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

Model tests on pipe-soil interaction in sand andnumerical analysis of lateral buckling ofsubmarine pipe-in-pipe pipelines
Jinjia Wang1, Guomin Sun2, Dang Zhao2, Ying Zhang2, Renjie Yang1, Menglan Duan1
1.College of Safety and Ocean Engineering, China University of Petroleum, Beijing, China
2. Offshore Oil Engineering Co. Ltd, Tianjin, China

excessive axial force which causes pipelines to be more prone to lateral
global buckling. Consequently, great attention should be paid to lateralbuckling which is an important issue in the design and in-service
assessment of submarine PIP pipelines.
Hobbs (1984) established analytical solutions for the lateral global
buckling of ideal straight pipelines on a rigid foundation, andinnovatively proposed the five modes of the lateral global buckling ofpipelines. But the shape of buried pipelines in project fields are neverfully straight owing to the installation process and/or uneven seabed, thisphenomenon is commonly known as initial imperfections of pipelines.
Taylor and Gan (1986) proposed analytical solutions for the global
buckling corresponding to imperfections of mode 1 and mode 2, whichis considered to be the classical analytical solutions for the lateral global
buckling of submarine pipelines with initial imperfections. In accordancewith submarine PIP pipelines, Vaz and Patel (1999) established ananalytical formulation of the coupled lateral buckling instability of a PIP
system based on the approach involving formulation of the governing
equation for pipe bending and of their numerical solution by aneigenvalue technique. However, in their studies, the nonlinearity of pipesoil interaction was neglected, or even the friction between the seabedand the outer pipe was not considered within the analysis.
As pointed out in Zhao (2007), it is hard to establish analytical formulas
analyzing the lateral global buckling of submarine PIP pipelines
considering all factors, making the FE method primarily being employed
to describe the lateral global buckling problem of exposed and shallow
buried submarine PIP pipelines. Sun (2009) created full-scale FE modelson the basis of pipe-soil interaction (PSI) elements to simulate thepipeline thermal expansion, upheaval and lateral buckling responses. TheFE method was used by Wang (2015) to investigate the upheaval
buckling response and obtain empirical formulas for critical bucklingforce of PIP systems with full-contact imperfections. Zhang (2018a)
utilized 3D FE numerical analysis to proposed a formula including
adequate parameters for the lateral buckling critical force of submarine
PIP pipelines. In their research, soil conditions and pipe-soil interaction
models, as necessary input for FE models, greatly influence the lateral
global buckling responses of subsea PIP pipelines.
Soil conditions plays an important role in the lateral buckling behaviorof submarine pipelines. Researchers have carried out many experimental
tests to investigate the soil resistance developed during pipeline
movement. Bruton (2006) carried out large-scale, small-scale andcentrifuge tests on lateral pipe-soil interaction of shallow buried

ABSTRACT
Exposed and shallow buried submarine PIP pipelines subjected to hightemperature and high pressure (HTHP) are more prone to lateral global
buckling, which is an important issue in the design and in-service
assessment of submarine PIP pipelines. Pipe-soil interaction resulting
from pipeline movement plays an important role in the lateral buckling
behavior of pipelines. In this paper, a series of lateral pullout tests werecarried out on model pipe segments having a diameter of 58mm buriedin sand, with different embedment ratios ranging from 0 to 1/2. Based on
the observed data of model tests, a nonlinear lateral pipe-soil interaction
model is proposed to describe the lateral resistance force-displacement
relation. 3D finite element numerical models in which the relation of thenonlinear pipe-soil interaction is employed are established to study thelateral buckling behavior of submarine pipe-in-pipe pipelines. A
combination of pipe-soil interaction elements, beam elements, and tubeto-tube elements is used in the FE models. The lateral buckling processof submarine PIP pipelines is simulated, and the influences of lateral
pipe-soil interaction models, pipe out-of-straightness (OOS) andstiffness ratio of the inner pipe to the outer pipe on the lateral buckling
behavior of submarine PIP pipelines are discussed. Results show that theexact pipe-soil interaction relation affects the lateral buckling responsesof submarine PIP pipelines. The capacity of submarine PIP pipelines
against lateral buckling increases with the increase of the embedment
ratio. It decreases with increasing pipe OOS and stiffness ratio of theinner pipe to the outer pipe.

KEY WORDS: model tests; pipe-soil interaction; submarine pipelines;
lateral buckling; pipe-in-pipe
INTRODUCTION
As shown in Fig. 1 referring to Zhang (2021), the PIP pipeline system
consists of an outer pipe, an inner pipe, centralizers, bulkheads, andinsulation material. The insulation material ensures the PIP system has
exceptional thermal insulation properties. Therefore, submarine PIP
pipelines have been used as one of the main means of transporting oil
and gas where heat needs to be retained and minimize flow assurance
risks. At high temperature and high pressure, exposed and shallow buried
submarine PIP pipelines constrained by the soil resistance suffer from1731