The tie-lugs on a 46” last stage blade (LSB) operated in a power plant first commissioned in the early 1960s experienced a long service history of cracking problems. A root cause investigation was performed, which identified the third mode of the bladed disc as operating near resonance. The original configuration is a 4-blade group structure with two tie-lugs. The third mode is a group torsional mode in which maximum stress occurs in the outer lugs. Dynamic stress throughout the rotating stage was calculated using a FE model. Based on the results of the investigation features of a retrofit were identified to detune the resonant mode and change the brazed lug to a more reliable forged design. A probabilistic analysis was used to demonstrate how the risk of cracking problem would be dramatically reduced.
Risk Assessment of an L-0 Stage Blade Retrofit
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Lam, TC, Shuster, LH, & Dewey, RP. "Risk Assessment of an L-0 Stage Blade Retrofit." Proceedings of the ASME 2004 Power Conference. ASME 2004 Power Conference. Baltimore, Maryland, USA. March 30–April 1, 2004. pp. 269-277. ASME. https://doi.org/10.1115/POWER2004-52058
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