X-100 steel is one of the most recently developed materials for production of gas transportation pipelines. This material is severely anisotropic. Smooth and notched round bars with different notch radius and flat notched specimens with different notch radius and notch depth in tension are tested to characterize the failure of this material under quasi-static loading condition.Triaxiality factor that embodies the effect of mean stress and Lode angle are the parameters that affect the failure. Lode angle is a recently introduced parameter in the fracture of ductile materials and contains the effect of third invariant of deviatoric stress tensor. The load-displacement curves and pictures taken by 2 photo camera are used to study the effects of anisotropy, triaxiality factor and Lode angle on the failure of this material. Finally an experimental failure criterion is developed to model the failure of this material. In this failure criterion, strain at fracture initiation is a function of X and TF. Models that take into account the effect of Lode angle, Triaxiality factor and anisotropy in plasticity and damage are the current state of the art in the research of ductile materials.