Abstract:
A flow device including a differential flow plate insertable into a flow path between pipe sections including a flow conduit supporting a flow interrupter and differential pressure taps. The flow conduit including a seamless interface between the flow interrupter and the pressure taps to reduce non-attributable pressure loss between differential pressure taps as well as reduce field installation labor including that of pressure testing the various pressure couplings.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     Reference id hereby made to co-pending application Ser. No. 09/395,688, filed Sep. 13, 1999 and entitled “PROCESS FLOW PLATE WITH HIGH ACCURACY TEMPERATURE FEATURE”. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to the process measurement and control industry. The measurement and control industry employs process variable transmitters to remotely monitor process variables associated with fluids such as slurries, liquids, vapors, gasses, chemicals, pulp, petroleum, pharmaceuticals, food and other food processing plants. Process variables include pressure, temperature, flow, level, turbidity, density, concentration, chemical composition and other properties. 
     FIG. 1 is an exploded view of a prior art process flow device  50  for measuring process variables, such as differential pressure and flow. As shown in FIG. 1, flow plate  52  is clamped between flanges  54 ,  56  in a flow path to produce a differential pressure across a constriction for measuring flow rate of fluids through a pipe  58 . Differential pressure across the flow constriction is measured at pressure taps  60 ,  62 . As illustrated in FIGS. 1-2, pressure taps  60 ,  62  are separate from flow plate  52  clamped between pipe flanges  54 ,  56  so that seams separate pressure taps  60 ,  62  from flow plate  52 . Pipe  58  conveys process fluid at a high pressure. Such pressure is a combination of the differential pressure developed in response to the constriction and the static pressure within the pipe which can be 1000 psi or more. The high pressure can cause fluid and pressure to leak from seams between the flow plate  52  and pressure taps  60 ,  62 . Vibration and other motion of the flow pipe can loosen the connection between the flow plate  52  and pressure taps  60 ,  62  contributing to fluid and pressure leakage at the seams. 
     Within device  50 , flow rate is calculated based upon differential pressure across a flow constriction, pipe diameter and constriction profile. Pressure loss and leakage at seams changes the measured differential pressure across the flow constriction and the pressure loss or change is not attributable to flow rate. The non-attributable pressure loss at the seams degrades flow calculations. Additionally, device  50  requires significant field installation time due to the necessity of joining all the couplings together and performing leak checking upon the couplings. Moreover, whenever maintenance is required for device  50 , significant disassembly/reassembly time is usually required which increases undesirable downtime. Thus, it is desirable to provide a process fluid flow measurement device with increased accuracy and reduced field installation time, downtime, and cost. 
     SUMMARY 
     Embodiments of the invention relate to a flow plate having a seamless interface between first and second pressure taps and flow interrupter to reduce non-attributable pressure loss at seams between first and second pressure taps and the flow interrupter. Reduced non-attributable pressure loss improves measurement accuracy, while the seamless interface reduces field installation time. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of a prior art flow plate inserted between pipe flanges. 
     FIG. 2 is a cross-sectional view taken along line  2 — 2  of FIG.  1 . 
     FIG. 3 is an environmental view of an embodiment of a process flow device of the present invention. 
     FIG. 4 is a schematic illustration of components of a process flow device of the present invention. 
     FIG. 5 is a cross-sectional view of an embodiment of a process flow device assembled in a flow pipe between flanges. 
     FIG. 6 is a detailed illustration of portion  6  of FIG.  5 . 
     FIG. 7 is a cross-sectional view of an alternate embodiment of a process flow device assembled in a flow pipe between flanges. 
     FIG. 8 is a cross-sectional view of an alternate embodiment of a process flow device assembled between pipe flanges having a detachable edge portion. 
     FIG. 9 is a detailed illustration of portion  9  of FIG.  8 . 
     FIG. 10 is a cross-sectional view of an alternate embodiment of a process flow device assembled between pipe flanges with exploded illustration of rings forming a conduit of the flow plate. 
     FIG. 11 is a perspective illustration of portion  11  of the flow plate of FIG. 10 
     FIG. 12 is a cross-sectional view of an embodiment of a process flow device assembled between pipe flanges with exploded illustration of an alternate embodiment of rings forming a conduit of the flow plate. 
     FIG. 13 is a perspective illustration of portion  13  of the flow plate of FIG.  12 . 
    
    
     DETAILED DESCRIPTION 
     FIGS. 3-4 are environment illustrations of an embodiment of a process flow device  100  of the present invention including an instrument base  102 , first and second different pressure passageways  104 ,  106  and a differential flow plate  108 . The differential flow plate  108  includes a flow conduit  110  supporting a flow interrupter  112  and first and second pressure taps  114 ,  116  open to the flow conduit  110  (illustrated schematically in FIG.  4 ). 
     As shown schematically in FIG. 4, instrument base  102  supports process instrumentation  120 . In FIGS. 3-5 and  7 , process instrumentation  120  includes a pressure sensor module  122  for isolating a differential pressure and transmitter  124  for transmitting process data to a computer or reading device  126  (FIG.  3 ). Transmitter  124 , or any other any other appropriate readout device, can sense process variables and provide a related output over a process loop to a control room or computer  126 , such that the process can be monitored and controlled. Computer  126  can be remote or locally integrated. The process loop can be a two-wire 4-20 mA process control loop. The loop may also have digital signals superimposed on the two-wire loop according to a process industry standard protocol such as the HART® (“Highway Addressable Remote Transducer”) digital protocol, as described in HART® Communication Foundation, Austin, Tex. 78759-6450. Local process control devices are connected to process control, for example, through a fieldbus interface and network system as described in “Fieldbus Technical Overview” Fisher-Rosemount Systems, Inc., Eden Prairie, Minn. Process transmitters  124  can also be configured to meet intrinsic safety requirements. 
     Instrument base  102  includes first and second differential pressure openings  130 ,  132  as shown in FIG.  4 . Instrument base  102  supports process instrumentation  120  for fluid connection to differential pressure passageways  104 ,  106 . FIG. 5 illustrates an embodiment of instrument base  102  that includes a manifold  134 . Although not necessary for embodiments of the invention, manifold  134  provides calibration and maintenance convenience. Manifold  134  includes valve ports  136  to selectively obstruct or permit flow through the manifold during maintenance. Pressure passageways  104 ,  106  are in fluid communication with manifold channels. Although three valve ports are shown, any appropriate number of valve ports  136  can be used. In FIG. 7, instrument base  102  includes a base flange  138  illustrated diagrammatically having pressure channels  140 ,  142  extending through flange  138  and opened to pressure passageways  104 ,  106 . 
     Pressure passageways  104 ,  106  fluidly couple pressure openings  130 ,  132  of the instrument base  102  to pressure taps  114 ,  116 . In FIGS. 5 and 7, pressure passageways  104 ,  106  are formed by coaxial channels  146 ,  148  in a solid stem  150 . Channels  146 ,  148  formed through stem  150  are straight for rodding the passageways for cleaning. In an alternative design, tubes can be used to form passageways  104 ,  106  and application is not limited to the solid stem  150  shown in FIGS. 5 and 7. Stem  150  can be bolted to instrument base  102  as illustrated in FIG. 3 or connected by other fasteners. 
     In FIG. 5, manifold  134  can be permanently connected to stem  150  to provide a permanent interface between stem  150  and manifold  134 . A permanent interface reduces leakage at the interface of the stem  150  and manifold  134  due to assembly and disassembly. 
     Differential flow plate is coupleable between pipe sections  58 - 1 ,  58 - 2 . In FIGS. 5 and 7, a sealing gasket  152  abuts a sealing surface of flow plate  108  and flanges  54 ,  56 . Flow conduit  110  supports flow interrupter  112  to separate flow conduit into two sides. Flow conduit  110  is seamless between flow interrupter  110  and first and second pressure taps  114 ,  116  to provide a seamless interface  154  (as schematically illustrated in FIG. 4) in flow conduit  110  between flow interrupter  112  and first and second pressure taps  114 ,  116 . Thus, the seams separating prior art flow plates from pressure taps as described in the Background of the Invention are eliminated. Elimination of the seams between the flow interrupter  110  and pressure taps  114 ,  116  limits non-attributable pressure loss at the seams which can degrade flow measurement. Additionally, such configuration reduces the likelihood of leak development and the associated undesirable fugitive emissions. Further, elimination of the seams reduces field installation time and cost because fewer seals need to be created and tested in the field. 
     In FIGS. 5 and 7, flow plate  108  is formed integrally with stem  150  to form a single assembly unit. The single assembly unit reduces connections between pressure taps  114 ,  116  and pressure openings  130 ,  132  to reduce non-attributable pressure loss. 
     Flow interrupter  112  can be an orifice plate  156  having a constricted flow orifice  158  as illustrated in FIG.  5 . Although a conical edge concentric orifice plate  156  is shown in FIG. 5, other orifice plates can be used. Flow interrupter  112  can be a nozzle plate  160  having a constricted nozzle opening  162  as illustrated in FIG.  7 . Detailed descriptions of various orifice plates and nozzle plates are described in Liptak, Beto,  Instrument Engineer&#39;s Handbook: Process Measurement and Analysis , 3rd. Ed., Chilton Book Company (1995) and Miller, Richard,  Flow Measurement Engineering Handbook , 3rd Ed., McGraw-Hill, Inc. (1996). 
     FIGS. 8-9 illustrate a flow interrupter  112  having a base portion  164  and a removable edge portion  166  including constricted flow passage  168 . Base portion  164  is integral with flow plate  108  and the edge portion  166  is removably coupleable (as illustrated) to the base portion  164 . When edge portion  166  wears, a new edge portion  166  is installed for continued use of the flow plate  108 , which extends the useful operating life of the flow plate  108 . In the embodiment illustrated in FIGS. 8-9, edge portion  166  is externally threaded  170  to mate with internal threads  170  on the base portion  164 . A mechanism to lock and seal plate  108  (not shown) is desirable to prevent the insert from dropping and/or falling out. Although a cooperating thread arrangement is shown for removably connecting base portion  164  and edge portion  166 , alternate coupling methods can be used employing, for example, screws, bolts, etc. 
     Differential pressure taps  114 ,  116  are in fluid communication with flow conduit  110 . The first pressure tap  114  is opened to the flow conduit  110  on a first side of the flow interrupter  112  and is in communication with the first differential pressure opening  130  through the first differential pressure passageway  104  as schematically illustrated in FIG.  4 . The second pressure tap  116  is opened to the flow conduit  110  on an opposite side of the flow interrupter  112  and in communication with the second differential pressure opening  132  through the second differential passageway  106 . 
     In FIGS. 5,  6 ,  7  and  8 , pressure taps  114 ,  116  are formed of a hole in flow conduit  110  on opposed sides of the flow interrupter  112 . In FIGS. 10-13, pressure taps  114 ,  116  include annular pressure channels  174 ,  176  extending about a perimeter of flow conduit  110  and in fluid communication with flow conduit  110 , on opposed sides of flow interrupter  112 , and differential pressure passageways  104 ,  106  to provide an average pressure measurement upstream and downstream of the flow interrupter  112 . 
     In FIGS. 10-11, an annular openings  178 ,  180  extend about the perimeter of conduit  110  on opposed sides of flow interrupter  112 . Openings  178 ,  180  fluidly couple flow conduit  110  to annular pressure channels  174 ,  176 , respectively. In FIGS. 12 and 13, a plurality of openings  182  are spaced about the perimeter of conduit  110  on opposed sides of the flow interrupter  112 . Openings  182  fluidly couple flow conduit  110  and annular pressure channels  174 ,  176  for pressure measurement. Openings  182  can be any suitable shape including holes, slots, and semicircles. 
     In FIGS. 5-7, flow plate  108  is formed of a unitary construction. In FIGS. 10-13, flow plate  108  is constructed of an outer block  184  and inner rings  186 ,  188 . Outer block  184  includes flow interrupter  112  extending into a central opening of outer block  184 . Rings  186 ,  188  are sized for insertion into central opening of outer block  184  on opposed sides of flow interrupter  112  to form conduit wall  110 . The inner diameter of rings  186 ,  188  can vary for sizing the flow plate  108  for various pipe inside diameters. In one embodiment, rings  186 ,  188  are welded to outer block  184  to provide a relatively fluid-tight connection for conduit walls  110 , although other connections can be used. 
     In FIGS. 10-11, edges of the rings  186 - 1 ,  188 - 1  are spaced from flow interrupter  112  to form the annular openings  178 ,  180  extending about the perimeter of the flow conduit  110  to fluidly couple conduit  110  to pressure channels  174 ,  176 . In FIGS. 12 and 13, rings  186 - 2 ,  188 - 2  include openings  182  extending about the perimeter of rings  186 - 2 ,  188 - 2  to fluidly couple conduit  110  and annular pressure channels  174 ,  176 . 
     Flow plate  108  is inserted into flowpath for process measurement and control. Flow through pipe  54  creates a differential pressure across flow interrupter  112 . Differential pressure across flow interrupter  112  is conveyed by first and second pressure taps  114 ,  116  on opposed sides of the flow interrupter  112  to process instrumentation  120  to measure differential pressure across first and second pressure taps  114 ,  116  and transmit measurement data to a computer  126 . Flow conduit  110  of flow plate  108  supporting flow interrupter  112  is seamless and includes pressure taps  114 ,  116  to provide a seamless interface between pressure taps  114 ,  116  and flow interrupter  112  for pressure measurement as previously described. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.