Risk-Based Stability Assessment for Semi-Submersible Platforms: Ballast System Failure

Abstract

Stability and buoyancy loss is a very current problem for semi-submersible platforms. New ballast system designs are developed to improve the safety of personnel and facility, but the effect of these is difficult to measure and document towards operators and authorities. The ultimate objective of this thesis has been to compare three modern ballast system designs with a fourth conventional system with respect to risk of stability and buoyancy loss. Fault tree analysis has been the main tool to establish failure frequencies for the defined top event unintended inclination induced or not corrected by ballast system. The systems have been evaluated for implementation on a semi-submersible production rig. Hydrostatic analyses for different relevant stability scenarios have been carried out as part of the consequence assessment. The final results indicate that an improved ballast system design can reduce the risk of stability loss by up to 40%, and at the same time decrease the capital cost for the system dramatically.