At the beginning of September, Liebherr delivered the second heavy lift offshore crane type MTC 78000 straight from its manufacturing plant in Rostock. The MTC 78000 is one of the biggest offshore slewing cranes worldwide. With a maximum dynamic torque of 78,000mt, the MTC 78000 is the most powerful machine within the extensive range of cranes and material handling machines offered by the Liebherr group of companies. Four units of the new heavy lift crane have already been ordered to date.
Despite its size, the MTC 78000 has been designed as a slewing crane and is supported by traditional large diameter antifriction bearings. With a weight of 70t, the swing ring has a diameter of approximately 9m. The manufacturing of such large mechanical parts can only be accomplished through complicated custom processes as conventional gear cutting machines are only available for
large diameter antifriction bearings up to a diameter of 5m. Therefore, Liebherr has acquired correspondingly sized machines and equipment specifically for the mechanical machining of these flanges.
Spectacular heavy lifting
The on-site erection and assembly of the large-size crane on the heavy load vessel OSA Sampson presented Liebherr engineers with special challenges: for example, the planning of the individual hoists so that the maximum permitted ground pressure of the pier was not exceeded. As the assembly starting date depended on the arrival of the heavy load vessel and the required lifting equipment needed to be ready on short notice, Liebherr exclusively used their own cranes for the assembly.
Two large LHM 600 mobile harbour cranes were used in tandem operation for the heavy duty lifts. Both cranes with their maximum load capacity of 208t each enabled parts weighing up to 400t to be mounted in tandem operation. The machines were equipped with the recently patented innovative Liebherr Sycratronic® control system. In combination with the dynamic anti collision system the Sycratronic controls the simultaneous operation of the mobile harbour cranes, ensuring best possible performance and protection for the cranes.
The assembly of the MTC 78000 required several spectacular heavy duty lifts. First, the slewing platform was mounted – at 370t, the heaviest of the components. Thereafter, the machinery compartment with the drive components (approximately 240t), the mast lower section (about 250t) and the mast upper section (around 160t) of which the lowest point needed to be hoisted up to over 43m above the pier level. This hoisting height was made possible by equipping the mobile harbour cranes with two corresponding tower extensions.
The last step in the assembly process involved putting the boom in place. In a tandem hoist operation, the 87m boom was positioned with millimetre precision at the respective connection points enabling 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 posed the rope assembly of four 1.6km 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 60t main hook.
Parallel to the assembly of the heavy lift offshore crane an offshore crane type CBO 3600 with a maximum lifting capacity of 100t was installed on the heavy load vessel OSA Sampson.
As first of all the base column of this crane also had to be welded onto the vessel the mechanics decided to assemble the crane on the test stand in Rostock before arrival of the vessel. The lifting and installation of the CBO 3600 on board was done in one step. This procedure reduced the duration of the project considerably. The crane transport from the test stand to the vessel was accomplished with a suitable platform trailer.
Due to precise project planning, the specially trained team of 50 mechanics was able to assemble the MTC 78000 in only 23 days.
Overload test offshore
The heavy lifting test of the large crane was carried out in the open sea with a 1,760t test weight – corresponding to 110% of the nominal load capacity. The test loads consisted of two water filled pontoons which were lifted out of the water and turned around.
After the successful test, the client could be delivered with the heavy load vessel OSA Sampson. The OSA Sampson is one of the largest heavy load vessels worldwide and is being used for platform reconditioning, pipe laying and to set up offshore wind power plants.
Unique performance characteristics
The MTC 78000 achieves a maximum lifting capacity of 1,600t at up to 35m radius. This corresponds to a maximum dynamic moment of 78,000mt, the crane still being able to slew over 360°. At a maximum radius of 74m for the main hoist the crane achieves a lifting capacity of almost 530t. The boom length of the crane currently delivered is 87m. In addition to the main hoist, the MTC 78000 offers two auxiliary hoists with lifting capacities of up to 500t and 50t respectively.
The dead weight of the new heavy-lift offshore crane is 1,420t without the base column which weighs approximately another 300t – depending on its design.
The size of the MTC 78000, which is derived from customer requirements, represents a new dimension in product development for Liebherr. Thereby, the crane’s design is characterised by state-of-the-art drive technology. The drive concept is based on an electro-hydraulic drive with 8 x 500kW or 4MW power. The two main winches offer a line pull of 500kN (50t) with a rope diameter of 48mm.
High safety standards are among the most important criteria to be fulfilled during the development of the new offshore crane. The standard equipment of the MTC 78000 features the proven Litronic control system with integrated display of load and radius as well as automatic load moment limitation. This is completed by special overload protections which are either activated electronically (AOPS ‘automatic overload protection system’) or manually (MOPS ‘manual overload protection system’). The crane’s auxiliary hoist is fitted with a constant tension system exerting a tensile force on the hoist rope in case of significant wave height, thus ensuring that the hook follows the moving load.