Thick-wall austenitic stainless steel full-focusing correction imaging method based on TRL probe

Abstract

The invention provides a thick-wall austenitic stainless steel full-focus correction imaging method based on a TRL probe, and the method comprises the steps: collecting a thick-wall austenitic stainless steel welding seam based on a TRL area array probe, obtaining full-matrix data, measuring an elastic stiffness matrix of a welding seam material, and solving a wave equation of ultrasonic waves based on the elastic stiffness matrix, the method comprises the following steps: acquiring a phase velocity and a group velocity, acquiring the magnitude and the direction of the phase velocity and the group velocity, calculating a propagation path of ultrasonic waves in an anisotropic medium based on a ray tracing technology and in combination with a Fermat principle, extracting an amplitude value of a corresponding moment from full matrix data according to propagation time, performing delay superposition on each imaging point in an imaging area, and completing correction of full-focus imaging. According to the thick-wall austenitic stainless steel welding seam correction imaging method based on the TRL area array probe, the detection precision of an imaging result and the detection signal-to-noise ratio are improved, and a more reliable and accurate technical scheme is provided for thick-wall austenitic stainless steel welding seam detection.

Description

Technical Field

[0001] The invention relates to the technical field of full-focus imaging of thick-walled austenitic stainless steel, and in particular to a full-focus correction imaging method of thick-walled austenitic stainless steel based on a TRL probe. Background Art

[0002] In solid media, there is a distinction between phase velocity and group velocity when ultrasonic waves propagate. Phase velocity refers to the propagation velocity of a certain phase when a single wave vibrates; group velocity refers to the propagation velocity of the maximum amplitude formed by the waves that make up the wavefront. When propagating in anisotropic media, the phase velocity and group velocity of ultrasonic waves are consistent only in a specific direction. As an anisotropic medium, austenitic stainless steel weld has a coarse-grained and polycrystalline macrostructure, and the grain orientations of adjacent grains are different, resulting in increased grain boundary scattering. When the sound beam passes through the grain boundary between grains, the phase velocity and group velocity change, which in turn causes the acoustic impedance between different grains to change, resulting in partial reflection and refraction at the grain boundary. At present, when using phased array instruments to perform ultrasonic detection calculations on austenitic stainless steel, the average sound velocity is used. This practice results in poor focusing effect of the defect image in the imaging result, low signal-to-noise ratio, and large positioning quantitative error, which has an adverse effect on defect detection and weld quality analysis. Therefore, it is very necessary to design a full-focus correction imaging method for thick-walled austenitic stainless steel based on TRL probe. Summary of the invention

[0003] In order to overcome the deficiencies of the prior art, the object of the present invention is to provide a full-focus correction imaging method for thick-walled austenitic stainless steel based on a TRL probe.

[0004] To achieve the above object, the present invention provides the following solutions:

[0005] The present invention provides a method for full-focus correction imaging of thick-walled austenitic stainless steel based on a TRL probe, comprising:

[0006] Based on the TRL area array probe, the thick-walled austenitic stainless steel weld is collected to obtain full matrix data;

[0007] The elastic stiffness matrix of thick-walled austenitic stainless steel weld material is measured. Based on the elastic stiffness matrix, the magnitude and direction of the phase velocity and group velocity of the ultrasonic wave in the austenitic stainless steel weld are obtained by solving the ultrasonic wave equation.

[0008] Based on ray tracing technology and combined with Fermat's principle, the propagation path of ultrasound in anisotropic media is calculated;

[0009] Based on the full matrix data, the full focusing imaging algorithm extracts the amplitude superposition at the corresponding moment from the full matrix data according to the propagation time, and finally compensates for the sound beam deflection in the full focusing imaging process of thick-walled austenitic stainless steel to complete the full focusing imaging.

[0010] Preferably, based on the elastic stiffness matrix of the thick-walled austenitic stainless steel weld material, the wave equation of the ultrasonic wave is solved to obtain the magnitude and direction of the phase velocity and group velocity of the ultrasonic wave in the austenitic stainless steel weld, specifically:

[0011] The crystal orientation analysis of the thick-walled austenitic stainless steel spectrum measured by the EBSD method was carried out, and the crystal orientation was characterized by the Euler angle method. According to the theory of elastic mechanics, the elastic constants of each anisotropic unit corresponding to the crystal orientation were assigned. The elastic stiffness matrix in the given coordinate system was obtained through the transformation matrix and the generalized Hooke's law, which is:

[0012] C' ijkl =MC ijkl M T (1)

[0013] In the formula, C ijkl is the elastic stiffness matrix in the normal coordinate system. Under different grain directions, the elastic constants can be obtained according to the transformation matrix M.

[0014] The sound velocity is compensated according to the incident angle of the sound wave. Assuming that the sound wave obeys the Christoffel equation when propagating in an infinite anisotropic elastic medium, we have:

[0015] C ijkl k j k l =ρω 2 δ il (2)

[0016] Where k is the acoustic wave vector, ρ is the material density, ω is the angular frequency, and δ il is the symbol for "Kroneckerdelta", C ijkl k j k l is the Christoffel sound tensor, expressed as:

[0017] Γ il =C ijkl u j u l (3)

[0018] Where u is the cosine of the wavefront normal vector, and from the wave velocity c = ω / k, the relationship between the sound velocity of the anisotropic medium and the sound wave incident angle and the elastic stiffness matrix is ​​obtained as follows:

[0019]

[0020] (ρc 2 ) is regarded as the eigenvalue of the sound tensor. According to the characteristics of the sound tensor, three real roots greater than 0 are obtained, namely two quasi-transverse wave speeds and one quasi-longitudinal wave speed, which are:

[0021]

[0022] For a specific wave vector direction n = (n1, n2, n3), solve the eigenvalue and eigenvector of the determinant and obtain the eigenvalue λ i and the eigenvector v i :

[0023]

[0024] v i =p i (7)

[0025] Where i = 1, 2, 3, m i =k i / ω is the component of slowness m, and p is the component of polarization vector. Phase velocity c pi and group velocity c gi The components can be expressed as:

[0026]

[0027] Preferably, the propagation path of ultrasound in anisotropic media is calculated based on ray tracing technology combined with Fermat's principle, specifically:

[0028] When ultrasonic waves propagate from one point to another in any medium, they propagate along the path that takes the shortest time, that is:

[0029]

[0030] When the medium is an anisotropic material, the first medium velocity c1 and the second medium velocity c2 change with the change of the incident direction of the wave and the grain direction. The points on the boundary of the weld area are discretized, and the time for the sound wave to propagate from the virtual source point to each discrete point on the boundary is calculated. The time for the sound wave to propagate from the discrete point on the boundary to the target point is calculated. The propagation direction of the wave is calculated based on the line connecting the discrete point and the target point. That is, the sound speed is known, and the shortest propagation path among all propagation paths is regarded as the propagation path of the sound wave.

[0031] Preferably, based on the full matrix data, the full focus imaging algorithm extracts the amplitude superposition at the corresponding moment from the full matrix data according to the propagation time, and finally realizes the compensation of the sound beam deflection in the full focus imaging process of thick-walled austenitic stainless steel, and completes the full focus imaging. Specifically, during the imaging process, the amplitude of a specific focus point (x, z) is expressed as:

[0032]

[0033] t in total focus imaging of anisotropic materials ij Depending on the angle of the sound wave and the discrete points chosen according to Fermat's theorem, it is revised to:

[0034]

[0035] Where, d ij , D ij is the propagation path length of the sound wave in the isotropic medium and the propagation path length of the sound wave in the anisotropic medium; c(θ) is a variable that changes with the angle θ between the sound wave and the grain.

[0036] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0037] The present invention provides a full-focus correction imaging method for thick-walled austenitic stainless steel based on a TRL probe, the method comprising collecting full matrix data of thick-walled austenitic stainless steel welds using a TRL array probe. The elastic stiffness matrix of the weld material is measured, and the magnitude and direction of the phase velocity and group velocity of the ultrasonic wave in the austenitic stainless steel weld are obtained by solving the Christoffel equation. Based on ray tracing technology, the propagation path of the ultrasonic wave in the anisotropic medium is calculated in combination with the Fermat principle, and the amplitude at the corresponding moment is extracted from the full matrix data according to the path propagation time and superimposed, and finally the compensation of the sound beam deflection in the full-focus imaging process of the thick-walled austenitic stainless steel is realized, and the full-focus imaging is completed. The present invention compares the TFM imaging results without correction imaging, and the TFM correction imaging method can effectively improve the problems of poor image focusing effect and large positioning error in the average sound velocity TFM imaging, and the defect amplitude is significantly improved, which effectively improves the defect positioning accuracy of the thick-walled austenitic stainless steel weld. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0039] Figure 1A flow chart of a method provided by an embodiment of the present invention;

[0040] Figure 2 This is a schematic diagram of the EBSD spectrum observation results of austenitic stainless steel weld;

[0041] Figure 3 This is a schematic diagram of the ray tracing principle;

[0042] Figure 4a Schematic diagram of TFM imaging results;

[0043] Figure 4b Schematic diagram of TFM correction imaging results. DETAILED DESCRIPTION

[0044] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not 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.

[0045] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0046] The main content of the present invention is a total focus correction imaging method for thick-walled austenitic stainless steel based on a TRL (Transmit-Receive Longitudinal) array probe. This method innovatively uses a low-frequency TRL array probe to perform total focus method (TFM) imaging on thick-walled austenitic stainless steel to improve the detection effect of phased array ultrasonic detection technology on thick-walled austenitic stainless steel welds. What is particularly critical is that in order to effectively overcome the problems of poor image focusing effect and large positioning quantitative errors generated when the average sound velocity is used to calculate the ultrasonic detection results, the present invention innovatively uses a TRL array probe to perform TFM imaging on thick-walled austenitic stainless steel welds; in response to the problems of poor focusing effect, low signal-to-noise ratio, and large positioning quantitative errors when the average sound velocity is used to perform phased array ultrasonic detection calculations on thick-walled austenitic stainless steel welds, the present invention provides a total focus correction imaging algorithm based on a TRL array probe. This algorithm has a very high suppression of artifacts and noise during the TRL-TFM imaging process, and the signal amplitude of the defect is relatively high, which makes the imaging results have higher accuracy and detection signal-to-noise ratio, providing more reliable and accurate technical support for the detection of thick-walled austenitic stainless steel welds. The following is a detailed introduction:

[0047] Figure 1 A flow chart of a method provided by an embodiment of the present invention, such as Figure 1 As shown, the present invention provides a method for full-focus correction imaging of thick-walled austenitic stainless steel based on a TRL probe, comprising:

[0048] Step 100: Collect data from thick-walled austenitic stainless steel welds using a TRL array probe to obtain full matrix data;

[0049] Step 200: measuring the elastic stiffness matrix of the thick-walled austenitic stainless steel weld material, and based on the elastic stiffness matrix, solving the wave equation of the ultrasonic wave to obtain the magnitude and direction of the phase velocity and group velocity of the ultrasonic wave in the austenitic stainless steel weld;

[0050] Step 300: Calculate the propagation path of the ultrasonic wave in the anisotropic medium based on ray tracing technology and Fermat's principle;

[0051] Step 400: Based on the full matrix data, the full focus imaging algorithm extracts the amplitude superposition at the corresponding moment from the full matrix data according to the propagation time, and finally realizes the compensation of the sound beam deflection in the full focus imaging process of thick-walled austenitic stainless steel, and completes the full focus imaging.

[0052] It should be noted that the TRL array probe used in this application is independently developed and designed, and the frequency and structural parameters of the probe are shown in Table 1 below;

[0053] Table 1 TRL array probe parameters

[0054] project Specification Array Model Dual Matrix Center frequency 2.0MHz Number of channels (n) 2-16*4elements Element length 3mm Element width 2.8mm Active axis array element center distance (Px) 3.2mm Active axis array element slot (IEx) 0.2mm Driven axis array element center distance (Py) 3.0mm Driven shaft array element slot (IEy) 0.2mm Active shaft effective aperture (Lx) 51.0mm Driven shaft effective aperture (Ly) 11.8mm Effective area (Lx*Ly) 2-51.0*11.8mm

[0055] Steps 200, 300 and 400 are introduced in conjunction with a specific embodiment:

[0056] In step 200, based on the elastic stiffness matrix of the thick-walled austenitic stainless steel weld material, the wave equation of the ultrasonic wave is solved to obtain the magnitude and direction of the phase velocity and group velocity of the ultrasonic wave in the austenitic stainless steel weld, specifically:

[0057] Crystal orientation analysis is performed based on the electron backscatter diffraction (EBSD) pattern of thick-walled austenitic stainless steel welds, where the pattern is as follows: Figure 2 As shown in the figure, it can be seen that the grains of austenitic stainless steel weld are arranged in a staggered manner, so the imaging area is divided. According to the atlas, the crystal orientation is characterized by the Euler angle method, and the elastic constant corresponding to the crystal orientation is given to each anisotropic unit according to the theory of elastic mechanics. The elastic stiffness matrix in a given coordinate system is obtained through the transformation matrix and the generalized Hooke's law, which is:

[0058] C' ijkl =MC ijkl MT (1)

[0059] In the formula, C ijkl is the elastic stiffness matrix in the normal coordinate system. Under different grain directions, the elastic constants can be obtained according to the transformation matrix M.

[0060] On this basis, the sound velocity is compensated according to the incident angle of the sound wave. Assuming that the sound wave obeys the Christoffel equation when propagating in an infinite anisotropic elastic medium, we have:

[0061] C ijkl k j k l =ρω 2 δ il (2)

[0062] In the formula, C ijkl k j k l is the Christoffel sound tensor, expressed as:

[0063] Γ il =C ijkl u j u l (3)

[0064] Where k is the acoustic wave vector, ρ is the material density, ω is the angular frequency, and δ il is the symbol for "Kroneckerdelta", C ijkl k j k l is the Christoffel sound tensor, expressed as:

[0065] Γ il =C ijkl u j u l (3)

[0066] Where u is the cosine of the wavefront normal vector, and from the wave velocity c = ω / k, the relationship between the sound velocity of the anisotropic medium and the sound wave incident angle and the elastic stiffness matrix is ​​obtained as follows:

[0067]

[0068] (ρc 2 ) is regarded as the eigenvalue of the sound tensor. According to the characteristics of the sound tensor, three real roots greater than 0 are obtained, namely two quasi-transverse wave speeds and one quasi-longitudinal wave speed, which are:

[0069]

[0070] For a specific wave vector direction n = (n1, n2, n3), solve the eigenvalue and eigenvector of the determinant and obtain the eigenvalue λ i and the eigenvector v i :

[0071]

[0072] v i =p i (7)

[0073] Where i = 1, 2, 3, m i =k i / ω is the component of slowness m, and p is the component of polarization vector. Phase velocity c pi and group velocity c gi The components can be expressed as:

[0074]

[0075] In step 200, based on ray tracing technology and combined with Fermat's principle, the propagation path of ultrasound in anisotropic media is calculated, specifically:

[0076] The principle of ray tracing correction imaging based on Fermat's theorem is as follows Figure 3 As shown in Figure 2, from Fermat's theorem, we know that when ultrasound propagates from one point to another in any medium, it propagates along the path that takes the shortest time, that is:

[0077]

[0078] When the medium is an anisotropic material, the first medium velocity c1 and the second medium velocity c2 change with the change of the incident direction of the wave and the grain direction. The points on the boundary of the weld area are discretized, and the time for the sound wave to propagate from the virtual source point to each discrete point on the boundary is calculated. The time for the sound wave to propagate from the discrete point on the boundary to the target point is calculated. The propagation direction of the wave is calculated based on the line connecting the discrete point and the target point. That is, the sound speed is known, and the shortest propagation path among all propagation paths is regarded as the propagation path of the sound wave.

[0079] In step 400, based on the full matrix data, the full focusing imaging algorithm extracts the amplitude superposition at the corresponding time from the full matrix data according to the propagation time to achieve focused imaging of any point in the detection area, wherein during the imaging process, the amplitude of a specific focused point (x, z) is expressed as:

[0080]

[0081] t in total focus imaging of anisotropic materials ij Depending on the angle of the sound wave and the discrete points chosen according to Fermat's theorem, it is revised to:

[0082]

[0083] Where, d ij , D ij is the propagation path length of the sound wave in the isotropic medium and the propagation path length of the sound wave in the anisotropic medium; c(θ) is a variable that changes with the angle θ between the sound wave and the grain.

[0084] The imaging area is divided into several sub-areas according to the grain orientation. The elastic matrix and sound speed between different areas are different. Points with equal spacing are discretized on each boundary. The shortest time for the sound wave to pass through these areas to reach the scattering point and the shortest time for the scattering point to reach the receiving source is calculated to obtain the corresponding position of the pixel point for a transmission and reception signal. Repeat this step to obtain the corrected ultrasonic image result.

[0085] The present invention provides an embodiment: FMC data collection is performed on a thick-walled austenitic stainless steel weld test block with a thickness of 100 mm. The weld of the test block is distributed with transverse through-hole defects with depths of 10 mm, 50 mm, and 90 mm and a diameter of 3.2 mm. The frequency and structural information of the TRL array probe used are shown in Table 1. The wedge block selects a wedge block with a longitudinal wave refraction angle of 45°, a Roof angle focusing depth of 50 mm, and a longitudinal wave sound velocity of 2337 m / s. The collected FMC data are subjected to TFM imaging and TFM correction imaging respectively. In the TFM imaging process, the propagation speed of the sound beam in the anisotropic medium is the average sound speed, while the sound speed of the TFM correction imaging is a variable, which varies with the angle between the propagation direction of the sound beam and the grain. The imaging area is 20 mm×90 mm, the pixel length and width are both 0.5 mm, and the imaging results are as follows Figure 4a and Figure 4b shown.

[0086] from Figure 4a and Figure 4bIt can be seen that due to the strong anisotropy of thick-walled austenitic stainless steel welds, even with full-focus imaging, the imaging results deviate far from the actual position, and the amplitudes of the three identical transverse through holes are quite different. The signal amplitude of the corrected imaging results is significantly improved. According to statistics, compared with the TRL-TFM imaging results, the amplitudes of the three transverse through hole defect images of the TRL-TFM corrected imaging results are increased from 97.29Pa, 173.18Pa, and 82.82Pa to 167.05Pa, 225.50Pa, and 105.67Pa, and the corresponding decibel values ​​are increased by 4.70dB, 2.29dB, and 2.13dB, respectively. This shows that the corrective imaging method in the present invention can effectively improve the focusing effect of the defect image. The reason is that the ray tracing technology is used and combined with the accurate calculation of the group velocity, so that the delayed superposition amplitude of the pixels of the corrected image can be improved. In addition, the TRL-TFM correction imaging results based on ray tracing technology have higher accuracy and defect signal-to-noise ratio: in the TRL-TFM imaging results, the defect image positioning error of hole 1 is the largest, reaching 4.80mm, and the average positioning error of the three holes is 4.09mm. Figure 4b As shown in the figure, the average positioning error is improved by 2.21mm compared with the TRL-TFM imaging results, and the average signal-to-noise ratio of defects is improved by 5.59dB.

[0087] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0088] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for full-focus correction imaging of thick-walled austenitic stainless steel based on a TRL probe, characterized in that: include: Based on the TRL area array probe, the thick-walled austenitic stainless steel weld is collected to obtain full matrix data; The elastic stiffness matrix of thick-walled austenitic stainless steel weld material is measured. Based on the elastic stiffness matrix, the magnitude and direction of the phase velocity and group velocity of the ultrasonic wave in the austenitic stainless steel weld are obtained by solving the ultrasonic wave equation. Based on ray tracing technology and combined with Fermat's principle, the propagation path of ultrasound in anisotropic media is calculated; Based on the full matrix data, the full focusing imaging algorithm extracts the amplitude superposition at the corresponding moment from the full matrix data according to the propagation time, and finally compensates for the sound beam deflection in the full focusing imaging process of thick-walled austenitic stainless steel to complete the full focusing imaging.

2. The method according to claim 1, characterized in that Based on the elastic stiffness matrix of thick-walled austenitic stainless steel weld material, the magnitude and direction of the phase velocity and group velocity of ultrasonic waves in the austenitic stainless steel weld are obtained by solving the wave equation of ultrasonic waves, specifically: The crystal orientation analysis of the thick-walled austenitic stainless steel spectrum measured by the EBSD method was carried out, and the crystal orientation was characterized by the Euler angle method. According to the theory of elastic mechanics, the elastic constants of each anisotropic unit corresponding to the crystal orientation were assigned. The elastic stiffness matrix in the given coordinate system was obtained through the transformation matrix and the generalized Hooke's law, which is: C' ijkl =MC ijkl M T (1) In the formula, C ijkl is the elastic stiffness matrix in the normal coordinate system. Under different grain directions, the elastic constants can be obtained according to the transformation matrix M. The sound velocity is compensated according to the incident angle of the sound wave. Assuming that the sound wave obeys the Christoffel equation when propagating in an infinite anisotropic elastic medium, we have: C ijkl k j k l =I am 2 d il (2) Where k is the acoustic wave vector, ρ is the material density, ω is the angular frequency, and δ il is the symbol for "Kroneckerdelta", C ijkl k j k l is the Christoffel sound tensor, expressed as: Γ il =C ijkl in j in l (3) Where u is the cosine of the wavefront normal vector, and from the wave velocity c = ω / k, the relationship between the sound velocity of the anisotropic medium and the sound wave incident angle and the elastic stiffness matrix is ​​obtained as follows: (ρc 2 ) is regarded as the eigenvalue of the sound tensor. According to the characteristics of the sound tensor, three real roots greater than 0 are obtained, namely two quasi-transverse wave speeds and one quasi-longitudinal wave speed, which are: For a specific wave vector direction n = (n1, n2, n3), solve the eigenvalue and eigenvector of the determinant and obtain the eigenvalue λ i and the eigenvector v i : in i =p i (7) Where i = 1, 2, 3, m i =k i / ω is the component of slowness m, and p is the component of polarization vector. Phase velocity c pi and group velocity c gi The components can be expressed as:

3. The method according to claim 1, characterized in that Based on ray tracing technology and combined with Fermat's principle, the propagation path of ultrasound in anisotropic media is calculated as follows: When ultrasonic waves propagate from one point to another in any medium, they propagate along the path that takes the shortest time, that is: When the medium is an anisotropic material, the first medium velocity c1 and the second medium velocity c2 change with the change of the incident direction of the wave and the grain direction. The points on the boundary of the weld area are discretized, and the time for the sound wave to propagate from the virtual source point to each discrete point on the boundary is calculated. The time for the sound wave to propagate from the discrete point on the boundary to the target point is calculated. The propagation direction of the wave is calculated based on the line connecting the discrete point and the target point. That is, the sound speed is known, and the shortest propagation path among all propagation paths is regarded as the propagation path of the sound wave.

4. The method according to claim 1, characterized in that: Based on the full matrix data, the full focusing imaging algorithm extracts the amplitude superposition at the corresponding moment from the full matrix data according to the propagation time to achieve focused imaging of any point in the detection area. In the imaging process, the amplitude I of a specific focused point (x, z) is expressed as: t in total focus imaging of anisotropic materials ij According to the angle of the sound wave and the discrete points selected according to Fermat's theorem, the sound beam propagation time t changes with the sound beam angle, written as: Where, d ij , D ij is the propagation path length of the sound wave in the isotropic medium and the propagation path length of the sound wave in the anisotropic medium; c(θ) is a variable that changes with the angle θ between the sound wave and the grain.

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