Pipes and tubular conduits – Flexible – Spirally wound material
Reexamination Certificate
2000-12-14
2001-07-03
Brinson, Patrick (Department: 3752)
Pipes and tubular conduits
Flexible
Spirally wound material
C138S133000, C138S138000
Reexamination Certificate
active
06253793
ABSTRACT:
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°) 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°; 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
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
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
xx
/moment of inertia I
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 ⅓), 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.
REFERENCES:
patent: 3858616 (1975-01-01), Thiery et al.
patent: 5275209 (1994-01-01), Sugier et al.
patent: 5730188 (1998-03-01), K
Dupoiron Francois
Espinasse Philippe François
Jung Patrice
Brinson Patrick
Corlexip
Ostrolenk Faber Gerb & Soffen, LLP
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