Relationship of Fracture Behaviours Between Full-Scale Pipe Bending and Small-Scale Toughness Tests

A comparison of the fracture behaviours for a full-scale (FS) pipe bending test and small-scale fracture toughness tests was carried out in this investigation. For the FS pipe test, two 4-meter long large diameter (914 mm) X70 pipes were girth-welded together to facilitate bend testing with an internal pressure of 72% of specified miniminm yield strength (SMYS). The test assembly also contained a semi-ellipical notch that was prepared by means of electrical discharge machining (EDM) from the outside surface in the heat-affected zone. Single-edge notched bend (SE(B) or SENB) and single-edge notched tension (SE(T) or SENT) test specimens were prepared from a duplicate girth weld produced with the same pipe and weld procedure with equivalent notch depths. The FS pipe test showed deformation along the pipe axis asymmetric to the girth weld centre. The comparison of fracture behaviours between small-scale and FS tests suggests that toughness measurements (crack-tip opening displacement or J-integral) at maximum load might be useful as a reference for strain-based design although further work is needed.