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Results
An Investigation About the Shape of the Collapse Mode of Flexible Pipes
Malta, Eduardo Ribeiro (Dept. of Mechanical Engineering, University of São Paulo) | de Arruda Martins, Clóvis (Dept. of Mechanical Engineering, University of São Paulo) | Neto, Alfredo Gay (Dept. of Mechanical Engineering, University of São Paulo) | Toni, Fernando Geremias (Dept. of Mechanical Engineering, University of São Paulo)
ABSTRACT: When the external layer of a flexible pipe is damaged, the seawater floods the annulus. The external pressure is then applied directly on the internal polymeric layer. That pressure, associated with an initial ovalization, can cause buckling of the interlocked carcass layer if it surpasses a critical value. In that context, a plane stress Finite Element model is developed in order to study the post buckling behavior of the flexible pipe, which is characterized by its particular geometric transition. The cross section of the deformed flexible pipe, depending on the initial conditions, may assume the form of an "eight" or a "heart" as they are commonly known. The analysis is conducted using a quasi-static method known as the Arc-Length method. This article intends to discuss the factors that influence the post buckling shape, including geometry of the layers of the tube and boundary conditions. INTRODUCTION The flexible pipe structure consists in several concentric layers. The dimensions and quantities of these layers are function of the load requirements of each tube. These loads, on the other hand, are a direct consequence of the environment in which the tube is inserted. This paper focuses on the region of the tube known as "structural nucleus". In this paper, the structural nucleus of a 4" flexible pipe is submitted to a particular load case causing a failure mode known as the "wet collapse". In that case, the external plastic layer has a crack, compromising its sealing function. Since the tensile armor and pressure layer cannot hold the water, the pressure is then applied directly to the internal polymeric layer. At the event of the collapse, when buckling occurs, the structural nucleus changes its shape. In that case it may assume a geometry that reminds the shape of an "eight" or a "heart".
Wet And Dry Collapse of Straight And Curved Flexible Pipes: a 3D FEM Modeling
Neto, Alfredo Gay (Department of Mechanical Engineering University of São Paulo) | de Arruda Martins, Clóvis (Department of Mechanical Engineering University of São Paulo) | Malta, Eduardo Ribeiro (Department of Mechanical Engineering University of São Paulo) | Godinho, Carlos Alberto Ferreira (Prysmian Cables and Systems) | Neto, Teofilo Ferreira Barbosa (Prysmian Cables and Systems) | de Lima, Elson Albuquerque (Prysmian Cables and Systems)
ABSTRACT: 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. INTRODUCTION Flexible pipes are structures composed by many layers used for offshore oil exploration. The layers are usually made of different materials. Flexible pipes can present many failure modes, being many of these related to structural causes. This work deals with two failure modes, named "dry collapse" and "wet collapse". Both are related to the flexible pipe failure when it is subjected to external pressure loads. The "dry collapse" failure mode can occur when the external polymeric layer has no damages.
- North America (0.46)
- South America > Brazil (0.28)