Welding and bonding method for butt joint of glass fiber reinforced plastic composite pipe

Abstract

The application discloses a welding and bonding method for butt joints of glass fiber reinforced plastic (FRP) composite pipelines, which comprises the following steps: after cutting the FRP composite pipeline, polishing the butt joint end of the inner lining pipe into a welding opening with a slope not less than 30 DEG and exposing the outer wall by not less than 10 mm, and polishing the butt joint end of the outer pipe into a groove with a slope not less than 1:6; assembling the FRP composite pipelines after cleaning and fixing the pipelines by three uniform points; adopting a push wire method to segmentally and layer by layer weld the welding opening, cleaning the welding seam after welding and detecting the welding seam by electric spark leak welding; coating the bonding surface with an epoxy resin mixed bonding agent, winding the bonding surface by layer and overlap with untwisted coarse glass fiber cloth, winding the bonding surface with untwisted fine glass fiber cloth until the bonding agent is completely soaked, and completing the operation after the bonding and winding layer is hardened, so that the process is reasonable and the process method meets the strength and quality requirements of the FRP composite pipeline.

Description

Technical Field

[0001] This invention relates to the field of fiberglass composite pipe construction technology, specifically to a welding and bonding method for the joints of fiberglass composite pipes. Background Technology

[0002] Fiberglass reinforced plastic (FRP) pipes are lightweight, high-strength, and corrosion-resistant non-metallic pipes. FRP composite pipes are formed by bonding thin-walled polyethylene (PE) pipes to the inner wall of FRP pipes. FRP composite pipes combine the corrosion resistance of polyethylene-lined pipes with the high strength and heat resistance of FRP, overcoming the shortcomings of polyethylene such as low pressure resistance at high temperatures and easy aging outdoors. This expands the application range of both single-layer polyethylene pipes and FRP pipes. FRP composite pipes are widely used in petroleum, chemical, metallurgical, and machinery industries due to their smooth surface, low frictional resistance, good corrosion resistance, temperature resistance, pressure resistance, wear resistance, strong interfacial adhesion, good impact resistance, low fluid resistance, and absence of electrochemical corrosion.

[0003] Currently, the construction of butt joints for FRP composite pipes mainly includes four processes: hot melt connection, electrofusion connection, flange connection, and socket sealing ring connection. Hot melt butt joint uses a hot melt machine to heat the ends of the two pipes to a molten state, pressurizes and cools them to form an integrated polyethylene sealing layer. It has high joint strength and low cost, but the butt joint time is long, pressure holding and cooling are required, and the outer FRP pipe at the joint must be manually reinforced. Electrofusion connection uses an electrofusion sleeve, which is heated by electricity to fuse the sleeve with the polyethylene at the pipe end. The construction speed is fast, but the cost is higher than hot melt connection. Similarly, the outer FRP pipe at the joint must be manually reinforced. Flange connection involves pre-installing flanges at the pipe end, sealing with gaskets and bolts. The seal depends on the gasket, and there is a risk of leakage with long-term use. It is also costly. Socket sealing ring connection uses an expanded socket at one end and a plug at the other end to form a flexible seal. It is quick to install, but the sealing reliability is lower than hot melt, and its application scenarios are limited. It is clear that the current construction processes for butt joints of FRP composite pipes have problems with low sealing reliability and construction efficiency that need to be improved. Summary of the Invention

[0004] The purpose of this invention is to provide a welding and bonding method for the joints of fiberglass composite pipes, so as to solve the technical problems mentioned in the background art.

[0005] The present invention achieves the above objectives through the following technical solutions: In a first aspect, the present invention provides a welding and bonding method for the joints of fiberglass composite pipes, wherein the fiberglass composite pipes use polyethylene pipes as inner lining pipes and fiberglass pipes as outer pipes, and includes the following steps: (1) Cut the fiberglass composite pipe; (2) Grinding: Grind the cut fiberglass composite pipe inner liner end to form a bevel with a slope of not less than 30° as a weld joint, and make the exposed length of the outer wall of the inner liner not less than 10mm. Grind the pipe wall of the outer pipe end to form a bevel with a length slope of not less than 1:6; and use the exposed part of the outer wall of the inner liner and the bevel of the outer pipe wall as the bonding surface. (3) Clean the weld joints and bonding surfaces; (4) Assembly: Assemble the two fiberglass composite pipes to be connected, and control the assembly gap between 0.5-1mm. (5) Welding: The weld joints of the two assembled fiberglass composite pipes are welded using the wire push method to form a weld filler layer in the weld joints of the two fiberglass composite pipes. (6) Adhesive wrapping: Apply epoxy resin mixed adhesive to the bonding surface, and use untwisted roving fiberglass cloth to layer and overlap the bonding surface to form an adhesive wrapping layer. After the untwisted roving fiberglass cloth is bonded, use untwisted fine fiberglass cloth to layer and overlap the bonding and wrapping, and gradually increase the wrapping force until the epoxy resin mixed adhesive completely penetrates the adhesive wrapping layer. (7) Once the adhesive wrapping layer has fully hardened, the welding and bonding operation of the fiberglass composite pipe joint is completed.

[0006] As a further optimization of the present invention, step (4) further includes, after the two fiberglass composite pipes to be joined are assembled, three-point hot air welding thermoplastic welding wire is used to fix them, and the three points are evenly fixed at a 120° interval on the circumference of the pipe and melt through the inner wall of the pipe.

[0007] As a further optimization of the present invention, the welding process in step (5) is specifically as follows: Preheat the hot air welding gun to 400-450℃. Use thermoplastic welding wire to perform segmented and layered welding on the joints of the two assembled fiberglass composite pipes. Weld 1 / 3 to 1 / 2 of each layer first, and continue welding the next section after the welded section has cooled and solidified. Before welding each layer, clean off any excess weld metal and ensure that each layer of weld is uniform and consistent until the joint is fully welded. After welding is completed, remove any weld seams that are higher than the outer wall of the inner liner pipe.

[0008] As a further optimization of the present invention, before performing step (6), a hot air weld electric spark detection process is also included, specifically: the voltage of the electric spark tester is set to 5kV / mm, and a complete circle is made along the weld filler layer to detect whether there is any missing weld.

[0009] As a further optimization of the present invention, in step (6), the epoxy resin adhesive includes component A and component B; Component A, by weight, includes 100 parts of bisphenol A epoxy resin, 8-10 parts of CTBN toughening agent, 25 parts of calcium carbonate, 5 parts of polyethersulfone pulp, 1-2 parts of silane coupling agent KH-560, and 1-2 parts of silica. Component B, by weight, includes 50-55 parts of phenolic amine curing agent, 20-25 parts of silica powder, and 1-2 parts of DMP-30 accelerator.

[0010] As a further optimization of the present invention, the mass ratio of component A to component B is 1:0.8-1.

[0011] As a further optimization of the present invention, the specific steps of step (6) of using untwisted roving fiberglass cloth to layer and overlap the bonding surface to form an adhesive winding layer are as follows: Untwisted roving fiberglass cloth is used to wrap the bonding surface coated with epoxy resin adhesive. During the wrapping process, each section is wrapped with 50% overlap until one layer is completed. Apply adhesive epoxy resin evenly between each layer until the untwisted fiberglass cloth is completely impregnated. When bonding and wrapping, increase the wrapping width on both sides layer by layer. When it reaches the same level as the outer tube, continue to increase the wrapping width on both sides by 50-200mm on each side, and make the edges of both sides tapered.

[0012] As a further optimization of the present invention, the specific steps of layering and overlapping bonding and winding of the untwisted fine fiberglass cloth after the untwisted coarse fiberglass cloth is bonded in step (6) are as follows: Wrap two layers continuously, increasing the wrapping force with each layer until the epoxy resin adhesive mixture completely saturates the adhesive wrapping layer. During the wrapping process, ensure 10% overlap in each section until one layer is completed. No epoxy resin adhesive mixture needs to be applied during the process.

[0013] As a further optimization of the present invention, in step (6), when the bonding surface is bonded and wrapped with untwisted roving fiberglass cloth in layers, two layers of polypropylene geotextile are laid along the length of the fiberglass pipe. During the laying process, each section is guaranteed to be 50% overlapped until one layer is completed. The two layers of polypropylene geotextile are carried out in steps during the bonding and wrapping of the untwisted roving fiberglass cloth. The distance between the two layers of polypropylene geotextile is 1 / 3 to 1 / 2 of the outer pipe wall thickness.

[0014] The beneficial effects of this invention are as follows: The welding and bonding method for the joints of fiberglass composite pipes provided by this invention involves, after cutting the pipe, grinding the butt joint of the inner liner pipe into a weld joint with a slope of not less than 30° (exposed outer wall ≥10mm), and grinding the butt joint of the outer pipe into a bevel with a slope of not less than 1:6; after cleaning, assembling the pipes (gap 0.5-1mm) and tack welding at three points evenly; using the push wire method to weld the joints in sections and layers, cleaning the weld seam after welding and performing electric spark leak detection; applying an epoxy resin mixed adhesive to the bonding surface, first wrapping it with layers of untwisted coarse fiberglass cloth, then wrapping it with untwisted fine fiberglass cloth until the adhesive is completely saturated, and completing the operation once the bonding and wrapping layer has hardened. The process is reasonable and the method meets the strength and quality requirements of fiberglass composite pipes. Furthermore, by optimizing the composition of the epoxy resin adhesive mixture and optimizing the construction operation, such as laying two layers of polypropylene geotextile in stages when the untwisted roving fiberglass cloth is layered and overlapped, the present invention improves the interfacial tensile strength of the fiberglass composite pipe at the joint, which helps to ensure the structural integrity and sealing reliability of the pipeline, reduce the risk of leakage and failure, extend the service life, and improve the safety and economy of the project. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of the fiberglass composite pipe after polishing, as provided in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the assembly of two fiberglass composite pipes to be connected, provided in Embodiment 1 of the present invention. Figure 3 This is a schematic diagram of the assembly and fixing of two butt-jointed fiberglass composite pipes provided in Embodiment 1 of the present invention. Figure 4 This is a schematic diagram of the interface of the welding filler layer provided in Embodiment 1 of the present invention; Figure 5 This is a schematic diagram illustrating the completed welding and bonding of the interface of the fiberglass composite pipe provided in Embodiment 1 of the present invention; Figure 6 This is a schematic diagram illustrating the completion of welding and bonding of the interface of the fiberglass composite pipe provided in Embodiment 2 of the present invention. Detailed Implementation

[0016] The present application will now be described in further detail with reference to the accompanying drawings. It should be noted that the following specific embodiments are only used to further illustrate the present application and should not be construed as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0017] Unless otherwise specified, all methods used below are conventional methods known to those skilled in the art, and all reagents and materials used are commercially available products.

[0018] Example 1

[0019] This embodiment provides a welding and bonding method for the joints of fiberglass composite pipes. The fiberglass composite pipe uses a polyethylene pipe as the inner lining and a fiberglass pipe as the outer pipe. The welding and bonding method includes the following steps: (1) Material cutting According to the required length of the fiberglass composite pipe for construction, mark the cutting point at the cutting location, clamp the pipe and protect it, such as by using cloth or rubber material to protect the pipe. Use a hacksaw or electric grinder to cut the pipe. After cutting, use a clean cloth or brush to remove burrs, dirt, debris and other debris, and set it aside for later use.

[0020] (2) Polishing The cut and assembled ends of the fiberglass composite pipes and their outer walls are then ground. Specifically: The end of the inner lining of the fiberglass composite pipe is ground into a bevel with a slope of not less than 30° to serve as a weld joint. In this embodiment, the slope is set to 30°, and the exposed length of the outer wall of the inner lining is not less than 10~20mm. In this embodiment, it is set to 10mm. The outer pipe of the fiberglass composite pipe is ground into a bevel with a length slope of not less than 1:6 or 1:7. In this embodiment, the length slope is set to 1:6. The exposed outer wall of the inner liner tube and the bevel of the outer tube wall are used as the bonding surface. The bonding surface is roughened during grinding, which is beneficial for subsequent bonding. A schematic diagram of the fiberglass composite pipe after polishing is shown below. Figure 1 As shown.

[0021] (3) Cleaning The polished fiberglass composite pipes are then cleaned to ensure smooth weld joints and a matte finish on the bonding surfaces. Specifically... Use a blower to remove dust and impurities from the weld joint and bonding surface. If necessary, use acetone to clean. Avoid contaminating the cleaned bevel before welding and ensure that welding is carried out within 1 hour after cleaning. If the time is exceeded, or if the surface becomes contaminated or wet, re-grind and clean.

[0022] (4) Pairs A pipe assembly tool is used to assemble two fiberglass composite pipes to be connected, with the assembly gap controlled between 0.5-1mm. A schematic diagram of the assembly of the two fiberglass composite pipes to be connected is shown below. Figure 2 As shown; After the team is assembled, hot air welding guns are used to weld thermoplastic welding wire to secure the welds at three evenly spaced points around the circumference of the pipe, at 120° intervals. Figure 3To ensure complete penetration of the pipe's inner wall, each tack weld should be at least 20mm long, and both ends of the tack welds should be rounded to facilitate subsequent hot air welding of the joints. The thermoplastic welding wire (materials such as PVC, PP, PE, etc.) is used; in this embodiment, PE thermoplastic welding wire is selected. (5) Welding The weld joints of the two assembled fiberglass composite pipes were welded using the wire-pushing method. Specifically, The hot air welding gun is preheated to 400-450℃, and in this embodiment, it is preheated to 400℃. The welding wire is preferably a PE thermoplastic welding wire with a diameter of 3.5mm. Hot air welding employs segmented and layered welding. Each weld bead is not completed in a single pass; instead, 1 / 3 to 1 / 2 of each layer is welded first. In this embodiment, 1 / 3 of each layer is welded first, and the next section is only welded after the previous section has cooled and solidified. This avoids weld deformation. Before each layer is welded, excess weld metal is removed with a blade to prevent welding defects and ensure uniformity in each weld bead until the weld joint is completely filled, forming a weld seam (i.e., weld filler layer) between the two FRP composite pipes. After welding, any weld seam protruding above the outer wall of the inner liner is removed to facilitate subsequent bonding. A schematic diagram of the weld filler layer interface is shown below. Figure 4 As shown; (6) Electrical spark detection Set the voltage of the electric spark tester to 5kV / mm (5kV per millimeter of wall thickness), and run it around the entire weld seam of the pipe to check for any leaks and ensure the weld seam is sealed.

[0023] (7) Bonding and wrapping of outer tube (7.1) After the electrical spark test is passed, use a blower to clean the weld and bonding area again until the bonding surface is clean and free of dust. (7.2) Preparation of epoxy resin adhesive: Component A: By weight, 100 parts of bisphenol A epoxy resin (E-51), 10 parts of CTBN toughening agent, 25 parts of calcium carbonate, 5 parts of polyethersulfone pulp, 2 parts of silane coupling agent KH-560, and 1 part of silica. Component B: By weight, 55 parts of phenolic amine curing agent, 20 parts of silica powder, and 1 part of DMP-30 accelerator; Bisphenol A epoxy resin was heated to 40°C, and the formulated amounts of CTBN toughening agent and silane coupling agent KH-560 were added. The mixture was stirred at a low speed of 300 r / min for 5 min until homogeneous. Then, calcium carbonate, aramid pulp and silica were added, and the mixture was stirred at 800 r / min for 20 min. Finally, the mixture was stirred and degassed for 15 min under a vacuum of ≥-0.09 MPa to obtain component A. Add DMP-30 accelerator to phenolic amine curing agent, stir at low speed of 300 r / min for 5 min to mix evenly, slowly add silica powder, stir at 800 r / min for 20 min, and finally stir and degas for 15 min under vacuum degree ≥ -0.09 MPa to prepare component B. The epoxy resin adhesive should be prepared and used immediately. Mix component A and component B in a dry container at a mass ratio of 1:0.8 for 5 minutes until the mixture is uniform in color. The prepared epoxy resin adhesive is a fluid. The mixing temperature should not exceed 25°C. The prepared epoxy resin adhesive should be used in an environment below 40°C and bonding should be completed within 10 minutes. (7.3) Bonding and winding untwisted roving fiberglass cloth Apply epoxy resin adhesive evenly to the outer wall of the inner lining tube, and wrap the adhesive surface coated with epoxy resin adhesive with untwisted coarse fiberglass cloth. During the wrapping process, ensure that each section overlaps by 50% until one layer is completed. Apply adhesive epoxy resin evenly between each layer until the untwisted fiberglass cloth is completely impregnated. When bonding and wrapping, increase the wrapping width on both sides layer by layer. When it reaches the same level as the outer tube, continue to increase the wrapping width on both sides, increasing by 50-200mm on each side, depending on the diameter of the outer tube. The larger the diameter of the outer tube, the wider the increase in width, and make the wrapping on both sides tapered. The bonding and wrapping process continues until the thickness reaches 1.5 times the outer tube wall thickness. During the operation, a roller is used to remove air holes and air bubbles. (7.4) Bonding and winding of untwisted fine fiberglass cloth After the untwisted coarse fiberglass cloth is wound, the untwisted fine fiberglass cloth is immediately tightened and wound. Two layers are wound continuously, and the winding force is increased layer by layer until the epoxy resin adhesive mixture completely saturates the entire adhesive winding layer. During the winding process, each section is guaranteed to overlap by 10% until one layer is completed. There is no need to apply epoxy resin adhesive mixture during the process.

[0024] (8) Hardening After the outer pipe of the fiberglass composite pipe is bonded and wrapped, wait 24 hours for the entire bonding and wrapping layer to harden. This completes the welding and bonding operation of the fiberglass composite pipe joints, as shown in the diagram. Figure 5 As shown.

[0025] Example 2

[0026] This embodiment provides a welding and bonding method for the interface of a fiberglass composite pipe with added polypropylene geotextile. The welding and bonding method differs from the steps in embodiment 1 in step (7) of bonding and wrapping the outer pipe. In this embodiment, the polypropylene geotextile is bonded and wound during the outer tube bonding and winding process in step (7). The specific difference lies in step (7.3) of bonding and winding the untwisted roving fiberglass cloth: Untwisted roving fiberglass cloth is used to wrap the bonding surface coated with epoxy resin adhesive. During the wrapping process, each section is wrapped with 50% overlap until one layer is completed. Apply adhesive epoxy resin evenly between each layer until the untwisted fiberglass cloth is completely impregnated. When bonding and wrapping, increase the wrapping width on both sides layer by layer. When it reaches the same level as the outer tube, continue to increase the wrapping width on both sides by 50-200mm on each side, depending on the diameter of the outer tube. The larger the diameter of the outer tube, the wider the increase in width, and make the wrapping on both sides tapered. The bonding and wrapping process continues until the thickness reaches 1.5 times the outer tube wall thickness. During the operation, a roller is used to remove air holes and air bubbles. During the bonding and winding of the untwisted roving fiberglass cloth, two layers of polypropylene geotextile are laid along the length of the fiberglass pipe. During the laying process, each section is ensured to overlap by 50% until one layer is completed. The two layers of polypropylene geotextile are bonded and wound in stages. The spacing between the two layers of polypropylene geotextile is 1 / 3 to 1 / 2 of the outer pipe wall thickness; in this embodiment, it is set to 1 / 3. (See schematic diagram). Figure 6 As shown; (4) Bonding and winding untwisted fine fiberglass cloth After the untwisted coarse fiberglass cloth is wound, the untwisted fine fiberglass cloth is immediately tightened and wound. Two layers are wound continuously, and the winding force is increased layer by layer until the epoxy resin adhesive mixture completely saturates the entire adhesive winding layer. During the winding process, each section is guaranteed to overlap by 10% until one layer is completed. There is no need to apply epoxy resin adhesive mixture during the process.

[0027] Example 3

[0028] This embodiment provides a welding and bonding method for fiberglass pipe joints based on different epoxy resin adhesives. The difference from Embodiment 1 is that: step (7.2) epoxy resin adhesive preparation: Component A: By weight, 100 parts of bisphenol A epoxy resin (E-51), 8 parts of CTBN toughening agent, 25 parts of calcium carbonate, 5 parts of polyethersulfone pulp, 1 part of silane coupling agent KH-560, and 2 parts of silica. Component B: By weight, 50 parts of phenolic amine curing agent, 25 parts of silica powder, and 2 parts of DMP-30 accelerator; Bisphenol A epoxy resin was heated to 40°C, and the formulated amounts of CTBN toughening agent and silane coupling agent KH-560 were added. The mixture was stirred at a low speed of 300 r / min for 5 min until homogeneous. Then, calcium carbonate, aramid pulp and silica were added, and the mixture was stirred at 800 r / min for 20 min. Finally, the mixture was stirred and degassed for 15 min under a vacuum of ≥-0.09 MPa to obtain component A. Add DMP-30 accelerator to phenolic amine curing agent, stir at low speed of 300 r / min for 5 min to mix evenly, slowly add silica powder, stir at 800 r / min for 20 min, and finally stir and degas for 15 min under vacuum degree ≥ -0.09 MPa to prepare component B. The epoxy resin adhesive should be prepared and used immediately. Mix components A and B in a 1:1 mass ratio in a dry container for 5 minutes until the mixture is uniform in color. The prepared epoxy resin adhesive is a fluid. The mixing temperature should not exceed 25°C. The prepared epoxy resin adhesive should be used in an environment below 40°C and bonding should be completed within 10 minutes.

[0029] Comparative Example 1 The comparative example provides a welding and bonding method for the interface of a fiberglass composite pipe with added polypropylene geotextile. The welding and bonding method differs from the steps in Example 1 in step (7) of bonding and wrapping the outer pipe. In this embodiment, the polypropylene geotextile is bonded and wound during the outer tube bonding and winding process in step (7). The specific difference lies in step (7.3) of bonding and winding the untwisted roving fiberglass cloth: Apply epoxy resin adhesive evenly to the outer wall of the inner lining tube, and wrap the adhesive surface coated with epoxy resin adhesive with untwisted coarse fiberglass cloth. During the wrapping process, ensure that each section overlaps by 50% until one layer is completed. Apply adhesive epoxy resin evenly between each layer until the untwisted fiberglass cloth is completely impregnated. When bonding and wrapping, increase the wrapping width on both sides layer by layer. When it reaches the same level as the outer tube, continue to increase the wrapping width on both sides by 50-200mm on each side, depending on the diameter of the outer tube. The larger the diameter of the outer tube, the wider the increase in width, and make the wrapping on both sides tapered. The bonding and wrapping process continues until the thickness reaches 1.5 times the outer tube wall thickness. During the operation, a roller is used to remove air holes and air bubbles. During the bonding and winding of the untwisted roving fiberglass cloth, two layers of polypropylene geotextile are bonded and wound. During the bonding and winding process, each section is ensured to have 50% overlap until one layer is completed. The two layers of polypropylene geotextile are bonded and wound in steps during the bonding and winding of the untwisted roving fiberglass cloth. The spacing between the two layers of polypropylene geotextile is 1 / 3 to 1 / 2 of the outer tube wall thickness; in this embodiment, it is set to 1 / 3. (See schematic diagram). Figure 5 As shown; (4) Bonding and winding untwisted fine fiberglass cloth After the untwisted coarse fiberglass cloth is wound, the untwisted fine fiberglass cloth is immediately tightened and wound. Two layers are wound continuously, and the winding force is increased layer by layer until the epoxy resin adhesive mixture completely saturates the entire adhesive winding layer. During the winding process, each section is guaranteed to overlap by 10% until one layer is completed. There is no need to apply epoxy resin adhesive mixture during the process.

[0030] Comparative Example 2 This comparative example provides a welding and bonding method for fiberglass pipe joints based on different epoxy resin adhesives. The difference from Example 2 is that: step (7.2) involves preparing the epoxy resin adhesive. Component A: By weight, 100 parts of bisphenol A epoxy resin (E-51), 10 parts of CTBN toughening agent, 25 parts of calcium carbonate, 5 parts of aramid pulp, 2 parts of silane coupling agent KH-560, and 1 part of silica. Component B: By weight, 55 parts of phenolic amine curing agent, 20 parts of silica powder, and 1 part of DMP-30 accelerator; Bisphenol A epoxy resin was heated to 40°C, and the formulated amounts of CTBN toughening agent and silane coupling agent KH-560 were added. The mixture was stirred at a low speed of 300 r / min for 5 min until homogeneous. Then, calcium carbonate, aramid pulp and silica were added, and the mixture was stirred at 800 r / min for 20 min. Finally, the mixture was stirred and degassed for 15 min under a vacuum of ≥-0.09 MPa to obtain component A. Add DMP-30 accelerator to phenolic amine curing agent, stir at low speed of 300 r / min for 5 min to mix evenly, slowly add silica powder, stir at 800 r / min for 20 min, and finally stir and degas for 15 min under vacuum degree ≥ -0.09 MPa to prepare component B. The epoxy resin adhesive should be prepared and used immediately. Mix component A and component B in a dry container at a mass ratio of 1:0.8 for 5 minutes until the mixture is uniform in color. The prepared epoxy resin adhesive is a fluid. The mixing temperature should not exceed 25°C. The prepared epoxy resin adhesive should be used in an environment below 40°C and bonding should be completed within 10 minutes.

[0031] Comparative Example 3 This comparative example provides a welding and bonding method for fiberglass pipe joints based on different epoxy resin adhesives. The difference from Example 2 is that step (7.2) involves preparing the epoxy resin adhesive: Component A: By weight, 100 parts of bisphenol A epoxy resin (E-51), 10 parts of CTBN toughening agent, 30 parts of calcium carbonate, 2 parts of silane coupling agent KH-560, and 1 part of silica. Component B: By weight, 55 parts of phenolic amine curing agent, 20 parts of silica powder, and 1 part of DMP-30 accelerator; Bisphenol A epoxy resin was heated to 40°C, and the formulated amounts of CTBN toughening agent and silane coupling agent KH-560 were added. The mixture was stirred at a low speed of 300 r / min for 5 min until homogeneous. Then, calcium carbonate, aramid pulp and silica were added, and the mixture was stirred at 800 r / min for 20 min. Finally, the mixture was stirred and degassed for 15 min under a vacuum of ≥-0.09 MPa to obtain component A. Add DMP-30 accelerator to phenolic amine curing agent, stir at low speed of 300 r / min for 5 min to mix evenly, slowly add silica powder, stir at 800 r / min for 20 min, and finally stir and degas for 15 min under vacuum degree ≥ -0.09 MPa to prepare component B. The epoxy resin adhesive should be prepared and used immediately. Mix component A and component B in a dry container at a mass ratio of 1:0.8 for 5 minutes until the mixture is uniform in color. The prepared epoxy resin adhesive is a fluid. The mixing temperature should not exceed 25°C. The prepared epoxy resin adhesive should be used in an environment below 40°C and bonding should be completed within 10 minutes.

[0032] First, the hardness of the joint of the fiberglass composite pipes welded and bonded according to the methods provided in Examples 1-3 and Comparative Examples 1-3 was tested. Specifically, according to the provisions of GB / T3854-2017 "Barcol Hardness Test Method for Fiber Reinforced Plastics", a digital display Barcol hardness tester was used to test the hardness of the joint. The hardness value of not less than 30 HBa is considered qualified.

[0033] Secondly, pressure resistance and sealing performance tests were conducted on the fiberglass composite pipes welded and bonded according to the methods provided in Examples 1-3 and Comparative Examples 1-3. The specific steps are as follows: (1) Sample preparation: After the fiberglass composite pipe sample has been welded and bonded by the method of the present invention and fully cured, sealing plugs are installed at both ends to ensure that there are no additional leakage points.

[0034] (2) Water injection and air release: Slowly inject clean water into the pipeline through the pressure test pump to completely remove the air in the pipe until it is full of medium, and then close the air release valve.

[0035] (3) Pressurize to test pressure: Start the test pressure pump and slowly increase the pressure to 1 bar, 5 bar, and 10 bar. Observe the pressure and confirm that the pressure is stable without sudden drop.

[0036] (4) Pressure holding test: The pressure is held continuously for 12 hours under the test pressure. During the test, the ambient temperature is kept stable and there is no obvious external disturbance.

[0037] (5) Leakage observation and inspection: During the pressure holding period, visually inspect the joint welding area, the bonding and wrapping area and the entire outer wall of the pipe to check for water droplet leakage, obvious wetting, continuous pressure drop, joint cracking, bulging and delamination. (6) Test judgment If there is no significant pressure drop during the pressure holding period, and there is no leakage or wetting at the interface or pipe wall, the water pressure sealing test is deemed qualified.

[0038] The results of hardness testing, pressure resistance testing, and sealing tests are summarized in Table 1.

[0039] Table 1 Statistical Table of Results ; As can be seen from Table 1, the joint hardness of the fiberglass composite pipes welded and bonded according to the methods provided in Examples 1-3 and Comparative Examples 1-3 is qualified, but the specific values ​​are different. This is because the composition of the epoxy resin adhesive is different. In addition, compared with Example 1, in Example 2, polypropylene geotextile is further laid along the length of the fiberglass composite pipe when bonding and wrapping the untwisted roving fiberglass cloth. The joint strength is better, the resin is fully cured, and the mechanical properties and toughness are well matched. Moreover, after pressure resistance and sealing tests, there is no leakage when the pressure is continuously maintained at 1-10 bar for 12 hours. It is suitable for most conventional working conditions such as municipal water supply and drainage, industrial circulating water buried pipelines, etc., and meets the requirements of high-quality engineering standards.

[0040] Furthermore, in accordance with GB / T5349-2005 "Test Method for Axial Tensile Properties of Fiber Reinforced Thermosetting Plastic Pipes", the interfacial tensile strength of the fiberglass composite pipes welded and bonded according to the methods provided in Examples 1-3 and Comparative Examples 1-3 was determined using a universal testing machine. The test temperature was (23±2)℃, the relative humidity was (50±5)%, and the loading rate was set to 2mm / min.

[0041] The specific testing method is as follows: Measure the inner / outer diameter and wall thickness of the gauge length of the specimen using vernier calipers, and calculate the effective tensile area of ​​the interface (A): A = π × (D) 2 -d 2 ) / 4 (D is the outer diameter, d is the inner diameter); Fix the sample in the fixture, adjust the centering, and ensure that the tensile force is along the tube axis to avoid lateral force; Apply an initial load (≤30% of the failure load), check the force on the fixture and the alignment of the specimen, and zero the load after confirming that there is no looseness. Load at the set rate and record the force-displacement curve in real time until interface separation, pipe fracture, or joint detachment occurs. Record the maximum destructive load (F). max ); Failure determination: Observe the failure location and mode, and distinguish between interface debonding, tube matrix failure, fiber breakage, etc. Calculate the interface tensile strength based only on the load at the time of interface debonding. Interfacial tensile strength (σ): σ = F max / A (unit: MPa); Each group had 3 replicates, and the results were averaged, as shown in Table 2.

[0042] Table 2 Statistical Table of Results ; As can be seen from Table 2, the FRP composite pipe joint welded and bonded according to the method provided in Example 2 achieved the maximum interfacial tensile strength. Further laying polypropylene geotextile along the length of the FRP composite pipe during the bonding and winding of untwisted roving fiberglass cloth is beneficial to improving the interfacial tensile strength at the joint of the FRP composite pipe. However, the polypropylene geotextile in Comparative Example 1, which is pasted and wound in the same way as the untwisted roving fiberglass cloth, does not have the same effect on improving the interfacial strength as Example 2. Improving the interfacial tensile strength at the joint of the FRP composite pipe is beneficial to ensuring the structural integrity and sealing reliability of the pipe, reducing the risk of leakage and failure, extending the service life, and improving the safety and economy of the project.

[0043] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A welding and bonding method for the joints of fiberglass composite pipes, characterized in that, Includes the following steps: (1) Cut the fiberglass composite pipe; (2) Grinding: Grind the cut fiberglass composite pipe inner liner end to form a bevel with a slope of not less than 30° as a weld joint, and make the exposed length of the outer wall of the inner liner not less than 10mm. Grind the pipe wall of the outer pipe end to form a bevel with a length slope of not less than 1:6; and use the exposed part of the outer wall of the inner liner and the bevel of the outer pipe wall as the bonding surface. (3) Clean the weld joints and bonding surfaces; (4) Assembly: Assemble the two fiberglass composite pipes to be connected, and control the assembly gap between 0.5-1mm. (5) Welding: The weld joints of the two assembled fiberglass composite pipes are welded using the wire push method to form a weld filler layer in the weld joints of the two fiberglass composite pipes. (6) Adhesive wrapping: Apply epoxy resin mixed adhesive to the bonding surface, and use untwisted roving fiberglass cloth to layer and overlap the bonding surface to form an adhesive wrapping layer. After the untwisted roving fiberglass cloth is bonded, use untwisted fine fiberglass cloth to layer and overlap the bonding and wrapping, and gradually increase the wrapping force until the epoxy resin mixed adhesive completely penetrates the adhesive wrapping layer. (7) Once the adhesive wrapping layer has fully hardened, the welding and bonding operation of the fiberglass composite pipe joint is completed.

2. The welding and bonding method for the joint of a fiberglass composite pipe according to claim 1, characterized in that, Step (4) further includes, after the two fiberglass composite pipes to be joined are assembled, three-point hot air welding thermoplastic welding wire is used to fix them, and the three points are evenly fixed at 120° intervals around the circumference of the pipe and melt through the inner wall of the pipe.

3. The welding and bonding method for the joint of a fiberglass composite pipe according to claim 1, characterized in that, The welding process in step (5) is specifically as follows: Preheat the hot air welding gun to 400-450℃. Use thermoplastic welding wire to perform segmented and layered welding on the joints of the two assembled fiberglass composite pipes. Weld 1 / 3 to 1 / 2 of each layer first, and continue welding the next section after the welded section has cooled and solidified. Before welding each layer, clean off any excess weld metal and ensure that each layer of weld is uniform and consistent until the joint is fully welded. After welding is completed, remove any weld seams that are higher than the outer wall of the inner liner pipe.

4. The welding and bonding method for the joints of fiberglass composite pipes according to claim 1, characterized in that, Before performing step (6), a hot air weld spark detection process is also included, specifically: the voltage of the spark tester is set to 5kV / mm, and a complete circle is made along the weld filler layer to check for any missing welds.

5. The welding and bonding method for the joints of fiberglass composite pipes according to claim 1, characterized in that, In step (6), the epoxy resin adhesive includes component A and component B; Component A, by weight, includes 100 parts of bisphenol A epoxy resin, 8-10 parts of CTBN toughening agent, 25 parts of calcium carbonate, 5 parts of polyethersulfone pulp, 1-2 parts of silane coupling agent KH-560, and 1-2 parts of silica. Component B, by weight, includes 50-55 parts of phenolic amine curing agent, 20-25 parts of silica powder, and 1-2 parts of DMP-30 accelerator.

6. The welding and bonding method for the joint of a fiberglass composite pipe according to claim 5, characterized in that, The mass ratio of component A to component B is 1:0.8-1.

7. The welding and bonding method for the joint of a fiberglass composite pipe according to claim 1, characterized in that, In step (6), the specific steps for using untwisted roving fiberglass cloth to layer and overlap the bonding surface to form an adhesive wrapping layer are as follows: Untwisted roving fiberglass cloth is used to wrap the bonding surface coated with epoxy resin adhesive. During the wrapping process, each section is ensured to overlap by 50% until one layer is completed. Apply adhesive epoxy resin evenly between each layer until the untwisted roving fiberglass cloth is completely impregnated. When bonding and wrapping, increase the wrapping width on both sides layer by layer. When it reaches the same level as the outer tube, continue to increase the wrapping width on both sides by 50-200mm on each side, and make the edges of both sides tapered.

8. The welding and bonding method for the joint of a fiberglass composite pipe according to claim 1, characterized in that, In step (6), the specific steps for layering and overlapping bonding and wrapping of untwisted fine fiberglass cloth after the untwisted coarse fiberglass cloth is bonded are as follows: Wrap two layers continuously, increasing the wrapping force with each layer until the epoxy resin adhesive mixture completely saturates the adhesive wrapping layer. During the wrapping process, ensure 10% overlap in each section until one layer is completed. No epoxy resin adhesive mixture needs to be applied during the process.

9. The welding and bonding method for the joints of fiberglass composite pipes according to claim 1, characterized in that, In step (6), when using untwisted roving fiberglass cloth to bond the bonding surface in layers, it also includes laying two layers of polypropylene geotextile along the length of the fiberglass pipe. During the laying process, each section is guaranteed to overlap by 50% until one layer is completed. The two layers of polypropylene geotextile are bonded and wrapped in steps during the process of bonding and wrapping the untwisted roving fiberglass cloth. The distance between the two layers of polypropylene geotextile is 1 / 3 to 1 / 2 of the outer pipe wall thickness.

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