Fracture behavior analysis of X80 girth welds considering misaligned and variable-wall-thickness geometric features via modified single-edge notched tensile (MSENT) specimens

Girth weld charactering misaligned and variable-wall-thickness geometric features are more susceptible to fracture at the root notch, yet the fracture behavior assessment of girth welds with such hybrid features remains mostly unexplored. In this paper, the fracture behaviors of X80 girth welds are thoroughly evaluated via experimental-numerical coupled analysis on the modified single-edge notch tensile (MSENT) specimens. The effects of misaligned and variable-wallthickness features on the fracture behavior are systematically elucidated. Controlled studies are carried out in quantitatively characterizing the crack tip constraint state of MSENT specimens; then the constraint-fracture toughness correlations are comparatively developed with a new constraint parameter 7M proposed, followed by discussions on the applicability of crack tip constraint characterization for the MSENT specimens. The results reveal that the misaligned and variable-wall-thickness features cause pronounced brittle fracture characteristics at low temperature and remarkable attenuations of fracture toughness CTODc with crack deflection at room temperature, which is consequently rationalized by the intensified crack tip constraint level. Simultaneously, the constraint parameter Ap is proven to be comparatively more appropriate for the constraint characterization of MSENT specimens. Also, the unique monotonic relationship between the newly developed constraint parameter 7M and fracture toughness is established. The research results provide a promising method of pipeline structures' integrity assessment and inservice evaluation.