EFFICIENT ANALYSIS OF OFFSHORE PIPELINE BUCKLING ON UNEVEN SEABEDS

ABSTRACT Many offshore pipelines are required to operate at high temperatures and pressures. This results in increased axial stress in the pipe-wall and potentially unexpected buckling, which may have serious consequences for the integrity of the pipeline if not taken into account during the design phase. In a buckling and stability analysis, a detailed representation of the interaction between the seabed and the pipeline is very important. To capture necessary geometric effects and to ensure accurate results, a full 3D description of the seabed is desirable. The present paper deals with recent developments related to efficient algorithms for accurate prediction and simulation of buckling effects in offshore pipelines on uneven seabeds. The algorithms include a full 3D representation of the seabed, special contact elements and automatic procedures to place the pipeline along a pre-defined route. The buckling and stability analysis capabilities of the new algorithms were verified by analyzing a section of one of the Ormen Lange import lines. Ormen Lange is a very challenging field when it comes to offshore pipe design because of extreme seabed topography, strong currents, large water depth and low temperatures. The paper presents the developed methods, analysis procedures and results from several analyses demonstrating both lateral buckling effects as well as comparison with results from a commercial FEA-solver. BACKGROUND During recent year's work with the Ormen Lange field Marintek has developed a new generation of 3D pipeline analysis tools. Ormen Lange is the largest natural gas field on the Norwegian continental shelf. The field is located 120 km northwest of Kristiansund. The seabed depths in the reservoir area vary between 800-1100m, and the terrain is very rough due remnants from the Storegga submarine slide 8200 years ago. In the period 2006-2007 two 30" import lines, two MEG lines, and two umbilicals were installed at the Ormen Lange field