Patent FR-2844330-A1 (FR)
Title: Production of high performance sealed tubular joint comprises internal expansion of male and female threaded tubes and axial displacement to give axial interference between two inclined shoulders
Inventor: VERGE ERIC
IPC: F16L15/06
Filed: 2002-01-03
Abstract: During the radial expansion, inclined shoulders formed in the outside peripheral surface of the male lip (43) turned away from the butting surfaces and the inside peripheral surface of the female seating (41) turned towards the butting surfaces, are subjected to a relative axial displacement to come into mutual contact with radial interference.  A male tube (1) with a male thread (3) and an annular lip (5) has a first axial butting surface at the free end of the first tube, and a female tube (2) with a female thread (4) matching the male thread has a seating matching the male lip with a second axial butting surface. The male thread is screwed into the female to bring the two butting surfaces into contact and the initial joint is subjected to a diametral expansion to cause plastic deformation using an expansion ball of greater diameter than the internal diameter of the tubes, moved axially in the joint. The peripheral surface of the seating has an annular groove with a concave arc profile and a flank turned axially towards the butting surfaces and a second flank turned axially away from the butting surfaces. The first inclined shoulder is defined by the first flank. The profile of the groove has a radius of curvature of 5-30 mm, preferably ca. 10 mm. The greatest radial height of the first and second flanks is 0.05-1 mm, preferably less than 0.5 mm. The first inclined shoulder of the lip and the seating are present in the initial tubular joint, axially opposite each other for at least part of their radial height. The part of the lip between the first inclined shoulder and the axial butting surface is at least partially pressed into the surface of the groove during expansion. The groove connects the side of the second axially butting surface to a first part of the peripheral wall and the opposite side to a second part of the peripheral wall of smaller diameter than the first part. The difference in diameter between the parts of the peripheral wall is less than or equal to 1 mm. Alternatively, the first inclined shoulder is formed by impressing at least part of it into the groove during expansion. The groove is adjacent to the second axially butting surface, with the second part of the peripheral having the same or greater diameter as the first part. The difference in diameter between the parts of the peripheral wall is less than or equal to 1 mm. The first part of the peripheral wall has a smaller diameter than the matching surface of the lip to produce an interference fit when they are screwed together. The first inclined shoulder of the lip and/or the seating are coated with a more ductile material than that of the substrate. The radial expansion of the joint is of the order of at least 10% and preferably 15%. A second inclined shoulder (42) is turned radially into the seating opposite to the first and forming a rounded rib with it. This shoulder has a greater radius of curvature than the first at the rib. The inclined shoulder of the male lip connects with a convex rounding in its external peripheral surface. The shoulders have an inclination of 5-20 degrees, preferably around 10 degrees relative to the longitudinal axis of the joint. The shoulders have a radial height of 0.2-1 mm, preferably ca. 0.5 mm. An Independent claim is also included for a tubular joint to carry out the above process.