Design of the Kilauea Jacket

Abstract

ABSTRACT Two objectives of the Kilauea jacket design were minimum schedule and minimum overall cost to the client. As part of a fast-track, turnkey project, extensive fabrication and installation considerations, as well as design considerations, shaped the jacket, The result was a competitive jacket that was fabricated two months ahead of what was initially seen as a tight schedule. The design, fabrication and installation considerations and a summary of the analyses performed is presented. INTRODUCTION The original Texaco bid-request package included a complete jacket and deck design for 690' depth. The jacket was a conventional design that could be built by most fabricators and required no special installation equipment. H had four main piles, eight skirt piles, half-width launch trusses and provisions for conventional surface pile driving. The bidders were allowed to use the Texaco jacket configuration and required to use the Texaco deck. Since the final water depth was 620', Texaco allowed for design time during bid preparation. Texaco also invited alternate jacket designs. To offer a more competitive bid, McDermott based its bid on an alternate design taking full advantage of its fabrication yard capabilities, offshore equipment and design expertise. This paper presents the framing philosophy Hudson Engineering used for the Kilauea jacket design including both fabrication and installation considerations along with a summary description of the analyses performed, CONFIGURATION PHILOSOPHY Background In 1985 Hudson Engineering Corporation performed an in-house study to develop more economical framing and installation concepts for deep water jackets to take full advantage of McDermott's equipment to reduce construction costs. The study compared economics of lifting versus launching for jackets weighing less than 10,000 tons. Additionally, framing configurations were optimized for weight and fabrication simplicity. This study and a subsequent 600' water depth jacket design formed the basis of much of the Kilauea jacket configuration. Design, fabrication and installation were all considered in Kilauea's final framing. Design Considerations Concentration of legs and piles around jacket corners was desired for efficient global stiffness, reduced pile loads and reduced pile penetrations. A four-leg, X-braced jacket with an essentially square base and with skirt piles at the corners seemed the most efficient overall configuration. Since the jacket was too heavy to lift with equipment expected to be in the Gulf in the summer of 1989, launch trusses would be required. To reduce wave load and launch truss weight, the size of the launch trusses was minimized. The launch truss length could be limited if the jacket was loaded out bottom first and launched top first. Based on previous studies, launch truss widths approximately half the jacket width were selected. The launch trusses were "boxed" together to simplify fabrication and to provide convenient supports for the conductors and pull-tubes. Supporting conductors on the launch box allowed efficient selection of conductor support levels and also allowed efficient selection of jacket vertical X-brace framing patterns independent from conductor support concerns.