A Parametric Study of Critical Buckling Force in Snaked Lay Pipelines under HP/HT Condition

Pipelines are an economical way for offshore oil and gas transportation. In operation conditions, flowing high pressure/high temperature (HP/HT) fluids may induce axial expansion. If this expansion is constrained, axial stresses will be created and they may cause pipeline buckling. In order to reduce damages and avoid buckling in unpredictable places, the controlled buckling concept is introduced. To use this concept in the present study, buckling is triggered at some predetermined locations by using the snaked laying method. This paper analyzes the global buckling process of a pipeline by using numerical simulation methods and the effects of loading (internal pressure and temperature) and section properties (diameter and thickness) are investigated on the critical buckling force of snaked lay pipelines under HP/HT conditions. Then, the analysis results of the finite element method (FEM) are compared with analytical solutions and previous simulation methods. This work includes performing nonlinear finite element analysis and modeling pipe-soil interaction of as-laid pipelines by the use of spring elements. The results show that the use of equivalent temperature instead of pressure difference, as already applied in previous studies, is not an authentic method and cannot introduce an accurate outcome. The analysis shows that by increasing pressure and decreasing temperature, the critical buckling force is decreased and the pipeline buckling occurs sooner. The investigation of section properties indicates that the most effective parameter is thickness. It is remarkable to know that at low values of thickness, the effect of diameter is negligible and by increasing thickness, the influence of diameter is increased. Comparing the analytical and numerical results reveals that at low values of circumferential stiffness (ratio of diameter to thickness), there are minor differences between numerical and analytical results.

Keywords:

Offshore Pipeline , Snake Lay Configuration , Lateral Buckling , Critical Buckling Force , High Pressure/ High Temperature