Technical Evaluation of Coatings for Corrosion Protection of Steel Structures in Nigeria’s Coastal Industrial Zone

This study presents a technical evaluation of protective coating systems applied to structural mild steel in the coastal industrial zone of Onne, Rivers State, South South Nigeria, assessing the performance durability and field application quality of epoxy, polyurethane, and zinc-rich primer systems. The Onne Free Port Zone supports extensive steel-intensive infrastructure exposed to one of the most corrosive atmospheric environments in Nigeria, characterised by high chloride deposition, elevated humidity, and industrial chemical contamination. Performance data are collected from coating condition surveys on forty tagged steel panels installed at three years prior at Port and factory structures. Panel assessments follow ISO 4628 for rust, blistering, and adhesion loss grading. Pull-off adhesion testing is conducted using a portable adhesion tester per ASTM D4541. Dry film thickness measurements are taken by electromagnetic gauge. Maintenance interval and cost records are analysed. Findings reveal that zinc-rich epoxy primer systems with polyurethane topcoat show significantly lower rust creep and adhesion loss after three years compared to non-zinc-primed epoxy systems. Application quality deficiencies including inadequate surface preparation and below-specification film thickness are documented in approximately 30 percent of assessed panels and are identified as primary drivers of premature coating failure. The study recommends mandatory third-party coating inspection during application for all critical structural steel in the Onne Port Zone. Keywords: protective coatings, corrosion, structural steel, coastal environment, Onne Free Port.