In early September, Liebherr completed a second heavy lift offshore crane type, MTC 78000, 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 mT, the MTC 78000 is the most powerful machine offered by the Liebherr Group. Four units of the new heavy lift crane have already been ordered.
Despite its size, the MTC 78000 has been designed as a slewing crane and is supported by traditional large diameter antifriction bearings. The swing ring weighs 70 t and has a diameter of approximately 9 m. The manufacture of such large mechanical parts can only be accomplished with custom processes, as conventional gear cutting machines are only available for large diameter antifriction bearings with a diameter up to 5 m. Liebherr has therefore specifically acquired correspondingly sized machines and equipment.
Spectacular heavy lifting
The onsite erection and assembly of the large size crane on the heavy load vessel OSA Sampson presented challenges for the Liebherr engineers, down to 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 a maximum load capacity of 208 t each, enabled parts weighing up to 400 t to be mounted in tandem operation. The machines were equipped with the Liebherr Sycratronic® control system. The Sycratronic® controls the simultaneous operation of the mobile harbour cranes, thereby ensuring the 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 370 t, the heaviest of the components. This was followed by the machinery compartment with the drive components and the lower mast section, weighing approximately 240 t and 250 t, respectively, then by the 160 t upper mast section, the lowest point of which needed to be hoisted up to over 43 m above the pier level. This hoist was achieved 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 87 m boom was positioned with millimetre precision at the respective connection points enabling it to be pinned to the slewing platform on both sides. The sheer size of the pins required a specially developed hydraulic pinning machine.
The four boom hoist winch and lifting ropes, each 1.6 km long, had to be handled with special auxiliary devices to finally fit the crane with the 60 t main hook. Thanks to the precise project planning, the specially trained team of 50 mechanics was able to assemble the MTC 78000 in just 23 days.
Parallel to the assembly of the MTC 78000, an offshore crane type CBO 3600 with a maximum lifting capacity of 100 t was installed on the OSA Sampson. The mechanics assembled the crane on the test stand in Rostock prior to the arrival of the vessel, when the base column would be welded onto it. The CBO 3600 was lifted and installed in one step. This simplicity of this procedure considerably reduced the duration of the project. The transportation of the crane from the test stand to the vessel was accomplished with a suitable platform trailer.
Overload test offshore
The heavy lifting test of the large crane was carried out in the open sea with a 1,760 t test weight –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 crane was ready to be delivered to the client with the 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 1600 t at up to 35 m radius. This corresponds to a maximum dynamic moment of 78 000 mt, the crane still being able to slew over 360°. At a maximum radius of 74 m from the main hoist, the crane achieves a lifting capacity of almost 530 t. The boom length of the crane currently delivered is 87 m. In addition to the main hoist, the MTC 78000 offers two auxiliary hoists with lifting capacities of up to 500 t and 50 t respectively.The dead weight of the new heavy-lift offshore crane is 1420 t without the base column which weighs approximately 300 t itself, 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 500 kW or 4 MW power. The two main winches offer a line pull of 500 kN (50 t) with a rope diameter of 48 mm.
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 Litronic control system with an 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 or manually. 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.
Read the article online at: https://www.worldcement.com/europe-cis/16112010/liebherr_delivers_further_1600_t_heavy_lift_offshore_crane/