Cordage institute guidelines for marine grade nylon and polyester rope-making yarns

The Cordage Institute (CI) recently published a new guideline for marine grade nylon yarn. This and an earlier, similar guideline for marine grade polyester yarn provide minimum performance criteria based on the yarn-on-yarn (YoY) abrasion test. The YoY abrasion test was developed by an Oil Companies International Marine Forum (OCIMF) study on the causes of failure of large single point mooring (SPM) hawsers in the early 1980s. Cyclic load tension testing of fiber ropes showed that internal abrasion was the principal cause of strength loss and failure. This problem is particularly acute in wet nylon ropes. OCIMF incorporated the YoY abrasion test into its “Guidelines for the Purchasing and Testing of SPM Hawsers”. The method has also been adopted as a standard test method by CI and ASTM and is referenced in other industry guidelines. At the request of the US Navy in the mid 1990s, CI set out to establish a definition and guideline for marinegrade yarn for use in mooring and towing hawsers. Wet YoY abrasion tests were performed on samples of four polyester and four nylon yarns which were claimed to be marine grade. All four polyester yarns exhibited very good performance. Based on this, CI published CI Guideline 2009P "Performance Requirements of Marine Grade Polyester Yarn for Fiber Rope" in 2002. Three of the tested nylon yarns exhibited very good wet YoY abrasion performance. But one nylon yarn performed relatively poorly. CI drafted a marine grade nylon yarn guideline in which the minimum performance criteria included the three good-performance yarns but excluded the poor-performance yarn. The producer of that excluded nylon yarn objected strongly, and the draft nylon guideline was not approved at that time. Additional YoY abrasion tests were recently performed on presently available nylon yarns. The nylon yarns used in the earlier CI tests are no longer made, at least by the original producers. Two present-day yarn producers provided samples of their regular and marine nylon grade yarns for testing. A rope producer also provided marine grade nylon yarn for testing. The marine grade yarns performed significantly better than the corresponding regular grade yarns. The marine grade nylon yarns all exceeded the earlier established CI minimum performance criteria. As a result, CI has now approved and published CI Guideline 2009N “Performance Requirements for Marine Grade Nylon Yarn For Fiber Rope” This paper explains the importance and advantages of using marine grade nylon yarn in ship mooring hawsers and other applications in which the rope is subjected to cyclic tension loading in wet condition. It presents the results of the OCIMF sponsored hawser study and the YoY abrasion test development trials. It describes the marine grade YoY test programs which were carried out by CI, including the results of the recent marine grade nylon yarn YoY abrasion test program. This paper will be of interest to yarn producers, rope manufacturers, and users of fiber ropes in the marine environment.