System and method for cathodic protection by distributed sacrificial anodes

Abstract

The invention relates to a system and method for cathodic protection by distributed sacrificial anodes. Disclosed is a method of reducing the total anode mass of a cathodic protection (CP) system by reducing or eliminating the total cathode area, said system comprising a metallic first layer coating (2) which is an anode to a component or substrate to be protected, which is bonded to the component or substrate, and which is electrically conductive. A sacrificial anode in the form of a metal second coating (3) is distributed on the first coating (2). The second layer of coating (3) has an open circuit potential equal to the first layer of coating, or is anode to the first layer of coating and to the substrate, the second layer of coating (3) being electrically conductive, bonded to the first layer of coating (2), and exposed to the ambient environment.

Description

This application is a divisional application of the invention patent application with the application date of 2017.03.01, application number 201780026615.3 (PCT / EP2017 / 054806), and the invention name is "System and method for cathodic protection by distributed sacrificial anodes". Technical Field of the Invention The present invention generally relates to cathodic protection of metal objects subject to corrosion. More specifically, the present invention relates to systems and methods for cathodic protection by depositing a protective sacrificial coating on the surface of a metal (ferrous or non-ferrous) object. Similarly, the present invention also relates to a subsea assembly carrying the cathodic protection system of the present invention.

[0001] The system and method of the present invention significantly reduces the total cathodic area by distributing sacrificial anodes over the structure to be protected, while still providing a degree of protection comparable to conventional sacrificial anodes. The present invention, hereinafter also referred to as cathodic protection by distributed sacrificial anodes (DSA), can effectively reduce the total cathodic area entirely, or reduce it to small defects that are a small fraction of the total surface area of the component, or be used in combination with conventional sacrificial anodes where larger areas must be conventionally coated, such as with paint systems and other non-conductive coatings. Background and prior art Electrochemical corrosion is a process initiated when conductive metal structures come into contact with conductive substances such as wet soil or water, which may contain various oxidants. In submarine systems, seawater acts as the electrolyte of a galvanic cell, where an electric current passes from the anodic to the cathodic sites of the submerged metal structure, causing electrochemical changes that produce corrosion products in the metal. During the uniform dissolution of ferrous metal structures submerged in seawater, for example, positively charged iron ions (Fe 2+ ) is released from the anode into the water, and the free electrons (e - ) moves to the cathode area on the metal surface. A reduction reaction occurs at the cathode area, where electrons are transferred to dissolved oxygen (O2) and water (H2O), generating hydroxide ions (OH - ) and hydrogen. Iron ions combine with hydroxide ions to form ferric hydroxide (Fe(OH) 2 ) or rust. If measures are not taken to prevent galvanic corrosion, it can affect the entire structure. Non-ferrous metals react in a similar way, forming different types of corrosion products.

[0002] In the absence of preventive measures (e.g., cathodic protection), the portion of the structure with the lowest free corrosion potential will undergo active dissolution.

[0003] Cathodic protection is a method of combating corrosion in which the structure to be protected is made a net cathode in a galvanic cell. When properly designed, a cathodic protection system can reduce the corrosion rate by more than 2 orders of magnitude, or completely inhibit corrosion.

[0004] In sacrificial cathodic protection, an active metal, i.e., a metal or alloy having a lower free corrosion potential than the structure to be protected, is electrically connected to the structure. In this circuit, the metal with the lowest (i.e., more negative) free corrosion potential becomes the net anode, while the structure becomes the net cathode. The corrosion of the more active metal polarizes the structure to a potential below its free corrosion potential, mitigating or inhibiting corrosion depending on the coupled potential. In subsea applications, for example, typical cathodic protection potentials by aluminum-based sacrificial anodes are on the order of -1.1 to -1.0 V relative to Ag / AgCl | seawater. However, as a rule of thumb, a structure is considered protected against corrosion when it is polarized below -0.8 V relative to Ag / AgCl | seawater.

[0005] Sacrificial anodes are made from metals and alloys that corrode easily in a given environment. The metals that form the anodes for most engineering alloys used in subsea oil and gas production are based on aluminum and zinc, which can be used as sacrificial anodes in essentially pure form or as alloys. Today, the oil and gas industry has standardized on the Al-Zn-In system, while the use of Zn-based anodes has been hampered by passivation and polarity reversal in seawater.

[0006] Sacrificial cathodic protection of submerged equipment in subsea oil and gas production and transportation typically requires considerable anode mass to protect remote subsea components. Anode requirements are traditionally determined by international standards such as DNV RP B401 (Det Norske Veritas' recommended practice) and ISO 12473. Total anode mass in the tens of tons is not uncommon for subsea oil and gas systems. This substantial tonnage of the CP system increases the overall weight and complexity of the structure, significantly adding to installation, operation, and maintenance costs.

[0007] In the past, several attempts have been made to avoid the need for large anode masses to achieve corrosion protection of buried or submerged equipment. One strategy that has several followers in the literature is to apply a thin coating on the outside of the object that needs protection.

[0008] An example of this strategy can be found in US 2015 / 226365 A1. In this invention, an iron-based piping component is coated with an inner layer that is anodic to the iron substrate. An outer layer, approximately 1-5 mm thick, is made of polyethylene or polypropylene resin. The outer layer provides a dielectric seal over the inner layer.

[0009] Another example from the same strategy can be found in CN 2536879. An oil pipe is coated with an inner layer that is anodic to the pipe base. The inner layer is protected by a top layer made of epoxy resin and is dielectric.

[0010] A similar approach can be found in CN 201187267, which discloses a multi-layered variant of corrosion protection via coating. A first passive layer of duplex stainless steel is applied to the exterior of an oil or gas pipe. A second layer, 100-150 μm thick, is applied to the first layer, acting anodic to the first layer and the pipe substrate. A sealing layer, 10-50 μm thick, is applied as a top coat.

[0011] Another multilayer coating system is disclosed in US Pat. No. 8,697,251 B2. A metal substrate is coated with an inner layer, an outer layer, and an intermediate layer. The inner layer is anodic to the metal substrate. The intermediate layer is anodic to one or both of the substrate and the inner layer. The outer layer is an oxide and acts as a dielectric coating, thereby preventing electrochemical contact between the underlying layers and the surrounding environment. Aluminum oxide (Al2O3) is described as a suitable dielectric in the outer layer of the multilayer coating system. The total thickness of the system reaches approximately 250 μm, while the thickness of the intermediate layer, which acts as a sacrificial anode, is approximately 50-75 μm.

[0012] A problem with multilayer coating systems, such as the one disclosed in US 8697251 B2, is that corrosion of the underlying layers can lead to blistering and interlayer separation. This problem arises when the underlying surface corrodes and corrosion products are generated. The corrosion products have poor mechanical properties and generally undergo swelling, which may be due to the formation of hydrates or because the corrosion products are soluble in water. An additional complication is that the outer layers of these systems, i.e. the layers exposed to the corrosive fluid, are dielectrics or electrical insulators. Therefore, the above solutions rely heavily on the integrity of the barrier coating. If forming part of a subsea system, those areas must be considered in the cathodic protection design. SUMMARY OF THE INVENTION In general, the present invention reduces or inhibits anode consumption by reducing or eliminating the total cathode area to be protected. The present invention significantly reduces anode mass while maintaining the same degree of corrosion protection as CP by conventional Al-based sacrificial anodes (e.g., bracket, embedded or bracelet anodes).

[0013] It is an object of the present invention to provide a cathodic protection system for corrosion protection of ferrous or non-ferrous metal substrates.

[0014] This object is met by the system defined in the accompanying system claims.

[0015] It is another object of the present invention to provide a method of applying cathodic protection to a ferrous or non-ferrous metal substrate.

[0016] This object is achieved by the method defined in the accompanying method claims.

[0017] Another object of the present invention is to provide a corrosion resistant subsea component intended for conveying hydrocarbon fluids through an internal cavity or passageway through a body made of ferrous or non-ferrous metal.

[0018] This object is met by the assembly as defined in the accompanying assembly claims.

[0019] Thus, in a first aspect, the present invention is a cathodic protection system for a metal component or substrate, the system comprising: a metallic first coating that is anodic to the substrate, bonded to the component or substrate, and electrically conductive, A sacrificial anode in the form of a metallic second coating layer distributed over the first coating layer, the second coating layer having an open circuit potential equal to that of the metallic first coating layer, or being anodic to the first coating layer, the second coating layer being conductive, bonded to the first coating layer, and exposed to the surrounding environment.

[0020] A fundamental aspect of the second coating layer exposed to the environment is that it matches the electrochemical properties (i.e., free corrosion potential and current capability) of the conventional sacrificial anode that is replaced in whole or in part by the second coating layer. Where appropriate, the second coating layer functions as a sacrificial anode that provides current to defects or uncovered areas or adjacent structures.

[0021] Since the sacrificial anodes are distributed across the structure, the total cathode area is reduced or eliminated.

[0022] Distributing the anodes also reduces problems associated with resistive voltage drops and improves current distribution.

[0023] Defects in the second coating that could potentially lead to exposure of the underlying first coating or substrate, for example, mechanically induced defects caused during operation or installation, can be assumed to be limited to a small portion of the total protected area. A total maximum of, for example, one percent (1%) defect area in the outer coating is a modest estimate and still illustrates the potential benefits that can be achieved by reducing the cathode area.

[0024] Since the proposed invention reduces the total cathode area by distributing the sacrificial anodes over the entire structure to be protected, there is a considerable saving in the total anode mass. The anode reduction by the proposed CP through DSA is illustrated by the following comparative example: When following DNV-RP-B401 guidelines, a planned pipeline terminal (PLET) assembly for an eight-well, three-manifold scheme for a gas field development approximately 130 km offshore in a tropical / subtropical water depth of approximately 200 m requires a calculated total mass of conventional anodes of approximately 26,000 kg in a sacrificial cathodic protection design.

[0025] Assuming a 1% defect area in the DSA, the same assembly would require a total conventional anode mass of approximately 2,000 kg, equivalent to a reduction of approximately 92% in conventional anode weight. This reduction in conventional anode mass is equivalent to approximately 20% of the total weight of the PLET.

[0026] The first coating layer comprises substantially pure metallic aluminum or an aluminum alloy.Selection of aluminum for the first coating layer results in a reduced requirement for sacrificial anode mass compared to the amount of anode mass required to protect a bare metal component or substrate.

[0027] Likewise, the second coating layer is made of an aluminum alloy that has the same open circuit potential as the first coating layer, or is anodic to the first coating layer. The second coating layer is also anodic to the component or substrate.

[0028] The chemical composition of the second coating layer exposed to the environment preferably matches the chemical composition of the conventional sacrificial anode that is fully or partially replaced by the sacrificial second coating layer.

[0029] Surfaces exposed to the environment should preferably be made of aluminum-zinc-indium (Al-Zn-In) alloy or other aluminum alloys with electrochemical properties matching those of Al-Zn-In alloy.

[0030] The second coating layer may be an Al alloy containing Zn in the range of 2-7% and In in the range of 0.01-0.05%.

[0031] The first coating layer preferably has a thickness in the range of 100-300 μm. The second coating layer preferably has a thickness in the range of 200-3,000 μm, preferably at least greater than 200 μm, most preferably 300 to 1,500 μm.

[0032] The thickness of the second coating layer exposed to the environment is determined based on the self-corrosion rate of the component or substrate, with the minimum required thickness determined by the end of the component's service life. Based on the results of internal research activities, a thickness of 50μm every 10 years is a conservative value for the PLET example discussed above.

[0033] The second coating layer is distributed over substantially the entire surface of the inner coating layer.

[0034] The first and second coating layers are preferably distributed over substantially the entire area of the component or substrate exposed to the corrosive environment, or to the greatest extent practically possible.

[0035] In a second aspect, the present invention is a method for cathodic protection of a metal component or substrate, the method comprising: applying a metallic first coating by a first deposition method, which coating is anodic to the component or substrate, Applying a metallic second coating by a second deposition method, distributing sacrificial anodes on the first coating, said metallic second coating having an open circuit potential equal to that of the metallic first coating or being anodic to the first coating.

[0036] The first and second deposition methods may be selected from deposition methods such as hot dip plating, co-lamination, co-extrusion and explosive bonding, and any deposition method known as metal spraying, including but not limited to one of detonation spraying, flame spraying, high velocity liquid fuel spraying, high velocity air fuel spraying, high velocity oxygen fuel spraying, plasma spraying, arc spraying and cold spraying, and the first and second deposition methods may be the same or different from each other.

[0037] An embodiment of the method includes depositing substantially pure metallic aluminum or an aluminum alloy to a thickness of 100-300 μm to form a first coating on a component or substrate.

[0038] Embodiments of the method further include depositing a metallic aluminum alloy having the same open circuit potential as or anodic to the metallic first coating layer to form a second coating layer having a thickness in the range of 200-3,000 μm, preferably at least greater than 200 μm, and most preferably 300 to 1,500 μm.

[0039] In a preferred embodiment, the method comprises feeding a metal composition comprising aluminum, zinc, and indium to a metal deposition process for depositing a sacrificial anodic coating onto a first coating.

[0040] In a third aspect, the present invention is a component made of ferrous or non-ferrous metal designed for subsea use, wherein the component is at least partially exposed to seawater when submerged. A first coating consisting of substantially pure aluminum or an aluminum alloy, which is protected from seawater by the following layers: A second coating in contact with seawater, the second coating comprising an aluminum alloy that is anodic to the aluminum and to the component.

[0041] The assembly may be designed to convey hydrocarbon fluids through a lumen or passageway through a body made of ferrous or non-ferrous metal.

[0042] The assembly may be covered with a sacrificial anodic coating comprising an aluminum-zinc-indium (Al-Zn-In) alloy.

[0043] According to the above, the sacrificial anode covering the component has a thickness in the range of 200-3,000 μm, preferably at least greater than 200 μm, most preferably 300 to 1,500 μm. The first coating preferably has a thickness of 100-300 μm.

[0044] Without excluding other components not mentioned, the component may be realized as at least one of the following subsea components: Tree BOP ·tool Pipeline ·Streamline Jumper wires Manifold Joints and connectors Pressure vessels Shell and hull Pump or compressor parts ·valve Flow meter ·sensor Control system module Umbilicals and related terminal assemblies Riser and riser base Suction anchor and anti-sinking plate Support structure and its connecting parts.

[0045] The invention is applicable not only to components for oil or gas related equipment but also, for example, to components for windmills, fish farming facilities, any cable or pipeline structure at least partially submerged in seawater, ships and vessels, etc.

[0046] According to the description of the above-mentioned cathodic protection system and method, the assembly is covered by a distributed sacrificial anode mass comprising an aluminum-zinc-indium alloy or other aluminum alloy having corresponding electrochemical properties. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be further described below with reference to the accompanying schematic drawings. Figure 1 Graphical illustration of anode requirements for bare and coated carbon steel. Figure 2 is a schematic cross-section through a cutaway portion of a sacrificial cathodic protection system applied to a metal substrate, and Figure 3 is a cross-section through an assembly intended for subsea transport of hydrocarbon fluids.

[0047] Figure 4a and 4b To show the protection current density as a function of exposure time in seawater for the prior art coating and the new coating respectively in comparison with anodic protection, and Figure 5a and 5b Photos of samples of the prior art coating and the new coating undergoing electrochemical testing under exposure to seawater. Detailed description of preferred embodiments The use of protective coatings is not only applicable to subsea structures, but also generally to buried pipelines or to provide protection against atmospheric exposure.

[0048] It should also be noted that any statements of percentages of ingredients given herein refer to percentages by weight unless otherwise indicated.

[0049] In submarine cathodic protection (CP), codes such as DNV-RP-B401 establish coating degradation factors that account for the normal aging process of different coating systems. Although the initial coating degradation factors are generally small, they approach a value of 1 at the end of the service life of the substructure.

[0050] In subsea CP design, the entire surface area of the component must be considered in the CP calculation because it is cathodic to conventional anodes. Conversely, the surface area of structures with the same open circuit potential as conventional sacrificial anodes should not be included in the CP calculation.

[0051] Figure 1 The diagram illustrates an example of a typical DNV-RP-B401 calculation. In this example, 2 Provide cathodic protection for components. Figure 1 As shown in Figure 1, a sacrificial anode must provide 150 mA to protect bare carbon steel (CS). For the same area of painted CS, applying a non-conductive protective coating, such as paint, reduces the average current demand to 33 mA. Thermal sprayed aluminum (TSA) can further reduce the current demand to 10 mA for the same area. As explained below, the distributed sacrificial anode (DSA) of the present invention will eliminate the current demand from conventional anodes for the surface area converted to DSA area.

[0052] exist Figure 2 In the drawings, reference numeral 1 refers to a bulk material of a metallic object forming a substrate to be protected by a cathodic protection system, the system comprising a first coating 2 applied to the surface of the substrate 1 and a second coating 3 applied over the first coating 2 .

[0053] The substrate 1 can be any object of ferrous or non-ferrous metal that needs to be protected from a corrosive environment (such as wet soil, water, and wet air), or an object that must be coated to reduce the overall anode consumption of the CP system. In subsea applications, the substrate is typically a component involved in the subsea production and / or transportation of oil, gas, or water, such as a pipeline, manifold structure, pump or compressor component, etc., and generally has an internal cavity or channel 4 for conveying fluid through the body of metal 1. Therefore, the substrate 1 can take virtually any form, including planar, curved, and hyperbolic shapes, and the coated surface of the substrate can be located on the exterior or interior of the substrate.

[0054] The first coating layer 2 may comprise any metal or metal alloy that is anodic to the substrate, electrically conductive, and capable of forming a bond to the substrate. The second coating layer 3 may comprise any metal or metal alloy that has an open circuit potential equal to that of the metallic first coating layer, or that is anodic to the first coating layer and the substrate, electrically conductive, and capable of forming a mechanical bond to the first coating layer. In all cases, the metals or metal alloys of the first and second coating layers should be related in the galvanic series such that the second coating layer 3 forms a sacrificial anode to the first coating layer 2 or the substrate, and the first coating layer should never be anodic to the second coating layer.

[0055] In a preferred embodiment, the first coating layer 2 comprises substantially pure aluminum or an aluminum alloy. In this case, pure aluminum or an aluminum alloy is preferred to reduce the amount of anode required to protect the substrate. The purity of the first coating layer can range from 85% to 100% Al. The first coating layer can be an aluminum alloy. In a preferred embodiment, the first coating layer 2 comprises 99.5% Al or an Al alloy containing 5% magnesium (Al5Mg).

[0056] Pure aluminum and aluminum alloys that are anodic to the substrate are preferred as the second coating 3. The most preferred composition for the second coating 3 is an aluminum-zinc-indium (Al-Zn-In) alloy, although other aluminum compositions that provide corresponding electrochemical properties may constitute alternatives. Other substances that can be combined with aluminum in the sacrificial second coating 3, in addition to zinc and indium, include, for example, cadmium (Cd), silicon (Si), tin (Sn), manganese (Mn), and titanium (Ti).

[0057] In a preferred Al-Zn-In alloy, zinc may comprise approximately 2-7% of the composition, indium may comprise approximately 0.01-0.05%, and aluminum makes up the remainder. It will be appreciated from the above that the composition of the second coating 3 may be similar to that of conventional sacrificial aluminum anodes used to protect subsea components.

[0058] The application of the first and second coating layers to the substrate may comprise any suitable application method, such as co-lamination, co-extrusion, and explosion bonding, for example, in any case where this is permissible with respect to the design of the substrate, for example, in connection with planar plates, tubes, and rods of continuous radius. For more complex shapes, metal spraying is the preferred method for depositing both the first coating layer 2 and the second coating layer 3.

[0059] Metal spraying is a generic name for several processes in which pure or alloyed metals are melted in a flame or electric arc and sprayed onto a substrate using compressed air or explosive gases. Micrometer-sized metal droplets are generated in this way and projected onto the substrate surface. By repeating this process, the droplets continuously accumulate to form a coating.

[0060] Under the general concept of metal spraying, several variants suitable for depositing the first and second coatings 2 and 3 can be distinguished, such as plasma spraying, detonation spraying, wire arc spraying, flame spraying, high velocity oxygen fuel spraying, warm or thermal spraying, cold spraying, etc.

[0061] The key feature of the present invention is the provision of a sacrificial anodic coating 3 distributed over substantially the entire area of the substrate / component exposed to the corrosive environment. The thickness of the second coating 3 is determined by the self-corrosion rate over the useful life of the component, while the total thickness is a function of the estimated current requirement to protect any defective areas in the second coating.

[0062] The Al-Zn-In anode composition of the second coating 3 of the preferred embodiment is assumed to be advantageous in order to achieve uniform corrosion and reduce the required layer thickness. Layer thicknesses in the range of 300-1,500 μm are preferred and well within the capabilities of the metal spraying process. This preferred range should also encompass most applications in terms of service life and operating conditions. However, it is within the scope of the present invention to increase the layer thickness of the second coating 3 up to approximately 3,000 μm if necessary, as above this range the weight reduction benefits compared to conventional anode assemblies are less pronounced. In any case, the thickness of the second coating 3 should not be less than 200 μm.

[0063] As already explained in other parts of this disclosure, the thickness of the inner coating layer 2 is preferably within the range of 100-300 μm.

[0064] From the above description of the cathodic protection system, it will be understood that the second coating 3 constitutes a sacrificial anode mass which is distributed over the substrate and the protected component and is in direct contact with the environment surrounding the component. The main substance in both the first and second coatings is metallic aluminum, which provides electrical conductivity and good bonding properties between the coatings themselves and to the substrate of ferrous and non-ferrous metals.

[0065] Distributed sacrificial anodes with a second coating can also be used in conjunction with conventional sacrificial anodes where larger areas would traditionally have to be coated (e.g., by paint systems or other non-conductive coatings). In all cases, the claimed invention provides a significant reduction in anode mass and weight whenever used in structures subject to corrosive environments.

[0066] Figure 4a and 4bIt is shown that a thermally sprayed Al2.5Zn0.02In alloy (DSA) coated on carbon steel is different from a thermally sprayed Al5Mg alloy (conventional TSA) coated on carbon steel with respect to electrochemical performance in seawater. In this example, the effectiveness of DSA versus TSA is illustrated by a protection current density-time graph. In terms of protection current density-time, DSA coated on carbon steel exhibits properties similar to or identical to conventional cast Al-Zn-In anode coupled to carbon steel, while TSA coated on carbon steel exhibits properties different from both DSA and cast Al-Zn-In anode coupled to carbon steel.

[0067] To conclude, Figure 4a and 4b It is shown that thermal sprayed Al2.5Zn0.02In alloy coated on carbon steel (DSA) is different from thermal sprayed Al5Mg alloy coated on carbon steel (conventional TSA) in terms of electrochemical performance in seawater, which is illustrated in this example by the protection current density-time graph.

[0068] For these tests, samples, designated DSA, were prepared by first applying an Al-Zn-In alloy to a carbon steel panel by thermal spraying, then cutting the sample to size, and finally preparing it for electrochemical testing by effectively sealing all of the carbon steel surfaces of the sample, leaving the DSA as the only metal portion of the sample exposed to seawater. Samples, designated TSA, were prepared for electrochemical testing in exactly the same manner as for DSA, except that an Al5Mg alloy was used during the thermal spraying process. Samples, designated CS, were prepared from bare carbon steel panels that were cut to size and sealed as needed to achieve the surface area ratios required for the various couplings.

[0069] Then, in electrochemical experiments in fresh, circulating natural seawater, the DSA sample was coupled to the CS sample at two different ratios: DSA:CS 100:1 (grey) and DSA:CS 10:1 (blue), which simulate different defect sizes (see Figure 4a ).

[0070] Likewise, TSA samples were coupled to CS samples at two different ratios; TSA:CS 100:1 (grey) and TSA:CS 10:1 (blue). For reference, anode samples cut directly from cast Al-Zn-In anodes were coupled to CS at a ratio of anode:CS 10:1 (red). Figure 4b .

[0071] exist Figure 4a and 4b The resulting protection current density (mA / m 2) show that (i) DSA is different from TSA, and (ii) DSA is similar or identical to conventional Al-Zn-In cast anodes.

[0072] Figure 5a and 5b The results show that after electrochemical testing, carbon steel coupled to thermally sprayed Al2.5Zn0.02In alloy (DSA) differs from carbon steel coupled to thermally sprayed Al5Mg alloy (conventional TSA) in terms of both the amount of calcareous deposits on the exposed carbon steel surface and the level of corrosion. The carbon steel samples, when coupled to thermally sprayed Al2.5Zn0.02In alloy (DSA) and exposed to seawater, showed significant accumulation of calcareous deposits and no signs of corrosion. In contrast, the carbon steel samples, when coupled to thermally sprayed Al5Mg alloy (TSA) and exposed to seawater, showed that carbon steel corrosion had occurred.

[0073] thus, Figure 5a The graph illustrates that after electrochemical testing as described above, a carbon steel (CS) sample showed no signs of corrosion (but had significant accumulation of calcareous deposits) when coupled to a thermally sprayed Al2.5Zn0.02In alloy (DSA) and exposed to seawater for 30 days. Figure 5b The image shows carbon steel corrosion when coupled to thermally sprayed Al5Mg alloy (TSA) and exposed to seawater for 30 days. The samples in the photo have an area ratio of DSA:CS 10:1 and TSA:CS 10:1.

[0074] Although illustrated by way of examples, the skilled person will recognize that the technical effects and benefits of the cathodic protection system of the present invention may be obtained to a certain extent, and thus it is possible to modify the invention within the language and wording of the claims, and any such modifications, if not literally satisfying the language of the claims, are also covered by the scope of protection defined and provided by the claims.

Claims

1. A method for cathodic protection of a metal component or substrate, the method comprising the steps of: applying a metallic first coating layer to a metallic component or substrate by a first deposition process, said metallic first coating layer being anodic to said metallic component or substrate, and A sacrificial anode is distributed on the metallic first layer of coating by applying a metallic second layer of coating via a second deposition method, said sacrificial anode having an open circuit potential equal to that of the metallic first layer of coating via the second deposition method.

2. The method of claim 1, wherein the first and second deposition methods are selected from the group consisting of hot dip plating, co-lamination, co-extrusion, explosion bonding, and any metal spray deposition method.

3. The method of claim 2, wherein the first and second deposition methods are the same.

4. The method of claim 2, wherein the first and second deposition methods are different.

5. The method of claim 1, further comprising depositing substantially pure metallic aluminum or aluminum alloy to a thickness of 100-300 μm to form the metallic first layer coating.

6. The method of claim 1, further comprising depositing an aluminum alloy anodic to aluminum to a thickness of 200-3,000 μm to form a metallic second coating.

7. The method of claim 1, further comprising feeding a metal composition comprising aluminum, zinc, and indium to a metal deposition process for depositing a sacrificial anodic coating onto the first coating.

8. The method of claim 1, wherein the metallic first coating is an aluminum alloy containing 5% magnesium.

9. The method of claim 1 wherein said metallic first coating layer consists of substantially pure aluminum.

10. The method of claim 1, wherein the metallic second coating is an aluminum-zinc-indium (Al-Zn-In) alloy comprising 2-7% zinc, 0.01-0.05% indium, and the balance aluminum and having a thickness of at least 200-3,000 μm.

11. The method of claim 2, wherein the metal spray deposition method is selected from the group consisting of detonation spray, flame spray, high velocity liquid fuel spray, high velocity air fuel spray, high velocity oxy-fuel spray, plasma spray, arc spray, and cold spray.

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