Accuracy of numerical analysis is always important but it is much more important in failure analysis of ductile materials. In ductile materials, the process of removing the effects of necking to obtain stress-strain curve usually need reverse identification methods which are based on iterative finite element analysis. Moreover, triaxiality factor and Lode angle (two parameters that control failure of ductile materials) are obtained from finite element analysis.

In this article based on some experiments, the effect of triaxiality factor and Lode angle on the failure strain of X100 pipeline steel is studied. In order to gain a better understanding of the response of triaxiality and Lode angle to deviations of stress, a sensitivity analysis is done on these two parameters before the start of finite elements (FE) analysis. This sensitivity analysis shows that the two parameters are really sensitive to stress deviations in some areas. Three geometries are selected and their FE analysis shows that it is necessary to reduce the element size lower than what is reported in literature in order to get convergence in triaxiality factor and Lode angle in critical areas.