Statistical Modeling of Shift in the Reference Temperature of Pressure Vessel Welds

Summary

Recently, regulators have used irradiated reference temperature estimates as a screening criterion for pressurized thermal shock evaluations adding increased emphasis to the accuracy with which shift predictions as measured by the Charpy impact curve are made. Since the evaluation of the pressure vessel structural integrity is directly linked to the prediction of shifts in reference temperature, a closer review of the methods used to model these predictions was required.

A data base consisting of automatic submerged-arc weld metals, made with copper plated wire and Linde 80 flux was assembled from surveillance capsule programs and a prediction model for shift was developed. Comparisons of predictions are given with the several models currently under consideration for revising regulatory requirements. The impact of the results of the analyses is that plants need not revise their operating schemes, but rather Reg. Guide 1.99 should be updated and its excessive conservatism removed.