In this paper, the authors present a finite element analysis (FEA)-based methodology for estimating the residual strength of degraded mooring chains. The paper presents work investigating FEA modeling parameter sensitivities and selection of appropriate parameters for FEA modeling. In addition, validation against break testing of full-scale chains is presented.
A typical offshore (e.g., floating production storage and offloading (FPSO)) mooring system may contain multiple components: chain stopper, fairlead or bending shoe, chain segments, wire rope, polyester rope, sockets, thimbles, anchors, and connectors or jewelry of various types. Because of its robust nature, chain is usually used at locations along the mooring line that are prone to the highest damage, such as at the top under high tension and in the touchdown or “thrash zone.” Two types of chain may be considered for mooring systems: studded and studless. Studded chains have a stud, or brace, placed between the bars in the midsection of the chain to prevent flexure and aid in fatigue endurance. Studless chains do not contain a bracing stud.