Wet And Dry Collapse of Straight And Curved Flexible Pipes: a 3D FEM Modeling

Flexible pipes for offshore applications can operate in deep water. In this situation the pipe must resist to the external pressure without collapse. Two different failure modes must be analyzed: the dry and the wet collapse. The first is possible to occur when the external polymeric layer of the flexible pipe has no damages. In the wet collapse scenario the external polymeric layer is damaged, permitting that the water floods the annulus. So, the internal polymeric layer receives the external pressure. In this case the limit external pressure to that the pipe can resist is usually smaller than in the former one. This work deals with both the failure modes, comparing their characteristics and collapse pressure values. For that purpose, a full 3D finite element model was constructed, including the interlocked carcass, the internal polymeric layer, the pressure armor and the external polymeric layer. The model considers all the cross section details of the pressure armor and interlocked carcass and contemplates self-contacts and interactions between layers. The length of pipe simulated corresponds to dozens of pitches of the interlocked carcass. The developed model can deal with a straight or curved flexible pipe to study the effect of curvature in the collapse pressure limit. Case studies are presented, compared and discussed.