Anisotropic Fracture Toughness Effects on Failure Modes of Piping

This paper summarizes various cases where anisotropic fracture toughness properties caused the failure mode to change during ductile fracture experiments on piping. It is noted that in particular for carbon steel piping, the anisotropy can cause an initial circumferential crack to propagate in a helical or even axial direction, even though there are only applied bending loads. This has implications that under combined loading, such pipes may have lower longitudinal stresses at failure than may be calculated by a leak-before-break analysis that only considers the longitudinal stresses and the toughness in the circumferential crack growth plane.