It is well known that lateral buckling of submarine pipelines is a partially displacement and load controlled phenomenon due to the restraint provided by the lateral friction on the seabed. In this paper, the proportion of displacement versus load control in terms of a percentage displacement control is quantified for various cases for a “short” pipeline. The method used to define the proportion of displacement control is the one developed by Collberg, Palmer, Aronsen and Hahn (2003) for a J-lay configuration. The definition of a “short” pipeline is given by Christensen (2005).
It is shown that using this new method the example pipeline in the post buckled condition is in fact within acceptable limits in accordance with the DNV-OS-F101 local buckling check. Had the conventional method assuming 100% load control or the HOTPIPE method (Mork, Collberg, Levold, and Bruschi, 1999) been used, it is shown that the pipeline would have instead failed the local buckling check.
Buckling of a pipeline due to temperature and/or pressure loading is different from “normal” column buckling in the sense that the buckling force reduces (releases) as the pipe feeds into the buckling region. The maximum bending moment is limited by the amount of feed-in into the buckling region and whereas buckling under constant force may lead to structural collapse this often does not happen for a buckling pipeline. The amount of feed-in is well predicted and can be calculated as the axial displacement due expansion of the pipeline into the buckling region less the resistance provided by the friction on the seabed. For a given axial friction force determined by the axial friction coefficient, μa, and pipeline submerged weight, w, the feed-in therefore is determined regardless of lateral friction or pipeline stiffness.