Article A-3000 of Appendix A in Section XI of the ASME Boiler and Pressure Vessel Code provides linear elastic fracture mechanics based calculation procedures for the determination of stress intensity factors. The 2015 Edition of ASME Section XI implements a number of significant improvements in Article A-3000. Major improvements include the implementation of an alternate method for calculation of the stress intensity factor for a surface flaw that makes explicit use of the Universal Weight Function Method and does not require a polynomial fit to the actual stress distribution, and the inclusion of closed-form equations for stress intensity factor influence coefficients for circumferential ID surface cracks. With the inclusion of the explicit weight function approach and the closed-form relations for influence coefficients, the procedures of Appendix A for the calculation of stress intensity factors can be used more efficiently.

Closed-form equations for stress intensity factor influence coefficients for axial ID surface cracks have been under development. Tabular data of influence coefficients for the cylinder geometry provided in API 579-1/ASME FFS-1 2007 are used as data source. A set of closed-formed equations for an axial semi-elliptical ID surface crack with depth a and length 2c in a cylinder were previously reported in a 2014 PVP paper. The smallest value for a/c is 0.03125 in the tabular data that were used to fit the equations. For practical applications, it is desirable to use axial flaw equations that allow a/c to approach zero without extrapolation. This issue is addressed in the current PVP paper.

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