Qualification Method for Cut Resistant Jackets for Fiber Mooring Ropes

Abstract

The Aasta Hansteen spar platform in the Norwegian Sea has a polyester rope mooring system. The anchors and large parts of the polyester ropes are outside of the safety exclusion zone granted by the Norwegian authorities. Fishing vessels cannot be denied as long as they are outside of the safety zone, and the polyester mooring ropes need to withstand abrasion loads from the possible fishing activity. A fishing activity study in 2013 defined probability for fishing, size of possible fishing vessels and type of fishing equipment. Numerical simulations of the mooring system and crossing fishing trawl equipment made it possible to establish trawl abrasion load cases, including trawl wire lengths, speed and contact pressure. No jacket design or jacket material was at the time confirmed to withstand the established abrasion loads. The jacket solution to be chosen for the project thus needed to be specially developed, designed, tested and approved to give sufficient resistance against the established abrasion loads. Several vendors developed and offered different jacket solutions, and the selection of cut resistant jacket was dependent on adequate testing. Based on input and comments from Equinor and rope vendors, DNV constructed a test rig extension to their 2500T horizontal test bed, where the required length of trawl wire was pulled over the polyester rope with the needed contact pressure. Full-size (diameter) ropes with the proposed cut resistant jackets were tested, including break strength testing after the abrasion test. This paper presents how the possible trawl activity was defined, the numerical simulation of trawl/mooring line interaction, the test rig setup and some test results of the trawl wire abrasion testing.