Assessing Strength Loss of Abraded and Damaged Fiber Rope

SummaryThis paper brings together two experiences from TTI (Tension Technology International) and the UoE (University of Exeter) and aims to quantify the damage that could be experienced by fibre mooring lines during the transit and commissioning phase of Marine Renewable Energy (MRE) devices.1. While deploying a new prototype of anchoring system for a MRE device, UoE experienced the failure of a new polyester mooring line during transit to site (90 minute duration). A thorough visual inspection supported by Scanning Electron Macroscopy (SEM) analysis and tensile test have established the physical conditions of the fibre rope before its failure.2. Wear testing led by TTI has investigated and established a relation between the degree of abrasion sustained and the residual strength of Dyneema ® fibre ropes. The ropes were submitted to friction forces via cycling over a roller and a fairlead with different abrasive surfaces (from 7.6 to 254.3μm). Negligible wear occurred with the low roughness surfaces and very high wear at the higher roughness surfaces.The load experienced by the polyester line during the deployment of the anchoring system was simulated with the software OrcaFlex TM . Dynamic modelling using representative conditions indicates that the polyester mooring line was loaded between 3 and 20% of its Minimum Breaking Load (MBL) which is well below the design load of the rope. IntroductionTo date there are only a few MRE designs which have achieved a pre-commercial development status. Experience in deploying such devices and specific guidance are missing. The approach of designers is thus conservative and based on the offshore oil and gas industry and anecdotal evidence [4].The use of synthetic fibre ropes for mooring systems has seen a sudden rise in marine applications over the last two decades [5] albeit mainly for deep water mooring [6]. Experience and feedback from the use of polyester ropes for MRE device moorings is still limited in terms of publications produced. This paper focuses on the commissioning phases of MRE devices, with a specific focus on the deployment of a novel anchoring system. Handling, lifting and rigging of mooring lines could result in damage during transport or installation as discussed in [7] and [8]. The strength of a rope will inevitably degrade from mishandling. Several research programs have been carried out to investigate the abrasion and twisting damage by rope manufacturers for towing systems. For example incorrect handling during transport could cause significant damage to the rope due to abrasion and the application of sudden high loads is one of the most severe conditions that a rope can experience [9].Certification standards and specific test methods have been developed to test the abrasion resistance of yarns [10] - [11]. The abrasion mechanism was described in [12] as a sequence of fibre peeling induced by surface shear forces. However the abrasion resistance of a fibre rope is not determined by standards and knowledge is only based on empirical test data.The exte...

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“…[21]; for a 12-strand polyester rope with a 40% damaged area the strength loss calculated with the Eq. 5.…”

Section: Existing Results On Residual Strength Estimation Of Damaged mentioning

confidence: 99%

Abrasion process between a fibre mooring line and a corroded steel element during the transit and commissioning of a marine renewable energy device

Herduin

Banfield²,

Weller

et al. 2016

Engineering Failure Analysis

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“…(12) considering the centroid of each unbroken rope component as the generic point (coordinates (z k , y k )). Based on this displacement field, the curvature of each unbroken rope component can be calculated in its deformed configuration.…”

Section: Proposed Analytical Modelmentioning

confidence: 99%

“…Several experimental [4][5][6][7][8][9][10][11][12] and theoretical [13][14][15][16][17][18] studies have shown that the impact of the presence of broken rope components on overall rope response (stiffness, residual strength and deformation capacity) depends on the length of the rope, number of broken rope components (degree of damage) and their distributions throughout rope cross-section (symmetric and asymmetric) and along the rope length, and rope construction. These studies have mainly been conducted on steel wire ropes and synthetic fiber ropes.…”

Section: Introductionmentioning

confidence: 99%

Assessment of static rope behavior with asymmetric damage distribution

Beltrán

Vico

2015

Engineering Structures

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“…In the aspect of the mechanical behavior of the damaged fiber ropes, the residual strength of damaged fiber ropes was experimentally investigated by Williams et al [18], Ward et al [19,20], and Flory [21]. All these studies adopted the method of cutting some sub-ropes or elements to create the initial damage state of specimens.…”

Section: Introductionmentioning

confidence: 99%

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

Lian

Yim

Zheng

et al. 2019

Journal of Offshore Mechanics and Arctic Engineering

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In this study, effects of damage levels of fiber ropes on the performance of a hybrid taut-wire mooring system are investigated. The analysis is performed using a numerical floating production storage and offloading (FPSO) model with a hybrid mooring system installed in 3000 m of water depth. An in-depth study was conducted using the numerical model, the dynamic stiffness equation of damaged fiber ropes, the time-domain dynamic theory, the rainflow cycle counting method, and the linear damage accumulation rule of Palmgren-Miner. Results indicate that, in a mooring line with an increasing damage level, the maximum tension decreases, while the offset of the FPSO increases. Particularly, when a windward mooring line failure occurs, in addition to the significant increase in the offset of the FPSO, the maximum tension, tension range, and annual fatigue damage levels of the remaining lines adjacent to the failed also increase significantly. The present work can be of great benefit to the evaluation of the offset of the floating platform, the tension response, and the service life of the hybrid mooring systems.

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Assessing Strength Loss of Abraded and Damaged Fiber Rope

Cited by 8 publications

References 0 publications

Abrasion process between a fibre mooring line and a corroded steel element during the transit and commissioning of a marine renewable energy device

Abrasion process between a fibre mooring line and a corroded steel element during the transit and commissioning of a marine renewable energy device

Assessment of static rope behavior with asymmetric damage distribution

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

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