Technical basis for the revised stress intensity factor equation for surface flaws in ASME Section XI Appendix A
- Aptech Engineering Services, Inc., Sunnyvale, CA (United States)
The flaw evaluation procedure for determining the acceptability of in service inspection indications detected in ferritic components is contained in Appendix A of the ASME Boiler and Pressure Vessel Code, Section 11. The flaw evaluation procedure is based on linear elastic fracture mechanics where the stress intensity factor (K) for the given flaw geometry and applied stress is used to evaluate fatigue crack growth and unstable fracture for the design basis transients. The original procedure for calculation of K for semielliptical surface cracks was based on a linearization method for conservatively estimating K for nonlinear stress variations. This method employed elastic superposition to determine K as the summation of stress intensity factors due to membrane and bending stresses where the membrane and bending stress components comprise the general linear equation for stress acting on the crack. To improve upon this approach, the K solution procedure has been revised to allow for the stress variation at the crack location to be represented by a cubic polynomial equation. The use of a cubic polynomial fit to the actual stress distribution will greatly improve the accuracy of the method for nonlinear stress fields such as those caused by thermal transient loadings and residual stresses. The technical basis and verification for this new procedure, which appears in the 1994 Addenda to ASME Section 11, is provided in this paper.
- OSTI ID:
- 136773
- Report Number(s):
- CONF-950740--; ISBN 0-7918-1344-4
- Country of Publication:
- United States
- Language:
- English
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