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Research Papers: Materials and Fabrication

The Revised Universal Slope Method to Predict the Low-Cycle Fatigue Lives of Elbow and Tee Pipes

[+] Author and Article Information
Hiun Nagamori

Graduate School of Engineering,
Yokohama National University,
79-5, Tokiwadai, Hodogaya,
Yokohama 240-8501, Japan
e-mail: nagamori-hiun-xk@ynu.jp

Koji Takahashi

Professor
Faculty of Engineering,
Yokohama National University,
79-5, Tokiwadai, Hodogaya,
Yokohama 240-8501, Japan
e-mail: takahashi-koji-ph@ynu.ac.jp

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the JOURNAL OF PRESSURE VESSEL TECHNOLOGY. Manuscript received February 7, 2017; final manuscript received June 3, 2017; published online August 2, 2017. Assoc. Editor: Kunio Hasegawa.

J. Pressure Vessel Technol 139(5), 051402 (Aug 02, 2017) (9 pages) Paper No: PVT-17-1024; doi: 10.1115/1.4037002 History: Received February 07, 2017; Revised June 03, 2017

The stress states of elbow and tee pipes are complex and different from those of straight pipes. The low-cycle fatigue lives of elbows and tees cannot be predicted by Manson's universal slope method; however, a revised universal method proposed by Takahashi et al. was able to predict with high accuracy the low-cycle fatigue lives of elbows under combined cyclic bending and internal pressure. The objective of this study was to confirm the validity of the revised universal slope method for the prediction of low-cycle fatigue behaviors of elbows and tees of various shapes and dimensions under conditions of in-plane bending and internal pressure. Finite element analysis (FEA) was carried out to simulate the low-cycle fatigue behaviors observed in previous experimental studies of elbows and tees. The low-cycle fatigue behaviors, such as the area of crack initiation, the direction of crack growth, and the fatigue lives, obtained by the analysis were compared with previously obtained experimental data. Based on this comparison, the revised universal slope method was found to accurately predict the low-cycle fatigue behaviors of elbows and tees under internal pressure conditions regardless of differences in shape and dimensions.

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References

Figures

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Fig. 1

Shape and geometries of elbow and tee specimens (unit: mm): (a) ES-1,3 [1], (b) ES-2 [1], (c) ES-4, EE-5, EC-6, ES-9,10, EC-11,12, EE-13-17 [2,47], (d) ES-7 and ES-8 [3], (e) TS-18, TB-19, 20 [8], and (f) TS-21, 22 [1]

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Fig. 2

Definition of each area of elbow and tee pipes: (a) elbow and (b) tee

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Fig. 3

Local wall thinning in elbow pipe specimen: (a) extrados and (b) crown

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Fig. 4

Local wall thinning at branch area in tee pipe specimen, the location of A–A′ line is denoted in Fig. 1(e): (a) TB-19 and (b) TB-20

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Fig. 5

Finite element models and their boundary conditions for elbow and tee pipes: (a) ES-10 (model of elbow), (b) EE-13 (local wall thinning), (c) TS-21 (model of tee), and (d) TB-20 (local wall thinning)

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Fig. 6

True stress–true strain curve: (a) STPT410 and (b) STS410

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Fig. 7

Comparison of failure mode between (a) result predicted by FEA and (b) experimental result of ES-10 (elbow pipe, 114.3 mm, 9 MPa, sound) [4]: (a) description chart of principal strain at inter surface and (b) view of fatigue crack at inner surface

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Fig. 8

Comparison of failure mode between (a) result predicted by FEA and (b) experimental result of TS-18 (tee pipe, 76.3 mm, 0 MPa, sound) [11]: (a) description chart of principal strain at outer surface and (b) view of fatigue crack at outer surface

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Fig. 9

Comparison of failure mode between (a) result predicted by FEA and (b) experimental result of TS-21 (tee pipe, 216.3 mm, 10.7 MPa, sound) [1]: (a) description chart of principal strain at inter surface and (b) view of fatigue crack at inner surface

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Fig. 10

Comparison between fatigue lives estimated by Manson's universal slope method and experimental fatigue lives: (a) elbow and (b) tee

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Fig. 11

Comparison between fatigue lives estimated by the revised universal slope method and experimental fatigue lives: (a) elbow and (b) tee

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