Composite strip, and methods for forming a junction between two conduits

A composite strip which extends in a main direction between first and second ends and which comprises a main strip comprising first fibres embedded in a matrix. The first fibres are made of carbon, an electrically conducting material, and the matrix is made up of at least one polymer. The composite strip further comprises a junction layer formed of an electrically conducting junction material. The junction layer is placed on the main strip.

RELATED APPLICATIONS

The present application is a National Phase entry of PCT Application No. PCT/FR2014/053126, filed Dec. 2, 2014, which claims priority from FR Patent Application 13 62506, filed Dec. 12, 2013, said applications being hereby incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The present invention relates to a composite strip for forming a joint between two pipes, and to the methods for forming the said joint.

BACKGROUND OF THE INVENTION

The invention relates to a composite strip that extends in a main direction between first and second ends, the said composite strip comprising a main strip comprising first fibres embedded in a matrix, the said first fibres being made of carbon, a material that conducts electricity, and the said matrix being made of at least one polymer.

Furthermore, an object of the invention is to form a joint between two pipes used for transporting a fluid, for example a fluid containing a hydrocarbon (a pipeline). Some of these pipes comprise an electrically conducting composite layer. This type of pipe is used, for example, in extremely cold environments, on land and at sea, and sometimes at sea at very great depths. Under these conditions, the fluid may freeze, coagulate, set, thicken or form deposits of paraffin or of hydrate. These transformations of the fluid may cause blockages and impede the transport of the fluid along the pipe. This is why these pipes are sometimes heated in order to avoid such disadvantages. One known technique is to heat these pipes electrically using conducting lines made of copper positioned around the pipes.

Document CN2800021-Y describes such a pipe for transporting a hydrocarbon, with a glass-fibre reinforced plastic tube and a first layer of carbon fibre supplied with electricity to heat the tube.

However, the pipes needed for transporting hydrocarbons are extremely long, potentially as much as several kilometres long. The abovementioned document does not propose any solution either for mechanically connecting pipes one after the other or for electrically connecting together the electricity-conducting layers of these pipes.

Document FR2958991 describes such an improved pipe for transporting a hydrocarbon, which further comprises a reinforcing layer suited to improving mechanical integrity. That document also describes means of assembling pipes with one another, further comprising means of supplying electricity to the heating layer.

However, these means of connection between the pipes are complex. It is therefore necessary to find other solutions for joining or connecting the pipes together.

SUMMARY OF THE INVENTION

It is an object of the present invention to improve a composite strip of the aforementioned type, notably in order to make the mechanical and electrical joint between carbon heating layers of pipes for transporting hydrocarbons.

To this end, the composite strip is characterized in that it further comprises a junction layer formed of an electrically conducting junction material, the said junction layer being placed on the main strip.

Thanks to these arrangements, the preformed composite strip is suited to being used immediately for making the electrical joint between heating layers of two pipes butted together end to end.

In addition, the electrical joint is highly effective because the materials of the heating layers and of the composite strip naturally weld together and because the junction layer of the composite strip has very good electrical properties. The composite strip is therefore able to form an electrical joint that has low electrical resistance, making it possible to avoid electrical losses through a Joule heating effect between each pipe, and making it possible to avoid localized overheating that could damage the assembled hydrocarbon pipeline.

In addition, the mechanical joint is mechanically very strong. The assembled hydrocarbon pipeline is almost continuous between the adjacent first and second pipes. Localized mechanical weaknesses at each joint are thus eliminated.

In various embodiments of the composite strip according to the invention, it is possible also to resort to one and/or another of the following measures.

According to one aspect of the invention, the junction layer is placed only at the first and second ends of the composite strip.

According to one aspect of the invention, the junction layer has the form of strips extending along the first and second ends, each of the said strips having, in the main direction, a width greater than 1 cm and preferably greater than 5 cm.

According to one aspect of the invention, the junction layer has a thickness of between 0.05 mm and 1 mm.

According to one aspect of the invention, the junction material is chosen from a list comprising a polymer filled with electrically conducting particles, a polymer filled with metallic particles, a polymer filled with silver particles, a polymer filled with metalized carbon fibres, a polymer filled with copper fibres, a polymer filled with braided copper fibres.

According to one aspect of the invention, the first fibres extend in the main direction.

According to one aspect of the invention, the first fibres extend substantially in a fibre direction forming a fibre angle with the main direction, the said fibre angle being between 0 degrees and 45 degrees and preferably between 0 degrees and 10 degrees.

According to one aspect of the invention, the composite strip has the shape of a trapezium having two lateral edges that extend in directions parallel to one another and two end edges which belong to the ends of the composite strip and which extend in directions that converge towards one another, the junction layer extending parallel to each end edge.

According to one aspect of the invention, the end edges form an angle of convergence of between 0.1 degree and 20 degrees, and preferably between 0.1 degree and 5 degrees.

According to one aspect of the invention, the composite strip further comprises a lateral portion in a secondary direction substantially perpendicular to the main direction, the said lateral portion not comprising the said first fibres and comprising second fibres embedded in the matrix, the said second fibres being formed of a second material that is not electrically conducting.

According to one aspect of the invention, the second material is glass.

The invention also relates to a method for forming a joint between a first pipe and a second pipe. Each pipe comprises an internal hollow tube and a heating layer situated in the thickness of the said pipe, the said heating layer comprising fibres formed of a conducting material.

In the method, a composite strip is provided and extends in a main direction between first and second ends, the said composite strip comprising a main strip comprising first fibres embedded in a matrix, the said first fibres being made of carbon, a material that conducts electricity, the said matrix being made of at least one polymer, and the said composite strip further comprising a junction layer formed of an electrically conducting junction material, the said junction layer being placed on the main strip.

In the method, an electrical joint is made between the first and second pipes by performing the following step: the composite strip is applied to each heating layer or to a layer placed beforehand on the said heating layers by winding around the tubes, the junction layer of the composite strip is brought into contact with the heating layer of the first pipe and with the heating layer of the second pipe.

In various embodiments of the method according to the invention, it is possible further to resort to one and/or the other of the following measures.

According to one aspect of the invention, the junction layer is placed only at the ends of the composite strip, and the junction layer of the first end is brought into contact with the heating layer of the first pipe and the junction layer of the second end is brought into contact with the heating layer of the second pipe.

According to one aspect of the invention, each pipe has an end of substantially conical shape at least in the thickness of the heating layer, and a composite strip is chosen that has a trapezium shape with a geometry matched to the shapes of the ends of the pipes so that during the electrical-jointing step, the composite strip forms a joint of a shape that substantially complements the conical ends of the heating layers of the pipes by the winding of the trapezium-shaped composite strip around the tubes.

According to one aspect of the invention, the first and second ends of the pipes are machined first of all in order to uncover a cylindrical portion of each tube and to make a conical shape in at least the heating layer of each tube.

According to one aspect of the invention, prior to the electrical-jointing step, a step of welding the tube of the first pipe to the tube of the second pipe is performed.

According to one aspect of the invention, an insulation-jointing step is performed after the welding step and before the electrical-jointing step, and involves applying an insulating strip comprising second fibres embedded in a matrix, the said second fibres being formed of a second material that is not electrically conducting, said second material being, for example, glass.

According to one aspect of the invention, after the step of applying a composite strip, a heating step is performed during which the composite strip applied between the first and second pipes is heated in order to crosslink the matrix of the composite strip.

The invention also relates to a method for forming a joint between a first pipe and a second pipe, in which method each pipe comprises an internal hollow tube and a heating layer situated in the thickness of the said pipe, the said heating layer comprising fibres formed of a conducting material.

In the method, a main strip is supplied and comprises first fibres embedded in a matrix, the said first fibres being made of an electrically conducting material, and the said matrix being made of at least one polymer.

In the method, an electrical junction is made between the first and second pipes by performing the following steps:a junction layer is applied to each heating layer or around a layer placed on the said heating layers beforehand, each junction layer being made up of an electrically conducting junction material, and the junction layers are brought into contact with the heating layer of the first pipe and with the heating layer of the second pipe, andthe main strip is applied to the said junction layer by winding around the tubes.

In the various figures, the same numerical references denote elements that are identical or similar.

DETAILED DESCRIPTION OF THE DRAWINGS

In the present description, the terms “front” and “rear” are used with reference to the longitudinal direction X. The terms “upper” or “upwards” and “lower” or “downwards” are used with reference to the vertical direction Z, upwards, perpendicular to the longitudinal direction X and to the transverse direction Y.

The term “pipe” in the present invention is to be understood as being a device comprising a tube for transporting a fluid at least between an inlet and an outlet, it being possible for the device to comprise other elements, such as a valve, or multiple branches.

FIGS. 1aand 1bshow a pipe1of the heating type, and comprising a composite material, depicted in longitudinal section on a plane XZ and in transverse section on a plane YZ. In these figures, only an upper half above the axis X is shown, the lower other half being substantially identical by symmetry with respect to the axis X.

The pipe1comprises a hollow tube2, extending in the longitudinal direction of axis X between a first and a second end1a,1bof the pipe. This tube2comprises an internal surface2anear the axis X, and an external surface2bfurther away from the axis X. On the inside of the internal surface2athere extends a cavity2cbetween an inlet and an outlet of the cavity which inlet and outlet are situated at each of the ends. The cavity2cis suited to transporting the fluid between the said inlet and the said outlet.

The pipe1has a cross section of substantially cylindrical shape in the YZ plane, although other shapes could be achieved.

The tube2may be produced using an electrically conducting material, such as steel, as has been depicted in the figures for the present embodiment of the pipe.

The tube2may be made from an electrically insulating material, for example a polymer. This material may advantageously be a polyamide (PA) or a polyvinylidene fluoride (PVDF).

On this tube2there are, for example, the following layers, from the inside (nearest the axis X) towards the outside (away from the axis X):a first insulating layer3a heating layer4, anda second insulating layer5.

The first and second electrically insulating layers3,5are electrically insulating. They are made up, for example, of a polymer or a composite containing glass fibres embedded in the polymer (matrix) or a composite containing Kevlar fibres embedded in the polymer. The polymer is advantageously suited to adhering well to the other layers: the tube2and the heating layer4. This polymer may be identical to the polymer used in the heating layer4and/or in the tube2as mentioned hereinabove.

The heating layer4is a composite comprising at least carbon fibres embedded in a polymer. This polymer may advantageously be a polyamide (PA) or a polyvinylidene fluoride (PVDF).

The carbon fibres are able to conduct an electrical current in order to heat the tube through a Joule heating effect. The electrical resistance R of such a heating layer4between the first and second ends (1a,1b) of the pipe can be calculated approximately using the following formula:

in which:

R=ρfibre·Lπ·Dmean·Ep·cos2⁢α·ρfibreis the resistivity of the carbon fibres, for example having the value ρfibre=1.9×10−5Ωm at a temperature of 20° C., which is substantially 1100 times more resistive than copper at 20° C.,L is a length of the heating layer4between the first and second ends (1a,1b) in the longitudinal direction X,Dmeanis a mean diameter of the heating layer3,Epis a thickness of the heating layer in a transverse direction, andα is an angle of inclination that carbon fibres make with respect to the direction of the axis X.

Because of the angle of inclination of the carbon fibres in the heating layer4it is possible to obtain a desired electrical resistance R of the heating.

By virtue of this heating layer4comprising carbon fibres well distributed in the polymer material of this layer, the heating around the tube2is more uniform. Furthermore, if one or several carbon fibres become broken at a point on the pipe, the electrical current can nevertheless continue to pass via the other carbon fibres that have not broken. Thus, the electrical properties (resistance) are not greatly downgraded.

The various layers of the pipe1may be manufactured by known means using preformed composite strips, each preformed strip extending in a direction and comprising fibres (carbon, glass or Kevlar) embedded in a polymer matrix. The fibres may be oriented in the said direction of the preformed strip.

It is an object of the present invention also to use composite strips in order to make a mechanical and electrical joint between the layers of two pipes1which are butted together end to end.

Notably, one object of the invention is to use a special-purpose composite strip10for making the joint between the heating layer4of the first pipe and the heating layer4of the second pipe.

InFIG. 2, the composite strip10extends in a main direction P between first and second ends10a,10b, the second end being the opposite end of the first end in the main direction P. Each end10a,10bcomprises an end edge13a,13b, respectively. In a secondary direction S substantially perpendicular to the main direction P it further comprises two lateral edges14a,14bwhich are opposite to one another. The lateral edges14a,14bextend between the two ends10a,10bof the composite strip. The composite strip10thus, for example, has the overall shape of a quadrilateral, which may be a square, a rectangle or a trapezium.

The composite strip10firstly comprises fibres11a(first fibres) embedded in a matrix11b. The matrix11band the fibres11aform an entity referred to as the main strip11, having a shape that is substantially planar in a plane of directions P-S. The main strip11thus has an upper face15aand a lower face15b.

These first fibres11aare formed of a first electrically conducting material and extend in a fibre direction F. The conducting first material is advantageously carbon, like for the fibres of the heating layer4of the pipe1.

The matrix11bis made up of at least one polymer. The polymer may advantageously be a polyamide (PA) or a polyvinylidene fluoride (PVDF), like for the matrix of the heating layer4of the pipe1.

The composite strip10of the first embodiment ofFIG. 2further comprises, near each of the ends or end edges13a,13b, a junction layer17formed of a junction material which is likewise electrically conducting. This junction layer17is situated on top of the main strip11, i.e. on top of the first fibres11aand of the matrix11b. This junction layer17has the purpose of improving conduction of electricity of the composite strip10at its ends, which are intended to be in contact with a heating layer4of a pipe1.

This junction layer17is visible in cross section inFIG. 3. It takes the form of a strip which extends along each end10a,10b, each one having a width in the main direction P, for example of 1 cm or more, and for example greater than 5 cm. It has a thickness of between 0.05 mm and 1 mm.

This composite strip10is therefore a compound ready for use to make the joint between the heating layers4of two pipes1.

The junction material is advantageously a polymer filled with electrically conducting particles, or a polymer filled with metallic particles, or a polymer filled with silver particles, or a polymer filled with metallized carbon fibres, or a polymer filled with copper fibres, or a polymer filled with braided copper fibres.

The particles are small-sized elements of spherical, elliptical or any other shape. They have a size (largest dimension) for example smaller than 0.1 mm, and preferably smaller than 0.01 mm. These particles may thus be mixed into or serve as a filler for a polymer without having a great effect on the viscosity thereof. These particles are therefore in the form of powder.

During a step of transforming the composite strip by heating, the junction material of the junction layer17will bond intimately with the matrix and with the first fibres11a, to improve the conduction of electricity of a zone around the said junction layer17at the end of the composite strip10. Electrical conduction and contact with a heating layer4of a pipe1are thus greatly improved.

The first fibres11apossibly extend in the main direction P of the composite strip10. The composite strip is thus easier to produce.

The first fibres11aadvantageously extend in a fibre direction F that is inclined with respect to the main direction P, with a predetermined fibre angle β. The fibre angle β is, for example, between 0 degrees and 45 degrees. Advantageously, it is between 0 degrees and 10 degrees.

The fibre angle β of the composite strip may possibly differ from the angle of inclination α of the carbon fibres of the heating layer4of the pipes1. Notably, the fibre angle β is advantageously smaller than the angle of inclination α. The linear electrical resistance in the direction of the axis X of the joint6is therefore lower than the linear electrical resistance of the pipe. Heating at the joint is therefore reduced, and may even be eliminated.

According to the embodiment ofFIG. 2, the composite strip10is of rectangular shape.

According to the embodiment ofFIG. 4, the composite strip10is in the shape of a trapezium: the end edges13a,13bextend in directions that converge towards one another, forming an angle of convergence x, for example of between 0.1 degree and 20 degrees, and preferably between 0.1 degree and 5 degrees.

This angle of convergence is advantageously suited to the shapes of the heating layers4of the pipes1that are to be joined.

According to the embodiment ofFIG. 5, the composite strip10comprises:a main portion18corresponding to the composite strip10of the embodiments ofFIGS. 2 to 4, namely comprising conducting first fibres11a, anda secondary portion19which extends in the secondary direction S from the lateral edge14aof the main portion18, the said secondary portion19not containing the said first fibres and containing second fibres20embedded in the matrix11b, the said second fibres20being formed of a second material that is not electrically conducting.

The second material is, for example, glass.

The composite strip10is a continuous assembly of material comprising, continuously and juxtaposed, the first and second portions18,20. This composite strip10is thus ready for use to form a joint between two heating layers4and a joint between two insulating layers3or5.

By virtue of this composite strip it is possible to make a joint of several or all the layers using a single winding of the special-purpose composite strip10, and notably to make a joint between an insulating layer and a heating layer (between two pipes).

According to another embodiment (not depicted), the composite strip comprises a main portion18and two secondary portions19one on each side of the said main portion18, in the secondary direction.

Thanks to this composite strip, it is possible to make a joint of several or all the layers using a single winding of the special-purpose composite strip10, and notably to make a joint of the heating layer4and the two insulating layers3and5one on each side of the heating layer (between two pipes).

According to alternative forms of all the above embodiments of the composite strip, the junction layer17may be situated at various points on (or in contact with) the main strip11.FIGS. 6 to 9show cross sections similar to the cross section ofFIG. 3, and which explain these various locations.

In the alternative form ofFIG. 6, the junction layer17is situated at each of the ends10a,10bin strips extending along the end edges and arranged on the upper face15aand under the lower face15bof the main strip11. The junction layer17thus comprises four strips.

In the alternative form ofFIG. 7, the junction layer is situated at each of the ends10a,10bin strips extending along the end edges, and covers a strip of the upper face15aand the end edge13a,13b. The junction layer17thus comprises two strips of L-shaped cross section.

In the alternative form ofFIG. 8, the junction layer17is situated at each of the ends10a,10bin strips extending along the end edges, on the upper face15a, under the lower face15b, and on the end edge13a,13bin order to connect the strips of the upper and lower faces. The junction layer17therefore comprises two strips of C-shaped cross section which includes each end edge.

In the alternative form ofFIG. 9, the junction layer17is situated on the entire surface of the upper face15a(and/or lower face15b). It thus connects each end10a,10b. The junction layer17therefore covers the entirety of the said surface of the main strip11.

In each of these alternative forms, the conduction of electricity that can be achieved in a joint between two pipes with such a composite strip is thus reduced.

A method for forming a joint between two pipes1of the type ofFIG. 1will now be explained. These pipes1comprise an internal hollow tube2and successive layers of materials. One of the layers is a heating layer4allowing the pipe to be heated by electrical conduction. This heating layer4is situated within the thickness of the pipe, i.e. in a range of radial distances relative to the axis X of the pipe. The heating layer4comprises fibres made of conducting material, such as carbon fibres.

This method employs one of the composite strips10previously described for connecting the heating layers4of two pipes1butted together end to end.

Notably, the method comprises an electrical jointing process in which at least the following step is performed:the composite strip10is applied to each heating layer4or to a layer placed beforehand on the said heating layers by winding around the tubes2. The junction layer17of the composite strip10is then brought into contact with the heating layer4of the first pipe and with the heating layer4of the second pipe.

FIGS. 10 to 13show a more detailed example of how this method is implemented.

InFIG. 10, the second end1bof a pipe1is formed for example with the shape shown either at the factory or at the time of joining two successive (adjacent) pipes together.

A cylindrical portion2dof the external surface2bof the tube is uncovered (with no layer on top), and the layers on top of the tube2are formed into a cone shape with the cone extending towards the end1bof the pipe.

This second end1bis, for example, formed by machining a completely cylindrical pipe as shown inFIG. 1.

InFIG. 11, two pipes1each having its ends shaped as explained hereinabove are brought together until they are coaxial of axis X and in contact via their ends in a median plan M: the second end1bof the first pipe is in contact with the first end1aof the second pipe. The two tubes2of each pipe are then welded together in a welding step to form a continuous internal tube2for transporting the hydrocarbon fluid. A tube joint2jis therefore formed by welding together the two tubes2of the pipes1.

InFIG. 12, junction layers are then created on the tube junction2jin order to join the respective layers of each pipe1. Thus, the following steps are performed:

a) a first insulation-jointing step, in which an insulating strip containing second fibres embedded in a polymer matrix is applied, the said second fibres being formed of a second material that is not electrically conducting, such as glass; a first insulation layer joint3jis thus formed and joins together the first insulating layers3of the two pipes1on top of the tube joint2j;
b) an electrical-jointing step in which a composite strip10is applied by winding around the insulating layer3j, the junction layers17of each end of the composite strip being in contact with each heating layer4of the two pipes1; a heating layer joint4jis thus made and joins the said heating layers4on top of the insulation layer joint3j; and
c) a second insulation-jointing step in which an insulating strip of the same type as in the first insulation-jointing step is applied on top of the heating layer joint4j; a second insulation layer joint5jis thus made and joins together the second insulating layers5of the two pipes1on top of the heating layer joint4j.

The joints,2jbetween tubes,3j,5jbetween insulating layers and4jbetween heating layers form a joint6between the two tubes1which reproduces the stack of layers of each of the pipes1to form mechanical and electrical continuity (conduction and insulation) between the pipes1.

Further, between each of the preceding steps or as a final step, a step of heating the joint6between the first and second pipes1may possibly be carried out in order to crosslink or solidify the matrices11b.

Each joint3j,5jbetween insulating layers, and4jbetween heating layers, may be made using independent suitable strips. That means to say an insulating composite strip for each insulation layer joint3j,5jand a composite strip10of the type ofFIG. 2orFIG. 4for the heating layer joint4j.

One single composite strip10of the type ofFIG. 5, comprising two secondary portions19, may potentially be used to form all three layers of the joint6in a single winding.

In the scenario as set out in the figures, in which the joint6has a conical shape, a composite strip10in the shape of a trapezium may advantageously be used. Thus, for each turn of the winding of the strip in the joint6, as depicted inFIG. 13, the end edges13a,13bnaturally offset from one another allowing better contact between the junction layer17and the heating layers4of each pipe1. That also allows material to diffuse from the junction layer17over the entire area of contact with each heating layer4. That improves the conductivity of this heating layer joint4j(reducing contact electrical resistance).

The trapezium shape of the composite strip10is advantageously matched to the shapes of the ends of the pipes1, so that as the composite strip10is wound it forms a joint6of a shape that complements the said ends of the pipes. Notably, the diameters of the pipes, the thickness of the composite strip10and the shape of the ends of the pipes need to be taken into consideration when establishing the trapezium shape of the composite strip10.

Another method for forming a joint between two pipes1of the type ofFIG. 1will now be explained.

This method requires only a main strip11and the material of the junction layer. There is therefore no need to have a composite strip10prepared in advance and incorporating a junction layer17. However, this method takes longer to implement in the field.

Finally, it is possible using one or more composite strips10and/or main strips11, as set out in the present description, to make joints between pipes that are substantially identical and have several heating layers within the thickness of the pipes.

Notably, a composite strip10having an alternation of insulating portions (such as the secondary portion19) and conducting portions (such as the main portion18) can be produced. All the layers, and notably all the heating layers4, are then jointed using one single winding of the said special-purpose composite strip10.

Various modifications to the invention may be apparent to one of skill in the art upon reading this disclosure. For example, persons of ordinary skill in the relevant art will recognize that the various features described for the different embodiments of the invention can be suitably combined, un-combined, and re-combined with other features, alone, or in different combinations, within the spirit of the invention. Likewise, the various features described above should all be regarded as example embodiments, rather than limitations to the scope or spirit of the invention. Therefore, the above is not contemplated to limit the scope of the present invention.