Usually when a large internal fluid pressure acts on the inner walls of flexible pipes, the carcass layer is not loaded, as the first internal pressure resistance is given by the internal polymeric layer that transmits almost all the loading to the metallic pressure armor layer. The last one must be designed to ensure that the flexible pipe will not fail when loaded by a defined value of internal pressure. This paper presents three different numerical models and an analytical nonlinear model for determining the maximum internal pressure loading withstood by a flexible pipe without burst. The first of the numerical models is a ring approximation for the helically rolled pressure layer, considering its actual cross section profile. The second one is a full model for the same structure, considering the pressure layer laying angle and the cross section as built. The last numerical model is a two-dimensional (2D) simplified version, considering the pressure layer as an equivalent ring. The first two numerical models consider contact nonlinearities and a nonlinear elastic-plastic material model for the pressure layer. The analytical model considers the pressure armor layer as an equivalent ring, taking into account geometrical and material nonlinear behaviors. Assumptions and results for each model are compared and discussed. The failure event and the corresponding stress state are commented.

Dry collapse is one of the possible failure modes of flexible pipes. It refers to the situation in which no damage occurs in the flexible pipe external sheath. In this scenario, all layers of the pipe withstand the external pressure loading in a deep-water application. Such a situation is addressed in this work, which proposes some simplified modeling techniques to represent straight and curved flexible pipes subjected to external pressure, undergoing dry collapse during simulation procedure. The results of the proposed models are compared to other reference results, from a fully three-dimensional (3D) finite element model. Good agreement has been got, even with the proposed simplifications with a large reduction in computational cost when compared to full 3D model.

Axial compressive loads can appear in several situations during the service life of a flexible pipe, due to pressure variations during installation or due to surface vessel heave. The tensile armor withstands well tension loads, but under compression, instability may occur. A Finite Element model is constructed using Abaqus in order to study a flexible pipe compound by external sheath, two layers of tensile armor, a high strength tape and a rigid nucleus. This model is fully tridimensional and takes into account all kinds of nonlinearities involved in this phenomenon, including contacts, gaps, friction, plasticity and large displacements. It also has no symmetry or periodical limitations, thus permitting each individual wire of the tensile armor do displace in any direction. Case studies were performed and their results discussed.

In order to study the axial compressive behavior of flexible pipes, a nonlinear tridimensional finite element model was developed. This model recreates a five layer flexible pipe with two tensile armor layers, an external polymeric sheath, an orthotropic high strength tape, and a rigid inner core. Using this model, several studies were conducted to verify the influence of key parameters on the wire instability phenomenon. The pipe sample length can be considered as one of these parameters. This paper includes a detailed description of the finite element model itself and a case study where the length of the pipe is varied. The procedure of this analysis is here described and a case study is presented which shows that the sample length itself has no practical effect on the prebuckling response of the samples and a small effect on the limit force value. The postbuckling response, however, presented high sensitivity to the changes, but its erratic behavior has made impossible to establish a pattern.

In order to study the compressive behavior of flexible pipes, a nonlinear finite element model was developed. This fully tridimensional model recreates a five-layer flexible pipe with two tensile armor layers, an external polymeric sheath, an orthotropic high strength tape, and a rigid inner nucleus. The friction coefficient is known as a key parameter in determining the instability response of flexible pipes’ tensile armor. Since the featured model includes all nonlinear frictional contacts between the layers, it has been used to conduct several experiments in order to investigate its influence on the response. This article includes a description of the finite element model itself and a case study where the friction between the layers of the pipe is changed. The procedure of this analysis is described here, along with the results.