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Research Papers: Seismic Engineering

Numerical Analysis of JNES Seismic Tests on Degraded Combined Piping System

[+] Author and Article Information
Tao Zhang1

 Engineering Mechanics Corporation of Columbus, 3518 Riverside Dr., Suite 202, Columbus, OH 43221tzhang@emc-sq.com

Frederick W. Brust, Gery Wilkowski, Do-Jun Shim

 Engineering Mechanics Corporation of Columbus, 3518 Riverside Dr., Suite 202, Columbus, OH 43221

Jinsuo Nie, Charles H. Hofmayer

 Brookhaven National Laboratory, Upton, NY 11973-5000

Syed A. Ali

 U.S. Nuclear Regular Commission, Office of Nuclear Regulatory Research, Division of Engineering, Rockville, MD 20852

1

Corresponding author.

J. Pressure Vessel Technol 134(1), 011801 (Dec 20, 2011) (12 pages) doi:10.1115/1.4005055 History: Received February 28, 2011; Revised August 17, 2011; Published December 20, 2011; Online December 20, 2011

Nuclear power plant safety under seismic conditions is an important consideration. The piping systems may have some defects caused by fatigue, stress corrosion cracking, etc., in aged plants. These cracks may not only affect the seismic response but also grow and break through causing loss of coolant. Therefore, an evaluation method needs to be developed to predict crack growth behavior under seismic excitation. This paper describes efforts conducted to analyze and better understand a series of degraded pipe tests under seismic loading that was conducted by Japan Nuclear Energy Safety Organization (JNES). A special “cracked-pipe element” (CPE) concept, where the element represented the global moment-rotation response due to the crack, was developed. This approach was developed to significantly simplify the dynamic finite element analysis in fracture mechanics fields. In this paper, model validation was conducted by comparisons with a series of pipe tests with circumferential through-wall and surface cracks under different excitation conditions. These analyses showed that reasonably accurate predictions could be made using the abaqus connector element to model the complete transition of a circumferential surface crack to a through-wall crack under cyclic dynamic loading. The JNES primary loop recirculation piping test was analyzed in detail. This combined-component test had three crack locations and multiple applied simulated seismic block loadings. Comparisons were also made between the ABAQUS finite element (FE) analyses results to the measured displacements in the experiment. Good agreement was obtained, and it was confirmed that the simplified modeling is applicable to a seismic analysis for a cracked pipe on the basis of fracture mechanics. Pipe system leakage did occur in the JNES tests. The analytical predictions using the CPE approach did not predict leakage, suggesting that cyclic ductile tearing with large-scale plasticity was not the crack growth mode for the acceleration excitations considered here. Hence, the leakage was caused by low-cycle fatigue with small-scale yielding. The procedure used to make predictions of low-cycle fatigue crack growth with small-scale yielding was based on the Dowling ΔJ procedure, which is an extension of linear-elastic fatigue crack growth methodology into the nonlinear plasticity region. The predicted moments from the CPE approach were used using a cycle-by-cycle crack growth procedure. The predictions compare quite well with the experimental measurements.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Post-test photograph of pipe specimen for experiment 1.2.1.3

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Figure 2

Illustration of crack growth for circumferential surface cracks

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Figure 3

Moment-rotation input curve for experiment 1.2.1.3

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Figure 4

Moment versus rotation-due-to-the-crack comparison between abaqus and test results from experiment 1.2.1.3

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Figure 5

Applied load versus load-line displacement curve comparison between abaqus and test results from experiment 1.2.1.3

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Figure 6

Illustration of JNES pipe system (combined-component) test

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Figure 7

Mesh and crack locations of the scaled PLR system

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Figure 8

Location and directions of simulated cracking of type A

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Figure 9

Applied acceleration histories for PLR system in test FTP-4 (load blocks CO 30, CO-33, and CO-35)

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Figure 10

Moment versus rotation-due-to-the-crack curves for type A flaws in the main pipe and branch pipe flaw locations at room temperature

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Figure 11

Moment versus rotation-due-to-the-crack curves for type A flaws in the main pipe and branch pipe flaw locations at high temperature (288 °C, 550 °F)

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Figure 12

Displacement measurement locations DO1, DO4, and DO7 for FTP-4 test system

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Figure 13

Comparison of displacement history between the measured and predicted values at location DO7

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Figure 14

Calculated applied moment (N-m) at elbow crack location at room temperature for loading block CO-35

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Figure 15

Calculated applied moment (N-m) at reducer crack location at room temperature for loading block CO-35

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Figure 16

Calculated applied moment (N-m) at branch connection crack at room temperature for loading block CO-35

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Figure 17

Calculated moment (N-m) at elbow crack location at high temperature (288 °C) using loading block CO-35

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Figure 18

Calculated moment (N-m) at reducer crack location at high temperature (288 °C) using loading block CO-35

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Figure 19

Calculated moment (N-m) at branch crack location at high temperature using loading block CO-35

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Figure 20

Broken FTP-4 combined-component system at room temperature

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Figure 21

Broken FTP-4 combined-component system at high temperature

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Figure 22

Predicted moment (N-m) versus time history for reducer crack for seismic loading case CO-30

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Figure 23

(Continued) Predicted moment (N-m) versus time history for reducer crack for seismic loading case CO-30

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Figure 24

(Continued) Predicted moment (N-m) versus time history for reducer crack for seismic loading case CO-30

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Figure 25

Binned stress cycles calculated from the predicted moments for all seismic loading history (CO-30 to CO-35)

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Figure 26

Low-cycle fatigue-crack-growth predictions

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