TUBULAR JOINT WITH TRAPPED MID-JOINT METAL TO METAL SEAL

Abstract: A joint (10) and male and female tubular element (30, 20) where the threads (70, 80) of the female and male members (20, 30) have negative load flanks (44) and have two or more radial steps axially separated one from another by a reverse angle torque shoulder (43) having one or two adjacent conical sealing surfaces (41, 42). The reverse angle torque shoulder (43) produces radial positional interference of the conical sealing surfaces (41, 42) when the male and female members (30, 20) are fully assembled and serves as a positive assembly stop. The negative load flank angle of the threads and the reverse angle torque shoulder combine to interlock the male and female members and to prevent differential radial separation of the conical sealing surfaces when the joint (10) is exposed to internal pressure, external pressure or both. Tapered threads and sealing surfaces and interference threads may advantageously be used in joint construction.

Description: TUBULAR JOINT WITH TRAPPED MID-JOINT METAL TO METAL SEAL This invention relates generally to oil and gas well tubing and more particularly has to do with the con¬ struction of high pressure tubular joints operable when made-up and run into a well to withstand extreme fluid pressures, both internal and external, that seek escape throlgh the tubular assembly at the joints. The search for oil and gas reserves has brought about the exploration of ever deeper formations. These deep3r formations require longer strings of production pipe, casiig, liners and drill pipe used in the exploration and production of oil and gas at .extremely high pressures. This increased length of tubular strings imposes the upper portion of the string to very high tensile loads and in addition, the tubular strings are exposed to extremes of pressure both from within the tubing and also from the exterior of the tubing. Prior art metal-to-metal sealing mechanisms have provided seals that resist mainly internal pressure or mainly external pressure, as long as the surrounding tubu- lar geometry remains in the elastic range. The prior art sealing mechanisms have not solved the sealing problem of withstanding extremes of internal pressure, or external pressure, either pressure acting during circumstances of high tension, torque or compression forces acting on the tubing. OMPI r U.S. Patent No. 2,992,019 to M.D. MacArthur shows a casing joint having metal-to-metal sealing means responsive primarily to extremes of inside fluid pressure. The dis¬ closed interior sealing for the pin and box provides a fourteen degree (14°) interior seal that is spaced a distance from the threaded inner connection to enable the deformation or strain on the pin, in response to the in¬ side fluid pressure, to flex the pin interior sealing sur¬ face against the box interior sealing surface and obtain a greater sealing force. In addition, during such strain, the sealing contact area decreases which increases the sealing force over the reduced area. In particular, the distance between the pin and the seal surface remains the same while the center of the sealing area moves slightly toward the thread during such sealing flexing. U.S. Patent No. 4,009.893 issued to Schatton, et al. discloses a tubing or casing joint with box and pin members having two axially spaced thread sections separated by a radial step zone which includes for the pin member, an annulus having an axial undercut. The endface of the an- nulus bears against a complementary face in the step zone of the box member and serves to act as a complementary thread stopface, in addition to a stopface at the end of the pin member and in the box member. There has been a long-felt need for metal-to- metal sealing mechanisms for use in tubular joints which are able to hold mating members together for complete leak resistance against both internal and external pressures, regardless of the forces of tension, compression, inter- nal pressure, external pressure, torque or any combina¬ tion thereof that are applied to the joint. It is therefore a primary object of this inven¬ tion to provide a trapping mechanism in a joint to hold the mating members together for complete leak resistance in the face of multiple forces acting on the joint. Not only must the joint be sealed, it must be capable of being made up and disassembled numerous times without galling and without the danger of stripping threads or cross-threading. It is of course, desirable and there¬ fore an advantage of the joint according to the invention disclosed herein in that it may be "stabbed" and that thereafter it can be made up with a relatively small num¬ ber of turns. It is common to use an integral or upset joint wherein the threaded portion of the pipe is thickened by a forging technique so as to provide more metal in the area where threads are cut. The invention disclosed below may advantageously be used with an integral or upset type of joint, and it may also be used with a threaded and coupled joint wherein both ends of the tubular elements are pro¬ vided with male joining elements and a coupling member is provided with female joint elements.. The present invention therefore provides a joint for tubular elements comprising, an internally threaded female member and an externally threaded male mem¬ ber adapted to be threadably connected, characterized in that the threads of the female and male members have negative angle load flanks and there are at least two radial steps axially separated from one another by a reverse angle torque shoulder having at least one adjacent conical sealing surface, said shoulder defining a positive assembly stop, said adjacent conical sealing surfaces providing radial positional interference when the male and female members are fully assembled the negative load flank angle of the threads and the reverse angle torque shoulder - interlocking the male and female members and preventing differential radial separation of the engaged conical sealing surfaces when the joint is exposed to internal pres¬ sure, external pressure or both. Further features and advantages of the invention will be better understood from the following description of preferred embodiments of the invention taken in con- OMPI NATlθ nec ion with the accompanying drawings in which: Figure 1 illustrates a longitudinal cross-sec¬ tional section through a joint according to the invention showing in detail in Figures 1A and IB, the negative flank angle and the reverse torque shoulder features of the in¬ vention; Figure 2 illustrates an alternative embodiment of the invention with a longitudinal cross-section showing threads cut on a taper angle with respect to the axis of the male and female members of the joint; Figure 3 and Figure 3A shows an embodiment of the invention where the conical sealing surfaces of the male and female members are machined at slightly different angles; and Figures 4 and 4B illustrate alternative embodi¬ ments of the invention where Figure 4A shows conical seal¬ ing surfaces on both sides of the reverse angle torque shoulder and Figure 4B illustrates the use of a reverse angle torque shoulder between two or more stepped threads. Figure 1 illustrates, according to the invention, a joint shown generally at 10 comprising female or box mem¬ ber 20 in threaded connection with pin or male member 30 and having two step threads shown generally at 70 and 80 inter- connectad by a conical sealing surface 40. The joint is characterized, according to the invention, by providing a negative angle load flank 44 on the threads shown general¬ ly in more detail in Figure 1A and a reverse angle torque shoulder 43 shown in more detail in Figure IB. Figure 1A illustrates that the load flank 44 on the thraads is at an angle ώ which is measured counter¬ clockwise from the vertical to the longitudinal plane of the threads. Figure IB illustrates that the sealing surfaces 41 and 42 of the pin and box members terminate in the tor- —que shoulder 43 which is at a reverse angle a. measured O PI clockwise from the perpendicular to the longitudinal axis of the joint. The initial sealing surface contact of surfaces 41 and 42 is established at assembly by metal-to-metal interference. Upon full, make up of the joint, the mating of the respective torque angle shoulders may induce additional radial positional interference into the contacting sealing surfaces 41 and 42, especially for steep shoulder angles. Thus, two sources of radial positional interference are pos- sible in the joint of the assembled members according to the invention: interference caused by the assembly of the sealing surfaces 41 and 42 and, for reverse torque angle shoulder provided with steep angles, interference caused by the mating of the respective shoulders. The seal pressure retention characteristic of the threaded connection is re¬ lated to the ability of the sealing surfaces 41 and 42 to remain in contact with one another as radial deflection of the joint occurs from either internal pressure or exter¬ nal pressure. The unique seal retention according to the invention results from the trapping effect of the nega¬ tive load flank threads of both the large step threads 70 and the small step threads 80 in combination with the re¬ verse angle shoulder 43 in the intermediate region between the steps thereby preventing loss of surface contact be- tween surfaces 41 and 42. The trapping effect causes the two surfaces 41 and 42 to deflect as one. The seal is established regardless of differences in the annular section areas of each member 41 and 42 thus providing a pressure containment wherein forces act from either side of the seal. In addition, the application of an axial tensile load will cause the seal surface to re¬ main in contact. Similarly, torque forces on the joint do not adversely affect the seal of the joint. Advantageously, the only way that the sealing surfaces can separate is for extreme forces acting on the joint to cause the threads to OMPI &/?N A TlO shear, the shoulder to shear, or both. Although Figure 1 shows the threads 70 and 80 to be cut parallel to the axis of box member 20 and pin member 30, an alternative embodiment is shown in Figure 2 where threads 70 and 80 are cut on a taper angle shown generally as J, Although Figure 2 illustrates the sealing surfaces 41 and 42 to be cut at the same taper angle^ as are the threads 70 and 80, they may advantageously be provided at a taper an¬ gle different from the thread taper. Figure 3 shows another alternative embodiment of the invention whereby the conical sealing surfaces 41 and 42 of the top step are machined to slightly different angles with respect to the axis of the joint. According to a fur¬ ther preferred aspect of the invention, the conical seal surface of the member having the thinner wall thickness at the seal surface may be machined to a smaller angle with respect to the axis of the threaded connection than the com¬ plementary conical seal surface of the mating member. In¬ dividual sealing shoulder members are shown in more detail in Figure 3A. Because the conical seal at the upper step illustrated in Figure 3A occurs at a region where the female member 20 wall thickness is less than the wall thickness of the male member, the sealing surface 42 of the female member is machined to an angle of incline which is slightly less than the angle of incline of sealing surface 41. Figure 3A indicates the angle difference to be t . The mismatch of the angles of inclines of conical sealing surfaces 42 and 41 is selected for any particular seal geometry such that at final make-up, the bearing load has a relatively even distribution across the entire sealing surface in contact, thus broadly distributing make-up stresses and minimizing their negative effects. Referring to Figure 3A where for the upper step having the female conical sealing surface 42 machined at an angle slightly less than that of male surface 41, when the OMPI pin member 30 initially mates with box member 20, the bear¬ ing load is substantially on the leading edge of the box sealing surface 42 with the trailing edge of the pin seal¬ ing surface 41. After the sealing surfaces are fully ade- up, the stress as a function of axial width becomes more uniform than for the case where the taper angles of the sealing surfaces are the same or where the taper angle of the box sealing surface is greater than the taper angle of the pin sealing surface. Metal-to-metal seal taper angles commonly are provided in a range of from two degrees (2°) to fourteen degrees (14°) . The exact angular taper mismatch of the sealing angles of surfaces 41 and 42 varies depending on the seal angle of the more rigid member, the width of the seal- ing surface, the thickness of the thinner member, desired tolerances and other factors. It can be shown that seal mismatch for very low angle seals of approximately one-half (1/2") inch in axial width can be as low as one-quarter degree (1/4°). High angle seals of equal axial width may require a mismatch of one degree (1°) or more for complete balancing of bearing loads upon full make-up. Finite ele¬ ment analysis may be used as a tool to verify the optimum seal angle mismatch on any given seal and connection geometry. Figure 3 also shows that threads 70 and 80 may be interference fitting threads. Figures 4A and 4B illustrate alternative embodi¬ ments of the invention. Figure 4A illustrates the reverse angle torque shoulder 43 between the two step threads and having not only.conical sealing surface 40 (as illustrated in Figure 1) on the large step, but also conical sealing surface 45 on the small step. Alternatively a conical seal¬ ing surface 45 could be provided solely on the small step with no sealing surface being provided on the large step. Thus, one conical sealing surface provided on either step adjacent the reverse angle torque shoulder, or two seal- ing surfaces, one provided on each of the steps, serve in conjunction with the reverse angle torque shoulder and the negative angle load flank threads to create th unique trapping effect of the invention. Where as illustrated in Figure 4A, a conical seal¬ ing surface is provided as at 45 on the small step and the female member 20 wall thickness is greater than the thick¬ ness of the male member, the sealing surface of the female member is machined to an angle of incline which is slightly greater than the angle of incline of the sealing surface of the male member. Figure 4B illustrates that the combination of negative load flank threads and reverse angle torque shoulder between stepped threads may be used for tubular connections or joints having two or more stepped threads. For example, triple radial step threads 170, 190, and 180 may advantageously be used for thick walled tubulars. Ac¬ cording to the invention, reverse angle torque shoulders 43' and 43" are provided between thread steps 170 and 190 " and between thread steps 190 and 180. Providing one conical sealing surface such as 40' or 40" on each axial side of shoulder 43' and one conical sealing surface such as 41' or 42' or both 41* and 42' on each axial side of shoulder 43" serves to achieve the trapping effect discussed above when used in combination with negative load flank threads. More stepped threads with intermediate reverse angle torque shoulders and associated conical sealing surfaces could ad¬ vantageously find applications for tubulars having extreme¬ ly thick walls. In all the embodiments of this invention the mag¬ nitude of the negative thread flank angle or the angle of the reverse angle shoulder should not exceed thirty degrees (30°) . In addition, it has been found that the magnitude of the angle of the conical sealing surfaces relative to the joint axis should not be greater than fifteen degrees (15°) . Finally, for that embodiment of the invention il¬ lustrated in Figure 3, the dissimilarity of the angles of incline of the sealing surfaces of the male and female members should be less than one degree where the angle of incline of the member having the greater wall thickness should be greater than that of the member having the les- ser wall thickness. From the foregoing, it is apparent that there has been provided a sealing surface for use in joints, and in¬ terconnecting tubular members especially useful in oil and gas wells. Various, modifications and alterations in the described structures will be apparent to those skilled in the art from the foregoing description which do not depart from the scope of the invention. OM£L

Claims: 1. A joint (10) for tubular elements comprising, an internally threaded female member (20) and an exter¬ nally threaded male member (30) adapted to be threadably connected, characterized in that the threads (70, 80) of the female and male members (20, 30) have negative angle load flanks (44) and these are at least two radial steps axially separated from one another by a reverse angle tor¬ que shoulder (43) having at least one adjacent conical sealing surface (41, 42) , said shoulder (43) defining a positive assembly stop, said adjacent conical sealing sur¬ faces (41, 42) providing radial positional interference when the male and female members (20, 30) are fully as¬ sembled the negative load flank angle (Φ) of the threads (70, 80) and the reverse angle torque shoulder (43) in¬ terlocking the male and female members (20, 30) and pre¬ venting differential radial separation of the engaged coni¬ cal sealing surfaces when the joint (10) is exposed to in¬ ternal pressure, external pressure or both. 2. The joint of claim 1, characterized in that said radial positional interference of said conical sealing surfaces (41, 42) is provided during joint make-up and by the mating of the reverse angle torque shoulders (43). 3. The joint of claim 1 or 2, characterized in that there are three radial steps (170, 180, 190) each axially separated from one another, at least one of said shoulders (43") between each step (170, 180, 190) providing said positive assembly stop. 4. The joint of claim 3, characterized in that each reverse angle torque shoulder (43") is between two ad¬ jacent conical sealing surfaces (40', 41', 42'). 5. The joint of claim 1, characterized in that the threads (70, 80) are angularly tapered with respect to the tubular axis. 6. The joint of claim 5, characterized in that the taper angle of the threads (70, 80) and the taper an¬ gle of the complementary conical sealing surfaces are the same. 7. The joint of claim 5, characterized in that said conical sealing surfaces (41, 42) are provided at a different taper angle from the taper angle of the threads (70, 80). 8. The joint of claim 1, characterized in that the respective angles of the negative load flanks and the reverse angle torque shoulder (44) are each less than thirty degrees and the taper angles of said conical sealing surfaces (41, 42) are less than fifteen degrees. 9. The joint of claim 1, characterized in that the threads (70, 80) of said female and male members (20, 30) when connected produce an interference fitting thread. 10. The joint of claim 1, characterized in that the taper angle of the conical sealing surface (42) of the member (20) having the thinner wall thickness at the seal surface is inclined at a smaller angle with respect to the axis of the threaded connection than the complementary conical seal surface (41) of the mating member (20) . 11. The joint of claim 10, characterized in that the member having the thinner wall thickness is the female member (20) whose sealing surface (42) is tapered with respect to the female member axis at a first angle, and the conical sealing surface (41) of the male member (30) is tapered with respect to the axis of the male mem¬ ber (30) at an angle greater than the taper angle of the female member (20) , and wherein initial mating of said male conical sealing surface (41) with the female coni¬ cal sealing surface (42) , develops a bearing load sub¬ stantially on the leading edge of the female sealing sur¬ face (42) with the CMPI trailing edge of the male sealing surface (41) and wherein the angle difference between the male sealing surface (41) and the female sealing surface (42) is selected such that the-bearing load across the- entire axial width of the seal of mating female conical sealing surface (42) and male coni¬ cal sealing surface (41) is a relatively even distribution at final make-up. 12. The joint of claim 11, characterized by a second adjacent conical seal between the lower step (80) and the reverse angle torque shoulder (43) where the second conical sealing surface (42) of the female member (30) is tapered with respect to the female axis at an angle and the second conical sealing surface (41) of the male member (30) is tapered with respect to the axis of the male member (30) at an angle less than the taper angle of the female mem¬ ber (20) , and wherein initial mating of the second male conical sealing surface (41) with the second female conical sealing surface (42) , the bearing load is substantially on the leading edge of the second male sealing surface (41) with the trailing edge of the second female sealing surface (42) , and wherein the angle difference between the second male sealing surface (41) and the second female sealing surface (42) is selected such that the bearing load across the entire axial width of the seal of mating second female conical sealing surface (42) and second male conical seal¬ ing (41) surface is a relatively even distribution at final make-up. 13. The joint of claim 10, characterized in that the member having the thinner wall thickness is the female member (20) whose sealing surface (42) is tapered with re¬ spect to the female member axis at a first angle, and the conical sealing surface (41) of the male member (30) is tapered with respect to the axis of the male member (30) at an angle less than the taper angle of the female member (20) , and wherein initial mating of the male conical seal- OMPI ing surface (41) with the female conical sealing surface (42) develops a bearing load substantially on the leading edge of said male sealing surface (41) with the trailing edge of the female sealing surface (42) and wherein the angle difference between the male sealing surface (41) and the female sealing surface (42) is selected such that the bearing load across the entire axial width of the seal of mating female conical sealing surface (42) and male conical sealing surface (41) is a relatively even distri¬ bution at final make-up. 14. A male tubular member (30) adapted for use for coaxial threaded interconnection with an associated female tubular member (20) , the female tubular member (20) having internal threads (80) with negative angle load flanks (44) and at least two radial steps axially separated from one another by a reverse angle torque shoulder (43) having at least one adjacent conical sealing surface (41, 42) , said male member characterized by: external threads (70) with negative angle load flanks (44) and at least two radial steps axially separated from one another by a reverse angle torque shoulder (43) having at least one adjacent conical sealing surface (41) for mating with said female sealing surface (42) , said male torque shoulder (44) when mated with said female torque shoulder (44) defining a posi¬ tive assembly stop, said male conical sealing surface (41) when mated with said female conical sealing surface (42) providing radial positional interference when the male and female members (20, 30) are assembled, the male negative angle load flank (44) and the male torque shoulder (43) being selected to mate with the female negative angle load flank (44) and the female torque shoulder (43) to interlock the male and female members (20, 30) and to prevent dif¬ ferential radial separation of the engaged conical sealing surfaces (41, 42) when the mated threads are exposed to in¬ ternal pressure, external pressures or both. 15. The male tubular member of claim 14, char¬ acterized in that the male or female member (20,. 30) having the thinner wall thickness at the seal surface is inclined at a smaller taper angle with respect to the axis of the threaded connection than the complementary conical seal surface of the mating member, and wherein initial mating of each of the male conical sealing surfaces (41) with the corresponding female conical sealing surface (42), the bearing load is substantially on the leading edge of the sealing surface of the member (20, 30) having the thinner wall thickness with the trailing edge of the sealing sur¬ face of the member (20, 30) having the thicker wall thickness, and wherein the angle difference between said male seal¬ ing surface (41) and said female sealing surface (42) is selected such that bearing load across the entire axial width of the seal of mating female conical sealing surface (42) and male conical sealing surface (41) has a relatively even distribution at final make-up. 16. The male tubular member of claim 14 or 15, characterized in that there are three radial steps (170, 130, 190) axially separated from one another at least one of said male torque shoulders (44) when mated with a corres¬ ponding female torque shoulder (44) providing said positive assembly stop. 17. A female tubular member (20) adapted for use for coaxial threaded interconnection with a male tubular member (30) , the male tubular member (30) having external threads (70) with negative angle load flanks (44) and two radial steps axially separated from one another by a re¬ verse angle torque shoulder (43) having at least one ad¬ jacent conical sealing surface (41) , said female tubular member (20 characterized by: internal threads (80) with negative angle load flanks (44) and at least two radial steps axially separated from one another by a conical seal¬ ing surface (42) and including a reverse angle torque shoulder (43) for mating with said male sealing surface (41) said female torque shoulder (43) when mated with said male torque shoulder (43) defining a positive assembly stop, said female conical sealing surface (42) when mated with said male conical sealing surface (41) providing radial positional interference when the male and female members (20, 30) are fully assembled, the female negative angle load flank (43) and the female torque shoulder (44) being ' selected to mate with the male negative angle load flank (43) and the male torque shoulder (44) to interlock the female and male members (20, 30) and to prevent differential radial separation of the engaged conical sealing surfaces (41, 42) when the mated threads (70, 80) are exposed to internal pressure, external pressure or both. 18. The female tubular member of claim 17, char¬ acterized in that there are three radial steps (170, 180, 190) axially separated from one another at least one said female torque shoulder (44) when mated with a corres¬ ponding male torque shoulder (44) providing said positive assembly stop. 19. The female tubular member of claim 17 or 18, characterized in that the male or female member (20, 30) having the thinner wall thickness at the seal surface is inclined at a smaller taper angle with respect to the axis of the threaded connection that the complementary conical seal surface of the mating member, and wherein initial mating of each of the female conical sealing surfaces (42) with the corresponding male conical sealing surface (41) , the bearing load is substantially on the leading .edge of the sealing surface of the member (20, 30), having the thinner wall thickness with the trailing edge of the seal¬ ing surface of the member (20, 30) having the thicker wall thickness, and wherein the angle difference between said female sealing surface (42) and said male sealing surface (41) is selected such that the bearing load across the en¬ tire axial width of the seal of mating female conical sealing / > W1PO surface (42) and the male conical sealing surface (41) has a relatively even distribution at final make-up. 20. The tubular member of claim 14 or 17, characterized in that each reverse angle torque shoulder (44) is between two adjacent conical sealing surfaces (41, 42) and the external threads (70) are adapted to convert with the internal threads (80) of the associated tubular member to produce an interference fit connections, 21. The tubular member of claim 14 or 17, characterized in that said threads (70, 80) are angular¬ ly tapered with respect to the tubular member (20, 30) longitudinal axis and are adapted to interconnect with said associated tubular member threads of the same taper angl . 22. The tubular member of claim 14 or 17, characterized in that the conical sealing surface (41, 42) is at a taper angle equal to the taper angle of said threads (70, 80) . 23. The tubular member of claim 14 or 19, characterized in that the negative angle of the load flank and the angle of the reverse angle torque shoulder (43) is less than thirty degrees. OMPΪ

Inventors: BLOSE THOMAS L, CHELETTE K DARREL, ORTLOFF DONALD J, REEVES DOYLE E, BLOSE, THOMAS, L., CHELETTE, K., DARREL, ORTLOFF, DONALD, J., REEVES, DOYLE, E.
Applicants: HYDRIL CO, HYDRIL COMPANY
Application year: 1984
Main classification: E21B17
IPC codes: E21B17, F16L15