Phased array-based defect detection method for 9% Cr steel pipeline elbow butt welds

Abstract

The present invention relates to a phased array-based method for detecting defects in butt welds of 9% Cr steel pipeline elbows. The method can detect internal defects in butt welds of 9% Cr steel pipeline special-shaped parts. The method adopts ultrasonic phased array detection technology to overcome the disadvantage that conventional non-destructive testing means can only detect surface defects of welds. The elbow side is used as the detection surface, and a probe coupled to the detection surface is used to find the optimal scanning path. By enhancing the coupling effect and increasing the effective scanning angle, full coverage scanning of the interior of the weld is achieved. The defect reflection signal is clearly visible and easy to identify, and the defect can be accurately quantified to prevent accidents such as pipeline leakage. The method is simple, has good use effect, and greatly improves detection efficiency and accuracy. After actual application, the accuracy rate reaches more than 99.9%. The method is an innovation in the phased array ultrasonic detection method for butt welds of 9% Cr steel pipeline special-shaped parts, and has good social and economic benefits.

Description

Technical Field

[0001] The invention belongs to the technical field of nondestructive detection of 9% Cr steel pipelines of thermal power units, in particular to a method for detecting defects in butt welds of 9% Cr steel pipeline elbows based on a phased array. Background Art

[0002] 9% Cr steel is widely used in supercritical and ultra-supercritical unit main and reheat steam piping due to its high oxidation and high-temperature corrosion resistance, good impact toughness, high and stable thermal strength, excellent thermal conductivity, and low coefficient of expansion. Therefore, it has become the primary material of choice for tees, elbows, and valve bodies in high-performance units. However, during the use of 9% Cr steel elbows, type IV cracks and even leaks have occurred in the connecting welds, seriously affecting the safe and stable operation of the units.

[0003] The Type IV creep cracking process in 9% Cr steel butt welds is a fine-grained creep damage process. During welding, carbides originally present on the coarse austenite grain boundaries in the base metal do not completely dissolve, but instead precipitate on the grain boundaries of the fine-grained zone formed after welding. During high-temperature creep, the carbides that originally served as reinforcement in the fine-grained zone decrease, while carbides on the grain boundaries grow and new coarse carbides form at the grain boundaries, becoming nucleation sources for creep vacancies and reducing the creep performance of the fine-grained zone. As creep vacancies on the grain boundaries grow, aggregate, and connect, grain boundary separation occurs. As the number of separated grain boundaries increases, microcracks form on the original austenite grain boundaries, until the component fractures.

[0004] With the improvement of steam parameters of units, special-shaped welded structures such as 9% Cr steel elbows to elbows are becoming more and more common in in-service metal parts. Since stress concentration is easily generated during the welding process of special-shaped parts, the probability of Type IV creep cracking is increasing. The welds of 9% Cr steel special-shaped parts are curved or there are steps at the joints, resulting in a small straight section position that is not enough for the probe to scan a certain distance away from one side of the weld as required by the process, making it impossible to inspect the inside of the weld. At present, for defects such as cracks in special-shaped welds of high-temperature and high-pressure pipelines in in-service supercritical units, existing non-destructive testing methods mainly use surface testing methods such as magnetic particle testing and penetrant testing to detect surface defects of welds, resulting in a large operational safety risk for such welds. Non-destructive testing of defects such as cracks in special-shaped welds of in-service thermal power units has become a problem that technicians in this field urgently need to solve. Summary of the Invention

[0005] In view of the above situation and to overcome the shortcomings of the prior art, the purpose of the present invention is to provide a phased array-based 9% Cr steel pipe elbow butt weld defect detection method, which can effectively solve the problem of non-destructive detection of internal crack defects in the butt welds of 9% Cr steel pipe elbows of different diameters in in-service thermal power units, thereby preventing crack propagation and causing pipeline leakage accidents.

[0006] The technical solution provided by the present invention is:

[0007] A phased array-based method for detecting defects in butt welds of 9% Cr steel pipe elbows comprises the following steps:

[0008] Step 1: Scan the path to determine

[0009] Taking the elbow-to-elbow butt weld of 9% Cr steel pipe as the inspection object, a three-dimensional graph of the elbow-to-elbow base material and weld is established. The three-dimensional graph is divided into N sections perpendicular to the weld direction. The N sections are converted into N two-dimensional graphs, that is, a two-dimensional graph of the side view of the inspected weld is established. The probe placement position is determined for each of the N two-dimensional models, specifically:

[0010] A simulated crack defect with a depth of 6 mm was set in the weld along the fusion line. Two linear simulated acoustic beams were drawn at the two end points of the defect. The simulated acoustic beam 1 formed an angle of 55° with the simulated defect, and the simulated acoustic beam 2 formed an angle of 105° with the simulated defect.

[0011] The arc surface of the outer ring of the elbow is the back arc of the elbow, the arc surface of the inner ring of the elbow is the inner arc of the elbow, and the arc surface in the transition area between the inner arc of the elbow and the back arc of the elbow is the neutral surface of the elbow;

[0012] For the elbow back arc section, the intersection of the simulated acoustic beam 2 and the elbow back arc is the probe placement position. The probe placement positions of all elbow back arc sections are connected into a smooth transition curve to form the first scanning path S1.

[0013] For the elbow neutral plane section, the intersection of the secondary reflection wave of the simulated acoustic beam 1 and the elbow neutral plane is the probe placement position. The probe placement positions of all elbow neutral plane sections are connected into a smooth transition curve to form the second scanning path S2;

[0014] For the inner arc section of the elbow, the intersection of the simulated acoustic beam 1 and the inner arc of the elbow is the probe placement position. The probe placement positions of all the inner arc sections of the elbow are connected into a smooth transition curve to form the third scanning path S3;

[0015] According to the selected scanning path, the acoustic beam simulation software is used to simulate N pairs of inner arcs of the two-dimensional model. The S scanning starting angle is 40° and the ending angle is 75°, and the acoustic beam simulation results are obtained;

[0016] The boundaries of the elbow back arc, the elbow neutral plane and the elbow inner arc are:

[0017] Taking the center of the elbow back arc (the highest point of the radial section of the pipe) 0° as the benchmark, the arc surface range of -75° to +75° is the elbow back arc range, the arc surface range of +75° to +105° and -75° to -105° are the neutral plane ranges of the elbow on both sides, and the arc surface range of +105° to 255° is the elbow inner arc range.

[0018] Step 2: Transducer determination

[0019] Due to the large change in curvature of the contact surface between the transducer and the scanning path, in order to ensure the coupling effect, the model was simulated using acoustic beam simulation software according to the size of the pipe curvature change. The S-scan starting angle was 40° and the ending angle was 75°. The transducers used in different scanning paths were determined so that the maximum gap between the probe contact surface and the inspected workpiece during the scanning process was ≤0.4mm. The following results were obtained:

[0020] A. When the pipe diameter is Φ<250mm, two different types of transducers are used, namely the first transducer and the second transducer;

[0021] The parameters of the first transducer are: array model is linear array, number of channels is 16, array element center distance is 0.6mm, array element length is 10mm, and center frequency is 2.25MHz;

[0022] The parameters of the second transducer are: array model is linear array, number of channels is 32, array element center distance is 0.5mm, array element length is 10mm, and center frequency is 5MHz;

[0023] The first scanning path S1 and the second scanning path S2 use the second transducer, and the third scanning path S3 uses the first transducer;

[0024] B. When the pipe diameter Φ≥250mm, all scanning paths use the first transducer;

[0025] Step 3: Instrument parameter setting

[0026] Perform performance tests on ultrasonic phased array instruments and set basic parameters and sensitivity of transducers;

[0027] Step 4: Scan

[0028] (1) When the pipe diameter is Φ<250mm, two transducer scanning methods can be used to achieve full coverage scanning inside the weld. The transducer is placed on the side surface of the weld elbow to be inspected, and the probe is facing the weld direction. The second transducer moves along the scanning path from the neutral plane of the elbow on one side to the back arc surface of the elbow to the neutral plane of the elbow on the other side, that is, along the second scanning path on one side to the first scanning path to the second scanning path on the other side. The first transducer moves along the scanning path of the inner arc surface of the elbow, that is, along the third scanning path. The horizontal axis of the sound beam is aligned with the weld direction to cover the inside of the weld. After the scanning is completed, the detection data is saved to obtain the scanning spectrum T;

[0029] (2) When the pipe diameter Φ ≥ 250 mm, the second transducer is used to move along the scanning path to scan the entire weld. The second transducer probe is directed toward the weld and moved along the scanning path from the neutral plane of the elbow on one side to the back arc surface of the elbow, the neutral plane of the elbow on the other side, and the inner arc surface of the elbow to the starting position. The horizontal axis of the sound beam is aligned with the weld direction to cover the weld interior. After the scanning is completed, the detection data is saved to obtain the scanning map T.

[0030] Step 5: Defect Identification

[0031] Import the acoustic beam simulation results obtained in step 1 into the ultrasonic phased array instrument, find the scan pattern T from the ultrasonic phased array instrument, adjust the S scan angle and the step position in the B scan, and look for defect reflection signals at the corresponding positions of the characteristic waves of the S scan and B scan patterns based on the acoustic beam simulation results. If a reflection signal exists, measure the amplitude of the defect wave in the A scan. A defect wave is identified if the amplitude is higher than 80% of the screen, thereby effectively detecting elbow-to-elbow defects.

[0032] Compared with the existing technology, the present invention can detect internal defects in butt welds of 9% Cr steel pipeline special-shaped parts. It adopts ultrasonic phased array detection technology to overcome the disadvantage that conventional non-destructive testing means can only detect surface defects of welds. The elbow side is used as the detection surface, and a probe coupled with the detection surface is used to find the optimal scanning path. By enhancing the coupling effect and increasing the effective scanning angle, full coverage scanning of the inside of the weld is achieved. The defect reflection signal is clearly visible and easy to identify, and the defects can be accurately quantified to prevent accidents such as pipeline leakage. The method is simple and has good use effect, which greatly improves the detection efficiency and accuracy. After actual application, the accuracy rate reaches more than 99.9%. It is an innovation in the phased array ultrasonic detection method of butt welds of 9% Cr steel pipeline special-shaped parts, and has good social and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram for determining the scanning area of ​​the present invention, wherein a is a schematic diagram for determining the scanning area of ​​the back arc and inner arc of the elbow; b is a schematic diagram for determining the scanning area of ​​the neutral plane of the elbow.

[0034] Figure 2 Schematic diagram of the scanning path of the present invention, where c is the first scanning path S1, b is the second scanning path S2, and a is the third scanning path S3.

[0035] Figure 3 This is a schematic diagram of the simulation of the sound beam coverage when the pipe diameter Φ is less than 250mm;

[0036] Among them, a is the double-probe sound beam coverage diagram on the back arc side of the weld, b is the single-probe sound beam coverage diagram on the back arc side of the weld, c is the single-probe sound beam coverage diagram on the back arc side of the weld, d is the double-probe sound beam coverage diagram on the inner arc side of the weld, e is the single-probe sound beam coverage diagram on the inner arc side of the weld, and f is the single-probe sound beam coverage diagram on the inner arc side of the weld.

[0037] Figure 4 This is a schematic diagram of the simulation of the sound beam coverage when the pipe diameter Φ is greater than or equal to 250 mm according to the present invention;

[0038] Among them, a is the double-probe sound beam coverage diagram on the back arc side of the weld, b is the single-probe sound beam coverage diagram on the back arc side of the weld, c is the single-probe sound beam coverage diagram on the back arc side of the weld, d is the double-probe sound beam coverage diagram on the inner arc side of the weld, e is the single-probe sound beam coverage diagram on the inner arc side of the weld, and f is the single-probe sound beam coverage diagram on the inner arc side of the weld.

[0039] Figure 5 Schematic diagram of the transducer structure of the present invention.

[0040] Figure 6 Schematic diagram of the test block structure for transducer delay and angle gain compensation and DAC curve production of the present invention, where a is the standard test block BZSK-1 and b is the standard test block BZSK-2.

[0041] Figure 7 Schematic diagram of artificial defects of comparison test block DBSK-D1 (elbow neutral surface).

[0042] Figure 8 Schematic diagram of artificial defects of comparison test block DBSK-D2 (inner arc of elbow).

[0043] Figure 9 Schematic diagram of artificial defects of comparison test block DBSK-D3 (elbow back arc). DETAILED DESCRIPTION

[0044] The specific implementation of the present invention is further described in detail below with reference to the accompanying drawings and examples.

[0045] This embodiment takes the internal defects of the elbow-to-elbow butt welds in thermal power plants as the detection object, and the specific detection method includes the following steps:

[0046] Step 1: Scan the path to determine

[0047] Taking the elbow-to-elbow butt weld of 9% Cr steel pipe as the inspection object, a three-dimensional graph of the elbow-to-elbow base material and weld is established. The three-dimensional graph is divided into N sections perpendicular to the weld direction. The N sections are converted into N two-dimensional graphs, that is, a two-dimensional graph of the side view of the inspected weld is established. The probe placement position is determined for each of the N two-dimensional models, specifically:

[0048] A simulated crack defect with a depth of 6 mm is set along the fusion line of the weld, and two straight simulated sound beams are drawn out at the two end points of the defect (such as Figure 1 As shown, they are simulated acoustic beam 1 and simulated acoustic beam 2, respectively. The simulated acoustic beam 1 forms an angle of 55° with the simulated defect, and the simulated acoustic beam 2 forms an angle of 105° with the simulated defect.

[0049] The arc surface of the outer ring of the elbow is the back arc of the elbow, the arc surface of the inner ring of the elbow is the inner arc of the elbow, and the arc surface in the transition area between the inner arc of the elbow and the back arc of the elbow is the neutral surface of the elbow;

[0050] For the elbow back arc section, the intersection position of the simulated sound beam 2 and the elbow back arc is the probe placement position An (e.g. Figure 1 As shown), the probe placement positions of all elbow back arc sections are connected into a smooth transition curve to form a first scanning path S1;

[0051] For the elbow neutral plane section, the intersection position of the secondary reflection wave of the simulated sound beam 1 and the elbow neutral plane is the probe placement position An (e.g. Figure 2 As shown), the probe placement positions of all elbow neutral plane sections are connected into a smooth transition curve to form a second scanning path S2;

[0052] For the inner arc section of the elbow, the intersection of the simulated acoustic beam 1 and the inner arc of the elbow is the probe placement position. The probe placement positions of all the inner arc sections of the elbow are connected into a smooth transition curve to form the third scanning path S3;

[0053] The contact surface curvatures of scanning paths S1 and S3 are large, while the contact surface curvatures of scanning path S2 are small. The contact surface curvatures of the three scanning paths vary greatly. In order to ensure the coupling effect, the scanning path is divided into three sections. According to the selected scanning path, the acoustic beam simulation software is used to simulate N pairs of two-dimensional model inner arcs. The starting angle of the S scan is 40° and the ending angle is 75°. The acoustic beam simulation results are obtained. After the acoustic beam coverage simulation, the acoustic beam can completely cover the inside of the butt weld, meeting the detection effect (such as Figure 2 and Figure 3 shown);

[0054] The boundaries of the elbow back arc, the elbow neutral plane and the elbow inner arc are:

[0055] Taking the center of the elbow back arc (the highest point of the radial section of the pipe) 0° as the benchmark, the arc surface range of -75° to +75° is the elbow back arc range, the arc surface range of +75° to +105° and -75° to -105° are the neutral plane ranges of the elbow on both sides, and the arc surface range of +105° to 255° is the elbow inner arc range.

[0056] Step 2: Transducer determination

[0057] Due to the large change in curvature of the contact surface between the transducer and the scanning path, in order to ensure the coupling effect, the model was simulated using acoustic beam simulation software according to the size of the pipe curvature change. The S-scan starting angle was 40° and the ending angle was 75°. The transducers used in different scanning paths were determined so that the maximum gap between the probe contact surface and the inspected workpiece during the scanning process was ≤0.4mm. The following results were obtained:

[0058] A. When the pipe diameter is Φ<250mm, two different types of transducers are used, namely the first transducer and the second transducer;

[0059] The parameters of the first transducer are: array model is linear array, number of channels is 16, array element center distance is 0.6mm, array element length is 10mm, and center frequency is 2.25MHz;

[0060] The parameters of the second transducer are: the array model is a linear array, the number of channels is 32, the center distance of the array element is 0.5mm, the array element length is 10mm, the center frequency is 5MHz, and the transducer structure diagram is as follows: Figure 5 shown.

[0061] The performance test of the phased array ultrasonic instrument specifically includes: testing the vertical linearity and horizontal linearity of the phased array ultrasonic instrument, requiring the vertical linearity error of the phased array ultrasonic instrument to be no more than 3% and the horizontal linearity error to be no more than 1%;

[0062] The basic transducer parameters are set to use ABS display mode, S scan start angle is 40°, end angle is 75°, step is 0.5°, focus type is true depth;

[0063] The first scanning path S1 and the second scanning path S2 use the second transducer, and the third scanning path S3 uses the first transducer;

[0064] B. When the pipe diameter Φ≥250mm, all scanning paths use the first transducer;

[0065] Step 3: Instrument parameter setting

[0066] Perform performance tests on ultrasonic phased array instruments and set basic parameters and sensitivity of transducers;

[0067] The performance test of the phased array ultrasonic instrument specifically includes: testing the vertical linearity and horizontal linearity of the phased array ultrasonic instrument, requiring the vertical linearity error of the phased array ultrasonic instrument to be no more than 3% and the horizontal linearity error to be no more than 1%;

[0068] The transducer settings are as follows:

[0069] On the ultrasonic phased array instrument, select Probe / Custom Probe, enter the relevant parameters of the first and second transducers, select Save, select Wedge / Custom Wedge, enter the relevant parameters of the first and second transducers, and select Save;

[0070] The basic transducer parameters are set as follows: ABS display mode, S-scan start angle of 40°, end angle of 75°, step of 0.5°, focus type: true depth;

[0071] Compensation of transducer delay and angle gain is completed on the R50 and R100 arcs of the standard test block BZSK-1; Figure 6 To create a DAC curve, set cross-drilled holes of different depths on the standard test block BZSK-1. Generate a weld map of the workpiece under test based on the specifications and dimensions of the workpiece in the ultrasonic phased array instrument. Then place the probe on the test block and align it with holes of 5mm, 10mm, 20mm, 30mm, 40mm, and 50mm, respectively. Find the highest wave of the corresponding cross-drilled hole and draw a distance-amplitude curve in the instrument. This distance-amplitude curve is the DAC curve, which is used to determine the equivalent size of the defect.

[0072] Step 4: Scan

[0073] (1) When the pipe diameter is Φ<250mm, two transducer scanning methods can be used to achieve full coverage scanning inside the weld. The transducer is placed on the side surface of the weld elbow to be inspected, and the probe is facing the weld direction. The second transducer moves along the scanning path from the neutral plane of the elbow on one side to the back arc surface of the elbow to the neutral plane of the elbow on the other side, that is, along the second scanning path on one side to the first scanning path to the second scanning path on the other side. The first transducer moves along the scanning path of the inner arc surface of the elbow, that is, along the third scanning path. The horizontal axis of the sound beam is aligned with the weld direction to cover the inside of the weld. After the scanning is completed, the detection data is saved to obtain the scanning spectrum T;

[0074] (2) When the pipe diameter Φ ≥ 250 mm, the second transducer is used to move along the scanning path to scan the entire weld. The second transducer probe is directed toward the weld and moved along the scanning path from the neutral plane of the elbow on one side to the back arc surface of the elbow, the neutral plane of the elbow on the other side, and the inner arc surface of the elbow to the starting position. The horizontal axis of the sound beam is aligned with the weld direction to cover the weld interior. After the scanning is completed, the detection data is saved to obtain the scanning map T.

[0075] Step 5: Defect Identification

[0076] Import the acoustic beam simulation results obtained in step 1 into the ultrasonic phased array instrument, find the scan pattern T from the ultrasonic phased array instrument, adjust the S scan angle and the step position in the B scan, and look for defect reflection signals at the corresponding positions of the characteristic waves of the S scan and B scan patterns based on the acoustic beam simulation results. If a reflection signal exists, measure the amplitude of the defect wave in the A scan. A defect wave is identified if the amplitude is higher than 80% of the screen, thereby effectively detecting elbow-to-elbow defects.

[0077] Verification of the method of the present invention:

[0078] Make elbow to elbow butt weld crack comparison test blocks DBSK1~DBSK3, such as Figure 6-8 As shown, the elbow specification is Φ220mm×20mm, and the comparison block DBSK1 (elbow neutral surface) has three artificial defects on the outer surface of the weld fusion line, defect 1 is 10mm long×0.2mm wide×4mm deep, defect 2 is 15mm long×0.4mm wide×4mm deep, and defect 3 is 10mm long×0.4mm wide×4mm deep; the comparison block DBSK2 (elbow inner arc) has three artificial defects on the outer surface of the weld fusion line, defect 1 is 10mm long×0.2mm wide×4mm deep, defect 2 is 10mm long×0.4mm wide×4mm deep, and defect 3 is 15mm long×0.4mm wide×4mm deep; the comparison block DBSK3 (elbow back arc) has three artificial defects on the outer surface of the weld fusion line, defect 1 is 10mm long×0.2mm wide×4mm deep, defect 2 is 10mm long×0.4mm wide×4mm deep, and defect 3 is 15mm long×0.4mm wide×4mm deep. The weld seams of elbow-to-elbow comparison test blocks are scanned and inspected according to the method of the present invention.

[0079] The test results are shown in the following table:

[0080]

[0081] After testing, the maximum reflection wave height of defect 1 in DBSK-1 is SL+9.9dB, and the measured length is 9.8mm; the maximum reflection wave height of defect 2 is SL+11.2dB, and the measured length is 14.8mm; the maximum reflection wave height of defect 3 is SL+10.3dB, and the measured length is 10.2mm; the maximum reflection wave height of defect 1 in DBSK-2 is SL+9.7dB, and the measured length is 10.2mm; the maximum reflection wave height of defect 2 is SL+10.1dB, and the measured length is 9.8mm; the maximum reflection wave height of defect 3 is SL+11.1dB, and the measured length is 14.9mm; the maximum reflection wave height of defect 1 in DBSK-3 is SL+9.2dB, and the measured length is 9.6mm; the maximum reflection wave height of defect 2 is SL+9.9dB, and the measured length is 9.4mm; the maximum reflection wave height of defect 3 is SL+10.6dB, and the measured length is 14.8mm.

[0082] The test results show that this detection method can effectively detect all artificial simulated defects in the comparison test blocks and accurately determine the defect location; it can relatively accurately measure the defect length with an error of less than or equal to 0.6mm. In summary, this detection method can realize the effective detection of cracks in the elbow-to-elbow butt weld.

Claims

1. A phased array-based method for detecting defects in butt welds of 9%Cr steel pipe elbows, characterized in that: The following steps are involved: Step 1: Scan the path to determine Taking the butt weld of the 9%Cr steel pipe elbow as the inspection object, a three-dimensional graph of the elbow base material and weld is established. The three-dimensional graph is divided into N sections perpendicular to the weld. The N sections are converted into N two-dimensional graphs, that is, a two-dimensional graph of the side view of the inspected weld is established. The probe placement position is determined for each of the N two-dimensional models. Specifically: A simulated crack defect with a depth of 6 mm was set in the weld along the fusion line. Two linear simulated acoustic beams were drawn at the two end points of the defect. The simulated acoustic beam 1 formed an angle of 55° with the simulated defect, and the simulated acoustic beam 2 formed an angle of 105° with the simulated defect. The arc surface of the outer ring of the elbow is the back arc of the elbow, the arc surface of the inner ring of the elbow is the inner arc of the elbow, and the arc surface in the transition area between the inner arc of the elbow and the back arc of the elbow is the neutral surface of the elbow; For the elbow back arc section, the intersection of the simulated acoustic beam 2 and the elbow back arc is the probe placement position. The probe placement positions of all elbow back arc sections are connected into a smooth transition curve to form the first scanning path S1. For the elbow neutral plane section, the intersection of the secondary reflection wave of the simulated acoustic beam 1 and the elbow neutral plane is the probe placement position. The probe placement positions of all elbow neutral plane sections are connected into a smooth transition curve to form the second scanning path S2; For the inner arc section of the elbow, the intersection of the simulated acoustic beam 1 and the inner arc of the elbow is the probe placement position. The probe placement positions of all the inner arc sections of the elbow are connected into a smooth transition curve to form the third scanning path S3; According to the selected scanning path, the acoustic beam simulation software was used to simulate the inner arcs of N two-dimensional models respectively, with the S-scan starting angle being 40° and the ending angle being 75°, and the acoustic beam simulation results were obtained; Step 2: Transducer determination Due to the large change in curvature of the contact surface between the transducer and the scanning path, in order to ensure the coupling effect, the model was simulated using acoustic beam simulation software according to the size of the pipe curvature change. The S-scan starting angle was 40° and the ending angle was 75°. The transducers used in different scanning paths were determined so that the maximum gap between the probe contact surface and the inspected workpiece during the scanning process was ≤0.4mm. The following results were obtained: A. When the pipe diameter is Φ<250mm, two different types of transducers are used, namely the first transducer and the second transducer; The parameters of the first transducer are: array model is linear array, number of channels is 16, array element center distance is 0.6mm, array element length is 10mm, and center frequency is 2.25MHz; The parameters of the second transducer are: array model is linear array, number of channels is 32, array element center distance is 0.5mm, array element length is 10mm, and center frequency is 5MHz; The first scanning path S1 and the second scanning path S2 use the second transducer, and the third scanning path S3 uses the first transducer; B. When the pipe diameter Φ≥250mm, all scanning paths use the first transducer; Step 3: Instrument parameter setting Perform performance tests on ultrasonic phased array instruments and set basic parameters and sensitivity of transducers; Step 4: Scan (1) When the pipe diameter is Φ<250mm, two transducer scanning methods can be used to achieve full coverage scanning inside the weld. The transducer is placed on the side surface of the weld elbow to be inspected, and the probe is facing the weld direction. The second transducer moves along the scanning path from the neutral plane of the elbow on one side to the back arc surface of the elbow to the neutral plane of the elbow on the other side, that is, along the second scanning path on one side to the first scanning path to the second scanning path on the other side. The first transducer moves along the scanning path of the inner arc surface of the elbow, that is, along the third scanning path. The horizontal axis of the sound beam is aligned with the weld direction to cover the inside of the weld. After the scanning is completed, the detection data is saved to obtain the scanning spectrum T; (2) When the pipe diameter Φ ≥ 250 mm, the first transducer is used to move along the scanning path to scan the entire weld. The first transducer probe is directed toward the weld and moved along the scanning path from the neutral plane of the elbow on one side to the back arc surface of the elbow, the neutral plane of the elbow on the other side, and the inner arc surface of the elbow to the starting position. The horizontal axis of the sound beam is aligned with the weld direction to cover the weld interior. After the scanning is completed, the detection data is saved to obtain the scanning map T. Step 5: Defect Identification Import the acoustic beam simulation results obtained in step 1 into the ultrasonic phased array instrument, find the scan pattern T from the ultrasonic phased array instrument, adjust the S scan angle and the step position in the B scan, and look for defect reflection signals at the corresponding positions of the characteristic waves of the S scan and B scan patterns based on the acoustic beam simulation results. If a reflection signal exists, measure the amplitude of the defect wave in the A scan. A defect wave is identified if the amplitude is higher than 80% of the screen, thereby effectively detecting elbow defects.

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