This paper discusses different finite element models to assess the structural integrity of pipeline bundles installed on uneven seabeds. A pipeline bundle consists of an outer carrier pipe and several internal flowlines. This concept offers many advantages compared to conventional pipelines such as fabrication and pressure testing onshore, simplified installation, thermal insulation and mechanical protection of the internal flowlines. The high bending stiffness of the bundle cross section implies that longer free spans can be accepted compared to the case where the flowlines are installed separately. However, large axial compression forces may develop in the bundle due to high operating temperatures and pressures in the internal flowlines. These forces may give raise to significant additional bending in free spans due to second order effects. Some of the compression force is released at the bundle ends due to axial expansion. Restraints at the ends and soil friction acting along the carrier pipe may, however, give raise to high compression forces, particularly for long bundles. The high bending stiffness in addition to the lateral soil resistance normally prevent lateral buckling when the bundle rests on a flat seabed. However, the second order bending effects caused by the compression forces have to be considered when the bundle is to be installed on an uneven seabed. In this paper the second order bending effects arising from the compression forces in bundles are addressed. Different finite element analysis models to assess the structural integrity are described. These models are applied to a real life case and the results are discussed.

INTRODUCTION

Often several interfield flowlines are needed to connect the subsea wells and the production and exportation facilities in an offshore oil/gas field. If several flowlines run in parallel it may be beneficial to bundle them into an outer carrier pipe. Then the internal flowlines are kept in place by spacers at regular intervals

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