Sea-Crossing Bridge Steel Box Girder Coating in China

Illustration notice. Process illustrations are not verified photographs of this installation.

Project reference basis. Figures and configuration details are reported in the supplied project brief. They are reference values for the stated application, rather than verified acceptance results or a guarantee for another installation. Confirm the source records, material, tooling, operating schedule and test method when assessing a comparable project.

A tier-one highway bridge engineering contractor in Eastern China deployed Haifeng’s autonomous diesel-hydraulic polyurea spray systems to execute external anti-corrosion coating across 65,000 m² of steel box girders on a major sea-crossing expressway bridge.

Marine construction presented extreme operational hurdles, including high ambient humidity exceeding 90%, strong coastal winds, and the absence of high-voltage power on suspended scaffolding platforms 45 meters above the sea. Conventional fluorocarbon and epoxy multi-coat paint systems required 24-hour drying intervals between coats, exposing wet films to salt aerosol contamination that resulted in early blistering and premature delamination.

Haifeng deployed two self-contained HF-BRG200-DSL diesel-hydraulic spraying rigs mounted directly on bridge inspection maintenance trucks. Providing onboard 40 kW electrical power, 21 MPa hydraulic pressure, and 90-meter total hose length serving the reported 45-meter elevation, the systems applied rapid-curing pure polyurea and aliphatic aspartic topcoats that set within seconds, achieving 8,000-hour salt spray durability without corrosion.

Haifeng engineered a completely self-contained marine protective spraying package housed in weatherproof sound-attenuated skids. Each unit integrates a 40 kW Tier 4 diesel generator powering heavy electric immersion heaters and a rotary screw air compressor, allowing independent operation on remote bridge decks.

Steel box girder surfaces were grit-blasted to Sa 2.5 cleanliness with an anchor profile of 70 µm. Technicians rolled on a 80 µm moisture-tolerant epoxy primer. The HF-BRG200-DSL proportioner drew aromatic polyurea components from 200 L drums, displacing fluids at 18.5 MPa through dual 9 kW instant heating blocks up to 70°C.

Heated hoses were routed 45 meters down to suspended scaffolding platforms beneath the bridge deck. Operators sprayed 2.0 mm of pure polyurea in two continuous passes, with the material gelling in 15 seconds to eliminate sagging in gusty marine winds. This was capped with a 100 µm aliphatic aspartic polyurea topcoat to ensure long-term UV gloss retention. The system’s rapid pressure-relief valves protected operators from hose surges during pauses on elevated platforms.