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July 2014 Issue

Setting new Industry Standards for Marine-Grade Yarns
John Flory

In the May 2002 issue of Sea Technology, I wrote a Soapbox entitled 'Know the Ropes, Commodity or Quality,' in which I said: 'fiber rope properties can vary greatly, depending on fiber material, rope construction, and quality.' I advised that 'using the wrong type of rope or a poor-quality rope can result in accidents and fatalities.' That article mentioned some of the standards and guidelines which were then available.

At that time there were no guidelines for yarn quality, making it difficult for users to judge fiber materials. It was not possible to specify fiber quality, except by referencing a brand name, and many users cannot specify brand names. Now, the Cordage Institute (CI) has established guidelines for nylon and polyester marine-grade, rope-making yarns.

The Oil Companies International Marine Forum (OCIMF) sponsored research in the early 1980s to determine the causes of failure and develop guidelines for large single-point mooring (SPM) hawsers. Wet cyclic tension testing was conducted on many different rope samples. A rope maker provided two nylon rope samples made of the same nylon yarn material from the same producer, one made with a good standard yarn and the other made with a new and improved marine-grade-finish yarn. These two nylon rope samples were identical in yarn material and rope construction, except for the yarn finish. The marine-finish nylon rope performed much better than the other rope. Similarly, another rope maker provided otherwise identical polyester ropes made with polyester yarns from two different producers. Again, the marine-finish rope performed best.

OCIMF commissioned a university examination of the rope specimens after wet-cyclic load testing revealed that interstrand abrasion was the principal cause of strength reduction and rope failure. It was recognized that a test method was needed to quantify the yarn abrasion resistance of rope-making yarns. A yarn-on-yarn (YoY) abrasion test method was then developed to compare yarn performance. OCIMF commissioned a university to evaluate the test method and compare the yarn performances. Samples of the good and the improved marine-finish nylon and polyester yarns were provided for blind testing.

The results showed a correlation between the ropes that performed very well in wet cyclic tension and the yarns that performed very well in the wet YoY abrasion testing. The nylon yarn with the marine-grade finish exhibited significantly improved resistance to wet yarn-on-yarn abrasion, and the marine-grade nylon rope exhibited significantly improved wet cyclic load fatigue performance. The better-performing polyester yarn correlated with the better-performing polyester rope.

OCIMF incorporated the YoY abrasion test into its 'Guidelines for the Purchasing and Testing of SPM Hawsers' in 2000. The YoY abrasion test was then published as a CI Standard Test Method in 2002.

In the late 1990s, at the request of the United States Navy, CI set out to establish a definition and guideline for marine-grade yarns for use in mooring and towing hawsers. Wet YoY abrasion tests were performed on samples of polyester and nylon yarns that claimed to be marine grade. All four polyester yarns exhibited very good performance. CI then published the 'Performance Requirements of Marine Grade Polyester Yarn for Fiber Rope,' CI 2009P.

Three of the tested nylon yarns exhibited very good wet YoY abrasion performance, but one performed relatively poorly. The producer of the poor-performing nylon yarn objected, and the draft nylon guideline was not approved at that time.

Additional YoY abrasion tests were recently performed on presently available nylon yarns. Two current yarn producers provided samples of their regular and marine-grade nylon yarns for testing. The marine-grade yarns performed significantly better than the regular yarns. Both marine-grade nylon yarns exceeded the earlier established CI performance criteria. As a result, CI finally published the 'Performance Requirements for Marine Grade Nylon Yarn for Fiber Rope,' CI 2009N.

The CI Technical Committee operates on a consensus basis. Although a majority might be in favor of an action, if there are major objections, an effort is made to resolve the conflict. Normally, CI cannot set standards or guidelines that exclude particular rope products, even those made by nonmember companies. In this case, a new category of product was being established that has special, superior, desirable properties. This allowed the Technical Committee to establish higher performance criteria that some products could not meet.

The marine-grade nylon yarn criteria took more than 30 years to develop. The YoY abrasion test was first developed and demonstrated by OCIMF in the early 1980s. The CI effort to develop marine-grade yarn criteria began in the mid-1990s. During this period, several producers stopped making marine-grade nylon yarn, but other producers have taken their place, so the guidelines remain relevant.

Nylon fiber is particularly affected by water. The nylon molecule absorbs water and swells, loses strength, and becomes less resistant to abrasion. A good marine-grade finish protects the nylon fiber from this effect. Thus a good marine-grade yarn is important for ropes used in marine service.

We hope that the effort is worth it. We hope ship owners and other marine operators will now realize ropes made of marine-grade yarn last much longer, and that they will specify marine-grade nylon and polyester yarns in accordance with these CI guidelines to uphold safety in the industry.

The CI standards and guidelines can be obtained from the Cordage Institute, www.ropecord.com.

John Flory is the president of Tension Technology International LLC (Morristown, New Jersey). He worked for Exxon Research and Engineering for 20 years, conducting research and development of mooring systems for tankers. He is a member of the Cordage Institute Technical Committee and chair of the subcommittee that developed the marine-grade, rope-making yarn guidelines.


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