Numerical study on thermal buckling analysis of different multilayer offshore pipelines

Thermal buckling is one of the major problems in offshore pipelines, which affects the structural integrity of the pipeline since it operates under extreme temperatures and high-pressure conditions. The temperature variations across the pipeline's radius govern the critical buckling temperature, arising from heat transfer, especially the natural convection between the working fluid medium and the surrounding fluid medium. In the present study, the finite element tool ANSYS is selected to execute a coupled steady-state thermal and linear eigenvalue buckling analysis on four different types of offshore pipelines: equivalent single-walled pipeline, lined pipeline, sandwich pipeline, and pipe-in-pipe system. The critical buckling temperature of these pipelines is evaluated under subsea and buried conditions, and in comparison, to that of an equivalent single-walled pipeline. The temperature variation and Von Mises stress across the radius of the pipelines are analyzed. The results show that the addition of insulation materials to the pipelines has a significant impact on their critical buckling temperature. The pipe-in-pipe system shows a higher critical buckling temperature than all the other pipelines, exhibiting a significant rise in temperature and outperforming the equivalent single-walled pipeline by 116% and the sandwich pipeline by 34%. Furthermore, the lined pipe's critical bucking temperature is almost the same as that of the equivalent single-walled pipeline.