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Project Number 416
Date of Summary June 1, 2006
Subject Damaged Polyester Rope-Large Scale Experiment
Performing Activity Texas A&M University, Offshore Technology Research Center (OTRC)
Principal Investigator Dr. E.G. Ward
Contracting Agency Minerals Management Service
Estimated Completion Completed
Description Full-scale polyester ropes were tested to determine the impact of damage on the strength of polyester rope used as mooring lines for deepwater structures.
Polyester ropes from four manufacturers were tested (Bexco, Marlow, Whitehill, and CSL) were tested to determine the impact of damage on the strength of polyester mooring lines.

Small-scale rope tests were tested to examine the effect of rope sample length on the break strength of damaged rope. Full-scale ropes at standard test lengths (15m) were tested to determine the relationship between break strength of damaged rope and level of damage. Longer full scale ropes were tested to further examine the impact of length on the break strength of damaged rope. Results will be useful in developing guidelines for deciding how best to handle polyester mooring lines damaged during installation or service. The project is being sponsored by the MMS and the industry through a JIP. Industry participants include BP, Unocal, Petrobras, Kerr-McGee, ConocoPhillips, ABB, and ChevronTexaco.
Progress All testing and analysis have been completed. The ultimate goal of this project - to provide information on the residual strength of damaged polyester rope for the industry and MMS to use in developing guidelines for mitigating damaged polyester rope mooring lines - has been accomplished.

A coherent interpretation of the overall results was developed from a simple qualitative analytical model; careful consideration of rope construction details; observations of subrope behavior mechanisms; and consistent analyses and interpretation of test results. Given that this is the first ever attempt at testing such large and long ropes, this comprehensive interpretation can provide useful understanding and guidance in studying damaged polyester ropes and the developing codes and regulation to deal with damaged polyester mooring lines.

Current codes and guidelines suggest that if a rope is damaged such that it looses 10 percent of its strength, it should be replaced. Further, it is suggested that that damage and strength loss are linearly related so that a 10% loss of cross sectional area due to damage would result in a 10% strength loss.

Our results indicate that polyester rope is not that damage tolerant. While the behavior and residual strength of damaged ropes was found to be dependent on the details of rope construction and terminations, the following general trends were noted. The strength loss in standard test samples (15m length) with a 10 % cut damage generally resulted in strength losses larger than 10%. Further, longer samples (50 - 60 m) generally had a significantly higher strength loss, confirming the presence of length effects noted in smaller scale tests.

The Final Report that documents the tests, analyses, results and conclusions is completed, but it is proprietary until 2011.
 

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