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Research Papers: Design and Analysis

Experimental Evaluation of the Bending Load Effect on the Failure Pressure of Wall-Thinned Elbows

[+] Author and Article Information
Jin-Weon Kim1

Department of Nuclear Engineering, Chosun University, 375 Seosuk-dong, Dong-gu, Gwangju 501-759, Republic of Koreajwkim@chosun.ac.kr

Yeon-Soo Na

 Kyungpoog National University Hospital, 200 Dongduk-ro, Jung-gu, Daegu 700-721, Republic of Korea

Sung-Ho Lee

Nuclear Power Laboratory, Korea Electric Power Research Institute, 103-16 Munji-dong, Yusung-gu, Daejon 305-380, Republic of Korea

1

Corresponding author.

J. Pressure Vessel Technol 131(3), 031210 (Apr 29, 2009) (8 pages) doi:10.1115/1.3122032 History: Received May 05, 2008; Revised January 05, 2009; Published April 29, 2009

During normal operating conditions, piping systems in nuclear power plants are subject to internal pressure and bending loads induced by deadweight, thermal expansion, and internal pressure. Thus, understanding the effect of bending load on the failure of wall-thinned elbows is important to understand failure behavior and to evaluate the failure pressure reliably. This study includes a series of burst tests using full-scale 4-in. schedule 80 elbow specimens with local wall-thinning under combined internal pressure and in-plane bending load. The results are compared with those tested under simple internal pressure only. In the tests, various circumferential thinning angles (θ/π=0.125, 0.25, 0.5, 1.0) and thinning locations (intrados, extrados, and full-circumference) were considered. Each specimen was initially subjected to a displacement controlled in-plane bending load, closing mode for extrados wall-thinned elbows, and opening mode for intrados wall-thinned elbows, and then internal pressure was applied up to the point of final failure. The results showed that the effect of in-plane bending on the failure pressure and failure mode was minor under all wall-thinning conditions. In addition, the dependence of failure pressure on the circumferential thinning angle and thinning locations was identical to that observed under simple internal pressure.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 2

Schematic of the testing apparatus used in the experiment

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Figure 3

Apparatus for burst tests of local wall-thinned elbows

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Figure 4

Failure pressure of wall-thinned elbows with different thinning angles and locations under simple internal pressure (20)

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Figure 5

Measured data from the burst tests under combined loading conditions

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Figure 13

Distributions of equivalent stress along the circumference of the full-circumference wall-thinned elbow specimen under closing- and opening-mode bendings without internal pressure

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Figure 11

Increase in outer diameter of wall-thinned elbow specimens

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Figure 10

Failure patterns of wall-thinned elbow specimens under simple internal pressure, combined internal pressure, and in-plane bending loads

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Figure 9

Comparison of circumferential strains at wall-thinned areas for different loading types

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Figure 8

Comparison of failure pressures tested under simple internal pressure and under a combined loading condition

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Figure 7

Failure pressures tested under combined internal pressure and in-plane bending load

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Figure 6

Variations in bending load for each specimen with increasing internal pressure

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Figure 1

Elbow specimen and geometries of wall-thinning defect

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Figure 12

Locations of the outer diameter measurement for post-test specimens

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