Comparative Study on the Collapse Response of Flexible Pipe Using Finite Element Methods

Abstract

Although the scope and use of flexible pipe systems in deepwater developments is expanding, the mechanical behavior for these environments is not fully understood. This is due to the complex response and interaction between multiple layers within the pipe system that introduces significant difficulties and constraints into the engineering analysis. As future developments look to extend the use of this technology to greater water depths and harsher operating conditions there is a need to develop advanced numerical tools that can evaluate the mechanical integrity of these complex hybrid pipe systems. Availability of increasingly advanced computational packages has enabled substantial improvements to be made in the complexity of simulation tools for combined loading, external pressure collapse and fretting. This study establishes a foundation for the development of advanced numerical modeling procedures to assess the collapse failure of composite flexible pipe systems for deepwater applications. Here, a continuum finite element model is constructed using the software package ABAQUS/Standard, and studied using non-linear (arc length) methods. The carcass, pressure armor and corresponding polymer layers are represented in detail and modeled with three dimensional solid brick elements in order to examine the interlayer relationships influencing collapse initiation. In many recent studies, an initial geometric imperfection in the form of general ovality is explored as the predominant bifurcation mode. A similar approach is adopted here, coupled with case studies chosen such as to facilitate validation against existing analytical and numerical data. The importance of element selection, contact mechanics, interface properties and initial imperfections on the system mechanical response and performance is presented and compared to the available literature.

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

“…Collapse studies have been conducted extensively by many researchers since the inception of the flexible risers around the 1970s [23]. Experiments are the most reliable way to predict the critical pressure of riser products.…”

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

“…In that regard, analytical and numerical approaches are developed to give a prediction of the critical pressure of the carcass. For the most part, the analytical approaches has been limited to highly simplified analytical models due to the complexity of the carcass profile, aided by experimental calibration [18]. The most difficult step in that simplification of flexible risers is how to address the complex carcass profile, which is in an interlocked shape ( Figure 5 [19]).…”

“…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.…”

Predicting the wet collapse pressure for flexible risers with initial ovalization and gap: An analytical solution

“…However, this critical pressure might be reduced by two initial imperfections: ovalization of the carcass, and inter-layer gap between the carcass/liner and pressure armor. The ovalization of the carcass is a defect generated from the manufacture process while the inter-layer gap is caused by the volume change or extrusion of the liner [10,11], as shown in Fig. 2 [12].…”

“…Although tensile armors can reduce the interlayer gaps by squeezing the pressure armor, it is hard to close these gaps completely if the pipe is under a low longitudinal tension. For a flexible riser facing the flooded annulus situation, its collapse strength is sensitive to those two imperfections [10,11,13,14]. Besides, those imperfections may also affect the collapse modes of an encased carcass [15].…”