Patent EA-003718-B1 (EA)
Title: Threaded tubular element for fatigue resistant threaded tubular joint and resulting threaded joint
Inventor: VERDILLON LIONEL
IPC: F16L15/00
Filed: 2001-03-26
Abstract: 1. A male or female threaded tubular element (1, 2) for a threaded tubular connection (100, 300) formed at the end of a pipe (101, 102, 202, 301, 302) and comprising an external male threading (3, 303, 303') or an internal female threading (4, 304, 304') depending on whether the threaded element is male or female in type, the threads of which (11, 12), viewed in longitudinal cross section passing through the axis of the threaded element, comprise a thread crest (17, 20, S1, S2), a thread root (18, 19, F1, F2), a rectilinear load flank (13, 14), a rectilinear stabbing flank (15, 16) and two tangential thread root junction zones (21, 22, 51, 52) each of these two zones being disposed between the thread root and one of the two flanks termed the corresponding flank and comprising an arc of a circle, characterized in that at least one of the two tangential thread root junction zones termed the "multiple radius zone" comprises an arc of a circle termed the principal arc (23, 24, 53, 54) where the support circle cuts the support straight line of the corresponding flank at a point termed the flank reference point (PRF1, PRF2, PRF3, PRF4), and a regular curve termed the secondary curve (25, 26, 27, 55, 56) either side of the principal arc, which tangentially joins this to the corresponding flank on one side and to the thread root on the other and in that: a) at the flank reference point, the tangent (61, 62, 67, 68) of the support circle of the principal arc makes an acute angle (D, F) which is strictly positive with the support straight line of the corresponding flank, the positive sense being such that the principal arc does not cut into the material of the thread flank; b) said support circle of the principal arc cuts or is tangential to the support straight line of the thread root, the tangent to said support circle (63) making, at the intersection point (PRR1 or at the tangent point under consideration, an angle (E) in the range -15[deg.] to +15[deg.] with the support straight line of the thread root. 2. A threaded tubular element according to claim 1, characterized in that at the flank reference point of the multiple radius zone under consideration, the angle (D, F) between the tangent to the support circle of the principal arc and the corresponding flank is comprised between 10[deg.] and the difference (70[deg.]-J) if J is the algebraic angle (A, B) between the corresponding flank and a normal to the axis of the threaded element. 3. A threaded tubular element according to claim 2, characterized in that at the flank reference point of the multiple radius zone under consideration, the angle (D, F) between the tangent to the support circle of the principal arc and the corresponding flank is comprised between 15 degree and the difference (45 degree -J) if J is the algebraic angle (A, B) between the corresponding flank and a normal to the axis of the threaded element. 4. A threaded tubular element according to any one of claims 1 to 3, characterized in that the radius (rP1, rP2) of the principal arc (23, 24) of the multiple radius zone is comprised between 150% and 250% of that (rH1, rH2) of the standard arc (29, 30) passing through the flank reference point which would alone constitute a tangential junction zone between the corresponding flank and the thread root. 5. A threaded tubular element according to any one of claims 1 to 4, characterized in that each secondary curve (25, 26, 27, 55, 56) of the multiple radius zone is an arc of a circle. 6. A threaded tubular element according to claim 5, characterized in that the ratio of the radius (rS1, rS2, rS3, rS4, rT1) of the arc of each secondary curve (25, 26, 27, 55, 56) to that (rP1, rP2, rP3, rP4) of the principal arc of a multiple radius zone is in the range 0.1 to 0.4. 7. A threaded tubular element according to any one of claims 1 to 6, characterized in that only the tangential junction zone of the thread root with the load flank (21, 22) is a multiple radius zone. 8. A threaded tubular element according to any one of claims 1 to 6, characterized in that each of the two tangential junction zones of the thread root is a multiple radius zone. 9. A threaded tubular element according to claim 8, characterized in that the radius (rP1, rP2) of the principal arc (23, 24) of the multiple radius zone on the load flank side is greater than or equal to that (rP3, rP4) of the principal arc (53, 54) of the multiple radius zone on the stabbing flank side. 10. A threaded tubular element according to any one of claims 1 to 9, characterized in that the angle (A, B) which each of the flanks makes with the normal to the axis of the threaded element is positive or zero. 11. A threaded tubular connection (100, 300) with a high resistance to static and dynamic stresses, comprising a male threaded tubular element (1) at the end of a first pipe (101, 301) connected by screwing to a female threaded tubular element (2) at the end of a second pipe (102, 302) by means of a male threading (3, 303, 303') on the male threaded tubular element and a female threading (4, 304, 304') on the female threaded tubular element, the threads (11, 12) of each of the male and female threadings comprising a thread crest (17, 20, S1, S2), a thread root (18, 19, F1, F2), a rectilinear load flank (13, 14), a rectilinear stabbing flank (15, 16) and four junction zones each comprising a circle of an arc, two of these zones, the tangential thread root junction zones (21, 22, 51, 52), each joining the thread root to one flank and two zones, the thread crest junction zones (31, 32, 41, 42), each joining the thread crest to a flank, the profile and disposition of each thread crest junction zone being adapted so as not to interfere with the tangential thread root junction zone of the mated threaded element, characterized in that at least one of the two threaded tubular elements is a threaded element termed an anti-fatigue profile element according to any one of claims 1 to 10. 12. A threaded tubular connection according to claim 11, characterized in that at least one thread crest junction zone of a threaded tubular element opposite a tangential thread root junction zone with multiple radii of a mated threaded tubular element with an anti-fatigue profile is a zone termed follower zone (31, 32) which comprises two arcs of a circle which join tangentially to each other, namely a principal arc (33, 34) and a secondary arc (35, 36), this latter to produce the tangential thread crest junction of the corresponding flank and in that at the point termed the high junction point (PRH1, PRH2) of the corresponding flank where the support circle of the principal arc of the follower zone cuts the support straight line of the corresponding flank, the tangent to said circle makes an acute angle (G, H) which is strictly negative with the support straight line of the flank under consideration. 13. A threaded tubular connection according to claim 11 or 12, characterized in that the two male and female elements of the threaded tubular connection are of the type defined in any one of claims 1 to 10. 14. A threaded tubular connection according to any one of claims 11 to 13, characterized in that the threadings are interference threadings, the thread crest (20) of one threading (4) radially interfering with the thread root (19) of the mated threading (3). 15. A threaded tubular connection according to any one of claims 11 to 13, characterized in that the two thread flanks (13, 15) of one threading (3) are in contact with or without contact pressure with the two thread flanks (14, 16) of the mated threading (4) over at least a portion of the length of the threadings (3, 4).