Direct Use of the Fracture Toughness Master Curve in ASME Code, Section XI, Applications

The ASME Code, Section XI, has adopted the indirect use of the fracture toughness Master Curve to define an alternative index (RT_T0) rather than RT_NDT for using the Code K_IC and K_Ia curves in Appendices A and G. RT_T0 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 K_IC 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 K_IC 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 K_IC curve.