Timely inspection and maintenance are essential requirements in maintaining the high Reliability, Availability and Maintainability (RAM) of gas turbine units. The timing of inspections is determined by using the concept of the amount of accumulated operating activities of units between the inspection intervals. In tradition, operating hours and number of startups are used to measure these activities. Indeed, they are two major factors of the activities.

Gas turbines in general run in various duties, environments and operation modes. Under these conditions, it is important to have a well-defined tool and correctly quantified total operating activities of components to plan for timely inspection and refurbishment.

In this paper, the single parameter of Total Equivalent Operating Hours (TEOH) is proposed to be used as a tool to serve the purpose. In developing the TEOH, the linear fraction rule of damage, a theory of interaction fraction rule of damage, a theory of interaction between the creep and fatigue damages is applied to find the equivalent operating hours from the number of startups.

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