Liebherr installs another 1600 tonner

In September Liebherr delivered the second heavy lift offshore crane type MTC 78000 and installed it on board ship at its manufacturing plant in Rostock, Germany.

The MTC 78000 is one of the biggest offshore slewing cranes in the world. With a maximum dynamic torque of 78,000 tonne-metres, the MTC 78000 is the most powerful Liebherr crane. At the time of writing four units had been ordered. OSA Sampson is one of the largest heavy load vessels in the world. Its duties include offshore platform reconditioning, pipe laying and erecting wind power turbines.

Erection and assembly of the crane on the heavy lifting ship OSA Sampson presented Liebherr engineers with challenges, for example, the planning of the individual lifts to remain with the pier's ground pressure limit. The assembly date depended on the arrival of the heavy load vessel so the necessary lifting equipment had to be ready at short notice. For the work Liebherr used two of its own LHM 600 mobile harbour cranes lifting in tandem. Their load capacity of 208 tonnes each meant components weighing up to 400 tonnes could be mounted.

Assembly of the MTC 78000 required several spectacular heavy duty lifts. First and heaviest at 370 tonnes was the slewing platform. Next was the machinery compartment with drive components at about 240 tonnes, the lower mast section at about 250 tonnes and the upper section section of the mast at around 160 tonnes. The lowest point of the latter component had to be hoisted more than 43 m above the pier level. To do this the two mobile harbour cranes were fitted with tower extensions.

Placing the boom was the last step in the assembly process. In a tandem lift the 87 m boom was positioned at the respective connection points precisely enough for the boom to be pinned to the slewing platform on both sides. The sheer size of the pins required a specially developed hydraulic pinning machine.

A big challenge was posed by the rope assembly of four 1.6 km long boom hoist winch and lifting ropes which was handled with special auxiliary devices and high work input to finally fit the crane with the 60 tonne main hook. Accurate project planning and special training allowed the team of 50 mechanics to assemble the MTC 78000 in 23 days.

Also installed on the ship at the same time as the .larger crane was a 100 tonne capacity offshore crane type CBO 3600. First, the base column of this crane had to be welded onto the vessel. Mechanics assembled the crane on the test stand in Rostock before the vessel arrived.

Heavy lift testing was done in open sea using a 1,760 tonne test weight corresponding to 110% of the nominal load capacity. The test loads were two water filled pontoons lifted out of the water and turned around.

Despite its size, the MTC 78000 is designed as a slewing crane and is supported by traditional large diameter slew bearings. The slew ring weighs 70 tonnes and is 9 m diameter. Manufacturing such large mechanical parts uses complicated custom processes because conventional gear cutting machines are only available for bearings up to a diameter of 5 m.

BOX

MTC 78000 in figures

Lifting capacity: 1,600 tonnes to 35 m radius.

Maximum dynamic load moment: 78,000 tonne-metres

Capacity at maximum radius (74 m) for the main hoist: 530 tonnes.

Boom length (as fitted to OSA Sampson): 87 m.

Two auxiliary hoists with lifting capacities of 500 and 50 tonnes.

Deadweight is 1,420 tonnes without the base column which adds around another 300 tonnes depending on design.