Buried flexible composite pipe external binning temperature control wax prevention and stress regulation method and device

Abstract

The application discloses a buried flexible composite pipe external binning temperature control wax-proofing and stress regulation method and device, and relates to the technical field of oil and natural gas transportation. The method comprises the following steps: determining a target pipe section, and determining the environmental boundary parameters and the operation boundary parameters of the target pipe section. Then, based on the parameters, the PCM phase change temperature is designed, the PCM phase change layer thickness is calculated, and the PCM phase change latent heat is calculated. Then, according to the calculation results, the selection and structure parameters of the PCM are determined. An outer wrapping PCM composite protective sleeve is installed outside the target pipe section, which comprises an anti-pressure wear-resistant outer protective layer, a PCM sealing cavity layer and a heat conduction enhancement layer. The outer wrapping PCM composite protective sleeve is used to absorb heat in the pipeline operation temperature rising stage and release heat in the temperature dropping or shutdown stage, so that the temperature control wax-proofing and stress regulation are realized. The problems that the existing measures such as external insulation, heat tracing or heating station often have high energy consumption, complex reconstruction, great construction influence and poor engineering implementability are solved.

Description

Technical Field

[0001] This application relates to the field of oil and gas transportation technology, and in particular to a method and device for temperature control, wax prevention and stress regulation of external compartments in buried flexible composite pipes. Background Technology

[0002] In buried oil transportation (or gathering) operations, daily / seasonal fluctuations in surface temperature affect the pipe's surrounding temperature field through soil heat transfer. When the fluid temperature inside the pipe decreases or cools, the pipe's inner wall temperature may approach or fall below the wax-sensitive temperature range, inducing wax deposition, leading to increased transportation resistance, increased cleaning frequency, and increased energy consumption. Simultaneously, the coupling effect of temperature gradient and internal pressure causes fluctuations in thermal stress between the flexible composite pipe layers, which, over long-term cycling, may lead to interface fatigue and performance degradation risks.

[0003] Existing measures such as external insulation, heat tracing, or heating stations often have problems such as high energy consumption, complex modification, and significant construction impact; if an embedded phase change layer is required for an in-service pipeline, the original laminated structure of the pipeline needs to be changed, resulting in poor engineering feasibility. Summary of the Invention

[0004] In this application embodiment, a method for temperature control, wax prevention, and stress regulation of external compartments in buried flexible composite pipes is provided. This solves the problems of high energy consumption, complex modification, significant construction impact, and poor engineering feasibility of existing measures such as external insulation, heat tracing, or heating stations. This application achieves wax prevention and thermal stress regulation without damaging the pressure-bearing structure of the pipe, while also considering soil pressure resistance, water and oil resistance, and wear resistance and durability in buried environments.

[0005] In a first aspect, embodiments of this application provide a method for external compartmentalized temperature control, wax prevention, and stress regulation of buried flexible composite pipes. The method includes: determining the target pipe section of the in-service buried flexible composite pipe and obtaining environmental boundary parameters and operational boundary parameters of the target pipe section; wherein the environmental boundary parameters include the ambient soil temperature and the minimum fluid temperature during normal operation of the target pipe section, and the operational boundary parameters include the instantaneous fluid temperature, the initial temperature when crude oil begins to enter the target pipe section, and the temperature reached by the crude oil at the end of the target pipe section; based on the environmental boundary parameters and operational boundary parameters, performing PCM phase change temperature design, PCM phase change layer thickness calculation, and PCM phase change latent heat calculation; and based on the designed PCM phase change temperature and the calculated PCM phase change latent heat... The PCM selection is determined, and its structural parameters are determined based on the calculated phase change layer thickness. An outer PCM composite protective sleeve is installed on the outside of the target pipe section, positioned on the outermost side of the buried flexible composite pipe and in contact with its outer protective layer. The outer PCM composite protective sleeve includes an outer pressure-resistant and wear-resistant outer protective layer, a middle PCM sealing cavity layer, and an inner thermally conductive reinforcement layer. The material for the middle PCM sealing cavity layer is selected based on the PCM selection, and its structure is designed based on the PCM's structural parameters. The installed outer PCM composite protective sleeve absorbs heat during the heating phase of the buried flexible composite pipe's operation and releases heat during the cooling or shutdown phases to achieve temperature control, wax prevention, and stress regulation.

[0006] In one possible implementation, the PCM phase change temperature is set between the crude oil wax precipitation point temperature and the lowest fluid temperature during normal operation of the target pipe section, expressed as: ;in, This refers to the wax precipitation point temperature of crude oil. To ensure a safe temperature control margin, This refers to the PCM phase transition temperature. This is the lowest fluid temperature during normal operation of the target pipe section.

[0007] In one possible implementation, the calculation of PCM phase change layer thickness and PCM phase change latent heat includes: setting an initial PCM phase change latent heat, substituting it into the PCM phase change layer thickness calculation formula to obtain the PCM phase change layer thickness; based on the obtained PCM phase change layer thickness, determining whether the initial PCM phase change latent heat is greater than or equal to a preset condition; if it is greater than or equal to the preset condition, using the initial PCM phase change latent heat as the actual PCM phase change latent heat, and using the PCM phase change layer thickness as the actual PCM phase change layer thickness; if it is less than the preset condition, using the new PCM phase change latent heat value calculated according to the preset condition formula as the initial PCM phase change latent heat, substituting it into the PCM phase change layer thickness calculation formula to obtain a new PCM phase change layer thickness, until the new PCM phase change latent heat value calculated based on the new PCM phase change layer thickness is greater than or equal to the preset condition, using the new value as the actual PCM phase change latent heat, and using the new PCM phase change layer thickness as the actual PCM phase change layer thickness.

[0008] In one possible implementation, the formula for calculating the thickness of the PCM phase change layer includes: ;in, The thickness of the PCM phase change layer. The outer radius of the target pipe section, The thickness of the slip-able interface layer, The overall heat transfer coefficient of the pipeline, The target pipe section's heat dissipation surface area. For operating temperature, This refers to the PCM phase transition temperature. For the ambient soil temperature, Target temperature control time / safe shutdown time The fluid mass within the target pipe section. Specific heat capacity of the fluid For the density of PCM, The initial latent heat of phase transition of the PCM. The length of the target pipe section, It is a mathematical constant.

[0009] In one possible implementation, the preset condition is: ;in, For time variables, The instantaneous temperature of the fluid. The ambient / surface temperature is a function that varies with time. For the integral of the time variable, For the quality of crude oil within the target pipeline section, For isobaric specific heat capacity, This is the initial temperature at which crude oil begins to enter the target pipe section. The temperature reached by the crude oil at the end of the target pipe section. The thickness of the PCM phase change layer.

[0010] In one possible implementation, the outer PCM composite protective sleeve adopts a segmented circumferential sleeve structure or a strip-wound structure, and is closed and fixed by mechanical locking components, clamps, ferrules or circumferential tensioning bands.

[0011] In one possible implementation, the pressure-resistant and wear-resistant outer protective layer is a composite structure of a load-bearing skeleton layer and a wear-resistant shell layer; wherein, the load-bearing skeleton layer is a honeycomb skeleton, circumferential reinforcing ribs, or a high-modulus composite strip layer, used to disperse soil pressure and local indentations caused by vehicle dynamic loads.

[0012] In one possible implementation, the PCM sealing cavity layer includes multiple independent sealing units, each filled with a phase change material, and a barrier layer is provided on the outside of the sealing unit to prevent soil moisture or oil from seeping in and causing the phase change material to fail.

[0013] In one possible implementation, the thermally conductive reinforcement layer is a high thermal conductivity sheet layer, a thermally conductive filler layer, or a thermally conductive mesh layer, used to improve the heat flux transfer between the phase change material and the outer sheath of the target pipe section; a slip-able interface layer is provided between the thermally conductive reinforcement layer and the outer sheath of the target pipe section to absorb the relative displacement caused by thermal expansion and contraction.

[0014] Secondly, embodiments of this application provide a buried flexible composite pipe external compartment temperature control, wax prevention, and stress regulation device. This device includes: an acquisition module, used to determine the target pipe section of the in-service buried flexible composite pipe and acquire the environmental boundary parameters and operational boundary parameters of the target pipe section; wherein the environmental boundary parameters include the ambient soil temperature and the minimum fluid temperature during normal operation of the target pipe section, and the operational boundary parameters include the instantaneous fluid temperature, the initial temperature when crude oil begins to enter the target pipe section, and the temperature reached by the crude oil at the end of the target pipe section; and a determination module, used to design the PCM phase change temperature, calculate the PCM phase change layer thickness, and calculate the PCM phase change latent heat based on the environmental boundary parameters and operational boundary parameters; and to determine the PCM phase change temperature and calculated PCM phase change latent heat based on the designed PCM phase change temperature and calculated PCM phase change latent heat. The latent heat of change determines the selection of the PCM, and the structural parameters of the PCM are determined based on the calculated phase change layer thickness. An installation module is used to install an outer PCM composite protective sleeve on the outside of the target pipe section, positioning it at the outermost edge of the buried flexible composite pipe and adhering to its outer protective layer. The outer PCM composite protective sleeve includes an outer pressure-resistant and wear-resistant protective layer, a middle PCM sealing cavity layer, and an inner thermally conductive reinforcement layer. The material for the middle PCM sealing cavity layer is selected based on the PCM type, and its structure is designed based on the PCM's structural parameters. The installed outer PCM composite protective sleeve absorbs heat during the heating phase of the buried flexible composite pipe's operation and releases heat during the cooling or shutdown phases, achieving temperature control, wax prevention, and stress regulation.

[0015] One or more technical solutions provided in this application embodiment have at least the following technical effects: This application embodiment provides a method for external compartmentalized temperature control, wax prevention, and stress regulation of buried flexible composite pipes. The method involves determining the target pipe section, its environmental boundary parameters, and operational boundary parameters. Based on these parameters, the PCM phase change temperature is designed, the PCM phase change layer thickness is calculated, and the PCM phase change latent heat is calculated. The selection and structural parameters of the PCM are then determined based on the calculation results. An external PCM composite protective sleeve is installed on the outside of the target pipe section, comprising a pressure-resistant and wear-resistant outer protective layer, a PCM sealing cavity layer, and a thermally conductive enhancement layer. The external PCM composite protective sleeve absorbs heat during the pipeline's heating phase and releases heat during cooling or shutdown phases to achieve temperature control, wax prevention, and stress regulation. This solves the problems of existing measures such as external insulation, heat tracing, or heating stations, which often suffer from high energy consumption, complex modifications, significant construction impact, and poor engineering feasibility. This application achieves wax prevention and thermal stress control without damaging the pressure-bearing structure of the pipe body, while also taking into account soil pressure resistance, water and oil resistance, and wear resistance and durability in buried environments. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments of this application or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 A flowchart illustrating a method for external compartmentalized temperature control, wax prevention, and stress regulation of buried flexible composite pipes, provided as an embodiment of this application.

[0018] Figure 2 This is a schematic diagram of the outer PCM composite protective sleeve provided in the embodiments of this application.

[0019] Figure 3 This is a schematic diagram of the PCM sealing cavity layer structure provided in the embodiments of this application.

[0020] Figure 4 A schematic diagram illustrating the construction and installation process of an in-service buried flexible composite pipe provided in this application embodiment.

[0021] Figure 5 This is a schematic diagram of an apparatus for external compartmentalized temperature control, wax prevention, and stress regulation of buried flexible composite pipes, provided in an embodiment of this application. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0023] The following description of some technologies involved in the embodiments of this application is provided to aid understanding and should be considered merely exemplary. Therefore, those skilled in the art should recognize that various changes and modifications can be made to the embodiments described herein without departing from the scope and spirit of this application. Similarly, for clarity and brevity, some descriptions of well-known functions and structures are omitted in the following description.

[0024] This application provides a method for external compartmentalized temperature control, wax prevention, and stress regulation of buried flexible composite pipes, such as... Figure 1 As shown, the method includes steps S101 to S105. Wherein, Figure 1 This is merely one execution sequence shown in the embodiments of this application and does not represent the only execution sequence for a buried flexible composite pipe external compartment temperature control, wax prevention, and stress regulation method. The execution sequence can be adjusted to achieve the desired final result. Figure 1 The steps shown can be performed in parallel or in reverse order.

[0025] S101: Identify the target pipe section of the in-service buried flexible composite pipe and obtain the environmental boundary parameters and operational boundary parameters of the target pipe section. The environmental boundary parameters include the ambient soil temperature and the minimum fluid temperature during normal operation of the target pipe section. The operational boundary parameters include the instantaneous fluid temperature, the initial temperature when crude oil begins to enter the target pipe section, and the temperature reached by the crude oil at the end of the target pipe section.

[0026] Specifically, a comprehensive assessment is conducted on in-service buried flexible composite pipes, including pipeline layout, length, diameter, burial depth, soil conditions, and operational history. Based on the assessment results, pipe sections with a high risk of wax deposition or significant temperature fluctuations are identified as target sections. Environmental boundary parameters refer to external environmental factors that affect the pipeline temperature field distribution and wax deposition risk. Operational boundary parameters refer to operational parameters that directly affect the fluid temperature and wax deposition risk within the pipeline.

[0027] S102: Based on environmental boundary parameters and operational boundary parameters, perform PCM phase change temperature design, PCM phase change layer thickness calculation, and PCM phase change latent heat calculation.

[0028] Specifically, PCM in this application refers to phase change material.

[0029] The PCM phase change temperature is set between the crude oil wax precipitation point temperature and the lowest fluid temperature during normal operation of the target pipe section. The expression is: .in, This refers to the wax precipitation point temperature of crude oil. To ensure a safe temperature control margin, This refers to the PCM phase transition temperature. This is the lowest fluid temperature during normal operation of the target pipe section.

[0030] Specifically, , , and All units are in °C.

[0031] Specifically, the design principle of PCM phase change temperature aims to ensure that when the fluid temperature inside the pipeline is close to or below the wax precipitation point of crude oil, the PCM can release latent heat through phase change, maintaining the pipe wall temperature above the wax-sensitive temperature, thereby preventing wax deposition. The crude oil wax precipitation point temperature refers to the temperature at which wax begins to precipitate from crude oil. When the pipe wall temperature is close to or below this temperature, the wax in the crude oil will begin to deposit on the pipe wall, increasing transport resistance. To ensure that the pipe wall temperature is always above the wax precipitation point, a temperature control safety margin needs to be considered in the design. The temperature control safety margin is usually determined based on pipeline operating experience, crude oil properties, and environmental conditions, and is generally taken as 3~5℃. The PCM phase change temperature refers to the temperature at which the PCM changes from a solid to a liquid (or from a liquid to a solid). At this temperature, the PCM absorbs or releases a large amount of latent heat. The minimum fluid temperature during normal operation of the target pipe section refers to the lowest temperature the fluid may reach during normal pipeline operation. This temperature is usually determined based on the pipeline's operating history, fluid characteristics, and environmental conditions.

[0032] The calculation methods for PCM phase change layer thickness and PCM phase change latent heat include the following:

[0033] Specifically, the calculation of the latent heat of phase change of the PCM is an iterative process designed to ensure that the latent heat of phase change of the selected PCM can meet the thermal requirements of the pipeline during shutdown or cooling phases.

[0034] It should be noted that the PCM phase change layer thickness refers to the radial thickness of the region where the phase change material is located in the PCM sealing cavity layer.

[0035] Set an initial latent heat of phase change for the PCM, and substitute it into the formula for calculating the PCM phase change layer thickness to obtain the PCM phase change layer thickness.

[0036] Specifically, the initial latent heat of phase change of the PCM can be set based on the physical properties of the material substrate.

[0037] Based on the obtained PCM phase change layer thickness, determine whether the initial PCM phase change latent heat is greater than or equal to the preset condition.

[0038] If the initial latent heat of phase change of the PCM is greater than or equal to the preset conditions, the latent heat of phase change of the PCM is taken as the actual latent heat of phase change of the PCM, and the phase change layer thickness of the PCM is taken as the actual phase change layer thickness of the PCM.

[0039] If the value is less than the preset condition, the new PCM phase change latent heat value calculated according to the preset condition formula will be used as the initial PCM phase change latent heat value. This value will be substituted into the calculation formula for the PCM phase change layer thickness to obtain a new PCM phase change layer thickness. This process will continue until the new PCM phase change latent heat value calculated based on the new PCM phase change layer thickness is greater than or equal to the preset condition. In this case, the new value will be used as the actual PCM phase change latent heat value, and the new PCM phase change layer thickness will be used as the actual PCM phase change layer thickness.

[0040] The formulas for calculating the thickness of the PCM phase change layer include: .in, The thickness of the PCM phase change layer. The outer radius of the target pipe section, The thickness of the slip-able interface layer, The overall heat transfer coefficient of the pipeline, The target pipe section's heat dissipation surface area. For operating temperature, This refers to the PCM phase transition temperature. For the ambient soil temperature, Target temperature control time / safe shutdown time The fluid mass within the target pipe section. Specific heat capacity of the fluid For the density of PCM, The initial latent heat of phase transition of the PCM. The length of the target pipe section, It is a mathematical constant.

[0041] Specifically, , , and The unit for all of them is meters (m). The unit is watts per square kelvin (W / m²). 2 ·K). The unit is square meters (m) 2 ). and The unit is ℃. The unit is seconds. The unit is kilogram (kg). The unit is joules per kilogram Kelvin (J / kg·K). The unit is kilograms per cubic meter (kg / m³) 3 ). The unit is joules per kilogram (J / kg).

[0042] The preset conditions are: .in, For time variables, The instantaneous temperature of the fluid. The ambient / surface temperature is a function that varies with time. For the integral of the time variable, For the quality of crude oil within the target pipeline section, For isobaric specific heat capacity, This is the initial temperature at which crude oil begins to enter the target pipe section. The temperature reached by the crude oil at the end of the target pipe section. The thickness of the PCM phase change layer.

[0043] Specifically, The unit is kilogram (kg). The unit is joules per kilogram Kelvin (J / kg·K). and All units are in °C.

[0044] S103: Determine the PCM selection based on the designed PCM phase change temperature and the calculated PCM phase change latent heat, and determine the PCM structural parameters based on the calculated phase change layer thickness.

[0045] Specifically, the phase change temperature range of the PCM is determined based on the pipeline operating environment and the wax-sensitive temperature zone. The selected PCM's phase change temperature should be between the crude oil wax precipitation point temperature and the lowest fluid temperature during normal operation of the target pipe section, with an appropriate safety margin (usually 3~5℃) to ensure that the pipe wall temperature remains above the wax precipitation point when the PCM releases its latent heat. If the surface temperature in the target pipe section fluctuates significantly, the PCM's phase change temperature range should be designed to be wider to cover a broader range of temperature changes; in areas with relatively stable temperatures, the PCM's phase change temperature can be designed more precisely to reduce unnecessary energy loss. Based on the previously calculated latent heat requirement of the PCM's phase change, a PCM (phase change material) with sufficient heat storage capacity is selected. The greater the latent heat of phase change, the more heat the PCM can release during the phase change process, and the more significant its effect on maintaining stable pipe wall temperature. Considering the long-term stability of the PCM, the selected material should have good chemical stability and thermal cycling stability to ensure that its latent heat of phase change does not significantly decrease after multiple phase change cycles. The feasibility of actual construction and installation can be considered, and the calculated phase change layer thickness can be adjusted appropriately to ensure that the PCM layer can be installed smoothly and fit well with other structural layers.

[0046] S104: Install an outer PCM composite protective sleeve on the outside of the target pipe section, so that it is located on the outermost side of the buried flexible composite pipe and is in contact with the outer protective layer of the buried flexible composite pipe.

[0047] Figure 2 This is a schematic diagram of the PCM composite protective sleeve provided in an embodiment of this application. The PCM composite protective sleeve includes an outer pressure-resistant and wear-resistant protective layer, a middle PCM sealing cavity layer, and an inner thermally conductive reinforcement layer. The material of the middle PCM sealing cavity layer is selected based on the type of PCM, and its structure is designed based on the structural parameters of the PCM.

[0048] The outer PCM composite protective sleeve adopts a segmented circumferential sleeve structure or a strip-wound structure, and is closed and fixed by mechanical locking parts, clamps, ferrules or circumferential tensioning bands.

[0049] The pressure-resistant and wear-resistant outer protective layer is a composite structure consisting of a load-bearing skeleton layer and a wear-resistant shell layer. The load-bearing skeleton layer is a honeycomb skeleton, circumferential reinforcing ribs, or a high-modulus composite strip layer, used to disperse soil pressure and localized indentations caused by vehicle dynamic loads.

[0050] Specifically, the compressive and abrasion-resistant outer protective layer is located on the outermost side, directly bearing external loads such as soil pressure, backfill compaction, vehicle dynamic loads, and localized stone indentations. It employs a composite structure of a load-bearing skeleton layer and a wear-resistant shell layer. The load-bearing skeleton layer can be a honeycomb skeleton, circumferential reinforcing ribs, or a high-modulus composite strip layer, used to distribute external loads and prevent localized indentations. The wear-resistant shell layer provides additional abrasion protection against soil particles and stones.

[0051] Figure 3 This is a schematic diagram of the PCM sealing cavity layer structure provided in the embodiments of this application. The PCM sealing cavity layer includes multiple independent sealing units, each of which is filled with phase change material, and a barrier layer is provided on the outside of the sealing unit to prevent soil moisture or oil from seeping in and causing the phase change material to fail.

[0052] Above the PCM sealing cavity layer, a barrier layer is provided to block water, oil, and seepage, further enhancing the barrier effect against external corrosive substances. An inspection / replacement port is also provided; this design facilitates partial replacement and maintenance of the sealing unit. When a sealing unit malfunctions, targeted treatment can be carried out through this inspection / replacement port, preventing the failure of a single unit from affecting the performance of the entire PCM sealing cavity layer. The overall structural design is reasonable, and the functions of each part are clearly defined, aiming to ensure that the outer PCM composite protective sleeve can stably perform its functions of temperature control and wax prevention in buried pressurized environments over a long period.

[0053] Specifically, the PCM sealing cavity layer, located in the middle layer, is the main housing space for the PCM (phase change material). The design of the sealing unit facilitates local replacement and maintenance, preventing the failure of individual units from affecting overall performance. A barrier layer is installed on the outside of the sealing unit to prevent soil moisture or oil from seeping in and causing phase change material failure. The barrier layer material must have good barrier properties to ensure the long-term stability of the PCM. The material for the sealing cavity layer is selected based on the chosen PCM type, and the structure is designed according to the PCM's structural parameters (such as the phase change layer thickness).

[0054] The thermally conductive reinforcement layer, which can be a high thermal conductivity sheet, a thermally conductive filler layer, or a thermally conductive mesh layer, is used to improve the heat flux transfer between the phase change material and the outer sheath of the target pipe section. A slip-type interface layer is provided between the thermally conductive reinforcement layer and the outer sheath of the target pipe section to absorb the relative displacement caused by thermal expansion and contraction.

[0055] Specifically, the thermally conductive reinforcement layer is located on the innermost side, closely attached to the outer protective layer of the buried flexible composite pipe. A sliding interface layer is provided between the thermally conductive reinforcement layer and the outer protective layer to absorb relative displacement caused by thermal expansion and contraction, reducing the risk of interface delamination.

[0056] Figure 4 A schematic diagram illustrating the construction and installation process of an in-service buried flexible composite pipe provided in this application embodiment. Figure 4 (a) in the diagram is a schematic of partial excavation. First, the target pipe section with a high risk of wax deposition or significant temperature fluctuations is identified, and an appropriate covering length, i.e., the length of the target pipe section, is set. Next, partial excavation is carried out on the target pipe section to expose the outer surface of the outer protective layer. Extra care must be taken during the excavation process to ensure that the outer protective layer is not damaged. After the excavation is completed, the exposed outer surface of the outer protective layer is cleaned and its dimensions are checked to prepare for subsequent processes and ensure that the outer covering structure can fit well with the pipe body. Figure 4 (b) in the diagram is a schematic diagram of the installation of the first module. Figure 4 (c) in the diagram shows the installation of the second module. After cleaning and verifying the outer surface of the pipe, a thermal coupling channel, i.e., a thermal enhancement layer, is laid according to the design requirements. If necessary during actual construction, an interface strain relief layer, i.e., a sliding interface layer, also needs to be laid. During the laying process, it is essential to ensure that the thermally conductive layer continuously adheres to the outer surface of the pipe, minimizing air gaps, as air gaps increase thermal resistance and affect heat transfer. Subsequently, the outer PCM composite protective sleeve is closed around the pipe using a segmented circumferential sleeve or strip-wound structure. After wrapping, circumferential locking and axial limiting of the outer wrapping structure are achieved using clamps, clips, or locking devices to ensure stable and good contact between the inner thermal coupling layer and the pipe body, thereby ensuring effective heat transfer. Figure 4(d) in the diagram illustrates the sealing and backfilling process. After the outer casing structure is installed, key areas such as longitudinal joints, end closures, and penetrations require continuous sealing and barrier treatment. Specifically, joint sealing tape can be used to seal the longitudinal joints. These measures create a complete and effective water-blocking, oil-blocking, and seepage-blocking path, preventing groundwater from seeping into the sealed chamber along the interface, thereby protecting the internal phase change materials and other structures from corrosion and maintaining their performance stability. Finally, during the backfilling stage, a layered backfilling method is adopted, with each layer compacted. This avoids large hard objects directly impacting the outer protective shell, ensuring that the outer casing structure maintains its shape stability and sealing performance during the backfilling process and in the subsequent long-term buried environment. This allows for rapid modification of in-service pipelines and ensures their long-term stable service.

[0057] S105: By utilizing the installed outer PCM composite protective sleeve, heat is absorbed during the heating phase of the buried flexible composite pipe and released during the cooling or shutdown phase, so as to achieve temperature control, wax prevention, and stress regulation.

[0058] Specifically, the PCM in the outer PCM composite protective sleeve has unique phase change characteristics, enabling it to absorb or release a large amount of latent heat within a specific temperature range. During the heating phase, the PCM (phase change material) absorbs and stores heat; during the cooling or shutdown phase, the PCM releases the stored latent heat, thereby maintaining the temperature stability of the environment surrounding the pipeline.

[0059] During the warm-up phase of buried flexible composite pipe operation, the temperature of the surrounding environment and the fluid inside the pipe rises, and heat is transferred to the external environment. At this time, the PCM (Polymer Complex) in the outer PCM composite protective sleeve begins to play the following roles: After reaching the phase change temperature, the PCM begins to absorb the heat transferred from the surrounding environment and the fluid inside the pipe, and undergoes a phase change (such as from solid to liquid), storing the heat as latent heat. Through the heat absorption of the PCM, the rate of temperature rise of the surrounding environment can be slowed down, reducing the impact of temperature fluctuations on the pipeline and reserving heat for the subsequent cooling phase. When the pipeline enters the cooling or shutdown phase, the temperature of the fluid inside the pipeline gradually decreases, and the pipe wall temperature also decreases accordingly. At this time, the PCM in the outer PCM composite protective sleeve begins to release the stored heat. The PCM releases a large amount of latent heat during the phase change process, transferring the stored heat back to the pipeline, maintaining the pipe wall temperature within a relatively stable range, and preventing the pipe wall temperature from dropping too quickly to the wax-sensitive temperature range. By maintaining the pipe wall temperature above the wax point, it effectively prevents the deposition of wax in the crude oil on the pipe wall, reduces transportation resistance, and reduces the frequency of pipe cleaning and energy consumption. In addition to its temperature control and anti-waxing functions, the outer PCM composite protective sleeve can effectively regulate thermal stress fluctuations in pipelines. During the heat absorption phase of heating and the heat release phase of cooling, the PCM can significantly mitigate changes in the radial temperature gradient of the pipeline, suppressing thermal stress fluctuations caused by temperature differences between the inside and outside of the pipeline. By mitigating the temperature gradient, it reduces structural stress caused by thermal expansion in the pipeline, lowers peak thermal stress and cyclic fluctuations, thereby reducing interlayer risks and improving the long-term stability and pressure resistance of the pipeline.

[0060] Through the aforementioned heat absorption and release processes, the outer PCM composite protective sleeve achieves the following effects throughout the entire operating cycle of the buried flexible composite pipe: It ensures the pipeline maintains a stable temperature environment under different operating conditions, reducing the impact of temperature fluctuations on pipeline performance. It effectively prevents wax deposition on the pipe wall, maintaining pipeline transport efficiency and reducing operating costs. It suppresses thermal stress fluctuations, improving the long-term stability and safety of the pipeline and extending its service life.

[0061] This application also provides a buried flexible composite pipe external compartment temperature control, wax prevention, and stress regulation device 500, such as... Figure 5 As shown, the device includes: an acquisition module 501, a determination module 502, and an installation module 503.

[0062] The acquisition module 501 is used to determine the target pipe section of the in-service buried flexible composite pipe and acquire the environmental boundary parameters and operational boundary parameters of the target pipe section. The environmental boundary parameters include the ambient soil temperature and the minimum fluid temperature during normal operation of the target pipe section. The operational boundary parameters include the instantaneous fluid temperature, the initial temperature when crude oil begins to enter the target pipe section, and the temperature reached by the crude oil at the end of the target pipe section.

[0063] The determination module 502 is used to design the PCM phase change temperature, calculate the PCM phase change layer thickness, and calculate the PCM phase change latent heat based on environmental boundary parameters and operational boundary parameters. Based on the designed PCM phase change temperature and the calculated PCM phase change latent heat, the PCM type is selected, and based on the calculated phase change layer thickness, the PCM structural parameters are determined.

[0064] The mounting module 503 is used to install an outer PCM composite protective sleeve on the outside of the target pipe section, positioning it at the outermost edge of the buried flexible composite pipe and adhering to its outer protective layer. The outer PCM composite protective sleeve includes an outer pressure-resistant and wear-resistant protective layer, a middle PCM sealing cavity layer, and an inner thermally conductive reinforcing layer. The material of the middle PCM sealing cavity layer is selected based on the type of PCM used, and its structure is designed based on the PCM's structural parameters. Utilizing the installed outer PCM composite protective sleeve, heat is absorbed during the heating phase of the buried flexible composite pipe's operation and released during the cooling or shutdown phases, achieving temperature control, wax prevention, and stress regulation.

[0065] Some modules in the apparatus described in this application can be described in the general context of computer-executable instructions that are executed by a computer, such as program modules. Generally, program modules include routines, programs, objects, components, data structures, classes, etc., that perform a specific task or implement a specific abstract data type. This application can also be practiced in distributed computing environments where tasks are performed by remote processing devices connected via a communication network. In distributed computing environments, program modules can reside in local and remote computer storage media, including storage devices.

[0066] The apparatus or module described in the above embodiments can be implemented by a computer chip or physical entity, or by a product with a certain function. For ease of description, the above apparatus is described by dividing it into various modules according to their functions. When implementing the embodiments of this application, the functions of each module can be implemented in one or more software and / or hardware. Of course, a module that implements a certain function can also be implemented by combining multiple sub-modules or sub-units.

[0067] The various embodiments described in this specification are presented in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on its differences from other embodiments. All or part of this application can be used in numerous general-purpose or special-purpose computer system environments or configurations.

[0068] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of this application.

Claims

1. A method for external compartmentalized temperature control, wax prevention, and stress regulation of buried flexible composite pipes, characterized in that, include: Identify the target pipe section of the in-service buried flexible composite pipe and obtain the environmental boundary parameters and operational boundary parameters of the target pipe section. The environmental boundary parameters include the ambient soil temperature and the minimum fluid temperature during normal operation of the target pipe section. The operational boundary parameters include the instantaneous fluid temperature, the initial temperature when crude oil begins to enter the target pipe section, and the temperature reached by the crude oil at the end of the target pipe section. Based on environmental boundary parameters and operational boundary parameters, we perform PCM phase change temperature design, PCM phase change layer thickness calculation, and PCM phase change latent heat calculation. The selection of PCM is determined based on the designed PCM phase change temperature and the calculated PCM phase change latent heat, and the structural parameters of PCM are determined based on the calculated phase change layer thickness. An outer PCM composite protective sleeve is installed on the outside of the target pipe section, positioned on the outermost side of the buried flexible composite pipe and in contact with the outer protective layer of the buried flexible composite pipe. The outer PCM composite protective sleeve includes an outer pressure-resistant and wear-resistant outer protective layer, a middle PCM sealing cavity layer, and an inner thermally conductive enhancement layer. The material of the middle PCM sealing cavity layer is selected based on the PCM type, and the structure is designed based on the PCM structural parameters. The installed PCM composite protective sleeve absorbs heat during the heating phase of the buried flexible composite pipe and releases heat during the cooling or shutdown phase, thereby achieving temperature control, wax prevention, and stress regulation.

2. The method for external compartmentalized temperature control, wax prevention, and stress regulation of buried flexible composite pipes according to claim 1, characterized in that, The PCM phase change temperature is set between the crude oil wax precipitation point temperature and the lowest fluid temperature during normal operation of the target pipe section. The expression is: ;in, This refers to the wax precipitation point temperature of crude oil. To ensure a safe temperature control margin, The phase transition temperature of PCM. This is the lowest fluid temperature during normal operation of the target pipe section.

3. The method for external compartmentalized temperature control, wax prevention, and stress regulation of buried flexible composite pipes according to claim 1, characterized in that, The methods for calculating the PCM phase change layer thickness and the PCM phase change latent heat include: Set an initial latent heat of phase change for the PCM, and substitute it into the formula for calculating the thickness of the PCM phase change layer to obtain the thickness of the PCM phase change layer. Based on the obtained PCM phase change layer thickness, determine whether the initial PCM phase change latent heat is greater than or equal to the preset condition. If the initial latent heat of phase change of the PCM is greater than or equal to the preset condition, the latent heat of phase change of the PCM is taken as the actual latent heat of phase change of the PCM, and the phase change layer thickness of the PCM is taken as the actual phase change layer thickness of the PCM. If the value is less than the preset condition, the new PCM phase change latent heat value calculated according to the preset condition formula will be used as the initial PCM phase change latent heat value. This value will be substituted into the calculation formula for the PCM phase change layer thickness to obtain a new PCM phase change layer thickness. This process will continue until the new PCM phase change latent heat value calculated based on the new PCM phase change layer thickness is greater than or equal to the preset condition. In this case, the new value will be used as the actual PCM phase change latent heat value, and the new PCM phase change layer thickness will be used as the actual PCM phase change layer thickness.

4. The method for external compartmentalized temperature control, wax prevention, and stress regulation of buried flexible composite pipes according to claim 3, characterized in that, The formulas for calculating the thickness of the PCM phase change layer include: ;in, The thickness of the PCM phase change layer. The outer radius of the target pipe section, The thickness of the slip-able interface layer, The overall heat transfer coefficient of the pipeline, The target pipe section's heat dissipation surface area. For operating temperature, The phase transition temperature of PCM. For the ambient soil temperature, Target temperature control time / safe shutdown time The fluid mass within the target pipe section. Specific heat capacity of the fluid For the density of PCM, The initial latent heat of phase transition of the PCM. The length of the target pipe section, It is a mathematical constant.

5. The method for external compartmentalized temperature control, wax prevention, and stress regulation of buried flexible composite pipes according to claim 4, characterized in that, The preset conditions are: ;in, For time variables, The instantaneous temperature of the fluid. The ambient / surface temperature is a function that varies with time. For the integral of the time variable, For the quality of crude oil within the target pipeline section, For isobaric specific heat capacity, This is the initial temperature at which crude oil begins to enter the target pipe section. The temperature reached by the crude oil at the end of the target pipe section. The thickness of the PCM phase change layer.

6. The method for external compartmentalized temperature control, wax prevention, and stress regulation of buried flexible composite pipes according to claim 1, characterized in that, The outer PCM composite protective sleeve adopts a segmented circumferential sleeve structure or a strip-wound structure, and is closed and fixed by mechanical locking parts, clamps, ferrules or circumferential tensioning bands.

7. The method for external compartmentalized temperature control, wax prevention, and stress regulation of buried flexible composite pipes according to claim 1, characterized in that, The pressure-resistant and wear-resistant outer protective layer is a composite structure of a load-bearing skeleton layer and a wear-resistant shell layer; wherein, the load-bearing skeleton layer is a honeycomb skeleton, circumferential reinforcing ribs or a high-modulus composite strip layer, used to disperse soil pressure and local indentations caused by vehicle dynamic load.

8. The method for external compartmentalized temperature control, wax prevention, and stress regulation of buried flexible composite pipes according to claim 1, characterized in that, The PCM sealing cavity layer includes multiple independent sealing units, each filled with phase change material, and a barrier layer is provided on the outside of the sealing unit to prevent soil moisture or oil from seeping in and causing the phase change material to fail.

9. The method for external compartmentalized temperature control, wax prevention, and stress regulation of buried flexible composite pipes according to claim 1, characterized in that, The thermally conductive reinforcement layer is a high thermal conductivity sheet layer, a thermally conductive filler layer, or a thermally conductive mesh layer, used to improve the heat flux transfer between the phase change material and the outer sheath of the target pipe section; A slip-able interface layer is provided between the thermally conductive reinforcement layer and the outer protective layer of the target pipe section to absorb the relative displacement caused by thermal expansion and contraction.

10. A device for external compartmentalized temperature control, wax prevention, and stress regulation of buried flexible composite pipes, characterized in that, The device performs the method as described in any one of claims 1 to 9, including: The acquisition module is used to determine the target pipe section of the in-service buried flexible composite pipe and acquire the environmental boundary parameters and operational boundary parameters of the target pipe section. The environmental boundary parameters include the ambient soil temperature and the minimum fluid temperature during normal operation of the target pipe section. The operational boundary parameters include the instantaneous fluid temperature, the initial temperature when crude oil begins to enter the target pipe section, and the temperature reached by the crude oil at the end of the target pipe section. The determination module is used to design the PCM phase change temperature, calculate the PCM phase change layer thickness, and calculate the PCM phase change latent heat based on environmental boundary parameters and operational boundary parameters; determine the PCM selection based on the designed PCM phase change temperature and the calculated PCM phase change latent heat; and determine the PCM structural parameters based on the calculated phase change layer thickness. The installation module is used to install an outer PCM composite protective sleeve on the outside of the target pipe section, positioning it at the outermost edge of the buried flexible composite pipe and adhering to its outer protective layer. The outer PCM composite protective sleeve includes an outer pressure-resistant and wear-resistant outer protective layer, a middle PCM sealing cavity layer, and an inner thermally conductive enhancement layer. The material of the middle PCM sealing cavity layer is selected based on the PCM type, and its structure is designed based on the PCM's structural parameters. The installed outer PCM composite protective sleeve absorbs heat during the heating phase of the buried flexible composite pipe's operation and releases heat during the cooling or shutdown phases to achieve temperature control, wax prevention, and stress regulation.

Images