A method of inhibiting galvanic and stray current corrosion of metals

Abstract

The application relates to the field of corrosion protection of metal materials in engineering applications, and provides a method for inhibiting metal galvanic corrosion and stray current corrosion. Existing methods usually directly coat a protective layer on a metal surface to isolate the interface between an anode and an environment, so as to inhibit metal galvanic corrosion and stray current corrosion, but the protective layer is still easy to be damaged, thereby failing to effectively inhibit galvanic corrosion and stray current corrosion. The method comprises the following steps: arranging an impressed cathode and anode in an environmental medium around a corrosion metal needing protection, and connecting the cathode and the anode to an external power supply through wires to form an impressed barrier current circuit; adjusting an external current of the barrier current circuit through the external power supply, and monitoring an anode current or potential of the corrosion metal until the monitored anode current or potential meets a preset condition.

Description

Technical Field

[0001] This application relates to the field of corrosion protection of metallic materials in engineering applications, and more specifically, to a method for suppressing galvanic corrosion and stray current corrosion of metals. Background Technology

[0002] Controlling galvanic corrosion is theoretically quite simple; it only requires disconnecting the electronic or ionic circuit through which the galvanic current flows. However, in practice, this simple solution is often difficult to implement. For example, consider a galvanic couple formed by bolting two different metals (e.g., magnesium alloy and stainless steel) together in an environmental medium (e.g., seawater). The potential difference between the cathode (e.g., stainless steel) with a more positive self-corrosion potential and the anode (e.g., magnesium alloy) with a more negative self-corrosion potential causes current to flow from the anode (e.g., magnesium alloy) into the environmental medium as ions. This current then travels through the environmental medium to the cathode (e.g., stainless steel), where it is converted into electrons. The electrons then flow back from the cathode (e.g., stainless steel) through the cathode / anode (e.g., stainless steel / magnesium alloy) interface to the anode (e.g., magnesium alloy), forming a complete closed-loop current circuit. The current flowing from the anode (e.g., magnesium alloy) through the anode / environmental medium (e.g., magnesium alloy / seawater) interface into the environmental medium corresponds to the dissolution corrosion of the anode (e.g., magnesium alloy), which is accelerated by the electric field or potential difference applied by the cathode (e.g., stainless steel) to this interface. For the anode (e.g., magnesium alloy), the electric field, potential difference, or galvanic current applied by the cathode (e.g., stainless steel) are all external factors. Therefore, galvanic corrosion of the anode (e.g., magnesium alloy) can be understood as damage accelerated by the applied electric field. Simply insulating the cathode / anode (e.g., stainless steel / magnesium alloy) interface can block the entire current loop, ensuring that the influence of the electric field or potential difference applied by the cathode (e.g., stainless steel) on the anode (e.g., magnesium alloy) falls entirely on the cathode / anode (e.g., stainless steel / magnesium alloy) interface, rather than on the anode / environmental medium (e.g., magnesium alloy / seawater), thus preventing galvanic corrosion of the anode (e.g., magnesium alloy). However, in practical applications, the cathode / anode (e.g., stainless steel / magnesium alloy) interface is sometimes used for conducting electrical signals and cannot be insulated; or adding insulation would significantly reduce the mechanical strength of the connection, making it unacceptable; or adding such an insulation layer would make production costs too high to bear. Therefore, in engineering, these problems are often not solved by simply isolating the direct electrical connection between the anode and cathode.

[0003] Stray current corrosion is a common form of metal damage in practical engineering. It shares some similarities with galvanic corrosion, as described above. Its accelerated corrosion is also caused by an applied electric field. The current leaving the corroded metal flows through the surrounding medium in ionic form, eventually returning to other parts of the corroded metal and re-entering the metal in electron form, forming a closed current loop. The difference between stray current corrosion and galvanic corrosion is that the applied potential field is not necessarily from other metals or electronic conductors directly connected to the corroded metal. It could be from other electrical equipment not directly connected to the corroded metal, where the leaked current flows through the surrounding medium and the corroded metal before returning to the equipment; or it could be an induced current generated by an electromagnetic field flowing through the corroded metal and the surrounding medium. For example, electricity used by trams on city streets may leak through underground metal pipes and flow back to the tram; or current induced by high-voltage power lines may flow through the pipes and the surrounding medium. Therefore, the stray current corrosion system can be approximated as a galvanic-like system: the anode is the corroded metal; the cathode is an electronic conductor located at a distance or even unknown location, and the potential difference between it and the corroded metal depends on the intensity of the stray source. In such a stray current corrosion system, the electronic current path is difficult to cut off because as long as the corroded metal is still in contact with the environmental medium after the cut-off, the current leaked by the electrical equipment or the current induced by it will still flow through the medium and the corroded metal.

[0004] Whether it's galvanic corrosion or stray current corrosion, the outflow location is relatively easy to determine based on the corrosion damage characteristics of the metal surface. However, the location of the corresponding cathode or electron conductor receiving the current is not obvious and difficult to determine, especially the induced stray current, which is even more difficult to determine due to the omnidirectional nature of the environmental medium. Currently, the most common practice is to directly coat the metal surface with a protective layer to isolate the anodic / environment interface. However, sometimes the metal surface is too deep (e.g., the inner wall of a pipe) or too hidden (e.g., in a crevice), making direct surface coating difficult. More often, the coating is damaged during the use of the component, leading to severe aggravation of corrosion damage at the damaged area. Therefore, practical engineering and industrial applications still urgently need other technologies that can effectively suppress galvanic corrosion and stray current corrosion. Summary of the Invention

[0005] The purpose of this application is to provide a method for suppressing galvanic corrosion and stray current corrosion of metals, in order to solve the problem that the existing method of directly coating a protective layer on the metal surface to isolate the interface between the anode and the environment to suppress galvanic corrosion and stray current corrosion is still easily damaged, resulting in the inability to effectively suppress galvanic corrosion and stray current corrosion.

[0006] To achieve the above objectives, the technical solution adopted in the embodiments of this application is as follows:

[0007] A method for suppressing galvanic corrosion and stray current corrosion of metals includes:

[0008] An external cathode and anode are installed in the environmental medium surrounding the corrosive metal that needs protection, and the external cathode and anode are respectively connected to an external power source through wires to form an external blocking current circuit.

[0009] The external current of the blocking current circuit is adjusted by the external power source, while the anodic current or potential of the corroded metal is monitored until the measured anodic current or potential meets a preset condition. The preset condition is that the current direction of the external current is opposite to the current direction of the anodic current, so that the anodic current or potential meets a certain threshold, so that the flowing anodic current is reduced to zero, or even reversed to protect the corroded metal.

[0010] According to the method for suppressing galvanic corrosion and stray current corrosion of metals described above, the step of adjusting the external current of the blocking current circuit by the external power supply, while monitoring the anodic current or potential of the corroded metal, until the measured anodic current or potential meets the preset conditions, specifically includes:

[0011] The external current of the blocking current circuit is adjusted by the external power source, and the potential of the corroded metal relative to the anode is monitored by the anode until the measured potential meets the preset conditions.

[0012] According to the method for suppressing galvanic corrosion and stray current corrosion of metals described above, the step of adjusting the external current of the blocking current circuit by the external power supply, while monitoring the anodic current or potential of the corroded metal, until the measured anodic current or potential meets the preset conditions, specifically includes:

[0013] A reference electrode is provided, which is inserted into the environmental medium between the corroded metal and the anode, and the potential of the corroded metal is monitored through the reference electrode;

[0014] The external current of the blocking current circuit is adjusted by the external power source until the measured potential of the corroded metal relative to the reference electrode meets the preset conditions.

[0015] According to the above-described method for suppressing galvanic corrosion and stray current corrosion of metals, in the step of setting an external cathode and anode in the environmental medium surrounding the corrosive metal to be protected, and connecting the external cathode and anode to an external power source through wires to form an external blocking current circuit, neither the cathode nor the anode contacts the corrosive metal or is an electronic conductor that has a direct electrical connection with the corrosive metal.

[0016] According to the above-described method for suppressing galvanic corrosion and stray current corrosion of metals, in the step of setting an external cathode and anode in the environmental medium surrounding the corrosive metal to be protected, and connecting the external cathode and anode to an external power source through wires to form an external blocking current circuit, the distance between the anode and the corrosive metal is smaller than the distance between the cathode and the corrosive metal.

[0017] According to the above-described method for suppressing galvanic corrosion and stray current corrosion of metals, in the step of setting an external cathode and anode in the environmental medium surrounding the corrosive metal to be protected, and connecting the external cathode and anode to an external power source through wires to form an external blocking current circuit, the cathode and anode are both set at locations in the environmental medium where the anodic current distribution is concentrated.

[0018] According to the above-described method for suppressing galvanic corrosion and stray current corrosion of metals, in the step of setting an external cathode and anode in the environmental medium surrounding the corrosive metal to be protected, and connecting the external cathode and anode to an external power source through wires to form an external blocking current circuit, the surface of the cathode and the surface of the anode are both parallel to the surface of the corrosive metal.

[0019] According to the above-described method for suppressing galvanic corrosion and stray current corrosion of metals, in the step of setting an external cathode and anode in the environmental medium surrounding the corrosive metal to be protected, and connecting the external cathode and anode to an external power source through wires to form an external blocking current circuit, the area of ​​the cathode and the area of ​​the anode are both not less than 0.1% of the surface area of ​​the corrosive metal.

[0020] According to the above-described method for suppressing galvanic corrosion and stray current corrosion of metals, in the step of adjusting the external current of the blocking current circuit by the external power supply and simultaneously monitoring the anodic current or potential of the corroded metal until the measured anodic current or potential meets the preset conditions, the potential difference applied by the external power supply is greater than 2V.

[0021] According to the above-described method for suppressing galvanic corrosion and stray current corrosion of metals, in the step of setting an external cathode and anode in the environmental medium surrounding the corrosive metal to be protected, and connecting the external cathode and the external anode to an external power source through wires to form an external blocking current circuit, the external power source is a DC power source, and the external power source can control the output potential, current or power to be constant or variable.

[0022] The beneficial effects of the method for suppressing galvanic corrosion and stray current corrosion provided in this application are at least as follows:

[0023] This application uses an applied current (external current) instead of an insulator to block the corrosion current loop. This application regulates the direction of the external current in the environmental medium around the corrosive metal by an external power source so that it is opposite to the direction of the original anodic current (galvanic current or stray current) of the corrosive metal, causing the anodic current or potential to meet a certain threshold, thus blocking the original galvanic current or stray current. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a flowchart illustrating a method for suppressing galvanic corrosion and stray current corrosion in an embodiment of this application.

[0026] Figure 2 This is a schematic diagram illustrating a method for suppressing galvanic corrosion and stray current corrosion in accordance with an embodiment of this application.

[0027] Figure 3 This is a schematic diagram of the structure of Embodiment 1 of a method for suppressing galvanic corrosion and stray current corrosion of metals provided in this application.

[0028] Figure 4 for Figure 3 A partial schematic diagram.

[0029] Figure 5 This is a schematic diagram illustrating the effect of external current on galvanic current in Embodiment 1 of a method for suppressing metal galvanic corrosion and stray current corrosion provided in this application.

[0030] Figure 6 This is a schematic diagram of Embodiment 2 of a method for suppressing galvanic corrosion and stray current corrosion of metals provided in this application.

[0031] Figure 7 This is a schematic diagram illustrating the effect of external current on galvanic current in Embodiment 2 of a method for suppressing metal galvanic corrosion and stray current corrosion provided in this application.

[0032] Figure 8 This is a schematic diagram of the structure of Embodiment 3 of a method for suppressing galvanic corrosion and stray current corrosion of metals provided in this application.

[0033] Figure 9This is a schematic diagram illustrating the effect of external current on galvanic current in Embodiment 3 of a method for suppressing metal galvanic corrosion and stray current corrosion provided in this application.

[0034] The following are the labeling elements in the figure:

[0035] 1. First ammeter; 2. Second ammeter; 3. DC power supply; 41. Aluminum bronze; 42. Carbon steel; 43. First titanium wire; 44. Second titanium wire; 45. Wire; 46. Epoxy resin; 47. First NaCl solution; 48. Water tank; 51. Magnesium alloy; 52. Stainless steel gasket; 53. Third titanium wire; 54. Fourth titanium wire; 55. Insulating flat washer; 56. Nylon hexagonal nut; 571. Nylon hexagonal screw head; 572. Nylon hexagonal screw tail; 58. Salt spray test chamber; 59. Second NaCl solution; 61. Aluminum bronze tube; 62. Carbon steel tube; 63. Fifth titanium wire; 64. Sixth titanium wire; 65. PP insulating tube; 66. Flange gasket; 67. Insulating flange cover. Detailed Implementation

[0036] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0037] It should be noted that when a component is referred to as "fixed to" or "set on" another component, it may be directly or indirectly located on that other component. When a component is referred to as "connected to" another component, it may be directly or indirectly connected to that other component. The terms "upper," "lower," "left," "right," "front," "rear," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate orientations or positions based on the accompanying drawings, and are for ease of description only, and should not be construed as limiting the technical solution. The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features. "A plurality" means two or more, unless otherwise explicitly defined.

[0038] Controlling galvanic corrosion is theoretically quite simple; it only requires disconnecting the electronic or ionic circuit through which the galvanic current flows. However, in practice, this simple solution is often difficult to implement. For example, consider a galvanic couple formed by bolting two different metals (e.g., magnesium alloy and stainless steel) together in an environmental medium (e.g., seawater). The potential difference between the cathode (e.g., stainless steel) with a more positive self-corrosion potential and the anode (e.g., magnesium alloy) with a more negative self-corrosion potential causes current to flow from the anode (e.g., magnesium alloy) into the environmental medium as ions. This current then travels through the environmental medium to the cathode (e.g., stainless steel), where it is converted into electrons. The electrons then flow back from the cathode (e.g., stainless steel) through the cathode / anode (e.g., stainless steel / magnesium alloy) interface to the anode (e.g., magnesium alloy), forming a complete closed-loop current circuit. The current flowing from the anode (e.g., magnesium alloy) through the anode / environmental medium (e.g., magnesium alloy / seawater) interface into the environmental medium corresponds to the dissolution corrosion of the anode (e.g., magnesium alloy), which is accelerated by the electric field or potential difference applied by the cathode (e.g., stainless steel) to this interface. For the anode (e.g., magnesium alloy), the electric field, potential difference, or galvanic current applied by the cathode (e.g., stainless steel) are all external factors. Therefore, galvanic corrosion of the anode (e.g., magnesium alloy) can be understood as damage accelerated by the applied electric field. Simply insulating the cathode / anode (e.g., stainless steel / magnesium alloy) interface can block the entire current loop, ensuring that the influence of the electric field or potential difference applied by the cathode (e.g., stainless steel) on the anode (e.g., magnesium alloy) falls entirely on the cathode / anode (e.g., stainless steel / magnesium alloy) interface, rather than on the anode / environmental medium (e.g., magnesium alloy / seawater), thus preventing galvanic corrosion of the anode (e.g., magnesium alloy). However, in practical applications, the cathode / anode (e.g., stainless steel / magnesium alloy) interface is sometimes used for conducting electrical signals and cannot be insulated; or adding insulation would significantly reduce the mechanical strength of the connection, making it unacceptable; or adding such an insulation layer would make production costs too high to bear. Therefore, in engineering, these problems are often not solved by simply isolating the direct electrical connection between the anode and cathode.

[0039] Stray current corrosion is a common form of metal damage in practical engineering. It shares some similarities with galvanic corrosion, as described above. Its accelerated corrosion is also caused by an applied electric field. The current leaving the corroded metal flows through the surrounding medium in ionic form, eventually returning to other parts of the corroded metal and re-entering the metal in electron form, forming a closed current loop. The difference between stray current corrosion and galvanic corrosion is that the applied potential field is not necessarily from other metals or electronic conductors directly connected to the corroded metal. It could be from other electrical equipment not directly connected to the corroded metal, where the leaked current flows through the surrounding medium and the corroded metal before returning to the equipment; or it could be an induced current generated by an electromagnetic field flowing through the corroded metal and the surrounding medium. For example, electricity used by trams on city streets may leak through underground metal pipes and flow back to the tram; or current induced by high-voltage power lines may flow through the pipes and the surrounding medium. Therefore, the stray current corrosion system can be approximated as a galvanic-like system: the anode is the corroded metal; the cathode is an electronic conductor located at a distance or even unknown location, and the potential difference between it and the corroded metal depends on the intensity of the stray source. In such a stray current corrosion system, the electronic current path is difficult to cut off because as long as the corroded metal is still in contact with the environmental medium after the cut-off, the current leaked by the electrical equipment or the current induced by it will still flow through the medium and the corroded metal.

[0040] Therefore, to suppress galvanic corrosion and stray current corrosion, engineering practices tend to block or impede the ion conduction path. While the outflow location of both galvanic and stray current corrosion is relatively easy to determine based on the corrosion characteristics of the metal surface, the location of the corresponding receiving current cathode or electron conductor is less obvious and difficult to determine, especially the induced stray current, which is even more difficult to pinpoint due to the interconnectedness of the surrounding environment. To block the ion loop of such stray currents, it is best to perform the operation near the corroded metal where the ion current originates.

[0041] The most common practice is to directly coat the metal surface with a protective layer to isolate the anodic / environment interface. However, sometimes direct surface coating is difficult because the metal surface is too deep (such as the inner wall of a pipe) or too concealed (such as in a crevice); more often, the coating is damaged during the use of the component, leading to severe accelerated corrosion at the damaged areas. Therefore, practical engineering and industrial applications still urgently need other technologies that can effectively suppress galvanic corrosion and stray current corrosion.

[0042] To address the aforementioned problems, this application employs an additional external loop current (an external electric field added to the ion-conducting loop) in the environmental medium to counteract or block galvanic currents or stray currents, thereby suppressing the dissolution of corrosive metals. Specifically, this application sets up an external cathode and anode in the environmental medium surrounding the corrosive metal to be protected, and connects the cathode and anode to an external power source via wires to form an external blocking current circuit. The external current of the blocking current circuit is adjusted by the external power source, while simultaneously monitoring the anode current or potential of the corrosive metal. This process continues until the measured anode current or potential meets a preset condition, wherein the preset condition is that the direction of the external current is opposite to the direction of the anode current, causing the anode current or potential to meet a certain threshold, reducing the flowing anode current to zero, or even reversing it to protect the corrosive metal.

[0043] It is foreseeable that this application uses an applied current (external current) instead of an insulator to block the corrosion current loop. This application regulates the direction of the external current in the environmental medium around the corrosive metal by an external power source so that it is opposite to the direction of the original anodic current (galvanic current or stray current) of the corrosive metal, and makes the anodic current or potential meet a certain threshold, thus blocking the original galvanic current or stray current.

[0044] For this purpose, please refer to Figure 1 This application provides a method for suppressing galvanic corrosion and stray current corrosion of metals, the method comprising:

[0045] S10. An external cathode and anode are installed in the environmental medium surrounding the corrosive metal that needs protection, and the external cathode and anode are respectively connected to an external power source through wires to form an external blocking current circuit.

[0046] S20. Adjust the external current of the blocking current circuit through the external power supply, and at the same time monitor the anodic current or potential of the corroded metal until the measured anodic current or potential meets the preset conditions.

[0047] Specifically, the preset condition is that the direction of the external current is opposite to the direction of the anode current, and the anode current or potential meets a certain threshold, causing the flowing anode current to drop to zero, or even reverse to protect the corroded metal. The external current is the current applied by the external power supply to block the anode current. Furthermore, the external current applied by the external power supply will pass through the external anode, the environmental medium, and finally flow back to the external power supply from the external cathode. The external current mainly flows between the external cathode and anode, which largely avoids the overprotection that may occur to surrounding metals that do not need protection, as is the case with traditional cathodic protection current.

[0048] The magnitude and direction of the external current can be adjusted by an external power source, so that the direction of the external current in the environmental medium surrounding the corrosive metal is opposite to the direction of the original anodic current (couple current or stray current) of the corrosive metal, thus blocking the couple current or stray current.

[0049] To illustrate the above method, please refer to Figure 2 This is a schematic diagram of the present embodiment. In the diagram, the corroded metal originally has a dissolution current I. g The current flows through the interface between the corrosive metal (the anode of the galvanic couple) and the ambient medium, through the ambient medium, and through the interface between the ambient medium and the electronic conductor (where the electronic conductor is the cathode material of a different corrosive metal, or it can be another part of the corrosive metal; it may be close to the corrosive metal, or it may be far away, or its location is unknown), reaching the electronic conductor (the cathode of the galvanic couple), and then flows back to the corrosive metal (the anode of the galvanic couple) by electronic conductivity, forming a closed corrosion current loop. When an externally applied blocking current circuit consisting of an anode, cathode, power source (external power supply), and wires is added, the external current I provided by the power source... e The current flows from the positive terminal of the power supply to the external anode, and then splits into two paths: 1) Inner loop current I e i After passing through the ambient medium, it reaches the external cathode and returns to the negative terminal of the external power supply; 2) External loop current I e e After passing through the environmental medium, it reaches the corrosive metal (i.e., the anode of the corrosion couple), flows electronically to the electronic conductor (i.e., the cathode of the corrosion couple or the collector of stray current), and passes through the interface between the electronic conductor (i.e., the cathode of the corrosion couple) and the environmental medium. It then flows through the environmental medium again, passes through the interface between the environmental medium and the applied cathode, and enters the interface between the applied cathode and I. e i The current converges and flows back to the negative terminal of the external power supply. The external current I generated by the externally applied, isolated current circuit consisting of the external anode, cathode, external power supply, and wires... e e Compared with the original corrosion metal dissolution current I g The direction is opposite, therefore the dissolution current of the corroded metal is suppressed and reduced to I. g e :

[0050] I g e =I g -I e e ;

[0051] Obviously I e e It can be adjusted by an external power supply, according to the external current I. e As it increases, I increases accordingly. ge The size decreases. This is the principle behind the anodic dissolution of corroded metal being hindered by an external blocking current. In practice, it is only necessary to adjust the external current I... e Real-time monitoring I g e , when I g e It's fine as long as it reaches an acceptable level.

[0052] Optionally, in one embodiment, in the step of setting an external cathode and anode in the environmental medium surrounding the corrosive metal to be protected, and connecting the cathode and anode to an external power source via wires to form an external blocking current circuit, the cathode, anode, and external power source do not contact the corrosive metal or any electronic conductor directly electrically connected to the corrosive metal, and the external current is not directly applied to the corrosive metal through wires. In other words, this embodiment differs from traditional cathodic protection currents. Traditional cathodic protection currents, whether from an external power source or flowing from the electronic circuit of the sacrificial anode, need to be directly applied to the corrosive metal through wire connections. Since the external power source, cathode, and anode in this embodiment do not have direct electrical connections to the corrosive metal, it greatly facilitates practical engineering applications.

[0053] Optionally, in laboratory verification, the corroded metal can be completely insulated from the electronic conductor, and then short-circuited with an ammeter so that the current measured by the ammeter is equal to the anodic current flowing through the corroded metal. When the external current of the blocking current circuit is adjusted by the external power supply, the anodic current of the corroded metal can be monitored simultaneously until the measured anodic current meets a preset condition. The specific steps include:

[0054] A first ammeter is provided, which is connected between the corroded metal and the electronic conductor, and the anodic current of the corroded metal is monitored through the first ammeter;

[0055] The external current of the blocking current circuit is adjusted by the external power source until the measured anode current or potential meets the preset conditions.

[0056] In practical applications, the anodic current flowing through the corrosive metal can only be inferred by measuring the potential of the corrosive metal relative to the applied anode or relative to the inserted reference electrode, as described above. Specifically, the external current of the blocking current circuit is adjusted by the external power supply, while the potential of the corrosive metal relative to the anode is monitored using the anode until the measured potential meets a preset condition. Alternatively, a reference electrode is provided and inserted into the environmental medium between the corrosive metal and the anode. The potential of the corrosive metal is monitored using the reference electrode, and the external current of the blocking current circuit is adjusted by the external power supply until the measured potential of the corrosive metal relative to the reference electrode meets a preset condition.

[0057] Optionally, in one embodiment, the distance between the anode and the corroded metal is smaller than the distance between the cathode and the corroded metal.

[0058] Optionally, in one embodiment, both the cathode and the anode are located at positions in the ambient medium where the anodic current (galvanic current or stray current) is concentrated, and the distance between the cathode and the anode should be as large as possible.

[0059] Optionally, in one embodiment, the surfaces of the cathode and the anode are as parallel as possible to the surface of the corroded metal, preferably both the surfaces of the cathode and the anode are parallel to the surface of the corroded metal.

[0060] Optionally, in one embodiment, the area of ​​the cathode and the area of ​​the anode disposed in the ambient medium are both as large as possible, wherein the area of ​​the cathode and the area of ​​the anode disposed in the ambient medium are both not less than 0.1% of the surface area of ​​the corroding metal, and multiple cathodes and anodes may be disposed according to the current distribution in the ambient medium.

[0061] Optionally, in one embodiment, both the cathode and the anode are chemically stable in the environmental medium, insoluble or poorly soluble, and both have low polarization resistance, or low oxygen evolution overpotential and low hydrogen evolution overpotential. In practical applications, the anode can be, but is not limited to, the anodes used in traditional impressed current cathodic protection systems, water electrolysis oxygen production systems, or water electrolysis chlor-alkali production systems. Examples include stainless steel, titanium alloys, titanium-plated steel mesh, nickel-plated steel mesh, graphite, even platinum alloys, rare earth compounds, and highly conductive metal oxides. Alternatively, commonly used traditional anodes can be used, such as stainless steel, titanium alloys, titanium-plated steel mesh, nickel-plated steel mesh, graphite, even platinum alloys, rare earth compounds, and highly conductive metal oxides.

[0062] In practical applications, the cathode can be, but is not limited to, the cathodes used in traditional water electrolysis hydrogen production systems or water electrolysis chlor-alkali production systems, such as graphite, ferroalloys, cobalt alloys, nickel alloys, or even platinum alloys, palladium alloys, gold alloys, silver alloys, etc.; or it can be, but is not limited to, commonly used traditional cathodes, such as graphite, ferroalloys, cobalt alloys, nickel alloys, or even platinum alloys, palladium alloys, gold alloys, silver alloys, etc.

[0063] Furthermore, in one embodiment, the anode and the cathode may undergo further post-processing. Processing methods include, but are not limited to: machining, heat treatment, partial or complete surface laser treatment, chemical reaction, electrochemical reaction, thermal diffusion, ion implantation, electron implantation, partial or complete surface machining, brushing, spraying, deposition, growth, etc.

[0064] Optionally, in one embodiment, the external power supply can control the output potential, current, or power to be constant or variable, and the anodic current of the corroding metal can be adjusted by the external power supply. When the anodic current flowing through the corroding metal can be measured, the smaller the measured anodic current of the corroding metal, the better. When the anodic current is 0, it indicates that the anodic dissolution of the corroding metal caused by galvanic or stray current has been completely suppressed; when the direction of the anodic current is reversed, it indicates that the self-corrosion of the corroding metal has also been suppressed.

[0065] When corroded metal can be directly electrically connected to the outside, the anodic current of the corroded metal needs to be obtained by adding a reference electrode between the corroded metal and the external anode. The closer the potential of the corroded metal relative to the external reference electrode is to the self-corrosion potential of the corroded metal, the better, indicating that the anodic dissolution of the corroded metal caused by galvanic couples or stray currents is more effectively suppressed. When the measured potential is even negative to the self-corrosion potential of the corroded metal, it indicates that the self-corrosion of the corroded metal is also suppressed.

[0066] When corroded metal cannot be directly electrically connected to the outside environment, the anodic current of the corroded metal needs to be estimated by applying a dual reference electrode between the corroded metal and the applied anode. The closer the potential difference of the applied dual reference electrode is to 0, the better, indicating that the anodic dissolution of the corroded metal caused by galvanic couples or stray currents is more effectively suppressed. When the corroded metal cannot be directly electrically connected to the outside environment, and it is also impossible to apply a reference electrode between the corroded metal and the applied anode, the anodic current of the corroded metal can be estimated by measuring the potential difference between the applied anode and cathode and the external current. The potential difference applied by the external power source should be greater than the self-corrosion potential difference between the applied cathode and anode in the environmental medium plus the total value of the potential polarization shift of the electrochemical system composed of the corroded metal and its corresponding electronic conductor when the external current is applied.

[0067] When corroded metal cannot be directly electrically connected to the outside world, and no external electrode can be placed between the corroded metal and the applied anode, although it is impossible to know how large a current the external power supply needs to be to completely suppress galvanic corrosion or stray current corrosion of the corroded metal, it is certain that the larger the applied external current, the better the suppression effect. The potential difference applied by the external power supply should ideally be greater than 2V. When the self-corrosion potential difference between the applied anode and cathode is large, it may be possible to eliminate the need for an external power supply and simply short-circuit the applied cathode and anode.

[0068] To verify the principle of this application, the inventors conducted three sets of experiments: Experiment 1 was the blocking of copper-steel galvanic current in a 3.5 wt.% NaCl solution; Experiment 2 was the blocking of AM60 magnesium alloy-304 stainless steel galvanic current in a 5 wt.% NaCl salt spray (pH=3.5); and Experiment 3 was the blocking of galvanic current in a copper pipe-insulating section-carbon steel pipe filled with artificial seawater.

[0069] Experiment 1:

[0070] The engineering background of Experiment 1 is as follows: In engineering applications, electrical connections between different metals are unavoidable. To study their galvanic corrosion, these different metals are often separated and exposed on the same surface in the laboratory. Then, they are connected by wires and an ammeter to measure the galvanic current between them. This embodiment builds upon this by adding the cathode and anode of an external current-blocking circuit to this measuring surface.

[0071] The thermocouple samples for Experiment 1 consisted of one Φ1×1cm round rod-shaped QAL10-4-4 aluminum bronze sample, two TA2 titanium wire samples (first titanium wire 43 and second titanium wire 44), and one Q235 carbon steel sample. Each sample was connected to a wire 45, arranged in a straight line, and encapsulated in an 8×2×1.5cm epoxy resin container. The axis distance between the aluminum bronze 41 and the first titanium wire 43 was 12mm, the axis distance between the first titanium wire 43 and the second titanium wire 44 was 15mm, and the axis distance between the second titanium wire 44 and the carbon steel 42 was 12mm. (See reference...) Figure 3 and Figure 4 Their cylindrical end faces are exposed on the bottom surface of epoxy resin 46. After being sanded smooth, this surface becomes the working surface of the galvanic couple sample.

[0072] The experimental setup for Experiment 1 was as follows: The working surface of the epoxy resin-sealed thermocouple sample was immersed horizontally downwards in a 12×10×7cm rectangular water tank 48 containing 700mL of 3.5wt.% NaCl solution, with the working surface 4cm below the NaCl solution 47. The first titanium wire 43, the second titanium wire 44, the DC power supply 3, and the second ammeter 2 were connected in series via wires connected to these cylindrical samples; the aluminum bronze 41 and carbon steel 42 were respectively connected to the first ammeter 1. (See reference...) Figure 3 and Figure 4 The reading of ammeter 1 represents the anodic current (couple current) of the corroding metal; the reading of ammeter 2 represents the external current of the applied blocking current circuit.

[0073] The measurement steps for Experiment 1 are as follows: Turn on DC power supply 3, and adjust the external current of the applied blocking current circuit by adjusting the voltage of DC power supply 3. After each adjustment of the DC power supply voltage, wait 2 minutes, and read the current values ​​of the first ammeter 1 and the second ammeter 2, while continuously changing the voltage and current of DC power supply 3. Record the current values ​​of the first ammeter 1 and the second ammeter 2. The entire experiment is conducted in a laboratory at a room temperature of 27 degrees Celsius.

[0074] The measurement results of Experiment 1 are as follows: as the external current measured by the second ammeter 2 increases, the copper-steel galvanic current slowly decreases. When the external current is large enough, the galvanic current drops sharply and even reverses. This fully demonstrates that the copper-steel galvanic current in a 3.5 wt.% NaCl solution can indeed be suppressed and blocked by the external current. (See [reference needed]) Figure 5 .

[0075] Experiment 2:

[0076] The engineering background of Experiment 2 is as follows: In engineering applications, magnesium alloys are often connected to other metals via bolts. All engineering metals have an accelerating effect on galvanic corrosion of magnesium alloys, especially steel. Therefore, this embodiment directly simulates the bolted connection between magnesium alloys and steel. For ease of current measurement, insulated bolts, nuts, and washers are used in this example. Furthermore, since the primary application of magnesium alloys is currently in atmospheric environments, to obtain experimental results quickly, this embodiment uses an extremely harsh salt spray test for environmental simulation.

[0077] The thermocouple sample for Experiment 2 is as follows: Prepare a 5.5×3×0.5cm AM60 sheet magnesium alloy sample, and drill a circular hole with a diameter of 8mm vertically in its center for later use; prepare two Φ1mm TA2 titanium wires (third titanium wire 53 and fourth titanium wire 54), and bend one end of each TA2 titanium wire into a 16mm diameter ring. Except for the part of the TA2 titanium wire that is bent into a ring and exposed, the remaining TA2 titanium wires are covered with heat shrink tubing to avoid contact with environmental salt spray; also prepare one M8×20×2 304 stainless steel washer, one M8×60 nylon hex screw (including nylon hex screw head 571 and nylon hex screw tail 572), one M8 nylon hex nut, and three M8×16×1.4 insulating flat washers 55. The prepared stainless steel washer 52, insulating flat washer 55, ring-shaped third titanium wire 53, insulating flat washer 55, ring-shaped fourth titanium wire 54, insulating flat washer 55, and magnesium alloy 51 are sequentially fitted onto the nylon external hexagonal screw. Finally, the nylon hexagonal nut 56 is tightened from the tail 572 of the nylon hexagonal screw towards the head 571, securing the materials sequentially fitted onto the nylon external hexagonal screw tightly. The outer surfaces of the rings of the third titanium wire 53 and the fourth titanium wire 54 are aligned with the outer diameter of the insulating flat washer 55. The stainless steel washer 52 and magnesium alloy 51 are each connected to the wire, and the joints are sealed with silicone. This multi-layer structure will be used as a thermocouple sample. See [reference needed]. Figure 6 .

[0078] The experimental setup for Experiment 2 is as follows: The prepared thermocouple sample is placed on the V-groove of the salt spray test chamber 58, with the stainless steel gasket 52 at the top. The angle between the axis of the nylon hexagonal screw and the horizontal plane is set to 45°. The third titanium wire 53 in the thermocouple sample inside the salt spray test chamber 58, the DC power supply 3 outside the salt spray test chamber, the first ammeter 1, and the fourth titanium wire 54 in the thermocouple sample inside the chamber are connected in series by wires. The third titanium wire 53 is connected to the negative terminal of the DC power supply, and the fourth titanium wire 54 is connected to the positive terminal of the DC power supply. The second ammeter 2 outside the salt spray test chamber is connected to the stainless steel gasket 52 and the magnesium alloy 51 in the thermocouple sample inside the salt spray test chamber by wires. In this way, the reading of ammeter 1 represents the external current of the applied blocking current circuit; the reading of ammeter 2 represents the anodic current (thermocouple current) of the corroding metal. The solution used in the salt spray test was a 5 wt.% second NaCl solution with pH = 3.5 (pH adjusted with dilute hydrochloric acid), and the salt spray test temperature was 35℃.

[0079] The measurement steps for Experiment 2 are as follows: First, run the salt spray test chamber 58 for 12 hours to stabilize the temperature, humidity, salinity and thermocouple current inside the chamber. Then, turn on the DC power supply 3 and adjust the voltage of the DC power supply 3 to regulate the external current. After each adjustment for 2 minutes, measure the external current on the externally applied blocking current circuit and the anode current (thermocouple current) on the magnesium alloy-stainless steel thermocouple circuit using the first ammeter 1 and the second ammeter 2, respectively.

[0080] The measurement results of Experiment 2 are as follows: (See attached document) Figure 7 Under salt spray conditions, the galvanic current of magnesium alloy-stainless steel is highly sensitive to the external current of the applied blocking current circuit. This further proves that the external current blocking technology can even effectively block the extremely active galvanic corrosion of magnesium alloy and stainless steel in the extremely harsh salt spray environment. This result is of great significance because galvanic corrosion is currently one of the main obstacles to the engineering application of magnesium alloy.

[0081] Experiment 3:

[0082] The engineering background of Experiment 3 is as follows: Surface ships, submarines, and offshore platforms all contain pipes made of various metals, through which highly corrosive seawater flows. Besides the ion current loop formed by the flowing seawater, many other electronic connection channels exist between these different metal pipes. Simply adding insulating sections between the different metal pipes, merely increasing the resistance of the ion loop, cannot block the electronic loop, and the suppression of galvanic corrosion is very limited. Therefore, this example, in addition to adding insulating sections, uses an external current blocking technique to completely suppress galvanic corrosion of the pipes.

[0083] The thermocouple samples for Experiment 3 consist of one QAL10-4-4 aluminum bronze tube, one PP insulating tube, and one Q235 carbon steel tube, each with a total length of 1m and an inner diameter of 3cm, and flanges welded to both ends with an outer diameter of 14cm. These are arranged in series, with flange gaskets 9 inserted between their flanges, and bolted together to secure them. Simultaneously, two 0.5m long Φ1mm TA2 titanium wires (the fifth titanium wire 63 and the sixth titanium wire 64) are prepared. One end of each titanium wire is bent into a spring-shaped loop with a diameter of 29mm and 5 turns. Except for the loop portion, the remaining titanium wire is sealed with heat-shrink tubing to insulate it from the ambient medium. Place the loop of the fifth titanium wire 63 at the end of the PP insulating tube 65 near the aluminum bronze tube 61. The end of the fifth titanium wire 63 passes through the flange gasket 66 between the aluminum bronze tube 61 and the PP insulating tube 65, ensuring that the fifth titanium wire 63 does not have direct electrical contact with the aluminum bronze tube 61. Place the loop of the sixth titanium wire 64 at the end of the PP insulating tube 65 near the carbon steel tube 62. The end of the sixth titanium wire 64 passes through the flange gasket 66 between the carbon steel tube 62 and the PP insulating tube 65, ensuring that the sixth titanium wire 64 does not have direct electrical contact with the carbon steel tube 62. Seal the outer ends of the aluminum bronze tube 61 and the carbon steel tube 62 with insulating flange covers 67. Before sealing the last insulating flange cover 67, fill the three fully connected pipes connected in series with artificial seawater (ASTM D1141-98). Refer to the complete pipeline thermocouple sample. Figure 1 .

[0084] The experimental setup for Experiment 3 is as follows: Connect the fifth titanium wire 63, the sixth titanium wire 64, the DC power supply 3, and the second ammeter 2 in series. The fifth titanium wire 63 is connected to the negative terminal of the DC power supply 3, and the sixth titanium wire 64 is connected to the positive terminal. Connect the aluminum bronze tube 61 and the carbon steel tube 62 to the first ammeter 1 using wires. Thus, the reading of the first ammeter 1 represents the thermocouple current of the corroded pipe, and the reading of the second ammeter 2 represents the external current of the applied, isolated current circuit. (See reference...) Figure 8 .

[0085] The experimental test for Experiment 3 is as follows: Turn on DC power supply 3, adjust the external current by adjusting the voltage of DC power supply 3, record the readings of the first ammeter 1 and the second ammeter 2 after each adjustment of 2 minutes, and obtain the thermocouple current between the external current and the stainless steel tube-PP insulating tube-aluminum bronze tube.

[0086] The results of the test samples in Experiment 3 are as follows: (See attached document) Figure 9In a carbon steel-aluminum bronze pipe filled with artificial seawater and featuring an insulated section, the galvanic current almost decreases with increasing external current, eventually disappearing. When the external current is zero, although a 1-meter-long insulated section separates the galvanic pipes, it is far from sufficient to suppress galvanic corrosion, with the galvanic current exceeding 800 μA. However, by applying an external current barrier, the galvanic corrosion can be effectively suppressed. This result further demonstrates the effectiveness of external current barrier technology in seawater pipeline applications.

[0087] In summary, this application provides a method for suppressing galvanic corrosion and stray current corrosion of metals. The method involves setting an external cathode and anode in the environmental medium surrounding the corrosive metal to be protected, and connecting the cathode and anode to an external power source via wires to form an external blocking current circuit. The external current of the blocking current circuit is adjusted by the external power source, while the anode current or potential of the corrosive metal is monitored until the measured anode current or potential meets a preset condition. The preset condition is that the current direction of the external current is opposite to the current direction of the anode current, causing the anode current or potential to meet a certain threshold, reducing the flowing anode current to zero, or even reversing it to protect the corrosive metal. It is foreseeable that this application uses an applied current (external current) instead of an insulator to block the corrosion current loop. This application regulates the direction of the external current in the environmental medium around the corrosive metal by an external power source, so that the direction of the current is opposite to the original anodic current (galvanic current or stray current) of the corrosive metal. This causes the anodic current or potential to meet a certain threshold, so that the flowing anodic current is reduced to zero, or even reversed to protect the corrosive metal. In this way, the original galvanic current or stray current can be blocked.

[0088] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for suppressing galvanic corrosion and stray current corrosion of metals, characterized in that, include: An external cathode and anode are placed in the surrounding environment of the corrosive metal requiring protection, and the external cathode and anode are connected to an external power source via wires to form an external blocking current circuit. Neither the cathode nor the anode is in contact with the corrosive metal or is a conductor directly electrically connected to it. The distance between the anode and the corrosive metal is less than the distance between the cathode and the corrosive metal. Both the cathode and the anode are located in areas where the anodic current distribution is concentrated in the environment. The surfaces of the cathode and the anode are parallel to the surface of the corrosive metal. The areas of both the cathode and the anode are not less than 0.1% of the surface area of ​​the corrosive metal. The external power source is a DC power source, and its output potential, current, or power can be controlled constantly or dynamically. The external current of the blocking current circuit is adjusted by the external power supply, while the anodic current or potential of the corroded metal is monitored until the measured anodic current or potential meets a preset condition. The preset condition is that the current direction of the external current is opposite to the current direction of the anodic current, so that the anodic current or potential meets a certain threshold, reducing the flowing anodic current to zero, or even reversing to protect the corroded metal. The potential difference applied by the external power supply is greater than 2V.

2. The method for suppressing galvanic corrosion and stray current corrosion as described in claim 1, characterized in that, The step of adjusting the external current of the blocking current circuit through the external power supply, while monitoring the anodic current or potential of the corroded metal until the measured anodic current or potential meets the preset conditions, specifically includes: The external current of the blocking current circuit is adjusted by the external power source, and the potential of the corroded metal relative to the anode is monitored by the anode until the measured potential meets the preset conditions.

3. The method for suppressing galvanic corrosion and stray current corrosion as described in claim 1, characterized in that, The step of adjusting the external current of the blocking current circuit through the external power supply, while monitoring the anodic current or potential of the corroded metal until the measured anodic current or potential meets the preset conditions, specifically includes: A reference electrode is provided, which is inserted into the environmental medium between the corroded metal and the anode, and the potential of the corroded metal is monitored through the reference electrode; The external current of the blocking current circuit is adjusted by the external power source until the measured potential of the corroded metal relative to the reference electrode meets the preset conditions.

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