Design of Guylines for the Lena Guyed Tower

Abstract

Exxon’s Mississippi Canyon 280-A (Lena) platform represents the first commercial application of the guyed tower concept for offshore drilling and production platforms. Unlike a conventional offshore platform, the guyed tower is held upright by an array of guylines attached near the upper end of the structure and radiating outward to anchor piles driven into the seabed. This paper describes the functional requirements of the various components of this unique guying system and shows how each component was designed to meet those requirements. Among the design parameters discussed are guying system stiffness and strength, fatigue and wear life, corrosion protection, and assembly. The major length of the guyline consists of spiral-wound bridge strand, most of which is sheathed in polyethylene. The cable constructions and terminations are described. Near the tower, the sheathed cable is connected to a length of bare cable which passes through a special fairlead arrangement to direct the cable to the upper attachment above the water line. The fairlead arrangement and the upper attachment are described as well as the means provided to protect the bare cable from corrosion. Unique pinned connections in the system are designed to ease assembly while still providing the required load capacity and service life. A special anchor pile attachment eye design allows for large tolerances in anchor pile orientation. A description of the clump weight shows how this component is designed to achieve the desired system stiffness while also providing stability against overturning or excessive settlement into the seabed.