The Influence of Pipeline Insulation on Installation Temperature, Effective Force and Pipeline Buckling

High-performance insulated pipelines are designed for long cool-down times in operation. During the installation of such pipelines, the heat within the pipe as it leaves the lay vessel is not easily lost to the surrounding seawater. The ambient temperatures on the lay vessel, combined with significant heat input during welding and field joint coating, will result in the pipeline leaving the lay vessel at a temperature well above ambient deck temperature. The insulation system ensures that a significant amount of this heat will remain within the pipeline as it descends to the seabed, resulting in a higher than ambient installation temperature. As the pipeline cools to ambient seabed temperature, it is restrained on the seabed by axial friction thus generating effective tension in the pipeline. The magnitude of the locked in tension will depend on various factors, including the overall heat transfer coefficient, the system heat capacity, the water depth, water column temperature and the lay rate. Any significant locked in tension will influence the buckling behaviour of the pipeline by inhibiting buckle formation and reducing feed-in to lateral buckles. This paper presents a method to assess the temperature loss through the water column during installation of an insulated pipeline and the location, relative to the touchdown point, at which the pipeline becomes fully constrained. The modified as-installed temperature will much improve the accuracy of predicted buckling response at hydro-test or in operation.