Spread moored FPSO (Floating Production and Storage Off-loading) vessels are typically used in the large West African oil fields. The oil from these vessels is transferred to shuttle tankers via an Oil Loading Terminal(OLT). This usually consists of 2 to 3 flexible offloading lines installed between the FPSO and a Single Point Mooring (SPM) with large internal diameter for 24 hour offloading. The final connection between the SPM and the shuttle tanker is made by floating hoses.Currently the flexible off-loading lines (OOL) are designed with steel wire armor, as typically used in the Offshore West Africa Fields. With pipes reaching 23Љ internal diameter and up to 2300m in length, the steel wires give the pipes a substantial weight generating the need for a large number of buoyancy modules to minimize the tension at the FPSO and OLT. These modules significantly add to both the cost and the installation time.Carbon Fiber Composite (CFC) is characterized by its light weight and exceptional fatigue performance, with the ability to be manufactured as an armor wire in a long continuous single length (more than 4000 meters). It can be used as an alternative to steel wire armors to design an optimized flexible pipe structure with significant advantages:• 45% decrease in submerged weight • Potential to install in double catenary configuration, without leading to excessive top tension • Buoyancy Modules are no longer required -installation is safer and quicker • Riser configuration is no longer impacted by fluid density These advantages allow greater flexibility in the position of the FPSO relative to the SPM with a fixed length of riser. Because CFC Armor is not susceptible to corrosion, service life of the flexible pipe is unaffected by breaching of the outer sheath and subsequent flooding of the annulus.This new design of flexible pipe, together with the installation and operational configurations, will be presented in this paper. In order to demonstrate the suitability of CFC, the material performance testing in severe fatigue and ageing conditions will be disclosed. The economic viability will be demonstrated by showing how the material cost is offset by the elimination of buoyancy modules and faster installation. Additionally this technology enables flexible OOL risers to be produced in a long single length.

The paper focuses on a Finite Element (FE) model developed at IFPEN, denominated 3D-Periodic, which is dedicated to flexible riser studies. It takes full advantage of the geometric and loading periodicities to reduce the model length and the CPU cost. The model is developed in a commercial FE software with dedicated pre- and post-treatment packages. The model can represent standard cyclic bending with internal pressure and axial tension as well as external pressures load cases to investigate the risk of lateral buckling of tensile armors or of pipe collapse.

The flexible riser global behavior is of major importance during the design phase of a flexible riser system configuration. Flexible riser design is an optimization loop involving several iterations. The flexible riser main mechanical characteristics are used as inputs into the global dynamic analysis. The dynamic analysis is performed to derive global loads that are then used for the flexible riser design. At each step of the riser design optimization loop, from the global configuration to flexible pipe cross-section, accurate knowledge of the flexible pipe mechanical characteristics is essential. One of the main mechanical characteristics of a flexible riser that drives its global behavior is its bending stiffness. Considering the flexible riser composition, the bending stiffness is much lower than its torsional and axial stiffnesses and therefore has a larger influence on its static and dynamic behavior. In order to simplify the global analysis, the first approach considered uses a linear bending stiffness. In this case, only the contribution of the polymer layers of the flexible is accounted for. The linear bending stiffness is therefore only impacted by thermal loads. In reality, because of the friction that can occur between the armor layers, the bending behavior is non-linear and the relation between bending moment versus curvature is hysteretic. This hysteretic behavior induces energy dissipation and therefore, when accounted in the global modeling of the riser, reduces the curvature response of the flexible riser. Technip and IFPEN previously developed a model to describe mechanical flexible pipe characteristics. This model is based on the finite difference method. To ensure the accuracy of stress prediction of this method in response to external loads (tension, curvature, internal pressure and external pressure), results are validated with both experimental and finite element methods. This paper presents the theory of bending behavior of a flexible riser and explains how the model is used to derive a hysteric bending model. The matrix of experimental tests campaigns performed on flexible pipe to characterize bending behavior of flexible risers, and comparisons with hysteretic behavior predictions from the FEA and finite difference models are presented. Finally results from experimental tests, FEA and calculated hysteretic bending models are implemented into the dynamic analysis model of a flexible riser system. Then the global behaviors of the flexible pipe configuration, with the different properties, are compared.

Spread moored FPSO (Floating Production and Storage Offloading) vessels are generally used for the large West African oil fields. The oil is transferred from the FPSO to shuttle tankers via an Oil Loading Terminal (OLT). 2 to 3 large diameter flexible lines are connecting the FPSO to the OLT. The final connection between the OLT and the shuttle tanker is made by floating hoses. The single length of each flexible pipe can be typically 2,300 meters or higher, and the internal diameter is generally very large in the order of 15_23″ to minimize the pressure drop and the offloading time. Conventional flexible pipe is the most suitable solution for this application. However, its long length and large diameter require a large number of buoyancy modules which are necessary to support the substantial weight generated by the steel armor wires. An alternative to steel is Carbon Fiber Composite (CFC). This material is not only twice as strong and five times lighter than a high strength steel but it is also characterized by its exceptional performance in fatigue. As the weight of the composite armor flexible pipe is significantly reduced, the use of buoyancy is no longer necessary. The pipe can also be manufactured in a single length without intermediate connection. A qualification program based on a 19″ internal diameter prototype has been launched. This is the first time that a large internal prototype with Carbon Fiber Composite Armor (CFA) and end-fittings have been designed and manufactured. The main goals are to confirm the suitability of the CFA flexible pipe for oil offloading application in accordance with the design tools. The mechanical behavior responses of the CFA are monitored by strain gages when the flexible pipe is in straight and curved positions under internal pressure and bending cycles. The paper will present the main mechanical properties and the overall performance of the flexible pipe designed and tested. The economic viability will be demonstrated by showing how the CFC material cost is positively offset by the removal of the buoyancy modules and a faster offshore installation.

Since the beginning of the 21st century FLow-Induced Pulsations (FLIP) has been more and more experienced. The phenomenon is characterized by an acoustic wave that is created inside of the flexible pipe and that may lead to significant fatigue failure of the adjacent equipment. Flexible pipe integrity is not called into question regarding this phenomenon. In this context, a FLIP joint test involving TOTAL E&P, IRPHE (Institut de Recherche des Phenomenes Hors Equilibre) / CNRS (Centre National de la Recherche Scientifique), LMA (Laboratoire de Mecanique et d'Acoustique) / CNRS and TechnipFMC was conducted end of 2016 at CESAME Poitiers (France). The test was performed in a 6" internal diameter and 18-meter-long TechnipFMC flexible pipe. Both flow directions were tested to assess the influence of the rounded edges of the carcass. On the one hand, this paper presents the experimental test setup and the main results that came out of the test. On the other hand, this paper also presents the comparison between tests results and TechnipFMC analytical model outcome. Moreover, combining experiments and theoretical point of view enabled reproducing the phenomenon. A better understanding of the phenomenon will allow flexible pipes suppliers to propose mitigations or cancellation of FLIP to companies.