Intermediate coupling for connecting rigid pipe elements for conveying a fluid, and associated pipe network and assembly method

A coupling that includes a rigid inner shell, a rigid outer shell positioned around the inner shell to define an intermediate space that contains an electric line and a thermally insulating layer, and an electric connecting line for heating fluid that flows in the inner shell.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a 35 U.S.C. § 371 National Phase conversion of PCT/EP2013/066740, filed Aug. 9, 2013, which claims benefit of French Application No. 1257879, filed Aug. 20, 2012, the disclosure of which is incorporated herein by reference. The PCT International Application was published in the French language.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to an intermediate coupling for connecting rigid pipe elements for conveying a fluid, comprising:an inner rigid shell, comprising:an inner section, the inner section delimiting an inner passage for a flow of fluid between a first end and a second end,at least one inner branch tapped on the inner section between the first end and the second end, the inner branch delimiting an inner aperture for a fluid flow emerging in the inner passage;at least one electric connecting line, intended to heat the fluid flowing in the inner shell, the electric line being positioned outside the inner shell, the electric line having a first electrical connecting point situated on a first side of the inner branch, and a second electrical connecting point situated on a second side of the inner branch.

BACKGROUND OF THE INVENTION

Such a coupling is in particular designed to be used in a network of underwater hydrocarbon transport pipes. The pipe network is submerged in an expanse of water, in particular at a significant depth.

This network is for example designed to connect different wellheads to each other, or different pipeline end terminations (PLET) in order to collect the fluid taken from the different wells of an underwater oilfield and bring it to the surface through at least one riser.

In some cases, in particular at great depths, the temperatures of the expanse of water in which the pipe network is submerged can be low, for example several degrees Celsius.

In that case, the fluids transported through the pipe network may become very viscous. This reduces the flow rate of the fluid extracted outside the facility.

In the worst-case scenario, hydrate plugs may form and completely block the recovery of fluid through part of the facility.

In order to offset this problem, it is known to heat the fluid flowing in the pipes, either by passing electric current directly through the metal tube guiding the fluid, or by providing an electric heating line positioned between an inner metal tube containing the fluid and an outer metal tube. The latter configuration is designated by the term “Electrical Tracing Heated Pipe-In-Pipe” (ETH-PIP).

The electric heating lines are relatively easy to install in the annular space between the inner tube and the outer tube of a linear rigid pipe element. A layer of high-quality thermally insulating material, for example formed by an aerogel, is also introduced into the annular space, to provide good thermal insulation between the outside of the pipe element and the fluid flowing in the pipe element.

In some configurations, a T coupling, made up of a single metal shell, is mounted between three linear pipe elements to hydraulically connect those elements. The T coupling is respectively connected to a first double-shell pipe element and a second double-shall pipe element each containing an electric heating line.

Then, a water resistant insulating material is poured around the metal shell of the coupling. An electric connecting line is also positioned in the expanse of water around the coupling to electrically couple the electric heating lines of the pipe elements mounted on the coupling.

Such a coupling is not fully satisfactory. The insulating material surrounding the coupling provides thermal insulation lower than that of an insulating material contained in a double shell of a linear pipe element. A cold point may therefore appear at the coupling.

Furthermore, the electric connecting line is connected to the heating lines in a wet environment, directly in the expanse of water. A deterioration of the electrical connection, or even short circuits, may appear.

SUMMARY OF THE INVENTION

One aim of the invention is therefore to provide an intermediate coupling for connecting rigid pipes that allows a reliable extraction of the fluids that pass through it, while providing the desired fluid connections.

To that end, the invention relates to a coupling of the aforementioned type, characterized in that the coupling comprises a rigid outer shell positioned around the inner shell, the outer shell at least partially covering the inner section on either side of the inner branch, and the inner branch, the outer shell and the inner shell delimiting an intermediate space between them extending around the inner section and the inner branch, the electric line being received in the intermediate space, the coupling comprising a thermally insulating layer positioned in the intermediate space across from the inner section and across from the inner branch.

The coupling according to the invention may include one or more of the following features, considered alone or according to any technically possible combination(s):the electric line is placed in thermal contact with the inner shell to heat the fluid contained in the inner passage;it comprises an additional electric line positioned in the intermediate space, the additional electric line having a first line segment extending across from the inner section and a second line segment extending across from the inner branch;the thermally insulating layer fills substantially all of the intermediate space;the thermally insulating layer comprises an aerogel;the inner section has a part protruding outside the outer shell at least at one of the first end and the second end;it comprises, for the or each protruding part, a cover attached on the outer shell to cover the protruding part;the length of the inner section is less than 10 m;the inner shell is made in a single piece, the outer shell advantageously being made in a single piece;the outer shell comprises an outer section at least partially covering the inner section on either side of the inner branch and an outer branch tapped on the outer section and at least partially covering the inner branch, the intermediate volume delimited between the inner section and the outer section communicating with the intermediate volume delimited between the inner branch and the outer branch.

The invention also relates to a pipe network for conveying a fluid, designed to be submerged in the expanse of water, characterized in that it comprises:a coupling as defined above;a first rigid pipe element for conveying a fluid, coupled to the first end of the inner section;a second rigid pipe element for conveying a fluid, coupled to the second end of the inner section;a third rigid pipe element for conveying a fluid coupled to the inner branch.

The network according to the invention may include one or more of the following features, considered alone or according to any technically possible combination(s):the first rigid pipe element and the second rigid pipe element each comprise an inner fluid guide tube coupled to the inner section and an outer tube delimiting an annular space with the inner tube, the annular space receiving a thermally insulating layer and at least one electric line designed to heat the fluid contained in the inner tube, the electric lines of the first rigid pipe element and the second rigid pipe element being electrically coupled to each other by the electric connecting line;the inner section has a part protruding outside the outer shell at least at one of the first end and the second end, the coupling comprising a cover coupled to the outer shell and the outer tube to cover the protruding part;the electric connection between the electric line present in at least one of the first rigid pipe element and the second rigid pipe element on the one hand, and the electric connecting line on the other hand, is positioned between the protruding part and the cover.

The invention also relates to a method for assembling a pipe network for conveying a fluid below an expanse of water, comprising the following steps:providing a coupling as described above;fastening a first rigid pipe element to a first end of the inner section;fastening a second rigid pipe element to a second end of the inner section;connecting a third rigid pipe element to the inner branch;electrical coupling between at least one first electric line designed to heat the fluid present in the first rigid pipe element, and the electric connecting line present in the coupling;electrical coupling between at least one second electric line designed to heat the fluid present in the second rigid pipe element, and the electric connecting line present in the coupling.

The invention also relates to a method for conveying fluid through an expanse of water comprising the following steps:providing a pipe network as defined above;causing fluid coming from the first rigid pipe element to flow through the coupling toward one and/or the other of the second rigid pipe element and the third rigid pipe element;heating the fluid flowing through the coupling via the electric connecting line.

DESCRIPTION OF PREFERRED EMBODIMENTS

A first intermediate connection coupling10according to the invention is diagrammatically illustrated inFIGS. 1 to 3.

The intermediate coupling10is designed to be mounted in a facility12for exploiting and conveying a fluid through an expanse of water14, shown in top view inFIG. 1.

The expanse of water14is for example a sea, ocean or lake. The depth of the expanse of water14is generally greater than 100 m and is for example comprised between 1000 m and 4000 m.

In the example ofFIG. 1, the facility12comprises a plurality of wells16arranged in the bottom of the expanse of water14to withdraw fluid.

The fluid withdrawn and conveyed in the facility12is advantageously a hydrocarbon such as oil or natural gas.

The facility12comprises a network18of rigid pipes placed on the bottom of the expanse of water14, coupling and fluid collection elements20, such as pipeline end terminations (PLET), and at least one riser22, designed to convey the fluid flowing in the network18toward the surface of the expanse of water14.

As illustrated byFIGS. 1 and 2, the network18comprises a first rigid pipe element24for conveying a fluid, a second rigid pipe element26for conveying a fluid, and a third rigid pipe element28for conveying a fluid, the elements24to28being coupled to each other by a coupling10according to the invention.

The rigid pipe elements26to28have similar structures. In reference toFIG. 2, each element26to28thus has an inner metal tube30designed to guide the fluid, an outer metal tube32delimiting an intermediate space34with the inner tube30, and a thermally insulating layer36positioned in the intermediate space34.

Each pipe element26to28further comprises at least one electric line38designed to heat the fluid flowing through the inner tube30, the line38being received in the intermediate space34.

The inner metal tube30delimits a central aperture40for the flow of a fluid that emerges at each end of the tube30. Near the coupling10, the tube30has a region42protruding outside the outer tube32.

The inner tube30for example has an outer diameter comprised between 10 cm and 100 cm.

The thermally insulating layer36fills substantially all of the intermediate space34. It is for example formed by an aerogel. It has an overall heat transfer coefficient (OHTC) for example below 1 W/m2K.

The electric line38is able to perform heating electric tracing on the inner tube30, outside the tube30. It is placed in thermal contact with the outer surface of the inner tube30, either placed directly against the surface, or placed on a protective layer43of the outer surface such as a layer of fusion-bonded epoxy.

The electric line38is for example made by a cord of conductive cables or wires received in a metal sheath.

It for example has an elongated cross-section with a width larger than its thickness.

Near the coupling10, the electric line38advantageously has an electric connecting termination44protruding outside the intermediate space34.

The outer tube32surrounds the inner tube30and the thermally insulating layer36. It generally has an outer diameter comprised between 10 cm and 100 cm.

As illustrated byFIGS. 2 and 3, the coupling10comprises a metal inner shell60, designed to guide the fluid, and according to the invention, a metal outer shell62surrounding the inner shell60and delimiting a continuous intermediate space64with the inner shell60.

The coupling10further comprises a thermally insulating intermediate layer66and at least one electric connecting line68A,68B, designed to heat the fluid, the layer66and each line68A,68B being received in a continuous intermediate space64.

In the example ofFIG. 2, the coupling10further comprises intermediate protective covers70, coupling the outer shell62to the outer tube32of an adjacent pipe element24,26.

The coupling10is short. Its length is for example shorter than 10 m.

The inner shell60is preferably made in a single piece from metal. It comprises a tubular inner section72and at least one tubular outer branch74tapped on the inner section72between the ends76,78of the inner section72.

In this example, the inner shell60comprises a single outer branch74. It is thus generally T-shaped. In one alternative (not shown), it is generally Y-shaped, or has several branches74.

The inner section72has an outer diameter substantially equal to the outer diameter of the inner tube30of the pipe elements24,26to which it is connected.

It delimits an inner passage80for the flow of a fluid emerging outwardly at the first end76and the second end78.

The inner branch74is tapped on the inner section72between the first end76and the second end78.

It advantageously has an outer diameter substantially equal to the outer diameter of the pipe element28on which it is coupled.

It inwardly defines an inner aperture82for a flow of fluid emerging in the inner passage80between the ends76,78.

In this example, the inner section72comprises a part84protruding outside the outer shell62at each end78.

The outer shell62has a shape similar to that of the inner shell60.

It is positioned around the inner shell60to at least partially cover that shell60. The outer shell62outwardly delimits the intermediate space64.

The outer shell62is made in a single piece from metal. It comprises a tubular outer section92positioned around the inner section72and, for each inner branch74, an outer branch94tapped on the outer section92.

Advantageously, the length of the outer section92is shorter than that of the inner section72. It covers the inner section72on either side of the branch74.

The outer section92has an outer diameter substantially equal to the outer diameter of the outer tube32of each pipe element24,26on which the coupling10is connected.

The outer branch94is positioned around the inner branch64.

The outer branch62is thus generally T-shaped. Alternatively, it is generally Y-shaped, or has several branches94each corresponding to an inner branch74.

The intermediate space64comprises a first annular intermediate volume96situated between the inner section72and the outer section92, and a second intermediate volume98situated between the inner branch74and the outer branch94.

According to the invention, the intermediate space64is continuous. The second intermediate volume98emerges in the first intermediate volume96between the tap of the inner branch74on the inner section72and the tap of the outer branch94on the outer section92.

The coupling10is fastened on the first pipe element24, for example by welding, at the first end76. It is fastened on the second pipe element26, for example by welding, at the second end78.

It is also fastened on the third pipe element28.

In particular, each protruding region42of a pipe element24,26is assembled on a protruding part84of the inner section72. Each inner aperture40of a pipe element24,26then emerges in the inner passage80and is hydraulically connected to the third pipe element28by the inner aperture82.

The thermally insulating layer66extends in the intermediate space64. It comprises a first part100positioned in the first inner volume96and a second part102positioned in the second inner volume98.

Advantageously, the first part100and the second part102are connected to each other to provide continuous thermal insulation in the coupling10.

Preferably, the thermally insulating layer66substantially completely fills, for example more than 50%, in particular more than 90%, the volume of the intermediate space64.

The thermally insulating layer66being contained between the outer shell62and the inner shell60, it is not placed in contact with the expanse of water14surrounding the coupling10. It for example comprises an aerogel.

It thus has an overall heat transfer coefficient (OHTC) for example lower than 1 W/m2K.

The coupling10therefore does not constitute a cold point in the pipe network18.

In this example, the coupling10comprises a first electric line68A for heating the fluid extending through the first inner volume96between the inner section72and the outer section92.

The coupling10advantageously has a second electric line68B for heating the fluid extending partially in the first inner volume96and partially in the second inner volume98.

Each electric line68A,68B is for example able to perform heating electric tracing on the inner shell60, outside the inner shell60. It is placed in thermal contact with the outer surface of the inner shell60, placed either directly against the surface or on a protective layer43of the outer surface, such as a layer of fusion-bonded epoxy.

The electric line68A,68B is for example made by a cord of conductive cables or wires received in a metal sheath.

It for example has an elongated cross-section with a width larger than its thickness.

In reference toFIGS. 2 and 3, the first electric line68A has, in this example, a first electric connecting end104situated near the first end76, advantageously outside the outer shell62, and a second electric connecting end106, situated near the second end78, advantageously outside the outer shell62.

As illustrated byFIG. 2, the end44of the electric line38of the first pipe element24is connected to the first end104, preferably by crimping.

The end44of the electric line38of the second pipe element26is connected to the second connecting end106, preferably by crimping.

Thus, the electric connecting line68A electrically couples the electric line38of the second pipe element26to the electric line38of the first pipe element24, in the intermediate space64, without being in contact with the expanse of water14.

This makes it possible to produce dry electric connections between the lines38,68A, which increases the reliability of the heating of the fluid passing through the network18.

Furthermore, the lines38,68A can be electrically coupled by simple crimping, without having to perform welding withstanding a wet environment.

As illustrated byFIG. 3, the second electric line68B comprises a first line segment110extending across from the inner section72in the first volume100and a second line segment112extending across from the inner branch74in the second inner volume102.

The second electric line68B is therefore able to electrically couple an electric line38contained in one of the first pipe element24and the second pipe element26with an electric line contained in the third pipe element28.

Each cover70is positioned around the protruding parts42,84, bearing between the outer tube32and the outer shell62. The cover70is for example formed by two half-shells assembled on one another. A thermally insulating sleeve108is positioned in the intermediate volume defined between the protruding parts42,84and the cover70.

A method for assembling the pipe network18according to the invention will now be described.

This assembly method is for example implemented on land, or on a placement ship, on the surface of the expanse of water14. Alternatively, this method is implemented directly below the expanse of water14, using a hyperbaric chamber.

Initially, the coupling10, a first pipe element24and a second pipe element26are provided.

For each end76,78of the coupling10, the exposed protruding parts42,84are placed end to end and are fastened on one another, for example by welding.

Then, the electric connecting end44of the line38is electrically coupled to an electric connecting end104,106of the connecting line68A, for example across from the protruding parts42,84.

Next, the thermally insulating sleeve108is formed around the protruding parts42,84. The cover70is next placed around the sleeve108bearing on the outer tube32and on the outer shell62.

Next, a third pipe element28is connected to the bridge74of the coupling10, either directly as previously described, or by means of a valve.

The pipe network18can then be used. The heating lines38are electrically powered, and are connected to one another by the intermediate line68A. The fluid flowing in the apertures40and the inner passage80is therefore heated respectively using the lines38and the line68A, which decreases its viscosity, and prevents plugs from forming.

Owing to the coupling10according to the invention, it is possible to couple at least three tubular pipe elements24,26,28to each other, without creating a cold point at the coupling10.

The double shell structure of the coupling10being similar to that of the pipe elements24,26,28, it is easy to connect the coupling10on the pipe elements24,26,28. This structure makes it possible to use high-quality thermal insulators in the coupling10, and provide heating lines68A,68B through the coupling10, without contact with the expanse of water14. The electric connections are therefore done dry, for example by simple crimping.