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RESEARCH PAPERS

Effects of Simulated Seismic Loading on LBB Assessment of High Energy Piping

[+] Author and Article Information
Suneel K. Gupta

 Bhabha Atomic Research Center, Reactor Safety Division, Hall-7, Mumbai, 400 085, Indiasuneelkg@barc.gov.in

Vivek Bhasin, K. K. Vaze, A. K. Ghosh, H. S. Kushwaha

 Bhabha Atomic Research Center, Reactor Safety Division, Hall-7, Mumbai, 400 085, India

J. Pressure Vessel Technol 129(1), 28-37 (Mar 13, 2006) (10 pages) doi:10.1115/1.2388998 History: Received August 26, 2005; Revised March 13, 2006

The current Leak Before Break (LBB) assessment is based primarily on the monotonic fracture tearing instability. In it the maximum design accident load is compared with the fracture-tearing resistance load. The effect of cyclic loading has not been generally considered in the fracture assessment of nuclear power plant piping. It is a well-known fact that reversible cyclic loading decreases the fracture resistance of the material, which leads to increased crack growth. Indian nuclear power reactors consider Operational-Basis-Earthquake (OBE) and Safe-Shutdown-Earthquake (SSE) events in the design of various structures, systems, and components. Keeping this in view a series of cyclic tearing tests have been conducted on straight pipes, made of ASTM SA333 Gr.6 carbon steel. This is the material of primary heat transport (PHT) piping material of Indian Pressurized Heavy Water Reactors (PHWR). In this series 13 tests have been carried out circumferentially through wall cracked seamless and circumferential seam welded straight pipes under reversible cyclic bending loading. All the tests have been conducted under quasistatic, i.e., slow loading rates and dynamic inertia effects are not considered. The cyclic test results have been compared with the corresponding monotonic pipe fracture test results. These test results and its comparison with corresponding monotonic tearing clearly illustrate the need of addressing the reduction in apparent fracture toughness of material under reversible cyclic loading and the safe number of load cycles in the LBB assessment.

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Copyright © 2007 by American Society of Mechanical Engineers
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References

Figures

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Figure 6

Load versus crack mouth opening displacement (CMOD) curves of cyclic tests “QCSP-8-60-L2-CSB” conducted on the circumferential TWC straight pipes

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Figure 7

Comparison of the load line displacement (LLD) versus load cycles (N) curves of cyclic tests conducted on the circumferential TWC straight pipes

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Figure 8

Comparison of the average projected crack size versus load cycles (N) curves of cyclic tests conducted on the circumferential TWC straight pipes

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Figure 9

Moment versus crack extension plots for the three monotonic fracture tests and five cyclic tearing tests conducted on the circumferential TWC straight pipes

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Figure 10

Comparison of the moment versus rotation curves of displacement controlled cyclic tearing tests and corresponding monotonic test results

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Figure 11

Comparison of the moment versus CMOD curves of displacement controlled cyclic tearing tests and corresponding monotonic test results

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Figure 1

(a) Schematic diagram of the cyclic tearing test on the circumferential through wall cracked straight pipes; (b) Picture of the setup of cyclic tearing test on the circumferential through wall cracked straight pipes

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Figure 2

The schematic of the loading for the incremental displacement controlled loading cyclic test

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Figure 3

The typical display of the online image acquisition system containing four child windows on the computer screen captured during cyclic testing

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Figure 4

(a) Load line displacement versus load cycles (N) curves of cyclic tests “QCSP-8-60-L2-CSB” conducted on the circumferential TWC straight pipes. (b) CMOD versus load cycles (N) curves of cyclic tests “QCSP-8-60-L2-CSB” conducted on the circumferential TWC straight pipes.

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Figure 5

Load versus load line displacement curves of cyclic tests “QCSP-8-60-L2-CSB” conducted on the circumferential TWC straight pipes

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Figure 12

Comparison of the J-R curves displacement controlled cyclic tearing tests and corresponding monotonic fracture test results

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Figure 13

Master curve for SA333 Gr.6 carbon steel pipes: plot of cyclic load amplitude (% of corresponding monotonic failure load) versus number of load cycles to failure (Nf)

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Figure 14

Envelope of moment versus rotation, moment versus crack extension, and crack extension versus rotation data for the two displacement controlled cyclic tests and the corresponding monotonic fracture test

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