Deployment and Testing of HMPE Rope for Long-Term Moorings

Abstract The objective of this study and paper is to gain a better understanding of long term HMPE mooring rope performance for permanent facility mooring applications. The study specifically applies to HMPE rope used to moor an FPSO for a duration of 7 years. The HMPE rope was in and on the seabed, connecting the mooring line to the anchor, in this application for long term mooring. The temporary Serpentina FPSO moorings (2013 - 2019) included an HMPE mooring rope in each of the 9 mooring lines. All ~350 ft length ropes were located at and under the mudline as forerunners to a drop-embedded anchor. The mooring lines were recovered in 2019 and stored quayside in Louisiana until being cut into samples and tested for this project. The HMPE (Dyneema® SK78 fiber) mooring rope underwent the following tests: Full scale MBL testsDissection & visual / MicroCT inspectionFiber testing (comparing used fibers with new fibers, including residual creep testing (ARELIS)) All results indicate that the ropes are suitable for long term use. Two full scale rope MBL tests were performed that indicated the residual rope strength was over the rated average break strength. Inspections indicated an absence of foreign particles within the rope. Fiber testing indicated a sufficient residual creep life for continued deployment in excess of the lives of most LTM systems. No long-term deployment of HMPE fiber ropes in/on the seabed mooring a permanent facility with subsequent testing has been documented in industry to the knowledge of the authors. The results from this study indicate new potential for mooring components that are not subject to corrosion and allow for enabling anchor technologies to be used in permanent facility, offshore wind/renewables, and other mooring system applications.