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How Allseas completed one of the world’s most ambitious subsea pipelaying projects

930km of pipeline. 2.2km below the surface. The world's largest construction vessel

This ambitious pipelaying project demanded the best in equipment and technology to ensure success, making slings made with Dyneema® the obvious choice.

High-strength, low-weight slings produced by BEXCO and made with Dyneema® SK78 allow flexible, safe and easy handling onboard the world’s largest offshore vessel.

Designed by the Swiss-based Allseas Group, Pioneering Spirit is the world’s largest construction vessel – capable of lifting entire oil and gas platform topsides up to 48,000 tonnes (t) and jackets up to 20,000t in a single piece, and installing record-weight pipelines in all water depths. After demonstrating her heavy lift credentials in the North Sea with the historic single-lift removal of the 24,000t Brent Delta topsides in April 2017, her next assignment involved laying the TurkStream pipeline in the Black Sea.

One of the most challenging pipelaying projects

Pioneering Spirit is the world’s largest pipelaying ship, boasting an S-lay tension holding capacity of 2,000(t) and pipelay equipment that makes it possible to install record-weight pipelines from shallow to deep water, and achieve high lay rates. That made her the first choice for one of the most challenging pipelaying projects ever undertaken: TurkStream, a twin 32-inch diameter gas pipeline running 930km through the Black Sea, from Russia to Turkey in waters up to 2,200 meters deep. It is the largest-diameter pipe ever to be laid at such depths.

This already-challenging combination of depth and pipe diameter is made even more difficult by the steep slope of the seabed.

Pioneering Spirit is fully equipped to meet this pipelaying challenge, which included the deployment of BEXCO slings made with Dyneema® SK78.

BEXCO and DSM Dyneema have partnered over recent years to develop innovative offshore mooring, heavy lift and towing solutions that use lighter, easier-to-handle synthetic rope in place of steel wire.

Tight tolerances with BEXCO slings with Dyneema®

A key step in pipeline installation involves the lowering of the stinger at a precise angle, to guide and support the pipeline on its way to the seabed. Allseas installed Bexco 169mm slings with Dyneema® on board to use in the stinger adjustment system. The slings were used to adjust the radius position of the stinger when deep-water pipelay commenced. Each sling has a minimum breaking load (MBL) of 1800t and a safe working load (SWL) of 500t. The slings are reeved in basket configuration making the actual SWL 1000t.

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

Noemie Panis, BEXCO’s Project Manager for the TurkStream project

“As part of the production and delivery program, BEXCO conducted extensive stiffness testing on its slings with Dyneema® at its R&D test bench facility in Belgium prior to deployment. The slings are also protected from harsh environmental conditions by a highly durable jacket that will prolong their life cycle.”

Smaller, more compact winches made with Dyneema®

“The use of slings made with Dyneema® is a proven technology for Allseas. Other vessels also use these slings for radius adjustment operations, which forms the basis for synthetic sling selection over steel slings.” comments Zylvester Nocua, R&D Engineer for Allseas.

“The reasons for this choice are the slings’ low D/d ratio, allowing us to limit the structural interfaces on the vessel. Additionally, stinger operations are carried out over the slot of Pioneering Spirit, making low-weight specifications very suitable in this case. The lightweight specifications of the slings allowed for a relatively compact design of the winch solution, i.e. including the fore- and after- runners. This allowed for smaller winches in the forecastles of the bows of the Pioneering Spirit.” 

“The reasons for this choice are the slings’ low D/d ratio, allowing us to limit the structural interfaces on the vessel.”

Zylvester Nocua, R&D Engineer for Allseas

Where to buy BEXCO slings made with Dyneema® SK78?