Development of Creep Constitutive Equation for Low-Alloy Steel

High-temperature creep tests were performed with an SA533B1 low-alloy steel under both constant load and constant stress conditions. Using the measured minimum creep strain rates as a function of stress and temperature, least-square fittings were made into a Bailey-Norton-type power law equation. Based on the constant stress test results, a constitutive equation was developed for steady-state creep. The constitutive equation was then implemented in elastic-viscoplastic analysis of the lower head of a pressurized water reactor's reactor pressure vessel using a commercial FEM code named ABAQUS 5.8. The FEM model was validated using measured data from the lower head failure experiment conducted at the Sandia National Laboratories. The FEM model using the creep constitutive equation was shown to be capable of accurately predicting the lower head deformation behavior. Additional work, however, is needed to rationalize apparent inconsistency between the constant load data and constant stress data.