(197c) Energy Based Risk Methodology for Collision Protection of Lng Carriers

LNG terminal developments are still the subject of major debate associated with potential hazards of marine accidental events. Prior risk studies have used estimates for potential hole size from accidental events that were based to a large degree on judgment, with hole size estimates from 0.75m to 5m.

A major sponsored project has undertaken a review of hole size from a detailed structural calculation methodology. This has used real collision data from the EU HARDER project to map known collision outcomes onto the actual structure of membrane and spherical LNG vessels. This showed that LNG vessels have great strength as the structures between the outer and inner hulls take and redistribute collision loads. However, once the inner hull starts to fail, the resistance to small increments in size of failure are relatively less than before inner hull failure. Results from the analysis concluded that it may be more accurate to nominate a specific energy level rather than a characteristic hole size.

This paper presents the results of the Finite Element Method (FEM) analysis for the two LNG vessel types and for several potential collision scenarios (size of vessel, speed, angle of collision). A consequence approach does not work well and only a risk-based approach leads to meaningful decision making. An example of the risk based approach is presented.