Maintainability reliability analysis of a fleet of shovels

Technological development has enabled the mining industry to deploy more complex and capital-intensive equipment to increase productivity, but inefficient operation and deficient maintenance often prevent utilization of its full capacity. Interest in the maintenance and operational reliability of all capital-intensive equipment has been stimulated by the current emphasis on reducing production costs. The failure and repair patterns of a fleet of four 10-m3 electric rope shovels were analysed statistically to ascertain their reliability and maintainability characteristic. Different subsystems and the types of failures in each subsystem were coded so that the failure and repair data of each subsystem could be collected and sorted and the faults therein classified separately. Common graphical tools, e.g. trend and serial correlation tests, were used to validate the assumption of independent and identically distributed failure/repair data for each subsystem before they were fitted with theoretical probability distributions. Chi-squared and K-S tests were carried out with the aid of Statgraphics software to select the best-fit distribution. For most subsystems Weibull and lognormal distributions were found to give the best fit to the failure and repair data, respectively. The reliability and maintainability characteristics of the different subsystems of the shovel and of the shovel as a whole were calculated on the basis of the best-fit distribution. Analysis of the total downtime, breakdown frequency, reliability and maintainability characteristics of different subsystems and the faults in these identified dipper and electrical subsystems as weak links in the chain of subsystems. It was found that the reliability of all four shovels dropped below 50% after 24 h of working and that 25-50% of the total number of failures usually required less time to repair. The analysis of the failure patterns for all four shovels together was employed to calculate maintenance intervals different values of reliability. These intervals were used to schedule preventive maintenance, i.e. inspection, repair, servicing or replacement, and modify inspection frequencies with reference to safety considerations, cost-effectiveness and the nature of the fault. As expected, this has resulted in a reduction of the total downtime of the shovels