Cofferdams for Spudcan Repairs
Challenge
SeaTec was tasked to create a dry working environment around the giant support feet (spudcans) of a jack up oil rig. The cofferdams system had to completely enclose each spudcan in turn and seal against the underside of the rigs hull. When in position the area around and above the spudcan would be drained, thus allowing surface workers to carry out required Class approved weld repairs.
Work was carried out in the port of Esbjerg, Denmark with only 10m of water available, and water visibility of less than 30cm.
Solution
SeaTec designed, manufactured and installed a unique cofferdam system that allowed afloat repair of all three spudcans of a jack up oil rig.
The design of the cofferdam consisted of a bolted hexagonal steel ring with intergrated ballast tanks and a flexible membrane that covered the underside of the spudcan, sealing around the steel ring. The benefits of this design over an all steel construction were reduced weight, manufacturing costs and clearance required for installation.
In addition to the main cofferdam system a series of inflatable seals were placed inside the steel ring and outside the spudcan; this further reduced the risk of leakage by providing a secondary sealing system.
The complete cofferdam system measured 16m across, 2m deep and weighed 35 tonnes.