Method for assembling tubular joining sleeve and a conduit lining tube by laser welding

Abstract

The present invention relates to a method and to a device for assembling together two tubes (1, 2) comprising a tubular junction sleeve and an internal pipe liner tube made of thermoplastic materials by laser welding two contact surfaces of revolution (1-1, 2-1) pressed one against the other at the ends of the tubular sleeve of said liner tube overlapping coaxially.

Claims

1. A method of assembling a sleeve to a liner comprising: providing a laser device configured to emit a laser beam having a wavelength; providing a sleeve comprising a thermoplastic material, wherein the sleeve a is transparent to the wavelength of the laser beam, and wherein the sleeve is tubular; providing a first steel pipe comprising: an inner surface and a first end; a first liner which covers a lined portion of the inner surface of the first steel pipe, wherein the first liner comprises a thermoplastic material, and wherein the first liner is absorbent to the wavelength of the laser beam; and an unlined portion adjacent the first end of the first steel pipe where the inner surface of the first steel pipe is not covered by the first liner, wherein a first end of the first liner is adjacent the unlined portion of the first steel pipe; providing a second steel pipe comprising: an inner surface and a second end; a second liner which covers a lined portion of the inner surface of the second steel pipe, wherein the second liner comprises a thermoplastic material, and wherein the second liner is absorbent to the wavelength of the laser beam; and an unlined portion adjacent the second end of the second steel pipe where the inner surface of the second steel pipe is not covered by the second liner, wherein a second end of the second liner is adjacent the unlined portion of the second steel pipe; inserting a first end of the sleeve into the first end of the first steel pipe such that the first end of the sleeve contacts the first end of the first liner and inserting a second end of the sleeve into the second end of the second steel pipe such that the second end of the sleeve contacts the second end of the second liner, wherein the inserting steps coaxially align the sleeve, the first steel pipe and the second steel pipe relative to a common longitudinal axis; applying pressure to an inner surface of the sleeve in a radial direction, wherein the pressure is applied at the first end of the sleeve; emitting the laser beam from the laser device; directing the laser beam toward the inner surface of the sleeve at the first end of the sleeve and rotating the laser beam about the common longitudinal axis through 360; wherein, during the step of directing the laser beam: the laser device is arranged inside the sleeve or the first liner; the step of applying pressure is simultaneously performed; the laser beam passes firstly through the first end of the sleeve in order to reach a zone of contact between the first end of the sleeve and the first end of the first liner; respective contacting surfaces of the first end of the sleeve and the first end of the first liner are pressed against each other; and the first end of the sleeve is fused to the first end of the first liner to form a first weld zone.

2. The method according to claim 1, wherein the first and second liners and the sleeve each have a thickness that is less than or equal to 5 mm.

3. The method according to claim 1, wherein: the first end of the first liner has a constant thickness and defines a cylindrical inner surface having a first diameter; the first end of the sleeve has a constant thickness and defines a cylindrical outer surface which has a diameter equal to the first diameter; in the step of inserting the first end of the sleeve into the first end of the first steel pipe, the first end of the sleeve is positioned in an overlapping manner with the first end of the first liner; and the respective contacting surfaces of the first end of the sleeve and the first end of the first liner comprise the cylindrical inner surface of the first end of first liner and the cylindrical outer surface of the first end of the sleeve.

4. The method according to claim 1, wherein: the first end of the first liner has a thickness which is smaller than a thickness of a main portion of the first liner and defines a concave portion of an inner surface of the first end of the first liner, the concave portion having an inner diameter that is greater than an inner diameter of the main portion of the first liner; the first end of the sleeve has a thickness which is smaller than a thickness of a main portion of the sleeve, the first end of the sleeve defining a convex portion suitable for overlapping and abutting against the concave portion of the first end of the first liner; in the step of inserting the first end of the sleeve into the first end of the first steel pipe, the concave portion of the first end of the first liner is positioned in an overlapping and abutting manner with the convex portion of the first end of the sleeve; and the respective contacting surfaces of the first end of the sleeve and the first end of the first liner comprise the concave portion of the first end of the first liner and the convex portion of the first end of the sleeve.

5. The method according to claim 1, wherein the first weld zone is a continuous weld zone having a helical shape or the first weld zone comprises a plurality of adjacent circular weld zones.

6. The method according to claim 1, wherein: the step of directing the laser beam toward the inner surface of the sleeve is performed by: directing the laser beam in a longitudinal direction parallel to the common longitudinal axis to a mirror in such a manner that a surface of the mirror reflects the laser beam toward the inner surface of the sleeve, the surface of the mirror being inclined at an angle of inclination relative to the common longitudinal axis, wherein the angle of inclination is from 30 to 60, and rotating the mirror through 360 about the common longitudinal axis.

7. The method according to claim 6, wherein the mirror is rotated at a speed of 10 revolutions per second to 1 revolution every 10 seconds.

8. The method according to claim 6, wherein during the step of directing the laser beam toward the inner surface of the sleeve the mirror is additionally moved in the longitudinal direction.

9. The method according to claim 8 wherein the steps of rotating the mirror and moving the mirror in the longitudinal direction are performed simultaneously such that the first weld zone is formed with a helical shape.

10. The method according to claim 6, wherein the angle of inclination is variable and is changed during the step of directing the laser beam toward the inner surface of the sleeve.

11. The method according to claim 10, wherein during the step of directing the laser beam toward the inner surface of the sleeve, the angle of inclination is changed after rotating the mirror about the common longitudinal axis through 360, such that the first weld zone is a circular weld zone, and successive steps of rotating the mirror through 360 about the common longitudinal axis and subsequently changing the angle of inclination are repeated in order to make a additional circular weld zones.

12. The method according to claim 1, wherein in the step of directing the laser beam toward the inner surface of the sleeve, the laser beam is directed perpendicular to the respective contacting surfaces, or is inclined at an angle of 0 to 30, relative to a perpendicular to the respective contacting surfaces.

13. The method according to claim 1, further comprising forming the first liner by performing steps of: positioning short lengths of transparent first tubes and long lengths of absorbent second tubes in an alternating manner such that each first tube meets an adjacent second tube at a respective annular contact plane, wherein each of the first and second tubes is positioned coaxially relative to a common first liner axis, positioning a laser head inside at least one of the first and second tubes, for each respective annular contact plane, emitting a laser beam from the laser head, the laser beam being inclined relative to the common first liner axis and being directed at a respective annular contact plane to form a fusion weld at the respective annular contact plane.

14. The method according to claim 12, wherein the respective contacting surfaces are cylindrical or frustoconical in shape.

15. The method according to claim 1, wherein the laser beam has an energy of 1 W/mm.sup.2 to 5 W/mm.sup.2.

16. The method according to claim 1, wherein further comprising: inspecting a quality of the first weld zone by directing an inspection laser beam onto the first weld zone using the laser device, and using a sensor to measure an amount of absorption by detecting light reflected from the first weld zone, the inspection laser beam having lower energy than the laser beam used to form the first weld zone, and the inspection laser beam having the same wavelength as the wavelength of the laser beam used to form the first weld zone.

17. A method of assembling pipes comprising: a) providing a sleeve comprising a thermoplastic material, wherein the sleeve is transparent to a wavelength of a laser beam, and wherein the sleeve is tubular; b) providing a first steel pipe comprising: an inner surface and a first end; a first liner which covers a lined portion of the inner surface of the first steel pipe, wherein the first liner comprises a thermoplastic material, and wherein the first liner is absorbent to the wavelength of the laser beam; and an unlined portion adjacent the first end of the first steel pipe where the inner surface of the first steel pipe is not covered by the first liner, wherein a first end of the first liner is adjacent the unlined portion of the first steel pipe; c) providing a second steel pipe comprising: an inner surface and a second end; a second liner which covers a lined portion of the inner surface of the second steel pipe, wherein the second liner comprises a thermoplastic material, and wherein the second liner is absorbent to the wavelength of the laser beam; and an unlined portion adjacent the second end of the second steel pipe where the inner surface of the second steel pipe is not covered by the second liner, wherein a second end of the second liner is adjacent the unlined portion of the second steel pipe; d) providing a welding device comprising: a mandrel comprising a central axis; an umbilical connected to the mandrel, the umbilical comprising optical fibers, electrical power supply circuits, and a compressed air feed circuit; a laser device configured to emit the laser beam, wherein the laser beam has the wavelength and the laser device is mounted to the mandrel; a mirror mounted to the mandrel wherein the mirror is mounted for rotation about the central axis and translation in a direction parallel to the central axis, and the mirror is mounted such that an angle of inclination between the mirror and the central axis can be changed; a first inflatable chamber comprising a first internal space and a first peripheral wall, wherein the first peripheral wall is transparent to the wavelength, the first peripheral wall is radially expandable by inflation of the first internal space, and the mirror is located within the first internal space; a second inflatable chamber comprising a second internal space and a second peripheral wall, wherein the second peripheral wall is radially expandable by inflation of the second internal space; e) inserting a first end of the sleeve into the first end of the first steel pipe such that the first end of the sleeve contacts the first end of the first liner and a second end of the sleeve protrudes from the first end of the first steel pipe; f) performing a first step of laser welding to weld the first end of the sleeve to the first end of the first liner; g) inserting the welding device into the sleeve such that the first inflatable chamber is arranged at the second end of the sleeve, and securing the welding device in place by inflating the second inflatable chamber against an inner surface of the sleeve; after or before performing step g) inserting and forcing the second end of the sleeve into the second end of the second steel pipe such that the second end of the sleeve contacts the second end of the second liner at respective contact surfaces; welding together the first end of the first steel pipe to the second end of the second steel pipe by metal welding around an outer surface of the first end of the first steel pipe and an outer surface of the second end of the second steel pipe; inflating the first inflatable chamber to apply pressure to the second end of the sleeve, emitting the laser beam from the laser device while simultaneously applying the pressure, and reflecting the laser beam with the mirror to direct the laser beam towards the second end of the sleeve and to create a weld zone by melting a portion of each of the respective contact surfaces of the second end of the sleeve and the second end of the second liner; inspecting a quality of the weld zone by directing an inspection laser beam onto the weld zone using the laser device and the mirror, and using a sensor to measure an amount of absorption by detecting light reflected from the weld zone; and deflating the first and second inflatable chambers and removing the welding device from the sleeve.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other characteristics and advantages of the present invention appear in the light of the following detailed description given with reference to the following figures.

(2) FIG. 1 is a side view in section of a pipe assembly of the invention using a tubular junction sleeve between two lined pipe elements or unit lengths of pipe of the invention and the liners having terminal portions that are frustoconical.

(3) FIG. 1A is a side view in section of the frustoconical end 2a of the internal liner 2 of a pipe element of FIG. 1, showing diagrammatically the traces of weld zones 3 on said frustoconical contact surface 2-1.

(4) FIG. 2 is a side view in section of the tubular junction sleeve presenting two ends of cylindrical type.

(5) FIG. 2A is a side view in section of a steel pipe 10 having an internal liner 2 machined to form a female cylinder of axis XX with an inside radius R.sub.1, and receiving a tubular sleeve as shown in FIG. 2 that is machined to form a male cylinder of axis XX and with an outside radius R.sub.1 that is substantially identical.

(6) FIG. 3 is a side view in section of a tubular junction sleeve presenting two front ends at right angles of the plane annular type.

(7) FIG. 3A is a side view in section of a steel pipe fitted with an internal liner machined on a plane perpendicular to the axis XX at a distance L2 from the end of said pipe, and receiving a tubular sleeve having the configuration of FIG. 3.

(8) FIG. 4 is a side view in section of a pipe assembly of the invention using a tubular junction sleeve between two lined pipe elements or unit lengths of pipe of the invention, with the sleeve and the liner having cylindrical terminal portions overlapping in superposed manner.

(9) FIG. 5 is a diagram showing an embodiment of said means for rotating R the mirror combined with the means for moving said mirror in relative translation in a device as shown in FIG. 4.

(10) FIG. 6A is a longitudinal section view through the junction between two tubes showing laser welding with a device 20 for performing an assembly method of the invention involving rotating an inclined mirror () about the longitudinal axis XX of said tubes, in combination with moving said mirror in relative translation along the axial direction XX.

(11) FIG. 6B is a longitudinal section view at the junction between two overlapping tubes contacting via frustoconical end contact surfaces and showing laser welding with a device 20 for performing an assembly method of the invention and involving rotating a mirror about the longitudinal axis XX of said tubes in combination with varying the angle of inclination of the surface 4a of the mirror with an angle of inclination that is variable.

(12) FIG. 7 shows a liner tube being made by assembling together end-to-end long lengths of absorbent liner tubes 2 and short lengths of transparent liner tubes 1.

(13) FIG. 8 shows details of the laser welding at the plane annular surfaces pressed end-to-end one against the other of said absorbent tubes and said transparent tubes.

(14) FIG. 9 is a diagram showing an embodiment in which a transparent sleeve tube 1 is placed inside an absorbent liner tube 2 of a pipe 10, showing diagrammatically a helical weld zone 3h between the transparent tube 1 and the absorbent tube 2, said laser welding being performed from inside the transparent tube 1.

(15) FIG. 10 is a side view of an installing ship fitted with a so-called J-lay tower.

(16) FIGS. 11 to 15 show various steps of putting into place and laser welding the sleeve 1 at one end of a pipe element by using a device of the present invention, as shown diagrammatically.

(17) FIGS. 16 to 22 show various steps of assembling together two pipe elements with the sleeve 1 at one end of a first pipe element being put into place and welded to the sleeveless end of a second pipe element by using a device of the present invention, as shown diagrammatically.

(18) FIGS. 23 and 24 show a device 20 for putting a sleeve into place and having two chambers that are suitable for performing laser welding.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

(19) FIG. 1A shows a pipe 10 of the invention having at least two pipe elements 10.sub.1, 10.sub.2 with internal liners 2 made of polyethylene or polypropylene, which elements are assembled together end-to-end, and the ends of two pipe elements are welded together at 11. Each pipe element has an internal liner 2 made of thermoplastic material having an axis XX coinciding substantially with the axis of the pipe elements 10.sub.1, 10.sub.2, and presenting at each end a conical terminal portion 2a having a half-angle at the apex lying in the range 5 to 15, and in particular about 10, and of thickness that is smaller than the thickness of the main portion 2b of said liner, defining a concave shape with a frustoconical inner surface of revolution having a contact surface 2-1 of inside diameter that is greater than the inside diameter of the main portion 2b of said liner and that terminates at a certain distance L from each end of said pipe elements. The outer surface of each said terminal portion 2a of the internal liner is possibly held in place by adhesive 2c between the end of the liner at or near said terminal portion 2a of reduced thickness of the liner and the corresponding inner surface of the steel wall of the pipe, which adhesive is preferably of the polyurethane type or of the two-component epoxy type.

(20) A tubular junction sleeve 1 made of thermoplastic material, preferably identical to the thermoplastic material of the internal liner 2, of axis XX coinciding substantially with the axis of the pipe elements 10.sub.1, 10.sub.2, and of the same outside diameter that is just slightly smaller than the inside diameter of the pipe, is inserted inside each of the abutting ends of the two pipe elements so as to overlap said terminal portions of the two liners, with this being done by means of a device 20 of the invention, as described below with reference to FIGS. 11 to 19.

(21) At each longitudinal end, said sleeve 1 presents a transparent terminal portion 1a of thickness that is smaller than the thickness of the adjacent main portion 1b of said sleeve, said terminal portion 1a of the sleeve defining a convex shape suitable for overlapping the opaque terminal portion of smaller thickness of said liner 2a with which it comes into contact. Said terminal portion 1a of the sleeve defines a frustoconical outer surface 1-1 of outside diameter smaller than the outside diameter of the adjacent main portion 1b of the sleeve and having the same angle at the apex as the frustoconical inner surface of said concave terminal portion of said liner. The terminal portions of conical shape of the sleeve define a cylindrical inner surface 1-2 having substantially the same inside diameter as the inside diameter of said main portion 2b of the liner and of said main portion 1b of the sleeve.

(22) In FIG. 1, in a central portion 1c, i.e. a portion about halfway along in the axial longitudinal direction XX, the sleeve presents a reduced outside diameter that is smaller than the outside diameter of its main portions 1b adjacent to said central portion 1c so as to leave an annular space 12 for receiving an annular thermal protection part 13 to protect the sleeve while the ends of the pipe elements are being welded together, said main portions 1b of the sleeve present an outside diameter that is substantially identical to the inside diameter of the ends of said assembled-together pipe elements that are not covered by said liners.

(23) The tubular wall of said sleeve presents a thickness that is substantially constant in its central portion 1c and in its adjacent main portions 1b, which thickness is substantially equal to the thickness of the main portion 2b of said internal liners 2, and said central portion 1c of the sleeve is suitable for deforming to adopt an inside diameter that is substantially identical to the inside diameter of the remainder of the sleeve under the effect of the internal pressure of a fluid flowing inside the pipe in operation, which pressure is at least 1 megapascal (MPa), and the thermal protection part 13 is itself likewise deformable under the same internal pressure conditions inside the pipe so as to adopt a smaller thickness, preferably a thickness of less than 5 mm, more preferably of less than 2 mm, said thermal protection part more preferably being constituted by ceramic fibers in a form similar to cotton wool.

(24) It can be understood that: because of its substantially constant thickness, the central portion of the sleeve presents a reduction of outside diameter and of inside diameter while it is being laid, the pipe being empty and at atmospheric pressure, and so long as it is subjected to pressures corresponding to pressure values of less than 1 MPa (10 bars); and as soon as the internal pressure exceeds 1 MPa (10 bars), the thickness, in particular of about 3 mm to 10 mm, and the stiffness of the plastics material such as polyethylene or polypropylene allow the inside and outside diameters of the central portion to increase as a result of deformation, e.g. when a fluid flows inside the pipe and the sleeve, in particular water under pressure, as applies to water-injection pipes for oil wells at pressures greater than 5 MPa, and in particular at pressures in the range 25 MPa to 70 MPa.

(25) Because the outside pressure P.sub.0 is much smaller than the inside pressure Pmax, the inside pressure has the effect of pressing the constricted central portion 1c of the tubular junction sleeve 1 hard against the wall of the steel pipe, with the ceramic fiber screen 13 also being flattened so as to present a residual thickness of no more than 1 mm to 2 mm.

(26) It is possible to use a laser device of the kind fabricated and sold by the supplier Trumpf (France).

(27) FIG. 1A shows diagrammatically a plurality of traces 3 of laser weld zones that may correspond to a plurality of circular weld zones arranged side by side in discontinuous and parallel manner when the mirror 4 is moved step by step in relative translation as described below, or that may correspond to a continuous weld zone of spiral shape in a spiral of increasing diameter.

(28) In FIGS. 2 and 2A, said inner surface of the terminal portion 2a of reduced thickness of the liner and said outer surface of the terminal portion 1a of reduced thickness of the sleeve, which are in contact with each other, present the same cylindrical shape about the same axis XX as said sleeve and said pipe, the end of the terminal portion of reduced thickness of the sleeve coming into abutment against a shoulder 2e defining the inner surfaces of said main portion 2b and of said terminal portion of reduced thickness 2a of the liner.

(29) In FIG. 2A, the internal liner has been subjected to machining to obtain a cylindrical shape of axis XX and of radius R over a length L.sub.3 and at a distance L.sub.4 from the end of said pipe.

(30) In this embodiment having a cylindrical contact surface, said sleeve is inserted against the terminal portion 2a of reduced thickness of the liner until the end 2f of the liner comes into abutment against a shoulder 1e defining said main portion 1b of the sleeve and said terminal portion 1a of smaller thickness of the sleeve, and/or said sleeve is inserted against the terminal portion 2a of reduced thickness of the liner until the end 1f of the sleeve comes into abutment against the shoulder 2e defining the main portion 2b and said terminal portion 2a of reduced thickness of the liner.

(31) As described in WO 2006/042925, the terminal portions of the liner are made at the end of the insertion process involving swagelining and possibly also adhesive, the liner then being cut flush with the steel pipe element, after which it is machined by a machine tool installed on the face of the first end of the pipe element.

(32) FIG. 3A shows machining to obtain a plane face perpendicular to the axis XX and situated at a distance L.sub.2 from the end of said pipe.

(33) The internal liners and the tubular junction sleeves may be assembled together in various ways, each presenting an advantage relative to the thickness of the internal liner 2. The value of the angle between the axis XX and the generator line of the surface of the terminal portion 1a of the sleeve in contact with the terminal portion 2a of the liner may lie in the range 0 to 90. For the embodiments of FIGS. 2 and 3, showing a terminal portion 1a of conical convex shape, the conical outer surface presents a half-angle at the apex lying in the range 0 to 90, the apex of the cone being on the left of the figure.

(34) In FIG. 3, there is shown a frontal shape: i.e. a shape that is equivalent to the conical shape, but in which the angle is 90.

(35) FIG. 2 shows a cylindrical shape: i.e. a shape equivalent to the conical shape in which the angle at the apex is 0, the apex of the notional cone then being located at infinity.

(36) For liners of small thickness, e.g. lying in the range 3 mm to 5 mm, it is advantageous to use the conical embodiment of FIGS. 1 and 1A with an angle lying in the range 5 to 45, and preferably being equal to 10. For medium thicknesses, e.g. in the range 6 mm to 12 mm, it is advantageous to use the cylindrical embodiment of FIG. 2. For large thicknesses, e.g. in the range 12 mm to 20 mm, it is advantageous to use the frontal embodiment with a section at right angles as shown in FIG. 3.

(37) When prefabrication is performed in a workshop, operating conditions are much simpler than on site, and the hourly cost of a pipe-laying ship is not involved. It can thus be appropriate to prepare tubular junction sleeves and pipe strings using assembly technologies that are different from those used on site. For this purpose, FIG. 3A shows a tubular junction sleeve of mixed type, possessing on the right an end of frontal type that is assembled in a workshop to the corresponding frontal end of an internal liner of the string, as shown with reference to FIG. 3A.

(38) FIG. 1 shows only a portion of the means of a device of the invention for assembly by laser welding comprising a laser device 3d arranged outside the tubes 1, 2 and connected by an umbilical 3c to a laser head 3b that is supported by an assembly device 20 (not shown). Said laser head 3b emits a laser beam 3a-1 along the axis XX, which beam is deflected by reflection on the surface 4a of the mirror 4 that is inclined at an angle of 45 relative to the axial direction XX. The beam 3a-2 reflects on the surface 4a and reaches the sloping frustoconical contact surfaces 1-1 and 2-1 with said beam being inclined at an angle .sub.2 of 90 a relative to said surfaces 1-1 and 2-1 (and by an angle .sub.1= relative to the perpendicular to said contact surfaces 1-1 and 2-1).

(39) An inspection laser beam 3a-3 reflected on the weld zone is analyzed by a receiver 3r comprising a sensor suitable for measuring the power that is absorbed so as to verify the quality of the weld when, as explained above, the beam delivered 3a-1, 3a-2 is a weld inspection laser beam of lower energy than the welding laser beam.

(40) FIG. 5 shows a portion of a device 20 of the invention for laser beam assembly, the device comprising a mandrel 20a arranged on the same longitudinal axis XX as the axis of the tubes 1 and 2 inside which it is inserted, the mandrel 20a supporting an axially arranged laser head 3b emitting a laser beam 3a-1 in the longitudinal direction XX. The mandrel 20a supports a first inflatable chamber 21 at the front, which chamber is made up of two stationary segments 21-b arranged transversely relative to the longitudinal axis XX of said first chamber and said tubes, the segments being spaced apart from each other in the direction XX, and being connected together by a transparent flexible sheet 21a made of silicone. Inside the chamber 21 there is a mirror 4 having its reflecting surface 4a inclined at an angle of about 45 so that the laser beam 3a-1 is deflected through 90 in the transverse direction. The beam 3a-2 reflected on the mirror reaches a point of incidence 3i on the frustoconical contact surface 2-1 of the chamfered end 2a of reduced thickness of the absorbent tube 2, after passing through the end 1a of reduced thickness of the transparent tube 1. The fusion heat of the contact surface 2-1 is transmitted by thermal conduction to the contact surface 1-1 in localized manner at the contact interfaces with the points 3i where the beam 3-2 impacts on the contact surface 2-1.

(41) FIG. 4 shows an embodiment in which the internal liner and the sleeve are of small thickness not exceeding 5 mm, with terminal portions that are not machined and that have the same thickness as the adjacent main portions of the liner and of the sleeve respectively. The terminal portions of the internal liner and of the sleeve are superposed without abutting one against another, giving rise to cylindrical contact surfaces 1-1 and 2-1 that are united by a continuous cylindrical weld zone 3.

(42) FIG. 6A is a diagram showing means for moving the mirror in relative translation T inside the stationary chamber 21. The chamber 21 is held in place by inflation and applying pressure against the cylindrical inner surface 1-2 of the tube 1 at the end portion 1a of reduced thickness. Moving the mirror in translation T makes it possible to move the point of incidence 3i of the beam 3a-1 to points 3i-1 to 3i-3 that are spaced apart so as to create the weld zone 3 at the frustoconical contact surfaces 2-1 and 1-1, as shown in FIG. 5.

(43) FIG. 5 shows in greater detail but diagrammatically the means for rotating R the mirror 4 relative to the longitudinal axis XX of the tubes and the means for moving the mirror in translation T relative to the device 20, which means are included in the transparent inflation chamber 21 (not shown in FIG. 5). The mandrel 20a supports a motor 20b that drives rotation of a gear system driving the rotation R of the mirror 4 about the longitudinal axis XX. More precisely, the motor 20b drives rotation of the gearwheel 20c, which drives rotation of a toothed wheel 19a relative to the same longitudinal axis XX and secured to a rotary structure 19 containing said mirror and thus enabling said mirror to be rotated about the axis XX by having a ball-bearing system 19c.

(44) In FIG. 5, it can be seen that the mandrel 20a may support the laser head 3b, or else it may support the laser device 3d directly.

(45) Furthermore, FIG. 5 shows an embodiment in which the rotation R of the mirror 4 relative to the longitudinal axis XX of said tubes is combined with continuous relative movement in translation T in a longitudinal direction by using a wormscrew 18 that operates as follows. The toothed wheel 19a drives a second toothed wheel 19b in rotation about the same longitudinal axis XX, which second toothed wheel 19b co-operates with a gearwheel 18b that drives rotation of the wormscrew 18 about a longitudinal axis X.sub.1X.sub.1 via a longitudinal shaft 18a. The wormscrew 18 co-operates with a mirror support 4b such that rotation of the wormscrew 18 about its axis X.sub.1X.sub.1 leads to relative movement in translation of the support 4b of the mirror 4. The mirror 4 is thus moved in translation by the wormscrew 18, which is constrained to rotate with the rotation R, e.g. at a rate of 3 millimeters per revolution, where one revolution corresponds to one pitch step of the screw of a helical weld zone 3h as obtained in this way. It can be understood that the gearwheel 18b and the wormscrew 18 form part of the rotary structure driven in rotation about the axis XX together with the support 4b and the mirror 4.

(46) In an alternative embodiment (not shown), instead of a wormscrew 18, it is possible to use a stepper system for movement in relative translation in contrast to a continuous system, such that rotation of the gearwheel 18b leads to discontinuous movement and thus makes it possible to obtain parallel circular weld zones that are arranged side by side and spaced apart by a translation stepsize in the longitudinal direction XX instead of a continuous weld zone in the form of a spiral or helix. Using movement in translation that is continuous, or that is in steps with a movement in translation steps of size corresponding to the width of the weld zone created by the width of the beam, makes it possible to obtain a weld zone 3 that extends over a continuous surface of revolution along the longitudinal direction of the movement in translation, as shown in FIG. 4.

(47) FIG. 6B shows an embodiment in which, instead of relative movement in translation T of the mirror 4 inside the inflation chamber 21, the angle of inclination of the surface 4a of the mirror 4 is varied so that the reflected beam 3a-2 as deflected by the surface 4a of the mirror reaches the contacting surfaces 1-1 and 2-1 at an angle of inclination .sub.1 lying in the range 0 to 30 relative to the perpendicular to said contact surfaces 1-1 and 2-1. The point of incidence 3i-1 corresponds to an angle of incidence .sub.1 of 0, the point 3i-2 to an angle of incidence .sub.1 of 10, and the point 3i-3 to an angle of incidence .sub.1 of 30. The means for varying the angle of inclination of the mirror 4a may be constrained to move with the rotation R of the mirror about the axis XX by equivalent means involving a gearing system and a wormscrew 18. For example, a wormscrew 18 may be used that meshes on an angle takeoff gear system with an outlet gearwheel of axis perpendicular to the axis of the wormscrew 18 and co-operating with a gearwheel of the mirror support driving the angle of inclination of the mirror as a result of the rotation of the mirror about the longitudinal axis XX of said tube. The wormscrew 18 may be driven in rotation in the same manner as in the embodiment of FIG. 5. By way of example, the angle of the surface 4a of the mirror relative to the axis XX may be caused to vary through 5, said variation in the angle of inclination being driven by the rotation R of the mirror at 0.5 per revolution so as to obtain a weld zone 3h of spiral or helical shape. Alternatively, it is possible once more to implement a plurality of parallel circular weld zones that are side by side, by making use of discontinuous variations in angle of inclination, obtained by using a spring and cam system serving to actuate a lug for triggering stepped angular changes of said angle of inclination, e.g. by 0.5 per step. The disclosed method makes it possible to obtain weld zones of excellent quality that are very strong with a weld width corresponding to the width of the laser beam, which is 2 mm to 3 mm along the axis XX, thus making it possible to weld tubes having thicknesses up to 25 mm, and more particularly tubes having thicknesses in the range 1 mm to 25 mm. It is thus possible to make a weld zone that extends in the axial direction by using a helical zone made up of a plurality of discontinuous circles side by side, e.g. at a spacing of 5 mm, with the zones together extending over a distance of 20 mm to 50 mm in the axial direction XX.

(48) FIG. 7 shows long absorbent tubes 2 being assembled end-to-end together with short transparent tubes 1 via annular plane frontal end surfaces lying in planes that are perpendicular to the longitudinal axis XX.

(49) FIG. 8 shows a plurality of concentric circular weld zones 3-1, 3-2, and 3-3 being made by varying the angle of inclination of the surface 4a of the mirror 4 relative to the longitudinal axis XX of the tubes 1 and 2. Varying the angle of inclination involves varying the angles .sub.1 and .sub.2 of the incident beam 3a-2, .sub.1 relative to the longitudinal axis XX which is itself perpendicular to the frontal plane contact surfaces 1-1 and 2-1, and .sub.2 relative to the frontal plane contact surfaces 1-1 and 2-1 that are perpendicular to the axis XX. Because of the plurality of circular weld zones 3-1, 3-2, 3-3, a weld is thus obtained that occupies 60% to 90% of the thickness of the tubes 1 and 2.

(50) FIG. 9 shows an implementation in which the transparent tube or sleeve 1 is placed inside the opaque absorbent tube or liner 2 for a pipe 10 to which it is to be assembled by laser welding via their non-machined cylindrical terminal portions or ends 1a, 2a that are of constant thickness, which is preferably not greater than 5 mm, which terminal portions or ends are superposed and overlap over a distance =2 mm to 5 mm. A continuous helical weld zone 3h is made using a laser beam device rotating about and relative to the axis XX inside the transparent tube 1 so that the laser beam passes initially through the inner transparent portion before being reflected on the outer absorbent portion. In this embodiment, the weld zone comprises turns of constant diameter since said contact surfaces are cylindrical.

(51) In contrast, in an implementation in which the contact surfaces 1-1 and 1-2 are frustoconical surfaces of revolution, as shown in FIGS. 4 and 6, the weld zone is spiral in shape with turns of increasing diameter, starting from the turn going through the point 3i-1 corresponding to the turn of smallest diameter to the point 3i-3 corresponding to the turn of greatest diameter, the envelope surfaces of said weld zones then being surfaces that are frustoconical and not cylindrical.

(52) FIGS. 10 to 15 show the various steps of installing a tubular junction sleeve 1 in an end of a pipe element 10.sub.1 using a device 20 for putting the sleeve into place. These operations may be performed on land or on the deck of the ship 100 while in a horizontal position.

(53) A device 20 of the invention for putting a sleeve 1 into place is shown in FIGS. 11 to 15 as having a mandrel 20a of cylindrical shape extending in an axial longitudinal direction XX and having a longitudinal cylindrical central orifice within which there is placed an umbilical 20d that also serves as a cord for handling the device 20.

(54) In FIGS. 10 to 21, the device 20 comprises a first inflatable chamber 21 having a transparent wall 21a, the device being fitted with the mirror 4 and with means for moving the mirror in translation and/or in inclination as described above, said chamber being arranged in the longitudinal direction XX at a distance d from a second inflatable chamber 22.

(55) The first and second chambers are spaced apart by a distance d such that when the second chamber 22 is arranged facing the constricted central portion 1c of the sleeve, the first chamber 21 is arranged facing one end of the sleeve in register with its terminal portion 1a of reduced thickness.

(56) In FIGS. 11 and 12, a device 20 of the present invention for putting a sleeve into place is inserted in such a manner that, as can be seen in the figure, when the second inflatable chamber 22 is fully inflated, it presses against the wall of the constricted central portion 1b of the sleeve 1. The assembly comprising the device 20 and the sleeve 1 is thus held together and can be moved in horizontal translation towards the open end without a sleeve of a pipe element 10.sub.1 until it comes into abutment against the end 2a of the liner 2 of the pipe element 1.sub.1 as shown in FIG. 13. At this moment, and as shown in FIG. 14, the transparent wall 21a of the first inflatable chamber 21 faces the frustoconical contact surfaces 1-1, 1-2 at one end of the sleeve, as shown in FIGS. 13 and 14. At this stage, the first inflatable chamber 21 can be inflated so as to press against the terminal portion 1a of the sleeve in abutment against the end 2a of the liner, and the laser beam 3a is delivered so as to melt the zone of the contact surfaces 1-1, 2-1 of the sleeve and of the liner 2, thereby enabling laser welding to be performed by melting the zone of the contact plane between the tubular junction sleeve 1 at its end 1a and the end 2a of the liner 2 by passage of the laser beam 3a, as described above. The first chamber 21 is expanded with pressure that serves to guarantee excellent compactness in the melt plane and the absence of any bubbles of air that would be harmful to obtaining good sealing at the melt surface.

(57) Thereafter, in order to perform the steps of inspecting the quality of the weld, the first chamber 21 is deflated into a deflated position relatively close to the walls of the sleeve, and an inspection laser beam is sent to the weld zone so that the beam reflected on the weld zone can be analyzed using a sensor 3r situated in the first chamber.

(58) Advantageously, this guidance can be performed manually or by means of a carriage or of other means for guiding movement in longitudinal translation.

(59) Once the weld has been inspected, it is possible to remove the device 20 in translation after previously deflating all of the inflatable chambers. Said first and second inflatable chambers 21 and 22, in the deflated position, remain relatively close to the walls of the sleeve such that the device 20 can be guided relatively easily in longitudinal translation inside the sleeve. Advantageously, this guidance can be performed manually or by means of a carriage or by other means for guiding movement in longitudinal translation.

(60) A pipe element 10.sub.1 fitted at one of its ends with a tubular junction sleeve 1 forming a male portion is thus ready for laying, which male portion can be engaged in the female portion without a tubular junction sleeve of a second pipe element.

(61) FIGS. 16 to 22 show two unit lengths of lined pipe being assembled together during installation on site that is performed on board a pipe-laying ship 100 fitted with a J-lay tower 100a, as shown in FIG. 10. A new lined pipe element 10.sub.1 fitted with a tubular sleeve 1 at one of its ends is transferred in known manner from the horizontal position to an oblique position corresponding to the angle of inclination of the tower so as subsequently to be positioned on the axis of the terminal pipe element 10.sub.2 at the end of the string that is being laid. Said pipe element 10.sub.1 for assembling is then moved axially towards the suspended terminal pipe element 10.sub.2. A portion of the sleeve 1 forming a male end of one of the two pipe elements then penetrates into the female end without a sleeve of the other pipe element that is to be assembled therewith, until the terminal portion 1a of the sleeve comes into contact with the terminal portion 2a of the liner 2 inside the other pipe element 10.sub.1. Since the two pipe elements are close to being vertical, a manipulator arm enables the terminal portion 1a of the sleeve to become fully inserted against the terminal portion of the liner in order to reach the configuration of FIG. 23 where the two pipe elements 10.sub.1 and 10.sub.2 are held apart by a few millimeters, e.g. using the same manipulator arm (not shown), so as to make it possible in known manner to make the weld 11 by means of an orbital welding robot known to the person skilled in the art. The figures show the chamfered steel pipe walls spaced apart by a few millimeters while they are being welded together, the screen 13 constituted by a mattress of ceramic foam serving to limit the transfer of heat and protecting the thermoplastic sleeve throughout the duration of the welding process. On the right-hand side, the weld 11 is shown as being terminated.

(62) In an implementation shown in FIGS. 16 to 22, a new terminal pipe element 10.sub.1 is fitted with a tubular junction sleeve 1 at its bottom end, thus forming a male end that is lowered towards the female top end of a first pipe element 10.sub.1 that does not have a sleeve and that forms the top terminal pipe element of a pipe that is being laid and that is held securely in suspension from the bottom of the tower.

(63) In a first step, the device 20 for putting the sleeve into place is lowered by the umbilical 20d so that the first inflatable chamber 21 is positioned facing the terminal portion 1a of the bottom end of the sleeve 1 and the terminal portion 1a. The second inflatable chamber 22 is thus facing the central junction 1c of the sleeve 1, as shown in FIG. 17. At this moment, the second chamber 22 is inflated so as to secure the device 20 with the sleeve 1, the device 20 now being lowered together with the pipe element 10.sub.1 until the male end of the sleeve projecting from the end of the pipe element 10.sub.1 becomes engaged inside the non-lined female portion of the pipe element 10.sub.2, such that the terminal portion 1a of the sleeve 1 comes into abutment against the terminal portion 2a of the liner 2 of the pipe element 10.sub.2, as shown in FIG. 19.

(64) At this stage, FIG. 20, in order to obtain melting by laser welding, the first inflatable chamber 21 is inflated and the laser radiation is delivered so as to obtain melting in a weld zone 3 between the terminal portion 1a of the sleeve 1 and the terminal portion 2a of the liner 2, the optical fiber being conveyed in a pipe inside the umbilical 20d.

(65) Thereafter, in order to inspect the weld by using an inspection laser beam, the two chambers 21 and 22 are partially deflated. The various inflatable walls 21, 22 can then be deflated and the device 20 can be raised for subsequent use in assembling a new pipe element.

(66) FIGS. 23 and 24 show an embodiment in which the two chambers 21 and 22 are fitted with transparent walls placed in such a manner that they can be positioned simultaneously facing the two ends 1a of the same sleeve 1, the assembly comprising the two chambers 21 and 22 being of a length that is longer than the sleeve 1 so that the two chambers can coincide and press against both ends 1a of the sleeve simultaneously.

(67) Alternatively, it is possible to lower a new pipe element 10.sub.2 that is already fitted with a tubular junction sleeve 1 at its top end, but having its bottom end without a sleeve so as to form a female end of said new pipe element lowered towards the male top end of a first pipe element 10.sub.1 fitted with a tubular junction sleeve 1 at its top end, the first pipe element 10.sub.1 forming the top terminal pipe element of a pipe that is being laid and that is held securely suspended from the bottom of the tower.