Lined pipe for transporting corrosive fluid

Abstract

The invention relates to a metal pipe (1) for transporting corrosive fluid, the internal wall (11) of which is lined with a protective coating (2) made of plastics material, the coating (2) including a plurality of openings (3) able to discharge gases trapped at the interface between the coating (2) and the pipe (1) during a drop in pressure of the transported fluid, at least some of the openings (3) extending towards the pipe (1) from the internal wall (22) of the coating (2) able to come into contact with the fluid over a depth (Pr) of between 70% and 97% of the thickness (Er) of the coating (2) leaving a connecting band (4) that is able to tear when the difference between the pressure at the interface between the coating and the pipe and the pressure of the transported fluid exceeds a predefined threshold.

Description

[0001] Description

[0002] Title of the invention: Jacketed corrosive fluid transport tube

[0003] technical field

[0004] [1] The invention relates to the field of corrosive fluid transport tubes, widely used in various fields of the energy industry such as oil and gas.

[0005] Technological background

[0006] [2] It is known to line the inner wall of corrosive fluid transport tubes which are metallic, in particular steel, with a 'liner' type coating, which is made of plastic material, in particular polymer which may contain amide functions, in order to protect the tube from corrosion which may be caused by the fluid flowing through it.

[0007] [3] However, one of the main characteristics of plastic is its high permeability to gases. Consequently, these gases end up at the interface between the coating and the tube, ultimately at the same pressure as in the transported fluid. When a rapid drop in the pressure of the transported fluid occurs, for whatever reason (maintenance, variations in inputs, failure, etc.), the gases trapped at the interface will take longer to escape, generating a differential pressure between the coating / tube interface and the inside of the tube. Nevertheless, the coating does not possess sufficient mechanical properties to withstand this pressure differential. The coating is therefore at risk of collapsing and blocking the tube. The gases trapped at the coating / tube interface must be able to be ventilated quickly in one way or another.

[0008] [4] Ventilation solutions for venting these gases exist in the prior art. Notably, an industrial program called COREL (for Corrosion Resistant Liner) was conducted in 1999–2000 to design and test such solutions. Three of these solutions emerged as promising: [5] The first solution involves venting the gases to the outside of the tube, as in US patent application 2018 / 0051841, where the ventilation system includes a vent that comprises a base portion and an exhaust portion. The base portion is located between the liner and the tube and includes at least one channel extending along the base portion to a central region of the base portion. The exhaust portion projects from the central region of the base portion and is designed to extend through the tube wall.The exhaust section has a central passage which is interconnected with the channel(s) of the base section, so that the vent is configured to eject trapped gases at the coating / tube interface to the outside of the tube.

[0009] [6] The lining proposed by COREL according to the first solution features external longitudinal grooves (i.e., at the lining / pipe interface). The concept is that of longitudinal ventilation, with gases being directed to a valve in the pipe wall, allowing them to vent to the outside. This solution, described in the Offshore Technology Conference publication "Corrosion Resisting Liners - The Results of an Investigation into Plastic Lining of Pipelines for Corrosive Hydrocarbon Service" by Steve Groves et al., has the following drawbacks:

[0010] [7] High-performance (efficient for rapid gas ejection) and robust (durable over time) valve sets must be designed and installed. The former will entail design and installation costs, while the latter will entail maintenance and monitoring costs. Cost control is a crucial factor in the profitability of CO2 transport and storage projects.

[0011] [8] Such a pipe adds further complexity to its burial, as a passage for the extracted gas must be ensured, and presents significant limitations for an offshore installation (i.e., one located in the open sea, on oil drilling platforms). Indeed, water pressure increases by 1 bar every 10 meters of depth. For example, at a depth of 100 m, a pressure of 11 bar will be applied to the external face of the pipe, reducing the effectiveness of the valve (the flow is linked to the pressure difference) and even preventing complete venting, as the interface will retain 11 bar of pressure. However, offshore projects are carried out in a more restrictive environment. As for onshore projects (as opposed to offshore), many will require burial (regulations, reuse of existing pipes).

[0012] [9] Anthropogenic CO2 presents an increased risk of toxicity due to the presence of impurities such as SO2, NO2, and H2S. Whether for terrestrial or marine conditions, environmental and human safety concerns may restrict the use of external ventilation solutions.

[0013]

[0010] A risk has been identified of groove closure over time due to coating creep (NACE Corrosion Conference 2000 - paper 00784:

[0014] “Effective Annular Venting Of Thermoplastic Liners For Added Value And Benefit” by J. Taylor et al.). It should be noted that for the transport of anthropogenic CO2, the swelling of the lining may be greater than for traditional hydrocarbon fluids, implying particular attention to the design of the grooves to avoid any risk of lining failure.

[0015]

[0011] The second solution consists of placing a gas-impermeable intermediate coating between the tube and the permeable coating. Solutions involving the use of an aluminum strip have been developed for applications requiring the transport of oil or potable water. This solution has the advantage of being self-sufficient (no valve, no external discharge from the tube) but has the disadvantage of being sensitive to unpredictable events based on the following arguments:

[0016]

[0012] It is necessary to ensure that the metal coating / plastic coating adhesion is durable over time; otherwise, the coating collapse problem is shifted from the tube / plastic coating interface to the metal coating / plastic coating interface.

[0017]

[0013] This second solution requires strict quality control during the installation of the linings inside the tube. The slightest detachment anywhere along the tube is likely to quickly lead to damage to the plastic lining.

[0018]

[0014] The third solution, described in AMPP paper C2024-20954 “Corrosion Prediction in Perforated Polymer Lined Pipelines (PLP) used for Oil & Gas Transportation” by Gaurav R. Joshi et al., consists of perforating the plastic lining in places. The lining has regular, complete perforations of controlled sizes. It has been theorized and also experimentally verified that the corrosion rate remains acceptable despite the presence of a continuous path for the fluid to the metal surface. The reason is the absence of convection, which restricts the replenishment of acidic gases; fairly quickly, corrosion products form (which can provide intrinsic protection and otherwise inhibit the supply of corrosive species), and the pH in the cavity rises to conditions acceptable for the steel.Specific recommendations have been established regarding the shape and arrangement of these holes: a 2.2 mm diameter hole every 12 m is sufficient to achieve a pressure drop at the interface within 30 minutes; however, taking into account coating swelling, the potential presence of debris, and coating deformation during installation, holes up to 3 mm in diameter, circumferentially spaced 1 m apart and oriented at 90° to the circumference, represent an optimal configuration. However, this technical solution presents a major drawback in the context of anthropogenic CO2: the risk of high corrosion of the steel at the holes is not fully controlled. Indeed, the theoretical model does not incorporate the risk of strong acid formation; a single drop falling into a hole can compromise the integrity of the tube.Regarding feedback from corrosion tests, they are either short-term, static tests focused on electrochemical investigations, or they are more representative tests conducted over several months in a corrosion loop with a fluid simulating a production fluid, but in the presence of a small amount of water. These latter tests, however, do not guarantee that the most critical situation—that of water entering the cavities—has been assessed. Furthermore, none of the studies consider the risk of stress corrosion cracking, which occurs at low corrosion rates, even though it is recognized as critical in anthropogenic CO2 environments due to the presence of H2S and CO, for example.

[0019] Summary

[0020]

[0015] There is therefore a need to improve prior art tube coatings, in particular by remedying their drawbacks, improving their anti-corrosion efficiency and increasing their durability.

[0021]

[0016] Metal tube

[0022]

[0017] The invention aims to meet this objective and relates, according to one of its aspects, to a metallic tube for transporting corrosive fluid whose inner wall is lined with a protective coating of plastic material, said coating having a plurality of openings suitable for evacuating gases trapped at the interface between the coating and the tube during a drop in pressure of the transported fluid, at least a part of the openings extending towards the tube from the inner wall of the coating suitable for contacting the fluid: a) over a depth of between 70% and 97% of the thickness of said coating leaving a ligament suitable for tearing when the difference between the pressure at the interface between the coating and the tube on the one hand and the pressure of the transported fluid on the other hand exceeds a predefined threshold;or b) throughout the thickness of the coating, each of these openings having their smallest dimension less than or equal to 0.5 mm and presenting on one or the other of the walls of the coating an open geometric shape, in particular a line, a cross or a star.;

[0023]

[0018] In option a), the inventors consider that if the depth of the opening exceeds 97%, the excessively thin ligament tears rapidly, and the non-penetrating opening quickly becomes a complete perforation. On the other hand, if the depth of the opening is less than 70%, the excessively thick ligament does not tear when the predefined pressure differential threshold is reached, which could endanger the coating.

[0024]

[0019] The small openings in option b) are considered to be cracks acting as valves for gas evacuation. Indeed, a crack is defined as an opening with a smallest dimension of 0.5 mm or less. Anything larger than this is considered a perforation.

[0025]

[0020] When the opening has a circular cross-section in option a), the thickness e of said ligament can be given by the formula:

[0026] [Math 1] e < 0.698 where R is the radius of the opening, DP is said predefined threshold of difference between the pressure at the interface between the coating and the tube on the one hand and the pressure of the transported fluid on the other hand and Rm is the ultimate tensile strength of the coating material (“Ultimate Tensile Strength” (UTS) in English).

[0027] Of course, in the DP / Rm ratio, the quantities DP and Rm will be converted to the same unit of measurement.

[0021] In the remainder of this document, "depressurization" or "negative overpressure" means that the pressure at the coating / tube interface is greater than the internal pressure of the tube.

[0028]

[0022] The term “positive pressure” means that the pressure at the coating / tube interface is lower than the internal pressure of the tube.

[0029]

[0023] The term "a non-closed geometric shape" means any plane shape whose line or lines cannot define a closed contour, as opposed to a circle or a polygon.

[0030]

[0024] The invention provides a ventilation solution that avoids complete perforations of the coating, thus limiting corrosion, since there is less contact between the corrosive medium and the tube, both in option a) with non-through openings and in option b) with through openings since the latter are of small dimensions.

[0031]

[0025] The invention according to option a) with non-through openings offers great flexibility regarding the number of openings required to vent trapped gases at the coating / tube interface. Indeed, it is always difficult to optimize the number of openings and anticipate all the scenarios that may occur during operation, such as the clogging of openings by debris, corrosion products, precipitates, etc. The tube system according to the invention with option a) decides for itself, during operation, the total number of joints to break and where. Thus, the system automatically optimizes ventilation to the inside since the openings are made where there is the highest depressurization, where gas accumulation is greatest. The system will adapt without external control to situations where it would be necessary to open new openings for whatever reason.

[0032]

[0026] In the invention according to option b), the principle of swelling of the coating, even slightly, following absorption of CO2, allows the cracks to provide a physical barrier to the flow of the corrosive fluid through their non-closed geometric shape.

[0033]

[0027] The invention makes it possible to ensure protection against generalized corrosion by the coating both during the commissioning of the tube and during the phase of its recommissioning.

[0034]

[0028] During the commissioning of the tube, the swelling of the coating with even a small amount of CO2 ensures an effective physical seal at the openings. The behavior of the coating lining a tube according to the invention is expected to be little different from that of a non-perforated coating. Moreover, even if the temporary positive pressure following commissioning causes fluid to flow into the openings, the ligaments in option a) and / or the cracks in option b) act as a buffer against aggressive substances (water, CO2, impurities); admittedly less effective than that provided by a full-thickness coating, but the small size of the open area is not sufficient to significantly accelerate the accumulation of said substances at the coating / tube interface.

[0035]

[0029] During the recommissioning phase of the tube, following a depressurization which has led to the tearing of a number of ligaments in option a) and / or the momentary passage of gases through the cracks in option b), the temporary positive pressure which is established ensures a repositioning of the coating at the level of the openings and adequate protection against the risk of corrosion.

[0036]

[0030] The invention provides an additional anti-corrosion benefit compared to a traditional perforated coating solution, namely, that of ensuring additional protection against the risk of stress corrosion cracking, a cracking mechanism that is established for corrosion situations with low generalized corrosion rates, given that permanent contact of the corrosive fluid with the tube is avoided.

[0037]

[0031] According to embodiments, the tube according to the invention may comprise one or more of the following characteristics.

[0038]

[0032] In the variant according to option a), said at least a part of the openings may extend over a depth of between 75% and 95% of the thickness of said coating, better between 80% and 90% of the thickness of said coating, even better between 85% and 87% of the thickness of said coating.

[0039]

[0033] In the variant according to option a), the predefined pressure threshold from which the ligament is likely to tear is preferably equal to 4 bar.

[0040]

[0034] The openings can be radially equidistant from each other.

[0041]

[0035] In the variant according to option a), the openings can each have their smallest dimension less than or equal to 0.5 mm.

[0042]

[0036] In one embodiment, the openings may each have their smallest dimension less than or equal to 0.3 mm.

[0037] These small dimensions of the openings limit the contact between the corrosive fluid and the tube, while ensuring efficient evacuation of gases trapped at the coating / tube interface.

[0043]

[0038] In the variant according to option a), the openings may present an open geometric shape to the inner wall of the lining. For example, this shape is a line of any shape, in particular a straight line, a cross or a star.

[0044]

[0039] Preferably, said at least part of the openings presents to the inner wall of the coating a shape defined by a straight line, a cross or a star.

[0045]

[0040] The star shape ensures an efficient flow path over the smallest possible surface area, while preserving total coverage of the coating on said surface.

[0046]

[0041] In one embodiment, the thickness of the coating is between 5 mm and 10 mm, the inner and outer diameters of the tube being between 130 mm and 360 mm for a tube thickness between 5 mm and 55 mm.

[0047]

[0042] The metal tube can be made of steel.

[0048]

[0043] Method for making the tube

[0049]

[0044] The invention also relates, according to another of its aspects, to a method of making a tube according to the invention comprising manufacturing the coating using an extruder and placing said coating in the tube at the exit of the extruder, the openings being made by punching during this placement at the time of the entry of the coating into the tube.

[0050]

[0045] Preferably, the punching is carried out by means of a punch with controlled force. This makes it possible to create openings of controlled size.

[0051]

[0046] The punch preferably has a shank whose length corresponds to the desired depth of the opening inside the coating.

[0052]

[0047] Preferably, the punch has at its end opposite to that capable of piercing the coating a base whose surface is adapted to serve as a stop against punching, this surface being in particular sufficiently large to oppose any further penetration of the punch beyond the desired depth of the opening.

[0053]

[0048] In one embodiment, the punch has the general shape of a “T”.

[0054] Brief description of the figures

[0049] The invention will be better understood, and other objects, details, features and advantages thereof will become more apparent during the following description of several particular embodiments of the invention, given solely by way of illustration and not limitation, with reference to the accompanying drawings.

[0055] [fig. 1] Figure 1 is a schematic view of a partial longitudinal section of a tube according to the invention in its option a);

[0056] [fig. 2] Figure 2 is a front view of the inner wall of a tube lining according to the invention;

[0057] [fig. 3] Figure 3 shows examples of open geometric shapes for tube liner openings according to the invention; and

[0058] [fig. 4] Figure 4 is analogous to figure 1 with representation of the punch used to create the opening.

[0059]

[0050] References in the figures:

[0060] 1: tube;

[0061] 2: coating;

[0062] 3: opening;

[0063] 4: ligament;

[0064] 5: punch;

[0065] 6: punch shank;

[0066] 7: base of the punch;

[0067] 8: surface of the base of the punch;

[0068] 11: inner wall of the tube;

[0069] 22: internal wall of the coating;

[0070] Pr: depth of openings in option a);

[0071] Er: coating thickness;

[0072] And: tube thickness; e: ligament thickness

[0073] Description of the implementation methods

[0074]

[0051] Figure 1 schematically illustrates a partial longitudinal section of a metal tube according to the invention in its option a).

[0075]

[0052] In this example, the tube 1 is made of steel and is used to transport corrosive fluids such as hydrocarbons. The tube 1 has a wall thickness Et of 12 mm, an outside diameter of 300 mm, and an inside diameter of 200 mm.

[0053] The tube 1 is lined on its inner wall by a plastic coating 2. The coating 2 can be made of polymer, in particular polyamide 12 (PA12) or high-density polyethylene (HDPE), and has a wall thickness Er of approximately 8 mm.

[0076]

[0054] The coating 2 has non-through openings 3 extending towards the tube 1 from the inner wall 22 of the coating 2 capable of coming into contact with the fluid over a depth Pr of 85% of the thickness Er of the coating 2 leaving a ligament 4 of thickness e, capable of tearing when the difference between the pressure at the interface between the coating and the tube on the one hand and the pressure of the transported fluid on the other hand exceeds a predefined threshold DP, generally equal to about 4 bar.

[0077]

[0055] When the opening 3 has a circular cross-section, the thickness e of the ligament 4 is given by the formula:

[0078] [Math 2] e < 0.698 where R is the radius of the opening 3 and Rm the ultimate tensile strength of the coating material 2, DP and Rm then having the same unit of measurement.

[0079]

[0056] If we take a top view of the cross-section shown in Figure 1, the opening 3 applied to the inner wall 22 of the coating 2 can have any shape. It can be a circle corresponding to a perforation made by a cylindrical punching tool. Alternatively, it can be an open geometric shape, such as the star illustrated in Figure 2 or other shapes like those illustrated in a) to c) in Figure 3.

[0080]

[0057] Figure 2 is a front view of the inner wall 22 of a coating 2 of a tube 1 according to the invention. As mentioned above, this can correspond to the embodiment of Figure 1, or to another embodiment of the invention according to option b) where the opening 3 is through-hole and has a smaller dimension of less than 0.5 mm. For example, in the case of the star, this dimension corresponds to the thickness of one of the points of this star. Due to this small dimension, the opening 3 is then a crack in the coating.

[0081]

[0058] Figure 3 shows some non-limiting examples of open geometric shapes for the opening 3: (a) a curved line, (b) a straight line, (c) a cross, (d) a star.

[0059] Whether through or not, the openings 3 in the invention are made by punching with controlled force.

[0082]

[0060] Figure 4 is analogous to Figure 1, but shows a punch 5 used to create the opening 3, which is not shown in that figure for ease of understanding. This punch 5 has a general "T" shape and has a shank 6 and a base 7 located at the end of the punch opposite to the end capable of piercing the coating 2.

[0083]

[0061] The length of the rod 6 corresponds to the desired depth of the opening 3 inside the coating 2.

[0084]

[0062] The base 7 has a surface 8 adapted to serve as a stop against punching. This surface 8 is sufficiently large to prevent any further penetration of the punch 5 beyond the desired depth of the opening 3.

[0085]

[0063] The invention is not limited to the embodiments described above. For example, the punch may have a different shape to fit that of the opening.

Claims

Demands

1. A metallic tube (1) for transporting corrosive fluid, the inner wall (11) of which is lined with a protective coating (2) of plastic material, said coating (2) having a plurality of openings (3) suitable for venting gases trapped at the interface between the coating (2) and the tube (1) during a drop in pressure of the transported fluid, at least a part of the openings (3) extending towards the tube (1) from the inner wall (22) of the coating (2) suitable for contacting the fluid over a depth (Pr) between 70% and 97% of the thickness (Er) of said coating (2) leaving a ligament (4) suitable for tearing when the difference between the pressure at the interface between the coating and the tube on the one hand and the pressure of the transported fluid on the other hand exceeds a predefined threshold.

2. Tube according to the preceding claim, said at least a portion of the openings (3) extending over a depth (Pr) between 75% and 95% of the thickness (Er) of said coating (2), better between 80% and 90% of the thickness (Er) of said coating (2), even better between 85% and 87% of the thickness (Er) of said coating (2).

3. Tube according to one of the two preceding claims, the predefined pressure threshold being equal to 4 bar.

4. Tube according to any one of the preceding claims, the openings (3) being radially equidistant from each other.

5. Tube according to any one of the preceding claims, where the opening (3) has a circular cross-section, the thickness e of said ligament (4) can be given by the formula: [Math 3] e < 0.698 where R is the radius of the opening, DP is said predefined threshold of difference between the pressure at the interface between the coating and the tube on the one hand and the pressure of the transported fluid on the other hand and Rm is the ultimate tensile strength of the coating material, DP and Rm having the same unit of measurement.

6. Tube according to any one of claims 1 to 4, the openings (3) each having their smallest dimension less than or equal to 0.5 mm.

7. Tube according to any one of the preceding claims except claim 5, the openings (3) each having their smallest dimension less than or equal to 0.3 mm.

8. Tube according to any one of the preceding claims except claim 5, the openings (3) having an open geometric shape on the inner wall (22) of the coating (2).

9. Tube according to any one of the preceding claims except claim 5, said tube having at least a portion of the openings (3) having on the inner wall (22) of the coating (2) a shape defined by a straight line, a cross or a star.

10. Tube according to any one of the preceding claims, the thickness (Er) of the coating being between 5 mm and 10 mm, the inner and outer diameters of the tube (1) being between 110 mm and 360 mm for a thickness (Et) of the tube between 5 mm and 55 mm.

11. Method of making a tube (1) according to any one of the preceding claims, comprising manufacturing the coating (2) using an extruder and placing said coating (2) in the tube (1) at the exit of the extruder, the openings (3) being made by punching during this placement at the time of the entry of the coating (2) into the tube (1).

12. Method according to the preceding claim, the punching being carried out by a punch (5) with controlled force.

13. Method according to the preceding claim, the punch (5) having a shank (6) whose length corresponds to the desired depth of the opening (3) inside the coating (2).

14. Method according to the preceding claim, the punch (5) having at its end opposite to that suitable for piercing the coating a base (7) having a surface (8) adapted to serve as a stop against punching, this surface (8) being in particular sufficiently large to oppose any further indentation of the punch (5) beyond the desired depth of the opening (3).

15. Method according to the preceding claim, the punch (5) having the general shape of a “T”.

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