FMC answers prelude call to arms

Having secured agreements to provide subsea and topsides equipment for Shell's massive Prelude floating LNG development, FMC Technologies recently revealed details of the FLNG unit's offshore loading arm systems. In Houston, Russell McCulley discusses the technology with FMC's Laurent Poidevin.

FMC has dubbed the loading arm system under development for Shell OLAF, shorthand for 'offshore loading arm footless’. The equipment will build on the company’s existing Chiksan marine loading technology, a design based on articulated rigid pipes equipped with Chiksan swivel joints and supported by a separate articulated structure to prevent thermal stresses in cryogenic conditions. For Prelude, in the race to become the world’s first floating LNG facility and the largest floating offshore structure, FMC will supply a total of seven loading systems: four for liquefied natural gas and three for liquefied petroleum gas.

The contract was awarded by Technip on behalf of the Technip Samsung Consortium (TSC), which is handling Prelude’s engineering, procurement, construction and installation activities.

The 488m-long floater, to be built at the Samsung Heavy Industries shipyard in Geoje, Korea, will produce an estimated 3.6 million tonnes per annum of LNG, 1.3mtpa of condensate and 0.4mtpa of LPG from the Browse Basin WA-371-P permit, in 280m water depths offshore Western Australia (OE July 2011).

Unlike conventional loading arms, the OLAF has no base riser; instead, the articulated assembly is bolted on a turntable at deck level, which allows a 20% reduction in the length of the arm and connection to carriers up to 10m below Prelude’s deck, says Laurent Poidevin, president and general manager of FMC’s loading system division in Sens, France.

FMC's loading system for the Shell Prelude FLNG project will feature four 16in diameter loading arms for LNG and three 12in diameter arms for loading LPG.

‘The OLAF is a brand new design,’ he explains. ‘It is specifically made for the very big floaters, like the Shell Prelude one.’ The advantage to the ‘footless’ design, he says, ‘is that the OLAF can reach a very low operating envelope. When you see the upper deck level on this very large floater from Shell and compare it with a normal shuttle tanker, the deck levels are totally different, which means that the arms installed on the floater deck have to reach a very low operating envelope.’

The four LNG units will have 16in diameter pipes, while the three LPG arms will measure 12in in diameter. FMC says the technology ‘will bring enough operability to the system to assure weekly side by side LNG transfers without interrupting the liquefaction unit operations,’ according to a fact sheet supplied to OE. ‘It permits to connect the standard fleet of carriers without modifications of the carriers’ manifolds, thanks to the targeting system to assist the connection and disconnection under significant relative motions between the FLNG [facility] and the shuttle carrier.’

‘The OLAF is a brand new design, specifically made for the very big floaters.’ Laurent Poidevin

The OLAF system is expected to withstand 25 years of weekly service; the design also permits in situ maintenance of critical components without the need for heavy lifting equipment, FMC points out.

Shell has emphasized that Prelude, despite its scale, will for the most part use proven technologies, which extends to the loading systems. ‘Most of the components we are using for this new design have been already proven, and Shell is using almost all the components already at their onshore terminals,’ Poidevin says.

The OLAF design eliminates the base riser, allowing the articulated assembly to reach carrier intakes up to 20m below Prelude’s deck.

Adapting the components to function in a system that connects two floaters, however, required significant design modifications for the OLAF. Shell has run basin tests for Prelude at the Marine Research Institute Netherlands (Marin), Poidevin says; using data from those tests, FMC is in the process of putting together a 1:4 scale prototype of the OLAF system to test in dynamic conditions. The company hopes to have the model ready for testing in early 2013.

Shell has also indicated that the Prelude FLNG facility will be the first in a series of mostly identical units, the next of which could be deployed at the Inpex-operated Abadi FLNG project in the Masela block in the Indonesian section of the Timor Sea. In July 2011, Shell acquired a 30% working interest in the block from Inpex, which now holds 60%. PT Energi Mega Persada holds the remaining 10%. Inpex has said it expects a final investment decision late next year with a possible startup in 2018.

‘[Prelude] is a design Shell wants to consider as a standard design for all floaters that they build,’ Poidevin says. ‘The agreement with the Technip and Samsung consortium is for the next 15 years of production of different floaters – up to eight floaters of the same design.’

Four years ago FMC Technologies built and was set to deliver a total of 12 double counterweighted marine arm (DCMA-S) systems for four FLNG vessels to be operated by Flex LNG, including the Flex LNG Producer, which at the time was tipped to become the world’s first FLNG vessel (OE October 2008). In December 2011, Flex LNG’s Gulf LNG project offshore Papua New Guinea was shelved and the FMC DCMA-S systems, although paid for, were shelved as well. OE