METERING DEVICE FOR A FLUID

Abstract: A metering device for multiphase fluid, for example, crude oil, comprises a gamma or X-ray densiometer incorporating windows for the metering radiation of boron carbide. The boron carbide windows can be provided by a sleeve guiding the fluid flow, the sleeve (51) being reinforced by a thin external layer (52) of carbon fibre embedded in expoxy resin. Alternatively, a steel tube (26) receiving the fluid flow has aligned transverse apertures (47) containing plugs (49) of boron carbide.

Description: METERING DEVICE FOR A FLUID DESCRIPTION The invention relates to a metering device for a fluid. Particularly in the context of oil extraction systems, it is required to measure the proportions of the components in a multi-phase fluid flow, for example, a crude oil flow containing gas and/or water in varying proportions. It has been proposed in WO 90/13859 (FD20) to provide a mixer apparatus for fluids incorporating a choke or venturi, and to associate measuring or metering equipment with the venturi to determine mass flow rates of the fluid phases flowing through it. Such metering equipment can include a densio eter employing a γ or X-ray source located at one side of the fluid flow for transmitting its radiation transversely through the fluid to a radiation sensor or detector located at the other side of the fluid flow. The use of a Ύ or X-ray source and detector presents a problem for such metering equipment in that the tubing within which the fluid flow is confined should be highly transparent to the metering radiation whilst being resistant to the fluid flow and having necessary strength and rigidity. The first of these requirements effectively precludes the use of steel tubing and it has been proposed in EP 0 236 623 to employ beryllium as the material of the wall of the tube across which the radiation is transmitted. The toxicity of beryllium however presents manufacturing problems. The present invention accordingly relates to a metering device in which radiation from a source is transmitted through a multiphase or other fluid to be entered to a sensor or detector responsive to the radiation from the source. The invention is concerned with the provision of a device of this kind in which tubing guiding a flowing fluid has appropriate mechanical and physical characteristics and does not unduly attenuate the radiation to be transmitted across it. The invention accordingly provides a metering device of the kind described in which the material of the tubing wall, or other tubing portion through which the radiation is transmitted, is boron carbide ( B 4 C ) . Boron carbide has appropriate absorption ( or transparency ) characteristics for γ or X-rays and is not adversely affected by exposure to such multiphase fluids as are encountered in oil production systems , namely, oil mixed with variable proportions of gas and/ or water. • Boron carbide is not however ideal in respect of its mechanical properties . The invention accordingly also provides a metering device of the kind described in which the tubing comprises an inner tube or sleeve of material having high transparency to the radiation , for example , boron carbide , and a reinf orcing or support ing outer layer providing additional mechanical strength. The outer layer should of course be as transparent as pos s ible to the radiation. The outer layer can comprise a thread or fibre or other elongate element wound around the sleeve, preferably embedded in a settable plastics material to force a coating of fibre reinforced plastics material . For example , carbon fibre can be wound externally around the boron carbide sleeve to preload the sleeve against the forces it will experience, and the fibre then embedded in the settable plastic s material, for example, an epoxy resin . The coating can be employed to bond the inner tube to an external support tube, for example, of steel, provided with apertures , conveniently in the form of aligned radial bores , which can function to collimate the radiation, for the unobstructed transmission of the radiation through it. The invention also provides a metering device of the kind described in which tubing guiding the f luid flow comprises a tube of material of appropriate mechanical properties , for example , steel , provided with aligned transverse apertures for the radiation, the apertures being closed by elements of material, for example, boron carbide, of relatively high transparency to the radiation. A steel tube can thus be provided with aligned radial bores closed by plugs of boron carbide. In such arrangements, the tube of steel or the like can function not only as a structural part of the metering device but also as a frame for supporting the radiation source and detector. The invention is further described below, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a part-sectional side view of part of a subsea installation including a metering device in accordance with the invention located downstream of a mixing unit; and Figure 2 is a part sectional side view of a pipe element included in the metering device of Figure 1, shown on a larger scale and illustrating a modification. The illustrated installation resembles that shown in Figures 4 and 5 of WO 90/13859 (FD20), the contents of which are incorporated herein by reference, in that outer tubing 4 forming part of an open-topped receptacle has received therein a cartridge 5 including a mixing unit 10. The mixing unit can correspond functionally to the mixing unit shown in Figure 2 of WO 90/13859 and has a discharge duct 20 incorporating a venturi, in which the mixing is effected, and which is associated with metering equipment including a gamma or X-ray densiometer 22. The discharge duct 20 comprises four axially aligned pipe elements 24,25,26 & 27 of which the uppermost 24 and the lowermost 27 connect the discharge duct into the cartridge 5. The outer walls of the pipe elements 24-27 are spaced inwardly of adjoining parts of the cartridge to define an annular chamber 29 bounded externally by a sleeve 30, which approximately continues the exterior of the shape of the cartridge . The upper intermediate pipe element 25 and the lowest element 27 have tapered interiors which guide the fluid flow towards and away from the lower intermediate element 26 which has the least internal diameter , to constitute the actual choke or venturi throat . The pipe element 26, shown also in Figure 2 , forms part of the T -ray densiometer 22 , which is one of the metering units included in the metering equipment associated with the mixing unit 10 . The densiometer comprises a source 40 of gamma radiation diametrically opposed across the element 26 to a sensor or detector 41 capable of detecting the radiation -from the source. The source 40 preferably provides radiation at multiple distinct energy levels , or it may comprise multiple sources of radiation at different energy levels . The detector 41 is then capable of distinguishing between radiation at the dif ferent energy levels , or comprises multiple detectors responsive to respective energy levels . The detector 41 cooperates with the radiation source 40 to provide output signals dependent on the amount of the radiation absorbed by the different components of multiphase f luid flow in the venturi . The detector output i s appropriate treated in processing equipment (not shown) to provide measures of the mass flow rates of the components of . the multiphase fluid flow. The pipe element 26 comprises an outer sleeve 44 , conveniently of steel, of which the external surface is flush with the outer surfaces of the adjoining pipe elements 25 & 27. The interior of the element includes end portions 45 , 46 for receiving interior axially extending locating ring portions of the adjoining pipe elements . Radial bores 47 extend along a diameter through the sleeve to provide passage for radiation from the source 40 through the interior of the element 26 to the detector 41 on the other. The bores also effect collimation of the radiation. As shown at the right-hand side of Figure 2, the interior of the pipe element 25 has a flange 50 near its lower end which supports an inner sleeve 51 of boron carbide of which the inner surface is continuous with those of the flange and of the adjoining pipe elements. The boron carbide inner sleeve 51 requires mechanical reinforcement or support and this is provided by tensioned carbon fibre winding wound around its exterior and embedded in an epoxy resin to form a layer 52, the thickness of which need not be so great as to cause substantial absorption of the radiation. The radiation source 40 and the detector 41 are mounted on the pipe element 26 within the annular chamber 29 between the tubular elements 24-27 and the sleeve 30 which is filled with an inert gas, for example, nitrogen. The sleeve 30 is preferably counterbalanced externally by a pressure generated between it and the outer tubing 4. The lower portion of the sleeve 44 is provided with a connection 55 for a pressure sensor included in the metering equipment for supplying to the processing equipment a signal dependent on the pressure drop experienced by the multiphase fluid as it travels through the venturi. A temperature sensor can be included in the metering equipment also. In a modification, indicated at the left-hand side of Figure 2, the sleeve 51 is omitted together with the layer 52 and the flowing fluid stream is guided by the interior of the outer steel sleeve 44 directly. The radiation source and the detector are shielded from the fluid by plugs 49 of material, for example boron carbide, of high transparency to the radiation, received in the bores 47. The inner ends of the plugs 49 are preferably flush with the inner wall of the sleeve 44 and shaped accordingly. Although shown as occupying the entire lengths of the bores 47, the plugs 49 preferably extend along only part of the axial length of the bores 47 to limit attenuation of the radiation. The invention can of course be embodied in a variety of ways other than as specifically described.

Claims: CLAIMS 1. A metering device in which radiation from a source (40) is transmitted through a fluid to be metered to a sensor (41) responsive to the radiation by way of window means (49;51) comprising boron carbide. 2. A metering device as claimed in claim 1 in which the boron carbide window means comprises a sleeve (51) for guiding within it a flowing stream of the fluid. 3. A metering device as claimed in claim 2 in which the sleeve (51) has an external mechanical reinforcement. 4. A metering device having a window means (51) for transmission through a fluid to be metered of radiation from a source (40) to a sensor (41) responsive to the radiation, the window means comprising a sleeve for guiding within it a flowing stream of the fluid, the sleeve having an external mechanical reinforcement (52). 5. A metering device as claimed in claim 4 in which the material of the sleeve (51) is boron carbide. 6. A metering device as claimed in claim 3, 4 or 5 in which the mechanical reinforcement comprises an elongate element wound around the sleeve (51). 7. A metering device as claimed in claim 6 in which the elongate element comprises carbon fibre. 8. A metering device as claimed in claim 6 or 7 in which the wound elongate element is embedded in a settable material. 9. A metering device as claimed in claim 8 in which the settable material comprises an epoxy resin. 10. A metering device as claimed in any one of claims 3-9 in which the sleeve (51) is set within a rigid pipe element (26) having apertures (47) aligned across the element for transmission of the radiation. 11. A metering device in which radiation from a source (40) is transmitted through a flowing fluid to be metered to a sensor (41) responsive to the radiation by way of window means (49) comprising plugs received in apertures (47) aligned across a rigid pipe element (26) for guiding within it the flowing fluid. 12. A metering device as claimed in claim 10 or 11 in which the pipe element (26) is of generally circular cross- section and the apertures (47) are aligned along a diameter. 13. A metering device as claimed in claim 11 or 12 wherein the material of the plugs (49) is boron carbide. 14. A metering device as claimed in claim 13 wherein the plugs (49) occupy only the inner end portions of the apertures (47). 15. A metering device as claimed in any one of claims 10-14 in which the apertures (47) are arranged to effect collimation of the radiation. 16. A metering device as claimed in any one of claims 10-15 having tubing (30) around and spaced from the pipe element (26) to define a chamber containing the radiation source (40) and sensor (41). 17. A metering device as claimed in claim 16 in which the chamber contains an inert gas. 18. A metering device as claimed in any one of claims 10-17 in which the pipe element (26) is included in the discharge duct (20) of a mixing unit. 19. A metering device as claimed in claim 18 in which the pipe element (26) constitutes a venturi in the discharge duct (20). 20. A metering device as claimed in any preceding claim in which the metering device comprises a gamma ray or X-ray densiometer.

Inventors: MOHN FRANK, MOHN, FRANK
Applicants: FRAMO DEV LTD, FRAMO DEVELOPMENTS (UK) LIMITED
Application year: 1992
Main classification: G01N23
IPC codes: G01N23