conduit for transporting fluids to drainage channels

Abstract

Pipeline for the transport of fluids with drainage channels The invention relates to a pipe (2-1) for the transport of fluids comprising a steel tube (4) intended to receive a flow of fluids to be transported, a protective lining (6) inserted inside the tube, a plurality of non-through drainage channels (10) formed in an external surface of the protective lining (6) and extending between two ends (10a) to allow the gas that has passed through the lining to move inside an interstitial space between the tube and the lining, and at least one discharge zone (12) comprising a plurality of openings (14) made through the lining to connect the interstitial space with the interior of the pipe in order to allow the gas that has passed through the lining to escape from the interstitial space during a depressurization of the pipe,the ends (10a) of the drainage channels (10) being separated from the evacuation zones (12) by barrier zones (16) devoid of openings and drainage channels. Figure for the abbreviation: Fig. 1.

Description

Title of the invention: Conduit for transporting fluids with drainage channels. Technical field

[0001] The present invention relates to the general field of coated steel subsea or land-based pipelines used for transporting fluids such as hydrocarbons, in particular oil and gas, or hydrogen or CO2.

[0002] It relates more specifically to a solution to avoid buckling of the internal lining of such pipes under the coating during a sudden depressurization of the line due to permeation and accumulation of gas. Previous technique

[0003] Subsea pipelines used for transporting hydrocarbons, particularly oil and gas, from subsea production wells are generally made of a steel tube.

[0004] The fluids transported are sometimes corrosive to the steel constituting the pipes due to one or more constituents such as carbon dioxide or hydrogen sulfide. Therefore, to protect them against corrosion, it is known to insert or apply a layer of corrosion-resistant nickel-based alloy steel—typically 3 mm or more thick—into the inside of the steel pipe. This layer of corrosion-resistant alloy steel protects the mechanical integrity of the steel pipe by isolating it from the transported fluid and preventing induced corrosion. This alloy steel layer can be inserted as a liner or applied by deposition of material onto the inner surface of the steel pipe (this technique is known in the industry as "CRA lining" for "Corrosion Resistance Alloy lining").This effective solution is, however, very expensive, particularly due to the material cost of these corrosion-resistant alloys.

[0005] A first alternative to alloy steel lining is the application of a protective anti-corrosion layer in the form of a thin coating, made, for example, with the application of epoxy polymer resin, more commonly known as "epoxies," typically having a thickness on the order of a few hundred micrometers. Although more economical to purchase and manufacture than the use of alloy steel lining, these thin coatings have the disadvantage of being susceptible to scratches and abrasion, which can result in the exposure of certain parts of the steel pipe, thus exposing it to the risk of corrosion. Anti-corrosion chemicals are usually injected preventively into the transported fluid. to reduce the risk of corrosion in potentially exposed areas of the steel pipeline, which increases the operational costs of using the pipeline.

[0006] As an alternative, this solution can be replaced by the insertion of a protective annular liner—typically around 10 mm thick—made of polymer material, for example, thermoplastic. The protective liner is typically inserted by pulling it through a diameter reduction system and then inside the steel pipe, pressing it against the inner surface of the pipe once the pulling force is released to obtain a tight fit. The protective liner then isolates the steel pipe from the transported fluid and protects it from the risk of induced corrosion. The thickness of the polymer liner protects it from scratches and abrasion during the pipe's service life. This technique is quite commonly used for pipelines transporting liquids such as injection water, for example, but less so for subsea pipelines transporting multiphase production fluids.

[0007] Although more economical than the usual "CRA lining" technique, polymer lining has the disadvantage of being permeable to gases and vapors from the transported fluids. Therefore, in practice, gas tends to penetrate the polymer material and pass through the protective lining to become lodged in the interstitial space between the lining and the inner wall of the steel tube.

[0008] Over time, gases and vapors will accumulate in the interstitial space. The permeation phenomenon is driven by the operating pressure of the transported fluid, and over time, since permeation phenomena are not usually instantaneous, this creates an accumulation of pressurized gas under the lining, more or less uniformly distributed along the length of the pipe. However, when the pipe is depressurized, the permeation rate of the protective lining is not high enough to allow the pressure inside the interstitial space to decrease at the same rate as the pressure drop inside the pipe. A pressure differential is then created, with overpressure on the interstitial side, and a risk of buckling or local collapse of the protective lining.

[0009] The local and uncontrolled collapse of the protective lining during pipeline depressurization can compromise the integrity of the lining and therefore its effectiveness in protecting the steel constituting the pipe against corrosion. Furthermore, when the pipeline is repressurized, there is a risk that the collapsed portion of the protective lining may not return to its original shape against the inner wall of the pipe, potentially altering the cross-sectional area for the transported fluid, which can lead to increases in pressure loss, for example, or to a change in the resistance capacity over time of the polymer lining.

[0010] Several solutions have been considered to address this problem of uncontrolled collapse of the protective liner during pipeline depressurization. Some involve applying an adhesive coating to the inner surface of the steel pipe to increase adhesion between the thermoplastic liner and the steel pipe, thereby increasing the liner's resistance to collapse while limiting the volume of the interstitial space under the liner and thus the amount of gas that could potentially accumulate there. Other known solutions consist of creating grooves on the outer face of the liner to collect the gases that have passed through the liner and venting them to the outside of the pipeline via external ports in the pipe. This degassing operation can be performed continuously or at regular intervals.

[0011] Yet another solution, notably described in publication WO 02 / 033298, consists of making cylindrical perforations in the protective lining so as to bring the interstitial space into contact with the inside of the lining. In the event of pipe depressurization, the gases that have passed through the lining will use these perforations to be evacuated from the inside of the lining so as to maintain the pressure differential below the collapse pressure of the lining.

[0012] All the prior art solutions presented above have drawbacks. In particular, the use of an adhesive coating on the inner surface of the steel tube presents the disadvantage of a highly complex implementation process that requires several application phases of different layers followed by curing phases to create adhesion. Furthermore, the use of external gas vents requires drilling the steel tube, which weakens the tube's mechanical integrity, and providing a gas vent line in the underwater environment, thus increasing the system's complexity, installation procedures, and the risk of leaks. Moreover, this solution requires maintenance operations to activate the degassing process. The grooves on the outer surface of the liner are also prone to clogging and liquid accumulation, which can reduce ventilation efficiency.

[0013] The solution of drilling cylindrical perforations in the protective lining has the disadvantage of continuously exposing the transported fluids to the steel tube, with the risk of localized corrosion. Furthermore, over their service life, these cylindrical perforations are prone to clogging, as they can easily fill with sand, wax, hydrocarbons, or even become breeding grounds for bacteria.

[0014] A solution is also known from publication WO 2023 / 111437 in which the protective liner comprises a plurality of slots extending lengthwise parallel to a longitudinal axis of the tube and passing through an inner and an outer face of the liner. Each slot is open on the inner face of the liner prior to insertion of the liner into the tube and is at least partially closed once the liner is inserted. These slots allow gas that has infiltrated the annular space between the tube and the liner to be evacuated into the tube when a line depressurization occurs, while minimizing the risk of dirt / solids ingress.

[0015] The main problem with existing solutions is that the gas which has infiltrated the annular space is then evacuated outside the pipe, which requires, on the one hand, a venting connection in the pipe to evacuate the gas, and on the other hand, a venting network (ventilation network).

[0016] However, in an offshore environment, for subsea pipelines, the stresses on the steel pipe during installation are significantly higher than for onshore pipelines, while response times in the event of a leak are significantly longer. Installing and designing an external ventilation system is also more complex. For these reasons, it is preferable to avoid external vents for subsea pipelines. Description of the invention

[0017] The present invention aims to overcome these drawbacks by proposing a conduit for the transport of fluids which allows the permeable gas to be evacuated in the conduit itself without resorting to external vents or other evacuation holes drilled in the steel conduit.

[0018] This objective is achieved by means of a fluid transport conduit comprising a steel tube intended to receive a flow of fluids to be transported, and an annular lining for protection against corrosion and / or abrasion made of polymer material and inserted inside the tube, and further comprising, according to the invention: - a plurality of non-through drainage channels formed in an external surface of the protective liner and extending longitudinally between two ends to allow gas that has passed through the liner to move longitudinally within an interstitial space between an internal surface of the tube and an external surface of the liner, and - at least one evacuation zone comprising a plurality of openings made through the protective lining to put in communication between the interstitial space and the inside of the pipe to allow gas that has passed through the lining to escape from the interstitial space during pipe depressurization, - the ends of the drainage channels being separated from the evacuation areas by barrier zones devoid of openings and drainage channels.

[0019] The conduit according to the invention is remarkable in that it allows the permeable gas to be evacuated within the conduit itself without having to modify the conduit (such as by drilling vent holes). The integrity of the steel tube is thus preserved. Furthermore, the drainage channels do not open into the inside of the conduit, so that, during production phases, there is no flow of gas or liquid from inside the conduit into the drainage channels and the interstitial space between the tube and the protective lining.

[0020] The protective lining can be inserted inside the tube by a tight fit.

[0021] The openings in the discharge area may be cylindrical in shape.

[0022] Alternatively, the openings of the evacuation zone may each have, in cross-section and prior to the insertion of the protective lining into the tube, an external opening at the level of the external surface of the lining which communicates via a groove with an internal opening at the level of an internal surface of the lining.

[0023] The openings of the evacuation zone can be circumferentially spaced from each other and connected to each other by at least one substantially circumferential groove.

[0024] The respective ends of the drainage channels can be offset from the openings of the evacuation zone in a longitudinal direction so as to form a barrier zone.

[0025] Alternatively, the respective ends of the drainage channels and axial channels can be offset from the openings of the evacuation zone in a circumferential direction so as to form a barrier zone.

[0026] Alternatively, the barrier zone can be achieved by weakened portions of protective lining separating the drainage channels from the openings of the evacuation zones and whose mechanical resistance to radial deformation is lower than that of the remaining portion of the lining.

[0027] The conduit may comprise two discharge zones offset longitudinally from each other and each associated with a set of drainage channels, the adjacent ends of the drainage channels of each set being offset circumferentially from each other and not connected.

[0028] Preferably, the internal surface of the tube is coated with an anti-corrosion coating, which makes it possible to eliminate or reduce as much as possible the risk of corrosion of the tube.

[0029] The drainage channels may be circumferentially spaced from one another and connected to each other by at least one substantially circumferential groove. Brief description of the drawings

[0030] [Fig-1] Fig. 1 is a longitudinal cross-sectional view of a pipe along a first embodiment of the invention.

[0031] [Fig.2] The [Fig.2] is a perspective and cutaway view of part of the conduit of the [Fig.1].

[0032] [[Fig.3] Fig.3 is a longitudinal cross-sectional view of a pipe along a second embodiment of the invention.

[0033] [Fig.4] The [Fig.4] is a longitudinal cross-sectional view of a pipe according to a third embodiment of the invention.

[0034] [Fig.5] The [Fig.5] is a longitudinal cross-sectional view of a pipe according to a fourth embodiment of the invention.

[0035] [Fig.6] The [Fig.6] is a longitudinal cross-sectional view of a pipe according to a fifth embodiment of the invention.

[0036] [Fig.7] The [Fig.7] is a longitudinal cross-sectional view of a pipe according to a sixth embodiment of the invention. Description of the implementation methods

[0037] The invention relates to any type of fluid transport conduit, in particular for hydrocarbons but also for hydrogen or CO2, comprising a steel tube inside which the fluids to be transported flow, and an annular lining for protection against corrosion and / or abrasion which is made of polymer material and inserted inside the tube against an internal surface thereof.

[0038] The invention finds a preferred (but not limiting) application in the underwater transport of hydrocarbons, in particular oil and gas, from underwater production wells.

[0039] Fig. 1 is a longitudinal cross-sectional view of a section of a conduit 2-1 for the transport of fluids according to a first embodiment of the invention.

[0040] The conduit section 2-1 comprises a steel tube 4, for example carbon steel, having a longitudinal axis XX and which is intended to receive the flow of fluids to be transported.

[0041] The conduit section also includes an annular protective sleeve 6 made of polymer material, inserted inside the tube 4 against a surface internal to it and intended to ensure protection of the steel against corrosion from fluids and / or abrasion.

[0042] By way of non-limiting example, the protective lining can be made by extrusion of a thermoplastic material such as: high-density polyethylene (HDPE), polyamide (PA), polyvinylidene fluoride or polyvinylidene difluoride (PVDF), polyetheretherketone (PEEK), etc.

[0043] Preferably, the protective liner is inserted into the tube by deformation with a tight fit. For this purpose, the liner, in its resting state (i.e., prior to its insertion into the tube), has an external diameter that is slightly larger than the internal diameter of the tube. In this way, the insertion of the liner into the tube generates contact pressure between the liner and the tube. Once inserted into the tube, the internal and external diameters of the liner are therefore reduced compared to the liner in its resting state.

[0044] In a known manner, the conduit section 2-1 further comprises, at each of its longitudinal ends, end connectors 8 allowing the conduit section 2-1 to be connected to other conduit sections (for example, using a compression ring 8a, by welding, etc.). These end connectors may also be provided with a protective layer of alloy steel 8b.

[0045] According to the invention, a plurality of non-through drainage channels 10 are formed in an external surface of the protective lining 6. By "non-through", it is understood that the drainage channels do not connect the external surface with the internal surface of the protective lining.

[0046] Each drainage channel 10 extends longitudinally between two opposite ends 10a to allow the gas that has passed through the liner to move longitudinally inside the interstitial space between the inner surface of the tube 4 and the outer surface of the protective liner 6.

[0047] According to the invention, the conduit section 2-1 further comprises at least one evacuation zone 12 (two evacuation zones in the example of [Fig.1]) formed by a plurality of openings 14 which are made through the protective lining 6 to connect the interstitial space with the interior of the conduit in order to allow the gas which has passed through the lining to escape from the interstitial space during a depressurization of the conduit.

[0048] Furthermore, also according to the invention (and as represented in particular in [Fig.2]), the ends 10a of the drainage channels 10 are spaced longitudinally from the two evacuation zones 12 by barrier zones 16 which are devoid of openings and drainage channels.

[0049] Thus, during the production phases, the gas that has passed through the protective jacket to infiltrate the interstitial space moves along the axis Longitudinal XX of the pipe, using drainage channels 10. During pipe depressurization, the gas accumulated in this interstitial space will be at higher pressure than the inside of the pipe. When the pressure differential between this interstitial space and the discharge zones exceeds a certain threshold, the accumulated gas will pass through the barrier zones to reach the openings of the discharge zones and return to the pipe.

[0050] It should be noted that the barrier zones are dimensioned so as to minimize the pressure differential between the drainage channels and the openings of the evacuation zones and thus prevent the collapse of the protective lining during the depressurization of the gas in the pipe.

[0051] It will also be noted that there may be an overlap between these barrier zones 16 and the protective alloy steel layer 8b of the end connectors 8 so that the steel pipe is protected from corrosion potentially brought about by the presence of the drainage zones connecting the inside of the pipe and the interstitial space.

[0052] It should also be noted that the openings 14 of the evacuation zones may have a cylindrical shape as shown in [Fig.2].

[0053] Alternatively, these openings may each have, in cross-section and prior to the insertion of the protective lining into the tube, an external opening at the level of the external surface of the lining which communicates via a groove with an internal opening at the level of an internal surface of the lining (reference may be made to publication WO 2023 / 111437 for a more detailed description of the shape of the openings).

[0054] Whatever the shape of the openings of the evacuation zones, these can be distributed on a single circumferential row or on several circumferential rows (spaced axially from each other).

[0055] In connection with [Fig.3], a 2-2 conduit section will now be described according to a second embodiment of the invention.

[0056] In this second embodiment, two evacuation zones 12 are provided at each of the longitudinal ends of the pipe section, as well as a central evacuation zone 12-c which is located between the two longitudinal ends of the pipe section and which is formed by a plurality of central openings 14-c which are made through the protective lining 6.

[0057] This embodiment makes it possible to multiply the evacuation zones in the case where the distance between two end connectors is very large by allowing more frequent evacuations for the gas that has permeated.

[0058] Furthermore, the conduit section 2-2 also includes, on either side of the central evacuation zone 12-c, two central barrier zones 16-c which are devoid of openings and drainage channels.

[0059] According to an advantageous embodiment of the invention (partially shown in [Fig. 3]), the inner surface of the tube 4 is coated with an anti-corrosion coating 24, for example, a layer of CRA alloy (for "Corrosion Resistant Alloys"). In particular, this anti-corrosion coating 24 is positioned opposite the central openings 14-c in order to prevent any corrosion problems under these openings in the central drainage zone 12-c located between the two longitudinal ends of the pipe section. At these longitudinal ends, the anti-corrosion coating is typically integrated into the end connectors (see the protective alloy steel layer 8b in [Fig. 1]).

[0060] In connection with [Fig.4], a 2-3 conduit section will now be described according to a third embodiment of the invention.

[0061] In this embodiment, the openings 14 of the evacuation zone 12 are circumferentially spaced from each other and are connected to each other by a substantially circumferential groove 18.

[0062] The use of such a circumferential groove 18 in the evacuation zone allows the gas to be distributed over the circumference of the tube and thus manages the risk that one of the openings is obstructed, blocked, etc. (for any reason) by redistributing the gas to the other openings of the evacuation zone.

[0063] Similarly, the drainage channels 10 can be connected to each other by one or more substantially circumferential grooves 20 (two in [Fig. 4]) to mitigate the risk of one of these drainage channels becoming blocked for any reason (presence of a solid, precipitation of hydrates, etc.). The groove 20 need not be exactly circumferential as long as it connects the drainage channels to each other.

[0064] Still in this embodiment, it will be noted that the respective ends 10a of the drainage channels 10 are offset from the openings 14 of the evacuation zone 12 along the longitudinal axis XX so as to form the barrier zone 16.

[0065] In connection with [Fig.5], a 2-4 conduit section will now be described according to a fourth embodiment of the invention.

[0066] In this embodiment, the openings 14 of the evacuation zone 12 are connected to each other by a circumferential groove 18 which is itself extended axially towards the center of the conduit by axial channels 19. The drainage channels 10 are also connected to each other by one or more substantially circumferential grooves 20.

[0067] Unlike the embodiment of [Fig.4], the barrier zones 16 are formed here by an offset in a circumferential direction between the respective ends 10a of the drainage channels 10 and the axial channels 19 extending axially from the circumferential groove 18.

[0068] The use of nested drainage channel networks minimizes the pressure difference between the circumferential grooves 20 while blocking the direct connection between the drainage channels 10 and the openings 14 of the drainage zones 12.

[0069] In connection with [Fig.6], a 2-5 conduit section will now be described according to a fifth embodiment of the invention.

[0070] In this embodiment, the conduit section 2-5 comprises two drainage zones 12-a, 12-b which are longitudinally offset from each other and which are each associated with a set of drainage channels 10, the adjacent ends 10b of the drainage channels of each set being circumferentially offset from each other and not connected.

[0071] This embodiment ensures that no flow in the drainage channels will be caused by the production flow in the pipe section. Since the drainage channels 10 of an assembly can be connected to discharge zones at both ends, it is not technically necessary for the drainage channels to be continuous from one end to the other; they can be divided in two in the middle of the pipe section, each half distributing the permeable gas to one end of it. Thus, each drainage channel is a dead end and no flow can pass from one discharge zone to the other.

[0072] In connection with [Fig.7], a 2-6 conduit section will now be described according to a sixth embodiment of the invention.

[0073] In this embodiment, the barrier zones 16 are made by weakened portions 22 of protective lining 6 which separate the drainage channels 10 from the openings 14 of the evacuation zones 12 and whose mechanical resistance to radial deformation is lower than that of the remaining portion of the lining.

[0074] With these portions 22 of the protective lining weakened at the barrier areas, it is thus possible to facilitate the connection between the drainage channels and the openings of the evacuation areas during a depressurization of the pipeline and to reduce the pressure drop associated with the barrier areas.

[0075] Thus, in the event of excessive differential pressure between the openings and the drainage channels (i.e., the depressurization is too rapid for all the gas to cross the barrier zone quickly enough to maintain the differential pressure below the collapse pressure of the protective jacket), it is these weakened portions of the jacket that would collapse, thus releasing the path for the gas to reach the openings of the venting areas. During the production phases, these weakened sections of the lining would be the first to be "pressed" against the inner surface of the tube during pressurization, and the barrier function would thus be restored.

Claims

Demands

1. Conduit (2-1 to 2-6) for the transport of fluids comprising a steel tube (4) for receiving a flow of fluids to be transported, and an annular protective liner (6) against corrosion and / or abrasion made of polymer material and inserted inside the tube, characterized in that it further comprises: - a plurality of non-through drainage channels (10) formed in an external surface of the protective liner (6) and extending longitudinally between two ends (10a) to allow the gas that has passed through the liner to move longitudinally within an interstitial space between an internal surface of the tube and an external surface of the liner, and - at least one discharge zone (12; 12a, 12b; 12c) comprising a plurality of openings (14;14-c) made through the protective lining to connect the interstitial space with the inside of the pipe in order to allow the gas which has passed through the lining to escape from the interstitial space during a depressurization of the pipe, - the ends (10a) of the drainage channels (10) being separated from the evacuation zones (12) by barrier zones (16; 16-c) without openings and drainage channels.

2. Conduct according to claim 1, wherein the protective sleeving (6) is inserted inside the tube (4) by a tight fit.

3. Conduct according to any one of claims 1 and 2, wherein the openings (14) of the evacuation zone (12) have a cylindrical shape.

4. Conduct according to any one of claims 1 and 2, wherein the openings (14) of the evacuation zone (12) each have, in cross-section and prior to the insertion of the protective lining into the tube, an external opening at the level of the external surface of the lining which communicates via a groove with an internal opening at the level of an internal surface of the lining.

5. Conduct according to any one of claims 1 to 4, wherein the openings (14) of the evacuation zone are spaced circumferentially to each other and are connected to each other by at least one substantially circumferential groove (18).

6. Conduct according to any one of claims 1 to 5, wherein the respective ends (10a) of the drainage channels (10) are offset from the openings (14) of the discharge zone (12) in a longitudinal direction so as to form a barrier zone.

7. Conduct according to any one of claims 1 to 5, wherein the respective ends (10a) of the drainage channels (10) and axial channels (19) are offset from the openings (14) of the discharge zone (12) in a circumferential direction so as to form a barrier zone.

8. Conducted according to any one of claims 1 to 5, wherein the barrier zone (16) is made by weakened portions (22) of protective lining (6) separating the drainage channels (10) from the openings (14) of the evacuation zones and whose mechanical resistance to radial deformation is lower than that of the remaining portion of the lining.

9. Conduct according to any one of claims 1 to 8, comprising two drainage zones (12) offset longitudinally from each other and each associated with a set of drainage channels (10), the adjacent ends (10b) of the drainage channels of each set being offset circumferentially from each other and not connected.

10. Conduct according to any one of claims 1 to 9, wherein the internal surface of the tube (4) is coated with an anti-corrosion coating.

11. A conduit according to any one of claims 1 to 10, wherein the drainage channels (10) are circumferentially spaced from each other and are connected to each other by at least one substantially circumferential groove (20).

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