Thermal stress self-adaptive compensation method for external heating pipeline of BOPP (biaxially-oriented polypropylene) film production line

Abstract

The invention relates to the technical field of pipeline safety monitoring, and discloses a thermal stress self-adaptive compensation method for an external heating pipeline of a BOPP film production line, which comprises the steps of high-temperature-resistant sensor arrangement and data acquisition, temperature-strain-vibration decoupling and basic parameter calculation in a high-temperature environment, and a BOPP production line exclusive multi-load coupling stress calculation model. The invention relates to an integrated technical path of multi-section hinge type corrugated pipe compensator parameter optimization, self-adaptive compensation adjustment and double-closed-loop iteration optimization, and high-temperature-resistant multi-dimensional sensing monitoring-parameter linkage type stress calculation-high-frequency response corrugated pipe compensation optimization-stress-thin film thickness double-closed-loop iteration. The thermal stress self-adaptive compensation of the external heating pipeline of the BOPP film production line under the working conditions of high temperature of 200-250 DEG C and high-frequency load is realized.

Description

Technical Field

[0001] This invention relates to the field of pipeline safety monitoring technology, and more specifically, to a method for adaptive thermal stress compensation of external heating pipelines in BOPP film production lines. Background Technology

[0002] External pipelines (especially external heating pipelines in BOPP film production lines) are critical infrastructure in industrial production. During long-term service, they not only experience thermal expansion due to ambient temperature fluctuations and significant thermal stress caused by pipeline laying constraints (such as soil fixation and support limitations), but also bear loads unique to BOPP production lines: fatigue stress caused by high-frequency temperature cycles fluctuating 2-3 times per minute within the 180-220℃ range, and periodic vibration loads induced by polymer melt flow. These loads, combined with internal pipeline pressure, soil loads, and longitudinal bending deformation caused by uneven foundation settlement, can easily lead to pipeline material deterioration and weld fatigue cracking under long-term effects.

[0003] However, existing thermal stress compensation technologies have significant shortcomings: they rely heavily on fixed structural compensation (such as traditional U-bends), which can only achieve passive compensation under preset working conditions and cannot dynamically and adaptively adjust according to the real-time stress state of the pipeline. Furthermore, they have large inertia and slow response, making it difficult to adapt to the high-frequency response requirements of small displacements in BOPP pipelines. Moreover, stress calculation models often ignore the coupling effect of longitudinal bending load, temperature and strain, and loads specific to BOPP production lines, resulting in insufficient accuracy in stress calculation and difficulty in accurately reflecting the actual stress state of the pipeline. They also lack a closed-loop control mechanism of "real-time monitoring - compensation adjustment - effect verification," and the sensor solution is not adapted to the high-temperature environment of BOPP pipelines (200~250℃), making it impossible to verify and correct the compensation effect in a timely manner, thus making it difficult to ensure the long-term service safety of the pipeline.

[0004] Therefore, the present invention provides a method for adaptive thermal stress compensation of external heating pipelines in BOPP film production lines, which improves the above-mentioned technical problems. Summary of the Invention

[0005] This disclosure aims to address the shortcomings of existing technologies by providing an adaptive thermal stress compensation method for external heating pipelines in BOPP film production lines. The invention adopts an integrated technical path of "high-temperature multi-dimensional sensing and monitoring - parameter-linked stress calculation - high-frequency response corrugated pipe compensation optimization - stress-film thickness dual closed-loop iteration" to achieve adaptive thermal stress compensation for external heating pipelines in BOPP film production lines under high temperature and high-frequency load conditions of 200~250℃, ensuring that the total stress of the pipeline is ≤110MPa and the film thickness deviation is ≤5%.

[0006] The above-mentioned technical objective of the present invention is achieved through the following technical solution: a method for adaptive thermal stress compensation of an external heating pipeline in a BOPP film production line, comprising the following steps: S1: High-temperature sensor placement and data acquisition. A combination of ROTDR, BOTDA, and metal-welded FBG sensors, all resistant to 250℃, is used. Fiber optic cables are equipped with fluoropolymer sheaths and air-cooled tubing, and are arranged at preset intervals in straight pipe sections, bends, and compensator areas to collect temperature change data. Brillouin frequency shift Bragg wavelength variation and parameters such as melt flow rate v; S2: Temperature-Strain-Vibration Decoupling and Basic Parameter Calculation under High Temperature Environment. The temperature change rate is obtained based on the data collected in S1 and the high-temperature resistant sensing principle. Bending strain Mechanical strain Frequency of temperature change and vibration amplitude The ROTDR+BOTDA combined temperature compensation and circumferential average strain calculation are used to ensure that the decoupling error is ≤0.5% at 220℃. S3: A dedicated multi-load coupled stress calculation for BOPP production lines. Integrating the output parameters of S2, it sequentially calculates bending stress, axial thermal stress, internal pressure coupled stress, shear stress, temperature alternating fatigue stress, and polymer adhesion vibration stress. The aspect ratio parameter is corrected through dynamic adaptation and calibration using the kn parameter to obtain the total stress. and stress deviation The safety is verified by both total stress and equivalent shear stress. S4: Parameter optimization of multi-segment hinged bellows compensator. Based on the stress parameters of S3 and the temperature change rate of S2, the compensator deformation energy, adaptive displacement, and adjustment coefficient are calculated by combining thermal expansion correction. Update compensator radius ; S5: Adaptive compensation adjustment and dual closed-loop iterative optimization, setting the compensation response speed and iteration number according to the stress grading strategy, combined with the total stress. Deviation in BOPP film thickness Iteratively adjust the compensator parameters until... and .

[0007] As a preferred technical solution of the present invention, in S1, the BOTDA sensor is welded to the top of the pipeline longitudinally, the ROTDR sensor is arranged along the top or bottom of the pipe and is not bonded, and the FBG sensor is arranged in pairs welded in the hoop direction and longitudinal direction, with a set of sensors every 2~5m. One pair of FBG sensors is arranged every 2π / N along the circumference of the pipeline, and the acquisition frequency is 5~10Hz.

[0008] As a preferred embodiment of the present invention, in step S2, the decoupling formula for the BOTDA sensor is: ; Temperature compensation error verification: When the error exceeds the limit, the decoupling coefficient is dynamically corrected. and ; Circumferential average strain calculation: Take the average strain value of N pairs of sensors. This counteracts the local strain deviation caused by longitudinal bending; in, For strain coefficient, The internal friction temperature coefficient, , is the decoupling coefficient.

[0009] As a preferred embodiment of the present invention, in step S2, the decoupling formula for the FBG sensor is: ; in, For apparent temperature sensitivity, it has been calibrated and corrected for high temperature. For mechanical strain sensitivity, The difference in thermal expansion coefficients between the pipeline and the optical fiber. is the FBG decoupling coefficient.

[0010] As a preferred embodiment of the present invention, the formula for calculating shear stress in step S3 is: ; in, This is the shear correction factor. It is a lateral force. Shear modulus; The dynamic calculation formula is: Where A is the cross-sectional area of ​​the pipeline. Let the moment of inertia of the cross section be... For static moment, The width of the cross section; kn dynamic adaptation verification: Calculate the pipeline segment length ratio n=L2:L1 and the length-to-diameter ratio parameter: ; Check if the following conditions are met: Automatic correction when the error exceeds 5%. ; High temperature adaptable elastic modulus ,in, The room temperature elastic modulus of 316L stainless steel. This is the temperature correction factor for the elastic modulus; Input S2 , Calculate the alternating temperature fatigue stress: ; in, This is a correction factor for the frequency of temperature changes. This is the fatigue stress amplification factor.

[0011] As a preferred embodiment of the present invention, in step S3, the formula for polymer adhesion vibration stress is: ; in, The adhesion coefficient, The melt flow rate collected by S2 The density of the melt. For reference strain amplitude, The vibration amplitude extracted from S2; Dual security checks satisfy: Constraints, and added equivalent shear stress verification: ; in, For circumferential stress, The total axial stress is The yield strength of 316L stainless steel; The formula for calculating total stress is: ; Stress deviation: ; in, This represents the allowable stress for BOPP pipelines.

[0012] As a preferred embodiment of the present invention, in step S4, the optimization of the compensator parameters includes thermal expansion correction: ; Formula for updating compensator radius: ; Aspect ratio adaptation parameters: ; in, This is the correction factor for the adjustment coefficient due to stress deviation. This is the initial adjustment coefficient. The temperature change rate sensitivity coefficient, This is the correction factor for stress deviation on the aspect ratio.

[0013] As a preferred embodiment of the present invention, in step S5, the stress grading strategy is as follows: Risk level classification: Level I (0~20%): Compensation response speed < 0.5s, number of iterations ≥ 3; Level II (20~40%): Compensation response speed < 0.4s, number of iterations ≥ 4; Level III (40~60%): Compensation response speed < 0.35s, number of iterations ≥ 5; Level IV (60~80%): Compensation response speed < 0.3s, number of iterations ≥ 6; Level V (>80%): Compensation response speed <0.25s, number of iterations ≥8.

[0014] As a preferred embodiment of the present invention, in step S5, the pipeline radius adjustment formula during iterative optimization includes thermal expansion correction: ; in, The correction factor for stress deviation on pipeline radius. in, The stress deviation is the correction factor for the pipeline radius, and the iteration termination condition is... And BOPP film thickness deviation .

[0015] As a preferred technical solution of the present invention, the multi-segment hinged bellows compensator has a response speed of <0.5s, the power of the heat transfer oil pump is reduced by 12%~15% after compensation, the peak vibration stress is reduced from 42MPa to below 8MPa, the total pipeline stress is ≤110MPa, and the BOPP film thickness deviation is ≤5%.

[0016] In summary, the present invention has the following beneficial effects: Firstly, it adopts ROTDR, BOTDA distributed sensors and metal-welded FBG sensors that can withstand 250℃, combined with a fluoropolymer sheath to prevent polymer adhesion and an air-cooled jacket to control temperature. By utilizing circumferential uniform distribution and combined temperature compensation, it can achieve accurate acquisition of temperature, strain, vibration and melt flow rate in all dimensions, effectively solving the problems of high temperature failure and easy adhesion interference of traditional sensors.

[0017] Secondly, by using a linkage calculation model of "decoupling parameters - basic stress - specific load stress", the model integrates the high-frequency temperature cycle fatigue and polymer adhesion vibration load of the BOPP production line. Through curved beam theory correction, dynamic calculation of shear stress, dynamic adaptation of kn and double safety verification, combined with dynamic correction of high-temperature adaptation elastic modulus, the total stress calculation error is reduced, which more accurately reflects the actual stress state of the pipeline compared with traditional models.

[0018] Third, a multi-segment hinged bellows compensator is adopted, with a response speed of <0.5s. Based on the dual-parameter optimization adjustment coefficient of stress deviation and temperature change rate, dynamic compensation under high-frequency loads with small displacements is achieved. Through a stress-graded compensation strategy, accuracy and energy efficiency are balanced. After compensation, the peak vibration stress is reduced from 42MPa to below 8MPa, effectively making up for the defects of traditional fixed structure compensation in "passive adaptation and response lag". A "stress-film thickness" dual closed-loop iterative mechanism is constructed to ensure that the total pipeline stress is controlled within the allowable range of 110MPa, while ensuring that the BOPP film thickness deviation is ≤5%.

[0019] Fourth, the sensor adopts a welded arrangement and air-cooled protection, eliminating the need for frequent disassembly and maintenance. The compensator parameters are adaptively optimized through algorithm iteration without manual intervention. It can be adapted to 316L stainless steel external heating pipelines of different specifications such as Φ89×3mm, and is compatible with temperature ranges of 180~250℃ and pressure conditions within 1.8MPa. It is suitable for external heating pipeline scenarios in various BOPP film production lines. Attached Figure Description

[0020] Figure 1 The flowchart illustrates a method for adaptive thermal stress compensation in an external heating pipeline of a BOPP film production line, as provided in an embodiment of the present invention. Detailed Implementation

[0021] The present application will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any way. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present application. These all fall within the protection scope of the present application.

[0022] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0023] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the scope of this application. The term "and / or" as used in this specification includes any and all combinations of one or more of the associated listed items.

[0024] Furthermore, the technical features involved in the various embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0025] This disclosure proposes an adaptive thermal stress compensation method for the external heating pipeline of a BOPP film production line. It employs an integrated technical path of "high-temperature multi-dimensional sensing and monitoring - parameter-linked stress calculation - high-frequency response compensator optimization - stress-film thickness dual closed-loop iteration." Specifically, it utilizes a 250℃-resistant ROTDR distributed temperature sensor, a BOTDA distributed strain sensor, and a metal-welded FBG key node sensor (equipped with a fluoropolymer sheath to prevent polymer adhesion and an air-cooled jacket for temperature control) to achieve accurate acquisition of temperature, strain, vibration, and melt flow rate in a high-temperature environment of 200~250℃. Based on the sensing principle, it decouples and obtains fundamental parameters such as bending strain, mechanical strain, and temperature change frequency, further... A multi-load coupled stress model was constructed, integrating high-temperature adaptive elastic modulus, bending stress, axial thermal stress, and internal pressure coupled stress, superimposed with the high-frequency temperature fatigue stress and polymer adhesion vibration stress unique to the BOPP production line, to obtain the total stress and stress deviation. A multi-segment hinged bellows compensator with a response speed of <0.5s was adopted, and the adjustment coefficient and length-to-diameter ratio were optimized by combining the temperature change rate and stress deviation, and the compensator parameters were dynamically updated. Finally, with the total stress ≤110MPa and the BOPP film thickness deviation ≤5% as dual constraints, a closed loop was formed through iterative adjustment to achieve adaptive thermal stress compensation, while reducing the power of the heat transfer oil pump by 12%~15%, significantly improving the safety, stability and production economy of the external heating pipeline of the BOPP production line.

[0026] Please refer to Figure 1 , Figure 1 A flowchart illustrating an adaptive thermal stress compensation method for an external heating pipeline in a BOPP film production line according to an embodiment of this disclosure is shown. The overall process mainly includes the following five steps: Step 1: Arrangement of high-temperature resistant sensors and data acquisition.

[0027] The combined monitoring solution of "high temperature resistant distributed fiber optic sensor + metal welded FBG sensor" is adopted, which is suitable for the high temperature environment of 200~250℃ in BOPP production line and realizes full-range, high-precision acquisition of temperature, strain and vibration.

[0028] ROTDR (Raman Time Domain Reflectometry) sensors with a temperature resistance of 250℃ are selected for distributed temperature monitoring, BOTDA (Brillouin Time Domain Analysis) sensors with a temperature resistance of 250℃ are selected for distributed strain monitoring, and metal-welded FBG sensors (replacing adhesive type) are used for accurate stress monitoring of key nodes. All optical fibers are sheathed with fluoropolymer to prevent polymer adhesion from covering the sensing area.

[0029] BOTDA strain sensors are welded to the top of the pipeline (longitudinal), and ROTDR temperature sensors are arranged along the top / bottom of the pipe (unbonded). Both are externally equipped with air-cooled sheaths to wrap the optical fiber, maintaining the sensing area temperature ≤150℃. FBG sensors are welded in pairs along the hoop direction (φ=0°) and longitudinal direction (φ=90°), with one pair placed every 2~5m, covering straight pipe sections, bends, and compensator areas. A circumferentially uniform distribution design is used: one pair of FBG sensors is placed every 2π / N (N=2~4) along the pipeline circumference to compensate for strain errors caused by longitudinal bending.

[0030] sampling frequency 5~10Hz, acquiring temperature changes Strain changes (BOTDA), Bragg wavelength variation Raw data such as (FBG) and vibration signals are collected simultaneously, along with process parameters such as melt flow rate v; the output monitoring parameters include: temperature change. Brillouin frequency shift Bragg wavelength shift Melt flow rate v.

[0031] Step 2: Temperature-Strain-Vibration Decoupling and Basic Parameter Calculation under High Temperature Environment.

[0032] Based on the data acquired by S1 and the high-temperature resistant sensing principle, temperature, strain, and vibration are decoupled, eliminating temperature cross-sensitivity and interference from high-temperature environments. This ensures that the decoupling error is ≤0.5% at 220℃, and the output parameters are directly used as input for S3 stress calculation. Temperature time series data based on S1 Calculate the rate of temperature change : ; in, The temperature change at position x at time i+1 is collected by S1; The temperature change at position x at time i is collected by S1; The temperature data acquisition time interval for S1 is determined by the acquisition frequency. Sure: (e.g., sampling frequency) ,but ); , The times of two consecutive temperature measurements. (The time interval is determined by the sampling frequency of S1); The temperature change rate is determined by taking the maximum value (absolute value) in the full time series data as the temperature change rate, and the S4 compensator is used to optimize the adjustment coefficient β.

[0033] Decoupling of BOTDA sensors (for high-temperature environments): Specifically, the coupling relationship between Brillouin frequency shift and temperature and strain: ; in, The Brillouin frequency shift at position x is collected by S1; The strain coefficient of the BOTDA sensor was obtained through high-temperature calibration. The original strain change at position x is directly acquired by BOTDA; The internal friction temperature coefficient (obtained through a 250℃ high-temperature calibration test); The temperature change at position x is collected by ROTDR.

[0034] Temperature-compensated bending strain (used for output to S3 bending stress calculation): ; in, The bending strain at position x is the output after decoupling; strain-frequency shift decoupling coefficient. Temperature-frequency shift decoupling coefficient All of these are decoupling coefficients.

[0035] Temperature compensation error verification: When the error exceeds the limit, the decoupling coefficient is dynamically corrected. and ; in, For the compensated strain, Real strain is used for error verification.

[0036] Decoupling of the FBG sensor (for high-temperature environments, used for output to S3 vibration stress calculation): The relationship between Bragg wavelength variation and temperature and strain: ; in, The change in the Bragg wavelength of the FBG sensor is acquired by S1; The initial Bragg wavelength of the FBG sensor is a sensor intrinsic parameter. For mechanical strain sensitivity, the inherent parameters of the FBG sensor; Mechanical strain at position, output after decoupling; For apparent temperature sensitivity, it has been calibrated and corrected for high temperature. The optical fiber's thermo-optic coefficient is an intrinsic parameter of the optical fiber. The difference in thermal expansion coefficients between the pipeline and the optical fiber; The coefficient of thermal expansion of the pipeline material; The coefficient of thermal expansion of optical fiber materials.

[0037] Mechanical strain extraction (used for output to S3 total stress superposition): ; Among them, the wavelength-strain decoupling coefficient Wavelength-temperature decoupling coefficient .

[0038] Circumferential average strain calculation: Take the average strain value of N pairs of sensors. This counteracts the local strain deviation caused by longitudinal bending; Where N is the number of circumferential sensor pairs (2~4). For strain of a single sensor.

[0039] Temperature frequency and vibration characteristic parameter extraction (for output to S3 load calculation): based on Time series data, calculate the frequency of temperature change: ; in, The frequency of temperature change reflects the speed of temperature cycling. For the temperature fluctuation period, by Time series data statistical acquisition; for The time of two adjacent peaks (or valleys) in the time series data (identified by the peak detection algorithm of the time series data); n is the number of statistical periods (e.g., take 10 consecutive periods and calculate the average).

[0040] Calculate the vibration amplitude based on BOTDA strain fluctuations: ; in, The amplitude of the vibration reflects the intensity of the pipeline vibration. The maximum value of the bending strain at position x within a certain time period; The minimum bending strain at position x within a certain time period.

[0041] Step 3: Calculation model of multi-load coupling stress specific to BOPP production line.

[0042] By integrating parameters such as bending strain, mechanical strain, and temperature frequency output from S2, and superimposing loads such as longitudinal bending, axial thermal load, internal pressure, soil load, high-frequency temperature cyclic fatigue, and polymer adhesion vibration, a full-condition stress calculation model is established: Input S2 : ; in, Indicates the bending stress at position x; To adapt the elastic modulus to high temperatures; The room temperature elastic modulus of 316L stainless steel; This is the temperature correction factor for the elastic modulus; Based on S2 Dynamic correction was performed and fitted using high-temperature elastic modulus tests on 316L stainless steel. (Based on elastic modulus test data in the 20~250℃ range) (This refers to the temperature change output by S2).

[0043] For curved sections of pipelines (such as elbows), the curved beam theory is used for correction, based on the neutral layer radius. Calculate bending stress to improve the accuracy of stress calculation for curved segments; among which, To integrate over the cross-sectional area A of the curved beam, the integration domain is the cross-section of the curved beam; Let be the area of ​​a small element of the cross-section of the curved beam; for the area of ​​the infinitesimal element The distance from the location to the center of curvature of the curved beam.

[0044] Input S2 Calculate the axial thermal stress and internal compressive stress: Axial thermal stress: ; Circumferential stress (initiated by internal pressure): ; Axial internal pressure coupling stress: ; Total axial foundation stress: ; in, t is the coefficient of thermal expansion of 316L stainless steel; p is the internal pressure (acquired by SCADA system); D is the nominal diameter of the pipeline; t is the wall thickness. The Poisson's ratio for 316L stainless steel.

[0045] Shear stress calculation: Based on curved beam theory and shear correction factor, the formula is as follows: ; in, This is the shear correction factor; The lateral force borne by the pipeline; shear modulus .

[0046] The dynamic calculation formula is: ; Where A is the cross-sectional area of ​​the pipeline; The moment of inertia of the cross section; The static moment is calculated from the cross-sectional geometry; This represents the width of the cross-section.

[0047] Input S2 , Calculate the alternating temperature fatigue stress: ; Among them, S2-based Dynamic calculation , This is a correction coefficient for the frequency of temperature changes, which is dynamically adjusted according to the temperature frequency. This is the fatigue stress amplification factor.

[0048] Input S2 , Calculate polymer adhesion vibration stress: ; in, The coefficient of adhesion; The melt flow rate collected by S2 The density of the melt; The reference strain amplitude is 0.001. The vibration amplitude extracted from S2; Calibrated through melt adhesion tests on BOPP production lines, with values ​​ranging from 0.02 to 0.05 (when melt flow rate...). hour, ), can be based on S1 collection Dynamic correction: ; In BOPP production, the melt is polypropylene (PP). The temperature-dependent parameters of PP melt are calculated using empirical formulas: ,in The actual pipeline temperature collected by S1 ( , (Ambient temperature).

[0049] Total stress calculation (for output to S4 compensator optimization): ; kn dynamic adaptation verification: Calculate the pipeline segment length ratio n=L2:L1 and the length-to-diameter ratio parameter: Check if the following conditions are met: Automatic correction when the error exceeds 5%. ; Where k is the length-to-diameter ratio parameter, reflecting the fit between pipeline geometry and stress; The length of the long section of the compensator is a parameter inherent to the compensator. The correction factor for stress deviation on aspect ratio; Stress deviation (used for output to S4 adjustment coefficient calculation): ; in, This is the allowable stress for BOPP pipelines, and the yield strength of 0.6×316L stainless steel.

[0050] Double security verification: Retain the original Constraints are applied to perform equivalent shear stress verification: ; in, For circumferential stress, The total axial stress is It features a yield strength of 316L stainless steel and a dual threshold to ensure safety.

[0051] Step 4: Parameter optimization of multi-segment hinged bellows compensator.

[0052] A multi-segment hinged bellows compensator is used as the core compensation structure, with a response speed of <0.5s. Based on the stress deviation and temperature parameters output by S3, dynamic parameter optimization is achieved. Input S3 Calculate the deformation energy of the compensator: Derivation of deformation energy from stress-strain relationship: .

[0053] in, Section modulus; It is an integral infinitesimal element; The moment of inertia of the 316L stainless steel pipeline section is... This refers to the length of the long section of the compensator.

[0054] Input S3 Calculating compensator displacement: Based on Castigliano's theorem, the compensator displacement is related to the stress deviation. ; in, The average total stress, For the cross-sectional area of ​​the pipeline, This is the displacement-stress conversion factor.

[0055] Input S3 S2 Optimization of compensator dimensions: Length-to-diameter ratio adaptation parameters (optimized for 316L stainless steel): ; Temperature change rate of input S2 Calculate the frequency compensation adjustment coefficient: ; Compensator radius update formula (used for output to S5 iteration): ; in, This is the correction factor for stress deviation with respect to the aspect ratio. This is the initial adjustment coefficient. The temperature change rate sensitivity coefficient is determined by FFT analysis of the S2 vibration spectrum. This is the correction factor for the adjustment coefficient due to stress deviation; The value is determined based on the structural characteristics of multi-segment hinged bellows, and is set to 0.95 (the default initial value for a Φ89×3mm pipeline, which can be corrected according to the pipeline diameter D). ); The calibration coefficient obtained by FFT analysis of the S2 vibration spectrum is 0.02 (when...). (time), if γ=0.03; : This is the stress deviation correction factor, based on the allowable stress. Derivation: (when hour, ); Determined by the pipeline length-to-diameter ratio (L / D), formula: (L is the length of the straight pipe section, and D is the nominal diameter).

[0056] Step 5: Adaptive compensation adjustment and dual closed-loop iterative optimization.

[0057] Based on the total stress, stress deviation, and BOPP film thickness feedback output by S3, and combined with the compensator parameters output by S4, a closed loop is formed through dynamic adjustment via an iterative algorithm: Iterative optimization process: 1) Initialize compensator parameters and pipeline radius The allowable deviation of film thickness is set to ≤5%; 2) Substitute into formulas S2-S3 to calculate the total stress. and stress deviation Collect BOPP film thickness deviation ; 3) Stress grade compensation: based on Risk levels are divided (Level I: 0~20%, Level II: 20~40%, ..., Level V: >80%). High-risk nodes (bends, supports) require a response speed of <0.3s and ≥5 iterations, while low-risk nodes require a response speed of <0.5s and ≥3 iterations.

[0058] 4) If or Update the compensator parameters using formula S4: ; in, The inner radius of the pipeline after iteration; The inner radius of the pipeline before iteration; The outer radius of the pipeline after iteration; The outer radius of the pipeline before iteration; This is the correction factor for stress deviation on the pipeline radius; (BOPP film thickness deviation): Data is collected through online thickness detection equipment on the production line (such as a laser thickness gauge, with a sampling frequency of 10Hz). Calculation method: ;in, This is the actual thickness. The target thickness (e.g., 25 μm); For: calibration based on the matching test between the compensator displacement and the pipeline radius, the value is taken as follows: (That is, for every 1 MPa stress deviation, the pipeline radius is adjusted) This ensures that the adjustment amount is within the range of minute displacement (<50mm).

[0059] 5) Substitute the updated compensator parameters into S2-S4 and recalculate. and Repeat steps 2-4 until... and Output the optimal parameters.

[0060] Example: Taking an external heating pipeline (Φ89×3mm, 316L stainless steel, design pressure 1.8MPa, design temperature 220℃) of a BOPP film production line as the application object, the pipeline is 35m long, uses heat transfer oil medium, has a flow rate of 2.5m / s, an operating temperature of 220℃, passes through the production workshop, and is laid by overhead support.

[0061] The implementation steps are as follows: S1. High-temperature resistant sensor arrangement: BOTDA strain sensors (spatial resolution 0.2m, sampling interval 5cm) are welded longitudinally along the top of the pipeline and equipped with an external air-cooled sleeve; A 250℃-resistant ROTDR temperature sensor (sampling interval 5cm, accuracy ±0.1℃) is arranged along the bottom of the pipe, and the optical fiber is sheathed with fluoropolymer resin. Fifteen FBG sensor pairs (hoop direction + longitudinal direction) are welded to pipeline bends and support nodes, all equipped with air-cooling protection devices.

[0062] S2. Data Acquisition and Preprocessing: collection The vibration signal and melt flow velocity v were used to calculate the result. , After circumferential averaging Temperature compensation error is 0.3% (≤0.5%).

[0063] S3. Substitute parameters for calculation: ; ,satisfy ,error .

[0064] (Below the allowable stress).

[0065] Equivalent shear stress The double verification passed.

[0066] S4. Compensator parameter optimization: The calculation yielded: ; .

[0067] S5. Dual Closed-Loop Adaptive Adjustment and Verification: According to risk level II The response time was set to 0.4 s and the number of iterations was 4. After iterations, the compensator radius stabilized at 29.2 mm. The film thickness deviation was 2.6%, and the power of the heat transfer oil pump decreased by 13.5%.

[0068] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for adaptive thermal stress compensation of external heating pipelines in a BOPP film production line, characterized in that, The method includes the following steps: S1: High-Temperature Sensor Placement and Data Acquisition: A combination of ROTDR, BOTDA, and metal-welded FBG sensors, all with a temperature resistance of 250℃, is employed. Fiber optic cables are equipped with fluoropolymer sheaths and air-cooled tubing, and are placed at predetermined intervals in straight pipe sections, bends, and compensator areas to collect temperature change data. Brillouin frequency shift Bragg wavelength variation and parameters such as melt flow rate v; S2: Temperature-Strain-Vibration Decoupling and Basic Parameter Calculation under High Temperature Environment: Temperature Change Rate Obtained Based on Data Acquired in S1 and High-Temperature Resistant Sensing Principles. Bending strain Mechanical strain Frequency of temperature change and vibration amplitude The ROTDR+BOTDA combined temperature compensation and circumferential average strain calculation are used to ensure that the decoupling error is ≤0.5% at 220℃. S3: BOPP Production Line Dedicated Multi-Load Coupling Stress Calculation: Integrating S2 output parameters, it sequentially calculates bending stress, axial thermal stress, internal pressure coupling stress, shear stress, temperature alternating fatigue stress, and polymer adhesion vibration stress. The aspect ratio parameter is corrected through dynamic adaptation and calibration using kn to obtain the total stress. and stress deviation The safety is verified by both total stress and equivalent shear stress. S4: Parameter optimization of multi-segment hinged bellows compensator: Based on the stress parameters of S3 and the temperature change rate of S2, the deformation energy, adaptive displacement and adjustment coefficient of the compensator are calculated by combining thermal expansion correction. Update compensator radius ; S5: Adaptive Compensation Adjustment and Dual-Loop Iterative Optimization: The compensation response speed and iteration number are set according to the stress grading strategy, combined with the total stress. Deviation in BOPP film thickness Iteratively adjust the compensator parameters until... and .

2. The adaptive thermal stress compensation method for the external heating pipeline of a BOPP film production line according to claim 1, characterized in that, In S1, the BOTDA sensor is welded to the top of the pipeline longitudinally, the ROTDR sensor is arranged along the top or bottom of the pipe and is not bonded, and the FBG sensor is arranged in pairs welded in the hoop direction and longitudinal direction, with a set set every 2~5m. One pair of FBG sensors is arranged every 2π / N along the circumference of the pipeline, and the acquisition frequency is 5~10Hz.

3. The adaptive thermal stress compensation method for the external heating pipeline of a BOPP film production line according to claim 1, characterized in that, In S2, the decoupling formula for the BOTDA sensor is: ； Temperature compensation error verification: When the error exceeds the limit, the decoupling coefficient is dynamically corrected. and ; Circumferential average strain calculation: Take the average strain value of N pairs of sensors. This counteracts the local strain deviation caused by longitudinal bending; in, For strain coefficient, The internal friction temperature coefficient, , is the decoupling coefficient.

4. The adaptive thermal stress compensation method for the external heating pipeline of a BOPP film production line according to claim 1, characterized in that, In S2, the decoupling formula for the FBG sensor is: ； in, For apparent temperature sensitivity, it has been calibrated and corrected for high temperature. For mechanical strain sensitivity, The difference in thermal expansion coefficients between the pipeline and the optical fiber. is the FBG decoupling coefficient.

5. The adaptive thermal stress compensation method for the external heating pipeline of a BOPP film production line according to claim 1, characterized in that, In S3, the formula for calculating shear stress is: ； in, This is the shear correction factor. It is a lateral force. Shear modulus; The dynamic calculation formula is: ; Where A is the cross-sectional area of ​​the pipeline. Let the moment of inertia of the cross section be... For static moment, The width of the cross section; kn dynamic adaptation verification: Calculate the pipeline segment length ratio n=L2:L1 and the length-to-diameter ratio parameter: ； Check if the following conditions are met: Automatic correction when the error exceeds 5%. ; High temperature adaptable elastic modulus ; in, The room temperature elastic modulus of 316L stainless steel. This is the temperature correction factor for the elastic modulus; Input S2 , Calculate the alternating temperature fatigue stress: ； in, This is a correction factor for the frequency of temperature changes. This is the fatigue stress amplification factor.

6. The adaptive thermal stress compensation method for the external heating pipeline of a BOPP film production line according to claim 1, characterized in that, In S3, the formula for polymer adhesion vibration stress is: ； in, The adhesion coefficient, The melt flow rate collected by S2 The density of the melt. For reference strain amplitude, The vibration amplitude extracted from S2; Dual security checks satisfy: Constraints and equivalent shear stress verification: ； in, For circumferential stress, The total axial stress is The yield strength of 316L stainless steel; The formula for calculating total stress is: ； Stress deviation: ; in, This represents the allowable stress for BOPP pipelines.

7. The adaptive thermal stress compensation method for the external heating pipeline of a BOPP film production line according to claim 1, characterized in that, In step S4, the compensator parameter optimization includes thermal expansion correction: ； Formula for updating compensator radius: ； Aspect ratio adaptation parameters: ； in, This is the correction factor for the adjustment coefficient due to stress deviation. This is the initial adjustment coefficient. The temperature change rate sensitivity coefficient, This is the correction factor for stress deviation on the aspect ratio.

8. The adaptive thermal stress compensation method for the external heating pipeline of a BOPP film production line according to claim 1, characterized in that, In S5, the stress grading strategy is as follows: Risk level classification: Level I (0~20%): Compensation response speed < 0.5s, number of iterations ≥ 3; Level II (20~40%): Compensation response speed < 0.4s, number of iterations ≥ 4; Level III (40~60%): Compensation response speed < 0.35s, number of iterations ≥ 5; Level IV (60~80%): Compensation response speed < 0.3s, number of iterations ≥ 6; Level V (>80%): Compensation response speed <0.25s, number of iterations ≥8.

9. The adaptive thermal stress compensation method for the external heating pipeline of a BOPP film production line according to claim 1, characterized in that, In S5, the pipeline radius adjustment formula during iterative optimization includes thermal expansion correction: ； in, The stress deviation is the correction factor for the pipeline radius, and the iteration termination condition is... And BOPP film thickness deviation .

10. The adaptive thermal stress compensation method for the external heating pipeline of a BOPP film production line according to claim 1, characterized in that, The multi-segment hinged bellows compensator has a response speed of <0.5s, and after compensation, the power of the heat transfer oil pump is reduced by 12%~15%, the peak vibration stress is reduced from 42MPa to below 8MPa, the total pipeline stress is ≤110MPa, and the BOPP film thickness deviation is ≤5%.

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