Factors Influencing The Endurance Of Steel Wire Ropes For Mooring Offshore Structures

Factors Influencing The Endurance Of Steel Wire Ropes For Mooring Offshore Structures A.E. Potts; A.E. Potts U. of Reading Search for other works by this author on: This Site Google Scholar C.R. Chaplin; C.R. Chaplin U. of Reading Search for other works by this author on: This Site Google Scholar N.R.H. Tantrum N.R.H. Tantrum U. of Reading Search for other works by this author on: This Site Google Scholar Paper presented at the Offshore Technology Conference, Houston, Texas, May 1988. Paper Number: OTC-5718-MS https://doi.org/10.4043/5718-MS Published: May 02 1988 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Potts, A.E., Chaplin, C.R., and N.R.H. Tantrum. "Factors Influencing The Endurance Of Steel Wire Ropes For Mooring Offshore Structures." Paper presented at the Offshore Technology Conference, Houston, Texas, May 1988. doi: https://doi.org/10.4043/5718-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll ProceedingsOffshore Technology ConferenceOTC Offshore Technology Conference Search Advanced Search ABSTRACTThe service factors influencing the endurance of steel wire rope moorings for offshore structures are discussed. A tension-tension fatigue S-N curve for six strand ropes is presented consideration of cumulative damage resulting from a typical TBP spectrum shows tensile fatigue as a non-critical upper bound on endurance. However, combined bending-tension fatigue at fairlead arrangements is considered to represent the most severe fatigue loading. This mechanism is discussed in relation to existing knowledge of wire rope fatigue behaviour which provides an indication of the influence of the principal variables. The effect of the seawater environment is also reviewed and it is concluded that adequate protection can be provided by combinations of galvanizing, blocking compounds and impressed current systems, while jacketing may also provide long term protection. Caution is expressed regarding the use of bright wires and the consequences of zinc dissolution resulting from extended exposure. The problems of inspection and NDT are also discussed and recommendations are made as to how this may be effected for the critical fairlead region with the mooring line in place. Recommendations are also made as to what further work is necessary to give operators and certifying authorities greater confidence in the endurance of wire ropes for permanent moorings.NTRODUCTIONAs the offshore oil industry seeks to recover oil from deep water locations and to exploit fields previously considered marginal, floating systems are seen in many cases as providing the most practical and economical solutions for supporting topside facilities. In turning towards permanently moored production platforms, operators, regulators and certifiers alike share a common concern as to the long term integrity of the mooring components. The types of flexible mooring elements currently under investigation include:chain cable;steel and composite tubulars;synthetic fibre and composite ropes; and,steel wire ropes.To date steel wire ropes and chain, either solely or together, have been used in most compliant mooring applications, whilst tubulars have been preferred for tension leg platforms (TLP's). Synthetic fibre ropes and composite tubulars and ropes are still undergoing development.At present very little is known about the endurance characteristics of large diameter wire ropes (70 mm and greater) under the service loads and exposure conditions which are experienced in offshore mooring applications. Nor are there any reliable inspection or testing techniques to determine when a wire rope in service has reached the end of its "safe working life".Current mooring line maintenance practice for semi-submersibles used for exploration involves periodic visual inspection, with cut-and-slip of damaged ends, combined with a complete change-out every two or three years. Here the primary loss of rope performance is due to local mechanical damage caused during retrieval of the rope for inspection and/or changes in operating location. For the long term mooring of production units, maintenance practice will be governed by fatigue of mooring lines, particularly in the fairlead region, corrosion in the splash zone and the difficulties involved in inspection. Keywords: strand, annual otc, steel wire rope, upstream oil & gas, amplitude, wire rope, mooring system, endurance, termination, proc Subjects: Offshore Facilities and Subsea Systems, Mooring systems This content is only available via PDF. 1988. Offshore Technology Conference You can access this article if you purchase or spend a download.