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Research Papers: Gas Turbines: Structures and Dynamics

Numerical Investigation of Creep–Fatigue Behavior in a Steam Turbine Inlet Valve Under Cyclic Thermomechanical Loading

[+] 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 Research Institute,
Shanghai Jiao Tong University,
Shanghai 200240, China
e-mail: wangwz0214@sjtu.edu.cn

Sihua Xu

Shanghai Electric Power Generation
Equipment Co., Ltd.,
Shanghai 200240, China
e-mail: xush@shanghai-electric.com

Yingzheng Liu

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

1Corresponding author.

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received November 29, 2016; final manuscript received May 1, 2017; published online June 21, 2017. Assoc. Editor: David Sanchez.

J. Eng. Gas Turbines Power 139(11), 112502 (Jun 21, 2017) (15 pages) Paper No: GTP-16-1554; doi: 10.1115/1.4036953 History: Received November 29, 2016; Revised May 01, 2017

The aim of this study was to investigate the cyclic creep–fatigue interaction behavior in a steam turbine inlet valve under cyclic thermomechanical loading conditions. Three years and nine iterations of idealized startup–steady-state operation–shutdown process were chosen. The Ramberg–Osgood model, the Norton–Bailey law, and continuum damage mechanics were applied to describe the stress–strain behavior and calculate the damage. The strength of the steam valve revealed that significant stress variation mainly occurred at the joint parts between the valve diffuser and the adjust valve body, due to the combination of the enhanced turbulent flow and assembly force at these areas. The contact stress at the region of component assembly was sensitive to the cyclic loading at the initial iterations. The maximum decrease amplitude in the normalized contact stress between the second and the fourth iterations reached 0.12. The damage analysis disclosed that the notch of the deflector in the adjust valve had the maximum damage due to the stress concentration.

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Figures

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Fig. 1

(a) Steam flow path, (b) structure of the valve, and (c) mesh and displacement constraints

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Fig. 2

(a) Startup phase, (b) steady-state operation phase, (c) shutdown phase (quick close), and (d) shutdown phase (natural cooling)

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Fig. 3

(a) Stress distribution in the valve and (b) variation of the normalized stress at the chosen location during a startup phase

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Fig. 4

Temperature field in the valve at different time points during a startup phase: (a) 0.13 h, (b) 0.59 h, (c) 1.42 h, (d) 1.7 h, (e) 6.5 h, and (f) 12 h

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Fig. 5

C–A distribution

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Fig. 6

(a) Variation of normalized von Mises stresses in a whole phases at chosen locations A/B/C and (b) at chosen locations D/E (σvM,nom=σvM/σvM,max, σvM,max is the maximum von Mises stress in the steam valve during the whole iterations)

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Fig. 7

Variation of normalized von Mises stresses at chosen locations A/B/C/D/E during (a) the shutdown phase within the first iteration, (b) the startup phase within the second iteration, (c) the shutdown phase within the seventh iteration, and (d) the startup phase within the eighth iteration (σvM,nom=σvM/σvM,max, σvM,max is the maximum von Mises stress in the steam valve during the whole iterations)

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Fig. 8

Variation of normalized von Mises stresses in a whole phases at chosen locations F/G/H (σvM,nom=σvM/σvM,max, σvM,max is the maximum von Mises stress in the steam valve during the whole iterations)

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Fig. 9

Variation of normalized von Mises stresses at chosen locations F/G/H during (a) the shutdown phase within the first iteration, (b) the startup phase within the second iteration, (c) the shutdown phase within the seventh iteration, and (d) the startup phase within the eighth iteration (σvM,nom=σvM/σvM,max, σvM,max is the maximum von Mises stress in the steam valve during the whole iterations)

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Fig. 10

At the chosen location C: comparison of the normalized von Mises stresses among the second, fourth, sixth, and eighth (a) shutdown phases, (b) zoomed shutdown phases, (c) startup phases, and (d) zoomed startup phases (σvM,nom=σvM/σvM,max, σvM,max is the maximum von Mises stress in the steam valve during the whole iterations)

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Fig. 11

At the chosen location D: comparison of the normalized von Mises stresses among the second, fourth, sixth, and eighth (a) shutdown phases, (b) zoomed shutdown phases, (c) startup phases, and (d) zoomed startup phases (σvM,nom=σvM/σvM,max, σvM,max is the maximum von Mises stress in the steam valve during the whole iterations)

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Fig. 12

At the chosen location E: comparison of the normalized von Mises stresses among the second, fourth, sixth, and eighth (a) shutdown phases, (b) zoomed shutdown phases, (c) startup phases, and (d) zoomed startup phases (σvM,nom=σvM/σvM,max, σvM,max is the maximum von Mises stress in the steam valve during the whole iterations)

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Fig. 13

At the chosen location H: comparison of the normalized von Mises stresses among the second, fourth, sixth, and eighth (a) shutdown phases, (b) zoomed shutdown phases, (c) startup phases, and (d) zoomed startup phases (σvM,nom=σvM/σvM,max, σvM,max is the maximum von Mises stress in the steam valve during the whole iterations)

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Fig. 14

Variation of normalized contact stresses at chosen three locations: v_p1, v_p2, and v_p3 (σcta,nom=σcta/σcat,max, σcta,max is the maximum contact stress at the valve seat during the whole iterations)

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Fig. 15

Variation of normalized contact stresses at chosen locations v_p1/v_p2/v_p3 during (a) the shutdown phase withinthe first iteration, (b) the startup phase within the seconditeration, (c) the shutdown phase within the seventh iteration, and (d) the startup phase within the eighth iteration (σcta,nom=σcta/σcat,max, σcta,max is the maximum contact stress at the valve seat during the whole iterations)

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Fig. 16

Variation of normalized contact stresses at chosen three locations: Df_p1, Df_p2, and Df_p3 (σcta,nom=σcta/σcat,max, σcta,max is the maximum contact stress at the contact regions between the diffuser and the steam valve during the whole iterations)

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Fig. 17

Variation of normalized contact stresses at chosen locations Df_p1/Df_p2/Df_p3 during (a) the shutdown phase within the first iteration, (b) the startup phase within the seconditeration, (c) the shutdown phase within the seventh iteration, and (d) the startup phase within the eighth iteration (σcta,nom=σcta/σcat,max, σcta,max is the maximum contact stress at the contact regions between the diffuser and the steam valve during the whole iterations)

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Fig. 18

At the chosen location v_p1: comparison of the normalized contact stresses among the second, fourth, sixth, and eighth (a) shutdown phases, (b) zoomed shutdown phases, (c) startup phases, and (d) zoomed startup phases (σcta,nom=σcta/σcat,max, σcta,max is the maximum contact stress at the contact regions between the diffuser and the steam valve during the whole iterations)

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Fig. 19

At the chosen location v_p3: comparison of the normalized contact stresses among the second, fourth, sixth, and eighth (a) shutdown phases, (b) zoomed shutdown phases, (c) start phases, and (d) zoomed startup phases (σcta,nom=σcta/σcat,max, σcta,max is the maximum contact stress at the contact regions between the diffuser and the steam valve during the whole iterations)

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Fig. 20

Comparison of the normalized contact stresses among the second, fourth, sixth, and eighth (a) shutdown phases and (b) startup phases at the chosen location Df_p1, (c) shutdown phases and (d) startup phases at the chosen location Df_p3 (σcta,nom=σcta/σcat,max, σcta,max is the maximum contact stress at the contact regions between the diffuser and the steam valve during the whole iterations)

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Fig. 21

Temperature distribution in the parts of deflector, adjust valve seat, and diffuser

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Fig. 22

Normalized temperature difference during a (a) startup phase and (b) shutdown phase along the direction at the locations C/H shown in the figure

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Fig. 23

Damage at the locations A/B/C/D/E/F/G/H

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