Abstract:
Methods and apparatus for positioning an orifice plate within a body having a straight flowbore. One embodiment includes a carrier supporting the orifice plate and a drive member operable to engage the carrier and move the carrier along a first axis perpendicular to the flowbore. The drive member is also operable to limit the movement of the carrier along a second axis perpendicular to the flowbore and perpendicular to the first axis. A pin is operable to engage the carrier so as to limit movement along the first axis.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     Not applicable.  
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not applicable.  
       BACKGROUND OF THE INVENTION  
       [0003]     The invention relates to methods and apparatus for monitoring characteristics of a flow stream in a pipeline, in particular to dual chamber orifice fittings. More precisely, the embodiments of the invention relate to an improved system for positioning an orifice plate within the fitting.  
         [0004]     In pipeline operations and other industrial applications, flow meters are used to measure the volumetric flow rate of a gaseous or liquid flow stream moving through a piping section. Flow meters are available in many different forms. One common flow meter is an orifice meter, which includes an orifice fitting connected to the piping section. The orifice fitting serves to orient and support an orifice plate that extends across the piping section perpendicular to the direction of flow stream. The orifice plate is generally a thin plate that includes a circular opening, or orifice, that is typically positioned concentric with the inner surface of the piping section.  
         [0005]     In operation, when the flow stream moving through the piping section reaches the orifice plate, the flow is forced through the orifice, thereby constricting the cross-sectional flow area of the flow. Due to the principles of continuity and conservation of energy, the velocity of the flow increases as the stream moves through the orifice. This velocity increase creates a pressure differential across the orifice plate. The measured differential pressure across the orifice plate can be used to calculate the volumetric flow rate of the flow stream moving through the piping section.  
         [0006]     A dual chamber orifice fitting embodies a special design that enables the orifice plate to be removed from the fitting without interrupting the flow stream moving through the piping section. This specially designed fitting has been known in the art for many years. U.S. Pat. No. 1,996,192, hereby incorporated herein by reference for all purposes, was issued in 1934 and describes an early dual chamber orifice fitting. Fittings with substantially the same design are still in use in many industrial applications today. Although the design has remained substantially unchanged, operating conditions continue to expand and dual chamber fittings are now available for piping sizes up to 48-inches in diameter and for working pressures up to 10,000 psi.  
         [0007]     A common dual chamber orifice fitting  12  is illustrated in  FIG. 1 . Orifice fitting  12  includes body  16  and top  18 . Body  16  encloses lower chamber  20  which is in fluid communication with the interior  34  of pipeline. Top  18  encloses upper chamber  22  and is connected to body  16  by bolts  17 . Aperture  30  defines an opening connecting upper chamber  22  to lower chamber  20 . Valve seat  24  is connected to top  18  and provides a sealing engagement with slide valve plate  56 , which is slidably actuated by rotating gear shaft  54 . Lower drive  36  and upper drive  38  operate to move orifice plate carrier  32  vertically within fitting  12 .  
         [0008]     Orifice  31  is located on an orifice plate  33  supported by orifice plate carrier  32 . Orifice plate carrier  32  is shown in a metering position in alignment with bore  34 . To remove orifice plate carrier  32  from fitting  12  the following steps are used. First, gear shaft  54  is rotated to slide valve plate  56  laterally and away from valve seat  24  and open aperture  30 . Once aperture  30  is opened, lower drive  36  is actuated to move orifice plate carrier  32  upwards into upper chamber  22 . Once orifice plate carrier  32  is entirely within upper chamber  22 , aperture  30  is closed to isolate the upper chamber from bore  34  and lower chamber  20 . Any pressure within upper chamber  20  can then be relieved and orifice plate carrier  32  can be removed from fitting  12  by loosening clamping bar screws  46  and removing clamping bar  44  and sealing bar  40  from top  18 .  
         [0009]     The location of the orifice  31  within bore  34  is closely controlled because any misalignment may cause inaccuracies in measuring the flow through the pipeline. American Petroleum Institute (API) 14.3 sets forth the dimensional standards and tolerances for the position of orifice  31  in bore  34 . Compliance with the requirements of API 14.3 adds complexity to the manufacture of conventional dual chamber orifice fittings. Many conventional designs rely on precisely positioned surfaces inside body  16  to guide and position orifice plate carrier  32 . Often, several machining steps are required to place these selected surfaces in the proper relationships in order to guarantee compliance with API 14.3.  
         [0010]     Thus, there remains a need in the art for dual chamber orifice fittings providing improved orifice plate positioning systems. The embodiments of the present invention are directed to plate alignment apparatus for dual chamber orifice fittings that seek to overcome these and other limitations of the prior art.  
       SUMMARY OF THE PREFERRED EMBODIMENTS  
       [0011]     The preferred embodiments include methods and apparatus for positioning an orifice plate within a body having a straight flowbore. One embodiment includes a carrier supporting the orifice plate and a drive member operable to engage the carrier and move the carrier along a first axis perpendicular to the flowbore. The drive member is also operable to limit the movement of the carrier along a second axis perpendicular to the flowbore and perpendicular to the first axis. A pin is operable to engage the carrier so as to limit movement along the first axis.  
         [0012]     In one embodiment, an apparatus for positioning an orifice plate comprises a carrier supporting the orifice plate and a drive member adapted to engage the carrier and move the carrier in a first direction perpendicular to a flowbore. The drive member also limits the movement of said carrier in a second direction. The apparatus also includes a pin assembly adapted to limit the movement of the carrier in the first direction. In certain embodiments, the drive member comprises a shaft, a gear rotatably fixed to the shaft, and a cylindrical stuffing box engaging the shaft and having an outer diameter larger than the gear. The gear engages teeth disposed on the carrier. The stuffing box contacts a side of the carrier, which is perpendicular to the second direction, is connected to the body and sealingly engages the shaft. In certain embodiments, the pin assembly comprises a stop pin adapted to engage the carrier and a spanner nut attached to the body so as to limit the movement of the stop pin in the first direction. The pin assembly may also include a jack screw adapted to engage the spanner nut and move the stop pin in the first direction.  
         [0013]     Thus, the embodiments of present invention comprise a combination of features and advantages that enable substantial enhancement of the operation of dual chamber orifice fittings. These and various other characteristics and advantages of the present invention will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention and by referring to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     For a more detailed understanding of the present invention, reference is made to the accompanying Figures, wherein:  
         [0015]      FIG. 1  is a partial sectional isometric view of a prior art dual chamber orifice fitting;  
         [0016]      FIG. 2  is an isometric view of a dual chamber orifice fitting;  
         [0017]      FIG. 3  is a cross-sectional view of the dual chamber orifice fitting of  FIG. 2 ;  
         [0018]      FIG. 4  is a partial sectional isometric view of one embodiment of a fitting having a plate positioning system in accordance with the present invention;  
         [0019]      FIG. 5  is a magnified view of the system of  FIG. 3 ;  
         [0020]      FIG. 6  is an isometric view of one embodiment of a lower drive system;  
         [0021]      FIG. 7  is a partial sectional elevation view of a horizontal positioning system; and  
         [0022]      FIG. 8  is a partial sectional elevation view of a vertical positioning system. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]     In the description that follows, like parts are marked throughout the specification and drawings with the same reference numerals, respectively. The drawing figures are not necessarily to scale. Certain features of the invention may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in the interest of clarity and conciseness.  
         [0024]     Referring now to  FIGS. 2 and 3 , one embodiment of a dual chamber orifice fitting  100  is shown. Fitting  100  includes body  110  and top  115  connected by bolts  117 . Body  110  encloses lower chamber  120  and provides fluid communication with the interior of the pipeline by way of flange  125 . Bottom pin assembly  155  seals the lower end of body  110 . Top  115  encloses upper chamber  130  and includes aperture  140 , which provides a passageway between the upper chamber and lower chamber  120 .  
         [0025]     Top  115  includes flange  160 , for connecting with body  110 , and wall  165  surrounding upper chamber  130 . Upper chamber  130  is isolated from atmospheric pressure by sealing bar  170  and sealing bar gasket  172 , which are retained with clamping bar  175  and clamping bar screws  177 . Wall  165  supports upper drive assembly  145  and includes port  185 , which provides access to upper chamber  130 . A preferred body and top are further described in U.S. patent application Ser. No. ______, entitled “Dual Chamber Orifice Fitting Body,” (Atty. Ref. 1787-15200), which is incorporated by reference herein for all purposes.  
         [0026]     Valve assembly  135  is used to open and close the aperture  140 , allowing orifice plate carrier  147  to move between lower chamber  120  and upper chamber  130 . One preferred valve assembly is described in U.S. patent application Ser. No. ______, entitled “Dual Chamber Orifice Fitting Valve,” (Atty. Ref. 1787-14900), which is incorporated by reference herein for all purposes. Orifice plate carrier  147  supports the orifice plate  149 . Upper drive assembly  145  and lower drive assembly  150  are used to move orifice plate carrier  147  between lower chamber  120  and upper chamber  130  when valve assembly  135  is opened.  
         [0027]     Referring now to  FIG. 4 , a partial-section isometric view of body  110  is shown revealing orifice plate carrier  200  with orifice plate  220 , lower drive assembly  150 , and bottom pin assembly  230 . Plate carrier  200  is shown in the fully down position with orifice plate  220  axially aligned with the bore. It is in this position that pipeline flow measurements would be taken. Lower drive assembly  150  includes shaft  240 , stuffing boxes  245 , retainer nuts  250 , and gears  255 . Pin assembly  230  includes spanner nut  260 , jack-screw  265 , and stop pin  285 . The horizontal position of carrier  200  is set by lower drive assembly  150  and the vertical position is set by pin assembly  230 .  
         [0028]     Lower drive assembly  150  is shown in  FIG. 5  and includes shaft  240 , stuffing boxes  245 , retainer nuts  250 , and gears  255 . Shaft  240  has a middle portion  242  with an increased diameter. On each side of middle portion  242  are rotational locators  243 , such as keys or faceted surfaces, which interface with gears  255 , which have a corresponding internal feature  257 . Gears  255  slide onto shaft  240  and are rotationally constrained by locators  243 . Gears  255  are preferably not permanently affixed to shaft  240 .  
         [0029]     Stuffing boxes  245  slide onto shaft  240  until they contact, and axially constrain, gears  255 . The inside of stuffing boxes  245  have internal seals (not shown) that seal against shaft  240 . The outer surface of stuffing boxes  245  have a threaded boss  246  that connects to corresponding threads on the body  110 . Retainer nuts  250  on the outer end of stuffing boxes  245  are used to rotate the boxes and also hold in place seals  251  which seal between the stuffing boxes and the fitting body  110 .  
         [0030]     Referring now to  FIG. 6 , gears  255  engage teeth  275  on carrier  200  to move the carrier vertically as the gears are rotated. Stuffing boxes  245  on the outside edge of gears  255  have a larger diameter than the gears and thus engage the outer edges  270  of carrier  200 . Outer edges  270  may also include machined surfaces  275  at the top of carrier  200 . Machined surfaces  275  project above outer edges  270  to provide a surface that can be machined to a close tolerance, in order to establish the overall width of carrier  200 . Although the entire length of outer edges  270  may be machined, surfaces  275  provide a localized area so as to minimize that the length of the outer edge that has a closely maintained tolerance.  
         [0031]     In accordance with API 14.3, the positioning of the orifice plate  220  within the flow bore must be closely controlled. Therefore, the relationship between carrier  200  relative to body  110  is preferably determined using machined surfaces, the dimensional tolerances of which can be tightly controlled. Referring now to  FIG. 7 , a cross-sectional view of body  110  including carrier  200  and lower drive assembly  150  is illustrated. The position of carrier  200  is controlled both vertically and laterally, relative to the cross-section plane of  FIG. 7 , so that orifice plate  220  is centered on the bore within the permissible limitations.  
         [0032]     The lateral position of orifice plate  220  is determined by carrier  200  and its relationship to body  110 , which is controlled by lower drive assembly  150 . Machined surfaces  275  on carrier  200  establish the width of carrier  200  and define the distance  277  between the center of orifice plate  220  and the outermost edge of carrier  200 . Machined surfaces  275  contact ends  247  of stuffing boxes  245 . The distance  282  from the inner face  253  of retainer nut  250  to the end  247  of the stuffing box  245  is closely controlled as it is determined by the machined length of stuffing box  245 . The lateral position of inner face  253  of retainer nut  250  is established by machined surfaces  280  on the outside of body  110 , which, during manufacturing, can be precisely positioned relative to the center of the flow bore. Thus, carrier  200  is positioned using a combination of machined parts and surfaces, all of which can be closely controlled during manufacturing.  
         [0033]     The vertical location of carrier  200  is controlled by pin assembly  230 . Referring now to  FIG. 8 , pin assembly  230  is shown supporting the bottom of carrier  200 . Pin assembly  230  includes stop pin  285 , spanner nut  260 , and jack screw  265 . Pin  285  includes seal  290  that sealingly engages seal bore  295  of body  110 . Spanner nut  260  threadedly attaches to body  110  and includes threaded bore  262  accommodating jack screw  265 . Pin  285  interfaces with slot  295  on carrier  200 . The length of pin  285  and the vertical position of spanner nut  260  can be adjusted to control the vertical position of carrier  200 . With spanner nut  260  engaged, pin  285  can be moved upward relative to body  110 , by jack screw  265 , without manipulating spanner nut  260 . Thus, if carrier  200  were to become stuck in body  110 , pin  285  can be moved upward by rotating jack screw  265  to push on the carrier without moving spanner nut  265 , such that once jack screw  265  is lowered, pin  285  will return to its original position.  
         [0034]     Thus, the combination of lower drive assembly  150  and pin assembly  230  provide both lateral and vertical positioning for orifice plate carrier  200 . The positions of both lower drive assembly  150  and pin assembly  230  are established off of machined surfaces positioned on the outside of body  110 .  
         [0035]     The preferred embodiments of the invention relate to apparatus for positioning and moving an orifice plate within a dual chamber orifice fitting. The invention is susceptible to embodiments of different forms. There are shown in the drawings, and herein will be described in detail, specific embodiments of the invention with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that illustrated and described herein. In particular, various embodiments of the invention provide a number of different arrangements to improve operation of the fitting. Reference is made to the application of the concepts of the invention to dual chamber orifice fitting with a plate orifice, but the use of the concepts of the invention is not limited to these applications, and can be used for any other applications including other dual chamber fittings and orifice fittings. It is to be fully recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce desired results.  
         [0036]     The embodiments set forth herein are merely illustrative and do not limit the scope of the invention or the details therein. It will be appreciated that many other modifications and improvements to the disclosure herein may be made without departing from the scope of the invention or the inventive concepts herein disclosed. Because many varying and different embodiments may be made within the scope of the inventive concept herein taught, including equivalent structures or materials hereafter thought of, and because many modifications may be made in the embodiments herein detailed in accordance with the descriptive requirements of the law, it is to be understood that the details herein are to be interpreted as illustrative and not in a limiting sense.