Fatigue performance of steam turbine blading

Steam turbine is a rotating machine and therefore fatigue is an important damage mechanism to consider already in turbine design, and it is remains necessary to consider the risk of initiation and growth of fatigue cracks in the later in-service inspection and maintenance activities. With successful design and fabrication, and operation within the intended limits, the expected fatigue life is relatively long but nevertheless finite and variable. The design features and materials of steam turbine blades are generally well established, and conventional methods of inspection and maintenance are widely applied to monitor and limit the evolution of in-service damage. As the fatigue performance of a blade is simultaneously sensitive to material characteristics, structural/loading geometry and surface condition, the combined potential range of these factors explains in principle the observed wide scatter in turbine blade life. In this paper, examples on reduced blade life are discussed based on recent experience with a case example.