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Research Papers: Seismic Engineering

Low Cycle Fatigue Behavior and Seismic Assessment for Pipe Bend Having Local Wall Thinning-Influence of Internal Pressure

[+] Author and Article Information
Yoshio Urabe

Japan Nuclear Safety Institute,
5-36-7, Shiba, Minato-ku,
Tokyo, 108-0014, Japan
e-mail: urabe.yoshio@genanshin.jp

Koji Takahashi

e-mail: ktaka@ynu.ac.jp

Kyohei Sato

e-mail: kyohei310@gmail.com

Kotoji Ando

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

1Corresponding author.

Contributed by the Pressure Vessel and Piping Division of ASME for publication in the Journal of Pressure Vessel Technology. Manuscript received May 22, 2012; final manuscript received April 30, 2013; published online June 11, 2013. Assoc. Editor: Spyros A. Karamanos.

J. Pressure Vessel Technol 135(4), 041802 (Jun 11, 2013) (8 pages) Paper No: PVT-12-1064; doi: 10.1115/1.4024444 History: Received May 22, 2012; Revised April 30, 2013

One of the concerned technical issues in the nuclear piping under operation is pipe wall thinning caused by flow accelerated corrosion. This paper focuses on influence of internal pressure on low cycle fatigue life of pipe bends with local wall thinning and evaluation of safety margin against seismic loading in order to apply the obtained knowledge to the nuclear piping. In-plane bending fatigue tests under several constant internal pressure magnitudes were carried out using carbon steel pipe bends with local wall thinning at the extrados. Also finite element analysis, code-based seismic evaluation and fatigue analysis based on calculated strain range were carried out. Obtained main conclusions are as follows: (1) the tested pipe bends with local wall thinning at the extrados have a strong resistance against fatigue failure based on nuclear seismic piping design in Japan at least up to 12 MPa. That is, the tested pipe bends with severe local wall thinning (eroded ratio = 0.5 and eroded angle = 180 deg) at the extrados have margins against fatigue failure, even though the wall thickness is less than the code-required minimum value based on the nuclear piping seismic design in Japan. (2) Combination of the conventional B2 index and the Ke factor provided in the JSME Design and Construction Code, which is referred by JEAC 4601-2008 overestimates fictitious stress amplitude, when sum of the primary and secondary stress is much greater than 3 Sm.

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References

Figures

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Fig. 1

Shape and geometries of pipe bend specimens undergoing local wall thinning (a) pipe bend specimen and (b) detail of eroded area

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Fig. 2

An example of crack behavior (E-P9-20) (a) crack at outer surface (main crack length = 40.3 mm) and (b) crack at inner surface (main crack length = 48.7 mm)

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Fig. 3

Influence of internal pressure on fatigue life of pipe bend specimens

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Fig. 4

Difference of loop strain behavior with level of internal pressure

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Fig. 5

A typical example of hoop and axial strain at outer surface of crown (Test No. E-P6-20)

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Fig. 6

True stress-true strain curve of carbon steel STPT410

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Fig. 7

Finite element model of pipe bend specimen (a) overall view of pipe bend specimen and (b) detail of eroded area

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Fig. 8

An example of load versus load point displacement relationship (E-P12-D20)

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Fig. 9

Comparison of hoop strain at the surface of crown between experimental result and FEM result (E-P9-20)

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Fig. 10

Comparison of present fatigue data with reference data

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Fig. 11

Comparison between fictitious stress amplitude and ASME Sec. III seismic criteria

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Fig. 12

Relationship between fictitious stress amplitude and fatigue life

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