Abstract:
The present invention relates to valve plugs for reducing erosion of the valve plug head and/or seat. More specifically, this invention comprises a valve plug incorporating a choke transfer trim that reduces the time of exposure of the plug head and/or seat to high velocity and high pressure drop at the interface of the plug head and seat when the valve is in the closed position. The choke transfer trim transfers the flow control area of the valve away from the plug head/seat interface to a location downstream, thereby reducing erosion at the interface between the valve plug head and/or seat that is typically used for fluid throttling and shut off.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Application 61/024,105, entitled “Choke Transfer Valve Trim”, which was filed on Jan. 28, 2008 and is hereby incorporated by reference. 
    
    
     FIELD OF INVENTION 
     The present invention relates to valve plugs for reducing erosion of a valve plug head and/or seat. More specifically, this invention relates to a valve plugs using a choke transfer trim to reduce erosion in the region where the plug head and valve seat come into contact if the valve is in the closed position. 
     BACKGROUND OF THE INVENTION 
     Various valve plugs have been used for some time to control fluid flow through a conduit and/or orifice. Typically, these prior devices tend to wear away quickly in erosive process streams. Specifically, erosion caused by high velocity flow can cause the plug head and/or seat inlet to fail. Moreover, these prior devices comprise various shapes and configurations to regulate process stream flow. For example, one prior device reduces pressure in valve trim by using stages, but such trim is often limited to a clean fluid process. However, many of these shapes and configurations, although satisfactory in their ability to regulate fluid flow, experience erosion of the valve plug heads and valve seats, and such erosion may often be attributed to the repeated high velocity flow, high pressure drops, and/or corrosive process streams through a flow control area. 
     Choked flow can cause erosion of the plug head and/or seat and can cause the plug head and/or seat inlet to fail. Due to this possibility of failure, it is advantageous to produce a valve that reduces erosion of the valve plug head and/or seat inlet and thus increases longevity of severe duty service valves. 
     SUMMARY OF THE INVENTION 
     The present invention relates to valve plugs for reducing erosion of the valve plug head and/or seat inlet and thus increasing longevity of severe duty service valves. More specifically, in an exemplary embodiment, a valve plug comprises a choke transfer trim that reduces the time of exposure of the plug head and/or seat inlet to the high velocity and high pressure drop of a process stream. The choke transfer trim transfers the flow control area, also referred to as the minimum flow area, of the valve away from the plug head seat interface to a location downstream, thereby reducing erosion at the interface between the valve plug head and/or seat inlet that is typically used for fluid throttling and shut-off. 
     In an exemplary embodiment, the valve plug comprises a plug head, a plug stem configured to actuate the plug head, and a choke section comprising a plug head and a choke transfer seat. In accordance with one exemplary embodiment, the choke transfer trim comprises any geometry configured to transfer the process flow control area of the valve plug away from the clearance between the plug head and seat inlet to a location downstream. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete understanding of the present invention, however, may best be obtained by referring to the detailed description when considered in connection with the drawing figures, wherein like numerals denote like elements and wherein: 
         FIG. 1  illustrates a typical prior art valve plug; 
         FIG. 2  illustrates a valve plug with a choke transfer trim assembly in accordance with an exemplary embodiment of the present invention; 
         FIG. 3  illustrates a choke transfer trim assembly in accordance with an exemplary embodiment of the present invention; 
         FIG. 4  illustrates another exemplary embodiment of a choke transfer trim assembly; 
         FIGS. 5A-5F  illustrate various exemplary embodiments of a choke transfer trim assembly; and 
         FIG. 6  illustrates an exemplary embodiment of a choke transfer valve assembled with a process vessel. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The detailed description of exemplary embodiments of the invention herein, shows various exemplary embodiments and the best modes, known to the inventors at this time. These exemplary embodiments and modes are described in sufficient detail to enable those skilled in the art to practice the invention and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the following disclosure is intended to teach both the implementation of the exemplary embodiments and modes and any equivalent modes or embodiments. Additionally, all included figures are non-limiting illustrations of the exemplary embodiments and modes, which similarly avail themselves to any equivalent modes or embodiments. 
       FIG. 1  shows a typical prior art valve plug, which is susceptible to failure due to erosion. A typical prior art valve plug  100  comprises a plug head  101 , a plug stem  102  configured to actuate plug head  101 , an exterior housing  103 , and a valve seat  104  comprising a seat inlet  105 . The plug head seat portion  105  may be configured to be held within housing  103  such that it can interface with plug head  101  to control the volume of flow passing through the valve. This flow control is metered by adjusting the distance, “h”, between seat inlet  105  and the surface of plug head  101 . This distance is controlled by the actuation of plug stem  102 . 
     Accordingly, the minimum flow area of the prior art valve plug, shown in  FIG. 1 , is equal to the diameter of the inlet of valve seat  104 , labeled as D INLET , adjacent to plug head  101  and seat inlet  105  interface, times π, times “h” [Prior Art Minimum Flow Area=π* (D INLET )*(h)]. As illustrated in  FIG. 1 , the prior art valve plugs typically comprise trim configurations  106 , which position the flow control area  107  of the valve, denoted as “d”, close to the interface of plug head  101  and seat inlet  105 , thereby exposing the plug head and/or seat inlet to erosion and possible valve trim failure. Stated another way, the minimum flow area  107  and the inlet to the valve inlet  104  are at substantially the same location. 
     In an exemplary embodiment, and with reference to  FIG. 6 , a process system comprises a process vessel  600 , an injection valve  601 , a blowdown vessel  602 , and a valve plug  200 . The injection valve  601  controls the pressure and/or temperature of process vessel  600 . For example, a high pressure steam may be injected into process vessel  600 , thereby raising the temperature and the pressure. In accordance with an exemplary embodiment, valve plug  200  is configured to substantially shut off any leakage through the valve while process vessel  600  is pressurized. Furthermore, in another embodiment, valve plug  200  is configured to open quickly to allow for a rapid release of the pressure of process vessel  600  into blowdown vessel  602 . Opening quickly can be opening the valve plug within one second or less, though other opening times are suitable as determined by how the valve plug is used. 
     In yet another exemplary embodiment, valve plug  200  is configured to handle a “non-clean fluid” process. In other words, various materials may exit through valve plug  200  and into blowdown vessel  602  without clogging or substantially impairing the valve. For example, in one embodiment, food products are contained in process vessel  600 . Parts of the food products and/or dirt may be included in the material that passes through valve plug  200 . 
     In accordance with an exemplary embodiment, and with reference to  FIG. 2 , a valve plug  200  comprises a plug head  201 , a plug stem  202  configured to actuate the plug head, a housing  203 , and a valve seat  204  (also referred to as the choke section) comprising a seat inlet  205  and a choke transfer trim portion  206 . In the exemplary embodiment, the flow control area  207 , also referred to as the minimum flow area or reduced flow area, is the location in a fluid stream where the flow area of the valve plug is minimal. In accordance with an exemplary embodiment of this invention, both  FIG. 2  and  FIG. 3  illustrate a side view, cross-section of valve device  200 . 
     In an exemplary embodiment, plug head  201  can be coupled to plug stem  202  by at least one of a compliant ring, a screw, a rivet, a bolt, a vise, a press fit, a glued joint, any weld, or any suitable means for coupling plug head  201  to plug stem  202  now known or hereinafter devised. 
     Furthermore, in accordance with an exemplary embodiment, plug stem  202  and/or housing  203  may comprise any metal and/or ceramic material. In an exemplary embodiment, plug stem  202  and/or housing  203  may comprise, but are not limited to, titanium and its alloys, zirconium and its alloys, niobium and its alloys, titanium-niobium alloys, alloy steels, carbon steels, iron-base superalloys, stainless steels, nickel and its alloys, nickel-base superalloys, copper based alloys, cobalt alloys, cobalt-base superalloys, aluminum and its alloys, magnesium alloys, tantalum and the like. Moreover, alternative materials with similar properties can be substituted without departing from the concept of this invention. 
     Additionally, in accordance with another exemplary embodiment, seat inlet  205  comprises any erosion/corrosion resistance materials and/or any shock absorption materials. In an exemplary embodiment, at least a portion of seat inlet  205  comprises at least one of a metal and a ceramic. Structural ceramics include, but are not limited to at least one of a silicon carbide, a silicon nitride, an alumina, a zirconia, a tungsten carbide, a whisker-reinforced blends of ceramics, a two-phase ceramics and the like. In an exemplary embodiment, metals include, but are not limited to at least one of a cast iron, a silicon iron, a white iron, a heat treated martensitic steel (such as 440 or 416 grade steel), and a CrCoFe alloy (such as stellite #3, stellite #6, and stellite #12). 
     In this exemplary embodiment, plug stem  202  further couples to an actuating device. This actuating device can be any device configured to move plug stem  202 , thereby changing the distance between the top surface of seat inlet  205  and plug head  201 . 
     In accordance with an exemplary embodiment, the valve plug may be used in on/off applications discussed above with a decreased rate of erosion and an increased service lifecycle by transferring the minimum flow area away from the plug head  201  and/or seat inlet  205 . For example, with reference to  FIG. 4 , in accordance with an exemplary embodiment, the minimum flow area of the presently disclosed valve is equal to the square of half of the diameter of the narrowest part of valve seat  204 , labeled as “d”, downstream of plug head  201  and seat inlet  205  interface, times π: [Minimum Flow Area=π*(d/2) 2 ]. 
     Unlike the prior art valve plugs, an exemplary plug head transfers the minimum flow area of the valve away from plug head  201  and/or seat inlet  205  to a location downstream, thus reducing erosion of the valve plug head and/or seat inlet and thus increasing longevity of severe duty service valves. Specifically, unlike the prior art valve plugs, in accordance with an exemplary embodiment, and with reference to  FIG. 2 , valve plug  200  comprises a choke transfer trim portion  206  configured to transfer the flow control area  207  of the valve away from plug head  201  and/or seat inlet  205  to a location downstream. 
     As stated above, and with reference now to  FIG. 3  and  FIG. 4 , in accordance with an exemplary embodiment, valve plug  200  comprises a choke transfer trim  206  configured to transfer the flow control area  207  of the valve, again, denoted by “d” in  FIG. 3 , away from plug head  201  and/or seat inlet  205  to a location downstream. In accordance with one exemplary embodiment, choke transfer trim  206  comprises any geometry configured to facilitate transferring the flow control area  207  to a location downstream. In accordance with an exemplary embodiment, if the minimum flow area, [π*(d/2) 2 ], is less than the inlet flow area, which is the same as the prior art valve device&#39;s minimum flow area, [π*(D INLET )*(h)], the erosive environment is shifted away from the plug head/seat inlet interface (the surfaces required for shutting off the fluid flow). In other words, the minimum flow area is between the plug head and the seat inlet until that area exceeds the flow area created by the minimum diameter, d, of the choke transfer trim  206 . In accordance with an exemplary embodiment of this invention, the shape of the choke transfer trim  206  can comprise any shape suitable for creating a minimum flow area, [π*(d/2) 2 ], which is less than the inlet flow area, same as prior art valve device&#39;s minimum flow area, [π*(D INLET )*(h)]. For example, and in accordance with an exemplary embodiment, the shape of choke transfer trim  206  can comprise can at least one of a rounded, a tapered, and a stepped shape. 
     Moreover, in accordance with an exemplary embodiment, choke transfer trim  206  may comprises a top portion  208 , which is closest to the plug head inlet, D INLET , an inner surface  209  configured to interface with fluid flow, which runs the length of valve seat  204 , and a bottom portion  210 , which is located closer to the exit of valve seat  204 . 
     The distance at the inlet of valve seat  204  from one side of the top portion  208  to the opposite side of the top portion  208  of the choke transfer trim  206  is denoted by D INLET  in  FIG. 3 . Preferably, in accordance with an exemplary embodiment, choke transfer trim  206  has a circular cross-sectional shape, thus D INLET  is the diameter of the inlet of valve seat  204 . In accordance with an exemplary embodiment, the inlet to choke transfer trim  206 , D INLET , may comprise any cross-sectional geometry suitable for passage of a fluid stream. 
     In an exemplary embodiment, inner surface  209  is configured to interface with the fluid flow. The shape of inner surface  209  may comprise any shape and/or geometry that transfers the flow control area  207  of the valve away from plug head  201  and/or seat inlet  205  to a location downstream, thereby decreasing the rate of erosion and a increasing the shut off and service life of the plug head and/or seat. Preferably, as illustrated in  FIG. 3  and in accordance with an exemplary embodiment, inner surface  209  may define a cone shape. For example, the symmetric inner surfaces  209  of choke transfer trim  206  may comprise two overlapping and inverted cone shaped trim sections, wherein the first cone shaped trim section  212  is widest at the inlet of valve seat  204 , D INLET , and narrowest at the flow control area  207  of the valve, “d”, and wherein the second cone shaped trim section  213  is narrowest at the flow control area  207  of the valve, “d”, and widest at the outlet of valve seat  204 . In other words, inner surface  209  may resemble an hourglass shape configured to transfer the flow control area  207  of the valve away from the plug head and/or seat to a location downstream, thereby decreasing the rate of erosion and a increasing the life of the plug head and/or seat. 
     Via comparison of  FIG. 1  and  FIG. 3 , it should be understood that any choke transfer trim  206  geometry or shape that transfers the flow control area  207  of the valve away from the inlet of valve seat  204 , D INLET , is contemplated herein and will allow for decreasing the rate of erosion and increasing the service life of the plug head and/or plug head seat. Preferably, in accordance with an exemplary embodiment of this invention, the cross-sectional flow area is maintained such that the flow area between plug head  201  and seat inlet  205 , defined as [π*D INLET *h], is greater than or equal to the flow area of the flow control area, defined as [π*(d/2) 2 ]. In another exemplary embodiment, flow control area  207  of the valve, “d”, is a percentage of the inlet of valve seat  204 , D INLET , in the range of about 20% to about 95%. For example, if D INLET  is 20 inches in diameter, and d is 90% of the inlet diameter, then d would be 19 inches in diameter. 
     In an exemplary embodiment, and with reference to  FIG. 5 , flow control area  207  of valve plug  200  may have various configurations. The minimum flow area may be at any point of inner surface  209  of valve seat  204  that is not the interface of plug head  201  and seat inlet  205 . As illustrated in  FIGS. 5A-5C , the flow control area may be at the end of valve seat  204 , or about ¼ of the distance from either end of valve seat  204 . Furthermore, the minimum flow area may be formed by more than an angled inner surface  209 . In an exemplary embodiment, and with reference to  FIGS. 5D-5F , inner surface  209  may be curved, tapered with a substantially straight portion, or comprise a protruding shape. 
     In accordance with an exemplary embodiment and for the purpose of a specific example, the D INLET  of valve seat  204  is about 0.1 inches to about 24 inches, depending on the specific valve application. Moreover in an exemplary embodiment, the D INLET  of valve seat  204  is any other suitable distance. 
     Additionally, as illustrated in  FIG. 2  and  FIG. 3  and in accordance with an exemplary embodiment, the distance from D INLET  to flow control area  207 , “d,” of the choke transfer trim  206  is about 0.1 inches to about 24 inches, depending on the specific valve application. Moreover, in an exemplary embodiment, the distance from D INLET  to the flow control area  207 , “d,” of the choke transfer trim  206  is any other suitable distance. Also, in accordance with an exemplary embodiment, the outer diameter of choke transfer trim  206  is about 0.1 inches to about 24 inches, depending on the specific valve application. Moreover, in an exemplary embodiment, the outer diameter of choke transfer trim  206  is any other suitable distance. 
     Finally, as used herein, the terms “comprise”, “comprises”, “comprising”, “having”, “including”, “includes”, or any variation thereof, are intended to reference a non-exclusive inclusion, such that a process, method, article, composition or apparatus that comprises a list of elements does not include only those elements recited, but can also include other elements not expressly listed and equivalents inherently known or obvious to those of reasonable skill in the art. Other combinations and/or modifications of structures, arrangements, applications, proportions, elements, materials, or components used in the practice of the instant invention, in addition to those not specifically recited, can be varied or otherwise particularly adapted to specific environments, manufacturing specifications, design parameters or other operating requirements without departing from the scope of the instant invention and are intended to be included in this disclosure. 
     Moreover, unless specifically noted, it is the Applicant&#39;s intent that the words and phrases in the specification and the claims be given the commonly accepted generic meaning or an ordinary and accustomed meaning used by those of reasonable skill in the applicable arts. In the instance where these meanings differ, the words and phrases in the specification and the claims should be given the broadest possible, generic meaning. If it is intended to limit or narrow these meanings, specific, descriptive adjectives will be used. Absent the use of these specific adjectives, the words and phrases in the specification and the claims should be given the broadest possible meaning. If any other special meaning is intended for any word or phrase, the specification will clearly state and define the special meaning.