IV-Oil & Gas awarded Conbit a contract to lift and install a cable riser protection frame on Tennet’s Dolwin Alpha substation, located offshore in the German sector of the North Sea.
The protection frame is a 1.8 x 1.3 m steel column, over 36 meters in height and with a total weight of approximately 14.5 tonnes. The lifting procedure involved using a ballasted winch, a hinged upending procedure, and the remote release of slings.
IV-Oil & Gas contracted Conbit because of its specialist lifting know-how, engineering capability, and thorough work preparations. Involving Conbit at the early stage of the riser design process allowed them to incorporate a special installation method.
The project was surveyed, certified, and monitored by DNV.
The main challenge was upending the riser. As the platform’s crane was inadequate to perform this task, the team used the substation’s height to upend the riser. It was slowly brought into the vertical position by first sliding it out of the platform and supporting it with a hinge point at one end. Then, it was lowered at the end with a winch.
Because the substation’s outer wall is airtight, caution was necessary to ensure that the riser did not impact and damage it. Therefore, during the installation, the team decided to execute the upending procedure with extra clearance between the riser and the outer wall.
The client wanted to keep the welding of temporary structures to a minimum. To comply, the Conbit engineers devised a novel solution. It enabled them to limit the welding to only a few shear plates.
Overboard working requires typically additional measures to maintain safety, including a standby rescue vessel. For this project, the client decided to prevent overboard working. As Conbit engineers were lifting overboard, they needed to release their lifting slings remotely. They used a remote release shackle to overcome this challenge.
"An excellent job, guys. Really a demonstration of professional approach, planning and execution of a very demanding challenge. I am fully satisfied with the job done, also with the personal approach of each individual throughout. - Thank you!"