A hot bending pipe outer spraying process

Abstract

The present application relates to the technical field of external anticorrosion coating of pipes, and discloses an external spraying process for hot-bending elbow pipes. The external spraying process for hot-bending elbow pipes comprises the following steps: S1. Pretreatment: performing sand blasting treatment and preheating on a hot-bending elbow pipe to be sprayed; S2. Spraying an epoxy powder layer: using nano-alumina-graphene oxide double-modified epoxy powder as a spraying material to spray an epoxy powder layer on the surface of the hot-bending elbow pipe after the pretreatment in step S1; S3. Forming an adhesive coating layer: coating a modified polyvinyl adhesive on the surface of the epoxy powder layer sprayed in step S2 to obtain an adhesive coating layer; and S4. Coating a polyethylene layer: coating polyethylene on the surface of the adhesive coating layer obtained in step S3 to obtain a polyethylene layer. The hot-bending elbow pipe coating prepared by the external spraying process for hot-bending elbow pipes has good adhesion, corrosion resistance, impact resistance and coating uniformity, and can meet the stringent use requirements of hot-bending elbow pipes in the fields of petroleum and natural gas.

Description

Technical Field

[0001] This invention relates to the field of external anti-corrosion coating technology for pipes, and more specifically, to an external spraying process for hot-bent pipes. Background Technology

[0002] In long-distance pipeline transportation systems for energy industries such as oil and natural gas, hot-bent pipes are critical and indispensable connection and steering components. Due to their special manufacturing process and complex geometry, hot-bent pipes serve in harsh outdoor environments for extended periods, placing extremely stringent requirements on the anti-corrosion coating on the outer wall of the pipe. Within the entire coating system, the epoxy powder coating, which is in direct contact with the steel pipe substrate, is the core and fundamental functional layer that determines anti-corrosion performance and adhesion. It must not only provide an excellent chemical corrosion barrier but also form extremely strong mechanical anchoring and chemical bonding with the metal substrate to resist stress peeling.

[0003] Currently, traditional epoxy powder coatings used for hot-bending pipes face two major bottlenecks: First, the coating material itself has insufficient performance; the adhesion, density, and impact toughness of conventional epoxy powders are insufficient to meet the long-term service requirements of pipes under complex stress conditions. Second, the application process is poorly adaptable; it is difficult to form a uniform, defect-free coating on the curved surface of the pipe through electrostatic spraying, and uneven thickness can easily lead to premature local failure. Although existing technologies attempt to modify the coating by adding single fillers, this often sacrifices other properties while improving one, or fails to achieve uniform dispersion and firm bonding on the pipe surface. This results in limited improvement in the overall performance of the coating and poor uniformity control, making it a weak link in the safety of the entire pipeline system.

[0004] Therefore, developing a novel epoxy powder coating and its matching spraying process specifically designed for hot bending of pipes and capable of solving the aforementioned bottlenecks from the material source has become an urgent need in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a hot-bent pipe external spraying process.

[0006] To achieve the above objectives, the present invention provides the following technical solution: One of the technical solutions of this invention: A nano-alumina-graphene oxide dual-modified epoxy powder for use in hot-bending pipe external spraying process, the preparation method of the nano-alumina-graphene oxide dual-modified epoxy powder includes the following steps: 1) First, place the silane coupling agent in an ethanol solution, then add nano-alumina and graphene oxide, stir and react to obtain nano-alumina-graphene oxide hybrid filler; 2) Mix the nano-alumina-graphene oxide hybrid filler obtained in step 1), bisphenol A type epoxy resin and phenolic curing agent to obtain a premix; 3) The premix obtained in step 2) is sequentially subjected to melt extrusion molding, mechanical slicing, and ball milling to obtain the nano-alumina-graphene oxide dual-modified epoxy powder.

[0007] Further, in step 1), the mass-to-volume ratio of the silane coupling agent, nano-alumina, graphene oxide, and ethanol solution is (3-5) g : (8-10) g : (0.5-1.5) g : 100 mL.

[0008] Further, in step 1), the stirring reaction specifically involves stirring at 80–90°C for 4–6 hours.

[0009] Further, in step 2), the mass ratio of the nano-alumina-graphene oxide hybrid filler, bisphenol A epoxy resin and phenolic curing agent is (5-8):(70-80):(10-15).

[0010] The second technical solution of the present invention: A hot-bending pipe external spraying process, using the aforementioned nano-alumina-graphene oxide dual-modified epoxy powder used in the hot-bending pipe external spraying process as the core raw material, prepares an external anti-corrosion coating for the hot-bending pipe, specifically including the following steps: S1. Pretreatment: Sandblasting and preheating are performed on the hot-bent pipe to be sprayed; S2. Spraying epoxy powder layer: Using nano-alumina-graphene oxide dual-modified epoxy powder as the spraying material, an epoxy powder layer is sprayed onto the surface of the hot-bent pipe after the pretreatment in step S1. S3. Forming an adhesive coating layer: A modified polyethylene adhesive is applied to the surface of the epoxy powder layer sprayed in step S2 to obtain an adhesive coating layer; S4. Coating with a polyethylene layer: The surface of the adhesive coating layer obtained in step S3 is coated with polyethylene to obtain a polyethylene layer.

[0011] Further, in step S1, the preheating specifically involves preheating at 220–230°C for 15–25 minutes.

[0012] Further, in step S2, the spraying specifically involves: controlling the distance between the spray gun and the pipe wall to be 150-180mm, the electrostatic voltage to be 60-80kV, and the powder output to be 80-100g / min, and spraying an epoxy powder layer onto the surface of the hot-bent pipe after the pretreatment in step S1.

[0013] Further, in step S3, the preparation method of the modified polyethylene-based adhesive includes the following steps: mixing high-density polyethylene and low-density polyethylene, adding maleic anhydride and butyl acrylate, grafting, and in-situ chlorination to obtain the modified polyethylene-based adhesive.

[0014] Furthermore, the mass ratio of the high-density polyethylene to the low-density polyethylene is (2-4):1.

[0015] Furthermore, the amount of maleic anhydride added is 5 wt.% to 8 wt.%; and the amount of butyl acrylate added is 2 wt.% to 3 wt.%.

[0016] Furthermore, in step S3, before coating the modified polyethylene adhesive onto the surface of the epoxy powder layer, the epoxy powder layer needs to reach a gelation degree of 40% to 60%.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: The hot-bent pipe coating prepared by the external spraying process provided by this invention has an adhesion of ≥12.5MPa, shows no corrosion abnormalities after 1000h neutral salt spray test, has an impact resistance height of ≥50cm, and exhibits excellent coating uniformity. It has good adhesion, corrosion resistance, impact resistance, and coating uniformity, and can meet the stringent requirements for hot-bent pipes in the petroleum, natural gas and other fields. Detailed Implementation

[0018] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0019] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included within this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0020] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0021] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be obvious to those skilled in the art. This specification and embodiments are merely exemplary.

[0022] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0023] In the following embodiments, a hot-bending pipe external spraying process includes the following steps: 1. Pretreatment The hot-bent pipe to be sprayed is sandblasted until the surface cleanliness of the hot-bent pipe reaches Sa2.5 level and the anchor pattern depth reaches 60-80μm. Then the hot-bent pipe is preheated. Specifically, the preheating process involves preheating at 220–230°C for 15–25 minutes. 2. Apply epoxy powder coating 1) According to the mass-volume ratio of silane coupling agent, nano alumina, graphene oxide and ethanol solution as (3-5) g: (8-10) g: (0.5-1.5) g: 100 mL, first place the silane coupling agent (KH-550) in the ethanol solution (90 vol.%), control the stirring speed at 200-300 rpm, stir for 20-40 min, then add nano alumina (particle size 20-30 nm) and graphene oxide (layer number ≤ 5 layers), control the stirring speed at 200-300 rpm, stir and react at 80-90 °C for 4-6 h, centrifuge, wash, and vacuum dry at 80 °C for 1-3 h to obtain nano alumina-graphene oxide hybrid filler; 2) According to the mass ratio of nano-alumina-graphene oxide hybrid filler, bisphenol A epoxy resin and phenolic curing agent of (5-8):(70-80):(10-15), the nano-alumina-graphene oxide hybrid filler, bisphenol A epoxy resin and phenolic curing agent (T-31) obtained in step 1) are mixed, and the stirring speed is controlled at 1500-2000 rpm at 70-90℃ for 10-30 min to obtain a premix. 3) The premix obtained in step 2) is sequentially subjected to melt extrusion molding, mechanical slicing, and ball milling to obtain nano-alumina-graphene oxide dual-modified epoxy powder; Specifically, the melt extrusion molding process involves controlling the temperature of the first zone of the extruder to be 90–110°C, the second zone to be 110–130°C, the third zone to be 130–150°C, and the die head to be 140–160°C, followed by extrusion after melt blending. Specifically, the mechanical slicing involves cutting the cooled and shaped extruded strip into thin sheets with a thickness of 0.1 to 2 mm. Specifically, the ball milling process involves using zirconia balls as grinding balls, controlling the ball-to-material ratio at 5:1, and rotating at 200-400 rpm to ball mill the mechanically sliced ​​flakes to a particle size of 50-200 nm. 4) Using the nano-alumina-graphene oxide dual-modified epoxy powder obtained in step 3) as the spraying material, control the distance between the spray gun and the pipe wall to be 150-180mm, the electrostatic voltage to be 60-80kV, and the powder output to be 80-100g / min, and spray an epoxy powder layer with a thickness of 120-150μm onto the surface of the hot bent pipe after the pretreatment in step 1. 3. Formation of adhesive coating layer 1) Mix high-density polyethylene and low-density polyethylene at a mass ratio of (2-4):1, and add 5wt.%-8wt.% maleic anhydride and 2wt.%-3wt.% butyl acrylate. Graft the mixture at 160-180℃ for 1-3 hours under nitrogen protection, and then chlorinate it in situ for 15-25 minutes in a chlorine atmosphere to obtain a modified polyethylene-based adhesive. 2) After the epoxy powder layer sprayed in step 2 has reached a gelation degree of 40% to 60%, the modified polyethylene adhesive obtained in step 1) is coated on the surface of the epoxy powder layer, kept at 170 to 180°C for 10 to 20 seconds, and pressed by a pressure roller at 0.1 to 0.2 MPa to obtain an adhesive coating layer with a thickness of 30 to 40 μm. 4. Coated with polyethylene layer By extrusion coating, polyethylene is coated onto the surface of the adhesive coating layer obtained in step 3, and then cooled to obtain a polyethylene layer with a thickness of 100-200 μm; Specifically, the extrusion coating involves controlling the vacuum level to -0.06 to -0.08 MPa, the ultrasonic compaction frequency to 20 to 30 kHz, and the pressure roller pressure to 0.2 to 0.3 MPa, and coating the adhesive coating layer with polyethylene. Specifically, the cooling process involves first using air cooling to lower the temperature to 120–130°C, and then allowing it to cool naturally to room temperature.

[0024] Example 1 A hot-bending pipe external spraying process 1. Pretreatment The hot-bent pipe to be sprayed is sandblasted until the surface cleanliness of the hot-bent pipe reaches Sa2.5 level and the anchor pattern depth reaches 60-80μm. Then the hot-bent pipe is preheated. Specifically, the preheating process involves preheating at 220°C for 15 minutes. 2. Apply epoxy powder coating 1) Following the mass-to-volume ratio of silane coupling agent, nano-alumina, graphene oxide, and ethanol solution of 3g∶8g∶0.5g∶100mL, the silane coupling agent (KH-550) was first placed in the ethanol solution (90 vol.%), and the stirring speed was controlled at 200 rpm for 20 min. Then, nano-alumina (particle size of 20-30 nm) and graphene oxide (layer number ≤ 5 layers) were added, and the stirring speed was controlled at 200 rpm. The mixture was stirred and reacted at 80℃ for 4 h. After centrifugation, washing, and vacuum drying at 80℃ for 1 h, nano-alumina-graphene oxide hybrid filler was obtained. 2) The nano-alumina-graphene oxide hybrid filler, bisphenol A epoxy resin and phenolic curing agent obtained in step 1) are mixed according to the mass ratio of 5:70:10. The mixture is stirred at 1500 rpm at 70°C for 10 min to obtain the premix. 3) The premix obtained in step 2) is sequentially subjected to melt extrusion molding, mechanical slicing, and ball milling to obtain nano-alumina-graphene oxide dual-modified epoxy powder; Specifically, the melt extrusion molding process involves controlling the temperature of the first zone of the extruder to be 90°C, the second zone to be 110°C, the third zone to be 130°C, and the die head to be 140°C, followed by extrusion after melt blending. Specifically, the mechanical slicing involves cutting the cooled and shaped extruded strip into thin slices with a thickness of 0.1 mm. Specifically, the ball milling process involves using zirconia balls as grinding balls, controlling the ball-to-material ratio at 5:1, and rotating at 200 rpm to ball mill the thin slices obtained from mechanical slicing to a particle size of 50-200 nm. 4) Using the nano-alumina-graphene oxide double-modified epoxy powder obtained in step 3) as the spraying material, the distance between the spray gun and the pipe wall is controlled to be 150mm, the electrostatic voltage is 60kV, and the powder output is 80g / min. A 120μm thick epoxy powder layer is sprayed onto the surface of the hot-bent pipe after the pretreatment in step 1. 3. Formation of adhesive coating layer 1) Mix high-density polyethylene and low-density polyethylene at a mass ratio of 2:1, add 5 wt.% maleic anhydride and 2 wt.% butyl acrylate, and graft at 160°C for 1 h under nitrogen protection. Then, chlorinate in situ for 15 min in a chlorine atmosphere to obtain modified polyethylene-based adhesive. 2) After the epoxy powder layer sprayed in step 2 has reached 50% gelation degree, the modified polyethylene adhesive obtained in step 1) is coated on the surface of the epoxy powder layer, kept at 170℃ for 10s, and pressed by a pressure roller at 0.1MPa to obtain an adhesive coating layer with a thickness of 30μm. 4. Coated with polyethylene layer By extrusion coating, polyethylene is coated onto the surface of the adhesive coating layer obtained in step 3, and then cooled to obtain a polyethylene layer with a thickness of 100 μm. Specifically, the extrusion coating involves controlling the vacuum level to -0.06 MPa, the ultrasonic compaction frequency to 20 kHz, and the pressure roller pressure to 0.2 MPa, and coating the surface of the adhesive coating layer with polyethylene. Specifically, the cooling process involves first using air cooling to lower the temperature to 120°C, and then allowing it to cool naturally to room temperature.

[0025] Example 2 A hot-bending pipe external spraying process 1. Pretreatment The hot-bent pipe to be sprayed is sandblasted until the surface cleanliness of the hot-bent pipe reaches Sa2.5 level and the anchor pattern depth reaches 60-80μm. Then the hot-bent pipe is preheated. Specifically, the preheating process involves preheating at 225°C for 20 minutes. 2. Apply epoxy powder coating 1) Following the mass-to-volume ratio of silane coupling agent, nano-alumina, graphene oxide, and ethanol solution of 4g:9g:1g:100mL, the silane coupling agent (KH-550) was first placed in an ethanol solution (90 vol.%), and the stirring speed was controlled at 250 rpm for 30 min. Then, nano-alumina (particle size of 20-30 nm) and graphene oxide (layer number ≤ 5 layers) were added, and the stirring speed was controlled at 250 rpm. The mixture was stirred and reacted at 85℃ for 5 h. After centrifugation, washing, and vacuum drying at 80℃ for 2 h, nano-alumina-graphene oxide hybrid filler was obtained. 2) The nano-alumina-graphene oxide hybrid filler, bisphenol A epoxy resin and phenolic curing agent obtained in step 1) are mixed according to the mass ratio of 6:75:12. The mixture is stirred at 1800 rpm at 80°C for 20 min to obtain the premix. 3) The premix obtained in step 2) is sequentially subjected to melt extrusion molding, mechanical slicing, and ball milling to obtain nano-alumina-graphene oxide dual-modified epoxy powder; Specifically, the melt extrusion molding process involves controlling the temperature of the first zone of the extruder to be 100°C, the second zone to be 120°C, the third zone to be 140°C, and the die head to be 150°C, followed by extrusion after melt blending. Specifically, the mechanical slicing involves cutting the cooled and shaped extruded strip into thin slices with a thickness of 1 mm. Specifically, the ball milling process involves using zirconia balls as grinding balls, controlling the ball-to-material ratio at 5:1, and rotating at 300 rpm to ball mill the thin slices obtained from mechanical slicing to a particle size of 50–200 nm. 4) Using the nano-alumina-graphene oxide double-modified epoxy powder obtained in step 3) as the spraying material, the distance between the spray gun and the pipe wall is controlled to be 170mm, the electrostatic voltage is 70kV, and the powder output is 90g / min. A 130μm thick epoxy powder layer is sprayed onto the surface of the hot bent pipe after the pretreatment in step 1. 3. Formation of adhesive coating layer 1) Mix high-density polyethylene and low-density polyethylene at a mass ratio of 3:1, add 6 wt.% maleic anhydride and 2.2 wt.% butyl acrylate, and graft at 170°C for 2 h under nitrogen protection. Then, chlorinate in situ for 20 min in chlorine atmosphere to obtain modified polyethylene-based adhesive. 2) After the epoxy powder layer sprayed in step 2 has reached 50% gelation degree, the modified polyethylene adhesive obtained in step 1) is coated on the surface of the epoxy powder layer, kept at 175℃ for 15s, and pressed by a pressure roller at 0.1MPa to obtain an adhesive coating layer with a thickness of 35μm. 4. Coated with polyethylene layer By extrusion coating, polyethylene is coated onto the surface of the adhesive coating layer obtained in step 3, and then cooled to obtain a polyethylene layer with a thickness of 150 μm. Specifically, the extrusion coating involves controlling the vacuum level to -0.07 MPa, the ultrasonic compaction frequency to 25 kHz, and the pressure roller pressure to 0.2 MPa, and coating the surface of the adhesive coating layer with polyethylene. Specifically, the cooling process involves first using air cooling to lower the temperature to 125°C, and then allowing it to cool naturally to room temperature.

[0026] Example 3 A hot-bending pipe external spraying process 1. Pretreatment The hot-bent pipe to be sprayed is sandblasted until the surface cleanliness of the hot-bent pipe reaches Sa2.5 level and the anchor pattern depth reaches 60-80μm. Then the hot-bent pipe is preheated. Specifically, the preheating process involves preheating at 230°C for 25 minutes. 2. Apply epoxy powder coating 1) Following the mass-to-volume ratio of silane coupling agent, nano-alumina, graphene oxide, and ethanol solution of 5 g: 10 g: 1.5 g: 100 mL, the silane coupling agent (KH-550) was first placed in the ethanol solution (90 vol.%), and the stirring speed was controlled at 300 rpm for 40 min. Then, nano-alumina (particle size of 20-30 nm) and graphene oxide (layer number ≤ 5 layers) were added, and the stirring speed was controlled at 300 rpm. The mixture was stirred and reacted at 90 °C for 6 h. After centrifugation, washing, and vacuum drying at 80 °C for 3 h, nano-alumina-graphene oxide hybrid filler was obtained. 2) The nano-alumina-graphene oxide hybrid filler, bisphenol A epoxy resin and phenolic curing agent obtained in step 1) are mixed according to the mass ratio of nano-alumina-graphene oxide hybrid filler, bisphenol A epoxy resin and phenolic curing agent (T-31) of 8:80:15. The mixture is stirred at 2000 rpm at 90°C for 30 min to obtain a premix. 3) The premix obtained in step 2) is sequentially subjected to melt extrusion molding, mechanical slicing, and ball milling to obtain nano-alumina-graphene oxide dual-modified epoxy powder; Specifically, the melt extrusion molding process involves controlling the temperature of the first zone of the extruder to be 110°C, the second zone to be 130°C, the third zone to be 150°C, and the die head to be 160°C, followed by extrusion after melt blending. Specifically, the mechanical slicing involves cutting the cooled and shaped extruded strip into thin slices with a thickness of 2 mm. Specifically, the ball milling process involves using zirconia balls as grinding balls, controlling the ball-to-material ratio at 5:1, and rotating at 400 rpm to ball mill the thin slices obtained from mechanical slicing to a particle size of 50–200 nm. 4) Using the nano-alumina-graphene oxide double-modified epoxy powder obtained in step 3) as the spraying material, the distance between the spray gun and the pipe wall is controlled to be 180mm, the electrostatic voltage is 80kV, and the powder output is 100g / min. A 150μm thick epoxy powder layer is sprayed on the surface of the hot bent pipe after the pretreatment in step 1. 3. Formation of adhesive coating layer 1) Mix high-density polyethylene and low-density polyethylene at a mass ratio of 4:1, add 8 wt.% maleic anhydride and 3 wt.% butyl acrylate, graft at 180°C for 3 h under nitrogen protection, and then chlorinate in situ for 25 min in chlorine atmosphere to obtain modified polyethylene-based adhesive. 2) After the epoxy powder layer sprayed in step 2 has reached 50% gelation degree, the modified polyethylene adhesive obtained in step 1) is coated on the surface of the epoxy powder layer, kept at 180℃ for 20s, and pressed by a pressure roller at 0.2MPa to obtain an adhesive coating layer with a thickness of 40μm. 4. Coated with polyethylene layer By extrusion coating, polyethylene is coated onto the surface of the adhesive coating layer obtained in step 3, and then cooled to obtain a polyethylene layer with a thickness of 200 μm. Specifically, the extrusion coating involves controlling the vacuum level to -0.08 MPa, the ultrasonic compaction frequency to 30 kHz, and the pressure roller pressure to 0.3 MPa, and coating the surface of the adhesive coating layer with polyethylene. Specifically, the cooling process involves first using air cooling to lower the temperature to 130°C, and then allowing it to cool naturally to room temperature.

[0027] Comparative Example 1 A hot-bending pipe external spraying process Same as Example 2, except that in step 2, when spraying the epoxy powder layer, the addition of graphene oxide is omitted in step 1), and nano-alumina hybrid filler is used as the raw material for spraying the epoxy powder layer. Specifically: Following a mass-to-volume ratio of silane coupling agent, nano-alumina, and ethanol solution of 4 g: 9 g: 100 mL, the silane coupling agent (KH-550) was first placed in an ethanol solution (90 vol.%), and the stirring speed was controlled at 250 rpm for 30 min. Then, nano-alumina (particle size of 20-30 nm) was added, and the stirring speed was controlled at 250 rpm. The mixture was stirred and reacted at 85 °C for 5 h. After centrifugation, washing, and vacuum drying at 80 °C for 2 h, the nano-alumina hybrid filler was obtained.

[0028] Comparative Example 2 A hot-bending pipe external spraying process Same as Example 2, except that in step 2, when spraying the epoxy powder layer, the addition of nano-alumina is omitted in step 1), and the epoxy powder layer is subsequently sprayed using graphene oxide hybrid filler as the raw material. Specifically: Following a mass-to-volume ratio of silane coupling agent, graphene oxide, and ethanol solution of 4 g: 1 g: 100 mL, the silane coupling agent (KH-550) was first placed in an ethanol solution (90 vol.%), and the stirring speed was controlled at 250 rpm for 30 min. Then, graphene oxide (≤5 layers) was added, and the stirring speed was controlled at 250 rpm. The mixture was stirred and reacted at 85 °C for 5 h. After centrifugation, washing, and vacuum drying at 80 °C for 2 h, the graphene oxide hybrid filler was obtained.

[0029] Comparative Example 3 A hot-bending pipe external spraying process Same as Example 2, except that in step 2, when spraying the epoxy powder layer, step 4) is: Using the nano-alumina-graphene oxide dual-modified epoxy powder obtained in step 3) as the spraying material, the distance between the spray gun and the pipe wall is controlled to be 170 mm, the electrostatic voltage is 70 kV, and the powder output is 60 g / min. An epoxy powder layer with a thickness of 130 μm is sprayed onto the surface of the hot-bent pipe after the pretreatment in step 1.

[0030] Comparative Example 4 A hot-bending pipe external spraying process Same as Example 2, except that in step 2, when spraying the epoxy powder layer, step 4) is: Using the nano-alumina-graphene oxide dual-modified epoxy powder obtained in step 3) as the spraying material, the distance between the spray gun and the pipe wall is controlled to be 170 mm, the electrostatic voltage is 70 kV, and the powder output is 120 g / min. An epoxy powder layer with a thickness of 130 μm is sprayed onto the surface of the hot-bent pipe after the pretreatment in step 1.

[0031] Comparative Example 5 A hot-bending pipe external spraying process Same as Example 2, except that in step 3, forming the adhesive coating layer, step 1) is: 6 wt.% maleic anhydride and 2.2 wt.% butyl acrylate were added to high-density polyethylene, and grafting was carried out at 170°C for 2 h under nitrogen protection. Then, in-situ chlorination was carried out in chlorine atmosphere for 20 min to obtain modified polyethylene-based adhesive.

[0032] Comparative Example 6 A hot-bending pipe external spraying process Same as Example 2, except that in step 3, forming the adhesive coating layer, step 2) is: After the epoxy powder layer sprayed in step 2 has reached a gelation degree of 30%, the modified polyethylene adhesive obtained in step 1) is coated on the surface of the epoxy powder layer, kept at 175°C for 15s, and pressed by a pressure roller at 0.1MPa to obtain an adhesive coating layer with a thickness of 35μm.

[0033] Comparative Example 7 A hot-bending pipe external spraying process Same as Example 2, except that in step 3, forming the adhesive coating layer, step 2) is: After the epoxy powder layer sprayed in step 2 has reached 70% gelation degree, the modified polyethylene adhesive obtained in step 1) is coated on the surface of the epoxy powder layer, kept at 175℃ for 15s, and pressed by a pressure roller at 0.1MPa to obtain an adhesive coating layer with a thickness of 35μm.

[0034] Effect verification: The adhesion, corrosion resistance, impact resistance and coating uniformity of the hot-bent pipe coatings prepared in Examples 1-3 and Comparative Examples 1-7 were tested, and the test results are shown in Table 1. Table 1 Performance Test Results

[0035] As shown in Table 1, the hot-bent pipe coating prepared by the external spraying process provided by this invention has an adhesion of ≥12.5MPa, shows no abnormal corrosion after 1000h neutral salt spray test, has an impact resistance height of ≥50cm, and exhibits excellent coating uniformity. It has good adhesion, corrosion resistance, impact resistance, and coating uniformity, and can meet the stringent requirements for hot-bent pipes in the petroleum, natural gas, and other fields.

[0036] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A nano-alumina-graphene oxide dual-modified epoxy powder for external spraying in hot-bending pipe processes, characterized in that, The preparation method of the nano-alumina-graphene oxide dual-modified epoxy powder includes the following steps: 1) First, place the silane coupling agent in an ethanol solution, then add nano-alumina and graphene oxide, stir and react to obtain nano-alumina-graphene oxide hybrid filler; 2) Mix the nano-alumina-graphene oxide hybrid filler obtained in step 1), bisphenol A type epoxy resin and phenolic curing agent to obtain a premix; 3) The premix obtained in step 2) is sequentially subjected to melt extrusion molding, mechanical slicing, and ball milling to obtain the nano-alumina-graphene oxide dual-modified epoxy powder.

2. The nano-alumina-graphene oxide dual-modified epoxy powder for external spraying process of hot-bending pipes according to claim 1, characterized in that, In step 1), the mass-to-volume ratio of the silane coupling agent, nano-alumina, graphene oxide and ethanol solution is (3-5) g : (8-10) g : (0.5-1.5) g : 100 mL.

3. The nano-alumina-graphene oxide dual-modified epoxy powder for external spraying in hot-bending pipe coating process according to claim 1, characterized in that, In step 1), the stirring reaction specifically involves stirring at 80–90°C for 4–6 hours.

4. The nano-alumina-graphene oxide dual-modified epoxy powder for external spraying in hot-bending pipe coating process according to claim 1, characterized in that, In step 2), the mass ratio of the nano-alumina-graphene oxide hybrid filler, bisphenol A epoxy resin and phenolic curing agent is (5-8):(70-80):(10-15).

5. A hot-bending pipe external spraying process, characterized in that, The hot-bending pipe external spraying process uses the nano-alumina-graphene oxide dual-modified epoxy powder as described in any one of claims 1 to 4 as the core raw material to prepare the external anti-corrosion coating of the hot-bending pipe, specifically including the following steps: S1. Pretreatment: Sandblasting and preheating are performed on the hot-bent pipe to be sprayed; S2. Spraying epoxy powder layer: Using nano-alumina-graphene oxide dual-modified epoxy powder as the spraying material, an epoxy powder layer is sprayed onto the surface of the hot-bent pipe after the pretreatment in step S1. S3. Forming an adhesive coating layer: A modified polyethylene adhesive is applied to the surface of the epoxy powder layer sprayed in step S2 to obtain an adhesive coating layer; S4. Coating with a polyethylene layer: The surface of the adhesive coating layer obtained in step S3 is coated with polyethylene to obtain a polyethylene layer.

6. The hot-bending pipe external spraying process according to claim 5, characterized in that, In step S1, the preheating specifically involves preheating at 220–230°C for 15–25 minutes.

7. The hot-bending pipe external spraying process according to claim 5, characterized in that, In step S2, the spraying specifically involves: controlling the distance between the spray gun and the pipe wall to be 150-180mm, the electrostatic voltage to be 60-80kV, and the powder output to be 80-100g / min, and spraying an epoxy powder layer onto the surface of the hot-bent pipe after the pretreatment in step S1.

8. The hot-bending pipe external spraying process according to claim 5, characterized in that, In step S3, the preparation method of the modified polyethylene-based adhesive includes the following steps: mixing high-density polyethylene and low-density polyethylene, adding maleic anhydride and butyl acrylate, grafting, and in-situ chlorination to obtain the modified polyethylene-based adhesive.

9. The hot-bending pipe external spraying process according to claim 8, characterized in that, The mass ratio of high-density polyethylene to low-density polyethylene is (2-4):1; the amount of maleic anhydride added is 5wt.% to 8wt.%; and the amount of butyl acrylate added is 2wt.% to 3wt.%.

10. The hot-bending pipe external spraying process according to claim 5, characterized in that, In step S3, before applying the modified polyethylene adhesive to the surface of the epoxy powder layer, the epoxy powder layer needs to reach a gelation degree of 40% to 60%.

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