Understanding particular properties of the HMSF mooring lines
OCIMF and SIGTTO have issued a guide for those involved in the procurement of High Modulus Synthetic Fibre (HMSF) mooring lines.
The guidance is provided with the aim of increasing the understanding of the particular properties of the HMSF mooring lines and to encourage the adoption of improved specifications and quality assurance processes. It should be noted that international standards exist for the construction of HMPE but the standards for Aramid and LCP fibres are very limited. This guide contains recommendations relating to the scope of procurement specifications and provides brief information on the relevance of the various specified requirements to the mooring line’s in-service performance.
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HMSF mooring lines may be considered as an alternative to traditional steel wire ropes owing totheir higher strength to weight properties and advantages associated with their relative ease ofhandling. Over the years, the marine industry has gained considerable experience using mooringsconstructed from HMPE, but the use of Aramid and LCP fibres for large ship moorings has not beenextensive. With regard to HMPE mooring lines, after many years of relatively incident-free use, the industry hasexperienced a number of failures recently, particularly on large liquefied gas carriers. Althoughanalysis of the failures has not identified any specific cause, a number of contributory factors havebeen highlighted as being of potential importance including rope design, manufacturing quality,ambiguity in the specification of minimum breaking load (MBL), impact and frequency of dynamicloads, consideration of creep and high ambient temperatures. As a result, the lack of a clear detailed industry specification for use in the procurement of HMPEmooring lines was considered significant. It was found that purchasers often specified an MBLbased, for example, on a shipyard specification, but did not appreciate how to define this numberand did not always specify other requirements such as line construction, minimum HMPE content,grade of HMPE and requirements for testing the finished product. |
Rope manufacturers and suppliers, represented by the industry associations Cordage Institute and the European Federation of Rope, Twine and Netting Industries (EUROCORD), have provided valuable technical contributions.
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Quality control HMSF mooring lines should be manufactured and supplied under quality assuranceprocesses that are independently verified, such as those required under ISO 9001 or equivalent. Effective control of raw materials and finished products is of critical importance andthe manufacturer’s quality assurance and control procedures should address materialcertification, traceability, and testing requirements. The design of individual rope types should be based on fully documented andindependently-verified prototype tests. Ropes should be constructed in accordancewith the agreed design specification. The manufacturer should have documentedprocedures that address the frequency of batch break tests to confirm that stated MBLcriteria is being met, in accordance with ISO 2307 or CI 1500 (references 2 and 3). The manufacturer should have an inspection and test plan that includes the following,as a minimum:
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Further details may be found by reading the Guide to Purchasing High Modulus Synthetic Fibre Mooring Lines here
