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Fatigue and Creep Interaction in Steam Turbine Bladed Disk

Suhas B, A R Anwar Khan

A steam turbine rotating system is loaded with time by the changes in stress levels as a result of start-up and shutdown procedures.Many of the most serious damage mechanisms in blades occur in the phase transition zone (PTZ) This region typically starts in low pressure (LP) turbines and fails typically because of low cycle fatigue and creep. The purpose of this paper is to investigate the low cycle fatigue failure of low pressure steam turbine blade, particularly near PTZ. The present work is primarily focused developing a technique to assess low cycle fatigue life of the blade and to determine the number of startups and shutdown cycles. Two approaches were employed. First approach is based on the elastic finite element (FE) analysis. Second approach is based on elastic-plastic FE analysis. Strain amplitude is determined directly from the FE analysis and fatigue life is assessed Morrow’s equation. Creep life due to strainhardening is also assessed by using creep laws.