Abstract:
A PTFE jacketed tantalum tipped thermowell that can be used 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.

Description:
RELATED APPLICATION 
     This application 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 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 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 PTFE jacketed tantalum tipped thermowell 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 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 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 any non-encapsulated, exposed thermowell elements. 
     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) while controlling costs by utilizing 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 which minimizes the wall thickness. 
     It is an object of the claimed invention to provide a thermowell that enables the use of commercially available thermocouples 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 and thermometers by creating a centering insertion guide using a highly conductive material such as copper at the tip. The copper guide also acts as a reinforcement for the thin wall cup 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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional schematic view of a PTFE jacketed tantalum tipped thermowell in accordance with an exemplary embodiment of the claimed invention; 
         FIG. 2  is a detailed cross-sectional schematic view of an area labeled “A” of the PTFE jacketed tantalum tipped thermowell in  FIG. 1 ; 
         FIGS. 3A-3B  show various schematic views of the flange of the PTFE jacketed tantalum tipped thermowell in accordance with an exemplary embodiment of the claimed invention; 
         FIG. 4  is a cross-sectional schematic view of the outer tubular section or shell of the PTFE jacketed tantalum tipped thermowell in accordance with an exemplary embodiment of the claimed invention; 
         FIG. 5  is a cross-sectional schematic view of the conductive well of the PTFE jacketed tantalum tipped thermowell in accordance with an exemplary embodiment of the claimed invention; 
         FIG. 6  is a cross-sectional schematic view of a section or sub-assembly of the PTFE jacket 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 in accordance with an exemplary embodiment of the claimed invention; 
         FIG. 8  is a cross-sectional schematic view of a tip of the PTFE jacketed tantalum tipped thermowell in accordance with an exemplary embodiment of the claimed invention; 
         FIG. 9  are various views of the tantalum cup of the PTFE jacketed tantalum tipped thermowell in accordance with an exemplary embodiment of the claimed invention; 
         FIG. 10  is a cross-sectional view of a threaded half coupling component/part of the PTFE jacketed tantalum tipped thermowell in accordance with an exemplary embodiment of the claimed invention; and 
         FIG. 11  is a cross-sectional view of a guide tube of the PTFE jacketed tantalum tipped thermowell in accordance with an exemplary embodiment of the claimed invention. 
     
    
    
     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,  FIG. 1  shows the thermowell  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 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 maximum allowable temperatures for the polytetrafluorethylene (PTFE) material, i.e., 288° C. (550° F.). 
     As shown in  FIG. 1 , the claimed thermowell device  20  has a shell comprising components or parts  21 ,  22  and  23 , that can be made from readily available metals. The shell provides the basic structure and strength of the thermowell  20 . The particular design features of the claimed thermowell  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 these components  21 ,  22  and  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. 1 and 5 , 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 or copper 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  FIG. 1 , in accordance with an exemplary embodiment of the claimed invention, the tubular section or shell  22  is welded or brazed to the flange  21 . As shown in  FIG. 2 , in accordance with an exemplary embodiment of the claimed invention, the conductive or copper well  23  is brazed to the tubular section  22 . 
     As shown in  FIG. 1 , to enhance the protection against corrosive environments, in accordance with an exemplary embodiment of the claimed invention, the metal components/parts  21 ,  22 ,  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 flange  21  of  FIGS. 3A-B , the outer tubular section  22 , and most of the conductive or copper well  23 . It is appreciated that other plastics can be used to achieve alternate properties. As shown in  FIGS. 6 ,  7  and  8 , in accordance with exemplary embodiment of the claimed invention, the PTFE jacket  24  comprises two components or parts  25 ,  26 . Preferably, these two components  25 ,  26  are fused or welded together to form the PTFE jacket  24 . 
     Turning now to  FIGS. 1 and 9 , because PTFE is not a good conductor, in accordance with an exemplary embodiment of the claimed invention, the bottom most portion of the conductive or copper well  23  is covered with a highly corrosion resistant tantalum cup  27 . As shown in  FIG. 2 , in accordance with an exemplary embodiment of the claimed invention, the 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 component/part  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. 
     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 these thermowells  20 . 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 or copper well  23 , the assembly can be used at higher fluid pressures than if just a thin unsupported cup is used. Second, because the tantalum cup  27  is smaller in diameter than the outer tubular shell  22 , it will permit higher pressures than the larger diameter cups typically used. 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. 
     Turning now to  FIGS. 1 ,  10  and  11 , in accordance with an exemplary embodiment of the claimed invention, the two remaining metal components or parts: the threaded half coupling component/part  28  is welded to the flange  21 , and the guide tube  29 , advantageously allows standard, commercially available thin temperature measuring devices (not shown) to be inserted into the conductive or copper well  23 , reach the bottom of the conductive or copper well  23 , and make contact with the tantalum cup  27  without bending or kinking. As shown in  FIG. 2 , in accordance with an exemplary embodiment of the claimed invention, to keep the guide tube  29  in place it is brazed to the conductive or copper well  23 . 
     As shown in  FIGS. 2 and 5 , to improve the response time to fluid temperature changes, in accordance with an exemplary embodiment of the claimed invention, the tip of the copper well  23  has a specially machined thin base with a hole  31  machined to fit the 1/16″ tip of the temperature measuring device (not shown). 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  FIG. 2 , in accordance with an exemplary embodiment of the claimed invention, the face at the base of the conductive or copper well  23  is also 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.