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Research Papers: Gas Turbines: Turbomachinery

Numerical Analysis of Fatigue Life Improvement by Optimizing the Startup Phase for a 1000 MW Supercritical Steam Turbine Inner Casing

[+] Author and Article Information
Weizhe Wang

Key Lab of Education Ministry for Power
Machinery and Engineering,
Shanghai Jiao Tong University,
Shanghai 200240, China
Gas Turbine Institute,
Shanghai Jiao Tong University,
Shanghai 200240, China
e-mail: wangwz0214@sjtu.edu.cn

1Corresponding author.

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received May 3, 2014; final manuscript received June 15, 2014; published online October 28, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(4), 042601 (Oct 28, 2014) (10 pages) Paper No: GTP-14-1219; doi: 10.1115/1.4028614 History: Received May 03, 2014; Revised June 15, 2014

The fatigue behavior of a specific inner casing of a 1000 MW supercritical steam turbine was investigated during a complete startup phase. The Ramberg–Osgood model and Manson–Coffin strain-life law were used to describe the stress–strain behavior and calculate the damage. The temperature variation during the startup phase revealed that the startup phase could be divided into a warming-up phase, transition phase, and elevated temperature phase. The thermal stress that dominated in the inner casing could also be divided into the same three phases. The damage caused by the alternating stress during the warming-up phase was around 70% of the total damage. The remaining 30% of the damage was contributed by the transition and elevated temperature phases. The fatigue life was improved by shortening the warming-up phase and extending the elevated temperature phase. The damage was reduced by approximately 20%.

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Figures

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Fig. 1

The inner casing's (a) geometry, (b) mesh model, and (c) constraint condition

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Fig. 2

The normalized startup curve: t, time

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Fig. 3

The temperature distribution at different times during the complete startup phase

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Fig. 4

The locations for investigating the temperature difference

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Fig. 5

Variations in the temperature difference during the complete startup phase at (a) Loc 1, (b) Loc 2, (c) Loc 3, and (d) Loc 4: ΔT, temperature difference; t, time

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Fig. 6

The stress distribution at different times during the complete startup phase: S, stress

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Fig. 7

The stress and temperature distributions in the cross-section region at different times during the complete startup phase: S, stress; t, time

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Fig. 8

The five chosen locations

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Fig. 9

The stress variations at the five locations during the complete startup phase: σ, stress; t, time

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Fig. 10

The strain variations at the five locations during the complete startup phase: ɛ, strain; t, time

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Fig. 11

The damage distribution at the cross section of the steam inlet region

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Fig. 12

The difference in the damage at the five locations during the complete startup phase: D, fatigue damage; t, time

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Fig. 13

Improving the startup phase—(a) a description of the strain variation and (b) a comparison of the original and optimal startup curves: ɛ, strain; t, time

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Fig. 14

A comparison of the strain variations at the five locations during the original and optimal startup phases: ɛ, strain; t, time

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Fig. 15

A comparison of the difference in the damage at the five locations during the original and optimal startup phases: D, fatigue damage; t, time

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