AU728380B2 - Flexible metal pipes comprising a retractable polymer sheath - Google Patents

Description

I-'IUU/U11 WWI19 Regulation 3.2(2)

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Application Number: Lodged: Invention Title: FLEXIBLE METAL PIPES COMPRISING A RETRACTABLE POLYMER

SHEATH

The following statement is a full description of this Invention, including the best method of performing it known to us FLEXIBLE METAL PIPES COMPRISING A RETRACTABLE POLYMER SHEATH The present invention relates to flexible metal pipes provided with a retractable polymer sheath, and in particular to flexible tubular conduits incorporating such a sheathed flexible metal pipe and offering significant mechanical resistance especially to internal pressure, permitting their use for instance in off-shore oil and gas production.

The flexible metal pipes may be produced in conventional fashion by the coiling of a profiled interlocking strip (for example as in FR 2 555 920) or of a wire with interconnected helical tumrns (for example as in FR 2 650 652) or by any other process which gives the pipe good flexibility.

Flexible tubular conduits generally incorporate a flexible metal pipe serving as the inner 1. t0 frame which is formed by a helically coiled, profiled metal strip, for instance with interlocking turns, which interlocking strip-coil frame is covered with an impervious polymer sheath and the entire assembly is covered with reinforcing layers to withstand pressure as well as the underwater environment. Such flexible conduits are described for example in patents FR 2 619 193 and in "Recommended Practice for Flexible Pipe API is Recommended Practice 17 B (RP 17 B) First Edition June 1, 1988'.

"Bending of the flexible metal pipes is enabled by providing spaces between the helical tums. The interconnection between the turns is never impervious to liquids or to gas :Consequently, an impermeable polymer sheath is fitted over the metal pipe. Vulcanised rubber, for example, can be used or, for conduits having greater mechanical strength, a thermoplastic polymer presenting the required mechanical properties, for example polyethylene, for moving water or degassed crude oil in the extraction of underwater deposits.

What is most wanted, however, is to find a polymer material which offers three qualities: low permeability to liquids and/or gas, resistance to a wide range of operating temperatures (both mechanical resistance and chemical insensitivity to high temperatures).

and easy industrial implementation. Certain semi-crystalline polymers possess all of these qualities, with the more crystalline types among them being of particular interest due to their low permeability. On the other hand, the higher the rate of crystallinity of a polymer, the higher its rate of physical stress as it passes from the molten state to its crystallised solid state.

If this shrinkage is prevented, as in the case of a sheath extruded around a metal pipe, residual stress is produced especially in the form of tension within the polymer, weakening the shock resistance and flexibility of the sheath.

Furthermore, when the polymer sheath is extruded onto the metal pipe, the polymer enters into the spaces between the helices, thus reducing the degree of flexible movement of the pipe. Depending on the required properties and the intended use of the flexible pipe, such interstitial penetration of the polymer is acceptable in many cases. For certain applications this penetration effect is even sought intentionally, as in FR 2 268 614.

ooooo S"However, given that high-resistance flexible conduits are envisioned for heavy-duty operating conditions, it has been found that the penetration of the polymer in the spaces between the helices can have a negative effect on the performance of the sheath. In particular, studies made by applicants have revealed initial fissures which can lead to is progressive ruptures and to leaks both locally and at the perimeter of the raised section of the sheath as a function of the degree of polymer penetration between the helical turns.

In flexible pipes used in oil or gas extraction where the sheath material must also stand up to live crude without blistering or inflating, the metal pipes can be sheathed with polyamide-11 (PA-11) or, for more demanding operating conditions, with a fluorinated polymer, in particular polyvinylidene fluoride (PVDF). Polyvinylidene fluoride, by virtue of .:i.its crystallinity, chemical near-insensitivity and imperviousness to liquids and gas as well as its resistance to a temperature of the order of 105°C over many years, is the material of choice for the sheathing of flexible metal pipes, yet its rigidity does not permit such use.

To overcome this drawback, the PVDF may be plasticised; however, experience shows that the plasticisers migrate out of the polymer, causing the latter to return to its original rigidity over a period of time, depending again on the temperature of the liquids flowing through the pipe.

Plasticised PA-11 can also be used here to produce a leak-proof polymer sheath for flexible metal pipes.

As an alternative to the modification of an expressively rigid polymer by the application or admixture of a plasticiser, another known approach has been to copolymerise a predominant part of the monomer corresponding to at least one other comonomer.

Nevertheless, the polymer sheaths which can be produced by known methodology have limitations in their potential uses, where the limitations are dependent on performance requirements, especially when the pipe is to carry live crude oil under high pressure and/or at high temperatures. On the one hand, plasticised polymers are affected by the migration of the plasticisers and, in spite of the plasticising, they also involve the risk of a weakening in the areas between the helices when subjected to severe operating conditions. On the other hand, certain extra high-performance polymers whose use would of interest with no or relatively little plasticising remain practically ineligible due to their "excessive rigidity.

It has now been found that it suffices to interpose an elastomer between the metal pipe and the retractable polymer.

The present invention accordingly covers a flexible tubular conduit incorporating an e.

e inner flexible metal pipe whose outer surface displays interstitial spacings and which is covered by a retractable polymer sealing sheath, characterised in that it incorporates :between the retractable polymer sheath and the metal pipe an intermediate elastomer layer such that the sealing sheath rests on the elastomer layer in the areas where said sheath covers an interstitial space and its penetration of the space is negligible or zero.

The prior art has not solved this problem satisfactorily. EP 166 385 describes the wrapping of a polyester tape around the flexible metal pipe to prevent the PVDF from penetrating the spaces. Applicants have tested that technique and have found that the tape partially overlaps itself which is practically unavoidable in an industrial production operation and which proved to be enough to indent the PVDF and bring about a rupture when bent.

US 3 771 570 describes flexible metal pipes made up of interlocking helices and covered with a polymer sheath, preferably of polyvinyl chloride (PVC). The problem posed was the shifting of the sheath relative to the metal pipe. An adhesive layer is therefore incorporated between the metal helices and the PVC to make the PVC sheath adhere to the metal helices. The PVC completely penetrates the spaces between the helical turns.

GB 373 302 describes flexible conduits without reinforcing armour which resist internal pressure, incorporating a flexible metal pipe constituted of interlocking helices covered with a rubber sealing sheath, and a thin, relatively strong layer consisting, for instance, of a sheet of cellophane sandwiched between the interlocking helices and the rubber for the s purpose of protecting the latter from the petroleum carried by the flexible pipe. Between the metal helices and the cellophane sheet a filler material can also be inserted. The cellophane is in the form of a tape wrapped around the helices or applied as a coating in the form of a solution. The rubber is then applied to the outside and vulcanised.

The vulcanisation serves to facilitate the adhesion and the penetration of the cellophane sheet which forms a trough-like fold in each space between two helical turns, with each such space corresponding to a very marked bulge on the inner surface of the rubber. That is exactly the opposite of what is intended by the present invention.

With the present invention, an elastomer. is applied around the flexible metal pipe in an amount large enough to prevent the retractable polymer from penetrating the spaces between the helices very much, if at all, with the elastomer thus forming around the flexible metal pipe an intermediate layer which may envelop the pipe either in one piece or in sections.

The elastomer penetrates each individual space between the helices either partly or entirely. Work done by applicants has shown that, due in particular to the right choice of elastomer material, the shrinkage of the polymer sheath which took place on cooling after extrusion causes a portion of the elastomer to penetrate the interstitial spaces and to substantially reduce or even eliminate essentially any residual stress on the polymer of the sealing sheath.

In addition, the amount of elastomer already in place in the interstitial spaces at the lime of the polymer extrusion can be selected, as a function of the respective viscosity values of the elastomer and the polymer of the extruded sheath, in such a way as to prevent the formation of significant bulges which are encountered in the fabrication of flexible conduits along earlier techniques. It is also possible to limit the penetration of the polymer sheath in the area where it covers an interstitial space such that the inner surface exhibits only a slight, not very high nor significantly curved enlargement. In particular, this inner surface can be essentially cylindrical with a nearly constant cross-section over the length of the flexible conduit.

Accordingly, the present invention is a flexible material pipe whose external surface exhibits interstices covered by a sealing sheath of retractable polymer characterised in that placed between the retractable polymer sheath and the metal pipe and immediately adjacent to the retractable polymer sheath is an intermediate elastomer layer, optionally vulcanised or reticulated, and/or TPE which is in the form of a continuous tubular envelope, as in Figures 1 to 3, or in the form of a tape placed in the interstices, as in Figures 4 to 6, and further characterised in that the elastomer has a stiffness less than that of the retractable polymer and that the retractable polymer sheath is formed by extrusion.

In an embodiment of the present invention, the elastomer layer constitutes a tubular sleeve covering the flexible metal pipe in one piece. In those areas where it covers the cylindrical median section of the helices making up the flexible metal pipe it has a nearly constant thickness which is preferably between 0.1 and 2 mm. The polymer sealing sheath does not touch the flexible metal pipe at any point.

In another embodiment, instead of covering the entire flexible metal pipe, the intermediate elastomer layer is placed only in the interstitial spaces between the helical turns. In this design the elastomer layer is in the form of a more or less thick, continuous tape having an approximately constant cross-section which is applied in a generally helical fashion around the axis of the flexible conduit .oooo) corresponding to the free space between adjacent helical turns of the constituent sections, such as interlocking helical strips, of the flexible metal pipe.

•go• S: 25 Alternatively, the elastomer layer may be comprised of two, three, or even o•.

more helicoidal elements, for instance tapes, when the flexible metal pipe consists of two, three or more sections.

In the above two embodiments the elastomer fills the outer part of each interstitial space to a more or less significant depth, with the elastomer coverage 30 of the free area within the spaces optionally being essentially complete. The amount of elastomer should preferably be between 25% and 75% of the free spatial volume within the spaces between the helices.

o The retractable polymer is defined as any one polymer or mixture of polymers whose mould shrinkage is greater than or equal to 1% or, better yet, The retractable polymer is preferably of the semi-crystalline polymer type.

The semi-crystalline polymers which are suitable for the purposes of the present invention are those described in the POLYMER HANDBOOK, Third Edition (published by BRANDRUP and E.H. IMMERGUT) VI/1 to 89, an in particular the following: the polyolefins, the polyamides, the polyurethanes and polyureas, oooo oo ego• the polyesters, -the polyethers, -the polyoxides, the Parax polysulfides (PPS), s the polyether-ether-ketones (PEEK) and their copolymers the fluorous polymers such as: -the home- and copolymers of vinylidene fluoride (VF 2 -the homo- and copolymers of trifluoroethylene (VF3) the copolymers, and especially terpolymers, associating remainders of the activators chlorotrifluoroethylene (CTFE), tetrafluoroethylene (TPE). hexafluoro propene (HFP) and/or ethylene and optionally the activators VF 2 and/or VF 3 Among the fluorous polymers, the more suitable ones are the vinylidene fluoride-based homo- and copolymers due to their excellent chemical insensitivity to live crude oil or gas and their stability at high temperatures. By way of example, especially for oil and natural gas, it has been noted that a copolymer having at least 50% by weight vinylidene fluoride activators in the polymeric chain could provide sufficient impermeability. The definition of fluorous polymers also refers to mixtures of at least 70% by weight of the above with other polymers.

Without departing from the scope of the present invention, the retractable and preferably semi-crystalline polymers may also contain plasticisers, fillers, pigments, stabilisers, anti-impact reinforcements, and other such conventional additives.

The elastomeric polymers which make suitable materials for producing the intermediate elastomer layer are defined by ASTM D 883 as materials which, at ambient temperature, quickly retum to their approximate initial dimensions and shapes after having undergone a significant deformation as a result of minor stress applied to the slack material.

Suitable elastomeric polymers not only include elastomers proper (applied in their vulcanised or reticulated state) but also thermoplastic elastomers (widely referred to as TPE) which exhibit an elongation at their flowage threshold of greater than 15%. The TPEs rank between thermoplastic resins which are easy to work with and versatile, but have limited temperature-resistance qualities or dynamic properties, and the elastomers having highly elastic properties but are difficult to work with, complex and often environmentally polluting. The structure of TPEs always displays two incompatible phases, one of which brings together the dispersed thermoplastic sequences in the elastomer phase. Five TPE categories are generally distinguished between: the thermoplastic polyolefin elastomers (TPO) are physical mixtures made from s polyolefins. There are those which contain more than 60% polypropylene and those with a preponderant elastomer phase (over 70%) and which may or may not be reticulated.

-the polystyrene-based copolymer units whose rigid phase consists of polystyrene sequences, while their pliant phase may be formed for instance by polybutadiene (SBS).

polyisoprene (SIS), or poly(ethylene-butylene) (SEBS) sequences.

the polyurethane-based copolymer units (TPU) which can be obrained by the joint reaction of a diol of high molecular mass constituting the crystallisable pliant sequence of the TPE, with a diisocyanate and a diol of low molecular mass which engenders the rigid sequence.

the polyester-based copolymer units such as those obtained by the copolymerisation of a polybutylene terephtalate (PBT) or a polyethylene terephtalate (PET) which constitutes the rigid and crystalline sequences, and a glycol of low molecular weight (butane diol.

diethylene glycol) which, in association with a polyalkylene ether glycol, forms the crystallisable pliant sequence.

the polyamide-based copolymer units whose rigid sequences are constituted by polyamide (PA) and the pliable crystallisable sequences of polyester, also known as polyetheramides.

The stiffness of the elastomer is preferably less than that of the retractable polymer: it can be evaluated in terms of torsion and/or flexion and/or tension moduli and/or Shore hardness values which are measured under the same conditions for both the elastomer and the retractable polymer. The stiffness of the elastomer should preferably remain below that of the retractable polymer irrespective of the operating conditions when in use, especially in terms of temperature and in due consideration of the ageing of these materials.

It is preferred for the elastomer to be of a Shore A hardness at 23'C of less than 92 (and ideally less than 70), or of a Shore D hardness of less than 50 when measured by the ISO 868 standard.

The torsion modulus of the elastomer at 23 0 C is preferably less than 100 N/mm 2 or.

better yet, less than 30 N/mm 2 and ideally less than 10 N/mm 2 (measured according to DIN standard 53447).

SIt is preferred that the tension modulus of the elastomer at 23*C is less than 400 MPa s or, better yet, less than 100 MPa (measured according to ISO 527).

The tensile strength, that is, break elongation of the elastomer at 23 0 C is preferably greater than In the case of TPEs, the preferred material is one which has a VICAT of less than 70 0

C

when measured by the A/50 method according to the ISO 306 standard.

It is best to use elastomers which simultaneously display the above-specified values in terms of hardness, VICAT level, torsion modulus and breaking elongation.

The torsion modulus of the elastomer preferably remains below 30 N/mm 2 (measured according to DIN standard 53447) over the course of its thermal ageing.

The elastomers and/or TPEs specially recommended within the scope of the present invention may be selected from among the EPDM copolymers, the acrylonitrile butadiene styrene copolymers, the methylmethacrylate butadiene styrene copolymers, the ethylene carbon oxide copolymers, the ethylene carbon oxide vinyl acetate terpolymers, the acrylic rubber types, the thermoplastic copolyethers esters, the polystyrene-based and polyisoprene-type, polybutadiene-type and the like, copolymer sequences, the styrene butadiene styrene copolymers, the ethylene ethylacrylate, ethylene ethylacetate and ethylene vinyl acetate copolymers as well as their terpolymers, the fluorous elastomers, the silicone elastomers, the fluorous silicone elastomers, the polyurethanes.

Within the scope of the present invention elastomer and/or TPE mixtures may also be used.

For the requirements of the present invention a thermoplastic polyurethane (TPU) elastomer of a Shore A hardness less than 92 as measured in accordance with ISO standard 868 can be used. Moreover, it is preferred that this elastomer can sustain a strong viscosity reduction during thermal ageing. This viscosity reduction is preferably at least 60% over days at 120 0 C. The thermoplastic polyurethane elastomer usually displays a viscosity at 9 which lies within the range shown below. The values take into account the RABINOWVITCH correction as applied to non-Newtonian liquids.

Corrected shear rate s-1 Viscosity in kPa.s s 4.09 0.7 1.3 13.64. 0.25 0.85 36.15 0.19 0.78 122.91 0.12 0.70 The shear rate shown is also the shear-deformation rate gradient.

The elastomer should generally and preferably have a high level of chemical insensitivity and temperature stability, especially in the case of conduits carrying live crude 4 10 which contains various components highly damaging to a great many plastic materials.

Especially in the case of live crude which generally includes a more or less significant water content, the selected elastomer should preferably be one which is not susceptible to the effect of hydrolysis on the relatively high temperature of the crude coming out of the well, nor to any other form of water-induced degradation.

15 Also, as a function on the one hand of the retractable polymer selected for the sealing sheath and, on the other hand, of the operating environment of the conduit and in particular the temperature and the liquids carried, the elastomer is preferably selected in a way that any possible degradation products do not pose the risk of affecting the 2 performance characteristics of the retractable polymer as they progressively migrate 20 through the sealing sheath.

An interesting example of elastomers possessing the desired properties of stability and chemical insensitivity is found in the silicone group, and in particular the elastomer silicones of the RTV type (vulcanisable at ambient temperature) or HCR type (cold-vulcanisable).

In the case of HCR as well as RTV silicones, the vulcanisation can be performed in continuous fashion so as to speed up the operation, with the flexible conduit being drawn through or past heating devices (such as a hot-air or radiant or other type of heating systems).

The elastomer is selected and applied in a way that its interposition prevents the penetration of the polymer of the sheath into the recesses between the helical turns; the flow of the hot material during the extrusion of the polymer sealing sheath and the effect of the stress applied by the sheath during its shrinkage will accordingly cause it to penetrate the open spaces of the outer surface of the flexible metal pipe corresponding to the interstitial spaces between the helical turns in a way that the polymer of the sheath is free to retighten itself around the metal pipe without generating within itself any internal stress.

s Figures 1 and 2 of the accompanying diagrams show the cross-sections along both axes of a flexible tubular conduit according to the first embodiment of the present invention.

Interlocking articulation lips (16,17) of flexible metal pipe create interstices and spaces between the helical metal turns. Elastomer layer covers the metal pipe, filling all the spaces between the metal helices. This elastomer layer serves as an intermediate layer ee 10 between the flexible metal pipe and outer, retractable polymer layer Figure 3 of the accompanying diagrams shows the cross-section of a flexible tubular conduit again according to the first embodiment of the present invention, but more specifically intended for carrying water, oil or gas in an offshore extraction operation.

Flexible metal pipe constituting the inner frame of flexible pipe is produced by is closely coiling an interlocking strip whose successive turns (4a, 4b. 4c, delimit an interstitial space which opens toward the outside in a generally helical configuration, as :well as internal interstices which open toward the inside of the pipe. and inner spaces which are more or less closed. Elastomer layer covers the flexible metal pipe in continuous fashion, filling all interstitial spaces between the helical turns. This elastomer layer serves as the intermediate layer between the flexible metal pipe and retractable polymer layer which constitutes the inner sealing sheath of the flexible conduit. The reinforcing armour cladding on the outside of the sealing sheath assures mechanical strength of the flexible conduit and in particular its resistance to internal pressure within the pipe when in use, where the effect of the internal pressure is fully transmitted to said armour through the sealing sheath. The plastic material of the sealing sheath is thus subjected to very specific working conditions, with a virtually uniform pressure stress field whose extremely high value, optionally reaching or exceeding 100 MPa, corresponds to the internal pressure, while deformations and shear stress remain quite low.

In the case of the example illustrated, the circumferential pressure or hoop stress resistance is substantially assured by said pressure-absorbing armour cladding consisting of a closely coiled wire or strip, preferably of the interlocking wire type such as 11 Zeta wire, while the axial components of the force are retained by the pair of armour sleeves (11 a, 11 b) consisting of a plurality of wires at opposing angles of, for instance, 300 or 40 0 in relation to each other. Alternatively, resistance to the internal pressure can be provided by a single pair of armour sleeves whose wires are wound in opposite direction to each other at an angle of about 550. The wires of armour sleeves (10, 11) typically consist of metal such as steel or aluminum, or of a preferably fibre-reinforced plastic, or even of a high-strength fibre material.

The flexible tubular conduit is protected by an outer sheath (12) preferably made by extrusion from a thermoplastic polymer.

The role of the flexible metal pip is to assure crush resistance of the flexible conduit and to prevent collapsing of sealing sheath under certain operating conditions.

Compared to bonded flexible pipes, flexible conduit is of the unbonded flexible type which incorporates separate structural elements; this is a particularly interesting aspect of the present invention.

In the case of the example in Figure 3, elastomer layer constitutes a continuous tubular sleeve which envelops flexible metal pipe and its outer surface, which is in contact with the inner surface of sealing sheath is approximately cylindrical, with a minor depression (18) at the location of interstitial spaces The elastomer of layer fills interstitial space essentially completely. Alternatively, depending especially on the viscosity and the amount of the elastomer as well as the fabrication process, it would be possible according ooooi to an embodiment, not illustrated, to produce intermediate layer with less o°°S penetration in interstitial spaces oo00 25 Figures 4 to 6 show an enlarges, partial longitudinal section through a flexible conduit according to a second embodiment, incorporating an intermediate elastomer layer consisting of an elastomer tape (8A) placed in interstitial space which separates cylindrical outer parts (13a, 13b, 13c, of the successive helical turns constituting flexible metal pipe The alternating succession of cylindrical outer parts (13) of the metal pipe and outer surfaces (14) 0 of elastomer tape (8A) produces an approximately cylindrical surface which supports sealing polymer sheath in continuous fashion.

In the event where the flexible metal pipe is made up of a continuous helical coil of a single strip such as an interlocking hoop-type strip elastomer layer is comprised of a single continuous tape Alternatively, the flexible metal pipe can incorporate one or several contoured sections coiled in parallel, with elastomer layer consisting of a number of tapes (8A, 8B, equal to the number of contoured sections (3A, 3B, of the flexible metal pipe.

Figure 4 which illustrates a variation of the second embodiment also shows the armour cladding of the flexible pipe, incorporating in this case a pressure shield (10) and two tension-absorbing sleeves (Ila, lib) as well as outer sheath (12).

i 10 In the case of the variations according to Figures 4 and 5 the elastomer partially penetrates into interstitial spaces with the inner end of the area occupied by the elastomer located at a radial distance of a relative to the cylindrical surface defined by outer i cylindrical parts (13) of the flexible metal pipe. The version according to Figure 6 incorporates an intermediate layer consisting of an elastomer tape penetrating interstitial S" 15 is spaces in approximately complete fashion.

Relative to the ideal configuration which would be a perfectly cylindrical surface along the extension of cylindrical sections (13) of the interlocked strip, outer surface (14) of the elastomer may display an irregular form such as a minor depression or bulge.

The irregularity in outer surface (14) would preferably be in the form of a hollow like :20 a meniscus whose concave side faces toward the outside as illustrated in Figures 4 and 6.

In this case, polymer sealing sheath exhibits on its inner side a slight bulge (15) whose thickness d in the radial direction relative to the cylindrical reference surface defined by cylindrical surfaces (13) of the interlocked strip is preferably less than or equal to 0.3 e, e being the thickness of sheath in its cylindrical section around surfaces (13).

Altematively, elastomer tape (8A) can be of a shape which is slightly convex toward the outside, as in Figure 5. Its outer surface (14) has a cylindrical central part which connects to the outer surface of interlocking strip in a gradual progression with a very slight curvature and which is marginally separated from said cylindrical reference surface, with the radial distance separating the two surfaces preferably being less than 0.2 e.

Generally, irrespective of the selected embodiment and in particular in the oase of the examples shown in Figures 1 to 6, good results are achieved if the curvature of the inner 13 surface of polymer sealing sheath remains limited to very low levels in the areas adjoining interstitial spaces where it can have minor irregularities. Preferably, the smallest radius of curvature which this inner surface should display is greater than 0.5 e and, better yet, greater than the e-value of the thickness of sheath with these radii of s curvature at least equal to 2 e permitting maximum utilisation of the intrinsic properties of the material.

The thickness of retractable polymer sheath may generally vary between 1 and mm and the average would be between 3 and 15 mm, depending primarily on the diameter of the flexible tubular conduit.

'e'e 10 The width 1 of interstitial space at the plane of its outer opening, that is, its width between cylindrical parts (13) of adjacent helical turns, may vary etween 2 and 40 mm. The .edges of the interlocked contoured section, such as interlocked strip which form the boundaries of space are preferably rounded so that the width of the interstitial space diminishes from the outside toward the inside. If measured at a plane corresponding to the 15 mid-point of the radial depth h of the interstitial space, the width of the space may be of the order of 1 to 15 mm. In practice, the depth h of the space may vary between 1.5 and 30 mm, meaning that the h/I ratio between the depth h and the outer width I may accordingly vary between 0.4 and 1.4.

The manufacture of substantial continuous lengths of the flexible conduit according to the present invention can be accomplished producing polymer sheath by conventional extrusion methods. Where elastomer layer constitutes a continuous tubular envelope around the flexible metal pipe, the elastomer can be applied by extrusion onto the flexible metal pips. In this case it is possible for instance to simultaneously coextrude the retractable polymer and the elastomer by means of two extruders and a double-headed flowdistribution box in which the flexible pipe to be sheathed is centred. The penetration of the elastomer into interstitial spaces between the helices of the flexible metal pipe now depends, especially in a first pass, on the viscosity of the thermoplastic elastomer in its molten state. It is also possible to sheathe the flexible metal pipe conventionally by extruding the elastomer sheath onto the metal pipe and then cover the assembly with a retractable polymer layer in a second, in-line ext ruding operation further downstream at the output end of the first extruder from which the elastomer-coated flexible pipe emerges (extrusion tandem), or in a separate extruding operation performed after the first extrusion, or even by sheathing the flexible metal pipe with the elastomer, optionally dissolved in a solvent and then, after perhaps reticulation and/or evaporation of the solvent, in a second pass, covering the assembly with a layer of retractable polymer by extrusion sheathing.

Alternatively, the intermediate elastomer layer can be produced either in the form of a continuous tubular sleeve as illustrated in Figure 3, or in the form of a tape (8A) placed in interstitial spaces as shown in Figures 4 to 6, by an induction process, or by spraying for instance with an aerosol or especially electrostatic precipitation, or by immersion in a liquid bath involving for instance the dissolving of the elastomer in a solvent, or in a 10 fluidised bed, or by any other known process for covering the surface and/or the interstitial surface gaps of the flexible metal pipe with the elastomer. In the case of vulcanisable elastomers, the elastomer can also be successively applied to the metal pipe in its raw state and then vulcanised, preferably prior to the extrusion of sealing sheath One advantageous process involves the application of the elastomer by passing the flexible is5 metal pipe in continuous fashion through a chamber filled with raw elastomer, for which metal pipe enters and exits the chamber through circular openings which may be provided for instance with a rubber collar whose diameter is calibrated in a way that it embraces the pipe or, leaving a certain amount of free space, that the intermediate elastomer layer can be produced in the form of a tape (8A) applied in the interstitial spaces 20 or in the form of a continuous tubular sleeve.

According to another application process, the elastomer can be put in place by helically wrapping it around in the form either of ties or of a continuous tape, where the elastomer is in the vulcanised or thermoplastic state. Tie rings can also be used if the material is sufficiently soft to permit adaptation to the desired shape of the elastomer tape A ring or tie in the form of an elastomer would preferably be used whose cross-section is such that it corresponds to the configuration of interlocking contoured sections which radially flank and delimit interstitial space on each side. Ties so shaped, having a cross-section corresponding to the profile of the interstitial spaces, can thus constitute for instance the tape (8A) illustrated in Figure 3.

Without departing from the scope of the present invention, an intermediate elastomer layer can be produced in the form of a continuous tubular sleeve by helically coiling an elastomer ribbon with the edges butting, with the elastomer being sufficiently soft to permit easy shaping especially under the effect of the extrusion of sealing sheath so as to produce a regular, fairly smooth outer surface without overlapping and without gaps between adjoining turns. On its inner surface the band may incorporate a raised midsection s which protrudes in adaptation to the profile of interstitial spaces so as to securely fill the spaces to a certain depth corresponding to the side wall a as in Figures 4 and A variation of the present invention, not illustrated here, consists in the interposing of a thin sheet produced by wrapping one or several layers of a tape, made for instance of a fabric, of fibres or of a plastic material optionally fibre-reinforced, between flexible metal pipe and intermediate elastomer layer For easier industrial production, the wrapping of the tape may take place by the overlaying of a sheet of regular characteristics; the elastomer material supporting the tape is not in contact with the surface of the flexible pipe and is therefore not affected and/or degraded by the surface irregularities created by such overlaying. Preferably, a tape of sufficient mechanical strength is used so that the 15 sheet permits easy partial and regular filling of interstitial spaces with the elastomer of the intermediate layer.

Within the scope of the present invention, and for the purpose of strengthening the 99*e adhesion between the elastomer and the retractable polymer, a certain amount of retractable polymer can be added to the intermediate elastomer layer and/or a certain 99 :20 amount of elastomer can be added to the retractable polymer prior to their extrusion for instance by one or the other of the methods described above. Between the intermediate elastomer layer and the retractable polymer sheath a layer may also be interposed consisting of a mixture of elastomer and retractable polymer; this can be accomplished for instance by coextruding a three-layer sheath of elastomer/elastomer+ retractable polymer/retractable polymer.

The thickness of the intermediate elastomer layer or the TPE may generally vary between 0.1 and 2 mm measured from the apex of the flexible conduit.

The thickness of retractable polymer sheath may generally vary between 1 and mm and is usually between 3 and 15 mm, depending primarily on the diameter of the flexible tubular conduit.

The flexible tubular conduit which is the object of the present invention is especially suitable for use in oil and gas exploration/extraction where the inner diameter of the flexible metal pipe may be of the order of 20 to 600 mm and more typically betwveen 50 and 400 mm, with the internal pressure in the conduit typically being greater than 1.450 psi and.

s depending on the diameter, can reach or exceed 7,250 psi or even 14,500 psi. Such flexible pipes are particularly well suited for use involving high temperatures which.

depending on the polymers selected, may reach or exceed values of the order of 100 0 C to 120°C which constitutes the limits currently possible.

The following examples illustrate the invention without being in any way limiting in S* 10 nature.

Around a flexible steel pipe 32 mm in diameter and made up of helical turns, or helices, between which there are hollows and interstitial spaces to permit articulated bending, an elastomer layer constituting a continuous tubular envelope or sleeve around the metal pipe is applied by the method indicated in each of the tables relating to is each of the examples given, and a semi-crystalline polymer layer is extruded or coextruded as indicated in the tables. For purposes of comparison, the same pipe is produced under the same conditions with the same semi-crystalline polymer sheath, but without the *intermediate elastomer layer.

The pipes are tested in the following manner: 5 20 The sheathed pipe is placed on two stationary supports. With the use of a bending wheel with a radius of 75 mm, pressure is exerted at a point equidistant from the two pipe supports.

A pressure of 50 bars is applied. The pipe bends around the wheel. The indentation depth of the wheel indicates the ability of the flexible pipe to deform.

In all the examples the Shore A and D hardness values are measured according to ISO standard 868.

Example 1 In all the tests the semi-crystalline polymer is polypropylene (PP) with a melt index of 3g/10 min measured according to ISO 1133, and a thickness of 5 mm. (APPRYL® 3030 FN1 by the APPRYL Co.).

The elastomer is: SPolyurethane polyether (UTAFLEX3 TB 1 by the UETWILLER Co.) Shore A hardness 50 after reticulation.

6 Copolymer of polyamide and polyether units combined by ester functions, s PEBAX 3 2355 ELF ATOCHEM Shore A hardness 75; bending modulus at 23 0 C MPa measured according to ISO standard 118.

Polymer VF 2

C

2

F

3 CI in a molar 50/50 proportion, having a bending modulus at 23°C of 250 MPa measured by ISO standard 178.

10 Test temperature: 0 0 C ra A mThickness, measured from Elastomer layer Application method Thickness, measured from apex of the helices Polyurethane- By induction followed by 2 components baking for 1 hour at 80C 0.5 mm Elastomer extrusion onto Polyether-esteramide-- the pipe followed by 1 mm extrusion of the PP Polymer--- Direct coextrusion of PP

VF

2

VF

3 onto the steel pipe 1mm a.

a The above test results show better deformability, and in particular better bending ability, of the flexible pipes sheathed with an intermediate elastomer layer sanrdwiched between the so-called skeleton or frame of the flexible steel pipe and the outer retractable polymer sheath according to the present invention.

Example 2 In all of these cases the elastomer is a polyester polyurethane having a Shore A hardness of 88 (ESTANE® 58271) and a thickness of the elastomer layer of 1.5 mm measured from the apex of the helices.

Test temperature: 0 C Semi-crystalline polymer constituting the sealing Application method Thickness sheath Polyet e By extrusion onto the pipe (n 10) extrusion-coated with 5 mm elastomer Polyamide-1 1 Coextrusion onto the 4mm (RILSAN BESNO TL) metal pipe 4 mm Copolymer py' Extrusion onto the metal ethylenepipe extrusion-coated 5 mm (TEFZEL 200 by DUPONT)with eastomer with elastomer___

S

S. *5

S

S40,000 s MN 45,000 Shore D 75, impact resistance at -55 0 C 187 J/m measured according to is ASTM D 256.

The above test results show improved deformability, and in particular better bending ability of the flexible pipes which are sheathed with an intermediate elastomer layer sandwiched between the frame of the flexible steel pipe and the outer retractable polymer 20 sheath, according to the present invention.

Example 3 Around a flexible steel pipe 32 mm in diameter and made up of helices between which there are hollows and interstitial spaces to permit articulated bending, the following sheathing is applied by successive extrusions: A layer of polyester polyurethane (ESTANE 58271) 0.5 mm thick from the apex of the helices, and then a vinylidene polyfluoride layer FORAFLON 1000 HD) (sample 5 mm thick. The polyester polyurethane has a Shore A hardness of 88 and displays a viscosity reduction of more than 70% over 30 days at 120 0

C.

For comparative purposes the same pipe is produced under the same conditions, except without the intermediate polyurethane layer (sample 2).

The two pipes are compared under the conditions shown below.

The sheathed pipe is placed on two stationary supports. With the use of a bending wheel having a radius of 75 mm, pressure is exerted at a point equidistant from the two 19 pipe supports. A pressure of 725 psi is applied. The pipe bends around the wheel. The indentation depth of the wheel indicates the deformability of the flexible pipe. The maximum height is 170 mm; it corresponds to the perfect circumflexion of the pipe over the radius of curvature of the wheel. If during the indentation process the flexible pipe s ruptures the depth is noted. The greater the depth, the greater the bending ability of the pipes.

10 1 Temperature Indentation depth __Sample 1 Sample 2 20"C 170 mm 120 mm No rupture No rupture -30"C Rupture at Rupture at 150mm 80 mm Example 4 The samples 3 and 4 are prepared in the same manner as samples 1 and 2, except that the vinylidene polyfluoride is plasticised, at 7.5% by weight, with N-butylbenzene sulfonamide.

Sample 3 has an intermediate layer of polyester polyurethane 1 mm thick above the apices of the helices, and an outer layer, 6mm thick, of plasticised vinylidene polyfluoride.

Sample 4 does not have an intermediate polyester polyurethane layer.

Successive bending tests of the sheathed pipes are performed on a mandrel having a radius of 68 mm. After each new bending test, the pipes are subjected to a temperature of 0 C for one hour.

Sample 3 could be bent five times without rupturing.

Sample 4 whitens after the fourth bending and splits at the fifth.

The sample pipes 3 and 4 are aged for one month at 150°C in a ventilated oven.

The same bending test is then performed at -10 0

C.

Sample 3 whitens at the third bending and cracks at the fourth.

Sample 4 breaks at the first bending.

Claims (12)

1. A flexible material pipe whose external surface exhibits interstices covered by a sealing sheath of retractable polymer characterised in that placed between the retractable polymer sheath and the metal pipe and immediately adjacent to the retractable polymer sheath is an intermediate elastomer layer, optionally vulcanised or reticulated, and/or TPE which is in the form of a continuous tubular envelope, as in Figures 1 to 3, or in the form of a tape placed in the interstices, as in Figures 4 to 6, and further characterised in that the elastomer has a stiffness less than that of the retractable polymer and that the retractable polymer sheath is formed by extrusion.

2. Flexible pipe as claimed in Claim 1, characterised in that the retractable polymer sheath is semi-crystalline.

3. Flexible pipe as claimed in Claim 1 or 2, characterised in that the elastomer is selected from among: the silicone elastomers, possibly fluorous, the polyamide-based TPEs, the TPUs, the EPDM copolymers, the acrylonitrile butadiene styrene copolymers, the methylmethacrylate butadiene styrene copolymers, the ethylene carbon oxide copolymers, the ethylene carbon oxide vinyl acetate terpolymers, the acrylic rubber types, the TPOs, the polyester based TPEs, the ethylene ethylacrylate, ethylene, ethylacetate and ethylene vinyl acetate copolymers as well as their terpolymers, the fluorous elastomers. pg

4. Flexible pipe as claimed in any one of Claims 1 to 3, characterised in that the retractable polymer(s) are selected from among: the polyolefins, the polyamides the polyurethanes and polyureas The polyesters the polyethers, S the polyoxides, the Parax polysulfides (PPS) (i 21 the polyether-ether-ketones (PEEK) and their copolymers the fluorous polymers such as: Sthe home- and copolymers of vinylidene fluoride (VF2), -the homo- and copolymers of trifluoroethylene (VF 3 s the copolymers, and especially terpolymers, associating remainders of the activators chlorotrifluoroethylene (CTFE), tetrafluoroethylene (TFE), hexafluoro propene (HFP) and/or ethylene and optionally the activators VF 2 and/or VF 3 and advantageously PVDF and the copolymers having at least 50% by weight vinylidene fluoride activators in the polymeric chain, said retractable polymers able to be alone in a mixture with other 10 polymers, said retractable polymers being present at the rate of at least 70% by weight in the mixture.

5. Manufacturing process of a sheathed flexible metal pipe as claimed in any one of Claims 1 to 4, characterised in that the intermediate elastomer layer and the sealing sheath 5s of retractable polymer are extruded simultaneously onto the flexible pipe.

6. Manufacturing process of a sheathed flexible metal pipe as claimed in any one of Claims 1 to 4, characterised in that in a first pass the elastomer is sheathed onto the flexible S.o 2 pipe by extrusion, induction, pulverisation, projection or immersion in a liquid or fluid bath, 20 then the whole is covered by extrusion by a retractable polymer layer.

7. Manufacturing process of a sheathed flexible metal pipe as claimed in any one of Claims 1 to 4, characterised in that the elastomer is placed onto the flexible pipe by taping such as by helicoidal wrapping of a rod or continuous strip, where the elastomer is either vulcanised or thermoplastic.

8. Manufacturing process of a sheathed flexible metal pipe as claimed in Claim 7, characterised in that the elastomer is placed onto the flexible metal pipe in the form of a continuous tubular envelope by helically unrolling an interlocking elastomer strip.

9. Manufacturing process of a sheathed flexible metal pipe as claimed in Claim 7. characterised in that the elastomer is placed on to the flexible pipe in the form of a rod placed in the interstice Manufacturing process of a sheathed flexible metal pipe as claimed in any one of Claims 5 to 9, characterised in that a thin sheet produced by wrapping one or several layers of a tape, made for instance of a fabric, of fibres or of a plastic material optionally fibre. reinforced, is interposed between the flexible metal pipe and the intermediate elastomer layer

11. Manufacturing process of a sheathed flexible metal pipe as claimed in Claim characterised in that a certain quantity of retractable polymer is added to the intermediate elastomer layer and/or a certain quantity of elastomer is added to the retractable polymer before their coextrusion, or between the intermediate elastomer layer and the retractable polymer sheath a layer is interposed consisting of a mixture of elastomer and retractable polymer and a three-layer sheath of elastomer/elastomer+ retractable polymer/retractable polymer is coextruded.

12. Flexible tubular conduit comprising a sheathed pipe as claimed in any one of Claims 1 to 4, preferably reinforced by armour, which can be used for transporting liquids. especially pressurised and/or at high temperatures.

13. Flexible tubular conduit as claimed in Claim 12 which can be used for the production of petrol and/or off-shore gas. DATED this 20'" day of December, 1999 ELF ATOCHEM S.A. AND COFLEXIP S.A. WATERMARK PATENT TRADEMARK ATTORNEYS 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA ;:JGC:PcP Doc 25 AU002995.WPC