Carlos Godinho

Crushing and Wet Collapse of Flowline Carcasses: A Theoretical-Experimental Approach

The present paper brings together theoretical predictions and experimental results, comparing crushing tests results as well as carcass wet collapse tests. The theoretical models are of two kinds: (i) numerical (FE) and (ii) analytical. The first kind is a restricted 3D version of a finite element model. The second kind is based on classic assumptions of equivalent ring behavior. Discussion is made on the real yield stress value to be adopted, as well as on the pertinence of geometric hypotheses. Sensitivity analyses, regarding ovalization and helical pitch are also presented.© 2010 ASME

Predictions of Armour Wire Buckling for a Flexible Pipe Under Compression, Bending and External Pressure Loading

During installation and operation a flexible pipe may be subjected to high compressive forces, high cyclic curvatures and external pressures leading to high reverse end-cap loads. Under such loading conditions, which occur particularly in the touchdown region for deep water applications, the limiting condition for the flexible pipe can be the compressive stability of the tensile armour wires. Two potential instability modes are possible: radial mode (birdcaging) and lateral mode (lateral wire disorganization). Previous work on the subject has established the key factors which influence the onset of each buckling mode [1],[2],[3] and [4].In order to ensure the feasibility of flexible designs for applications with increasing water depth, it is important to improve the knowledge of the mechanisms which can lead to instability of armour wires and enhance the ability to predict with greater assurance, the particular conditions which increase the risk of wire instability.The focus of this work is the comparison of finite element prediction of radial buckling (birdcaging) with physical testing results under loading states that lead a pipe to birdcaging failure.The numerical model incorporates all tensile armor wires and their interactions with each other and adjacent layers. The outer sheath and reinforcing tape layers are explicitly represented, while the inner layers of the pipe (pressure armour and carcass sheath) are idealized using a homogeneous representation. The model also incorporates the effects of manufacturing pre-tension and hoop strength in the anti-birdcaging tape layers which are critical determinants for the onset of buckling.A key aspect of the method presented is the means by which the loading is applied. Specifically, the modeling handles the simultaneous and controlled application of end rotations, axial compression and radial resistance of the tapes through to the point of tape failure, pipe ovalisation and subsequent radial displacement and buckling of individual wires.In summary, in this paper a solid modeling approach is presented, which is compared with full a scale sample test data, that enables the simulation of a flexible pipe undergoing large combined compression, curvatures and pressure loading.© 2012 ASME

Simplified Finite Element Models to Study the Dry Collapse of Straight and Curved Flexible Pipes

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.

A Nonlinear Analytical Model for Flexible Pipe Crushing Analysis

This paper discusses a nonlinear analytical model for flexible pipe crushing analysis, improving analytical models previously published in OMAE2003, 2010 and 2011. Following that path, and still based on the concept of equivalent pipes and rings, the present model discusses a strategy to cope with an elastic-to-plastic analysis. Such a model considers the combined action of squeezing and concentrated loads applied as representing those due to the caterpillar shoes. Experimental results and finite element analysis are used to assess the pertinence of analytical modeling hypotheses.Copyright

Crushing of flexible pipes under traction: a theoretical-experimental assessment

The paper presents a theoretical-experimental comparison concerning standard crushing-traction tests of flexible pipe prototypes. The theoretical model for crushing is analytical and based on classic assumptions of equivalent pipes, applying model previously published in OMAE2003, and OMAE2010. Such a model considers the combined action of squeezing, concentrated loads due to the caterpillar shoes as well as the effect of initial ovalization. The experimental measures include a detailed internal geometrical mapping of the deformed carcass, until plastic deformation becomes evident. Discussion is made on the pertinence of modeling hypotheses. Sensitivity analyses, regarding initial ovalization and helical pitch of the pressure armor are also addressed.Copyright

Structural Behavior of Umbilicals: Part I—Mathematical Modeling

Umbilicals for offshore application are very complex, since they combine elements of different mechanical behavior, such as steel tubes, thermoplastic hoses and power cores in a single structure, not to mention helically laid-up armouring layers and polymeric sheathes. This motivates continuous research on their mechanical modeling. This paper presents research undertaken in the structural behavior of umbilicals and focus on the mathematical modeling of the elements, which are gathered into concentric layers. Interaction between layers is included as well as helical lay-up of elements. The model here presented will be compared to a set of experimental results in a separate paper (Part II). An analytical model was developed combining equilibrium equations, geometric compatibility and constitutive relations to obtain a set of equations that describe the umbilical behavior under external loads. This set of equations is numerically solved to obtain contact pressures (or gaps) among layers, radial variations and strains in the elements (used to calculate the stresses). The model was built to be general in order to be able to cope with complex cross-sections designs often encountered. It was then implemented in a tailor made local analysis software, called UTILFLEX®. Both modeling and software resulted from a development program partnership between Prysmian Cables & Systems and University of Sao Paulo. The paper will present modeling hypotheses and structural models that were used for steel tubes, hoses (thermoplastic and reinforced) and power cables and how the interaction among them has been treated.Copyright

Effect of Material Plasticity and Metallic Layer Profiles on the Crushing Resistance of Flexible Pipes

This paper presents a numerical 3D finite element model to simulate a flexible pipe under crushing-traction condition, which is a typical situation found during its laying operation. This model considers the geometry of some layers from the flexible pipe, responsible of providing the most contribution to its radial strength (e.g., interlocked carcass, internal polymeric layer, pressure armor, and external polymeric layer) and geometry of laying system shoes. It also considers the flexible pipe initial ovalization and the squeezing effect due to the tensile armor layers under traction. A numerical-experimental comparison is presented, in order to show the model validity.Copyright

CRUSHING TESTS OF FLOWLINES INTERNAL LAYERS: AN EXPERIMENTAL APPROACH VIA OPTICAL MOTION CAPTURE AND IMAGE PROCESSING

New optical measurement approach for crushing tests of flow lines internal layers is detailed, based on an accurate tracking of the deformed carcass section through image processing. The results are compared to those from standard procedures based on discrete measurements using calipers. The new approach shows to be not only appropriate for the standard measurement requirements but also enables a comprehensive understanding of the crushing behavior.© 2010 ASME

Structural Behavior of Umbilicals: Part II—Model-Experimental Comparisons

A set of tests was performed in a non-armored Steel Tube Umbilical (STU), including pure pressure loading, constant and variable tension loads and combinations of constant and cyclic bending moment and tension. Tests were made for pressurized and non pressurized conditions. Strains were measured with strain gages attached to the external surface of selected tubes. Instrumentation was performed in four windows that were opened on the umbilical outer sheath to provide access to the tubes. Besides the strains, tension, internal pressure and imposed angle were measured. Comparisons with results obtained using the model presented in Part I, [1], are presented for different load conditions.Copyright