Flexible Pipe Curved Collapse Resistance Calculation

Abstract

In the design of flexible pipelines for offshore field developments, the determination of the pipe resistance while subjected to external pressure and bending is very important in deepwater and is now required by the ISO and API standards. One of the critical failure modes being associated with this type of loads is the hydrostatic collapse. The collapse value of flexible pipe is calculated with a model validated with over 200 tests performed on all possible pipe constructions. This model has an analytical basis, and has been established in the past, leading to a fast and straightforward use. In order to address the bent collapse failure mode, Technip and IFP have therefore developed and improved over the past few years an analytical calculation model, based on the collapse model for straight pipes. The purpose of this paper is to present this design methodology and its validation. The modelling principles of the collapse calculation of straight flexible pipes are firstly presented, along with the main hypotheses. The adaptation to the case of curved pipes is detailed in the sequel of the paper. Many types of flexible pipe samples have been tested up to collapse both in straight and curved configurations. The results of these tests have been used to validate this model. In the paper, several tests results will be presented and compared with the calculations. This model is effective, of straightforward use, and has been certified by a third party. It allows Technip to optimize the flexible pipe design in particular for ultra-deep water applications, where external pressure resistance is very important.

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

“…Determining the critical pressure through the collapse tests ( Figure 4) of flexible risers is always the most reliable way for the anti-collapse analyses [10], [15], [16]. However, such hydrostatic tests require specialized hyperbaric chambers, which are very limited worldwide [17].…”

“…To prevent such kind of incidents, the flexible risers applied to deep/ ultra-deep water production, is thus required adequate anti-collapse capability. This capability often becomes a govern factor of pipe wall thickness and production cost [10], [11]. Therefore, the understanding of collapse failure and related riser performance characteristics is important for give a reliable prediction of critical pressure and guide the anti-collapse design of flexible riser systems [12].…”

Flexible Pipes: Influence of the Pressure Armor in the Wet Collapse Resistance

“…(8) and (9) leads to the thick ness of the equivalent ring (11) (8) and (9) leads to the thick ness of the equivalent ring (11)…”

“…However, the influence of the pressure armor was neglected, and this can play a role as a constraint to the inner layers, making the wet col lapse more difficult to occur. The two types of col lapse modes are addressed by Paumier et al [8] when they say: "Two collapse failure modes of flexible pipes have been experi mentally identified; the first one is called ovalization collapse mode; the second one is the heart collapse mode." Gay Neto et al [6] already made a comparison of these different approaches for the flexible pipe burst problem.…”

Buckling collapse study for the carcass layer of flexible pipes using a strain energy equivalence method

“…A similar equivalence method was also applied to study the mechanical behaviors of a pipe under axial loads (Wang and Chen, 2011;Yue et al, 2012). After an equivalent model is created, further studies on wet collapse (Pesce et al, 2010) or collapse with curvature (Paumier et al, 2009, Clevelario et al, 2010 can easily be conducted either analytically or with the finite element method.…”