Abstract：We present the study of unbonded flexible pipe and provide a case of 8 inch unbonded flexible riser at the water depth of 300 m. Firstly, the theoretical calculation formulae are introduced for the analysis of axial and torsional stiffness of the unbonded flexible riser. On the basis of the theoretical calculation, finite element analysis is carried out by modelling all layers separately to reflect the mechanical behavior of each layer. The numerical results are compared with the theoretical results for tensile load and torsion. The different contributions of each layer are discussed. Under the axial load or torque, the theoretical results are consistent with the numerical results, and the theoretical results of torsional stiffness are more conservative. During the actual engineering design, the appropriate calculation method can be chosen according to the design stage.
