Fracture Toughness of X100 Pipe Girth Welds Using SE(T) and SE(B) Tests

Extensive single-edge notched tension (SE(T)) and single-edge notched bend (SE(B)) tests were performed to apply the SE(T) procedure developed at CANMET and the standard SE(B) procedure of ASTM E1820 to pipeline girth welds as a contribution to a broader project on strain-based design (SBD) for pipeline girth weld integrity. Specimens were precracked from the pipe inner surface to target lengths of 3 and 6 mm to represent surface-breaking weld flaws of single- and double-pass height, respectively. It was found that resistance curves for weld metal (WM) were much lower than those for base metal (BM) or heat affected zone (HAZ) specimens even though the WM strength overmatched the BM, owing to effects from the WM microstructure. The small crack-tip opening angle observed in post-test WM specimens was consistent with the low crack propagation resistance, which in turn results in small tearing resistance, T_R. In general, toughness decreases with increase in initial crack length. J values and tearing resistance are found to be influenced by loading mode; toughness is higher in tension, SE(T), than in bending, SE(B) for a given crack length and test temperature.