Hydrolysis-resistant and high-temperature-resistant thermal repair pipeline and preparation process thereof

Abstract

The present application belongs to the technical field of heat pipe repair, and provides a hydrolysis-resistant and high-temperature-resistant heat repair pipe and a preparation process thereof, which comprises the following steps: taking the melt pressure pulsation phase change signal from the outlet of a spiral head to the inlet area of a sizing sleeve as a synchronous reference to construct an interlayer rheological asymmetric index; calculating the solidification rate change and freezing time difference of the inner lining layer, the barrier layer and the reinforcing layer in the cooling and sizing process according to the interlayer rheological asymmetric index to construct a pipe wall interlayer thermal stress distribution model; extracting the stress gradient and peak area of the interface between the inner lining layer and the barrier layer to form a non-uniform residual stress field through gradient heat setting; performing an accelerated aging test on the samples drawn from the repair pipe with the non-uniform residual stress field under alternating humidity and freezing-thawing cycle conditions to determine the residual stress distribution deviation of each region; and mapping the residual stress distribution deviation of each region to the stress concentration position to output the interlayer stability manufacturing parameters.

Description

Technical Field

[0001] This invention belongs to the field of thermal pipeline repair technology, specifically a hydrolysis-resistant and high-temperature-resistant thermal repair pipeline and its preparation process. Background Technology

[0002] With the continuous operation of urban centralized heating systems, some underground heating pipelines will experience problems such as aging, corrosion and local leakage. In order to reduce the construction impact of traditional excavation and replacement methods, existing technologies usually use thermal repair pipes to repair the original pipelines without excavation. These repair pipes generally adopt a flexible composite structure and are inserted into the pipeline to be repaired by dragging. During operation, the pipeline shape is maintained by the pressure of the internal heat medium.

[0003] However, in the cold regions of northern my country, centralized heating systems have seasonal operation characteristics. During the shutdown period, the repair pipe is in a state of no internal pressure for a long time. The flexible pipe wall is easily affected by external constraints and its own stress, resulting in local radial deformation or changes in cross-sectional roundness. During the restart of heating, there is a difference in the temperature rise rate inside and outside the pipe wall, which leads to asynchronous thermal deformation of the repair pipe. The local deformation area is prone to stress concentration during the recovery process, causing the inner lining layer and the reinforcing skeleton to bear a large interfacial force.

[0004] Existing technologies typically focus on the temperature resistance, hydrolysis resistance, and pressure resistance of thermal repair pipes under normal operating conditions, while paying relatively little attention to the morphological stability during seasonal shutdowns and the thermal response process during restart. This results in the repair pipes being prone to interlayer delamination between the inner lining and the reinforcing skeleton after multiple heating cycles, which can further lead to local crack propagation and pipe wall structural instability. Summary of the Invention

[0005] In order to overcome the shortcomings of the prior art, at least one technical problem raised in the background art is solved.

[0006] The technical solution adopted by the present invention to solve its technical problem is as follows: taking the melt pressure pulsation phase change signal from the screw head outlet to the shaping sleeve inlet area as a synchronization reference, collecting the intrinsic viscosity decay rate of the inner liner melt, the residence time of the barrier layer melt and the wetting state parameters of the reinforcing layer melt, and performing correlation processing on the melt state parameters of each layer to construct the interlayer rheological asymmetry index. Based on the interlayer rheological asymmetry index, the curing rate changes and freezing time differences of the inner lining, barrier layer and reinforcement layer during the cooling and shaping process are calculated to obtain the volume shrinkage rate differences of each layer. Combined with the thermal conduction hysteresis characteristics of the barrier layer, the interlayer shrinkage mismatch is quantitatively corrected to construct the interlayer thermal stress distribution model of the pipe wall. Based on the interlayer thermal stress distribution model of the pipe wall, the stress gradient and peak region of the interface between the inner lining layer and the barrier layer are extracted, the stress concentration location is located, and the heating power, traction disturbance amplitude and cooling airflow parameters are matched with the interlayer shrinkage rate according to the interface stress characteristics. A non-uniform residual stress field adapted to the interlayer shrinkage difference is formed through gradient thermal shaping. For repaired pipes with non-uniform residual stress fields, accelerated aging tests were conducted on sampled pipes under alternating damp heat and freeze-thaw cycles. The radial deformation response sequence of the pipe wall and the evolution characteristics of interlayer peeling were collected under different water content conditions. Based on the correspondence between the amount of residual stress release and the interface deformation change, the deviation of residual stress distribution in each region was determined. The residual stress distribution deviation in each region is mapped to the stress concentration location. The interface bonding strength attenuation rate, which is determined by the peeling cycle, is used as a constraint to adjust the co-extrusion rheological properties and gradient heat setting process in a feedback linkage manner, and output interlayer stability manufacturing parameters that are compatible with the interlayer shrinkage matching relationship.

[0007] The beneficial effects of this invention are as follows: By introducing a multi-layer rheological state sensing mechanism based on the phase synchronization of melt pressure pulsation during the co-extrusion molding process of multi-layer thermal repair pipes, a synergistic characterization of the melt characteristics, residence behavior, and wetting state of the inner liner, barrier layer, and reinforcing layer is achieved. Furthermore, by constructing an interlayer rheological asymmetry index, the flow differences, viscosity decay differences, and interface matching relationships of different material systems during the molding process are quantitatively described, thereby improving the control capability for the consistency of multi-layer structure molding. Further, by combining the changes in curing rate, differences in freezing sequence, and the thermal conduction hysteresis characteristics of the barrier layer, the interlayer volume shrinkage mismatch behavior during the cooling and shaping process is corrected, and an interlayer thermal stress distribution model of the pipe wall is established, enabling accurate identification of the interface thermal stress concentration area and its evolution trend. Based on the stress distribution characteristics, the heating power, traction disturbance amplitude, and cooling gas... By co-regulating flow parameters and guiding the release and redistribution of residual stress through gradient thermal setting, a residual stress state adapted to the shrinkage characteristics of different layers of materials is formed inside the pipe wall, reducing the risk of interfacial cracking, delamination, and structural instability caused by differences in interlayer thermal shrinkage. Simultaneously, by monitoring the radial deformation response and interlayer peeling evolution under alternating wet heat and freeze-thaw cycles, a correlation between residual stress release behavior and interfacial bond strength attenuation is established, enabling dynamic assessment of interfacial stability in long-term service environments. Finally, based on the residual stress distribution deviation and interfacial bond strength attenuation law, feedback optimization of co-extrusion rheological parameters and thermal setting process parameters is performed, resulting in thermally repaired pipes with superior hydrolysis resistance, high-temperature resistance, and interfacial bond stability under long-term cyclic conditions, improving the reliability of the pipes in complex underground thermal conditions. Attached Figure Description

[0008] The invention will now be further described with reference to the accompanying drawings.

[0009] Figure 1 This is a flowchart of the steps involved in the preparation process of a hydrolysis-resistant and high-temperature-resistant thermal repair pipe and its manufacturing process, as provided in Embodiment 1 of the present invention. Figure 2 This is a schematic diagram of the process framework for a hydrolysis-resistant and high-temperature-resistant thermal repair pipe and its preparation process provided in Embodiment 1 of the present invention. Detailed Implementation

[0010] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0011] Example 1: Please refer to Figure 1-2 As shown in the embodiment of the present invention, a hydrolysis-resistant and high-temperature-resistant thermal repair pipe and its preparation process include the following steps: Step S10: Using the melt pressure pulsation phase change signal from the screw head outlet to the shaping sleeve inlet area as a synchronization reference, collect the intrinsic viscosity decay rate of the inner liner melt, the residence time of the barrier layer melt, and the wetting state parameters of the reinforcing layer melt. Correlate the melt state parameters of each layer to construct the interlayer rheological asymmetry index.

[0012] In step S10, the process of constructing the interlayer rheological asymmetric index is as follows: During the multi-layer co-extrusion molding process, melt pressure fluctuation signals are continuously collected from the screw die outlet area and the shaping sleeve inlet area. Phase change nodes within the pressure pulsation cycle are extracted, and the pressure phase synchronization points of adjacent areas are used as time calibration benchmarks for different detection parameters. High-precision, high-frequency melt pressure sensors are fixedly installed at the screw die outlet and shaping sleeve inlet of the three-layer co-extrusion production equipment for thermal repair pipelines. The sensors are selected to suit the high-temperature and high-pressure conditions of the polymer melt, and a uniform 50–100 Hz high-frequency sampling frequency is set. The raw pressure fluctuation signals during the melt flow process are continuously collected. The collected raw signals are processed by a built-in noise reduction and filtering algorithm in the industrial control system to filter out mechanical noise. Vibration, ambient temperature interference, and power grid fluctuations cause noise interference. Only the periodic effective pressure pulsation waveform generated by the viscoelastic flow of the melt is retained. The system identifies and accurately extracts key feature nodes such as peaks, troughs, and phase zero-crossing abrupt changes of the pressure waveform cycle by cycle. The phase timing relationship of the pressure pulsation at the screw head outlet and the shaping sleeve inlet is compared synchronously. The time nodes with a phase deviation of less than 0.02s are selected as the global phase synchronization reference points. This synchronization point is used as the unified time scale for the acquisition, recording, and calculation of all rheological parameters. This completely solves the problem of parameter timing misalignment caused by sampling time difference and signal transmission lag of different detection modules, and ensures the consistency and accuracy of the time dimension of the melt state parameters of each subsequent layer.

[0013] The intrinsic viscosity decay rate of the liner melt during shear flow, the residence time change of the barrier layer melt in the flow channel, and the wetting and diffusion degree of the reinforcing layer melt on the fiber-reinforced structure were obtained separately to establish a sequence of melt state parameters for each layer. Precise parameter acquisition and sequence construction were carried out for the molding characteristics of the three functional layers of the pipeline. For the liner layer, an online high-temperature rheological detection device was used to capture the dynamic viscosity change of the melt during extrusion shear flow in real time. Real-time intrinsic viscosity values ​​of the melt were continuously recorded at a fixed sampling interval of 0.1 s. Combined with the initial steady-state viscosity of the melt, the viscosity decay amplitude and decay rate per unit shear time were calculated in real time. Data from the entire molding process was continuously recorded to form a time-series parameter sequence of the liner layer viscosity decay rate. For the barrier layer, flow rate, [missing information - likely a parameter or parameter] were embedded inside the co-extrusion distribution channel. The pressure real-time monitoring component tracks the entire process of the barrier layer melt entering the flow channel, flowing through the flow channel, and converging during co-extrusion. It dynamically captures the changes in residence time caused by fluctuations in equipment speed, melt temperature, and extrusion load, and statistically analyzes the residence time differences at different molding moments to construct a time-series parameter sequence of the barrier layer melt residence time change. For the reinforcement layer, it is paired with a high-definition infrared microscopic imaging and interface wetting detection system to observe the spreading, penetration, filling, and diffusion behavior of the molten matrix resin in the gaps between the continuous fiber reinforcement skeleton in real time. It quantifies the fiber pore wetting coverage, wetting depth, and diffusion rate at different moments, accurately characterizes the degree of melt wetting of the fiber structure, and continuously collects data to form a time-series parameter sequence of the reinforcement layer melt wetting state. The three sets of parameter sequences completely cover the melt rheology and interface state changes throughout the multi-layer co-extrusion process.

[0014] Based on the pressure pulsation phase synchronization relationship, the melt state parameter sequences of each layer are time-aligned. Taking the same phase node in the pressure pulsation signal of the screw head outlet area and the shaping sleeve inlet area as the time calibration reference point, the sampling timestamps in the melt state parameter sequences of the inner liner, barrier layer and reinforcement layer are respectively mapped to the time coordinate system of the reference point. The parameter sequences of each layer after mapping are resampled in the interval between the reference points using linear interpolation or spline interpolation, so that the parameter sequences of each layer have a unified time sampling node under the same phase reference.

[0015] The time-aligned melt state parameter sequences of each layer are interpolated under the same phase reference, and the variance and mean deviation of the resulting difference sequences are calculated. The weighted combination of variance and mean deviation is used as the correlation processing result characterizing the coupling deviation between the rheological state changes of each melt layer. Using the time-aligned liner layer state parameter sequence as a reference, the differences between the barrier layer and reinforcement layer state parameter sequences and the liner layer at the same phase node are calculated to form an interlayer difference sequence. The variance of this interlayer difference sequence is calculated to characterize the dispersion of the deviation at each phase node, and the mean deviation is calculated to characterize the overall offset direction and magnitude of the deviation. The calculated variance and mean deviation are weighted and summed according to preset weight ratios, where the weight ratios of the variance and mean deviation are preset fixed ratios, and the sum of the two weight ratios is the overall weight sum. The result of the weighted sum is used as the correlation processing result. The larger the result value, the greater the coupling deviation between the rheological state changes of each layer.

[0016] Based on the correlation processing results, rheological asymmetry features characterizing the degree of asynchronous melt response in each layer are extracted. According to the differences in rheological response between the liner and barrier layer, and between the barrier layer and reinforcement layer, weights are assigned to the amplitude of state change and response delay time of each layer to construct an interlayer rheological asymmetry index describing the interlayer rheological matching state. Considering the functional priority, rheological sensitivity, and impact on the final product performance of each layer of the thermal repair pipeline, weight coefficients are set differently. The liner-barrier layer interface, which directly determines the pipeline's high-temperature resistance and hydrolysis resistance and has the greatest impact on interlayer stress due to rheological response differences, is given high weight for its amplitude of state change and rheological response delay time. The barrier-reinforcement layer interface is given corresponding auxiliary weight. During normalized weighting calculations, the coupling deviation between the liner and barrier layer, and between the barrier layer and reinforcement layer, is first divided by the reference deviation of each interface under steady-state conditions, and the response delay time of both interfaces is then divided by... The characteristic period of pressure pulsation is used to obtain the dimensionless deviation ratio and dimensionless delay ratio. Then, based on the sensitivity coefficient of melt viscosity to temperature and the difference in shear rate of each layer, the deviation amplitude contribution factor and delay time contribution factor are determined. The dimensionless deviation ratio and dimensionless delay ratio of each interface are weighted and summed to obtain the comprehensive rheological asymmetry component of that interface. The comprehensive rheological asymmetry component of the interface between the inner liner and the barrier layer is multiplied by its high weight coefficient, and the comprehensive rheological asymmetry component of the interface between the barrier layer and the reinforcement layer is multiplied by its auxiliary weight coefficient. The sum obtained is the interlayer rheological asymmetry index. This index can intuitively and quantitatively characterize the interlayer rheological matching accuracy during multilayer co-extrusion molding. The larger the index value, the worse the synchronization of interlayer melt rheological response and the higher the molding matching disorder. The closer the index is to zero, the better the consistency of melt flow and rheological evolution of each layer. This provides a core quantitative basis for subsequent interlayer shrinkage mismatch quantification, thermal stress modeling and process closed-loop control.

[0017] Step S20: Based on the interlayer rheological asymmetry index, calculate the curing rate changes and freezing time differences of the inner lining, barrier layer and reinforcement layer during the cooling and shaping process, obtain the volume shrinkage rate differences of each layer, and combine the thermal conduction hysteresis characteristics of the barrier layer to quantitatively correct the interlayer shrinkage mismatch and construct the interlayer thermal stress distribution model of the pipe wall.

[0018] In step S20, the process of obtaining the difference in volume shrinkage rate of each layer is as follows: Based on the differences in response delay time and amplitude of each layer in the interlayer rheological asymmetry index, the phase hysteresis is converted into temperature hysteresis using a time-temperature equivalent translation factor. The response delay time value of each layer during the pressure pulsation cycle and the difference in state change amplitude at each phase node are extracted from the interlayer rheological asymmetry index. Using the relaxation time spectrum of each layer of melt material at the reference temperature as a reference, the translation factor calculation method described in the time-temperature equivalence principle is adopted. That is, based on the activation energy parameters of each layer of melt material within a specific temperature range and the temperature difference between the current processing temperature and the reference temperature, the time-temperature equivalent translation factor corresponding to each layer is calculated. The translation factor is multiplied by the response delay time value of each layer to obtain the temperature hysteresis corresponding to each layer in the cooling stage. This temperature hysteresis is used to characterize the phase shift of the temperature field generated by the asynchronous rheological response of each layer of melt during the cooling process.

[0019] Based on the temperature hysteresis, the additional heat accumulation value and the decrease in molecular chain motion degrees of freedom of each layer during the cooling stage are calculated, thereby converting the differences in rheological state into changes in heat release and the degree of restriction of molecular chain motion during the cooling stage. The calculated temperature hysteresis value of each layer is multiplied by the average isobaric specific heat capacity of the material in the cooling temperature range and the melt density of the layer to obtain the additional heat accumulation value generated by the rheological response hysteresis of each layer during the cooling stage. At the same time, based on the glass transition temperature range and free volume shrinkage characteristics of the melt of each layer during the cooling process, the temperature hysteresis value is substituted into the correlation between the known molecular chain motion activation energy parameters and temperature of the material in that layer to calculate the decrease in molecular chain segment transition probability caused by temperature hysteresis. This decrease is then normalized according to the equilibrium molecular chain motion degrees of freedom of the material in that layer at the cooling termination temperature to obtain the decrease in molecular chain motion degrees of freedom. The calculated additional heat accumulation value is used to characterize the degree of abnormal heat release during the cooling stage, and the decrease in molecular chain motion degrees of freedom is used to characterize the degree of restriction of molecular chain motion, thereby realizing the conversion of differences in rheological state into changes in heat release and the degree of restriction of molecular chain motion during the cooling stage.

[0020] The temperature change trajectories of the inner lining layer, barrier layer, and reinforcement layer within the shaping and cooling zone are acquired. Combined with the thermal diffusion characteristics of each layer, the migration rate of the curing interface and the curing completion time of each layer are calculated. Multiple high-precision temperature sensors are uniformly deployed along the radial and axial directions of the pipe within the shaping and cooling zone, with a sampling frequency set to 50Hz. Real-time temperature data of the three layers (inner lining, barrier layer, and reinforcement layer) are continuously acquired throughout the entire cooling and shaping process. Independent dynamic temperature trajectory curves of each layer as a function of molding time are generated, accurately capturing the gradual cooling of the melt from its molten high temperature state to its glass transition temperature and complete solidification temperature. By analyzing the temperature change characteristics throughout the process, the fundamental thermophysical parameters such as the inherent thermal diffusivity, specific heat capacity, and thermal conductivity of the three-layer material were retrieved. Combined with the real-time temperature gradient of each layer and the pipe wall thickness, the dynamic migration position and migration rate of the solidification interface of each layer were solved in real time through the unsteady-state heat conduction equation to obtain the real-time migration speed of the solidification interface. The time node when the melt temperature of each layer drops to the critical temperature for complete solidification of the material and the temperature no longer fluctuates significantly is taken as the end point of solidification completion. The overall solidification completion time of the inner lining layer, barrier layer, and reinforcement layer is accurately calculated, and the differences in the interface advancement rhythm and solidification sequence of the three-layer structure during the cooling and solidification process are clearly distinguished.

[0021] Based on the time interval between the completion times of each layer's curing, the differences in freezing sequence between different layers are determined. Combined with the initial melt temperature, cooling rate, and thermal expansion coefficient of each layer, the volume shrinkage rate change in the corresponding region is calculated. By comparing the curing completion times of the inner lining layer, barrier layer, and reinforcing layer, the curing time difference between adjacent layers is accurately calculated. This time difference represents the interlayer freezing sequence difference of the multi-layer pipe wall structure, directly reflecting the asynchronous nature of the three layers' transformation from a molten, plastic state to a solid, shaped state. Based on this, the initial temperature, average cooling rate, and inherent thermal expansion coefficient of each layer's melt entering the shaping and cooling zone are extracted. A quantitative calculation model for the thermal shrinkage of multi-layer materials is constructed. For different radial thickness regions and different axial forming positions of the pipe wall, corresponding process parameters and material parameters are substituted into each region to dynamically calculate the instantaneous volume shrinkage and unit-time volume shrinkage change of each layer's melt during the cooling and curing process. This accurately obtains the dynamic change law of the volume shrinkage rate of each layer throughout the entire cooling and shaping process, effectively capturing the shrinkage rate deviation caused by differences in freezing sequence, thermal properties, and cooling conditions in different layers and positions.

[0022] By correlating the volume shrinkage rate changes of different layers according to their radial position and axial forming direction, interlayer shrinkage difference parameters reflecting the synchronous shrinkage capability of multi-layer structures are obtained. Using the radial thickness dimension of the pipe wall as the zoning benchmark for the inner, middle, and outer layers, and the axial forming length of the pipe as the continuous extension dimension, the volume shrinkage rate change data of each layer calculated above are spatially correlated and matched to achieve a one-to-one correspondence between shrinkage rate data and the spatial position of the pipe. The radial shrinkage rate difference of the three layers at the same axial position and the shrinkage rate fluctuation value of the same layer along the axial forming direction are coupled and statistically analyzed to eliminate the one-sidedness of single-dimensional data and integrate interlayer shrinkage characteristic data that can comprehensively characterize the forming state of the pipe. Through normalized difference processing, the shrinkage rate deviation data of each group are quantified into a unified standard interlayer shrinkage difference parameter. This parameter can intuitively and quantitatively reflect the synchronous shrinkage capability of the multi-layer composite pipe wall during the cooling and shaping process. The larger the parameter value, the higher the degree of interlayer shrinkage mismatch and the greater the potential for internal stress during forming. This provides accurate quantitative data support for subsequent interlayer thermal stress modeling, shrinkage mismatch correction, and residual stress control.

[0023] In step S20, the process of constructing the interlayer thermal stress distribution model of the pipe wall is as follows: Based on the interlayer shrinkage difference parameters, the radial shrinkage differences of the lining layer, barrier layer, and reinforcement layer during the cooling process are obtained, and the initial shrinkage mismatch relationship of different interlayer interfaces is established. Using the pre-calculated global interlayer shrinkage difference parameters as input conditions, and combining the thickness dimensions, real-time cooling rate, and volume shrinkage rate dynamic curves of the lining layer, barrier layer, and reinforcement layer, the cumulative radial shrinkage of each functional layer during the entire shaping and cooling process is calculated by integrating across different regions. This accurately yields the total actual shrinkage deformation of each layer in the radial direction of the pipe wall. By comparing the radial shrinkage deformation differences between the lining layer and the barrier layer, and between the barrier layer and the reinforcement layer, the adjacent layers are quantified. The shrinkage deformation deviation of two layers under the same cooling time and forming position accurately captures the asynchronous shrinkage behavior of multi-layer composite pipes caused by differences in material thermophysical properties, curing and freezing time, and rheological forming. Based on this, taking the interlayer bonding interface of the pipe wall as the boundary, an initial interface shrinkage mismatch dataset is established with radial shrinkage difference, shrinkage start and end time difference, and local shrinkage gradient deviation as the core. This clarifies the deformation constraint contradictions and the source of original stress generation of each interface in the early stage of cooling and forming, and constructs an initial shrinkage mismatch relationship that can truly reflect the interlayer deformation incoordination during the forming process, providing original boundary conditions for subsequent thermal stress correction calculations and model building.

[0024] The temperature gradient change data along the thickness direction of the barrier layer is collected, the heat transfer delay time inside the barrier layer is calculated, and the actual shrinkage response state of the barrier layer is compensated for based on the heat conduction hysteresis characteristics. Due to the special material structure characteristics of the dense, water- and oxygen-barrier barrier layer, its heat conduction rate is significantly lower than that of the inner lining and reinforcing layer, exhibiting a significant heat transfer hysteresis effect. In this step, three layers of high-precision micro-temperature sensing points are uniformly distributed along the thickness direction of the barrier layer, respectively attached to the inner layer interface, the thickness center, and the outer layer interface. Real-time temperature data along the thickness direction of the barrier layer is collected throughout the cooling and shaping process at a sampling frequency of 50Hz, generating a multi-dimensional temperature gradient dynamic change curve along the thickness direction. Based on the time difference and temperature decay rate of the temperature response at each measuring point, combined with the thermal conductivity coefficient and thickness parameters of the barrier layer, the lag time for the complete transfer of heat from the inside to the outside of the barrier layer is accurately calculated using a one-dimensional unsteady-state thermal conduction delay calculation formula. The heat transfer delay time at different axial and radial positions is quantified. Based on this heat transfer delay time, the original shrinkage response time sequence curve of the barrier layer is positively compensated and corrected to offset the shrinkage response lag caused by the heat transfer lag. This ensures that the corrected shrinkage behavior of the barrier layer can truly match its actual internal temperature curing state, eliminates the calculation deviation of the shrinkage state caused by single temperature monitoring, and guarantees the accuracy of the deformation response characterization of the barrier layer.

[0025] The shrinkage response state of the time-compensated barrier layer is synchronously matched with the shrinkage state of adjacent layers to calculate the transient shrinkage constraint amount of each interface region. The dynamic shrinkage rate, real-time shrinkage deformation, and curing shrinkage time sequence characteristics of the barrier layer after heat conduction time-series compensation are synchronously matched with the real-time shrinkage states of the inner lining layer and the outer reinforcing layer on a time-by-time and spatial-position basis, respectively. This unifies the molding time reference and spatial position reference of the three-layer structure, eliminating the deformation asynchrony error caused by the interlayer heat transfer time sequence difference. Based on time synchronization, and relying on the deformation constraint principle of the multi-layer composite structure interface... Theoretically, when there is a difference in shrinkage rate and deformation between two adjacent layers, the interlayer interface will exert an elastic constraint on each other. By calculating the theoretical free shrinkage deformation difference on both sides of the interface at the same moment, and combining the radial deformation constraint boundary conditions of the pipe wall, the transient deformation constraint value of each interlayer interface at different cooling stages can be accurately solved, which is the transient shrinkage constraint of the interface. This constraint can accurately characterize the degree of mutual compression and tension constraint caused by shrinkage mismatch between layers, and can intuitively reflect the real-time generation and accumulation law of interface stress during the cooling process, providing accurate dynamic load input conditions for multi-dimensional thermal stress solution.

[0026] Based on the correspondence between material elastic modulus, interfacial bonding parameters, and shrinkage constraint, a pipe wall interlayer thermal stress distribution model is established, including radial stress, tangential stress, and interfacial shear stress distribution. Inherent mechanical parameters such as elastic modulus, Poisson's ratio, and thermal deformation stiffness of each layer are retrieved from both room temperature and high temperature ranges. Interfacial bonding characteristic parameters such as interlayer bonding strength, interfacial friction coefficient, and interfacial adhesion stiffness are also introduced. The previously calculated global transient shrinkage constraint is used as the dynamic stress load boundary to construct a multi-layer pipe wall thermo-mechanical coupled finite element calculation model. Using the pipe's radial thickness, axial forming length, and circumferential annular angle as three-dimensional calculation dimensions, a detailed analysis of the pipe wall structure is performed. By discretizing the mesh, the shrinkage constraints at different locations and times are successively substituted into the mesh elements for mechanical solution. The real-time values ​​and distribution patterns of radial compressive stress, circumferential tangential stress, and interlayer interface shear stress over the entire pipe wall are calculated. By fitting the spatial distribution curve and temporal evolution curve of the stress data over the entire area, a pipe wall interlayer thermal stress distribution model is finally established. This model contains three-dimensional stress components, has spatiotemporal evolution characteristics, and can accurately characterize the interlayer thermal stress concentration and stress distribution patterns. It can accurately locate high stress concentration areas and stress peak intervals, providing reliable model support and data basis for subsequent stress concentration identification and gradient thermal shaping parameter control.

[0027] Step S30: Based on the interlayer thermal stress distribution model of the pipe wall, extract the stress gradient and peak region at the interface between the lining layer and the barrier layer, locate the stress concentration location, and match the heating power, traction disturbance amplitude, and cooling airflow parameters with the interlayer shrinkage rate according to the interface stress characteristics. Through gradient thermal shaping, form a non-uniform residual stress field adapted to the difference in interlayer shrinkage. In step S30, the process of locating the stress concentration location is as follows: Based on the interlayer thermal stress distribution model of the pipe wall, the interface region between the lining layer and the barrier layer is spatially discretized to obtain interface stress distribution data at different radial positions. Using the previously constructed interlayer thermal stress distribution model as the computational basis, the interface between the lining layer and the barrier layer is selected as the core analysis region. Abandoning the global uniform mesh generation mode, an interface-refined spatial discretization strategy is adopted to perform fine mesh generation. The interlayer interface is segmented axially, evenly divided circumferentially, and subjected to radial thin-layer refinement. Axially, the interface is uniformly divided into units with a 5mm equidistant step size, and circumferentially, it is discretized into rings with a 1° central angle. The radial region is tripled in mesh density within a 0.2mm thickness range above and below the interlayer interface, while the remaining matrix region uses a conventional mesh transition. This effectively reduces redundant computational power loss while ensuring computational accuracy. After discretization, the mechanical solution results corresponding to the thermal stress model are retrieved independently for each mesh cell. Real-time radial stress, tangential stress, and interface shear stress values ​​at different radial depths, axial positions, and circumferential angles are extracted in batches. A complete dataset of continuous stress distribution across the entire interface is collected, accurately obtaining the original distribution state of interface stress at each discrete point. This provides refined and comprehensive raw data support for subsequent stress gradient calculation and feature analysis.

[0028] The radial stress gradient, tangential stress gradient, and shear stress amplitude within the interface region were calculated separately to establish a multidimensional stress gradient feature matrix. Based on the discrete mesh stress data of the entire interface, the differential gradient algorithm was used to solve the gradient of the three core stress parameters point by point. The radial stress gradient in the radial direction of the pipe wall, the tangential stress gradient in the circumferential direction, and the fluctuation amplitude of the interlayer interface shear stress were calculated respectively. The radial stress gradient represents the rate of increase or decrease of stress in the thickness direction, the tangential stress gradient represents the uniformity of stress change in the circumferential direction of the pipe, and the shear stress amplitude represents the extreme level of the stress constrained by the mutual displacement of the interlayer interface. The multidimensional stress characteristic parameters were quantitatively calculated for each mesh cell. Using the discrete mesh spatial coordinates as the row dimension and the three types of stress gradient characteristic parameters as the column dimension, the parameters were structurally integrated and normalized to unify the dimensions, eliminating the analytical bias caused by the difference in the numerical magnitude of different stress parameters. Finally, a four-dimensional multidimensional stress gradient feature matrix containing spatial location, radial stress gradient, tangential stress gradient, and shear stress amplitude was constructed to realize the structured and digital representation of the stress change characteristics of the interlayer interface.

[0029] Based on the stress gradient feature matrix, regions of rapid stress change are identified. Regions where the stress gradient amplitude at any spatial discrete point within the interface region exceeds twice the average stress gradient amplitude of the interface region, and the rate of change of stress gradient between two adjacent discrete points exceeds a preset threshold, are defined as regions of rapid stress change. The stress peak value, duration, and spatial diffusion range at the corresponding locations are extracted. Following the axial and radial discrete grid division of the interface region, the stress gradient amplitude at each spatial discrete point is calculated point by point, and the arithmetic mean of the stress gradient amplitudes at all discrete points is taken as the average stress gradient amplitude of the interface region. Twice this average stress gradient amplitude is used as the first judgment threshold, based on the material yield strength... The upper limit of the gradient change rate of the strength of the material and the interface bonding strength is set as the second judgment threshold; each discrete point is scanned point by point along the axial direction, and the continuous segment that simultaneously satisfies the stress gradient amplitude exceeding the first judgment threshold and the stress gradient change rate between the point and its adjacent downstream discrete point exceeds the second judgment threshold is marked as the stress rapid change region; for each marked stress rapid change region, the maximum value of the stress gradient amplitude among all discrete points in the region is extracted as the stress peak value, the product of the length of the region continuously distributed along the axial direction and the time history experienced by the melt within the length range is extracted as the duration, and the span distance between the start position and the end position of the region along the axial direction is extracted as the spatial diffusion range.

[0030] Spatially mapping the stress peak region with the interlayer shrinkage mismatch region identifies stress concentration locations where interfacial delamination may occur during long-term humid heat and temperature cycling. A unified three-dimensional spatial coordinate mapping system for the pipe is established, matching and associating the coordinates of the previously identified stress peak anomaly regions with the previously calculated and calibrated interlayer shrinkage mismatch spatial regions point-to-point and block-to-block. The overlap and coverage matching degree between high-stress regions and shrinkage mismatch regions are verified. If the stress peak region highly overlaps with the core regions of interlayer shrinkage rate mismatch, curing time mismatch, and heat transfer hysteresis mismatch, then the region is considered... The region is a high-risk area for structural stress concentration caused by inherent defects in the forming process. Combining the actual service environment characteristics of the pipeline, the mechanism of cyclic loads caused by seasonal start-up and shutdown of heating in northern China, including water absorption, freeze-thaw expansion, and temperature alternation, is simulated. The stress accumulation and stress release laws of this high-risk area under repeated tension and compression and alternating wet and dry conditions are analyzed. The evolution trend of microcrack initiation, expansion, and peeling at the interface is predicted. Finally, all fixed stress concentration locations with long-term peeling failure risk at the interface between the inner lining and the barrier layer of the pipe wall are accurately located. This provides a clear target control area for subsequent gradient thermal shaping zonal stress control and precise reconstruction of the residual stress field.

[0031] In step S30, the process of forming a non-uniform residual stress field that adapts to the interlayer shrinkage difference is as follows: Based on the location of stress concentration, the stress level range of each axial region is determined, and the target compensation shrinkage amount required for each region is calculated according to the interface stress gradient characteristics. The stress level range of each axial region is mapped and matched with the target compensation shrinkage amount. Based on the mapping and matching results, the correspondence between each stress concentration region and the local heating power, traction disturbance amplitude, and cooling airflow intensity is established. Based on the coordinate location of interlayer stress concentration, the magnitude of the stress peak, the rate of change of the stress gradient, and the spatial diffusion range of stress, combined with the shrinkage mismatch level at different axial and radial positions of the pipe wall, all stress concentration regions are divided into three levels according to the stress gradient amplitude: mild mismatch, moderate mismatch, and severe mismatch. At the same time, the interlayer shrinkage timing difference, volume shrinkage rate deviation, and heat conduction hysteresis characteristics of the corresponding regions are matched to eliminate... Interlayer contraction constraint stress and equilibrium interface stress gradient are the control targets. The stress gradient amplitude is used as the reference input for heating power; the larger the stress gradient amplitude, the higher the corresponding local heating power setting. The spatial diffusion range of the stress peak is used as the reference input for the width of the cooling airflow; the larger the diffusion range, the wider the corresponding cooling airflow width. The duration of the stress peak is used as the reference input for the duration of the cooling airflow; the longer the duration, the longer the corresponding cooling airflow duration. The contraction mismatch level of the stress concentration area is used as the reference input for the amplitude of the traction disturbance; the higher the mismatch level, the larger the corresponding traction disturbance amplitude. Based on this, a quantitative relationship is established between local heating power, traction disturbance amplitude, cooling airflow intensity, and stress peak, stress gradient, and contraction mismatch degree.

[0032] To address the shrinkage mismatch in different axial regions, the local heating power, traction disturbance amplitude, and cooling airflow intensity during the gradient heat setting process were adjusted. The heat setting area along the pipe axis was divided into several independent temperature control units, each capable of independent and precise control of heating, traction, and cooling parameters. The interlayer shrinkage time difference in each region was used as the adjustment benchmark for heating power. The ratio of the shrinkage time difference to the total curing time of the pipe in that region was used as the adjustment ratio for heating power. That is, based on the benchmark heating power, the heating power was increased or decreased proportionally according to this adjustment ratio. Regions with larger shrinkage time differences had a higher increase in heating power to prolong the time the melt in that region remained in the relaxation temperature range. The deviation in volumetric shrinkage rate in each region was used as the adjustment benchmark for cooling airflow intensity. The ratio of the volumetric shrinkage rate deviation to the total curing time of the pipe in that region was adjusted proportionally according to this adjustment ratio. The ratio of the material's baseline shrinkage rate is used as the adjustment ratio for the cooling airflow. That is, based on the baseline cooling airflow, the cooling airflow is adjusted in reverse according to this adjustment ratio. The larger the deviation in shrinkage rate, the greater the reduction in cooling airflow, in order to slow down the cooling rate and reduce the time difference in curing between layers. The ratio of the stress gradient amplitude at the interface of each region to the average stress gradient amplitude of the region is used as the adjustment benchmark for the traction disturbance amplitude. Based on the baseline traction disturbance amplitude, the disturbance amplitude is increased or decreased proportionally according to this ratio. The larger the stress gradient, the greater the disturbance amplitude, in order to promote the rearrangement of molecular chains and stress relaxation at the interlayer interface through mechanical disturbance. Through the above-mentioned regional differentiated parameter control, regions with different shrinkage mismatch levels can obtain heat setting conditions that are compatible with their shrinkage mismatch characteristics, and the problem of inconsistent interlayer shrinkage can be compensated from the process end.

[0033] During the heat setting process, data on the radial dimensional changes and temperature response of the pipe wall are collected, and the deviation between the actual shrinkage trajectory and the target shrinkage matching trajectory is calculated in real time. Throughout the gradient heat setting process, dynamic response data such as the radial outer diameter of the pipe wall, the overall temperature of the pipe wall, and the interlayer interface temperature of each axial control unit are collected in real time and continuously using a high-precision laser diameter gauge and a pipe wall infrared temperature sensing array. The sampling frequency is uniformly set to 50Hz. The complete dimensional shrinkage trajectory and temperature evolution trajectory of the pipe from the high-temperature plastic state to complete cooling and setting are recorded. Combined with the standard target shrinkage trajectory preset by the interlayer shrinkage matching model, and using the same molding time and the same axial position as the matching benchmark, the differences between the actual radial shrinkage deformation, shrinkage rate, and cooling rate and the target theoretical curve are compared time-by-time and region-by-region. The three core deviation indicators of radial dimensional deviation, shrinkage rate deviation, and temperature response lag deviation are calculated respectively, and the real-time shrinkage matching deviation of each region is quantified. This accurately captures molding anomalies such as local over-shrinkage, under-shrinkage, and asynchronous shrinkage, providing accurate deviation data support for iterative correction of process parameters.

[0034] Based on the deviation results, the heat setting parameters of different regions are iteratively adjusted to form a non-uniform residual stress field corresponding to the shrinkage differences of each layer. A negative feedback iterative adjustment mechanism is established based on the real-time shrinkage trajectory deviation values ​​of each axial region. Dynamic parameter correction is implemented for regions with excessive shrinkage deviation. When the actual shrinkage is less than the target shrinkage, the local heating power is appropriately increased and the cooling wind speed is reduced to promote sufficient relaxation and shrinkage of the melt. When the actual shrinkage is too large and there is excessive stretching residual stress, the heating temperature is appropriately reduced and the cooling intensity is slightly increased to quickly lock the forming shape and suppress excessive deformation. This process is repeated multiple times. Real-time iterative correction gradually brings the actual shrinkage trajectory of each layer and region closer to the theoretical optimal matching trajectory, accurately offsetting the original tensile and compressive stress caused by the asynchronous curing and shrinkage of multi-layer heterogeneous materials. Ultimately, a non-uniform residual stress field is actively constructed inside the pipe wall that is perfectly matched with the shrinkage characteristics, interlayer mismatch locations, and stress concentration distribution of the three-layer materials. The pre-fabricated reverse equilibrium residual stress offsets the additional interfacial stress generated by damp heat, freeze-thaw cycles, and temperature cycling during service, completely suppressing the problems of interlayer stress concentration, microcrack initiation, and interfacial peeling failure, and significantly improving the interlayer bonding stability and long-term service life of multi-layer composite pipes.

[0035] Step S40: For the repaired tube with a non-uniform residual stress field, accelerated aging tests are conducted on sampled tubes under alternating damp heat and freeze-thaw cycles. The radial deformation response sequence of the tube wall and the interlayer peeling evolution characteristics under different water content conditions are collected. Based on the correspondence between the residual stress release and the interface deformation change, the residual stress distribution deviation in each region is determined.

[0036] In step S40, the process of collecting the radial deformation response sequence of the pipe wall and the evolution characteristics of interlayer peeling under different water content states is as follows: For the repaired tube that has formed a non-uniform residual stress field, samples are taken from the tube based on the high-stress areas and corresponding environmentally sensitive areas determined by the interlayer thermal stress distribution model of the tube wall. On the repaired tube that has undergone gradient heat setting and formed a non-uniform residual stress field, the stress peak position coordinates in the axial and radial directions of the tube wall are extracted based on the stress distribution map output by the previously constructed interlayer thermal stress distribution model of the tube wall. Sections where the stress gradient amplitude exceeds twice the average stress gradient amplitude of the region and the rate of change of stress gradient between adjacent discrete points exceeds a preset threshold are identified as high-stress areas. By combining the hydrolysis resistance characteristics of the inner lining material and the water vapor permeability coefficient of the barrier layer material, the environmentally sensitive area most prone to interfacial hydrolysis and degradation in a humid and hot environment was identified. The spatial overlap between the high-stress area and the environmentally sensitive area was used as the sampling target area. A standard annular sample with a length three times the nominal outer diameter of the pipe was cut from the pipe using a water-cooled cutting method. During the cutting process, sufficient cooling was maintained to prevent the introduction of additional residual stress disturbance by the cutting heat. After cutting, the end face of the sample was mechanically ground flat to ensure that the perpendicularity deviation between the end face of the sample and the axis of the pipe does not exceed 0.1 mm.

[0037] For the samples, environmental loading treatment for accelerated aging tests was carried out by selecting the frequency of wet and heat alternation, the path of water content change, and the range of freeze-thaw temperature cycles corresponding to the actual service conditions. The standard annular samples were installed on a special clamping fixture in a programmable environmental test chamber. The clamping fixture simulated the axial constraint stiffness and radial free expansion conditions of the pipe under actual buried or overhead laying conditions. Based on the actual service conditions of the thermally repaired pipeline, the frequency of wet and heat alternation was set to complete one full wet-dry cycle every 24 hours. During the high-humidity phase, the relative humidity was maintained at 95%±3% and the temperature at 60℃±2℃ for 12 hours to simulate the immersion state of the pipeline in saturated water-containing soil. During the drying phase, the relative humidity was maintained at 30%±5% and the temperature at 60℃±2℃ for 12 hours. The process of desorption of water from a pipeline under dry conditions was simulated by maintaining the temperature at 0℃±2℃ for 12 hours. The water content state change path was gradient-loaded in the order of "dry state → surface adsorption state → saturated water absorption state → frozen state". The surface adsorption state was achieved by continuously spraying deionized water mist onto the sample surface, the saturated water absorption state was achieved by completely immersing the sample in a 60℃ deionized water bath, and the frozen state was achieved by transferring the saturated water-absorbing sample into a -20℃±2℃ low-temperature chamber for 6 hours. The freeze-thaw temperature cycle range was set from -20℃ to 60℃, and the heating and cooling rate was controlled within 5℃ / min to avoid thermal shock introducing additional stress. The number of cycles was not less than 30 to ensure that the accelerated aging effect could fully expose the potential peeling evolution trend of the interlayer interface.

[0038] During cyclic loading, the moisture content changes, radial expansion displacement response, axial deformation, and interlayer interface acoustic wave propagation characteristics of different regions of the sample were simultaneously collected. In each cycle of environmental loading, miniature dielectric constant sensors embedded at the interfaces of the lining, barrier, and reinforcement layers of the sample were used to collect real-time moisture content change data for each layer. The sensor sampling frequency was set to 1 time / minute. The real-time moisture content of each layer was calculated using the differences in the response of the dielectric constants of different polymer materials to moisture content. The radial expansion displacement response was collected using six non-contact laser displacement sensors evenly arranged along the circumference of the outer wall of the sample. The sensor resolution was no less than 0.1 μm, and the sampling frequency was [not specified in the original text]. The frequency was set to 10Hz to record the radial expansion and contraction of the sample under different moisture contents in real time. The axial deformation was collected by high-precision linear variable differential transformer displacement sensors installed on both ends of the sample to monitor the axial expansion and contraction of the sample during hygrothermal expansion and freeze-thaw cycles in real time. The acoustic wave propagation characteristics of the interlayer interface were detected by ultrasonic pulse reflection method. The focused ultrasonic probe was scanned circumferentially along the outer wall of the sample and emitted longitudinal wave pulses with a frequency of 5MHz. By analyzing the amplitude attenuation and propagation time offset of the reflected echo at the interface of the inner liner layer-barrier layer and the interface of the barrier layer-reinforcing layer, the contact state and micro-peeling degree of the interlayer interface were characterized in real time.

[0039] Based on the water content migration state at different cycle stages, the radial deformation response sequence was divided into stages and time-series synchronization was performed. The deformation rate difference and recovery characteristics corresponding to the hygrothermal water absorption stage and the freeze-swelling stage were extracted. The radial deformation response sequence within each complete cycle was divided into four characteristic stages according to the water content change path: dry state reference stage, surface adsorption swelling stage, saturated water absorption swelling stage, and freeze-swelling stage. The time node when the water content reaches steady state in each stage was used as the stage division boundary, and the radial deformation data and water content data were time-series synchronized and aligned. For the hygrothermal water absorption stage, the dimensions of the sample from the dry state reference size to the saturated water absorption steady-state size were extracted. The total radial expansion, expansion rate curve, and time constant required to reach 90% saturation expansion were recorded. For the freeze expansion stage, the additional radial expansion increment, freeze expansion rate, and volumetric abrupt change characteristics of the sample from the saturated water-absorbing state to the frozen steady state were extracted. At the same time, the radial dimensional recovery rate and irreversible residual deformation during the recovery from the frozen state to the room temperature dry state were recorded. The irreversible residual deformation is a direct quantitative characterization of the interlayer interface damage accumulation under this cycle. By comparing the difference in the wet heat water absorption deformation rate and the freeze expansion deformation rate of different cycles, the decay law of interlayer interface bonding strength with the aging process was evaluated.

[0040] By combining the relationship between the changes in acoustic wave propagation at the interlayer interface and the distribution of local deformation anomalies, the evolution characteristics of interlayer peeling with each cycle are extracted. The acoustic wave reflection echo amplitude data collected at each cycle are spatially registered with the radial deformation anomaly areas of the sample. A spatial distribution map of the interface peeling state is established with the axial position of the sample as the abscissa and the circumferential angle as the ordinate. When the amplitude of the reflected echo from the liner-barrier layer interface at a certain location decreases by more than 6 dB relative to the initial state, it is determined that initial micro-peeling of the interface has occurred at that location. When the echo amplitude decreases by more than 12 dB and... When the radial deformation increases abnormally locally, it is determined that the location has developed into macroscopic interlayer peeling. Through statistical analysis of the number, area, and distribution of peeling determination areas under different cycle cycles, four interlayer peeling evolution characteristic parameters are extracted: peeling initiation cycle cycle, peeling propagation rate, peeling area connectivity, and peeling area ratio. Correlation analysis is performed between the peeling propagation rate and the residual stress release in the corresponding area to establish the correspondence between peeling evolution characteristics and interlayer residual stress attenuation, providing a quantitative basis for determining the subsequent residual stress distribution deviation and adjusting process parameters.

[0041] In step S40, the process of determining the residual stress distribution deviation in each region is as follows: Based on the interlayer peeling evolution characteristics, the interface deformation expansion and peeling growth rate under different cycle cycles were obtained. Using the interlayer peeling evolution characteristic dataset collected from previous wet-heat freeze-thaw cycle tests as a basis, and with a fixed cycle cycle as the time node, interface defect evolution data of high-risk stress areas and conventional areas of the pipeline were extracted cycle by cycle. Relying on the acoustic attenuation rate, waveform distortion degree, and defect spatial diffusion range obtained from ultrasonic detection, the actual expansion area of ​​interlayer micro-debonding and micro-cracks and the interface deformation expansion depth were accurately defined after each cycle, quantifying the cumulative expansion of interface deformation under different cycle cycles. By performing differential calculations on the peeling defect increments of adjacent cycles, the dynamic growth rate of interlayer peeling within a single cycle was obtained, distinguishing the rate differences in the initial micro-defect initiation stage, the stable defect expansion stage, and the rapid defect deterioration stage. A complete dynamic characteristic curve of peeling expansion and peeling growth rate changing with cycle cycles was constructed, accurately characterizing the interface damage evolution law of different pipe wall regions under alternating environmental loads, and providing original damage characteristic parameters for the quantitative calculation of residual stress release.

[0042] The residual stress release in each region before and after environmental cycling was calculated. Using the residual stress release in each region as the independent variable and the radial deformation response at the interface as the dependent variable, a piecewise linear interpolation method was used to establish a mapping curve between the two. The same pipe wall monitoring area before and after the environmental cycling test was selected as a comparison benchmark. The initial non-uniform residual stress field value before environmental cycling was conducted after pipe forming and finalization was used as the benchmark stress value. Combining the stress release and deformation coupling mechanism of polymer composite materials, the total residual stress released during wet-heat freeze-thaw cycles was calculated based on the degree of interface peeling expansion, radial deformation increment, and cumulative residual deformation in each region at different cycling stages, according to the cycle stages. The total residual stress released during wet-heat freeze-thaw cycles due to interface relaxation, molecular chain reconstruction, and micro-defect initiation was calculated in different regions. By correlating real-time radial expansion deformation, shrinkage and rebound deformation, and stress attenuation data in the same region, a multivariate coupling fitting algorithm was used to establish the corresponding relationship. The residual stress release measured in each monitoring region at different cycle cycles was used as the dependent variable, and the radial expansion deformation rate, cumulative radial deformation, and residual deformation in the corresponding cycle of the same region were used as independent variables. Temperature, moisture content, and external force constraints were used as interference variables. A multivariate coupled dataset was constructed. Next, each variable was normalized to eliminate dimensional differences. Temperature was normalized based on the material's glass transition temperature, moisture content on the material's saturated water absorption rate, and external force constraints on the initial axial constraint force of the pipe. Then, with residual stress release as the output target, radial deformation parameters as the main effect term, and the cross-product term of temperature, moisture content, and external force constraints as the interference correction term, the normalized dataset was fitted using the least squares method with multiple linear regression to obtain the relationship between residual stress release and radial deformation parameters. The quantitative correspondence between deformation parameters is established. Based on the fitted quantitative correspondence, the residual stress release data points measured in each monitoring area at different cycle counts are used as interpolation nodes. A linear function is used to connect adjacent data points to construct a piecewise linear interpolation mapping curve with residual stress release as the horizontal axis and interface radial deformation response as the vertical axis. This curve serves as the mapping relationship between residual stress release and interface radial deformation response. Based on this mapping relationship curve, the residual stress release in each area can be inverted and calculated from the measured radial deformation response data.

[0043] The radial deformation response of each region's interface is compared with the deformation response under the theoretical steady state. The deviation between the two is substituted into the mapping curve for back calculation to obtain the residual stress release offset of the region. For each monitoring region, the difference between the measured radial deformation response of the interface after environmental cyclic loading and the radial deformation response of the region under the theoretical steady state is calculated to obtain the radial deformation deviation of each region. The radial deformation deviation of each region is substituted into the established piecewise linear interpolation mapping curve with the residual stress release as the horizontal axis and the radial deformation response of the interface as the vertical axis. The deviation is used as the input value in the vertical direction to locate the corresponding horizontal axis coordinate value on the curve. This horizontal axis coordinate value is the estimated value of the residual stress release of the region after environmental cyclic loading due to the actual deformation deviating from the theoretical steady state. The difference between this estimated value and the initial reference residual stress value of the region after heat setting is compared. The difference between the two is the residual stress release offset of the region. This offset is used to characterize the degree of deviation of the current residual stress distribution of the region from the initial design state.

[0044] By comparing the residual stress release offset of each region with the initial non-uniform residual stress distribution, the residual stress distribution deviation at different locations is determined. Spatial distribution data of the initial non-uniform residual stress field constructed by gradient thermal shaping after pipe forming are retrieved to clarify the initial residual stress peak value, stress distribution gradient, and stress equilibrium state of each region in the axial and radial directions of the pipe wall. The calculated residual stress release offset of each region is superimposed and compared with the initial residual stress distribution parameters at the corresponding spatial locations. The difference between the initial stress preset value and the actual service stress release behavior is analyzed, distinguishing regions of excessive stress, insufficient stress, and unbalanced stress gradient. Through normalized deviation calculation, the amplitude and direction of the residual stress distribution deviation at each point are quantified and statistically analyzed. Finally, the residual stress distribution deviation characteristics of all regions of the pipe wall are calibrated across the entire domain, accurately locating the core region of residual stress matching failure. This provides a precise quantitative basis for subsequent closed-loop feedback correction of process parameters and iterative optimization of interlayer stability parameters.

[0045] Step S50: Map the residual stress distribution deviation in each region to the stress concentration location, and use the interface bonding strength attenuation rate determined by the peeling cycle to constrain the feedback linkage adjustment of co-extrusion rheological properties and gradient heat setting process, and output interlayer stability manufacturing parameters that are compatible with the interlayer shrinkage matching relationship.

[0046] In step S50, the process of outputting interlayer stability manufacturing parameters that are compatible with the interlayer shrinkage matching relationship is as follows: Based on the residual stress distribution deviation, the residual stress offset in each region is mapped to the corresponding stress concentration location in the interlayer thermal stress distribution model of the pipe wall, thus determining the area of ​​influence of the residual stress deviation on interface stability. Using the global pipe wall residual stress distribution deviation data as a correction basis, a coordinate-to-coordinate spatial mapping mechanism is established based on the previously constructed three-dimensional interlayer thermal stress distribution model of the pipe wall. The quantitative data such as the residual stress release offset, stress excess deviation, and stress deficiency deviation in each axial, radial, and circumferential region measured in the experiment are accurately projected to the coordinate points of the corresponding grid cells in the thermal stress model. Through spatial superposition and comparison, the residual stress deviation area is verified to be consistent with the original model. By analyzing the overlap and deviation amplitude matching relationship between stress concentration areas and interlayer shrinkage mismatch areas, we can distinguish between areas affected by single stress deviations and areas with defects caused by multiple coupled factors. This allows us to accurately identify weak interfacial areas corresponding to various deviation problems such as uneven residual stress distribution, insufficient stress compensation, and excessive release of residual stress. Furthermore, by combining the stress transmission law of interlayer interfaces in thermal pipelines, we can analyze the secondary accumulation and release mechanism of residual stress deviations during hygrothermal water absorption, freeze-thaw expansion, and temperature alternation cycles. Ultimately, we can accurately pinpoint the core influencing areas of micro-debonding, microcrack propagation, and interlayer peeling induced by residual stress deviations, thus providing clear and precise control targets for subsequent process targeted corrections.

[0047] Based on the changes in interlaminar peeling propagation rate under different cycles, the attenuation rate of interfacial bonding strength was calculated. The attenuation rate of bonding strength in each region was numerically fitted with the deviation of residual stress distribution at the corresponding location, and the fitted regression equation or interpolation function was used as the constraint relationship between the two. Based on the interlaminar peeling evolution time-series data collected from multiple rounds of wet-heat freeze-thaw cycles, the dynamic changes in defect propagation area, peeling depth, and interfacial acoustic attenuation coefficient under different cycles were extracted. The instantaneous velocity and average propagation rate of interlaminar peeling propagation were calculated cycle by cycle using a differential algorithm, distinguishing the damage characteristics of the three stages: initial slow propagation, mid-term stable propagation, and late-term rapid unstable propagation. Using a composite material interlaminar shear strength testing method, the initial and remaining interfacial bonding strengths of the original unaged sample and samples after different cycles were detected. The interfacial bonding strength of each defect region was calculated using an exponential decay degradation model. Attenuation rate: Using the residual stress distribution deviation in each region as the independent variable and the interface bond strength attenuation rate as the dependent variable, the residual stress distribution deviation in each stress concentration region is normalized. The stress peak value in the initial non-uniform residual stress field of the region is used as the normalization benchmark to obtain the dimensionless residual stress deviation. A spatial position correction coefficient is introduced, which is determined based on the axial distance between the stress concentration location and the pipe end. The closer the location is to the end and the weaker the constraint, the larger the correction coefficient is assigned. An environmental cycle correction coefficient is introduced, which is the ratio of the actual cycle number to the design reference cycle number. Using the dimensionless residual stress deviation as the base and the product of the spatial position correction coefficient and the environmental cycle correction coefficient as the exponent, a power function-form quantitative constraint relationship is constructed. Through this power function relationship, the corresponding predicted value of the interface bond strength attenuation rate can be calculated from the residual stress distribution deviation value in any region.

[0048] Based on the constraint relationship, the melt viscosity control parameters of the inner liner layer, the residence time of the barrier layer, and the wetting state parameters of the reinforcing layer in the co-extrusion molding stage are adjusted in reverse. At the same time, the heating power distribution, traction disturbance amplitude, and cooling airflow parameters in the gradient heat setting stage are adjusted. Based on the strength attenuation-stress deviation constraint quantification relationship, a closed-loop correction logic is formed to control the molding process in reverse from the interface failure characteristics. Precise parameter optimization is implemented in two major stages. In the multi-layer co-extrusion molding stage, for areas with large residual stress deviation and severe interface attenuation, the extrusion temperature of the inner liner layer and the screw shear speed are specifically fine-tuned to precisely control the intrinsic viscosity of the melt and reduce the difference in melt rheological response between layers. The opening of the barrier layer diversion channel and the extrusion conveying are optimized. The rate is precisely controlled to manage the residence time of the melt flow channel in the barrier layer, mitigating the shrinkage timing deviation caused by heat conduction lag. The impregnation tension of the reinforcing layer fiber and the die pressure are adjusted to improve the uniformity of melt wetting and diffusion onto the fiber skeleton, reducing interlayer rheological asymmetry and initial molding stress from the source. During the gradient heat setting stage, the heating power density of each defect area along the tube wall axis is redistributed to appropriately balance the heat input in areas with high stress deviation. The amplitude of low-frequency reciprocating disturbance of the traction mechanism is optimized to match the interlayer relaxation rate. The cooling fan pressure, air volume, and air delivery uniformity are adjusted in zones to correct the shrinkage mismatch caused by excessively fast or slow local cooling, achieving coordinated correction of co-extrusion rheological parameters and heat setting control parameters.

[0049] The manufacturing parameters are iteratively corrected based on the interface stability response results after cyclic loading to obtain a combination of co-extrusion rheological parameters and gradient heat setting parameters that satisfy the interlayer shrinkage matching relationship, and the interlayer stability manufacturing parameters are output. The preliminarily corrected co-extrusion rheological parameters and gradient heat setting parameters are then implemented into the production line for trial production and sample preparation. The trial-produced repaired tubes are then subjected to a standard alternating damp heat-freeze-thaw cycle accelerated aging verification test. The interlayer peeling propagation rate, residual stress release uniformity, interface bonding strength retention rate, and tube wall deformation stability are monitored throughout the process. The interface stability response data after multiple rounds of tests are compared to determine the interlayer shrinkage matching effect under the current process parameter combination. If there are still problems with local stress deviation and excessive strength attenuation, the closed-loop process of stress deviation mapping, strength attenuation calculation, and process reverse adjustment is repeated to carry out multiple rounds of iterative correction, gradually reducing the differences in interlayer rheology, curing time, and shrinkage mismatch. When the sample has completed the rated number of cycles, the test is completed. When there is no obvious interlayer delamination, the residual stress is uniformly distributed, and the attenuation rate of the interface bonding strength meets the design threshold requirements, the current parameter combination is determined to have reached the optimal matching state. Finally, standardized interlayer stability manufacturing parameters that are suitable for the interlayer shrinkage matching relationship of multi-layer structures and for long-term wet and hot freeze-thaw cycles are locked and output. The interlayer stability manufacturing parameters consist of a co-extrusion rheological parameter group and a gradient heat-setting parameter group. The co-extrusion rheological parameter group includes the extrusion temperature of the inner liner, the screw shear speed of the inner liner, the opening of the flow channel of the barrier layer, the extrusion conveying rate of the barrier layer, the impregnation tension of the fiber of the reinforcing layer, and the die pressure of the reinforcing layer. The gradient heat-setting parameter group includes the heating power density of each axial zone, the low-frequency reciprocating disturbance amplitude of the traction mechanism, the cooling fan pressure of each axial zone, the cooling fan air volume of each axial zone, and the air supply uniformity index of each axial zone. Based on the interlayer stability manufacturing parameters, the stable mass production of thermally repaired pipes with high hydrolysis resistance, high temperature resistance, and high interface stability is achieved.

[0050] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A hydrolysis-resistant and high-temperature-resistant thermal repair pipe and its preparation process, characterized in that: Includes the following steps: Using the melt pressure pulsation phase change signal from the screw head outlet to the shaping sleeve inlet area as a synchronization reference, the intrinsic viscosity decay rate of the inner liner melt, the residence time of the barrier layer melt, and the wetting state parameters of the reinforcing layer melt are collected. The melt state parameters of each layer are correlated and processed to construct the interlayer rheological asymmetry index. Based on the interlayer rheological asymmetry index, the curing rate changes and freezing time differences of the inner lining, barrier layer and reinforcement layer during the cooling and shaping process are calculated to obtain the volume shrinkage rate differences of each layer. Combined with the thermal conduction hysteresis characteristics of the barrier layer, the interlayer shrinkage mismatch is quantitatively corrected to construct the interlayer thermal stress distribution model of the pipe wall. Based on the interlayer thermal stress distribution model of the pipe wall, the stress gradient and peak region of the interface between the inner lining layer and the barrier layer are extracted, the stress concentration location is located, and the heating power, traction disturbance amplitude and cooling airflow parameters are matched with the interlayer shrinkage rate according to the interface stress characteristics. A non-uniform residual stress field adapted to the interlayer shrinkage difference is formed through gradient thermal shaping. For repaired pipes with non-uniform residual stress fields, accelerated aging tests were conducted on sampled pipes under alternating damp heat and freeze-thaw cycles. The radial deformation response sequence of the pipe wall and the evolution characteristics of interlayer peeling were collected under different water content conditions. Based on the correspondence between the amount of residual stress release and the interface deformation change, the deviation of residual stress distribution in each region was determined. The residual stress distribution deviation in each region is mapped to the stress concentration location. The interface bonding strength attenuation rate, which is determined by the peeling cycle, is used as a constraint to adjust the co-extrusion rheological properties and gradient heat setting process in a feedback linkage manner, and output interlayer stability manufacturing parameters that are compatible with the interlayer shrinkage matching relationship.

2. The hydrolysis-resistant and high-temperature-resistant thermal repair pipe and its preparation process according to claim 1, characterized in that, The process of constructing the interlayer rheological asymmetric index is as follows: During the multi-layer co-extrusion molding process, the melt pressure fluctuation signals of the screw head outlet area and the shaping sleeve inlet area are continuously collected, and the phase change nodes within the pressure pulsation cycle are extracted. The pressure phase synchronization points of adjacent areas are used as the time calibration reference for different detection parameters. The intrinsic viscosity decay rate of the inner liner melt during shear flow, the change in residence time of the barrier layer melt in the flow channel, and the degree of wetting and diffusion of the reinforcing layer melt on the fiber-reinforced structure were obtained respectively, and a sequence of melt state parameters for the corresponding layers was established. Based on the pressure pulsation phase synchronization relationship, the sequence of melt state parameters of each layer is time-aligned; The time-aligned melt state parameter sequences of each layer are subjected to difference calculation under the same phase reference, and the variance and mean deviation of the obtained difference sequence are calculated. The weighted combination value of variance and mean deviation is used as the correlation processing result characterizing the coupling deviation between the changes in the rheological state of each layer of melt. Based on the correlation processing results, rheological asymmetry features characterizing the degree of asynchronous melt response of each layer are extracted. According to the differences in rheological response between the inner liner and the barrier layer, and between the barrier layer and the reinforcement layer, the amplitude of state change and response delay time of each layer are weighted and an interlayer rheological asymmetry index is constructed to describe the interlayer rheological matching state.

3. The hydrolysis-resistant and high-temperature-resistant thermal repair pipe and its preparation process according to claim 1, characterized in that, The process of obtaining the difference in volume shrinkage rate of each layer is as follows: Based on the differences in response delay time and amplitude of each layer in the interlayer rheological asymmetry index, the phase hysteresis is converted into temperature hysteresis through time and temperature equivalent translation factors. The additional heat accumulation value and the decrease in molecular chain motion degrees of freedom of each layer during the cooling stage are calculated based on the temperature hysteresis, thereby converting the differences in rheological state into changes in heat release and the degree of restriction of molecular chain motion during the cooling stage. The temperature change trajectories of the inner lining layer, barrier layer and reinforcement layer in the shaping and cooling area are obtained, and the migration speed of the curing interface and the curing completion time of each layer are calculated in combination with the thermal diffusion characteristics of each layer material. Based on the time interval between the completion times of each layer's curing, the differences in freezing sequence between different layers are determined, and the changes in volume shrinkage rate of the corresponding region are calculated by combining the initial melt temperature, cooling rate, and thermal expansion coefficient of each layer. By correlating the changes in volume shrinkage rate of different layers according to radial position and axial forming direction, interlayer shrinkage difference parameters reflecting the synchronous shrinkage capability of multilayer structures are obtained.

4. The hydrolysis-resistant and high-temperature-resistant thermal repair pipe and its preparation process according to claim 1, characterized in that, The process of constructing the interlayer thermal stress distribution model of the pipe wall is as follows: Based on the interlayer shrinkage difference parameter, the radial shrinkage difference of the inner lining, barrier layer and reinforcement layer during the cooling process is obtained, and the initial shrinkage mismatch relationship of different interlayer interfaces is established. Data on the temperature gradient change along the thickness direction of the barrier layer are collected, the heat transfer delay time inside the barrier layer is calculated, and the actual shrinkage response state of the barrier layer is compensated in time based on the heat conduction hysteresis characteristics. The time-compensated barrier layer shrinkage response state is synchronously matched with the shrinkage state of adjacent layers to calculate the transient shrinkage constraint amount of each interface region. Based on the correspondence between the material's elastic modulus, interface bonding parameters, and shrinkage constraint, a model for the distribution of interlayer thermal stress in the pipe wall, including radial stress, tangential stress, and interface shear stress distribution, is established.

5. The hydrolysis-resistant and high-temperature-resistant thermal repair pipe and its preparation process according to claim 1, characterized in that, The process of locating stress concentration points is as follows: Based on the interlayer thermal stress distribution model of the pipe wall, the interface region between the inner lining and the barrier layer is spatially discretized to obtain interface stress distribution data corresponding to different radial positions. Calculate the radial stress gradient, tangential stress gradient, and shear stress amplitude within the interface region respectively, and establish a multidimensional stress gradient characteristic matrix. Based on the stress gradient feature matrix, the local stress rapidly changing region is identified. The segment where the stress gradient amplitude at any spatial discrete point in the interface region exceeds twice the average stress gradient amplitude of the interface region and the stress gradient change rate between two adjacent discrete points exceeds a preset threshold is determined as the stress rapidly changing region. The stress peak value, duration and spatial diffusion range at the corresponding location are then extracted. By spatially mapping the stress peak region with the interlayer shrinkage mismatch region, the location of stress concentration that may lead to interfacial delamination evolution during long-term humid heat and temperature cycling can be determined.

6. The hydrolysis-resistant and high-temperature-resistant thermal repair pipe and its preparation process according to claim 1, characterized in that, The process of forming a non-uniform residual stress field that adapts to the difference in interlayer shrinkage is as follows: The stress level range of each axial region is determined based on the location of stress concentration, and the target compensation shrinkage amount required for each region is calculated based on the characteristics of the interface stress gradient. The stress level range of each axial region is mapped and matched with the target compensation shrinkage amount. Based on the mapping and matching results, the correspondence between each stress concentration region and the local heating power, traction disturbance amplitude and cooling airflow intensity is established. To address the degree of shrinkage mismatch in different axial regions, the local heating power, traction disturbance amplitude, and cooling airflow intensity during the gradient heat setting process were adjusted accordingly. Collect data on the radial dimension change and temperature response of the tube wall during the heat setting process, and calculate the deviation between the actual shrinkage trajectory and the target shrinkage matching trajectory in real time. Based on the deviation results, the heat setting parameters of different regions are iteratively adjusted to form a non-uniform residual stress field corresponding to the shrinkage differences of each layer.

7. The hydrolysis-resistant and high-temperature-resistant thermal repair pipe and its preparation process according to claim 1, characterized in that, The process of collecting the radial deformation response sequence of the pipe wall and the evolution characteristics of interlayer peeling under different water content states is as follows: For the repaired tube that forms a non-uniform residual stress field, samples are taken from the tube based on the high stress area and corresponding environmentally sensitive area determined by the interlayer thermal stress distribution model of the tube wall. For the samples, select the frequency of wet and hot alternation, the path of water content change and the range of freeze-thaw temperature cycles that correspond to the actual service conditions, and carry out environmental loading treatment for accelerated aging tests. During the cyclic loading process, the changes in moisture content, radial expansion displacement response, axial deformation, and acoustic wave propagation characteristics of different regions of the sample were collected simultaneously. Based on the water migration state in different cyclic stages, the radial deformation response sequence is divided into stages and time sequence synchronization is performed to extract the deformation rate difference and recovery characteristics corresponding to the wet heat water absorption stage and the freeze expansion stage. By combining the relationship between the changes in acoustic wave propagation at the interlayer interface and the distribution of local deformation anomalies, the interlayer peeling evolution characteristics that change with the number of cycles are extracted.

8. The hydrolysis-resistant and high-temperature-resistant thermal repair pipe and its preparation process according to claim 1, characterized in that, The process of determining the residual stress distribution deviation in each region is as follows: Based on the interlayer peeling evolution characteristics, the amount of interface deformation expansion and peeling growth rate under different cycle cycles were obtained; The residual stress release of each region before and after environmental cycling is calculated. The residual stress release of each region is the independent variable and the radial deformation response of the interface is the dependent variable. A piecewise linear interpolation method is used to establish the mapping relationship curve between the two. The radial deformation response of each region interface is compared with the deformation response under the theoretical steady state. The deviation between the two is substituted into the mapping relationship curve for back calculation to obtain the regional residual stress release offset. The residual stress release offset of each region is compared with the initial non-uniform residual stress distribution state to determine the residual stress distribution deviation at different locations.

9. The hydrolysis-resistant and high-temperature-resistant thermal repair pipe and its preparation process according to claim 1, characterized in that, The process of outputting interlayer stability manufacturing parameters that are compatible with the interlayer shrinkage matching relationship is as follows: Based on the residual stress distribution deviation, the residual stress offset of each region is mapped to the corresponding stress concentration location in the interlayer thermal stress distribution model of the pipe wall to determine the area where the residual stress deviation affects the interface stability. Based on the change in the interlayer peeling propagation rate under different cycles, the attenuation rate of interfacial bonding strength is calculated, and the attenuation rate of bonding strength in each region is numerically fitted with the deviation value of residual stress distribution at the corresponding position. The fitted regression equation or interpolation function is used as the constraint relationship between the two. Based on the constraint relationship, adjust the melt viscosity control parameters of the inner liner, the residence time of the barrier layer and the wetting state parameters of the reinforcing layer in the co-extrusion molding stage, and adjust the heating power distribution, traction disturbance amplitude and cooling airflow parameters in the gradient heat setting stage. The manufacturing parameters are iteratively corrected by the interface stability response results after cyclic loading to obtain a combination of co-extrusion rheological parameters and gradient thermal setting parameters that satisfy the interlayer shrinkage matching relationship, and the interlayer stability manufacturing parameters are output.

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