Prelude Hull Cargo Containment System

Abstract

The Prelude FLNG is the first application of a cryogenic containment system in the largest turret moored offshore LNG/LPG and condensate production system suitable for a cyclonic environment. This paper discusses the rigorous safety processes, specialized technologies and the innovation required to realize a hull design suitable for a floating LNG facility. The Prelude hull evolved from innovation, continuous improvement and best offshore and LNG Carrier engineering practice. Prelude has been subject to extensive analytical and model studies to realize the design. The analysis of global motions, structural analysis and cargo tank fluid motions has resulted in a cargo tank arrangement of 2-rows each of 5 tanks which allows partial filling in the offshore environment. Rigorous safety assessment required a new LNG cargo tank dome to be developed to protect against blast pressures and maintain integrity of the cargo tanks. Operational safety has also driven design to ensure maintainability in the field. The world's first 2-row 5 cargo tank arrangement utilizing membrane containment technology solved several requirements. Maximizes storage capacity within hull sizing constraints, provides a flat deck for process design, provides an optimized hull design to satisfy topside and hull loads. The hull comprises a complete double hull at the bottom, side and deck, a novel centre line ballast tank separating the two rows of cargo tanks and cofferdams between tanks. The centre line ballast tank arrangement enables a significant proportion of the topsides module weight to be directly opposed by buoyancy forces. To satisfy stringent safety requirements, the double deck is designed to absorb process explosion events and provides space to locate the cargo tank L/G domes. The tank domes located between the main-deck and the cargo tank are filled with N2 gas to improve detectability of LNG leakage. Such a novel design has not been applied on standard LNG carriers and required diligent application of the IGC code to prove the design. Shell, Samsung Heavy Industry and GTT successfully achieved and constructed a cargo containment system with safe dome design on the Prelude FLNG. From engineering stage to the cold test into the tank, enormous building works have been conducted in South Korea, and then the offshore execution for LNG/LPG offtake in Australia was successfully carried out.