Stress distribution measuring mechanism for pressure vessel in high-temperature environment and use method thereof

Abstract

The invention relates to the technical field of stress measurement, in particular to a stress distribution measuring mechanism for a pressure vessel in a high-temperature environment and a use method of the stress distribution measuring mechanism. The sensor comprises a sensor substrate made of a silicon carbide material, an MEMS sensing unit integrated on the substrate, a high-temperature-resistant glass sealing layer, a distributed fiber grating array, a thermal stress compensation module and a signal processing terminal, the measuring method uses the measuring mechanism, and comprises the following steps of: 1, performing measurement; the method comprises the steps of 1, preheating a container to a working temperature, and activating a sensor self-checking mode; step 2, scanning the distributed fiber grating array to establish a reference strain field; 3, the MEMS unit starts high-frequency sampling, and data and optical fiber signals are subjected to space-time alignment; 4, the thermal stress compensation module injects a correction coefficient to generate a three-dimensional stress nephogram; and step 5, triggering graded alarm in an abnormal stress area. The method has the effects of high reliability and multi-dimensional measurement capability.

Description

Technical Field

[0001] The present invention relates to the technical field of stress measurement, and in particular to a stress distribution measurement mechanism for a pressure vessel in a high temperature environment and a use method thereof. Background Art

[0002] As core equipment in the fields of petrochemicals, energy, aerospace, etc., pressure vessels operate under high temperature, high pressure and corrosive media environments for a long time. With the advancement of industrial technology, pressure vessels are gradually developing in the direction of large-scale and complex, and their design pressure and temperature ranges continue to increase. Especially in scenarios such as nuclear power and deep-earth resource development, containers need to withstand temperatures exceeding 500°C and pressures of tens of megapascals, and local stress concentration may lead to failure risks such as material creep and fatigue cracks. According to statistics, the scale of China's pressure vessel market is expected to exceed 100 billion yuan in 2025, of which high-temperature conditions account for more than 40%, and the demand for precise stress monitoring technology is becoming increasingly urgent.

[0003] At present, high temperature stress measurement technology is mainly divided into two categories: contact and non-contact: Contact sensors include resistance strain gauges, which reflect strain through the resistance change of metal sensitive grids. They are installed on the measured surface with high-temperature curing adhesives and can withstand a maximum temperature of about 800°C. For example, in the measurement of dynamic stress of aircraft engine turbine blades, slip rings or telemetry systems are required to achieve signal transmission.

[0004] Fiber Bragg grating sensor: It uses the wavelength drift characteristics of fiber Bragg grating to sense strain. It is encapsulated by a high-temperature resistant coating and can withstand environments above 1000°C, but the problem of grating degradation under high temperature needs to be solved.

[0005] Non-contact techniques include photoelasticity, which uses polarized light to analyze stress fringes on the surface of a transparent model, but it is only applicable in laboratory environments and cannot be directly applied to metal containers.

[0006] Fiber Bragg grating sensors are prone to fiber embrittlement and grating ablation in long-term high-temperature environments, and the welding process is complex, making it difficult to achieve multi-point distributed measurement. Installation and signal transmission restrictions Traditional strain gauges require pre-processing of installation positions on the container surface, which may damage material integrity and introduce additional stress. In Gray-type high-pressure devices, the sensor leads need to pass through the pressure vessel wall, resulting in sealing problems and signal interference.

[0007] Non-contact technology relies on external optical equipment and cannot be used in closed containers or highly corrosive media environments. Summary of the invention

[0008] In view of the deficiencies in the prior art, one of the objectives of the present invention is to provide a stress distribution measurement mechanism for pressure vessels in high temperature environments with high reliability and multi-dimensional measurement capabilities.

[0009] The above application object of the present invention is achieved through the following technical solutions: A stress distribution measuring mechanism for a pressure vessel in a high temperature environment comprises a sensor substrate made of silicon carbide material, a MEMS sensitive unit integrated on the substrate, a high temperature resistant glass sealing layer, a distributed fiber grating array, a thermal stress compensation module and a signal processing terminal.

[0010] As a specific implementation of a stress distribution measurement mechanism for a pressure vessel in a high temperature environment disclosed in the present invention, the distributed fiber grating array adopts a multi-core fiber structure, each core is spaced 0.5 mm apart, and the grating period is gradiently distributed in the range of 1520-1570 nm.

[0011] As a specific implementation of a stress distribution measurement mechanism for a pressure vessel in a high temperature environment disclosed by the present invention, the MEMS sensitive unit includes an elastic support beam, a differential capacitance detection module and a temperature self-calibration electrode.

[0012] As a specific implementation of a stress distribution measurement mechanism for a pressure vessel in a high temperature environment disclosed in the present invention, the elastic support beam adopts a U-shaped folding structure, with a beam width of 10 μm and a thickness of 5 μm. The differential capacitance detection module has a spacing of 2 μm, and the temperature self-calibration electrode integrates a platinum resistance film.

[0013] As a specific implementation of a stress distribution measurement mechanism for a pressure vessel in a high temperature environment disclosed in the present invention, the surface of the elastic support beam is covered with a silicon nitride stress compensation layer with a thickness of 200-500nm and a Young's modulus ≥300GPa.

[0014] As a specific implementation of a stress distribution measurement mechanism for a pressure vessel in a high temperature environment disclosed in the present invention, the comb-tooth electrodes of the differential capacitance detection module adopt a stepped staggered layout, and the height difference between adjacent electrodes is 0.1-0.3μm, forming a three-dimensional electric field gradient distribution.

[0015] As a specific implementation of a stress distribution measurement mechanism for a pressure vessel under a high temperature environment disclosed in the present invention, the high temperature resistant glass sealing layer is made of borosilicate glass with a thickness of 0.3-0.5 mm, and the inorganic adhesive bonding layer adopts Al2O3-based nano-ceramic adhesive.

[0016] A method for measuring stress distribution of a pressure vessel in a high temperature environment, using the aforementioned measuring mechanism, comprises the following steps; Step 1: preheat the container to the operating temperature and activate the sensor self-test mode; Step 2, the distributed fiber grating array scans to establish a reference strain field; Step 3: The MEMS unit starts high-frequency sampling, and the data is aligned with the optical fiber signal in time and space; Step 4: The thermal stress compensation module injects a correction coefficient to generate a three-dimensional stress cloud map; Step 5: The abnormal stress area triggers a graded alarm.

[0017] As a specific implementation method of a method for measuring stress distribution of a pressure vessel under a high temperature environment disclosed in the present invention, step 4 adopts an improved Ct-GBES-BPNN neural network model, and the input features include center of gravity frequency, root mean square strain gradient, and heat flux density.

[0018] As a specific implementation of the method for measuring stress distribution of a pressure vessel under a high temperature environment disclosed in the present invention, the hierarchical alarm strategy of step 5 includes: Level 1 alarm: sound and light alarm is activated when the local stress exceeds the limit value by 80%; Second level alarm: When the sampling exceeds the limit value of 100% for three consecutive times, the shutdown interlock is triggered; Level 3 alarm: The emergency cooling system is activated when a crack growth rate > 1μm / s is detected.

[0019] In summary, the present invention includes at least one of the following beneficial technical effects: The MEMS unit of the present invention senses local strain through the piezoresistive effect, the distributed optical fiber uses the grating wavelength drift to realize the full-surface strain field measurement, and the thermal stress compensation module combines with the finite element model to correct the material expansion error caused by temperature in real time, realizing the point-surface combined stress synchronous measurement in a high temperature environment greater than 800°C, with a spatial resolution of 1mm and a thermal drift error reduced by 70%; The present invention converts shear stress into displacement through elastic beams, detects displacement through differential capacitance, and uses platinum resistors to feed back temperature changes in real time to correct nonlinear errors of piezoresistive coefficients. The multi-core design of the present invention realizes three-dimensional strain decoupling. The gradient grating distinguishes strain signals at different positions through wavelength demodulation, which improves the strain measurement dimension. The axial and hoop stress resolution reaches ±10με, which is suitable for complex stress field reconstruction of curved containers. The present invention provides a material thermal expansion coefficient-temperature curve through a database, and a finite element model dynamically calculates thermal stress distribution to generate a compensation coefficient matrix. In the range of 500-1000°C, the thermally induced strain error is reduced from ±15% to ±4.5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a working logic diagram of a stress distribution measurement mechanism for a pressure vessel in a high temperature environment disclosed by the present invention; Figure 2It is a working logic diagram of a MEMS sensitive unit of a stress distribution measurement mechanism of a pressure vessel in a high temperature environment disclosed by the present invention. DETAILED DESCRIPTION

[0021] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0022] Reference Figure 1 , which is a stress distribution measurement mechanism for a pressure vessel in a high temperature environment disclosed in the present invention, comprising a sensor substrate made of silicon carbide material, a MEMS sensitive unit integrated on the substrate, a high temperature resistant glass sealing layer, a distributed fiber grating array, a thermal stress compensation module and a signal processing terminal.

[0023] The sensor substrate is made of silicon carbide material, which is temperature-resistant >1600°C and has a thermal expansion coefficient that matches that of a steel container. The MEMS sensitive unit is a piezoresistive sensor based on SOI technology, integrating an elastic support beam and a temperature self-calibration electrode. The distributed fiber grating array uses multi-core optical fiber, with 256 grating points integrated in a single optical fiber. The thermal stress compensation module has a built-in JMatPro material database to calculate the thermal expansion strain correction coefficient in real time.

[0024] The sensor base is fixed to the inner wall of the container through a high-temperature bonding process. The MEMS unit senses local strain through the piezoresistive effect. The distributed optical fiber uses the grating wavelength drift to realize full-surface strain field measurement. The thermal stress compensation module combines with the finite element model to correct the material expansion error caused by temperature in real time, and realizes point-to-surface combined stress synchronous measurement in a high temperature environment greater than 800°C. The spatial resolution reaches 1mm, and the thermal drift error is reduced by 70%.

[0025] The MEMS sensitive unit includes an elastic support beam, a differential capacitance detection module and a temperature self-calibration electrode. The elastic support beam adopts a U-shaped folding structure, with a beam width of 10μm and a thickness of 5μm. The differential capacitance detection module has a spacing of 2μm. The temperature self-calibration electrode integrates a platinum resistor film. The elastic beam converts shear stress into displacement, the differential capacitance detects the displacement, and the platinum resistor feeds back temperature changes in real time to correct the nonlinear error of the piezoresistance coefficient.

[0026] As a specific embodiment of the present invention, a silicon nitride stress compensation layer may be covered on the surface of the elastic support beam, the thickness of which is 200-500nm and the Young's modulus is ≥300GPa. It should be understood that the silicon nitride sealing layer is formed by a low-pressure chemical vapor deposition process, with a thickness of 1-2μm, and a micropore array may be opened on the surface with a pore size of ≤0.5μm. The micropore array releases packaging stress while blocking the intrusion of external contaminants. According to tests, the packaging life is extended to 100,000 thermal cycles, and the airtightness reaches 10⁻ 8 Pa·m³ / s.

[0027] The comb-tooth electrodes of the differential capacitance detection module adopt a staggered layout, with a height difference of 0.1-0.3μm between adjacent electrodes, forming a three-dimensional electric field gradient distribution. The staircase layout enhances the electric field edge effect, making the capacitance change linearly related to the displacement, increasing the capacitance sensitivity by 3 times, and achieving a resolution of 0.1nm.

[0028] The temperature self-calibration electrode is composed of a platinum-titanium composite film with a thickness of 50-100nm and a resistance temperature coefficient of 0.00385 / ℃. The resistance of the platinum film changes linearly with temperature, and a temperature compensation signal is output through a Wheatstone bridge circuit. In the range of -40~800℃, the temperature measurement error is <±0.5℃.

[0029] The distributed fiber grating array adopts a multi-core fiber structure, with each core spaced 0.5mm apart, and the grating period is gradiently distributed in the range of 1520-1570nm. It adopts a hybrid technology of time division multiplexing (TDM) and wavelength division multiplexing (WDM). The multi-core design realizes three-dimensional strain decoupling, and the gradient grating distinguishes strain signals at different positions through wavelength demodulation, which improves the strain measurement dimension. The axial and hoop stress resolution reaches ±10με, which is suitable for the reconstruction of complex stress fields of curved containers.

[0030] The thermal stress compensation module includes a high-temperature material database based on JMatPro software and a real-time nonlinear finite element calculation unit. The database provides the material thermal expansion coefficient-temperature curve, and the finite element model dynamically calculates the thermal stress distribution and generates a compensation coefficient matrix. In the range of 500-1000℃, the thermal strain error is reduced from ±15% to ±4.5%.

[0031] The high temperature resistant glass sealing layer can be made of borosilicate glass with a thickness of 0.3-0.5mm, and the inorganic adhesive bonding layer uses Al2O3-based nano-ceramic adhesive with a curing temperature of ≥600°C. The glass layer isolates the corrosive medium, and the nano-ceramic adhesive realizes the chemical bonding between the substrate and the container wall. The heat shock cycle is >1000 times, and the sealing life is increased to 5000 hours, avoiding the high temperature carbonization failure of traditional adhesives.

[0032] The signal processing terminal has a built-in multi-channel synchronous acquisition card with a sampling rate of ≥100kHz and supports TDM / WDM hybrid multiplexing technology. Time-wavelength hybrid multiplexing enables parallel processing of 256 sensing points with a data delay of <1ms. The dynamic stress measurement bandwidth is extended to 10kHz, which is suitable for monitoring transient working conditions such as explosion impact.

[0033] The measuring mechanism provided by the present invention also includes a wireless transmission module, which adopts the LoRa spread spectrum communication protocol, has an operating frequency band of 868MHz and a transmission power of 27dBm. The sensor data is encrypted and uploaded to the cloud through the LoRa gateway, supporting relay-free transmission within 10km, realizing remote real-time monitoring of closed containers, and improving the anti-electromagnetic interference capability by 50dB.

[0034] A method for measuring stress distribution of a pressure vessel in a high temperature environment, using the aforementioned measuring mechanism, comprises the following steps; Step 1: preheat the container to the operating temperature and activate the sensor self-test mode; Step 2, the distributed fiber grating array scans to establish a reference strain field; Step 3: The MEMS unit starts high-frequency sampling, and the data is aligned with the optical fiber signal in time and space; Step 4: The thermal stress compensation module injects a correction coefficient to generate a three-dimensional stress cloud map; Step 5: The abnormal stress area triggers a graded alarm.

[0035] Among them, step 4 uses the improved Ct-GBES-BPNN neural network model, and the input features include center of gravity frequency, root mean square strain gradient, and heat flux density. The neural network performs fusion analysis on multi-source data to identify defect modes such as stress concentration and creep cracks. The defect classification accuracy is >95%, and the misjudgment rate is reduced by 80% compared with the traditional threshold method.

[0036] The hierarchical alarm strategy of step 5 includes: Level 1 alarm: sound and light alarm is activated when the local stress exceeds the limit value by 80%; Level 2 alarm: shutdown interlock is triggered when the sampling exceeds the limit value by 100% for three consecutive times; Level 3 alarm: emergency cooling system is activated when the crack growth rate>1μm / s is detected. Through the hierarchical risk management, unplanned shutdown caused by malfunction can be avoided.

[0037] The following is a comparison of some experimental data: Experimental design description: Test environment: 800℃ high temperature / 25MPa pressure environment.

[0038] Comparison object: Mechanism, aluminum oxide substrate resistance strain gauge and aluminum oxide substrate resistance strain gauge of the present invention Test indicators include: strain measurement accuracy, temperature drift error, dynamic response bandwidth, seal life, and anti-interference ability.

[0039] Key experimental data comparison table index System of the present invention Alumina substrate resistance strain gauge Alumina substrate resistance strain gauge Advancedness improvement Temperature range (℃) 20-1200 20-800 20-1000 Temperature limit +400℃ Strain measurement accuracy (με) ±0.5 (MEMS) ±2 (fiber optic) ±15 ±5 Accuracy improved by 3-30 times Thermal drift error (με / 100°C) ≤1.2 (after compensation) ≥15 (no compensation) ≥8 (without compensation) Error reduction of 87%-93% Dynamic response bandwidth (kHz) 10 (MEMS) 1 (optical fiber) 0.5 0.2 Bandwidth increased by 20-50 times Sealing life (h@800℃) ≥5000 ≤200 3000 Lifespan extended 25 times Electromagnetic interference suppression (dB) ≥40 (copper nickel shielding layer) ≤10 (unshielded) 25 (aluminum foil shielding) Anti-interference increased by 60% The embodiments of this specific implementation method are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, any equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A stress distribution measurement mechanism for a pressure vessel in a high temperature environment, characterized in that: It includes a sensor substrate made of silicon carbide material, a MEMS sensitive unit integrated on the substrate, a high-temperature resistant glass sealing layer, a distributed fiber grating array, a thermal stress compensation module and a signal processing terminal.

2. The stress distribution measuring mechanism for a pressure vessel in a high temperature environment according to claim 1, characterized in that: The distributed fiber grating array adopts a multi-core fiber structure, each core is spaced 0.5 mm apart, and the grating period is gradiently distributed within the range of 1520-1570 nm.

3. The stress distribution measuring mechanism for a pressure vessel in a high temperature environment according to claim 1, characterized in that: The MEMS sensitive unit includes an elastic support beam, a differential capacitance detection module and a temperature self-calibration electrode.

4. The stress distribution measuring mechanism for a pressure vessel in a high temperature environment according to claim 3, characterized in that: The elastic support beam adopts a U-shaped folding structure, with a beam width of 10 μm and a thickness of 5 μm. The differential capacitance detection module has a spacing of 2 μm, and the temperature self-calibration electrode integrates a platinum resistance film.

5. The stress distribution measuring mechanism for a pressure vessel in a high temperature environment according to claim 3, characterized in that: The surface of the elastic support beam is covered with a silicon nitride stress compensation layer, the thickness of which is 200-500nm and the Young's modulus is ≥300GPa.

6. The stress distribution measuring mechanism for a pressure vessel in a high temperature environment according to claim 3, characterized in that: The comb-teeth electrodes of the differential capacitance detection module adopt a staggered layout, and the height difference between adjacent electrodes is 0.1-0.3 μm, forming a three-dimensional electric field gradient distribution.

7. The stress distribution measuring mechanism for a pressure vessel in a high temperature environment according to any one of claims 1 to 6, characterized in that: The high temperature resistant glass sealing layer is made of borosilicate glass with a thickness of 0.3-0.5 mm, and the inorganic adhesive bonding layer adopts Al2O3-based nano ceramic adhesive.

8. A method for measuring stress distribution of a pressure vessel in a high temperature environment, characterized in that: Using the measuring mechanism as described in any one of claims 1 to 7 comprises the following steps; Step 1: preheat the container to the operating temperature and activate the sensor self-test mode; Step 2, the distributed fiber grating array scans to establish a reference strain field; Step 3: The MEMS unit starts high-frequency sampling, and the data is aligned with the optical fiber signal in time and space; Step 4: The thermal stress compensation module injects a correction coefficient to generate a three-dimensional stress cloud map; Step 5: The abnormal stress area triggers a graded alarm.

9. The method for measuring stress distribution of a pressure vessel in a high temperature environment according to claim 8, characterized in that: Step 4 uses the improved Ct-GBES-BPNN neural network model, and the input features include center of gravity frequency, root mean square strain gradient, and heat flux density.

10. The method for measuring stress distribution of a pressure vessel in a high temperature environment according to claim 8, characterized in that: The hierarchical alarm strategy of step 5 includes: Level 1 alarm: sound and light alarm is activated when the local stress exceeds the limit value by 80%; Second level alarm: When the sampling exceeds the limit value of 100% for three consecutive times, the shutdown interlock is triggered; Level 3 alarm: The emergency cooling system is activated when a crack growth rate > 1μm / s is detected.

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