Fracture-toughness and fatigue crack growth evaluation in the transversal direction of the longitudinal weld of an API X52 steel pipeline

In this paper, the fracture-toughness and fatigue crack growth rates of the deposited seam weld on the longitudinal pipeline API 5L X52 were evaluated. The study was performed with nonstandard curved specimens, which were machined in the transversal direction of the seam weld with a crack-initiating notch aligned perpendicular to the direction of the deposited seam weld metal. The fractographic analysis showed that the low fracture toughness of the weld can be attributed to the the existence of elements capable of nucleating brittle fracture and the fact that the intrinsic porosity in the transversal direction provided a favorable crack path for separating the fracture plane, resulting in low fracture-toughness values. Finally, the resistance decrease with respect to the fatigue crack growth was attributed to the small grain size because of the effect of roughness-induced crack closure as well as the interaction of the crack and the inherent porosity.