Fatigue Failure Paths for Offshore Platform Inspection

Abstract

A closed‐form, reliability‐based, procedure is developed to identify fatigue failure paths of offshore structures and assess the notional probability of system failure through these paths. The procedure utilizes the Miners rule node fatigue failure reliability model developed by Wirsching. Effects of load redistribution following the fatigue failure of a node on the time to failure of remaining unfailed nodes is taken into consideration. Primary fatigue failure paths are identified through use of a branch and bound procedure. The components that fall in these paths are relatively critical to platform integrity. A platform inspection, therefore, needs to be planned around these components, as the failure of these would ultimately lead to system failure. The use of the procedure is demonstrated by application to a plane frame representation of a fixed shallow‐water offshore jacket. The procedure is general in nature and neither imposes any restrictions in terms of uniform strengths of members nor requires loads to confirm to a specific pattern or be shared equally among members.