Precision lifting key to riser caisson success

The job saw Jumbo deploy its heavy-lift vessel Fairplayer to handle the 120-metre long and 1.3-metre diameter caisson.

“This job involved the careful handling of fragile offshore equipment. But with our experienced crews and engineering teams, combined with the dual cranes of the Fairplayer, Jumbo Offshore had the technical capabilities and offshore expertise that made this precision operation a success,” said Carol Granneman, project manager, Jumbo.

“Technip FMC is a very valued client of ours and we look forward to working with their team in the future.”

Finely-tuned

The Fairplayer picked up the caisson from the Scottish port of Nigg, an operation that demanded a finely-tuned rigging arrangement due to the high flexibility of the caisson.

To this end, each of the Fairplayer’s 900-tonne cranes used double slings and a total of five connection points.

After transporting the caisson to the offshore location, Jumbo then executed the wet storage scope of the project. Wet storage is the temporary storage of offshore components on the sea bed, which in the case of this particularly delicate caisson, called for careful operations.

The offshore scope was the most challenging, said Mr Granneman. 

“Due to the motions of the waves and the buoyancy of the caisson, the most critical moment was when we lowered the caisson through the splash zone, and then we had to lower it evenly through the water column to avoid excessive stresses in the caisson,” he said.

The preparatory engineering of this project is also notable. Having worked together on numerous occasions in the past, Technip FMC and Jumbo Offshore have a good working relationship.

For this riser caisson project, the two companies worked together on the project engineering. Technip FMC carried out the calculations for the rigging, and Jumbo worked on the vessel-specific calculations regarding the Fairplayer’s movement at different phases of the operation.

Once positioned on the seabed, Jumbo used an ROV to disconnect the caisson, leaving two rigging points in position to allow Technip FMC to pick it up for installation at a later date.