Device and method for testing dynamic stress of top cover bolt of pumped storage unit

Abstract

The invention discloses a device and a method for testing the dynamic stress of a top cover bolt of a pumped storage unit, which are used for solving the problems of insufficient bolt dynamic stress test precision and poor dynamic response in the prior art. The device comprises an ultrasonic stress monitoring module, an environmental parameter acquisition module, a data transmission module and a data processing module, and real dynamic stress is calculated by synchronously acquiring bolt ultrasonic signals, temperature and vibration parameters and utilizing a coupling and decoupling formula. The method comprises the steps of sensor calibration, multi-working-condition signal acquisition, data decoupling and fatigue evaluation. Compared with single ultrasonic monitoring of CN112525520B, the method has the advantages that the error is reduced to + / -3 MPa through two-parameter correction; compared with CN117910288A finite element simulation, 1kHz high-frequency dynamic monitoring is achieved, transient stress fluctuation can be captured, real-time data is provided for bolt safety assessment, and monitoring precision and engineering practicability are improved.

Description

Technical Field

[0001] This invention relates to the field of pumped storage unit condition monitoring technology, and in particular to a dynamic stress testing device and method for the top cover bolts of a pumped storage unit. Background Technology

[0002] The top cover bolts of pumped storage units are key components connecting the top cover and the seat ring, and their dynamic stress state directly affects the safe operation of the unit. In existing technology, CN112525520B discloses an online monitoring method for the top cover bolts, which obtains stress change values ​​through an ultrasonic stress monitoring system and compares them with a reference value to trigger an alarm. However, this technology only monitors the absolute value of stress and does not consider the interference of environmental factors such as temperature and vibration on the ultrasonic propagation characteristics, resulting in a large error in dynamic stress measurement (the error rate is usually >5%). CN117910288A proposes a bolt stress calculation method based on a finite element model, analyzing the force distribution through contact constraints and material models. However, this method is an offline simulation and cannot capture stress fluctuations under dynamic operating conditions of the unit in real time, and it does not address the multi-physics coupling problem in actual testing.

[0003] Therefore, existing technologies have the drawback of being unable to accurately obtain the true dynamic stress of bolts under dynamic working conditions. There is an urgent need for a testing scheme that combines multi-parameter synchronous monitoring and dynamic decoupling algorithms to meet the requirements of high-head pumped storage units for the accuracy of bolt dynamic stress testing. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a dynamic stress testing device and method for the top cover bolts of pumped storage units, thereby solving the problems of large environmental interference and inability to decouple in real time in existing dynamic stress testing technologies.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A dynamic stress testing device for the top cover bolts of a pumped storage unit includes an ultrasonic stress monitoring module, an environmental parameter acquisition module, a data transmission module, and a data processing module. The ultrasonic stress monitoring module includes an ultrasonic signal generator, an ultrasonic sensor, and a time-difference acquisition unit. The ultrasonic sensor is installed on the end face of the top cover bolt and is used to emit and receive ultrasonic signals. The time-difference acquisition unit is used to acquire the change in ultrasonic propagation time Δt within the bolt. The environmental parameter acquisition module includes a temperature sensor and a vibration sensor, used to acquire the ambient temperature T and vibration acceleration around the bolt. The data transmission module uses coaxial cables to connect each sensor to the data processing module; the data processing module has a built-in stress calculation model, which satisfies the following: ; in, This represents the dynamic stress value of the bolt (MPa). The ultrasonic stress coefficient of the bolt material is (μs / (MPa·m)). The effective length of the bolt (m). This is the temperature correction factor (MPa / ℃). The vibration correction factor is (MPa / (m / s²)).

[0006] Furthermore, there are six ultrasonic sensors, symmetrically distributed on the top cover segmented structure in a circular pattern. Three bolts are selected for each segment, respectively arranged on both sides and the center of the segmented surface. The temperature sensor and vibration sensor correspond one-to-one with the ultrasonic sensor and are installed on the top cover surface 5±1cm outside the bolt axis.

[0007] Furthermore, the coaxial cable of the data transmission module is wrapped with a shielding layer, and the grounding resistance of the shielding layer is ≤4Ω; the cable fixing spacing is 30±5cm, and it is double-fixed with stainless steel strip and insulating tape, and the ground laying section is protected by metal corrugated pipe with a thickness of ≥2mm.

[0008] Furthermore, the excitation pulse width of the ultrasonic signal generator is 50-200ns, and the repetition frequency is 1-10kHz; the measurement accuracy of the time difference acquisition unit is ≤0.1ns, and it supports the synchronous acquisition of the primary bottom wave time difference t1 and the secondary bottom wave time difference t2, and Δt=t2-t1.

[0009] Furthermore, the data processing module also includes a dynamic stress spectrum analysis unit, used to calculate the stress amplitude under different working conditions: ; in, This is a real-time stress time series under a certain working condition.

[0010] This invention also provides a method for testing the dynamic stress of the top cover bolts of a pumped storage unit, using the aforementioned stress testing device, and comprising the following steps: S1. Sensor Calibration: Select a standard bolt of the same type as the bolt to be tested, apply a gradient load on the tensile testing machine, and simultaneously record Δt, temperature, and vibration data. Obtain the sensor calibration result using the least squares method. , , The value; S2. Measuring point installation: Clean the bolt end face to a roughness Ra≤1.6μm, and use epoxy adhesive to attach the ultrasonic sensor with an adhesive layer thickness ≤0.1mm; the temperature sensor and vibration sensor are fixed by magnetic base; S3. Signal Acquisition: Synchronously acquire Δt, T, and T values ​​under unit start-up / shutdown, full-load operation, and sudden load changes. The signal sampling frequency is set to 1kHz; S4. Data processing: Substitute the collected data into the stress calculation model described in claim 1 to obtain the dynamic stress value and generate a stress-time curve; S5. Result Analysis: Based on the calculations... Amplitude is used to assess the fatigue damage of bolts under dynamic loads.

[0011] Furthermore, in step S1, the gradient load is applied within the range of 0-1.2 times the bolt's rated load, with each load level held for 5 minutes, and at least 3 sets of data collected. The fitting error of the value is ≤2%.

[0012] Furthermore, the epoxy adhesive mentioned in step S2 is a two-component structural adhesive with a curing temperature of 25±5℃, a curing time of ≥24h, and a shear strength of ≥15MPa after curing.

[0013] Furthermore, the load change rate of the load change condition described in step S3 is 0.5-2MW / s, and the system is allowed to run stably for 10 minutes after each change before the next test is conducted.

[0014] Furthermore, the fatigue damage calculation in step S5 adopts Miner's rule: ; in, For cumulative damage, For the first Number of cycles under primary stress, For the fatigue life corresponding to the stress level, according to The amplitude can be obtained from the material's SN curve.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. Improved accuracy: Through dual-parameter correction of temperature and vibration, the dynamic stress measurement error rate is ≤3%, which is more than 40% higher than the single ultrasonic monitoring accuracy of CN112525520B.

[0016] 2. Dynamic response: The sampling frequency reaches 1kHz, which can capture the stress transient fluctuations when the unit load changes suddenly, making up for the deficiency of CN117910288A offline simulation in that it cannot monitor in real time.

[0017] 3. The proposed fatigue damage calculation method can directly guide the formulation of bolt maintenance cycles, and adds full life cycle management support capabilities compared with existing technologies. Attached Figure Description

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1This is a diagram showing the arrangement of measuring points for the top cover and seat ring bolts in an embodiment of the present invention. Figure 2 This is a front view of the bolt measuring point location in an embodiment of the present invention; Figure 3 This is a schematic diagram of the installation of the bolt stress measuring point protective cap by drilling holes in an embodiment of the present invention; Figure 4 The stress-time curves are simulated for comparing the embodiments of the present invention with two comparative documents.

[0019] The components include: seat ring 1, ultrasonic sensor 2, and bolt 3. Detailed Implementation

[0020] The technical solutions of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0021] Example 1 A dynamic stress testing device for the top cover bolts of a pumped storage unit includes an ultrasonic stress monitoring module, an environmental parameter acquisition module, a data transmission module, and a data processing module.

[0022] Ultrasonic stress monitoring module: The ultrasonic signal generator used is the RITEC RAM-5000 model from the United States, with an excitation pulse width of 100ns and a repetition frequency of 5kHz. Ultrasonic sensor 2 is a 5MHz longitudinal wave probe, model: Olympus V156-RM, diameter 10mm, compatible with M36-M64 bolts. The time difference acquisition unit uses the NIPXIe-5122 high-speed acquisition card with a measurement accuracy of 0.05ns. It supports synchronous acquisition of t1 and t2, and the Δt calculation is achieved through a built-in algorithm.

[0023] Environmental parameter acquisition module: The temperature sensor is a PT1000 platinum resistance thermometer, with a measurement range of -40~150℃ and an accuracy of ±0.1℃. The vibration sensor used is a PCB352C33 accelerometer with a range of ±50g and a sensitivity of 10mV / g.

[0024] Data transmission module: The coaxial cable is of type RG-213, with an impedance of 50Ω. The shielding layer adopts a double-layer shielding of multi-strand copper mesh and aluminum foil, and the grounding resistance is 3Ω. Fixing method: The wall section is fixed with 304 stainless steel strip (12mm wide) every 30cm, and the ground section is covered with φ25mm galvanized metal corrugated pipe and covered with 5mm thick stainless steel cover plate.

[0025] Data processing module: The hardware uses an industrial control computer, equipped with a Core i7-12700 processor and 32GB of memory; Built-in stress calculation model parameters: For bolt 3 made of 34CrNi3Mo material, =2.3×10 -9 μs / (MPa·m), =0.0025MPa / ℃, =0.08MPa / (m / s²), dynamic stress is calculated in real time using the stress calculation model formula.

[0026] Example 2 The present invention also provides a dynamic stress testing method for the top cover bolts 3 of a pumped storage unit, which uses the above-mentioned stress testing device and includes the following steps: S1. Sensor Calibration: Select M48 standard bolt 3 made of 34CrNi3Mo material, which is from the same batch as bolt 3 to be tested. Apply a gradient load of 0-800kN on a 1000kN tensile testing machine, with each level being 100kN, and hold for 5 minutes. Simultaneously collected Δt (mean), ambient temperature (constant 25℃), and vibration acceleration (≤0.01g), and fitted using the least squares method, yielded the following: =2.3×10-9μs / (MPa·m), fitting error 1.8%, which meets the requirements.

[0027] S2. Measurement point installation: Bolt 3 end face treatment: radial grinding with 120 grit sandpaper, axial polishing with 800 grit sandpaper, and cleaning with alcohol 3 times. The roughness Ra was measured to be 1.2μm. Sensor bonding: Loctite E-20HP epoxy adhesive was used, with a layer thickness of 0.08mm. Curing time was 24 hours at 25℃, and the shear strength test value was 18MPa. Installation location is as follows... Figures 1-3 As shown, the test points are arranged on the end faces of the bolts connecting the top cover and the seat ring. Three bolts are selected for each segment, located at both ends of the segment face and the center of the segment, for a total of 6 test points. Environmental sensor installation: The temperature sensor and vibration sensor are fixed to the outside of bolt 3 by magnetic base 5cm away, and keep in the same axial plane as ultrasonic sensor 2.

[0028] S3. Signal Acquisition: The test conditions include: unit startup (0-300MW, lasting 10min), full load operation (300MW, lasting 30min), and load change (300MW→150MW, rate 1MW / s, stabilization for 10min). The sampling frequency was set to 1kHz, and three sets of data were continuously collected for each operating condition, with each set of data being ≥1GB.

[0029] S4. Data Processing: Let Δt, T, Substituting the data into the stress calculation model formula, for example, data at a certain moment under full load conditions: Δt = 0.23 μs, T = 35℃, =0.5m / s², =0.3m, calculated as follows: ; Generate stress-time curves, such as Figure 4 As shown, the peak stress during the startup phase reaches 380 MPa, and stabilizes at 340 ± 5 MPa during the full load phase. This indicates that the stress of this invention rises rapidly during the startup phase (0-100s), stabilizes at 340 ± 2 after full load, and has a small drop during sudden changes (322→330), demonstrating strong adaptability. Test CN112525520B shows a rapid increase during the startup phase (315→390), but a sharp drop during sudden changes (350→305), indicating poor stability. Test CN117910288A shows a smooth startup phase (310→365), remains almost unchanged after full load, has a small change during sudden changes (335→325), but has a slow startup response.

[0030] S5. Results Analysis: According to Miner's rule, the number of stress cycles for each working condition is counted: During the initial stage, N1 = 50 cycles (σ1 = 380 MPa, Np1 = 1 × 10⁻⁶). 4 ), at full load stage N2=300 times (σ2=340MPa, Np2=5×10), 4 ), calculated to be: This indicates that bolt 3 has not yet suffered fatigue damage, and it is recommended that the next testing cycle be 6 months.

[0031] The core innovation of this invention lies in establishing a coupling and decoupling model of "ultrasonic propagation characteristics - environmental interference - dynamic stress": Utilizing the propagation characteristics of ultrasound in a stress field (Δt and (linear relationship), breaking through the limitation of CN112525520B which only monitors stress changes; Introducing a temperature correction factor and vibration correction factor This method quantitatively eliminates environmental interference and addresses the issue that the CN117910288A simulation model does not consider the actual environmental impact. By using dynamic stress spectrum analysis and Miner's rule, a complete technical solution from stress testing to fatigue assessment is achieved, which expands the engineering application scenarios compared to existing technologies.

[0032] This device and method have been applied to Unit 3 of a pumped storage power station. The test results are consistent with the actual flaw detection results of bolt 3, verifying the effectiveness of the technology.

[0033] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A dynamic stress testing device for the top cover bolts of a pumped storage unit, characterized in that, The system includes an ultrasonic stress monitoring module, an environmental parameter acquisition module, a data transmission module, and a data processing module. The ultrasonic stress monitoring module comprises an ultrasonic signal generator, an ultrasonic sensor, and a time-difference acquisition unit. The ultrasonic sensor is mounted on the end face of the top cover bolt and is used to emit and receive ultrasonic signals. The time-difference acquisition unit is used to acquire the change in ultrasonic wave propagation time Δt within the bolt. The environmental parameter acquisition module includes a temperature sensor and a vibration sensor, used to acquire the ambient temperature T and vibration acceleration around the bolt. The data transmission module uses coaxial cables to connect each sensor to the data processing module; the data processing module has a built-in stress calculation model, which satisfies the following: ； in, This represents the dynamic stress value of the bolt (MPa). The ultrasonic stress coefficient of the bolt material is (μs / (MPa·m)). The effective length of the bolt (m). This is the temperature correction factor (MPa / ℃). The vibration correction factor is (MPa / (m / s²)).

2. The dynamic stress testing device for the top cover bolts of a pumped storage unit as described in claim 1, characterized in that, There are 6 ultrasonic sensors, which are symmetrically distributed on the top cover segment structure in a circular pattern. Three bolts are selected for each segment and are respectively arranged on both sides and the center of the segment surface. The temperature sensor and vibration sensor correspond one-to-one with the ultrasonic sensor and are installed on the top cover surface 5±1cm outside the bolt axis.

3. The dynamic stress testing device for the top cover bolts of a pumped storage unit as described in claim 1, characterized in that, The coaxial cable of the data transmission module is wrapped with a shielding layer, and the grounding resistance of the shielding layer is ≤4Ω; the cable fixing spacing is 30±5cm, and it is double fixed with stainless steel strip and insulating tape. The ground laying section is protected by metal corrugated pipe with a thickness of ≥2mm.

4. The dynamic stress testing device for the top cover bolts of a pumped storage unit as described in claim 1, characterized in that, The excitation pulse width of the ultrasonic signal generator is 50-200ns, and the repetition frequency is 1-10kHz; the measurement accuracy of the time difference acquisition unit is ≤0.1ns, and it supports the synchronous acquisition of the primary bottom wave time difference t1 and the secondary bottom wave time difference t2, and Δt=t2-t1.

5. The dynamic stress testing device for the top cover bolts of a pumped storage unit as described in claim 1, characterized in that, The data processing module also includes a dynamic stress spectrum analysis unit for calculating stress amplitudes under different working conditions: ； in, This is a real-time stress time series under a certain working condition.

6. A method for testing the dynamic stress of the top cover bolts of a pumped storage unit, characterized in that, Using the stress testing apparatus as described in any one of claims 1 to 5, the steps include: S1. Sensor Calibration: Select a standard bolt of the same type as the bolt to be tested, apply a gradient load on the tensile testing machine, and simultaneously record Δt, temperature, and vibration data. Obtain the sensor calibration result using the least squares method. , , The value; S2. Measuring point installation: Clean the bolt end face to a roughness Ra≤1.6μm, and use epoxy adhesive to attach the ultrasonic sensor with an adhesive layer thickness ≤0.1mm; the temperature sensor and vibration sensor are fixed by magnetic base; S3. Signal Acquisition: Synchronously acquire Δt, T, and T values ​​under unit start-up / shutdown, full-load operation, and sudden load changes. The signal sampling frequency is set to 1kHz; S4. Data processing: Substitute the collected data into the stress calculation model described in claim 1 to obtain the dynamic stress value and generate a stress-time curve; S5. Results Analysis: Based on the calculations... Amplitude is used to assess the fatigue damage of bolts under dynamic loads.

7. The method for testing the dynamic stress of the top cover bolts of a pumped storage unit as described in claim 6, characterized in that, The gradient load applied in step S1 is within the range of 0-1.2 times the bolt's rated load, with each load level held for 5 minutes, and at least 3 sets of data collected. The fitting error of the value is ≤2%.

8. The method for testing the dynamic stress of the top cover bolts of a pumped storage unit as described in claim 6, characterized in that, The epoxy adhesive mentioned in step S2 is a two-component structural adhesive with a curing temperature of 25±5℃, a curing time of ≥24h, and a shear strength of ≥15MPa after curing.

9. The method for testing the dynamic stress of the top cover bolts of a pumped storage unit as described in claim 6, characterized in that, The load change rate of the load change condition described in step S3 is 0.5-2MW / s. After each change, the system should be kept stable for 10 minutes before the next test is conducted.

10. The method for testing the dynamic stress of the top cover bolts of a pumped storage unit as described in claim 6, characterized in that, The fatigue damage calculation in step S5 adopts Miner's rule: ； in, For cumulative damage, For the first Number of cycles under primary stress, For the fatigue life corresponding to the stress level, according to The amplitude can be obtained from the material's SN curve.

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