Type III cylinders use a load-bearing metal liner, commonly aluminium, beneath a fibre-reinforced overwrap. CT can support evaluation of liner-wall variation, winding irregularity, delamination, inclusions, impact damage and local anomalies at the liner–composite interface. Type IV cylinders replace the metal liner with a non-load-bearing polymer liner and typically require attention to the composite overwrap, liner deformation, boss–liner region, local gaps, porosity and winding consistency. Industrial X-ray computed tomography provides cross-sectional and 3D internal views without cutting the cylinder, supporting product development, process validation, comparative quality studies and failure investigation. Detectability depends on cylinder size, material density, geometry, scan energy, resolution and reconstruction artefacts. CT results require qualified interpretation and engineering acceptance criteria, and complement—not replace—mandatory visual, leak, proof, burst, acoustic-emission or other statutory inspections.