Jacking technique for FPSO topsides accelerates hook-up process
Technip has devised a new concept for FPSO topsides assembly. The tech-niques employed are designed to sim-plify and shorten the installation pro-cedure and to reduce hook-up and commissioning. This in turn gives greater flexibility in terms of hull/topsides delivery schedules, the main cause of floater project delays and cost over-runs.
Typical layout for a 23,000-tonne jack deck FPSO topsides. Utilities and process equipment are contained in two side-by-side modules.
null
Large FPSOs for deepwater projects off West Africa are typically being designed to carry topsides of 20-23,000 metric tonnes. According to Technip, these may be configured in one of two formats:
- Around 13 mid-size modules, with interconnecting pipe racks and living quarters; and 20 associated lifts, varying from 300 to 2,000 tonnes, with 20 main horizontal interfaces (or an even greater number of modules, lifts, and interfaces)
- Six large modules, plus living quarters, involving seven lifts, from 3,000 to 5,000 tonnes, with eight main horizontal interfaces.
The constituent packages are typically sourced from a variety of sub-contractors, and delivery must be coordinated to fit the lifting schedule. This in itself can be constrained by the lifting capacity and reach of the yard's cranes and the attendant problems of transferring heavy loads safely to a 60-m wide, 300-m long FPSO hull, with the deck often protruding 30 m above the quayside loading station. This arrangement is also inefficient, as it complicates work access. Additionally, the large number of modules leads to more interfaces, further extending the schedule. Hook-up for Shell's Bonga topsides at the Amec yard in Wallsend, UK, involved installing 23 modules brought in from four different locations. The overall operation took around 1 million man-hours to complete.
Technip's concept, known as FPSO Jack Deck, splits the entire deck into two large, self-contained modules. For a 23,0000-tonne topsides, these would comprise utilities (10,000 tonnes) and process equipment (13,000 tonnes). According to Chris-tian Nygaard, vice president of technology marketing (tech-nology, petroleum & gas), "Both modules would be assembled on land, as you would any deck. This facilitates the hook-up and commissioning as well as improving the safety aspects. The modules would then be loaded onto a barge stationed alongside the quay in two separate skidding operations."
Once the topsides modules have been secured to the jackup legs, the barge withdraws.
null
Once the first module has been loaded onto the barge, eight legs are attached to pre-assembled connection points on two sides of the module's structure. The legs are lowered until contact is made with the sea floor, and the module is then elevated by 20-30 m at a rate of 0.45 m/min using hydraulically driven jacks. This method is based on the same rack-and-pinion principle applied for installation of the TPG 500 jackup platforms on the North Sea Elgin and Harding fields. The lift capability is around 2,480 tonnes/leg.
Subsequently, the barge is retracted, making way for the FPSO's hull, complete with a bearing support structure for the Jack deck frame and topsides, to take its place between the legs. The integrated module is then lowered onto the support structure by jacking down the legs. When a connection has been effected, the legs are removed and are re-used for lifting the other module. Once in position, each module is then split transversely into three sub-modules to aid structural flexibility with regard to hull hogging and sagging.
The legs have been designed for future re-use on other projects. The system is also reversible for future field decommissioning.
The FPSO with its newly installed topsides.
The entire operation for both modules is completed within three weeks, Nygaard says. "But the main point is that installing two self-contained modules is much more efficient than a process involving 20 or more lifts. This way, we can cut two to three months off the typical hook-up schedule, which is very significant for an FPSO project." He adds that two (modules) is not considered the magic number.
For the installation to work, the seabed alongside the yard's quayside, or dry dock, would need to be reasonably prepared. Technip has already investigated yards with suitable facilities – "some may not be capable of performing all the integration," Nygaard says.
