As subsea technology has developed, the use of satellite templates from marginal oil and gas fields has become more common. The connecting pipelines are usually buried in trenches in order to reduce the interference with activities such as fishing equipment, anchors, installation of cables and other offshore structures. However, experience shows that the burying itself may cause problems for the pipelines in operation due to high temperature of the transported oil or gas, inducing large axial stresses. These stresses may cause vertical pipe instability or buckling. This paper presents analytical methods for prediction of buckling potential, i.e. buckling load, length and amplitudes. The predicted behaviour will be presented as a function of geotechnical properties such as breakout resistance and an equivalent coefficient of friction between the pipe and the surrounding soil. The analytical models presented in the paper have been applied on the 9" Tommeliten-Edda North pipeline, which recently has experienced buckling type of behaviour. The calculation results show that the pipe should develop vertical buckling, with span lengths of 40–45 m and amplitudes of 4–6 m. It should further be expected buckling deformations to occur at an intermediate distance of 1.9–3.3 km. These analytical results correspond closely to the actual behaviour, which showed that the deformation pattern had a span length at seabed of 30 m and an amplitude of 5 m.
Compression forces will be induced in pipelines by the restraint of axial extensions caused by temperature increases during oil/gas transportation. These forces may cause vertical buckling of a buried pipeline, Fig. 1. This buckling mode involves an overall column-type response without gross distortion of the pipeline cross-section. Analytical methods for prediction of vertical buckling behaviour, i.e. buckling load, length, amplitude and distance between adjacent but independent pipe deformations, are presented.
