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Research Papers: Gas Turbines: Structures and Dynamics

Comparative Study of Flange-to-Seal Contact Couplings With Bolt Relaxation Under Creep Condition

[+] Author and Article Information
Jianfeng Mao

Key Lab of Education Ministry
for Power Machinery and Engineering,
School of Mechanical Engineering,
Shanghai Jiao Tong University,
Shanghai 200240, China
College of Mechanical Engineering,
Zhejian University of Techology,
Hangzhou 310014, China
e-mail: jianfeng-mao@163.com

Weizhe Wang

Key Lab of Education Ministry
for Power Machinery and Engineering,
School of Mechanical 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

Yingzheng Liu

Key Lab of Education Ministry
for Power Machinery and Engineering,
School of Mechanical 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

Junhui Zhang

Design & Research Institute,
Shanghai Electric Power
Generation Equipment Co., Ltd.,
Shanghai 200240, China
e-mail: zhangjh3@shanghai-electric.com

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 January 9, 2014; final manuscript received January 13, 2014; published online February 27, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 136(7), 072504 (Feb 27, 2014) (8 pages) Paper No: GTP-14-1013; doi: 10.1115/1.4026656 History: Received January 09, 2014; Revised January 13, 2014

Future coal-fired steam turbines promise increased efficiency and low emissions. However, this comes at the expense of increased thermal load from higher inlet steam temperatures and pressures leading to severe creep that significantly influences the sealing behavior and high temperature strength of bolted flange-seal couplings. Flanges with different thicknesses were employed for a comparative study. The important stress/creep values in the flanges and U-type seals had been obtained for variations in flange thickness and bolt relaxation while maintaining other leading parameters constant. The variation of contact stresses due to creep deformation plays an important role in achieving a leak proof sealing. In this paper, a two-dimensional finite element analysis of bolted flange-seal couplings has been carried out by taking the relaxation of bolt stress under full-loading turbine service. The creep strength of flanges and U-type seals are investigated by Cocks–Ashby (C–A) equivalent strain method. The multiaxial state of stresses is considered in this method by using C–A multiaxial coefficient. According to ASME allowable creep limit, the C–A equivalent strains of three flange-seal couplings are evaluated and compared. Furthermore, based on the results of contact stresses, the creep behavior of U-type seals is analyzed varying flange thickness. Finally, analysis shows that the thinner flange-seal coupling has larger long-term contact stress, while the U-type seal with the thicker flange has the least creep strength.

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References

Figures

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Fig. 1

Finite element mesh and assembly profile of flange-seal coupling

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Fig. 2

The relaxation curve of bolt stress

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Fig. 3

Distribution of contact stress with varying the creep time under max. thickness flange: (a) with bolt relaxation; (b) without bolt relaxation

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Fig. 4

Distribution of contact stress varying with increasing creep time under mid. thickness flange: (a) with bolt relaxation; (b) without bolt relaxation

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Fig. 5

Distribution of contact stress varying with increasing creep time under min. thickness flange: (a) with bolt relaxation; (b) without bolt relaxation

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Fig. 6

Variation of contact stresses at different key locations during creep time under three thickness flanges

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Fig. 7

The comparison of contraction quantities of U-type seals under different thickness flanges

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Fig. 8

(a) Temperature and (b) von Mises stress distributions of different thickness flanges at initial creep stage

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Fig. 9

(a) Temperature and (b) von Mises stress distributions of the U ring under different thickness flanges at initial creep stage

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Fig. 10

The multiaxial factor FCA varies with creep time

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Fig. 11

(a) Multiaxial coefficient; (b) C–A equivalent strain plot for different thickness flanges at 0.2 106 creep hours

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Fig. 12

(a) Multiaxial coefficient; (b) C–A equivalent strain plot for U ring with bolt relaxation under different thickness flanges at 0.2 106 creep hours

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