ABSTRACT:

The excessive build up of marine growth on submersed structures poses a significant problem for structural integrity. Left unchecked, it substantially alters the structures overall load on the seabed, increases hydrodynamic drag through increased seacurrent resistance and impedes effective periodic visual inspections by occluding important views. This problem is particularly pertinent to platforms and structures in warm, temperate waters, such as West Africa, Gulf of Mexico and the Mediterranean where marine growth proliferates under these favourable sea conditions. Until now, this problem could only be addressed by employing commercial divers to manually clear the debris. This however was restricted to either shallow depths of only of approximately 20 metres with air diving or deeper if using expensive saturation diving systems. Traditional large hydraulic ROV's were not a viable option as their large dimensions restricted their entrance inside the subsea structures and limited their manoeuvrability around critical zones. The evolution of the powerful, compact electric ROV's such as The Cougar allowed DNT to develop an innovative and highly effective ROV supported cleaning system. The Cougar ROV with its unique size and power ratio is small and agile enough to enter and manoeuvre around all the structures, whilst being robust enough to support such powerful tool. In July/August 2006, DNT Offshore Srl successfully conducted the first completely diverless subsea structure marine growth removal campaign, in Sicily, Italy. DNT Offshore Srl's revolutionary prototype cleaning system averaged a massive 6.5 cubic metres per hour, cleaning hard, built-up marine growth, with less than a 1.7% downtime. The system has a current maximum depth capacity of 120 metres. The system requires just two technicians for each 12 hour day operation. The Marine Growth Cleaning Tool (MGCT) promises not only to dramatically cut maintenance costs for existing production platforms and Offshore structure maintenance activities, but to be extremely useful for the localised cleaning requirements for the installation of add on structures such as risers, clamp reinforcements etc to existing platforms. Furthermore, with increasing emphasis on deepwater facilities, time and cost efficiency and safety for personnel and the environment alike, the DNT Cougar MGCT proposes the most advanced solution on all fronts

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