Reliability-based maintenance optimization of walking draglines

Gölbaşı, Onur
Dragline is an earthmover extensively utilized in open cast coal mines for overburden stripping activities. Since the machinery breakdowns may induce high amount of production losses, draglines are required to be operated with high availability. In this sense, effective maintenance policies are essential to improve longevity of dragline component and sustainability of operations. In this research study, it is aimed to develop a reliability-based maintenance optimization models for two walking draglines, Page and Marion, currently operated in Tunçbilek coal mine. The study methodology consists of four main phases as: i) characterizing the machinery components via reliability models, ii) implementing a decision platform for preventive replacement of components, iii) generating risk-based maintenance importance models for the machinery components, and iv) developing an optimization algorithm for inspection intervals of the draglines. Component and system characterization was achieved generating deductive reliability models. Preventive component replacement models were created considering preventive and corrective cost factors and investigating applicability of preventive replacements for components. Risk model was developed regarding indirect and direct maintenance costs and maintenance criticality scores were estimated for system elements. Optimization algorithm on inspection intervals was implemented including random lifetime and repair behaviors of components, functional effect of each other during failures, scheduled halts in shifts and regular inspections, and direct and indirect costs of maintenance activities. The results of reliability models revealed that dragging and bucket units were expected to fail most frequently. On the other hand, boom unit was detected to sustain its functionality for the longest time compared to the other units. Moreover, machinery house components generally lead to the longest repairing time and the highest production loss. Considering individual components and their associated structural and functional dependencies, Marion and Page draglines are expected to keep operation going for 34.04 and 35.62 hours without any breakdown, respectively. In addition, optimization algorithm for inspection intervals showed that interval lengths of 184 and 232 hours are economically optimal for Page and Marion, respectively. Maintenance costs of the draglines using these intervals are expected to decrease with 5.9% for Page and 6.2% for Marion. Moreover, risk-based reliability allocation models showed that reliability improvement in motor, generator, rotation, and walking had the greatest impact on overall system reliability considering failure frequencies and their consequences. It was revealed from the risk model that maintenance for these components should be carried out in more controlled and planned manner. This research study provides a new perspective on dragline maintenance. The main novelty and expected industrial contribution of this study is to provide a new inspection optimization model and implementation of risk factors to identify draglines’ component maintenance criticality considering reliability allocation which has not been considered previously in literature.