Improvements in oil recovery have resulted in many offshore structures staying in service beyond their designated service lives. Offshore structures are subject to severe environmental loading, leading to degradation of the structures, and many have deteriorated to the extent that their capacities have been reduced. Corrosion is one of the main damage mechanisms of offshore structures, it can be relatively uniform over the surface or localized with thickness reduction concentrated over a small portion of the member (patch corrosion). Structural capacity may be significantly reduced by corrosion of bracing members or legs. Such damage to an offshore structure may have consequences on the platform functionality and can induce serious safety, environmental and economic consequences. It is important to estimate the residual capacity of degraded tubular members as it promotes the safe usage and assessment of the structural integrity of the load-bearing structure.Formulae for the ultimate capacity of corroded tubular members were formerly addressed in NORSOK N-004 2004. However, in the superseding versions, it has been removed because of the insufficient information&nbsp;on the strength of corroded tubular members. Now practicing structural analysts can only estimate the capacity of such members by relying on the limited experimental work available or numerical work without being validated against standards and recommended practices.This paper provides a comprehensive finite element analysis to investigate the corroded members' ultimate capacity. A parametric study is then performed to investigate the effect of geometric parameters on the capacity. The paper presents a comparison between documented laboratory tests to the formulae of superseded standards and recommended practices, and numerical analysis using non-linear finite element methods. It also provides guidance on how to use modified NORSOK N-004 2004 formulas to estimate the capacity of degraded columns as well as guidance for the use of non-linear finite element analysis.

Residual Strength of Tubular Columns With Localized Thickness Loss

Paper Proceedings: https://asmedigitalcollection.asme.org/OMAE/OMAE2021/volume/85116

OMAE 2021

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