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Numeric Optimization for a J-Lay Subsea Pipeline Launching System

Economical and political factors have changed the conventional point of view on the development of new submarine pipelines crossings. In fact, the laying of present lines is now driven by the increasing globalization of the market, with longer distances covered from producers to end-users, and not only by the exploitation of new offshore resources. Therefore, new capabilities to operate in deep waters are needed more and more, with ongoing development plans considering projects in water depths up to 3500 m and more. This paper is following another paper issued by the same authors in which the strains and deformations of the very same J-Lay launching system were calculated. Now the authors go a step further in order to optimize the geometry and dimensions of the structural arrangement of the launching ramps in order to have the smallest stresses inside the subsea pipe during launching. The integrity of the subsea pipe during launching from a J-Lay vessel is the most important criteria to judge a successful launching. In the J-Lay systems as the one presented in this paper the vessel launching structure is stressing the pipe sometimes beyond the elastic domain and the verification of the stresses inside the pipe is of a paramount importance. This paper is providing a modern involvement of Finite Element Method in calculating the optimum launching system arrangement in order to have the minimum equivalent stress inside the subsea pipe during launching. After optimization the maximum calculated stress inside the pipe is 8.06e7 Pa instead of 9.97e7 Pa before optimization, therefore a reduction of 19% is to be reached by simply lowering the upper ramp and decreasing the force developed by the Tensioner 1.