The Nuclear Regulatory Commission (NRC) is currently reviewing Section III, Division 5 of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPVC) for potential endorsement. Prior reviews sponsored by the NRC on the application of the design rules in Section III, Division 5 for elevated-temperature reactors have identified issues currently not in the code that need to be addressed.  These issues include an inadequate knowledge of the effects of geometrical discontinuities, such as notches on the weakening of the material and the impact of a multiaxial stress state on creep-rupture properties. Through the use of different notch geometries, this work qualitatively evaluates Alloy 617 as notch strengthening or notch weakening and investigates the impact of multiaxial stress on Alloy 617 creep behavior. Alloy 617 was chosen for this study because of the extensive characterization and data generated necessary for its recent inclusion into Section III, Division 5. Code Cases N-872 and N-898 permit nuclear reactor construction with Alloy 617 for low- and elevated-temperature service, respectively.

Multiaxial stress does not impact the short-term creep-rupture properties of Alloy 617. This was concluded from the following observations: 1.) Alloy 617 is notch strengthening, and 2.) multiaxial creep resides on or to the right of the Larson-Miller curve for uniaxial creep. Long‑term and intermediate creep‑rupture tests are in progress in order to determine whether notch behavior will cross over from strengthening to weakening at lower stresses and longer rupture life times. A nondestructive characterization methodology using X‑ray computed tomography is explored to attempt to detect the failure location on the specimen prior to rupture. 


The Impact of Geometric Discontinuities on Alloy 617 Creep-Rupture Behavior

Division / Sponsors: 
Pressure Vessels & Piping (PVP)


Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2020/volume/83815

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