A Novel Correlation Model Between the Critical CTOD and Crack Tip Constraint of High-Grade Pipeline Girth Weld

Abstract Under the action of external load, the crack driving force of the girth weld is greater than the fracture toughness of the material, which will lead to the fracture failure accident of the girth weld of the pipeline. As an important parameter of the failure limit state prediction model, the fracture toughness of the material is affected by the constraint state of the structural crack tip. Therefore, it is necessary to establish an accurate correlation between the fracture toughness of the material and the crack tip constraint. In this paper, based on the theory of meso-damage mechanics, a multi-scale numerical simulation model of crack propagation resistance of girth welds is established to accurately describe the complete fracture behavior of crack tip passivation, crack initiation and tearing. An accurate characterization method of crack tip constraint difference of weld metal based on the equivalent plastic zone area of crack tip is proposed. A unified correlation between the CTOD of girth welds and the crack tip constraint is established, which is suitable for different material properties. The accuracy of the established constraint-fracture toughness correlation is verified by the finite element calculation results of full-scale pipeline girth welds, and the average relative error is less than 4 %. The research results can provide theoretical guidance for the accurate determination of fracture toughness of pipeline girth welds in fracture evaluation.