Technical basis for flaw shape change formulations proposed for appendix a to section XI

摘要

Appendix A to Section XI of the ASME Boiler and Pressure Vessel Code provides an analytical procedure for determinign the acceptability of flaws that have been detected during inservice inspection of ferritic components. The procedure requires the evaluation of the end-of-period flaw size from a cumulative fatigue flaw growth analysis which is carried out by determining the range of the stress intensity factor associated with each transietn and applying the result to the appropriate fatigue crack growth rate curve. The stress intensity factor calculation can be quite sensitive to the flaw shape which changes during flaw growth. The 1998 Edition of the Code specifies that flaw shape change should be accounted for but provides no guidance on how this is to be done. The inclusion of explicitly stated flaw shape change methodology eliminates a source of uncertainty in the flaw growth calculation.