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| Crane Design Life Issues | ||
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There are various clauses within the Provision and Use OF Work Equipment Regulations 1998 (PUWER) and Lifting Operations and Lifting Equipment Regulations 1998 (LOLER) which give guidance to manufacturers on how they should be looking after various items of plant both from a maintenance and statutory inspection position. Clauses that are particularly relate to design life issues and inspections are attached for clarity. As an example Clause 103 from PUWER indicates that the equipment must be suitable for its intended use ‘by design’, this would included its original ‘design life’ which is related to the total number of operating cycles the structure and mechanisms have been designed to undertake. During the initial design phase of a crane, to establish an intended ‘Design Life’ for the equipment, the designers collect various data. The purchaser is requested to supply detailed information on the number of expected operations and the individual loads to be carried at each stage of the operations. If detailed information cannot be provided then guidance is given in the appropriate British Standards (BS466:1984, BS2573 Parts 1 &2:1983). This guidance indicates a range of classifications for different types of cranes. For Electric Overhead Travelling (EOT) cranes this would be BS466 Tables 5 to 16. The crane structure and mechanisms will be designed with sufficient robustness to perform the estimated number of Operating Cycles. An operating cycle is defined as when the crane first lifts a load until the load is set down and the crane is ready to take up the next load. Each operating cycle can potentially include many fatigue cycles as the structure and mechanisms are stressed during initial load take up, followed by stress changes as long or cross travel is undertaken and braking is introduced. Fatigue cycles are also introduced when the crane is in motion with no load at the hook. The crane structure would be designed to withstand these fatigue cycles, generated during construction, testing and operation of the crane during its total design life. For detailed information on the design of the mechanisms BS466 refers out to BS2573-2. As an example consider that a crane was designed for ‘Light Workshop Duty’, the mechanisms are most likely to have been designed as T3 items. This gives an intended service life of 1600 hours for each motion. Within BS2573-2 indication is given that, for gearing in particular, expected daily use is 0.8 hours for a T3 mechanism. If the service life (1600hrs) is divided by the designed daily use (0.8hrs) the resulting number of days use is 2000. In the example above if the crane was installed in 1977, then by 2004 it would be 27 years old. From the results above, if the age of the crane (27yrs) is divided into the number of available days (2000days) the result is the number of available days each year (74dys) at 0.8 hours use each of those days. If the actual usage is higher than this then the crane is operating beyond its design life. To comply with the requirements of PUWER & LOLER appropriate maintenance, inspections and surveys are required to ensure that deterioration does not effect the safe use of the lifting equipment. As an owner of the crane the company has a ”duty of care” to make certain the equipment is operating within its design intent. In addition an annual statutory inspection is required by an accredited organisation such as Royal Sun Alliance. As there are in the majority of cases, no structural maintenance undertaken on most cranes or their support structure, there is a risk of potential faults, which could compromise the safety of the lifting equipment. In addition to fatigue, which causes sudden failure, the wear of the interfaces of moving parts can restrict the life of a crane. In the case of toothed gear wheels when the fit becomes loose then slipping can become a potential problem. Examples of structural/mechanism fatigue/environmental issues on old cranes are: Brake caliper fracture Structural bolt replacement on portal and tower Racking Gearbox failure following vibration testing. Bolt replacement on crane rails. Drive gear train fracture on travel bogie. End carriage buffer protection dropping off crane. Notes. In the attached sheets we have highlighted in the statutory regulations associated with LOLER and PUWER where reference is specifically related to design & fatigue issues. Download LOLER and PUWER Specific Regulations / Clauses by right clicking the following link and selecting 'save target as'. |
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