PROCESS AND DEVICE FOR LAYING A PIPE-IN-PIPE

摘要

The invention concerns a process and a device for laying a subsea pipeline according to the J-lay or S-lay method wherein straight sections are mounted onshore, dried and degassed then closed by plugs. The sections are loaded on a pipe-laying ship, are separated from their plugs before the welding. At the welding of each bulkhead a short pumping is operated to reduce the pressure in the part of the annulus located between the two last bulkheads and then the opening leading to the annulus are sealed.

主权项

1. A laying process according to the J-lay or S-lay method for a subsea pipeline used to transport a fluid and which comprises an inner casing arranged coaxially in an outer casing, thereby delimiting an annulus, the pipeline being formed of straight sections, the process comprising:
mounting the sections onshore, each section comprising an inner pipe coaxially arranged using positioning and thermal insulation elements inside an outer pipe, loading the sections onto a J-lay or S-lay method pipe-laying ship, welding the sections end to end, at sea, in order to form the portions of pipeline, bulkheads being welded between two successive portions of pipeline, the bulkheads delimiting, between each other, closed parts of annulus, wherein prior to loading the sections onto the pipe-laying ship, the process comprises the steps of: drying and degassing a space between the inner pipe and the outer pipe of each section, after drying and degassing, placing two plugs at the ends of each section to temporarily close at least the space between the inner pipe and the outer pipe, removing the plugs before welding the sections together, after the welding of at least one of the bulkheads, executing a short pumping operation to reduce the pressure in the part of the annulus located between this bulkhead and the previously installed bulkhead, via at least on opening made facing this part of the annulus, and sealing said opening facing this part of the annulus.