Prediction of Creep Void Growth in Heat-Affected Zone of High Chromium Steel Weldments Considering Multiaxial Stress State

Abstract

This paper deals with a method for predicting creep void growth in heat-affected zone (HAZ) of high chromium steel weldments. The method has been proposed by authors based on the relationship between creep void density increasing rate and multiaxial stress state. In this study, internal pressure creep tests of ASME grade 91 (9Cr-1Mo-Nb-V) tubes 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 of 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 void distributions revealed that stress triaxiality factor predominantly 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 there is a proportional relationship between creep void density increasing rate and the parameter to represent stress multiaxiality on the logarithmic graph. To verify proposed 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 were in good agreement with experimental results.