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

Propagation Buckling of High Pressure Large Wall Thickness Submarine Pipeline
Xiaoxia Liu1，Ruichao Wu2 and Xu Jia1

1. CNOOC Research Institute Co., Ltd., Beijing China; 2. Det Norske Veritas (China) Co., Ltd., Shanghai China

the pipeline is due to the cross section of the pipeline losing its roundshape, becoming flat, and consequently losing its load carrying capacity.
The collapse capacity defines the resistance of an intact pipe to theexternal pressure, however, the damage resulting in the decrease of thepipe strength shall be considered in the design. The damage caused by
the collision of a heavy object, by excessive bending during installation,by environmental factors such as earthquakes, ocean currents, etc. andby thickness reduction caused by corrosion and/or wear can reduce thestrength of the pipeline to external pressures. The initial size of thedamaged section will characterize the initiation propagation pressure(Pinit) which is the pressure required to start a propagating buckle from agiven buckle/damage.

ABSTRACTThe external pressure collapse and propagation buckling of 8-inch
submarine pipeline with design pressure of 56MPa are analyzed by 3-D
finite element method in this paper (ABAQUS 6.14-4). The results showthat the finite element analyses results are almost the same as analyticalresults using the criteria in DNVGL-ST-F101 2017. The propagation
buckling criteria is limited to pipeline within 15<D/t<45 in DNVGL-STF101 2017, the criteria in this code can be used in the design of highpressure and large wall thickness pipeline within D/t≤15 and checked byfinite element method.

KEY WORDS: submarine pipeline, finite element, high pressure,large wall thickness, propagation buckling

The propagating pressure (Ppr) is the pressure required to continue a
propagating buckle. Depending on the external pressure, the local failure
can propagate with a high speed. A propagating buckle will stop when
the pressure is less than the propagating pressure or when it reaches alocal structural reinforcement called buckle arrestor. The propagatingpressure depends mainly on the relation between diameter and thickness
D/t and material properties, such as yield stress and strain hardening. The
propagating buckle, once initiated, can propagate at any pressure
bounded by the collapse pressure Pc (upper limit) and the propagatingpressure Ppr (lower limit). However, the pipeline must first be locallydamage to initiate the propagation. The relation between the differentpressures is: Pc > Pinit > Ppr.

INTRODUCTION
With rapid development and application of offshore oil and gas resourcesin China, the significance of submarine pipeline is increasing in theoffshore oil and gas projects (Liu, X, and Jia, X 2015). It has become the"artery". Submarine pipeline has the remarkable characteristics of large
investment, high technical difficulty and high operation risk. It is one of
the most challenging technical links in offshore oil and gas development
resources. In recent years, more and more long-distance, ultra-deep waterand large diameter submarine oil and gas pipelines have been studied andapplied. High pressure leads to large design wall thickness of pipeline.
At present, the high pressure large wall thickness submarine pipe has noapplication in China, and is rarely used abroad. The propagation bucklingformula specifies the limitation 15<D/t<45 in DNVGL-ST-F101 (DNVGL, 2017), It is necessary to study the propagation buckling of highpressure and large wall thickness submarine pipeline within D/t≤15.

Fig. 1 shows some geometric parameters of the propagation collapse.
The transition region defined by length (L) represents the pipeline
section whose one end is perfect, and the other end is totally collapsed.
External pressure acts in such a way that the pipeline walls touch eachother at point C in the final balance condition. The speed of propagation(V) depends on the relation between the pressure load and propagatingpressure (P/Ppr), and the density of the fluid medium in which thepipeline is immersed.

In this paper, the external pressure collapse and propagation buckling of
8-inch submarine pipeline with design pressure of 56MPa are calculatedby 3-D finite element method, and the stress state of submarine pipeline
is analyzed, so as to reasonably determine the wall thickness ofsubmarine pipeline and ensure the safe application of submarine
pipeline.

PROPAGATING BUCKLING BACKGROUND
With the tendency to produce oil and gas in deep and ultra-deep waters,
the external pressure can be considered the governing design parameter
since this can cause catastrophic failure of the pipeline. The collapse ofFig. 1 Geometric Parameters of Propagation Collapse

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