Failure Investigation and Crack Propagation Analysis of LP Blade Steam Turbine 220 MW

Abstract:

The cracked blade in L-0, L-1 governor side, and L-1 generator side were found when A 220 MW low-pressure steam turbine was checked in the serious inspection. However, the crack population more dominant at L-1 Gen compared to L-0 Gov and L-1 Gov. Most of the cracks were located on 300-400 mm from the root of the blade span, and it did not associate with the pitting defect. In this study, the root cause of L-1 blade failure was investigated. There is three-stage of analyzing process, firstly capturing the airfoil and dimension of L-1—secondly, the material properties analysis, and finally stress analysis of L-1 by the finite element analysis software. L-1 is the blade with the chord length on the tip L-1 blade longer than root as 2.1% and the angle of an airfoil from root to tip twisted as 24 degrees. The type of material did not look precisely similar to AISI 422 because its hardness-strength is lower than AISI 422 as 5.1%. The finite element analysis shows that there was a symptom of the imprecise shroud gap that promoted maximum stress at 300-400 mm from the root area of the L-1 blade span. Moreover, a lack of hardness-strength material cannot accommodate the excessive movement of the blade and promoted the initial crack of L-1. A crack length blade as 16 mm shows a lower number of cyclic (N_f) to failure tremendously compared to standard blades such as 32,367 of the number cyclic for regular blade and 42.6 for the crack blade. Increasing 2 mm of initial crack will decrease significantly the number of cyclic N_f of the blade. It was tearing mode crack propagation of L-1 results a significant stress intensity factor compared to other modes, especially at 16 mm length of the crack.

• Periodical: Key Engineering Materials (Volume 876)
• Pages: 67-76
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.876.67
• Online since: February 2021
• Authors: Natalina Damanik*, Hendery Dahlan
• Keywords: Cracks, LP Blade, Number of Cyclic, SIF, Stress Analysis

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