Fabiano Bertoni

A FE Model to Predict the Stress Concentration Factors in the Tensile Armor Wires of Flexible Pipes Inside End Fittings

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.© 2013 ASME

A Novel Concept of Flexible Pipe End Fitting: Tensile Armor Foldless Assembly

The structural behavior of the flexible pipe tensile armors inside the end fitting (EF) is different from the one observed in the pipe body. The actual design methodology shows that the end fitting of the riser top section (at the interface with the floating unit) is critical with respect to fatigue, as stress concentration that occurs in this region during the end fitting assembly leading to significant plastic strains.Aiming at improving the structural performance of flexible risers, Petrobras designed and patented a novel concept of flexible pipe end fitting in which its assembly can be carried out without the need of folding the tensile armor thus avoiding the introduction of plastic strains and residual stresses in this layer.In order to assess and quantify the benefits of this new concept, in this work, a comparative study between the current end fitting concept used by the industry and the new technology proposed by Petrobras was conducted. This study comprises not only the stress distribution along the wire inside the end fitting but also the fatigue performance. For this purpose, finite element analyses have been carried out considering the entire end fitting mounting process and also the operational loads.These analyses were calibrated with results from midscale tests in which a longitudinal slice of the real end fitting was simulated. An instrumented tensile armor wire was embedded in the resin epoxy and pulled out from a test device.The results obtained show that the using of the proposed technology results in a considerably end fitting fatigue performance improvement.Copyright