First Subsea Decommissioning Tool recovers Caisson within a Caisson within a Caisson

Published May 18, 2016
First Subsea tool
First Subsea tool recovers difficult to reach caisson (photo: ProServ)

Energy services company Proserv, has leased First Subsea Ltd’s Ballgrab gripping technology for a decommissioning project in Norwegian waters for the recovery of a caisson. In this case the application required the tool to descend down within a foundation caisson of 30-inch to 20-inch to 13-3/8-inch to access the inner 9-7/8-inch API 5CT Q125 section.

The tool is part of the company’s rental fleet that covers over 300 stock tools for lifting / handling and recovery of API line pipes, deployment and handling of manifolds, monopiles, suction piles and flexible risers for both Oil & Gas and Renewables sectors.

At 30 inches in diameter the foundation caisson protruded 8 metres vertically above the seabed in a water depth of approximately 90 metres and contained three inner caissons of reducing diameters.

Recovering the inner caisson required a simplified rigging methodology to overcome the shackle geometry constraints which prevented access to the inner 9-7/8-inch caisson. The shackle could only accommodate the 20-inch casing section and a 2.5m modular extension was added to the tool extending its reach to access the inner 9-7/8-inch (ID 8.625 inches) caisson.

The Ballgrab tool was lowered into the caisson and then remotely activated topside through a 120-metre twin Siamese hose on a reeler complete with HPU (hydraulic power unit).

“Ballgrab gripping technology is ideal for this kind of application where caisson and pipes have to be removed from often inaccessible locations,” says John Shaw, Managing Director, First Subsea Ltd.

Tags: First Subsea Ltd, Preserve


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