Anti-corrosion maintenance process for large-diameter carbon steel pipeline and large-diameter carbon steel pipeline

Abstract

The invention discloses an anti-corrosion maintenance process for a large-diameter carbon steel pipeline and the large-diameter carbon steel pipeline, and the anti-corrosion maintenance process comprises the following steps: firstly, removing impurities attached to the surface of the pipeline, secondly, repairing an uneven area on the surface of the pipeline, and finally, coating the surface of the pipeline with a composite anti-corrosion layer consisting of a fiber material and an epoxy resin material. The process is suitable for various complex pipeline systems, corrosion prevention can be conducted on special parts, the limitation of a traditional process in the aspects of complex structures and special corrosion prevention requirements is broken through, and therefore the performance and reliability of the pipeline system are remarkably improved. Through the net-shaped structure formed by combining the fiber material and the epoxy resin, the composite anti-corrosion layer can effectively prevent corrosion, the service life of the pipeline is prolonged, and the local structural strength of the pipeline is enhanced. In addition, the composite material can form good interface bonding with the pipe wall in the curing process, the risk of anti-corrosion layer stripping is further reduced, and durability and stability of the anti-corrosion effect are ensured.

Description

Technical Field

[0001] The present invention relates to the field of pipeline maintenance, and particularly to an anti-corrosion repair process for large-diameter carbon steel pipelines. Background Art

[0002] In the water desalination industry, the large-diameter pump outlet pipeline system is a key component of the entire technological process, and its safe and stable operation is crucial for production. At present, carbon steel lined pipelines are widely used as the main pipeline materials for transporting seawater in this industry, especially in unconventional pipelines and pipe fittings. These pipelines face severe corrosion challenges during long-term operation. Seawater, as a medium with high salinity and high corrosivity, continuously erodes the inner wall of the pipeline. After long-term seawater erosion, the lining layer of carbon steel pipelines often shows varying degrees of peeling. Once the lining layer peels off, seawater will directly contact the carbon steel substrate, accelerating the corrosion process, seriously threatening the structural integrity and service life of the pipeline, and even possibly leading to unplanned shutdowns of the production system, causing significant economic losses.

[0003] In response to the problem of peeling of the carbon steel pipeline lining, the prior art mainly adopts two repair methods:

[0004] (1) For detachable pipeline parts, the traditional method is to disassemble the pipe section and outsource it for sandblasting as a whole, and then re-perform internal anti-corrosion treatment, or directly replace it with a new pipe section. Although this method has good anti-corrosion effect, it is extremely costly and has a long repair cycle, which will have a greater impact on production. Especially for large-diameter pipelines, the disassembly and transportation themselves pose great difficulties and safety hazards.

[0005] (2) For key parts such as non-detachable wall-piercing pipes, the prior art mainly adopts the process of on-site painting of anti-corrosion paint. This method is relatively simple to operate, but the anti-corrosion paint has a short service life in an environment of long-term seawater erosion and chemical corrosion, and requires frequent maintenance and re-painting, increasing the maintenance cost and downtime. Summary of the Invention

[0006] The purpose of the present invention is to provide an anti-corrosion repair process and a large-diameter carbon steel pipeline for large-diameter carbon steel pipelines, so as to improve the service life of the pipeline and reduce the anti-corrosion cost.

[0007] The present invention discloses an anti-corrosion repair process for large-diameter carbon steel pipelines, including:

[0008] Removing impurities attached to the pipeline surface;

[0009] Repairing uneven areas on the pipeline surface;

[0010] Coating an anti-corrosion layer on the pipeline surface, wherein the anti-corrosion layer includes a composite material composed of a fiber material and an epoxy resin material.

[0011] Further, removing impurities attached to the pipe surface includes:

[0012] Rusting the pipe surface at least twice;

[0013] And, grinding and removing the failed inner lining on the pipe surface.

[0014] Further, repairing uneven areas inside the pipe includes:

[0015] Filling and repairing the uneven areas with a depression depth within the first set threshold range;

[0016] Patch welding and repairing the uneven areas with a depression depth within the second set threshold range.

[0017] Further, the first set threshold range is less than or equal to 30% of the pipe wall thickness, and the second set threshold range is less than or equal to 50% of the pipe wall thickness and greater than 30% of the pipe wall thickness.

[0018] Further, the materials for the filling and repairing include at least one of epoxy putty, conductive polymer putty, polyurethane elastic glue, and glass fiber putty.

[0019] Further, the fiber material includes at least one of chopped strand mat, glass fiber, carbon fiber, aramid fiber, and polyester fiber.

[0020] Further, the epoxy resin material includes at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, phenolic epoxy resin, alicyclic epoxy resin, and waterborne epoxy resin.

[0021] Further, coating an anti-corrosion layer on the pipe surface includes:

[0022] Sequentially coating an epoxy resin layer, a fiber material, and an epoxy resin layer on the pipe surface.

[0023] Further, the thickness range of the anti-corrosion layer is 3 - 5 mm.

[0024] Further, the coating layer is set to extend to the flange waterline position and smoothly transition at the flange connection.

[0025] On the other hand, the present invention also provides a large-diameter carbon steel pipe repaired by using the above anti-corrosion repair process for large-diameter carbon steel pipes.

[0026] Compared with the prior art, the present invention has at least the following technical effects:

[0027] The present invention discloses a three-step treatment process. First, impurities attached to the surface of the pipeline are removed. Second, uneven areas on the surface of the pipeline are repaired. Finally, a composite anti-corrosion layer composed of a fiber material and an epoxy resin material is coated on the surface of the pipeline. This process is not only applicable to various complex pipeline systems but also can carry out anti-corrosion treatment for special parts, breaking through the limitations of traditional processes in terms of complex structures and special anti-corrosion requirements, thereby significantly improving the performance and reliability of the pipeline system. Through the network structure formed by the combination of the fiber material and the epoxy resin, the composite anti-corrosion layer can not only effectively prevent corrosion and extend the service life of the pipeline but also enhance the local structural strength of the pipeline. In addition, during the curing process, this composite material can form a good interfacial bond with the pipe wall, further reducing the risk of anti-corrosion layer peeling and ensuring the durability and stability of the anti-corrosion effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic flow chart of the anti-corrosion repair process for large-diameter carbon steel pipelines in an embodiment of the present invention;

[0029] Figure 2 It is a schematic structural diagram of a large-diameter carbon steel pipeline repaired by using the anti-corrosion repair process in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] The following will describe an anti-corrosion repair process for large-diameter carbon steel pipelines and large-diameter carbon steel pipelines of the present invention in conjunction with the schematic diagrams. The preferred embodiments of the present invention are shown, and it should be understood that those skilled in the art can modify the present invention described herein while still achieving the beneficial effects of the present invention. Therefore, the following description should be understood as broad guidance for those skilled in the art and not as a limitation to the present invention.

[0031] In the following paragraphs, the present invention will be described more specifically by way of example with reference to the accompanying drawings. According to the following description, the advantages and features of the present invention will be clearer. It should be noted that the drawings are all in a very simplified form and use non-precise scales, only for the purpose of conveniently and clearly assisting in explaining the purpose of the embodiments of the present invention.

[0032] Please refer to Figure 1 , the present invention provides an anti-corrosion repair process for large-diameter carbon steel pipelines, and the process includes the following steps:

[0033] S1. Remove impurities attached to the surface of the pipeline;

[0034] S2. Repair uneven areas inside the surface of the pipeline;

[0035] S3. Coat an anti-corrosion layer on the surface of the pipeline, wherein the anti-corrosion layer includes a composite material composed of a fiber material and an epoxy resin material.

[0036] In this embodiment, the present invention discloses a three-step treatment process. First, impurities attached to the surface of the pipeline are removed. Second, uneven areas on the pipeline surface are repaired. Finally, a composite anti-corrosion layer composed of fiber materials and epoxy resin materials is coated on the pipeline surface. This process is not only applicable to various complex pipeline systems but also can perform anti-corrosion on special parts, breaking through the limitations of traditional processes in terms of complex structures and special anti-corrosion requirements, thus significantly improving the performance and reliability of the pipeline system. Through the network structure formed by the combination of fiber materials and epoxy resin, the composite anti-corrosion layer can not only effectively prevent corrosion and extend the service life of the pipeline but also enhance the local structural strength of the pipeline. In addition, during the curing process of this composite material, a good interfacial bond can be formed with the pipe wall, further reducing the risk of anti-corrosion layer peeling and ensuring the durability and stability of the anti-corrosion effect.

[0037] In this embodiment, the complex pipeline system includes, but is not limited to, pipeline systems with multiple segments of connection, special-shaped structures, or complex environments; the special parts include, but are not limited to, the lap joints between carbon steel through-wall pipes and concrete in concrete water tanks, pipeline flange joints, and valve joints, etc., which are difficult to handle by traditional processes. The anti-corrosion repair process for large-diameter carbon steel pipelines disclosed by the present invention can be used in any of the above situations.

[0038] In step S2, removing impurities attached to the pipeline surface includes: rust removal from the pipeline wall at least twice; and, grinding to remove the failed lining on the pipeline wall. Among them, failure includes physical and chemical failures, such as linings that are about to fall off, worn, have lost their anti-corrosion function, and the materials have degraded.

[0039] Specifically, the number of times of rust removal can be selected according to the actual situation. Generally speaking, it can be determined according to the degree of rust, pipeline material, and subsequent anti-corrosion requirements. For pipelines with mild rust, two rust removals can be adopted; for pipelines with moderate rust, it is recommended to perform three rust removals, namely primary rust removal, intermediate rust removal, and fine rust removal; for pipelines with severe rust, four or more rust removals may be required, respectively targeting rust layers with different depths and properties. The particle size of the tools used for each rust removal should gradually become finer. For example, P40 - P60 particle size can be used for the first time, P80 - P100 particle size for the second time, and P120 - P180 particle size for the last time to achieve an ideal surface state.

[0040] In a specific embodiment, removing impurities attached to the pipeline surface includes:

[0041] S11. Perform primary rust removal on the pipeline surface;

[0042] S12. Grind to remove the failed lining attached to the pipeline surface;

[0043] S13. Perform secondary rust removal on the surface of the pipeline.

[0044] In a specific embodiment of step S11, large pieces of rust inside the pipeline are manually removed, and electric tools can also be used as an auxiliary for rust removal. The purpose of the preliminary rust removal treatment is to mainly remove the loose rust on the surface and create conditions for subsequent fine treatment. Therefore, at this stage, relatively rough grinding tools can be selected. For example, a grinding machine equipped with a wire wheel or a grinding wheel disc is used to perform preliminary rust removal on the inner wall of the pipeline. When operating, apply force evenly along the axial direction of the pipeline to avoid excessive damage to the base material.

[0045] In step S12, grinding tools such as an electric angle grinder, a handheld grinder, a wire wheel brush, and a small impact removal tool can be used to grind and remove the failed inner lining on the pipe wall.

[0046] In a specific embodiment of S13, an electric tool is used to remove rust from the pipeline until the metal color of the pipeline is reached, meeting the rust removal standard. The purpose of the secondary rust removal is to remove the remaining oxides and inner lining adhesives, enabling the subsequent repair materials to tightly bond with the pipe wall base material. Therefore, at this stage, relatively rough grinding tools can be selected. For example, a fine grinding wheel or sandpaper (such as P120 - P180 grit) is used to perform secondary fine rust removal on the pipe wall area where the inner lining has been removed. When operating, a grinding method combining rotation and axial direction is preferably adopted to make the surface roughness suitable for the subsequent coating adhesion.

[0047] In step S2, the repair of the uneven areas inside the pipeline includes:

[0048] S21. Perform filling repair on the uneven areas where the depression depth is within the first set threshold range;

[0049] S22. Perform welding repair on the uneven areas where the depression depth is within the second set threshold range.

[0050] The uneven areas include corrosion pits, uneven welds, pits left after the removal of the inner lining, transition areas after local repair, and other surface defects that may affect the uniformity of the subsequent anti-corrosion layer.

[0051] In step S21, filling repair is suitable for shallow uneven areas. Preferably, filling repair is performed on areas where the depression depth is less than 30% of the pipe wall thickness of the pipeline. For example: perform filling repair on uneven areas with an original wall thickness of 10 mm and a depth less than or equal to 3 mm.

[0052] Further preferably, for uneven areas with a depression depth less than or equal to 20% of the pipe wall thickness, single filling is performed. For areas with a depression depth greater than 20% and less than 30%, layered filling can be adopted according to the actual situation, for example, divided into two layers for filling. The reason for such treatment is that during the filling process, if the filling material is too thick, shrinkage stress is likely to occur during the curing of the material, resulting in cracking or hollowing.

[0053] In a specific embodiment, the filling and repairing material includes at least one of epoxy putty, conductive polymer putty, polyurethane elastic glue, and glass fiber putty. Those skilled in the art can understand that the choice of filling and repairing material should be determined according to the specific use environment and conditions of the pipeline. For pipelines that are subject to large temperature changes, polyurethane elastic glue with good elasticity can be preferably selected, which can absorb the stress caused by thermal expansion and contraction. For occasions requiring electrical conductivity, such as in cases where anti-static or cathodic protection systems are required, conductive polymer putty can be selected. For emergency repairs that require rapid curing, fast-curing epoxy putty can be used. And for areas subject to large mechanical stress, glass fiber-reinforced putty has better strength performance.

[0054] A complete operation step is as follows: Use a stainless steel scraper or a special filling tool to evenly apply the mixed filling and repairing material on the identified uneven area, making the filler flush with the surrounding surface. For deeper pits or gaps in this step, layered filling is required. Wait until the previous layer is semi-cured before filling the next layer to prevent air bubbles or shrinkage cracks from appearing inside the filler.

[0055] In step S22, repair by welding is suitable for uneven areas with medium depth. Preferably, for areas with a depression depth greater than 30% and less than 50% of the pipe wall thickness, repair by welding is performed. For example: For an uneven area with an original wall thickness of 10 mm, a depth greater than 3 mm and less than 5 mm, repair by welding is performed.

[0056] During the actual operation process, first, a thickness gauge or depth gauge needs to be used to accurately measure the depth of the corrosion area to determine whether it meets the conditions for repair by welding. For areas that meet the conditions, the area around the corrosion part should be ground first to form a bevel transition at a suitable angle, for example: form a bevel transition of 30° - 45°, so that the welding material can fully penetrate and form a firm bond.

[0057] When welding, electrodes or welding wires of the same or similar material as the original pipeline are selected. For example, electrodes of type E4303 or E7016 are selected. The welding process should adopt the method of small current and multi-layer surfacing to reduce the heat-affected zone and control deformation. The thickness of each layer of weld is controlled within a suitable range, for example, 2 - 3 mm. After welding one layer, the welding slag should be removed in time to ensure good interlayer bonding.

[0058] For relatively regular corrosion pits, a spiral welding path from the outside to the inside can be adopted; for irregularly shaped corrosion areas, a segmented welding method is used to avoid deformation of the pipe wall caused by concentrated heat. Special attention should be paid to controlling the heat input during welding. When necessary, intermittent welding can be used, allowing the weld to cool before continuing, to prevent overheating deformation of the pipe wall or the formation of harmful metallographic structures.

[0059] After welding is completed, the weld should be ground smooth and non-destructive testing should be carried out to improve the welding quality. Commonly used testing methods include magnetic particle inspection or penetrant inspection. The repaired welding area also needs to be subjected to local stress relief treatment, which can be carried out by heating with a gas flame and then cooling slowly.

[0060] After repairing the uneven area inside the pipe, step S3 is carried out.

[0061] Specifically, in step S3, the fiber materials include but are not limited to chopped strand mat, glass fiber, carbon fiber, aramid fiber, and polyester fiber. Chopped strand mat or glass fiber is preferred. The reason is that chopped strand mat or glass fiber is preferably selected because it has good tensile strength and impact resistance, so that the pipe coated with this material can effectively resist the anisotropic stress generated by seawater scouring. At the same time, these two materials have good wettability and compatibility with epoxy resin, and can form a composite anti-corrosion layer with a uniform structure.

[0062] The epoxy resin materials include but are not limited to bisphenol A epoxy resin, bisphenol F epoxy resin, phenolic epoxy resin, alicyclic epoxy resin, and waterborne epoxy resin. Bisphenol A epoxy resin is preferred. The reason is that bisphenol A epoxy resin has excellent adhesion performance to the surface of metal pipes, shows excellent chemical resistance in a seawater environment, and can form a high-density network structure after curing, effectively blocking the penetration of corrosive media.

[0063] During the actual operation process, ensure that the surface of the pipe has been completed with rust removal, lining removal, and leveling treatment, and the surface is dry, free of oil and dust. Before coating, the surface can be finally cleaned with alcohol or acetone to improve the coating adhesion.

[0064] Cut the chopped strand mat into an appropriate size so that it can completely cover the inner surface of the pipe that needs anti-corrosion. The specifications of the chopped strand mat can be selected according to the actual situation. For example: select a product with a fiber length of 25 - 50 mm and a surface density of 300 - 450 g / m 2 This specification is not only convenient for operation but also can provide sufficient strengthening effect. According to the mixing ratio requirements, mix bisphenol A epoxy resin and curing agent in a certain proportion, and stir well until uniform to avoid generating too many bubbles.

[0065] Use a roller brush to evenly coat the inner surface of the pipe with the mixed epoxy resin. The thickness of the first layer of coating is controlled within a suitable range, such as: 1.2mm, 0.8mm, 1mm, preferably 1mm. Subsequently, place the prepared chopped strand mat on the surface coated with epoxy resin and use a roller brush or a special tool to squeeze it from the middle to the periphery, so that the chopped strand mat is saturated with epoxy resin and has no bubbles or wrinkles.

[0066] After the chopped strand mat is completely saturated, apply a second layer of epoxy resin to cover all fiber layers and form a smooth surface. The total thickness of the anti-corrosion layer should be controlled within a suitable range, preferably 3 - 5mm. If it is too thin, it may not provide sufficient protection, and if it is too thick, it may crack due to excessive internal stress.

[0067] In addition, please refer to Figure 2 , in the pipeline system, the flange connection (the overall connection area formed after two flange plates are fastened by bolts) is a key area for anti-corrosion treatment and also the weakest link where corrosion failure is most likely to occur. The flange waterline position refers to the intersection of the flange sealing surface and the inner wall of the pipe. Due to the special structure of this area, geometric discontinuities often occur, resulting in the formation of turbulence, eddy currents or stagnant areas of the fluid here, which exacerbates corrosion. At the same time, the presence of the flange connection makes the stress distribution in this area complex and prone to stress concentration.

[0068] During the actual operation process, the anti-corrosion layer needs to extend from the inner wall of the pipe to the flange waterline. In addition, at the junction of the anti-corrosion layer and the flange, a smooth slope transition area needs to be formed, preferably gradually thinning at an oblique angle of 15° - 30°. The smooth transition design avoids the formation of right-angled or acute-angled edges of the anti-corrosion layer at the flange junction, reduces the turbulence and scouring effects generated when the fluid passes through, and effectively reduces the risk of local corrosion. Secondly, the gradually changing thickness distribution evenly disperses the stress, preventing the anti-corrosion layer from cracking or peeling off due to stress concentration during temperature changes or mechanical vibrations.

[0069] After completing step S3, after the anti-corrosion layer has solidified, grind the flange connection.

[0070] In summary, the present invention adopts a fiber-epoxy resin composite material system that can be constructed on-site. This material has excellent fluidity and plasticity, enabling it to conform to irregular surfaces and narrow spaces. At the same time, the layered construction technology is adopted, allowing the anti-corrosion material to penetrate into areas that are difficult to reach by conventional coatings. Coupled with the graded repair strategy for different corrosion depths, it can flexibly handle various pipeline damage conditions. The special treatment process for special structures such as flange connections solves the adaptability problem of traditional anti-corrosion technologies in complex structural parts. It can not only handle straight pipe sections but also effectively deal with complex configurations such as elbows, tees, reducers, and the connections between pipelines and other structures (such as concrete). In addition, compared with traditional anti-corrosion repair methods, the process of the present invention does not require pipeline disassembly, reducing maintenance costs and downtime.

[0071] Embodiment 2

[0072] Based on the same inventive concept, this embodiment provides a large-diameter carbon steel pipeline, which is repaired using the anti-corrosion repair process for large-diameter carbon steel pipelines in Embodiment 1. The strength and anti-corrosion properties of the large-diameter carbon steel pipeline obtained through the above process are both relatively high.

[0073] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these changes and modifications.

Claims

1. A corrosion protection and maintenance process for large-diameter carbon steel pipelines, characterized in that: The process comprises: Remove impurities attached to the surface of the pipe; Repairing the uneven area on the surface of the pipeline; An anti-corrosion layer is coated on the surface of the pipeline, wherein the anti-corrosion layer comprises a composite material consisting of fiber material and epoxy resin material.

2. The anti-corrosion maintenance process for large-diameter carbon steel pipelines according to claim 1, characterized in that: Removal of impurities attached to the pipe surface includes: Derusting the surface of the pipeline at least twice; and grinding to remove the failed lining on the surface of the pipeline.

3. The anti-corrosion maintenance process for large-diameter carbon steel pipelines according to claim 1, characterized in that: Repairing the uneven area on the pipeline surface includes: Filling and repairing the uneven area whose depression depth is within a first set threshold range; The uneven area whose depression depth is within the second set threshold range is repaired by welding. The first set threshold range is less than or equal to 30% of the pipe wall thickness, and the second set threshold range is less than or equal to 50% of the pipe wall thickness and greater than 30% of the pipe wall thickness.

4. The anti-corrosion maintenance process for large-diameter carbon steel pipelines according to claim 3 is characterized in that: The filling and repairing material includes at least one of epoxy putty, conductive polymer putty, polyurethane elastic glue and glass fiber putty.

5. The anti-corrosion maintenance process for large-diameter carbon steel pipelines according to claim 1, characterized in that: The fiber material includes at least one of chopped strand mat, glass fiber, carbon fiber, aramid fiber and polyester fiber.

6. The anti-corrosion maintenance process for large-diameter carbon steel pipelines according to claim 1, characterized in that: The epoxy resin material includes at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, novolac epoxy resin, alicyclic epoxy resin and water-based epoxy resin.

7. The anti-corrosion maintenance process for large-diameter carbon steel pipelines according to claim 1, characterized in that: The anti-corrosion coating on the pipeline surface includes: An epoxy resin layer, a fiber material and an epoxy resin layer are sequentially coated on the surface of the pipeline.

8. The anti-corrosion maintenance process for large-diameter carbon steel pipelines according to claim 1, characterized in that: The thickness of the anti-corrosion layer is in the range of 3-5 mm.

9. The anti-corrosion maintenance process for large-diameter carbon steel pipelines according to claim 1, characterized in that: The coating layer is arranged to extend to the flange waterline position and to smoothly transition at the flange connection.

10. A large diameter carbon steel pipeline, characterized in that: The repair is carried out using the anti-corrosion maintenance process for large-diameter carbon steel pipelines as described in any one of claims 1 to 9.

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