Threaded joint for pipes provided with seal

1. Threaded joint, defining a longitudinal axis, comprising a first and a second pipe segment,

the first pipe segment defining a male member ( 1 ) of the joint,

the second pipe segment defining a female member ( 2 ) of the joint,

wherein the first pipe segment ( 1 ) is provided with at least one male thread at one end, and the second pipe segment ( 2 ) is provided with at least one female thread ( 7 ) adapted to be screwed to the male thread to constitute the joint,

wherein there are provided a first seal surface on the first segment ( 1 ) and a second seal surface ( 4 ) on the second segment ( 2 ) arranged between one end of the female thread and the nearest end of the second pipe segment,

the first and the second ( 4 ) seal surfaces having dimensions such as to generate a reciprocal interference by deformation of the material of the first and second segments of pipe, at least in the end of make up position, thus constituting a metal-metal type joint seal,

wherein there is provided a reinforcement section ( 5 ), positioned at the end of the second pipe segment which protrudes beyond the female thread ( 7 ) and having at all points an internal diameter larger than the external nominal diameter of the first pipe segment, the joint being characterised in that said reinforcement section ( 5 ) has a minimum axial length L minimum given by the following formula

L minimum =5(ln(wt) /OD 0.125 ),

in which OD is the nominal external diameter of first and second pipe segments and wt is the nominal thickness of the wall of first and second segments of pipe, such as not to generate any contact between the first and second pipe segments throughout the length of the reinforcement section ( 5 ).

2. Joint as claimed in claim 1 , wherein the reinforcement section ( 5 ) has a wall thickness T given by the following formula

0.1wt≦T≦0.3wt.

3. Joint as claimed in claim 2 , wherein the reinforcement section ( 5 ) has an axial length L given by the following formula

L< 20(ln(wt)// OD 0125 ).

4. Joint as claimed in claim 3 , wherein said axial length L is between approximately 6 and 26.5 mm.

5. Joint as claimed in claim 4 , wherein the distance between the starting point of the female thread ( 7 ) and the seal surface ( 4 ) is between 0.5 and 5 times the value of the thread pitch.

6. Joint as claimed in claim 5 , wherein there are provided on the first pipe segment ( 1 ) at least one first shoulder face ( 6 ′) and on the second pipe segment ( 2 ) at least one second shoulder face ( 6 ″) having a shape complementary to the first shoulder face, the first and second shoulder faces defining an end of the making up position of the threaded joint, wherein said first and second shoulder faces ( 6 ′, 6 ″) are arranged in an intermediate position to the male and female threads.

7. Joint as claimed in claim 5 , wherein there are provided on the first pipe segment ( 1 ) at least one first shoulder face ( 6 ′) and on the second pipe segment ( 2 ) at least one second shoulder face ( 6 ″) having a shape complementary to the first shoulder face, the first and second shoulder faces defining an end of screwing position of the threaded joint, in which said first and second shoulder faces ( 6 ′, 6 ″) are arranged at corresponding ends of the male and female threads.

8. Joint as claimed in claim 6 , wherein the joint threads have a tapered shape in a section plane passing through the axis of the joint.

9. Joint as claimed in claim 7 , wherein the joint threads have a tapered shape in a section plane passing through the axis of the joint.

10. Joint as claimed in claim 6 , wherein the joint threads have a cylindrical shape in a section plane passing through the axis of the joint.

11. Joint as claimed in claim 7 , wherein the joint threads have a cylindrical shape in a section plane passing through the axis of the joint.