Pipe for transporting fluids with drainage channels

Abstract

The invention relates to a pipe (2-1) for transporting fluids, which pipe comprises a steel tube (4) for receiving a flow of fluids to be transported, a protective liner (6), blind drainage channels (10) formed in an outer surface of the protective liner (6) to allow gas having passed through the liner to move within an interstitial space between the tube and the liner, and at least one discharge zone (12) comprising a plurality of openings (14) made through the liner to allow the interstitial space to communicate with the interior of the pipe in order to allow the gas having passed through the liner to escape from the interstitial space upon depressurisation of the pipe, the ends of the drainage channels being spaced apart from the discharge zones (12) by barrier zones (16) not provided with any openings or drainage channels.

Description

Description Title of the invention: Conduit for the transport of fluids with drainage channels; conduit for the transport of 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, including oil and gas, or hydrogen or CO2.

[0002] It relates more specifically to a solution to prevent the 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 steel tubing.

[0004] The fluids transported are sometimes corrosive to the steel of the pipes due to one or more constituents such as carbon dioxide or hydrogen sulfide. Therefore, to protect them against corrosion, it is common practice to insert or apply a layer of corrosion-resistant nickel-based alloy steel to the inside of the steel pipe – typically 3 mm or more thick. 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 – a technique known in the industry as "CRA lining" for "Corrosion Resistance Alloy lining." This effective solution is, however, very expensive, primarily 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, for example, using epoxy polymer resin, more commonly known as "epoxies," typically a few hundred micrometers thick. Although more economical to purchase and manufacture than alloy steel lining, these thin coatings have the disadvantage of being susceptible to scratches and abrasion, which can result in exposing parts of the steel pipe and thus making it vulnerable to corrosion. Anti-corrosion chemicals are usually injected preventively into the transported fluid to reduce the risk of corrosion in any areas of the steel pipe that may be exposed, thereby increasing the pipeline's operating costs.

[0006] As an alternative, this solution can be replaced by inserting a protective annular sleeve—typically around 10 mm thick—made of polymer material, such as thermoplastic. The protective sleeve is typically inserted by pulling it through a diameter reduction system and then inside the steel pipe. Once the pulling force is released, it presses against the inner surface of the pipe to achieve a tight fit. The protective sleeve then isolates the steel pipe from the fluid being transported and protects it from the risk of induced corrosion. The thickness of the polymer sleeve 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, 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, becoming lodged in the interstitial space between the lining and the inner wall of the steel tube.

[0008] Over time, gases and vapors accumulate in the interstitial space. The permeation process is driven by the operating pressure of the transported fluid, and over time, since permeation is not usually instantaneous, this creates an accumulation of pressurized gas beneath 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 then develops, with overpressure occurring in the interstitial space, creating a risk of buckling or localized collapse of the protective lining.

[0009] The localized 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 pipe against corrosion. Furthermore, when the pipeline is repressurized, there is a risk that the collapsed portion of the lining may not return to its original shape against the inner pipe wall, potentially altering the localized flow area for the transported fluid. This can lead to increased pressure losses, for example, or a change in the long-term strength of the polymer lining.

[0010] Several solutions have been considered to address the 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 beneath 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 vent 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, involves drilling cylindrical perforations in the protective lining 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, thus maintaining the pressure differential below the lining's collapse pressure.

[0012] All the prior art solutions presented above have drawbacks. In particular, using an adhesive coating on the inner surface of the steel tube presents the disadvantage of a highly complex implementation process, requiring multiple application phases of different layers followed by curing phases to create adhesion. Furthermore, using external gas vents necessitates drilling the steel tube, which weakens its mechanical integrity, and providing a gas vent line in the underwater environment, increasing system complexity, installation procedures, and the risk of leaks. Moreover, this solution requires maintenance to activate the degassing operation. The grooves on the outer surface of the liner are also prone to clogging and fluid 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 lifespan, 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 lining comprises a plurality of slots extending lengthwise parallel to a longitudinal axis of the tube and passing through an inner and outer face of the lining. Each slot is open on the inner face of the lining prior to insertion of the lining into the tube and at least partially closed once the lining is inserted. These slots allow gas that has infiltrated the annular space between the tube and the lining 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, the stresses on the steel pipe during installation of subsea pipelines are significantly higher than for onshore pipelines, while response times in the event of a leak are also significantly longer. Installing and designing an external venting system is also more complex. For these reasons, it is best 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 within 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 connect the interstitial space with the interior of the pipe in order to allow gas that has passed through the lining to escape from the interstitial space during a depressurization of the pipe, - 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 requiring any modification to the conduit (such as drilling vent holes). The integrity of the steel tube is thus preserved. Furthermore, the drainage channels do not open into the interior of the conduit, so that during production phases, there is no flow of gas or liquid from inside the conduit into the drainage channels or the interstitial space between the tube and the protective lining.

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

[0021] The openings in the evacuation zone may have a cylindrical shape.

[0022] Alternatively, the openings in 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 in the evacuation zone can be spaced circumferentially 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 include 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 helps to eliminate or minimize the risk of tube corrosion.

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

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

[0031] [Fig. 2] Figure 2 is a perspective and cutaway view of part of the pipe in Figure 1.

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

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

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

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

[0036] [Fig. 7] Figure 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 privileged (but not limiting) application in the underwater transport of hydrocarbons, in particular oil and gas, from underwater production wells.

[0039] Figure 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 2-1 conduit section includes 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 jacket 6 which is made of polymer material, inserted inside the tube 4 against an internal surface thereof and intended to provide protection of the steel against corrosion from fluids and / or abrasion.

[0042] As a 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 sleeve is inserted into the tube by deformation, ensuring a tight fit. For this purpose, the sleeve, in its resting state (i.e., prior to insertion into the tube), has an external diameter slightly larger than the tube's internal diameter. This creates contact pressure between the sleeve and the tube as the insertion of the sleeve. Once inserted, the sleeve's internal and external diameters are therefore reduced compared to its resting state.

[0044] As is known, the pipe section 2-1 further includes, at each of its longitudinal ends, end connectors 8 allowing the pipe section 2-1 to be connected to other pipe 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 within 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 Figure 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, according to the invention (and as shown in particular in Figure 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 production phases, the gas that has passed through the protective lining to infiltrate the interstitial space moves along the longitudinal axis XX of the pipeline through the drainage channels 10. During pipeline depressurization, the gas accumulated in this interstitial space will be at higher pressure than the inside of the pipeline. When the pressure differential between this interstitial space and the venting areas exceeds a certain threshold, the accumulated gas will pass through the barrier zones to reach the venting area openings and return to the pipeline.

[0050] It should be noted that the barrier zones are sized 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 should 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 figure 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] Regardless of the shape of the openings in the evacuation zones, these can be distributed over a single circumferential row or over several circumferential rows (spaced axially from each other).

[0055] In connection with figure 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 allows for multiple evacuation zones in cases where the distance between two end connectors is very large, enabling more frequent evacuations for the gas that has permeated.

[0058] Furthermore, the 2-2 conduit section 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 Figure 3), the inner surface of the tube 4 is coated with an anti-corrosion coating 24, for example, a layer of CRA (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 Figure 1).

[0060] In connection with figure 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 spaced circumferentially 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 of one of the openings being obstructed, blocked, etc. (for any reason) by redistributing the gas to the other openings in 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 Figure 4), thus mitigating 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.

[0064] In this embodiment, it should 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 figure 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 in Figure 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 evacuation zones 12.

[0069] In connection with figure 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 pipeline 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 split in two at the midpoint of the pipeline section, with each half distributing the permeable gas to one end of that section. Thus, each drainage channel is a dead end, and no flow can pass from one discharge zone to the other.

[0072] In connection with figure 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 22 portions of weakened protective lining at the barrier zones, it is thus possible to facilitate the connection between the drainage channels and the openings of the evacuation zones during a depressurization of the pipeline and to reduce the pressure drop associated with the barrier zones.

[0075] Thus, in the event of excessive differential pressure between the openings and the drainage channels (i.e., depressurization is too rapid for all the gas to pass through the barrier zone quickly enough to maintain the differential pressure below the collapse pressure of the protective liner), these weakened sections of the liner would collapse, thereby clearing the path for the gas to reach the openings of the vent zones. During production phases, these weakened sections of the liner 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) intended to receive a flow of fluids to be transported, and an annular protective lining (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 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 (12; 12a, 12b; 12-c) comprising a plurality of openings (14; 14-c) made through the protective lining to connect the interstitial space with the interior of the pipe in order to allow 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; 16-c) devoid of 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. A conduit according to any one of claims 1 to 4, wherein the openings (14) of the discharge zone are circumferentially spaced from one another and are connected to one another 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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