Case study: Creep Analysis for a Blade with Cover Lifting
Stage: Stages 10 in a reheated IP steam turbine
Issue: Severe cover lifting found, and potentially caused by creep damage as suggested by OEM
Objectives: FEA creep analysis to assist operator to understand the underlying mechanism and evaluate the modification
proposed by OEM
Diagnosis: Creep at the juncture between cover and tenon leads to cover lifting
Solution: New cover design verified by analysis
Issue of cover lifting on 8th to 11th stages of IP turbine was encountered. The 10th stage experienced the most severe cover lifting among all stages.
OEM believed that creep was involved.
TTI was solicited to perform a FEA creep analysis to identify the root cause of cover lifting.
An important goal of the study was to assess the control value or allowable limit specified by OEM.
Another objective was to evaluate the cover band modification proposed by OEM.
Summary of Analyses
Results from FEA analysis confirm root cause of the cover lifting in multiple stages of IP turbine is principally due to elevated temperature creep in conjunction with appreciable localized stress.
FEA analysis establishes the relationship between creep damage at critical locations and the amount of cover lifting.
Improvement of new cover design proposed by OEM is verified by FEA calculations in comparison against the current cover design.