Bridge steel structure anticorrosion coating process

Abstract

The present application relates to the technical field of bridge manufacturing, in particular to a bridge steel structure anticorrosion coating process. The mode of combining main coating in the factory with local supplementary coating at the bridge site is adopted to improve the overall coating efficiency, quality and environmental performance. The coating of the outer surface, inner surface, steel bridge deck and friction surface of high-strength bolt connection parts of the steel structure is completed in the factory coating room, and the exposed surface of the girth weld, high-strength bolt connection part and coating damage part after installation is only supplemented at the bridge site. The coating system is designed differently for different parts: the outer surface adopts the system of "epoxy zinc-rich primer + epoxy cloud iron intermediate paint + acrylic polyurethane topcoat + fluorocarbon topcoat"; the inner surface adopts the thinned system of "epoxy zinc-rich primer + epoxy thick paste intermediate paint" to avoid excessive coating in the low corrosion risk area. The present application can shorten the site construction period by 20% to 30%, reduce the coating amount and VOCs emission, and improve the coating quality stability.

Description

Technical Field

[0001] This invention relates to the field of bridge manufacturing technology, and in particular to an anti-corrosion coating process for bridge steel structures. Background Technology

[0002] Traditional anti-corrosion coating for bridge steel structures often employs a phased process of "factory application of primer and intermediate coats, followed by on-site application of topcoat." This process has the following drawbacks: the uncontrollable temperature and humidity of the on-site environment easily leads to quality problems such as whitening, sagging, and decreased adhesion of the topcoat; the intermediate coat layer is prone to impact damage during transportation and hoisting, resulting in decreased interlayer adhesion and creating weak points in corrosion protection; the on-site coating work is extensive, and it is difficult to guarantee consistent quality with manual spraying; the overlapping of multiple processes can easily delay the construction period; in addition, the fugitive emissions of VOCs on-site pose a significant environmental burden.

[0003] On the other hand, existing processes typically apply a uniform coating system and thickness to all parts of the steel structure, without fully considering the differences in corrosion environments in different parts. For example, the inner surface of a steel box girder in a closed or semi-closed environment is coated with the same or similar thickness as the outer surface directly exposed to the atmosphere, resulting in over-coating of low-corrosion-risk areas, increasing paint usage and material costs.

[0004] Therefore, there is an urgent need for a bridge steel structure coating process that can significantly improve coating quality stability, construction efficiency and environmental friendliness, and achieve differentiated corrosion protection. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a corrosion protection coating process for bridge steel structures, which combines full-body coating completed in the factory with local touch-up coating at the bridge site, and designs a coating system with different parts for different parts. At the same time, it introduces intelligent sandblasting and spraying equipment to achieve an overall improvement in coating efficiency, quality and environmental performance.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is: a bridge steel structure anti-corrosion coating process, the innovation of which is: including the completion of the main coating in the factory and the local touch-up coating at the bridge site; The painting of the outer and inner surfaces of the bridge steel structure, the steel bridge deck, and the friction surfaces of the high-strength bolt connections is completed in the factory's painting room. Repair and coating of exposed surfaces and damaged areas of circumferential welds and high-strength bolt connections after the installation of the bridge steel structure were completed at the bridge site; Painting or touch-up methods include: Surface pretreatment: Before sandblasting and rust removal and touch-up coating, the surface of the component must be inspected and marked. Use manual or power tools to grind and clean areas that are not conducive to painting, including removing surface defects such as weld slag, spatter, and oxide scale. Trim sharp corners, burrs, flash, and other edge defects to make them smooth. Repair surface depressions, scratches, and damaged edges of old coatings. Before painting, all exposed edges of the rods should be chamfered with a chamfer radius ≥2mm. Before steel components are sandblasted in the blasting room, surface cleaning work needs to be carried out at the temporary storage point. This includes removing oil stains and surface deposits from the steel surface; and testing the surface salt content according to the method specified in GB / T 18570.9-2022, with a content ≤5μg / cm³. 2 ; Coating application: The first coating should be applied within 4 to 12 hours after sandblasting and rust removal.

[0007] Furthermore, the environmental requirements for the coating room are as follows: the ambient temperature is 5-38℃, the relative humidity is ≤85%, and the surface temperature of the steel to be coated is at least 3℃ higher than the dew point temperature of the air. When the working environment in the coating room does not meet the standards, dehumidifiers, heating dryers and other equipment are used for adjustment.

[0008] Furthermore, the specific steps for the main body painting in the factory are as follows: S1. Clean the surface of the components to be painted, removing oil, dust and other contaminants; S2. Perform surface pretreatment inspection on the components to be coated in S1 to confirm that the chamfering of the edges is qualified, there is no visible oil on the surface, and the salt content test meets the standard. If the inspection is passed, proceed to S3; otherwise, proceed to S1. S3. Sandblasting and rust removal treatment: The inner and outer surfaces are sandblasted using a multi-axis joint linkage intelligent sandblasting equipment to achieve a cleanliness level of Sa2.5 and a roughness of Rz40~80μm. S4. Check the sandblasting quality. If the cleanliness and roughness are not up to standard, return to S3 for re-sandblasting. S5. Pre-coat or spray primer on the surface of the components to be coated; S6. Pre-coat and spray intermediate paint on the surface of the components; S7. Pre-coat and spray topcoat the surface of the components; S8. After the component painting is completed, the final quality inspection is carried out.

[0009] Furthermore, during the sandblasting and rust removal process, an intelligent sandblasting equipment with multi-axis joint linkage is used for sandblasting and rust removal on both the inner and outer surfaces. The specific parameters are as follows: compressed air 0.6MPa~0.8MPa, spray distance 500mm, moving speed 0.05~0.24m / s, spray width 800mm~900mm, overlap width 80mm~120mm, and nozzle outlet diameter 8mm~12mm. During the spraying process, intelligent spraying equipment is used to carry out overall spraying of the steel bridge deck, outer surface and outer side of the inner diaphragm of the beam segment. The relevant parameters are as follows: compressed air 0.4MPa~0.6MPa, spraying distance 300mm~500mm, moving speed 0.05~0.3m / s, spray width 800mm~900mm, and overlap width 400~500mm.

[0010] Furthermore, after completing steps S5, S6, or S7, it is necessary to check whether the process is qualified before proceeding to the next step. The adhesion of the coating must be ≥5MPa, as tested by the pull-off method.

[0011] Furthermore, the measured values ​​of the coating film thickness must meet the double 90% rule for the outer surface and the double 85% rule for the inner surface. That is, more than 90% of the measured values ​​on the outer surface must meet the specified thickness requirements, and the thickness of the remaining 10% of the measured values ​​that do not meet the thickness requirements must not be less than 90% of the specified thickness. On the inner surface, more than 85% of the measured values ​​must meet the specified thickness requirements, and the thickness of the remaining 15% of the measured values ​​that do not meet the thickness requirements must not be less than 85% of the specified thickness.

[0012] In addition, the measurement was done at 10m. 2 For each measurement unit, at least three reference surfaces should be selected, and five points should be measured on each reference surface, with the arithmetic mean taken. (100 m) 2 Choose any three 10m rods from the following list. 2 Measurements were taken at 100m. 2 The above-mentioned members should be measured for the first 100m using the method described above. 2 For each of the remaining 100m 2 Choose any 10m 2 (Measurement is performed).

[0013] Furthermore, the repair method completed at the bridge site is as follows: using a combination of power tool grinding and manual sanding, the surrounding coating of the area to be repaired is sanded into a stepped transition layer with a 1:3 slope. After dust removal and cleaning, a pneumatic or electric portable spray gun is used to apply each layer of coating according to the corresponding coating system for that area, with the interlayer interval meeting the requirements of the paint product instructions.

[0014] Furthermore, the bridge steel structure includes steel box girders and steel-concrete composite beams, and its differentiated coating system is as follows; The requirements for the outer surface coating of steel box girders are as follows: The steel plate surface is sandblasted to remove rust, Sa2.5 grade, Rz40~80μm; epoxy zinc-rich primer, 1 coat, thickness ≥80μm; epoxy micaceous iron oxide intermediate paint, 2 coats, total thickness ≥140μm; acrylic polyurethane topcoat, 1 coat, thickness ≥40μm; fluorocarbon topcoat, 1 coat, thickness ≥40μm. Requirements for coating the inner surface of steel box girders: The steel plate surface is sandblasted to remove rust, Sa2.5 grade, Rz40~80μm; epoxy zinc-rich primer, 1 coat, thickness ≥60μm; epoxy thick intermediate paint, 2~3 coats, total thickness ≥200μm; Steel bridge deck coating requirements: The steel plate surface is sandblasted to remove rust, Sa2.5 grade, Rz40~80μm; epoxy zinc-rich primer, 1 coat, thickness ≥80μm. Since the steel bridge deck will be subsequently poured with concrete pavement, epoxy zinc-rich primer can be used as the anti-rust layer. Coating requirements for friction surfaces of high-strength bolt connections: The steel plate surface is sandblasted to remove rust, Sa3 grade, Rz50~80μm; inorganic zinc-rich anti-rust and anti-slip coating, 1 coat, thickness ≥80μm; Painting requirements for exposed splicing plates at high-strength bolt connection points: Remove oil and dirt, and mechanically grind the exposed parts of bolts, nuts and washers to St3 grade; epoxy micaceous iron oxide intermediate paint, 3 to 4 coats, thickness ≥300μm; fluorocarbon topcoat, 2 coats, total thickness ≥80μm; The coating requirements for the inner and outer surfaces of steel-concrete composite beams are the same as those for the inner and outer surfaces of steel box girders.

[0015] The advantages of this invention are: 1. This invention combines full-body coating in the factory with localized touch-up coating at the bridge site, controlling over 90% of the coating workload within a factory-controlled environment. This significantly improves coating quality stability and shortens the on-site construction period by 20%–30% compared to traditional processes. The differentiated coating system allows for appropriate thinning in low-corrosion-risk areas such as inner surfaces, reducing paint usage and material costs. The application of intelligent equipment improves coating efficiency and consistency. On-site VOC emissions are significantly reduced, demonstrating clear environmental advantages.

[0016] 2. The anti-corrosion coatings on the inner and outer surfaces of the bridge steel structure in this invention are specifically designed to avoid applying excessive coatings on the inner surface of the bridge steel structure where the protection requirements are relatively weak, thereby reducing the amount of coating used and lowering costs. Detailed Implementation

[0017] To further illustrate the technical means and effects of the present invention in achieving the intended purpose, the following detailed description of the specific implementation methods, structures, features and effects of the present invention, in conjunction with preferred embodiments, is provided below.

[0018] A bridge steel structure anti-corrosion coating process includes main coating completed in the factory and local touch-up coating at the bridge site; The painting of the outer and inner surfaces of the bridge steel structure, the steel bridge deck, and the friction surfaces of the high-strength bolt connections is completed in the factory's painting room. Repair and coating work was completed at the bridge site, including circumferential welds and high-strength bolt connections after the bridge steel structure was installed, as well as damaged areas. The environmental requirements for the coating room are as follows: ambient temperature is 5-38℃, relative humidity is ≤85%, and the surface temperature of the steel to be coated is at least 3℃ higher than the dew point temperature of the air. When the working environment in the coating room does not meet the standards, dehumidifiers, heating dryers and other equipment are used for adjustment.

[0019] Painting or touch-up methods include: Surface pretreatment: Before sandblasting and rust removal and touch-up coating, the surface of the component must be inspected and marked. Using manual or power tools, areas unsuitable for coating should be sanded and cleaned according to the requirements in the table below. This includes removing surface defects such as weld slag, spatter, and oxide scale, and smoothing sharp angles, burrs, and flash to make the edges smooth. Surface depressions, scratches, and damaged edges of old coatings should also be repaired. Before coating, all exposed edges of the rods should be chamfered with a chamfer radius ≥2mm. Table 1. Grinding and cleaning requirements for areas unsuitable for painting.

[0020] Specifically, in the sandblasting and rust removal process, a multi-axis joint linkage intelligent sandblasting equipment is used to sandblast and remove rust from the inner and outer surfaces. The relevant parameters are as follows: compressed air 0.6 MPa ~ 0.8 MPa, spray distance 500 mm, moving speed 0.05 ~ 0.24 m / s, spray width 800 mm ~ 900 mm, overlap width 80 mm ~ 120 mm, and nozzle outlet diameter 8 mm ~ 12 mm. Before steel components are sandblasted in the blasting room, surface cleaning work needs to be carried out at the temporary storage point. This includes removing oil stains and surface deposits from the steel surface; and testing the surface salt content according to the method specified in GB / T 18570.9-2022, with a content ≤5μg / cm³. 2 ; Coating application: The first coating should be applied within 4 to 12 hours after sandblasting and rust removal.

[0021] Specifically, during the spraying process, intelligent spraying equipment is used to carry out overall spraying of the steel bridge deck, outer surface, and outer side of the inner diaphragm of the beam segment. The relevant parameters are as follows: compressed air 0.4MPa~0.6MPa, spraying distance 300mm~500mm, moving speed 0.05~0.3m / s, spray width 800mm~900mm, and overlap width 400~500mm.

[0022] The aforementioned bridge steel structure includes steel box girders and steel-concrete composite beams; The requirements for the outer surface coating of steel box girders are as follows: The steel plate surface is sandblasted to remove rust, Sa2.5 grade, Rz40~80μm; epoxy zinc-rich primer, 1 coat, thickness ≥80μm; epoxy micaceous iron oxide intermediate paint, 2 coats, total thickness ≥140μm; acrylic polyurethane topcoat, 1 coat, thickness ≥40μm; fluorocarbon topcoat, 1 coat, thickness ≥40μm.

[0023] The coating requirements for the inner surface of steel box girders are as follows: The steel plate surface is sandblasted to remove rust, Sa2.5 grade, Rz40~80μm; epoxy zinc-rich primer, 1 coat, thickness ≥60μm; epoxy thick intermediate paint, 2~3 coats, total thickness ≥200μm.

[0024] The requirements for steel bridge deck coating are as follows: The steel plate surface is sandblasted to remove rust, Sa2.5 grade, Rz40~80μm; epoxy zinc-rich primer, 1 coat, thickness ≥80μm.

[0025] The coating requirements for the friction surfaces of high-strength bolt connections are as follows: The steel plate surface is sandblasted to remove rust, Sa3 grade, Rz50~80μm; inorganic zinc-rich anti-rust and anti-slip coating, 1 coat, thickness ≥80μm.

[0026] The coating requirements for exposed splice plates at high-strength bolt connection points are as follows: Remove oil and dirt, and mechanically grind the exposed parts of bolts, nuts and washers to St3 grade; apply 3-4 coats of epoxy micaceous iron oxide intermediate paint with a thickness ≥300μm; apply 2 coats of fluorocarbon topcoat with a total thickness ≥80μm.

[0027] The coating requirements for the inner and outer surfaces of steel-concrete composite beams are the same as those for the inner and outer surfaces of steel box girders.

[0028] The specific steps for the main body painting in the factory are as follows: S1. Clean the surface of the components to be painted, removing oil, dust and other contaminants; S2. Perform surface pretreatment inspection on the components to be coated in S1 to confirm that the chamfering of the edges is qualified, there is no visible oil on the surface, and the salt content test meets the standard. If the inspection is passed, proceed to S3; otherwise, proceed to S1. S3. Sandblasting and rust removal treatment: The inner and outer surfaces are sandblasted using a multi-axis joint linkage intelligent sandblasting equipment to achieve a cleanliness level of Sa2.5 and a roughness of Rz40~80μm. S4. Check the sandblasting quality. If the cleanliness and roughness are not up to standard, return to S3 for re-sandblasting. S5. Pre-coat or spray primer on the surface of the components to be coated; S6. Pre-coat and spray intermediate paint on the surface of the components; S7. Pre-coat and spray topcoat the surface of the components; S8. After the component painting is completed, the final quality inspection is carried out.

[0029] Furthermore, after completing steps S5, S6, or S7, it is necessary to check whether the process is qualified before proceeding to the next step. The adhesion of the coating is required to be ≥5MPa by the pull-off test.

[0030] Furthermore, the measured values ​​of the coating film thickness must meet the double 90% rule for the outer surface and the double 85% rule for the inner surface. That is, more than 90% of the measured values ​​on the outer surface must meet the specified thickness requirements, and the thickness of the remaining 10% of the measured values ​​that do not meet the thickness requirements must not be less than 90% of the specified thickness. On the inner surface, more than 85% of the measured values ​​must meet the specified thickness requirements, and the thickness of the remaining 15% of the measured values ​​that do not meet the thickness requirements must not be less than 85% of the specified thickness.

[0031] In addition, the measurement was done at 10m. 2 For each measurement unit, at least three reference surfaces should be selected, and five points should be measured on each reference surface, with the arithmetic mean taken. (100 m) 2 Choose any three 10m rods from the following list. 2 Take measurements, 100m 2 The above-mentioned members should be measured for the first 100m using the method described above. 2 For each of the remaining 100m 2 Choose any 10m 2 (Measurement is performed).

[0032] The repair method completed at the bridge site was as follows: using power tools to grind and hand sandpaper to sand the surrounding coating of the area to be repaired into a stepped transition layer with a 1:3 slope. After dust removal and cleaning, a pneumatic or electric portable spray gun was used to apply each layer of coating according to the corresponding coating system for that area, with the interlayer interval meeting the requirements of the paint product instructions.

[0033] Taking the outer surface of the steel box girder of the G5 section of the bridge steel structure of a cross-river passage as an example, its coating process is as follows: 1. Surface pretreatment: Remove oil and contaminants from the steel surface. Test the surface salinity according to GB / T 18570.9-2022: ≤4μg / cm³ 2 All exposed edges of the members shall be chamfered with a chamfer radius ≥ 2mm; defects such as weld slag, spatter, and oxide scale shall be ground and cleaned according to the requirements of Table 1.

[0034] 2. Sandblasting and rust removal: The equipment adopts a multi-axis joint linkage intelligent sandblasting equipment with key parameters of 0.7MPa compressed air, 500mm spray distance, 10mm nozzle outlet diameter, 0.15m / s moving speed, surface cleanliness reaching Sa2.5 level, and roughness Rz50~70μm.

[0035] 3. Primer application: Within 4 hours after sandblasting, pre-coat edges, corners, welds, and other areas manually, then apply an epoxy zinc-rich primer (dry film thickness 85μm) using intelligent spray painting equipment. After complete drying, perform a pull-off adhesion test according to "Paints and Varnishes Pull-Off Adhesion Test" (GB / T 5210-2006), with an adhesion ≥6MPa.

[0036] 4. Intermediate coat application: After the primer has fully dried (24 hours at 25℃), apply two coats of epoxy micaceous iron oxide intermediate coat, with each coat having a dry film thickness ≥70μm and a total thickness ≥140μm.

[0037] 5. Topcoat application: After the intermediate coat has fully dried (48 hours at 25℃), spray the acrylic polyurethane topcoat (≥40μm) and fluorocarbon topcoat (≥40μm) in sequence.

[0038] 6. Quality Inspection: The total dry film thickness is approximately 310μm, meeting the double 90% rule; adhesion is ≥5.5MPa; and there are no defects such as missed coating, sagging, or blistering in the appearance.

[0039] Coating of the inner surface of steel box girder The inner surface of the steel box girder is in a closed environment, where the corrosive environment is milder than that of the outer surface. A differentiated thinning coating system is adopted. Sandblasting and rust removal of steel plate surface: Sa2.5 grade, Rz40~80μm; epoxy zinc-rich primer, 1 coat, dry film thickness ≥60μm; epoxy thick-film intermediate paint, 2 coats, total dry film thickness ≥200μm; total dry film thickness ≥260μm.

[0040] This design ensures long-term corrosion protection of the inner surface while reducing paint usage by approximately 20% to 30% compared to traditional uniform coating systems.

[0041] The painting room in the factory is equipped with a VOCs catalytic combustion treatment device, and the exhaust gas emissions meet the requirements of the "Integrated Emission Standard of Air Pollutants" (GB 16297-1996). For on-site touch-up coating, low VOCs coatings with a VOCs content of ≤420g / L are preferred, which meet the requirements of the "Limits of Hazardous Substances in Industrial Protective Coatings" (GB 30981-2020).

[0042] This invention combines in-plant main coating with on-site touch-up coating, achieving an overall improvement in coating efficiency, quality, and environmental performance. In-plant coating is applied to the outer and inner surfaces of the steel structure, the steel bridge deck, and the friction surfaces of high-strength bolt connections. At the bridge site, only the circumferential welds, exposed surfaces of high-strength bolt connections, and areas with damaged coating are touched up. The in-plant coating environment requires an ambient temperature of 5–38℃, relative humidity ≤85%, and a steel surface temperature ≥ air dew point temperature +3℃. Multi-axis articulated intelligent sandblasting and painting equipment are used for sandblasting and painting operations. Different coating systems are designed for different areas: the outer surface uses an "epoxy zinc-rich primer + epoxy micaceous iron oxide intermediate coat + acrylic polyurethane topcoat + fluorocarbon topcoat" system; the inner surface uses a thinned "epoxy zinc-rich primer + epoxy thick intermediate coat" system to avoid over-coating low-corrosion-risk areas.

[0043] In this invention, the anti-corrosion coatings on the inner and outer surfaces of the bridge steel structure are respectively designed for specific purposes, avoiding the need for excessive coatings on the inner surface of the bridge steel structure where the protection requirements are relatively weak, thereby reducing the amount of coating used and lowering costs.

[0044] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A corrosion-resistant coating process for bridge steel structures, characterized in that: This includes completing the main body painting within the factory and partial touch-up painting at the bridge site; The painting of the outer and inner surfaces of the bridge steel structure, the steel bridge deck, and the friction surfaces of the high-strength bolt connections is completed in the factory's painting room. Repair coating was completed at the bridge site, including the exposed surfaces of circumferential welds and high-strength bolt connections after the bridge steel structure was installed, as well as areas with damaged coatings. Painting or touch-up methods include: Surface pretreatment: Before sandblasting and rust removal and touch-up coating, the surface of the component must be inspected and marked. Use manual or power tools to grind and clean the parts that are not conducive to painting. Before painting, all exposed edges of the rods should be chamfered with a chamfer radius ≥2mm. Before entering the sandblasting room, steel components need to undergo surface cleaning at a temporary storage point, specifically including the removal of oil stains and surface adhering substances from the steel surface; the surface salt content of the steel components before coating should be ≤5μg / cm³. 2 ; Coating application: The first coating should be applied within 4 to 12 hours after sandblasting and rust removal.

2. The anti-corrosion coating process for bridge steel structures according to claim 1, characterized in that: The environmental requirements for the coating room are as follows: ambient temperature is 5-38℃, relative humidity is ≤85%, and the surface temperature of the steel to be coated is at least 3℃ higher than the dew point temperature of the air. When the working environment in the coating room does not meet the standards, dehumidifiers and heating dryers are used for adjustment.

3. The anti-corrosion coating process for bridge steel structures according to claim 1, characterized in that: The specific steps for the main body painting in the factory are as follows: S1. Clean the surface of the components to be painted, removing oil, dust and other contaminants; S2. Perform surface pretreatment inspection on the components to be coated in S1 to confirm that the chamfering of the edges is qualified, there is no visible oil on the surface, and the salt content test meets the standard. If the inspection is passed, proceed to S3; otherwise, proceed to S1. S3. Sandblasting and rust removal treatment: The inner and outer surfaces are sandblasted using a multi-axis joint linkage intelligent sandblasting equipment to achieve a cleanliness level of Sa2.5 and a roughness of Rz40~80μm. S4. Check the sandblasting quality. If the cleanliness and roughness are not up to standard, re-sandblast. S5. Pre-coat or spray primer on the surface of the components to be coated; S6. Pre-coat and spray intermediate paint on the surface of the components; S7. Pre-coat and spray topcoat the surface of the components; S8. After the component painting is completed, the final quality inspection is carried out.

4. The anti-corrosion coating process for bridge steel structures according to claim 3, characterized in that: During the sandblasting and rust removal process, an intelligent sandblasting equipment with multi-axis joint linkage is used to sandblast and remove rust from the inner and outer surfaces. The relevant parameters are: compressed air 0.6 MPa~0.8 MPa, spray distance 500 mm, moving speed 0.05~0.24 m / s, spray width 800 mm~900 mm, overlap width 80 mm~120 mm, and nozzle outlet diameter 8 mm~12 mm. During the spraying process, intelligent spraying equipment is used to carry out overall spraying of the steel bridge deck, outer surface and outer side of the inner diaphragm of the beam segment. The relevant parameters are as follows: compressed air 0.4MPa~0.6MPa, spraying distance 300mm~500mm, moving speed 0.05~0.3m / s, spray width 800mm~900mm, and overlap width 400~500mm.

5. The anti-corrosion coating process for bridge steel structures according to claim 3, characterized in that: In steps S5, S6 or S7, after each coating is fully dried, the coating quality and dry film thickness must be checked to ensure they are up to standard. Only after confirming that they are up to standard can the next step be carried out. The adhesion of the final coating system must be ≥5MPa by the pull-off test.

6. The anti-corrosion coating process for bridge steel structures according to claim 5, characterized in that: The measured thickness of the coating film must meet the double 90% rule for the outer surface and the double 85% rule for the inner surface.

7. The anti-corrosion coating process for bridge steel structures according to claim 1, characterized in that: The repair method completed at the bridge site was as follows: using power tools to grind and hand sandpaper to sand the surrounding coating of the area to be repaired into a stepped transition layer with a 1:3 slope. After dust removal and cleaning, a pneumatic or electric portable spray gun was used to complete the repair of each coating layer according to the corresponding coating system of the area.

8. The anti-corrosion coating process for bridge steel structures according to claim 1, characterized in that: The bridge steel structure includes steel box girders and steel-concrete composite beams; The requirements for the outer surface coating of steel box girders are as follows: The steel plate surface is sandblasted to remove rust, Sa2.5 grade, Rz40~80μm; Epoxy zinc-rich primer, 1 coat, thickness ≥80μm; Epoxy micaceous iron oxide intermediate paint, 2 coats, total thickness ≥140μm; Acrylic polyurethane topcoat, 1 coat, thickness ≥40μm; Fluorocarbon topcoat, 1 coat, thickness ≥40μm; Requirements for coating the inner surface of steel box girders: The steel plate surface is sandblasted to remove rust, Sa2.5 grade, Rz40~80μm; Epoxy zinc-rich primer, 1 coat, thickness ≥60μm; Epoxy thick intermediate paint, 2-3 coats, total thickness ≥200μm; Steel bridge deck coating requirements: The steel plate surface is sandblasted to remove rust, Sa2.5 grade, Rz40~80μm; Epoxy zinc-rich primer, 1 coat, thickness ≥80μm; Coating requirements for friction surfaces of high-strength bolt connections: The steel plate surface is sandblasted to remove rust, Sa3 grade, Rz50~80μm; Inorganic zinc-rich anti-rust and anti-slip coating, 1 coat, thickness ≥80μm; Painting requirements for exposed splicing plates at high-strength bolt connection points: Remove oil and dirt, and mechanically grind the exposed parts of bolts, nuts and washers to St3 grade; Epoxy micaceous iron oxide intermediate paint, 3-4 coats, total thickness ≥300μm; Fluorocarbon topcoat, 2 coats, total thickness ≥80μm; The coating requirements for the inner and outer surfaces of steel-concrete composite beams are the same as those for the inner and outer surfaces of steel box girders.

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