SS: Fiber Moorings, Recent Experiences and Research: Updating API RP 2SM on Synthetic Fiber Rope for Offshore Moorings
Authors: Petruska David Joseph , Kelly Pat , Stone Barbara , Ahjem Vidar , Zimmerman Evan H. , Garrity Robert , Veselis Todd 
Published: July 2010

The 1st Edition of API RP 2SM — Recommended Practice for Design, Manufacture, Installation and Maintenance of Synthetic Fiber Ropes for Offshore Mooring — was released in March 2001. Prior to then, most of the actual synthetic fiber rope mooring applications were installed in Brazil by Petrobras. Since the publication of RP 2SM, polyester moorings have been used in other deepwater basins, including the Gulf of Mexico, for both temporary drilling MODUs and permanent FPSs. Much has been learned from the actual design, manufacture, installation and operation of these systems by other operators and contractors throughout the past decade. This work has created an extensive knowledge base in the areas of both synthetic fiber rope behavior and mooring system design. To best capture these new learnings, an API Task Group assembled to perform a major update in developing a 2nd Edition.

API RP 2SM is the recognized standard for synthetic fiber offshore moorings in the Gulf of Mexico as well as other deepwater basins of the world. It is used in conjunction with API RP 2SK (Design and Analysis of Stationkeeping Systems for Floating Structures, 2005) and API RP 2I (In-Service Inspection of Mooring Hardware for Floating Structures, 2008) for the design, manufacture, installation and maintenance of both temporary and permanent synthetic fiber mooring systems.

This paper will present the key changes in the update of this API RP. Reasons for the changes and significance on a synthetic fiber offshore mooring project will be discussed. Major changes in the RP include sections on elongation and stiffness testing, contact with the seafloor, creep rupture and axial tension compression fatigue. The new guidance in the RP will allow for improved synthetic fiber mooring systems design, installation and operation while also potentially reducing cost.

Introduction

In 1997, Petrobras installed a 12-point taut leg polyester mooring system on its P-27 semisubmersible floating production system in the Campos Basin, offshore Brazil. This installation was a first in the offshore industry, and since then Petrobras has installed more than 20 polyester mooring systems on semis, FSOs and FPSOs. In 2004, BP was the first to install a polyester mooring system in the Gulf of Mexico (GoM) on its Mad Dog spar. Anadarko followed shortly by installing a polyester system on its Red Hawk cell spar. Since then several other projects (Gomez, Tahiti, Blind Faith, Independence Hub, Thunder Hawk, Mirage and Perdido) have used polyester mooring systems in the GoM. Polyster moorings are planned for future GoM projects, including Petrobras's Chinook and Cascade development. Additionally, polyester has been used for the Kikeh spar moorings in Malaysia as well as several CALM buoy moorings and turret moorings throughout the world.

Similarly on the MODU side, in 2001 both Shell and BP successfully performed a full scale field trial of polyester mooring systems from a MODU. Since then, such systems have become more commonly used. In particular, after the 2004 and 2005 hurricanes, the use of polyester mooring on the MODUs has greatly increased as a possible means to mitigate overload failure or damage to infrastructure on the seafloor should a mooring system failure occur and the MODU go adrift during a hurricane.