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Landing, risers, wellhead piping and their tie-in works
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Landing, risers, wellhead piping and their tie-in works
Conduits to transfer materials from the seafloor to production and drilling facilities atop the water’s surface, as well as from the facility to the seafloor, subsea risers are a type of pipeline developed for this type of vertical transportation. Whether serving as production or import/export vehicles, risers are the connection between the subsea field developments and production and drilling facilities.
Similar to pipelines or flowlines, risers transport produced hydrocarbons, as well as production materials, such as injection fluids, control fluids and gas lift. Usually insulated to withstand seafloor temperatures, risers can be either rigid or flexible.
Types Of Risers
There are a number of types of risers, including attached risers, pull tube risers, steel catenary risers, top-tensioned risers, riser towers and flexible riser configurations, as well as drilling risers.
The first type of riser to be developed, attached risers are deployed on fixed platforms, compliant towers and concrete gravity structures. Attached risers are clamped to the side of the fixed facilities, connecting the seabed to the production facility above. Usually fabricated in sections, the riser section closest to the seafloor is joined with a flowline or export pipeline, and clamped to the side of the facility. The next sections rise up the side of the facility, until the top riser section is joined with the processing equipment atop the facility.
Also used on fixed structures, pull tube risers are pipelines or flowlines that are threaded up the center of the facility. For pull tube risers, a pull tube with a diameter wider than the riser is preinstalled on the facility. Then, a wire rope is attached to a pipeline or flowline on the seafloor. The line is then pulled through the pull tube to the topsides, bringing the pipe along with it.
Building on the catenary equation that has helped to create bridges across the world, steel catenary risers use this curve theory, as well. Used to connect the seafloor to production facilities above, as well as connect two floating production platforms, steel catenary risers are common on TLPs, FPSOs and spars, as well as fixed structures, compliant towers and gravity structures. While this curved riser can withstand some motion, excessive movement can cause problems.
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