Evaluation on fracture toughness of welded joint of X65+Inconel 625 composite pipeline

The fracture failure phenomenon of welded joint of composite pipeline was analyzed in this paper. The fracture toughness of welded joint of X65+Inconel 625 composite pipeline in different zones (weld metal zone, fusion zone and heat affected zone) at 0 ℃ was tested by single edge notched three-point bending fracture toughness test. Surface cracks and through-thickness cracks were prepared in different zones of welded joints and compared with the variation trend of CTOD values in different areas of welded joints. The results demonstrate that the structure inhomogeneity has great influence on the dispersity of CTOD value. The research shows that the fracture toughness of welded joints of the composite pipeline varies with zones. Among them, the CTOD value is high in strain aging zone of heat affected zone, and is low with not large dispersity in weld zone, while the CTOD value in weld fusion zone and composite fusion zone are low with large dispersity. So the fusion zone and composite fusion zone are the weak links of the X65+Inconel625 composite pipeline welded joint.