During the end fitting (EF) assembly, the tensile armors of flexible pipes are folded and then unfolded to allow the assessment to the inner sheath and the activation of the inner sealing system. This procedure leaves residual stresses and plastic deformations on these armors, which affect their fatigue resistance and, consequently, the overall performance of the pipe. Hence, in this work, a methodology to predict the fatigue resistance of tensile armors inside an EF is proposed. This methodology relies on stresses calculated with a previously presented three-dimensional finite element (FE) approach and is employed to analyze the fatigue response of a 6” production riser in catenary configuration. This fatigue analysis not only addresses the effects from several irregular sea states but also the local stress concentrations associated with the EF assembly and pre-operational tests (e. g., Factory Acceptance Test, FAT). The results obtained indicate that the EF entrance may be a critical point for fatigue failure and, moreover, the lower fatigue resistance is related to a region where higher alternate stresses occur despite the very high mean stresses are observed in other regions along the tensile armors.

In this work, a solid three-dimensional finite element (FE) approach is proposed to investigate the stress distribution along the tensile armors of flexible pipes inside their end fittings (EFs). This approach employs two different models. The first model consists of a single tensile armor, which is meshed with solid FEs, and a rigid surface that represents the EF. A toroidal template is also considered and the EF mounting process is simulated. In the second model, the deformed armor and the stress state from the first model are considered and the voids between the armor and the EF are filled with resin, which is also modeled with solid FEs. Geometric and material nonlinearities are addressed and the interaction between the different components are ensured with contact elements. A case study is conducted to observe the stress distribution along the tensile armor considering typical operational loads. The results obtained are compared to those calculated with a previously proposed analytical model showing good agreement, but also evidencing the need to adequately simulate the EF mounting process and the pre-operational tests. Moreover, intense stress concentrations at the entrance of the EF are observed thus indicating that this region can be critical in fatigue analyses.

During the end fitting (EF) mounting process, the tensile armor wires of flexible pipes are folded and then unfolded. This process usually leaves plastic deformations and generates sharp curvatures on these wires just at the EF entrance. Dissections performed in several flexible risers, which were in operation or subjected to qualification tests, revealed that this region is especially prone to fatigue failure thus affecting the overall performance of these structures. In this work, an analytical approach devoted to predict the stresses induced in the tensile armor wires at the EF entrance is combined with a previously presented methodology to compute the fatigue life of flexible risers in order to account for the EF mounting process. A parametric study is also conducted aiming at evaluating the effect of the folding radius, the stress level induced during pre-operational tests and the contact conditions between the epoxy resin and the tensile armor wires on the fatigue resistance of a free hanging flexible riser. These analyses indicate that the choice of the mean stress correction model, the folding radius and the stress level induced during the pre-operational tests significantly modify the fatigue resistance of the tensile armor wires. The contact conditions also influence the fatigue resistance, but their effect is less significant.

A torpedo base is a type of conductor casing that embeds into the seabed mainly by free fall using its own weight as driving energy. One of the advantages of this concept is to install the conductor casing before the dynamic positioned (DP) drillship arrival at the location. This reduces the time of the well drilling leading to significant cost saving. However, the need to withstand the challenging loads of the ultra-deep water scenarios pushed the typical torpedo base design to its limit and, consequently, modifications to its original geometry and more accurate design models are needed. Therefore, in this work, a new torpedo base, designed to sustain high axial loads in very soft clays, is analyzed with a three-dimensional finite element (FE) model. This model accounts for the setup-effects of the soil with the use of a previously proposed analytical approach to estimate the stress state of the soil at any time after the installation of the base. The results obtained indicate that the axial holding capacity of the base varies along time. The holding capacity increase rapidly at the beginning of the installation, but this rate reduces after the first days. Depending on soil characteristics, full axial capacity may be reached more than one year after the installation of the base. Moreover, the use of more than four fins welded to the shaft of the conductor casing modifies the shear zone along the base, but does not contribute to a significant increase in the axial holding capacity.

Torpedo anchors have been used in various offshore applications especially due to its low cost installation and the ability to withstand high inclined loads. This anchor consists of a shaft in which flukes are welded in order to increase the soil-anchor contact region and, consequently, its holding capacity. Since this anchor presents a singular geometry, different from a regular cylindrical anchor/pile, the computation of the holding capacity of a torpedo anchor is not straightforward. In a previously presented work, the holding capacities of typical torpedo anchors were assessed with a finite element (FE) model in which both the anchor and the surrounding soil are represented with three-dimensional finite elements. However, this FE model demands a significant computational effort and, consequently, simpler approaches would be desirable in order to design these anchors. Relying on the FE model and a parametric study, this paper presents simple formulae to predict the holding capacities of torpedo anchors embedded into cohesive soils. These formulae are employed to predict the holding capacities of two different torpedo anchors, which are compared to those estimated with the FE model. Results agreed very well indicating that this simpler approach may be employed to quickly evaluate the holding capacities of these anchors.

In this work, a bidimensional finite element (FE) approach is proposed to estimate the stresses induced in the tensile armor wires inside end fittings (EF) of flexible pipes. This approach accounts for the residual stresses caused by the mounting procedure and the deformed configuration of the wire. The resin and its interaction with the wires are also addressed. A parametric study was performed aiming at investigating the influence of three parameters on the stress state along the wire, i. e. , the contact conditions between the resin and the wire inside the EF, the stress levels induced during the factory acceptance test (FAT) or the offshore leak test (OLT) and the resin elastic properties. The study pointed that high stress concentration is induced in the transition between the flexible pipe’s body and the EF and the stress distribution along the wire may be significantly affected by these parameters. Moreover, the apparent axial stiffness of the wire is also modified by its anchoring conditions, which may lead to non-uniform stress distributions among the wires of the tensile armor layers.

Torpedo anchors have proven to be one of the most important alternatives for mooring systems, especially in Brazilian offshore fields. Their installation involves many hydrodynamic and soil-structure interaction aspects and, therefore, their vertical stability cannot be always assured. This often results, after their installation, in an inclination between the anchor and a vertical axis called tilt angle. The traditional approach to assess the holding capacity of torpedo anchors relies on the hypothesis that the relative angle between the load direction and the axis of the anchor may be used in conjunction with a finite element model in which a perfectly vertical anchor is considered. In this work, this assumption is discussed. A parametric study in which four different tilt angles are combined to various load inclinations was conducted. The study relied on a previously proposed FE model. The results obtained indicate that the use of the traditional approach is safe for relative angles higher than 40° and lower than 140° For other angles, the approach leads to values slightly higher than those predicted with the direct consideration of the tilt angle.

This paper studies the structural response of a 6.0 ″ flexible pipe under pure tension considering two different situations: the pipe is intact or has five wires broken in its outer tensile armor. A three-dimensional nonlinear finite element model devoted to analyze the local mechanical response of flexible pipes is employed in this study. This model is capable of representing each wire of the tensile armors and, therefore, localized defects, including total rupture, may be adequately represented. Results from experimental tests are also presented in order to validate the theoretical estimations. The theoretical and experimental results indicate that the imposed damage reduced the axial stiffness of the pipe. High stress concentrations in the wires near the damaged ones were also observed and, furthermore, the stresses in the inner carcass and the pressure armor are affected by the imposed damage, but, on the other hand, the normal stresses in the wires of the inner tensile armor are not.

Despite being largely used to install flexible risers, neither the loads imposed by hydraulic collars nor the response of the flexible riser to these loads have been previously studied. Hence, this paper aims at presenting a finite element (FE) model to calculate not only the loads imposed by a typical hydraulic collar to a flexible riser, but also the response of this structure to the imposed loads. A 9,5” flexible riser is analyzed and the obtained results are compared to the ones from experimental tests carried out by PETROBRAS and COPPE/UFRJ.