Study On Major Problems For Submarine Pipeline Laying By Surface Tow Method

As the lifeline of the offshore oil and gas fields, submarine pipelines play a key role in oil exploitation, production and transportation. The pipeline installation approaches mainly consist of tow method and pipelaying vessel method. The tow method is further divided into surface tow, off-bottom tow and bottom tow methods. With the advantages of simple equipment and less cost, surface tow method is widely used in the current development of offshore marginal oil fields in China. However, the on-site data show that various forms of failure for the pipeline laid by surface tow method may occur, which would disturb pipeline construction and normal operation. Therefore, it is of necessity for the pipelines laid by surface tow to study the loading processes, uncover the causes of pipe failure, and finally propose the controlling measurements.In view of the above reasons, the research work done in this paper can be summarized into three aspects listed as follows.(1) Mechanics analysis and numerical simulation for pipe lifting are carried out at first. Ignoring pipeline and seabed interaction, the mechanical model of pipe lifting is established. Based on the theory of the beam with large deflection, the differential equations to pipeline lifting are derived. Using MATLAB program, the procedures to solve double sling lifting problem are presented. Meanwhile, considering the interaction between pipeline and seabed, a nonlinear contact finite element model to simulate lifting process on the base of ANSYS program is built.(2) Based on the theoretical research of pipe-soil interaction, the mechanism of thermal expansion for pipeline is analyzed using soil spring of ANSYS program.(3) Based on FE method, a numerical procedure to simulate the whole life cycle loading history for submarine pipeline laying by surface tow method is proposed. The weld imperfections in welded joints are introduced. The typical local buckling modes of the pipeline are obtained. A parametric study is performed. The effects of cyclic loading on the critical buckling load are analyzed at last.