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

Abstract

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 review on predicting critical collapse pressure of flexible risers for ultra-deep oil and gas production

“…Owing to the geometric complexity of the interlocked layer profile, analytical approach has been limited to highly simplified analytical models, aided by experimental calibration. The main difficulty in using those analytical models is always the necessity to determine an equivalent ring thickness or width and, eventually, an equivalent material [31]. The equivalent ring width method, proposed by Pesce et al [32], is often used for crushing analysis where the crushing loads were limited in a small region (shoes region) [33].…”

“…Since the carcass and pressure armor are the main components for preventing from wet collapse, the other layers, e.g. tensile armors, anti-wear and insulation layers, are generally omitted in the numerical models [31].…”

“…11. Such kind of FE models preserve the layer geometric details and therefore can be used to investigate the issues related to stress concentrations [31].…”

Prediction of the critical collapse pressure of ultra-deep water flexible risers-a: Literature review

“…The 3D full model refers to modelling the interlocked layers, carcass and pressure armour, with their actual rolled shapes. Such kind of FE models were constructed by Neto et al [18], [26] and could be used to investigate stress concentrations for their preservation of layer geometric details. However, the full FE models are still impractical for design purpose of flexible risers due to the onerous modelling producedure and time-consuming computation.…”

“…These simplified models are often employed to conduct sensitivity analysis of collapse resistance on geometric imperfections (initial ovalization and gaps) [27] as well as the post-buckling mode investigation of carcass [28], [29]. Although the simplified models simplify the modelling procedure and reduce the computational time, they may lead to incorrect predictions of stress concentrations due to the loss of geometric profile details [26].…”