Analyses of Different FE Models for HP/HT-Pipeline Walking With Sliding End Structures

Non-buried subsea pipelines subjected to high internal pressures and high operational temperatures (HP/HT) might experience significant axial expansion. If this movement is restrained by an end structure, considerably high loads can be imposed to the system. Sliding foundations have been used to minimize this effect, allowing free end displacements. Regarding the aforementioned loads, the thermo-mechanical behavior of HP/HT pipelines interacts with the end restraints in a complex manner. Axial displacements can accumulate over the operational cycles, in a phenomenon known as “pipeline walking”. If the sliding foundation design does not account for these accumulated displacements, axial loads (not considered in the pipeline design) might be imposed. As a result, the overall thermo-mechanical behavior in terms of lateral buckling and walking can change significantly. Two recently published papers present the results of different analysis methodologies for the same structure. The corresponding analyses were performed using two different tools: (1) a non-linear three-dimensional finite element model considering pipe-soil interaction with full 3D seabed bathymetry and (2) a simplified one-dimensional model published in OMAE 2011. In both cases, the limited sliding range was imposed to the model ends. Both calculation tools show similar overall results of pipeline global behavior, but the results of the end reaction after a few operational cycles are somewhat different. Stimulated by these recently published papers, which present the results of different performed finite element analyses; this paper was developed to investigate the same problem, but now starting off with a third software, and rerunning the two previous analyses in the same software and adding an intermediate modeling level.