Comparative vibration analysis and resonance reliability of LP steam turbine blades: a comprehensive study

This study examined a healthy 250 MW LP steam turbine blade (X10CrNiMoV1222) through experimental modal analysis (EMA) and finite element (FE) modelling, with both methods showing strong agreement in natural frequencies and mode shapes validating the FE approach for further analysis. The research then compared five blade materials (X10CrNiMoV1222, X20CrMoV121, 17-4PH, ASTM 410 stainless steel, and Ti-6Al-4V) under two critical scenarios: (1) crack progression (10–90% of the fir tree root top serration) and (2) blade-root contact variations altering fixity conditions (FCs). For all materials, the first ten vibration modes were analysed alongside Campbell diagrams to identify critical speeds. Results revealed that the X20CrMoV121 blade outperformed the other materials tested, as its critical speeds consistently remained outside the rotor's operating range, positioning it as the safest replacement option. Beyond material selection, the study provides practical and actionable insights crucial for industrial application, including guidance for blade installation, detailed procedures for maintenance inspections (such as overhauls and over-speed balancing), and recommendations for frequency tuning. These findings offer engineers the necessary technical basis to enhance overall turbine reliability and effectively mitigate the risk of resonance-related failures.