TABLE OF CONTENTS The design of High-Pressure/High-Temperature (HP/HT) pipelines on an uneven seabed has become an important issue in the recent years. The need to gain further insight into how expansion, seabed friction and free spans influence on the pipeline behavior through selected load cases is the background for this chapter. The behavior of such pipelines is largely characterized by the tendency to undergo global buckling, either vertically if trenched or covered, or laterally if the pipeline is left fully exposed on the seabed. The main concern in the design of slender pipelines operating under HP/HT conditions is to control global buckling at some critical axial force. The large horizontal and/or vertical displacements induced by global buckling may result in high stresses and strains in the pipe wall that exceed code limits.
The simulation of the designed pipeline in a realistic three-dimensional environment obtained by measurements of the seabed topography, allows the engineers to exploit any opportunities that the pipeline behavior may offer to develop both safe and cost-effective solutions. For example, the designer can first analyze the pipeline behavior on the original seabed. If some of the load cases result in unacceptably high stress or strain, seabed modification can be simulated in the finite-element model and the analysis re-run to confirm that the modifications have lead to the desired decrease in stress or strain.
The finite element model may be a tool for analyzing the in-situ behavior of a pipeline. By the pipeline in-situ behavior it is here meant the...
