Adaptation of hydrocarbon pipelines for hydrogen transport.

Description

1 / 19 Adaptation of hydrocarbon pipelines for hydrogen transport.

[001] The present invention relates to the transport of hydrogen gas through pipelines that were previously used for the transport of hydrocarbons, such as oil or natural gas. The invention relates, in particular, to techniques for adapting, reinforcing or modernizing previously used or decommissioned steel pipelines for the transport of hydrogen.

[002] The transition from current hydrocarbon pipelines to bulk hydrogen gas transport is expected to play a key role in decarbonizing the energy sector. However, achieving this goal is not simply a matter of replacing hydrocarbon fluids with hydrogen. This is because most large hydrocarbon pipelines are made of carbon steel. Hydrogen absorption tends to decrease the ductility and crack resistance of the pipeline's steel wall, making it susceptible to failure.

[003] Hydrogen embrittlement of steel can occur even under static conditions, although the problem can be exacerbated by the dynamic or cyclic loading of a pipeline, caused by fluctuations in internal pressure or by thermal cycles. Thus, existing hydrocarbon pipelines that were not designed for the transport of hydrogen must be adapted so that they can transport hydrogen at high pressure.

[004] Conventionally, used pipelines are retrofitted with a polymer coating. However, fluid permeation through polymeric materials makes this technique unsuitable for some applications, for example, for hydrogen transport or carbon capture involving the transport of CO2 for storage in depleted oil reservoirs. In such applications, a polymer coating may not provide sufficient protection. Petition 870250088104, dated 09 / 29 / 2025, page 6 / 45 2 / 19 against gas permeation, leading to degradation of the surrounding steel pipe due to embrittlement or corrosion.

[005] Several studies have suggested that hydrogen absorption by pipeline steel could be mitigated by adding other fluids, such as carbon monoxide, natural gas, or water, to dilute the hydrogen. However, such measures would increase the complexity and reduce the efficiency of hydrogen transport.

[006] Currently, there is no known technology that can coat the interior of a long, pre-installed in-situ steel pipeline to mitigate hydrogen absorption in the pipeline wall, especially if the pipeline is used to transport pure hydrogen under high pressure. In this regard, pipeline electroplating has been explored, but no practical solutions have been found.

[007] Copper electroplating of steel pipes is known in the field. For example, US patent 3875027 describes the electroplating of copper and nickel layers within a ferrous pipe. For this purpose, the pipe is immersed in an ionic solution while an electric current is applied. However, this method cannot be used to refurbish an existing pipeline, which is usually submerged or buried, as an in-situ pipeline cannot be immersed in an ionic solution to perform electrolysis.

[008] Document EP 3710177 describes a pig with embedded anodes for cleaning and protecting a pipe that serves as a cathode. There is no instruction on metal deposition, which would be prevented by the electric field arrangement in any case.

[009] In this context, the invention consists of a method for electrodepositing a metallic coating on the inner surface of a pipe wall. The method comprises transporting a pig along the pipe while an electric current is conducted through a body of electrolytic fluid extending from an electro Petition 870250088104, dated 09 / 29 / 2025, p. 7 / 45 3 / 19 of the pig's length extends to the pipe wall. The electric current can be conducted by a voltage source, such as a set of battery cells carried by the pig.

[0010] The method of the invention is suitable for being performed on a steel pipeline in situ after the pipeline has been used to transport hydrocarbons, and is also suitable for being followed by the transport of hydrogen along the pipeline.

[0011] The electrolytic fluid body may be part of an electrical circuit comprising an additional connection extending between the pig and the pipe wall. In this case, the additional connection may be separated from a pig chamber containing the electrolytic fluid body and the pig electrode.

[0012] The pig electrode can be an anode, for example, made of copper, in which case the pipe wall serves as a cathode. When the coating is copper, the electrolytic fluid may contain a copper salt, such as copper sulfate.

[0013] The method may involve transporting at least one slug of the electrolytic fluid along the pipeline, this slug being delimited by the pig. There may be a succession of these slugs along the pipeline.

[0014] At least one slug of a washing fluid, such as an acid wash, or a hydrocarbon solvent, such as glycol, may be driven along the pipeline ahead of the electrolytic fluid slug or slugs. The washing fluid slug or slugs may be accompanied by at least one brush pig adapted for scraping the inner surface of the pipeline wall. At least one slug of water may be driven along the pipeline after the washing fluid slug or slugs and / or to remove the electrolytic fluid. A gas may then be carried along the pipeline to remove the water. Petition 870250088104, dated 09 / 29 / 2025, page 8 / 45 4 / 19

[0015] The various slugs mentioned can transit through the pipeline in series as part of a continuous sequence of pigs, and the liquids from these slugs can be recovered in respective tanks as they reach the end of the pipeline. Residual gas, such as nitrogen, can be expelled from inside the pipeline ahead of the pig sequence.

[0016] The inventive concept also encompasses a pig for electrodeposition of a metallic coating on the inner surface of a pipe wall, the pig being thus adapted to implement the method of the invention. The pig of the invention comprises: a body supporting a voltage source, which may be internally sealed and insulated by the body; at least one sealing disc mounted on and extending radially from the body; at least one electrode mounted on the body and electrically connected to a first pole of the voltage source; and at least one electrically conductive connecting element extending from the body in a radial extent substantially corresponding to that of each sealing disc, the connecting element(s) being electrically connected to a second pole of the voltage source. The connecting element(s) may also extend longitudinally from the body.

[0017] Where the first pole is a positive terminal of the voltage source, the one or each electrode serves as an anode. Such an anode may be made of copper.

[0018] The electrode or each electrode may be arranged between sealing discs spaced longitudinally along the body. At least one of the sealing discs may be arranged in a longitudinal position between the electrode or each connecting element and the electrode or each electrode.

[0019] Thus, the invention explores the potential for repurposing decommissioned offshore hydrocarbon pipelines for a new use in the transportation of hydrogen gas. For example, such pipelines are Petition 870250088104, dated 09 / 29 / 2025, page 9 / 45 5 / 19 riam suitable for transporting hydrogen that is produced offshore using electrolyzers powered by renewable energy from wind or solar sources.

[0020] The inventive concept can be exemplified by cleaning the internal pipe left in situ, followed by coating its radially inner surface with a thin layer of a metal, such as copper, formed by electroplating using a copper anode pig and a copper sulfate slug. In principle, the denser copper coating will form a less absorbent barrier that restricts the degree of hydrogen absorption in the steel wall of the pipe.

[0021] The internal cleaning and copper coating processes of the invention aim to leave an internal copper coating approximately 0.01 mm thick. This coating forms an internal radial layer to reduce the permeation of hydrogen atoms into and through the steel pipe wall. By reducing the permeation of hydrogen atoms into the pipe wall, the amount of hydrogen that can be pumped through an old hydrocarbon main line can be increased to the point where offshore hydrogen production becomes a commercially viable option.

[0022] The embodiments of the invention implement a method for modernizing a used steel pipeline, the method comprising at least the steps of: acid washing of the pipeline, optionally after preliminary cleaning and washing of the pipeline; washing the acid with fresh water; and depositing a layer of a second type of metal, such as copper. The method may further comprise the deposition of another layer, or an intermediate layer, of a third type of metal, such as tin or nickel, in the case of hard steels.

[0023] Each step of the method may comprise the circulation or transport of a volume or slug of an appropriate fluid from a pri Petition 870250088104, dated 09 / 29 / 2025, page 10 / 45 6 / 19 One end of the pipeline is moved to a second end of the pipeline between at least two pigs that are displaced or propelled along the pipeline by a pressure differential. The method may further comprise the selective recovery of the respective fluids at the second end of the pipeline for evacuation and disposal.

[0024] Copper deposition as the second type of metal may involve supplying copper anode pigs and circulating these pigs within the pipeline with a volume of liquid copper sulfate or other copper salt disposed between the pigs. Copper electroplating is feasible only with some types of steel or other ferrous alloys, due to galvanic corrosion, but the practical limitations in this respect are well understood in the art. For example, many older offshore pipelines are made of X50 to X60 steel alloys, which do not present problems with copper deposition.

[0025] The embodiments of the invention also provide a copper anode pig for electrodeposition of copper on the inner wall of a pipeline, for example, derived from copper sulfate. The pig comprises: a pig structure comprising a sealed and insulated body and external sealing discs mounted on the body to guide the pig along the inner wall of the pipeline; at least one copper anode outside the body; at least one electric battery inside the body, comprising two electric poles, one pole of the battery being electrically connected to the copper anode; and at least one electrically conductive cathode drag arm outside the body, electrically connected to the other pole of the battery, one end of the cathode drag arm being in contact with the inner wall of the pipeline.

[0026] In summary, a metallic coating is electrodeposited on the inner surface of a pipe wall, guiding a pig along the pipe and conducting an electric current through it. Petition 870250088104, dated 09 / 29 / 2025, page 11 / 45 7 / 19 a body of electrolytic fluid extending from an electrode on the pig to the pipe wall. To deposit an internal copper coating, the pig may support a copper anode and the electrolytic fluid may be copper sulfate.

[0027] The electrodeposition method can be applied to a steel pipeline in situ, after the transport of hydrocarbons through the pipeline, and can then be followed by the transport of hydrogen along the pipeline. The internal coating attenuates the migration of hydrogen atoms to the pipeline wall and the consequent risk of steel embrittlement.

[0028] In order to make the invention more easily understood, reference will now be made, by way of example, to the accompanying drawings, in which:

[0029] Figure 1 is a schematic plan view of an offshore oil / gas field comprising platforms connected directly or indirectly to an onshore terminal;

[0030] Figure 2 is a piping and instrumentation diagram showing a typical piping system on an offshore oil / gas platform that transports production fluid to a subsea export pipeline;

[0031] Figure 3 is a piping and instrumentation diagram showing a typical piping system of an onshore terminal receiving production fluid from a subsea export pipeline, as shown in Figure 2;

[0032] Figure 4 is a schematic side view of a pig of the invention;

[0033] Figure 5 is a schematic view of the end of the pig shown in Figure 4;

[0034] Figure 6 is a schematic cross-sectional view along line VI-VI of Figure 4; Petition 870250088104, dated 09 / 29 / 2025, page 12 / 45 8 / 19

[0035] Figures 7, 8 and 9 are schematic side views of pigs that can be used in methods of the invention;

[0036] Figure 10 is a flow diagram that describes the steps of the invention method;

[0037] Figures 11a and 11b are schematic side views of the piping systems of Figures 2 and 3 connected by a subsea export pipeline, showing pre-existing hydrocarbons being purged from the pipeline in a first stage of the method established in Figure 10;

[0038] Figures 12a to 12g are schematic side views of a submarine export pipeline undergoing additional steps of the method established in Figure 10;

[0039] Figure 13 is a schematic side view of a sequence of pigs of the invention in transit along a submarine export pipeline; and

[0040] Figure 14 is a cross-sectional view of a pipe with an internal copper lining applied in accordance with the invention.

[0041] Figure 1 illustrates how an offshore oil / gas field 10 typically comprises a set of individual platforms 12. In this example, the hydrocarbon production fluid is collected by internal pipelines 14 that extend from satellite platforms 12 to a single collection platform 12, from which a single export pipeline 16 or trunk line extends along the seabed and crosses the coast 18 to reach a terminal 20 located on the coast.

[0042] Figure 2 shows an example of a surface piping system on an offshore platform 12 for hydrocarbon production. The hydrocarbon production fluid flows along an export line 22 through production export valves 24 and an embarkation valve 26, before descending below Petition 870250088104, dated 09 / 29 / 2025, p. 13 / 45 9 / 19 from sea level 28 through a riser 30 and enter a subsea export pipeline 16 that leads to an onshore terminal 20, as shown in Figures 1 and 3.

[0043] A pig system comprises an offshore pig chamber that can be loaded with pigs through a chamber door 34 at one end. The pigs are launched onto the export line 22 through a launch pipe 36 at the other end of the pig chamber 32. Isolation valves 38 are arranged in the launch pipe 36 downstream of the pig chamber 32, upstream of the confluence between the launch pipe 36 and the export line 22.

[0044] When pig chamber 32 is used to launch pigs, pig chamber 32 is supplied with production fluid via a branch of the export line 22 through bypass valves 40 and pig chamber valves 42. Pig chamber 32 can also be supplied with other fluids, such as glycol for cleaning or water for discharge, via a flanged inlet 44 controlled by double shut-off valves 46.

[0045] Correspondingly, Figure 3 shows an example of a surface pipeline system of an onshore terminal 20. The submarine export pipeline 16 emerges above sea level 28 as it crosses the coastline 18 and extends through an in-line dune valve 48 to a production and import pipeline 50 which extends to the onshore processing facilities via production and import valves 52.

[0046] In a mirrored arrangement of the pig capture system shown in Figure 2, an onshore pig chamber 54 can receive pigs via a receiving pipe 56 branched off from the production and import pipeline 50. Chamber isolation valves 58 are arranged in the receiving pipe 56 upstream of the pig chamber. Petition 870250088104, dated 09 / 29 / 2025, page 14 / 45 10 / 19 54, downstream of the branch between the production and import pipeline 50 and the receiving pipe 56.

[0047] Again, where the onshore pig chamber 54 is used to launch pigs back along the subsea export pipeline 16 through the production and import pipeline 50, the pig chamber 54 is supplied with production fluid by a branch of the production and import pipeline 50 through bypass valves 40 and pig chamber valves 42. The pig chamber 54 may also be supplied with other fluids through a flanged inlet 44 controlled by double shut-off valves 46.

[0048] Figures 4 to 9 illustrate various pigs that can be used to implement the invention. Similar numbers are used for similar features.

[0049] Figures 4, 5 and 6 show a copper anode pig comprising a cylindrical body 62, from which longitudinally spaced pairs of sealing discs 64 extend radially. The sealing discs 64 are arranged in parallel planes orthogonal to the central longitudinal axis 66 of the body. The sealing discs 64 rest on the inner surface of the surrounding wall 68 of the pipe 16, as shown in Figure 4, to allow the pig 60 to be driven by the differential pressure of the fluid within the pipe 16, ahead of and behind the pig 60. The longitudinal spacing between the pairs of sealing discs 64 defines an annular chamber 70 between the body 62 and the pipe wall 68.

[0050] Body 62 is sealed and electrically insulated and contains an onboard power source exemplified here by batteries 72 embedded in body 62. The positive terminals of batteries 72 are connected to an array of longitudinally extending copper anodes 74 that are angularly spaced around body 62. The copper anodes 74 are arranged in the space between the pairs of Petition 870250088104, dated 09 / 29 / 2025, page 15 / 45 11 / 19 sealing discs 64, therefore being exposed to the electrolytic fluid in the annular chamber 70. In this example, an aqueous solution of copper sulfate (CuSO4) is considered as the electrolytic fluid.

[0051] The negative terminals of the batteries 72 are connected to cathodic connections which are exemplified here by conductive rear arms 76 extending outward from one end of the body 62. The arms 76 extend longitudinally and radially outward in respective radial planes which are angularly spaced around the central longitudinal axis 66. The arms 76 are resiliently polarized to rest elastically against the inner surface of the tube wall 68 at locations longitudinally outward from the annular chamber 70. By sliding in contact with the tube wall 68, the arms 76 complete a circuit between the tube wall 68 which serves as a cathode and the copper anodes. 74 which are opposite the wall of the tube 68 through the annular chamber 70, this circuit extending through the electrolytic fluid in the annular chamber 70. The arms 76 are segregated from the annular chamber 70 by the intermediate sealing discs 64.

[0052] In this example, the 72 batteries each have a cylindrical shape and extend longitudinally on parallel axes arranged in concentric arrays around the central longitudinal axis 66. The 72 batteries are connected in parallel by ring connectors 78 that connect their like terminals to each other and to the copper anodes 74 and the rear arms 76, respectively. Other onboard power sources or other battery shapes or arrangements are possible.

[0053] Figure 7 shows a bidirectional brush pig 80. Again, the pig 80 comprises a cylindrical body 62 from which pairs of longitudinally spaced sealing discs 64 extend radially. The sealing discs 64 are arranged in Petition 870250088104, dated 09 / 29 / 2025, page 16 / 45 12 / 19 planes parallel to the central longitudinal axis 66 of the body 62, resting against the inner surface of a surrounding pipe wall 68, allowing the pig 80 to be driven by differential fluid pressure, as is conventional. In the longitudinal gap between the pairs of sealing discs 64, the body 62 supports sets of angularly spaced wire brushes 82 that support and wear down the inner surface of the surrounding pipe wall 68 as the pig 80 advances along the pipe 16, thus removing deposits and exposing the bare metal. Magnets 84 supported on the body 62 of the pig 80 capture ferrous particles that are dislodged from the pipe wall 68 by the cleaning action of the brushes 82.

[0054] Figure 8 shows a bidirectional discharge pig 86 that is similar to the brush pig 80 of Figure 7, but omits the brushes 82. Optionally, as in this example, the body 62 of the pig 86 supports circumferential sets of magnets 84 to capture ferrous particles that may be dislodged from the tube wall 68.

[0055] Figure 9 shows a foam pig 88 comprising a resilient foam body, usually cylindrical 62, whose circular cross-section is a tight sliding fit within the surrounding tube wall 68. Circumferential ribs 90 spaced longitudinally around the body 62 improve the seal between the body 62 and the tube wall 68.

[0056] An exemplary method of the invention is summarized in the Figure and will be described in detail in Figures 11a to 13. As shown in Figure 10, the pipe 16 is first purged of hydrocarbons at 92 and then internally cleaned at 94, for example, with a hydrocarbon solvent such as glycol. After a freshwater wash at 96, the pipe 16 is internally washed with a diluted acid at 98, washed again with freshwater at 100, and internally galvanized at 102 using a solution of Petition 870250088104, dated 09 / 29 / 2025, page 17 / 45 13 / 19 copper sulfate to form a copper coating on the inner surface of the pipe wall 68. Finally, after a further flush with fresh water at 104, the contents of pipe 16 are purged with nitrogen at 106.

[0057] Figures 11a and 11b illustrate the initial purge stage 92 applied to a pipeline 16 that was previously used to transport natural gas. A bidirectional pig 86, as shown in Figure 8, is launched from the offshore pig chamber 32, as shown in Figure 11a, and along the pipeline 16 in the landward direction, propelled by compressed nitrogen. The piston effect of the in-transit pig 86 propels the residual natural gas towards the landward end of the pipeline 16, where the gas is flared. When the pig 86 reaches the shore, it is diverted to the onshore pig chamber 54, as shown in Figure 11b. The entire pipeline 16 is then purged with a stream of nitrogen, which can be released into the atmosphere at the landward end.

[0058] Figure 12a shows step 94 of internal surface cleaning, which involves injecting glycol into the pipeline through the offshore pig chamber 32 and using the offshore pig chamber 32 to launch a succession of brush pigs 80, as shown in Figure 7. The objective of this step 94 is to remove residual hydrocarbon deposits from the internal surface of the pipe wall 68 and begin to bring that surface back to the pure metal state. For this purpose, it is foreseen that at least three brush pigs 80 can be fired from the offshore pig chamber 32 at intervals so that the pigs 80 of the resulting pig sequence are separated from each other by glycol spheres 108. These spheres 108 can, for example, be about 100 m long.

[0059] Figure 12b shows the first washing stage 96, involving the injection of a freshwater slug 110 into the pipe 16 Petition 870250088104, dated 09 / 29 / 2025, page 18 / 45 14 / 19 through the offshore pig chamber 32. The water slug 110 removes residual glycol 108, continues to clean the inner surface of the pipe wall 68 to a pure metal state and acts as a neutral barrier for the subsequent acid wash. The water slug 110 is bounded by brush pigs 80, which may also be about 100 m apart. The front pig 80 is the rear pig 80 of the pig sequence carrying the glycol pigs 108 injected in the previous step 94. The rear pig 80 is launched from the offshore pig chamber 32 to be added to the pig sequence, which therefore now also involves the water slug 110.

[0060] Figure 12c shows the acid washing step 98, involving the injection of a diluted acid slug 112 into the pipe 16 through the offshore pig chamber 32. The acid slug 112 continues to clean the inner surface of the pipe wall 68 to a pure metal state and is bounded by brush pigs 80, which may also be about 100 m away. The front pig of these pigs 80 is a rear pig 80 of the pig sequence, which carries the glycol and water slugs 108 and 112 injected in the previous steps 94 and 96. The rear pig of these pigs 80 is launched from the offshore pig chamber 32 to be added to the pig sequence, which therefore now also involves the acid slug 112. The diluted acid injection propels the pig sequence along the pipe 16 in the onshore direction.

[0061] Figure 12d shows the second washing stage 100, involving the injection of a second freshwater slug 114 into the pipe 16 through the offshore pig chamber 32. The second water slug 114 removes residual acid 112, continues to clean the inner surface of the pipe wall 68 to a pure metal state and acts as a neutral barrier for the copper sulfate slugs that will follow. Again, this second water slug 114 is delimited by brush pigs 80 which may, for example, be spaced at cer Petition 870250088104, dated 09 / 29 / 2025, page 19 / 45 15 / 19 ca of 100 m. The front pig of these 80 pigs is the rear pig 80 of the pig sequence that carries the glycol, water, and acid slugs 108, 110, 112 injected in the previous stages 94, 96, 98. The rear pig 80 is launched from offshore pig chamber 32 to be added to the pig sequence, which now also includes the second water slug 114. The water injection propels the pig sequence further along pipeline 16 in the onshore direction.

[0062] Optionally, the last pig in the extended pig sequence, at the rear end of the second water slug 114, may be a copper anode pig 60 as shown in Figures 4 to 6. This possibility is shown in Figure 12e, which illustrates the electroplating step 102, where pieces of copper sulfate solution 116 are injected into the pipe 16 via the offshore pig chamber 32. The offshore pig chamber 32 is used to launch a succession of copper anode pigs 60 as shown in Figures 4 to 6. The copper sulfate solution fills the annular chamber 70 of each copper anode pig 60 bounded by the pipe wall 68, the body 62 and the longitudinally spaced sealing disc pairs 64, thus bathing the copper anodes 74 in that electrolytic fluid to complete the electrical circuit.

[0063] The objective of the electroplating step 102 is to deposit a thin copper coating on the bare metallic inner surface of the tube wall 68. Thus, elemental copper derived from copper sulfate present in the electrolytic fluid is deposited on the wall of tube 68, which serves as the cathode. In other words, during electrolysis, copper atoms derived from copper sulfate form a coating on the wall of tube 68, leaving residual sulfur in the electrolytic solution.

[0064] It is foreseen that at least three 60 copper anode pigs can be fired from the offshore pig chamber 32 at intervals so that the 60 pigs of the resulting set are separated from each other. Petition 870250088104, dated 09 / 29 / 2025, page 20 / 45 16 / 19 others by slugs of copper sulfate solution 116. These slugs 116 may, for example, be about 200 m long. As noted above, the first of the copper anode pigs 60 is the last pig 60 in the sequence of pigs carrying the glycol, water, acid and the second water slugs 108, 110, 112, 114 that were injected in the previous steps 94, 96, 98, 100. The other copper anode pigs 60 launched from the offshore pig chamber 32 are added to the sequence of pigs, which therefore now also comprises the copper sulfate slugs 116. The continuous injection of copper sulfate solution propels the sequence of pigs further along the pipeline 16 in a landward direction.

[0065] Figure 12f shows the third discharge stage 104, involving the injection of at least a third slug of fresh water 118 into the pipeline 16 through the offshore pig chamber 32. In this example, there are a third and a fourth water slug 118 arranged in succession to remove the residual copper sulfate solution from the pipeline. Each of these slugs 118 may, for example, be about 100 m long.

[0066] The third water slug 118 is bounded at its forward end by the rear copper anode pig 60 of the previous pig sequence and at its rear end by a discharge pig 86 such as that shown in Figure 8, therefore also disposed at the forward end of the fourth water slug 118. The fourth water slug 118 is further bounded at its rear end by a second discharge pig 86. The discharge pigs 86 are launched from the offshore pig chamber 32 to be added to the pig sequence, which now also encompasses the third and fourth water slugs 118. The water injection propels the pig sequence further along the pipeline 16 in the landward direction.

[0067] Figure 12g shows the first and second nitro slugs. Petition 870250088104, dated 09 / 29 / 2025, page 21 / 45 17 / 19 nitrogen 120 injected into pipeline 16 via offshore pigging chamber 32. In this example, the first and second nitrogen slugs 120 are arranged in succession to clean the various liquids 108 to 116 previously injected from the pipeline 16 pigging sequence. Again, each of these slugs 120 may, for example, be about 100 m long.

[0068] The first nitrogen slug 120 is bounded at its forward end by the rear discharge pig 86 of the previous pig sequence and at its rear end by a foam pig 88 like the one shown in Figure 9, therefore also disposed at the forward end of the second nitrogen slug 120. The second nitrogen slug 120 is further bounded at its rear end by a second foam pig 88. The foam pigs 88 are launched from the offshore pig chamber 32 to be added to the pig sequence, which therefore now also encompasses the first and second nitrogen pigs 120. The nitrogen injection propels the pig sequence further along the pipeline 16 in the landward direction.

[0069] When there are slugs of the same fluid in immediate succession within the pipeline, the pigs that separate these slugs can be considered as subdividing a larger slug of that fluid.

[0070] Figure 13 is a schematic representation of the various fluid volumes of the pig sequence moving along pipe 16 in the landward direction. The pig sequence may, for example, transit at a speed of about 0.1 m / s. In order, from the front end to the rear end of the pig sequence, the slugs are glycol 108, water 110, dilute acid 112, water 114, copper sulfate solution 116, water 118, and nitrogen 120. Finally, the pig sequence is pushed towards the shore, with each volume of the pig sequence being received sequentially by the pig chamber. Petition 870250088104, dated 09 / 29 / 2025, p. 22 / 45 18 / 19 terrestrial 54.

[0071] In each of the steps shown in Figures 12a to 12g, and as also shown in Figure 13, the residual nitrogen 122 left in the initial purge step and discarded ahead of the pig sequence is expelled into the atmosphere from the land end of the pipe 16, as the pig sequence extends and advances along the pipe 16.

[0072] As each slug of liquid reaches terminal 20 at the land end of pipeline 16, the slugs are selectively captured by the onshore pig chamber 54 and drained into the respective tanks provided at terminal 20, namely, a glycol tank 124, a water tank 126, an acid tank 128 and a copper sulfate tank 130. The nitrogen 120, 122 at the front and rear ends of the pig sequence can simply be vented to the atmosphere, after which pipeline 16 is completely purged with nitrogen.

[0073] Returning finally to Figure 14, this cross-sectional view of a steel pipe 16 with an inner lining of the invention shows a copper lining 132 with a thickness of, for example, 0.01 mm. The wall of the steel pipe 68 may, for example, have a thickness of 13 mm and an outer diameter of 24 inches (610 mm). In this example, the pipe 16 has an outer anti-corrosion coating 134 of fusion-bonded epoxy, typically with a thickness of 0.6 mm, surrounded by a weight coating 136 of concrete which may be 50 mm thick. Other corrosion-resistant or thermally insulating coatings are possible.

[0074] Many variations are possible within the inventive concept. For example, anodes and cathodes of various metals can be used to deposit copper from an electrolytic fluid containing a salt. Petition 870250088104, dated 09 / 29 / 2025, page 23 / 45 19 / 19 copper. Furthermore, in principle, copper cathode elements in a pig could be used to transfer copper to the pipe wall that serves as the anode, if the resulting erosion of the copper cathode were controllable.

[0075] It would be possible to deposit a layer of a different metal, such as tin or nickel, using similar techniques, with corresponding adjustments to electrolytes and electrodes. Such a layer could, for example, be deposited on or below a layer of copper.

[0076] The electrical connection between the pig and the pipeline, made through the drag arms, could be made through one or more sealing discs.

[0077] When the invention is applied to an offshore pipeline, it would be possible, in principle, to transport the sequence of pigs and associated slugs in the opposite direction to that described above, i.e., from the landward end towards the offshore end of the pipeline. Furthermore, although the invention has been described in the context of an offshore pipeline, the inventive concept can also be applied to an onshore pipeline. Petition 870250088104, dated 09 / 29 / 2025, page 24 / 45

Claims

1 / 4 CLAIMS 1. A method for electrodepositing a metallic coating on an inner surface of a pipe wall, characterized in that it comprises carrying a pig along the pipe and conducting an electric current through a body of electrolytic fluid extending from an electrode of the pig to the pipe wall.

2. Method according to claim 1, characterized in that the electrolytic fluid body is part of an electrical circuit comprising an additional connection extending between the pig and the pipe wall.

3. Method according to claim 2, characterized in that it comprises segregating the additional connection of a pig chamber containing the electrolytic fluid body and the pig electrode.

4. A method, according to any of the preceding claims, characterized in that the electric current is conducted by a voltage source carried by the pig.

5. A method, according to any of the preceding claims, characterized in that the pig electrode is a copper anode and the pipe wall serves as the cathode.

6. A method, according to any of the preceding claims, characterized in that the coating is made of copper.

7. A method, according to any of the preceding claims, characterized in that the electrolytic fluid comprises a copper salt.

8. Method according to claim 7, characterized in that the copper salt is copper sulfate. Petition 870250096367, dated 10 / 22 / 2025, page 14 / 20 2 / 4 9. A method, according to any of the preceding claims, characterized in that it comprises transporting a slug of electrolytic fluid along the pipeline, this slug being delimited by the pig.

10. Method according to claim 9, characterized in that it comprises transporting a succession of such slugs along the pipeline.

11. A method according to claim 9 or 10, characterized in that it comprises transporting at least one slug of a washing fluid along the piping ahead of the electrolytic fluid slug.

12. Method according to claim 11, characterized in that it comprises accompanying one or more slugs of washing fluid with at least one brush pig that is adapted to abrade the inner surface of the pipe wall.

13. Method, according to claim 11 or 12, characterized in that it comprises transporting at least one slug of water along the pipeline following the one or more slugs of washing fluid.

14. A method according to any one of claims 11 to 13, characterized in that the washing fluid slug or slug comprises an acid wash.

15. A method according to any one of claims 11 to 14, characterized in that the washing fluid slug or slug comprises a hydrocarbon solvent.

16. Method according to claim 15, characterized in that the hydrocarbon solvent is a glycol.

17. Method, according to any of the preceding claims, characterized in that it is followed by the transport of at least one slug of water along the pipeline to release the electrolytic fluid.

18. Method, according to claim 17, characterized in that it is followed by the transport of a gas along the pipeline to release the water.

19. A method according to any one of claims 10 to 18, characterized in that the slugs pass through the piping in series as part of a continuous pigging sequence.

20. Method according to claim 19, characterized in that it comprises recovering liquid slugs in respective tanks as the slugs from the pig sequence arrive at one end of the pipeline.

21. Method according to claim 20, characterized in that it comprises venting gas from inside the piping ahead of the pigging sequence.

22. A method, according to any of the preceding claims, characterized in that it is carried out in a steel pipeline in situ after the pipeline has transported hydrocarbons, and followed by the transport of hydrogen along the pipeline.

23. Pig for electrodeposition of a metallic coating on an inner surface of a pipe wall, characterized in that it comprises: a body supporting a voltage source; at least one sealing disc mounted on and extending radially from the body; at least one electrode mounted on the body and electrically connected to a first pole of the voltage source; and Petition 870250096367, dated 10 / 22 / 2025, page 16 / 20 4 / 4 at least one electrically conductive connecting element extending from the body to a radial extent substantially corresponding to that of the or of each sealing disc, the or of each connecting element being electrically connected to a second pole of the voltage source.

24. Pig, according to claim 23, characterized in that the first pole is a positive terminal of the voltage source and the other or each electrode is a copper anode.

25. Pig, according to claim 23 or 24, characterized in that the electrode or each electrode is disposed between sealing discs spaced longitudinally along the body.

26. Pig, according to any one of claims 23 to 25, characterized in that at least one of the sealing discs is arranged in a longitudinal position between the one or each connecting element and the one or each electrode.

27. Pig, according to any one of claims 23 to 26, characterized in that the one or each connecting element also extends longitudinally from the body.

28. Pig, according to any one of claims 23 to 27, characterized in that the voltage source is sealed inside and insulated by the body. Petition 870250096367, dated 10 / 22 / 2025, p. 17 / 20

Images