Modulift has refurbished two subsea spreader beams for a major subsea installation contractor before they were used to lift 260 tonnes and 280 tonnes manifolds for a field development offshore Libya
The standard Modulift SUB 380 beams originally provided up to 380 tonnes at nine metres and up to 16 metres at a lower capacity. However, in this case, Modulift re-rated the capacity to 364 tonnes working load limit (WLL) with +1.5 dynamic amplification factor (DAF). The drop links were re-rated to 200 tonnes WLL, also with 1.5 DAF, and new data plates were added accordingly.
Chris Schwab, account executive at Modulift, explained that the identical spreaders’ original DAF was 1.8. He added, “The principle reason for refurbishing the beams was so they could be reused on another project that required an additional strut to achieve a new span, and they needed to be re-rated to a higher capacity, yet lower DAF.”
This was necessary to manufacture new 0.95 metre struts for each beam and shotblast all existing components. Extensive testing was conducted on welds, plus new spans and capacities. The drop links had already been tested to a sufficient capacity as part of an earlier project, thus, additional testing for these was not required.
Also included within the scope of work was the supply of new bolts and preparation of a calculations report so DNV could carry out verification against its Loadout, Transport and Installation of Subsea Objects criteria (DNV-OS-H206).
Modulift's new subsea range has an open section design that aims to eliminate risks of cavity or pressure issues, said the company.
The physical size of the manifolds—fabricated in Ravenna, Italy—meant that they could only be brought offshore via a barge. Ground loading and crane capacity issues on site resulted in a requirement for a tandem crane lift. The installation vessel, however, had a single crane so as to simulate the installation lift a single point lift was required.
To achieve a simulated offshore single point lift, Modulift provided a MOD250/400 spreader beam and associated rigging to ‘join’ the two site cranes together using an inverted spreader bar arrangement. The SUB 380 spreader bar on each structure was connected to the structure via high-performance synthetic slings and ROV-friendly shackles to form the installation rigging arrangement on the structures.
