Case study: Evaluation of L-1 Steeple Repair Strategy 

Stage: L-1 stage in a base load LP steam turbine

Issue: Crack indications have been found in the L‐1 steeples with axial curved entry blade roots 

Objectives: FEA analyses to evaluate the stresses resulting from modifications by grinding out cracks in the steeple grooves

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Background

  • Crack indications have been found in the L‐1 steeples with axial curved entry blade roots.

  • Modifications by grinding out cracks with different profiles were proposed.

  • FEA was performed to evaluate the impact on stresses and associated risk as a result of modification to repair the damage steeple.

Summary of Analyses

  • FEA analysis shows that steady stresses in the original and modified L-1 steeples are NOT excessive to pose a significant threat to the structure integrity under a base load operation.

  • Cracking might be associated with corrosion assisted fatigue.  

  • The proposed modifications were studied and optimal configuration was recommended.

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