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Conceptual Analysis of Stinger for Ultra-deepwater S-lay

Lin WangFabrication Sub-company, China Offshore Oil Engineering Co. Ltd., Tianjin, China

Xiangfeng Zhang, Wei Lv, Qianjin YueDepartment of Engineering Mechanics Dalian University of Technology, Dalian, China

Ning He, Lei ZhouEngineering Technology Center, China Offshore Oil Engineering Co. Ltd., Tianjin China

ABSTRACT

As a traditional offshore pipelay technology, S-lay is still frequently

utilized even in the deep water pipelays. It has two important devices:stinger and tensioner. Stinger controls the overbend of pipeline. Itsgeometry, length, and curvature, are the function of water depth, laytension requirement and geometry and material of the pipeline. In this

paper, an analytical method and the finite element methods arepresented for researching the relationships of these parameters.

Suggestions on the conceptual design of a novel deepwater stinger andthe upgrade of an actual stinger have been provided as a favor ofdecision-making.

KEY WORDS: pipelay; pipeline; stinger; S-lay; ultra-deepwater.

INTRODUCTION

As the exploration of oil and gas resources goes into deep and ultradeep water, subsea pipeline installation in such area has become a real

challenge. Nowadays, S-lay and J-lay are two important pipelaytechniques, which have made great success in shallow and moderatewater depth respectively. It once seemed that J-lay is the only choice

for deep water pipelay, but recently, to keep project costs low and stillmeeting the challenges of pipeline installation, S-lay has been made

break through based on the improvement of equipment capacities.These equipments include stinger, tensioner, and dynamic positioningsystem. These enhancements make the S-lay in ultra deep waters

possible (Vermeulen, 2000). Other successful deep and ultra deep water

pipelays were conducted by S-lay vessels Lorelay and Solitaire. Theyhave laid the 12/14 inch pipeline into 932 meters in Oil Export Pipeline

project in 1991, and laid the 8/12 inch pipeline in the water depth of

1676 meters in 2001. Even more success in 2005, they laid the 8/10inch pipeline into 2750 meters in the Gulf of Mexico, and so on. The

pipelay depth for S-lay is shown in Fig. 1.

In the case of S-lay, there are several working stations located on thelay-barge, and pipes are welded, coated and tested horizontally, then

pipe string passes through the stinger suspended from the back of bargeinto water in nearly a vertical slope. It is finally laid on the seabed. Theconfiguration of the pipeline during laying process resembles S, and

it is divided into the overbend on stinger and the sagbend from lift-ofpoint to touch down point on the seabed, as shown in Fig. 2. The

curvature of the overbend is controlled by 6 to 14 rollers installed onthe stinger. The rollers are normally spaced in 5 to 10 m. The sagbend

curvature is controlled by tension at the tensioner on the lay-barge.

Fig. 1: The Lay Depth Using S-lay Technique

In the deep and ultra deep water, large tension and high curvaturestinger are required in order to achieve the nearly vertical departure

Such setup can lead to large plastic deformation in overbend area. Howto design the geometry of the stinger to prevent pipeline in theoverbend form (plastic) collapse becomes extremely challenging. Thisis also a main focus of this study.

As an efficient pipelay technique, S-lay has always being the focapoint of offshore industry. A great deal of efforts has been carried intoexecution. Firstly, design and safety analysis of pipeline became themain tasks in early research using numerical and finite elemen

methods (Kruppa and Clauss, 1976; Heedo, 2004), and then theconfiguration of pipeline during S-lay was studied by means of singular

perturbation technique (Guarracino, 1999). Lately, parameters analysisof S-lay, such as water depth, tension and stinger, was put forward(Daley, 1974; Zhu, 1997). In these studies, the stinger was supposed to

be articulated stinger controlled by buoyancy, which is so differenfrom the stinger controlled by given equipment, such as A-frame or S-

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Proceedings of the Third (2009) International Deep-Ocean Technology Symposium

Beijing, China, June 28-July 1, 2009

Copyright 2009 by The International Society of Offshore and Polar Engineers (ISOPE)

ISBN 978-1-880653-73-9