Fatigue Failure Mechanisms in Critical Tubular Joints of Gulf of Guinea Jackets: S–N, Fracture Mechanics and Corrosion Ageing Interaction

Abstract

This paper analyses the fatigue failure mechanisms that govern the residual life of critical tubular joints on a representative Gulf of Guinea (GoG) steel jacket platform. Both the conventional S–N (Palmgren–Miner cumulative damage) and fracture-mechanics (Paris–Erdogan crack-growth) approaches are applied, with explicit inclusion of time-dependent corrosion and structural ageing effects. Six representative joints (J1–J6) are examined under realistic operational loading. Deterministic S–N calculations yield a 25-year damage ratio of 1.85 and an implied residual life of 13.5 years for the governing lower-bay K-joint (J5). Independent fracture-mechanics analysis, initiated from a representative surface crack depth a₀ = 0.5 mm, produces a crack-propagation life of 13.5 years for the same joint, confirming consistency between the two methodologies. Parametric studies incorporating corrosion rates in the range 0.1–0.4 mm/year demonstrate that progressive wall thinning and associated stress elevation reduce remaining fatigue life by 9%–28%. The results highlight the necessity of integrating corrosion-fatigue interaction into residual-life assessments of ageing GoG jackets and provide a validated basis for inspection prioritisation and life-extension decisions.