Flexible Pipes: Influence of the Pressure Armor in the Wet Collapse Resistance

When subjected to large valued external pressures, flexible pipes may collapse. If the external sheath is damaged, all the external pressure is directly applied to the internal polymeric layer that transmits the loading to the carcass layer. When the carcass layer fails due to this effect, the wet collapse occurs. This failure mode must be taken into account in the flexible pipe design. The study for this problem can be done neglecting the influence of the pressure armor, but this assumption may underestimate the wet collapse pressure value. This work aims to study the pressure armor effect in the numerical prediction of wet collapse. The main contribution of the pressure armor to the flexible pipe resistance to collapse is to be a constraint to the radial displacement of the carcass and the internal polymeric layers. Two models were developed and compared with the purpose of calculating the critical value of the external pressure that causes carcass layer to collapse. The first and most complete study is done using a ring 3D FEM model that takes into account both the real pressure armor and carcass real profiles. In the second model, the pressure armor is considered adopting an equivalent ring simplification. The comparison of the results of both the models clarifies how the behavior of the pressure armor in the wet collapse situation is. Parametric studies of initial ovalization of the carcass and initial gaps in manufacturing of flexible pipes are made and discussed.