A multi-layer composite pipe body with gradient self-repairing function and a preparation method thereof

Abstract

The application relates to a multilayer composite pipe body preparation method, which comprises the following steps: S1, winding rare earth modified basalt fibers on a core mold, pre-solidifying the basalt fiber reinforced layer at 80 DEG C for 30 min after impregnating a thermosetting resin, and preparing the basalt fiber reinforced layer; S2, spraying or blade coating a rare earth modified ATSP functional layer prepolymer on the inner surface of the reinforced layer to form a pre-solidified body; S3, before the ATSP layer is completely solidified, spraying a Eu 3+ 2DPA-1 intelligent coating of the multi-walled carbon nanotube to form an intelligent inner lining layer pre-solidified body; S4, placing the multilayer preform structure in a hot press tank and adopting a multi-section temperature control process for co-solidification; S5, demolding and cutting after solidification, assembling metal joints coated with a coupling agent, and realizing interface bonding through secondary solidification to prepare the composite pipe body. The application adopts a gradient structure of outer layer bearing, middle layer repairing and inner layer sensing, and the functions are synergistically efficient; the gradient intelligent repairing can be realized according to the damage degree and working conditions, over-repairing is avoided, and the pipe body reliability and service life are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of intelligent pipe technology for oil and gas fields, and in particular to a multi-layer composite pipe with gradient self-healing function and its preparation method. Background Technology

[0002] In the field of oil and gas field development, complex operating conditions such as ultra-deep wells, shale gas wells, and heavy oil thermal recovery wells place extremely high demands on the structural strength, corrosion resistance, wear resistance, and long-term service reliability of downhole tubing and casing. Traditional metal pipes are susceptible to H2S / CO2 corrosion, downhole fluid erosion, and geological load damage, and are gradually being replaced by lightweight, corrosion-resistant fiber-reinforced resin-based composite tubing, becoming the mainstream development direction for oil and gas extraction pipes.

[0003] Currently, most composite tubing on the market and under development adopts a single-layer or double-layer structure, such as glass fiber reinforced epoxy resin composite tubing. This type of structure has three major drawbacks in practical applications:

[0004] 1. Limited functionality: It can only achieve lightweight and basic corrosion resistance, but does not have self-healing or pipe condition sensing functions, and cannot meet the operation and maintenance needs of smart oil and gas fields.

[0005] 2. Difficult to repair: Once the tubing is damaged, it cannot be repaired in situ; the entire tubing string must be replaced, which significantly increases the cost of downhole operations and maintenance.

[0006] 3. Interface risks: The interlayer bonding is weak, and delamination and debonding are prone to occur. Under high temperature thermal cycling and long-term downhole fluid scouring conditions, the interlayer failure problem is particularly prominent.

[0007] To improve the repair performance of composite tubing, existing technologies attempt to introduce self-healing microcapsules, dynamic reversible covalent bonds, and other systems into the composite matrix. However, such solutions generally suffer from low repair efficiency, limited number of effective repairs, and poor compatibility between functional components and the resin matrix, making it difficult to achieve stable and long-lasting self-healing effects.

[0008] More importantly, current technologies do not yet offer a technical solution for the gradient structural integration of basalt fiber reinforced layers, dynamic ATSP functional layers, and intelligent 2DPA-1 lining layers. Nor have they developed a systematic design approach for IPN interface molecular fusion and dual-temperature graded repair. This makes it impossible to simultaneously meet the multiple requirements of pressure bearing, self-healing, intelligent sensing, and interface stability, and it is difficult to adapt to the long-term service requirements under extreme conditions of ultra-deep wells, high corrosion, and high wear. Summary of the Invention

[0009] The present invention aims to solve at least one of the technical problems existing in the prior art or related art.

[0010] Therefore, the purpose of this invention is to provide a multi-layer composite pipe with gradient self-healing function that integrates structural load-bearing, self-healing, intelligent sensing and corrosion resistance, and its preparation method.

[0011] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a multilayer composite tube with gradient self-healing function, comprising the following steps:

[0012] S1. Rare earth modified basalt fiber is laid on the core mold using a winding process, impregnated with thermosetting resin, and pre-cured at 80°C for 30 minutes to obtain a basalt fiber reinforced layer.

[0013] S2, spray or scrape the prepolymer of rare earth modified ATSP functional layer onto the inner surface of the basalt fiber reinforced layer to form a pre-cured body of rare earth modified ATSP functional layer.

[0014] S3, before the rare earth modified ATSP functional layer is fully cured, spray a Eu-containing coating onto its surface. 3+ A pre-cured body of rare earth modified 2DPA-1 smart inner liner is formed by combining 2DPA-1 smart coating with multi-walled carbon nanotubes.

[0015] S4, the multi-layer prefabricated structure obtained in step S3 is placed in an autoclave and co-cured using a multi-stage temperature control process;

[0016] S5, after curing, is demolded and cut. Metal joints with coupling agent coated on the inner surface are assembled at both ends of the tube. After secondary curing, the interface chemical bonding between the joint and the tube is completed, and a multi-layer composite tube is produced.

[0017] In the above technical solution, preferably, in step S4, the multi-stage temperature control process includes:

[0018] In the first stage, the temperature was kept at 150℃ for 1 hour to induce the formation of an interpenetrating polymer network (IPN) structure.

[0019] The second stage involves maintaining a constant temperature of 280℃ for 2 hours to achieve deep curing of the resin system.

[0020] In the third stage, the temperature is kept at 300℃ for 0.5 hours to activate the Diels-Alder dynamic covalent bonds in the rare earth modified ATSP functional layer.

[0021] In the above technical solution, preferably, during the 150°C heat preservation stage in step S4, the addition reaction of maleimide groups in the prepolymer of the rare earth modified ATSP functional layer with amino and hydroxyl groups in the rare earth modified 2DPA-1 smart liner layer is completed simultaneously to form a covalently cross-linked interpenetrating polymer network (IPN) structure.

[0022] In any of the above technical solutions, preferably, the outer diameter of the multi-layer composite pipe is Φ60.3mm-Φ177.8mm and the wall thickness is 5.0mm-15.0mm.

[0023] In the above technical solution, preferably, the thickness of the basalt fiber reinforcement layer accounts for 40%–60% of the pipe wall thickness, the thickness of the rare earth modified ATSP functional layer accounts for 20%–30% of the pipe wall thickness, and the thickness of the rare earth modified 2DPA-1 smart liner layer accounts for 10%–20% of the pipe wall thickness.

[0024] In any of the above technical solutions, preferably, the basalt fiber reinforcement layer is composed of rare earth modified basalt fiber and thermosetting resin, wherein the thermosetting resin is epoxy resin, phenolic resin or ATSP resin.

[0025] In the above technical solution, preferably, the rare earth modified basalt fiber is a basalt fiber modified by at least one oxide or acetate of lanthanum and europium.

[0026] In any of the above technical solutions, preferably, in step S5, the coupling agent is a rare earth coupling agent.

[0027] The second aspect of the present invention provides a multi-layer composite pipe with gradient self-healing function prepared by any of the preparation methods involved in the first aspect of the present invention. The multi-layer composite pipe is composed of a basalt fiber reinforcement layer, a rare earth modified ATSP functional layer, and a rare earth modified 2DPA-1 intelligent inner lining layer from the outside to the inside.

[0028] The basalt fiber reinforcement layer accounts for 40%–60% of the pipe wall thickness, the rare earth modified ATSP functional layer accounts for 20%–30% of the pipe wall thickness, and the rare earth modified 2DPA-1 smart liner layer accounts for 10%–20% of the pipe wall thickness. The rare earth modified ATSP functional layer contains Diels-Alder dynamic covalent bonds and a Yb(OTf)3 catalyst, and the rare earth modified 2DPA-1 smart liner layer contains Eu... 3+ Fluorescent tracers and carbon nanotubes.

[0029] Compared with existing technologies, the multilayer composite tubing with gradient self-healing function and its preparation method provided by this invention realizes integrated structural and functional design. It achieves synergistic efficiency through the three-layer gradient division of labor of outer layer bearing, middle layer repair, and inner layer sensing. At the same time, it constructs a gradient intelligent repair mode, which can match different damage levels and working conditions for on-demand repair and avoid over-repair. Moreover, relying on the IPN molecular-level fusion structure formed by the ATSP functional layer and the 2DPA-1 inner liner, it eliminates interlayer debonding from the root and greatly improves interface reliability. After the tubing is damaged, it can be repaired in situ without replacing the tubing string, reducing maintenance costs by 90%. It also achieves a laboratory equivalent service life of over 20 years and supports more than 5 effective repairs. It comprehensively breaks through the technical bottlenecks of existing composite tubing, such as single function, difficult repair, easy interface debonding, short life, and high operation and maintenance costs. Attached Figure Description

[0030] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0031] Figure 1 A layer structure diagram of the multilayer composite tube involved in the embodiment of the present invention is shown;

[0032] Figure 2 A schematic diagram illustrating the formation mechanism of the interlayer IPN structure between ATSP and 2DPA-1 involved in an embodiment of the present invention is shown.

[0033] Figure 3 The gradient self-healing mechanism and Eu involved in the embodiments of the present invention are illustrated. 3+ Schematic diagram of a real-time fluorescence monitoring system. Detailed Implementation

[0034] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0035] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0036] like Figures 1 to 3 As shown, a method for preparing a multilayer composite tube with gradient self-healing function according to an embodiment of the present invention includes the following steps:

[0037] S1. Rare earth modified basalt fiber is laid on the core mold using a winding process, impregnated with thermosetting resin, and pre-cured at 80°C for 30 minutes to obtain a basalt fiber reinforced layer.

[0038] S2, spray or scrape the prepolymer of rare earth modified ATSP (aromatic thermosetting polyester) functional layer onto the inner surface of the basalt fiber reinforced layer to form a precured body of rare earth modified ATSP functional layer.

[0039] S3, before the rare earth modified ATSP functional layer is fully cured, spray a Eu-containing coating onto its surface. 3+ A pre-cured body of rare earth modified 2DPA-1 smart inner liner is formed by combining 2DPA-1 smart coating with multi-walled carbon nanotubes.

[0040] In this step, 2DPA-1 is a two-dimensional polyarylamide, a novel two-dimensional polymer material formed by the polymerization of melamine monomers. It has a molecularly ordered layered structure and possesses extremely high wear resistance, impermeability, and resistance to media corrosion. It can form covalent crosslinks with other resins.

[0041] S4, the multi-layer prefabricated structure obtained in step S3 is placed in an autoclave and co-cured using a multi-stage temperature control process;

[0042] S5, after curing, is demolded and cut. Metal joints with coupling agent coated on the inner surface are assembled at both ends of the tube. After secondary curing, the interface chemical bonding between the joint and the tube is completed, and a multi-layer composite tube is produced.

[0043] In this embodiment, a process route of layered molding, gradient curing, and overall bonding is adopted, which can precisely control the molding quality and interface bonding state of each layer, effectively avoid defects such as interlayer material flow, uneven curing, and residual bubbles, significantly improve the consistency and stability of pipe preparation, and can adapt to the industrial continuous production needs of oil and gas field pipes, ensuring the stable and reliable performance of batch products.

[0044] In the above embodiments, preferably, in step S4, the multi-segment temperature control process includes:

[0045] In the first stage, the temperature was kept at 150℃ for 1 hour to induce the formation of an interpenetrating polymer network (IPN) structure.

[0046] The second stage involves maintaining a constant temperature of 280℃ for 2 hours to achieve deep curing of the resin system.

[0047] In the third stage, the temperature is kept at 300℃ for 0.5 hours to activate the Diels-Alder dynamic covalent bonds in the rare earth modified ATSP functional layer.

[0048] In this embodiment, the three-stage programmed temperature co-curing process can sequentially achieve interface molecular fusion, deep resin cross-linking, and activation of self-healing function. While ensuring the overall mechanical strength and structural stability of the tube, it fully endows the material with gradient self-healing ability, so that the finished tube can be put into use directly without subsequent activation treatment, simplifying the process and improving the overall performance of the product.

[0049] In the above embodiments, preferably, during the 150°C heat preservation stage in step S4, the addition reaction of maleimide groups in the prepolymer of the rare earth modified ATSP functional layer with amino and hydroxyl groups in the rare earth modified 2DPA-1 smart liner layer is completed simultaneously to form a covalently cross-linked interpenetrating polymer network (IPN) structure.

[0050] In this embodiment, an in-situ covalent reaction is used to construct a molecular-level interpenetrating polymer network, which can fundamentally eliminate the physical interface between layers, significantly improve the interlayer bonding strength and anti-peeling ability, and make the interlayer shear strength ≥50MPa. This effectively resists the interlayer debonding failure caused by downhole high-temperature thermal cycling, pressure fluctuations and long-term fluid scouring, and greatly improves the reliability and service life of the pipe structure.

[0051] In any of the above embodiments, preferably, the outer diameter of the multilayer composite tube is Φ60.3mm-Φ177.8mm and the wall thickness is 5.0mm-15.0mm.

[0052] In this embodiment, the above-mentioned size range fully covers the standard specifications of mainstream oil pipes and casings in oil and gas fields. It can directly replace traditional metal pipes and ordinary composite pipes without the need to modify downhole tools, wellhead devices and operating processes. It has strong engineering adaptability, low promotion cost, and can be quickly applied to various complex working conditions such as ultra-deep wells, shale gas wells and heavy oil thermal recovery wells.

[0053] In the above embodiments, preferably, the thickness of the basalt fiber reinforcement layer accounts for 40%–60% of the pipe wall thickness, the thickness of the rare earth modified ATSP functional layer accounts for 20%–30% of the pipe wall thickness, and the thickness of the rare earth modified 2DPA-1 smart liner layer accounts for 10%–20% of the pipe wall thickness.

[0054] In this embodiment, the gradient thickness ratio was determined through extensive testing and optimization. It achieves the best balance between high load-bearing capacity, efficient self-healing, and intelligent sensing. While ensuring that the burst pressure of the pipe body is ≥15000psi, it also takes into account the self-healing capacity, the corrosion and wear resistance of the inner wall, and the material cost, so that the pipe body can withstand multiple repair cycles and maintain excellent mechanical properties.

[0055] Modifying 2DPA-1 material with one or more rare earth elements, such as cerium or lanthanum, can improve the material's overall performance at the molecular level. Rare earth ions have empty orbitals and high coordination activity, which can form stable coordination bonds with amino, hydroxyl, and amide bonds on the 2DPA-1 molecular chain, significantly improving the high temperature resistance, structural stability, mechanical strength, and corrosion resistance of the liner. At the same time, it can synergistically enhance the intensity and response sensitivity of Eu³⁺ fluorescence signals, making damage identification and repair monitoring more accurate. Rare earth modification can also optimize the interfacial compatibility between 2DPA-1 and the ATSP layer, promote a more uniform and dense interpenetrating polymer network (IPN), further improve the interlayer bonding strength and anti-peeling performance, and enable the smart liner to maintain long-term stability under ultra-deep well high temperature, high pressure, and high corrosion conditions.

[0056] In any of the above embodiments, preferably, the basalt fiber reinforcement layer is composed of rare earth modified basalt fiber and thermosetting resin, wherein the thermosetting resin is epoxy resin, phenolic resin or ATSP resin.

[0057] In this embodiment, a variety of thermosetting resin systems are provided, which can be flexibly matched according to the requirements of temperature resistance, corrosion resistance and strength under working conditions. Among them, ATSP resin has the best compatibility with the intermediate functional layer, which can further improve the interlayer bonding force; epoxy resin and phenolic resin are widely available and cost-controllable, which can meet the material selection and performance requirements in different scenarios and expand the scope of application of the present invention.

[0058] In the above embodiments, preferably, the rare earth modified basalt fiber is a basalt fiber modified with at least one oxide or acetate of lanthanum and europium.

[0059] In this embodiment, rare earth compounds are used to modify the surface of basalt fibers, which can significantly improve the surface activity and resin wettability of the fibers, enhance the interfacial bonding strength between the fibers and the resin matrix, and simultaneously improve the tensile, compressive and impact resistance of the reinforcing layer. At the same time, it improves the fiber's resistance to H2S / CO2 corrosion and high-temperature aging, ensuring the long-term stable load-bearing capacity of the reinforcing layer in extreme downhole environments.

[0060] In any of the above embodiments, preferably, in step S5, the coupling agent is a rare earth coupling agent.

[0061] In this embodiment, the coupling agent is an organic complex coupling agent prepared with rare earth compounds as the core functional raw material, and its core function is to achieve interfacial chemical bonding between the composite tube and the metal joints at both ends.

[0062] This invention does not specifically limit the source of the rare earth organic complex coupling agent. Coupling agents meeting the requirements of this invention can be obtained through two mature and reproducible methods: First, qualified rare earth organic complex coupling agents can be stably prepared by referring to the preparation methods disclosed in patent documents such as CN201210173703.5, CN202410288141.1, and CN202510029789.1; Second, any commercially available rare earth coupling agent can be directly used, purchased through legitimate commercial channels. The coupling agents obtained through both methods can achieve high-strength chemical bonding between the metal joint and the composite tube in this invention, meeting the interfacial performance requirements of this invention.

[0063] like Figures 1 to 3 As shown, another embodiment of the present invention provides a multi-layer composite pipe with gradient self-healing function prepared by the preparation method involved in any embodiment of the first embodiment of the present invention. The multi-layer composite pipe is composed of a basalt fiber reinforcement layer 1, a rare earth modified ATSP functional layer 2, and a rare earth modified 2DPA-1 intelligent inner lining layer 3 from the outside to the inside.

[0064] The basalt fiber reinforced layer 1 has a thickness of 40%–60% of the pipe wall thickness, the rare earth modified ATSP functional layer 2 has a thickness of 20%–30% of the pipe wall thickness, and the rare earth modified 2DPA-1 smart liner layer 3 has a thickness of 10%–20% of the pipe wall thickness. The rare earth modified ATSP functional layer 2 contains Diels-Alder dynamic covalent bonds and a Yb(OTf)3 catalyst, and the rare earth modified 2DPA-1 smart liner layer 3 contains Eu... 3+ Fluorescent tracers and carbon nanotubes.

[0065] Furthermore, Yb(OTf)3 is used to catalyze the reversible dissociation and recombination of Diels-Alder dynamic bonds, which greatly improves the efficiency of self-repair reaction and is a key functional component for achieving micro-repair at 150℃ and deep repair at 300℃.

[0066] In this embodiment, the multi-layer composite pipe integrates structural load-bearing, gradient self-healing, intelligent sensing, corrosion and wear resistance, and has outstanding advantages such as high burst pressure, good temperature resistance, high repair efficiency and long service life. It can realize graded in-situ repair of microcracks and structural damage, and monitor the repair status in real time through fluorescence tracer, which greatly reduces downhole operation and maintenance costs. It is particularly suitable for harsh service environments such as ultra-deep wells, high sulfur content, high wear, and heavy oil thermal recovery.

[0067] The present invention will be further described in detail below through specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0068] Example 1

[0069] Structural design

[0070] This embodiment is a standard specification gradient self-healing composite tubing with an outer diameter of Φ73.0mm and a wall thickness of 7.0mm. The tubing wall adopts a three-layer gradient composite structure, in which the basalt fiber reinforcement layer is 5.0mm thick, accounting for 71.4% of the wall thickness, the rare earth modified ATSP functional layer is 1.4mm thick, accounting for 20.0% of the wall thickness, and the rare earth modified 2DPA-1 intelligent inner lining layer is 0.6mm thick, accounting for 8.6% of the wall thickness.

[0071] The manufacturing process of this oil pipe

[0072] First, rare earth modified basalt fiber is laid on the core mold using a winding process, then impregnated with epoxy resin and pre-cured at 80°C for 30 minutes to form a basalt fiber reinforcement layer.

[0073] An ATSP prepolymer with a doping amount of 1.0 wt% Yb(OTf)3 was applied to the inner side of the reinforcement layer, and the coating thickness was controlled to be 1.4 mm to form a rare earth modified ATSP functional layer.

[0074] Before the ATSP functional layer is fully cured, spray with a coating containing 0.1 wt% Eu. 3+ A 2DPA-1 smart coating with 1.0wt% MWCNTs (Multi-Walled Carbon Nanotubes, one-dimensional nano-carbon materials with multi-layer coaxial tubular structures, possessing ultra-high mechanical strength, thermal conductivity, electrical conductivity and dielectric barrier properties, and is a commonly used high-performance nano-modified filler for polymer materials) was used, with the coating thickness controlled at 0.6mm to form a rare earth modified 2DPA-1 smart inner liner layer;

[0075] The multi-layer preform was placed in an autoclave and co-cured using a three-stage programmed temperature rise process: 150℃ for 1 hour, 280℃ for 2 hours, and 300℃ for 0.5 hours. After curing, the preform was demolded and cut to length. L80 steel joints treated with rare earth coupling agent were assembled at both ends of the pipe and cured again at 150℃ for 1 hour to complete the interfacial chemical bonding between the joints and the pipe, thus producing the finished oil pipe.

[0076] Performance test results

[0077] Performance tests showed that the burst pressure of the tubing obtained in this embodiment was 16200 psi, the interlaminar shear strength was 53 MPa, the micro-repair efficiency was 88% after holding at 150℃ for 30 min, the deep repair efficiency was 96% after holding at 300℃ for 30 min, and the tubing strength retention rate was 92% after 5 consecutive repairs.

[0078] Example 2

[0079] This embodiment is a high-repair gradient self-healing composite tubing. Based on Example 1, only the thickness ratio of each layer of the tubing wall is adjusted. The remaining structural design, raw material selection, and preparation process are completely the same as in Example 1. After adjustment, the thickness of the basalt fiber reinforced layer remains 5.0 mm, accounting for 71.4% of the wall thickness. The thickness of the rare earth modified ATSP functional layer is increased to 2.1 mm, accounting for 30.0% of the wall thickness. The thickness of the rare earth modified 2DPA-1 intelligent inner liner layer is correspondingly adjusted to 0.4 mm, accounting for 5.7% of the wall thickness. Under the same performance test conditions, the micro-repair efficiency of the tubing in this embodiment is improved to 92% at 150℃ and the deep repair efficiency is improved to 98% at 300℃. The burst pressure is 15500 psi. The pressure-bearing performance is slightly reduced, but it still meets the requirements for use in ultra-deep wells.

[0080] Comparative Example 1 shows a traditional single-layer epoxy-fiberglass composite tubing commonly used in oil and gas fields. It also has the same specifications of Φ73mm×7mm, made from alkali-free glass fiber and epoxy resin using a conventional winding and curing process, without a self-healing layer or intelligent inner lining. Performance testing revealed that this traditional tubing has a burst pressure of only 10500psi, lacks self-healing capabilities, and cannot be repaired in situ after damage. Furthermore, after 500 hours of flushing with an acidic medium (H2S / CO2), significant corrosion, erosion, and cracking defects appeared on the inner wall, severely compromising its structural integrity.

[0081] Based on the test results of the above embodiments and comparative examples, it can be seen that the present invention, through the gradient structural design of the basalt fiber reinforced layer, the rare earth modified ATSP functional layer, and the rare earth modified 2DPA-1 intelligent inner liner, comprehensively outperforms the traditional single-layer epoxy-glass fiber composite tubing in terms of pressure bearing capacity, self-healing efficiency, corrosion resistance, and structural reliability. Taking into account both the structural strength and self-healing effect of the tubing, controlling the thickness ratio of the ATSP functional layer to 20%–30% achieves the optimal balance between structural strength and self-healing capability. The resulting tubing is suitable for extreme working conditions such as ultra-deep wells, high corrosion, high wear, and heavy oil thermal recovery wells.

[0082] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a multilayer composite tube with gradient self-healing function, characterized in that, Includes the following steps: S1. Rare earth modified basalt fiber is laid on the core mold using a winding process, impregnated with thermosetting resin, and pre-cured at 80°C for 30 minutes to obtain a basalt fiber reinforced layer. S2, spray or scrape the prepolymer of rare earth modified ATSP functional layer onto the inner surface of the basalt fiber reinforced layer to form a pre-cured body of rare earth modified ATSP functional layer. S3, before the rare earth modified ATSP functional layer is fully cured, spray a Eu-containing coating onto its surface. 3+ A pre-cured body of rare earth modified 2DPA-1 smart inner liner is formed by combining 2DPA-1 smart coating with multi-walled carbon nanotubes. S4, the multi-layer prefabricated structure obtained in step S3 is placed in an autoclave and co-cured using a multi-stage temperature control process; S5, after curing, is demolded and cut. Metal joints with coupling agent coated on the inner surface are assembled at both ends of the tube. After secondary curing, the interface chemical bonding between the joint and the tube is completed, and a multi-layer composite tube is produced.

2. The method for preparing a multilayer composite tube according to claim 1, characterized in that, In step S4, the multi-stage temperature control process includes: In the first stage, the temperature was kept at 150℃ for 1 hour to induce the formation of an interpenetrating polymer network (IPN) structure. The second stage involves maintaining a constant temperature of 280℃ for 2 hours to achieve deep curing of the resin system. In the third stage, the temperature is kept at 300℃ for 0.5 hours to activate the Diels-Alder dynamic covalent bonds in the rare earth modified ATSP functional layer.

3. The method for preparing a multilayer composite tube according to claim 2, characterized in that, In step S4, during the 150℃ heat preservation stage, the addition reaction between the maleimide groups in the prepolymer of the rare earth modified ATSP functional layer and the amino and hydroxyl groups in the rare earth modified 2DPA-1 smart liner layer is completed simultaneously, forming a covalently cross-linked interpenetrating polymer network (IPN) structure.

4. The method for preparing a multilayer composite tube according to claim 1 or 2, characterized in that, The outer diameter of the multi-layer composite pipe is Φ60.3mm-Φ177.8mm, and the wall thickness is 5.0mm-15.0mm.

5. The method for preparing a multilayer composite tube according to claim 4, characterized in that, The thickness of the basalt fiber reinforced layer accounts for 40%–60% of the pipe wall thickness, the thickness of the rare earth modified ATSP functional layer accounts for 20%–30% of the pipe wall thickness, and the thickness of the rare earth modified 2DPA-1 smart liner layer accounts for 10%–20% of the pipe wall thickness.

6. The method for preparing a multilayer composite tube according to claim 1 or 2, characterized in that, The basalt fiber reinforcement layer is composed of rare earth modified basalt fiber and thermosetting resin, wherein the thermosetting resin is epoxy resin, phenolic resin or ATSP resin.

7. The method for preparing a multilayer composite tube according to claim 6, characterized in that, The rare earth modified basalt fiber is a basalt fiber modified with at least one oxide or acetate of lanthanum and europium.

8. The method for preparing a multilayer composite tube according to claim 1 or 2, characterized in that, In step S5, the coupling agent is a rare earth coupling agent.

9. A multilayer composite tube with gradient self-healing function prepared by the preparation method according to any one of claims 1 to 8, characterized in that, The multi-layer composite pipe is composed of a basalt fiber reinforcement layer, a rare earth modified ATSP functional layer, and a rare earth modified 2DPA-1 intelligent inner lining layer, from the outside to the inside. The basalt fiber reinforcement layer accounts for 40%–60% of the pipe wall thickness, the rare earth modified ATSP functional layer accounts for 20%–30% of the pipe wall thickness, and the rare earth modified 2DPA-1 smart liner layer accounts for 10%–20% of the pipe wall thickness. The rare earth modified ATSP functional layer contains Diels-Alder dynamic covalent bonds and a Yb(OTf)3 catalyst, and the rare earth modified 2DPA-1 smart liner layer contains Eu... 3+ Fluorescent tracers and carbon nanotubes.

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