Polyethylene zero-hollowing full-automatic winding anti-corrosion process for hot-bending elbow

Abstract

The invention relates to the technical field of hot bent pipes, and discloses a hot bent pipe polyethylene zero-hollowing full-automatic winding anti-corrosion process which comprises the following steps: carrying out sand blasting on the outer surface of a hot bent pipe to remove rust to Sa2.5 level, cleaning, and then coating an epoxy primer; uniformly preheating the surface of the bent pipe to 40-60 DEG C by adopting infrared heating; a polyethylene belt is spirally wound along the axis of the bent pipe to form a winding layer, the winding tension is constantly 50-80 N, and the lap joint rate is 30-50%; the surface of the winding layer is covered with a flexible vacuum film, negative pressure of-0.1 MPa to-0.08 MPa is applied, and the negative pressure is maintained for 5-10 min. According to the method, the cleanness of a base surface is ensured through sand blasting derusting and epoxy primer coating, infrared preheating, constant tension winding and lap joint rate control are combined, a polyethylene belt is tightly attached to the curved surface of the bent pipe, negative pressure is applied through a flexible vacuum film, bubbles in a winding layer are removed in time, then gradient temperature control curing is conducted, and the zero-hollowing structure of the polyethylene layer is achieved; and the bonding strength and the long-term sealing performance of the anti-corrosion layer and the base body are greatly enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of hot-bent pipes, and particularly to a fully automatic winding anti-corrosion process for polyethylene with zero air pockets on hot-bent pipes. Background Art

[0002] In the field of anti-corrosion of hot-bent pipes, traditional polyethylene winding processes often result in air pocket defects in the anti-corrosion layer due to uneven manual operation tension and inaccurate curing temperature control, seriously affecting the corrosion resistance and service life of the bent pipes. Although existing technologies have attempted to improve the winding method or optimize the material formula, it is still difficult to achieve full-process automatic control and quantitative detection of air pockets. In particular, there is a lack of an efficient solution for air pocket problems in the curved surface area of the bent pipes. There is an urgent need for a full-process technology integrating automatic winding, negative pressure defoaming, gradient curing, and intelligent air pocket detection to achieve the goal of "zero air pockets".

[0003] A prior patent discloses a new anti-corrosion process for modified asphalt polyethylene steel pipes (publication number CN104119686A). In this process, the steel pipe is first derusted, the conveying connection pipe is made, medium-frequency heating is carried out, and powder spraying is performed. Then, the modified asphalt powder is put into a high-speed mixer and uniformly formed through high-speed mixing. Then, it is extruded and coated or side-wound and coated on the outer surface of the steel pipe through an extruder circular die to form an anti-corrosion layer. Then, another plastic extruder circular die is used to extrude and coat or side-wound and coat a layer of PE outside the modified asphalt anti-corrosion layer to form a protective layer, thus forming a complete anti-corrosion structure for modified asphalt polyethylene steel pipes, and the above raw materials are in parts by weight. In the technology disclosed in this patent, after side-winding and coating a layer of PE on the modified asphalt anti-corrosion layer, there is often an "air pocket" phenomenon due to technical problems. This "air pocket" can only be judged by workers knocking on the pipe to listen to the echo, and its efficiency is very low and the accuracy is insufficient. Summary of the Invention

[0004] The present invention provides a fully automatic winding anti-corrosion process for polyethylene with zero air pockets on hot-bent pipes to solve the existing technical problems, and solves the problem of air pockets occurring when winding the anti-corrosion layer on the pipe surface.

[0005] To solve the above technical problems, according to one aspect of the present invention, more specifically, a fully automatic winding anti-corrosion process for polyethylene with zero air pockets on hot-bent pipes includes the following steps: S1. Sandblast and derust the outer surface of the hot-bent pipe to Sa2.5 level, and apply an epoxy primer after cleaning; S2. Uniformly preheat the surface of the bent pipe to 40 - 60 °C by infrared heating; S3. Spirally wind the polyethylene tape along the axis of the bent pipe to form a winding layer, and the winding tension is kept constant at 50 - 80 N, and the overlap rate is 30 - 50%; S4. Cover a flexible vacuum film on the surface of the winding layer, apply a negative pressure of -0.1 to -0.08 MPa and maintain it for 5 to 10 minutes; S5. Move the elbow into a gradient temperature-controlled curing oven and increase the temperature step by step to 80 °C at a rate of 10 °C / min; S6. Based on infrared thermal imaging, obtain the shadow contour pictures of the air pockets that appear in the vacuum film and the winding layer; S7. According to the relationship between the characteristics in the shadow contour pictures and the quality of the manually sampled and detected hot-bent elbows, construct a detection model for the air pocket defects of the hot-bent elbows; S8. Based on the air pocket coefficient output by the air pocket defect detection model and the actual use environment of the hot-bent elbow, establish a defect judgment comparison table.

[0006] Furthermore, in the step S1, the thickness of the epoxy primer is 80 to 120 .

[0007] Furthermore, in the step S4, the vacuum film is made of silica gel and has a temperature resistance of ≥150 °C.

[0008] Furthermore, the width of the polyethylene tape is 50 to 100 mm, the melting point is 130 °C, and the polyethylene tape contains the following components: High-density polyethylene, with a mass percentage of 85 to 92%; Maleic anhydride grafted polyethylene, with a mass percentage of 5 to 8%; Nano-silica, with a mass percentage of 3 to 5%.

[0009] Furthermore, in the step S5, the temperature control curve of the gradient temperature-controlled curing oven is as follows: 1). After rising from 40 °C to 50 °C, maintain the temperature of 50 °C for 10 minutes; 2). After rising from 50 °C to 60 °C, maintain the temperature of 60 °C for 10 minutes; 3). After rising from 60 °C to 70 °C, maintain the temperature of 70 °C for 10 minutes; 4). After rising from 70 °C to 80 °C, maintain the temperature of 80 °C for 30 minutes.

[0010] Furthermore, in the step S7, the specific steps for obtaining the characteristics in the shadow contour pictures are as follows: 1). Input all the shadow contour pictures into a neural network to obtain the pixel area feature x of the shadow contour; 2). Based on the shadow contour corresponding to the pixel area feature x, extract the average temperature difference feature y between the inner and outer edges of the corresponding shadow contour; 3). According to the pixel area feature x and the average temperature difference feature y, obtain the approximate volume v of the air pocket shown by the corresponding shadow contour.

[0011] Furthermore, in step S7, the specific steps for constructing the hollow defect detection model of the hot-bent pipe are as follows: S701. Determine the hollow coefficient of the hot-bent pipe according to the ranking of the number of surface defects detected by manual sampling in the sample. S702. Respectively establish a characteristic relationship between the hollow coefficient of the hot-bent pipe, the ratio of the approximate volume v of the maximum shadow contour to the approximate volume v of the minimum shadow contour, and the variance of the average temperature difference feature y of all shadow contours in the hot-bent pipe. S703. Establish a hollow defect detection model based on this characteristic relationship.

[0012] Furthermore, the specific calculation formula for the hollow defect detection model to output the hollow coefficient is: ; In the formula, represents the hollow coefficient output by infrared thermal imaging to obtain the characteristics of the shadow contour picture of the hot-bent pipe; represents the ratio of the approximate volume v of the maximum shadow contour to the approximate volume v of the minimum shadow contour in the hot-bent pipe; represents the variance of the average temperature difference feature y of all shadow contours in the hot-bent pipe.

[0013] Furthermore, the division of the actual use environment in step S8 includes oil and gas transportation environment, chemical and high-temperature liquid transportation environment, tap water transportation environment, and sewage transportation environment.

[0014] A fully automatic winding anti-corrosion process for polyethylene with zero hollows in hot-bent pipes provided by the present invention, compared with the prior art, the effects achieved by this method are as follows: 1. The present invention ensures a clean base surface through sandblasting and rust removal and epoxy primer coating. By combining infrared preheating, constant tension winding, and overlap rate control, the polyethylene tape is tightly attached to the curved surface of the bent pipe, and a flexible vacuum membrane is used to apply negative pressure to immediately remove the bubbles in the winding layer, and then gradient temperature control curing is carried out to achieve a zero-hollow structure of the polyethylene layer, greatly enhancing the bonding strength and long-term sealing performance between the anti-corrosion layer and the matrix.

[0015] 2. The present invention captures the hollow shadow contour based on infrared thermal imaging technology, extracts the pixel area feature and the average temperature difference feature between the inner and outer edges, constructs an approximate hollow volume calculation model, and further combines the maximum / minimum hollow volume ratio and temperature difference variance to establish a hollow coefficient formula, realizing the digital and automatic evaluation of anti-corrosion layer defects. This model can accurately predict the surface defect density grade of hot-bent pipes by associating sample training with manual sampling data, replacing traditional destructive testing.

[0016] 3. The polyethylene tape formulation in the present invention contains high-density polyethylene, maleic anhydride-grafted polyethylene, and nano-silica. Among them, the grafted component enhances the interfacial adhesion force, and the nano-particles improve the material stiffness and thermal stability. Combining with the melting point of 130 °C and the customized width, it ensures the molten fluidity and covering uniformity during the winding process, is suitable for the complex curvature of the elbow pipe, and can withstand the high temperature of gradient curing at the same time, avoiding material degradation.

[0017] 4. The present invention realizes automatic control throughout the whole process from surface treatment, preheating, winding, negative pressure exhaust to gradient curing, reducing human error. By establishing a defect judgment comparison table of the hollowing coefficient and the actual use environment, the quality acceptance standard is dynamically adjusted to ensure the anti-corrosion reliability under different corrosion environments and improve the engineering applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a flow chart of the present invention; Figure 2 is a graph showing the relationship between the hollowing coefficient c and the ratio m of the approximate volume of the present invention; Figure 3 is the hollowing coefficient c and variance s of the present invention 2关系图； Figure 4 is the ratio m of the hollowing coefficient c to the approximate volume and variance s of the present invention 2关系图。 DETAILED DESCRIPTION OF THE INVENTION

[0019] To make the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] As Figures 1-4 shown, in a fully automatic winding anti-corrosion process for polyethylene with zero hollowing of a hot-bent elbow pipe, the specific acquisition steps of the features in the shadow contour picture are as follows: 1). Input all the shadow contour pictures into the neural network to obtain the pixel area feature x of the shadow contour.

[0021] 2). Based on the shadow contour corresponding to the pixel area feature x, extract the mean temperature difference feature y between the inner and outer edges of the corresponding shadow contour.

[0022] 3). According to the pixel area feature x and the mean temperature difference feature y, obtain the approximate volume v of the hollowing shown in the corresponding shadow contour.

[0023] Among them, the specific steps for constructing a hollowing defect detection model of a hot-bent elbow pipe according to the above features are as follows: S701. Determine the hollowing coefficient of the hot-bent elbow pipe according to the ranking of the number of surface defects detected by manual sampling in the sample.

[0024] Among them, the hollow coefficient c output by infrared thermal imaging to obtain the picture features of the shadow contour of the hot-bent pipe can be represented by the ranking of the number of surface defects of the hot-bent pipe detected by manual sampling in the sample.

[0025] For example, when collecting data on 100 hot-bent pipe samples, if after manual evaluation, the defect density of a certain hot-bent pipe exceeds the data in other 50 samples, it means that the hollow coefficient c = 50% output by infrared thermal imaging to obtain the picture features of the shadow contour of the hot-bent pipe.

[0026] All other data are then used for subsequent calculations and fitting statistics with the collected data.

[0027] S702. Respectively establish a feature relationship with the ratio of the hollow coefficient of the hot-bent pipe to the approximate volume v of the maximum shadow contour and the approximate volume v of the minimum shadow contour, and the variance of the mean temperature difference feature y of all shadow contours in the hot-bent pipe.

[0028] Establish a mathematical model for the relationship between the hollow coefficient c and the ratio m of the approximate volume (as shown in Figure [not provided], the red dots in the figure are the distributions of the 100 samples collected), then there is: Figure 2 shown in the figure, the red dots in the figure are the distributions of the 100 samples collected), then there is: (Formula 1); In the above Formula 1, k represents an empirical constant for adjusting the sensitivity of the above model.

[0029] For the relationship between the hollow coefficient c and the variance s 2之间的关系建立数学模型（如图 as shown in Figure [not provided], the blue dots in the figure are the distributions of the 100 samples collected), then there is: (Formula 2); In the above Formula 2, k represents an empirical constant for adjusting the sensitivity of the above model.

[0030] S703. Establish a hollow defect detection model based on this feature relationship.

[0031] For the ratio m of the hollow coefficient c to the approximate volume and the variance s 2之间的关系建立数学模型（如图 as shown in Figure [not provided], it can be known through this model that the ratio m of the approximate volume and the variance s 2呈正相关的关系），并结合由上述公式 1 and the feature relationship of Formula 2, then there is: c = (Formula 1) × (Formula 2); Then according to the above derivation, it can be known that the specific calculation formula for the hollow defect detection model to output the hollow coefficient is: ; In the formula, represents the hollow coefficient output by infrared thermal imaging to obtain the picture features of the shadow contour of the hot-bent pipe; It represents the ratio of the approximate volume v of the largest shaded contour in the hot-bent pipe to the approximate volume v of the smallest shaded contour. It represents the variance of the mean temperature difference feature y of all shaded contours in the hot-bent pipe.

[0032] The explanations of the parameters in this model formula are as follows: Among them, the calculation formula for the approximate volume v of any shaded contour is: ; Among them, represents the approximate volume of this shaded contour; 表示该阴影轮廓的像素面积特征，单位㎜2； represents the mean temperature difference feature between the inner and outer edges in this shaded contour, with the unit of mm. There is: ; In the formula, y represents the mean temperature difference feature between the inner and outer edges in the shaded contour, with the unit of °C; among them, a, b, and c are all material-related fitting parameters (the data in the hot-bent pipe are: a = 0.8, b = 1.2, c = -0.3).

[0033] The ratio of the approximate volume v of the largest shaded contour in the hot-bent pipe to the approximate volume v of the smallest shaded contour is: ; The variance of the mean temperature difference feature y of all shaded contours in the hot-bent pipe is: ; In the formula, represents the mean temperature difference feature of the i-th shaded contour in the same hot-bent pipe; represents the average value of the mean temperature difference features of all shaded contours in this hot-bent pipe; represents the number of all shaded contours in this hot-bent pipe.

[0034] Examples of this model formula are as follows: When calculating the variance of the mean temperature difference feature y of all shaded contours in the hot-bent pipe, the mean temperature difference feature y of all shaded contours in the same hot-bent pipe is collected: Table 1 Mean temperature difference feature of the shaded contour of any hot-bent pipe

[0035] Then, the sample variance formula for the 10 groups of data in Table 1 above is: (°C); Then, the calculation of the variance is: ; Based on the above calculations, it can be known that the variance of the mean temperature difference feature y of all the shadow contours in the hot-bent pipe is 0.024.

[0036] Moreover, when the ratio of the approximate volume v of the largest shadow contour to the approximate volume v of the smallest shadow contour in the hot-bent pipe is taken then there is: ; According to the above calculations, it can be known that in the hot-bent pipe, the variance of the mean temperature difference feature y of all the shadow contours is 0.024, and when the ratio of the approximate volume v of the largest shadow contour to the approximate volume v of the smallest shadow contour is taken the hollowing coefficient output by the infrared thermal imaging for obtaining the shadow contour picture features of the hot-bent pipe is 54.5%. Then there is: Table 2 Defect Judgment Comparison Table of the Relationship between Partial Implementation Data and the Quality of Hot-Bent Pipes

[0037] According to the data in Table 2 above, it can be known that when the sample data tends to infinity, the number of surface defects of the hot-bent pipe is divided by the hollowing coefficient c. For example, when the required number of surface defects of the hot-bent pipe is ≤ 5 per 100 mm × 100 mm, then c ≤ 47%; when the required number of surface defects of the hot-bent pipe is ≤ 3 per 100 mm × 100 mm, then c ≤ 42.3%.

[0038] Example 1 As Figure 1 shown, a fully automatic winding anti-corrosion process for polyethylene with zero hollows in hot-bent pipes is provided. The hot-bent pipe for oil and gas transportation prepared according to this process includes the following steps: Step 1: Sandblast and derust the outer surface of the hot-bent pipe to Sa2.5 level, and apply an epoxy primer after cleaning; the thickness of the epoxy primer is 100 .

[0039] Step 2: Uniformly preheat the surface of the bent pipe to 50 °C by infrared heating; Step 3: Spirally wind the polyethylene tape along the axis of the bent pipe to form a winding layer, and the winding tension is kept constant at 70 N, and the overlap rate is 40%; Step 4: Cover a flexible vacuum film on the surface of the winding layer, apply a negative pressure of -0.1 MPa and maintain it for 10 min. The width of the polyethylene tape is 100 mm, the melting point is 130 °C, and the polyethylene tape contains the following components: High-density polyethylene, with a mass percentage of 90%; Maleic anhydride grafted polyethylene, with a mass percentage of 6%; Nano-silica, with a mass percentage of 4%.

[0040] Step 5: Move the bent pipe into a gradient temperature-controlled curing oven and increase the temperature step by step to 80°C at a rate of 10°C / min; the temperature control curve of the gradient temperature-controlled curing oven is as follows: 1). After rising from 40°C to 50°C, maintain the temperature of 50°C for 10 minutes; 2). After rising from 50°C to 60°C, maintain the temperature of 60°C for 10 minutes; 3). After rising from 60°C to 70°C, maintain the temperature of 70°C for 10 minutes; 4). After rising from 70°C to 80°C, maintain the temperature of 80°C for 30 minutes.

[0041] Step 6: Obtain the shadow contour pictures of the air pockets that appear in the vacuum film and the winding layer based on infrared thermal imaging, and obtain the air pocket coefficient based on the air pocket defect detection model.

[0042] Among them, one standard for the hot-bent pipe used for oil and gas transportation is that the number of surface defects of the hot-bent pipe ≤ 3 per 100mm×100mm. Then it means that the detected and output air pocket coefficient needs to be ≤ 42.3%.

[0043] Example 2 As Figure 1 shown, a fully automatic winding anti-corrosion process for hot-bent pipe polyethylene with zero air pockets is provided. The hot-bent pipe prepared according to this process for chemical and high-temperature liquid transportation includes the following steps: Step 1: Sandblast and derust the outer surface of the hot-bent pipe to Sa2.5 level, and apply an epoxy primer after cleaning; the thickness of the epoxy primer is 120 .

[0044] Step 2: Uniformly preheat the surface of the bent pipe to 60°C by infrared heating; Step 3: Spirally wind the polyethylene tape along the axis of the bent pipe to form a winding layer, and the winding tension is kept constant at 80N, and the overlap rate is 50%; Step 4: Cover the flexible vacuum film on the surface of the winding layer, apply a negative pressure of -0.1MPa and maintain it for 10 minutes. The width of the polyethylene tape is 70mm, the melting point is 130°C, and the polyethylene tape contains the following components: High-density polyethylene, with a mass percentage of 87%; Maleic anhydride grafted polyethylene, with a mass percentage of 8%; Nano-silica, with a mass percentage of 5%.

[0045] Step 5: Move the bent pipe into a gradient temperature-controlled curing oven and increase the temperature step by step to 80°C at a rate of 10°C / min; the temperature control curve of the gradient temperature-controlled curing oven is as follows: 1). After rising from 40°C to 50°C, maintain the temperature of 50°C for 10 minutes; 2), After rising from 50°C to 60°C, maintain the temperature of 60°C for 10 min; 3), After rising from 60°C to 70°C, maintain the temperature of 70°C for 10 min; 4), After rising from 70°C to 80°C, maintain the temperature of 80°C for 30 min.

[0046] Step Six: Obtain the shadow contour pictures of the air voids in the vacuum film and the winding layer based on infrared thermal imaging, and obtain the air void coefficient based on the air void defect detection model.

[0047] Among them, one standard for the hot-bent pipe used for chemical industry and high-temperature liquid transportation is that the number of surface defects of the hot-bent pipe ≤ 3 per 100 mm × 100 mm. Then it means that the detected and output air void coefficient needs to be ≤ 42.3%.

[0048] Example 3 As Figure 1 shown, a fully automatic winding anti-corrosion process for polyethylene zero air void of a hot-bent pipe is provided. The hot-bent pipe prepared according to this process for tap water transportation includes the following steps: Step One: Sandblast and rust-remove the outer surface of the hot-bent pipe to Sa2.5 level, and apply epoxy primer after cleaning; the thickness of the epoxy primer is 90 .

[0049] Step Two: Uniformly preheat the surface of the bent pipe to 50°C by infrared heating; Step Three: Spirally wind the polyethylene tape along the axis of the bent pipe to form a winding layer, and the winding tension is constantly 50 N, and the lap rate is 30%; Step Four: Cover the flexible vacuum film on the surface of the winding layer, apply a negative pressure of -0.09 MPa and maintain it for 6 min. The width of the polyethylene tape is 70 mm, the melting point is 130°C, and the polyethylene tape contains the following components: High-density polyethylene, with a mass percentage of 92%; Maleic anhydride grafted polyethylene, with a mass percentage of 4%; Nano-silica, with a mass percentage of 4%.

[0050] Step Five: Move the bent pipe into a gradient temperature control curing box and increase the temperature step by step to 80°C at a rate of 10°C / min; the temperature control curve of the gradient temperature control curing box is: 1), After rising from 40°C to 50°C, maintain the temperature of 50°C for 10 min; 2), After rising from 50°C to 60°C, maintain the temperature of 60°C for 10 min; 3), After rising from 60°C to 70°C, maintain the temperature of 70°C for 10 min; 4), After rising from 70°C to 80°C, maintain the temperature of 80°C for 30 min.

[0051] Step 6: Obtain the shadow contour pictures of the air voids in the vacuum film and the winding layer based on infrared thermal imaging, and obtain the air void coefficient based on the air void defect detection model.

[0052] Among them, one standard for the hot-bent pipe used for tap water transportation is that the number of surface defects of the hot-bent pipe ≤ 5 per 100 mm × 100 mm. Then it means that the detected and output air void coefficient needs to be ≤ 47%.

[0053] Example 4 As Figure 1 shown, a fully automatic winding anti-corrosion process for polyethylene zero air void of a hot-bent pipe is provided. The hot-bent pipe prepared according to this process for sewage transportation includes the following steps: Step 1: Sandblast and rust-remove the outer surface of the hot-bent pipe to Sa2.5 level, and apply an epoxy primer after cleaning; the thickness of the epoxy primer is 80 .

[0054] Step 2: Uniformly preheat the surface of the bent pipe to 40 °C by infrared heating; Step 3: Spirally wind the polyethylene tape along the axis of the bent pipe to form a winding layer, and the winding tension is kept constant at 50 N, and the overlap rate is 30%; Step 4: Cover the flexible vacuum film on the surface of the winding layer, apply a negative pressure of -0.08 MPa and maintain it for 5 min. The width of the polyethylene tape is 50 mm, the melting point is 130 °C, and the polyethylene tape contains the following components: High-density polyethylene, with a mass percentage of 85%; Maleic anhydride grafted polyethylene, with a mass percentage of 5%; Nano-silica, with a mass percentage of 3%.

[0055] Step 5: Move the bent pipe into a gradient temperature control curing oven and increase the temperature step by step to 80 °C at a rate of 10 °C / min; the temperature control curve of the gradient temperature control curing oven is: 1). After rising from 40 °C to 50 °C, keep the temperature at 50 °C for 10 min; 2). After rising from 50 °C to 60 °C, keep the temperature at 60 °C for 10 min; 3). After rising from 60 °C to 70 °C, keep the temperature at 70 °C for 10 min; 4). After rising from 70 °C to 80 °C, keep the temperature at 80 °C for 30 min.

[0056] Step 6: Obtain the shadow contour pictures of the air voids in the vacuum film and the winding layer based on infrared thermal imaging, and obtain the air void coefficient based on the air void defect detection model.

[0057] Among them, one standard for the hot-bent pipe used for sewage transportation is that the number of surface defects of the hot-bent pipe ≤ 15 per 100mm × 100mm. Then it means that the detected and output hollowing coefficient needs to be ≤ 54.5%.

[0058] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent for the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent for the present invention shall be subject to the appended claims.

Claims

1. A fully automatic winding anti-corrosion process for polyethylene with zero air pockets in hot-bent pipes, characterized in that It includes the following steps: S1. Sandblast and derust the outer surface of the hot-bent pipe to Sa2.5 level, and apply epoxy primer after cleaning; S2. Uniformly preheat the surface of the bent pipe to 40 - 60 °C by infrared heating; S3. Spirally wind the polyethylene tape along the axis of the bent pipe to form a winding layer, and the winding tension is constantly 50 - 80 N, and the overlap rate is 30 - 50%; S4. Cover the flexible vacuum film on the surface of the winding layer, apply a negative pressure of -0.1 - -0.08 MPa and maintain it for 5 - 10 min; S5. Move the bent pipe into a gradient temperature control curing box and stepwise heat it to 80 °C at a rate of 10 °C / min; S6. Based on infrared thermal imaging, obtain the shadow contour pictures of the air pockets that appear in the vacuum film and the winding layer; S7. According to the relationship between the characteristics in the shadow contour pictures and the quality of the hot-bent pipe detected by artificial sampling, construct an air pocket defect detection model for the hot-bent pipe; S8. Based on the air pocket coefficient output by the air pocket defect detection model and the actual use environment of the hot-bent pipe, establish a defect judgment comparison table.

2. The fully automatic winding anti-corrosion process for polyethylene with zero air pockets in hot-bent pipes according to claim 1, characterized in that: In the step S1, the thickness of the epoxy primer is 80~120 .

3. The fully automatic winding anti-corrosion process for polyethylene with zero air pockets in hot-bent pipes according to claim 1, characterized in that: In step S4, the vacuum film is made of silica gel material with a temperature resistance of ≥150 °C.

4. The full-automatic winding anti-corrosion process for polyethylene with zero air pockets in hot-bent pipes according to claim 1, wherein: The width of the polyethylene tape is 50 - 100 mm, the melting point is 130 °C, and the polyethylene tape contains the following components: High-density polyethylene, with a mass percentage of 85 - 92%; Maleic anhydride grafted polyethylene, with a mass percentage of 5 - 8%; Nano-silica, with a mass percentage of 3 - 5%.

5. The full-automatic winding anti-corrosion process for polyethylene with zero air pockets in hot-bent pipes according to claim 1, characterized in that: In step S5, the temperature control curve of the gradient temperature control curing box is as follows: 1). After rising from 40 °C to 50 °C, maintain the temperature of 50 °C for 10 min; 2). After rising from 50 °C to 60 °C, maintain the temperature of 60 °C for 10 min; 3). After rising from 60 °C to 70 °C, maintain the temperature of 70 °C for 10 min; 4). After rising from 70 °C to 80 °C, maintain the temperature of 80 °C for 30 min.

6. The fully automatic winding anti-corrosion process for polyethylene with zero air pockets in hot-bent pipes according to claim 1, characterized in that: In step S7, the specific steps for obtaining the characteristics in the shadow contour pictures are as follows: 1). Input all the shadow contour pictures into the neural network to obtain the pixel area feature x of the shadow contour; 2). Based on the shadow contour corresponding to the pixel area feature x, extract the average temperature difference feature y between the inner and outer edges in the corresponding shadow contour; 3). According to the pixel area feature x and the average temperature difference feature y, obtain the approximate volume v of the air pocket shown in the corresponding shadow contour.

7. The fully automatic winding anti-corrosion process for polyethylene with zero air pockets in hot-bent pipes according to claim 6, characterized in that: In step S7, the specific steps for constructing the air pocket defect detection model for the hot-bent pipe are as follows: S701. Determine the air pocket coefficient of the hot-bent pipe according to the ranking of the number of surface defects of the hot-bent pipe detected by artificial sampling in the sample; S702. Respectively establish a feature relationship between the air pocket coefficient of the hot-bent pipe, the ratio of the approximate volume v of the largest shadow contour to the approximate volume v of the smallest shadow contour, and the variance of the average temperature difference feature y of all shadow contours in the hot-bent pipe; S703. Based on the feature relationship, establish an air pocket defect detection model.

8. The full-automatic winding anti-corrosion process for polyethylene with zero air pockets on hot-bent pipes according to claim 6, characterized in that: The specific calculation formula for the air pocket coefficient output by the air pocket defect detection model is: ； In the formula, represents the hollow coefficient output by infrared thermal imaging to obtain the picture features of the shadow contour of the hot-bent pipe; represents the ratio of the approximate volume v of the largest shadow contour to the approximate volume v of the smallest shadow contour in the hot-bent pipe; represents the variance of the mean temperature difference feature y of all shadow contours in the hot-bent pipe.

9. The fully automatic winding anti-corrosion process for polyethylene with zero air pockets in hot-bent pipes according to claim 1, wherein: In step S8, the division of the actual use environment includes oil and gas transportation environment, chemical and high-temperature liquid transportation environment, tap water transportation environment, and sewage transportation environment.

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