C8-C11 Holistic Design Review
• Purpose - To provide an update of the Holistic Design Review of C8-C11 turbines.
• No Board action is being requested.
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Last Update – Sept. 2014
• Holistic Design Review
– Anticipated completion Nov. 2014
• 1st Unit Outage Start – June 2015
• Project Budget: $42- $44 Million
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Holistic Design Review
• Objective
– To evaluate the stresses and fatigue lives of the major components of the turbine.
• Why
– To maximize the remaining life of the complete turbine. Are there other components that could fail sooner than expected?
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Holistic Design Review • Why
– Stress and fatigue calculations only performed for the turbine blades and hub by the manufacturer.
– Multiple components from C10 appeared to have been overstressed (piston rod, headcover, blade bushings, cylinder spider).
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Holistic Design
• Finite Element Stress Analysis (FEA)
– An engineering calculation used to determine stresses in the individual components at various operating conditions. The calculated stress is compared to a safe allowable stress.
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Holistic Design
• Fatigue Analysis
– An engineering calculation used to evaluate the components undergoing cyclical loading and to determine when a crack will start (fatigue life-years). Goal is to achieve a minimum of 30 years of additional service.
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Holistic Design
• Fracture Analysis
– An engineering calculation used to determine the time until a component undergoing cyclical loading will fail after a flaw (0.080” crack) has already started. Goal is to achieve a minimum of 30 years of additional service.
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Green components – Stress and fatigue life met criteria. Red components did not meet stress or fatigue life criteria.
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Blue Components – Engineering evaluation is complete. Red Components – Engineering evaluation is ongoing.
Summary
• Additional FEA and Fatigue evaluation required for:
– Turbine shaft
– Wicket gates
– Piston rod
– Servomotor eye bolts
• Estimated Engineering Cost - $350k
• Anticipated Completion – Late May 2015
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Potential additional Costs
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– Modify Turbine Shaft, $320k for 4 units.
– Modify existing Wicket gates, $400k for 4 units; or
New wicket gates,
$3 Million for 4 units.
Potential Extra Costs
– Modify Link Pins $10k for 4 units.
– New Servomotor Eye Bolts $500k for 4 units.
– New Cylinder spider cover bolts $30k for 4 units.
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Total cost: range $1.6 M to $4.2 Million
Summary
1st Unit Outage Schedule Impact
• None expected for:
– Turbine shaft
– Wicket gates
– Servomotor eye bolts
• Uncertain:
– Piston rod (know more in May)
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Conclusion
Sept. 2014 Update
• Holistic Design Review – Anticipated completion
Nov. 2014.
March 2015 Update
• Holistic Design Review – Original scope completed
Jan. 2015.
– Additional analysis anticipated to be complete by May 2015.
• Required Budget (4 Units) – $43.6 to $48.2 Million
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• Current project Budget (4 Units) – $42 to 44 Million
C8-C11 Turbine Repairs O&M Improvement Items
• Considering New Blade Trunnion Seal Design
– Reduces risk of oil leak.
– Estimated Cost: $670k for 4 units
• Relocate Hub oil vent plug – Est. $80k, 4 units
• Redesigned Blade Dowel Plugs – Est. $60k, 4 units
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