This study proposes a limit state equation for steel pipelines under complex loading conditions, based on the unified yield criterion (UYC). The equation accounts for various loads, including internal pressure, axial forces, and bending moments, and is validated through full-scale burst tests. The study shows that the UYC-based model can accurately predict failure pressure under complex loading conditions. The model considers the influence of the second principal stress on failure, which is critical for pipelines under combined loading. The study also compares the performance of different yield criteria, finding that the von Mises criterion provides the most accurate predictions, followed by the ASSY criterion. The results demonstrate that the proposed model is effective in assessing failure pressure and selecting appropriate yield criteria based on load conditions. The study also highlights the importance of considering circumferential stress in pipelines under complex loading, as it is a key indicator of internal pressure failure. The model was validated using finite element analysis and experimental data, showing good agreement between predicted and observed failure pressures. The study concludes that the UYC-based limit state equation is a reliable tool for assessing the integrity of pipelines under complex loading conditions.This study proposes a limit state equation for steel pipelines under complex loading conditions, based on the unified yield criterion (UYC). The equation accounts for various loads, including internal pressure, axial forces, and bending moments, and is validated through full-scale burst tests. The study shows that the UYC-based model can accurately predict failure pressure under complex loading conditions. The model considers the influence of the second principal stress on failure, which is critical for pipelines under combined loading. The study also compares the performance of different yield criteria, finding that the von Mises criterion provides the most accurate predictions, followed by the ASSY criterion. The results demonstrate that the proposed model is effective in assessing failure pressure and selecting appropriate yield criteria based on load conditions. The study also highlights the importance of considering circumferential stress in pipelines under complex loading, as it is a key indicator of internal pressure failure. The model was validated using finite element analysis and experimental data, showing good agreement between predicted and observed failure pressures. The study concludes that the UYC-based limit state equation is a reliable tool for assessing the integrity of pipelines under complex loading conditions.