Abstract:
A two or three piece seal apparatus and method is described for providing a positive seal of threads in extreme temperature ranges up to 2000° F. for at least 20 minutes. A stainless steel compression/retaining nut is utilized in combination with a high temperature alloy ring or diamond-shaped seal to effect sealing of the threads.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is related to U.S. Pat. No. 4,887,631, entitled &#34;Fire Isolation Device&#34;, and assigned to the assignee of this application. 
     BACKGROUND OF THE INVENTION 
     This invention concerns seals designed to fit pipe or straight threads, and more particularly to seals that provide positive sealing of threads in extreme temperature environments. 
     Seals for pipe couplings are known from U.S. Pat. Nos.: 3,004,776 (Sebardt); 2,342,425 (Parker); 1,071,585 (Rossell); 2,343,235 (Bashark); 3,009,722 (Augustin); and 3,259,404 (Papenguth). These prior art arrangements use elastomer elements which are not suitable for the extreme temperature environments contemplated by the invention. 
     Other bushing, ring, and boss type sealing arrangements of the prior art are known from U.S. Pat. Nos.: 2,704,676 (Harding); 3,462,539 (Winston); 3,106,413 (Hamlin); 2,825,584 (Badger et al.); 2,199,647 (Mueller et al); and 3,756,628 (St. Clair). 
     A pipe or tube coupling device is described in U.S. Pat. No. 3,356,391 in which nuts are formed with an annular packing ring or gland which may be made of deformable metallic or plastic material. This prior art reference does not recognize the critical material requirements for effective thread sealing at the extreme temperature environments contemplated by the invention. 
     The purpose of the invention is to solve the problem of sealing threads at system pressures up to 3,000 psi and temperatures up to 2,000° F. for 20 minutes, as well as cryogenic (-455° F.) temperatures. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to provide a two or three piece thread sealing apparatus to withstand a 2,000° F. temperature environment for 20 minutes as well as being suitable for cryogenic (-455° F.) temperature environments. 
     Another object of the invention is to provide a sealing method to ensure effective sealing using the apparatus according to the invention and without the requirement of special tooling. 
     According to the broader aspects of the invention, the apparatus consists of a threaded ring and a compression nut designed to interlock and compress the ring to effectively seal the total surfaces of the thread connections. 
     The method of the invention consists of installing the compression nut on the male thread of the connection a number of turns, threading the ring on the same male thread a lesser number of turns, inserting the male thread into the female threaded coupling and tightening the male and female coupling, and tightening the compression nut sufficiently to bottom the compression nut on the coupling or face thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and features of the invention will become apparent by reference to the following description taken in conjunction with the accompanying drawings in which: 
     FIG. 1A illustrates the two piece sealing apparatus as installed; 
     FIG. 1B illustrates the two piece sealing apparatus as torqued in place; 
     FIG. 2 illustrates another embodiment of the two piece sealing apparatus; 
     FIG. 3A illustrates the three piece sealing apparatus as installed; and 
     FIG. 3B illustrates the three piece sealing apparatus as torqued in place. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The sealing apparatus and method of the invention will effectively seal pipe and straight threads for zero fluid drop leak tight systems up to and including 3,000 psi, 4,500 PSIG proof and 7,500 PSIG min. burst at elevated temperatures of 2,000° F. for 20 minutes minimum. The inventive apparatus and method is also suitable for cryogenic (-455° F.) temperature environments. 
     Referring now to FIG. 1A, there is shown a two piece sealing apparatus consisting of a high temperature alloy, such as red brass, manganese bronze, manganese silver bronze and the like, threaded ring seal 1, and a 316/316L stainless steel compression/retaining nut 2 having an undercut 2A to receive seal 1. The material is critical to effect sealing according to the invention. A male threaded fitting 3 is threaded into a female threaded coupling 4 also having an undercut (but female coupling need not be undercut) 4a to receive seal 1. FIG. 1B shows the apparatus of FIG. 1A torqued in-place in which the ring seal 1 and the nut 2 interlock and compress the ring seal to effectively seal the total surfaces of the threaded connections. 
     Referring now to FIG. 2, a diamond-shaped high temperature alloy ring seal 21 is shown with the nut 22 having a chamfered face 22A to accommodate the diamond-shaped seal 21. The female threaded coupling 24 for receiving the male threaded fitting 23 also has a chamfer 24a for the diamond-shaped seal. 
     The method of the invention for FIGS. 1 and 2 comprises installing the nut on the male thread of the connection and rotating the nut onto the thread at least seven thread turns. The ring or diamond-shaped seal is then threaded onto this same male thread and rotated approximately five thread turns or a couple less turns than the nut. No special tools are required for installation of the nut and seal, since they may be installed by hand using finger assembly. The threaded male fitting is then threaded into the female coupling in the normal manner and tightened some three turns plus or minus a half turn. The nut is then tightened sufficiently to bottom the nut against the female coupling or face thereof as shown in FIGS. 1B and 2. The torque applied to the nut is transmitted to the ring or diamond seal, and the seal is forced into the total threaded surface area including the thread root. 
     FIGS. 3A and 3B show respectively the three piece apparatus as installed and as torqued. The high temperature alloy ring seal 31 and the 316/316L stainless steel nut 32 are installed on male threaded fitting 33. Female threaded coupling 34 has a chamfer 34a and mounted on the outer diameter of ring seal 31 is a 316/316L stainless steel washer 35. The method of implementing the three piece arrangement is the same as for the two piece arrangement except that the washer is placed on the ring seal prior to insertion of the male thread into the female coupling. 
     The invention has particular application as a fire seal in that it is able to withstand 2,000° F. flame for up to 20 minutes without failure to meet fire safe connection requirements in fuel and hydraulic systems in aircraft, commercial and industrial heating and processing systems, and for fuel and hydraulic systems in automotive and naval equipments. 
     While the present invention has been disclosed in connection with the preferred embodiments thereof, it should be understood that there may be other embodiments which fall within the spirit and scope of the invention as defined by the following claims.