Predictability of Long-Term Creep and Rupture in a Nozzle-to-Sphere Vessel Model

Abstract

The results of a long-term (approximately 2-1/2 yr), high-temperature failure test of a pressurized nozzle-to-spherical-shell model made of a well-characterized heat of type 304 stainless steel are presented and compared with inelastic deformation and failure predictions. The model, which was tested at 593°C (1100°F), was instrumented with capacitive strain gages in key locations. In addition to recording strains, the surface of the model in the junction region was periodically examined throughout the test for the formation and progression of the creep cracking that ultimately led to a leakage failure. The inelastic analysis predictions were based on guidelines developed and used for design of elevated-temperature nuclear components. Similarly, the failure model used was that upon which the ASME elevated-temperature Code Case N-47 for nuclear components is based. Thus, the reasonable agreement observed between experimental results and predictions adds confidence in the overall design methodology for elevated-temperature components. The results also demonstrated the leak-before-break nature of failure and the fact that pressure-induced stresses do not necessarily relax with time.

Report on an Assessment of the Application of EPP Results from the Strain Limit Evaluation Procedure to the Prediction of Cyclic Life Based on the SMT Methodology

“…However, ultimately the EPP method will be used in conjunction with the isochronous stress/strain curves and the "D" diagrams in the Division 5. This section and the corresponding appendix also compare the EPP method directly to experimental data from a component test conducted at ORNL in the 1980s [8]. This comparison demonstrates the conservatism of the EPP method for realistic component geometries and loading conditions.…”

High-Temperature Creep Test Suite for Grizzly

“…The nozzle-to-sphere vessel assessment case is based on one of the experimental tests conducted at ORNL as part of a United States Department of Energy program to develop the elevated-temperature structural design methodology for liquid-metal and other advanced reactors [29 ].…”

Historical Context and Perspective on Allowable Stresses and Design Parameters in ASME Section III, Division 5, Subsection HB, Subpart B

“…Because lowering the allowable stress values by this magnitude would be at odds with commercial practice and other international standards, it was deemed appropriate to reexamine the original time-to-tertiary criterion rather than immediately change the allowable stresses. The goal of this revaluation was to see if the tertiary creep criterion was more generally applicable to thicker walled components such as in the ORNL nozzle-to-sphere test by Corum and Battiste [9]. The current status of these assessments is that the original capsule failures were equally or better explained by multiaxial effects, the data used to establish the onset of tertiary was compromised by irregularities in the creep curves, and the nozzle-to-sphere failure data did not correlate with the onset of tertiary creep.…”