AU1836199A - Flexible metal pipes comprising a retractable polymer sheath - Google Patents

Description

Requ a' fim 3 242)

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Application Number: Lodged: invention Title: FLEXiBLE METAL PIPES COMPRISING A RETRACTABLE POLYMER

SH-EATH

The following statoment Is a lull description of t1his Invention, Including the best method of performing it known to us 1 P- 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.

S 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 turns (for example as in FR 2 650 652) or by any other process which gives the pipe good flexibility.

j Fexible tubular conduits generally incorporate a flexible metal pipe serving as the inner I. to 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 S 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. 19S8'.

Bending of the flexible metal pipes is enabled by providing spaces between the helical turs. 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 :0 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 andior gas. resistance to a wide range of operating 2s 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 s 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 to applications this penetration effect is even sought intentionally, as in FR 2 268 614.

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 Sup 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 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 ;l 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 sa 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.

h As an alternative to the modifiction of an exoprssiveKy rigid poymer by the application or admixture of a piasticiser, another known approach has been to copolvmerise a predominant part of the monomer corresponding to at least one other comonomer.

Nevertheless, the polymer sheaths which can be produced by known methodology s have limitations in their potential uses. where the limitations are dependent on performance requirements, especially when the pipe is to cary live crude oil under high pressure and/or at high temperatures. On the one hand. plasticised polumers 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 a conditions. On the other hand. certain extra high-performance polymers whose use would be of interest with no or relatively little plasticising remain practicaiy 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.

i s The present invention accordingly covers a flexible tubular conduit incorporating an S 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 :a 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 PUDF 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 2s 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 3o 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 with out reinf:orcinrg aouwhch- reist nternai pressure. incoporatng a flex ibi !et CCP- ccsZot-ute- &r 1tez-!c6,ing hzElces covered with a rubber sealing sheath, and a thin, relatively s:ronq lauYer consisting, "'or instance. of a sheet of cellcphane sandwiched between the interlocking helices and the rubber for the purpose of protecting the latter from the Petroleum Carried by the fie\ib~e pipe. Betwveen the metal helices and the celloohiane sheet a filler- material can aLso be insertLed. The cellophane is in the form of a tape wrapped around thne helices or applied as a coating in the form of a solution. The rubber is then applied to the outside and -ulcanisec.

T he vulcanisation serves to facilitate the adhesion and the penetration of the To cellophane sheet which forms a trough-like -told in each space betwveen two helical turns.

with each such space corresponding to a very marked bulge on the inner surface of the &--rubber- That is exactly the opposize of wkhaz is intended by the presen, invention.

With the present invention, an elastomer is applied around the flexible metal pipe in an amount large enough to prevent -he retractable Polymner from penetraling the spaces Is between the helices very much, it-at all,. with thie elastorner thus forming a-ound the flexible metal pipe an intermediate lave.r which may envelop the pipe either in one piece or in sections.

j. Te elstorer enetrates each individuapl space between the heLices eithe partlyor entirely. Work done by applicants has shovwn that, due in particular to t~he right choice o; elastomer material, the shrinkage of the polymner shez!:h which took place on cooling after extrusion causes a portion o' the elastone to penerrate the intersttia[ spaces and to substanl~ai~y reduce or even eiiminiate essentially any residual stress on th e polymer of the sealing sheath.

In addition, the amount of elastomer alreadY in p lace inthe inters-iial spaces at the 2S lime of the polymer extrusion ca., be selected, as a function of the respective viscosity values of the elastomer and the polymer of the ex-truded sheath. in such a way as to prevent the formation of significant bulges w-;hich 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 interstiial space such that the inner surface exhbi~onl a ligt, ot eryhig no sgn ficantly curved enlargement. In particular, this inner surface can be essentially cylindrical with a nearly constant cross-section over the length of the flexible conduit.

in a first embodiment of the present invention, the elastomer layer constitutes a tubular Isleeve covering the flexible metal pipe in one piece. In those areas where it covers the s 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 a second embodiment, instead of covering the entire flexible metal pipe. the intermediate elastomer layer is placed only in the interstitial spaces between the helical o1 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 corresponding to the free space between adjacent helical turns of the constituent sections, such as interlocking helical strips, of the flexible metal pipe.

is Alternatively, the elastomer layer may be comprised of two. three, or even more Shelicoidal 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 eiastomer coverage 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.

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) Vill to 89. and in particular the following: the polyolefins, 3 the polyamides.

the polyurethanes and polyureas, the polyeSters.

-the polyoxides.

the Parax polysulfides (PPS), the polyether-ether-ketones (PEEK) and their copolymers the fluorous polymers such es: the home- and copolymners of vinylidene fluoride the homno- and copolymers of trifluoroethylene the copolymers. and especially terpolymers. asscciating remainders of the activatOrs Ch[orotrifluoroethyfiene (CTFE). ItetraIoroeth,,Jene iTE.hexcaflt.oro propene (HFP) an&or ethylene and optionaly, the activators \JF, an~d;or VCF 3 Among the fluorous polymers. the more suitable ones are e vinlildene fluoridle-based hono- and copolymers dlue to their excellent chemical insensifivity to live crude oil or gas and their stability at high temperatures. By wLav 0f examnple, especially for oil and natural IS gas. it has been noted that a copolymer having at least 50%0 by -,;eight Vinylid ene fluoride activators in the oolyrneric chairn could provide sufficient imperme11ability. The definition of fluorous pclymners also refers to mixtures of at least 70% by weight of ah above ith ot polymers.

Without departing from the scope of- the present invention, the retractable and opreferably semi-crtvstalline polymers may also contain 01as'.cisers. filters, pigments.

sta-biliser.s, anti-impact reinforcements, and other such conventional additives.

The elastomeric polymers which make2 suitable materials for pro-ducing the intermediate elastomer layer are defined by ASTM D 6S3 as materials which, a: ambient temperature, quickly return to thieir approxi-iate initial dimensions and shapes after having 2S undergone a significant deformation as a resurt of minor stress-- aooiied to the sla ck mate rial1.

Suitable elastomeric polymers rot only include elastorners proper (applied in their vulcanised or reticulated state) but also thermorilastic elastomers (widely referred to as TPE) whnich exhibit an elongation at their flo'wvage threshold of greater han 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 I7 polluting- h In czueo t oaz:e; zle categories are genlerally dLrtinguished betw-een: -the the-oplasflc polyolefin elastorners (TPO1 are vhm:al mi-cu7,res trade from pobolefinps. There are those which contain more than 60Fpl- ropc!-zne and those with a preponderant elastorner phiase (iover 70"-C' and which me,, or a. no-, be reizulated.

the poiystvene-based copolvnier units whose ri idphs oSso pstrn sequences, while their pliant phase may' be normed for inst4an:e 'oobtde potyisoprene (SIS). or pohvteihylen-e-bu-v2ene, (ES eauences.

To the polyurethane-based c-opolynier nis(TU) which can be cbaine by' thi? join-, reaction of a diol of hi,-h mnolecular mnass constituting the c-rvs-rallisable -1iant sequence o'.

the TPE. withi a dilsocyanate arnd a di-ol of lowe M0o!ecU'ar ma1ss -hich engoend ers the rigidl sequence- -the polyester- based conolyrie, Lmits suchl as those obta led by -he copo hnicmeation !s of a polybutylene terepha-ae (PBT) or a po-,ethlene terephtzaae (PEI: w;ihich conlstitlutes the rigid and crystalline sequences. and a slvco! OF 'Low, mojecular '-?ight (buzane diol.

diethylene glycol! which, in awscciation ivith a PO!V el-l ethe- .hlcol. forms the crystailisable pliant sequenice- -the polyamide-based copo lymner units wvhose ricid secuenc es ar-e cons:1tnited by o0 poiyamide and the pliable c7sls a1 esq.csO oyetr lokona polyetherarnides.

he stffness of the elas-zorner is Dre'erably less than that of: Jh ret.acta be olymer i; can be evaluated in terms of torsion arndo.- flexion and!or tension Ym'Z Culi and.'or Shore hardness values which aremeasured under th 'e samne conditions for both t.he elestomer and 211the retractable polymer. The stir.'ess of th-e elastorner should preferablyremain below, thaz of the retractable polymer irrespective of the? o:)eratinq conditions when in use. especially in terms of temperature and in due consideration of 4.he gigofheemera.

It is prefeired for the elastorner to be of a Shore A harcnes, at 23:C ot less than 92 (and ideally less than 70). or of a Shore D hardness Of less ffhan 50 when m.easured by the 33 ISO 863 standard- Thte torsion modulus of th~e elastomer at 23-C is pre era bIV lessM. _Ln10N t t beterv~et. less thfan 30 \-rr 2 and ideal less than 10 N"m ;mrneaSurC-acorQn to DIN standard 53447]t spreferredi that the tenision modulus of the elastomer at 23YC islesta40 la or, better yet. less than 1±00 MPa (measured according to ISO 527]T The tensile strength. that is, break elongation of the elastorner at 23 C is p-referab!,y greater than In the case of TPEs. the preferred material is one which has a VICAT of less than when measured by the AN50 method according to the ISO 306 standard.

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

~The torsion modulus oif the elastorner preferably remains below 30 Nirm kimleaSUr~en according to DIN standard 53-447) over the course of, its thermial ageing- The elastomers ancLor TPEs specially recommended wvithin the scope of zho, presen: is inuention may be selected from among the EPDN' copolymers, the acryloni-TriI'? butaciiene IF ethylene carbon oxide copolymers. the ethylene carbon oxide iYn-.'l acetate terpolymers. the acrylilc rubber types. the thermoplastic copolvethers esters, the polystyrene-based and polvisoprefle-bype. polybutadiene-type andi the ldke. copolymer ~u seuences the styrene -butadiene styrene copolymers the ethylene ethylacrylate.

~ethylene ethylacetate and ethylene vIinyl acetate copoymners as; well as tzheir :erpolyrnes.

the fluorous elastomers. the silicone ejastomers. The fluorous silicorie elastomers. the polyurethanes.

Wvithin the scope of the present invention elastorner and,'or TPE mixtLures may also be ~sused.

For the requirements of the present invention a thermoplastic po!lyirethane

(TPUI)

elastomer of a Snore A hardness less than 9-2 as mreasured in accordance w.'Ath ISO standard 868 can be used. Moreover, it is preferred that this elastomner can sustain a strong viscosity, reduction during thermnal ageing- T his viscosity reduction is preferably at least over days at 120'C. The therm 1 oplastic polyurethane elastomner usually displays a v.iscosity a: 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 t 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.

SAlso, 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 .i performance characteristics of the retractable polymer as they progressively migrate 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 2s 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 ress applied by the sheath during its shrinka-ge wil 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 to 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 s1 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 2s 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 NPa. 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 Zeta wire, while the axial components of the force are retained by the pair of armour i sleeves (lla. lib) consisting of a plurality of wires at opposing angles of. for instance. or 40°. 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 s to each other at an angle of about 55*. The wires of armour sleeves (10. 11) typically s 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.

10 The role of the f.exible metal pipe is to assure crush resistance of the flexible conduit and to prevent ciaptai-- 5saea~g sheath under certain operating conditions.

B Compared to bon ppF~, flexible conduit is of the unbonded flexible type which incorporates sepr e c'.'cu l lements: this is a particularly interesting aspect of the present invention: S" s In the case of the epa ie V, Riure 3, elastomer layer constitutes a continuous St"" ubular sleeve which en-eopf ilekibtle 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 elastnmer of layer fills interstitial spaces essentially completely. Alternatively, dependin 3 i-specilly on the 0 viscosity and the amount of the elastomer as well as the fabrication process, it 'would be possible according to an embodiment, not illustrated, to produce intermediate layer with less penetration in interstitial spaces corresponding to side a illustrated in Figures 3A and 3B.

Figures 4 to 6 show an enlarged, partial longitudinal section through a flexible conduit 7s according to a second embodiment, incorporating an intermediate elastomer layer (8) consisting of an elastomer tape (SA) 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 cuter pates (13) of the metal pipe and outer surfaces (14) of elastomer tape (8A) produces an approximately cylindrical o3 surface which supports Fealing polymer sheath in continuous fashion.

I 2 In the event where the flexible metal pipe is made up of a continuous helical coil of a single stip 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 s of tapes (8A, SB, 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 la, 11b) as well as outer sheath (12).

i 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 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 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 a meniscus whose concave side faces toward the outside as illustrated in Figures 4 and 6.

In this case. nolymer sealing sheath exhibits on its inner side a slight bulge (15) whose thickness a 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).

.2s Alternatively, 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.

S Generally, irrespective of the selected embodiment and in particular in the oase of the Sexamples shown in Figures 1 to 6, good results are achieved if the curvature of the inner L 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 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.

t* o The width 1 of interstitial space at the plane of its outer opening, that is. its width S between cylindrical parts (13) of adjacent helical turns. may vary etween 2 and 40 mm. The S. 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 S- s mid-point of the radial depth h of the interstitial space, the width of the space may be of Sthe 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/l ratio between the depth h and the outer width I may accordingly vary between 0.4 and 1.4. 'i The manufacture of substantial continuous lengthr 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. Ir this case it is possible for instance to simultaneously coextrude the retractable i polymer and the elastomer by means of two extruders and a double-headed flow- S2 distribution 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 0 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 iW (extrusion tandem), or in a separate extruding operation performed after ith first extrusion.

or even by sheathing the flexible metal pipe with the e!astomer, 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.

s 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 (SA) 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 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 s metal pipe in continuous fashion through a chamber filled with raw e!astomer, 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 S 0 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 2s 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 (SA) 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 T i..

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 Sto 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 eiastomer 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 :s sheet permits easy partial and regular filling of interstitial spaces wi:h the elastomer of the intermediate layer.

V: Within the scope of the present invention, and for the purpose of strengthening the 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 .zo 0 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/retractabe 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.

I---8 The flexible tubular conduit which is the object of the present invention is especially suitable for use in oil and gas expiorationextraction where the inner diameter of the flexible metal pipe may be of the order of 20 to 600 mm and more typically between 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'C to 120C which constitutes the limits currently possible.

The following examples illustrate the invention without being in any way limiting in 0to 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 i s 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: 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.

2s 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 0o 3g/10 min measured according to iSO 1133, and a thickness of 5 mm. (APPRYL 3 3030 FN by the APPPYL Co.).

1 The elastomner is: SPolyurethane poiyether (UJTAFLEX3 TB 1 by the UETWII I ER Co.) Shore A hardness 50 after reticulation.

Copolymer of polyamide and polyether units combined by ester functions.

S PEBAX-' 2355 ELF ATOCHEM1 Shore A hardness 75; bending modulus at 23"C MPa measured according to ISO standard 118.

Polymer VIF, CQF.CI in a molar -50i,50 proportion, having a bending modulus at 23C of 250 MPa measured by ISO standard 178.

to Test temEoerature: 0 0

C

111 Elastomer layer Application meihod Tikes esrdfo of the helices Polyurethane- By induction followed by 2 components Ibaking for j. hour at 801C Elastomer extrusion onto Polyether-esteramide- the pipe followed by 1 mm extrusion of the PP Polymer... Direct coextrusion of PP VF, VF 3 onto the steel pipe I1mm The above test results show better deformability, and in particular better bending ability, of the flexible Pipes sheathed with an intermediate elastomer layer sandwiched 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 eiastcmer is a polyester polyurethane having a Shore A of 88 (ESTAINE* 58271) and a thickness of the elastomer layer of 1.5 mm measured from the apex off the helices.

Test temperature: 0'C Semi-crystalline polymer Thickness constituting the sealing Application method sheath By extrusion onto the pipe s Polyethylene extrusion-coated with 5 mm (Mn 10) elastomer Poiyamide-1 Coextrusion onto the 4 mm (RILSAN BESNO TL) metal pipe Copolymer Extrusion onto the metal 1o ethylene pipe extrusion-coated 5 mm (TEFZEL 200 by DUPONT) with elastomer .40,000 MN 45.000 Shore D 75. impact resistance at -55*C 187 J/m measured according to ASTM D256.

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 a sheath, according to the present invention.

I 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 2s sheathing is applied by successive ex-tusions: 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 I A hardness of 83 and displays a viscosity reduction of more than 70% over 30 days at 120*C.

C 3 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 r|\ pipe supports. A pressure of 725 psi is applied. The pipe bends around the wheel. The indentation depth of the wheel indicates the deforability 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 ruptures the depth is noted. The greater the depth, the greater the bending ability of the pipes.

Temperature Indentation depth Sample 1 Sample 2 20C 170 mm 120 mm No rupture No rupture -30"C Rupture at Rupture at 150 mm 80 mm (s 'a Example 4 The samples 3 and 4 are prepared in the same manner as samples 1 and 2, except that is the vinylidene polyfluoride is piasticised. 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.

2c 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 for one hour.

Sample 3 could be bent five times without rupturing.

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

2s 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 Sample 3 whitens at the third bending and cracks at the fourth.

Sample 4 breaks at the first bending.

Claims (13)

1. A flexible met-_l piLpev whose external surface exhibits intersticgs cov.ered by a sealing sheath of retractable polymer, preferably semi-crystalline. characterised in that placed between the retractable polymer sheath and the metal pipe 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. to

2. Flexible pipe as claimed in Claim 1. characterised in that the elastomer has a stiffness less than that of the retractable polymer.

3. Flexible pine as claimied in Claim 1 or 2. characterised in that the elastomer is selected is from among the silicone elastomers, possibly fluorous. and,'or polyarnide-based TPEs and/or TPUs and/or the EPDivl copolynars, and/or the acrylonitrile butadiene styrene copolymers, and~or the rrethylmethacrylate butadiene styrene copolymers, and/or the ethylene carbon oxide copolyrners and/or the ethylene carbon oxide vinyl acetate I. .terpolymers, andfor the acrylic rubber types, and/or the TPOs and/or the polyester-based ~a TPEs and/or the ethylene ethylacrylate. ethylene ethylacetate and ethylene vinyl acetate copolymers as well as their terpolymers. and/or the fluorous elastomers.

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. -the polyoxides, -the Parax polysulfides (PPS). 'A' the polyether-ether-ketones (PEEK) and their copolymers the fluorous polymers such as: Sthe home- and copolymers of vinylidene fluoride the homo- and copoiymers of trifluoroethylene (VF 3 s the copolymers. and especially terpolymers, associating remainders of the activators chlorotifluoroethylene (CTFE), tetrafluoroethylene (TFE). hexafluoro propene (HFP) and/or ethylene and optionally the activators VF, and/or VF 3 and advantageously PVDFand 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 S to 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 i to 4. characterised in that the intermediate elastomer layer and the sealing sheath :s 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 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 2s vulcanised or thermoplastic.

S. 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. r i} 1

9. LNanufacturng process oit a sheathed flexibie metal pioe as claimed in Claim 7. characterised in that the elastomer is placed on to the flexible pipe in thie form of a rod placed in the interstice s

10. Manufacturing process of a sheathed flexible metal pipe as claimed in any one of Claims 5 to 9. charact erised in that a thin sheet produced by wrTapping one or several layers of a tape. made for instance of a fabric. of fibres or of a plastfic material optionally fibre- reinforced, is interposed betwveen the flexible metal pipe and the inter,-ediate elastomer layer

11. Manufacturinlg process of a sheathed flexible metal pipe as claimied in Claim characterised in that a certain quantity of retractable polymer is added to the intermediate, elastomner layer and/or a certain quantity of retractable polymer is added to the retractable polymer before their coextrusion. or betw~een the intermediate elastomer layer and the s 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 I. to 4, preferably reinforced by armour, which can be used for transporting liquids. especially pressurised and/or at high tempIeratures.

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 22nd day of Febrwary, 1999 ELF ATOCHEM S.A. AND CFLEXIP S.A. WATERMARK PATENT TRADEMARK ATTORNEYS 290 BURWOOD ROAD HAWTHORN VICTORIA 3122 AUSTRALIA LCG:JGC:PCP Doc 2s Auoa2995swPCA