Building a Giant for Single Platform Lifts

Abstract

Abstract This paper describes the design, building and functioning of a ship forsingle-lifting of topsides of offshore platforms up to 53,000 short tons(48,000 metric tons) and jackets up to 27,500 short tons (25,000 metrictons). The vessel will have a wide slot at the bow which fits around platformsubstructures and is equipped with a hydraulically operated topsides liftingsystem. For installing or removing platform jackets she will have a system oftwo tilting lift beams at the stern. Very large lifts can substantially reduce offshore hook-up costs in topsidesinstallation. In topsides decommissioning, single-lifting can make laborious module removalunnecessary. The offshore environment is spared and the safety of personnel atwork offshore is enhanced. In rough areas such as the North Sea, a motion elimination system is anecessity to avoid re-impact of a lifted structure onto its base structure, which could cause severe damage. The vessel may not always find sufficient occupancy in very heavy lifting workand therefore will also be a pipelayer with an S-lay tension capacity up to2200 short tons (2000 metric tons) for installing heavy pipelines in shallowand deep water. The building of the vessel and equipment is in progress; she is scheduled to becommissioned by the end of 2013. Traditional modular lifting versus topsides float-overs Installing large offshore platforms has so far generally been done with cranevessels. Large topsides have to be installed module by module to ensure thatthe lifts remain within the capacity of the cranes. This can lead to considerable offshore hook-up costs to complete the topsides, which is more expensive than when done on land. However, by single-lifting the offshore hook-up costs can be significantlyreduced. If a topside structure is completed on land and installed in onepiece, the making of all the connections between elements or modules -structural, electrical, hydraulic and piping - is faster and less costly. Installation of large integrated topsides by a "float-over" method has alreadybeen proposed since the 1970s, and in benign waters has been applied by severalcontractors. In the Gulf of Mexico, Versatruss successfully applies single-lifting with aninnovative system of large frames on two barges in still water. The large semi-submersible crane vessels of Heerema and Saipem havesuccessfully done integrated lifts of up to 12,000 short tons (11,000 metrictons) with two cranes, in very favorable weather conditions. Removing large topsides by traditional crane vessels requires the topsides tobe removed module by module, or by more time-consuming, hazardous and expensivedismantling offshore in small pieces. When removing topsides in a modular way, every module must be cut loose fromthe surrounding modules, lift points must be re-installed, and lift riggingmust be attached. Platform walkways, escape routes and safety plans must beadjusted several times during the removal process. Several "make safecampaigns" are required offshore and onshore. At an early stage theaccommodation facilities will have to be removed because of their outsideposition and then will no longer be available to the dismantling crew.