Spooling and installing trace-heated pipelines of pipe-in-pipe configuration

摘要

A transition section disposed between two electrically trace-heated Pipe-in-Pipe pipelines connected end-to-end, the transition section comprising: an inner pipe, an outer pipe and an annulus between them. The annulus contains heating cables that extend longitudinally between annuli of the pipelines and longitudinally-spaced seals that, when deactivated, allow fluid communication between the annuli of the pipelines and, when activated, isolate the annuli of the pipelines from each other. Longitudinally-spaced blocking plates close the lumen of the inner pipe and define an inner chamber between them. Longitudinally-spaced openings penetrate a wall of the inner pipe at locations longitudinally inboard of the blocking plates and the seals to effect fluid communication between the annulus of the transition section and the inner chamber and also define a diversion path for the heating cables that extends from the annulus of the transition section to the inner chamber and back to the annulus of the transition section. Embodiments include a method comprising drawing down a partial vacuum in annuli of the pipelines when the annuli are in mutual fluid communication via an inner chamber in a radially inner pipe of the transition section, which inner chamber is isolated from radially inner pipes of the pipelines.