Abstract: To reveal the local damage mechanisms of natural gas pipelines subjected to high-speed rigid projectile penetration, a unified analytical solution for the plastic radius of pipeline local damage was established by high-speed projectile experiments, mesoscale numerical simulations, and theoretical analysis based on the unified strength theory. An analytical investigation was carried out to provide a physically reasonable and engineering-oriented description of the local plastic deformation behavior of cylindrical pipelines subjected to high-speed impact loading. The high-speed projectile experiments were conducted on L415M natural gas pipeline using rigid bullets and the key damage characteristics were obtained, including the impact morphology of the pipeline striking face, the distribution of the plastic zone, and the maximum plastic radius. Based on the analysis of experimental results and with ANSYS/Workbench, a dynamic numerical model was established to simulate the penetration process. The local stress and strain distributions of the pipeline subjected to high-speed projectile penetration were analyzed. The material behavior of the steel pipeline was described using a bilinear elastoplastic constitutive model to represent yielding and linear strain hardening during penetration. To evaluate the influence of the intermediate principal stress under complex three-dimensional stress states, the sensitivity of the intermediate principal stress parameter b was systematically analyzed based on the unified strength theory. Moreover, by coupling the unified strength theory with a finite cylindrical cavity expansion model, an analytical expression for the plastic radius of pipeline local damage was derived. Based on the derived solution, a unified local damage failure criterion for natural gas pipelines subjected to high-speed penetration was proposed. According to this criterion, local damage failure of the pipeline subjected to high-speed impact loading could be identified when the measured maximum plastic radius exceeded the critical value r_max which was determined both by the material uniaxial tensile fracture strain ε_f and the model parameter A including the intermediate principal stress parameter b. The comparisons between theoretical predictions and experimental results indicate that the proposed analytical solution provides a reasonable description of the local plastic deformation behavior of the natural gas pipeline. Especially, when b=0.2, the theoretical predictions shown the best agreement with experimental measurements and relative errors were less than 10%. The proposed method effectively characterizes the evolution of the plastic zone and local damage patterns of pipelines subjected to high-speed impact loading. The results provide theoretical comprehension and engineering reference for safety assessment and protective design of long-distance natural gas pipelines subjected to high-speed impact loading.