eddy current testing can only detect near-surface defects of materials, and has poor detection effect on structures with complex shapes. Magnetic flux leakage testing can only be used to detect ferromagnetic materials, and cannot detect some weakly magnetic or non-magnetic alloy materials. X-ray testing is not easy to operate and is harmful to the human body. At this time, it is the best choice to choose ultrasonic testing, a non-destructive testing technology with the advantages of low cost, high efficiency, high safety and easy operation, to detect corrosion defects on the inner surface of metal structures. The detection methods using ultrasound to detect defects at home and abroad are already quite mature, but the detection methods for the corrosion state of defects on the inner surface of structural parts have been relatively less studied.

[0004] In summary, the current corrosion defect detection methods for the inner surface of metal structures are not comprehensive enough. Some methods only evaluate the degree of corrosion by the depth of the defect, while others only evaluate the degree of corrosion by the surface area of ​​the defect, resulting in the technical problem that the degree of corrosion is not accurately evaluated by a single parameter. Therefore, it is urgent to propose a more comprehensive detection and evaluation method for the corrosion state of the inner wall defects of metal structures, which can realize the imaging and quantitative detection of corrosion defects on the inner surface of metal structures. Summary of the invention

[0005] The purpose of the present invention is to provide a quantitative ultrasonic detection and evaluation method for corrosion defects on the inner surface of a structural part, which solves the technical problem that the existing technology cannot comprehensively evaluate the corrosion state of the inner surface defects of metal structural parts through ultrasonic detection technology, resulting in inaccurate detection of the shape of the inner surface corrosion defects and inaccurate evaluation of the corrosion degree. The present invention mainly realizes the quantitative detection of corrosion defects by performing positioning ultrasonic C-scan detection; then, by establishing a physical model of typical corrosion defects, the positioning ultrasonic C-scan detection is compared with the 3D digital detection of high-precision laser sensing and the ultrasonic analysis and characterization algorithm is corrected to realize the detection and evaluation. The method of the present invention can quantitatively detect the corrosion defects on the inner surface of metal structural parts and evaluate the detection accuracy, which provides an accurate reference for the corrosion detection of metal structural parts in actual production, improves the detection efficiency, and greatly reduces the detection cost, which is of great significance to actual production.

[0006] The above-mentioned object of the present invention is achieved by the following technical solutions: The quantitative ultrasonic detection and evaluation method for corrosion defects on the inner surface of structural parts mainly realizes the quantitative detection of corrosion defects by performing positioning ultrasonic C-scan detection; then, by establishing a physical model of typical corrosion defects, the positioning ultrasonic C-scan detection is compared with the 3D digital detection of high-precision laser sensing and the ultrasonic analysis and characterization algorithm is corrected to realize the detection and evaluation. It includes the following steps: Step 1: Positioning ultrasonic C-scan detection: ultrasonic waves are incident from the outer surface of the structural part, and positioning ultrasonic C-scan detection is performed according to the reflected echo on the inner surface, and the detection data is recorded; Step 2: Quantitative analysis of corrosion defects: perform a parametric quantitative analysis of the corrosion state of the inner surface of the structural parts based on the ultrasonic detection signal feature analysis, including the parametric characterization of the corrosion area and corrosion ratio, the corrosion degree, and the graphical characterization of the corrosion state degree; Step 3: Establish a corrosion defect assessment model: First, establish a physical model of typical corrosion defects, establish a CAD 3D digital defect model through model design, and then prepare a corrosion defect assessment model, and prepare defects on the structural parts through laser digital 3D engraving; finally, detect the model, and use high-precision laser sensing 3D digital detection technology to detect the 3D digital defect model; Step 4: Calibrate the evaluation model: After positioning the physical model with ultrasonic C-scan detection, analyze the ultrasonic signal characteristics; then make a 3D image representation of the corrosion state based on the ultrasonic signal analysis, and finally compare it with the 3D digital image based on laser sensing and correct the ultrasonic analysis and characterization algorithm.

[0007] The positioning ultrasonic C-scan detection described in step 1 is: by selecting the characteristic value of the scanning point in the ultrasonic A wave to perform characteristic imaging analysis detection, and by selecting different characteristic value information to detect the internal cross-sectional state of the structural part at different depths; in the ultrasonic detection process of corrosion defects of the structural part, the ultrasonic probe will emit ultrasonic waves through the water coupling agent to enter the interior of the carbon steel material, and will generate defect echoes when encountering corrosion defects. When there are no defects inside the structural part, the ultrasonic wave will propagate to the bottom of the structural part and reflect. The pulse echo signal received by the ultrasonic probe will be converted into an electrical pulse signal, which will be displayed on the display screen of the industrial computer after ultrasonic A / D signal conversion, thereby obtaining a positioning ultrasonic C-scan detection image.

[0008] Ultrasonic filter processing technology is used to pre-process the positioning ultrasonic C-scan detection image; The mean filtering method is used to take the average data value of the pixel size of all data points inside the detection window as the effective pixel size of the central pixel; if the original pixel of the image is f(x,y) , then the pixel after mean filtering is g (x,y) ,Right now:

[0009] In the formula, the coordinates of each pixel are S, and the sum of all pixels is M; the average value of the pixels in the excluding neighborhood is used to represent the pixel value of the point; the neighborhood processed by the mean filter is selected from 3×3, 5×5, 7×7, etc. N × N , N is an odd number; f ( m , n ) are the original pixels at each coordinate of the image.

[0010] The corrosion area described in step 2 is calculated by calculating the small areas of the corrosion defects and then accumulating them. First, all the scanning line information in the scanning path of the positioning ultrasonic C-scanning detection image after image processing is extracted, entered into the computer, and the defect lengths in all scanning lines in the scanning path of the positioning ultrasonic C-scanning detection image are calculated through the ultrasonic characteristic curve algorithm. Then, the area formed by two adjacent scanning lines and the edge of the corrosion defect is regarded as a trapezoid. The height h of the trapezoid is the moving step length of the detection probe. The area S between each two adjacent scanning lines is regarded as the area of ​​the trapezoid. The defect areas between all adjacent ultrasonic detection scanning lines are added together to obtain the defect area of ​​the corrosion defect on the inner surface of the structural part, that is, the formula

[0011] In the formula a is the length of the upper scanning line, and b is the length of the lower scanning line; The expression of corrosion ratio is: , where S 表 is the surface area of ​​the structural member; The parametric evaluation of the corrosion degree is expressed based on the parameterization of the corrosion depth, thereby achieving the purpose of parametric characterization of the defect corrosion degree. The corrosion depth is calculated by measuring the ultrasonic signal sound path of the corrosion defect on the inner wall of the structural part; the corrosion depth H of the corrosion defect on the inner wall of the structural part to be tested is: H=TS; where T is the thickness of the structural part to be tested, and S is the ultrasonic signal sound path of the corrosion defect on the inner wall of the structural part to be tested; thus, the maximum corrosion depth H is obtained. max =TS min , average corrosion depth ; The determination of the degree of corrosion of structural parts is affected by the corrosion area, corrosion ratio and corrosion depth.

[0012] The high-precision laser sensing 3D digital detection technology described in step three is: using a two-dimensional laser ranging sensor to detect the surface of the prepared 3D digital defect model. The laser emitted by the two-dimensional laser ranging sensor is a line laser, and what is collected is a two-dimensional data point cloud that constitutes the surface contour image of the defect model. Then all the contour data points on the surface of the 3D digital defect model are fitted in three-dimensional space.

[0013] The 3D digital image based on laser sensing described in step 4 is: extracting the three-dimensional morphology of the overall surface of the structural part, performing feature analysis on the single defect contour line, that is, processing the data of each point on a cross section of the defect; in order to more intuitively display the appearance characteristics of complex defects, the overall appearance of the complex defects is visualized, all contour data points on the surface of the 3D digital defect model are fitted in three-dimensional space, and a three-dimensional point cloud representing the appearance morphology of the defect is output.

[0014] The beneficial effects of the present invention are: The current research on quantitative detection and evaluation methods for corrosion defects on the inner surface of metal structural parts at home and abroad is limited to evaluating the degree of corrosion by a single parameter. There is almost no research method for restoring 3D digital images of corrosion defects on the inner surface of structural parts. With the continuous development of ultrasonic detection technology, the method of the present invention can quantitatively detect corrosion defects on the inner surface of metal structural parts and evaluate the detection accuracy, which provides an accurate reference for corrosion detection of metal structural parts in actual production, improves detection efficiency, and greatly reduces detection costs, which is of great significance to actual production. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The drawings described herein are used to provide further understanding of the present invention and constitute a part of this application. The illustrative examples of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0016] Figure 1 It is a schematic diagram of the evaluation method flow of the present invention; Figure 2 It is a schematic diagram of the 3D digital defect model of the present invention; Figure 3 Selecting a neighborhood method for the mean filtering process of the present invention; Figure 4 A schematic diagram for solving the corrosion defect area of ​​the present invention; Figure 5 It is a schematic diagram of ultrasonic radio frequency of defect depth of the present invention. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0018] See also Figures 1 to 5 As shown, the quantitative ultrasonic detection and evaluation method of corrosion defects on the inner surface of metal structural parts based on ultrasonic technology of the present invention mainly realizes quantitative detection by performing positioning ultrasonic C-scan detection on the non-corroded surface on the metal structural part, and then performing parameterized quantitative analysis on the corrosion state of the inner surface of the structure based on the characteristics of the ultrasonic detection signal, and performing graphical characterization of the degree of corrosion state. Then, by establishing a physical model of typical corrosion defects, the results of positioning ultrasonic C-scan detection and 3D digital detection by high-precision laser sensing are compared and the ultrasonic analysis and characterization algorithm is corrected to realize detection and evaluation. This method can quantitatively detect corrosion defects on the inner surface of metal structural parts and evaluate their detection accuracy, providing an accurate reference for corrosion detection of metal structural parts in actual production, improving detection efficiency, and greatly reducing detection costs, which is of great significance to actual production.

[0019] See also Figure 1 As shown, the detection method comprises the following steps: Step 1: Positioning ultrasonic C-scan detection: ultrasonic waves are incident from the outer surface of the structural part, and positioning ultrasonic C-scan detection is performed according to the reflected echo on the inner surface, and the detection data is recorded.

[0020] Step 2: Quantitative analysis of corrosion defects: Carry out parametric quantitative analysis of the corrosion state of the inner surface of the structural parts based on the characteristic analysis of ultrasonic detection signals. This includes parametric characterization of the corrosion area, corrosion ratio, and corrosion degree, as well as graphical characterization of the corrosion state degree.

[0021] Step 3: Establish a corrosion defect assessment model: First, establish a physical model of typical corrosion defects, and then establish a CAD 3D digital defect model through model design, such as Figure 2 As shown, a corrosion defect evaluation model is then prepared, and defects are prepared on the structural parts through laser digital 3D engraving; finally, the model is detected, and the 3D digital defect model is detected using high-precision laser sensing 3D digital technology.

[0022] Step 4: Calibrate the evaluation model: After positioning the physical model with ultrasonic C-scan detection, analyze the ultrasonic signal characteristics. Then, make a 3D image representation of the corrosion state based on the ultrasonic signal analysis, and finally compare it with the 3D digital image based on laser sensing and correct the ultrasonic analysis and characterization algorithm.

[0023] In step one, the positioning ultrasonic C-scan detection is: by selecting the characteristic value of the scanning point in the ultrasonic A wave to perform characteristic imaging analysis detection, the internal cross-sectional state of the structural part can be detected at different depths by selecting different characteristic value information. In the ultrasonic detection process of corrosion defects of the structural part of the present invention, the ultrasonic probe will emit ultrasonic waves through the water coupling agent to enter the interior of the carbon steel material, and will generate defect echoes when encountering corrosion defects. If there are no defects inside the structural part material, the ultrasonic wave will propagate to the bottom of the structural part and reflect. The pulse echo signal received by the ultrasonic probe will be converted into an electrical pulse signal, which will be displayed on the display screen of the industrial computer after ultrasonic A / D signal conversion, thereby obtaining a positioning ultrasonic C-scan detection image.

[0024] Ultrasonic filter processing technology is used to pre-process the positioning ultrasonic C-scan detection image; The average data value of the pixel size of all data points inside the detection window is taken as the effective pixel size of the central pixel; if the original pixel of the image is f(x,y) , then the pixel after mean filtering is g(x,y) ,Right now:

[0025] In the formula, the coordinates of each pixel are S, and the sum of all pixels is M; the average value of the pixels in the removed neighborhood is used to represent the pixel value of the point; f ( m , n ) is the original pixel of each coordinate of the image; the neighborhood of mean filter processing is selected as 3×3, 5×5, 7×7...N × N , N is an odd number, such as Figure 3 shown.

[0026] The corrosion area described in step 2 is calculated by calculating the small areas of the corrosion defects and then accumulating them. First, all the scanning line information in the scanning path of the positioning ultrasonic C-scanning detection image after image processing is extracted, entered into the computer, and the defect lengths in all scanning lines in the scanning path of the positioning ultrasonic C-scanning detection image are calculated through the ultrasonic characteristic curve algorithm. Then, the area formed by two adjacent scanning lines and the edge of the corrosion defect is regarded as a trapezoid. The height h of the trapezoid is the moving step length of the detection probe, and the area S between each two adjacent scanning lines is regarded as the area of ​​the trapezoid, such as Figure 4 As shown in the figure, the defect area between all adjacent ultrasonic inspection scanning lines is added to obtain the corrosion defect area on the inner surface of the structural part, that is, the formula

[0027] Where a is the length of the upper scanning line, and b is the length of the lower scanning line; The expression of corrosion ratio is: , where S 表 is the surface area of ​​the structural member; The parametric evaluation of the corrosion degree is expressed based on the parameterization of the corrosion depth, thereby achieving the purpose of parametric characterization of the degree of defect corrosion. The corrosion depth can be calculated by measuring the ultrasonic signal sound path of the corrosion defect on the inner wall of the metal structure. The corrosion depth H of the corrosion defect on the inner wall of the structure to be tested is: H=TS; where T is the thickness of the structure to be tested, and S is the ultrasonic signal sound path of the corrosion defect on the inner wall of the structure to be tested, such as Figure 5 As shown. It can be deduced that the maximum corrosion depth H max =TS min , average corrosion depth ; The determination of the degree of corrosion of structural parts is affected by the corrosion area, corrosion ratio and corrosion depth.

[0028] The high-precision laser sensing 3D digital detection technology described in step three is: using a two-dimensional laser ranging sensor to detect the surface of the prepared 3D digital defect model. The laser emitted by the two-dimensional laser ranging sensor is a line laser, and what is collected is a two-dimensional data point cloud that constitutes the surface contour image of the defect model. Then all the contour data points on the surface of the 3D digital defect model are fitted in three-dimensional space.

[0029] The 3D digital image based on laser sensing described in step 4 is: extracting the three-dimensional morphology of the overall surface of the structural part, performing feature analysis on the single defect contour line, that is, processing the data of each point on a cross section of the defect; in order to more intuitively display the appearance characteristics of complex defects, the overall appearance of the complex defects is visualized, all contour data points on the surface of the 3D digital defect model are fitted in three-dimensional space, and a three-dimensional point cloud representing the appearance morphology of the defect is output. Example

[0030] In this embodiment, quantitative ultrasonic testing and evaluation is performed on carbon steel materials widely used in metal structural parts. The plate size is 180mm×120mm×10mm. Laser digital 3D engraving is used to prepare corrosion defects of size S and area on the plate. 1 =25mm 2 , depth H 1 =3mm defect, and corrosion defect 2 area size S 2 =10mm 2 , depth H 2 =1mm defect; positioning ultrasonic C scanning detection is adopted, the center frequency of the excitation probe is 5MHz, and the excitation incident angle is 90°. The detection and evaluation method of the present invention is used to detect carbon steel materials and perform characteristic analysis on ultrasonic signals, and a 3D image representation of the corrosion state is made based on the ultrasonic signal analysis. The 3D digital image based on laser sensing is then detected by using high-precision laser sensing 3D digital detection technology for comparison and correction of the ultrasonic analysis and characterization algorithm; in order to verify the accuracy of the evaluation model, its determination coefficient and root mean square error are calculated, and the determination coefficient is 0.9753, indicating that the fitting effect is good, and the root mean square error is 1.0537, indicating that the error between the predicted value and the actual value is small. The results show that the corrosion defect results detected by the method of the present invention are compared with the actual corrosion defect results, and the accuracy rate is as high as 97%.

[0031] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made to the present invention shall be included in the protection scope of the present invention.

Claims

1. A quantitative ultrasonic detection and evaluation method for corrosion defects on the inner surface of a structural part, characterized in that: The quantitative detection of corrosion defects is achieved by positioning ultrasonic C-scan detection, and then the physical model of typical corrosion defects is established, and the detection evaluation is achieved by comparing the positioning ultrasonic C-scan detection with the 3D digital detection of high-precision laser sensing and correcting the ultrasonic analysis and characterization algorithm; the following steps are included: Step 1: Positioning ultrasonic C-scan detection: ultrasonic waves are incident from the outer surface of the structural part, and positioning ultrasonic C-scan detection is performed according to the reflected echo of the ultrasonic waves on the inner surface, and the detection data is recorded; Step 2: Quantitative analysis of corrosion defects: perform a parametric quantitative analysis of the corrosion state of the inner surface of the structural parts based on the ultrasonic detection signal feature analysis, including the parametric characterization of the corrosion area and corrosion ratio, the corrosion degree, and the graphical characterization of the corrosion state degree; Step 3: Establish a corrosion defect assessment model: First, establish a physical model of typical corrosion defects, establish a CAD 3D digital defect model through model design, and then prepare a corrosion defect assessment model, and prepare defects on the structural parts through laser digital 3D engraving; finally, detect the model, and use high-precision laser sensing 3D digital detection technology to detect the 3D digital defect model; Step 4: Calibrate the evaluation model: After positioning the physical model with ultrasonic C-scan detection, analyze the ultrasonic signal characteristics; then make a 3D image representation of the corrosion state based on the ultrasonic signal analysis, and finally compare it with the 3D digital image based on laser sensing and correct the ultrasonic analysis and characterization algorithm.

2. The quantitative ultrasonic detection and evaluation method for corrosion defects on the inner surface of a structural part according to claim 1 is characterized in that: The positioning ultrasonic C-scan detection described in step 1 is: by selecting the characteristic value of the scanning point in the ultrasonic A wave to perform characteristic imaging analysis detection, and by selecting different characteristic value information to detect the internal cross-sectional state of the structural part at different depths; in the ultrasonic detection process of corrosion defects of the structural part, the ultrasonic probe will emit ultrasonic waves through the water coupling agent to enter the interior of the carbon steel material, and will generate defect echoes when encountering corrosion defects. When there are no defects inside the structural part, the ultrasonic wave will propagate to the bottom of the structural part and reflect. The pulse echo signal received by the ultrasonic probe will be converted into an electrical pulse signal, which will be displayed on the display screen of the industrial computer after ultrasonic A / D signal conversion, thereby obtaining a positioning ultrasonic C-scan detection image.

3. The quantitative ultrasonic detection and evaluation method for corrosion defects on the inner surface of a structural part according to claim 2 is characterized in that: Ultrasonic filter processing technology is used to pre-process the positioning ultrasonic C-scan detection image; The mean filtering method is used to take the average data value of the pixel size of all data points inside the detection window as the effective pixel size of the central pixel; if the original pixel of the image is f(x,y) , then the pixel after mean filtering is g(x, y) ,Right now: ； In the formula, the coordinate of each pixel is S, and the sum of all pixels is M; The pixel value of a point is expressed by using the average pixel value of the denoted neighborhood. The neighborhood processed by the mean filter is selected from 3×3, 5×5, 7×7, etc. N × N , N is an odd number; f ( m , n ) are the original pixels at each coordinate of the image.

4. The quantitative ultrasonic detection and evaluation method for corrosion defects on the inner surface of a structural component according to claim 1 is characterized in that: The corrosion area described in step 2 is calculated by calculating the small areas of the corrosion defect and then accumulating them. First, all the scanning line information in the scanning path of the positioning ultrasonic C-scanning detection image after image processing is extracted, entered into the computer, and the defect lengths in all scanning lines in the scanning path of the positioning ultrasonic C-scanning detection image are calculated by the ultrasonic characteristic curve algorithm. Then, the area formed by two adjacent scanning lines and the edge of the corrosion defect is regarded as a trapezoid. The height h of the trapezoid is the moving step length of the detection probe. The area S between each two adjacent scanning lines is regarded as the area of ​​the trapezoid. The defect areas between all adjacent ultrasonic detection scanning lines are added together to obtain the defect area of ​​the corrosion defect on the inner surface of the structural part, that is, the formula: ； In the formula a is the length of the upper scanning line, and b is the length of the lower scanning line; The expression of corrosion ratio is: , where S 表 is the surface area of ​​the structural member; The parametric evaluation of the corrosion degree is based on the parametric expression of the corrosion depth to achieve the purpose of parametric characterization of the corrosion degree of the defect. The corrosion depth is calculated by measuring the ultrasonic signal sound path of the corrosion defect on the inner wall of the structural part; the corrosion depth of the corrosion defect on the inner wall of the structural part to be tested is H=TS; where T is the thickness of the structural part to be tested, and S is the ultrasonic signal sound path of the corrosion defect on the inner wall of the structural part to be tested; thus, the maximum corrosion depth H is obtained. max =TS min , average corrosion depth ; The determination of the degree of corrosion of structural parts is affected by the corrosion area, corrosion ratio and corrosion depth.

5. The quantitative ultrasonic detection and evaluation method for corrosion defects on the inner surface of a structural component according to claim 1, characterized in that: The high-precision laser sensing 3D digital detection technology described in step three is: using a two-dimensional laser ranging sensor to detect the surface of the prepared 3D digital defect model. The laser emitted by the two-dimensional laser ranging sensor is a line laser, and what is collected is a two-dimensional data point cloud that constitutes the surface contour image of the defect model. Then all the contour data points on the surface of the 3D digital defect model are fitted in three-dimensional space.

6. The quantitative ultrasonic detection and evaluation method for corrosion defects on the inner surface of a structural component according to claim 1, characterized in that: The 3D digital image based on laser sensing described in step 4 is: extracting the three-dimensional morphology of the overall surface of the structural part, performing feature analysis on the single defect contour line, that is, processing the data of each point on a cross section of the defect; visualizing the overall appearance of the complex defect, fitting all contour data points on the surface of the 3D digital defect model in three-dimensional space, and outputting a three-dimensional point cloud representing the appearance of the defect.

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