Anti-slide device for the self-centering of an inner tube inside an outer tube of an element of unit length of a subsea pipeline for transporting fluids

Abstract

An anti-slip and self-centering device for an inner tube inside an outer tube of a unit length element for an undersea fluid transport pipe, the device having a ring (4) made of elastomer material sandwiched between two annular metal plates (6, 8) having an inside diameter that corresponds substantially to the diameter of the inner tube and an outside diameter that corresponds substantially to the diameter of the outer tube, the device further having a clamp (10, 12) for clamping the plates together to compress the ring.

Claims

1. A unit length element for an undersea fluid transport pipe, the element comprising an inner tube, an outer tube mounted coaxially around the inner tube, and at least one anti-slip and self-centering device that is interposed between the inner tube and the outer tube and disposed around an annular shoulder of the inner tube, each anti-slip and self-centering device comprising a ring made of elastomer material sandwiched between two annular metal plates having an inside diameter (d) that corresponds substantially to the outside diameter of the inner tube and an outside diameter (D) that corresponds substantially to the inside diameter of the outer tube, and a clamp to force the plates together to compress the ring.

2. The unit length undersea pipe element according to claim 1, wherein the anti-slip and self-centering device is interposed between the inner tube and the outer tube at each longitudinal end of said unit length pipe element.

3. The unit length undersea pipe element according to claim 2, wherein the anti-slip and self-centering device is assembled around an annular shoulder of the outer tube positioned facing the shoulder of the inner tube.

4. The unit length undersea pipe element according to claim 1, wherein the anti-slip and self-centering device maintains in position at least one heating cable and/or at least one optical fiber.

5. The unit length undersea pipe element according to claim 1, wherein the clamp comprises a plurality of screws that pass through the two plates and the ring, and that are suitable for being tightened in nuts.

6. The unit length undersea pipe element according to claim 5, wherein the screws each have a tensile grade of 12.9.

7. The unit length undersea pipe element according to claim 1, wherein at least one of the two plates of the anti-slip and self-centering device is made from at least two angular plate sectors.

8. The unit length undersea pipe element according to claim 1, wherein the ring of the anti-slip and self-centering device is made of ethylene propylene diene monomer having a Shore hardness lying in the range 30 to 90, a Young's modulus of less than 1 MPa, and a Poisson's ratio of the order of 0.5.

9. The unit length undersea pipe element according to claim 1, wherein the plates of the anti-slip and self-centering device are made of steel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other characteristics and advantages of the present invention appear from the following description given with reference to the accompanying drawings which show an embodiment having no limiting character. In the figures:

(2) FIG. 1 is an exploded perspective view of the device according to an embodiment of the invention;

(3) FIG. 2 is an assembled view of the device of FIG. 1;

(4) FIGS. 3A and 3B are fragmentary section views of the device of FIGS. 1 and 2 in the non-compressed state and in the compressed state, respectively; and

(5) FIG. 4 is a view of a unit length undersea pipe element of the PIP type fitted with devices of the invention.

DETAILED DESCRIPTION OF THE INVENTION

(6) The invention applies to any type of fluid transport pipe, and in particular to undersea coaxial pipes of the pipe in pipe (PIP) type, i.e. a pipe that comprises an inner tube for transporting hydrocarbons coming from production wells and an outer tube coaxial around the inner tube and also referred to as the outer envelope, which is in direct contact with the surrounding water.

(7) This type of undersea coaxial pipe is typically used in the offshore production of hydrocarbons at great depths. In the context of such installations, undersea coaxial pipes can be assembled on land as a plurality of pipe sections of unit length (also referred to as joints, in particular double joints for two unit elements assembled together, triple joints for three unit elements assembled together, and quadruple joints for four unit elements assembled together, or more generically quad-joint for quadruple tube sections), of the order of 10 m to 100 m, depending on the loading capacity of the laying system. During laying, these unit length elements of undersea pipe are connected to one another on board the vessel progressively as they are laid in the sea.

(8) In particular, the operation of connecting a unit length element to the undersea pipe that has already been lowered into the sea requires the unit length pipe element to be positioned vertically, and to be held in this position during welding of the bottom end of its inner tube to the top end of the inner tube of the undersea pipe, and then requires the outer tube to be slid in order to weld the top end of the outer tube of the undersea pipe.

(9) The invention aims to provide an anti-slip self-centering device that serves, during the connection operation, to hold the inner tube of the unit length pipe element vertical and stationary inside the outer tube, while ensuring it is centered inside the outer tube.

(10) An example of such a device 2 is shown in exploded perspective view in FIGS. 1 and 2.

(11) The device 2 comprises in particular a ring 4 made of elastomer material, which is sandwiched between two annular plates 6, 8 made of metal (preferably steel) having an inside diameter d that corresponds substantially to the outside diameter of the inner tube of the unit length pipe element on which the device is designed to be assembled, and having an outside diameter D that corresponds substantially to the inside diameter of the outer tube of said unit length pipe element.

(12) The device 2 further comprises clamping means for clamping plates 6, 8 together to compress the ring 4 made of elastomer material, the ring tending to swell radially towards both the inside and the outside of the plates under the compression force.

(13) The clamping means may be made by means of a plurality of screws 10 passing through both of the plates 6, 8 and the ring 4 made of elastomer material and by clamping nuts 12. In the embodiment shown in FIG. 1, there are ten screws 10 that are regularly spaced apart about an axis of revolution X-X of the device.

(14) FIG. 3A shows the device of FIGS. 1 and 2 in the assembled rest position, i.e. without compression of the ring 4 made of elastomer material, while FIG. 3B shows the same device after application of a clamping force by the nuts 12 on the screws 10 leading to compression of the ring 4, and thus to deformation of said ring that can be seen by a radial expansion both towards the inside and outside.

(15) When the device is interposed between an inner tube and an outer tube of a unit length undersea pipe element, this compression of the ring of the device thus makes it possible to ensure that the inner tube is blocked in position inside the outer tube.

(16) The elastomer material used for making the ring of the device, as well as the characteristics of the screws and nuts and of their clamping force, are selected and calibrated as a function of the requirements for blocking the inner tube of the undersea unit length pipe element inside the outer tube.

(17) In particular, for the particular application envisaged (i.e. connecting a unit length element vertically to an undersea pipe), these selections and calibrations are defined to be able to support the weight of the inner tube but no more. In particular, the characteristics of the device must not prevent the outer tube from sliding relative to the inner tube once said inner tube is connected to the inner tube of the undersea pipe.

(18) Thus, the characteristics of the device of the invention could be selected and calibrated so as to enable it to absorb a compression load lying in the range 1 MPa to 5 MPa (with an acceptable compression load of 3.5 MPa, the device can support up to 4.7 (metric) tonnes at the inner tube and up to 5.8 tonnes at the outer tube of the unit length pipe element, these values being given purely by way of indication and depending on the diameters and dimensions of the contact surfaces).

(19) To this end, and by way of example, ethylene propylene diene monomer (EPDM) may be selected as the elastomer material for making the ring of the device having a Shore hardness lying in the range 30 to 90, a Young's modulus of less than 1 MPa, and a Poisson's ratio of the order of 0.5. Thus, with such a Poisson's ratio, the vertical pressure on the plates exerted by the clamping of the screws is almost equal to the contact pressure on the side walls of the tubes.

(20) With such characteristics, the screws 10 used for clamping the plates 6, 8 may each have a tensile grade of 12.9 in order for their clamping to enable the plates to move closer together by about 0.5 mm.

(21) FIG. 4 shows two devices 2 of the invention assembled together at each longitudinal end of an undersea pipe element 14 of unit length.

(22) As described above, the pipe element 14 of unit length comprises an inner tube 16 disposed coaxially inside an outer tube 18.

(23) At each of its longitudinal ends, the inner tube 18 is provided with an annular shoulder 20 where more precisely there is a device 2 of the invention. This shoulder 20 is thin (so as not to prevent the controlled slipping of the outer tube) and can be obtained by adding a small length of inner tube incorporated in the shoulder at both ends (it projects radially outwards).

(24) Preferably, the outer tube 18 also comprises, on its inside surface, an annular shoulder 20 positioned facing the shoulder 20 of the inner tube in such a manner as to reinforce the safety of the device (the shoulder 20 projects radially inwards).

(25) While the unit length pipe element is still in the horizontal position, the ring 4 made of elastomer material of the device is thus slid around an inner tube from one of its longitudinal ends in order to cover the corresponding shoulder 20.

(26) The two annular plates 6, 8 are then positioned on each side of the ring 4, the plate situated on the side opposite the end of the inner tube (in this embodiment the plate 6) preferably being made from at least two angular plate sectors 6a, 6b (see FIG. 1) in such a manner as to facilitate its assembly around the inner tube.

(27) The screws 10 and nuts 12 are thus mounted on the device (at this stage without tightening the nuts) with the screw heads advantageously turned towards the corresponding longitudinal end of the inner tube.

(28) The outer tube 18 of the unit length pipe element is then slid longitudinally around the inner tube until it reaches the desired position. The screws 10 are thus clamped in the nuts 12 in such a manner as to compress the ring 4 made of elastomer material. As mentioned above, the clamping force is calibrated depending on the weight of the inner tube in order to enable the two devices to support the weight of the inner tube (with a safety margin of 15% to 20% more).

(29) The annular space defined between the two devices 2 may be filled with an insulating material, in particular a resin. To this end, the devices of the invention may advantageously serve as a stop wall or mold during injection of the resin in order to hold said resin inside a fixed volume that is suitable for being evacuated.

(30) The unit length pipe element 14 as assembled in this way can thus be mounted vertically by means that are known per se in order to be assembled to an undersea pipe that has already been lowered into the sea.

(31) In advantageous manner, it should be observed that the device of the invention may be used to block various parts, such as heating cables, optical fibers, etc., in position around the inner tube of the unit length pipe element.

(32) To this end, the heating cables, optical fibers, or others that extend longitudinally along the inner tube are interposed between the inner tube and the ring made of elastomer material of the device such that compression of said device ensures they are blocked in position.