Epoxy flangeWith excellent chemical corrosion resistance, mechanical strength, and insulation properties, it is widely used in fields with high corrosion risks such as petrochemicals, water supply and drainage, and marine engineering. However, if there are defects or improper construction of the epoxy coating on its surface, it is prone to problems such as coating peeling and substrate corrosion, which can affect the service life and operational safety of the equipment. This plan is based on the corrosion characteristics of different working conditions, and develops a full process anti-corrosion treatment measure of "pretreatment coating construction curing and post protection" to ensure that the anti-corrosion effect meets the standard.
1、 Scope of application and anti-corrosion objectives of the plan
1. Scope of application
This scheme is applicable to the anti-corrosion treatment of newly produced epoxy flanges before leaving the factory, the repair of epoxy flange coatings during use, and the strengthening of anti-corrosion treatment under special working conditions (such as strong acidic and alkaline media, high humidity, marine atmospheric environment), covering common types of epoxy flanges such as flat welding, butt welding, socket welding, etc.
2. Anti corrosion objectives
Newly made flanges: form a continuous and uniform anti-corrosion coating, with an adhesion of ≥ 5MPa (checked by cross cutting method), salt spray corrosion resistance of ≥ 1000 hours (neutral salt spray test), and no foaming or peeling phenomenon.
Repair flange: Thoroughly remove the corroded area, and after repair, the coating should be smoothly connected to the original coating, with the same anti-corrosion performance as the original coating, ensuring the overall anti-corrosion integrity of the flange.
Special working condition flange: For highly corrosive environments, a composite anti-corrosion process is adopted to ensure that the chemical corrosion resistance meets the requirements of medium immersion (such as resistance to 30% sulfuric acid immersion for ≥ 6 months without damage).
2、 Core preparation before anti-corrosion treatment
1. Assessment of working conditions and flange status
Working condition investigation: Clarify the type of corrosive medium (such as acidic, alkaline, salt spray), concentration, temperature (normal or high temperature), and pressure of the flange usage environment, determine the corrosion level (mild, moderate, severe), and provide a basis for process selection.
Flange inspection: Newly made flanges need to be inspected for defects such as pinholes, scratches, and dents on the surface epoxy layer; When using flanges, it is necessary to check the area of coating detachment, degree of rust, and whether there are cracks. Use a thickness gauge to measure the coating thickness and record the location and size of defects.
2. Preparation of materials and tools
Anti corrosion materials: Select suitable materials according to the corrosion level, and choose epoxy zinc rich primer+epoxy topcoat for mild corrosion; For moderate corrosion, choose epoxy zinc phosphate primer+epoxy mica iron intermediate paint+fluorocarbon topcoat; For severe corrosion, epoxy glass flake coating or epoxy coal tar coating should be used. The materials must have product certification and testing reports, and be stored in a cool and dry place, away from direct sunlight.
Tools and equipment: Prepare surface treatment tools (sandpaper, wire brush, sandblasting equipment, degreasing cotton), coating construction tools (spray gun, brush, drum), testing tools (grid cutter, coating thickness gauge, salt spray test chamber), and safety protective equipment (gas mask, chemical protective suit, goggles).
3. Construction environment control
The construction environment should meet the requirements of a temperature of 5-35 ℃, relative humidity ≤ 85%, and no weather conditions such as strong winds, rainfall, or dust. If it is outdoor construction, temporary protective shelters need to be built; Indoor construction requires opening ventilation equipment to ensure air circulation in the construction area and avoid safety risks caused by solvent evaporation.
3、 Core anti-corrosion treatment process
1. Surface pretreatment (key step)
The quality of surface pretreatment directly affects the adhesion of the coating, and it is necessary to thoroughly remove oil stains, rust, defects, and residual old coatings.
Degreasing and degreasing: Using solvent degreasing method, wipe the flange surface with degreasing cotton dipped in anhydrous ethanol or acetone, focusing on cleaning the flange sealing surface, bolt holes and other parts, repeatedly wiping 2-3 times until there is no oil residue, and let it dry naturally.
Rust removal treatment: If there is slight rust on the newly made flange, manually polish it with 120-180 grit sandpaper; When the flange is severely corroded or the old coating falls off, dry sandblasting treatment is used (quartz sand with a particle size of 0.5-1.0mm is selected as the abrasive), and the sandblasting pressure is controlled at 0.4-0.6MPa to achieve a surface roughness of Ra25-50 μ m. After exposing the metallic color, the surface dust is blown off with compressed air.
Defect repair: For defects such as pinholes and dents on the flange surface, fill them with epoxy putty, smooth them out, and sand them with sandpaper until they are flush with the surrounding surface; If there are burrs on the edge of the bolt hole, use a file to smooth it out and avoid scratching the coating.
2. Coating construction process
Adopting the principle of "multiple coating, thin coating multiple times" to ensure uniform and defect free coating, the construction interval of different coatings should comply with the requirements of the material manual (usually 4-6 hours).
Primer construction: Select a suitable primer, and give priority to using epoxy zinc rich primer (with a zinc content of ≥ 80%) for newly made flanges to enhance the cathodic protection effect. Spray with a spray gun, with a distance of 20-30cm from the flange surface and a spraying thickness of 30-50 μ m, to ensure no leakage or sagging. Cure at room temperature for 4 hours.
Intermediate paint construction (moderate and above corrosion conditions): Apply epoxy cloud iron intermediate paint to enhance coating thickness and shielding performance, spray a thickness of 50-80 μ m, and after curing, lightly polish the surface with sandpaper to remove particle impurities.
Topcoat construction: Select topcoat according to working conditions, fluorocarbon topcoat for outdoor or humid environments, and epoxy glass flake topcoat for chemical corrosion environments. The spraying thickness should be 40-60 μ m, and the total coating thickness should meet the design requirements (mild corrosion ≥ 120 μ m, moderate corrosion ≥ 200 μ m, severe corrosion ≥ 300 μ m). After the last coat of paint is applied, it should be naturally cured for more than 7 days (or baked and cured according to material requirements).
Special part treatment: The flange sealing surface needs to be pasted with special protective tape to avoid coating contamination; Hand brushing is used around the bolt holes to ensure complete coating coverage; After the welding between the flange and the pipeline is completed and cooled, the surface treatment of the weld area should be carried out again and the coating should be applied.
3. Curing and post-treatment
Curing and curing: After the coating construction is completed, it should be left to cure in the construction environment. During the curing period, it is forbidden to touch or squeeze the flange to avoid damage to the coating; The flange under high temperature conditions can be accelerated by low-temperature baking (60-80 ℃) for curing, and the baking time is determined according to the material manual.
Post treatment: After curing is complete, remove the protective tape from the sealing surface and clean the residual impurities on the surface with degreased cotton; Gently polish the surface of the coating with fine sandpaper (400 mesh or more) to achieve a smooth surface with slight sagging and particles.
4、 Quality Inspection and Acceptance Standards
1. Appearance inspection
Visually inspect the coating surface to be smooth, uniform in color, and free of defects such as bubbles, peeling, pinholes, and sagging; Use a 5-10 times magnifying glass to inspect bolt holes, corners, and other areas to ensure complete coating coverage.
2. Performance testing
Coating thickness: Use a coating thickness gauge to measure the thickness at different parts of the flange (at least 5 points), with a deviation within ± 10%, in accordance with the design requirements.
Adhesion testing: Use the grid cutting method for testing, with a grid spacing of 2mm (coating thickness ≤ 120 μ m) or 3mm (coating thickness>120 μ m). After grid cutting, use adhesive tape to peel off, and the coating peeling area is ≤ 5% to be qualified.
Corrosion resistance testing: Sampling is conducted for salt spray testing (neutral salt spray, 35 ℃, 5% sodium chloride solution), with mild corrosion conditions lasting ≥ 1000 hours, moderate corrosion conditions lasting ≥ 1500 hours, and severe corrosion conditions lasting ≥ 2000 hours. After the test, the coating shows no significant corrosion.
3. Acceptance Record
Fill out the "Epoxy Flange Anti corrosion Treatment Acceptance Record Form", which includes the construction date, working condition information, material model, construction process, testing data, and acceptance results. The form shall be jointly signed and confirmed by the construction personnel, quality inspection personnel, and the user.
5、 Post maintenance and protective measures
Regular inspection: Under normal working conditions, inspections should be conducted every 3 months. For special corrosive working conditions, inspections should be conducted monthly to check whether the coating has peeled off, cracked, or rusted. If small defects are found, they should be promptly sanded and the corresponding coating should be applied.
Cleaning and maintenance: Regularly rinse the flange surface with clean water to prevent dust and impurities from adhering to corrosive media; If in contact with acidic or alkaline media, immediately rinse with plenty of water and air dry. If necessary, apply topcoat.
Service life management: Based on the service life of the anti-corrosion coating (usually 3-5 years, special working conditions 1-2 years), a re coating plan should be developed in advance to avoid corrosion of the flange substrate caused by coating failure.