Probabilistic Risk-based Integrity Assessment of Corroded Aging Marine Pipelines

Abstract

This study developed a risk-based integrity management strategy for aging marine pipelines, emphasizing corrosion degradation, structural reliability, failure risk, and life extension of the Uyeghe–Stubb Creek buried oil pipeline system in Rivers State, Nigeria. The study used a case-study approach, drawing on historical inspection data and operating parameters, along with Melchers tri-linear and Paik non-linear corrosion models, marine-growth modelling, time-dependent reliability analysis, and Monte Carlo simulation. Two corroded pipeline segments were examined, with recorded pit depths of 0.33 mm and 2.53 mm, while corrosion rates of 0.0779, 0.1423, and 0.3672 mm/year were considered for low, moderate, and high degradation conditions. The results showed progressive environmental and material deterioration. Marine growth increased from 0 mm at commissioning to approximately 25 mm after 50 years, while biomass accumulation approached 14 kg/m². The Melchers model predicted approximately 3.8 mm corrosion depth at 50 years, compared with 2.45 mm from the Paik model; the marine-growth-enhanced model reached about 3.0 mm at 40 years, approximately 35% above the unfouled condition. For a nominal 20 mm wall, the predicted loss corresponded to substantial reductions in structural and pressure capacity. Reliability declined nonlinearly with age: the simulated reliability index decreased from 3.2 at commissioning to 2.0 after 25 years and 1.4 after 50 years, while failure probability increased from 0.0007 to 0.08. At year 25, mean wall thickness reduced to 18.3 mm, representing an 8.5% loss. The study demonstrates that integrating degradation modelling, probabilistic reliability and consequence-based risk assessment provides a practical basis for proactive integrity management of aging marine pipelines.