The balance between safety and economic requirements is becoming more and more important with the turbine age. The main criteria for an efficient operation are a high life endurance and high availability. The latter is restricted by periodic inspections of the most loaded components, whereby at the same time, these inspections are very important to guarantee a safe operation, e.g. by early identification of damage or cracks. The remaining life of the turbine components, as well as the frequency of the periodic inspections, are generally determined by mechanical calculations which take the prevailing damage processes and the possible mechanisms of sudden failure into account. In this way it is evident that a design life extension and longer intervals between inspections and overhauls might be possible under some circumstances (based on the modern NDE techniques) due to application of advanced non-linear computational methods such as elasto-plastic fracture mechanics (J-Integral approach) and creep crack initiation and propagation assessment (C{sup}* approach) in the frame of finite-element analysis. Some field examples show the applicability of the advanced assessment methods.
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