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

Abstract

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...

Condition Monitoring Technologies for Synthetic Fiber Ropes - a Review

“…Note that it is the internal abrasion that generates heat in the rope such that the fibers melt together, reducing the strength of the rope. Herduin, Banfield, Weller, Thies, and Johanning (2016) show through experimental tests that there is a linear relationship between the strength loss due to external abrasion and the surface roughness.…”

Stability Analysis and Environmental Influence Evaluation on a Hybrid Mooring System for a Floating Offshore Wind Turbine

“…Castillo et al (2020) have confirmed that synthetic fiber ropes serve as optimization tools for achieving a cost-effective and reliable mooring system design [1]. Synthetic fiber ropes are advantageous in terms of reduced corrosion problems, with wet polyester experiencing lower abrasion rates compared to dry polyester ropes, as proposed by Herduin et al (2016) [16]. However, it is crucial to note several adverse effects associated with synthetic fiber ropes.…”