This paper deals with analysis of lateral instabilities of submarine pipelines caused by thermal expansion and internal pressure effects. A pipeline resting on the sea bed is to some degree axially restrained by the soil friction. Due to high operating temperatures and internal pressures, large axial compressive forces may develop. This will cause the pipeline to buckle laterally at some critical force level to release its potential axial expansion. Such an event may damage the pipeline severely. One way of controlling this behaviour is to install the pipeline with curves to initiate lateral deflection at pre-defined intervals and, thus, release the expansion force in a controlled way. A numerical method for analysis of expansion curves based on the non-linear finite element method is described. The model includes a soil friction element to represent the interaction between pipeline and sea bed and a three-dimensional material model taking into account hoop and radial stresses and to be used with a standard beam element. These new features give a significant improvement, both in terms of efficiency and accuracy, when analysing expansion curves and other similar subsea pipeline problems.
During operation, some subsea pipelines are exposed to fluids of high pressures and temperatures. Since the pipeline is partially restrained from axial movement by soil friction, high compressive forces build up in the pipe. At some critical axial force the pipeline buckles laterally to release its effective axial compressive force. During post-buckling the pipeline is heavily deformed by bending and may be critically damaged. The usual way of preventing such a failure mode is to restraint the pipeline from buckling laterally or vertically by some overburden. This may be done by trenching and backfill, rockdump, concrete mats or pipe supports. However, all these methods are related with high costs.
