Composite tube comprising an inner casing

[0002] The present invention relates to a composite tubular pipe structure intended to carry liquid or gaseous products, in particular for offshore petroleum production.

[0003] Composite tubes usually consist of parallel fiber layers such as glass fibers, carbon fibers, aramid fibers, embedded in a matrix. Each one of these layers has a given thickness and forms a given angle with the axis of the tube so as to meet criteria relative to the mechanical resistance to the stresses applied to the tube. The matrix can be a thermosetting matrix, an epoxy resin for example. However, the present invention is not limited to a thermosetting matrix, other materials can be used without departing from the scope of the present invention, thermoplastics for example.

[0004] Documents U.S. Pat. No. 5,110,644, U.S. Pat. No. 5,499,661, U.S. Pat. No. 5,091,230 describe composite tubes.

[0005] Such tubes can be used in particular in offshore oil prospecting and production operations, for example as risers connecting the sea bottom to the surface support for carrying the effluent produced. These composite tubes can notably advantageously replace, entirely or partially, rigid steel catenary risers, which are very heavy and subjected to stresses, notably bending stresses at the base, which can be very great and detrimental. A solution consists in using composite materials, much lighter, more flexible and fatigue resisting. The invention is not limited to these risers, it also relates to all the composite tubes having a sealing sheath that can be subjected to an external pressure.

[0006] In these types of tube, sealing against internal fluids is obviously fundamental, notably for the safety of the operations. It is however well-known that this type of composite is not considered to be sufficiently gas, water or hydrocarbon tight and at least one specific internal tube, referred to as liner, is required to provide sufficient sealing. This liner is generally made of organic materials, polymers of polyamide type or equivalent as regards sealing and implementation.

[0007] This polymer liner solution has the advantage of providing fluid tightness, good aging stability in a hydrocarbon environment, and it is compatible with the deformations of the composite, unlike a metal liner, for example in form of a continuous metal tube, cylindrical or corrugated. It however has several drawbacks, since it is notably difficult to obtain perfect and lasting sticking of the plastic layer to the upper composite layers made of fibers embedded in a matrix. Furthermore, gas permeation through the material of the inner liner, or permeation of sea water under pressure through the thickness of the composite layers is likely to produce a collapse pressure on this inner liner, which may eventually collapse.

[0008] The present invention thus relates to a multilayer tube comprising at least one layer of a composite material consisting of reinforcing fibers embedded in a matrix, at least one sealing sheath made of a polymer material intended to improve the tightness of this tube. The inner part of the tube consists of a metal carcass intended to protect the sheath against a possible external pressure.

[0009] According to the invention, the carcass is a flexible metal tube, for example made of a stapled steel tape or equivalent.

[0010] In a variant, the tube according to the invention comprises, on the outer surface thereof, a flexible metal tube, preferably made of stapled steel tape, intended to provide an external protection.

[0011] The tube according to the invention can comprise several sealing sheaths.

[0012] The present invention can be applied to constitute production risers of catenary or taut type, drilling risers, and even export lines connecting a production support and a loading buoy.

[0013] Other features and advantages of the present invention will be clear from reading the description hereafter of non limitative examples, with reference to the accompanying drawings wherein:

[0014] FIG. 1 illustrates an example of a structure according to the invention,

[0015] FIGS. 2A, 2B, 2C and 2D illustrate examples of tube casings according to the invention,

[0016] FIG. 3 shows a variant according to the invention,

[0017] FIG. 4 illustrates various applications of the present invention.

[0018] FIG. 1 shows, from reference numbers 1 to 9, a series of layers forming a tube according to the invention. Reference number 1 designates the sealing layer made of plastic material thermoplastic polymer or elastomer. Reference numbers 2 to 8 refer to layers comprising each fibers arranged at equal angles or symmetrical in relation to the axis of the tube, and embedded in a matrix. This matrix adheres to the fibers. Some of these layers can be suited to withstand more particularly the pressure prevailing inside the tube or internal pressure, and others more particularly withstand traction. The pressure-resisting layers comprise then groups of fibers wound at a high angle in relation to the axis of the tube (2, 4, 6 and 8 for example), whereas the traction-resisting layers comprises fibers wound at a small angle in relation to the axis of the tube (3, 5, 7 for example). According to the invention, sealing sheath 1 is implemented on a metal carcass 9. Thus, sheath 1 is supported by the carcass so as to withstand the external pressure. The external pressure that can be exerted on the sheath can come from the external fluid flowing through the non impermeable composite layers, for example as a result of matrix cracking, or because of the gas that has flowed through the sheath by permeability and remains trapped by the upper layers.

[0019] The flexible structure of the metal tube forming the carcass is such that it follows without detrimental stresses the longitudinal bending and tensile deformations of the composite tube which are much greater than the deformations of steel. As regards the internal pressure stresses, it undergoes no circumferential deformation because it remains pressure balanced since it is not liquid or gas tight.

[0020] Furthermore, this internal structure protects mechanically the sealing sheath from wear and destruction that may be caused by the bit passing into the inner space of the tube.

[0021] Finally, in the non limitative case of composite catenary tubes, the latter are penalized, in particular in the case of gas production, by their too low weight. The metal carcass according to the invention also acts as a ballast.

[0022] FIGS. 2A-D illustrate types of flexible metal carcass:

[0023] FIG. 2A shows a carcass made of stapled steel tape,

[0024] FIG. 2B shows a carcass made-of self-stapled Zeta,

[0025] FIG. 2C shows a T-shaped carcass stapled by a U-shaped staple, or T-shaped (not shown),

[0026] FIG. 2D shows a C-shaped (or U-shaped) carcass.

[0027] The structures shown are not described more in detail here since they are known to the man skilled in the art of hydrocarbon production. These flexible metal tube structures are made from stapled or self-stapled wires, but they can also be made with rings of suitable section stapled to one another.

[0028] The example of FIG. 2A is preferred because it currently corresponds to a good quality-price ratio.

[0029] FIG. 3 illustrates variants of the composite tube according to the invention. Reference number 10 refers to a metal carcass on which a sealing sheath 15 is applied, by extrusion for example. On this core, several composite layers (11, 13) made of coated fibers are deposited by filament winding. In order to protect them against external mechanical stresses, a metal layer made of steel tape 14 can surround the whole of the tube. In a variant, another sealing sheath made of polymer material 12 can be interposed between reinforcing fiber layers so as to reinforce or to complete the sealing function.

[0030] FIG. 4 shows various possible applications of the composite tubes according to the invention. Reference number 1 refers to a catenary production riser. Reference number 2 refers to all of the production risers of a TLP type production platform. Reference number 3 refers to an export line for carrying the effluent produced, for example by the TLP, to the loading means. Reference number 4 refers to a drilling riser. These various lines can consist of at least one more or great length of a tube according to the present invention.