Method for corrosion protection of spiral steel pipes

Abstract

The present application provides a kind of anticorrosion method of spiral steel pipe, and the present application belongs to the field of steel pipe anticorrosion, comprising the following steps: step S100, detection and screening, the corrosion degree of steel pipe and surface defect are detected, and the qualified spiral steel pipe is screened out;Step S200, rust removal treatment, the inner wall and outer wall of steel pipe are treated by rust removal;Step S300, spraying, after anticorrosive powder is sprayed on the inner wall and outer wall of steel pipe, anticorrosive material is coated to form anticorrosive coating, and then solidification treatment is carried out;Step S400, coating detection, the coating effect of steel pipe after spraying is detected;Step S500, code spraying package.The purpose is to solve the problem of weak corrosion resistance of spiral steel pipe.The technical effect achieved is: effectively guarantee the corrosion resistance of spiral steel pipe, and meet the long-period safe operation demand.

Description

Technical Field

[0001] This invention relates to the field of steel pipe corrosion protection technology, and in particular to a method for corrosion protection of spiral steel pipes. Background Technology

[0002] Spiral steel pipes, with their high strength and large diameter, have become core components in long-distance pipeline projects for oil, natural gas, and municipal water supply and drainage. However, due to their long-term service in open-air, buried, or acidic / alkaline environments, oxygen, soil salinity, and the transported medium can easily penetrate to the surface of the steel pipe, causing uniform corrosion or localized corrosion at weak points such as welds and pipe ends. This leads to thinning of the pipe wall, sealing failure, and in severe cases, leakage accidents, requiring frequent maintenance and replacement, significantly increasing project costs. Current methods for preventing corrosion of spiral welded steel pipes have the following problems: First, relying solely on visual inspection to screen steel pipes in the early stages fails to accurately identify hidden defects such as rust depth and micro-cracks. Spiral steel pipes that are substandard before the anti-corrosion coating is applied are prone to failure in subsequent processes. Second, the rust removal stage often neglects inner wall treatment, leaving residual rust that hinders the coating's adhesion to the substrate. Third, coatings are often applied using a single material or simple layers, resulting in poor interlayer adhesion and a tendency for pinholes to appear after curing. Inspection focuses only on thickness, neglecting integrity and adhesion. These problems directly lead to short anti-corrosion coating lifespans and weak corrosion resistance in spiral steel pipes, making it difficult to meet the requirements for long-term safe operation. Summary of the Invention

[0003] This invention provides a method for corrosion protection of spiral steel pipes to solve the above-mentioned problems.

[0004] This invention provides a method for corrosion protection of spiral steel pipes, comprising the following steps: Step S100, Inspection and Screening: Inspect the degree of corrosion and surface defects of the steel pipes, and screen out qualified spiral steel pipes. Step S200: Rust removal treatment, rust removal treatment is performed on the inner and outer walls of the steel pipe; Step S300: Spraying. After spraying anti-corrosion powder onto the inner and outer walls of the steel pipe, anti-corrosion material is applied to form an anti-corrosion coating, followed by curing. Step S400: Coating inspection, inspecting the coating effect of the steel pipe after spraying; Step S500: Inkjet printing and packaging.

[0005] In addition, the spiral steel pipe anti-corrosion method according to the present invention may also have the following additional technical features: In some embodiments of the present invention, step S100, detecting the degree of corrosion and surface defects of the steel pipe, includes the following steps: Step S110: Take a full-view photo of the steel pipe to determine the distribution of rust, the distribution of surface defects, the type of surface defects, and the type of rust. Step S120: Measure the thickness of the corroded part of the steel pipe and calculate the wall thickness loss rate; Step S130: Determine the corrosion grade of the steel pipe based on the corrosion distribution, corrosion type, and wall thickness loss rate; Step S140: Measure the depth and wall thickness of the defective parts on the steel pipe surface, and determine the surface defect level of the steel pipe based on the distribution of surface defects.

[0006] In some embodiments of the present invention, step S200, rust removal treatment, includes the following steps for removing rust from the inner and outer walls of the steel pipe; Step S210: Apply mechanical force to the outer wall of the steel pipe to remove oxide scale, rust and impurities, forming anchor patterns, and the rust removal of the outer wall is completed; Step S220: Pump the pickling solution into the steel pipe through a sequential pump, circulate it continuously for the first preset time, then use a neutralizing solution to circulate and neutralize it, then rinse it with clean water and dry it. The rust removal of the inner wall is completed.

[0007] In some embodiments of the present invention, in step S300: the steel pipe is heated by medium frequency before spraying.

[0008] In some embodiments of the present invention, step S300, spraying anti-corrosion powder onto the inner and outer walls of the steel pipe, includes the following steps: Step S310: Apply fusion-bonded epoxy powder to the inner wall of the steel pipe to form an inner wall fusion-bonded epoxy powder coating, and apply fusion-bonded epoxy powder to the outer wall of the steel pipe to form an outer wall fusion-bonded epoxy powder coating. Step S320: Apply polyethylene powder coating to the outer wall of the steel pipe.

[0009] In some embodiments of the present invention, step S300, which involves coating the inner and outer walls of the steel pipe with an anti-corrosion material to form an anti-corrosion coating, includes the following steps: Step S330: Quality inspection of the fusion-bonded epoxy powder coating surface on the inner wall of the steel pipe and the polyethylene powder coating surface on the outer wall of the steel pipe. Step S340: Applying adhesive layer to the inner wall of the steel pipe; Step S350: After the polyethylene surface layer is wrapped around the inner wall of the steel pipe to form an inner anti-corrosion coating, the coating is cooled and cured. Step S360: Applying adhesive layer to the outer wall of the steel pipe; Step S370: After the polyethylene surface layer is wrapped around the outer wall of the steel pipe to form an anti-corrosion coating, it is cooled and cured.

[0010] In some embodiments of the present invention, step S310, applying fusion-bonded epoxy powder coating to the inner and outer walls of the steel pipe, includes the following steps: Step S312: Heat the steel pipe to the set temperature; Step S314: Atomize the fusion-bonded epoxy powder and spray it onto the inner wall of the steel pipe to form an inner wall fusion-bonded epoxy powder coating; atomize the fusion-bonded epoxy powder and spray it onto the outer wall of the steel pipe to form an outer wall fusion-bonded epoxy powder coating. Step S316: After the inner wall fusion-bonded epoxy powder coating and the outer wall fusion-bonded epoxy powder coating are heat-insulated and cured, they are cooled with water mist.

[0011] In some embodiments of the present invention, step S320, forming a polyethylene powder coating by spraying polyethylene powder onto the outer wall of the steel pipe, includes the following steps: Step S322: High-frequency heating is applied to the steel pipe at a temperature of 300℃ to 350℃; Step S324: Use the first set of annular spray guns to spray polyethylene powder onto the outer wall of the steel pipe to form a base coating; Step S326: Use the second set of annular spray guns to spray polyethylene powder onto the steel pipe, and after curing, a polyethylene powder coating is formed.

[0012] In some embodiments of the present invention, step S400, which involves detecting the coating effect of the steel pipe, includes the following steps: Step S410: Take a photo of the steel pipe coating and check the size of the coating damage. If the size of the coating damage is larger than the preset size, it is a defective product and needs to be reworked. Step S420: Check the coating thickness. If the coating thickness is not within the preset thickness range, it is a defective product and needs to be reworked. Step S430: Detect the coating adhesion. If the coating adhesion is less than the preset adhesion, it is a defective product and needs to be reworked.

[0013] In some embodiments of the present invention, step S400, which involves detecting the coating effect of the steel pipe, further includes the following steps: Step S440: Detect leaks using electric spark testing. If the number of leaks detected exceeds the preset number or the area of ​​at least one leak exceeds the preset area, the product is considered unqualified and must be reworked.

[0014] In summary, this application includes the following beneficial technical effects: This method removes unqualified spiral steel pipes before the application of anti-corrosion coating by detecting hidden defects such as rust depth and micro-cracks, avoiding the failure of the anti-corrosion coating due to the uncoated spiral steel pipe, ensuring the qualification rate of the spiral steel pipe coating while ensuring the anti-corrosion effect of the coating; By thoroughly removing rust from the inner and outer walls of the spiral steel pipe, residual rust layers are removed, laying the foundation for coating adhesion and preventing the penetration of oxygen, soil salts, etc., thus avoiding thinning of the spiral steel pipe wall; The double-layer anti-corrosion coating of anti-corrosion powder spraying combined with anti-corrosion material coating can reduce the problems of poor interlayer adhesion and easy pinhole formation in the spiral steel pipe coating, forming a dense coating, isolating acid and alkaline media, extending service life, and meeting the needs of long-distance pipelines; By comprehensively testing the coating effect, not only focusing on thickness, integrity and adhesion are ensured, reducing the risk of leakage; The above methods effectively ensure the corrosion resistance of the spiral steel pipe, meeting the requirements for long-term safe operation. Attached Figure Description

[0015] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. Figure 1 A flowchart illustrating the process of a spiral steel pipe corrosion protection method according to some embodiments of the present invention is shown.

[0016] Figure 2 A cross-sectional view of a spiral steel pipe with an anti-corrosion coating, according to some embodiments of the present invention, is shown schematically.

[0017] Figure labels 1. Spiral steel pipe; 2. Inner wall fusion bonded epoxy powder coating; 3. Inner wall anti-corrosion coating; 4. Outer wall fusion bonded epoxy powder coating; 5. Polyethylene powder coating; 6. Outer wall anti-corrosion coating. Detailed Implementation

[0018] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0019] It should be understood that the terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “” used herein may also indicate the inclusion of the plural forms. The terms “comprising,” “including,” “containing,” and “having” are inclusive and therefore indicate the presence of the stated features, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, elements, components, and / or combinations thereof. The method steps, processes, and operations described herein are not construed as requiring them to be performed in a particular order described or illustrated, unless the order of performance is explicitly indicated. It should also be understood that additional or alternative steps may be used.

[0020] Although terms such as first, second, third, etc., may be used in this document to describe multiple elements, components, regions, layers, and / or segments, these elements, components, regions, layers, and / or segments should not be limited by these terms. These terms may be used only to distinguish one element, component, region, layer, or segment from another. Unless the context clearly indicates otherwise, terms such as "first," "second," and other numerical terms used herein do not imply order or sequence. Therefore, the first element, component, region, layer, or segment discussed below may be referred to as the second element, component, region, layer, or segment without departing from the teachings of the exemplary embodiments.

[0021] For ease of description, spatial relative terms may be used in the text to describe the relationship of one element or feature relative to another element or feature, as shown in the figure. These relative terms include, for example, "inside," "outside," "middle," "outer," "below," "below," "above," "over," etc. Such spatial relative terms are intended to include different orientations of the device in use or operation, other than those depicted in the figure. For example, if the device in the figure is flipped, an element described as "below other elements or features" or "below other elements or features" would subsequently be oriented "above other elements or features" or "above other elements or features." Therefore, the example term "below" can include both upper and lower orientations. The device may also be rotated 90 degrees or in other orientations, and the spatial relative descriptors used in the text will be interpreted accordingly.

[0022] like Figure 1 and Figure 2 As shown, according to an embodiment of the first aspect of the present invention, a method for preventing corrosion of a spiral steel pipe 1 is proposed, comprising the following steps: Step S100, Inspection and Screening: Inspect the degree of corrosion and surface defects of the steel pipes, and screen out qualified spiral steel pipes 1; Step S200: Rust removal treatment, rust removal treatment is performed on the inner and outer walls of the steel pipe; Step S300: Spraying. After spraying anti-corrosion powder onto the inner and outer walls of the steel pipe, anti-corrosion material is applied to form an anti-corrosion coating, followed by curing. Step S400: Coating inspection, inspecting the coating effect of the steel pipe after spraying; Step S500: Inkjet printing and packaging.

[0023] In the above embodiments, it should be noted that the inkjet printing packaging method includes the following steps: Step S510: In the middle of the outer wall of the steel pipe Select locations on the outer and inner walls of the steel pipe that are free from coating damage, easy to observe, and not easily obscured by transportation friction. Then, use an inkjet printer to print the corresponding locations on the outer and inner walls of the steel pipe. Specifically, print the code on the outer wall of the steel pipe at a location 500-1000mm from one end of the steel pipe and outside the weld seam area, and on the inner wall of the steel pipe at a location less than 500mm from both ends and outside the weld seam area.

[0024] The technical effects achieved by the above embodiments are as follows: This method removes unqualified spiral steel pipes 1 before the anti-corrosion coating is applied by detecting hidden defects such as rust depth and micro-cracks, thus avoiding the failure of the anti-corrosion coating due to the spiral steel before the coating is applied, ensuring the qualification rate of the spiral steel pipe 1 coating while ensuring the anti-corrosion effect of the coating; by thoroughly removing rust from the inner and outer walls of the spiral steel pipe 1, residual rust layers are removed, laying the foundation for coating adhesion and preventing the penetration of oxygen, soil salts, etc., thus avoiding the thinning of the pipe wall of the spiral steel pipe 1; the double-layer anti-corrosion coating of anti-corrosion powder spraying combined with anti-corrosion material coating can reduce the problems of poor interlayer adhesion and easy pinhole formation of the spiral steel pipe 1 coating, forming a dense coating, isolating acid and alkali media, extending service life, and meeting the needs of long-distance pipelines; the above methods effectively ensure the corrosion resistance of the spiral steel pipe and can meet the requirements of long-term safe operation.

[0025] The above methods effectively ensure the corrosion resistance of the spiral steel pipe 1, which can meet the requirements of long-term safe operation.

[0026] Optional, such as Figure 1 and Figure 2 As shown, step S100, detecting the degree of corrosion and surface defects of the steel pipe includes the following steps: Step S110: Take a full-view photo of the steel pipe to determine the distribution of rust, the distribution of surface defects, the type of surface defects, and the type of rust. Step S120: Measure the thickness of the corroded part of the steel pipe and calculate the wall thickness loss rate; Step S130: Determine the corrosion grade of the steel pipe based on the corrosion distribution, corrosion type, and wall thickness loss rate; Step S140: Measure the depth and wall thickness of the defective parts on the steel pipe surface, and determine the surface defect level of the steel pipe based on the distribution of surface defects.

[0027] In the above optional embodiments, it should be noted that step S110, taking a full-view photograph of the steel pipe to determine the rust distribution, surface defect distribution, surface defect type, and rust type, specifically includes: The inner wall of the steel pipe was photographed and recorded using an endoscope camera to show the distribution of rust, surface defects, types of surface defects, and types of rust. The outer wall of the steel pipe was photographed and recorded using a vision camera, along with the distribution of rust, surface defects, types of surface defects, and types of rust on the inner wall of the steel pipe.

[0028] Step S120: Measure the thickness of the corroded portion of the steel pipe and calculate the wall thickness loss rate. This specifically includes: The wall thickness at the rust location of moderately rusted and heavily rusted steel pipes after rust removal treatment was measured using an ultrasonic thickness gauge, and the wall thickness loss rate was calculated. Wall thickness loss rate = (mean value of baseline wall thickness - mean value of wall thickness in corroded area) / (mean value of baseline wall thickness) × 100%.

[0029] Step S130, determining the corrosion grade of the steel pipe based on the corrosion distribution, corrosion type, and wall thickness loss rate, specifically includes: If the surface of the steel pipe is only partially oxidized and there are no visible rust marks, it is considered to be slightly corroded and is a qualified product. If light brown rust spots appear locally on the surface of the steel pipe, the number of rust spots is less than five, and the area of ​​each rust spot is less than 0.25 square centimeters, then it is considered moderate corrosion and is a qualified product. If the steel pipe surface shows obvious rust marks or more than five light brown rust spots, or if the area of ​​a single rust spot is greater than 0.25 square centimeters, it is considered severely rusted and is a substandard product that needs to be repaired.

[0030] If the wall thickness loss rate is ≤5% and the minimum wall thickness is ≥95% of the designed wall thickness, the substrate meets the coating construction requirements; if it is >5% or the minimum wall thickness is <95% of the designed wall thickness, repair welding should be performed.

[0031] Step S140: The depth and wall thickness of the defective portions on the steel pipe surface are measured, and the surface defect level is determined based on the distribution of surface defects. This specifically includes: Inspect the inner and outer surfaces of the steel pipe for defects, including cracks, pits, or weld beads. If the total number of defects exceeds 5, the steel pipe is considered unqualified and needs to be repaired. If the total number of defects is less than 5, the defect size needs to be analyzed. If the length or width of any defect is greater than 0.5cm, the steel pipe is unqualified and needs to be repaired.

[0032] If all defect dimensions are less than 1cm, then a specific analysis based on the defect type is required: If the defect type is a crack, it needs to be repaired directly.

[0033] If the defect type is a pit, an ultrasonic flaw detector must be used to check the pit depth. If the pit depth is greater than 1.5mm, the steel pipe is unqualified and needs to be repaired.

[0034] If the defect type is weld bead, the height of the weld bead needs to be checked. If the height of the weld bead is greater than 0.5mm, the steel pipe is unqualified and needs to be repaired.

[0035] The beneficial effects of the above optional embodiments are as follows: by analyzing the surface defect level and corrosion level of the steel pipe, it can be effectively ensured that the surface of the spiral steel pipe 1 is more suitable for spraying during the spraying process, thereby ensuring the spraying effect of the spiral steel pipe 1 while increasing the reliability and pass rate of the spiral steel pipe 1 after spraying.

[0036] Optional, such as Figure 1 and Figure 2 As shown, in step S200, the rust removal process, which involves removing rust from the inner and outer walls of the steel pipe, includes the following steps: Step S210: Apply mechanical force to the outer wall of the steel pipe to remove oxide scale, rust and impurities, forming anchor patterns, and the rust removal of the outer wall is completed; Step S220: Pump the pickling solution into the steel pipe through a sequential pump, circulate it continuously for the first preset time, then use a neutralizing solution to circulate and neutralize it, then rinse it with clean water and dry it. The rust removal of the inner wall is completed.

[0037] In the above optional embodiments, it should be noted that, specifically, mechanical force is applied to the outer wall of the spiral steel pipe 1 with a wall thickness loss rate ≤5%, light corrosion and moderate modification to remove the oxide scale, rust and impurities on the outer wall, form anchor patterns, and the rust removal of the outer wall is completed. For spiral steel pipes with a wall thickness loss rate of ≤5%, light corrosion, and moderate modification, pickling solution is pumped into the steel pipe through a sequential pump and continuously circulated for a first preset time. Then, neutralizing solution is circulated and neutralized. Finally, the pipe is rinsed with clean water and dried, and the rust removal of the inner wall is completed.

[0038] In step S210, the mechanical force applied to the outer wall of the steel pipe can be obtained by existing methods such as shot blasting, sandblasting, brushing, or grinding to remove oxide scale, rust, and impurities from the outer wall of the spiral steel pipe 1, forming anchor patterns, thus completing the outer wall rust removal.

[0039] The beneficial effects of the above optional embodiments are as follows: by performing rust removal treatment on both the inner and outer walls of the steel pipe, the smooth spraying of the spiral steel pipe 1 can be further guaranteed, while ensuring the spraying effect and increasing the qualification rate of the spiral steel pipe 1 product.

[0040] Optional, such as Figure 1 and Figure 2 As shown, in step S300: before spraying, the steel pipe is heated by medium frequency.

[0041] In the above optional embodiments, it should be noted that the method for medium-frequency heating of the steel pipe is: using a medium-frequency heating furnace to perform medium-frequency heating on the spiral steel pipe 1 to achieve rapid heating of the steel pipe.

[0042] The beneficial effect of the above optional embodiments is that the setting of medium-frequency heating of the steel pipe provides effective heating conditions for the subsequent spraying of the steel pipe.

[0043] Optional, such as Figure 1 and Figure 2 In step S300, spraying anti-corrosion powder onto the inner and outer walls of the steel pipe includes the following steps: Step S310: Apply fusion-bonded epoxy powder to the inner wall of the steel pipe to form an inner wall fusion-bonded epoxy powder coating 2, and apply fusion-bonded epoxy powder to the outer wall of the steel pipe to form an outer wall fusion-bonded epoxy powder coating 4. Step S320: Apply polyethylene powder coating 5 to the outer wall of the steel pipe.

[0044] Optional, such as Figure 1 and Figure 2 As shown, step S310, the fusion-bonded epoxy powder coating of the inner and outer walls of the steel pipe, includes the following steps: Step S312: Heat the steel pipe to the set temperature; Step S314: Atomize the fusion-bonded epoxy powder and spray it onto the inner wall of the steel pipe to form an inner wall fusion-bonded epoxy powder coating 2; atomize the fusion-bonded epoxy powder and spray it onto the outer wall of the steel pipe to form an outer wall fusion-bonded epoxy powder coating 4. Step S316: After the inner wall fusion-bonded epoxy powder coating 2 and the outer wall fusion-bonded epoxy powder coating 4 are heat-insulated and cured, they are cooled with water mist.

[0045] In the above optional embodiments, it should be noted that in step S312, before heating the steel pipe to the set temperature, high-pressure compressed air is output from an air compressor to blow the inner and outer walls of the spiral steel pipe 1 to ensure that there are no residual steel shot or dust on the inner and outer surfaces of the spiral steel pipe 1.

[0046] The steel pipe is heated to the set temperature by using a medium-frequency heating furnace to heat the spiral steel pipe to the set temperature, which is between 230°C and 280°C. Then, an infrared thermometer is used to monitor the temperature in real time to ensure that the inner and outer wall temperatures of the steel pipe remain at the set temperature during the spraying process.

[0047] In step S314, the specific method for atomizing the fusion-bonded epoxy powder and spraying it onto the inner wall of the steel pipe to form an inner wall fusion-bonded epoxy powder coating 2, and for atomizing the fusion-bonded epoxy powder and spraying it onto the outer wall of the steel pipe to form an outer wall fusion-bonded epoxy powder coating 4, is as follows: A retractable inner wall spray gun is inserted from one end of the steel pipe and moved at a constant speed of 0.5 m / min to 1 m / min along the axial direction. Then, the fusion-bonded epoxy powder is delivered to the inner wall spray gun through an air compressor. After being physicochemically treated by the inner wall spray gun, the fusion-bonded epoxy powder becomes negatively charged and is adsorbed onto the inner wall of the positively charged spiral steel pipe 1, forming an inner wall fusion-bonded epoxy powder coating 2 on the inner wall of the spiral steel pipe 1. Then, a medium-frequency heating furnace is used to maintain the temperature of the spiral steel pipe between 220°C and 250°C, so that the epoxy powder can be fully melted and leveled to form a continuous coating without pinholes. Then, the temperature of the spiral steel pipe 1 is cooled by air to below 150°C and then cooled to room temperature by water mist. The epoxy powder coating on the inner wall of the spiral steel pipe 1 is then cured.

[0048] The spiral steel pipe is heated to a set temperature of 230°C to 280°C using a medium-frequency heating furnace. Then, a ring-shaped electrostatic spray gun is used to spray fusion-bonded epoxy powder onto the outer wall of the spiral steel pipe 1 while moving along the axial direction at a speed of 1m / min to 2m / min. This forms an outer wall fusion-bonded epoxy powder coating 4 on the outer wall of the spiral steel pipe 1. The spiral steel pipe 1 is then transported to a hot air circulating curing tunnel oven to melt and cure the fusion-bonded epoxy powder coating. Finally, a cold air blower is used to cool the curing temperature to room temperature to prevent coating deformation.

[0049] The beneficial effects of the above optional embodiments are as follows: by setting the inner wall fusion-bonded epoxy powder coating 2 and the outer wall fusion-bonded epoxy powder coating 4, the inner wall of the spiral steel pipe 1 can have strong adhesion and corrosion resistance; while the outer wall of the spiral steel pipe 1 has strong weather resistance and impact resistance, it also has good corrosion resistance.

[0050] Optional, such as Figure 1 and Figure 2 As shown, step S320, forming a polyethylene powder coating 5 by spraying polyethylene powder onto the outer wall of the steel pipe, includes the following steps: Step S322: High-frequency heating is applied to the steel pipe at a temperature of 300℃ to 350℃; Step S324: Use the first set of annular spray guns to spray polyethylene powder onto the outer wall of the steel pipe to form a base coating; Step S326: Use the second set of annular spray guns to spray polyethylene powder onto the steel pipe, and after curing, a polyethylene powder coating 5 is formed.

[0051] In the above optional embodiments, it should be noted that the method for high-frequency heating of the steel pipe is to use a high-frequency heating furnace to heat the spiral steel pipe 1 at high frequency.

[0052] Infrared thermometers were used to monitor the temperature of the outer wall of the spiral steel pipe 1 in real time throughout the entire process of forming a polyethylene powder coating 5 by spraying polyethylene powder onto the outer wall of the steel pipe.

[0053] In step S324, the first group of annular spray guns consists of 2 to 3 guns arranged around the circumference of the steel pipe, and moves at a constant speed of 0.5 m / min to 1 m / min along the axial direction of the steel pipe to spray polyethylene powder to form a base coating. In step S326, one to two ring-shaped spray guns are used to spray polyethylene powder onto the steel pipe, which then cures to form a polyethylene powder coating 5.

[0054] In step S326, the method for curing polyethylene powder is as follows: the coated spiral steel pipe 1 is fed into the pipe anti-corrosion spraying oven using a conveying device. The hot air of the pipe anti-corrosion spraying oven is used to assist in leveling, so that the polyethylene powder coating 5 is fully leveled, eliminating pinholes and shrinkage cavities. Then, the leveled polyethylene coating is conveyed to the water cooling device using a conveying device to rapidly cool the temperature of the spiral steel pipe 1 to below 60°C, so that the polyethylene powder coating 5 is set and cured.

[0055] The conveying device uses existing belt conveyors or roller conveyors, and the specific structure will not be discussed in detail. The water cooling device uses existing water cooling devices, and the specific structure will not be discussed in detail.

[0056] The beneficial effects of the above optional embodiments are as follows: the setting of polyethylene powder coating 5 increases the low temperature resistance, impact resistance and soil stress resistance of spiral steel pipe 1, and effectively increases the corrosion resistance of spiral steel pipe 1.

[0057] Optional, such as Figure 1 and Figure 2 As shown, step S300, coating the inner and outer walls of the steel pipe with anti-corrosion material to form an anti-corrosion coating, includes the following steps: Step S330: Quality inspection of the surface of the fusion-bonded epoxy powder coating 2 on the inner wall of the steel pipe and the surface of the polyethylene powder coating 5 on the outer wall of the steel pipe. Step S340: Applying adhesive layer to the inner wall of the steel pipe; Step S350: After the polyethylene surface layer is wrapped around the inner wall of the steel pipe to form an inner anti-corrosion coating 3, the coating is cooled and cured. Step S360: Applying adhesive layer to the outer wall of the steel pipe; Step S370: After the polyethylene surface layer is wrapped around the outer wall of the steel pipe to form an anti-corrosion coating, the coating is cooled and cured.

[0058] In the above optional embodiments, it should be noted that the method for quality inspection of step S330, the surface of the fusion-bonded epoxy powder coating 2 on the inner wall of the steel pipe, and the surface of the polyethylene powder coating 5 on the outer wall of the steel pipe is as follows: The smoothness of the polyethylene powder coating 5 on the outer wall of the spiral steel pipe 1 is measured using a visual camera, and the smoothness of the fusion-bonded epoxy powder coating on the inner wall of the spiral steel pipe 1 is measured using an endoscope camera. If there are no obvious orange peel, pinholes, bubbles, runs, bumps, depressions, cracks, missed coatings, or delamination on the inner and outer walls of the spiral steel pipe 1, then the inspection is considered qualified. Then, a colorimeter is used to detect the color difference between the surface of the fusion-bonded epoxy powder coating 2 on the inner wall of the spiral steel pipe 1 and the surface of the polyethylene powder coating 5 on the outer wall of the spiral steel pipe 1. If there is no color difference, the second test is qualified. Then, a thickness gauge is used to check the coating thickness of the inner wall and outer wall of the spiral steel pipe 1. Products with coating thickness less than 10% of the preset thickness are considered qualified. Among them, the preset thickness of polyethylene powder coating 5 is 750μm, and the preset thickness of fusion bonded epoxy powder coating is 300μm, which are the final qualified spiral steel pipes 1.

[0059] It should be noted that the quality inspection of the fusion-bonded epoxy powder coating 2 on the inner wall of the steel pipe is carried out during the cooling and curing process of the fusion-bonded epoxy powder coating; the quality inspection of the polyethylene powder coating 5 on the outer wall of the steel pipe is carried out during the cooling and curing process of the polyethylene powder coating 5.

[0060] Step S340: Applying adhesive layer to the inner wall of the steel pipe; The method for coating the inner wall of the steel pipe is as follows: the coating on the inner wall surface of the spiral steel pipe 1 is finally qualified. When the temperature of the inner wall surface of the spiral steel pipe 1 drops to between 160°C and 210°C, the adhesive is applied to the inner wall of the spiral steel pipe 1 using an inner wall applicator to form an inner wall adhesive layer.

[0061] Step S350: After the polyethylene surface layer is wrapped around the inner wall of the steel pipe to form an inner anti-corrosion coating 3, the coating is cooled and cured. When the inner wall surface temperature of the spiral steel pipe 1 drops to between 140°C and 160°C, the polyethylene melt is uniformly coated onto the fusion-bonded epoxy powder coating surface of the inner wall of the spiral steel pipe 1 using an internal pipe coating machine. The cooling and curing treatment method adopts the existing natural cooling, air cooling, or water cooling, which will not be discussed in detail.

[0062] Step S360: Applying adhesive layer to the outer wall of the steel pipe; The outer wall surface coating of the spiral steel pipe 1 is finally qualified. When the surface temperature of the spiral steel pipe 1 is between 190℃ and 210℃, a single screw extruder is used to uniformly extrude the molten adhesive onto the surface of the rotating steel pipe to form a continuous adhesive layer.

[0063] Step S370: After the polyethylene surface layer is wrapped around the outer wall of the steel pipe to form an anti-corrosion coating, the coating is cooled and cured.

[0064] The outer wall surface coating of the spiral steel pipe 1 is finally qualified. After the adhesive is applied to the outer wall surface of the spiral steel pipe 1, when the temperature of the outer wall surface of the spiral steel pipe 1 drops to between 140°C and 160°C, the polyethylene particles are heated and melted using a screw extruder to form a molten polyethylene melt. Then, the molten polyethylene melt is uniformly extruded through a ring die to coat the surface of the adhesive layer. The cooling and curing treatment uses existing natural cooling, air cooling, or water cooling methods, which will not be discussed in detail.

[0065] The advantages of the above-mentioned optional embodiments are as follows: by coating the inner wall of the spiral steel pipe 1 with a polyethylene coating combined with an adhesive and a fusion-bonded epoxy powder coating, the anti-corrosion effect of the inner wall of the steel pipe can be effectively guaranteed. By coating the outer wall of the spiral steel pipe 1 with a molten polyethylene coating, an adhesive, a polyethylene powder coating 5, and a fusion-bonded epoxy powder coating, the anti-corrosion effect of the outer wall of the steel pipe can be effectively guaranteed. The differentiated anti-corrosion treatment of the inner and outer walls of the spiral steel pipe 1 reduces material utilization while ensuring the anti-corrosion effect, saving materials and indirectly reducing costs. By setting up the setting of testing the inner and outer wall surfaces of the spiral steel pipe 1 before coating with polyethylene coating, the pass rate of the spiral steel pipe 1 at the factory can be effectively increased, the probability of rework after the anti-corrosion coating of the spiral steel pipe 1 is fully coated can be reduced, and the anti-corrosion effect is increased while efficiency is increased.

[0066] Optional, such as Figure 1 and Figure 2 As shown, step S400, the detection of the coating effect on the steel pipe includes the following steps: Step S410: Take a photo of the steel pipe coating and check the size of the coating damage. If the size of the coating damage is larger than the preset size, it is a defective product and needs to be reworked. The preset size here is 3mm in length and 2mm in width.

[0067] The method for photographing the coating of the spiral steel pipe 1 and detecting the size of coating damage is as follows: Multiple vision cameras are arranged along the circumference of the spiral steel pipe 1. Then, a conveyor device is used to move the spiral steel pipe 1 while gradually photographing the defects of the coating on the outer wall of the spiral steel pipe 1 along the axial direction and measuring the size of the defects. Alternatively, an endoscope camera is used to move along the axial direction of the spiral steel pipe 1 while gradually photographing the defects of the coating on the inner wall of the spiral steel pipe 1 and measuring the size of the defects.

[0068] Step S420: Check the coating thickness. If the coating thickness is not within the preset thickness range, it is a defective product and needs to be reworked. The preset thickness range here refers to the total thickness range of the coating, and the specific dimensions are between 2mm and 2.3mm.

[0069] The method for detecting the coating thickness is as follows: use a magnetic thickness gauge to move along the inner and outer walls of the spiral steel pipe 1 and measure the thickness of the anti-corrosion coating of the spiral steel pipe 1 in sequence.

[0070] Step S430: Detect the coating adhesion. If the coating adhesion is less than the preset adhesion, it is a defective product and needs to be reworked. The preset adhesion here is 7.0 MPa.

[0071] The adhesion of a coating can be tested using the existing pull-off method, or other feasible methods. Specific methods will not be discussed in detail.

[0072] Optional, such as Figure 1 and Figure 2 As shown, step S400, the inspection of the coating effect on the steel pipe further includes the following steps: Step S440: Detect leaks using electric spark testing. If the number of leaks detected exceeds the preset number or the area of ​​at least one leak exceeds the preset area, the product is considered unqualified and must be reworked.

[0073] In the above optional embodiments, it should be noted that the inner wall area of ​​the spiral steel pipe 1 is 1 square millimeter and the outer wall area is 1 square millimeter.

[0074] Step S440: Detect leaks by electric spark. If the number of leaks detected is greater than the preset number or the area of ​​at least one leak is greater than the preset area, the product is considered unqualified. The preset number is 2.

[0075] The method for detecting leaks by electric spark is to use an electric spark leak detector to detect leaks on the inner and outer walls of the spiral steel pipe 1.

[0076] The advantages of the above optional embodiments are that the above method can effectively ensure the anti-corrosion effect of the coating.

[0077] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for corrosion protection of spiral steel pipes, characterized in that, Includes the following steps: Step S100, Inspection and Screening: Inspect the degree of corrosion and surface defects of the steel pipes, and screen out qualified spiral steel pipes (1). Step S200: Rust removal treatment, rust removal treatment is performed on the inner and outer walls of the steel pipe; Step S300: Spraying. After spraying anti-corrosion powder onto the inner and outer walls of the steel pipe, anti-corrosion material is applied to form an anti-corrosion coating, followed by curing. Step S400: Coating inspection, inspecting the coating effect of the steel pipe after spraying; Step S500: Inkjet printing and packaging.

2. The anti-corrosion method for spiral steel pipes according to claim 1, characterized in that, In step S100, detecting the degree of corrosion and surface defects of the steel pipe includes the following steps: Step S110: Take a full-view photo of the steel pipe to determine the distribution of rust, the distribution of surface defects, the type of surface defects, and the type of rust. Step S120: Measure the thickness of the corroded part of the steel pipe and calculate the wall thickness loss rate; Step S130: Determine the corrosion grade of the steel pipe based on the corrosion distribution, corrosion type, and wall thickness loss rate; Step S140: Measure the depth and wall thickness of the defective parts on the steel pipe surface, and determine the surface defect level of the steel pipe based on the distribution of surface defects.

3. The anti-corrosion method for spiral steel pipes according to claim 1, characterized in that, In step S200, the rust removal process, which involves removing rust from the inner and outer walls of the steel pipe, includes the following steps: Step S210: Apply mechanical force to the outer wall of the steel pipe to remove oxide scale, rust and impurities, forming anchor patterns, and the rust removal of the outer wall is completed; Step S220: Pump the pickling solution into the steel pipe through a sequential pump, circulate it continuously for the first preset time, then use a neutralizing solution to circulate and neutralize it, then rinse it with clean water and dry it. The rust removal of the inner wall is completed.

4. The anti-corrosion method for spiral steel pipes according to claim 1, characterized in that, In step S300: Before spraying, the steel pipe is heated by medium frequency.

5. The anti-corrosion method for spiral steel pipes according to claim 1, characterized in that, In step S300, spraying anti-corrosion powder onto the inner and outer walls of the steel pipe includes the following steps: Step S310: Apply fusion-bonded epoxy powder to the inner wall of the steel pipe to form an inner wall fusion-bonded epoxy powder coating (2), and apply fusion-bonded epoxy powder to the outer wall of the steel pipe to form an outer wall fusion-bonded epoxy powder coating (4). Step S320: Apply polyethylene powder to the outer wall of the steel pipe to form a polyethylene powder coating (5).

6. The anti-corrosion method for spiral steel pipes according to claim 5, characterized in that, In step S300, coating the inner and outer walls of the steel pipe with anti-corrosion material to form an anti-corrosion coating includes the following steps: Step S330: Quality inspection of the surface of the fusion-bonded epoxy powder coating (2) on the inner wall of the steel pipe and the surface of the polyethylene powder coating (5) on the outer wall of the steel pipe; Step S340: Applying adhesive layer to the inner wall of the steel pipe; Step S350: After the polyethylene surface layer is wrapped around the inner wall of the steel pipe to form an inner anti-corrosion coating (3), it is cooled and cured. Step S360: Applying adhesive layer to the outer wall of the steel pipe; Step S370: After the polyethylene surface layer is wrapped around the outer wall of the steel pipe to form an anti-corrosion coating (6), it is cooled and cured.

7. The anti-corrosion method for spiral steel pipes according to claim 6, characterized in that, Step S310, applying fusion-bonded epoxy powder coating to the inner and outer walls of the steel pipe, includes the following steps: Step S312: Heat the steel pipe to the set temperature; Step S314: Atomize the fusion-bonded epoxy powder and spray it onto the inner wall of the steel pipe to form an inner wall fusion-bonded epoxy powder coating (2); atomize the fusion-bonded epoxy powder and spray it onto the outer wall of the steel pipe to form an outer wall fusion-bonded epoxy powder coating (4). Step S316: After the inner wall fusion-bonded epoxy powder coating (2) and the outer wall fusion-bonded epoxy powder coating (4) are heat-insulated and cured, they are cooled with water mist.

8. The anti-corrosion method for spiral steel pipes according to claim 6, characterized in that, Step S320, forming a polyethylene powder coating by spraying polyethylene powder onto the outer wall of the steel pipe (5), includes the following steps: Step S322: High-frequency heating is applied to the steel pipe at a temperature of 300℃ to 350℃; Step S324: Use the first set of annular spray guns to spray polyethylene powder onto the outer wall of the steel pipe to form a base coating; Step S326: Use the second set of annular spray guns to spray polyethylene powder onto the steel pipe, and after curing, a polyethylene powder coating is formed (5).

9. The anti-corrosion method for spiral steel pipes according to claim 1, characterized in that, In step S400, the detection of the coating effect of the steel pipe includes the following steps: Step S410: Take a photo of the steel pipe coating and check the size of the coating damage. If the size of the coating damage is larger than the preset size, it is a defective product and needs to be reworked. Step S420: Check the coating thickness. If the coating thickness is not within the preset thickness range, it is a defective product and needs to be reworked. Step S430: Detect the coating adhesion. If the coating adhesion is less than the preset adhesion, it is a defective product and needs to be reworked.

10. The method for corrosion protection of spiral steel pipes according to claim 9, characterized in that, In step S400, the detection of the coating effect of the steel pipe after spraying also includes the following steps: Step S440: Detect leaks using electric spark testing. If the number of leaks detected exceeds the preset number or the area of ​​at least one leak exceeds the preset area, the product is considered unqualified and must be reworked.

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