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Polyurea spraying is a widely adopted method for applying high-performance anti-corrosion coatings in demanding environments such as pipelines, storage tanks, marine structures, and chemical processing facilities. The following detailed guidelines cover surface preparation, equipment setup, application parameters, and quality control to ensure optimal coating performance and durability.
Proper surface preparation is critical for adhesion and long-term protection. The substrate must be free of contaminants including oil, grease, rust, mill scale, and moisture. For steel surfaces, abrasive blasting to achieve a minimum cleanliness of Sa 2.5 (near-white metal) and a surface profile of 75-125 microns is recommended. Concrete surfaces should be dry, cured for at least 28 days, and free of laitance. Apply a compatible Primer if specified by the polyurea manufacturer. Mix polyurea components (resin and isocyanate) in the correct ratio, typically 1:1 by volume, using a mechanical stirrer at low speed to avoid air entrapment. Pot life is usually short (15-30 seconds), so prepare only the amount that can be applied immediately.
Use a plural-component spray system with heated hoses and a proportioning pump capable of maintaining precise ratio control. Set the material temperature between 60-80°C (140-176°F) to reduce viscosity and ensure proper mixing. Adjust air pressure to 3-5 bar (45-75 psi) depending on the desired film thickness and spray pattern. Maintain a spray gun distance of 30-50 cm (12-20 inches) from the substrate, moving at a consistent speed of 0.5-1.0 meters per second. Apply in multiple passes to achieve the specified dry film thickness (typically 500-2000 microns per coat). Overlap each pass by 50% to ensure uniform coverage and avoid pinholes.
For edges, corners, welds, and bolt heads, apply a stripe coat using a brush or small spray gun before the full coating. This ensures adequate thickness in areas prone to thin coverage. For vertical or overhead surfaces, use a lower air pressure and faster gun speed to prevent sagging. In confined spaces, ensure adequate ventilation and use explosion-proof equipment. For repairs or touch-ups, abrade the existing coating, clean the area, and apply a fresh coat using the same parameters. Allow sufficient curing time (typically 24 hours at 25°C) before subjecting the coating to mechanical stress or immersion.
Inspect each coat for defects such as runs, sags, blisters, or contamination. Use a wet film thickness gauge during application and a dry film thickness gauge after curing. Perform adhesion tests (pull-off or cross-cut) as per ASTM D4541 or ISO 2409. For immersion service, conduct holiday detection (spark testing) at 5-10 volts per micron of coating thickness. Ensure all operators wear full personal protective equipment including chemical-resistant gloves, safety goggles, respirators with organic vapor cartridges, and protective clothing. Maintain proper ventilation to keep airborne isocyanate levels below permissible exposure limits. Dispose of waste materials in accordance with local environmental regulations.