Method for installation and implementation of a rigid tube from a ship or floating support

Abstract

A method of installing and implementing a rigid tube (10) referred to as a main tube, wherein the following steps are performed: a) lowering an end of the main tube from a floating support or vessel (13) on the surface (14) to below sea level (14) to be connected to undersea equipment (16) that is immersed (17); and b) maintaining the main tube as immersed in this way for a given period of time. The said main tube (10) is caused to pass through a cylindrical orifice (4) of circular section in a stress limiter device, the orifice having a slippery internal coating (3) secured to a support structure (9) secured to the floating support or vessel, the service tube thus being suitable for sliding in contact against the slippery coating during steps a) and b).

Claims

1. A method of installing and operating a rigid tube referred to as a main tube, the method comprising the following steps: a) lowering an end of said main tube from a floating support or vessel on the sea surface to below sea surface level in order to be connected to undersea equipment that is immersed; and b) maintaining the main tube as immersed with the lower end of the main tube suspended below the sea surface for a given period of time; wherein said main tube is passed through a cylindrical orifice of circular section referred to as a first orifice, in a stress limiter device referred to as a sliding stiffener, said first orifice having an internal lubricating coating, said sliding stiffener being secured to a support structure, said support structure secured to said floating support or vessel and extending outside said floating support or vessel over the sea surface, a top portion of said main tube being held in suspension above said sliding stiffener, such that said main tube is suitable for sliding in contact against said lubricating coating during steps a) and b).

2. The method according to claim 1, wherein said sliding stiffener comprises a solid rigid part having said first orifice having a vertical axis (ZZ) passing through its material, said rigid part comprising a main portion presenting an outside surface of revolution about the axis of said first orifice of diameter that decreases progressively and continuously going down said sliding stiffener to the bottom end of said sliding stiffener.

3. The method according to claim 2, wherein at said main portion of the rigid part constituting said sliding stiffener presents an outside surface of frustoconical shape extending from and below a top portion of said rigid part defining a fastener flange around the top end of said first orifice.

4. The method according to claim 3, wherein said fastener flange forms a fastener plate fastened to or formed integrally with the top end of said main portion, said fastener plate resting on and being fastened to a horizontal platform of said support structure, said fastener plate extending on a plane surface on top of said platform of dimension D2 that is greater than the dimension D1 of the greatest section of said main portion, said plane plate surface being of circular circumference coaxial with the circumference of said first orifice.

5. The method according to claim 1, wherein said first orifice of said sliding stiffener is covered on its surface which is in contact with said main tube by a material comprising said internal lubricating coating constituted by a solid material in the form of a plastics film layer, made of a thermoplastic or of an elastomer material, said plastics coating being further coated on its surface in contact with said main tube with a low friction anti-abrasion material selected from an oil and a grease.

6. The method according to claim 1, wherein said main tube is coated in a low friction anti-abrasion material selected from an oil and a grease, and wherein the treatment for performing said coating is performed after step a) and before inserting the main tube in said first orifice.

7. The method according to claim 1, wherein said sliding stiffener is pre-fitted with a tube portion referred to as a connection tube that is fastened and/or suspended in reversible manner to said support structure and/or to said sliding stiffener, said connection tube being engaged in said first orifice and having a connection element at its bottom end beneath said stiffener, the connection element being connected or suitable for being connected to a piece of equipment and prior to step a), the following steps are performed: connecting the end of said main tube to the top end of said connection tube; separating said connection tube from said sliding stiffener device; and beginning the descent by descending said connection tube.

8. The method according to claim 7, wherein said connection tube includes a removable clamping collar around a portion of said connection tube projecting above said first orifice.

9. The method according to claim 1, step a), the following steps are performed: a.1) unwinding said main tube wound on a winding support on said floating support or said vessel, and passing said main tube through a device for tensioning and reducing residual curvature associated with winding and then through a grease box and a trimming collar, prior to inserting it in said sliding stiffener; and a.2) lowering said main tube below sea level by causing it to slide through said sliding stiffener.

10. The method according to claim 1, wherein in step b), said main tube unwound from a floating support or a vessel at the sea surface down to the sea bottom passing through a said sliding stiffener is maintained and stabilized after said descent and implementation for a period of at least 24 hours before raising it to the sea surface and/or without unwinding any additional length.

11. The method according to claim 1, wherein an undersea pipe and/or a wellbore at the sea bottom is verified and/or maintained by sending a liquid or a gas via said main tube having its bottom end connected to said undersea pipe and/or a wellbore at the sea bottom.

12. An installation suitable for performing a method according to claim 1, the installation comprises a support structure secured to a floating support or vessel on the sea surface, the support structure having fastened thereto a sliding stiffener comprising a solid rigid part having an outside surface of revolution of diameter that decreases progressively and continuously going down said sliding stiffener to the bottom end of said stiffener having an axial orifice referred to as a first orifice with an internal lubricating coating, said internal coating being suitable for enabling sliding of a main tube inserted into said first orifice in contact with said main tube.

13. The installation according to claim 12, wherein said first orifice of said rigid stiffener part is covered on its surface in contact with said main tube by a material comprising said internal lubricating coating constituted by a solid coating of a layer of plastics film made of a thermoplastic material or of an elastomer, said layer of plastics film being further coated on its surface in contact with said main tube with a low friction anti-abrasion material selected from an oil and a grease.

14. The installation according to claim 12, wherein said sliding stiffener is fitted with a tube portion referred to as a connection tube that is reversibly fastened to said sliding stiffener, said connection tube having the same diameter as said main tube, said connection tube being engaged in said first orifice and having at its bottom end, below said stiffener, said connection element that is connected to or suitable for being connected to a piece of equipment or a flexible or semi-rigid pipe.

15. The installation according to claim 14, wherein said connection tube includes a removable clamping collar around a portion of said connection tube projecting above said first orifice.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other characteristics and advantages of the present invention appear in the light of the following detailed description made with reference to the figures, in which:

(2) FIGS. 1A to 1C are a side view (FIG. 1A) and axial vertical section views (FIGS. 1B and 1C) of a sliding stiffener 1 of the present invention pre-fitted with a connection tube 5 (FIG. 1B) and without a connection tube (FIG. 1C);

(3) FIG. 2 is a view of a bottom-to-surface connection installation fitted with a stiffener device of the present invention referred to below as a sliding stiffener;

(4) FIG. 3 shows the portion of the installation on board the vessel; and

(5) FIG. 3A shows a detail at the junction between the sliding stiffener 1 and a support structure or beam 9 of the vessel.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

(6) The sliding stiffener 1 as shown in the figures is constituted by a solid part made of rigid solid material such as steel, possibly reinforced by glass or synthetic fibers and comprising the following two portions: a conical main portion 2a and a top fastener plate 2b. The bottom main portion 2a having an outside surface in the form of a frustoconical surface of revolution extends over a length L1. It is pierced by a said first cylindrical orifice 4 of circular axis on the same axis ZZ as the frustoconical outer surface and passing right through the main part. The diameter of the frustoconical outer surface of the main portion 2a varies between a maximum value D1 at its top end to a minimum value d1 at its bottom end. In the figures, the conical part is shown as having a linear generator line with diameters that vary in linear manner. Nevertheless, in another embodiment, the generator line of the surface of revolution of the current portion 2a could be parabolic, but in any event the diameter varies in progressive and continuous manner between the maximum value D1 and its minimum value d1.

(7) The frustoconical main portion 2a is surmounted by a perforated plate forming a coaxial annular part 2b perforated by the top end of said first cylindrical orifice. The annular top plate 2b is of cylindrical shape of greatest diameter D2 that is greater than D1, and of thickness e1. The greatest diameter D2 of the annular plate 2b enables its underface 2b1 to rest on and be fastened by bolting and/or welding to the top face of a platform of a support structure 9 secured to the floating support or vessel described below with reference to FIG. 2.

(8) In an embodiment, the main portion 2a of the frustoconical outer surface may be made by machining a tubular perforated part having a cylindrical outer surface of circular section, said machining enabling its thickness and thus its outside diameter to be reduced progressively in continuous manner all along its length.

(9) The part 2 may also and preferably be made in the form of a forging having the top plate 2b made integrally with the bottom main portion 2a, said part 2 having said first axial cylindrical orifice 4 passing continuously therethrough.

(10) In another embodiment, the annular top plate 2b is welded to the top end of the main portion 2a having the frustoconical surface.

(11) The part 2 has a slippery coating 3 in the form of an inner jacket of plastics material, preferably of thermoplastic material, for said first orifice and referred to as a liner. Such lining may be performed by swagelining as described in FR 2 876 773. To do this, the following steps are performed:

(12) a) preparing a liner pipe 3-1 of flexible and elastic thermoplastic material inside said first orifice, said liner pipe presenting a diameter that is slightly greater than the diameter of said first orifice;

(13) b) heating said liner pipe by passing it through a heater oven and then through a die in order to leave the die going towards said first orifice with an outside diameter that is slightly less than the inside diameter of said first orifice;

(14) c) a first end of the liner pipe is inserted into a first end of said first orifice. Said first end of the liner pipe is fitted with a traction head connected to a winch outside said first orifice beyond its second end;

(15) d) applying traction to the liner pipe from the second end of the orifice 4. During this traction, the liner pipe thus has its diameter diminished and also its nominal length increased. During a stage of preparing the pulling, the inside wall of said first orifice is coated with an adhesive, e.g. an adhesive of epoxy or two-component polyurethane type; and

(16) e) after said liner pipe has been pulled inside said first orifice to its second end, traction on the liner pipe is released once it has passed through the entire first orifice. Because it initially presented a diameter greater than the diameter of the first orifice, said released liner pipe then presses against the steel inside surface of the first orifice and adheres thereto by melting as a result of being heated, with adhesion possibly being reinforced by the adhesive. Advantageously, the fastener flange 2b is provided on its top surface with a portion 3b of internal coating extending continuously with the cylindrical coating 3a inside said first orifice 4. This plane top portion 3b serves to protect the top face of the fastener flange 2b.

(17) In another embodiment, the thermoplastic internal coating is pressed against the inside surface of said first orifice as an interference fit.

(18) In order to use a steel service tube having a diameter 3.5 (89 mm) with an elastic limit of 555 MPa that is to be deployed over a length of more than 2 km in order to be installed at a depth of about 2000 m.

(19) Use is made of a sliding stiffener presenting the following dimensional characteristics:

(20) L1=2 m to 7 m;

(21) e=thickness of the steel cone of stiffness varying from: e max=10 mm to 50 mm at the top; to e min=2 mm to 3 mm at the bottom; and

(22) thickness of the polyethylene (PE) coating=5 mm to 25 mm.

(23) The flange 2b connected by welding to the top of the stiffener 2a presents a thickness e1 greater than the maximum thickness e max of the stiffener.

(24) In FIGS. 1A and 1B, the sliding stiffener 1 is fitted with a connection tube 5 having the same diameter and the same thickness as the service tube with which it is to be connected at its chamfered top end 5a. Its bottom end is fitted with a male or female element of an automatic connector 6, once more as an interference fit or by welding. The greatest outside diameter D3 of said connector element 6 is greater than the inside diameter of said first orifice d2. The top end 5a of the connection tube 5 extends above the top fastener plate 2b.

(25) In an embodiment, the connection tube 5 is thus held in suspension with its top end 5a extending above the plate 2b by a clamp 7 clamped around the outside surface of the connection tube and resting on the top face of the plate 2b.

(26) The outside diameter of the connection tube d3 in its main portion provides minimum clearance relative to the inside diameter d2 of the first orifice coated with said internal liner 3 so as to enable the tube 5 to slide via its top end 5a inserted into the bottom end of the first orifice in the conical part 2.

(27) FIGS. 2 and 3 show a complete bottom-to-surface connection installation showing how a rigid steel service tube 10 wound on a drum 12 on the deck of a floating support or vessel 13 is deployed. The steel service tube 10 is unwound and passes through a straightener device 11 and then through a device 18 for greasing and smoothing its outside surface. Thereafter, its end is welded to the top end 5a of the connection tube 5 that is secured to a sliding stiffener 1 having its top annular plate 2b fastened to the top plate 9a of a platform of a support structure 9, the frustoconical main portion 2a of the sliding stiffener passing through an orifice 8 in the platform 9 (FIG. 1C). Thereafter, the connection tube 5 is disconnected from the stiffener 1 so as to enable the connection tube 5 together with the service tube to slide and be deployed in immersion down to the sea bottom. For this purpose, the clamp or collar 7 that was holding the connection tube in suspension in the sliding stiffener as shown in FIG. 1A is disengaged.

(28) FIG. 2 shows the service tube after unwinding and immersing the end of the steel service tube fitted with its connection tube.

(29) In FIG. 2, the connection element 6 at the end of the connection tube 5 is connected to a complementary connection element 6 of an automatic connector at the end of a flexible pipe 15 having its other end giving access to and enabling maintenance and/or tests to be performed on undersea equipment 16 resting on the sea bottom 17, such as a well head or an undersea oil production pipe.

(30) The equipment 16 may be connected to the bottom end of the connection tube 5 before or after separating and lowering in immersion the connection tube 5 relative to the stiffener by using an undersea robot of the ROV type.