Thick-wall austenitic stainless steel welding seam full-focusing imaging method based on TRL area array probe

Abstract

The invention discloses a thick-wall austenitic stainless steel welding seam full-focusing imaging method based on a TRL area array probe, and belongs to the technical field of nondestructive testing. According to the method, a phased array detection instrument which comprises a TRL area array probe and has a full-matrix acquisition function is adopted. The method comprises the following steps: firstly, acquiring full-matrix data of a thick-wall austenitic stainless steel weld joint based on a TRL area array probe, and calculating three types of space coordinates required by imaging according to parameters of the probe and a wedge block; then, a refraction point calculation path is optimized by using sound propagation characteristics and the Snell theorem, and the imaging speed is increased; and finally, calculating propagation path time consumption of any pixel point in the imaging area according to the obtained space coordinates, carrying out delay superposition to obtain a detection image with a high signal-to-noise ratio, and carrying out positioning and quantification on defects on the basis. According to the method, the pseudo-focusing characteristic of the TRL area array probe and the space averaging of the full-focusing imaging algorithm are combined, the imaging signal-to-noise ratio of the thick-wall austenitic stainless steel welding seam is increased, and the method has good engineering application value.

Description

Technical Field

[0001] The invention relates to a full-focus imaging method for a thick-walled austenitic stainless steel weld based on a TRL area array probe, and belongs to the technical field of non-destructive testing. Background Art

[0002] Phased array ultrasonic testing is an important nondestructive testing technology for thick-walled austenitic stainless steel main pipeline welds. However, due to the presence of coarse columnar crystals in thick-walled austenitic stainless steel welds and strong elastic anisotropy, conventional phased array ultrasonic testing technology has problems such as low signal-to-noise ratio and difficulty in quantifying defect locations.

[0003] Phased array ultrasonic testing based on a transmit-receive dual-crystal longitudinal wave (TRL) phased array probe and full-focus imaging based on a linear array phased array probe are currently commonly used to improve the ultrasonic imaging signal-to-noise ratio of thick-walled austenitic stainless steel welds. Among them, the phased array ultrasonic testing method based on the TRL array probe uses the "pseudo-focusing" characteristics of the TRL array probe structure to improve the focusing ability of the ultrasonic beam and the imaging signal-to-noise ratio within the focusing range. However, the imaging effect within the non-focusing range is not ideal, the effective detection range of a single imaging is small, and it is necessary to change the position and scan multiple times to cover the entire detection area, and the detection efficiency is low.

[0004] The full focusing method is based on full matrix data, and can achieve point-by-point focusing of the area to be inspected, generating high-quality images with high resolution and large effective detection coverage. It is called the "gold standard" of phased array ultrasonic testing by some scholars and is a commonly used imaging method in ultrasonic testing engineering applications. The current full focusing method is mainly based on phased array linear array probes, and the imaging calculation is assumed to be performed in a two-dimensional plane. Since the columnar crystals in austenitic stainless steel welds have a divergent effect on ultrasonic waves, the detection signal-to-noise ratio is insufficient, and artifacts caused by noise are prone to appear in the image background, affecting the positioning and quantitative analysis of weld defects. Summary of the invention

[0005] The purpose of the present invention is to provide a full-focus imaging method for thick-walled austenitic stainless steel welds based on a TRL area array probe, which combines the focusing characteristics of the TRL area array probe and the imaging characteristics of the full-focus method to obtain a detection image with a high signal-to-noise ratio, high imaging resolution and a large imaging range.

[0006] The technical solution adopted by the present invention is: a full-focus imaging method for thick-walled austenitic stainless steel welds based on a TRL array probe, which belongs to the field of non-destructive testing technology. The method adopts a set of phased array detection instruments including a TRL array probe and a full-matrix acquisition function. First, the full matrix data of the thick-walled austenitic stainless steel weld is collected based on the TRL array probe, and the three types of spatial coordinates required for imaging are calculated according to the probe and wedge parameters. Then, the refraction point calculation path is optimized using the sound propagation characteristics and Snell's theorem to improve the imaging speed. Finally, the propagation path time of any pixel point in the imaging area is calculated based on the obtained spatial coordinates, and delayed superposition is performed to obtain a detection image with a high signal-to-noise ratio, on which the defects are located and quantified. The method adopts the following steps:

[0007] (1) Determine ultrasonic testing parameters

[0008] Determine appropriate ultrasonic testing parameters according to the condition of the workpiece being inspected, mainly including workpiece parameters, probe parameters and wedge parameters. Workpiece parameters include workpiece thickness, material sound velocity, etc.; probe parameters include the number of array elements, array element width, array element spacing, etc.; wedge parameters include wedge sound velocity, wedge inclination, roof angle, first array element height, etc.

[0009] (2) Collecting full matrix data

[0010] Based on the workpiece to be inspected, the probe and the wedge determined in step (1), the probe is placed at a suitable position on the workpiece surface, and the full matrix acquisition function of the phased array ultrasonic detector is used to obtain the ultrasonic full matrix data of the thick-walled austenitic stainless steel weld.

[0011] (3) Calculate the transmit-receive array element coordinates

[0012] The three-dimensional coordinates of the transmitting and receiving array elements in the TRL array probe are calculated according to the array element center distance, wedge inclination angle, roof angle, and first array element height in the probe parameters and wedge parameters. The receiving array element coordinates are symmetrical with the transmitting array element coordinate axis.

[0013] (4) Calculate the coordinates of the pixels in the imaging area

[0014] Determine the scope of the imaging area, select the appropriate image resolution, discretize the imaging area, and obtain the spatial coordinates of each pixel.

[0015] (5) Calculate the coordinates of the double-medium refraction point

[0016] Considering the three-dimensional structure of the TRL array probe, the range of the double-medium refraction point is the wedge area, and the appropriate discrete interval is selected. The number of discrete points N can be expressed as:

[0017]

[0018] Where, Lwedge is the wedge length, W wedge is the wedge width, d step is a discrete interval.

[0019] To improve the efficiency of refraction point calculation, the wedge sound velocity is set to c 1 , the workpiece sound speed is c 2 According to Snell's theorem, the refraction relationship of the heterogeneous interface can be expressed as:

[0020]

[0021] In the formula, θ 1 is the incident angle of the ultrasonic wave inside the wedge, θ 2 is the refraction angle of ultrasonic wave inside the workpiece.

[0022] It is known that the sound velocity of the wedge is often smaller than the sound velocity of the workpiece being tested. According to Fermat's theorem, the range of the refraction point is further narrowed to reduce the calculation time of the refraction point.

[0023] (6) Delayed superposition of pixel signals

[0024] Calculate the propagation path time of each transmitting-receiving array element pair at each pixel point respectively. The array element transmitting coordinate is (x 1 ,y 1 ,z 1 ), the pixel coordinates are (x 2 ,y 2 ,z 2 ), the receiving array element coordinates are (x 3 ,y 3 ,z 3 ), the propagation path time t is expressed as:

[0025]

[0026] Among them, d 1 d 2 d 3 d 4 It is expressed as:

[0027]

[0028] Among them, (x, y, z) and (X, Y, Z) represent the coordinates of the refraction point at the transmitting end and the refraction point at the receiving end, respectively. The t value of all the transmitting-receiving signals in the full matrix data for the pixel point is calculated, and the pixel point can be delayed and superimposed:

[0029]

[0030] Among them, S ij(t) is the amplitude of the signal from transmitting element i to receiving element j at the time of delay t, and h() is the Hilbert transform. According to formula (5), the imaging amplitude of any pixel in the imaging area can be calculated, and the fully focused image can be formed after the amplitudes of all pixels in the imaging area are obtained.

[0031] (7) Image normalization and interpolation processing

[0032] The amplitudes of all pixels in the imaging area are normalized, and the calculation process can be expressed as:

[0033]

[0034] Among them, I(x,z) is the pixel amplitude, max() is the maximum value, and || is the absolute value.

[0035] The Spline interpolation polynomial in the piecewise interpolation polynomial is used to interpolate the image to make the image smooth and avoid distortion. At the same time, the image is processed by dB threshold to obtain dB threshold imaging with different dynamic ranges:

[0036]

[0037] Based on the obtained full-focus image, defects can be located and quantitatively detected.

[0038] The beneficial effects of the present invention are as follows: The method first collects full matrix data of thick-walled austenitic stainless steel welds based on the TRL array probe, and calculates the three types of spatial coordinates required for imaging based on the probe and wedge parameters. Then, the refraction point calculation path is optimized using the sound propagation characteristics and Snell's theorem to improve the imaging speed. Finally, the propagation path time of any pixel point in the imaging area is calculated based on the obtained spatial coordinates, and delayed superposition is performed to obtain a high signal-to-noise ratio detection image, on which the defects are located and quantified.

[0039] This method combines the "pseudo-focusing" characteristics of the TRL array probe and the spatial averaging of the full-focusing imaging algorithm to improve the imaging signal-to-noise ratio of phased array ultrasonic testing of thick-walled austenitic stainless steel main pipeline welds and suppress artifacts caused by coarse-grained structures. This method has no additional requirements for the hardware system and is suitable for nondestructive testing of large-thickness elastic anisotropic materials similar to thick-walled austenitic stainless steel welds, and has good engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present invention will be further described below with reference to the accompanying drawings and examples.

[0041] Figure 1 This is a real picture of the test block.

[0042] Figure 2 This is a schematic diagram of the TRL array probe location and defect setting.

[0043] Figure 3 This is a real picture of the probe.

[0044] Figure 4 This is a schematic diagram of the full-focus imaging of the TRL array probe.

[0045] Figure 5 These are the fully focused normalized image and dB threshold image of the thick-walled austenitic stainless steel weld produced by the TRL area array probe.

[0046] Figure 6 This is the phased array sector scan image of the TRL area array probe. DETAILED DESCRIPTION

[0047] The full-focus imaging method of thick-walled austenitic stainless steel welds based on the TRL array probe, the specific detection and imaging steps are as follows:

[0048] (1) Parameter setting. Austenitic stainless steel weld defect test block Figure 1 As shown in the figure, the test block was processed with 3.2mm diameter transverse through hole defects with depths of 10mm, 30mm, 50mm and 70mm respectively (such as Figure 2 ). The probe structure is as follows Figure 3 As shown, the center frequency is 2.25MHz, the array element arrangement is 16×4, and it is equipped with a wedge with a refraction angle of 55° and a roof angle focusing depth of 20mm.

[0049] (2) Collect full matrix data. Place the TRL array probe at a suitable position on the surface of the test block, such as Figure 2 As shown, full matrix data is collected.

[0050] (3) Calculate relevant coordinates. Calculate the three-dimensional coordinates of the transmitting and receiving array elements in the TRL array probe based on the array element center distance, wedge inclination, roof angle, and first array element height in the probe and wedge parameters; after selecting the imaging area and image resolution, obtain the coordinates of all pixel points in the detection area; discretize the dual-medium acoustic beam refraction point area and record the coordinates of each discrete refraction point. According to Snell's law combined with Fermat's theorem, optimize the refraction point range and reduce the time-delay superposition full-focus imaging time of the TRL array probe. The number of refraction points can be expressed as:

[0051]

[0052] Where, L wedge is the wedge length, W wedge is the wedge width, d step is a discrete interval. According to Snell's theorem, the refraction relationship of the heterogeneous interface can be expressed as:

[0053]

[0054] In the formula, θ 1 is the incident angle of the ultrasonic wave inside the wedge, θ 2 is the refraction angle of ultrasonic wave inside the workpiece.

[0055] (4) Delayed superposition of pixel signals.

[0056] Calculate the propagation path time of each transmitting-receiving array element pair at each pixel point respectively. The array element transmitting coordinate is (x 1 ,y 1 ,z 1 ), the pixel coordinates are (x 2 ,y 2 ,z 2 ), the receiving array element coordinates are (x 3 ,y 3 ,z 3 ), the propagation path time t is expressed as:

[0057]

[0058] Among them, d 1 d 2 d 3 d 4 It is expressed as:

[0059]

[0060] Among them, (x, y, z) and (X, Y, Z) represent the coordinates of the refraction point at the transmitting end and the refraction point at the receiving end, respectively. The t value of all the transmitting-receiving signals in the full matrix data for the pixel point is calculated, and the pixel point can be delayed and superimposed:

[0061]

[0062] Among them, S ij (t) is the amplitude of the signal from the transmitting element i to the receiving element j when the delay is t, and h() is the Hilbert transform. According to formula (5), the imaging amplitude of any pixel point in the imaging area can be calculated. After obtaining the amplitude of all pixel points in the imaging area, a fully focused image can be formed, as shown in Figure 4 shown.

[0063] (5) Normalization and interpolation processing.

[0064] Normalize all pixel amplitudes in the imaging area, and the calculation process can be expressed as

[0065]

[0066] Among them, I(x,z) is the pixel amplitude, max() is the maximum value, and || is the absolute value.

[0067] Use the above formula to normalize, and interpolate the image through the Spline interpolation polynomial in the piecewise interpolation polynomial. The result is as follows: Figure 5 As shown in (a);

[0068] The Spline interpolation polynomial in the piecewise interpolation polynomial is used to interpolate the image to make the image smooth and avoid distortion. At the same time, the image is processed by dB threshold to obtain dB threshold imaging with different dynamic ranges:

[0069]

[0070] Using the above formula to perform dB threshold imaging, the result is as follows Figure 5 As shown in (b). Based on the fully focused image obtained, the defects can be located and quantitatively detected. TRL sector scanning imaging ( Figure 6 (b)) cannot detect the 10mm deep cross-hole defect. This method can image all the cross-hole defects in the sample ( Figure 6 In (a), the signal-to-noise ratio of the defect image can reach up to 20.83dB, and the average defect positioning error is 0.52mm. Compared with the TRL sector scanning imaging results, the signal-to-noise ratio of the defect image is increased by an average of 2.76dB, and the average positioning error is reduced by 1.15mm, meeting the engineering requirements.

Claims

1. A full-focus imaging method for thick-walled austenitic stainless steel welds based on a TRL array probe, characterized by: The device used in the method is a phased array detection instrument including a TRL array probe and a full matrix acquisition function; the method adopts the following steps: (1) Determine ultrasonic testing parameters Determine ultrasonic testing parameters according to the condition of the workpiece to be inspected, including workpiece parameters, probe parameters and wedge parameters; the workpiece parameters include workpiece thickness and material sound velocity; the probe parameters include the number of array elements, array element width, and array element center distance; the wedge parameters include wedge sound velocity, wedge inclination, roof angle, and first array element height; (2) Collecting full matrix data Place the probe on the workpiece surface and use the full matrix acquisition function of the phased array ultrasonic detector to obtain the ultrasonic full matrix data of the thick-walled austenitic stainless steel weld. (3) Calculate the transmit-receive array element coordinates The three-dimensional coordinates of the transmitting and receiving array elements in the TRL array probe are calculated according to the array element center distance, wedge inclination angle, roof angle, and first array element height in the probe parameters and wedge parameters. The receiving array element coordinates are symmetrical with the transmitting array element coordinate axis. (4) Calculate the coordinates of the pixels in the imaging area Determine the range of the imaging area, select the image resolution to discretize the imaging area, and obtain the spatial coordinates of each pixel point; (5) Calculate the coordinates of the double-medium refraction point Considering the three-dimensional structure of the TRL array probe, the range of the double-medium refraction point is the wedge area, and the number of discrete points N is expressed as: Where, L wedge is the wedge length, W wedge is the wedge width, d step is a discrete interval; Assuming the wedge sound velocity is c1 and the workpiece sound velocity is c2, according to Snell's theorem, the refraction relationship of the heterogeneous interface is expressed as: Where θ1 is the incident angle of the ultrasonic wave inside the wedge, and θ2 is the refraction angle of the ultrasonic wave inside the workpiece; (6) Delayed superposition of pixel signals Calculate the propagation path time of each transmitting-receiving array element pair at each pixel point respectively. The array element transmitting coordinates are (x1, y1, z1), the pixel point coordinates are (x2, y2, z2), and the receiving array element coordinates are (x3, y3, z3). The propagation path time t is expressed as: Among them, d1, d2, d3, and d4 are expressed as: Among them, (x, y, z) and (X, Y, Z) represent the coordinates of the refraction point at the transmitting end and the refraction point at the receiving end, respectively. Calculate the t value of all the transmitting-receiving signals in the full matrix data for the pixel point, and perform delay superposition on the pixel point: Among them, S ij (t) is the amplitude of the signal transmitted by element i and received by element j at the time of delay t, and h() is the Hilbert transform. According to formula (5), the amplitude of any pixel point in the imaging area can be calculated, and after the amplitudes of all pixel points in the imaging area are obtained, a fully focused image can be formed; (7) Image normalization and interpolation processing Normalize the amplitudes of all pixels in the imaging area: Among them, I(x,z) is the pixel amplitude, max() is the maximum value, and || is the absolute value; The Spline interpolation polynomial in the piecewise interpolation polynomial is used to interpolate the image, and the image is processed by dB threshold to obtain dB threshold imaging with different dynamic ranges: Based on the obtained full-focus image, the defects are located and quantitatively detected.

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