For large gas turbine new make or standard customer value program always aims for higher power and efficiency which calls for an incremental stage loading in terms of higher gas pressure and temperatures distributions for the new upgrade with less ownership costs. To bring down the ownership cost without compromising on the performance or operating hours it becomes important to squeeze and optimize the current design to its maximum limits. This leads to a situation where existing static components fails to meet the MI Strength and Lifing requirements due to change in pressure and temperature.

This paper describes the design challenges and the applied mitigations in the design optimizations of aft stage Ring Segment Hooks and Rails to meet requirements for higher loads at higher performance.

Several sensitivity studies were carried out and transfer functions were developed to bring down the hook loads and hook stresses for steady state max temperature and pressure conditions. Two strategies were adopted to optimize the hook loads. The first is to find the adequate gap between hook and slot and the other one is to vary the hook stiffness by changing the circumferential length.

This paper also presents a systematic approach and check points to decide the optimum gaps and the stiffness of the hooks. For that purpose, a co-relation was developed between hook load and hook to slot gap and the hook circumferential length and hook stiffness.

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