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Research Papers: Materials and Fabrication

Stress Corrosion Crack Shape Development Using AFEA

[+] Author and Article Information
D. Rudland1

Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission, Mail Stop: C-05C04, Washington, DC 20555-0001david.rudland@nrc.gov

A. Csontos

Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission, Mail Stop: C-05C04, Washington, DC 20555-0001

D.-J. Shim

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

As noted later in this paper, some of the differences in the plots are due to the curve fit of the Anderson solution.

1

Corresponding author. Views expressed herein are those of the author and do not represent an official position of the US NRC.

J. Pressure Vessel Technol 132(1), 011406 (Jan 05, 2010) (7 pages) doi:10.1115/1.4000349 History: Received November 19, 2008; Revised May 28, 2009; Published January 05, 2010; Online January 05, 2010

Typical ASME Section XI subcritical cracking analyses assume an idealized flaw shape driven by stress intensity factors developed for semi-elliptical shaped flaws. Recent advanced finite element analyses (AFEA) conducted by both the United States Nuclear Regulatory Commission (U.S.NRC) and the nuclear industry for long circumferential indications found in the pressurizer nozzle dissimilar metal welds at the Wolf Creek power plant suggest that the semi-elliptical flaw assumption may be overly conservative in some cases. The AFEA methodology that was developed allowed the progression of a planar flaw subjected to typical stress corrosion cracking (SCC)-type growth laws by calculating stress intensity factors at every nodal point along the crack front, and incrementally advancing the crack front in a more natural manner. Typically, crack growth analyses increment the semi-elliptical flaw by considering only the stress intensity factor at the deepest and surface locations along the crack front, while keeping the flaw shape semi-elliptical. In this paper, a brief background to the AFEA methodology and the analyses conducted in the Wolf Creek effort will be discussed. In addition, the predicted behavior of surface cracks under normal operating conditions (plus welding residual stress) using AFEA will be investigated and compared with the semi-elliptical assumption. Conclusions on the observation of when semi-elliptical flaw assumptions are appropriate will be made. These observations will add insight into the conservatism of using an idealized flaw shape assumption.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Examples of arbitrary crack fronts developed by PIPEFRACCAE (cracked areas in white, remaining ligament in gray)

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Figure 2

Crack shape prior to leakage assuming semi-elliptical crack growth and natural crack growth for relief nozzle geometry

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Figure 3

Crack depth and length versus time for relief nozzle case

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Figure 4

Welding residual stress profiles

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Figure 5

Normalized crack fronts to illustrate shape factor calculation

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Figure 6

Definition of shape factor

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Figure 7

Effects of welding residual stress on final surface crack shape

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Figure 8

Effects of initial crack size on final shape

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Figure 9

Crack growth comparison between small and short crack

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Figure 10

Effects of pipe diameter (Ri/t) on final crack shape

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Figure 11

Effect of bending stress on final crack shape

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Figure 12

Predictions of time to leakage for cases with no welding residual stress

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Figure 13

Predictions of crack length at leakage for cases with no welding residual stress

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Figure 14

Predictions of time to leakage for cases with welding residual stress

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Figure 15

Predictions of crack length at leakage for cases with welding residual stress

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Figure 16

Predictions of leakage time for original Wolf Creek relief nozzle crack with influence function curve fit and look-up table

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Figure 17

Example of case with semi-elliptical final crack shape

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