As many deep-sea oil and gas fields are being developed, floating platforms becomes larger with more complicated topsides. However, the construction time is demanded to be shorter to meet the overall project schedule. The use of very large topside modules is one of the effective ways to reduce the integration time and decrease the possibility of fabrication defects.
The Ichthys Project’s CPF (Central Process Facility) is currently being constructed at Samsung Heavy Industries (SHI). The CPF will be the world’s largest production semi-submersible platform. The hull is constructed on the Offshore Floating Dock and most of the topside modules are prepared at workshops and integrated by floating cranes on the hull.
To maximize production efficiency in terms of reduced integration time and reworks, several topside modules are assembled into a larger module weighing up to 7,400 tonne spanning 150m long. Such large module cannot be handled by a single 8,000 tonne F/C, the largest crane that SHI owns. This fact initiated the idea of dual-lifting with a combination of the two F/Cs (8,000 tonne and 3,600 tonne) which enables lifting, transportation and integration of the mega-modules properly and safely without building a larger capacity F/C. Using different sized F/Cs increases the flexibility of the operation of the F/Cs.
To ensure safety during the dual-lifting, the two F/Cs are synchronized to be controlled as a single crane unit. During hoisting, all the measured data such as loads and positions of the hooks, and rotation of the module, are monitored in real time basis and used to hoist the module automatically. All the systems are designed to be redundant. Additional engineering works are performed to check the safety such as 1) structural analysis to investigate the structural safety with out-of-phased motions at boom-tip 2) time-domain analysis and 3) model test in ocean basin with the operation scenarios in real environments to obtain the dynamic load factors and the guidance on the operation limits in terms of wave heights. The two crane barges are moored side-by-side using fenders and mooring lines, and tug operation conditions are planned not only to move but also to push the two barges from sideways to be moored tightly, which minimizes the possibility of relative motions between the two barges.
The developed system had been applied to the integration of all the modules successfully weighing from 4600 to 7400 tonne. It is expected to be applied to many other offshore projects to keep the construction schedule on time. This paper will address and share the technical experiences obtained during the dual lifting of the mega-modules for the Ichthys Project’s CPF.