A £1 million investment in developing its largest subsea Chopsaw to date has paid off for Decom Engineering (Decom) following impressive results on its first deployment.

The C1-46 Chopsaw played a pivotal role in a subsea infrastructure decommissioning project on behalf of DeepOcean in the Northern North Sea.

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

The Decom team was tasked with cutting a wide range of pipe sizes, from 1,042mm OD concrete-coated carbon steel pipes to 220mm OD super duplex pipes. These subsea pipelines needed to be segmented into 9.5 meter sections for efficient recovery to the vessel deck.

Powered from topside and ROV using a Hydraulic Power Unit (HPU), reeler, hot stabs and control panel, the C1-46 exceeded all expectations, proving its worth in the harshest of subsea environments. The smaller C1-24 chopsaw was utilized for certain tasks and also operated with a mix of topside and ROV controls.

Decom Engineering’s C1-46 Chopsaw deployed in North Sea on cutting campaign on large concrete coated pipelines. (Image credit: Decom Engineering)

The C1-46 averaged 15 cuts before requiring a blade change, significantly reducing the need for recovery to the surface and impressively completed 79 cuts on its first deployment, showcasing a remarkable 100% success rate.

Substantial time savings of almost 300% were achieved compared to using traditional diamond wire saws which typically have longer cut times, carry a risk of wires breaking, and require multiple trips to the surface vessel for blade replacement. Using customized insertable and replaceable tips voided the need for blade changes, reducing costs and increasing efficiency by minimizing vessel time.

In contrast, the C1-46 completed some cuts in as little as 20 minutes, while the C1-24 saw excelled in cutting super duplex and flexible risers - materials that traditional shears can’t handle.

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.

Established in the United Kingdom in 2011, Decom is an R&D specialist focusing on the design and fabrication of cutting solutions and innovative decommissioning equipment, with a growing reputation for providing complex deepwater project solutions.

A pipe section cut using Decom Engineering’s C1-46 Chopsaw and lifted to surface using a custom-built pipe grab. (Image credit: Decom Engineering)

Decom Engineering managing director, Sean Conway, said: “The C1-46 Chopsaw is a remarkable piece of subsea engineering which was designed, developed, and deployed in under six months, specifically for this North Sea decommissioning campaign.

“This project underlined our commitment to engineering innovation and underlined our credentials for pushing the limits of what’s achievable in subsea decommissioning. To efficiently cut through a submerged 1,042mm reinforced concrete coated pipe is not without its challenges, but the C1-46 was more than up to this difficult task.

“It’s been a valuable learning experience and the performance of the C1-46 Chopsaw sets the benchmark for going on to roll out our technologies which offer multiple benefits to contractors and operators engaged in complex subsea decommissioning projects.”

Sean Conway, Managing Director, Decom Engineering Ltd, (Photo credit: Decom Engineering) 

The C1-46 Chopsaw has been designed to cut tubulars and other materials up to 46” diameter and is able to cut a wide range of materials, including inconel alloys, duplex and concrete.

It can be operated in water depths of up to 2,000 meters, has the ability to cut in any orientation, and is capable of multiple cuts per blade (20-100), resulting in large cost savings and increased efficiency. Blade changes are efficient and safe and the Chopsaw can be supplied set up in a number of configurations and settings to suit project requirements.

Project Statistics:

Total Cuts Completed: 74.
Pipe Sizes Cut: Ranging from 1042mm OD concrete-coated carbon steel to 220mm OD super duplex.
Cut Length: All pipes were segmented into 9.5-meter sections for efficient recovery.
Equipment Used: C1-46 Chopsaw , C1-24 Chopsaw .
Blades Used (24"): 2 blades for flexible production riser (8 cuts), 1 blade for PU-coated carbon steel (12 cuts), 1 blade for super duplex (5 cuts).
Teeth Used for the C1-46: 941 teeth on a single blade.
Fastest Cut (C1-46): 20 minutes on 1042mm OD concrete-coated carbon steel.
Fastest Cut (C1-24): 14 minutes on 220mm OD super duplex.