Enabling Ultra-Deepwater Mooring with Aramid Fiber Rope Technology

Abstract

New high-strength synthetic ropes constructed of para-bonded aromatic polyamide (aramid) fiber are being developed for ultra-deepwater mooring applications. This paper highlights new laboratory tensile/fatigue testing of rope assembly, computer modeling analysis of mooring performance under operating conditions, and the potential economic impact.As the industry moves into ultra-deep water, traditional steel wire rope and chain moorings are being gradually displaced by polyester ropes. These synthetic ropes have been used in water depths between 3,000 feet and 8,000 feet. Questions arise, however, about whether polyester mooring ropes provide enough stiffness to maintain acceptable platform offsets in increasingly deeper water in all cases. Aramid fiber ropes are inherently stiffer and stronger than polyester ropes and therefore offer new solutions for ultra-deepwater mooring, as well as for other applications where production platform offsets may be critical.Advanced technologies are being developed to optimize aramid fiber performance and rope design configurations. New laboratory tensile and fatigue data are presented to demonstrate aramid fiber rope properties, performance capabilities, and minimum tension settings meeting API RP 2SM guidelines. Mooring analysis comparing the performance of an aramid mooring system with that of a polyester mooring system under simulated hurricane and loop current conditions shows significant reductions in platform offsets are achieved with the aramid system without compromising safety. This paper describes a new technology for ultra-deepwater mooring. The new approach offers the opportunity to design mooring systems for deeper water without modifying certain platform components and systems by incorporating stiffer, high-strength aramid fibers in the platform mooring system. Potential benefits include achieving optimal offsets for production risers in ultra-deep water, easier handling and installation due to smaller rope size, and greater flexibility in mooring system design. Economic analyses are presented to illustrate the advantages of the new technology as well as the financial impact.

A creep–rupture model of synthetic fiber ropes for deepwater moorings based on thermodynamics

“…After that polyester ropes have become the preferred option for depths down to 1500 m. However, with numerous discoveries of natural resources in deeper waters, the question of whether polyester ropes can be utilized and provide enough stiffness to maintain acceptable platform offsets at all depths has been raised. Based on the fact that aramid and HMPE fiber ropes have shown higher stiffness than polyester ropes on the condition of equivalent minimum breaking load, they are considered as alternatives to polyester ropes [5,[8][9][10]. However, compared to polyester, HMPE has a lower break extension, easier creep failure and a higher modulus which will cause a larger cyclic load range in storm.…”

“…In 1983, the first attempt that aramid fiber ropes are utilized as the main part of mooring lines was made, although it failed attributed to not considering the fiber axial compression fatigue [2]. Therefore, aramid fiber ropes appeared to be a good choice for deepwater moorings provided that compression loading can be avoided [3][4][5]. In 1992, experimental researches about the mechanical behavior of polyester ropes were first systematically performed by Del Vecchio [6].…”

Effects of Damaged Fiber Ropes on the Performance of a Hybrid Taut-Wire Mooring System

“…In 1997, the first polyester taut-wire mooring system was successfully installed in the Campos Basin, offshore Brazil [6]. Since then, the polyester ropes used in taut-wire mooring systems have become the preferred option for depths up to 1500 m. However, with numerous discoveries of natural resources in deeper waters, the question of whether the polyester ropes can provide sufficient stiffness to maintain acceptable platform offsets at various depths has been raised [7][8][9]. Based on the observation that the stiffness of high modulus polyethylene (HMPE) ropes is higher than that of the polyester ropes at the same minimum breaking strength, the HMPE ropes were considered as alternatives to the polyester ropes [7,9].…”

Lifetime prediction of high-modulus polyethylene yarns subjected to creep using the Larson–Miller methodology

“…Along the past three decades, extensive research was done with different materials, studying different mechanical properties. An interesting overview of different examples of synthetic mooring ropes, including several materials and properties, can be found in the literature, 3 –6 and general guidance and recommendations regarding these systems can be found in the literature. 7 –9 More specifically, studies dealing with long-term behavior of fibers under constant tension, that is, creep, are of utmost importance when it comes to mooring systems.…”