When you’re laying 930 km of pipeline 2.2 km underwater – and using the world’s largest construction vessel to do it – you need the very best in equipment and technology. For the Swiss-based Allseas Group, slings made from Dyneema® were the go-to solution.

Diamond Background

Wave upon wave of challenges

Designed by Allseas, the Pioneering Spirit offshore vessel is capable of lifting entire oil and gas platform topsides weighing up to 48,000 tonnes and jackets up to 20,000 tonnes in a single piece. It can also install record-weight pipelines in all water depths.

With the historic single-lift removal of the 24,000-tonne Brent Delta topsides in 2017, the Pioneering Spirit had proved its world-leading credentials. Its next assignment? Laying the TurkStream pipeline in the Black Sea.

Even for the world’s largest pipelaying ship, TurkStream posed a major challenge. A twin 32-inch diameter gas pipeline running 930 km through the Black Sea from Russia to Turkey, it was the largest-diameter pipe ever to be laid at depths up to 2,200 meters. As if that wasn’t daunting enough, the challenge was compounded by the steep slope of the seabed.

Synthetic slings: The smarter choice

But Allseas was well prepared: the Pioneering Spirit was equipped with BEXCO slings made with Dyneema® SK78 fiber. These slings were the result of careful collaboration between Dyneema® and BEXCO on the development of innovative offshore mooring, heavy-lifting, and towing solutions that use lighter, easier-to-handle synthetic rope in place of steel wire.

In this particular case, Allseas installed BEXCO 169 mm slings containing Dyneema® to use in the stinger adjustment system (a critical piece of apparatus in guiding pipelines onto seabeds). Each sling came with a minimum breaking load of 1,800 tonnes and a safe working load of 500 tonnes – rising to 1,000 tonnes once the slings were reeved in their eventual basket configuration.

Prior to deployment, BEXCO conducted extensive stiffness testing on its Dyneema®-based slings at its R&D test bench facility in Belgium. The slings were also protected from harsh environmental conditions by a highly durable jacket designed to prolong their lifetime.

“The key requirement from Allseas was to ensure the smooth and safe adjustment of the stinger radius. That meant tight tolerances on both length and elongation of the BEXCO slings.”

Noemie Panis, Project Manager for the TurkStream project, BEXCO

Diamond Backgroun

Smaller, more compact winches with Dyneema®

Better yet, the BEXCO slings delivered on deck as well as underwater. “Using slings made with Dyneema® is a proven technology for Allseas,” said Zylvester Nocua, R&D Engineer at Allseas. “Our other vessels also use these synthetic slings for radius adjustment operations. One key benefit is their low D/d ratio, which allows us to limit the structural interfaces on the vessel. Additionally, stinger operations are carried out over the slot of the Pioneering Spirit, making lightweight specifications important. This also enables a relatively compact design for the winch solution, including the fore- and after- runners, in the vessel’s forecastles.”

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