Larger images: Low res jpg (40k) Hi res jpg (1.6mb) Hi res tif (15mb) (Photo courtesy of IHI, Japan) The service for specific installations will be defined in the class notation using combinations of the following symbols: F – Floating G – Gravity Base P – Gas Processing Facility L – Liquefaction Facility S – Storage Facility O – LNG Offloading R – Re-gasification Facility T- Terminal Without Processing Equipment The "ABS Guidance Notes for Building and Classing Offshore LNG Terminals" is publication No. 106 and is available for free download from the "Rules & Guides" section.

ince announcing the Guidance Notes at the Offshore Technology Conference in Houston in early May, ABS Offshore has received worldwide interest in its roadmap for classification of offshore LNG terminals. With the global LNG—liquefied natural gas—market forecast to double in size over the next decade, industry is preparing to provide ample capacity to meet demand. In the United States alone, LNG imports reached 4.9 million tons in 2000—about 5 percent of the global LNG trade—and up from 3.4 million tons in 1999. LNG Drivers Terminal Locations Roadmap for Guidelines Relative Motions, Sloshing and Temperatures LNG Drivers Drivers for the rapid LNG growth include continued demand for a cleaner-burning fuel and the need to bring "stranded" gas from deepwater and remote areas to market. In the U.S., concern over long-term gas supply, a larger number of new supply projects and lower LNG infrastructure costs from a decade ago also are contributors to the LNG growth spurt in recent years. The reality of September 11 is a contributing motivator for considering—for the first time—the development LNG terminals in an offshore environment remote from high-risk populated areas.

"There’s a lot of public and government concern with regard to the security of storing quantities of LNG on land. Offshore provides a more isolated environment," says Sember.

Terminal Locations

Industry forecasts, he adds, estimate that anywhere from five to 20 offshore terminals could be built for US installation in the next 10 years. Planned locations include the East and West Coasts as well as the Gulf of Mexico.

Other locations where offshore LNG terminals are under consideration include Australia, West Africa, Japan and the Mediterranean. Offshore LNG terminals will be designed for site-specific environmental conditions and are expected to be predominantly purpose-built.

Global sites for offshore LNG terminals, adds Sember, will facilitate continued growth among emerging countries eager to find new and accessible markets for gas production.

"Industry will be able to expand and build on its excellent record of safely and efficiently transporting and offloading LNG to many regions of the world, thus spurring development of burgeoning markets," says Sember.

There are two basic functional types of offshore LNG terminals: loading terminals and discharge terminals. Loading terminals receive gas directly from one or more wells or from another offshore facility where it may or may not have been processed. The gas is liquefied in an onboard liquefaction facility and stored for offloading as LNG to a trading LNG carrier.

Discharge terminals receive LNG from trading LNG carriers and store the LNG until it is vaporized in a re-gasification facility for pipeline transmission to shore. However, offloading LNG in a lightering operation also is envisioned.

ABS brings substantial experience to support the energy industry in its potential development of offshore LNG terminals, says Sember: experience with both LNG carriers and site-specific offshore structures designed to operate uninterrupted for long service periods in harsh environments as well as an intrinsic knowledge of the US and global regulatory arena.

Roadmap for Guidelines

"These particular attributes will contribute to the value of the Guidance Notes to the industry," says Sember. He adds that the Guidance Notes will provide industry with a comprehensive document that outlines ABS procedures for LNG terminal classification. A significant part of that process includes cross-references with ABS Rules and other relevant industry documents such as API, NFPA, ASME and the IMO Gas Code.

Within the Guidance Notes, class notations are clearly defined to effectively describe the function of each LNG configuration. The appropriate combination of notations will be included in the ABS RECORD and on the classification certificate to clearly indicate the specific function of the facility. Areas of emphasis within the Guidance Notes include the terminal structure; the mooring system; the offloading system; LNG containment systems; process facilities; and support and safety systems.

The document also addresses LNG terminal installation, hook-up and commissioning, and surveys during construction and throughout its continued operation.

Safety is a critical issue here, adds Sember, as industry considers taking facilities that are historically on land and putting these gas processing and cryogenic storage facilities offshore.

"Industry has successfully dealt with oil and gas processing facilities on Floating Production Storage Units for a number of years. However, the liquefaction and cryogenic storage of LNG offshore is a whole new arena. This transition requires a comprehensive approach toward the integration of marine and typically shore-based gas processing facilities in the design of an offshore LNG terminal," says Sember.

Relative Motions, Sloshing and Temperatures

A key issue for the floating terminal concepts, adds Sember, is designing for the motions likely to occur on a floating terminal as well as the relative motion between the terminal and LNG carrier during loading/offloading operations.

"Transfer of LNG—at subzero temperatures—through a loading hose presents industry with a technological challenge. Industry is presently evaluating appropriate technologies to create more reliability and flexibility for the LNG transfer in an offshore environment," says Sember.

The technology surrounding containment systems also is part of the critical evolution of offshore LNG terminals, says Todd Grove, ABS Director of Offshore Project Development. There are three basic containment system designs: membranes, spherical tanks and self-supporting prismatic tanks.

"To date, 43 LNG carriers have been built to ABS class and have incorporated every type of containment system available," says Grove.

While the shipping industry has perfected LNG containment systems for LNG transportation, the systems, in general, can be migrated in a straightforward manner to terminal applications, says Grove.

"We see viable applications being considered for use of both the membrane as well as independent tank concepts presently in use," says Grove.

Grove advises that the shipping industry has enhanced the basis of design for membrane systems, thus enabling containment systems to handle partial loading conditions and to sustain the associated sloshing loads.

"An industry ‘by-product’ of this technology improvement," says Grove, "is advancement toward development of offshore LNG terminals, which also will require partial-loading capability for floating terminal concepts."

LNG carriers building today have cargo containment systems ranging in sizes up to 145,000 cubic meters, with future designs expected to increase to 200,000 cubic meters. Designs for offshore LNG terminals currently under development can be at least twice that size.

Prospects on when the industry’s first offshore LNG terminal will be built and installed are still uncertain, particularly in the United States, where regulatory issues regarding jurisdiction are presently being addressed. ABS is well-positioned with comprehensive documentation in place to assist industry once these regulatory matters are resolved, says Grove.

"ABS is ready to go. We know the technology—both in terms of LNG and marine issues—and we have a documented plan in place to meet industry requirements in an efficient manner," says Grove.

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