Typhoon SeaStar TLP
Authors: Matten R.B. , Provost M.J. , Pastor S. , Young W.S. 
Published: October 2008

This paper describes the design, fabrication, installation and hook-up and commissioning of the Typhoon SeaStar.

The Typhoon SeaStar TLP was installed in 2097' water depth in Green Canyon 236/237 and produced First Oil on July 28th 2001, just eighteen months after project sanction. The Atlantia scope of project was completed on budget and on schedule.

A reimbursable contract with a cost based management fee proved to be effective in maintaining alignment between Owner and Contractor to minimize changes and avoid cost growth. Detailed planning and execution of onshore precommissioning was key to achieving the very fast schedule.

Repeat of a proven design with incentives to improve the design where possible was key to the successful outcome.

Introduction

The Typhoon SeaStar is the third SeaStar TLP to be installed in the Gulf of Mexico, and follows the Sir Douglas Morpeth Seastar (installed 1998) and the Allegheny SeaStar (installed 1999). Both platforms have been trouble free in operation since installation.

The SeaStar TLP design features a monocolumn hull with 3 pontoons radiating outwards at the base. The platform stability against overturning is provided by 6 near neutrally buoyant tendons which run vertically from the top connectors mounted on tendon porches located at the extremities of each pontoon to piles driven in the seabed. The tendon system also acts as the station keeping system.

In principle, the buoyant pontoons tension the tendons and the column buoyancy supports the topsides payload to minimize the moment transfer at the pontoon/ column connection.

The four-legged deck is supported on the hull and incorporates a K braced jacket structure to transmit the shear loads. The SeaStar is relatively transparent to the crests of extreme waves, thereby avoiding "ringing" loads experienced by other TLPs.

The Typhoon deck is comprised of two main levels, a grated main deck and a plated production deck, which provide support for the process and auxiliary equipment, an under deck truss, a small cellar deck, a support frame for the quarters building and a flare/vent boom.

The deck's design is based on a conventional deck structure consisting of commonly available tubular sizes and wide flange members. It is supported by four main columns arranged in a square pattern to align with the hull's outer diameter of 58-ft. The under-deck truss, located beneath the Cellar deck, frames into the deck legs in a cross pattern to provide support for the deck's wing sections and provide bracing to the deck. Between deck levels, the legs have been designed to minimize diagonal bracing wherever possible to allow for clear unobstructed equipment access.

Health, Safety, Environmental, and Regulatory concerns impacted nearly every aspect of the design. Equipment layouts and deck surface selection were no exception. The deck surfaces were selected to optimize containment and ventilation.

Two stairways provide access between the main and production deck levels and a stairway and ladder provide access between the production and cellar deck levels and cellar deck and top of the hull utility space (H.U.S.).