Special technology using so-called flush-tanks allows the world’s largest lifting vessel to lift a single offshore platform in a matter of hours and sail it ashore to be scrapped or refurbished. The lifting operation entails emptying eight large containers of water, like flushing water out of a cistern. In that way the lifting vessel, the MPU Heavy Lifter, removes oil rigs and drilling platforms proficiently or places new and renovated platforms in the North Sea and elsewhere in the world.
The floating lifting vessel which is undergoing construction at the Keppel Verolme shipyard in Rotterdam can complete such offshore jobs faster, more cheaply and more safely than traditional heavy cranes. While the giant lifting vessel only uses one lift to remove platform and one to remove sub-structure, traditional floating cranes need up to 200 lifts to remove a platform and its sub-structure.The MPU Heavy Lifter cuts out the multiple dangers involved in divers having to cut the sub-structure into smaller sections. Instead, the lifting vessel sails the scrapped structures ashore to be cut up on dry land, thus minimising the number of working hours at sea where the wind and weather in general are often unstable.
"The floating crane is being built to meet the growing need to provide a more environmentally sustainable way of removing oil rigs, many of which are out-dated and have outlived their useful lives. These rigs have to be disposed of. In the Ekofisk field alone, one of the oldest oil fields in the North Sea, there are some 20 platforms which will soon have to be pensioned off," explains COWI engineer Jørgen Visholm.Visholm is consultant for the Norwegian client MPU Offshore Lift ASA on contract management and time planning for the colossal floating lifting vessel, which will be 87 metres long, 110 metres wide and 62 metres high. Construction of the lifting vessel will be completed in the summer of 2009.
The background to the concept is an eight-year period spent developing and testing the floating crane, which is built of a special innovative lightweight concrete, which weighs a third less than normal concrete. This concept has a major advantage, according to Jørgen Visholm:"The innovative lightweight concrete means we can build the vessel of concrete instead of steel. As a result the lifting vessel is more robust and, with a net weight of 53,000 tons, is more stable in the face of offshore weather and waves." By Christina Tækker, cht@cowi.comPublished: