Abstract: Rolled plate processing induces texture evolution and directional variations in the mechanical properties of pipeline steels, leading to pronounced differences in yielding, hardening, and deformation behavior along different directions, and consequently affecting localized plastic deformation and failure during pipeline service. To address the limitation of conventional isotropic constitutive models in characterizing the direction-dependent plastic behavior of pipeline steels, X52 pipeline steel was selected as the research material in this study. In-situ tensile tests were conducted along different orientations to obtain the stress-strain responses and plastic strain ratio parameters, and five hardening models were comparatively evaluated to identify the most suitable hardening law for describing the plastic-stage response of X52 pipeline steel. On this basis, a non-associated anisotropic constitutive framework was established by combining the Hill48 yield function, an independent plastic potential function, and the Multi-Voce hardening model. Its ability to predict macroscopic plastic deformation was validated through comparison with a numerical model based on the von Mises yield criterion. The results show that X52 pipeline steel exhibits pronounced strength anisotropy, whereas the variation in plastic flow anisotropy is relatively limited. Both the isotropic and anisotropic models can accurately reproduce the load-displacement responses of specimens with different orientations. Compared with the isotropic model, the anisotropic model provides an integrated description of the plastic responses in different orientations within a unified parameter framework, demonstrating better physical consistency and parameter transferability. The proposed model can provide a theoretical basis for analyzing the direction-dependent plastic behavior of pipeline steels, as well as for evaluating plastic failure and predicting ductile fracture of pipeline structures under complex service conditions.