Abstract:
A method for forming a fluid tight seal is disclosed. The method may make use of a first component having a first sealing surface, and a second component having a second sealing surface. The method may further involve coating one of the first and second sealing surfaces with a metallic film layer adapted to transform into a liquefied metallic layer when a temperature of one of the first and second surfaces exceeds a melting temperature of a metal used to form the metallic film layer. Once it becomes liquefied, the liquefied metallic layer forms a pressure-tight seal between the sealing surfaces.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 12/201,449, filed Aug. 29, 2008 (now U.S. Pat. No. 8,317,233). The entire disclosure of the above application is incorporated herein by reference. 
    
    
     STATEMENT OF GOVERNMENT RIGHTS 
     The subject matter of the present disclosure was made with support from the U.S. Government under Contract No. F33615-98-9-2880 awarded by the U.S. Air Force. The U.S. Government has certain rights in the subject matter disclosed herein. 
    
    
     FIELD 
     The present disclosure relates to metal-to-metal couplings, and more particularly to a metal-to-metal coupling with a localized liquid metal film that is able to extend the operational temperature of high temperature metal-to-metal fittings used to join tube and pipe sections carrying high temperature gas flows. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     Mechanical joints between sections of metallic tubing are necessary in order to provide for ease of joining during assembly of high pressure gas lines. For applications involving gas temperatures less than 1300° F., sections can be joined using metal fittings that rely on elastic deflection of internal sealing surfaces. Such “dynamic seal” fittings cannot be used at temperatures above 1300° F. because the internal sealing surfaces plastically deform and permanently set into their deflected shape, loosing their elasticity and ability to provide a leak-free seal. 
     To achieve leak-free joints in high temperature (i.e., above 1300° F.) pressurized gas lines, it has typically been necessary to resort to fusion welding. Use of conventional fusion welding operations to join tube segments requires sufficient 360° access to the full circumference of the tube joint to accommodate manual or automated orbital fusion welding equipment. In applications that require dense packing to conserve volume and minimize weight, providing such access often results in suboptimum packing designs that unduly penalize the performance of end items that are weight and/or size critical. Examples of end items where low weight and size are critical include high performance aircraft and high performance missile systems and propulsion systems such as turbine engines. 
     In one aspect the present disclosure relates to a method for forming a fluid tight seal. The method may comprise providing a first component having a first sealing surface, and providing a second component having a second sealing surface. The method may further comprise coating one of the first and second sealing surfaces with a metallic film layer adapted to transform into a liquefied metallic layer when a temperature of one of the first and second sealing surfaces exceeds a melting temperature of a metal used to form the metallic film layer. The liquefied metallic layer helps to form a pressure-tight seal between the sealing surfaces. 
     In another aspect the present disclosure relates to a method for forming a dynamic beam seal coupling device. The method may comprise providing a first tubular component having a first, generally planar sealing surface. A second tubular component having a second, generally planar sealing surface may also be provided. The first and second sealing surfaces may be arranged on their respective first and second tubular components such that the first and second sealing surfaces are in a facing relationship with one another when the first and second tubular components are coupled together. A metallic film layer may be applied to one of the first and second sealing surfaces. The metallic film layer may exist in a solid state prior to a pressurized, heated fluid of at least about 500 psi being flowed through the first and second tubular components. The metallic film layer may transform into a liquefied metal layer when the metallic film layer is exposed to the pressurized, heated fluid, and wherein the pressurized, heated fluid has a temperature that exceeds a melting temperature of a metal from which the metallic film layer is formed. The liquefied metal layer forms a liquid seal between the sealing surfaces while the metallic film layer is maintained in a liquefied state by heat from the pressurized, heated fluid. 
     In still another aspect the present disclosure relates to a method for forming a dynamic beam seal that is effected upon exposure to a pressurized, heated fluid having a pressure of at least about 500 pounds per square inch. The method may comprise providing a first tubular component having a first sealing surface, and providing a second tubular component having a second sealing surface. The first and second sealing surfaces may be arranged on their respective first and second tubular components such that the first and second sealing surfaces are in a facing relationship with one another when the first and second tubular components are coupled together. A metallic film layer may be applied to one of the first and second sealing surfaces. The metallic film layer may exist in a solid state prior to the pressurized, heated fluid being flowed through the first and second tubular components. The metallic film layer may transform into a liquefied metal layer when the metallic film layer is exposed to the pressurized, heated fluid having a temperature that exceeds a melting temperature of a metal from which the metallic film layer is formed. The metallic film layer may further be provided with a thickness greater than about 0.001 inch and up to about 0.002 inch, prior to the metallic film layer transforming into the liquefied metal layer. 
     SUMMARY 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a partial side cross sectional view of a dynamic beam seal coupling apparatus of the present disclosure that incorporates a metallic film layer to aid in sealing the mating surfaces of the coupling together while a high temperature, high pressure, gas is flowing through the apparatus; 
         FIG. 2  is an enlarged portion showing where a metallic layer may be deposited on one of the components of the beam seal coupling apparatus of  FIG. 1 ; 
         FIG. 3  is a magnified view of a portion of the dynamic beam seal coupling apparatus of  FIG. 2  showing how surface tension effects have caused the liquefied metal film to wick and partially flow out from between the mating sealing surfaces after being exposed to a temperature that exceeded the melting temperature of the metallic film layer; 
         FIG. 4  is a side view of a three piece coupling apparatus incorporating a V-ring seal component that includes a metallic film layer thereon; 
         FIG. 5  is a highly enlarged photograph of a circled portion  5  of the V-ring seal shown in  FIG. 4  after the V-ring seal has been coated with a metallic coating and then exposed to a temperature sufficient to melt the metallic film layer, and evidencing flow of the liquefied metal after 160 second exposure to a 2000° F., 680 PSI hot gas flow through the sealing apparatus containing the V-ring seal; 
         FIG. 6  illustrates a series of graphs showing temperature and internal pressure versus time for a hot gas flow test performed on a dynamic beam seal incorporating a metallic coating to show a relatively constant pressure being maintained over time while the temperature of the seal components was maintained above about 1800° F.; and 
         FIG. 7  is a flowchart setting forth various operations that may be used in forming a coupling device in accordance with the teachings of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
     Referring to  FIG. 1 , a dynamic beam seal apparatus  10  including a metallic film layer is shown. The beam seal apparatus  10  is illustrative of merely one form of coupling device with which the teachings of the present disclosure may be used to form a high temperature, high pressure seal joining two conduits that carry a high temperature, high pressure gas. The dynamic beam seal apparatus  10  typically includes a first coupling component  12  and a second coupling component  14  that are coupled together by a threaded member  16  associated with one of the components, in this example component  14 , that engages a threaded end  18  of component  12 . The first and second components  12  and  14  may be made from any materials that are suitable for use in a high temperature, high pressure coupling device, but in one example the components  12  and  14  are made from Inconel 718. 
     Referring to  FIGS. 2 and 3 , an illustration of an enlarged portion of the sealing surfaces of the components  12  and  14  is shown. First component  12  includes a first sealing surface  20  while second component  14  includes a second sealing surface  22 . One of the two sealing surfaces includes a metallic film layer  24  deposited thereon, and in this example that surface is sealing surface  20  of the first component  12 . However, it will be recognized that the metallic film layer may just as readily be used on the second sealing surface  22 . The metallic film layer  24  may comprise a variety of metals such as gold, silver, and copper, as well as other commercially available alloys used in well known brazing practices. The metallic film layer  24  may be deposited onto the sealing surface  20  using well known electroplating techniques. Alternatively, an alloyed metallic film layer may be formed using well known physical vapor deposition or sputtering techniques. The metallic film layer  24  may also vary in thickness to suit specific applications, but in most instances a suitable thickness is expected to be between about 0.001 inch to 0.002 inch (0.0254 mm-0.0508 mm). The specific metallic material chosen for the metallic film layer  24  also should be able to liquefy in response to the temperature of the gas that will be flowing through the coupling apparatus  10  during normal operation of the coupling apparatus  10 . For gold, the melting temperature is about 1948° F. and for silver it is about 1761° F. Prior to the electroplating of the metallic metal layer  24  on to the sealing surface  20 , it is also preferred that the sealing surface  20  be polished to a surface finish of about 8-32 RA. 
     During the first few seconds of initial operation of the coupling apparatus  10 , the heat from the high temperature gas flowing through the apparatus  10  will fuse the electroplated metallic film layer  24  to the sealing surface  20 . Thereafter, as the hot gas flowing through the coupling apparatus  10  heats up the sealing surfaces  20  and  22  past the melting temperature of the metallic film layer  24 , the metallic film layer transforms into a liquid state (i.e., liquefies). The hot gas flowing through the apparatus  10  is a high pressure gas typically under a pressure of at least about 500 PSI, and more typically about 680 PSI to about 800 PSI, or possibly even higher. One might expect the liquefied metal to simply squirt out from between the sealing surfaces  20  and  22  when exposed to a hot flow gas at such high pressure. However, laboratory tests using electroplated gold have shown that even pressures as high as 800 PSI are insufficient to overcome the capillary forces that hold the molten metal of the metallic film layer  24  in the gap between the two sealing surfaces  20  and  22 . Thus, the liquefied metallic film layer forms an effective seal between the sealing surfaces  20  and  22  in a matter of just a few seconds after being exposed to the hot, high pressure gas flow. 
     With brief reference to  FIG. 3 , the metallic film layer  24  is shown after it has cooled after being exposed to a high temperature, high pressure gas flow. It will be noted that the great majority of the metal of the metallic film layer  24  is still present on the sealing surface  20 , although a small portion  24   a  has wicked out from between the surfaces  20  and  22  on to an inner surface  12   a  of component  12 . 
     Referring now to  FIG. 4  a three piece coupling apparatus  100  in accordance with another embodiment of the present disclosure is provided. The apparatus  100  includes a first component  102 , a second component  104  in the form of a V-ring seal component, and a third component  106 . The V-ring seal component  104  is interposed between sealing surface  108  of the first component  102  and sealing surface  110  of the third component  106 . The sealing surfaces  108  and  110  generally face each other. A male threaded member  112  of the first component  102  engages a female threaded portion  114  of the third component  106  to clamp the V-ring seal component  104  tightly between the sealing surfaces  108  and  110 . The V-ring seal component  104  in this example is a Haynes 188 seal, although it will be appreciated that essentially any form of sealing component that is able to be plated with a metallic film layer, capable of sustaining the hot, high pressure gas, and able to be held between two adjacent sealing surfaces, could be used as the sealing component that interfaces with the two sealing surfaces  108  and  110 . 
     In this example the V-ring seal component  104  has its entire outer surface coated with a metallic film layer  116 , although it will be appreciated that only the areas of the V-ring seal component  104  that physically abut the sealing surfaces  108  and  110  require the metallic film layer to be formed thereon. Alternatively, the sealing surfaces  108  and  110  may be coated with a metallic film layer. The metallic film layer  116  may be gold, silver, copper, or other commercially available alloys used in well know brazing practices and be of a thickness as described above. 
     The apparatus  100  operates in essentially the same manner as apparatus  10 . As hot, high pressure gas begins to flow through the apparatus  100  the metallic film layer  116  fuses to the outer surface of the V-ring seal component  104 . Thereafter as the temperature of the V-ring seal component  104  passes the melting temperature of the metallic film layer  116 , the metallic film layer liquefies to form an airtight, pressure tight seal between the sealing surfaces  108  and  110  of the first and third components  102  and  106 .  FIG. 5  illustrates an enlarged portion of the metallic film layer  116  corresponding to circled area  5  in  FIG. 4  after the metallic film layer  116  has been exposed to a hot gas flow. A portion of the material of the metallic film layer  116  has migrated into a peripheral area  116   a  to form a meniscus, thus indicating that metallic film layer  116  had previously liquefied and that some small degree of flow has taken place. 
     Referring briefly to  FIG. 6 , laboratory test data showing the temperature-pressure-time history for a tube containing both dynamic beam and V-ring seals is shown. As will be noted, the internal pressure of the tube, indicated by curve  200 , stayed essentially constant—pressure tight and leak-free—while the bare tube temperature indicated by curve  202  stayed above the melting temperature of the metallic film layer. The other two curves shown in  FIG. 6  represent data acquired from temperature sensors mounted on the test apparatus that is unrelated to the present disclosure. 
     Referring to  FIG. 7 , a flowchart  300  is shown that sets forth operations in forming a coupling apparatus with a metallic film layer on one of its sealing surfaces. It will be understood that the flowchart  300  applies to both two piece dynamic beam seal coupling devices and three piece coupling devices making use of a V-ring seal component. At operation  302  the sealing surfaces of the apparatus are polished to a surface finish of about 8-32 RA. At operation  304  a metallic film layer is deposited, by electroplating or other suitable techniques, onto one of the sealing surfaces. At operation  306  the components of the apparatus are assembled. At operation  308  the assembled apparatus is exposed to a high temperature, high pressure gas flow where the metallic film layer liquefies and forms a pressure tight seal between the sealing surfaces. 
     The present disclosure is expected to find utility in any device that makes use of a metal-to-metal contacting sealing surface. The various embodiments described herein are able to provide leak free couplings for hot gas flows having a pressure of up to 800° F. and potentially even higher. The ability to provide a liquid metal seal eliminates the need for extra space around the circumference of the coupling to facilitate 360° welding of the sealing surfaces, and therefore can significantly reduce the packaging and space requirements for systems that require the use of couplings that can handle extremely high temperature, pressurized gas flows. The various embodiments are also expected to help significantly reduce the weight of subsystems that require high temperature/pressure couplings due to greater packing efficiency. 
     While various embodiments have been described, those skilled in the art will recognize modifications or variations which might be made without departing from the present disclosure. The examples illustrate the various embodiments and are not intended to limit the present disclosure. Therefore, the description and claims should be interpreted liberally with only such limitation as is necessary in view of the pertinent prior art.