MMS JIP: Full Scale Experiments on Damaged Polyester Rope

Summary

Objective

Tests are being conducted to experimentally determine the effect of damage on the remaining strength of polyester rope. The goal is to provide information on the remaining strength of polyester mooring lines damaged either during installation or while in service. That information can then be used by the industry and the MMS to develop guidelines for dealing with damaged polyester mooring lines.

Approach

Commercially available ropes with standard splices from Bexco, Whitehill, CSL, and Marlow are being tested. The program consists of three series of tests as shown in the test matrix below:

1. Length Effect Tests – Develop qualitative information on the influence of rope sample length on tests of damaged ropes. Small-scale rope will be used for these tests.
2. Damaged Full-Scale Tests – Develop quantitative data on the influence of damage on full-scale rope strength. These tests are the main focus of this project.
3. Verification Tests – Verify the results of the Damaged Full-Scale Rope Tests with a limited number of tests on longer full-scale rope samples.

The MMS is funding one-half of the project costs, and industry JIP participants are funding the remaining half.

This project is one of several integrated projects sponsored by the MMS and/or the OTRC to assess the impact of damage to polyester rope mooring lines for deepwater structures. In addition to the project to develop a numerical model to predict the strength of damaged rope, other projects have addressed (1) characterizing installation and in-service damage, and (2) small-scale experiments of rope components up to and including subropes to provide data to calibrate the rope model and develop better understanding of damaged full-scale rope performance (CEAC). The ultimate goal of these integrated projects is to develop information for the industry and MMS to use in developing API guidelines for mitigating damaged polyester rope mooring lines.

Deployment of Results

The test data can be directly useful in determining mitigation strategies, guidelines and criteria, and should provide valuable insight on how damaged rope fails. Results should be useful in developing API guidelines for mitigating damaged polyester rope mooring lines. Additionally, the data will be useful (1) to validate the numerical model of damaged rope being developed by Dr. Eric Williamson in a related OTRC project and (2) in developing scaling relationships for testing damaged ropes that could lead to less expensive test procedures for determining the strength and damage tolerance of new rope designs.

Project Plan

Previous Results: The project test matrix is shown below. Test conditions include cyclic loading followed by a break test of undamaged ropes and ropes with simulated damage (5 to 15 percent of the cross-sectional area).

The Length Effect Tests were completed in October 2003, and the Damaged Full Scale Tests were initiated in February 2004. Results from the Length Effect Tests showed that most failures were in rope body, and some evidence of length effects and strain localization due to damage. Damaged Full-Scale testing will be completed in October 2004.

Scope of Work: Following completion of the Damaged Full-Scale Tests in October 2004, test data and observations from the Length Effect Tests (35t) and Damaged Full-Scale Tests (700t) will be analyzed and interpreted to determine:

• Performance (failure characteristics, damage tolerance, etc.) vs construction differences
• Length effects
  • Observations – 35t tests vs 700t tests
  • Potential causes of length effects
• Scale effects – 35t vs 700t tests
• Damage tolerance of ropes of different constructions

These results will be used to select the damage conditions for the Verification Tests.

The goal of the Verification Tests is to verify critical results from the Damaged Full-Scale Test with a longer test sample. The damage level and pattern that caused the most significant damage tolerance finding for each rope will be re-tested using longer rope samples (60 m vs 10 m). The Verification Tests are expected to be completed in December 2004.

Results for the Verification Tests will then be analyzed and incorporated with results from the Length Effect tests and the Damaged Full-Scale Tests to develop overall results and conclusions regarding

• the impact of damage on the performance of polyester ropes on different constructions
• the damage tolerance of different polyester ropes
• practical implications
• testing and length effects

Related Publications

E. G. Ward, R. R. Ayers, S. Banfield, N. O’Hear, C. E. Smith, (2005) “Experimental Investigation of the Damage Tolerance of Polyester Ropes”, Fourth International Conference on Composite Materials for Offshore Operations. Houston, TX, October 4-6.

E. G. Ward, R. R. Ayers, S. Banfield, N. O’Hear, C. E. Smith, T. Laurendine (2006) “The Residual Strength of Damaged Polyester Rope”, Offshore Technology Conference, Paper 18150, Houston, May