Intelligent 3PE anti-corrosion production process adopting gas heating-spraying infiltration

Abstract

The invention relates to the technical field of 3PE anti-corrosion production, and provides a gas heating-spraying infiltration type intelligent 3PE anti-corrosion production process which comprises the following steps: adding a steel pipe into a gas heating furnace for heating at the heating temperature of 280 DEG C to 260 DEG C, uniformly spraying for 10-30 seconds by adopting a spray gun until the temperature of the steel pipe is 240 DEG C, translating the steel pipe to an AD (adhesive) station, and then transferring the steel pipe into a spraying station; the temperature is 210-220 DEG C, opening an AD vulcanization tank (the length of the vulcanization tank is matched with the length of the steel pipe), infiltrating the bottom of the rotating steel pipe into vulcanized AD powder, rotating for one circle, translating the steel pipe to a polyethylene powder infiltration station at the temperature of 190-200 DEG C and at the moment, opening a PE vulcanization tank, infiltrating the bottom of the rotating steel pipe into vulcanized PE powder, rotating for one circle, translating the steel pipe to a polyethylene powder infiltration station at the temperature of 190-200 DEG C and at the moment, the method has the beneficial effects that a new technical route of fuel gas heating and gradient spraying infiltration is adopted for external corrosion prevention, meanwhile, a three-stage powder recovery system is designed, the production efficiency is improved by 10-15%, the heating energy consumption is reduced by 30-45%, and the dust emission is reduced by 20-50%.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of 3PE anti-corrosion production, and particularly relates to a gas heating-spraying infiltration type intelligent 3PE anti-corrosion production process. BACKGROUND

[0002] Current situation and development trend at home and abroad (1) 3PE anti-corrosion technology and equipment 3PE is a short name of three-layer polyethylene anti-corrosion layer, and is one of two main pipeline anti-corrosion technologies in the world (the other one is FBE), and is the most popular and main anti-corrosion technology for buried steel pipelines in China. 3PE adopts a three-layer structure: the bottom layer is an epoxy resin powder, the middle layer is an adhesive, and the outer layer is polyethylene. The composite structure mainly utilizes the strong adhesion of the epoxy powder to the surface of the steel pipe to improve the adhesion, and utilizes the excellent mechanical strength, chemical stability, insulation, resistance to plant root penetration, and resistance to water penetration of the extruded polyethylene to improve the overall performance, so that the overall performance of the anti-corrosion coating is more outstanding and comprehensive.

[0003] 3PE anti-corrosion production line is a device for producing three-layer polyethylene anti-corrosion layer, and its main working process includes steel pipe surface treatment, primer coating, outer layer polyethylene coating, and heating and curing. First, the steel pipe is subjected to surface treatment such as shot blasting and polishing to ensure that the surface is clean and smooth; then primer coating is performed to enhance the anti-corrosion effect; then outer layer polyethylene coating is performed to form a 3PE structure; and finally, heating and curing are performed to ensure that the coating is firm. Such an anti-corrosion coating can effectively prolong the service life of the steel pipe, is suitable for various pipeline conveying systems, and has been widely used in pipeline protection in the fields of natural gas, petroleum, and chemical industry.

[0004] (2) Development status of 3PE anti-corrosion production line 3PE anti-corrosion production line was successfully developed in Europe in the 1980s and began to be used. In the early 1980s, Mannesmann Company in Germany introduced the performance advantages of 3-layer polyolefin coating (MAPEC) and extruded polyolefin coating developed by the company's research institute and BASF Chemical Industry Company. The performance advantages overcome the performance deficiencies of the two coatings when used alone. 3PE anti-corrosion has been applied in many projects since its inception, especially in European countries, and its application range has rapidly expanded.

[0005] In 1994, China Petroleum and Natural Gas Group decided to introduce 3PE coating technology, which was first applied to the external corrosion protection coating of Shaanxi-Beijing Gas Pipeline and Kuche-Shanshan Oil Pipeline. In December of the same year, experts from China Petroleum Construction Bureau, Pipeline Bureau, Sichuan Petroleum Design Institute and Northwest Pipeline Command jointly visited the United States, Italy, Turkey and other countries to investigate 3PE coating lines. In 1995, Liaohe Oil Construction Company I was responsible for bidding to introduce the first 3PE coating line from Canada's Genware Company. It went into normal production in early 1996, marking the official application of 3PE corrosion protection technology in China. In 1999, China's first self-developed 3PE corrosion protection production line was successfully launched, marking the beginning of the 3PE domestic era and breaking the long-term monopoly of foreign technology. Since 2000, more and more 3PE corrosion protection production lines have been developed and constructed, and 3PE corrosion protection technology has been widely used in China. 3PE corrosion protection layer has become the mainstream of corrosion protection materials.

[0006] After decades of application and development, 3PE corrosion protection production lines and their corrosion protection pipeline products have been widely used in many fields such as petroleum, natural gas, ventilation, water supply and drainage, heat and electricity, and communication. In recent years, the research on 3PE corrosion protection equipment has mainly focused on improving material performance, optimizing coating process, and improving the quality of corrosion protection layer and intelligent automation level. New version of national standard technical requirements, low-temperature coating technology, and powder spraying type 3PE technology have been proposed. Currently, 3PE corrosion protection technology has become the preferred technology for domestic oil and gas long-distance pipeline projects, and its application status and technical improvement have attracted widespread attention.

[0007] (3) Urgency of 3PE corrosion protection equipment update and iteration China's oil and gas pipeline mileage has exceeded 160,000 kilometers, but the direct loss caused by corrosion averages more than 30 billion yuan per year. The future 3,000 kilometers of corrosion protection pipeline (about 60 billion yuan in output value) are needed for China-Russia East Line and West-to-East Gas Pipeline Phase IV, and the traditional production capacity gap is 40%. On the other hand, the new version of the "Integrated Emission Standard of Air Pollutants" tightens the dust limit from 50 mg / m³ to 30 mg / m³, and 90% of the existing equipment needs to be modified.

[0008] Although domestic 3PE corrosion protection production lines have made great technical progress and achieved self-development and manufacturing, there are still problems such as high energy consumption, low efficiency, dust pollution, and substandard corrosion protection life, especially the high energy consumption, which has always kept the manufacturing cost of downstream product enterprises high, restricting the high-quality development of the entire industry. In addition, the domestic rate of 3PE equipment parts is only 65%, and some key parts still rely on imports. In the face of the increasingly tense international economic situation, developing a completely domestic next-generation 3PE corrosion protection equipment has become a very urgent task; 3PE is the most popular and primary anti-corrosion technology for buried steel pipelines in China, boasting advantages such as strong corrosion resistance, reliable mechanical properties, ease of construction and maintenance, and long service life. In recent years, domestically produced 3PE anti-corrosion production lines have made significant progress in optimizing coating processes, improving the quality of the anti-corrosion layer, and enhancing intelligent automation levels, achieving independent research and development and manufacturing. However, they still rely on traditional electric heating and spray-wrapping processes. The prolonged electric heating of the steel pipe and the maintenance of the PE material's molten state during wrapping result in substantial energy consumption. Furthermore, these processes suffer from low efficiency, dust pollution, and insufficient anti-corrosion lifespan. Summary of the Invention

[0009] In view of this, the present invention provides a gas-fired heating-spraying immersion intelligent 3PE anti-corrosion production process, which solves the problems of high energy consumption caused by long-term electric heating and spraying wrapping of steel pipes and maintaining the molten state of PE material during wrapping, as well as low efficiency, dust pollution and failure to meet anti-corrosion life.

[0010] The technical solution is as follows: A gas-fired heating-spraying immersion intelligent 3PE anti-corrosion production process, step one: after the outer and inner walls of the steel pipe are derusted by shot blasting equipment, they are put into a gas-fired heating furnace with a heating temperature of 280℃ and heated to 260℃. The temperature is detected before it is taken out of the furnace, and the error is within (±3℃). Step 2: Transfer the steel pipe to the first layer epoxy resin powder coating equipment within 1-2 minutes, and spray it evenly with a spray gun for 10-30 seconds. At this time, the temperature of the steel pipe is 240℃, and the first layer of epoxy resin powder coating is completed. Step 3: Move the steel pipe to the AD (adhesive) station at a temperature of 210-220℃, open the AD vulcanizing tank (the length of the vulcanizing tank matches the length of the steel pipe), and immerse the bottom of the rotating steel pipe in the vulcanized AD powder. After rotating once, the AD anti-corrosion is completed, and the second layer of adhesive powder is impregnated. Step 4: Move the steel pipe to the polyethylene powder impregnation station. The temperature is 190-200℃. The transfer vehicle moves the steel pipe to the PE (polyethylene) powder station. At this time, the temperature is about 190-200℃. Open the PE vulcanization tank. The bottom of the rotating steel pipe is impregnated into the vulcanized PE powder, completing the third layer of polyethylene powder impregnation. Step 5: Move the steel pipe to the cooling station for cooling.

[0011] Preferably, the heating process of the gas-fired heating furnace is as follows: The gas-fired heating furnace is divided into three parts: a heating section, a heat preservation section, and an outlet transition section. The heating section occupies 1 / 3 of the furnace width, with the flame tip temperature controlled at 950-1050℃. The heat preservation section occupies 2 / 3 of the furnace width, with the flame tip temperature reduced to 850-900℃, using a gentle radiation + convection method. The outlet transition section is located 5m from the end of the furnace, with the flame tip temperature reduced to 700-750℃. It works in conjunction with the furnace insulation layer to achieve a buffer transition, preventing a sudden drop in temperature after the steel pipe exits the furnace. The distance between the flame tip and the steel pipe surface is 150-200mm to prevent the flame from directly burning the steel pipe surface and causing the oxide scale to thicken. The flame nozzle at the flame tip sprays flames in a flat fan shape with a diffusion angle of 30° and the flames sprayed between adjacent flame nozzles overlap by 10%. The flame nozzles are linearly and evenly distributed at the top of the gas heating furnace, and each flame nozzle is equipped with a valve for individual control. The gas-fired heating furnace is equipped with one set of K-type thermocouples (temperature measurement accuracy ±0.5℃) at the inlet, the end of the heating section, and the end of the outlet transition section, for a total of 4 detection points, to collect the surface temperature of the steel pipe in real time. An infrared thermometer (response time ≤0.1s) is installed at the outlet of the gas-fired heating furnace to perform 100% online detection of the steel pipe outlet temperature, ensuring that the outlet temperature is accurately controlled at 260℃ (allowable deviation ±3℃).

[0012] Preferably, the heating time of the gas-fired heating furnace is set according to the specifications of the steel pipe. For small-diameter pipes (diameter 150-300mm, wall thickness 6-8mm), the total heating time is 18-22 minutes, with a heating phase of 12-15 minutes and a heat preservation phase of 6-7 minutes. For medium-diameter pipes (diameter 300-800mm, wall thickness 8-12mm), the total heating time is 25-30 minutes, with a heating phase of 18-20 minutes and a heat preservation phase of 7-10 minutes. For large-diameter pipes (800-1400mm diameter, 12-20mm wall thickness), the total heating time is 35-45 minutes, with a heating phase of 25-30 minutes and a heat preservation phase of 10-15 minutes.

[0013] Preferably, the spraying process for the first layer of epoxy resin powder coating is as follows: (1) Pre-treatment connection before spraying: The steel pipe enters the front end of the first layer epoxy resin powder spraying equipment and sets up a pre-treatment stage that occupies 1 / 5 of the width of the spraying equipment. In the pre-treatment stage, a 0.4-0.6MPa high-pressure air purging + 30-50kV electrostatic adsorption secondary purification device is added to remove surface dust (residual amount ≤5mg / m²) to ensure that the temperature is stable at 230-245℃ (fluctuation ≤±5℃) when entering the spraying station and the surface cleanliness reaches Sa2.5 level or above. The high-pressure air purging is connected to an external gas heating furnace to make the temperature of the sprayed gas 240℃. (2) Powder pretreatment: Modified EP powder (containing 5% KH-550 silane coupling agent) with a particle size of 20-80μm (D50=50μm) and an angle of repose of ≤32° is used after drying at 80℃ for 2h (moisture content ≤0.1%) and sieving with 100 mesh. (3) Customized spraying: High-temperature resistant suspended water-cooled spray guns are used. The gun bar on the spray gun adopts a suspended spray bar system. The heating zone is equipped with a double-layer stainless steel water-cooled gun bar to prevent powder falling and dripping caused by the vibration of the stabilizer during steel pipe spraying. The number of spray guns is designed to be 4 for small pipe diameter, 8 for medium pipe diameter, and 16 for large pipe diameter. The axis is at an angle of 30-35° with the surface of the steel pipe. The parameters are set according to the pipe diameter: spraying pressure 0.35-0.65MPa, powder amount per gun 1000-1500g / min, spraying speed 0.5-1.5m / min, electrostatic voltage 60-90kV, and spraying time 10-30 seconds. (4) Real-time control: The temperature and coating thickness are monitored in real time by infrared thermometer (response time ≤ 0.1s) and laser thickness gauge (accuracy ± 0.01mm). AI vision detection identifies surface defects ≥ 0.1mm. The parameters are automatically adjusted when the temperature exceeds the window or the thickness deviation exceeds ± 5%.

[0014] Preferably, the high-temperature resistant suspended water-cooled spray gun includes a water-cooling system. This water-cooling system continues the design of the high-temperature resistant suspended water-cooled spray gun, with a fully enclosed water circulation zone volume ≥5L, a circulating water flow rate of 0.8-1.2m / s, an inlet water temperature ≤25℃, and an outlet water temperature ≤45℃. A closed-loop cooling system is formed by a stainless steel water tank, a plate cooler, and a variable frequency circulating pump, ensuring that the surface temperature of the spray gun head is ≤60℃. The temperature of the spray gun is reduced by the flow of circulating water, preventing the EP powder from solidifying and forming a skin.

[0015] Preferably, the amount of epoxy resin powder sprayed in the first layer is calculated according to Q_pwder=(π×D×L_unit×δ_target×ρ_pwder) / η_recvery×V in: D: Outer diameter of steel pipe (m) L_unit: Unit length = 1m (used to calculate the amount of paint sprayed per meter) δ_target: Target coating thickness (m), taken as 100μm = 0.0001m (median value) ρ_pwder: Density of epoxy resin powder, taken as 1.4 g / cm³ = 1400 kg / m³ η_recvery: Powder recycling rate, taken as 0.90 (i.e., 90% effective adhesion). V: Speed ​​of steel pipe travel (m / min); The design formula is: Q_pwder(g / min)=0.44×D×V. The distance between the high-temperature resistant suspended water-cooled spray gun and the pipe diameter is 180mm. Spraying starts 0.5 seconds before the steel pipe enters the spraying area and ends 0.3 seconds after the steel pipe leaves the spraying area.

[0016] Preferably, the second layer of adhesive powder is impregnated and the third layer of polyethylene powder is impregnated, and the specific process is as follows: Second layer of adhesive powder impregnation: ① Pre-treatment connection: After the first layer of epoxy resin powder is sprayed and before entering the second layer of adhesive powder impregnation, the loose powder is removed by hot air blowing at 0.15-0.2MPa. The hot air outlet temperature is 210-220℃, and the surface temperature of the steel pipe is stabilized at 210-220℃ (fluctuation ≤±3℃). The gel rate of EP coating is 70-80%. ②Powder pretreatment: Modified cplyPP type AD powder (containing 3% MAH-g-PP thickener) with a particle size of 30-90μm (D50=60μm) is used after vacuum drying at 90℃ for 1.5h (moisture content ≤0.08%) and ultrasonic dispersion. ③ Customized impregnation: A closed segmented vulcanizing tank is adopted, and the steel pipe is horizontally moved (0.5-1.5m / min) and rotated at a uniform speed (10-40r / min) by a stepping hydraulic lifting vehicle. The parameters are set according to the pipe diameter: the powder temperature of the vulcanizing tank is 165-180℃, impregnation is 1 round, and the AD layer thickness is 0.8-1.2mm (uniformity error ≤±6%). ④ Transition and connection: After being kept warm by hot air at 195-205℃ for 40-80 seconds, the AD coating melt rate is ≥85%, and the surface is leveled before being transported to the PE station; Third layer of polyethylene powder impregnation ① Pre-treatment connection: After the steel pipe is impregnated with AD and heat-insulated, it is transported to the third layer of polyethylene powder impregnation (PE station). The surface temperature of the steel pipe is stabilized at 190-200℃ (fluctuation ≤ ±4℃), and the curing degree of AD coating is 30-40%. ②Powder pretreatment: HDPE modified powder (containing 5% EVA toughening agent) with a particle size of 40-120μm (D50=80μm) is used. It is dried at 100℃ for 2h (moisture content ≤0.05%) and sieved through an 80-mesh sieve before being put into use. ③ Customized impregnation: The lifting multi-zone vulcanizing tank is adopted. Through 1-3 cycles of impregnation + touch-up coating, the parameters are set according to the pipe diameter: vulcanizing tank powder temperature 175-190℃, steel pipe rotation speed 8-35r / min, PE layer thickness 2.5-3.5mm (uniformity error ≤±7%). Cooling: The PE coating is cooled through a cooling channel, achieving a curing degree of ≥95% and an internal stress of ≤2MPa.

[0017] Preferably, the first layer of epoxy resin powder spraying, the second layer of adhesive powder impregnation, and the third layer of polyethylene powder impregnation are all connected to a three-stage powder recovery system. The process of the three-stage powder recovery system is as follows: (1) Primary source control and recovery unit: including a pipe front end + pipe rear end synchronous following powder suction hood, a variable frequency centrifugal fan and a primary filter box; the powder suction hood adopts a flexible sealing skirt (the gap with the steel pipe surface is ≤5mm), and is linked with a step-type hydraulic lifting and lifting vehicle to automatically adapt to DN159-1400mm pipe diameter and 0.5-1.5m / min translation speed. The air volume is set according to the pipe diameter as 3000-10000m³ / h and the suction pressure is -7~-18kPa. The primary filter box intercepts large particle impurities through a 50-mesh screen and is equipped with a pressure difference trigger back-blowing device; (2) Secondary dead angle capture and recovery unit: including a telescopic pipe inner wall suction device, a workstation fully sealed cover, a side suction port array and a double cone cyclone separator; the suction... The pipe and the internal anti-corrosion spray gun move synchronously, and the umbrella-shaped suction nozzle captures dust on the inner wall of the pipe with an air volume of 800-2000 m³ / h; the sealed cover has built-in infrared heat lamps to maintain 50-60℃, and the side suction port array is arranged in 1 group every 1m along the axial direction to capture suspended dust at the work station; the cyclone separator separates powder with a particle size ≥10μm and has a separation efficiency ≥92%; (3) Three-level terminal refining and recycling unit: including 16 sets of membrane filter cartridge dust collectors (pore size 1μm, filtration efficiency ≥92%) The equipment includes an ultrasonic dispersing device (≥99.99%), a vacuum drying device, a three-layer vibrating sieve, and a grading and mixing chamber. The recovered powder is ultrasonically dispersed (20kHz×10-15s), vacuum dried (60-80℃×30-60min, moisture content ≤0.05%), and graded and sieved (60-120 mesh screen) before being mixed with new powder in the following proportions: EP powder 1:3, AD powder 1:2, PE powder 1:1.5, with a reuse rate ≥85%.

[0018] As a preferred option, multi-tube simultaneous spraying is also included, with the specific process steps as follows: Step 1: Multiple steel pipes are transported into the powder coating booth via a transmission device. Sensors detect the position and speed of the steel pipes and transmit the signals to the control system.

[0019] Step two: The control system selects the appropriate spraying mode based on the type and quantity of steel pipes, and adjusts the working parameters of the spraying equipment, such as production cycle, spraying speed, and powder quantity.

[0020] Step 3: The control system sends a spraying command to the spraying device, which then sprays the steel pipe internally according to the preset spraying trajectory and speed. At the same time, the intelligent following function enables the spraying device to move synchronously with the steel pipe.

[0021] Step four: The control system monitors the status and quality of the spraying process, collects and analyzes spraying data, and optimizes and adjusts the spraying equipment to improve spraying efficiency and quality.

[0022] Preferably, a stepping hydraulic lifting trolley is also included for moving the steel pipe horizontally, enabling the transfer of the steel pipe between different process steps. The stepping hydraulic lifting trolley includes components such as a base, column, hydraulic cylinder, hydraulic pump, hydraulic pin, lifting arm, and lifting head, as well as vision sensors and a control system. The process flow is as follows: Step one: The vision sensor acquires and processes images of the steel pipe through the camera to obtain the position and orientation information of the steel pipe, such as the coordinates of the center point, length, diameter, and tilt angle. Then, this data is transmitted to the control system.

[0023] Step two: The control system calculates the target position and attitude of the lifting vehicle based on the data from the vision sensor, such as the moving distance, rotation angle, and lifting height of the lifting vehicle. Then, it converts this data into corresponding control signals and sends them to the hydraulic pump and motor actuator.

[0024] Step three: The hydraulic pump and motor, etc., control the movement and lifting of the base, column, lifting arm and other components of the lifting vehicle according to the control signal, so that the lifting head of the lifting vehicle is aligned with the support point of the steel pipe, and finally realizes automatic sensing, precise positioning and multi-stage lifting of the steel pipe.

[0025] The beneficial effects of this invention after adopting the above technical solution are as follows: It is the first domestic research and development project to utilize a gas-heated, spray-coating, and impregnating intelligent 3PE anti-corrosion production line. The external anti-corrosion process adopts a new technical route of "gas heating + gradient spray-coating and impregnation," and simultaneously designs a three-stage powder recovery system. Compared with mainstream domestic and international equipment—spray-coating and wrapping 3PE anti-corrosion equipment—it increases production efficiency by 10-15%, reduces heating energy consumption by 30-45%, and reduces dust emissions by 20-50%. It solves the problems of high energy consumption, low efficiency, and severe dust pollution in existing 3PE anti-corrosion equipment, providing a highly intelligent, automated, green, and energy-saving processing solution for long-term anti-corrosion of steel pipes in harsh environments. This effectively ensures the safe and stable transportation of important industries such as marine, petroleum, and water conservancy, and has high strategic value. The segmented gas-fired heating furnace design significantly improves heat utilization efficiency through temperature gradient control in the heating section, heat preservation section, and outlet transition section, as well as uniform radiant heating with a flat fan-shaped flame. Based on customized heating parameters for steel pipes of different diameters, the total heating time is reduced by 30%-49% compared to traditional electric heating, with the most significant efficiency improvement (35%-48%) for small-diameter steel pipes. At the same time, the energy cost of gas heating is lower than that of electricity. Combined with the buffer heat preservation design of the outlet transition section to reduce heat loss, the heating energy consumption per unit of steel pipe is further reduced, significantly improving production economy. Precise temperature control is achieved throughout the entire process of steel pipe heating, spraying, and impregnation, with errors kept within ±5℃ (heating and exiting the furnace error ±3℃). This ensures that each coating material completes curing and melting within its optimal temperature range, significantly improving the interfacial bonding between the epoxy resin layer, adhesive layer, and polyethylene layer. It also prevents coating peeling and delamination defects caused by temperature fluctuations. Customized processes enhance coating uniformity: different numbers of spray guns, spraying parameters, impregnation speeds, and rotation speeds are matched to steel pipes of different diameters. Combined with the vibration-resistant design of the suspended water-cooled spray guns and the circulating impregnation design of the liftable multi-zone vulcanization tank, the uniformity error of the epoxy resin layer thickness is ≤±5%, the AD layer ≤±6%, and the PE layer ≤±7%. The coating surface has high smoothness, with no powdering, dripping, or uneven thickness issues. Multiple pretreatments ensure coating cleanliness: targeted pretreatment before each process (shot blasting, high-pressure air blowing + electrostatic adsorption, hot air blowing) and powder drying and sieving treatment ensure that the surface cleanliness of the steel pipe reaches Sa2.5 or above, the dust residue is ≤5mg / m², and the powder moisture content is ≤0.1%, effectively avoiding the impact of impurities and moisture on the coating quality and improving the density and corrosion resistance of the anti-corrosion layer; The three-tiered powder recycling system covers the entire process, achieving efficient recycling and reuse of powder resources. First-level source control reduces powder dispersion, second-level blind spot capture fills the gaps in traditional recycling, and third-level final refining, through processes such as ultrasonic dispersing, drying, and sieving, brings the recycled powder performance close to virgin powder standards. Ultimately, the reuse rate of EP, AD, and PE powders is ≥85%, significantly reducing powder waste. Simultaneously, the membrane-coated cartridge dust collector (filtration efficiency ≥99.99%) effectively intercepts fine dust, preventing dust pollution and meeting green production requirements. By circulating water to lower the temperature of the spray gun, the melting and solidification of powder inside or outside the spray gun can be avoided, ensuring that epoxy resin powder can be sprayed at high temperatures, improving spraying efficiency and quality, while reducing the frequency and cost of cleaning and maintaining the spray gun. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a design drawing of the present invention; Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0029] like Figure 1 As shown, a smart 3PE anti-corrosion production process using gas heating and spray immersion is employed. Step 1: After removing rust from the outer and inner walls of the steel pipe using shot blasting equipment, place it into a gas-fired heating furnace with a heating temperature of 280℃ and heat it to 260℃. Before removing it from the furnace, check the temperature, with an error within ±3℃. Step 2: Transfer the steel pipe to the first layer epoxy resin powder coating equipment within 1-2 minutes, and spray it evenly with a spray gun for 10-30 seconds. At this time, the temperature of the steel pipe is 240℃, and the first layer of epoxy resin powder coating is completed. Step 3: Move the steel pipe to the AD (adhesive) station at a temperature of 210-220℃, open the AD vulcanizing tank (the length of the vulcanizing tank matches the length of the steel pipe), and immerse the bottom of the rotating steel pipe in the vulcanized AD powder. After rotating once, the AD anti-corrosion is completed, and the second layer of adhesive powder is impregnated. Step 4: Move the steel pipe to the polyethylene powder impregnation station. The temperature is 190-200℃. The transfer vehicle moves the steel pipe to the PE (polyethylene) powder station. At this time, the temperature is about 190-200℃. Open the PE vulcanization tank. The bottom of the rotating steel pipe is impregnated into the vulcanized PE powder, completing the third layer of polyethylene powder impregnation. Step 5: Move the steel pipe to the cooling station for cooling.

[0030] The heating process of the gas-fired heating furnace is as follows: The gas-fired heating furnace is divided into three parts: a heating section, a heat preservation section, and an outlet transition section. The heating section occupies 1 / 3 of the furnace width, with the flame tip temperature controlled at 950-1050℃. The heat preservation section occupies 2 / 3 of the furnace width, with the flame tip temperature reduced to 850-900℃, using a gentle radiation + convection method. The outlet transition section is located 5m from the end of the furnace, with the flame tip temperature reduced to 700-750℃. It works in conjunction with the furnace insulation layer to achieve a buffer transition, preventing a sudden drop in temperature after the steel pipe exits the furnace. The distance between the flame tip and the steel pipe surface is 150-200mm to prevent the flame from directly burning the steel pipe surface and causing the oxide scale to thicken. The flame nozzle at the flame tip sprays flames in a flat fan shape with a diffusion angle of 30° and the flames sprayed between adjacent flame nozzles overlap by 10%. The flame nozzles are linearly and evenly distributed at the top of the gas heating furnace, and each flame nozzle is equipped with a valve for individual control. The gas-fired heating furnace is equipped with one set of K-type thermocouples (temperature measurement accuracy ±0.5℃) at the inlet, the end of the heating section, and the end of the outlet transition section, for a total of 4 detection points, to collect the surface temperature of the steel pipe in real time. An infrared thermometer (response time ≤0.1s) is installed at the outlet of the gas-fired heating furnace to perform 100% online detection of the steel pipe outlet temperature, ensuring that the outlet temperature is accurately controlled at 260℃ (allowable deviation ±3℃).

[0031] The heating time of the gas-fired heating furnace is set according to the specifications of the steel pipe. For small pipe diameters (150-300mm in diameter and 6-8mm in wall thickness), the total heating time is 18-22 minutes, with a heating phase of 12-15 minutes and a heat preservation phase of 6-7 minutes. For medium-diameter pipes (diameter 300-800mm, wall thickness 8-12mm), the total heating time is 25-30 minutes, with a heating phase of 18-20 minutes and a heat preservation phase of 7-10 minutes. For large-diameter pipes (800-1400mm diameter, 12-20mm wall thickness), the total heating time is 35-45 minutes, with a heating phase of 25-30 minutes and a heat preservation phase of 10-15 minutes.

[0032] The heating time is based on the standard that "the entire steel pipe reaches a core temperature of 280℃ and the temperature gradient in the wall thickness direction is ≤5℃". It is precisely set according to the steel pipe diameter (DN) and wall thickness (t). The specific parameters are as follows: Steel pipe specification (pipe diameter DN x wall thickness t) Total heating time (min) Ramp-up time (min) Soak time (min) Traditional electric heating time (min) Efficiency improvement ratio DN159x6-8mm (small pipe diameter) 18-22 12-15 6-7 30-35 35%-48% DN300-800x8-12mm (medium pipe diameter) 25-30 18-20 7-10 40-50 30%-45% DN800-1400x12-20mm (large pipe diameter) 35-45 25-30 10-15 55-70 36%-49% The spraying process for the first layer of epoxy resin powder coating is as follows: (1) Pre-treatment connection before spraying: The steel pipe enters the front end of the first layer epoxy resin powder spraying equipment and sets up a pre-treatment stage that occupies 1 / 5 of the width of the spraying equipment. In the pre-treatment stage, a 0.4-0.6MPa high-pressure air purging + 30-50kV electrostatic adsorption secondary purification device is added to remove surface dust (residual amount ≤5mg / m²) to ensure that the temperature is stable at 230-245℃ (fluctuation ≤±5℃) when entering the spraying station and the surface cleanliness reaches Sa2.5 level or above. The high-pressure air purging is connected to an external gas heating furnace to make the temperature of the sprayed gas 240℃. (2) Powder pretreatment: Modified EP powder (containing 5% KH-550 silane coupling agent) with a particle size of 20-80μm (D50=50μm) and an angle of repose of ≤32° is used after drying at 80℃ for 2h (moisture content ≤0.1%) and sieving with 100 mesh. (3) Customized spraying: High-temperature resistant suspended water-cooled spray guns are used. The gun bar on the spray gun adopts a suspended spray bar system. The heating zone is equipped with a double-layer stainless steel water-cooled gun bar to prevent powder falling and dripping caused by the vibration of the stabilizer during steel pipe spraying. The number of spray guns is designed to be 4 for small pipe diameter, 8 for medium pipe diameter, and 16 for large pipe diameter. The axis is at an angle of 30-35° with the surface of the steel pipe. The parameters are set according to the pipe diameter: spraying pressure 0.35-0.65MPa, powder amount per gun 250-375g / min, spraying speed 0.5-1.5m / min, electrostatic voltage 60-90kV, and spraying time 10-30 seconds. (4) Real-time control: The temperature and coating thickness are monitored in real time by infrared thermometer (response time ≤ 0.1s) and laser thickness gauge (accuracy ± 0.01mm). AI vision detection identifies surface defects ≥ 0.1mm. The parameters are automatically adjusted when the temperature exceeds the window or the thickness deviation exceeds ± 5%.

[0033] The high-temperature resistant suspended water-cooled spray gun includes a water-cooling system. This water-cooling system is consistent with the high-temperature resistant suspended water-cooled spray gun, with a fully enclosed water circulation zone volume ≥5L, a circulating water flow rate of 0.8-1.2m / s, an inlet water temperature ≤25℃, and an outlet water temperature ≤45℃. A closed-loop cooling system is formed by a stainless steel water tank + plate cooler + variable frequency circulating pump, so that the surface temperature of the gun head is ≤60℃. The temperature of the spray gun is reduced by the flow of circulating water to prevent EP powder from solidifying and forming a skin.

[0034] The amount of epoxy resin powder sprayed in the first layer is as follows: Q_pwder=(π×D×L_unit×δ_target×ρ_pwder) / η_recvery×V in: D: Outer diameter of steel pipe (m) L_unit: Unit length = 1m (used to calculate the amount of paint sprayed per meter) δ_target: Target coating thickness (m), taken as 100μm = 0.0001m (median value) ρ_pwder: Density of epoxy resin powder, taken as 1.4 g / cm³ = 1400 kg / m³ η_recvery: Powder recycling rate, taken as 0.90 (i.e., 90% effective adhesion). V: Speed ​​of steel pipe travel (m / min); The design formula is: Q_pwder(g / min)=0.44×D×V. The distance between the high-temperature resistant suspended water-cooled spray gun and the pipe diameter is 180mm. Spraying starts 0.5 seconds before the steel pipe enters the spraying area and ends 0.3 seconds after the steel pipe leaves the spraying area.

[0035] Parameters are set according to the steel pipe diameter to ensure that the coating thickness (design value 0.4-0.6mm) uniformity error is ≤±5%. Specific parameters are as follows: Steel pipe specification (pipe diameter DN x wall thickness t) Spraying pressure (MPa) Single gun powder quantity (g / min) Spraying speed (m / min) Spray gun moving speed (mm / s) Electrostatic voltage (kV) DN159x6-8mm (small pipe diameter) 0.35-0.45 250-375 (4 guns in total 1000-1500) 1.2-1.5 80-100 60-70 DN300-800x8-12mm (medium pipe diameter) 0.45-0.55 150-200 (8 guns in total 1200-1600) 0.8-1.2 60-80 70-80 DN800-1400x12-20mm (large pipe diameter) 0.55-0.65 100-150 (16 guns in total 1600-2400) 0.5-0.8 40-60 40-60 The second layer of adhesive powder impregnation and the third layer of polyethylene powder impregnation are carried out through the following specific processes: Second layer of adhesive powder impregnation: ① Pre-treatment connection: After the first layer of epoxy resin powder is sprayed and before entering the second layer of adhesive powder impregnation, the loose powder is removed by hot air blowing at 0.15-0.2MPa. The hot air outlet temperature is 210-220℃, and the surface temperature of the steel pipe is stabilized at 210-220℃ (fluctuation ≤±3℃). The gel rate of EP coating is 70-80%. ②Powder pretreatment: Modified cplyPP type AD powder (containing 3% MAH-g-PP thickener) with a particle size of 30-90μm (D50=60μm) is used after vacuum drying at 90℃ for 1.5h (moisture content ≤0.08%) and ultrasonic dispersion. ③ Customized impregnation: A closed segmented vulcanizing tank is adopted, and the steel pipe is horizontally moved (0.5-1.5m / min) and rotated at a uniform speed (10-40r / min) by a stepping hydraulic lifting vehicle. The parameters are set according to the pipe diameter: the powder temperature of the vulcanizing tank is 165-180℃, impregnation is 1 round, and the AD layer thickness is 0.8-1.2mm (uniformity error ≤±6%). ④ Transition and connection: After being kept warm by hot air at 195-205℃ for 40-80 seconds, the AD coating melt rate is ≥85%, and the surface is leveled before being transported to the PE station; Parameters are set according to the steel pipe diameter to ensure that the uniformity error of the AD layer thickness (design value 0.8-1.2mm) is ≤±6%. The specific parameters are as follows: Steel pipe specification (pipe diameter DN x wall thickness t) Vulcanizing tank powder temperature (℃) Steel pipe rotation speed (r / min) Translation speed (m / min) Infiltration time (s / circle) Powder bulk density (g / cm³) DN159x6-8mm (small pipe diameter) 175-180 30-40 1.2-1.5 1.5-2 0.65-0.7 DN300-800x8-12mm (medium pipe diameter) 170-175 20-30 0.8-1.2 2-2.5 0.6-0.65 DN800-1400x12-20mm (large pipe diameter) 165-170 10-20 0.5-0.8 2.5-3 0.55-0.6 Third layer of polyethylene powder impregnation ① Pre-treatment connection: After the steel pipe is impregnated with AD and heat-insulated, it is transported to the third layer of polyethylene powder impregnation (PE station). The surface temperature of the steel pipe is stabilized at 190-200℃ (fluctuation ≤ ±4℃), and the curing degree of AD coating is 30-40%. ②Powder pretreatment: HDPE modified powder (containing 5% EVA toughening agent) with a particle size of 40-120μm (D50=80μm) is used. It is dried at 100℃ for 2h (moisture content ≤0.05%) and sieved through an 80-mesh sieve before being put into use. ③ Customized impregnation: The lifting multi-zone vulcanizing tank is adopted. Through 1-3 cycles of impregnation + touch-up coating, the parameters are set according to the pipe diameter: vulcanizing tank powder temperature 175-190℃, steel pipe rotation speed 8-35r / min, PE layer thickness 2.5-3.5mm (uniformity error ≤±7%). Parameters are set according to the steel pipe diameter and target thickness to ensure that the uniformity error of the PE layer thickness (design value 2.5-3.5mm) is ≤±7%. The specific parameters are as follows: Steel pipe specification (pipe diameter DN x wall thickness t) Vulcanizing tank powder temperature (℃) Steel pipe rotation speed (r / min) Translation speed (m / min) Infiltration times (times) Single infiltration time (s / circle) DN159x6-8mm (small pipe diameter) 185-190 25-35 1.0-1.3 1-2 2-3 DN300-800x8-12mm (medium pipe diameter) 180-185 15-25 0.7-1.0 2 3-4 DN800-1400x12-20mm (large pipe diameter) 175-180 8-15 0.4-0.7 2-3 4-5 Cooling: The PE coating is cured to ≥95% and internal stress is ≤2MPa through a cooling channel. Water cooling (water temperature 40-50℃) is used at a cooling rate of 5-8℃ / min until it reaches room temperature.

[0036] The first layer of epoxy resin powder spraying, the second layer of adhesive powder impregnation and the third layer of polyethylene powder impregnation are all connected to the three-level powder recovery system. The process of the three-level powder recovery system is as follows: (1) First-level source control and recovery unit: including the front end of the pipe and the rear end of the pipe synchronously following the powder suction hood, the variable frequency centrifugal fan and the primary filter box; the powder suction hood adopts a flexible sealing skirt (the gap with the steel pipe surface is ≤5mm), and is linked with the stepping hydraulic lifting trolley, automatically adapting to the DN159-1400mm pipe diameter and the 0.5-1.5m / min translation speed, and setting the air volume to 3000-10000m³ / h and the suction pressure to -7~-18kPa according to the pipe diameter. The primary filter box intercepts large particle impurities through a 50-mesh screen and is equipped with a pressure difference trigger back-blowing device; (2) Second-level dead angle capture and recovery unit: including the telescopic pipe inner wall suction device, the work station full sealing cover, the side suction port array and the double cone section cyclone separator; the suction pipe and the inner wall of the pipe are connected to the primary filter box. The anti-corrosion spray gun moves synchronously, and the umbrella-shaped suction nozzle captures dust on the inner wall of the pipe with an air volume of 800-2000 m³ / h; the sealed cover has built-in infrared heat lamps to maintain 50-60℃, and the side suction port array is arranged in 1 group every 1m along the axial direction to capture suspended dust at the work station; the cyclone separator separates powder with a particle size ≥10μm and has a separation efficiency ≥92%; (3) Three-level terminal refining and recycling unit: including 16 sets of membrane filter cartridge dust collectors (pore size 1μm, filtration efficiency ≥ The equipment includes an ultrasonic dispersing device (99.99%), a vacuum drying device, a three-layer vibrating sieve, and a grading mixing chamber. The recovered powder is ultrasonically dispersed (20kHz×10-15s), vacuum dried (60-80℃×30-60min, moisture content ≤0.05%), and graded and sieved (60-120 mesh sieve) for refining. Then, it is mixed with new powder in the following proportions: EP powder 1:3, AD powder 1:2, PE powder 1:1.5, with a reuse rate ≥85%.

[0037] In practical operation: A segmented gas-fired heating furnace design is adopted. Through temperature gradient control in the heating section, insulation section, and outlet transition section, as well as uniform radiant heating with a flat fan-shaped flame, heat utilization efficiency is significantly improved. Based on customized heating parameters for steel pipes of different diameters, the total heating time is reduced by 30%-49% compared to traditional electric heating, with the most significant efficiency improvement (35%-48%) for small-diameter steel pipes. Simultaneously, the energy cost of gas heating is lower than that of electricity. Combined with the buffer insulation design of the outlet transition section to reduce heat loss, the heating energy consumption per unit of steel pipe is further reduced, significantly improving production economics. Precise temperature control is achieved throughout the entire process of steel pipe heating, spraying, and impregnation, with errors kept within ±5℃ (heating and exiting the furnace error ±3℃). This ensures that each coating material completes curing and melting within its optimal temperature range, significantly improving the interfacial bonding between the epoxy resin layer, adhesive layer, and polyethylene layer. It also prevents coating peeling and delamination defects caused by temperature fluctuations. Customized processes enhance coating uniformity: different numbers of spray guns, spraying parameters, impregnation speeds, and rotation speeds are matched to steel pipes of different diameters. Combined with the vibration-resistant design of the suspended water-cooled spray guns and the circulating impregnation design of the liftable multi-zone vulcanization tank, the uniformity error of the epoxy resin layer thickness is ≤±5%, the AD layer ≤±6%, and the PE layer ≤±7%. The coating surface has high smoothness, with no powdering, dripping, or uneven thickness issues. Multiple pretreatments ensure coating cleanliness: targeted pretreatment before each process (shot blasting, high-pressure air blowing + electrostatic adsorption, hot air blowing) and powder drying and sieving treatment ensure that the surface cleanliness of the steel pipe reaches Sa2.5 or above, the dust residue is ≤5mg / m², and the powder moisture content is ≤0.1%, effectively avoiding the impact of impurities and moisture on the coating quality and improving the density and corrosion resistance of the anti-corrosion layer; The three-tiered powder recycling system covers the entire process, achieving efficient recycling and reuse of powder resources. First-level source control reduces powder dispersion, second-level blind spot capture fills the gaps in traditional recycling, and third-level final refining, through processes such as ultrasonic dispersing, drying, and sieving, brings the recycled powder performance close to virgin powder standards. Ultimately, the reuse rate of EP, AD, and PE powders is ≥85%, significantly reducing powder waste. Simultaneously, the membrane-coated cartridge dust collector (filtration efficiency ≥99.99%) effectively intercepts fine dust, preventing dust pollution and meeting green production requirements. By circulating water to lower the temperature of the spray gun, the melting and solidification of powder inside or outside the spray gun can be avoided, ensuring that epoxy resin powder can be sprayed at high temperatures, improving spraying efficiency and quality, while reducing the frequency and cost of cleaning and maintaining the spray gun. Example

[0038] Based on Example 1, the process also includes multi-tube synchronous spraying, with the specific steps as follows: Step 1: Multiple steel pipes are transported into the powder coating booth via a transmission device. Sensors detect the position and speed of the steel pipes and transmit the signals to the control system.

[0039] Step two: The control system selects the appropriate spraying mode based on the type and quantity of steel pipes, and adjusts the working parameters of the spraying equipment, such as production cycle, spraying speed, and powder quantity.

[0040] Step 3: The control system sends a spraying command to the spraying device, which then sprays the steel pipe internally according to the preset spraying trajectory and speed. At the same time, the intelligent following function enables the spraying device to move synchronously with the steel pipe.

[0041] Step four: The control system monitors the status and quality of the spraying process, collects and analyzes spraying data, and optimizes and adjusts the spraying equipment to improve spraying efficiency and quality.

[0042] It also includes a stepping hydraulic lifting trolley, used to move steel pipes horizontally and realize the transfer of steel pipes between different process steps. The stepping hydraulic lifting trolley includes components such as a base, column, hydraulic cylinder, hydraulic pump, hydraulic pin, lifting arm, and lifting head, as well as vision sensors and a control system. The process flow is as follows: Step one: The vision sensor acquires and processes images of the steel pipe through the camera to obtain the position and orientation information of the steel pipe, such as the coordinates of the center point, length, diameter, and tilt angle. Then, this data is transmitted to the control system.

[0043] Step two: The control system calculates the target position and attitude of the lifting vehicle based on the data from the vision sensor, such as the moving distance, rotation angle, and lifting height of the lifting vehicle. Then, it converts this data into corresponding control signals and sends them to the hydraulic pump and motor actuator.

[0044] Step three: The hydraulic pump and motor, etc., control the movement and lifting of the base, column, lifting arm and other components of the lifting vehicle according to the control signal, so that the lifting head of the lifting vehicle is aligned with the support point of the steel pipe, and finally realizes automatic sensing, precise positioning and multi-stage lifting of the steel pipe.

[0045] In practice: internal anti-corrosion is integrated with the external anti-corrosion immersion station using roller coating; by developing a multi-pipe synchronous spraying system, up to three pipes can be operated in parallel, which increases production efficiency by 25% and shortens the production cycle by 40%. Example

[0046] Based on the above embodiments: the cooling adopts a three-stage combination mode of "front air cooling pre-cooling → middle water cooling main cooling → rear air cooling slow cooling", and the specific steps are as follows: (1) Pre-cooling: After the steel pipe is impregnated with PE powder, it enters a 5m long cooling hood. The annular air curtain cooling hood is activated, and the air source is heated air at 25-30℃. The air velocity is set according to the pipe diameter at 5-8m / s (5-6m / s for small pipe diameter, 6-7m / s for medium pipe diameter, and 7-8m / s for large pipe diameter). The temperature of the PE coating is reduced from 190-200℃ to 120-150℃, with a cooling rate of 3-5℃ / min. The distance between the air hood and the steel pipe is 150-200mm. The uniformity of the air velocity is ensured to be ≤±5% through the flow equalization plate. (2) Medium water cooling main cooling: Start the low pressure atomizing spray chamber, use softened water at 40-50℃, set the total water volume to 5-15m³ / h according to the pipe diameter (5-8m³ / h for small pipe diameter, 9-12m³ / h for medium pipe diameter, and 12-15m³ / h for large pipe diameter), spray pressure 0.3-0.5MPa, atomization particle size 50-100μm, reduce the coating temperature from 120-150℃ to 60-80℃, cooling rate 5-8℃ / min, water recycling rate ≥95%; (3) Post-air cooling and slow temperature reduction: Start the uniform flow layer air cooling cover, the air source is a constant temperature air of 30-35℃, and the air speed is set to 3-5m / s according to the pipe diameter (3-4m / s for small pipe diameter, 5m / s for large pipe diameter) to reduce the coating temperature from 60-80℃ to 25-30℃, with a cooling rate of 2-3℃ / min; This process precisely controls parameters using the convective heat transfer formula Q=h×A×ΔT and the cooling rate formula dτdT=m×ch×A×ΔT, ensuring that the coating thermal stress σ=α×E×ΔTmax≤2MPa. This solves the problems of coating cracking and interlayer delamination caused by traditional rapid water cooling, achieving a coating cracking rate ≤0.1% and a curing degree ≥95%. Specifically: 1. Basic formula for convective heat transfer

[0047] Convective heat transfer (Q) is the core of the cooling process, and the formula is as follows: Q = h × A × ΔT • Symbol explanation: Q: Convective heat transfer (W);

[0048] h: Convection heat transfer coefficient (W / (m²·℃), air-cooled hair≈15-30 W / (m²·℃), water-cooled hwater≈500-1500 W / (m²·℃)); A: Heat exchange area (m²), calculated based on the outer surface area of ​​the steel pipe: A=π×D×L (D is the outer diameter of the steel pipe, and L is the effective length of the cooling section); ΔT: The average temperature difference (°C) between the heat exchange medium and the coating surface, ΔT=2(Tcating, in−Tmedium)+(Tcating, ut−Tmedium) (Tcating, in is the inlet coating temperature of the stage, Tcating, ut is the outlet coating temperature of the stage, and Tmedium is the air / water temperature). 2. Cooling rate formula

[0049] The cooling rate (dT / dτ) is determined by the heat exchange, the mass of the object (m), and the specific heat capacity (c), and the formula is as follows: dτ / dT = m × cQ = m × ch × A × ΔT Symbol explanation: dτdT: cooling rate (°C / min); m: Total mass (kg) of steel pipe + three-layer coating, m = msteel + mEP + mAD + mPE (mass of steel pipe msteel = π × (D − tsteel) × tsteel × L × ρsteel, coating mass is calculated by volume × density, ρEP≈1.4g / cm3, ρAD≈1.1g / cm3, ρPE≈0.95g / cm3); c: Total specific heat capacity (J / (kg・℃)), calculated by mass-weighted average: c=mmsteelcsteel+mEPcEP+mADcAD+mPEcPE (csteel=460, cEP=1800, cAD=1900, cPE=2200, all units are J / (kg・℃)). 3. Thermal stress verification formula (core control index)

[0050] The essence of coating cracking is that thermal stress exceeds the allowable stress of the material. The formula for thermal stress (σ) is as follows: σ = α × E × ΔTmax Symbol explanation: σ: Coating thermal stress (MPa); α: Coefficient of thermal expansion of coating (1 / ℃), αPE≈18×10−6, αAD≈15×10−6, αEP≈6×10−6; E: Coating elastic modulus (MPa), EPE≈800, EAD≈1200, EEP≈3500 (at room temperature). ΔTmax: Maximum temperature difference of the coating (°C), which is the maximum temperature difference between the surface and interior of the coating during the cooling process (this design controls the temperature by gradient cooling).

[0051] Allowable stress requirement: The allowable stress of the PE coating is approximately 3 MPa. In this design, σ is controlled to be less than or equal to 2 MPa to avoid cracking.

[0052] (III) Example Calculation (Taking DN800×12mm steel pipe as an example) 1. Basic parameters

[0053] Steel pipe parameters: D=800mm=0.8m, tsteel=12mm=0.012m, L=15m (total cooling length), ρsteel=7850kg / m3; Coating parameters: tEP=0.5mm, tAD=1.0mm, tPE=3.0mm; Cooling parameters: front air cooling ℃, middle water cooling ℃, rear air cooling ℃. 2. Key Calculation Steps

[0054] (1) Calculate the total mass (m): Steel pipe mass: msteel=π×(0.8−0.012)×0.012×15×7850≈3480kg; Coating weight: mEP = π × 0.8 × 15 × 0.0005 × 1400 ≈ 26.4 kg, mAD = π × 0.8 × 15 × 0.001 × 1100 ≈ 41.5 kg, mPE = π × 0.8 × 15 × 0.003 × 950 ≈ 107.4 kg; Total mass: m = 3480 + 26.4 + 41.5 + 107.4 ≈ 3655.3 kg.

[0055] (2) Calculate the total specific heat capacity (c): ℃ (3) Heat exchange and cooling rate in the pre-air cooling stage: Heat exchange area: A = π × 0.8 × 5 ≈ 12.57 m2 (front air-cooled section length 5 m); Average temperature difference: ℃; Convection heat transfer coefficient: 2℃ (at a wind speed of 7m / s); Heat exchange: Q1 = 25 × 12.57 × 147 ≈ 46300 W; Cooling rate: ℃ (actual design 3-5℃ / min, h value can be adjusted by increasing wind speed).

[0056] (4) Thermal stress check: Maximum temperature difference of PE coating: ℃; Thermal stress: σ = 18 × 10−6 × 800 × 25 = 0.36 MPa ≤ 2 MPa, which meets the requirement of no cracking.

[0057] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from its spirit and scope. All such changes and modifications fall within the scope of the present invention as claimed, which is defined by the appended claims and their equivalents.

Claims

1. A smart 3PE anti-corrosion production process employing gas heating-spray immersion coating, characterized in that, The process includes the following steps: Step 1: After removing rust from the outer and inner walls of the steel pipe using shot blasting equipment, it is placed in a gas-fired heating furnace for heating at a temperature of 280℃. The temperature is then reduced to 260℃. The temperature is checked before the pipe is removed from the furnace, with an error within ±3℃. Step 2: Transfer the steel pipe to the first layer epoxy resin powder coating equipment within 1-2 minutes, and spray it evenly with a spray gun for 10-30 seconds. At this time, the temperature of the steel pipe is 240℃, and the first layer of epoxy resin powder coating is completed. Step 3: Move the steel pipe to the AD (adhesive) station at a temperature of 210-220℃, open the AD vulcanizing tank (the length of the vulcanizing tank matches the length of the steel pipe), and immerse the bottom of the rotating steel pipe in the vulcanized AD powder. After rotating once, the AD anti-corrosion is completed, and the second layer of adhesive powder is impregnated. Step 4: Move the steel pipe to the polyethylene powder impregnation station. The temperature is 190-200℃. The transfer vehicle moves the steel pipe to the PE (polyethylene) powder station. At this time, the temperature is about 190-200℃. Open the PE vulcanization tank. The bottom of the rotating steel pipe is impregnated into the vulcanized PE powder, completing the third layer of polyethylene powder impregnation. Step 5: Move the steel pipe to the cooling station for cooling.

2. The intelligent 3PE anti-corrosion production process using gas heating-spraying immersion as described in claim 1, characterized in that, The heating process of the gas-fired heating furnace is as follows: The gas-fired heating furnace is divided into three parts: a heating section, a heat preservation section, and an outlet transition section. The heating section occupies 1 / 3 of the furnace width, with the flame tip temperature controlled at 950-1050℃. The heat preservation section occupies 2 / 3 of the furnace width, with the flame tip temperature reduced to 850-900℃, using a gentle radiation + convection method. The outlet transition section is located 5m from the end of the furnace, with the flame tip temperature reduced to 700-750℃. It works in conjunction with the furnace insulation layer to achieve a buffer transition, preventing a sudden drop in temperature after the steel pipe exits the furnace. The distance between the flame tip and the steel pipe surface is 150-200mm to prevent the flame from directly burning the steel pipe surface and causing the oxide scale to thicken. The flame nozzle at the flame tip sprays flames in a flat fan shape with a diffusion angle of 30° and the flames sprayed between adjacent flame nozzles overlap by 10%. The flame nozzles are linearly and evenly distributed at the top of the gas heating furnace, and each flame nozzle is equipped with a valve for individual control. The gas-fired heating furnace is equipped with one set of K-type thermocouples (temperature measurement accuracy ±0.5℃) at the inlet, the end of the heating section, and the end of the outlet transition section, for a total of 4 detection points, to collect the surface temperature of the steel pipe in real time. An infrared thermometer (response time ≤0.1s) is installed at the outlet of the gas-fired heating furnace to perform 100% online detection of the steel pipe outlet temperature, ensuring that the outlet temperature is accurately controlled at 260℃ (allowable deviation ±3℃).

3. The intelligent 3PE anti-corrosion production process using gas heating-spraying immersion as described in claim 2, characterized in that, The heating time of the gas-fired heating furnace is set according to the specifications of the steel pipe. For small pipe diameters (150-300mm in diameter and 6-8mm in wall thickness), the total heating time is 18-22 minutes, with a heating phase of 12-15 minutes and a heat preservation phase of 6-7 minutes. For medium-diameter pipes (diameter 300-800mm, wall thickness 8-12mm), the total heating time is 25-30 minutes, with a heating phase of 18-20 minutes and a heat preservation phase of 7-10 minutes. For large-diameter pipes (800-1400mm diameter, 12-20mm wall thickness), the total heating time is 35-45 minutes, with a heating phase of 25-30 minutes and a heat preservation phase of 10-15 minutes.

4. A gas-heated, spray-coating, immersion-type intelligent 3PE anti-corrosion production process according to claim 1, characterized in that, The spraying process for the first layer of epoxy resin powder coating is as follows: (1) Pre-treatment connection before spraying: The steel pipe enters the front end of the first layer epoxy resin powder spraying equipment and sets up a pre-treatment stage that occupies 1 / 5 of the width of the spraying equipment. In the pre-treatment stage, a 0.4-0.6MPa high-pressure air purging + 30-50kV electrostatic adsorption secondary purification device is added to remove surface dust (residual amount ≤5mg / m²) to ensure that the temperature is stable at 230-245℃ (fluctuation ≤±5℃) when entering the spraying station and the surface cleanliness reaches Sa2.5 level or above. The high-pressure air purging is connected to an external gas heating furnace to make the temperature of the sprayed gas 240℃. (2) Powder pretreatment: Modified EP powder (containing 5% KH-550 silane coupling agent) with a particle size of 20-80μm (D50=50μm) and an angle of repose of ≤32° is used after drying at 80℃ for 2h (moisture content ≤0.1%) and sieving with 100 mesh. (3) Customized spraying: High-temperature resistant suspended water-cooled spray guns are used. The gun bar on the spray gun adopts a suspended spray bar system. The heating zone is equipped with a double-layer stainless steel water-cooled gun bar to prevent powder falling and dripping caused by the vibration of the stabilizer during steel pipe spraying. The number of spray guns is designed to be 4 for small pipe diameter, 8 for medium pipe diameter, and 16 for large pipe diameter. The axis is at an angle of 30-35° with the surface of the steel pipe. The parameters are set according to the pipe diameter: spraying pressure 0.35-0.65MPa, powder amount per gun 1000-1500g / min, spraying speed 0.5-1.5m / min, electrostatic voltage 60-90kV, and spraying time 10-30 seconds. (4) Real-time control: The temperature and coating thickness are monitored in real time by infrared thermometer (response time ≤ 0.1s) and laser thickness gauge (accuracy ± 0.01mm). AI vision detection identifies surface defects ≥ 0.1mm. The parameters are automatically adjusted when the temperature exceeds the window or the thickness deviation exceeds ± 5%.

5. The intelligent 3PE anti-corrosion production process using gas heating-spraying immersion as described in claim 4, characterized in that, The high-temperature resistant suspended water-cooled spray gun includes a water-cooling system. This water-cooling system is consistent with the high-temperature resistant suspended water-cooled spray gun, with a fully enclosed water circulation zone volume ≥5L, a circulating water flow rate of 0.8-1.2m / s, an inlet water temperature ≤25℃, and an outlet water temperature ≤45℃. A closed-loop cooling system is formed by a stainless steel water tank + plate cooler + variable frequency circulating pump, so that the surface temperature of the gun head is ≤60℃. The temperature of the spray gun is reduced by the flow of circulating water to prevent EP powder from solidifying and forming a skin.

6. The intelligent 3PE anti-corrosion production process using gas heating-spraying immersion as described in claim 5, characterized in that, The amount of epoxy resin powder sprayed in the first layer is calculated according to Q_pwder=(π×D×L_unit×δ_target×ρ_pwder) / η_recvery×V in: D: Outer diameter of steel pipe (m) L_unit: Unit length = 1m (used to calculate the amount of paint sprayed per meter) δ_target: Target coating thickness (m), taken as 100μm = 0.0001m (median value) ρ_pwder: Density of epoxy resin powder, taken as 1.4 g / cm³ = 1400 kg / m³ η_recvery: Powder recycling rate, taken as 0.90 (i.e., 90% effective adhesion). V: Speed ​​of steel pipe travel (m / min); The design formula is: Q_pwder(g / min)=0.44×D×V. The distance between the high-temperature resistant suspended water-cooled spray gun and the pipe diameter is 180mm. Spraying starts 0.5 seconds before the steel pipe enters the spraying area and ends 0.3 seconds after the steel pipe leaves the spraying area.

7. The intelligent 3PE anti-corrosion production process using gas heating-spraying immersion as described in claim 6, characterized in that, The second layer of adhesive powder impregnation and the third layer of polyethylene powder impregnation are carried out through the following specific processes: Second layer of adhesive powder impregnation: ① Pre-treatment connection: After the first layer of epoxy resin powder is sprayed and before entering the second layer of adhesive powder impregnation, the loose powder is removed by hot air blowing at 0.15-0.2MPa. The hot air outlet temperature is 210-220℃, and the surface temperature of the steel pipe is stabilized at 210-220℃ (fluctuation ≤±3℃). The gel rate of EP coating is 70-80%. ②Powder pretreatment: Modified cplyPP type AD powder (containing 3% MAH-g-PP thickener) with a particle size of 30-90μm (D50=60μm) is used after vacuum drying at 90℃ for 1.5h (moisture content ≤0.08%) and ultrasonic dispersion. ③ Customized impregnation: A closed segmented vulcanizing tank is adopted, and the steel pipe is horizontally moved (0.5-1.5m / min) and rotated at a uniform speed (10-40r / min) by a stepping hydraulic lifting vehicle. The parameters are set according to the pipe diameter: the powder temperature of the vulcanizing tank is 165-180℃, impregnation is 1 round, and the AD layer thickness is 0.8-1.2mm (uniformity error ≤±6%). ④ Transition and connection: After being kept warm by hot air at 195-205℃ for 40-80 seconds, the AD coating melt rate is ≥85%, and the surface is leveled before being transported to the PE station; Third layer of polyethylene powder impregnation ① Pre-treatment connection: After the steel pipe is impregnated with AD and heat-insulated, it is transported to the third layer of polyethylene powder impregnation (PE station). The surface temperature of the steel pipe is stabilized at 190-200℃ (fluctuation ≤ ±4℃), and the curing degree of AD coating is 30-40%. ②Powder pretreatment: HDPE modified powder (containing 5% EVA toughening agent) with a particle size of 40-120μm (D50=80μm) is used. It is dried at 100℃ for 2h (moisture content ≤0.05%) and sieved through an 80-mesh sieve before being put into use. ③ Customized impregnation: The lifting multi-zone vulcanizing tank is adopted. Through 1-3 cycles of impregnation + touch-up coating, the parameters are set according to the pipe diameter: vulcanizing tank powder temperature 175-190℃, steel pipe rotation speed 8-35r / min, PE layer thickness 2.5-3.5mm (uniformity error ≤±7%). Cooling: The PE coating is cooled through a cooling channel, achieving a curing degree of ≥95% and an internal stress of ≤2MPa.

8. A gas-heated, spray-coating, immersion-type intelligent 3PE anti-corrosion production process according to any one of claims 1-7, characterized in that, The first layer of epoxy resin powder spraying, the second layer of adhesive powder impregnation and the third layer of polyethylene powder impregnation are all connected to the three-level powder recovery system. The process of the three-level powder recovery system is as follows: (1) First-level source control and recovery unit: including the front end of the pipe and the rear end of the pipe synchronously following the powder suction hood, the variable frequency centrifugal fan and the primary filter box; the powder suction hood adopts a flexible sealing skirt (the gap with the steel pipe surface is ≤5mm), and is linked with the stepping hydraulic lifting trolley, automatically adapting to the DN159-1400mm pipe diameter and the 0.5-1.5m / min translation speed, and setting the air volume to 3000-10000m³ / h and the suction pressure to -7~-18kPa according to the pipe diameter. The primary filter box intercepts large particle impurities through a 50-mesh screen and is equipped with a pressure difference trigger back-blowing device; (2) Second-level dead angle capture and recovery unit: including the telescopic pipe inner wall suction device, the work station full sealing cover, the side suction port array and the double cone section cyclone separator; the suction pipe and the inner wall of the pipe are connected to the primary filter box. The anti-corrosion spray gun moves synchronously, and the umbrella-shaped suction nozzle captures dust on the inner wall of the pipe with an air volume of 800-2000 m³ / h; the sealed cover has built-in infrared heat lamps to maintain 50-60℃, and the side suction port array is arranged in 1 group every 1m along the axial direction to capture suspended dust at the work station; the cyclone separator separates powder with a particle size ≥10μm and has a separation efficiency ≥92%; (3) Three-level terminal refining and recycling unit: including 16 sets of membrane filter cartridge dust collectors (pore size 1μm, filtration efficiency ≥ The equipment includes an ultrasonic dispersing device (99.99%), a vacuum drying device, a three-layer vibrating sieve, and a grading mixing chamber. The recovered powder is ultrasonically dispersed (20kHz×10-15s), vacuum dried (60-80℃×30-60min, moisture content ≤0.05%), and graded and sieved (60-120 mesh sieve) for refining. Then, it is mixed with new powder in the following proportions: EP powder 1:3, AD powder 1:2, PE powder 1:1.5, with a reuse rate ≥85%.

9. The intelligent 3PE anti-corrosion production process using gas heating-spraying immersion as described in claim 8, characterized in that, This also includes multi-pipe simultaneous spraying, with the specific process steps as follows: Step 1: Multiple steel pipes are transported into the powder coating booth via a transmission device. The position and speed of the steel pipes are detected by sensors, and the signals are transmitted to the control system. Step two: The control system selects the appropriate spraying mode based on the type and quantity of steel pipes, and adjusts the working parameters of the spraying equipment, such as production cycle, spraying speed, and powder amount. Step 3: The control system sends a spraying command to the spraying device, so that the spraying device sprays the inside of the steel pipe according to the preset spraying trajectory and speed. At the same time, the intelligent following function realizes the synchronous movement of the spraying device and the steel pipe. Step four: The control system monitors the status and quality of the spraying process, collects and analyzes spraying data, and optimizes and adjusts the spraying equipment to improve spraying efficiency and quality.

10. A gas-heated, spray-coating, immersion-type intelligent 3PE anti-corrosion production process according to claim 1 or 9, characterized in that, It also includes a stepping hydraulic lifting trolley, used to move steel pipes horizontally and realize the transfer of steel pipes between different process steps. The stepping hydraulic lifting trolley includes components such as a base, column, hydraulic cylinder, hydraulic pump, hydraulic pin, lifting arm, and lifting head, as well as vision sensors and a control system. The process flow is as follows: Step 1: The vision sensor acquires and processes images of the steel pipe through the camera to obtain the position and orientation information of the steel pipe, such as the coordinates of the center point, length, diameter, and tilt angle of the steel pipe, and then transmits this data to the control system. Step two: The control system calculates the target position and attitude of the lifting vehicle based on the data from the vision sensor, such as the moving distance, rotation angle, and lifting height of the lifting vehicle. Then, it converts this data into corresponding control signals and sends them to the hydraulic pump and motor actuator. Step three: The hydraulic pump and motor, etc., control the movement and lifting of the base, column, lifting arm and other components of the lifting vehicle according to the control signal, so that the lifting head of the lifting vehicle is aligned with the support point of the steel pipe, and finally realizes automatic sensing, precise positioning and multi-stage lifting of the steel pipe.

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