Best-in-class maintenance benchmarks in Chilean open pit mines
In 2001, the Catholic University of Chile undertook a maintenance benchmarking study of six open pit copper mines having mill capacities varying between 18,000 t/d and 156,000 t/d, and collectively responsible for 58% of Chilean copper production. Key performance indices were selected to measure the effectiveness, efficiency, and development of the maintenance process.
Key effectiveness indices used in the mining industry are equipment availability, reliability, and maintainability and safety indices. Reliability is often measured by mean time between failures (MTBF) and maintainability as the mean time to repair or restore service (MTTR). At the time of undertaking the benchmarking study (2001), only two of the six participating mines routinely measured these parameters. For this reason, the study focused on comparing fleet availabilities. Accident rate and accident severity (expressed as the number of lost time incidents and lost time hours per million man hours, respectively) were solicited for all permanent and contracted maintenance personnel.
Financial data provided by the participating companies included total annual maintenance and mining costs, as well as a breakdown of labour, materials, and contractor costs. This data, when combined with ore and waste production data, enabled the unit costs of maintenance to be calculated.
Internal efficiency indicators were solicited for:
the percentage of planned maintenance (preventive, predictive, and programmed major component replacement) carried out on each equipment fleet (blasthole drills, hydraulic and cable shovels, wheel loaders, haul trucks, and auxiliary equipment);
scheduled maintenance compliance (actual planned hours versus scheduled planned hours);
organizational efficiency in terms of the ratio of supervisors to maintenance technicians;
investment in maintenance planning as evident from the ratio of planners to maintenance technicians (planning clerks and statisticians were also considered to be maintenance planners); and
efficiency in inventory practices as evident from the stores turnover ratio and service level.
Development indices were solicited for the educational level of maintenance employees and the level of commitment to maintenance training by both the companies and their collaborators, in terms of annual training hours and investment per employee.
The principal conclusions of the study were as follows:
For the six open pit mines that participated in the study, maintenance costs were found to average 44% of mining costs. This highlights the importance of the direct cost of maintenance to the financial performance of mines.
Percentage planned maintenance of equipment fleets were low by world standards, averaging 35%, 56%, and 44%, respectively, for blasthole drill, shovel, and haul truck fleets.
Fleet availabilities were significantly influenced by the percentage of planned maintenance achieved. For example, haul truck fleet availabilities were found to increase on average by 1% for every 4% increase in planned maintenance over the range examined.
Maintenance cost per equipment was found to decrease non-linearly with increases in percentage planned maintenance. An empirical relationship was determined that can be used to estimate potential cost savings as a result of improved planned maintenance practices (see figure).
The ratio of maintenance planning staff to maintenance technicians varied between 1:10 and 1:24, indicating improvement opportunities for some of the participating companies. Investment in technical training (including planned maintenance practice) was found to be low by global industry standards.
It was concluded that fleet availability and maintenance costs in Chilean open pit operations could be considerably improved by improving and/or developing maintenance planning standards, and training personnel in planned maintenance techniques.