CONTROLLED TOWOUT AND LAYING OF VERY LONG PIPELINE SECTIONS

The feasibility of towing very long prefabricated pipeline sections from sheltered sea areas to an installation site are investigated and analysed. The sections are carried by buoys with spacings in the order of 100m or more, depending on the type of pipeline. The towout is performed by a for and aft tug in 40m depth. The response of the system of buoys and pipeline to wave and current action is determined. Two methods for laying the pipeline are presented, direct sinking by releasing the carrying buoys and a system where the pipeline is run over an intermediate barge on which the carrier buoys are dismantled and the pipeline is then laid conventionally with a stinger system. The major problem turns out to be accurate positioning of the long pipeline sections. A simulation procedure for the positioning is presented.