Floating LNG: New Rule Note for the Classification of LNG FPSO
Authors: Guillaume Gourdet , Toderan Catalin 
Published: May 2011

Offshore LNG terminals are today broadly considered by the industry to respond to the world thirst of energy in a rapid and efficient manner. In order to match these technical developments, Bureau Veritas has completed, in May 2009, the first phase of a rule development project for the classification of floating offshore gas terminals.

Combining BV's experience with the classification of liquefied gas carriers and FPSOs, this resulting guidance note provides requirements for structural safety and cargo containment system assessment. These requirements are applicable for offshore units including LNG FPSOs, FSRUs, gas production units or FSOs. In September 2010, BV has completed this guidance note with specific requirements for stability, electrical installations, safety and offloading of offshore LNG terminals.

The paper will describe the work and conclusions of this guidance note and focus on the 2 main challenges faced during the work:

On one hand culture differences between shipping, gas and offshore industries. Although modern design techniques are largely using sophisticated numerical calculation tools for both ships and offshore units, there is still a notable cultural difference between the shipping and the offshore industries in the fact that the design of offshore platforms has historically been inclined to be quite based on first principles and direct risk analyses as opposed to ships, the design of which integrates, to a large extent, the return of experience in service in a more empirical way.

On the other hand, the difficulty to built standards for a new technology. Despite the long experience in gas transportation at sea and in offshore units, LNG FPSO projects need to identify the risk induced by transferring new technologies from shipping or from onshore industry to offshore floating gas project.

The difficulties encountered will be illustrated with practical examples.

Introduction

In the last decades we have seen oil & gas markets focusing on LNG. This new focus initiated a technology development phase of LNG production chains.

Among the new technologies concerning marine and offshore industry that came to life in this decade, we can mention:The LNG regasification vessel, LNG carriers that are designed to regas their cargo moored in offshore condition, moored at buoy before to offload gas to shore by a submarine pipes.Larger LNG carrier than ever built, with a huge capacity increase compared with large " traditional?? LNG carriersDiesel electric LNG carrier, with boil-off reliquefaction;New membrane tank systems developedShip to ship LNG transferFSRU, Floating Storage and regasification Units. These units, generally converted LNG carriers, are receiving the LNG from conventional LNG Carriers and regasifying it for onshore distribution as gas. If the 1st of them were moored at quay in sheltered areas, the latest projects are more and more going towards offshore units.

All these projects were involving third parties, like classificaition societies, which use this technological breakthrought to develop rules and methodologies, applicable to LNG units.

When going throught these developments, we can notice they are covering only 2 parts of the LNG chain, sea transportation and regasification. The other end of the LNG chain, offshore production liquefaction is still waiting for its first LNG FPSO, or FLNG. However several projects are being studied and designed going from very large LNG FPSO to smaller but modular LNG FPSO concepts, from mild offshore conditions to not so mild conditions.