The aim of this study is the assessment of the mechanical performance reduction due to manufacturing-induced gaps and voids (delaminations) in thermoplastic composite pipes. The effects of gaps are assessed based on the finite element modeling of an internal pressure load case and is validated by experimental tensile coupon testing. Results show a stress increase through-the-thickness in the layers having the same orientation, which depends linearly on the gap width. The assessment of voids is based on the modeling of external pressure and lateral crushing, in which the latter is also experimentally tested for validation purposes. No reduction in performance is observed for external pressure and an onset of delamination growth is observed for lateral crushing. A tool is proposed for a fast and computational inexpensive assessment of manufacturing-induced gaps in thermoplastic composite pipes to improve the design and manufacturing process and contribute to an improved integrity management system.