Unbonded flexible risers are key components in offshore oil and gas production, enabling safe hydrocarbon transport under extreme deepwater conditions. The pressure armour (PA) layer is the primary metallic layer, which is designed to resist internal pressure; however, its complex helical geometry poses significant modelling challenges. This study presents a comprehensive numerical and analytical investigation of the burst behaviour of the PA layer under internal pressure. Three FE modelling strategies are developed and compared with theoretical predictions: a simplified axisymmetric 2D model, a fully detailed 3D helical model, and an efficient periodic boundary condition (PBC) model. The proposed PBC-based approach offers a practical balance between accuracy and efficiency, providing an effective tool for parametric analysis and design optimisation of flexible risers.