Exploration • Drilling • Field Services


Walking the torque Karel Devos looks at torque-matched fibre rope solutions for offshore mooring.


stated advantages of lower overall weight, easier deployment and potentially lower environmental impact using polyester rope have already been demonstrated in numerous drilling rig mooring installations.


T What has been less commented upon is the


importance of considering the overall approach towards typical deep sea mooring installations. In


he trend which has emerged in recent years of the deployment of fibre rope solutions instead of steel wire and chain for deepwater mooring solutions has been well-documented. Te


the case of temporary moorings for Mobile Offshore Drilling Units (MODU), this will require either a combination of fibre rope and steel wire (Fig. 1), or a combination of steel wire, fibre rope and chains (Fig. 2).


A steel wire commonly used in offshore mooring such as a six or eight strand, will have the tendency to un-twist when load is applied. A polyester rope which has been built as torque neutral is by its very nature flexible and acts like a swivel when twisted. As a result, the steel wire in combination with polyester rope will be impacted by cyclical twist to the point where a repair of the steel wire


Fig. 1. Right lay wire matched with right lay torque-matched polyester. 30 www.engineerlive.com


Fig. 2. Right lay wire matched with right lay torque-matched polyester and torque- neutral chain.


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