Asset Risk Management of Bulk Materials Handling Equipment
Large materials handling machines such as stackers, reclaimers and shiploaders are typically of welded steel construction balanced by a large counterweight. They are normally capable of long traveling, slewing and luffing motions and must withstand repetitive dynamic loads. Historically, such machines have experienced higher failure rates than other types of structures. The main risks are typically machine collisions, corrosion and structural fatigue cracking. The structural integrity of a machine is dependent on the structural, mechanical, electrical, and control systems operating correctly. The distinguishing feature of mobile equipment for continuous handling of bulk materials is the inherent high level of risk and the very large cost of addressing the failure consequences.
Bulk Materials Handling Machines
The increasing level of coal and mineral exports from Australia has created a strain on existing export facilities and has resulted in the need for expansions to existing facilities and new export facilities. Larger bulk material carrier sizes up to 360,00 DWT are now in service, however many existing ports can only handle vessels up to a maximum of 220,000 DWT. Thus there will be a need for new berths designed for these vessels and continuing pressure on existing terminals to accept larger ships.
Behavior of Steel Ropes
A wire rope consists of many wires twisted to make a complex structure combining axial strength and stiffness with flexibility in bending. Modern ropes offer a wide range of constructions with different levels of helical complexity and wires of different diameters in combinations to achieve an acceptable performance in a wide range of applications.
Mine and port facilities typically have significant investment in structures required for their on-going operations. These are often specialised, highly loaded and exposed to harsh operating conditions, and therefore have higher risks of collapse than ordinary structures. Current Australian legislation and standards do not provide specific guidance on how to manage these risks. This article summarises the general requirements for managing these risks from a number of pieces of legislation and the Australian Standards and gives guidance on how this may be applied in practice.
The increasing level of mineral exports from Australia has resulted in the need for expansions to existing facilities and new export facilities. Rail-mounted materials handling machines such as shiploaders, stackers and reclaimers are significant investment items for the ports and mines involved in the supply chain for export of these commodities. Australia is one of the few countries to have its own standard for such equipment: AS4324.1.
Materials handling equipment for the mining industry has shown failure rates much higher than standard static structures. The equipment comprises large moving structures with onerous load conditions compared to standard building structures. There is a strong need for owners, operators, designers, and manufacturers to adopt a proactive approach throughout the asset lifecycle, including procurement, design, manufacture, installation, and ongoing asset management and maintenance to ensure safe use of the equipment.
Many sites involved in mining and heavy industry own and operate a number of cranes and hoists, which are used to assist maintenance operations. Often these cranes are used infrequently, and a result maintenance and inspection of this equipment can be overlooked. However, a breakdown of one of these cranes, especially during critical maintenance operations can lead to lengthy delays and costly losses of production while the crane is repaired or an alternative found. Statutory compliance can also be important from a legal standpoint. As a result, it is important for owners and operators of these cranes to be aware of the maintenance/inspection requirements for this equipment.
The payload capacity of trucks used in any materials handling operation has a significant effect on the overall materials handling cost per tonne. For an existing facility considering upgrading their mining trucks, the potential benefits of moving higher volumes of material has to be weighed against the possibility that the infrastructure the trucks use may have to be upgraded. Mining trucks today are designed to carry much larger loads and more commonly have a rear dumping action. These are now being used for coal hauling as well as overburden stripping, whereas previously, bottom dump trucks were used for coal hauling.
Trippers are widely used to deliver material from a yard or wharf conveyor to a stacker or shiploader. The design of the tripper should be integrated with the design of the yard or wharf conveyor because the optimum tripper profile depends on the belt tensions. The lift radius of the belt should be calculated at the head and tail ends of the yard conveyor for full, empty, start and stop conditions. Trippers should be profiled with a convex "buffer curve" near the toe to prevent edge buckling of the belt which results in spillage.