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Improvement of the LBB.ENG2 Circumferential Through-Wall Crack J-Estimation Scheme

[+] Author Affiliations
Richard Olson

Battelle Memorial Institute, Columbus, OH

Sureshkumar Kalyanam, Frederick W. Brust

Engineering Mechanics Corporation of Columbus, Upper Arlington, OH

Jeong Soon Park

Korea Institute of Nuclear Safety, Daejeon, Korea

Paper No. PVP2016-63264, pp. V003T03A075; 6 pages
doi:10.1115/PVP2016-63264
From:
  • ASME 2016 Pressure Vessels and Piping Conference
  • Volume 3: Design and Analysis
  • Vancouver, British Columbia, Canada, July 17–21, 2016
  • Conference Sponsors: Pressure Vessels and Piping Division
  • ISBN: 978-0-7918-5039-8
  • Copyright © 2016 by ASME

abstract

The LBB.ENG2[1] circumferential through-wall crack (TWC) J-estimation scheme forms the basis for the Extremely Low Probability of Rupture (xLPR)[2] probabilistic pipe fracture analysis for TWC elastic-plastic fracture mechanics (EPFM) stability assessment. The LBB.ENG2 methodology uses a reduced thickness pipe wall analogy to approximate the behavior of actual cracked pipe and sets the thickness of the reduced section by making the usual cracked pipe limit load assumption. Sometime during the original LBB.ENG2 development process, it was discovered that LBB.ENG2 was not as good as desired at predicting the maximum moment carrying capacity of pipe fracture experiments with longer cracks. Accordingly, the effective thickness equation was modified to be 1.0 at crack angles less than π/4, 4/π at angles greater than π/3, and linear between these values using a so-called ψ function.

When LBB.ENG2 was coded for the TWC stability module for xLPR, TWC_fail, the behavior described above was implemented. Quite unexpectedly, with the new coding, exploration of TWC_fail’s bounds uncovered two discontinuities in the complete moment-pressure-critical crack size failure surface. Subsequently, it was found that these discontinuities were caused by the discontinuity in the derivative of the ψ function.

This paper documents the approach used to smooth the TWC_fail moment-pressure-critical crack size surface by making a ψ function fit that minimizes the difference between J from LBB.ENG2 and J from finite element analyses results. The results of the finite element analyses and fitting methodology are described and the basic equations for the solution are presented. Following this, the new ψ function is applied to cases to evaluate the efficacy of the approach.

Copyright © 2016 by ASME

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