Abstract This article presents the conceptual design of a pipe separator, the multiphase model of the coupled reservoir-production network and experimental results from large scale multiphase experiments carried out in StatoilHydro's multiphase test rig. An application of the pipe separator tied in to the Troll B Floating Production Unit (FPU) has been studied by StatoilHydro and FMC and is used to exemplify the pipe separator's applications and benefits. Introduction The pipe separator concept is a novel compact separator principle patented by Hydro. The primary use of the pipe separator is as a subsea separator for bulk water knock out and or for low pressure production. The separator is in the latter case combined with subsea pumps. The pipe separator concept utilizes the effect of a small diameter and a short residence time. The small pipe diameter leads to a short transport distance for the water and oil, thus the separation is efficient. Due to the difference in flow speed of the oil and water phase, a shear force is developed in the interface area that breaks down emulsion of oil and water. Accumulation of emulsion in the separator is not an issue because the pipe has a horizontal flow. The pipe separator concept has been studied for the use for low pressure production (LPP) located subsea and tied in to the Troll B floating production platform (FPU) on the Troll oil and gas field. The separated water was planned to be used for water injection (WI) into the Troll reservoir for pressure support and stabilization of the oil column while the commingled oil and gas stream is pumped to the Troll B topside process facilities by means of a multiphase pump (MPP). The lowered pressure in the pipe separator is achieved by. means of the MPP, that maintains a reduced receiving pressure at the sea bottom by pumping the commingled oil and gas flow to the topside 1st stage separator. The reduced receiving pressure increases oil recovery since the differential pressure between the well head and the reservoir is reduced. Other beneficial effects of the reduced well head pressure are: increased regularity, accelerated production and a more robust system for reservoir uncertainties. The pipe separator concept has been developed to a pre-engineering maturity for the Troll B use. A significant experimental test program has been carried out using live crude under pressure in a pressurized scaled test rig. The experimental set up, key findings and some key learning points from the experiments are described in the article. Section two in this article contains a brief description of the Troll field. Section three presents the pipe separator concept used together with the Troll B floating production platform, section four presents the results from the multiphase simulations executed on a coupled reservoir-production network utilizing the coupled Eclipse-FlowManager simulator. Section five outlines the experimental set-up and section six presents the experimental results from the tests carried out on the multiphase test rig. The last section contains some key learning from the project.