A wind power bolt safety detection method based on phased array

Abstract

The present invention relates to a phased array-based wind power bolt safety detection method. The phased array device is cleverly used to quickly judge the pre-tightening force of the bolt. By adjusting the amplitude to calculate the gain difference, the bolt stress state can be judged simultaneously with the bolt crack detection, thus saving working time. The upper limit warning values ​​for over-tightening and over-loosening of the bolt are set through calibration experiments, and the gain difference is used to achieve simple and rapid judgment of the bolt pre-tightening state, thereby greatly improving the detection efficiency and achieving good social and economic benefits.

Description

Technical Field

[0001] The present invention relates to the field of wind power, and in particular to a safety evaluation method for high-strength bolts used in wind power, mainly involving a method for evaluating bolt stress and internal defects. Background Art

[0002] Currently, the capacity of wind turbines is getting larger and larger. Wind turbine blades and tower bolts play an important role in the connection of wind turbines. Phased array inspection of bolts is required regularly to determine whether there are internal defects through waveforms, but it is impossible to determine the stress state of the bolts.

[0003] At present, my country's wind power industry has maintained a rapid growth trend in terms of both total installed capacity and newly installed capacity. Bolts in wind power equipment are the main connecting components of wind turbines. If there are quality risks and insufficient bolt preload, the bolts will fail, thus affecting the safety of the wind turbine. In terms of bolt preload measurement, Gu Yuefei determined the bolt stress corresponding to the residual magnetization intensity of the bolt based on the relationship between the residual magnetization intensity of the bolt and the bolt stress in his patent "A method, device and equipment for non-destructive testing of stress". In the article "Ultrasonic measurement of bolt stress", Hu Chunhua derived the linear relationship between ultrasonic sound time difference and stress and proposed a method for online real-time monitoring of the axial stress of wind turbines. It is impossible to identify internal defects of the bolt while checking the bolt preload.

[0004] When determining internal defects in bolts, phased arrays are generally used to inspect the location of the defects. In his article "Application of 3D Fully Focused Phased Array Detection Technology in Nondestructive Testing of Wind Turbine Bolts," Li Wang explains the capabilities of phased array technology in detecting internal defects in bolts, achieving 3D full-focus imaging detection through image recognition. In his patent application, "A High-Strength Bolt Defect Detection Device," Xiao Jian designed a high-strength bolt detection device consisting of an ultrasonic phased array mainframe and a phased array probe connected to it via a cable. A cover secures and positions the phased array probe, enabling it to quickly locate the center of the bolt. A protective film applied to the probe tip significantly reduces probe wear and extends its life. Phased arrays are widely used to inspect internal bolt defects, but research on their use in bolt stress measurement has been limited. Summary of the Invention

[0005] In view of the above situation, in order to overcome the defects of the prior art, the purpose of the present invention is to provide a wind power bolt safety detection method based on phased array, which can effectively solve the problem of efficient safety detection of wind power bolts.

[0006] The technical solution provided by the present invention is: a wind power bolt safety detection method based on phased array, comprising the following steps:

[0007] Step 1: Bolt stress calibration

[0008] Select bolts with the same material and specifications as the part to be measured for calibration, make a calibration platform with the same structural dimensions as the part to be measured, install the bolts into the bolt holes of the calibration platform, and fix them with nuts screwed onto the bolts;

[0009] The bolt surface is pasted with a strain gauge for detecting bolt stress;

[0010] The strain gauge is connected to a strain meter, which is connected to a display for displaying stress readings, thereby obtaining the preload force of the bolt;

[0011] Placing a phased array probe on the end face of the bolt at the section where the nut is located, and connecting the phased array probe to a phased array detection device (7);

[0012] Use a torque wrench to turn the nut and apply the target preload force F1. First, adjust the initial wave of the phased array to 80% of the amplitude and record the gain value dB1. Under this condition, adjust the bottom wave amplitude to 80% and record the dBla at this moment. Calculate the difference between the two: ΔdB1 = dB1 - dB1a.

[0013] Use a torque wrench to turn the nut and apply the target preload upper limit F2. First, adjust the phased array initial wave to 80% of the amplitude and record the gain value dB2. Under this condition, adjust the bottom wave amplitude to 80% and record the dB2a at this moment. Calculate the difference between the two: ΔdB2 = dB2 - dB2a.

[0014] Use a torque wrench to turn the nut and apply the target preload lower limit F3. First, adjust the phased array initial wave to 80% of the amplitude and record the gain value dB3. Under this condition, adjust the bottom wave amplitude to 80% and record the dB3a at this moment. Calculate the difference between the two: ΔdB3 = dB3 - dB3a.

[0015] Step 2: On-site testing

[0016] Place the phased array probe on the end face of the bolt on site. If other waveforms appear before the bottom wave or no bottom wave is seen, it indicates that the bolt has internal defects and is directly rejected.

[0017] If a bottom wave appears and no waveform between the initial wave and the bottom wave is seen, it means that no internal defect is found. Adjust the initial wave to 80% of the amplitude and record the gain value dBx at this time. Then adjust the bottom wave amplitude to 80% and record the gain value dBxa. Calculate the difference between the two: ΔdBx = dBx - dBxa.

[0018] If ΔdBx is between ΔdB2 and ΔdB3, it is qualified;

[0019] If ΔdBx is greater than ΔdB2, it is judged that the bolt is overtightened;

[0020] If ΔdBx is less than ΔdB3, it is judged that the bolt is loose.

[0021] The present invention is simple and cleverly uses phased array equipment to quickly determine the preload condition of a bolt. When the bolt is subjected to axial stress, the size of the internal grains of the bolt changes, resulting in slightly different gain values ​​when adjusting the initial wave to 80%. Therefore, the initial wave gain value must be recorded first. When the bolt is subjected to different axial tensions, the changes in the internal grains of the bolt and the change in bolt length cause different attenuation of the initial wave, and the gain value required to adjust the bottom wave to 80% of the amplitude also varies. The gain value when the bottom wave is adjusted to 80% minus the original gain value of 80% of the initial wave amplitude is the gain value change caused by stress. The gain difference is large when the stress is large, and small when the stress is small. Therefore, the stress state of the bolt can be determined by the difference in gain. Compared with the existing technology, the present invention can determine the stress state of the bolt by calculating the gain difference by adjusting the amplitude, thereby saving work time. The upper limit warning value for overtightening and underloosening of the bolt is set through calibration experiments, and the preload state of the bolt can be simply and quickly determined by the gain difference, greatly improving detection efficiency and achieving good social and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the bolt stress calibration connection of the present invention.

[0023] Figure 2 The figure is a logic flow chart of the method of the present invention. DETAILED DESCRIPTION

[0024] The specific embodiments of the present invention are further described in detail below with reference to the accompanying drawings.

[0025] Depend on Figure 1-2 The present invention provides a wind power bolt safety detection method based on a phased array, comprising the following steps:

[0026] Step 1: Bolt stress calibration

[0027] Select bolts with the same material and specifications as the part to be measured for calibration, make a calibration platform with the same structural dimensions as the part to be measured, install the bolts in the bolt holes of the calibration platform, and fix them with nuts 4 screwed on the bolts;

[0028] A strain gauge 6 for detecting bolt stress is attached to the bolt surface;

[0029] The strain gauge is connected to the strain meter 8, and the strain meter 8 is connected to a display for displaying the stress reading, thereby obtaining the preload force of the bolt;

[0030] The specific conversion method is as follows:

[0031] σ=∈×E

[0032] Where: σ represents stress, ∈ represents strain, and E represents elastic modulus;

[0033] F=σ×S

[0034] Where: F represents the axial stress of the bolt, that is, the preload force, and S represents the cross-sectional area of ​​the bolt;

[0035] Placing a phased array probe 5 on the end face of the bolt at the section where the nut is located, and connecting the phased array probe to a phased array detection device (7);

[0036] Use a torque wrench to turn the nut and apply the target preload force F1. First, adjust the initial wave of the phased array to 80% of the amplitude and record the gain value dB1. Under this condition, adjust the bottom wave amplitude to 80% and record the dB1a at this moment. Calculate the difference between the two: ΔdB1 = dB1 - dB1a.

[0037] Use a torque wrench to turn the nut and apply the target preload upper limit F2. First, adjust the phased array initial wave to 80% of the amplitude and record the gain value dB2. Under this condition, adjust the bottom wave amplitude to 80% and record the dB2a at this moment. Calculate the difference between the two: ΔdB2 = dB2 - dB2a.

[0038] Use a torque wrench to turn the nut and apply the target preload lower limit F3. First, adjust the phased array initial wave to 80% of the amplitude and record the gain value dB3. Under this condition, adjust the bottom wave amplitude to 80% and record the dB3a at this moment. Calculate the difference between the two: ΔdB3 = dB3 - dB3a.

[0039] Step 2: On-site testing

[0040] Place the phased array probe on the end face of the bolt on site. If other waveforms appear before the bottom wave or no bottom wave is seen, it indicates that the bolt has internal defects and is directly rejected.

[0041] If a bottom wave appears and no waveform between the initial wave and the bottom wave is seen, it means that no internal defect is found. Adjust the initial wave to 80% of the amplitude and record the gain value dBx at this time. Then adjust the bottom wave amplitude to 80% and record the gain value dBxa. Calculate the difference between the two: ΔdBx = dBx - dBxa.

[0042] If ΔdBx is between ΔdB2 and ΔdB3, it is qualified;

[0043] If ΔdBx is greater than ΔdB2, it is judged that the bolt is overtightened;

[0044] If ΔdBx is less than ΔdB3, it is judged that the bolt is loose.

[0045] To ensure the use effect, the calibration platform includes a first flange 1 and a second flange 2. The first flange 1 and the second flange 2 are provided with bolt through holes corresponding to the bolts and passing through from top to bottom. The first flange 1 and the second flange 2 are stacked together up and down, and the bolts are installed in the bolt through holes and are tightened and fixed by the nut 4 screwed on the bolt thread section 3a.

[0046] The strain gauge 6 is pasted on the non-threaded section of the bolt, and the strain gauge has multiple (such as Figure 1 As shown in the figure, there are 2 strain gauges), and the bolt strain finally collected is the average value of the measurement results of multiple strain gauges.

[0047] The target preload force F1 (F) is calculated by the following formula:

[0048]

[0049] Where:

[0050] M-torque; k-torque coefficient; d-nominal thread diameter, F=F1, is the target preload force;

[0051] The target preload upper limit F2 and lower limit F3 are selected according to "VDI2230 System Calculation of High Strength Bolt Connections":

[0052] When tightening bolts using the on-site torque method, F2 is set to 1.17F;

[0053] When pre-tightening bolts using the on-site torque method, F3 is set to 0.83F;

[0054] When hydraulic tightening is used to pre-tighten bolts on site, F2 is 1.09F;

[0055] When hydraulic tightening is used on site for bolt pre-tightening, F3 is taken as 0.91F.

[0056] The present invention has achieved good technical effects through practical application, and the application examples are as follows:

[0057] For a tower connection bolt, the torque method is used to control the bolt preload. The bolt specification is M36mm, the bolt length is 150mm, the torque coefficient is 0.1, and the design torque is 1500Nm.

[0058] Step 1: Calculate the bolt design preload and upper and lower limits;

[0059]

[0060]

[0061]

[0062] The preload force applied to the bolt is 417KN, that is, F1 = 417KN; σ1 = 409.88MPa

[0063] The upper limit of the applied preload force is 1.17P; that is, F2 = 1.17 × 417 = 487.89 KN, σ2 = 479.56 MPa;

[0064] The lower limit of the applied preload force is 0.83P; that is, F2 = 0.83 × 417 = 346.11KN; σ3 = 340.20MPa

[0065] Step 2: Apply preload on the test bench

[0066] 2.1 Place the bolt to be calibrated on the calibration platform and apply a preload of 417 kN. The stress data is controlled by a strain gauge, and the strain gauge control data is 409.88 MPa. Place the phased array probe on the bolt end face. Adjust the initial wave to 80% of the amplitude and record the gain value at this time: dB1 = 42.6 dB. Due to acoustic wave attenuation, the bottom wave amplitude is less than 80% at this time. Adjust the gain value to 80% and record the gain value at this time: dB1a = 63.2 dB. Calculate the difference between the two: ΔdB1 = dB1 - dB1a = 20.6 dB.

[0067] 2.2 Apply a preload of 487.89 kN. The stress data is controlled by a strain gauge. Place the phased array probe on the bolt end face. Adjust the initial wave to 80% of the amplitude and record the gain value at this time: dB2 = 42.9 dB. Due to acoustic wave attenuation, the bottom wave amplitude is less than 80% at this time. Adjust the gain value to 80% and record the gain value at this time: dB21 = 66.7 dB. Calculate the difference between the two: ΔdB2 = dB2 - dB2a = 23.8 dB.

[0068] 2.3 Apply a preload of 346.11 kN. The stress data is controlled by a strain gauge. Place the phased array probe on the bolt end face. Adjust the initial wave to 80% of the amplitude and record the gain value at this time: dB3 = 42.1 dB. Due to acoustic wave attenuation, the bottom wave amplitude is less than 80% at this time. Adjust the gain value to 80% of the bottom wave amplitude and record the gain value at this time: dB31 = 58.9 dB. Calculate the difference between the two: ΔdB3 = dB3 - dB3a = 16.8 dB.

[0069] Step 3: Field testing

[0070] A wind turbine blade bolt test was conducted on 20 bolts. Based on the results of the previous calibration experiment, the gain difference was less than 16.8dB, indicating that the bolts were loose. The gain interpolation was between 16.8-23.8dB, indicating normal stress. The gain difference was greater than 23.8dB, indicating that the bolts were overtightened.

[0071] The test results are shown in Table 1. After inspection, it was found that the gain difference of bolts No. 1, 8, 10, 14, and 18 was less than 16.8dB, indicating that the bolts were loose, and the gain difference of bolt No. 13 was greater than 23.8dB, indicating that the bolt was too tight.

[0072] The current positions of bolts 1, 8, 10, 14, and 18 were recorded. A 1500 NM torque wrench was used to tighten the bolts. The presence of changes in the bolt positions indicated that the bolts were indeed loose. The test results were accurate.

[0073] Record the position of bolt No. 13, loosen the bolt, and retighten it with a 1500NM bolt torque wrench. Measure again and record the gain difference of 20.5dB. The bolt stress is normal.

[0074] Table 1 On-site inspection results

[0075]

Claims

1. A wind power bolt safety detection method based on phased array, characterized in that: The following steps are involved: Step 1: Bolt stress calibration Select bolts with the same material and specifications as the part to be measured for calibration, make a calibration platform with the same structural dimensions as the part to be measured, install the bolts in the bolt holes of the calibration platform, and fix them with nuts (4) screwed onto the bolts; A strain gauge (6) for detecting bolt stress is attached to the bolt surface; The strain gauge is connected to a strain meter (8), and the strain meter (8) is connected to a display for displaying stress readings, thereby obtaining the preload force of the bolt; Placing a phased array probe (5) on the end face of the bolt at the section where the nut is located, and connecting the phased array probe to a phased array detection device (7); Use a torque wrench to turn the nut and apply the target preload force F1. First, adjust the initial wave of the phased array to 80% of the amplitude and record the gain value dB1. Under this condition, adjust the bottom wave amplitude to 80% and record the dB1a at this moment. Calculate the difference between the two: ΔdB1 = dB1 - dB1a. Use a torque wrench to turn the nut and apply the target preload upper limit F2. First, adjust the phased array initial wave to 80% of the amplitude and record the gain value dB2. Under this condition, adjust the bottom wave amplitude to 80% and record the dB2a at this moment. Calculate the difference between the two: ΔdB2 = dB2 - dB2a. Use a torque wrench to turn the nut and apply the target preload lower limit F3. First, adjust the phased array initial wave to 80% of the amplitude and record the gain value dB3. Under this condition, adjust the bottom wave amplitude to 80% and record the dB3a at this moment. Calculate the difference between the two: ΔdB3 = dB3 - dB3a. Step 2: On-site testing Place the phased array probe on the end face of the bolt on site. If other waveforms appear before the bottom wave or no bottom wave is seen, it indicates that the bolt has internal defects and is directly rejected. If a bottom wave appears and no waveform between the initial wave and the bottom wave is seen, it means that no internal defect is found. Adjust the initial wave to 80% of the amplitude and record the gain value dBx at this time. Then adjust the bottom wave amplitude to 80% and record the gain value dBxa. Calculate the difference between the two: ΔdBx = dBx - dBxa. If ΔdBx is between ΔdB2 and ΔdB3, it is qualified; If ΔdBx is greater than ΔdB2, it is judged that the bolt is overtightened; If ΔdBx is less than ΔdB3, it is judged that the bolt is loose.

2. The wind power bolt safety detection method based on phased array according to claim 1 is characterized in that: The calibration platform comprises a first flange (1) and a second flange (2). The first flange (1) and the second flange (2) are provided with bolt through-holes corresponding to the bolts and extending through the first and second flanges. The first flange (1) and the second flange (2) are stacked together, and the bolts are inserted into the bolt through-holes and are tightened and fixed by nuts (4) screwed onto the bolt thread sections (3a).

3. The wind power bolt safety detection method based on phased array according to claim 1 is characterized in that: The strain gauge (6) is pasted on the non-threaded section of the bolt, and there are multiple strain gauges evenly distributed along the axial direction of the bolt. The bolt strain amount finally collected is the average value of the measurement results of the multiple strain gauges.

4. The wind power bolt safety detection method based on phased array according to claim 1 is characterized in that: The target preload force F1 is calculated by the following formula: Where: M-torque; k-torque coefficient; d-nominal thread diameter, F=F1, is the target preload force; When tightening bolts using the on-site torque method, F2 is set to 1.17F; When pre-tightening bolts using the on-site torque method, F3 is set to 0.83F; When hydraulic tightening is used to pre-tighten bolts on site, F2 is 1.09F; When hydraulic tightening is used on site for bolt pre-tightening, F3 is taken as 0.91F.

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