Developing a Structural Integrity Management System for Offshore Fixed Platform Jacket Structures in the Nigerian Offshore Environment

Nigeria's offshore petroleum production infrastructure in the South South geopolitical zone includes several hundred fixed platform jacket structures, many of which have exceeded their original 20 to 25-year design lives and operate in a regulatory environment that lacks a comprehensive national framework for structural integrity management. This study develops a structural integrity management system for offshore fixed platform jackets in the Nigerian offshore environment, integrating risk-based inspection planning, structural reliability updating with inspection evidence, and fatigue life management under a unified management framework adapted to the operational and regulatory context of the Nigerian Upstream Petroleum Regulatory Commission. The structural integrity management system is built on a Bayesian updating methodology that incorporates inspection data from underwater visual surveys, magnetic particle inspection, and eddy current testing into probabilistic fatigue crack growth models for tubular joints under West African wave loading. A consequence-based risk categorisation system classifies nodes into five criticality tiers, driving inspection interval selection and acceptance criteria. The system was piloted on a 12-leg jacket platform in the Bonga Field using archived inspection data from six inspection campaigns over 18 years. Results demonstrate that the risk-based inspection planning component of the system correctly identified the three nodes exhibiting the most advanced fatigue crack growth, which had been missed by the previous time-based equal-interval inspection programme. Life extension feasibility assessments conducted for four platform sections indicate that targeted repair and monitoring-based life extensions of 10 to 15 years are structurally supportable for sixty-two percent of assessed nodes. The study provides the first Nigeria-specific offshore structural integrity management framework grounded in probabilistic structural mechanics. Keywords: structural integrity management, offshore jacket platforms, risk-based inspection, fatigue, Nigeria offshore.