Hull girder reliability assessment for FPSOs

Abstract

A methodology for reliability assessment for hull girder ultimate strength of FPSOs is presented in the paper. The hull girder ultimate strength of a FPSO is calculated by a progressive collapse analysis using the Smith method. Uncertainty of still-water bending moment (SWBM) is evaluated based on the loading conditions from FPSO operational manuals. A stochastic model of the extreme value of vertical wave-induced bending moment (VWBM) is developed in accordance with the extreme value theories based on the long-term distribution of VWBM. A first-order reliability method coupled with finite difference methods is proposed for reliability estimate dealing with the complicated implicit limit state function for hull girder ultimate strength assessment. Reliability assessments for four FPSOs are performed to demonstrate the capability of the methodology developed. The effects of the return period of the extreme value of VWBM, environmental severity factor and corrosion effects on hull girder reliability are investigated. A sensitivity analysis for each random variable is also conducted.