Effects of Fiber Rope – Seabed Contact on Subsequent Rope Integrity

Abstract A 15-month research project was initiated in September 2012, funded by the Research Partnership to Secure Energy for America (RPSEA) and industry partners, with the goal of investigating the effects of polyester mooring rope segments contacting the seafloor prior to installation as part of a deep-water mooring system. It is possible for some soil particles to bypass the particle filter, become embedded in the rope core, and intensify normal fretting wear damage as the installed ropes respond to the cyclic loads resulting from extreme weather forces (such as hurricanes). Potential soil ingress into rope due to accidental contact with the seabed may affect the long-term integrity of the mooring system and increase the risk for failure. This situation, in turn, places nearby subsea and surface infrastructure at risk. This investigation may also provide the ability to qualify particular rope designs for pre-installation on the seabed prior to hook-up. This option would greatly reduce overall risk by reducing the time required to attach mooring lines to a floating facility, thereby reducing time to reach a safely moored condition before arrival of severe weather. This paper is a 2014 continuation of the 2013 OTC paper on the same subject, OTC 24027, and describes:results from extraction of subropes from seabed-soiled full rope 15-meter inserts,laboratory experiments on water and soil particle ingression and migration, andthe initial full-scale subrope cyclic wear testing to determine the impact of seabed soil contact on the long-term performance of a mooring system. In summary, all of the experimentation and testing performed to date are showing that with multiple layers of filtering material and with the one alternative filtering system we evaluated, the tentative conclusion is that the rope designs tested can completely protect the mooring ropes from soil ingression, and thus there is no reason to avoid having such ropes drop to the seafloor or be laid on the Gulf of Mexico seafloor. This tentative result assists in working toward the important project goal of reaching agreement between industry participants and U.S. regulatory agencies to qualify polyester mooring ropes for incidental seabed contact and seabed pre-installation.