FMC loading arms go offshore

In the coming months specially designed loading arms from FMC will go into operation serving two groundbreaking offshore LNG projects

The handling of LNG at offshore terminal locations has posed challenges for cargo transfer equipment designers and manufacturers. The relative, wave-induced motions between offshore LNG terminals and the LNG shuttle carriers that serve them make it virtually impossible for conventional marine loading arms (MLAs) to ensure the safe side-by-side transfer of cargo.

In recent years FMC Technologies has brought to bear its impressive MLA engineering pedigree, not least in the LNG sector, to develop and test several technical solutions to address new challenges related to the offshore environment. FMC supplied the first LNG offloading arms ever built in 1956 and over the last 50 years has manufactured more than 300 all-metal loading arms which are currently in service at onshore LNG export and import terminals worldwide.

Further, FMC provided the first LNG boom-to-tanker (BTT) system to go into service, at the Shell Brunei export terminal some 25 years ago, and the first loading arms for the handling of liquefied gases at an offshore location. The latter were supplied for BP’s Ardjuna floating LPG production barge located off the coast of Indonesia. These arms are utilised in side-by-side cargo transfer operations.

In the most recent developments FMC Technologies is supplying the MLAs for two new ‘offshore’ LNG projects. One set of arms will be utilised on ExxonMobil’s Adriatic LNG gravity based structure (GBS) import terminal that will be positioned off the coast of Italy near Venice. The second set will be provided for the Golar Frost floating storage and regasification unit (FSRU) conversion project.

The loading arms for the Adriatic LNG terminal have been placed on the GBS at its building site in Spain prior to the terminal being towed to the northern reaches of the Adriatic where it will be ballasted into position. The three arms for the Golar Frost FSRU, comprising two units for LNG and one for vapour, will be positioned on the main deck between two of the ship’s spherical cargo tanks.

Because the Adriatic LNG GBS will be ballasted into a permanent position, the range of possible motions between the terminal and shuttle LNG tanker will be reduced but the shuttle tanker will still be exposed to the effects of the wind, waves and current and the MLAs will be required to accommodate the movements of the ship’s hull.

The Golar Frost FSRU project is based on the 137,000m3 LNG carrier Golar Frost that Golar LNG has recently sold to OLT Offshore LNG Toscana (OLT-O) for conversion into an FSRU. Once converted, Golar Frost will be placed on station 35km off the coast of Livorno in Italy. OLT-O is the operator of the project which is expected onstream in the latter half of 2010.

FMC Technologies has been working for several years to develop special MLA systems suitable for use at offshore locations and the Adriatic and Golar LNG contracts signify the first fruits of this R&D programme. The projects also necessitated further focused design and testing work to meet their specific requirements. A series of full-scale dynamic trials was carried out at the company’s Sens testing facility in France to determine the effects of the relative, wave-induced motions that will be encountered with the particular offshore terminal facilities. FMC points out that the test programme demonstrated the full operability of the arms in extreme sea conditions.

For the Adriatic LNG terminal project, ExxonMobil, one of the terminal’s owners and operators, and FMC carried out an extensive design and qualification phase of the specially designed MLAs. Because the work commenced as early as 2003 and was carried out through the pre-front-end engineering and design (pre-FEED) and FEED project phases, the loading arm design features were well advanced by the time the project go-ahead was given.

The Adriatic LNG terminal arms incorporate not only a unique structural design but also a number of other special features, including a cable targeting system, constant motion swivel joints and a customised quick connect/disconnect coupler (QC/DC) system. FMC and ExxonMobil also used a failure mode effect criticality analysis (FMECA) to verify the viability of the final engineered system in the anticipated working environment.

The cable targeting system enables the operators to ensure the ability to safely and reliably connect to and disconnect from the manifold flange, irrespective of the wave-induced motions of the LNG carrier while at the terminal. The targeting system was tested in the full-scale trials during the yard erection test in Sens and it was also evaluated during the comprehensive FMECA study.

In addition to ExxonMobil and Golar LNG, Shell, Total, StatoilHydro and Hunt Oil have also qualified FMC’s cable targeting system and the technology has been certified by the classification society DNV. The first-ever FMC cable targeting system was installed at Statoil’s Mongstad refinery and terminal complex in Norway a year ago and has provided a fully satisfactory service since startup.

Going forward, engineering companies developing LNG cargo transfer systems have to balance their commitment to meeting the burgeoning demand for their established equipment for use at conventional terminals with the major R&D commitment needed to develop the sophisticated systems required for offshore applications. The growing interest in LNG floating production, storage and offloading vessels (FPSOs) as well as FSRUs is only intensifying the challenges facing the engineers.

For its part, FMC Technologies believes that it is well placed to take advantage of the offshore opportunities opening up due to its unparalleled experience with conventional MLAs, the extensive offshore research already carried out, the new MLA equipment technologies it is introducing and the breakthrough orders with Golar LNG and Adriatic LNG. Furthermore, FMC stands ready with its BTT technology for use in applications where LNG has to be transferred in tandem loading operations in particularly harsh environments. LNG