Study On Towing Method Of Submarine Pipeline In Installation And Its Software

The towing method is an important pipe laying technique which is usually adopted in the exploitation of offshore oil and gas resources in our country. With the advantages of simple equipment and less cost, it will be widely applied in the current and future development of offshore marginal oil fields. According to the studying project "Research on the installation techniques of offshore engineering facilities for marginal oil fields" supported by Offshore Oil Engineering Co., LTD, in this paper, three types of towing methods are systematiclly studied, which are respectively bottom towing method, surface towing method and off-bottom towing method. Taking into account the corresponding construction techniques and ocean environment conditions, the mechanical analysis models of submarine pipeline during the towing are reasonably created, and the finite element method is applied to analyze the stress states of various segments of pipeline. The software "Submarine Pipeline Towing Method Analysis System" (SPTMAS3.0) is specially developed for stress analysis during the laying. The main studying results are summarized as follow.(1) For the bottom towing method, the seabed is divided into many parts, the formula of pipeline traction of each part is established. The problems of the maximal suspended-span length and the obstacle height are discussed.(2) As to the surface towing and off-bottom towing methods, the pipeline at the static equilibrium conditions in the seawater is analyzed to resolve the configuration problems of the buoy and towline. The mechanical analysis model of pipeline in the towing process is established and three-dimensional finite element method is used to compute the stress and deformation of the pipeline.(3) Concerning the software SPTMAS3.0, in addition to the computation of construction configuration, it is capable of carrying out the analysis of stress and deformation for the towing pipeline using 3D FEM, the output of the calculating results is in the forms of intuitional graphics and documents.After the example analysis of surface towing method and off-bottom towing method, the different influencing factors such as the towing velocity and the tension of tail-ship on the maximum stress of pipeline are discussed. These results have an important referenced value in the actual application of the submarine pipeline projects.