Collision Risk Analysis Fixed Platform and Semisubmersible

by Jan K. Lund, Safety and Reliability Services, Norway,
Bj?rn Arstad, Safety and Reliability Services, Norway,



Document Type: Proceeding Paper

Part of: Structural Safety and Reliability

Abstract:

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: Failure analysis | Risk management | Stochastic processes | Mooring | Offshore structures | Cables | Structural failures

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