Abstract Ductile failure of X100 pipeline steel is studied. In order to study the effect of anisotropy, triaxiality factor and Lode angle on the failure, a series of specimens with different geometries are tested. Measurements of deformation in three dimensions are done to check the variation of elongation and lateral deformations during loading. Extensive fractography is done using pictures taken by SEM to study the fracture surfaces completely. The results show that triaxiality causes the failure to occur sooner and Lode angle has no effect on the failure in triaxialities higher than that of simple tension. Moreover, delamination has occurred in some of the specimens. This phenomenon is studied and the causes of delamination are explained in macro scale.