High strength heavy plates from Dillinger for a heavy lift offshore crane

The heavy lift offshore crane, type MTC 78000 is part of one of the largest heavy lift vessels worldwide. The maximum load capacity of the crane amounts to 1,600 t. Dillinger delivered extraordinary heavy plates with maximum weights of up to 35 t, thicknesses up to 200 mm and enhanced properties in through thickness direction. With extra large-size plates, the number of components of the swing ring and the welding costs are minimized.

The Gulf of Mexico is an important area for oil production. To tap the oil reserves at depths of up to 10 km under the sea heavy barges are required to erect platforms and dismantle the platforms later. The barges lay miles of pipelines for oil and gas. A new field of application: Installation of foundations and towers for offshore wind - energy.

The OSA Goliath, one of the largest heavy lift vessels worldwide, is equipped with a heavy lift crane, type MTC 78000. The maritime unit of Liebherr fabricated this offshore crane in Rostock. The classification number 78,000 stands for the maximum dynamic moment of the crane. This is the lifted weight in tons multiplied by the radius in meters multiplied by the so-called impact factor. The maximum load capacity of the crane amounts to 1,600 t: 4 empty ICE-3 trains. Even with a maximum radius of 74 metres for the main hoist the crane achieves a lifting capacity of almost 530 tonnes.

Dillinger supplied about 1,400 tons of steel. Thereof about 1,200 tons are high-strength heavy plates with minimum yield strength of 690 MPa. Approximately 900 tons of heavy plates where supplied according to project related customer specifications. Extraordinary heavy gage plates with a thickness of 200 mm are needed for the connection of the boom with the hoist of the crane. The huge forces are transmitted from the hoist into the hull via the 145 mm thick slewing platform. This causes stresses in the slewing platform perpendicular to the plate surface. To match this challenge Dillinger delivered plates with enhanced properties in through thickness direction: the so-called z-grade.

Dillinger is one of the few manufacturers of high strength steel who offers these improved properties and the technical capabilities to produce the required thicknesses in the MTC 78000. With a manual welding process more than 100 individual weld seams will be necessary to weld the 145 mm thick plates. Thus, Dillinger supplied the swing ring plates with large dimensions and with maximum weights of up to 35 tons a plate. Advantage: the swing ring could assembled only of a few parts. The number of welds and the welding costs are reduced.