Background <p>The bandgap characteristics of phononic crystals (PCs) can effectively suppress the propagation of elastic waves in fluid-conveying pipeline. However, most prior studies assume idealized conditions and give limited attention to how boundary constraints influence the bandgap behavior of periodic composite PC pipelines.</p> Methods <p>Euler-Bernoulli beam theory is combined with the dynamic stiffness method and the transfer matrix method (TMM) to compute the band structure and frequency response of periodic composite PC pipelines conveying fluid. Typical engineering boundary conditions are considered to systematically evaluate their effects on bandgap formation and wave attenuation. Furthermore, the tuning mechanisms associated with structural parameters, material properties, and internal fluid velocity are investigated, and their impacts on bandgap characteristics are also quantified.</p> Results <p> The analytically derived results are validated through experiments on a finite periodic PC pipeline and corresponding finite element simulations. Bandgap-induced attenuation depends on both the excitation location and the support configuration. Nevertheless, strong suppression performance is preserved under non-ideal boundary conditions.</p> Conclusions <p> These findings provide practical guidance for the vibration control design of fluid-conveying PC pipelines under realistic support constraints, highlighting the robustness of bandgap effects beyond idealized assumptions.</p>