Steel pressure vessel outer wall surface crack detection method based on array surface waves

Abstract

The invention discloses a steel pressure vessel outer wall surface crack detection method based on array surface waves, which comprises the following steps: S1, arranging a phased array probe on a detection object and carrying out scanning detection to obtain a detection signal and a detection image feature; s2, fan-shaped scanning parameters and array surface wave focusing rules of the phased array are set; s3, analyzing the detection signal and the detection image features, and calculating the crack length and the wall thickness of the pressure vessel according to the time of the crack opening end reflection pulse f1, the crack tip reflection pulse f2 and the conversion shear wave reflection pulse f3; s4, confirming the crack and correcting the length of the crack; according to the method, the detection efficiency and the quantitative detection capability of the surface opening crack defect are greatly improved.

Description

Technical Field

[0001] The present invention belongs to the field of surface crack detection, and particularly relates to a method for detecting surface cracks on the outer wall of a steel pressure vessel based on array surface waves. Background Art

[0002] The surface of components often becomes a high-risk area for crack initiation under complex loading environments. These cracks not only seriously damage the load-bearing performance and corrosion resistance of workpieces, but also cause stress concentration phenomena, becoming potential causes of structural fracture. The crack depth is an important parameter for equipment safety assessment. Compared with buried cracks, the open form of surface-opening cracks is more easily identifiable; timely and effective depth detection of surface-opening cracks can not only ensure the load-bearing performance of components, but also be of great significance for improving the operation safety and reliability of equipment. Currently, the commonly used detection methods for surface-opening cracks include ultrasonic, penetrant, magnetic particle, and eddy current detection; ultrasonic detection measures the crack morphology and depth through the diffraction or scattering effect of surface waves; both the penetrant method and the magnetic particle method can effectively identify cracks and measure the length, but the depth measurement accuracy is insufficient; although the eddy current detection has the advantages of high efficiency and sensitivity, it has technical limitations such as being unable to accurately distinguish the nature of cracks, being affected by many interference factors, and having a large degree of uncertainty.

[0003] Surface waves are particularly sensitive to surface and subsurface defects of workpieces, and have the advantages of being non-dispersive, not easily attenuated, and having a relatively long detection distance, and are particularly suitable for the detection of material surface defects; the ultrasonic phased array technology can control the deflection and focusing of the sound beam through the time-delay rule, and has relatively high detection accuracy. By using the combination of an ultrasonic phased array probe and a wedge block to perform oblique incidence excitation of surface waves on the workpiece surface, the sound beam control ability of the ultrasonic phased array can form a surface wave focal zone in a specific area on the surface of the test block for the excited surface waves, and can directly display the surface wave reflection echo images at the opening end and the tip of the surface-opening crack, and perform positioning and quantitative detection based on the sound path of the surface wave reflection echo pulses at the opening end and the tip of the surface-opening crack. Therefore, by combining the ultrasonic phased array technology with surface waves, a method for detecting opening cracks based on array surface waves is proposed, which greatly improves the detection efficiency and quantitative detection ability for surface-opening crack defects. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention proposes a method for detecting surface cracks on the outer wall of a steel pressure vessel based on array surface waves, which greatly improves the detection efficiency and quantitative detection ability for surface-opening crack defects.

[0005] The technical solution provided by the present invention is as follows:

[0006] A method for detecting surface cracks on the outer wall of a steel pressure vessel based on array surface waves, comprising the following steps:

[0007] Step S1: Arrange the phased array probe on the detection object and perform scanning detection to obtain detection signals and detection image features;

[0008] Step S2: Set the fan-shaped scanning parameters and array surface wave focusing rules of the phased array;

[0009] Step S3: Analyze the detection signals and detection image features, and calculate the crack length and the wall thickness of the pressure vessel according to the time of the crack opening end reflection pulse f1, the crack tip reflection pulse f2, and the converted shear wave reflection pulse f3;

[0010] Step S4: Confirm the crack and correct the crack length.

[0011] Preferably, the parameters of the phased array probe in Step S1 are: the center frequency of the probe is 5 MHz, the number of array elements is 32, the size of the array element is 0.4 mm × 10 mm, the center spacing of the array elements is 0.5 mm, the wedge angle is 38°, and the minimum distance from the array element to the bottom of the wedge after installing the wedge is 7.5 mm.

[0012] Preferably, Step S1 includes the following sub-steps:

[0013] Sub-step S11: Arrange the probe on the outer wall of the pressure vessel, rotate and scan with the front end of the probe as the center, and observe the reflected echoes in the detection area with a radius of 50 mm;

[0014] Sub-step S12: When a reflected echo appears in this area and the amplitude ≥ 15% of the full screen, fine-tune the direction of the probe with the center of the probe as the center to make this reflected echo reach the highest and record the detection data.

[0015] Preferably, the detection data includes signals and images.

[0016] Preferably, Step S2 includes the following sub-steps:

[0017] Sub-step S21: Set the ultrasonic phased array scanning mode to the fan scan mode, and the maximum fan scan angle is 89°;

[0018] Sub-step S22: Number the array elements from 1 to n from one side to the other side;

[0019] Sub-step S23: Set the origin coordinates (0, 0) at the bottom of the wedge and directly below the 1st array element;

[0020] Sub-step S24: The distance h from the 1st array element to the bottom of the wedge after installing the wedge is 7.5 mm;

[0021] Sub-step S25: The focusing position is the incident point position of the surface wave excited by the nth array element.

[0022] Preferably, the delay of the ith array element in Sub-step S22 is ti , the t i is expressed as:

[0023]

[0024] In the formula, the longitudinal wave sound velocity c 1 of the wedge is 2337 m / s, the surface wave sound velocity c 2 of the workpiece is 2990 m / s, the angle α between the sound beam main axis of each element emitting the surface wave and the normal of the detection surface is 50°, the minimum distance h between the element and the bottom of the wedge after installing the wedge is 7.5 mm, the wedge angle γ is 38°, and the element pitch d is 0.5 mm.

[0025] Preferably, step S3 includes the following sub-steps:

[0026] Sub-step S31: In the defect detection image, display the echo pulses f1, f2, f3 and the corresponding reflected wave fringes F1, F2, F3 and the positions of the fringes;

[0027] Sub-step S32: The relative positions between the reflected wave fringes F1, F2, F3 corresponding to the echo pulses f1, f2, f3 do not change with the forward and backward movement of the probe;

[0028] Sub-step S33: Based on the time difference between the echo pulses f1 and f2, the surface crack length l can be calculated:

[0029]

[0030] In the formula, t 1 , t 2 are the arrival times of the reflected echo pulses f1 and f2 respectively, and c B is the surface wave sound velocity;

[0031] Sub-step S34: Based on the time difference between the echo pulses f2 and f3, the wall thickness of the container can be calculated. According to the times of the echo pulses f2 and f3 and the calculated value l of the crack length, the wall thickness H of the pressure vessel can be obtained c as:

[0032]

[0033] In the formula, t 2 , t 3 are the times of the reflected echo pulses f2 and f3 respectively, and c s is the shear wave sound velocity.

[0034] Preferably, step S4 includes the following sub-steps:

[0035] Sub-step S41: Compare the wall thickness measurement value H c with the actual value H tThe crack can be further determined, and the criterion for determining the crack is as follows:

[0036]

[0037] Among them, H t represents the actual value, and H c represents the measured value;

[0038] Sub-step S42: Further correct the crack calculated value l, and the correction formula is:

[0039]

[0040] In the formula, l represents the crack calculated value, represents the correction value.

[0041] The beneficial effects of the method for detecting surface cracks on the outer wall of a steel pressure vessel based on array surface waves of the present invention are as follows:

[0042] An open crack detection method based on array surface waves is proposed by combining ultrasonic phased array technology with surface waves, which greatly improves the detection efficiency and quantitative detection ability of surface open crack defects. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] To more clearly elaborate the purpose, design concept and innovation of the method for detecting surface cracks on the outer wall of a steel pressure vessel based on array surface waves proposed by the present invention, the present invention will be described in detail below with reference to the drawings and attached tables.

[0044] Figure 1 It is a schematic diagram for calculating the delay law of the present invention.

[0045] Figure 2 is a schematic diagram for detecting cracks in an array surface wave of the present invention.

[0046] Figure 2(a) is an A-scan signal diagram of an 89° sound beam of the present invention.

[0047] Figure 2(b) is a fan scan diagram of an array surface wave of the present invention.

[0048] Figure 3 It is a schematic diagram for arranging a test block and a probe of the present invention.

[0049] Figure 4 It is a schematic diagram for calculating the delay law of the present invention.

[0050] Figure 5 It is a diagram of element delay of the present invention.

[0051] Figure 6 It is a propagation path diagram of a reflected wave at an open end of the present invention.

[0052] Figure 7It is the propagation path diagram of the tip reflection wave of the present invention.

[0053] Figure 8 It is the propagation path diagram of the tip converted shear wave reflection wave of the present invention.

[0054] Figure 9 is the array surface wave detection diagram of the present invention.

[0055] Figure 9(a) is the 89° sound beam A-scan signal diagram of the present invention.

[0056] Figure 9(b) is the array surface wave sector scan diagram of the present invention. Detailed implementation manners

[0057] The present invention will be described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0058] The following describes the specific implementation manners of the present invention to facilitate those skilled in the art to understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation manners. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concept of the present invention are within the scope of protection.

[0059] A method for detecting cracks on the outer wall surface of a steel pressure vessel based on array surface waves includes the following steps:

[0060] Step S1: Arrange a phased array probe on the detection object and perform scanning detection to obtain detection signals and detection image features;

[0061] Step S2: Set the fan-shaped scanning parameters of the phased array and the array surface wave focusing rule;

[0062] Step S3: Analyze the detection signals and detection image features, and calculate the crack length and the wall thickness of the pressure vessel according to the time of the crack opening end reflection pulse f1, the crack tip reflection pulse f2, and the converted shear wave reflection pulse f3;

[0063] Step S4: Confirm the crack and correct the crack length.

[0064] The parameters of the phased array probe in Step S1 are as follows:

[0065] The center frequency of the probe in this implementation scheme is 5 MHz, the number of array elements is 32, the array elements are linearly arranged, the size of the array element is 0.4 mm × 10 mm, and the center distance between array elements is 0.5 mm; the wedge angle is 38°, and the minimum distance from the array element to the bottom of the wedge after installing the wedge is 7.5 mm.

[0066] The method for arranging the phased array probe in Step S1 of this implementation scheme is specifically as follows:

[0067] Place the probe on the outer wall of the pressure vessel, rotate and scan with the front end of the probe as the center, observe the reflected echoes within the detection area with a radius of 50 mm. When there are reflected echoes in this area and the amplitude ≥ 15% of the full screen, fine-tune the probe direction with the center of the probe as the center to make the reflected echo reach the highest point and record the detection data (signals and images).

[0068] The phased array sector scan parameters and the array surface wave focusing law in step S2 of this implementation plan are as follows:

[0069] Set the ultrasonic phased array scanning mode to the sector scan mode, and the maximum sector scan angle is 89°; the element numbers from left to right are 1, 2, 3, …, i, …, n. Assume the origin coordinates (0, 0) are at the bottom of the wedge and directly below element 1. After installing the wedge, the distance h from element 1 to the bottom of the wedge is 7.5 mm, and the focusing position is the incident point position of the surface wave excited by the last element (element n), as Figure 1 shown. The delay of the i-th element is t i :

[0070]

[0071] In the formula, the longitudinal wave sound velocity c 1 of the wedge is 2337 m / s, and the surface wave sound velocity c 2 of the workpiece is 2990 m / s. The angle α between the main axis of the sound beam of the surface wave emitted by each element and the normal of the detection surface is 50°. After installing the wedge, the minimum distance h from the element to the bottom of the wedge is 7.5 mm, the wedge angle γ is 38°, and the element pitch d is 0.5 mm.

[0072] Therefore, the delays of each element are calculated as follows:

[0073] Table 1 Element delay values (μs)

[0074]

[0075] The detection signal, the characteristics of the detection image, and the calculation methods of the crack and wall thickness in step S3 of this implementation plan are as follows:

[0076] In the defect detection image, the echo pulses f1, f2, f3 and the corresponding reflected wave stripes F1, F2, F3 (Figure 2) and the positions of the stripes are shown; the relative positions between the echo pulses f1, f2, f3 (reflected wave stripes F1, F2, F3) do not change with the forward and backward movement of the probe. Based on the time difference between the echo pulses f1 and f2, the surface crack length l can be calculated:

[0077]

[0078] In the formula, t 1 、t2 are the arrival times of the reflected echo pulses f1 and f2 respectively, and c B is the surface wave sound velocity.

[0079] Based on the time difference between the echo pulses f2 and f3, the wall thickness of the container can be calculated. According to the times of the echo pulses f2 and f3 and the calculated crack length l in Equation (2), the wall thickness H of the pressure vessel can be obtained c is:

[0080]

[0081] In the formula, t 2 and t 3 are the times of the reflected echo pulses f2 and f3 respectively, and c s is the shear wave sound velocity.

[0082] The wall thickness criterion and correction method in step S4 of this implementation scheme are as follows:

[0083] Compare the measured wall thickness value H c with the actual value H t to further determine the crack. The criterion is as follows:

[0084]

[0085] The calculated crack value l is further corrected as follows:

[0086]

[0087] In the formula, l represents the calculated crack value, represents the correction value.

[0088] When this implementation scheme is implemented,

[0089] 1. Probe arrangement

[0090] Use an ultrasonic phased array probe combined with a wedge for oblique incidence detection. The parameters of the selected ultrasonic phased array probe are: the center frequency of the probe is 5 MHz, the number of array elements is 32, the array elements are linearly arranged, the size of the array element is 0.4 mm (width) × 10 mm (length), and the center spacing of the array elements is 0.5 mm; the parameters of the wedge are: the longitudinal wave sound velocity is 2337 m / s, and the wedge angle is 38°. After the phased array probe and the wedge are installed forward and connected to the instrument, gradually input the probe and wedge parameters, and the workpiece sound velocity is the surface wave sound velocity of the detection object.

[0091] Machine a narrow groove with a depth of 5 mm in the middle of the top view surface of the steel test block to simulate a surface opening crack. The thickness of the test block is 60 mm, and the size of the narrow groove is 5 mm (length) × 0.3 mm (width); as Figure 3It is a schematic diagram of the test block and probe arrangement. The probe is arranged on the outer wall of the pressure vessel and rotated for scanning with the front end of the probe as the center. Observe the reflected echoes within the detection area with a radius of 50 mm. When there are reflected echoes in this area and the amplitude ≥ 15% of the full screen, fine-tune the probe direction with the probe center as the center to make the reflected echo reach the highest and record the detection data (signals and images).

[0092] 2. Parameter settings and focusing rules

[0093] Set the ultrasonic phased array scanning mode to the sector scan mode, and the maximum sector scan angle is 89°; the array element numbers from left to right are 1, 2, 3, …, i, …, n. Assume that the origin coordinates (0, 0) are located at the bottom of the wedge block and directly below the 1st array element. After installing the wedge block, the distance h from the 1st array element to the bottom of the wedge block is 7.5 mm, and the focusing position is the incident point position of the surface wave excited by the last array element (the nth array element), as Figure 4 shown. The delay of the ith array element is t i :

[0094]

[0095] In the formula, the longitudinal wave sound velocity c 1 of the wedge block is 2337 m / s, the surface wave sound velocity c 2 of the workpiece is 2990 m / s, the included angle α between the sound beam main axis of the surface wave emitted by each array element and the normal of the detection surface is 50°, the minimum distance h from the array element to the bottom of the wedge block after installing the wedge block is 7.5 mm, the wedge block angle γ is 38°, and the array element pitch d is 0.5 mm.

[0096] Thus, the delays of each array element are calculated as shown in Table 1, and the delay diagram is as Figure 5 shown. The delay of the 1st array element is 0, and the delay increases with the increase of the number.

[0097] Table 1 Array element delay values (μs)

[0098]

[0099]

[0100] 3. Image analysis

[0101] When detecting surface cracks by the surface wave pulse reflection method, it is necessary to excite surface waves on the surface of the detection object; the probe can receive three kinds of reflected echoes generated by the surface wave at the surface opening crack, namely: when the surface wave propagates in the shallow layer of the detection object surface and encounters an opening crack, the reflected echo f1 generated at the crack opening end( Figure 6 ); the tip reflected echo f2 formed by part of the surface wave propagating along the crack surface to the crack tip( Figure 7);At the same time, converted shear waves are also generated at the crack tip. The shear wave is incident on the bottom surface and then reflected back to the crack tip and propagates back along the crack surface as the reflected wave f3( Figure 8 ).

[0102] The sound velocity of the workpiece is set to the surface wave sound velocity of 2990 m / s. At this time, a focused surface wave can be formed at the front end of the ultrasonic phased array probe. According to the above test method, the probe is arranged on the detection surface for detection, and the array surface wave detection image of the narrow groove can be measured. At this time, the distance between the front end of the probe and the narrow groove is 35 mm. Figure 9(a) is the A-scan signal diagram at a sound beam angle of 89°, and Figure 9(b) is the fan-scan detection image of the narrow groove. The defect detection image shows the echo pulses f1, f2, f3 (Figure 9(a)) and the corresponding reflected wave fringes F1, F2, F3 (Figure 9(b)) and the positions of the fringes. Among them, the echo pulse f1 has the highest amplitude, the reflected wave fringe F1 has the darkest color and the strongest reflected wave; the relative positions between the echo pulses f1, f2, f3 (reflected wave fringes F1, F2, F3) do not change with the forward and backward movement of the probe. Since the distance between the front end of the probe and the narrow groove is 35 mm, and the distance between the sound beam incident point of the probe and the front end of the probe is 9.1 mm, the fringe formed by the narrow groove reflected echo pulse f1 appears at the half-path value of 44.1 mm; the position of the f2 pulse is related to the depth of the narrow groove and appears at the half-path of 49.1 mm; the position of the f3 pulse is related to the depth of the narrow groove and appears at the half-path of 49.1 mm.

[0103] 4. Crack calculation

[0104] The distance between the echo pulses f1, f2 (reflected wave fringes F1, F2) is related to the depth of the narrow groove. Based on the time difference between the echo pulses f1, f2, the surface crack length l can be calculated:

[0105]

[0106] In the formula, t 1 , t 2 are the arrival times of the reflected echo pulses f1, f2 respectively, and c B is the surface wave sound velocity.

[0107] The distance between the echo pulses f2 and f3 (reflected wave fringes F2 and F3) is related to the wall thickness. Based on the time difference between the echo pulses f2 and f3, the wall thickness of the container can be calculated. According to the time of the echo pulses f2, f3 and the calculated value l of the crack length in formula (2), the wall thickness H of the pressure vessel can be obtained c is:

[0108]

[0109] In the formula, t 2 , t 3They are the times of the reflected echo pulses f2 and f3 respectively, and c s is the shear wave velocity.

[0110] Compare the measured wall thickness value H c with the actual value H t The crack can be further determined, and the criteria are as follows:

[0111]

[0112] It can be calculated from Eqs. (2), (3), and (4) that the calculated values of the narrow groove length and the wall thickness are 5.40 mm and 59.994 mm respectively; the relative errors with the actual dimensions are 8% and 0.01% respectively; the relative error of the wall thickness calculation is less than 2%, and it is determined that the defect is a surface-opening crack defect.

[0113] Substitute the calculated value l of the narrow groove into Eq. (5) for correction to obtain a high-precision quantitative result of the narrow groove depth:

[0114]

[0115] The relative error of the corrected dimension is -2.8%. The relative error of the measured value of the corrected narrow groove length is small and can be used for measuring the depth of the surface-opening narrow groove. Using the ultrasonic phased array technology to excite the array surface wave and form a surface wave focal zone can perform high-precision quantitative detection of the surface-opening crack.

Claims

1. A method for detecting cracks on the outer wall of a steel pressure vessel based on array surface waves, characterized in that: The following steps are involved: Step S1: placing a phased array probe on a detection object and performing scanning detection to obtain detection signals and detection image features; Step S2: setting the sector scanning parameters of the phased array and the array surface wave focusing law; Step S3: analyzing the detection signal and the detection image features, and calculating the crack length and the pressure vessel wall thickness according to the time of the crack opening end reflection pulse f1, the crack tip reflection pulse f2, and the converted shear wave reflection pulse f3; Step S4: Confirm the crack and correct the crack length.

2. The method for detecting cracks on the outer wall of a steel pressure vessel based on array surface waves according to claim 1, characterized in that: The parameters of the phased array probe in step S1 are: the probe center frequency is 5 MHz, the number of array elements is 32, the array element size is 0.4 mm×10 mm, the array element center spacing is 0.5 mm, the wedge angle is 38°, and the minimum distance between the array element and the bottom of the wedge after the wedge is installed is 7.5 mm.

3. The method for detecting cracks on the outer wall of a steel pressure vessel based on array surface waves according to claim 1, characterized in that: The step S1 comprises the following sub-steps: Sub-step S11: placing the probe on the outer wall of the pressure vessel, rotating and scanning with the front end of the probe as the center, and observing the reflected echo in the detection area with a radius of 50 mm; Sub-step S12: When a reflected echo appears in the area and its amplitude is ≥ 15% of the full screen, the probe direction is fine-tuned with the probe center as the center of the circle to make the reflected echo reach the highest and record the detection data.

4. The method for detecting cracks on the outer wall of a steel pressure vessel based on array surface waves according to claim 3, characterized in that: The detection data includes signals and images.

5. The method for detecting cracks on the outer wall of a steel pressure vessel based on array surface waves according to claim 1, characterized in that: The step S2 comprises the following sub-steps: Sub-step S21: setting the ultrasonic phased array scanning mode to a sector scanning mode, with a maximum sector scanning angle of 89°; Sub-step S22: numbering the array elements from one side to the other side as 1 to n; Sub-step S23: Assume that the origin coordinate (0,0) is located at the bottom of the wedge and directly below the array element No. 1; Sub-step S24: After the wedge is installed, the distance h between the array element No. 1 and the bottom of the wedge is 7.5 mm; Sub-step S25: The focusing position is the incident point position of the excited surface wave of the array element No. n.

6. The method for detecting cracks on the outer wall of a steel pressure vessel based on array surface waves according to claim 1, characterized in that: The delay of the i-th array element in the sub-step S22 is t i , the t i The expression is: Wherein, the longitudinal wave speed c1 of the wedge is 2337m / s, the surface wave speed c2 of the workpiece is 2990m / s, the angle α between the main axis of the sound beam of each array element emitting the surface wave and the normal of the detection surface is 50°, the minimum distance h between the array element and the bottom of the wedge after the wedge is installed is 7.5mm, the wedge angle γ is 38°, and the array element spacing d is 0.5mm.

7. The method for detecting cracks on the outer wall of a steel pressure vessel based on array surface waves according to claim 1, characterized in that: The step S3 comprises the following sub-steps: Sub-step S31: displaying the echo pulses f1, f2, f3 and the corresponding reflected wave fringes F1, F2, F3 and the positions of the fringes in the defect detection image; Sub-step S32: the relative positions of the reflected wave fringes F1, F2, F3 corresponding to the echo pulses f1, f2, f3 do not change with the forward and backward movement of the probe; Sub-step S33: The surface crack length l can be calculated based on the time difference between the echo pulses f1 and f2: Where t1 and t2 are the arrival times of the reflected echo pulses f1 and f2 respectively, c B is the surface wave speed; Sub-step S34: The wall thickness of the pressure vessel can be calculated based on the time difference between the echo pulses f2 and f3. The wall thickness H of the pressure vessel can be obtained based on the time difference between the echo pulses f2 and f3 and the calculated crack length l. c for: Where t2 and t3 are the times of reflected echo pulses f2 and f3 respectively, c s is the shear wave speed.

8. The method for detecting cracks on the outer wall of a steel pressure vessel based on array surface waves according to claim 1, characterized in that: The step S4 comprises the following sub-steps: Sub-step S41: Compare the wall thickness measurement value H c and the actual value H t The cracks can be further determined, and the criterion for determining the cracks is: Among them, H t Indicates the actual value, H c Indicates the measured value; Sub-step S42: further correcting the crack calculation value l, the corrected formula is: Where l represents the calculated crack value, Indicates the correction value.

Images