Collision Risk Analysis Fixed Platform and Semisubmersible

by Jan K. Lund, Safety and Reliability Services, Norway,
Bjørn Arstad, Safety and Reliability Services, Norway,

Document Type: Proceeding Paper

Part of: Structural Safety and Reliability


This paper summarizes the North Sea experience pertaining to mooring line failures of conventional 8 and 12 anchor line systems. Mooring system calculations, experience and test results are used to predict increased line tension after failure of one single line. A stochastic domino model for a sequential failure process is applied to predict the probability of multiple line failure as a function of the line tension level. An event tree model describes the conditions for collision and estimates the collision frequency between a fixed platform and a nearby anchored semisubmersible. The risk reduction effect of providing the semisubmersible with an automatic thruster assisted anchoring system as well as a simple cost benefit evaluation of this measure are presented.

Subject Headings: Risk management | Cables | Stochastic processes | Anchors | Tension members | Failure analysis | Offshore structures | Mooring

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