Full-scale tests and numerical investigation on the bending strain failure of low-strength-matched X80 pipeline girth welds

The fracture behavior and strain capacity of girth welds in large-diameter high-grade steel pipelines are crucial for their structural design and safe operation. This study conducts full-scale four-point bending tests on X80 steel pipelines (D1219×22 mm) under low-strength matching conditions to obtain the pipeline strain capacity under conditions close to actual service scenarios. The main goal is to systematically investigate the effects of internal pressure, external loads, and crack geometric dimensions on the strain-bearing capacity. Digital image correlation (DIC) technology and a multi-point strain monitoring system are integrated to real-time collect key data, including strain response, load-displacement, internal pressure, and crack mouth opening displacement (CMOD). A finite element numerical model is established based on the results of small-scale material mechanical property tests. Moreover, a comparative analysis is performed between the simulation results and the test data. The results indicate that the numerical simulation is in good agreement with the test results; pipelines with defects under low strength matching conditions still maintain a certain load-bearing capacity, and their failure is mainly caused by the through-thickness propagation of cracks. This study enriches the global pipeline strain capacity database and provides a systematic experimental framework and theoretical support for the research on the fracture behavior of large-diameter high-grade steel pipelines.