Ultrasonic imaging method for pipeline axial defects based on modified mode synthetic aperture focusing

Abstract

The present invention belongs to the field of nondestructive testing technology and proposes a method for ultrasonic imaging of pipeline axial defects based on modified mode synthetic aperture focusing. This method utilizes a detection system consisting of a phased array ultrasonic detector, a phased array probe, and an angle wedge to acquire a B-scan image from one side of the pipeline area to be inspected. For each reconstruction point, all 21 mode waves are selected from the B-scan image to perform a nonlinear correction of the propagation time to account for curvature. Delayed superposition processing is then performed to select the mode wave image with the strongest response, thereby enabling contour reconstruction and quantitative detection of a priori unknown defects. This method takes into account the influence of pipeline curvature on ultrasonic propagation. Through nonlinear correction of the propagation time, delayed superposition processing, and mode selection, the contour reconstruction of pipeline axial defects is achieved, significantly improving the quantification accuracy of defects.

Description

Technical Field

[0001] The present invention relates to the technical field of nondestructive testing, and in particular to a pipeline axial defect ultrasonic imaging method based on modified mode synthetic aperture focusing. Background Art

[0002] Pipeline structures are widely used in the industrial field. However, during the manufacturing and service process, internal defects can occur due to factors such as processing technology and operating environment, seriously affecting the service life of the pipeline and production safety. Based on the characteristics of the pipeline structure, defects can be divided into two categories: circumferential defects are those whose major axis is perpendicular to the pipeline axis; axial defects are those whose major axis is parallel to the pipeline axis.

[0003] At present, ultrasonic testing and post-processing technology has been widely used in pipeline structural defect detection. When ultrasonically detecting circumferential defects, the sound beam is incident from a plane and intersects with the detection surface where the defect is located. The pipeline detection and processing methods are not much different from those of flat plates. In contrast, when detecting axial defects, due to the curvature of the inner and outer surfaces of the pipeline, the incident and exit paths of the sound beam change, making it difficult to directly use the ultrasonic detection and post-processing methods for circumferential defects. At present, some studies have focused on the impact of pipeline curvature on ultrasonic detection. For example, when using TOFD technology to detect axial defects in pipelines, the defects can be effectively located in depth by combining the arc shape characteristics in the B-scan image (Jin SJ, Zhang B, Sun X, Lin L. Reduction of layered dead zone in time-of-flight diffraction (TOFD) for pipeline with spectrum analysis method [J]. Journal of Nondestructive Evaluation. 2021, 40(2): 48). It should be pointed out that this method can only obtain diffraction waves at the end points of the defect, and it is difficult to clearly determine the shape contour and orientation information of the defect; at the same time, TOFD technology is not sensitive to volume defects, and there are certain difficulties in its application in the engineering field.

[0004] Synthetic aperture focusing technology extracts the array A-scan signal from the B-scan image and selects the direct mode for time-delayed superposition processing, which helps to obtain the contour features of a priori unknown defects, thereby achieving accurate defect quantification and location (Xiang Bo. Research on ultrasonic imaging methods of welds based on synthetic aperture [D]. Wuhan: Wuhan University of Technology, 2018). However, the above research focuses on defects in flat plates, and the influence of pipe curvature on the beam path and acoustic timing cannot be ignored. Therefore, it is necessary to modify the conventional synthetic aperture focusing technology and select the optimal detection mode to obtain the most intuitive defect detection image, thereby achieving defect property identification and quantitative detection. Summary of the Invention

[0005] This invention provides a method for ultrasonic imaging of axial defects in pipelines based on modified synthetic aperture focusing. This method aims to address the problem of increased error in quantitative defect detection caused by acoustic time calculation deviations due to pipeline curvature. By using a phased array probe (2) to capture B-scan images, nonlinear acoustic time corrections are performed for 21 modes of wave propagation, taking into account pipeline curvature. By applying time-delayed superposition processing and mode selection to each reconstruction point in the inspected area, the defect contour is reconstructed, enabling quantitative defect detection.

[0006] The present invention employs the following technical solution: a method for ultrasonic imaging of pipeline axial defects based on modified mode synthetic aperture focusing. The method comprises a detection system consisting of a phased array ultrasonic detector 1, a phased array probe 2, and an angle wedge 3. A B-scan image is acquired from one side of the pipeline's inspection area. For each reconstruction point, all 21 mode waves are selected from the B-scan image to perform a nonlinear correction of the propagation time of sound, taking curvature into account. A time-delayed superposition process is performed to select the mode wave image with the strongest absolute amplitude, thereby enabling contour reconstruction and quantitative detection of a priori unknown defects.

[0007] The specific steps are as follows:

[0008] Step 1. Determine the detection parameters

[0009] According to the material, shape and size information of the pipeline to be tested, the center frequency and number of array elements of the phased array probe 2 and the angle wedge 3 that matches the curvature of the surface of the sample to be tested are selected;

[0010] Step 2. B-scan image acquisition

[0011] Connect the phased array ultrasonic detector 1, phased array probe 2 and angle wedge 3 in sequence, and place the phased array probe 2 on one side of the area to be detected; when the number of array elements of the phased array probe 2 is N, a B scan image containing N A scan signals is collected, and the coordinates of the i-th array element are (x i ,y i ), the array element transmit and receive signals are defined as L i (); where 1≤i≤N;

[0012] Step 3. Reconstruct the regional mesh

[0013] The axis of the pipeline to be tested is used as the coordinate origin, and the area to be tested is gridded. Each grid node is defined as an image reconstruction point, forming a reconstruction area with m×n reconstruction points. The coordinates of any reconstruction point P are (a l ,b w ), where 1≤l≤m, 1≤w≤n;

[0014] Step 4. Correction model calculation

[0015] Determine the transmitting and receiving array elements i and the reconstruction point P. Considering the mode conversion of the sound wave on the pipeline and defect surface, a total of 21 different mode waves are generated. According to the characteristics of the sound beam path, the imaging mode is divided into direct mode, half-span mode and full-span mode. L represents the longitudinal wave and T represents the shear wave. The direct mode includes three mode waves: LL, TT and LT. The half-span mode includes eight mode waves: LLL, LTL, LTT, LLT, TTT, TLL, TTL and TLT. The full-span mode includes ten mode waves: LLLL, LTLL, TLLL, LLTT, TLLT, TLTL, LTTL, TLTT, LTTT and TTTT. For each mode wave, the total acoustic time t of the Gth mode wave is obtained through the reconstruction point P. i-G (a l ,b w ) Take the incident sound time t ip-G (a l ,b w ) and the emitted sound time t pi-G (a l ,b w ), where 1≤G≤21;

[0016] t i-G (a l ,b w )=t ip-G (a l ,b w )+t pi-G (a l ,b w )1)

[0017] When the axial defect detection of the pipeline to be tested is performed, the coupling surface of the angle wedge (3) and the pipeline to be tested is a curved surface, and the coordinates of the incident point and the exit point of the i-th array element sound beam are A(x j ,y j ) and B(x k ,y k ), then the nonlinear propagation of sound satisfies:

[0018]

[0019] When the outer surface radius of the pipe to be measured is R1, the angle wedge 3 and the interface between the pipe to be measured, incident point A and exit point B, satisfy the following conditions:

[0020]

[0021] Correction calculation is performed for each mode. The imaging modes are divided into direct mode, half-span mode and full-span mode. Different imaging modes have different incident sound time t ip-G (a l ,b w ) and the emitted sound time tpi-G (a l ,b w ) is calculated differently;

[0022] When the imaging mode is direct mode, the transmitted and received signals only pass through the interface between the angle wedge 3 and the outer surface of the pipe to be measured, and only the influence of the curved surface is considered. At this time, t ip-G (a l ,b w ) and t pj-G (a l ,b w ) are:

[0023]

[0024] Where c0 represents the longitudinal wave speed in the angle wedge 3, c d1 、c d2 are the sound velocities corresponding to the path of the sound beam in the pipe to be tested during the incident and exit processes, respectively, and are the longitudinal wave speed or shear wave speed of the pipe material to be tested;

[0025] When the imaging mode is half-span mode, the transmitted signal is reflected on the inner surface of the pipe to be measured. The radius of the inner surface of the pipe is R2, and the coordinates of the reflection point are Q(x q ,y q )satisfy

[0026]

[0027] The inner and outer surfaces of the incident sound beam where the mode conversion occurs are both curved surfaces, and the outgoing sound beam is only affected by the curvature of the outer surface of the pipe to be tested, so t ip-G (a l ,b w ) and t pj-G (a l ,b w ) are:

[0028]

[0029] Where c h1 with c h2 is the corresponding sound velocity of the two sections of the sound beam path in the pipe during the incident process, c h3 is the sound velocity corresponding to the path of the sound beam in the pipe during the emission process, c h1 、c h2 、c h3 is the longitudinal wave sound velocity or shear wave sound velocity of the pipeline material;

[0030] When the imaging mode adopts the full-span mode, both the transmitting and receiving signals are reflected on the inner surface of the pipe. At this time, the reflection point coordinates Q1(x q1 ,y q1) and the reflection point coordinates Q2(x q2 ,y q2 )satisfy

[0031]

[0032] In the full-span mode, both the incident and outgoing sound beams undergo mode conversion on the inner and outer surfaces of the pipe to be tested, so t ip-G (a l ,b w ) and t pj-G (a l ,b w ) are respectively

[0033]

[0034] Where c f1 with c f2 is the corresponding sound velocity of the two sections of the sound beam path in the pipe to be measured during the incident process, c f3 with c f4 is the corresponding sound velocity of the two sections of the sound beam path in the pipe to be measured during the emission process, c f1 、c f2 、c f3 、c f4 is the longitudinal wave velocity or shear wave velocity of the pipeline material to be tested;

[0035] From L i Select the sound time t in () i-G (a l ,b w ) corresponds to the amplitude L i (t i-G (a l ,b w )) is the signal amplitude of the Gth mode wave of the array element i at the reconstruction point P;

[0036] Step 5. Time-lapse overlay and mode selection

[0037] The N A-scan signals in the B-scan image are subjected to 21 types of delayed superposition processing of mode waves. The process is as follows:

[0038]

[0039] Select the strongest response I from all mode waves at all reconstruction points max , the process is expressed by the following formula:

[0040]

[0041] In the formula, (a l ,b w ) are the coordinates of any point in the imaging area;

[0042] Then, the strongest response I max The corresponding mode wave G is used as the mode wave for final imaging and defect assessment; Step 6. Qualitative and quantitative detection of defects

[0043] The optimal mode wave obtained in step 5 is used to image the reconstructed area, obtain the contour reconstructed image of the unknown defect and perform qualitative identification; finally, the -6dB method is used to quantify the depth, size and tilt angle of the defect.

[0044] The present invention has the following beneficial effects: This method for ultrasonic imaging of axial defects in pipelines based on modified synthetic aperture focusing takes into account the influence of pipeline curvature on ultrasonic propagation. Through nonlinear correction of propagating sound, time-delayed superposition processing, and mode selection, it reconstructs the contours of axial defects in pipelines, significantly improving the accuracy of defect quantification. Furthermore, this method can be integrated into phased array ultrasonic detectors and implemented in conjunction with scanners, demonstrating its promising application prospects and potential for widespread adoption. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Schematic diagram of the detection system used in the present invention.

[0046] Figure 2(a) is a schematic diagram of a carbon steel pipe specimen with an axial crack machined with an inclination angle of -45°.

[0047] Figure 2(b) is a schematic diagram of a carbon steel pipe specimen machined with an axial crack with an inclination angle of 0°.

[0048] Figure 2(c) is a schematic diagram of a carbon steel pipe specimen with an axial crack machined at an inclination angle of 45°.

[0049] Figure 3(a) shows the imaging result of an axial crack at an inclination angle of -45° based on conventional synthetic aperture focusing technology.

[0050] Figure 3(b) shows the imaging result of an axial crack at a tilt angle of 0° based on conventional synthetic aperture focusing technology.

[0051] Figure 3(c) shows the imaging result of an axial crack at an inclination angle of 45° based on conventional synthetic aperture focusing technology.

[0052] FIG4( a ) is an imaging result of an axial crack with an inclination angle of -45° obtained based on the method of the present invention.

[0053] FIG4( b ) is an imaging result of an axial crack with an inclination angle of 0° obtained based on the method of the present invention.

[0054] FIG4( c ) is an imaging result of an axial crack with an inclination angle of 45° obtained based on the method of the present invention.

[0055] In the figure: 1-phased array ultrasonic detector; 2-phased array probe; 3-angle wedge. DETAILED DESCRIPTION

[0056] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0057] The ultrasonic imaging method of pipeline axial defects based on modified mode synthetic aperture focusing adopts a detection system such as Figure 1 As shown, it includes a phased array ultrasonic detector 1, a phased array probe 2, and an angle wedge 3 of tilted organic glass. The dotted box of the pipeline to be inspected is the area to be inspected. The specific inspection and processing steps are as follows:

[0058] In step (a), the inspected pipes were carbon steel pipe specimens with a wall thickness of 20 mm and an outer diameter of 200 mm. Axial cracks were machined into the specimens, each with a length of 5 mm and a center depth of 10 mm. The cracks had inclination angles of -45°, 0°, and 45°, with the vertical direction set at 0° and the clockwise direction considered positive, as shown in Figures 2(a), 2(b), and 2(c).

[0059] Step (b) uses a phased array ultrasonic detector 1, a phased array probe 2 with a center frequency of 5 MHz and 32 array elements, and an angle wedge 3 with a 55° curved surface to detect defects, wherein the sampling frequency is 100 MHz, the longitudinal wave speed of the angle wedge 3 is 2330 m / s, the shear wave speed of the carbon steel test block is 3230 m / s, and the longitudinal wave speed is 5900 m / s.

[0060] Step (c): using the B-scan acquisition function of the phased array ultrasonic detector 1 to acquire signals from one side of the area to be detected, and obtaining 32 A-scan signals containing different mode waves.

[0061] Step (d) establishes a rectangular coordinate system and divides the area to be inspected into 100×100 rectangular grids. Figures 3(a), 3(b) and 3(c) show the imaging results of cracks at different tilt angles based on conventional synthetic aperture focusing technology. The image can give some features of the defect, but the contour is incomplete, which is not conducive to the accurate identification and quantitative detection of the defect properties. The coordinates of the crack endpoints are read from the imaging image for calculation. The length quantitative errors of -45°, 0° and 45° axial cracks are 3.02mm, 1.11mm and 0.53mm respectively, the angle quantitative errors are 4.09°, 17.97° and 4.54° respectively, and the depth quantitative errors are 2.95mm, 8.15mm and 0.25mm respectively. The defect quantitative error is large, and the 0° crack is even misjudged as an inner surface open crack.

[0062] Step (e), for the ultrasonic imaging method for pipeline axial defects based on modified pattern synthetic aperture focusing proposed by the present invention, for each grid point in the area to be detected, the propagation acoustic time of 21 different mode waves between each group of transmitting and receiving array elements is obtained by nonlinear correction calculation. On this basis, the 21 mode waves are delayed superposition, imaging and mode comparison are performed, and the mode wave image corresponding to the strongest response in the imaging area is selected as the defect imaging result, as shown in Figure 4 (a), Figure 4 (b) and Figure 4 (c). The contours of each crack are completely reconstructed, and the length quantitative errors are 0.62mm, 0.10mm and 0.05mm respectively, the angle quantitative errors are 0°, 1° and 0° respectively, and the depth quantitative errors are 0.25mm, 0.25mm and 0.05mm respectively. The quantitative, positioning and orientation measurement errors of pipeline axial cracks are significantly reduced. In summary, this method realizes the contour reconstruction of pipeline axial defects, and the quantitative and positioning errors are small, meeting engineering requirements.

[0063] The descriptions presented in the above exemplary embodiments are only intended to illustrate the technical solutions of the present invention and are not intended to be exhaustive or to limit the present invention to the precise forms described. Obviously, it is possible for a person of ordinary skill in the art to make many changes and variations based on the above teachings. The exemplary embodiments are selected and described in order to explain the specific principles of the present invention and its practical applications, so that other persons skilled in the art can easily understand, implement and utilize the various exemplary embodiments of the present invention and its various selected forms and modified forms. The scope of protection of the present invention is intended to be defined by the appended claims and their equivalents.

Claims

1. A pipeline axial defect ultrasonic imaging method based on modified mode synthetic aperture focusing, characterized in that: The method is based on a detection system composed of a phased array ultrasonic detector (1), a phased array probe (2) and an angle wedge (3), and collects a B-scan image from one side of the pipeline to be detected area; for each reconstruction point, all 21 mode waves are selected from the B-scan image to perform a propagation sound time nonlinear correction considering curvature; a time delay superposition process is performed to select the mode wave image with the strongest absolute amplitude, thereby realizing contour reconstruction and quantitative detection of a priori unknown defects; The specific steps are as follows: Step 1. Determine the detection parameters According to the material, shape and size information of the pipeline to be tested, the center frequency and number of array elements of the phased array probe (2) and the angle wedge (3) that matches the curvature of the surface of the sample to be tested are selected; Step 2. B-scan image acquisition Connect the phased array ultrasonic detector (1), the phased array probe (2) and the angle wedge (3) in sequence, and place the phased array probe (2) on one side of the area to be detected; when the number of array elements of the phased array probe (2) is N, a B scan image containing N A scan signals is collected, and the coordinates of the i-th array element are (x i ,y i ), the array element transmit and receive signals are defined as L i (); where 1≤i≤N; Step 3. Reconstruct the regional mesh The axis of the pipeline to be tested is used as the coordinate origin, and the area to be tested is gridded. Each grid node is defined as an image reconstruction point, forming a reconstruction area with m×n reconstruction points. The coordinates of any reconstruction point P are (a l ,b w ), where 1≤l≤m, 1≤w≤n; Step 4. Correction model calculation Determine the transmitting and receiving array elements i and the reconstruction point P. Considering the mode conversion of the sound wave on the pipeline and defect surface, a total of 21 different mode waves are generated. According to the characteristics of the sound beam path, the imaging mode is divided into direct mode, half-span mode and full-span mode. L represents the longitudinal wave and T represents the shear wave. The direct mode includes three mode waves: LL, TT and LT. The half-span mode includes eight mode waves: LLL, LTL, LTT, LLT, TTT, TLL, TTL and TLT. The full-span mode includes ten mode waves: LLLL, LTLL, TLLL, LLTT, TLLT, TLTL, LTTL, TLTT, LTTT and TTTT. For each mode wave, the total acoustic time t of the Gth mode wave is obtained through the reconstruction point P. i-G (a l ,b w ) Take the incident sound time t ip-G (a l ,b w ) and the emitted sound time t pi-G (a l ,b w ), where 1≤G≤21; t i-G (a l ,b w )=t ip-G (a l ,b w )+t pi-G (a l ,b w ) (1) When the axial defect detection of the pipeline to be tested is performed, the coupling surface of the angle wedge (3) and the pipeline to be tested is a curved surface, and the coordinates of the incident point and the exit point of the i-th array element sound beam are A(x j ,y j ) and B(x k ,y k ), then the nonlinear propagation of sound satisfies: When the radius of the outer surface of the pipeline to be measured is R1, the angle wedge (3) and the interface between the pipeline to be measured, the incident point A and the exit point B satisfy: Correction calculation is performed for each mode. The imaging mode is different and the incident sound time t ip-G (a l ,b w ) and the emitted sound time t pi-G (a l ,b w ) is calculated differently; When the imaging mode is direct mode, the transmitted and received signals only pass through the interface between the angle wedge (3) and the outer surface of the pipe to be measured, and only the influence of the curved surface is considered. At this time, t ip-G (a l ,b w ) and t pj-G (a l ,b w ) are: Where c0 represents the longitudinal wave speed in the angle wedge (3), c d1 、c d2 are the sound velocities corresponding to the path of the sound beam in the pipe to be tested during the incident and exit processes, respectively, and are the longitudinal wave speed or shear wave speed of the pipe material to be tested; When the imaging mode is half-span mode, the transmitted signal is reflected on the inner surface of the pipe to be measured. The radius of the inner surface of the pipe is R2, and the coordinates of the reflection point are Q(x q ,y q )satisfy The inner and outer surfaces of the incident sound beam where the mode conversion occurs are both curved surfaces, and the outgoing sound beam is only affected by the curvature of the outer surface of the pipe to be tested, so t ip-G (a l ,b w ) and t pj-G (a l ,b w ) are: Where c h1 with c h2 is the corresponding sound velocity of the two sections of the sound beam path in the pipe during the incident process, c h3 is the sound velocity corresponding to the path of the sound beam in the pipe during the emission process, c h1 、c h2 、c h3 is the longitudinal wave speed or shear wave speed of the pipe material; When the imaging mode adopts the full-span mode, both the transmitting and receiving signals are reflected on the inner surface of the pipe. At this time, the reflection point coordinates Q1(x q1 ,y q1 ) and the coordinates of the reflection point Q2(x q2 ,y q2 )satisfy In the full-span mode, both the incident and outgoing sound beams undergo mode conversion on the inner and outer surfaces of the pipe to be tested, so t ip-G (a l ,b w ) and t pj-G (a l ,b w ) are respectively Where c f1 with c f2 is the corresponding sound velocity of the two sections of the sound beam path in the pipe to be measured during the incident process, c f3 with c f4 is the corresponding sound velocity of the two sections of the sound beam path in the pipe to be measured during the emission process, c f1 、c f2 、c f3 、c f4 is the longitudinal wave velocity or shear wave velocity of the pipeline material to be tested; From L i Select the sound time t in () i-G (a l ,b w ) corresponds to the amplitude L i (t i-G (a l ,b w )) is the signal amplitude of the Gth mode wave of the array element i at the reconstruction point P; Step 5. Time-lapse overlay and mode selection The N A-scan signals in the B-scan image are subjected to 21 types of delayed superposition processing of mode waves. The process is as follows: Select the strongest response I from all mode waves at all reconstruction points max , the process is expressed by the following formula: In the formula, (a l ,b w ) are the coordinates of any point in the imaging area; Then, the strongest response I max The corresponding mode wave G is used as the mode wave for final imaging and defect assessment; Step 6. Qualitative and quantitative detection of defects The optimal mode wave obtained in step 5 is used to image the reconstructed area, obtain the contour reconstructed image of the unknown defect and perform qualitative identification; finally, the depth, size and tilt angle of the defect are quantified.

2. The pipeline axial defect ultrasonic imaging method based on modified mode synthetic aperture focusing according to claim 1 is characterized in that: In step 6, the -6dB method is used to quantify the depth, size and tilt angle of the defect.

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