Case study: Design Evaluation of a L-0 Blade

Stage: L-0 stage in a combined cycle LP steam turbine

Issue: Blade failure with the crack initiated at the trailing edge near hub 

Objectives: Design evaluation and root cause analysis using FEA

Diagnosis: Water droplet erosion under partial load operation



  • A L-0 blade failure occurred during an over-speed and trip operation.  Numerous L-0 blades experienced similar cracking on the airfoil trailing edge.

  • Finite element analysis (FEA) was used to examine the structure characteristics, such as frequencies, steady and dynamic stresses.

  • FEA was also applied to perform a fracture mechanics analysis to predict the critical crack size under different operating speeds.

  • Computational fluid dynamics (CFD) was employed to study the effect of load conditions on the flow patterns and its association with erosion.   

Summary of Analyses

  • The analytical results and metallurgical evidence both support a scenario where sustained and significant erosion first weakened the material and introduced stress risers along the trailing edge.

  • The initial cracks were then propagated by HCF (high cycle fatigue) most likely induced by a resonant or near resonant condition of a lower fundamental mode vibration.

  • CFD simulation identified that flow re-circulation occurring approximate to the trailing edge was the potential source for TE erosion.

  • Recommendations include: 1) Limiting number of partial load operations to prevent droplet erosion on trailing edge; 2) Blending damaged trailing edge.

  • The predicted critical crack size appears to be consistent with the crack dimension observed from the metallurgical examination. 

This site was designed with the
website builder. Create your website today.
Start Now