Guide For Selection Of Polyurethane Paint For Steel Pipes

Polyurethane paint is a mainstream topcoat system for steel pipe anti-corrosion coating due to its excellent weather resistance, chemical corrosion resistance, high adhesion and mechanical properties. Its selection must strictly follow the core principles of “environment adaptation, performance matching, system compatibility, and construction feasibility”, and combine with the steel pipe’s service environment, corrosion level, operating conditions and construction conditions to select scientifically to ensure anti-corrosion life and structural safety.

The core premise of selection is to clarify the service environment and exposure state of the steel pipe: For outdoor overhead, exposed municipal pipe networks, and steel pipes in coastal and chemical industrial areas that are long-term exposed to ultraviolet radiation, rain and snow, and salt spray, aliphatic polyurethane paint should be preferred. With HDI and IPDI as curing agents, it has outstanding light and color retention, no yellowing or chalking, and can ensure 5-10 years of outdoor anti-corrosion life. For indoor pipe trenches, underground direct-buried, and concealed steel pipes in pipe galleries without ultraviolet radiation, aromatic polyurethane paint can be selected, which has excellent acid and alkali resistance, oil resistance, lower cost, and avoids performance redundancy. For steel pipes transporting drinking water, food-grade polyurethane paint that meets the “Hygienic Safety Evaluation Specification for Drinking Water Transmission and Distribution Equipment and Protective Materials” must be selected to prevent the precipitation of harmful substances.

Secondly, it is necessary to match the corrosion level and service temperature: For steel pipes with mild corrosion in conventional atmospheric environments, two-component acrylic polyurethane topcoat can meet the requirements; for steel pipes with moderate to severe corrosion in industrial pollution areas, coastal high salt spray, and chemical medium contact, high-solid-content polyurethane heavy anti-corrosion paint should be selected to improve the film density and medium resistance. The conventional applicable temperature of polyurethane paint is -40℃~120℃. For steel pipes transporting high-temperature media, high-temperature resistant modified products should be selected, and polyurethane system is not recommended when the temperature exceeds 150℃.

The coating supporting system is the key to selection. Polyurethane paint is mostly used as a topcoat and needs to be compatible with primers and intermediate coats (it is strictly prohibited to match with inferior alkyd primers to avoid interlayer peeling). At the same time, it is necessary to control technical indicators and construction adaptability. The film adhesion must reach Grade 1 of GB/T 5210 standard, the salt spray resistance ≥ 500h, the construction environment must be controlled at a temperature of 5-35℃ and a relative humidity ≤ 85%, and the steel pipe surface treatment must reach sandblasting Sa2.5 level or power tool St3 level.

The selection of polyurethane paint for steel pipes should focus on working conditions, give priority to matching the exposure state and corrosion level, scientifically design the supporting system, and control surface treatment and construction details to achieve the optimal balance between anti-corrosion performance and economy.