Parametric analysis of an offloading hose under internal pressure via computational modeling

An offloading hose is a complex structure, mainly composed of rubber, cords and steel coil, which is used worldwide for oil production and transport systems such as offloading operations in Catenary Anchor Leg Mooring (CALM) buoy. The cords play a vital role on the hose, being responsible for resisting to the applied internal pressure. In this work, finite element models with axisymmetric and 3D elements have been developed to estimate burst pressure of a double carcass floating hose with nominal diameter 20″ and design pressure of 21 bar. Finite element models have been developed in commercial software using reinforcement bars (rebars) to represent cords behavior. A parametric analysis has been performed, and mesh convergence was also evaluated to predict stress concentration in the failure regions. In addition, complex non-linear calculations for the contact between the hyperelastic rubber, which was modelled with Arruda-Boyce's, and the polyester, polyamide and hybrid reinforcement cords, modelled with Marlow's theory, were considered in the FEM. Maximum load in the REBAR layers was used to predict failure in the cords. Actual full-scale experiments were carried out for comparisons, prototypes with different number of layers and cord material have been manufactured. Burst pressure tests of the carcasses was the criterion used to evaluate the minimum requirements of the Oil Companies International Marine Forum (OCIMF). A maximum deviation of 7.5% was found between computational predictions and experimental results. Therefore, the proposed computational model was considered suitable to be used in the design of these hoses, especially for parametric analysis.