Following the 2018 campaign, the client reordered the 40Te Scanmachine to support the footprint of a drilling rig at two locations. The 2020 scope covered: 

• Rock remedial work to DNV design criteria, fulfilling foundation stabilisation while avoiding the use of additional gravel and minimising seabed disturbance
• Debris removal
• Pipe uncovering in preparation for DWS
• Relocation of two pipes that had already been cut and left

Given the volume of material to be processed, the 2018 campaign had already shown that a grab setup was more efficient than a traditional ejector. To improve seabed preparation further, a 2.1 m tilting levelling bucket was selected as the maintool. 

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At short notice, the client also asked whether Scanmudring could provide a tool capable of lifting and relocating pipes from 3" to 20". Scanmudring sourced a conventional onshore log grapple, then modified and tested it at its own facilities. A ripper tooth was brought offshore to handle debris and harder material. 

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Challenges

• Strong tidal currents
• Low visibility
• No ROV support
• Precise placement of rock dump
• Minimising disturbance to the surrounding area
• Debris
• Maximising efficiency across the scope

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Specific Toolin

• 40Te Scanmachine, capable of mounting heavy-duty tooling
• High production rate combined with high placement precision.
• No hose handling required
• Reduced ROV support
• Works within a tolerance of +-200mm
• Accepts standard excavation tools from our onshore partners.

Pad remedial

The design aimed to reduce overall berm thickness, removing side walls and the outer edges of top pad arragnements where necesarry (scalloping) and re-depositing that rock within the footprint of the proposed berm. The large tilt bucket was used throughout and proved highly efficient, holding level regardless of machine roll, monitored in PDS, with a thin and precise blade.

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Pipe uncovering and debris removal

• The log grapple manoeuvred pipes of various sizes that were inaccessible to the crane, lifting and shifting a 5-6 m section of 20" pipe 60-70 m within minutes.
• The ripper tooth broke through hard layers to reach pipe depth, and was also used to drag longer pipe sections choked with softslings.
• Suction nozzles were the preferred method for uncovering pipes and creating room for future DWS cutting, primarily to maintain visibility.

• The poject was executed safely and effectively
• Close planning with the contractors was a significant factor in the outcome
• Depth readings can be challenging in shallow water, where wave action affects accuracy. - This is an area to improve on future campaigns
• The 40Te Scanmachine proved reliable, running dives of continious heavy excavation up to 87 hours without issue.

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