ABSTRACT
Time-directed maintenance (TDM) enables an organization to exchange lost opportunity and intangible costs of an unscheduled system downing event with maintenance costs to replace an unfailed part.
Time-directed maintenance uses the hazard function of part failure to determine when a part is replaced based on the organization’s definition of allowable risk. Part replacement occurs when the part has been exposed to a load that approaches or exceeds the likelihood of failure based on interference theory. There are no condition indicators, as are used in condition-based maintenance (CBM). No part is risk free and parts will fail at different instantaneous failure rates under different operating and operational conditions of use. The part mean time between failure (MTBF) is of little economical value for TDM replacement intervals. The part hazard function is characterized from the reliability-centered maintenance (RCM) failure analysis and describes the behavior of part failure resulting from loads and operational and ambient conditions of use that are specific to the system.
