Subsea gravity separation is a field proven, robust and reliable technology implemented on several fields such as Troll, Tordis, Pazflor and Marlim. Among other solutions, SAIPEM has developed a deepwater gas separation and liquid boosting system based on its proprietary "Multipipe" separator concept. This paper presents an alternate design having the same throughput range as the original design – the “Modular Multipipe” - allowing easy retrieval and maintenance of individual separator pipes thanks to a new structural, piping and connection arrangement. Both designs provide a good flexibility in handling a wide range of steady and un-steady multiphase input streams using a relatively simple mechanical arrangement. The Multipipe concept features an array of vertical pipes for gas/liquid separation by gravity and adequate liquid hold-up volumes. The operating principle is the same as standard gravity separation vessels. The limited diameter and wall thickness of the vertical pipes make the Multipipe concept particularly suited for deep and ultra-deepwater applications and/or high pressure conditions where the selection of a single separator vessel could lead to unpractical wall thicknesses. In most cases, standard API or ASME pipes can be utilized for the Multipipe Separator, thus enabling conventional fabrication methods, and in turn reducing cost and delivery time and also opening opportunities for local content. After a qualification campaign, confirming a simple control principle (same as single vessels), and demonstrating the separation efficiency with real crude, a new design has been developed, allowing for individual pipe retrieval. This new design is anticipating the needs for even deeper applications and the flexibility required to comply with a wider number of IMR support vessels. The paper reminds the qualification work performed on the Multipipe technology and presents the design of this new “Modular Multipipe”.
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