Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Experimental Observations on Collapse Mechanisms of Faceted Subsea Pipeline
Mahmoud Alrsai a, Hassan Karampour b and Husam Alsanat a.
a

Department of Civil Engineering, School of Engineering, Al-Hussein Bin Talal University (AHU).
Ma'an, Jordan.
b Griffith School of Engineering and Built Environment, Griffith University.
Gold Coast, QLD, Australia.

the ocean environment and ecosystem system (Drumond et al., 2018).
Therefore, this phenomenon causes fracture in the pipe wall which isinvestigated by several researchers (Yeh and Kyriakides, 1986; Gong etal. 2013; He et al. 2014; Alrsai et al. 2018b) or leads to local buckling.
A local buckle, ovalization, dent, or corrosion in the pipe wall canquickly transform the pipe cross-section into a dumb-bell shape that
propagates along the pipeline as long as the external pressure is highenough to sustain propagation.

ABSTRACTThis study investigates the collapse mechanisms and capacity of thefaceted pipe against the conventional pipe under external hydrostaticpressure. The experimental protocol is comprised of additivelymanufactured (3D-printed) faceted and conventional titanium pipes(Ti6Al4V-0406) tested inside a 30MPa hyperbaric chamber. A finite
element analysis (FEA) is presented and is validated against theexperimental results. Using the validated FE model, the major geometricparameters affecting the collapse capacity of faceted pipe wereinvestigated. The proposed FE model can accurately predict the collapsepressure of faceted and conventional pipes. Results showed that thefaceted pipe can boost the collapse capacity by at least an 80% increase
compared to the conventional pipe. Also, the collapse mode wasobserved

A number of solutions to mitigate collapse pressure (and the necessary
increase in wall-thickness of the pipeline) were proposed such as pipein-pipe system (PIPs) (Karampour et al. 2017; Alrsai et al. 2018a; Li2018), sandwich pipe system (SP) (Gong et al. 2018; Wan et al. 2020)
and textured pipelines (Karampour et al. 2021; Albermani et al. 2011;
Khalilpasha and Albermani 2013).
Many literatures have been published in the past 40 years investigating
the collapse of conventional subsea pipelines, under different
combinations of axial tension, bending and external pressure were
performed by Yeh and Kyriakides (1986), Corona and Kyriakides(2000), Kyriakides and Corona (2007), Gong et al. (2011, 2012) Alrsaiet al. (2019,ISOPE), Zhang and Pan (2020). Evidently, that the problemof collapse of tubular structures is by no means new. In order to mitigate
the collapse pressure, Alrsai et al. (2018) studied the pipe-in-pipe systemand the collapse mechanism of the inner pipe of PIPs and found that thecollapse problem is affected by a combination of parameters under
combined actions like external pressure, propagation buckling and axial
tension. Therefore, to overcome these challenges, their work proposed
empirical expressions to predict the collapse pressure of the conventional
inner pipe of the PIPs. Moreover, Most recent research on collapse
failure of pipelines suggested that the wall thickness of the pipe should
be increased in order to increase the collapse capacity, which means
more material and high cost.

KEY WORDS: Subsea pipelines; Faceted pipeline; external pressure;collapse pressure; collapse; cylindrical tube, textured tube.

INTRODUCTION
In today’s world, subsea pipeline systems are construed as the mostinfluential means to transport oil and gas. The rapid development that theoil and gas industry has witnessed necessitates the construction ofthousands of kilometres of pipelines across the world. Given that thesepipelines are lengthy, it is highly probable that they cross active faults(on land and in the sea); accordingly, they are in constant exposure tovarious catastrophic hazards. The characteristic distinguishing this kindof pipeline from other structures constructed on the ground is that theinertial forces exerted by the pipe’s weight and its content are not very
important.

Only marginal works have been done on faceted (textured) pipe, like
Albramani et al. (2011), Karampour et al. (2021). Their work suggested
that the faceted pipe could be used to increase the collapse andpropagation buckling capacity of a pipeline without increasing the wall

The most important structure damages occurring in pipelines are causedby collapse pressure if the external hydrostatic pressure of the pipeline islarger than its critical pressure. As a failure form, collapse will not only
produce enormous economic loss but also result in large catastrophe to1616