Flexible pipe with i-shaped wire winding

A flexible tubular pipe having an internal sheath and a pressure vault around the sheath with a helically would short pitch metal wire. The metal wire has an I-shaped cross-section with a narrowed central web and greater thickness internal and external flanges. Recesses in at least one set of the flanges enable fastening elements to be installed for holding to adjacent wire windings. The ratios of widths of the flanges, height and width of the wire, moments of inertia in the width wise and radial direction are disclosed.

BACKGROUND OF THE INVENTION
 The present invention relates to a flexible pipe for transporting, over
 long distances, a fluid which is under pressure and possibly at a high
 temperature, such as a gas, petroleum, water or other fluids. The
 invention relates most particularly to a pipe intended for offshore oil
 exploration. It relates especially first, to the flow lines, that is to
 say flexible pipes unwound from a barge in order to be laid generally on
 the bottom of the sea and connected to the subsea installations, such
 pipes working mainly in static flexible pipes which are unwound from a
 surface installations and most of which do not lie below the seabed, such
 pipes working essentially in dynamic mode.
 The flexible pipes used offshore must be able to resist high internal
 pressures and/or external pressures and also withstand longitudinal
 bending or twisting without the risk of being ruptured.
 They have various configurations depending on their precise use but in
 general they satisfy the constructional criteria defined in particular in
 the standards API 17 B and API 17 J drawn up by the American Petroleum
 Institute under the tile "Recommended Practice for Flexible Pipe".
 Reference may also be made to documents FR 2 654 795 A, WO 938/25 063 A,
 FR 2 727 738 A and FR 2 744 511 A.
 A flexible pipe generally comprises, from the inside outward:
 an internal sealing sheath made of a plastic, generally a polymer, able to
 resist to a greater or lesser extent the chemical action of the fluid to
 be transported;
 a pressure vault resistant mainly to the pressure developed by the fluid in
 the sealing sheath and consisting of the winding of one or more
 interlocked profiled metal wires (which may or may not be
 self-interlockable) wound in a helix with a short pitch (i.e. with a wind
 angle close to 90.degree.) around the internal sheath;
 at least one ply (and generally at least two crossed plies) of tensile
 armor layers whose lay angle measured along the longitudinal axis of the
 pipe is less than 55.degree.; and
 an external protective sealing sheath made of a polymer.
 Such a structure is that of a pipe with a so-called smooth bore. In a pipe
 with a so-called rough bore, a carcass consisting of an interlocked metal
 strip, which serves to prevent the pipe being crushed under external
 pressure, is also provided inside the internal sealing sheath. However,
 the pressure vault also contributes to the crushing strength.
 Attempts are made to reduce the weight of flexible pipes, particularly for
 applications at great depth, where, in order to rests being crushed, it is
 necessary to considerably increase the moment of inertia of the profiled
 wire constituting the pressure vault. The weight of the flexible pipe also
 plays an important role when laying it; this is because its weight must be
 limited so as to allow it no be laid by existing means (for example 600
 tonnes for a conventional system).
 The pressure vault consists of a profiled wire, usually of the Z or T type,
 or derivatives (teta and zeta) thereof, which is wound with a short pitch.
 The profiled wire is generally such that the ratio of its height to its
 width is less than 1, so as to prevent warping in winding the vault. In
 addition, it is known to dimension the pressure vault so that it helps to
 delay the onset of ovalization of the carcass under the increase in
 internal pressure (this onset resulting in the ruin of the carcass), but
 promotes the extension of the preferred cardioidal deformation mode: the
 delay in ovalization is all the greater the higher the moment of inertia
 I.sub.xx, of the profiled wire constituting the vault.
 For applications at great depth, it is therefore desired to increase the
 moment of inertia of the profiled wire usually employed, in order to
 resist the crushing pressure; for example, it would be desirable to use a
 teta wire 16 mm in height. However, this would result in drawbacks, such
 as the increase in the weight of the pipe which may exceed the limit of
 the laying system, or even exceed the limits of resistance of the pipe
 itself being able to support its own weight when laying it; and a more
 complex implementation of this type of profiled wire; all these drawbacks
 increase the manufacturing cost of such a pipe.
 The oil industry is therefore seeking an interlockable profiled wire having
 a high moment of inertia I.sub.xx for a low weight.
 It has already been proposed, in document U.S. Pat. No. 4,549,581 A, to use
 interlockable U-shaped profiled wires, but the improvement made to the
 moment of inertia/weight ratio has not been significant. Moreover, it
 appears not to be easy to envision lightening the known S-, Z- or T-shaped
 sections by providing hollows, for manufacturing reasons.
 SUMMARY OF THE INVENTION
 The objective of the invention is therefore to propose a novel type of
 interlockable section allowing the moment of inertia/weight ratio to be
 very favorably increased.
 The objective of the invention is achieved by providing a flexible tubular
 pipe comprising at least, from the inside outward, an internal sealing
 sheath, a cylindrical pressure vault consisting of the winding of an
 interlocked profiled metal wire wound in a helix with a short pitch, at
 least one ply of tensile armor layers wound with a long pitch, and an
 external protective sealing sheath made of a polymer, characterized in
 that the profiled wire constituting the vault has an I-shaped cross
 section.
 I-shaped (or H-shaped) sections have already been proposed within the
 specific framework of flexodrilling, for example in documents FR 2 210 267
 A or FR 2 229 913 A. However, these sections are used to produce the
 tensile armor layers, that is to say they are in the form of windings of
 non-interlockable wires with a long pitch, whereas the pressure vault is
 always produced with S- or Z-shaped interlockable profiled wires.
 Moreover, in this flexodrilling application, the proposed wires have a
 height/width ratio greater than 1 and a moment of inertia I.sub.xx /moment
 of inertia I.sub.yy ratio of preferably between 1.5 and 2. Such a wire
 would neither allow the necessary bending nor the stability during winding
 with a short pitch (warping phenomenon).
 Also known, from document GB 1 081 339 A, is a hose formed from a
 short-pitch winding of a box strip having an I-shaped cross section, the
 flanges of the I being flexible enough to be able, by deformation, to be
 imbricated one with respect to another. The hose in question has nothing
 to do with the pipes of the invention since it does not have either a
 pressure vault or any tensile armor layers, and is not intended for the
 same application. The winding does not in itself present any difficulty
 because it is a strip which, even boxed, remains very flexible. Besides,
 the height-to-width ratio of the I formed by the strip is very low
 (typically less than 1/3), which allows it to be easily wound.
 The present invention differs from this in that it is a true profiled wire,
 that is to say a wire of relatively large cross section (with a mean
 diameter generally greater than 10 mm), which cannot be likened to a
 simple strip. In addition, according to the invention, the ratio of the
 height to the width of the I is preferably between 0.5 and 1 and even
 between 0.7 and 0.8.
 Advantageously, the wire forms an I with thick flanges in which recesses
 are formed, these being intended to at least partially house fasteners,
 for example the flanges of U-shaped fasteners.
 These recesses may be formed on the inside of the flanges, but are
 preferably formed on the outside of the flanges, in order to facilitate
 the fastening. They may be formed toward the ends of the flanges or indeed
 formed at the center of the flanges.
 The invention will be clearly understood with the aid of the description
 which follows, with reference to the appended schematic drawings showing,
 by way of example, embodiments of the flexible pipe according to the
 invention. Further advantages and features will become apparent on reading
 the description.

DESCRIPTION OF PREFERRED EMBODIMENTS
 It should be noted that in some of the figures the spaces between the
 constituent elements have sometimes been intentionally exaggerated in
 order to make the drawings clearer.
 As FIG. 1 shows, and in general, a pipe of the smooth-bore type comprises,
 from the inside outward, a polymeric internal sealing sheath 1, a metal
 vault 2 consisting of the winding of at least one profiled metal wire
 wound in a helix with a short pitch, an armor layer 30 resistant to the
 axial tension in the longitudinal direction of the pipe and usually
 consisting of one or more pairs of crossed plies 31, 32 of a winding with
 a long pitch in opposite directions, and a polymeric external sealing
 sheath 33. Other layers (not shown) may be provided, depending on the type
 and the application of the pipe, such as, for example, an internal carcass
 underneath the internal sealing sheath 1 (for so-called rough-bore pipes
 which are the preferred type of application of the invention), a hoop
 reinforcement layer consisting of a winding of a rectangular wire with a
 short pitch, interposed between the pressure vault 2 and the first armor
 ply 31, and intermediate sheaths placed between various armor plies.
 FIG. 2 shows, in longitudinal cross section, an example of a pressure vault
 2 according to the invention, formed from a profiled wire 10 of large
 cross section and therefore of large moment of inertia, but lightened
 since it consists of a profiled wire having a cross section in the form of
 an upright I (or an H on its side), which has a web 3 and flanges 4, 5, 6
 and 7, the web 3 being wound approximately radially over and around the
 internal sheath 1 in a helix with a short catch, the external flanges 4, 5
 and the internal flanges 6, 7 of the consecutive turns facing each other
 and together forming an approximately confined volume 8 helically
 traversing the vault 2.
 The shape of the flanges may be highly varied, as may be seen below, as
 long as the flanges 6, 7 on the internal side, or the flanges 4, 5 on the
 external side, allow the wire to be interlocked. This is achieved either
 by self-interlocking by virtue of a special section given to the profiled
 wire, or by an attached interlocking wire which it is generally preferred
 to place on the outer face of the vault (so-called fastening "from above")
 both for reasons of ease of manufacture and of better strength of the
 pipe, especially when it is used in dynamic mode (riser).
 In the embodiment shown in FIG. 2, the I-shaped metal wire 10 of the
 pressure vault 2 of the flexible pipe is interlocked by a fastener 11 on
 the external face of the vault; the fastener 11 consists of a wire in the
 form of a flat U wound helically in recesses 14 of the external face of
 the vault 2, that is to say by the outer flanges 4 and 5 of the metal wire
 10, and it joins together, at these outer flanges 4 and 5, the consecutive
 turns of the helically wound metal wire 10. The fastener 11 is
 advantageously placed slightly set back with respect to the volume
 envelope of the external face so as to prevent the armor layers from
 bearing on the fastener 11, which would run the risk of inducing fatigue
 in dynamic use.
 To give a pipe flexibility, the metal wire 10 is wound helically by leaving
 internal and external helical gaps on the respectively internal and
 external faces of the pressure vault, these caps opening onto the internal
 volume 8. In order to prevent the possibility of the sheath 1 creeping
 between the flanges 6 and 7 of two consecutive turns, it is advantageous
 to provide an anti-creep device consisting of an overlay element 12
 produced, in FIG. 2, by the overlap of the parts 20, 21 of the
 unsymmetrical flanges 6, 7 facing the internal sheath 1. These parts 20,
 21 overlap longitudinally so that they allow the formation of the
 longitudinal gap 9 but, on the other hand, leave virtually no passage in
 the thickness direction of the flanges, so as to bar access between the
 sheath 1 and the confined volume 8.
 FIG. 3 shows in greater detail a preferred embodiment of the I-shaped
 profiled wire fastened from above by means of a fastener 11 similar to
 that in the embodiment of FIG. 2 and intended for dynamic applications.
 The anti-creep overlay element 12 consists here of a flat wire, for
 example made of PTFE-coated metal, wound helically in the inner face of
 the vault 2, in the symmetrical inner flanges 6 and 7 of the metal wire 3,
 by means of facing recessed parts 13 made over the length of the flanges 6
 and 7 of the consecutive turns of the metal wire 3 which are the furthest
 inside the pipe. These recessed parts 13 are substantially in shape
 correspondence with said overlay element 12 so that the latter 12 can be
 easily housed therein, at least partially.
 The wire 10 is in the form of a I with a height H and a width L, its web 3
 having a thickness l. The flanges have a height a and are joined to the
 web by a surface 15 approximately in the form of a dihedron with a rounded
 peak, the dihedron making an angle .alpha. with a plane parallel to the
 base of the flanges, this angle being determined by the rolling conditions
 for and the constraints on the I (the position of the center of gravity,
 distribution of the stresses, weight). These surfaces 15 are joined to the
 web by a rounded piece whose radius of curvature is defined by the rolling
 options. It has been discovered according to the invention that, in order
 to obtain the desired weight saving for the same moment of inertia, it is
 preferable to have:
 (1) I.sub.xx /I.sub.yy &lt;1 (xx and yy denoting the respective horizontal and
 vertical axes with respect to the I);
 (2) 0.5&lt;H/L&lt;1 and preferably, (2'), 0.7&lt;H/L&lt;0.8;
 (3) 0.2&lt;l/L&lt;0.6 and preferably, (3'), 0.3&lt;l/L&lt;0.5;
 (4) 0&lt;.alpha.&lt;45.degree. and preferably, (4'),
 10.degree.&lt;.alpha.&lt;30.degree..
 With regard to the interlocking, this is achieved so as to allow the
 adjacent interlocked wires to be separated by a clearance of between a
 zero minimum clearance (see the two wires on the left in FIG. 3) and a
 maximum clearance (see the two wires on the right in FIG. 3), to which
 clearances a minimum pitch and a maximum pitch correspond, the half-sum of
 which pitches is the mean pitch P.sub.m. The recesses 14, of width C, are
 limited by a rim of width J and of height M and are separated by a
 distance F. The recesses, which are here represented by right-angled
 walls, may be flared; in this case, the profile of the fastener is
 modified accordingly. The U-shaped fasteners 11 have a thickness e and a
 width D and their feet 17 have a height G and a width U. The back of the
 fasteners 11 is set in by a small distance b with respect to the level of
 the I-shaped section. Preferably:
 (5) G and M&gt;0.5 mm and preferably G and M&gt;1 mm, with G&lt;M;
 (6) C&gt;1 mm and preferably 2 mm, with C&lt;U+10%P.sub.m ;
 (7) P.sub.m &lt;10L/9;
 (8) thickness e&gt;1 mm, and preferably 2 mm;
 (9) set-back b of about 0.1 mm;
 (10) D+F&lt;L;
 (11) I-2J&lt;10%P.sub.m.
 To be more specific, the characteristic dimensions of the preferred
 embodiment in FIG. 3 are the following: H=22 mm; L=28.6 mm; H/L=0.77; 1=12
 mm; maximum pitch=33 mm; mean pitch=30.8 mm; e=G=2 mm; D=13.3 mm; depth of
 the recesses 14=4.2 mm. For the same moment of inertia, it may be shown
 that this I-shaped cross section allows a weight saving of 25% over a
 conventional teta-shaped cross section. This is illustrated in FIG. 17 in
 which the relationship between the moment of inertia.times.modulus as a
 function of the weight per meter of the structure (for a 12", i.e.
 approximately 30 cm, pipe) has been compared for various profiled wire
 sections, namely conventional steel and aluminum teta-shaped and steel
 U-shaped sections and steel I-shaped sections according to the invention.
 It may be seen that, apart from the aluminum teta, which is necessarily
 lighter, the steel I according to the invention favorably decreases he
 weight/moment of inertia ratio compared with the teta-shaped and even the
 U-shaped wire.
 Although the "cactus-shaped" section in FIG. 3 represents a preferred
 embodiment of the invention, many other forms are possible, including some
 of those illustrated in FIGS. 4 to 16.
 In FIGS. 4 and 5, the I-shaped section 10 has, at its base, recesses 14'
 intended for interlocking from the bottom by means of a U-shaped fastener
 11 similar to that described in the previous embodiment. This method of
 interlocking from below is, in principle, reserved for use of the pipe in
 static mode.
 FIGS. 6 to 9 illustrate possible sections for the wire 10, the arrangements
 corresponding to the method of interlocking adopted not having been shown
 in some of these figures.
 In FIG. 6, the width of the upper flanges 4 and 5 of the symmetrical
 section has been reduced. This section is advantageously interlocked on
 the inside, as shown in FIG. 13, by U-shaped fasteners 11 placed in
 housings 14" formed on the upper part of the lower flanges 6, 7 and an
 element, such as a seal, may be placed on top of the fastener 11.
 FIG. 7 shows a section similar to a basic I, the upper flanges 4, 5 of
 which have been modified so as to include self-interlocking hooks 18.
 FIG. 8 shows a section 10 with unsymmetrical flanges 4, 5 and 6, 7,
 allowing self-interlocking from above and from below, the latter solution
 being illustrated in FIG. 14, which shows self-interlocking hooks 18
 formed in a complementary manner on the flanges 6, 7.
 FIG. 9 shows a I-shaped section 10 with a very high moment of inertia by
 virtue of the large thickness of the flanges 4 to 7, which terminate in a
 rim 19. The rim 19 may serve for the interlocking, unless an interlocking
 method like that in FIGS. 15 or 16 (described later) is chosen.
 Previously, interlocking via the flanges, either on the top side or on the
 bottom side, where the flanges of the U-shaped fasteners 11 are housed in
 recesses 14 placed entirely in the flanges of the I-shaped section, was
 described. This allows the fastener 11 to be completely retracted but it
 requires making the flanges which receive the recesses 14 sufficiently
 thick.
 Provision may also be made for the recesses 14 for housing he fasteners to
 be closer to the mid-plane of the section 10, or even at the point of
 forming only a single central groove housing the flanges of the two
 adjacent U-shaped fasteners 11, as shown in FIG. 10 (interlocking from
 above) and FIG. 11 (interlocking from below). In this case, the fasteners
 11 are no longer retracted.
 Up until now U-shaped fasteners have been described, but it goes without
 saying that other fastener sections may be adopted, for example a zeta
 section like that illustrated in FIG. 12 which shows a zeta fastener 11'",
 the edges of which are housed in recesses 14'" provided on the respective
 lower and upper faces of the flanges 6 and 7 (interlocking from below).
 FIG. 15 shows an embodiment of interlocking by straddling, which does not
 require a recess for housing the flanges of the fasteners; in this case,
 the fasteners 11' in the form of a wide U straddle two I-shaped sections
 10, the upper fasteners being offset with respect to the lower fasteners
 so that the combination of the two fastener wires allows the sections 10
 to be effectively held together between their flanges.
 In FIG. 16, the straddling fasteners 11' are similar to those in the
 previous figure, except that they are housed in central grooves 14,
 alternatively at the top and at the bottom, of the sections 10 which are
 similar to those in FIGS. 10 and 11.