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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

Bending Moment Analysis of High Pressure Submarine Pipeline Based on Finite Element Method
Xiaoxia Liu1 , Jun Huang1 , Yi Liu1 and Ruichao Wu2
1. CNOOC Research Institute Co., Ltd., Beijing China; 2. Det Norske Veritas (China) Co., Ltd., Shanghai China

Combined loading of pipelines has been studied by many researchers andengineers. De Winter et al.(1985) published some work on combined
loading, Bruschi (1995) presented ten years later an interesting study
using finite element analyses to establish the load carrying capacity
under combined loading due to bending moment, pressure and axialforce. Mørk et al. (1997) and Vitaly et al.(1999) published work with thesame focus, coming up with an improved criterion for combined loading.
The formulation is based on plasticity theory, modified for strain
hardening and, finally, adjusted for findings/observations made by finite
element analyses. For a detailed explanation of the background and thetheoretical derivation please see the paper by Collberg and Levold (2016)
where the theoretical basis for the different versions of the criterion isdeducted. Combined loading in DNVGL-ST-F101 is focusing on thepeak bending moment including the detrimental effects of pressure andaxial force. For a straight pipe this is typically due to yielding andovalisation (reducing the section modulus). The bending moment
capacity will typically reduce as the effective axial force come into playregardless of the sign of the force (compression or tension). In DNV-STF101, the bending moment capacity under combined loading condition
is defined by equation (5.19), also stated in the following Equation 1.
This equation limits the D/t ratio in the range of 15~45.

ABSTRACTThe 3-D FE model is established to simulate the bending moment of thelarge wall thickness submarine pipeline with high pressure of 56MPa in
this paper (Liu, X, and Jia, X 2015). The results show that the bending
moment resistance capacity from the FE simulations are higher than that
calculated by the equation of DNVGL-ST-F101 2017. DNV GL equationis relatively conservative. DNV GL specifies the limitation (15≤D/t≤45),
the bending moment equation in this code can be used in the design ofhigh pressure large wall thickness submarine pipeline within D/t<15, andchecked by finite element method. It is suggested that DNV GL-ST-F101
remove the restriction of D/t≥15 for the bending moment analysis
through further research.

KEY WORDS: bending moment, submarine pipeline, finite element,over pressure, large wall thickness

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 (ABAQUS 6.14-4). Submarine pipeline has
the remarkable characteristics of large investment, high technicaldifficulty and high operation risk. It is one of the most challenging
technical links in offshore oil and gas development resources. In recentyears, more and more long-distance, ultra-deep water and large diametersubmarine oil and gas pipelines have been studied and applied. Highpressure leads to large design wall thickness of pipeline. At present, thehigh pressure large wall thickness submarine pipe has no application inChina, and is rarely used abroad.

2  m  SC  S sd ( pi ) M sd+ m SC c  M p (t2 )   c  S p (t2 ) 22pi − pe + p 1 c  Pb (t2 ) 

15  D / t2  45, Pi  Pe , Ssd / S p  0.4(1)

Where,t2 is pipeline characteristic wall thickness.
In the derivation of the combined loading criterion, the following steps
were performed.

The bending moment equation is specified the limitation 15≤D/t≤45 in
DNVGL-ST-F101 (DNV GL, 2017), it is necessary to study the bending
moment of high-pressure and large wall thickness submarine pipeline
within D/t≤15.

• Validate a FE model versus tests• Use the FE model to establish a database of results• Develop an analytical basis for the failure mode
• Adjust the analytical basis with the FE-database results to derive thefinal criterion.

In this paper, the 3-D finite element simulation is used to analyze thebending moment of the large wall thickness submarine pipeline with highpressure of 56MPa, and the stress state of submarine pipeline is analyzed,
so as to reasonably determine the wall thickness of submarine pipeline
and ensure the safe application of submarine pipeline.

Based on the database established during the derivation of the combined
loading criterion, we carry out several FE analyses under the definedloading conditions to check against the existing database, thereby to checkthe validity of the equation for the pipelines with D/t ratios less than 15.

BENDING UNDER COMBINED LOADING CONDITION1743