Abstract:
A stabilized mounting assembly ( 15 ) and method for sensing pressure in a conduit, such as a pipeline, is disclosed wherein the load on the NPT threaded taps ( 31 ) is reduced and transferred from the NTP threads.

Description:
This application claims the benefit of Provisional application Ser. No. 60/123,175, filed Mar. 5, 1999, and 60/138,535, filed Jun. 10, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the remote sensing of pressure drops across an orifice plate in a pipeline and particularly to an orifice saddle to facilitate, stabilize and reduce vibration of the transmitter and associated apparatus, such as valved manifold blocks connecting the transmitter to taps straddling the orifice plate. 
     2. Description of the Related Art 
     The gas industry makes extensive use of orifice plates for volume measurements. Orifice plates are artificial constrictions in a pipeline. As a result of this constriction there is a pressure drop from the upstream side of the orifice plate to the downstream side of the orifice plate. There is a relationship between the pressure drop and the amount of gas flowing through the pipeline. The pressure drop can be measured which in turn allows a determination of the flow through the pipeline. 
     The pressure drop is measured using electronic transmitters. These transmitters actually measure the pressures on both the upstream and downstream sides of the orifice plate and then record the difference between the two. Devices of this type are referred as differential pressure transmitters. There are numerous manufacturers of this type of device (e.g. Rosemount, Honeywell, Foxboro and others). 
     Orifice plate fittings (such as the type manufactured by Daniel Industries) and orifice flanges (manufactured by Daniel and others) are provided with holes (called taps) both upstream and downstream of the orifice plate. The taps are generally threaded holes, typically ½″ female NPT (National Pipe Thread—a tapered thread designed to seal pressure tight). 
     It is necessary to incorporate valving systems between the orifice taps and the differential pressure transmitters. These valving systems need to include the following functions. Block valves to isolate the flow through the upstream and downstream taps (generally referred to as the high pressure side and the low pressure side), between the orifice flange or fitting and the transmitter. An equalizer valve, or valves, to control the connection between the high pressure passages and the low pressure passages. A vent valve, or valves, to allow trapped pressures to be bled off or to allow the passages to be purged of entrapped gases or liquids. Sometimes the vent valve(s) are incorporated into the transmitters. 
     The natural gas industry has evolved a number of specifications and requirements to minimize errors in the measurement of flow and to provide improved accuracy and response time. Some of these are: 
     1. The closer the transmitter is to the orifice plate the better. 
     2. The orifice size through the valving system from the orifice taps to the transmitter must be ⅜″ in diameter. 
     3. The flow passages between the orifice taps to the transmitter should be as straight as possible. The ideal is a straight through passage. One 90 degree turn in the flow passage is permitted. 
     Another consideration is mounting the valve system and the transmitters to the orifice plate assembly. Conventional mounting, valving, and transmitter assemblies can weigh 40 pounds and, depending on the complexity of the assembly and the products used, up to 70 pounds. The pipeline system and the orifice flanges or fittings are subject to vibration. The valving and transmitter assemblies also tend to be leaned on by the instrumentation personnel. It is necessary to spread the loads arising from these factors off of the typical ½″ NPT tap connections and transfer the loads onto the orifice fitting or flange. Currently available products use individual taps with attachments to spread the load. These are called stabilized connection flanges or stabilized futbol flanges. An example of such a stabilized connector flange is shown in U.S. Pat. No. 4,920,626 assigned to Precision General, Inc. of Houston, Tex. 
     In this patent is provided a stabilizer foot which is a generally parallelpiped body portion and/or containing pair of stabilizer feet attached to the body portion which feet project axially toward the orifice plate assembly. The body portion is provided with a bore through which is fitted an NPT threaded connector flange so that the body and/or the stabilizer feet are radially outward of the NPT threads and provide outriggers for engagement with the external surface of the orifice plate assembly. 
     However, if the orifice plate assembly is curved the body and/or stabilizer feet only make point contact along the curved surface. The provision of a flat boss on the orifice plate assembly will increase the contact with the parallelpiped body surface and/or projecting stabilizer feet but then the requirement of a planar boss limits the applicability of the usage of the device in U.S. Pat. No. 4,920,626 to only certain types of orifice fittings. 
     Notwithstanding the use of the device of U.S. Pat. No. 4,920,626 on the limited planar or curved surfaces, the shear forces exerted by the dead load of the transmitters (and any associated block manifolds) and live load exerted by instrumentation personnel leaning on the transmitter (and block manifold) will be borne by the NPT threads tending to disturb the seal between the threads and the orifice taps, resulting in the possibility of leaks. 
     Thus, there is a continuing need to provide an alternative connection method and apparatus to operatively fluidly couple the high and lower pressure taps about an orifice plate with a transmitter. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a method and apparatus for operatively fluidly connecting the high and low pressure taps of an orifice plate with a transmitter. 
     In a particularly preferred embodiment an orifice saddle is provided which orifice saddle preferably has one round hole and one elongated hole, though two round holes can be provided. 
     The threaded end of the taps are inserted through these holes and tightened into the ½″ NPT holes of the orifice fittings or orifice flange. The end of the taps, distal from the threaded end tightened into the ½″ NPT holes, is known as the “hex end” due to their configuration and are larger than the threaded end. 
     The saddle is forced outward of the taps toward the hex end by a series of adjustable feet which may take the form of adjustable stabilizing bolts extending from the saddle toward the orifice assembly. 
     This forcing places the taps in tension and forms a stable platform to attach the rest of the assembly. Any further live or dead loads are carried by the stabilizer bolts. 
     When the nature of the orifice fitting does not provide a sufficient area upon which the stabilizer bolts may bear, in a further embodiment of the invention a lower plate may be provided to increase the area of the orifice fitting assembly upon which the adjustable stabilizing bolts may bear. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded view of a typical transmitter and block manifold assembly for use with the saddle of the invention; 
     FIG. 2 is a schematic cross sectional view of the saddle assembled on a 12″ 600# flange; 
     FIG. 3 is an enlarged view of FIG. 2 to show detail thereof; 
     FIG. 4 is a schematic cross sectional view of the saddle of FIGS. 2-3 assembled on a 3″ 600# flange; 
     FIG. 5 is an exploded view of an alternative orifice fitting assembly showing use of a lower plate in connection with the saddle of the invention; 
     FIG. 6 is a schematic representation of FIG. 5 in assembled form; 
     FIG. 7 is an exploded view of a typical transmitter and block assembly for use with a second embodiment of the invention; 
     FIG. 8 is a perspective view of a ½″ socketweld tap; 
     FIG. 9 is a top view of FIG. 8; 
     FIG. 10 is a side view partially sectional of the tap of FIG. 8; 
     FIG. 11 is a perspective view of a socketweld tap nut designed to interfit with the ½″ socketweld tap of FIG. 8; 
     FIG. 12 is a top view of the tap nut of FIG. 11; 
     FIG. 13 is a side view, partially sectional of the tap nut of FIG. 11; 
     FIG. 14 is a perspective view of the assembled socketweld tap and tap nut in combination with the saddle of the second embodiment of the invention; 
     FIG. 15 being a side view of FIG. 14; 
     FIG. 16 being a side, sectioned view of FIG. 14; 
     FIG. 17 being an end view of FIG. 14; 
     FIG. 18 is an enlarged view of the stabilizer bolts of FIG. 17; and 
     FIG. 19 being a sectioned view of FIG.  18 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The apparatus of the invention can best be understood by reference to FIG. 1 in which a transmitter module  1  is placed in fluidly coupled connection with a pair of taps  31  representing the high and low pressure (or upstream and downstream sides, respectively) on either side of an orifice plate in a pipeline (not shown). 
     Block manifold assembly  17  and transmitter manifold assembly  15  generally shown in FIG. 1 complete the fluid connection between transmitter module  1  and taps  31 , generally ½″ NPT threaded. 
     In order to provide a stable platform on which to mount the transmitter assembly, an orifice saddle  34  is provided. 
     The device is assembled as follows. The taps  31  are inserted through holes  35 ,  36  in the orifice saddle  34 . The orifice saddle  34  includes one round hole  35  for the NPT taps and one elongated hole  36 . The elongated hole  36  is to allow for variation between the center to center spacings of the orifice taps in either the orifice flange or the orifice fitting. The distance between the orifice taps is conventionally 2⅛″, however this spacing can vary somewhat. The slot A in the orifice saddle allows for center to center spacings between 2″ and 2¼″. 
     The taps  31  are tightened into the ½″ NPT holes in the orifice fitting or orifice flange  37  (See FIG.  3 ). Once the taps  31  are fitted pressure tight and have been checked to ensure that the hex end  38  of the taps  31  are approximately in the same plane, the orifice saddle  34  is drawn up towards the hex end  38  of the taps  31 . The hex end  38  of the taps  31  is larger than the threaded end. There is a shelf  39  (FIG. 3) machined in the tap hole.  40  in the orifice saddle  34 . The tap  31  bears on the shelf  39  in the orifice saddle  34 . 
     The orifice saddle  34  is machined with four lobes  41 , each containing a threaded hole  42  (See FIG.  3 ). A stabilizing bolt  32  is threaded through each hole  42 . As the bolts  32  are threaded through the orifice saddle  34  they bear on the orifice flange or the orifice fitting  37  (See FIG.  3 ). The bolts  32  press the orifice saddle  34  against the taps  31 . When fully tightened the orifice saddle  34  now becomes a stable platform to attach the rest of the assembly. The loads imposed by the saddle  34  and the balance of the assembly is also transferred along the bolts  32  and to the orifice fitting or flange  37  (See FIG.  3 ). Thus, some of the load on the taps  31  has been relieved. The stabilizing bolts  32  can be locked in place using either locknuts  43  on the stabilizer bolts  32  or grub screws (not shown) installed through the side of the lobes  41  on the orifice saddle  34 . 
     The block manifold  17  assembly is then bolted directly to the orifice saddle  34 , using  4  bolts  12 . There is a pressure tight seal between the hex end  38  of the taps  31  and the bottom  44  of the block manifold  17  using teflon gaskets  30 . There is a single ⅜″ bore  45  (See FIG. 3) through each tap  31 . Those ⅜″ bores  43  line up with the corresponding ⅜″ bores  46  provided in the block manifold  17 . Each ⅜″ bores  46  in the block manifold is controlled by a conventional block valve assembly  18 ,  28 . When the manifold assembly  17  is securely bolted to the orifice saddle  34  its&#39; top surface (not visible) proves a stable platform to attach the transmitter manifold  15 . 
     Two gasket grooves (not visible) are provided in the top surface (not visible) of the block manifold  17  around the outlet of each ⅜″ bore  46 . Teflon gaskets  16  are inserted into these grooves to provide the pressure tight seal between the block manifold assembly  17  and the transmitter manifold  15  assembly. The transmitter manifold  15  (with transmitter  1  mounted) is attached to the block  17  manifold with 4 bolts  12 . There are two ⅜″ bores  47  straight through the transmitter manifold  15  which match to the ⅜″ bores  46  in the block manifold  17  on one side and to the transmitter process connections (not shown) on the other side. 
     The transmitter  1  is attached to the transmitter manifold  15  using  4  socket bolts  14 . The transmitter shown in this embodiment is a Rosemount  1151  . This transmitter has a 2⅛″ spacing between the high and low pressure inlets. Transmitters from other manufacturers can be attached to this device. Transmitters with other center to center spacings between the high and low side can also be attached to a modified version of this device. The transmitter  1  must be attached to the transmitter manifold  15  before the transmitter manifold  15  is attached to the block manifold  17 . 
     The transmitter manifold  15  can be fitted with various valves as required by the specific application. The transmitter manifold  15  shown has a total of four valves  3 ,  7 ,  9 ,  11 . Two of the valves  7 ,  9  are equalizer valves. These valves  7 ,  9  control the flow of gas between the high pressure side and the low pressure side. It is necessary to allow the high pressure side and the low pressure side of the assembly to communicate with each other to allow for calibration of the transmitter  1 . The natural gas industry requires two equalizer valves to minimize the potential for any pressure leakage between the high pressure side and the low pressure side when the transmitter is in use. Such leakage, if it were to occur, would impair the accuracy of the flow measurements. The other two valves  3 ,  11  are vent valves. In the configuration shown these vent valves permit each side (high pressure or low pressure) to be vented or purged separately. The vented gas of other fluids exits the assembly through a ¼″ NPT outlet. A standard commercially available NPT to tube fitting connection  13  can be installed in the ¼″ NPT outlet if it is necessary to capture the vented gas or fluid. 
     The internal flow passages of the transmitter manifold can be modified to allow for any number of different combinations of equalizer and vent valves, e.g.  1  equalizer and no vents,  1  equalizer and  1  vent,  1  equalizer and  2  vents,  2  equalizers and no vents,  2  equalizers and  1  vent, etc. 
     The device as shown allows for a ⅜″ bore straight from the orifice tap  31  through the transmitter  1 . The distance between the orifice taps  31  and the transmitter has been minimized and although no dimensions are shown, the distance is approximately 4½″. The orifice saddle  34  arrangements allows for a stable platform for the balance of the assembly, transfers load away from the NPT taps  31  and onto the orifice fitting or orifice flange. As shown in FIG. 3, each adjustable foot  32  is in the form of a bolt which has a foot axis angled with respect to a central axis of the tap  31 . According to the method of the invention, bolts  32  are adjusted to move the orifice saddle away from the conduit and to transfer the load from the tap to the feet and thereby relieve the load on the NPT threads. Each foot is preferably angled such that the foot axis is substantially perpendicular to the engaging surface of the conduit, as shown in FIG.  3 . The arrangement, because of the stabilizing effect of the bolts through the orifice saddle bearing on the orifice flange or fitting  37  (See FIG. 3) and minimizes the effects of vibration on the mounted assembly. 
     In an alternative embodiment, where the orifice fitting  50  (FIGS. 5 and 6) does not provide sufficient area adjacent threaded orifices  51 ,  52  to mount the orifice saddle  34  directly a lower plate  53  can be employed through which taps  31  pass. 
     In such a case, the stabilizer bolts  32  can then bear upon lower plate  53  by means of an upper plate  54  which places taps  31  in tension thereby forming a stable platform upon which to mount the remaining assembly. 
     Other types of manifold such as the five valve manifold  55  of FIGS. 5-6 may be used instead of the manifolds  15 ,  17  of FIGS. 1-4. 
     A further embodiment of the stabilized mounting assembly is shown generally in FIGS. 8-19. (Similar elements in different embodiments utilize the same numbering system throughout the views.). 
     Turning now to FIG. 7, the orifice saddle  34  is provided with ½″ socketweld taps  55 ,  56 , which pass through apertures  57 ,  58 , in orifice saddle  34 , so as to mate with socketweld tap nuts  59 ,  60 . Seals (only one of which is shown)  61  are captured between the socketweld taps  55 ,  56  and block manifold  80  (FIG. 7) to fluidly seal them together. A plurality of stabilizing bolts  62  is optionally provided with a lock nut  63  to adjustably position orifice saddle  34 . 
     FIGS. 8-10 show an enlarged view of socketweld tap  55  ( 56  being similar) provided with a through aperture  64  and a sealing well  68  into which seal  61  is positioned. A lip  67  is provided to engage with the lower portion of saddle  34  which is held snug by interfitting tap nut  60  with the threads  65  of tap  55 . Tap  55  is optionally provided with a chamfer at  66 . 
     As seen in FIGS. 11-13 tap nut  60  is provided with internal threads  70  so as to threadedly engage with threads  65  of tap  55 . Tap nut  60  is optionally counterbored at  78 , so as not to contact block manifold  80  (FIG.  7 ). FIG. 19 shows, at  82 , an elongated slot for adjustment of the saddle  34 . 
     Enlarged and sectional views of the saddle  34  are shown in FIGS. 14-19.