May 2024, Vol. 251, No. 5

Tech Notes

Subsea Decommissioning Pays Off in North Sea

(P&GJ) — Development of its largest subsea chop saw paid off for Decom Engineering following its first deployment in a subsea infrastructure decommissioning project on behalf of DeepOcean in the Northern North Sea.

Deployment took place on a cutting campaign, involving large concrete coated pipelines.

The ambitious project involved the removal of pipelines, control umbilicals and various other subsea structures from the seabed in water depths of up to 590 feet (180 meters), each requiring precise and efficient cutting. 

Cutting pipe sizes ranging from 41-inch outer-diameter, concrete-coated carbon steel pipes to 8.6 inches outer diameter, the C1-46 Chopsaw was used to cut into 18-inch (9.5-meter) sections to allow efficient recovery to the vessel deck.  

Powered from topside and ROV using a hydraulic power unit (HPU), the C1-46 Chopsaw exceeded expectation in the harsh of subsea environments, the company said, while a smaller C1-24 Chopsaw was used for certain tasks. 

The C1-46 averaged 15 cuts before requiring a blade change, reducing the need for recovery to the surface and completing 79 cuts on its first deployment, the company said, savings almost 300% of the amount of time needed by traditional diamond wire saws. 

Furthermore, Decom’s innovative approach to reducing seabed dredging time by modifying the saw’s clamps reduced dredge time from 3.5 hours to just 30 minutes.  

Sean Conway, Decom Engineering managing director, called the project “a valuable learning experience,” which “sets the benchmark for going on to roll out our technologies.” 

The C1-46 Chopsaw can be operated in depths of 6,560 feet (2,000 meters) and ca cut in any orientation, he said. 

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