Research on the strain capacity of girth welds in pipelines containing fusion line crack defects

Abstract In response to the lack of research into the impact of fusion line cracking on the strain capacity of girth welds in high-grade steel pipelines, this paper focuses on the fusion line cracked pipeline on the inner surface of the girth weld. Using a combination of experimental testing and finite element analysis, we create a numerical simulation model of the strain capacity of the girth weld. It takes into account differences in the intrinsic material curves of the base, heat-affected, and weld zones, as well as the Gurson-Tvergaard-Needleman (GTN) damage parameters. Based on the behaviour of the crack tip during tearing, a method for determining crack initiation failure and characterising strain capacity is established. The influence of geometrical factors is systematically discussed. The results show that, based on the experiment-simulation hybrid method, testing of the local ontology of the pipe girth weld and calibration of the GTN damage parameters can be achieved. Wall thickness is the key geometrical factor affecting strain capacity, and its influence decreases with increasing pipe diameter. The outer diameter has little influence. Changes to small cracks significantly affect strain capacity, and the influence of crack depth on strain capacity is greater than that of crack length. The magnitude of strain capacity reduction caused by changes in single-dimensional crack size converges over a wide range. This study provides a basis for reference in the safety assessment and failure control of pipeline ring welds with fusion line cracks.