By Lindsay Gale22 October 2015
Italian contractor Despe carried an unusual demolition project in the Italian port of Taranto, where it deconstructed a harbour unloader crane belonging to ILVA, one of the largest steel production and processing companies in Europe. Having reached the end of its working life, ILVA required that the unit be removed within a tight deadline of 20 days.
Despe proposed dismantling the unloader crane using 750 tonne mobile cranes and hydraulic platforms and then cutting up the metal framework on the ground using excavators equipped with hydraulic shears suitable for processing such metal structures, piping, and small/medium-size equipment.
The DM4 unloader crane was a gantry apparatus consisting of a metal framework, travelling on 20 m (65.6 ft) gauge railway-type tracks. The maximum height of the structures relative to ground level was approximately 50 m (164 ft), while the maximum reach on the sea side was about 46 m (151 ft).
The unloader crane was a complex machine consisting of mechanical components such as gear reducers, winches, steel cables, return and hoist pulleys, etc. In addition, there were electrical components such as electrical panels, power cables, signal cables and instrument cables, and finally, miscellaneous metal structural components and piping for fluids.
Before starting the demolition work, the work-site was established and the area was marked off with suitable mobile metal fences. The locations of the offices, equipment stores, chemical toilets, and fuel depots were defined and all requirements to which they were subjected were fulfilled. The disassembly operations started immediately after the preparations on the site where the material processing was to be carried out following its removal from the main structure was completed.
The dismantling activities were organised in a distinctly designed sequence. First, all "non-structural" accessory frameworks such as conveyor belt frames and hoppers were dissassembled and transported to the work site. Then all the mechanical components of the unloader, such as gear reducers, were similarly removed and transported, with carre being taken to not cause damage to them while also avoiding any potential spills of oil and grease. The components designated for recovery by the ILVA technicians were placed in a suitable area near the unloader crane, and segregated from those designated to be scrapped. Work then moved to the electrical systems and associated panels. Similarly, those being retained were segregated from those to be scrapped.
The final stage of the demolition was the disassembly of the crane’s main structures. This was carried out using 750 tonne capacity mobile cranes, with the assistance of 130 tonne cranes, which were used for accessory and support activities. The various parts to be dismantled were cut up using oxy-propane torches. The operators used both the various levels of the unloader crane and two work platforms 38 and 80 m (125 and 263 ft) in height respectively. A detailed design was prepared for the dismantling activities that defined the parts to be cut off and the disassembly sequence, the weight of the various structures, the strapping methods and the sectioning points.
The material placed at the worksite was then cut into pieces of "furnace-ready" size, using an excavator fitted with hydraulic shears, or by manual cutting with oxy-propane torches in the case of the thicker parts.
A scaffolding was built prior to commencing the dismantling activities, with a protection guard for the belts connecting the unloader crane to be dismantled with those still in operation. During the hot-cutting operations, the various structures were protected with fire-resistant fabric near the cutting points. In addition, a fire-fighting team was always present during the hot-cutting operations.
The challenge in the removal of the unloading crane related both to the limited time available for disassembly and also the limited space available to place the parts of the unloader crane as they were removed.
The customer required that the disassembly of the DM4 unloader crane, meaning the removal of the 1,300 tonne machine from the track, be carried out in about 20 calendar days (to be specific, it was carried out between 27/05/2014 and 16/07/2014). The waste material was then to be cut into furnace-ready size pieces and removed to the various recovery plants by 31/07/2014.
It was necessary to schedule and design the disassembly sequence in a way that optimised the capacity of the mobile crane and reduced the cutting points to a minimum. The parts placed at the site had to be processed appropriately: the parts to be recovered had to be segregated and those to be scrapped had to be cut to furnace-ready size. At the same time, the parts to be recovered had to be transported to ILVA storage areas and the parts to be scrapped to disposal plants, all this fast enough to free the space at the site to allow dismantling another portion of the crane. To prevent any congestion on site that could potential slow down or even bring a halt to disassembly activities, it was necessary to prepare an area (about 800 m away) where the parts were cut to furnace-ready size; large dismantled portions could be transported to this area by trucks.