Patent FR-2863030-A1 (FR)
Title: Tubular joint, e.g. for hydrocarbon casing, has lip extending male thread and curved seating on female threaded part, so that after plastic deformation by radial expansion, joint becomes sealed
Inventor: DUBEDOUT LAURENT
IPC: F16J15/04
Filed: 2003-11-28
Abstract: The second and third butting surfaces are respectively convex and concave, at the same angle to the longitudinal axis of the tube, so they press together to give a sealed radial grip between the first internal surface and second external surface. The first external surface and third internal surface are constrained to give a local sealed grip when radial expansion causes plastic deformation : A first tubular element (EM) has a first part with a male thread and a second part (P2) extending the first part and including a first annular lip (L1) with a first axially butting surface (SB1), a first internal surface and a first external surface, and a second butting surface (SB2). A second tubular element (EF) has a female thread matching the male thread and screwing onto it, a second annular lip (L2) with a third butting surface (SB3) pressing against the second butting surface, a second external surface placed opposite the first internal surface and a second internal surface, a fourth butting surface (SB4) and a third internal surface facing the female thread and defining with the second external surface and the fourth butting surface an annular seating (LO) for the first lip. The angles are initially between 5 and 30[deg]. The first and second lips are shaped so the first internal surface and the second external surface do not make a gripping contact until after the second and third butting surfaces. The first butting surface is designed to press against the fourth butting surface during tightening in a way which provokes axial compression of the first lip in elastic deformation. The second external surface of the second lip has an inclined annular portion at the level of contact with the third butting surface, at an angle of between 8 and 12[deg], preferably 10[deg]. The first internal surface of the first lip is inclined at an angle of between 0.1 and 15[deg]. The male and female threads have threads with a bearing flank with a negative angle of between -3 and -15[deg]. and an engaging flank with a positive angle of between +10 and +30[deg]. The threads are designed after screwing and before deformation to leave an axial play between their engaging flanks of between 0.1 and 0.3mm. The first tubular element has at the level of its first external surface and before its first part, a conical chamfer defining a local annular seat inwards. This chamfer has a continuous slope of between 8 and 12[deg]. A second part of the first tubular element has a local annular over- thickness at the level of a fourth internal surface extending the second butting surface in the direction of the first part, and a third internal surface with a groove in a selected place in which the local over- thickness will fit. At the level of the first external surface of the first lip, during radial expansion, an annular shoulder matching at least part of the groove is in gripping and sealing contact with the groove. The groove has two curvilinear portions with identical radii of curvature of between 2 and 20mm, separated by a cylindrical central part. An independent claim is made for a process to make the above joint by screwing the parts together and then expanding them radially using an axially displaced expansion tool.