Session: CS-08-02 The Warren H. Bamford Memorial Symposium on Recent Developments in ASME Codes and Standards: ASME Code Section XI Activities-2

Paper Number: 155922

155922 - Clarification on Definition of Membrane-to-Gradient Stress Ratio Used in the Development of Asme Code Section Xi Appendix L Flaw Tolerance Procedures 

Abstract: 

ASME Code, Section XI, Nonmandatory Appendix L prescribes flaw tolerance procedures for determining an allowable operating period for operating plant components and piping subjected to cyclic (fatigue) loadings. The procedures require qualified nondestructive examination (NDE) confirmation that the location of interest has an absence of flaws deeper than the IWB-3500 Section XI Flaw Acceptance Standards. The flaw tolerance analysis postulates a pre-existing flaw at the location of interest. The flaw depth is based on the Acceptance Standards, and the flaw aspect ratio is determined based on the material type and the ratio of the cyclic membrane to gradient stress. Currently, Appendix L does not provide a procedure or guidance on how to specifically calculate membrane to gradient (M-G) stress ratios for individual cyclic stress profiles, which can lead to uncertainties and inconsistencies in Appendix L flaw tolerance evaluations. A detailed review of the technical basis documents for the latest revision to Appendix L (2008 Addenda) was performed to obtain clarification on the definition of the M-G cyclic stress ratio for determining the equivalent single crack (ESC) tables of flaw aspect ratio that currently reside in Appendix L. From this review, it was confirmed that the original Appendix L technical basis calculations used a fixed stress profile of through-wall linear and nonlinear gradient stresses, and the total stress values at the component internal surface. Independent, new calculations were performed to confirm the review findings. This conference paper will report the review findings and suggest an improved approach to determine and calculate the varying degree of M-G stress gradient in the individual cyclic stress profiles for use in Appendix L evaluations.

 

Presenting Author: Gary Stevens Consultant to Electric Power Research Institute

Presenting Author Biography: later

Authors:

Nathan Glunt EPRI
Gary Stevens Consultant to Electric Power Research Institute
Steven Xu Kinectrics