FR2779797A1 - A flexible pipeline for conveying hydrocarbon fluids includes a compressible core - Google Patents

Abstract

The pipeline consists of a spirally wound flexible metal frame with non-connecting coils, a compressible core arranged in the gap between consecutive coils, an inner extruded and impervious thermoplastic sheath on the metal frame, a layer of armoring wrapped around the inner sheath and an outer sheath arranged around the armoring. The core has a volumetric deformation of at least 50% when compressed.

Description

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  IMPROVED FLEXIBLE CONDUCT FOR TRANSPORT

FLUIDS

  The present invention relates to a flexible pipe capable of being used for the transport of fluids such as hydrocarbons by

example.

  Several types of flexible pipes are used. Some flexible pipes include, from the inside to the outside, an internal sealing sheath made of plastic, elastomer or other relatively flexible suitable material; an unsealed flexible metal tube which must resist the forces developed by the pressure of the fluid flowing in the pipe; one or more layers of armor and at least one external sealing sheath made of polyvinyl material. This type of flexible driving

  is often called "smooth-bore" by specialists in the field.

  Other flexible pipes called "roughi-bore" include

  nent, from the inside to the outside, a non-waterproof flexible metallic tube, called a carcass, constituted by a profile wound in turns stapled one on the other, like for example a stapled strip or plain wire of stapled form such as a T, U, S or Z wire. an internal sealing sheath made of polymeric material. one or more layers of armor capable of withstanding the forces developed by the pressure of the fluid flowing in the pipe and the external forces to which the flexible pipe is subjected,

  and at least one external protective sheath of the polymeric type.

  In the latter type of flexible pipes, the internal sealing sheath is directly extruded, continuously, onto said carcass which has

  between the coiled turns or interstices.

  To ensure good contact between the internal sealing sheath and the metal carcass, it is necessary that the internal diameter of the internal sealing sheath be as close as possible and even equal to the diameter

  of the flexible metal carcass.

  When manufacturing a flexible pipe of the rough-

  boron ", the internal sealing sheath which is extruded on the carcass

  metallic, contracts on the latter during cooling.

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  Depending on the materials used for the production of the internal sealing sheath, there are, after cooling, deformations called "shrinkage" which appear on the internal face of said internal sealing sheath and in particular on either side of the joints between the turns of the metal frame. Such shrinkage is due, it seems, to the differential shrinkage of the material used for the internal sealing sheath, due to the variation of the cooling gradient in the thickness of the internal sealing sheath, cumulated with l effect of the junctions of the turns of the metal carcass. Indeed, the extruded plastic sealing sheath being in contact by its internal face on the metal carcass which is at room temperature, it follows that the cooling of said internal face is very rapid, which causes surface irregularities or shrinkage; this phenomenon is amplified at the junctions of the turns of the metal carcass, the differential constriction in these places causing variations in local thickness of the internal sealing sheath. When the sealing sheath is made of semi-crystalline polymer, sensitive to the presence of surface defects causing the sheath to lapse, possibly going as far as breaking, such as PVDF for example, this very often results, in operation, in a degradation of said sealing sheath (rupture) which

  no longer performs its sealing function.

  To remedy such a drawback and to solve the problem posed by the appearance of retassutires, it was found and adopted the solution which consists in having, between the metal carcass and the internal sealing sheath, a low sacrificial sublayer thickness, in a suitable material such as PVDF. The internal sealing sheath is then extruded on said sacrificial sublayer but making sure that there is no "weld" or intimate connection between the sealing sheath and the sacrificial sublayer ", in order that the fissures which propagate from the internal face of the underlayer towards the outside are blocked at the interface of the sealing sheath and the sacrificial underlayer. This is what is described in

WO 95/2478.

  The major drawback of this solution is the slippage suscep-

  tible to occur between the internal sealing sheath and the sacrificial sublayer at the ends of the flexible pipe, as well as the

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  additional raw material and processing costs (manufacturing)

  caused by the presence of said sacrificial sublayer.

  Other solutions have been sought to eliminate the appearance

  shrinkage or mitigate their effects.

  Among these latter solutions which relate to the establishment of an internal sealing sheath having, after cooling, a cylindrical and smooth internal face implement a conformation which is either

  internal, with the main drawback of creating longitudinal cracks

  dinales on the internal face of the sealing sheath and a single fold of material on l0 the external face, ie external with a drawback the total absence

  anchoring the sealing sheath on the metal frame.

  In the technique of manufacturing flexible pipes of the type

  "smooth-bore", which consists in separately producing the internal sheath of

  chéité by any appropriate means such as extrusion, and the metal carcass, it was recommended to heat the sealing sheath or the metal carcass, once the two elements are assembled in order to maintain or make plastic the sheath tightness to force it to flow in the gaps of the turns of the metal carcass. Such manufacturing processes are described in particular in FR-B-74 14 398 (COFLEXIP) and the addition

no 71 16 880 (IFP).

  However, these methods have the sole purpose of causing permanent creep of the polymeric sealing sheath between the turns of the metal carcass, after or at the same time as stresses are developed in the internal sealing sheath to achieve intimate contact, the constraints developed being for example due to an implementation

  pressure of said internal sealing sheath.

  In an exemplary implementation described in patent FR-B-74 14 398 and concerning a flexible pipe comprising a peripheral sheath extruded on an assembly comprising from the inside to the outside, an internal sealing sheath, united arch pressure, two layers of armor and a wire mesh. it is recommended to heat the assembly before the extrusion of the peripheral sheath so as to maintain at least the internal face of said peripheral sheath in the plastic state or more exactly in the thermoplastic state so, and this is the goal sought, to creep the internal face in the meshes of the wire mesh, to fill them

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  totally and thus achieve total attachment of the peripheral sheath to the wire mesh. Under these conditions, it is imperative to strongly heat the assembly, to temperatures which are of the order of several hundred degrees Celsius. Such techniques gave such poor results that they were abandoned very quickly, since filling both the interstices of the pressure vault and the mesh of the wire mesh stiffened the pipe and consequently reduced the essential property of

  flexibility that it must present imperatively.

  In US Patent 3,311,133, a pipe is described comprising an internal metal carcass constituted by a stapled strip

  in the shape of an S and in the gaps of which a compressible rod is interposed.

  The aim is to control the clearance between the turns of the strip while

  providing a certain flexibility to said carcass.

  In application 96 10 490 filed by the applicant, it is recommended to heat the metal carcass to a temperature below

   C, upstream of the extrusion means, so as to avoid cooling

  roughly brutal of the internal face of the sealing sheath during its extrusion on the metal carcass. The work carried out on the flexible pipes with pre-heated carcass showed that the thermoflowing of the internal sealing sheath was increased and that, sometimes, this led to a blocking of the strip. The consequence of such a blockage is to displace the neutral fiber during the bending stress and thereby. increase the deformation on the upper surface of the internal sealing sheath or pressure sheath. However, when the complete flexible pipe is bent with MBR (Minimum Bending Radius) and if the strip is blocked, it is easy to understand that for a deformation of the order of 6% on the upper surface of the pressure sheath, it a deformation of approximately 10 to

  12% on the lower surface, which is not acceptable. In addition, thermo-

  plastics have an elongation at the threshold which decreases as the temperature decreases, which means that their deformation capacity is also decreased at low temperatures. This phenomenon is only of relative importance with materials with significant elastic deformation, typically greater than 12% at the stressing temperature, provided that their capacity to deform is preserved over time. On the other hand, with materials whose elastic deformation is limited, typically

2779797

  less than 10-12% at the stress temperature, a rupture may occur

  produce due to exceeding this deformation capacity.

  The use of thermoplastics with a high deformation capacity (greater than 10%) has not given good results because the known thermoplastics do not withstand temperatures above 130-150 C (homo or PVDF copolymer) or present

  other disadvantages such as poor creep resistance (PFA).

  This is the reason why, for an effluent temperature of around C, plasticized PVDF homopolymer is used. However, the plasticizer gradually disappears over time, which leads to an unplasticized thermoplastic which does not withstand thermal and mechanical stresses. The loss of the plasticizer is also problematic in the

  part of the pipe which is housed in the end fitting.

  In addition, the industrial implementation of the heated carcass and the subsequent extrusion of the internal sealing sheath poses real problems. Indeed, depending on the viscosity of the plastic used for the internal sealing sheath and the heating temperature of the metal carcass, a more or less significant thermofluage occurs in the joints. As the physicochemical characteristics of said plastic material can vary from one batch to another, it is practically impossible to control the thermofluage under normal conditions of setting

  in industrial work; often, a total thermofluage has been observed, that is to say

  tell a full fill of the breakfasts. It is easy to understand that a total thermofluage can lead to blockage of the metal carcass and therefore to reduced flexibility of the pipe. For example, above 90% filling of the gap with the internal sealing sheath, there is a risk

  blocking in certain places of the flexible pipe.

  The object of the present invention is to remedy the aforementioned drawbacks and to propose a flexible pipe in which at least the internal sealing sheath is produced with thermoplastic materials having alone or in combination a significant thermofluage and a visco-elastic elongation of less than 10 -12% over the entire temperature range between the limits of use and without formation of shrinkage.

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  To do this, we combine. on the one hand, the effects of heating the carcass so as to avoid the formation of shrinkage as explained in the application previously analyzed and filed in the name of the applicant and, on the other hand, by limiting the thermofluage of the internal sealing sheath in the gaps of the turns of the carcass so as not to block the movement of the strip constituting said carcass, while obtaining a positive attachment of the internal sealing sheath on said

  carcass, said attachment resulting from limited thermofoil in the joints.

  An object of the present invention is a method of manufacturing a flexible pipe for the transport of fluids such as hydrocarbons, of the type comprising, from the inside to the outside, a flexible metal carcass with helical winding of non-contiguous turns , a compressible rod disposed in the gap between the consecutive turns of said helical winding, an internal sealing sheath extruded on said metal carcass, at least one armor ply wound around said internal sealing sheath and at least one sheath external sealing arranged around said armor ply. and it is characterized in that the compressible rod is made of a material having a high volume compressibility under a low stress which is less than one Newton per linear millimeter of said rod for a

displacement of 60% of material.

  The fact of using a rod which is highly compressible under a low stress load allows the thermofoil to occur during the extrusion of the internal sealing sheath on the metal carcass while

  limiting penetration to a predetermined value.

  According to another characteristic, the metal carcass is heated before the extrusion of the sealing sheath, which facilitates thermofoiling while

  avoiding the formation of retassutires.

  According to another characteristic, the material is alveolar comprising between 40 and 60% by volume of hollow cells and having a first modulus of elasticity El of the cell part and a second modulus of elasticity E, of the dense part, the ratio of two E1 / E2 modules being at

less than 10.

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  Other advantages and characteristics will appear more clearly

  on reading the description of a preferred embodiment of the invention,

  as well as the appended figures in which - Figure 1 is a partial perspective view and cut away of a flexible pipe, - Figure 2 is a schematic and partial view of a part of the metal carcass coated with a part of an internal sealing sheath according to the present invention, - Figure 3 shows a curve of the stress in N / mm

  linear as a function of displacement in percent.

  The flexible pipe I according to the invention is of the type comprising from the inside to the outside - a metal carcass 2 produced by a helical winding of a metal wire with non-contiguous turns 3 and of predetermined section, by

  example in S as in the example shown in Figure 2.

  - an internal sealing sheath 4 arranged by extrusion around the metal carcass 2, - a pressure vault 5, - one or more layers of armor 6, - optionally an intermediate strip 7, and

  - an external sealing sheath 8.

  The external sealing sheath 8 can also be extruded on the intermediate strip 7 when it exists or on the external armor ply 6, the internal 4 and external 8 sealing sheaths being produced

  in a common plastic or in different plastics

  according to the needs and destination of the flexible pipe 1.

  The metal carcass being with non-contiguous turns 3, a space or gap 9 is provided between two consecutive turns 3. During or after the manufacture of the metal carcass 2, a compressible rod 10 is placed in the gaps 9 (FIG. 2). The compressible rod 10 can, depending on the manufacturing step during which it is inserted in the joints, be positioned at the bottom of the latter or at a certain height from the bottom of the said joints. In all cases, it is positioned so that at most 75% of the volume of each gap can be filled with the material of the internal sealing sheath 4, said material coming to bear on the compressible rod. Of course, the

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  geometry of the compressible ring is adapted to the shape of the gap; in

  preferred embodiment of the invention, the section of said rod compres-

  sible has a cross section at least equal to 25% of the cross section of the gap with the mean pitch of the stapled strip having been used for the manufacture of the metal carcass so as to ensure, as specified above, that at most 75 % of the volume is available for the thermofluage of the

internal sealing sheath.

  The material from which the compressible rod is manufactured must meet certain characteristics and in particular A - have a volume compression ratio at least equal to% and it is chosen from the family of hydrogen-carbon elastomers and, preferably, from the family of silicone elastomers or silicofluorinated, - resist at least five milILnutes at the temperature to which the internal sealing sheath is brought during its extrusion on the carcass

metallic.

  According to a preferred embodiment of the invention, the compressible rod is made of a cellular material which has a high volume compressibility under a low load, the dense material of said rod occupying a volume of between 40 and 60% of the total volume of said rod . Referring to FIG. 3, which represents, on the one hand, a first curve CI (left part) representing the stress in Newton per linear millimeter and a second curve C2 representing the elastic return after compression, on the other hand, we notes that the material has a first elastic modulus El relative to the hollow part of said material and a

  second modulus of elasticity E2 relative to the dense part of the same material.

  The modulus El is determined by the straight line Dl which is tangent to the curve CI for the abscissa point of approximately 40%, while the elasticity modulus E, is determined by the straight line D2 which is tangent to the curve C2 for the abscissa point of approximately 75%. The E1 / E ratio is in all cases greater than 10 and preferably greater than 30. On the curve C1, it is found that for a displacement in volume (or compression) of 40% of the rod, the stress which it must be applied to obtain such a displacement is 0.4 N / mm linear and that for 65% of displacement. the stress is of the order of 1.3 N / mmrn linear, the total compression of the alveolar part of the rod corresponding to a displacement of 80% for a stress of 4 N / rmm

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  linear. Curve C2 shows that the material tested has an elastic return of at least 60%, that is to say that the material, when the

  compression ceases, practically regains its original shape and volume.

  In all cases, the volume compressibility is important under a low stress which is less than I Newton per linear millimeter for

  a displacement of 60% of material of said rod.

  In order to allow the recovery of the tensile force necessary for its installation in the gaps 9 of the metal carcass, a reinforcement 11 is embedded in the mass of the compressible rod 10. the reinforcement being unidirectional and produced in a mineral material, organic or vegetable. The unidirectional reinforcement also gives a certain longitudinal stiffness to the rod, which further facilitates its installation in the joints as well as the resumption of the tensile force to which it may be subjected when it is placed in the joints of the strip , which thus avoids the variation (reduction) in section of the rod. This maintains the compactness of the rod in the gaps as it was initially (40 to 60%) before its

implementation.

  Of course. if the tensile force is relatively low during installation in the joints, then it is possible not to use a

reinforcement in the rod.

  A method of manufacturing the flexible pipe described above, consists in interposing the compressible rod when the metal carcass 2 is under axial tension and before the plastic sheath 4 is extruded on said metal carcass. The axial tensioning of the metal carcass has the consequence of allowing the gap 9 to be at their maximum opening, so that the rod can be easily accommodated in the open gaps. When the axial tension is released, the dimensions of the joints are reduced, which allows the compressible rod to be maintained in the appropriate position to limit the creep of the sheath 4 in the

lunches.

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Claims (12)

  1. Flexible pipe (1) for the transport of fluids such as hydrocarbons, of the type comprising, from the inside to the outside, a flexible metal carcass (2) with helical winding of non-contiguous turns (3), a rod compressible (10) disposed in the gap (9) between the consecutive turns of said helical winding, an internal sealing sheath (4) extruded on said metal carcass, at least one armor ply (6) wound around said sheath internal seal (4) and at least one external seal sheath (8) disposed around said armor ply, characterized in that the compressible rod is made of a material having a high volume compressibility under a low stress which is less than one Newton per linear millimeter of said   rod for a displacement of 60% of material.   2. flexible pipe (1) according to claim 1, characterized in that the rod material is a cellular material constituted by a part of dense material and by hollow cells, the dense material occupying a volume of between 40 and 60% of the total volume of said rod (10), in that said material has a first elasticity module (El) corresponding to a compression of the crucified cells and a second elasticity module (E2) corresponding to a compression of said dense material, the ratio (E, / E2) of the first modulus of elasticity to the second modulus of elasticity being at less than 10.   3. flexible pipe (1) according to claim 2, characterized in that the cellular material has a low stress ufine up to 50% of the compression, said stress being less than Lun Newton per millimeter linear of said rod (10).   4. Flexible pipe (1) according to claim 3, characterized in that   that said stress is less than 0.6 N per linear millimeter of said rod.   5. Flexible pipe according to claim 1, characterized in that the material has a stress greater than one Newton per millimeter   linear of the rod from 65% compression.   6. flexible pipe (1l 1) according to claim 1, characterized in   that the ratio E1 / E2 of said elastic moduli is greater than 30.   il 2779797 7. flexible pipe (1) according to claim 1, characterized in that the penetration depth of the internal sealing sheath (4) in the   gaps (9) is at most equal to 75% of the depth of the gaps.   8. Flexible pipe (1) according to claim 6, characterized in that the penetration depth is advantageously 50% and preferably 30%.   9. Flexible pipe according to claim 1 or 2, characterized in that the cellular material is an elastomer containing silicon and   preferably a silica-fluorinated elastomer.   lo 10. Flexible pipe according to one of claims 1 to 9, characterized   in that a unidirectional reinforcement (11) is housed in the compressible rod (10), so as to give the latter a longitudinal stiffness facilitating   placing said rod in the gaps (9) of the metal carcass (2).   11. Flexible pipe (1) according to claim 10, characterized in that the unidirectional reinforcement (11) is in mineral or organic or vegetable matter. 12. A method of manufacturing the flexible pipe according to claim 1, characterized in that the compressible rod (10) is wound in the gaps (9) of the metal carcass (2) when the latter is   under axial tension and that the joints (9) are at their maximum opening.