1 Copyright © 2011 by ASME Proceedings of OMAE2011 30 th International Conference on Ocean, Offshore and Arctic Engineering 19 – 24 June 201, Rotterdam, the Netherlands OMAE2011-49524 CRUSHING OF FLEXIBLE PIPES UNDER TRACTION: A THEORETICAL- EXPERIMENTAL ASSESSMENT Guilherme R. Franzini 1 (gfranzini@usp.br ) Celso P. Pesce 1 (ceppesce@usp.br ) Fernanda C.M. Takafuji 1 (fernanda.takafuji@gmail.com ) Rodolfo T. Gonçalves 2 (rodolfo_tg@tpn.usp.br ) Rafael Tanaka 3 (rafael.tanaka@prysmian.com ) Marcelo Silva 3 (marcelo.silva@prysmian.com ) Teófilo Barbosa 3 (teofilo.barbosa@prysmian.com ) Carlos A. Godinho 3 (carlos.godinho@prysmian.com ) Escola Politécnica – University of São Paulo São Paulo, SP, Brazil 1 LIFE&MO – Fluid Structure Interaction and Offshore Mechanics Laboratory 2 TPN – Numerical Offshore Tank 3 Prysmian Cables and Systems Vila Velha, ES, Brazil ABSTRACT 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. Keywords: Flexible pipe, crushing tests, analytical model, experimental results. INTRODUCTION The structural behavior of flexible pipes has been the focus of theoretical and experimental studies since the early 80’s. Many important aspects have been addressed, from the general flexural and axial-torsional behavior, see, e.g., [1]-[4], to specific ones, as those related to structural modeling under crushing loading, see, e.g., [5]-[11]. In particular, references [5], [8], [9]and [10] address the crushing loading structural behavior mainly through computational methods, while references [6] and [7] rely on analytical approaches. These approaches essentially model the behavior of carcasses and pressure armors as those of equivalent pipes or rings. Response to similar local loading, as those imposed by hydraulic collars may be also found, see [12]. More specifically, reference [11] combines crushing [13] and wet collapse experiments of typical carcass reinforced flowlines with computational techniques, improving the representativeness of the simple linear model presented in [7]. The present paper aims at assessing the ability of the simple analytical equivalent ring approach presented in [7] and applied in [11], now considering initial ovalization and squeezing effects provided by the action of the helical tensile layers to represent the geometric deformation of typical pressured armored flexible pipes. This is carried out through an experimental-theoretical comparison. A SIMPLE LINEAR ANALYTICAL MODEL This section presents an application of a simple linear analytical model, given in [7] and [11], to determine the elastic line of an equivalent circular ring, which shall represent the joint action of the pressure armor and the internal carcass. The ring is simultaneously submitted to a uniformly distributed radial load and to concentrated loads. The model also considers the effect of initial ovalization. The mathematical model given in [7] and [11] is based on usual hypothesis of the linear theory of elastic structures and can be straightforwardly derived from any good text book, as the classical reference [14], chapter 7. Use is made of the concepts and nomenclature described in [7] and [11], recalling the definition of the nondimensional load parameter, n λ , Proceedings of the ASME 2011 30th International Conference on Ocean, Offshore and Arctic Engineering OMAE2011 June 19-24, 2011, Rotterdam, The Netherlands OMAE2011-49524 1 Copyright © 2011 by ASME