Abstract:
A pipeline flow meter orifice fitting includes a first body, a flow bore through the first body, a chamber in the first body adjacent to the flow bore, an orifice plate supported in alignment with the flow bore by an orifice plate carrier, wherein the orifice plate carrier is exposed to the chamber and divides the flow bore into a first region to one side of the orifice plate and a second region to the other side of the orifice plate, a second body coupled to said first body, a first flow path fluidicly coupling the first region and the chamber through the second body, and a second flow path fluidicly coupling the second region and the chamber through the second body. In some embodiments, a three way valve is mounted on the first body, the three way valve selectably actuatable to open a first flow path between the first region and the chamber or a second flow path between the second region and the chamber.

Description:
BACKGROUND 
     This disclosure relates generally to orifice fittings for measuring fluid flow rates through pipes or other conduits. More particularly, the disclosure relates to a pressure equalization system for use in orifice fittings. 
     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 the flow stream. The orifice plate is generally a thin plate that includes a circular opening, or orifice, that is typically positioned concentric with the flow stream. 
     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. 
     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 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 a wide range of piping sizes and working pressures. 
     A cross-sectional view of 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 bore  34  of a 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  by bolts  28  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 bore  34  and fitting  12  between lower chamber  20  and upper chamber  22 . Orifice plate carrier  32  can be removed from fitting  12  through upper chamber  22  by loosening bolts  46 , which engage locking bar  44  to compress sealing bar  40  and sealing gasket  42  against top  18 . Orifice plate carrier is thus selectably disposable between the fully seated position in bore  34  and the upper portions of fitting  12 . 
     In operation, as shown in  FIG. 1 , aperture  30  is closed by slide valve plate  56  hydraulically isolating upper chamber  22  and lower chamber  20 . Pressurized fluid flow in bore  34  passes through orifice  52 , which is located on an orifice plate  50  supported by orifice plate carrier  32  that sealingly engages the wall of bore  34 . Pressure up and downstream of orifice plate  50  is measured via meter tap holes or communication ports  66 . The measured pressure differential across orifice plate  50  is then used to estimate the rate of fluid flow through fitting  12 . In order to obtain accurate estimates of the flow rate through fitting  12 , all of the flow moving through the pipeline must pass through orifice  52 . If any flow by-passes or flows around orifice  52 , an error in the measurement of the pressure differential across orifice plate  50  occurs. To prevent flow from bypassing orifice  52 , a seal  64  is placed around orifice plate  50 , between plate  52  and carrier  32 . 
     When lower chamber  20  has a lower pressure than bore  34 , the pressure in bore  34  will tend to urge orifice plate carrier  32  upward and into lower chamber  20 , potentially causing misalignment between orifice  52  and bore  34  that can decrease measurement accuracy. Further, seal  64 , which is usually constructed from an elastomer or polymer, may fail due to the pressure differential between bore  34  and lower chamber  20 . In order to counter the pressure differential, an equalization flow path or weephole  60  is included between lower chamber  20  and bore  34 . Weephole  60  provides fluid communication between bore  34  and lower chamber  20 , and thus, allows pressure to equalize across orifice plate carrier  32 . Weephole  60  is located upstream of orifice  52  so as to be located in the region of highest pressure within bore  34 . 
     In some applications, such as metering for bulk storage facilities, it may be desirable to be able to operate an orifice fitting with flow in either direction through the fitting, in order to measure the alternating flow into and out of the facility. However, if weephole  60  is positioned downstream from orifice  52 , the pressure in bore  34  proximate weephole  60  will be less than the pressure in bore  34  that acts on orifice plate carrier  32 , thereby creating a pressure differential across carrier  32  and urging carrier  32  into lower chamber  20 . Further, seal  64  may tend to expand radially off of orifice plate  50 . Once seal  64  is compromised in this manner, pressure differential measurement accuracy is lost. 
     To enable the measurement of fluid passing through a fitting in either direction, the weephole may be sealed by welding, and a bypass system coupled to the fitting. In some configurations, the bypass system, which replaces the weephole, includes two tubes. One tube is coupled between a meter tap hole to one side of the orifice plate and the lower chamber, while the other tube is coupled between a meter tap hole to the other side of the orifice plate and the lower chamber. A valve is positioned along each tube to permit or prevent fluid flow therethrough. 
     In operation, the valve positioned along the tube coupled to the upstream meter tap hole is open, while the other valve is closed. Some pressurized fluid passes from the bore through the upstream tube into the lower chamber to provide pressure equalization between the lower chamber and the bore of the fitting upstream of the orifice plate. Thus, the upstream tube of the bypass system performs the same function as a weephole in a uni-directional fitting. Pressure differential measurements may be taken across the orifice plate, as described above. 
     When the direction of flow through the bi-directional fitting is reversed, the position of each valve is also reversed. What was previously the upstream valve, now the downstream valve, is closed. Similarly, what was previously the downstream valve, now the upstream valve, is opened. With the valve positions reversed and the upstream tube again performing the function of a weephole, pressure differential measurements may be taken across the orifice plate with flow passing through the fitting but in the opposite direction. 
     While these types of bypass systems offer a means for converting a fitting from uni-directional to bi-directional, these bypass systems are not without their shortcomings. The individual components of the bypass system are costly and can be difficult to install. Once installed, these systems often leak. Since the bypass system is external to the fitting, the tubing and valves are vulnerable to surrounding conditions. An inadvertent impact to the tubing and/or valves, e.g., during transport of the fitting, may cause damage to the bypass system. 
     Therefore, there remains a need in the art for a bi-directional dual chamber orifice fitting that provides pressure equalization across the orifice plate carrier while overcoming these and certain other limitations of the prior art. 
     SUMMARY 
     The disclosure includes methods and apparatus for a bi-directional dual chamber orifice fitting comprising a first body, a flow bore through the first body, a chamber in the first body adjacent to the flow bore, an orifice plate supported in alignment with the flow bore by an orifice plate carrier, wherein the orifice plate carrier is exposed to the chamber and divides the flow bore into a first region to one side of the orifice plate and a second region to the other side of the orifice plate, a second body coupled to said first body, a first flow path fluidicly coupling the first region and the chamber through the second body, and a second flow path fluidicly coupling the second region and the chamber through the second body. In some embodiments, fluid flow through the flow bore in a first direction will flow through the first flow path but not the second flow path. A fluid flow through the flow bore in the opposite direction will flow through the second flow path but not the first flow path. 
     In some embodiments, a method for equalizing the pressure on an orifice plate carrier disposed within a flow bore through an orifice fitting and exposed to a chamber within the orifice fitting adjacent the flow bore comprises flowing a fluid through the flow bore in a first direction, equalizing a pressure between a first upstream region of the flow bore and the chamber through a first flow path in the body, flowing the fluid through the flow bore in an opposite direction of the first direction, actuating a second flow path in the body, and equalizing a pressure between a second upstream region of the flow bore and the chamber through the second flow path. 
     In further embodiments, an orifice fitting comprises a first body having a flow bore therethrough and a chamber disposed therein adjacent the flow bore, an orifice plate supported in alignment with the flow bore by an orifice plate carrier, wherein the orifice plate carrier is exposed to the chamber and divides the flow bore into a first region to one side of the orifice plate and a second region to the other side of the orifice plate, and a three way valve mounted on the first body, the three way valve selectably actuatable to open a first flow path between the first region and the chamber or a second flow path between the second region and the chamber. 
     Thus, the embodiments of the disclosure 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 disclosure will be readily apparent to those skilled in the art upon reading the following detailed description and by referring to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more detailed understanding, reference is made to the accompanying Figures, wherein: 
         FIG. 1  is a cross-sectional view of a dual chamber orifice fitting; 
         FIG. 2  is a perspective view of a bi-directional orifice fitting with a pressure equalization system in accordance with the principles disclosed herein; 
         FIG. 3  is a partial cross-sectional view of the bi-directional orifice fitting of  FIG. 2  with the pressure equalization system coupled thereto; 
         FIGS. 4A and 4B  are cross-sectional views of another embodiment of a pressure equalization system with a slidable valve; 
         FIG. 5  is a partial cross-sectional view of the bi-directional orifice fitting of  FIG. 3  showing flow in a first direction; and 
         FIG. 6  is a partial cross-sectional view of the bi-directional orifice fitting of  FIG. 3  showing flow in a second direction. 
     
    
    
     DETAILED DESCRIPTION 
     In the drawings and description that follow, like parts are typically 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. The present disclosure is susceptible to embodiments of different forms. Specific embodiments are described in detail and are shown in the drawings, with the understanding that the present disclosure is to be considered an exemplification of the principles of the disclosure, and is not intended to limit the disclosure to that illustrated and described herein. 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. 
     Unless otherwise specified, any use of any form of the terms “connect”, “engage”, “couple”, “attach”, or any other term describing an interaction between elements is not meant to limit the interaction to direct interaction between the elements and may also include indirect interaction between the elements described. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ”. The various characteristics mentioned above, as well as other features and characteristics described in more detail below, will be readily apparent to those skilled in the art upon reading the following detailed description of the embodiments, and by referring to the accompanying drawings. 
     Referring now to  FIG. 2 , a perspective view of an orifice fitting  100  coupled to a pipeline  103  is shown. Orifice fitting  100  includes a body  102  having a meter tap boss  105 . A pressure equalization system  110  is coupled to body  102  at boss  105 . Pressure equalization system  110  may also be referred to as a bypass system. Bypass system  110  includes a body or block  115  through which one or more bolts  120  extend to couple block  115  to body  102  of fitting  100 . Bypass system  110  further includes a valve  125  (visible in  FIG. 3 ) disposed within block  115 . A handle  130  is coupled to valve  125  and is selectably moveable to change the position of valve  125 . In this exemplary embodiment, valve  125  is actuated by manually moving handle  130  from one position to another. In other embodiments, however, valve  125  may be actuated in other ways known in the art, including but not limited by electrical means. 
     Referring now to  FIG. 3 , a cross-section of bypass system  110  coupled to orifice fitting  100  is shown. Meter tap boss  105  of orifice fitting  100  includes a lower chamber  135 , which is in fluid communication with a flow bore  140  of pipeline  103 . An orifice plate carrier  145  is disposed within flow bore  140 , thereby dividing flow bore  140  into a first region  150  and a second region  155 . Plate carrier  145  includes an orifice plate  160  with an orifice  165  therethrough and a seal  170  surrounding plate  160  between plate  160  and carrier  145 . 
     Meter tap boss  105  of fitting  100  further includes an inner surface  175 , an outer surface  180 , two meter tap holes  185 ,  190  extending therebetween, and a flow bore  195  extending between outer surface  180  and lower chamber  135 . Meter tap holes  185 ,  190  are positioned on opposite sides of orifice plate  160  and configured to permit the measurement of fluid pressure within flow bore  140 . Outer surface  180  is configured to engage block  115  of bypass system  110 . In some embodiments, body  102  and boss  105  are cast or machined to create outer surface  180  such that outer surface  180  may sealingly engage block  115 . In other embodiments, body  102  and block  115  are manufactured as integral components, or as a uniform body including the components of block  115  as described herein. 
     As described above, valve  125  of bypass system  110  is seated within block  115 . In this exemplary embodiment, valve  125  is a rotatable valve, including but not limited to a ball valve. Handle  130  is coupled to valve  125  and is selectably moveable to vary the position of valve  125 . Bypass system  110  further includes three flow bores  200 ,  205 ,  210  extending between valve  125  and an inner surface  207  of block  115 . Inner surface  207  is configured to engage boss  105  of fitting  100 . In some embodiments, block  115  is cast or machined to create inner surface  207  such that inner surface  207  may sealingly engage fitting  100  when installed thereon. In other embodiments, fitting  100  and block  115  are manufactured as integral components, or as a uniform body including the components of block  115  as described herein. When block  115  is installed on fitting  100 , as shown in  FIG. 3 , flow bores  200 ,  205  align with meter tap holes  185 ,  190 , respectively. Also, flow bore  210  aligns with flow bore  195  of fitting  100 . 
     Depending on the position of valve  125 , a flow path may be opened from flow bore  140  of pipeline  103  through meter tap boss  105  of fitting  100  and block  115  of bypass system  110  to lower chamber  135 . When valve  125  assumes a first position, as shown, a first flow path  215  is opened and extends from first region  150  of flow bore  140  through meter tap hole  190 , flow bore  205 , valve  125 , flow bore  210  and flow bore  195  to lower chamber  135 . When valve  125  assumes a second position (shown in  FIG. 6 ), a second flow path  220  is opened and extends from second region  155  of flow bore  140  through meter tap hole  185 , flow bore  200 , valve  125 , flow bore  210  and flow bore  195  to lower chamber  135 . Valve  125  is selectably actuated by rotation of handle  130  to open first flow path  215  and simultaneously close second flow path  220 , or vice versa. By virtue of the communicating flow bores and selectively useable flow paths just described, valve  125  may also be referred to as a three way valve. First flow path  215  provides a selectively useable fluidic coupling between first region  150  and chamber  135  through body  115 , and second flow path  220  provides another selectively useable fluidic coupling between second region  155  and chamber  135  also through body  115 . 
     To prevent the loss of fluid from fitting  100  and bypass system  110 , bypass system  110  further includes a plurality of sealing elements  225  disposed between block  115  of bypass system  110  and meter tap boss  105  of fitting  100  surrounding the junctions between flow bore  200  and meter tap hole  185 , between flow bore  210  and flow bore  195 , and between flow bore  205  and meter tap hole  190 . Bypass system  110  further includes a plurality of sealing elements  230  at the junctions between valve  125  and flow bores  200 ,  205 ,  210 . Lastly, bypass system  110  further includes a plug  235 . Plug  235  in inserted into block  115  after flow bores  200 ,  205  are manufactured. 
     As described above, in this exemplary embodiment, bypass system  110  includes rotatable valve  125 . Other embodiments of a pressure equalization system may include another type of valve. By way of example,  FIG. 4A  depicts a bypass system  665  including a slidable valve  625 . Bypass system  665  includes a block  620  which may be coupled to boss  105  of fitting  100  ( FIG. 2 ). Block  620  includes a cavity  635  therein, which is bounded by a surface  675 . Valve  625  is disposed within cavity  635  and slidably engages surface  675  of block  620 . A handle  630  is coupled to valve  625  and is selectably moveable to vary the position of valve  625  within cavity  635 . Block  620  further includes three flow bores  600 ,  605 ,  610  extending between valve  625  and an inner surface  607  of block  620 . Inner surface  607  is configured to engage boss  105  of fitting  100  ( FIG. 2 ). In some embodiments, block  620  is cast or machined to create inner surface  607  such that inner surface  607  may sealingly engage fitting  100  when installed thereon. When block  620  is installed on fitting  100 , flow bores  600 ,  605  align with meter tap holes  185 ,  190 , respectively. Also, flow bore  610  aligns with flow bore  195  of fitting  100 . 
     Valve  625  includes an elongate member  685  having projections  650  forming two chambers  640 ,  645  inside cavity  635 . Handle  630  is coupled to member  685 . Each projection  650  includes a groove  690  disposed therein. Each groove  690  is configured to receive a sealing element  695  prior to insertion of valve  625  within block  620 . When valve  625  is slidably disposed within cavity  635 , as shown, elements  695  enable sealing engagement between valve  625  and block  620 . 
     Depending on the position of valve  625 , a flow path may be opened from flow bore  140  of pipeline  103  through meter tap boss  105  of fitting  100  and block  620  of bypass system  665  to lower chamber  135 . When valve  625  assumes a first position, as shown, a first flow path  700  is opened and extends from first region  150  of flow bore  140  through meter tap hole  190 , flow bore  605  of valve  625 , chamber  645 , flow bore  610  and flow bore  195  of body  105  to lower chamber  135 . When valve  625  assumes a second position, as shown in  FIG. 4B , a second flow path  705  is opened and extends from second region  155  of flow bore  140  through meter tap hole  185 , flow bore  600  of valve  625 , chamber  640 , flow bore  610  and flow bore  195  of body  105  to lower chamber  135 . Valve  625  is selectably actuated by translation of handle  630  to open first flow path  700  and simultaneously close second flow path  705 , or vice versa. By virtue of the selectively useable flow paths  700 ,  705 , valve  625  may also be referred to as a three way valve. Flow paths  700 ,  705  provide separate fluidic couplings between regions  150 ,  155  and chamber  135  through body  620 . 
     During operation of orifice fitting  100 , fluid may pass through flow bore  140  of pipeline  103  in either direction. Depending on the direction of flow, either bypass system  110 ,  665  is actuated to provide a flow path between flow bore  140  upstream of orifice plate  160  and lower chamber  135 . By opening such a flow path, some fluid is allowed to pass from the upstream side of flow bore  140  into lower chamber  135 . As a result, pressures loads acting on orifice plate carrier  145 , orifice plate  160 , and orifice plate seal  170  may be substantially equalized. 
     For example, referring to  FIG. 5 , a cross-section of bypass system  110  coupled to orifice fitting  100  is shown with fluid flowing through fitting  100  in the direction  400  indicated. As shown, fluid flows from first region  150  through orifice  165  to second region  155 . By virtue of the flow direction  400 , first region  150  is the upstream region of flow bore  140 , while second region  155  is the downstream region of flow bore  140 . To provide pressure equalization between upstream region  150  and lower chamber  135 , handle  130  is rotated to actuate valve  125  such that first flow path  215  is opened and second flow path  220  is closed. As a result, a portion of fluid passing through flow bore  140  of pipeline  103  is diverted from upstream region  150  along first flow path  215  to lower chamber  135 . Thus, the pressure of fluid acting on an outer surface  240  of orifice plate carrier  145  is substantially equalized or balanced with the pressure of fluid acting on upstream faces  405 ,  410 ,  415  of orifice plate carrier  145 , plate  160  and seal  170 , respectively. 
     Alternatively, referring to  FIG. 6 , a cross-section of bypass system  110  coupled to orifice fitting  100  is shown with fluid flowing through fitting  100  in the opposite direction, or in the direction  500  indicated. As shown, fluid flows from second region  155  through orifice  165  to first region  150 . By virtue of the flow direction  500 , second region  155  is the upstream region of flow bore  140 , while first region  150  is the downstream region of flow bore  140 . To provide pressure equalization between upstream region  155  and lower chamber  135 , handle  130  is rotated to actuate valve  125  such that second flow path  220  is opened and first flow path  215  is closed. As a result, a portion of fluid passing through flow bore  140  of pipeline  103  is diverted from upstream region  155  along second flow path  220  to lower chamber  135 . Thus, the pressure of fluid contained within lower chamber  135  and acting on outer surface  240  of orifice plate carrier  145  is substantially equalized or balanced with the pressure of fluid acting on upstream faces  505 ,  510 ,  515  of orifice plate carrier  145 , plate  160  and seal  170 , respectively. 
     As described, with fluid passing through flow bore  140  of pipeline  103  in either direction, valve  125  of bypass system  110  may be actuated to open a flow path between the upstream region of flow bore  140  and lower chamber  135 . By opening such a flow path, some fluid is allowed to pass from the upstream region of flow bore  140  (region  150  of  FIG. 5 ; region  155  of  FIG. 6 ) into lower chamber  135 . Thus, pressure of fluid contained within lower chamber  135  and acting on outer surface  240  of orifice plate carrier  145  can be controllably and substantially equalized or balanced with the upstream pressure regardless of the fluid flow direction. 
     The equalization of pressure acting on orifice plate carrier  145 , plate  160  and seal  170  enables the radial position of plate carrier  145  to remain unchanged, and the eccentricity of orifice  165  to be maintained. Further, the equalization of pressure acting on seal  170  promotes the structural integrity of seal  170  and minimizes any tendency for seal  170  to displace. Promoting the eccentricity of orifice  165  and eliminating leakage by supporting seal  170  both enable accuracy of differential pressure measurements across orifice plate  160 . Thus, by providing a pressure equalization flow path on either side of orifice  165 , fitting  100  can be operated to obtain accurate flow estimates with fluid moving in either direction through pipeline  103 . 
     While certain embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teaching herein. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the system and apparatus are possible and will become apparent to those skilled in the art once the above disclosure is fully appreciated. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied. Furthermore, the flow paths between the pipeline bore through the fitting and equalization pressure system to the lower chamber of the fitting may vary in shape and orientation. Accordingly, it is intended that the following claims be interpreted to embrace all such variations and modifications.