Simplified Prediction of Creep Void Density in Heat-Affected Zone of Grade 122 Steel Considering Multiaxial Stress State

Abstract

This paper deals with a simplified method for approximately predicting creep void growth in heat-affected zone (HAZ) of ASME grade 122 (11Cr-2W-0.4Mo-Cu-Nb-V) steel weldments. Authors have proposed a simplified prediction method based on the relationship between creep void density increasing rate and multiaxial stress state. This method has been applied to prediction of creep void growth behavior for grade 91 (9Cr-1Mo-Nb-V) tubular specimens with longitudinal weldments. In this study, the method has been also applied to grade 122 steel to clarify the applicability of the method. Internal pressure creep tests of grade 122 tubular specimens with longitudinal weldments subjected to several internal pressures have been conducted to reveal creep void growth behavior in HAZ. In addition, finite element creep analyses for the specimens at different creep strain rates in base metal, weld metal and HAZ have been carried out to investigate distribution of stresses and stress triaxiality factor in HAZ. A comparison between stress distributions and creep void distributions revealed that stress triaxiality factor affects growth behavior of creep voids. From the result, the relationship between creep void density increasing rate and the parameter as a function of principal stress and triaxiality factor was established. It was found that the slope of this relationship for 122 steel has a tendency to be slightly small compared with grade 91 steel. To demonstrate the applicability of the proposed simplified prediction method, the method was applied to the internal pressure creep test specimens at different experimental conditions. As a result, the predicted void distribution and void density increasing rates for grade 122 steel were in good agreement with the experimental results.