AU2005259096B2

AU2005259096B2 - Monitoring of stiffeners for flexible sea pipes

Info

Publication number: AU2005259096B2
Application number: AU2005259096A
Authority: AU
Inventors: Antoine Felix-Henry; Patrice Joel Louis Jung; Philippe Lembeye
Original assignee: Technip France SAS
Current assignee: Technip Energies France SAS
Priority date: 2004-06-11
Filing date: 2005-06-08
Publication date: 2010-12-09
Anticipated expiration: 2025-06-08
Also published as: DK1759085T3; AU2005259096A1; DE602005003364D1; EP1759085A1; NO334201B1; NO20065432L; EP1759085B1; WO2006003308A1; FR2871511B1; BRPI0511946A; FR2871511A1; ATE378499T1

Abstract

The invention concerns a device for controlling stiffeners (18) of flexible marine pipes, said stiffeners (18) wherein are fitted said flexible pipes (10) are adapted to bend while limiting the curvature of said flexible pipes, said device comprising a deformable rigid rod (26, 34, 42) having a central axis (C), said deformable rigid rod being configured to be embedded in the thickness of said stiffener (18) substantially parallel to said pipe (10), at least two deformation sensors being maintained pressed against the periphery of said deformable rigid rod (26, 34, 42); said deformable rigid rod (26, 34, 42); being maintained locked in rotation about said central axis (C) in said stiffener (18).

Description

Monitoring of stiffeners for flexible sea pipes The present invention refers to a monitoring system for flexible sea pipe suitable for the conveyance of 5 hydrocarbons, an assembly including such a system, and process for producing such an assembly. We know of stiffeners forming sleeves, which are suitable for encircling said flexible pipes to rigidify them and limit their curvature when they are subjected to 10 the effects of the tide and of marine currents. According to a particular application of these stiffeners to risers, which link a bottom installation to a surface installation, these have a top end solidly fixed to the surface installation by a flange and extend along the pipe 15 over a variable distance of the order of one metre. The flexible pipe is sleeved coaxially by the stiffener such that, despite the effects of the tide or the marine current near the surface, the flexible pipe conserves a radius of curvature greater than its Minimum Bending 20 Radius (MBR) and therefore does not deteriorate. These stiffeners are also capable of sleeving pipe sections extending near the seabed to again limit their curvature. However, whilst these stiffeners allow the magnitude 25 of pipe movements to be limited, the pipes do nevertheless deteriorate in these areas under stress. Systematic recording of deformations in these stiffeners has therefore been imagined using monitoring systems embedded in their thickness to monitor not only aging of the pipe 30 sections under stress, but also the stiffeners themselves. It is indeed possible to deduce a state of aging for the pipe by combining all the stresses sustained by it over time, in terms of both frequency and magnitude. Known monitoring systems comprise a deformable rigid -2 rod with a central axis of revolution, the deformable rigid rod being fitted with three deformation sensors spaced around its periphery (these known systems are commercialized under the name Smart Rod). When the rod is 5 bent, these sensors are capable of delivering signals allowing the direction of the rod bending plane and the bending magnitude to be determined. This deformable rigid rod fitted with sensors is then embedded in the thickness of the stiffener in a section 10 capable of bending and parallel to the axis of the stiffener and to the pipe. When the flexible pipe is in service, the movements of the stiffener thereby cause bending of the deformable rigid rod and the sensors therefore deliver signals 15 representing the curvature of the stiffener. The cumulative stresses sustained by the stiffener and therefore its degree of damage can be calculated by recording these signals delivered by the sensors during its service life, 20 However, a disadvantage of this type of monitoring system resides in the displacement of the rigid rod fitted with sensors relative to the stiffener. To ensure installation of these systems, a bore of circular symmetry is effectively created in the thickness of the stiffener 25 and the deformable rigid rod is inserted under friction into this bore. The rod is then partially locked in rotation such that, during the service life of the stiffener, it can move significantly in rotation within the bore, which distorts interpretation of the signals 30 delivered by the sensors, To remedy this and, above all, to limit the error in evaluating the real curvature of the stiffener, installation of at least two monitoring systems in the thickness of the stiffener, for example at 90" to each 35 other with respect to its axis, has been imagined. However, this causes an even greater increase in the cost -3 of the monitoring system. A problem raised is thus to provide a monitoring system allowing reliable measurement of the stresses sustained by the stiffener during its service life at a 5 more advantageous cost. According to a first aspect of the present invention, there is provided a monitoring system for a stiffener for a flexible sea pipe suitable for the conveyance of hydrocarbons, in which stiffener said flexible pipe is 10 sleeved, said stiffener being adapted for bending, whilst limiting the curvature of said flexible pipe, said system comprising a deformable rigid rod having a central axis, said deformable rigid rod being suitable for embedment in the thickness of said stiffener approximately parallel to 15 said pipe, at least two deformation sensors adapted to be kept pressed against the periphery of said deformable rigid rod, said deformation sensors being suitable for delivering a signal representing the curvature when said stiffener bends and causes deformation of said deformable 20 rigid rod, wherein said deformable rigid rod is able to be kept locked in rotation about said central axis in said stiffener. According to a second aspect of the present invention, there is provided an assembly comprising a 25 stiffener for flexible sea pipes suitable for the conveyance of hydrocarbons and a system according to the first aspect, wherein the deformable rigid rod is embedded in the thickness of the stiffener to be generally parallel with said pipe and locked in rotation about said central 30 axis, and the deformation sensors are pressed against the periphery of the rod. The deformable rigid rod can, by being locked in rotation within a bore of the stiffener during the service life thereof, be held in a fixed position with respect to 35 the stiffeners, whereby signals delivered by the sensors always allow the curvature of the stiffener to be -4 calculated. Again, there is no need to provide several deformable rigid rods fitted with sensors, but simply one, which allows the cost of the monitoring system to be reduced. 5 According to a particularly advantageous embodiment of the invention, said deformable rigid rod has a non circular determined normal cross section, whilst said stiffener has a bore with a non-circular normal cross section corresponding to said determined normal cross 10 section to marry the shape of said deformable rigid rod. The deformable rigid rod is thereby locked in rotation within the bore because of the dissymmetry of the deformable rigid rod and the corresponding bore. According to a particular embodiment of the 15 invention, said bore is formed longitudinally in a cylindrical body, said cylindrical body being suitable for embedment in the thickness of said stiffener. Whilst it is not easy to embed directly the deformable rigid rod, fitted with its sensors, in the thickness of the stiffener 20 without damaging the rod and its sensors, the cylindrical body, previously bored and- embedded in the stiffener, allows the deformable rigid rod to be subsequently inserted safely into said bore. Obviously, the material of the cylindrical body must be of sufficient strength to 25 resist compression during moulding of the stiffener. Particularly advantageously, said sensors may comprise optical fibers, in which Bragg gratings are written. The optical fibers thus allow both the sensor and the signal conduction means to be obtained in a single 30 element. The Bragg gratings are written by laser means, for example to form the sensor at one end of the optical fiber, and both fiber and sensor are held in a fixed position within a longitudinal groove created in the surface of the deformable rigid rod, which comprises, for 35 example, a cord made of composite material reinforced by glass fibers, Such a material is both rigid and flexible -5 and well-suited to support the sensors. Moreover, this material is suitable for following the longitudinal deformations of the stiffener, The end of the optical fiber then constitutes the deformation sensor, whilst the 5 optical fiber itself is suitable for the optical transmission of signals representing the stresses. According to a particularly advantageous alternative embodiment, said sensors comprise three optical fibers spaced around the periphery of said deformable rigid rod. 10 Thus, the three optical fibers have, especially at their ends, Bragg gratings allowing full determination of the direction of the bending plane of the deformable rigid rod, the bending magnitude and thereby even the deformation of the stiffener. Two of the three optical 15 fibers allow full determination of the bending plane of the rigid rod and the magnitude of this bending, the third optical fiber allowing correction of the signal delivered by the other two when the cord is axially deformed, This axial deformation of the cord inside the stiffener is 20 essentially due to frictional forces and/or temperature. Owing to preferred embodiments of the invention, the stiffener is likely to be perfectly monitored throughout its service life because the signals delivered by the sensors reflect the reality of the deformation and, in 25 addition, is likely to be produced at an advantageous cost because only one monitoring system is required. According to a third aspect of the present invention, there is provided a production process for an assembly in accordance with the second aspect, in which assembly said 30 deformable rigid rod has a non-circular determined normal cross section, and said stiffener has a bore with a non circular normal cross section corresponding to said normal cross section to marry the shape of said deformable rigid rod, and in which assembly said stiffener is provided with 35 a cylindrical body embedded in the thickness thereof and said bore is formed longitudinally in the cylindrical -6. body, wherein said stiffener is moulded in a single piece by embedding the bored cylindrical body in said thickness. A bore can thereby be created in the thickness of the stiffener in a simplified manner by selecting a 5 cylindrical body, whose material is sufficiently rigid with respect to the stresses which are exerted on it during moulding. According to the prior art, this bore was effectively created in the thickness of the stiffener by moulding it incorporating a draw rod and this draw rod 10 was subsequently extracted to reveal the bore. The material of the cylindrical body is moreover selected such that it is locked in rotation within the thickness of the stiffener. To achieve this, and in a particularly advantageous 15 manner, said stiffener may be moulded from plastic having a first modulus of elasticity, with said bored cylindrical body being made of a similar plastic having a second modulus of elasticity greater than the first modulus of elasticity. The cylindrical body can thus be frictionally 20 locked with respect to the stiffener and the bore not deformed during moulding. According to the process conforming to preferred embodiments of the invention, said deformable rigid rod fitted with said sensors -is then advantageously inserted 25 into said bore after said cylindrical body has been embedded in the thickness of said stiffener. Other particular characteristics and advantages of the invention will emerge on reading the description given hereafter of the particular embodiments of the invention, 30 given as indications but without limitation, in reference to the appended drawings on which: - Figure 1 is a vertical cross-sectional diagrammatic view of an arrangement comprising a stiffener for flexible pipes embodying the invention; - 6A - Figure 2 is a detailed diagrammatic view of Figure 1; Figure 3 is a normal cross-sectional diagrammatic view of the system according to a first alternative embodiment of the invention; 5 - Figure 4 is a normal cross-sectional diagrammatic view of the system according to a second alternative embodiment of the invention;' - Figure 5 is a normal cross-sectional diagrammatic view of the system according to a third alternative 10 embodiment of the invention; and - Figure 6 is a normal cross-sectional diagrammatic view of the system according to a particular method of implementation. Figure 1 shows a flexible pipe 10, commonly called a 15 "riser", which extends approximately vertically from the surface 12 to the seabed 14. This flexible pipe 10 W02006/003308 - 7 - PCT/FR2005/001412 has a surface end 16, which is solidly connected to an unrepresented surface installation. Moreover, this surface end 16 is sleeved by a stiffener 18, whose top end 20 is held in a fixed position on a platform and 5 whose bottom end 22 is extends around the pipe 10 towards the seabed 14 over a distance of between S and 10 metres, for example. This stiffener 18 has an axis of symmetry, when it is at rest and not curved. The stiffener 18 is made of a material more rigid 10 than the flexible pipe 10, for example polyurethane, such that the bending magnitude of the pipe 10 is limited near the surface 12. Figure 2 illustrates in greater detail the stiffener 18, having an annular cross section, which 15 reduces from the top end 20 towards the bottom end 22. Deformation sensors 24 are installed over the whole length of the stiffener 18 for monitoring both the bending magnitude of the stiffener 18 and the direction of the bending plane. 20 We will now refer to Figure 3 for describing the monitoring system conforming to the invention according to a first alternative embodiment. Figure 3 illustrates in a normal cross section a fiberglass cord 26, with a triangular cross section and 25 a central axis C, embedded in the thickness of the stiffener 18 up to near its bottom end 22, illustrated in Figure 2. This cord 26 has faces, whose normal cross-sectional dimensions are of the order of a millimetre, for example between 5 and 8 mm. A 30 longitudinal central form groove 28 is created on each face over the whole length of the cord 26. A wave guide formed from an optical fiber 30 is held in position using resin, for example epoxy, in these grooves 28. These optical fibers 30 extend longitudinally over the 35 whole length of said cord 26, which itself extends over the whole length of the stiffener 18 illustrated in Figure 2. The optical fibers 30 thereby extend from the bottom end 22 up to the top end 20 and beyond for connection to signal processing means.

W02006/003308 - 8 - PCT/FR2005/001412 Moreover, between the top end 20 and the bottom end 22, the optical fibers 30 have a multiplicity of zones in which a structure comprising Bragg gratings is created and which form the deformation sensors 24. 5 As shown in Figure 3, the cord 26 with a triangular cross section is inserted in a bore 32, again triangular, which is created longitudinally in the thickness of the stiffener 18 along axis A. The triangular bore 32 marries the shapes of the cord 26 10 such that the latter is locked in rotation about its axis C. Whatever the deformations of the stiffener 18, the cord 26 thereby holds, in a fixed position with respect to the stiffener 18, the optical fibers 30 and, in particular, the deformation sensors 24 made up of 15 Bragg gratings. Thus, the signals delivered by the deformation sensors 24, which are previously calibrated, remain representative of a similar deformation of the stiffener 18. In Figure 4, the monitoring system conforming to 20 the invention is represented in another alternative embodiment according to which the cord no longer has a triangular normal cross section but, in this case, a hexagonal cross section. This Figure 4 shows in a normal cross section the stiffener 18 and a cord 34 of 25 hexagonal cross section, extending longitudinally in the thickness of the stiffener 18 along a bore 3b, also of hexagonal normal cross section. The walls of the bore 36 also marry the shape of the cord 34 such that the latter is locked in rotation about its central axis 30 C. A groove 38 is created longitudinally and alternately on three faces of the cord 34 such that three optical fibers 40 are located therein. Two of the optical fibers 40 make it possible to determine the bending plane of the stiffener and the bending 35 magnitude, whilst the third optical fiber allows the values given by the other two optical fibers to be corrected when the cords sustain an axial deformation. This axial deformation is, in particular, due to frictional forces and/or temperature.

W02006/003308 - 9 - PCT/FR2005/001412 According to a third alternative embodiment, we have represented in Figure 5 a fiberglass cord 42, whose cross section is approximately U-shaped and corresponds to a bore 44 formed in the thickness of the 5 stiffener 18 which has the same U-shaped configuration. According to this configuration, the cord 42 is also locked in rotation in the thickness of the stiffener 18. Moreover, the cord also has three grooves 46 spaced around its periphery and in which three optical fibers 10 48 are respectively installed. We will now refer to Figure 6, which illustrates the invention according to a particular, advantageous embodiment. In this Figure 6, we find a cross section through 15 the thickness of the stiffener 18 perpendicular to its axis of symmetry A and a bore 50 of triangular cross section. This bore 50 is no longer created directly in the thickness of the stiffener 18, but in the cylindrical body 52, which is itself inserted in the 20 thickness of the stiffener 18. To do this, the cylindrical body 52 is made of a rigid plastic material, preferably of circular cross section so that the radial stress field exerted on it is uniform, and the central bore 50 is created 25 symmetrically inside. This triangular bore 50 obviously has dimensions compatible with the deformable rigid rod suitable for crossing it. Moreover, the cylindrical body 52 extends over at least a part of the length of the stiffener 18 such that the rigid rod can be 30 inserted from the top end 20 to the bottom end 22. The stiffener 18 is therefore moulded in a single piece around the cylindrical body 52 using polyurethane-type plastic less rigid than that of the cylindrical body 52. The cylindrical body 52 is thereby 35 sufficiently rigid to resist the stresses and not to deform during moulding. In this way, the bore 50 remains undeformed and the deformable rigid rod can be threaded into it without excessive friction.

-10 The cylindrical body 52 will thereby remain permanently in the thickness of the stiffener 18 and will be locked in rotation in the stiffener 18 because of the contraction of the moulded plastic. Furthermore, by 5 selecting a cylindrical body 52 made of polyurethane-type material and by moulding the stiffener 18 using the same type of material, the adhesion forces between the two contact surfaces are sufficiently great to lock in rotation the cylindrical body 52 in the thickness of the 10 stiffener 18. Moreover, due to the cylindrical shape, generated by revolution, of the cylindrical body 52, the molten material is distributed uniformly around said cylindrical body 52 during injection. When the material has become rigid, the stiffener thereby has neither 15 anisotropy nor incipient crack, despite the presence of the cylindrical body 52, Thus, after the body of the stiffener 18 has been fully moulded with the cylindrical body 52 incorporated in its thickness, the deformable rigid rod comprising a 20 fiberglass cord of triangular cross section, which is fitted with optical fibers just like the cord 26 shown in Figure 3, is suitable for threading into the bore 50. Obviously, the optical fibers are then connected to a computer-controlled emission and reception device, itself 25 being connected to an analysis device, such that the bending movements of the stiffener can be recorded. Many modifications will be apparent to those skilled in the art without departing from the scope of the present invention, 30 Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but 35 not the exclusion of any other integer or step or group of -11 integers or steps, The reference in this specification to any prior publication (or information derived from it) , or to any matter which is known, is not, and should not be taken as 5 an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Claims

1. A monitoring system for a stiffener for a flexible sea pipe suitable for the conveyance of hydrocarbons, in which stiffener said flexible pipe is sleeved, said stiffener 5 being adapted for bending, whilst limiting the curvature of said flexible pipe, said system comprising a deformable rigid rod having a central axis, said deformable rigid rod being suitable for embedment in the thickness of said stiffener approximately parallel to said pipe, at least two 10 deformation sensors adapted to be kept pressed against the periphery of said deformable rigid rod, said deformation sensors being suitable for delivering a signal representing the curvature when said stiffener bends and causes deformation of said deformable rigid rod, wherein said 15 deformable rigid rod is able to be kept locked in rotation about said central axis in said stiffener.

2, The monitoring system as claimed in claim 1, wherein said sensors comprise optical fibres in which Bragg gratings are written. 20

3. The monitoring system as claimed in claim 2, wherein said sensors comprise three optical fibres spaced around the periphery of said deformable rigid rod.

4. The monitoring system as claimed in any one of claims 1 to 3, wherein said deformable rigid rod is formed by a 25 fibreglass cord.

5. A monitoring system substantially as hereinbefore described with reference to the drawings and/or Examples.

6. An assembly comprising a stiffener for flexible sea - 13 pipes suitable for the conveyance of hydrocarbons and a system according to any one of the preceding claims, wherein the deformable rigid rod is embedded in the thickness of the stiffener to be generally parallel with said pipe and locked 5 in rotation about said central axis, and the deformation sensors are pressed against the periphery of the rod.

7. The assembly as claimed in claim 6, wherein said deformable rigid rod has a non-circular determined normal cross section, and said stiffener has a bore with a non 10 circular normal cross section corresponding to said determined normal cross section to marry the shape of said deformable rigid rod.

8. The assembly as claimed in claim 7, wherein said stiffener is provided with a cylindrical body embedded in 15 the thickness thereof, said bore being formed longitudinally in the cylindrical body.

9. A production process for the assembly of claim 8, wherein said stiffener is moulded in a single piece by embedding said bored cylindrical body in said thickness. 20

10. The production process as claimed in claim 9, wherein said stiffener is moulded from plastic having a first modulus of elasticity, and said cylindrical body is made of plastic having a second modulus of elasticity greater than the first modulus. 25

11. The production process as claimed in claim 9 or 10, wherein said deformable rigid rod, fitted with said sensors, is inserted into said bore after said cylindrical body has been embedded in said thickness. -14

12. An assembly according to any one of claims 6 to 8, substantially as hereinbefore described with reference to the drawings and/or Examples.

13. A production process according to any one of claims 9 5 to 11, substantially as hereinbefore described with reference to the drawings and/or Examples,