An Approach for Estimating the Corrosion Rates on Aging FPSO Hull Structures

Abstract

This paper presents a methodology to estimate the thickness loss on hulls of Floating, Production, Storage and Offloading (FPSO) platforms under general corrosion. The main purpose is to define characteristic corrosion rates for structural reassessment of the extension of life of FPSOs considering results of previous in-life inspections. The steel wear generates sectional loss and capacity reduction, possibly leading to structural failure. Being capable of estimating FPSO’s plates and stiffeners thickness along the operational life would be a considerable safety improvement for the whole industry, benefiting operators and classifications societies. During this research, different models were investigated to define the proposed methodology: (a) Model A (Garbatov and Soares [1,2]); (b) Model B (Melchers et al. [3–11] and, the one considered more appropriate to this study, Model C (Paik et al. [12,16]). The proposed approach, based on Paik et al (2003), considers that the results of thickness loss readings in inspections during the operational life of the FPSO may be modeled by the Weibull model. Then, this model is applied to estimate the characteristic corrosion rate for the structural reassessment of FPSO extension life. Results of the proposed methodology are presented for four structural components of a typical converted FPSO single hull in operation at Campos Basin, Brazil offshore.