Abstract:
An improvement to the sealing ring of U.S. Pat. No. 4,085,951 is disclosed, wherein the sealing ring is of a special design including an in situ sealing flange generating corner, and the stepped thread pin and box members have been modified in the shoulder areas between the thread sections thereof to provide a pressure transmitting area for transmitting torque to the ring, and to provide room for the in situ sealing flange to form and extend beyond the faces of the improved ring. 
     With the improved design, the sealing ring is capable of retaining hot gases or liquids with a pressure differential in at least a given direction across the sealed joint exceeding the yield pressure of the rubber or plastic of which the ring is made.

Description:
BACKGROUND OF THE INVENTION 
     Joints used for the purpose of connecting drill pipe lengths or tubing lengths must be made up with a tight fit on tapered lateral contact surfaces in order to provide the required degree of rigidity needed to resist lateral bending stress with a minimum of fatigue. It is, however, difficult to produce sealed joints having both a tight fit on tapered, lateral contact surfaces, and a longitudinally compressed ring gasket, as even very small variations in the machining of the tapered lateral contact surfaces results in significant displacement variations in the longitudinal make up of the joints, with resultant differences of degree in the amount of compression applied to the ring gasket, which will sometimes be damaged by too great a compression, or may be compressed insufficiently to adequately seal the joint. 
     Difficulties of this nature have led to the use of special pipe and tubing joints which have stepped threads and tapered seating elements employing highly polished metal-to-metal fits as a means of sealing against very high oil pressure, and such joints, when made up carefully under ideal conditions, are entirely capable of sealing against such high well pressures. This type of joint, referred to hereinafter as the Hydril-type connector or joint, is generally more costly to manufacture than more conventional pipe and tubing joints, and the polished sealing surfaces or seats are quite susceptible to damage when the joints are made up and broken out under operating conditions encountered in the oil fields. Damage may occur as a result of direct or sliding impact of the pin seal against the end of the box when the lower end of a suspended, relatively heavy pipe stand is stabbed into a joint on the upper end of the pipe which precedes the suspended pipe stand into the well. 
     Furthermore, the polished metal-to-metal sealing areas or seats are also quite susceptible to damage at the time the joints are screwed together, as even quite small particles of dirt or sand, if trapped between the mating seats, are capable of scoring or producing galling which may completely destroy the effectiveness of the metal-to-metal seal. Excessive friction, caused by overtightening, lack of lubrication, or rapid make up, will occasionally cause the tight fitting metal-to-metal seats to gall during the last fraction of a turn as the joints are screwed together. 
     In an effort to avoid the entrapment of dirt and sand particles between the seating surfaces as the joints are screwed together, the prior art has customarily made the metal-to-metal contact area between the seats relatively narrow. The prior art may provide one joint member with an arcuate seating surface and the mating member with a conical seating surface to obtain a line of contact between the two surfaces. However, such narrow seating surfaces are not generally desirable because they are quite vunerable to attack by the corrosive fluids which are often present in oil and gas wells. In this regard, the corrosive need penetrate only a relatively short distance in order to completely destroy the line of metal-to-metal contact existing between the two joint surfaces, and thereby destroy the seal. 
     Thread damage is frequently caused by the vertical stabbing of threaded pin ends of suspended heavy pipe stands into threaded box ends of pipe or pipe collars supported beneath the pipe stands. This damage usually occurs when the entire stabbling load falls on the relatively thin and frail thread ends of the threaded pin and box members. A damage end thread on one joint member will often damage, and occasionally destroy, a number of additional threads on both members should the pin and box be screwed together before the thread end damage is discovered. 
     The Hydrill-type connectors, because of their relatively delicate sealing areas, are thus easily damaged. Damage to the Hydril-type connector sealing areas has heretofore required that the unit be scraped, or shop repaired at great expense. 
     In oil fields, drill strings and other tubular goods are frequently connected by Hydril-type connectors, which involve a two-step thread design, as is well known to those skilled in the art. For instance, hydril-type connectors are disclosed in U.S. Pat. No. 2,532,632, the disclosure of which is hereby incorporated by reference for the teachings of Hydril-type connectors therein. 
     The prior art has made extensive use of &#34;O&#34; rings and similar sealing means, in the sealing of pipes and the like. See for instance, U.S. Pat. Nos. 3,054,628; 3,167,333; 2,980,451; 2,889,773; 2,813,567; 2,770,477; and 2,553,340. Generally, the sealing rings or gaskets of these prior art patents have been made of Teflon or similar plastic material. 
     The use of rings of plastic or rubber or the like in rotary tools is also known in the art, see, for instance, U.S. Pat. Nos. 2,102,072, and 2,110,127. Finally, the use of Teflon as a sealing ring in Hydril-type connectors is disclosed in U.S. Pat. Nos. 2,907,589 and 3,100,656. In these patents, the Teflon seal ring is located in the area of the free terminal forward end of the pin member of the Hydril-type connector. If such sealing rings are so located on the pin member, they are highly susceptible to damage, and if located on the box member they are quite difficult to install, and subject to a tendency to be locally deranged in an unpredictable manner as the joint is made up. 
     Many different designs of screw threaded pin and box type tubing and drill pipe joints have been proposed by the prior art. However, in spite of the many proprosals, a number of problems have remained unsolved, especially those problems having to do with a method of adequately and enduringly sealing a Hydrill-type connector after the metal-to-metal seating surfaces have been damaged, which is a frequent occurrence, against the extremely high fluid pressures which are encountered in deep drilled oil and has wells. For instance, such pressures might range as high as 15,000 psi. 
     The Hydril Company commercially offers a patented tubing connection, with a Teflon ring located in the box member at a location such that when the connection is made up the ring will be at the free terminal end of the pin. It is indicated that the prime purpose of this ring is to complete the corrosion protection afforded by plastic coated pipe. The advertising material also indicates that the connection may be specified where an additional high-pressure seal is desired. 
     The Rucker Atlas Bradford Company has offered leakproof tubing to the trade, using conventional thread profile, but modifying the coupling by machining out one and one-half threads near each end of the internally threaded coupling and installing a Teflon ring in the resultant retaining groups. In another version, a pin and box member design is provided wherein a groove is machined inside the box member to retain a Teflon seal ring. 
     U.S. Pat. No. 4,085,951 to James B. N. Morris, issued April 25, 1978, discloses the use of a secondary sealing means between the stepped threaded areas of a Hydril-type tubing or casing connector or joint. The secondary seal is an annular ring of relatively rigid internally tenacious plastic or rubber material, such as polytetrafluoroethylene, which serves to contain well pressure if the metal-to-metal sealing surfaces on the pin and/or box members of the Hydril-type connector are damaged. With the sealing rings disclosed in the Morris patent, damaged Hydril-type connectors can be used without having to undergo extensive repair of the damaged area, or even scrapping. 
     FIGS. 5, 6, 7 and 8 of the Morris patent disclose various forms of sealing rings which can be used therein, with various modifications of the inner wall of the annular ring being made to facilitate installation of the ring over a portion of the threads of the Hydril-type connector. Column 5, lines 3-9 of the Morris patent also suggest that a ring of square cross-sectional area, as illustrated in FIG. 8, may be installed by heating the ring until the ring expands enough to permit it to be slipped over the pin member threads, or alternatively suggest the ring could be actually molded in place in the ring-receiving groove. 
     The sealing ring of the Morris patent has been found to work very effectively, especially when used to contain liquids. However, the sealing ability of the sealing ring of the Morris patent is pressure limited by the contact pressures which can be applied to the ring, and it has been found that high pressure gases can leak relatively easily past the relatively small sealing area of the sealing ring of the Morris patent. 
     U.S. Patent Application Ser. No. 517,415, filed July 26, 1983 now Pat. No. 4,591,195 in the names of K. Darrel Chelette and Merle Edward Evans is directed to an improvement of the Morris U.S. Pat. No. 4,085,951, wherein the sealing ring is of a special design including in situ sealing flange generating corners located along each side of the ring, and the stepped thread pin and box members have been modified in the shoulder areas between the thread sections thereof to provide a pressure transmitting area for transmitting torque to the ring, and undercut areas to provide room for formation of the in situ sealing flange between the radially inner and outer portions of the ring. The in situ sealing flange extends beyond the faces of the improved ring, which is capable of retaining hot gases or liquids with a pressure differential across the sealed joint in at least one given direction exceeding the yield pressure of the rubber or plastic of which the ring is made. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an improvement in the Morris U.S. Pat. No. 4,085,951, the disclosure of which is hereby incorporated by reference, wherein the male and female members of the Hydril-type joint are modified, and wherein the annularly continuous ring of plastic or rubber material is of a special design, whereby at least one in situ sealing flange is formed on a surface of said ring upon exposing the ring to joint assembly pressure. Thus the present invention relates to improvements in threaded-type joints, and in particular relates to the design and construction of sealed, screw threaded oil well tubing and casing or other tubular joints which are capable of being rapidly made up to positive pressure seal condition, and rapidly broken apart without damage to the seals or threads during either make up or breaking of the joint under conditions of repeated severe usage in the field. The present invention is directed to improvements in Hydril-type connectors wherein the connector is capable of maintaining a pressure differential in at least one direction across the annular ring which is in excess of the yield pressure of the material of which the annular ring is made. The present invention is applicable to inserted joints, wherein one pipe end is screwed directly into the end of another pipe end, to couplings in which the opposed ends of two pipes are threaded into a tubular collar, and into other similar types of tubular goods connections. 
     A ring receiving groove is located in the vicinity of the shoulder between the stepped threads of a male or female member of a Hydril-type connector, and preferably on the male member of the Hydril-type connector. The ring receiving groove is radially located at least about as far from the pipe axis as the thread roots. The shoulder includes a pressure transmitting area for transmitting make up torque to the face of the annular ring located in the groove. A chamfer is provided in the shoulder area of the male or female member which does not have the ring receiving groove located thereon to provide room for formation of the in situ sealing flange which extends beyond the face of the annular ring. The generally flat chamfer extends at an angle of about 15° to 75°, preferably about 45°, to the axis of the pipes. Preferably the other shoulder, which is preferably on the pin member, also has a chamfer which is at an angle of about 15° to 75∞, preferably about 45°, to the axis of the pipes. The take off points of the chamfers are preferably at least substantially the same distance from the axis of the pipes, thereby permitting the ring room to expand on either side thereof to form said in situ sealing flange. The preferred annular ring which is used in the present invention has corners located on the radially inner or outer surface depending upon whether the groove is on the female or the male member, respectively) thereof in order to assist in the generation of the in situ sealing flange. A stiffening portion of the ring is preferably provided on the ring remote from said corners to support and stabilize the ring in the ring receiving groove upon make up of the Hydril-type joint. The ring includes face areas for receiving pressure from the pin and box members upon make up of the joint, to transmit pressure to the corners mentioned above to cause the in situ sealing flange to form. At least one in situ sealing flange will be located proximate the radially inner or outer surface of the ring. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention will be more readily understood with reference to the accompanying drawings, wherein 
     FIG. 1 is a cross-sectional view of a typical joint of the present invention illustrated before the joint has been fully made up (the male and female member shoulders are just touching the sealing ring); 
     FIG. 2 is a cross-sectional view of a sealing ring being threaded on a male member of a Hydril-type joint; 
     FIG. 3 is a cross-sectional view of a portion of the joint of FIG. 1, showing greater detail at the sealing ring; 
     FIG. 4 is a cross-sectional view of the joint of FIG. 3 showing the formation of the in situ sealing flanges on the annular ring upon joint make-up; 
     FIG. 5 is a perspective view of the sealing ring illustrated in FIGS. 1-4; 
     FIG. 6 is a cross-sectional view of a different embodiment of the sealing ring; 
     FIG. 7 is a cross-sectional view of a yet further embodiment of the sealing ring; 
     FIG. 8 is a cross-sectional view of the sealing ring of FIG. 5, in a different embodiment of the Hydril-type joint; 
     FIG. 9 is a cross-sectional view of the sealing ring of FIG. 7, used in a different embodiment of the Hydril-type joint; and 
     FIG. 10 is a cross-sectional view of the sealing ring of FIG. 7, used in a yet further embodiment of the Hydril-type joint of the present invention. 
    
    
     In FIGS. 1, 2, 3 and 4, a joint 1 includes a pin member 2 and a box member 3 having interengaged two step threads, with threads 4 and 5 interengaged in one step and threads 6 and 7 interengaged in a second step. The pin and box members are of the two-step type, with pin threads 4 and 6 cut on steps 8 and 9 respectively, and being of the same pitch and outline characteristics. In a similar manner, box member threads 5 and 7 are complimentary to pin threads 4 and 6 and are cut on steps 10 and 11, respectively. At the outer end of the box there is provided a tapered box stop shoulder 12 which is complimentary to a opposed pin stop shoulder 13, while at the inner end of the box there is a square cut box shoulder 14 and a complimentary square cut pin shoulder 15. When the joint 1 is fully made up, tapered pin and box stop shoulders 16 and 17 are in compressive engagement near the forward end of the pin. 
     The box and pin members have rather shallow bevels or chamfers 18 and 19 intersecting the box and pin bores 20 and 21 and also intersecting the box shoulder 14 and the pin shoulder 15, respectively. The chamfers are generally coaxial and typically will extend at around 20° angularity with the bores 20 and 21 as illustrated. 
     The mating shoulders provide metal-to-metal seating surfaces, serving to seal the joint against outward escape of high fluid pressure from the joint. However, upon damage of one or more of the shoulders, the joint may no longer be capable of retaining full well pressure. The present invention is directed to providing a Hydril-type connector or joint having a secondary sealing means which will contain full well pressure in the pipe, even though the mating metal-to-metal shoulders are damaged. 
     To provide this secondary sealing means, which seals the interior of the pipe against the fluid pressure therein, in the pin shoulder area 22 between steps 8 and 9 of the pin member 2 a groove 23 is provided. An annular ring 24 of resilient plastic or rubber material, such as, for instance, of Teflon (polytetrafluoroethylene) is provided in the groove. It is preferred that the ring include a fillter to increase the strength thereof, and suitable inorganic fillers include glass fibers, fine particle size ceramic materials, and fine particle size metals. The ring may be pigmented if desired. 
     As more clearly illustrated in FIG. 2, the unstressed ring includes an upper portion 25 and a lower portion 26. Corners 60 are located in the area between side walls 30, 31 and outer surface 29. Corners 27 are located in the area between upper portion 25 and lower portion 26. The ring 24 includes an inner surface 28, an outer surface 29, substantially vertical sidewalls 30, 31, and flats 32 extending between corners 27 and lower portion 26. Lower portion 26 includes beveled walls 33, 34, so that lower portion 26 is in the form of a trapezoid. As illustrated in FIG. 2, the shape of lower portion 26 is such as to fit between threads 35 of pin member 2. As will be seen in FIG. 5, a circumferential gap 36 of at least 15° and generally no more than 45°, and preferably about 30°, is formed in lower portion 26, so that ring 24 will be readily threadable over threads 35. 
     The modifications to a conventional Hydril-type connector can be noted most readily with respect to FIG. 3 of the drawings. An undercut area 37 is formed in the region pin shoulder ares 22. The innermost portion 38 of undercut 37 is radiused in order to prevent stress concentration, and preferably the radius of innermost portion 38 is at least 0.01 inches. A chamfer 39 joins innermost portion 38 to pressure transmitting face 40, which upon joint make up transfers make up torque to ring 24 in combination with a corresponding face 42 on box member 3. A chamfer 41 on box member 3 corresponds in take-off point and angle to chamfer 39, and is associated with pressure transmitting face 42 on box member 3 which as indicated cooperates with pressure transmitting face 40 on pin member 2. Undercut area 61 is formed on box member 3 in the region of the box member shoulder area. A chamfer 62 joins inner portion 63 and face 42 of box member 3. A chamfer 64 on pin member 2 corresponds in take-off point and angle to chamfer 62, and is associated with pressure transmitting face 40 on box member 3. 
     The lower portion 26 of ring 24 serves as a stiffening and support for the upper portion 25, which receives pressure from the pressure transmitting faces and functions to seal the joint against high pressure fluids by forming two pairs of in situ sealing flanges, one at corners 27 and one at corners 60. This is more clearly noted with reference to FIGS. 3 and 4, wherein Figure 3 is an expanded cross-sectional view of the joint of FIG. 1, with a joint made up to a point wherein the pressure transmitting faces are just beginning to engage the sidewalls 30, 31 or ring 24. After the joint has been made up, the ring 24 is placed under compression between pressure transmitting faces 40, 42, as illustrated in FIG. 4, with the resulting formation of sealing flanges 43, 44 in the region of corners 27 and sealing flanges 65,66 in the region of corners 60. With the formation of sealing flanges 43,44 and 65,66 in the embodiment of FIG. 4, the resulting joint can withstand high pressures exerted from the inside of the pipe to the outside of the pipe, or from the outside of the pipe to the inside of the pipe with the pressure differential across the pipe walls exceeding the yield pressure of the material of which the ring is made, especially when the ring contains inorganic filler material. Preferably the amount of filler utilized is between 15 and 45%, suitably about 30%, by weight. It is preferred that a substantial proportion more preferably the majority, of the filler be glass fibers in view of their excellent strength reinforcement characteristics, but the glass fibers can be in part or even fully replaced by other inorganic fillers such as ceramic or metal filler. Organic fillers are not preferred because of cost and generally poorer strength characteristics, but can be utilized if desired if capable of withstanding the processing and use temperatures to which such organic fillers may be exposed. 
     With the use of a suitable filled polytetrafluoroethylene ring, or other suitable ring, an increase of the pressure differential across the pipe wall, from the inside to the outside of the pipe, or from the outside to the inside of the pipe, increases the sealing ability of ring 24 of FIG. 4. The increased pressure from the inside of the pipe acts upon sealing flanges 43, 44 to cause the flanges to be pressed into even tighter sealing engagement with chamfers 39, 41, respectively to thereby increase the sealing ability of ring 24. Likewise, the increased pressure from the outside of the pipe acts upon sealing flanges 65,66 to cause the flanges to be pressed into even tighter sealing engagement with chamfers 62,64 respectively to thereby increase the sealing ability of ring 24 against a pressure differential from the outside to the inside of the pipe. This permits the joint of the present invention to be utilized in situation wherein conventional joints are highly likely to fail, and especially for the sealing of high pressure gases in hot corrosive conditions. Thus in the preferred embodiment of the present invention two pairs of sealing flanges are formed, so that the fully made-up joint resists pressure differential in either direction across the pipe walls, unlike the joint disclosed in copending application Ser. No. 517,415. 
     The axial width of the lower portion 26 of ring 24 is preferably at least 40% of the axial width of the upper portion 25 in order to provide adequate stiffening and reinforcing of the upper portion. 
     Chamfers 39, 41 are substantially at the same angle to the axis of the pipes and preferably at identical angles, with the angles varying from about 15° to 75°, preferably about 30° to 60°, and most preferably about 45°. The take off points of the chamfers 39, 41 are at least substantially the same distance from the axis of the pipes, and preferably are of identical distances from the axis of the pipes, and are no further from the axis of the pipes than the radial mid-point of the upper portion 25. The width of the chamfer 39 is at least equal to the width of chamfer 41. The concave radius of innermost portion 38 is not less than 0.01 inches, preferably not less than 0.015 inches. Chamfers 62,64 are substantially at the same angle to the axes of the pipes and preferably at identical angles, with the angles varying from about 15° to 75°, preferably about 30° to 60°, and most preferably about 45°. The take-off points of the chamfer 62,64 are at least substantially the same distance from the axes of the pipes, and preferably are of identical distances from the axes of the pipes. These chamfers are at least as far from the axes of the pipes as a radial midpoint of the upper portion 25. It is important that the width of faces 40,42 be at least 25% of the widths of faces 30,31. 
     While the present description is with respect to a sealing ring 24 installed on a pin member 2, it will be readily appreciated that the ring may be installed on the box member of a pin and box Hydril-type connector. However, due to the difficulty of ring installation and inspection, it is greatly preferred to have the ring located on the pin member. 
     It is preferred that the ring be made of a filled polytetrafluoroethylene which has a compressive strength of at least 1500 psi, and more preferably of at least 2,000 psi. 
     The corners 27 and the corners 60 of ring 24 are preferably right angle corners, but it will be readily apreciated that angles greater or less than 90° may be utilized if desired. The corner should have a dimension of at least 0.01 inches per side, and preferably at least 0.02 inches per side. 
     Other forms of sealing rings may be utilized in the joint of the present invention without departing from the scope of this invention. For instance, a sealing ring 46 as illustrated in FIG. 6 may be utilized, or alternatively a sealing ring 47 as illustrated in Figure 7 may be utilized. Sealing ring 46 includes an upper portion 48 and a lower portion 49, with lower portion 49 being rectangular or square in cross-section, as opposed to the trapezoidal shape of the lower portion 26 of ring 24 of FIG. 2. Corners 50,67 of ring 46 will perform the same functions as corners 27,60 of ring 24, so that a pair of the in situ sealing flanges will be formed in a joint utilizing ring 46 and the pin and box members of FIG. 3. Likewise, corners 51 on ring 47 will form an in situ sealing flange. In this embodiment, the sealing ring 47 is of rectangular cross-section, and bulges will be formed on surfaces 68,69, but will not be as pronounced as the sealing flanges which will be formed at corners 51, due to the much greater distance of corner 70 from pressure transmitting faces 40,42. 
     It is anticipated that the dimensions of the sealing ring will be substantially the same as that disclosed in the aforesaid copending Ser. No. 517,415, the disclosure of which is hereby incorporated by reference. 
     FIG. 8 illustrates the sealing ring of FIG. 5, utilized in a different embodiment of the male and female hydril-type connector. Female member 71 has an undercut area 72 provided at the shoulder ares 73 thereof. Undercut area 72 includes a innermost portion 74 and a chamfer 75. Chamfer 76 is provided on male member 77, and chamfer member 76 has substantially the same takeoff point, and extends at substantially the same angle as chamfer 75. Other than chamfer 76 and undercut 72, the female member 71 and male member 77 are of conventional hydril-type connector design, with no undercut provided on female member 71 or male member 77 in the vicinity of corners 27. Thus only corners 60 will form an in situ sealing flange, so that sealing ring 29 will be more effective in sealing against pressure from the outside to the inside of the pipe than vice versa. 
     FIG. 9 illustrates the use of the male and female member joint of FIG. 8 with a rectangular cross-section sealing ring 47, which is the same as that of FIG. 7. Chamfers 75,76 cause in situ sealing flanges to form at corners 51 upon joint make-up. Similar to the arrangement of FIG. 8, no inner in situ sealing flange will be formed. 
     In the embodiment illustrated in FIG. 10, a sealing ring 47, which is the same as the ring of FIGS. 7 and 9, is utilized in a yet further embodiment of the male and female hydril-type connector. In this embodiment, ring 47 projects a distance A above flat 80 of male member 81. Female member 82 has an undercut area 83 provided in the vicinity of shoulder 84, and undercut area 83 includes an inner area 85 and a chamfer 86. The chamfer 86 allows a portion B of ring 47 to extend above contact of ring 47 with pressure-transmitting face 87, which pressure-transmitting face 87 contacts an area of width C of ring 47. For all of the embodiments of the present invention it is preferred that distances B and, where applicable, A be no greater than distance C, the radial distance of contact of the pressure-transmitting face with the sealing ring. The embodiment of FIG. 10 is quite similar to the embodiment of FIG. 9, except no chamfer 76 has been provided in the embodiment of FIG. 10. 
     In all of the embodiments of FIGS. 3, 7, 8, 9 and 10 the sealing rings have not been placed under compression by the respective pressure-transmitting faces, with the Figures illustrating that the joint at that point wherein the pressure-transmitting faces have just contacted both sides of the sealing ring.