Bespoke Cofferdam Design Enables Dry Pontoon Repairs in the North Sea

Following the identification of cracks in the pontoon of a semi-submersible rig, Global Energy Solutions were contracted to provide a repair solution. This involved the design and fabrication of a cofferdam that would enable dry weld repairs to be carried out by the Aventus offshore construction team.

A bespoke cofferdam was design-engineered to ensure a secure and watertight fitment around an intricate arrangement of braces, stiffener plates, and access ladders. The assembly was developed to allow a team of construction personnel to work safely over an extended period. The cofferdam was designed to withstand expected wave conditions, which dictated both the wall height and structural stiffening arrangement. The design also featured an innovative twin-sealing system, providing sufficient sealing performance to accommodate any anticipated surface irregularities that might otherwise compromise the integrity of the seal.

Due to the required size of the cofferdam, transportation to the repair site was addressed by prefabricating each wall panel section at the Aventus facility, prior to transport for final assembly and NDT on the deck of the rig in the North Sea. The cofferdam included a boat landing platform to enable safe access and egress at all times, along with valves to assist with water displacement. Once the cofferdam was positioned, the remaining water was pumped out, creating a dry workspace for the pontoon weld repairs to be carried out by Global Energy Solutions personnel.

Following a successful period of NDT, the pontoon repairs were accepted by the classification society, and the cofferdam was removed from site.