Linear elastic fracture mechanics based flaw evaluation procedures in Section XI of the ASME Boiler and Pressure Vessel Code require calculation of the stress intensity factor. Article A-3000 of Appendix A in ASME Section XI prescribes a method to calculate the stress intensity factor for a surface or subsurface flaw by making use of the flaw location stress distribution obtained in the absence of the flaw. The 2015 Edition of ASME Section XI implemented a number of significant improvements in Article A-3000, including closed-form equations for calculating stress intensity factor influence coefficients for circumferential flaws on the inside surface of cylinders. Closed-form equations for stress intensity factor influence coefficients for axial flaws on the inside surface of cylinders have also been developed. Ongoing improvement efforts for Article A-3000 include development of closed-form relations for the stress intensity factor coefficients for flaws on the outside surface of cylinders. The development of closed-form relations for stress intensity factor coefficients for axial flaws on the outside surface of cylinders is described in this paper.
General Design Criteria (GDC) 1, 2, 4, 14, 30, 31 and 32 of 10 CFR Part 50, Appendix A, define requirements for the reactor coolant pressure boundary (RCPB) with respect to structural and leakage integrity [1]. Steam generator tubing and tube repairs constitute a major fraction of the RCPB surface area. Steam generator tubing and associated repair techniques and components, such as sleeves, must be able to maintain reactor coolant inventory and pressure. The Structural Integrity Performance Criterion (SIPC) from Nuclear Energy Institute (NEI) 97-06 [2] was developed to provide reasonable assurance that a steam generator tube will not burst during normal or postulated accident conditions. This paper presents the SIPC and its technical basis.
The ASME Code, Section XI, has adopted the indirect use of the fracture toughness Master Curve to define an alternative index (RTT0) rather than RTNDT for using the Code KIC and KIa curves in Appendices A and G. RTT0 is defined as T0 + 19.7°C (T0 + 35°F), where T0 is the Master Curve reference temperature as defined in ASTM Standard Test Method E 1921. This alternative approach was first approved in ASME Code Case N-629 for Section XI and Code Case N-631 for Section III. Most recently this approach has been integrated directly into the Code, Section XI, and will be published in the 2013 Edition. When this alternative indexing approach was developed, it was recognized that the direct use of the Master Curve itself also could be used as an alternative to the Code KIC curve. A Code Case for the direct use of the fracture toughness Master Curve has been developed and has been presented to Section XI for approval. This paper provides the technical basis for using the fracture toughness Master Curve as an alternative to the Section XI KIC curve. An adjustment to the Master Curve at very low temperatures is included which alleviates a potential problem for low temperature overpressure (LTOP) protection setpoints as would be determined using the existing Code KIC curve.
Nondimensional stress intensity factors have been numerically determined for a straight-fronted edge crack located at the thread root of a fastener. An influence-function or weight-function approach was used in determining KI for several fastener sizes: diameters ranging from 1 to 6 in. (2.5 to 15.2 cm) and thread pitches of 4, 8, and 12 threads per inch. Several analytical approximations are used in simplifying the stress analysis problem and the development of the weight function. The results for the nondimensional stress intensity factor, KI/σ(πa)1/2, are provided as a function of crack depth, bolt size, and thread pitch. The effects of bolt size and thread form play an important role only when cracks are relatively small. These results indicate that local differences caused by thread form and root radius are limited to crack depths within 2% of the net section. All major contributions to elevation in KI, caused by the presence of the threads appear to diminish for cracks extending beyond 25% of the minor diameter.
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