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A coaxial pipe element (1) includes an outer pipe (1a) and an inner pipe (1b), and at each of its ends a junction forging (2a, 2b), each forging having at least an inner first branch (32) set back (L1) from an outer first branch (31), in which all of the circular welds between the inner and the oute

A coaxial pipe element (1) includes an outer pipe (1a) and an inner pipe (1b), and at each of its ends a junction forging (2a, 2b), each forging having at least an inner first branch (32) set back (L1) from an outer first branch (31), in which all of the circular welds between the inner and the outer pipe and the junction forgings are made on the outside of the pipes.

대표청구항 ▼

1. A coaxial pipe element comprising: an inner pipe;an outer pipe spaced from said inner pipe, thereby forming an annular space therebetween; anda sealed closure positioned at each end of said inner and outer pipes and annular space, each said sealed closure being constituted by a junction forging i

1. A coaxial pipe element comprising: an inner pipe;an outer pipe spaced from said inner pipe, thereby forming an annular space therebetween; anda sealed closure positioned at each end of said inner and outer pipes and annular space, each said sealed closure being constituted by a junction forging in the form of a body of revolution, each of said junction forgings being constituted as a single integral block for joining with another coaxial pipe element,each of said junction forgings comprising at least two first branches of revolution, in which an inner first branch of revolution is welded directly to one end of said inner pipe with a circular weld bead and an outer first branch is welded directly to the end of said outer pipe with a circular weld bead,said inner first branches of revolution being longer than said outer first branches by a length L, in the axial longitudinal direction of said coaxial pipe element,each of said junction forgings at each end of said pipe element being designed to be assembled at one end to the ends of said outer and inner pipes of said coaxial pipe element, and at an opposite end directly to another said junction forging, itself assembled by welding to the end of another or second unit comprising two coaxial pipes,wherein, all of said circular weld beads are located on the outside of the inner and outer pipes, andwherein each respective end of the outer pipe is connected to the respective sealed closure by a single weld and there are no intervening welds on the outer pipe. 2. The coaxial pipe element according to claim 1, wherein said inner pipe is subjected to traction stress exerted by each of said junction forging at each end when said coaxial pipe element is not in service. 3. The coaxial pipe element according to claim 2, wherein when said coaxial pipe element is not in service, said inner pipe is subjected to traction stress that is less than about 90% of the elastic limit of the steel constituting said inner pipe. 4. The coaxial pipe element of claim 3, wherein said inner pipe is subjected to traction stress that is in the range of from about 5% to about 75% of the elastic limit of the steel constituting said inner pipe. 5. The coaxial pipe element according to claim 1, wherein said pipe element is designed for use in assembling steel undersea pipes, and presents a length lying in the range of from about 10 m to about 100 m. 6. The coaxial pipe element according to claim 1, wherein, at their one ends, said inner and outer first branches of said junction forgings are respectively of substantially the same thicknesses as said inner and outer pipes. 7. The coaxial pipe element according to claim 1, wherein said pipe element includes at each end a said forging defined as follows: in a radial direction relative to a longitudinal axis XX′ of revolution of said forging, it is defined by a cylindrical inner wall having substantially the same diameter as the main portion of said inner pipe, and by a cylindrical outer wall of diameter substantially equal to the outer diameter of the main portion of said outer pipe; andin the longitudinal axial direction XX′,at the end of said junction forging that is assembled by welding to the ends of said outer and inner pipes, said outer and inner walls of said junction forging form, in longitudinal section, respective outer and inner first branches that are substantially of the same thicknesses as said outer and inner pipes to which they are assembled, said outer and inner first branches defining a first annular cavity; andthe opposite end of said junction forging that is to be assembled to another said junction forging said outer and inner walls forming, in longitudinal section, respective outer and inner second branches defining a second annular cavity;the ends of said first and second cavities being spaced apart in said longitudinal direction XX′ so as to define a solid zone of said junction forging in which said outer and inner walls form the outer and inner faces of a single cylindrical wall. 8. The coaxial pipe element according to claim 1, wherein said pipe element includes at each end a said forging defined as follows: in a radial direction relative to a longitudinal axis XX′ of revolution of said forging, it is defined by a cylindrical inner wall having substantially the same diameter as the main portion of said inner pipe, and by a cylindrical outer wall of diameter substantially equal to the outer diameter of the main portion of said outer pipe; andin the longitudinal axial direction XX′,at the end of said junction forging that is assembled by welding to the ends of said outer and inner pipes, said outer and inner walls of said junction forging form, in longitudinal section, respective outer and inner first branches that are substantially of the same thicknesses as said outer and inner pipes to which they are assembled, said outer and inner first branches defining a first annular cavity; andthe opposite end of said junction forging that is to be assembled to another said junction forging, said outer and inner walls forming, in longitudinal section, respective outer and inner second branches defining a second annular cavity;the ends of said first and second cavities being spaced apart in said longitudinal direction XX′ so as to define a solid zone of said junction forging in which said outer and inner walls form the outer and inner faces of a single cylindrical wall;the free end of said outer second branch presents a shape, making it suitable for being welded from outside the pipe to the free end of another said outer second branch of another junction forging to which it is to be assembled, said other junction forging itself being assembled to the end of the second unit; andthe free end of said inner second branch is of a shape enabling it to make contact in abutment against the free end of another said inner second branch of another said junction forging assembled to the end of a said second coaxial pipe assembly element, without being welded thereto; andthe free ends of said outer and inner second branches of a single junction forging coming to substantially the same level in said longitudinal direction; andsaid two outer second branches of said two junction forgings that are to be assembled together by welding having the same thickness. 9. The coaxial pipe element of claim 8, wherein each said shape is a chamfer. 10. The coaxial pipe element of claim 8, wherein the thickness of said welding is greater than the thickness of said inner second branch of said junction forging. 11. An assembly constituted by assembling together at least two coaxial pipe elements according to claim 8, a said junction forging assembled by welding to a junction forging of an other said coaxial pipe assembly element, each of said two junction forgings being welded to each other solely via the ends of outer second branches, the non-welded ends of two inner second branches coming into abutting contact against each other during assembly of said junction forgings, such that second inner cavities are not sealed from the inside of inner walls of the forgings and said inner pipes of the another said coaxial pipe element. 12. An assembly constituted by assembling together at least two coaxial pipe elements according to claim 1, a said junction forging of one coaxial pipe element assembled by welding to a junction forging of the other said coaxial pipe element. 13. The coaxial pipe element according to claim 1, wherein the length of the pipe element is in the range of from about 20 m to about 50 m. 14. The coaxial pipe element of claim 1, wherein said annular space is filled with an insulating material. 15. The coaxial pipe element according to claim 14, wherein the insulating material is one of a microporous or nanoporous material. 16. The coaxial pipe element according to claim 15, wherein the insulating material is an aerogel. 17. The coaxial pipe element according to claim 14, wherein the insulating material is in the form of grains having a diameter lying in the range of from about 0.5 mm to about 5 mm. 18. A method of fabricating the coaxial pipe element of claim 1, comprising the following successive steps: 1) welding the cylindrical end of said inner first branch of a first junction forging to a first end of said inner pipe that is not covered by the outer pipe, said welding being performed from the outside of said inner pipe;2) moving said outer pipe coaxially around said inner pipe so that a first end of said outer pipe makes end-to-end contact with the corresponding end of the outer first branch of said first junction forging, the second end of said inner pipe being set back from the corresponding second end of said outer pipe by a length L3 that is not less than L1; and3) welding the end of said outer first branch of said first junction forging to the end of said outer pipe, from the outside of said outer pipe;4) reversibly expanding along the axial longitudinal direction said second end of said inner pipe so that it projects by a length L2 from said corresponding second end of said outer pipe;5) from the outside of said inner pipe, while said inner pipe is in the expanded position, welding said second end of said inner pipe to the end of the inner first branch of a second said forging;6) resorbing at least part of the expansion of said inner pipe until said outer first branch of said second forging comes end-to-end with said second end of said outer pipe; and7) from the outside of said outer pipe, welding the end of said outer first branch of said second forging to said second end of said outer pipe,wherein each respective end of the outer pipe is connected to the respective junction forging by a single weld and there are no intervening welds on the outer pipe. 19. The method according to claim 18, wherein: in step 2), said second end of the outer pipe at its end for connection to said second forging is adjusted so as to project beyond said corresponding second end of the inner pipe by a length L3=L1+e; andin step 4), said inner pipe is expanded by a length L2 greater than or equal to L1+e, such that in step 6), part of said expansion is resorbed, and at the end of the welding in step 7), said inner pipe is subjected to traction corresponding to residual elongation less than or equal to e. 20. The method according to claim 18, wherein, in step 4), said inner pipe is expanded by being heated. 21. The method according to claim 18, wherein in step 4), said expansion is performed by applying mechanical traction to said inner pipe with the help of a traction device comprising a winch or an actuator placed outside said inner pipe. 22. The method according to claim 21, wherein, in step 4), said expansion is performed by applying longitudinal traction to said inner pipe and simultaneous longitudinal compression to said outer pipe via their said second ends. 23. The method according to claim 22, wherein said welding is performed with a device comprising a stationary welder head, and said pipe element is caused to rotate about the longitudinal axis of said pipe element. 24. The method according to claim 23, wherein said traction device comprises or co-operates with: means for blocking said inner pipe, thus enabling said inner pipe to be caused to move in longitudinal translation in expansion when the traction device is actuated, while allowing said inner pipe to rotate about the longitudinal axis of the inner pipe; andmeans for blocking said outer pipe, preventing any movement in longitudinal translation of said outer pipe, and allowing the outer pipe to rotate about the longitudinal axis of the outer pipe. 25. The method according to claim 24, wherein said traction device comprises or co-operates with at least one tie member constituted by a rigid rod or a cable, suitable for being moved in longitudinal translation by a winch or an actuator connected to a second blocking device for blocking said inner pipe by applying radial compression to the inner wall of said inner pipe. 26. The method according to claim 25, wherein said traction device comprises at least two actuators disposed substantially evenly about said stationary first peripheral body having pistons secured to rods that come into abutment against said stationary first peripheral body supporting said first bearing, said actuators being connected to said tie member via a second bearing, said second bearing being suitable for co-operating with a support secured to said tie member, such that by applying pressure to said actuators, the tie member exerts traction on the inner pipe while allowing said pipe element to rotate about the longitudinal axis of the pipe element, said first peripheral body and a second peripheral body and the rods of the actuators remaining stationary relative to the ground, thereby enabling the use of a stationary welder head. 27. The method according to claim 26, wherein said second bearing comprises a crossed roller bearing and the second peripheral body is stationary relative to the ground supporting said actuators. 28. The method according to claim 23, wherein said means for blocking the outer pipe comprise: a first device for blocking by radial compression that is disposed in stationary manner around said outer pipe; anda first peripheral body that is stationary relative to the ground, co-operating with said first blocking device via a first bearing allowing said outer pipe to rotate about the longitudinal axis of the outer pipe. 29. The method according to claim 28, wherein said first bearing comprises crossed roller bearings in and between an inner cage secured to a collar and an outer cage secured to said stationary first peripheral body. 30. The coaxial pipe element according to claim 1, wherein said pipe element includes at each end a said forging defined as follows: in a radial direction relative to a longitudinal axis XX′ of revolution of said forging, it is defined by a cylindrical inner wall having substantially the same diameter as the main portion of said inner pipe, and by a cylindrical outer wall of diameter substantially equal to the outer diameter of the main portion of said outer pipe; andin the longitudinal axial direction XX′,at the end of said junction forging that is assembled by welding to the ends of said outer and inner pipes, said outer and inner walls of said junction forging form, in longitudinal section, respective outer and inner first branches that are substantially of the same thicknesses as said outer and inner pipes to which they are assembled, said outer and inner first branches defining a first annular cavity;the opposite end of said junction forging that is to be assembled to another said junction forging, said outer and inner walls forming, in longitudinal section, respective outer and inner second branches defining a second annular cavity;the ends of said first and second cavities being spaced apart in said longitudinal direction XX′ so as to define a solid zone of said junction forging in which said outer and inner walls form the outer and inner faces of a single cylindrical wall; andthe free end of said outer second branch presents a chamfer shape making the free end suitable for being welded from outside the pipe to the free end of another said outer second branch of another junction forging to which it is to be assembled, said other junction forging itself being assembled to the end of the second unit. 31. An assembly constituted by assembling together at least two coaxial pipe elements according to claim 1, each junction forging assembled by welding to a junction forging of an other said coaxial pipe assembly element, each of said two junction forgings being welded to each other solely via the ends of outer second branches, the non-welded ends of two inner second branches coming into abutting contact against each other during assembly of said junction forgings, such that second inner cavities are not sealed from the inside of inner walls of the forgings and said inner pipes of the another said coaxial pipe elements.