Fatigue analysis of deepwater hybrid mooring line under corrosion effect

Abstract

In the deepwater exploitation of oil and gas, replacing the polyester rope by a wire in the chain-wire-chain mooring line is proved to be fairly economic, but this may provoke some corresponding problems. The aim of this paper is to compare the fatigue damage of two mooring system types, taking into account corrosion effects. Using a semisubmersible platform as the research object, two types of mooring systems of the similar static restoring stiffness were employed. The mooring lines had the chain-wire-chain and chain polyester-chain structure, respectively. Firstly, the numerical simulation model between the semi-submersible platform and its mooring system was built. The time series of mooring line tension generated by each short-term sea state of South China Sea S4 area were calculated. Secondly, the rain flow counting method was employed to obtain the fatigue load spectrum. Thirdly, the Miner linear cumulative law model was used to compare the fatigue damage of the two mooring system types in long-term sea state. Finally, the corrosion effects from zero to twenty years were considered, and the comparison between the fatigue damage of the two mooring system types was recalculated.