This paper documents important details of the technical bases for changes to Appendix L. Calculations identified aspect ratios for equivalent single cracks (ESC) between the extremes of a 6:1 ratio and a full circumferential crack that can be used in Appendix L flaw tolerance assessments to account for the initiation, growth, and linking of multiple fatigue cracks. Probabilistic fracture mechanics (PFM) calculations determined ESC aspect ratios that result in the same through-wall crack probability as multiple small cracks (0.02 inch depth) that initiate and coalesce. The computations considered two materials (stainless and low alloy steels), three pipe diameters, five cyclic membrane-to-gradient stress ratios and a wide range of primary loads. Subsequent deterministic calculations identified the ESC aspect ratio for the hypothetical reference flaw depth assumptions in Appendix L. This paper also describes computations that compare the Appendix L flaw tolerance allowable operating period for the ESC models with results obtained when the a single default 6:1 aspect ratio reference flaw.
Revised: May 19, 2011 |
Published: July 1, 2005
Citation
Gosselin S.R., F.A. Simonen, and R.G. Carter. 2005.Flaw Tolerance for Multiple Fatique Cracks. In Proceedings of the ASME Pressure Vessels and Piping Conference 2005 - Materials and Fabrication, PVP2005, Denver, CO, Jul 17-21 2005, 6, 73-86. New York, New York:American Society of Mechanical Engineers.PNNL-SA-44392.