This study provides an engineering application of a continuum damage model to analyze the ductile tearing of axial surface cracks in X80 pipelines. Compact tension experiments were conducted to examine the behavior of large crack extension of X80 pipeline steel. The test results were used to verify the optimized parameter set of the proposed damage model. In the numerical model, progressive damage was restricted within a predetermined fracture process zone (FPZ). The material’s damage behavior in FPZ was described in terms of the Gurson–Tvergaard-Needleman (GTN) micro-mechanical damage model. The measured load versus load line displacement curve of CT specimens was numerically predicted using the damage model developed. T* integral was calculated to determine the limiting crack size in X80 pipelines. The damage model was then used to analyze the axial subcritical crack extension. It can help Leak-Before-Break (LBB) assessment.