One of the most important facilities in the oil and gas industry is the pipeline. These pipelines convey high pressure with high temperature (HPHT) fluids and transit several kilometers traveling through different seafloor soils. The topography of seabed which acts as viscoelastic foundation to the pipeline is rough and irregular, thereby making the pipelines to be slightly curved. This erratic behavior of these soils presents several problems to the constructor and threatens the lifespan of the pipeline. The nonlinear governing partial differential equations (PDEs) were derived and solved using energy and eigenfunction expansion methods, respectively. The resultant ordinary differential equations (ODEs) were truncated after the fourth mode and solved numerically using eighth-seventh order Runge–Kutta code in matlab. Two types of foundations were investigated: both with viscous damping but one was with linear spring, while the other was with nonlinear spring. Bifurcation and orbit diagrams with their corresponding phase portraits that show periodic and chaotic motions of the system trajectories are generated and presented. It was examined that foundation, initial curvature, and tension could stiffen the pipe, while pressure and temperature did the rule of softening. Nonlinear stiffness made the pipe to undergo chaotic oscillation which was absent in the linear case, meaning that linear foundations could enhance the life span of pipelines than the nonlinear ones.

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