In 2014 Williams Companies delivered a Spar-based FPS to be used by the Hess Corporation for developing their “Tubular Bells” field as well as for future tiebacks for other developments. Tubular Bells is located in the Mississippi Canyon region of the Gulf of Mexico.

The Spar hull is the ‘Classic hull form’, 584 ft (178 m) long, 85 ft (26 m) in diameter with 60 ft (18 m) hull freeboard. The mooring system consists of 9 mooring lines in 3 groups composed of a chain-polyester-chain configuration.

This paper describes the tools and methodology Williams plans to use for assessing the fatigue damage of the mooring chain over the operating life of the platform. The basic plan is to collect field-measured data for parameters that impact mooring fatigue damage, such as: environmental conditions, Spar motions (particularly Vortex Induced Motions data) and mooring line tensions, then process that data with specialized software so it can be effectively compared to the applicable data that was used in the design of the mooring system for fatigue.

A key element in the plan to compare the field data with the design data is new computer software developed specifically to process the field measured data and generate the field measured, fatigue design parameters on a regular basis and in a form that is readily comparable to the design data. Additionally, a graphic user interface in this software will provide a clear visualization of the Spar motions that is linked with the associated environmental conditions for the same time periods.

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