Preparation method of glass fiber reinforced plastic outer protective layer for low-temperature medium conveying pipeline

Abstract

The invention relates to the technical field of composite material preparation, particularly discloses a preparation method of a glass fiber reinforced plastic outer protective layer for a low-temperature medium conveying pipeline, and aims to solve the technical bottlenecks of a traditional metal or glass fiber reinforced plastic outer protective layer in the aspects of low-temperature adaptability, corrosion resistance and manufacturing efficiency. The method comprises the steps that glass cloth and a single-component light-cured resin system are adopted, the surface of a pretreated pipeline is subjected to annular winding forming, then rapid curing is achieved through ultraviolet light irradiation, an anti-aging gel coat is sprayed on an original station, secondary curing is conducted, and finally the method is completed. According to the technical scheme, the axial tensile strength and the structural stability of the outer protective layer can be remarkably improved, the service life is prolonged to 15-25 years, the production efficiency is improved by 62.5%, the production capacity per day reaches 6-9 pieces, and meanwhile the comprehensive cost is reduced by 40-50%.

Description

Technical Field

[0001] This invention belongs to the field of composite material preparation technology, specifically relating to a method for preparing a fiberglass outer sheath for cryogenic medium transport pipelines. Background Technology

[0002] In the field of cryogenic media transportation, especially in the long-distance transportation of ultra-low temperature fluids such as liquefied natural gas (LNG), the pipeline outer sheath serves as a critical barrier to ensure the safe and stable operation of the system. It must simultaneously meet requirements for excellent corrosion resistance, resistance to low-temperature embrittlement, and long-term environmental durability. Currently, the industry generally adopts two mainstream outer sheath structures: one is a metal outer sheath represented by aluminum alloys or stainless steel, relying on its inherent mechanical strength to provide physical protection; the other is a fiberglass outer sheath composed of glass fiber reinforced resin matrix composites, formed through manual or semi-automatic winding processes, and supplemented with surface gel coat or anti-corrosion coatings to enhance performance. Although both are widely used in engineering, they both reveal significant technical bottlenecks and economic shortcomings in harsh operating environments such as extreme low temperatures, high humidity, and high salinity.

[0003] While metal outer sheaths possess high initial strength, their coefficient of thermal expansion differs significantly from that of the pipe's base steel. Under repeated hot and cold cycles, this difference can easily lead to weld cracking and the risk of cold leakage. Furthermore, metal materials have limited lifespan in corrosive coastal or industrial environments; after coating damage, the corrosion rate can reach 0.2–0.5 mm / year, resulting in short maintenance cycles and high annual operating costs. Traditional fiberglass outer sheaths, while lower in cost, are limited by their unidirectional fiberglass yarn winding structure, exhibiting significant anisotropy in mechanical properties. Localized stress concentrations can easily induce microcracks. Moreover, their manufacturing process involves multiple discrete steps such as impregnation, winding, curing, and spraying, with frequent process connections. The damage rate of semi-finished products during transfer can reach 10%–15%, severely restricting production efficiency and finished product consistency.

[0004] Existing technologies are further limited by the high dependence of room-temperature curing resin systems on ambient temperature and humidity. At low temperatures, additional heating is required to maintain reactivity, significantly increasing energy consumption. Simultaneously, the gel coat layer is typically applied separately after the main body has cured, resulting in weak interfacial adhesion and difficulty in forming an integrated protective structure. These issues collectively lead to a difficulty in simultaneously achieving structural stability, service life, and manufacturing efficiency in existing outer protective layer solutions, particularly failing to meet the urgent needs of modern cryogenic pipelines for high-performance, long-life, and low-cost integrated protective systems. Therefore, a novel fiberglass outer protective layer preparation method is urgently needed, capable of achieving in-situ integration throughout the entire process and possessing both excellent mechanical properties and environmental adaptability. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a fiberglass outer protective layer for cryogenic medium transport pipelines, which can effectively solve the problems in the background art.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a fiberglass outer sheath for a cryogenic medium transport pipeline includes the following specific steps: Step 1: Prepare the reinforcing material and resin system. Select glass fiber cloth as the reinforcing material and prepare a single-component photocurable resin system. The resin system includes epoxy vinyl ester prepolymer, photoinitiator and flame retardant. Step 2: Impregnation and winding molding. The fiberglass cloth is impregnated with a single-component light-cured resin by ultrasonication through an impregnation device. Multiple layers are laid on the surface of the pipe using a ring winding process, with the number of layers being 1-10. Step 3: UV curing treatment. Use UV curing equipment to irradiate and cure the wound pipe at the original work site. The UV wavelength range is 365-405nm, and the curing time is 20-30min. Step 4: Gelcoat spraying and secondary curing. Directly spray the light-cured anti-aging gelcoat onto the cured fiberglass surface, and then perform secondary curing for 50-70 minutes.

[0007] Preferably, the fiberglass fabric in step 1 includes plain-weave fiberglass cloth and basalt glass composite cloth, and the basis weight of the fiberglass fabric is 100-1000 g / m². 2 The difference in strength between the warp and weft directions is ≤5%; the epoxy vinyl ester prepolymer in the single-component light-curing resin system includes styrene-free flame-retardant epoxy vinyl ester resin and / or flame-retardant epoxy vinyl ester resin.

[0008] Preferably, in step 2, the ultrasonic power is 250-300W, the frequency is 40-50Hz, the ultrasonic impregnation time is 1-10s, and the adhesive content after impregnation is 45-55%; the overlap width of adjacent layers is 1 / 10-9 / 10 of the fabric width, the winding speed is 0.5-10m / min, the pipe rotation speed is 3-4r / min, and the winding tension is 100-500N.

[0009] Preferably, in step 3, the UV curing equipment has a lamp power of 800-1500W, an irradiation distance of 15-25cm, and a curing temperature of 35-45℃.

[0010] Preferably, the photocurable anti-aging gel coat in step 4 comprises the following components by weight: 100 parts matrix resin, 0.3-0.8 parts UV absorber, 0.2-0.5 parts light stabilizer, and 2-8 parts filler; the matrix resin comprises any one of isophenylene / neopentyl glycol unsaturated polyester and epoxy vinyl ester resin; the UV absorber is a benzotriazole absorber; the light stabilizer is a hindered amine stabilizer; and the filler comprises any one of carbon black, iron oxide red, and titanium dioxide. Preferably, the UV absorption band of the photocurable anti-aging gel coat is 365-405nm, the curing time is 50-70min, the coating thickness is 0.1-0.3mm, the spraying speed is 0.3-0.8m / min, and the spraying distance is 15-30cm.

[0011] Compared with the prior art, the present invention has the following beneficial effects: By employing a fiberglass cloth wrapping structure and a single-component UV-curable resin system, combined with an integrated on-site operation mode, the axial tensile strength and structural stability of the outer sheath are significantly improved, extending its service life to 15-25 years. The UV curing process greatly shortens the curing time, improves production efficiency, and increases daily capacity to 6-9 pieces. The on-site mobile spraying design ensures good adhesion between the gel coat layer and the substrate, reduces transfer damage rate, and lowers overall costs by 40-50%. This method comprehensively solves the technical bottlenecks of traditional metal and fiberglass outer sheaths in terms of low-temperature adaptability, corrosion resistance, and manufacturing efficiency. Attached Figure Description

[0012] Figure 1 A flowchart illustrating the steps of a method for preparing a fiberglass outer sheath for a cryogenic medium transport pipeline provided by the present invention. Detailed Implementation

[0013] The technical solution of this application is further illustrated below through specific embodiments. These specific embodiments will be described in detail with reference to the accompanying drawings.

[0014] Unless otherwise specified, all raw materials used in this application are derived from commercially available materials.

[0015] Example 1 The basics are as follows: Figure 1 As shown, this embodiment provides a method for preparing a fiberglass outer sheath for a cryogenic medium transport pipeline, including the following steps: Step 1: Prepare the reinforcing material and resin system. Select glass fiber cloth as the reinforcing material and prepare a single-component photocurable resin system. The resin system includes epoxy vinyl ester prepolymer, photoinitiator and flame retardant. Specifically, plain-weave fiberglass cloth or basalt glass composite cloth is selected as the reinforcing material, with basalt glass composite cloth being suitable for pipelines requiring higher pressure (≥2MPa). In this embodiment, plain-weave fiberglass cloth is selected, with a warp and weft strength difference of no more than 5% and a basis weight of 100-1000g / m². 2 The preferred value is 400-600g / m³. 2 This plain weave structure uses warp and weft yarns interwoven in a one-over-one pattern to form a highly symmetrical two-dimensional grid, effectively eliminating the anisotropy of mechanical properties caused by the entanglement of traditional unidirectional fiber yarns. Its warp-to-weft tensile strength ratio is controlled between 0.95 and 1.05, ensuring that the outer sheath has a balanced load-bearing capacity in both the circumferential and axial directions when the pipeline is subjected to internal pressure, external impact, or thermal stress, thus preventing localized stress concentration that could lead to microcrack propagation.

[0016] In this embodiment, the resin system includes epoxy vinyl ester prepolymer, photoinitiator and flame retardant. The epoxy vinyl ester prepolymer includes styrene-free flame-retardant epoxy vinyl ester resin and / or flame-retardant epoxy vinyl ester resin.

[0017] Step 2: Impregnation and winding molding. The fiberglass cloth is impregnated with a single-component light-cured resin by ultrasonication through an impregnation device. Multiple layers are laid on the surface of the pipe using a ring winding process, with the number of layers being 1-10. Specifically, plain-weave glass cloth is conveyed to the impregnation tank via guide rollers and fully impregnated with single-component UV-curable resin. During impregnation, an ultrasonic component is activated with an ultrasonic power of 250-300W, a frequency of 40-50Hz, and an ultrasonic impregnation time of 1-10s. Multiple layers are laid on the pipe surface using a ring-winding process, with 1-10 layers, preferably 3-4 layers. Specifically, the overlap width between adjacent layers is 1 / 10-9 / 10 of the cloth width, preferably 1 / 4-3 / 4, the winding speed is controlled at 0.5-10m / min, the ambient temperature is maintained at 15-30℃, and the relative humidity is ≤70%. The impregnation device consists of a resin tank, guide rollers, a scraper roller, and a tension control system. The plain-weave glass cloth enters the resin tank via the guide rollers and is completely immersed in the liquid resin. It is then passed through a pair of precision scraper rollers with a roller gap of 0.6-0.8mm, controlling the resin content within the range of 45-55%. After the adhesive is applied, the wet glass cloth enters the winding station. The winding head is equipped with a servo motor-driven feeding mechanism and a tension sensor, which provides real-time feedback and closed-loop control of the tension. The winding tension is controlled between 100-500N, with a typical setting of 300N, ensuring that the cloth layer adheres tightly to the pipe surface without wrinkles, looseness, or slippage.

[0018] Step 3: UV curing treatment. Use UV curing equipment to irradiate and cure the wound pipe at the original work site. The UV wavelength range is 365-405nm, and the curing time is 20-30min. Specifically, ultraviolet (UV) curing equipment is used to irradiate and cure the wound pipe at the original work station. The UV wavelength range is 365-405nm, the UV curing equipment lamp power is 800-1500W, and the curing time is 20-30 minutes. The UV curing unit is located downstream of the winding station and consists of a ring-shaped UV lamp array, a temperature control system, an inert gas protective shroud, and a motion control mechanism. The lamp array is distributed along the pipe axis, covering the maximum winding area to ensure uniform irradiation along the entire length. The main peak of the mercury lamp emission spectrum is located at 365nm, matching the absorption peak of the photoinitiator used; the LED light source allows for precise wavelength control at 385nm, resulting in lower energy consumption and a longer lifespan. The irradiation intensity is calibrated in real time using a power meter, with a set value of 1000mW / cm². 2 Tolerance ±200mW / cm 2 During the curing process, the pipeline rotates at a uniform speed of 4 r / min, while the lamp array moves slowly along the axial direction or is controlled independently in multiple sections to eliminate shadowing effects and ensure uniform light intensity distribution in three-dimensional space. The irradiation distance is set at 15-25 cm to balance light intensity attenuation and thermal management requirements. The curing process is accompanied by slight heat release, and the curing temperature is controlled at 35-45℃ by a temperature control system. After curing, a degree of cure of over 95% is achieved.

[0019] Step 4: Gelcoat spraying and secondary curing. Directly spray the light-cured anti-aging gelcoat onto the cured fiberglass surface, and then perform secondary curing for 50-70 minutes.

[0020] Specifically, the gelcoat application and secondary curing process involves directly spraying a UV-cured anti-aging gelcoat onto the cured fiberglass surface. The gelcoat thickness is controlled at 0.1-0.3 mm. After coating, a secondary curing process is performed, with a curing time controlled at 50-70 minutes. The UV-cured anti-aging gelcoat comprises the following components by weight: 100 parts base resin, 0.3-0.8 parts UV absorber, 0.2-0.5 parts light stabilizer, and 2-8 parts filler. The base resin includes any one of isophenylene / neopentyl glycol unsaturated polyester and epoxy vinyl ester resin. The UV absorber is a benzotriazole absorber, the light stabilizer is a hindered amine stabilizer, and the filler includes any one of carbon black, iron oxide red, and titanium dioxide. The secondary curing of the gelcoat layer is completed at room temperature for 50-70 minutes.

[0021] The following table shows a comparison of the preparation efficiency and cost of the metal outer sheath using the technical solution of this invention with that of the prior art: Table 1. Comparison of the differences between the present invention and the prior art In summary, this embodiment constructs a high-efficiency, high-quality, and low-cost fiberglass outer protective layer preparation system by using core technologies such as in-situ integration of the entire process, cross-winding of plain weave fabric, single-component photocurable resin, and integrated gel coat spraying, fundamentally overcoming the structural defects of existing technologies.

[0022] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered exemplary and not restrictive in all respects. Furthermore, it should be understood that although this specification describes embodiments, it does not encompass only one technical solution. This descriptive method is merely for clarity, and those skilled in the art should consider the specification as a whole. The technical solutions in the embodiments can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a fiberglass outer sheath for a cryogenic medium transport pipeline, comprising the following specific steps: Step 1: Prepare the reinforcing material and resin system. Select glass fiber cloth as the reinforcing material and prepare a single-component photocurable resin system. The resin system includes epoxy vinyl ester prepolymer, photoinitiator and flame retardant. Step 2: Impregnation and winding molding. The fiberglass cloth is impregnated with a single-component light-cured resin by ultrasonication through an impregnation device. The fiberglass cloth is then wound in multiple layers on the surface of the pipe using a ring winding process, with the number of layers ranging from 1 to 10. Step 3: UV curing treatment. Use UV curing equipment to irradiate and cure the wound pipe at the original work site. The UV wavelength range is 365-405nm, and the curing time is 20-30min. Step 4: Gelcoat spraying and secondary curing. Directly spray the light-cured anti-aging gelcoat onto the cured fiberglass surface, and then perform secondary curing for 50-70 minutes.

2. The method for preparing the fiberglass outer sheath for cryogenic medium transport pipelines according to claim 1, characterized in that: The fiberglass fabric in step 1 includes plain-weave fiberglass cloth and basalt glass composite cloth, and the basis weight of the fiberglass fabric is 100-1000 g / m². 2 The difference in strength between the warp and weft directions is ≤5%; the epoxy vinyl ester prepolymer in the single-component light-curing resin system includes styrene-free flame-retardant epoxy vinyl ester resin and / or flame-retardant epoxy vinyl ester resin.

3. The method for preparing the fiberglass outer sheath for cryogenic medium transport pipelines according to claim 1, characterized in that: In step 2, the ultrasonic power is 250-300W, the frequency is 40-50Hz, the ultrasonic impregnation time is 1-10s, and the adhesive content after impregnation is 45-55%; the overlap width of adjacent layers is 1 / 10-9 / 10 of the fabric width, the winding speed is 0.5-10m / min, the pipe rotation speed is 3-4r / min, and the winding tension is 100-500N.

4. The method for preparing the fiberglass outer sheath for cryogenic medium transport pipelines according to claim 1, characterized in that: In step 3, the UV curing equipment has a lamp power of 800-1500W, an irradiation distance of 15-25cm, and a curing temperature of 35-45℃.

5. The method for preparing the fiberglass outer sheath for a cryogenic medium transport pipeline according to claim 1, characterized in that: In step 4, the photocurable anti-aging gel coat comprises the following components by weight: 100 parts matrix resin, 0.3-0.8 parts UV absorber, 0.2-0.5 parts light stabilizer, and 2-8 parts filler; the matrix resin comprises any one of isophenylene / neopentyl glycol unsaturated polyester and epoxy vinyl ester resin, the UV absorber is a benzotriazole absorber, the light stabilizer is a hindered amine stabilizer, and the filler comprises any one of carbon black, iron oxide red, and titanium dioxide.

6. The method for preparing the fiberglass outer sheath for a cryogenic medium transport pipeline according to claim 5, characterized in that: In step 4, the UV absorption band of the photocured anti-aging gel coat is 365-405nm, the curing time is 50-70min, the coating thickness is 0.1-0.3mm, the spraying speed is 0.3-0.8m / min, and the spraying distance is 15-30cm.

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