Fractography of burst-tested linepipe

The fracture mechanism of fast running ductile crack was investigated from the viewpoint of microscopic fracture appearance. Fracture surfaces were sampled from burst linepipes after full-scale burst tests, and examined by scanning electron microscope (SEM). In spite of sufficient thickness reduction due to local necking, the macroscopic appearance of the burst-tested specimens was a slanted fracture in the wall thickness direction. The microscopic observations revealed an equiaxed dimple pattern on the fracture path in the thickness direction tilted to the maximum shear stress direction. The Charpy impact test, drop weight tear test (DWTT), plate tensile test and round bar tensile test were also performed with the same materials as in the full-scale burst tests. The size and frequency of the primary dimples on the fracture surface of the laboratory specimens were compared with those of the full-scale burst linepipe. The stress state at the running crack tip in the full-scale burst test was also investigated based on the dimple morphology.

► Microscopic fractography on full-scale linepipes burst test samples was examined.
► Charpy impact test, DWTT, and tensile test were conducted with the same materials.
► Dimples size and its morphologies were compared with laboratory specimens.
► DWTT showed similar dimple morphology to full-scale burst linepipes.