Reinforced tubular joint for improved sealing-tightness after plastic expansion

Tubular joint according to one of the preceding claims, characterised in that the sealing surface of the lip and the opposite surface are cylindrical and are disposed with slight clearance from one another after screwing together and before diametric expansion.

Tubular joint according to one of the preceding claims, characterised in that each of the first and second tubular elements (11, 12) comprises a non-threaded lip (38, 5) extending between its thread and its free end and having a sealing surface (40, 7) capable of being in sealing-tight contact with the opposite surface (41, 8) of the other element after screwing together and diametric expansion, followed by generation of springback forces of the first and second tubular elements, and in that it comprises two tubular sleeves (34, 36) capable of being threaded on to the second element (12) before screwing together, of being positioned in order to extend axially substantially opposite to the lips (38, 5) respectively, and of generating a springback force which is added to that of the second element in order to counteract the spring back force of the first element, thus effecting at least the shrink-fitting of the tubular sleeve over the second element.

Tubular joint according to one of the preceding claims, characterised in that each tubular sleeve (34;

• 36) has an overlap length (lm2;
• lm1) roughly equal to the length of the lip opposite, optionally with the addition of at most 8 times the pitch of the threads.

Tubular joint according to one of the preceding claims, characterised in that the tubular sleeve (34) extending opposite to the lip (38) of the second element has a radial projection (42) capable of coming into contact with a radial surface (39) disposed at the end of the second element (12) and capable of facilitating the positioning of the tubular sleeve (34).

Tubular joint according to one of the preceding claims, characterised in that the tubular sleeve (34;

• 36) is held in position relative to the second element (12) by adhesion of at least part of the surfaces of the second element and of the sleeve opposite.

Tubular joint according to one of the preceding claims, characterised in that the tubular sleeve (34;

• 36) is positioned axially on the second element (12) by means of shrink-fitting at least by cooling of the second element (12).

Tubular joint according to one of the preceding claims, characterised in that the tubular sleeve (34;

• 36) is positioned axially on the second element (12) by means of shrink-fitting at least by heating of the tubular sleeve.

Tubular joint according to one of the preceding claims, characterised in that the second element (12) has a mark which is disposed on its external peripheral surface (37) and which is capable of facilitating positioning of the tubular sleeve.

Tubular joint according to one of the preceding claims, characterised in that the radial thickness of the tubular sleeve is at least equal to 1.5 mm.

Tubular joint according to one of the preceding claims, characterised in that the material of the tubular sleeve has a yield strength higher than the yield strength of the material of the first and second elements.

Tubular joint according to one of the preceding claims, characterised in that the yield strength of the material of the tubular sleeve is adjusted by heat treatment.

Method of forming a sealing-tight threaded tubular joint, characterised in that one starts off with a tubular threaded joint according to one of the preceding claims, known as an “initial tubular threaded joint”, and in that this initial threaded joint is subjected to diametric expansion in the sense of plastic deformation by means of an expansion ball (30) of a diameter greater than the inner diameter (DI) of the tubular elements, which is moved axially in the threaded joint in the region where each sleeve generates, after expansion, a springback force which is added to that of the second element in the region covered thereby.