(Houston, TX---) Focused on the improved safety and operation of tension leg platforms (TLPs) and spars and in response to emerging technological advances, ABS has announced its industry-first guidance on building and classing the specialized deepwater floating production units. This guidance comes in the form of a supplement to the ABS “Guide for Building and Classing Floating Production Installations” (FPI) and is available to the offshore industry for free. In developing the supplement, ABS has applied its extensive knowledge and experience in classing TLPs and spars while emphasizing the global performance issues and motion characteristics unique to these floating structures, says Ernesto Valenzuela, ABS manager of Offshore Technology. “The requirements noted in the new supplement address the special design and operational attributes associated with TLPs and spars. We believe the critical evaluation applied in the development of this supplement, together with future inspections, will assist industry in reducing installation losses and avoiding potential production shutdowns due to components failure on a unit,” said Valenzuela. He adds that the intrinsic value to the customer is improved integrity of the structure and reduced operational risk. “Through classification of these units, the customer has the long-term benefit of unified design criteria for follow-up inspections and surveys to ensure the reliability of the unit,” said Valenzuela. There are presently some 20 TLPs and some 10 spars installed worldwide, with an estimated 20 new TLPs and another 30 spars expected over the next decade. Of the units installed, ABS has classed 13 of the TLPs and all of the spars. While the existing FPI Guide addresses column-stabilized units and other types of floaters, the supplement addresses the structural performance and demands specifically associated with TLPs and spars. Key areas of emphasis include global performance requirements, load and environmental issues, stability parameters and structural strength criteria.

Neptune, the offshore industry’s first spar, helped set the stage for frontier development. ABS ANTICIPATES CONTINUED DEEPWATER DEVELOPMENT USING FLOATING PRODUCTION INSTALLATIONS, RESPONDS TO EMERGING TECHNOLOGIES WITH FIRST GUIDANCE ON BUILDING, CLASSING FPIs. Installed in 1996 on Viosca Knoll Block 825 in 1,930 feet of water in the Gulf of Mexico, Kerr-McGee’s Neptune spar became the industry’s first spar. The classic spar design has led to further emerging technologies, including the truss spar and cell spar innovations. Focused on the continued safe operation of spars and tension leg platforms (TLPs), ABS has announced its industry-first guidance on building and classing the specialized deepwater floating production units. There are presently some 20 TLPs and some 10 spars installed worldwide, with an estimated 20 new TLPs and another 30 spars expected over the next decade. Of the units installed, ABS has classed 13 of the TLPs and all of the spars, including Neptune. >View larger image - low res (33kb) >View larger image - hi res (8mb)

Representing an industry-first in FPI classification, advises Tuanjie Liu, ABS engineer, the supplement requires that owners of these units perform global performance analyses to fully address the comprehensive effects of environmental loads on an overall platform and its components, including the deck, hull, tendons, mooring system and risers. Loading and response predictions for each of these components can be completed separately or in an integrated form.

Elements of these analyses include frequency domain analysis, addressing the six degrees of freedom, i.e. surge, sway, heave, pitch, roll and yaw; time domain analysis, deck clearance and model testing to calibrate design parameters and analytical tools.

“We anticipate that this level of investigation will assist owners in verifying the safe design of their floating systems, particularly in terms of the mooring and riser systems design unique to TLPs and spars,” said Liu.

The guide, adds Liu, is particularly useful in addressing risk issues associated with potential loss of vessel and environmental protection. In terms of vessel stability, the guide discusses requirements for tendon tension to ensure TLP platform integrity and specifies ballasting requirements in the event of collision damage or accidental flooding.

“For instance, in the event of a vessel collision and considering only one compartment damaged, a TLP must be able to maintain adequate tendon tension, with the vessel capable of sustaining a full range of possible center of gravity variations. While these issues are not new to the FPI, they receive enhanced detail in the supplement,” said Liu.

With regard to spars, however, the supplement for the first time provides operators and owners with specific design parameters for maintaining stability. The guide now requires that all emergency and safety systems, including life saving and abandonment equipment, are to be operational at parameters specified for storm survival and specific wind conditions. The detailed parameters define wind speed and list angle limits for varying operational scenarios.

In terms of load and environmental issues, says Liu, the supplement delineates the modes of operation for both pre-service and in-services conditions. Relevant issues or impacts include gravity loads together with the effects of wind, waves, current and other phenomena, such as earthquake, temperature, fouling, ice, etc., depending on the specific installation site.

“Specifically, the supplement provides that TLPs and spars must be designed for loading conditions to sustain the most severe local and global effects on a structure,” said Liu.

Load issues addressed include: environmental loads, hydrostatic pressures and buoyancy, gravity and inclination-induced loads, inertia loads, operational loads, mooring and riser loads, marine operation loads, vortex-induced vibration (VIV) loads, green water loads and slamming loads during both transportation and operation.

“VIV loads are new to the guide and are particularly important to the safe operation of spars. The supplement provides that VIV loads and fatigue strength are to be fully assessed and that the mooring system fully analyzed, considering VIV effects,” said Liu.

The guide also clarifies operational scenarios for TLPs and spars, providing for expanded environmental conditions, including specific design environmental conditions, design operating conditions, reduced extreme conditions and calm conditions.

“This level of detail is new to the guide and should assist operators in designing for site-specific conditions, including the 100-year return response,” said Liu.

The guide also now provides new requirements for modules and topside buildings, such that the design of these components is consistent with the overall structural analysis.

“Structural verification of topsides modules and buildings will help to ensure safety of personnel on these deepwater installations,” said Liu.

As part of ABS’ normal review process for its new guides, industry professionals have provided comments to the FPI supplement, providing appropriate enhancements for increased value, advises Liu.

Industry comments have addressed TLP deck clearance, in terms of seabed subsidence, and criteria for compressed air ballast systems.

“Our critical industry review is now completed and we look forward to providing offshore designers and operators with a document that will facilitate continued frontier development,” said Liu.

The “Guide for Building and Classing Floating Production Installations” is available for free download at: http://www.eagle.org/rules/downloads.html. See publication Number 82, Supplement 2, August 2003.

Founded in 1862, ABS is a leading international classification society devoted to promoting the security of life, property and the marine environment through the development and verification of standards for the design, construction and operational maintenance of marine-related facilities.

For more information, contact:
Susan Gonzalez,
ABS
1-281-877-5853
or sgonzalez@eagle.org