Abstract:
A corrosion resistant thermowells with thin wall tips for use in unusually difficult industrial applications such as pharmaceutical and chemical process plants and semiconductor manufacturing facilities. These facilities have process environments that may include at least one of the following: highly corrosive fluids, difficult mechanical conditions such as rapid or turbulent fluid flows, and/or reasonably high process temperatures and/or pressures. The corrosion resistant thermowells provide isolation between a temperature sensor and a fluid to be measured.

Description:
RELATED APPLICATION 
     This application is a continuation-in-part of application Ser. No. 13/652,315 filed Oct. 15, 2012, which claims the benefit of U.S. Provisional Application No. 61/546,796 filed Oct. 13, 2011, which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The claimed invention relates to PTFE (polytetrafluorethylene) jacketed tantalum tipped and also PTFE tipped thermowells, more particularly to thermowells for use in unusually difficult industrial applications. 
     BACKGROUND OF THE INVENTION 
     Thermowells are commonly used in industry to protect sensitive temperature measurement instruments such as thermocouples, RTDs (Resistance Temperature Detectors), or thermometers from conditions of process fluids that may cause the bare instrument to suffer damage. The claimed invention relates to a new configuration for the construction of such thermowells for use in unusually difficult industrial applications such as pharmaceutical and chemical process plants, semiconductor manufacturing facilities and other similar facilities with process environments that may include some or all of:
         Highly corrosive fluids   Difficult mechanical conditions such as rapid or turbulent fluid flows   Reasonably high process temperatures and/or pressures.       

     In such industrial applications, maintaining tight control over process temperatures via quick detection and feedback of temperature changes is highly desirable to maintain the most efficient and effective processes. This problem is usually taken care of by employing carbon steel, stainless steel or other common metal thermowells. For highly corrosive environments where common metals do not stand up, the wells may be coated with corrosions resistant materials such as PTFE or made from solid PTFE or similar material. 
     In certain cases where unusually aggressive instances of the situations described above are encountered, PTFE jackets much thicker than coatings are employed, often with corrosion resistant tantalum cups to improve the sensitivity may be employed. 
     However all the above solutions have limitations that prevent their use in the most aggressive environments while achieving sensitivities that foster efficient processes. They may:
         Have length limitations   Not be strong enough to handle fast moving or agitated fluids or   If fabricated to overcome such limitations, lose sensitivity slowing reaction times to process temperature changes.       

     These situations provide an opportunity to overcome such limitations by using a combination of some previously employed design elements plus new design elements in a unique combination that allows much improved fluid temperature measurement and control in aggressive fluid environments. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     In view of the above-described shortcomings in the art, it is an object of the claimed invention to provide a corrosion resistant thermowells with thin wall tips, preferably, one that can be used in unusually difficult industrial applications such as pharmaceutical and chemical process plants, semiconductor manufacturing facilities and other similar facilities with process environments that may include some or all of: highly corrosive fluids, difficult mechanical conditions such as rapid or turbulent fluid flows, and/or reasonably high process temperatures and/or pressures. 
     The importance of well-designed, high quality thermowells used widely in industrial applications cannot be overemphasized. They need to be strong, highly corrosion resistant, and allow for quick response to changes in temperature. Further, there is a need to provide a design with the flexibility to be tuned to avoid vibrations that can be induced by fluid flows. 
     There have been many instances of thermowell failures, many of which have been attributed to such vibrations induced by fluid flows. One such well-publicized event occurred in 1995, when the failure of a thermowell from vibration at the Monju nuclear power plant in Japan caused leakage of molten sodium coolant resulting in the shutdown of the plant. 
     It is an object of the claimed invention are to provide a thermowell that protects the most sensitive and responsive thermocouples, RTDs, or thermometers that are usually thin to provide high sensitivity; for example, those as small as 1/16″ diameter. 
     It is an object of the claimed invention to provide a thermowell that provides high corrosion resistance by allowing the basic metal well to be encapsulated by a jacket made from a corrosion resistant material, preferably a highly corrosion resistant material, such as polytetrafluoroethylene (PTFE). 
     It is an object of the claimed invention to provide a thermowell that enables the basic metal well to be made from commercially available pipes or tubes. Such pipe or tube enable a wide choice in preparing a design that is flexible enough to incorporate as needed, large diameters, heavy wall thicknesses, high strength metals and/or corrosion resistant metals where users require that for a wide variety of fluid measurement applications. 
     It is an object of the claimed invention to provide a thermowell that provides enhanced conductivity and thus responsiveness by employing a cup, at the point which temperature needs to be measured, made from corrosion resistant metal conductive material (such as tantalum) or from a thin-walled corrosion resistant plastic material (such as PTFE) while controlling costs by utilizing at the point which temperature needs to be measured, a small diameter and thin wall design. 
     It is an object of the claimed invention to provide the thermowell as aforesaid that further enhances conductivity and responsiveness while controlling costs by utilizing a step-down diameter for the tip. 
     It is an object of the claimed invention to provide a thermowell that enables the use of commercially available thermocouples, RTDs, and thermometers that feature thin diameters and spring loading. The former enables greater instrument sensitivity and the latter ensures close contact of the tip to the metal housing at the bottom. 
     It is an object of the claimed invention to provide the thermowell as aforesaid that allows for comparatively easy and accurate insertion of thin diameter thermocouples, RTDs, and thermometers by creating a centering insertion guide using a strong metal tube (such as a stainless steel tube) that leads to a conductive material such as copper at the tip. In the tantalum tipped embodiment the copper at the tip also acts as a reinforcement for the thin wall cup to permit use of the wells at higher pressures. In the PTFE tipped embodiment the copper at the tip also acts as a reinforcement for the thin PTFE wall at the tip to permit use of the wells at higher pressures. 
     It is an object of the claimed invention to provide the thermowell as aforesaid whose design permits the manufacture of varying lengths—short ones to be used in piping systems, often inserted into elbows or tees, and long ones to reach far into large process vessels and normally installed in vessel nozzles 
     It is an object of the claimed invention to provide the thermowell as aforesaid that can be tuned to avoid vibrations induced by fluid flows by utilizing a highly flexible arrangement of design elements. 
     It is an object of the claimed invention to provide the thermowell as aforesaid that can be specified with flanged connections to ensure strong connections to industry standard piping and vessel systems. 
     It is an object of the claimed invention to provide the thermowell as aforesaid that further ensures quick response to fluid temperature changes by incorporating a conductive paste at the critical contact surface. 
     In accordance with an exemplary embodiment of the claimed invention, a device provides isolation between a temperature sensor and a fluid to be measured. A metal guide tube of the device receives the temperature sensor. The metal guide tube has a top end and a bottom end. A conductive well of the device has a top end and a bottom end having a base. The top end has an outer diameter greater than an outer diameter at the bottom end. The outer diameter at the bottom end being partially threaded with buttress threads. The conductive well surrounds the bottom end of the metal guide tube. The conductive well is brazed to the metal guide tube. A metal tube of the device surrounds the top end of the conductive well and a remaining portion of the metal guide tube. The conductive well is brazed to the metal tube. A corrosion resistant jacket subassembly of the device has at least two outer diameters excluding a corrosion resistant flare and encapsulates the metal tube and a remaining portion of the conductive well not surrounded by the metal tube. A thin walled, corrosion resistant and heat conductive metal cup of the device has an outer diameter smaller than a larger of the two outer diameters of the corrosion resistant jacket subassembly. The corrosion resistant and heat conductive metal cup is located at a base of the conductive well and entirely covers a bottom end of the corrosion resistant jacket subassembly. A metal flange of the device secures a top end of the device and surrounds the metal guide tube at the top end opposite the corrosion resistant and heat conductive cup. A metal half coupling of the device is connected to the metal flange. The corrosion resistant flare at the end of the corrosion resistant jacket subassembly seals to a bottom face of the metal flange. The corrosion resistant flare has an outside diameter covering part or all of the bottom face of the flange and an inside diameter substantially equal to the larger of two outer diameters of the corrosion resistant jacket subassembly. The base of the conductive well comprises an opening to receive a tip of the temperature sensor. 
     In accordance with an exemplary embodiment of the claimed invention, the aforesaid conductive well is a copper conductive well. 
     In accordance with an exemplary embodiment of the claimed invention, the aforesaid corrosion resistant and heat conductive cup is a tantalum cup covering the base of the conductive well to provide a quick response to temperature changes. 
     In accordance with an exemplary embodiment of the claimed invention, the aforesaid corrosion resistant and heat conductive cup is a vanadium cup covering the base of the conductive well to provide a quick response to temperature changes. 
     In accordance with an exemplary embodiment of the claimed invention, the aforesaid metal tube is made from one of the following: carbon steel, stainless steel or alloy. 
     In accordance with an exemplary embodiment of the claimed invention, the aforesaid corrosion resistant jacket subassembly is a polytetrafluoroethylene (PTFE) jacket. 
     In accordance with an exemplary embodiment of the claimed invention, the aforesaid conductive well is a threaded conductive well and the corrosion resistant jacket subassembly is threaded to fit onto the threaded conductive well. 
     In accordance with an exemplary embodiment of the claimed invention, the aforesaid corrosion resistant and heat conductive cup is swaged over the corrosion resistant jacket subassembly to provide a leak tight seal. 
     In accordance with an exemplary embodiment of the claimed invention, the aforesaid corrosion resistant jacket subassembly comprises two components that are fused or welded together. 
     In accordance with an exemplary embodiment of the claimed invention, a face at the base of the aforesaid conductive well is installed using a thin layer of conductive paste to further improve response time. 
     In accordance with an exemplary embodiment of the claimed invention, a device provides isolation between a temperature sensor and a fluid to be measured. A metal guide tube of the device receives the temperature sensor. The metal guide tube has a top end and a bottom end. A conductive well of the device has a top end and a bottom end having a base. The top end has an outer diameter greater than an outer diameter at the bottom end. The conductive well surrounds the bottom end of the metal guide tube. The conductive well is brazed to the metal guide tube. A metal tube of the device surrounds the top end of the conductive well and a remaining portion of the metal guide tube. The conductive well is brazed to the metal tube. A corrosion resistant jacket subassembly of the device has at least two outer diameters excluding a corrosion resistant flare and encapsulates the metal tube and a remaining portion of the conductive well not surrounded by the metal tube. A thin walled, corrosion resistant plastic tip of the device has an outer diameter smaller than a larger of the two outer diameters of the corrosion resistant jacket subassembly. The corrosion resistant plastic tip is located at a base of the conductive well and entirely covers and contiguous with the bottom end of the corrosion resistant jacket subassembly. A metal flange of the device secures a top end of the device and surrounds the metal guide tube at the top end opposite the corrosion resistant plastic tip. A metal half coupling of the device is connected to the metal flange. The corrosion resistant flare at the end of the corrosion resistant jacket subassembly seals to a bottom face of the metal flange. The corrosion resistant flare has an outside diameter covering part or all of the bottom face of the flange and an inside diameter substantially equal to the larger of two outer diameters of the corrosion resistant jacket subassembly. The base of the conductive well comprises an opening to receive a tip of the temperature sensor. 
     In accordance with an exemplary embodiment of the claimed invention, the aforesaid corrosion resistant plastic tip is a corrosion resistant plastic film or membrane covering the base of the conductive well and responsive to temperature changes. 
     In accordance with an exemplary embodiment of the claimed invention, the aforesaid corrosion resistant jacket subassembly is threaded to fit onto the conductive well that is partially threaded with buttress threads. 
     In accordance with an exemplary embodiment of the claimed invention, the aforesaid corrosion resistant plastic tip is a contiguous part of the corrosion resistant jacket subassembly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-B  are cross-sectional schematic views of a corrosion resistant thermowell with thin wall tip in accordance with an exemplary embodiment of the claimed invention; 
         FIGS. 2A-2B  are detailed cross-sectional schematic views of the respective thin wall tip area of the corrosion resistant thermowells of  FIGS. 1A-B  in accordance with an exemplary embodiment of the claimed invention; 
         FIGS. 3A-3B  show various schematic views of the metal flange of the corrosion resistant thermowell in accordance with an exemplary embodiment of the claimed invention; 
         FIG. 4  is a cross-sectional schematic view of the metal tube of the corrosion resistant thermowells in accordance with an exemplary embodiment of the claimed invention; 
         FIGS. 5A-B  are cross-sectional schematic views of the respective conductive wells of the corrosion resistant thermowells of  FIGS. 1A-B  in accordance with an exemplary embodiment of the claimed invention; 
         FIGS. 6A-6B  are cross-sectional schematic views of a respective section or sub-assembly of the PTFE jacket of the corrosion resistant thermowells of  FIGS. 1A-B  in accordance with an exemplary embodiment of the claimed invention; 
         FIG. 7  is a cross-sectional schematic view of a section or sub-assembly of the PTFE jacket of the corrosion resistant thermowell in accordance with an exemplary embodiment of the claimed invention; 
         FIGS. 8A-B  are cross-sectional schematic views of a respective tip of the PTFE jacket of the corrosion resistant thermowells of  FIGS. 1A-B  in accordance with an exemplary embodiment of the claimed invention; 
         FIG. 9  is a schematic view of the heat conductive cup of the corrosion resistant thermowell of  FIG. 1A  in accordance with an exemplary embodiment of the claimed invention; 
         FIG. 10  is a schematic view of the conductive support tip of the corrosion resistant thermowell of  FIG. 1B  in accordance with an exemplary embodiment of the claimed invention; 
         FIG. 11  is a cross-sectional view of a threaded half coupling component/part of the corrosion resistant thermowell in accordance with an exemplary embodiment of the claimed invention; 
         FIG. 12  is a cross-sectional view of the metal guide tube of the corrosion resistant thermowell in accordance with an exemplary embodiment of the claimed invention, and 
     
    
    
     While in the illustrated embodiments features of the invention have been put forward, it is to be understood that the invention is not limited to the precise form illustrated, and the changes may be made thereto without departing from the spirit or substance of the invention. 
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Referring to the drawings in detail,  FIGS. 1A-B  show the thermowells  20  in accordance with an exemplary embodiment of the claimed invention. Thermowells are commonly used in process containment devices such as process vessels or pipes to protect sensitive temperature measuring devices such as thermocouples, RTDs, or thermometers from damage due to rapid fluid flows and/or aggressively corrosive environments. The claimed thermowell provides extreme corrosion resistance at temperatures up to the allowable temperatures for the polytetrafluorethylene (PTFE) material, i.e., 260° C. (500° F.). 
     As shown in  FIGS. 1A-1B , the claimed thermowell  20  has a shell comprising a metal flange  21 , a metal tube  22  and a conductive well  23 , that can be made from readily available metals. The shell provides the basic structure and strength of the thermowells  20 . The particular design features of the claimed thermowells  20  allow for the use of an unusually wide range of lengths and diameters. Long lengths (up to 4 meters or more) are often needed to provide quick response to changes in fluid temperature at a remote point, one that can be reached by insertion of long length thermowell  20  into a flanged opening in a process vessel or pipe. Large diameters (up to 100 mm or more) are often needed to provide extra strength to such long length thermowells  20  to resist rapid and/or turbulent fluid flows. 
     The common metals used for the metal flange  21 , the metal tube  22  and the conductive well  23  can be, but not limited to, carbon steel, stainless steel, or other alloys such as Monel®. Monel® is a registered trademark of Huntington Alloys Corporation. As shown in  FIGS. 1A-B  and  5 A-B, in accordance with an exemplary embodiment of the claimed invention, a highly conductive material such as copper can be used at the tip to provide the conductive well  23  with superior sensitivity to changes in temperature at the remote point where the measuring tip of the thermocouple or thermometer is located. As shown in  FIGS. 1A-B , in accordance with an exemplary embodiment of the claimed invention, the metal tube  22  is welded or brazed to the metal flange  21 . As shown in  FIGS. 2A-B , in accordance with an exemplary embodiment of the claimed invention, the conductive well  23  is brazed to the metal tube  22 . 
     As shown in  FIGS. 1A-B , to enhance the protection against corrosive environments, in accordance with an exemplary embodiment of the claimed invention, the metal components/parts (metal flange  21 , metal tube  22 , conductive well  23 ) that would normally come into contact with the fluid requiring temperature measurement are covered with highly corrosion resistant materials. In accordance with an exemplary embodiment of the claimed invention, a jacket  24  made of PTFE (or PTFE jacket  24 ) covers the face of the metal flange  21  of  FIGS. 3A-B , the metal tube  22 , and most of the conductive well  23 . It is appreciated that other plastics can be used to achieve alternate properties. As shown in  FIGS. 6A-B ,  7  and  8 A-B, in accordance with exemplary embodiment of the claimed invention, the PTFE jacket  24  comprises corrosion resistant flare  35  and two components or parts  25  and  26 . Preferably, these two components  25  and  26  are fused or welded together to form the PTFE jacket  24 . 
     A feature of the conductive well  23  and the mating jacket tip  26  is a thread  40 . The PTFE jacket  24  tends to expand in length with the increasing temperature, thereby causing the heat conductive cup  27  or the thin corrosion resistant tip  27 ′ to move away from the tip of the temperature measuring device, the thermocouple, RTD or thermometer residing in a pocket  31 . If such expansion is not constrained or minimized, the transmission or conduction of the changing temperatures would slow dramatically, which would be counter to the basic purpose of the thermowells. In accordance with an exemplary embodiment of the claimed invention, the PTFE jacket  24  is shrunk over the metal tube  22  to constrain the expansion of the PTFE jacket  24 . In accordance with another embodiment of the claimed invention, the PTFE jacket  24  is mechanically fastened to its mating conductive well  23  to constrain the expansion of the PTFE jacket  24 , for example by pinning or threading the PTFE jacket  24  to the conductive well  23 . Alternatively, in accordance with an exemplary embodiment of the claimed invention, as shown in  FIGS. 1A-B ,  2 A- 2 B,  5 A- 5 B,  6 A- 6 B,  8 A- 8 B, the PTFE jacket  24  and the conductive well  23  have mating buttress threads  40 , which, because of their flat, shelf-like mating surfaces, form a strong constraint preventing the undesirable movement of the heat conductive cup  27  or the thin corrosion resistant tip  27 ′ away from the temperature measuring device. 
     Turning now to  FIGS. 1A-B ,  9  and  10 , because PTFE is not a good conductor, in accordance with an exemplary embodiment of the claimed invention, the bottom most portion of the conductive well  23  is covered with a highly corrosion resistant tantalum cup  27  or thin corrosion resistant tip  27 ′. As shown in  FIG. 2A , in accordance with one exemplary embodiment of the claimed invention, the heat conductive cup or tantalum cup  27  is swaged over the PTFE jacket  24  to provide a leak tight seal between its inner surface and the outer surface of the jacket tip  26 . In addition to its excellent corrosion resistance, tantalum is an excellent conductor of heat thus providing the potential for a quick response to changes in fluid temperature. Alternatively, as shown in  FIG. 2B , in accordance with an exemplary embodiment of the claimed invention, a thin corrosion resistant tip  27 ′, integral with jacket tip  26  as shown in  FIG. 8B , provides a leak tight seal with the main body of the jacket tip  26 . Of course the material, PTFE, of the thin corrosion resistant tip  27 ′, is not a good conductor. But when certain extremely corrosive fluids attack tantalum, PTFE may be necessary for those applications. In accordance with an exemplary embodiment of the claimed invention, the corrosion resistant tip  27 ′ is made very thin to provide adequate response time. 
     In accordance with an exemplary embodiment of the claimed invention,  FIG. 9  shows a small size thin walled tantalum cup  27  that is used for all lengths and diameters of the corrosion resistant theremowells with thin wall tantalum tips  20  (hereinafter “tantalum tipped thermowells”  20 ) of  FIG. 1A . The small diameter of the tantalum cup  27  allows for use of a thin cup with advantages described herein. First, when the tantalum cup  27  is supported by the base machined at the tip of the conductive well  23 , the assembly can be used at higher fluid pressures than if just a thin unsupported cup is used. Second, the tantalum cup  27  is smaller in diameter than the metal tube  22 , thereby permitting the tantalum cup  27  to be subjected to higher pressures than the typically used larger diameter cups. Third, the use of the small thin walled tantalum cup  27  in the claimed invention reduces the cost of the device because tantalum is a high cost material. 
     In accordance with an exemplary embodiment of the claimed invention,  FIG. 2B  shows the thin corrosion resistant PTFE tip  27 ′. The PTFE tip  27 ′ is supported by a thin, small diameter conductive support tip  38  that allows for the PTFE corrosion resistant tip  27 ′ to be thin walled. So even though PTFE is not a good conductor, the thin wall of the PTFE tip  27 ′ minimizes its resistance to temperature transmission. Thus the temperature probe residing in the pocket  31  will still be sensitive to temperature changes, albeit more slowly than with the tantalum cup  27 . In certain cases, where needed, corrosion resistant metals other than tantalum, for example vanadium, may be substituted for the tantalum, and achieve much the same advantages gained with the tantalum. 
     Turning now to  FIGS. 1A-B ,  11  and  12 , in accordance with an exemplary embodiment of the claimed invention, the two remaining metal components or parts: the threaded metal half coupling  28  is welded to the metal flange  21 , and the metal guide tube  29 , advantageously allows standard, commercially available thin temperature measuring devices to be inserted into the conductive well  23 , reside in the pocket  31 , reach the bottom of the conductive well  23 , and make contact with the tantalum cup  27  as shown in  FIG. 2A  or make contact with a thin wall metal tip  38  that supports the PTFE tip  27 ′ as shown in  FIG. 2B , without bending or kinking As shown in  FIGS. 2A-B , in accordance with an exemplary embodiment of the claimed invention, to keep the metal guide tube  29  in place it is brazed to the conductive well  23 . 
     As shown in  FIGS. 2A-B  and  5 A-B, to improve the response time to fluid temperature changes, in accordance with an exemplary embodiment of the claimed invention, the tip of the conductive well  23  has a specially machined thin base with a hole or pocket  31  for thermocouple, RTD, or thermometer, machined to fit the 1/16″ or larger tip of the temperature measuring device. The design of the claimed invention advantageously allows for such small diameter thermocouples, even in long length thermowells  20 . It is noted that the small diameter thermocouples improve response times. Also, as shown in  FIGS. 2A-B , in accordance with an exemplary embodiment of the claimed invention, the face  45  at the base of the conductive well  23  or face  45  of the conductive support tip  38 , may also be installed using a thin layer of conductive paste  30  to further improve the response time. 
     Various omissions, modifications, substitutions and changes in the forms and details of the device illustrated and in its operation can be made by those skilled in the art without departing in any way from the spirit of the present invention. Accordingly, the scope of the invention is not limited to the foregoing specification, but instead is given by the appended claims along with their full range of equivalents.