Advancing Ultrasonics-Based Structural Health Monitoring Theory for Steel Offshore Platforms in the Nigerian Continental Shelf

Steel offshore platforms on the Nigerian continental shelf in the Gulf of Guinea are subjected to fatigue loading from wave action, corrosion in the marine environment, and impact from vessel berthing, creating structural health monitoring requirements that demand advanced ultrasonic inspection capabilities beyond conventional periodic manual inspection. This study advances the theoretical foundations and experimental implementation of guided wave ultrasonic structural health monitoring for tubular joint connections and plate structures representative of Nigerian offshore platform construction. A theoretical framework for guided wave propagation in fluid-loaded cylindrical shells, accounting for corrosion-induced wall thickness variation and wave mode conversion at structural discontinuities, is developed using the Global Matrix Method extended to visco-elastic media. Novel damage-sensitive features based on the Hilbert-Huang transform of guided wave signals are derived theoretically and demonstrated experimentally to improve delamination and corrosion detection sensitivity by 34 percent relative to conventional time-of-flight features. A long-term structural health monitoring system architecture integrating piezoelectric actuator-sensor networks with machine learning-based damage classification is designed, implemented on a representative laboratory-scale platform joint, and evaluated over 12 months of accelerated fatigue testing. Keywords: structural health monitoring, guided waves, offshore platform, Nigeria, piezoelectric