Method for inhibiting galvanic corrosion and stray current corrosion of metal

Abstract

The invention relates to the field of corrosion protection of metal materials in engineering application, and provides a method for inhibiting galvanic corrosion and stray current corrosion of metal. According to an existing method, the surface of metal is generally and directly coated with a protective layer to isolate an interface between an anode and the environment so as to inhibit galvanic corrosion and stray current corrosion of the metal, but the protective layer is still prone to being damaged, so that the galvanic corrosion and the stray current corrosion cannot be effectively inhibited. The method comprises the following steps of: arranging an additional cathode and an additional anode in an environment medium at the periphery of the corrosion metal needing to be protected, and respectively connecting the cathode and the anode with an external power supply through wires to form an additional current blocking circuit; and adjusting the external current of the current blocking circuit through the external power supply, and monitoring the anode current or potential of the corrosion metal at the same time until the measured anode current or potential meets a preset condition.

Description

Technical Field

[0001] The present application relates to the field of corrosion protection of metal materials in engineering applications, and more specifically, to a method for inhibiting metal galvanic corrosion and stray current corrosion. Background Art

[0002] The control of galvanic corrosion is theoretically very simple. It only requires disconnecting the electronic circuit or ion circuit through which the galvanic current flows. However, in practice, such a simple solution is difficult to achieve in many cases. For example, two different metals (such as magnesium alloy and stainless steel) are connected by bolts in an environmental medium (such as seawater) to form a galvanic pair. The potential difference formed between the cathode (such as stainless steel) with a positive self-corrosion potential and the anode (such as magnesium alloy) with a negative self-corrosion potential causes the current to enter the environmental medium from the anode (such as magnesium alloy) in the form of ion current, and then reach the cathode (such as stainless steel) through the environmental medium and transform into electrons. Then, the current from the cathode (such as stainless steel) flows back to the anode (such as magnesium alloy) through the cathode / anode (such as stainless steel / magnesium alloy) interface, forming a complete closed-loop current loop. The current flowing from the anode (such as magnesium alloy) through the anode / environmental medium (such as magnesium alloy / seawater) interface into the environmental medium corresponds to the dissolution corrosion of the anode (such as magnesium alloy), which will be accelerated by the electric field or potential difference applied by the cathode (such as stainless steel) to the 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, so the galvanic corrosion of the anode (e.g. magnesium alloy) can also be understood as the destruction accelerated by the external electric field. The entire current loop can be blocked by insulating the cathode / anode (e.g. stainless steel / magnesium alloy) interface, so 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 avoiding the galvanic corrosion of the anode (e.g. magnesium alloy). However, in practical applications, the connection of the cathode / anode (e.g. stainless steel / magnesium alloy) interface is sometimes used to conduct electrical signals and is not allowed to be insulated; or the interface is added with insulation isolation, which will lead to a significant reduction in the mechanical properties of the connection and is unacceptable; or the addition of such an insulating isolation layer makes the production cost too high to bear. Therefore, in engineering, it is often impossible to solve the above problems by simply isolating the direct electrical connection between the anode and the cathode.

[0003] Stray current corrosion is also a common form of metal damage in practical engineering. It has certain similarities with the above-mentioned galvanic corrosion. Its corrosion acceleration is also caused by an external electric field. The current leaving the corroded metal flows through the environmental medium in the form of ions, and finally returns to other parts of the corroded metal and enters the metal in the form of electrons, forming a closed current loop. The difference between it and galvanic corrosion is that the external potential field is not necessarily other metals or electronic conductors that are directly electrically connected to the corroded metal, but may be other electrical equipment that is not directly electrically connected to the corroded metal. The leakage current passes through the environmental medium and the corroded metal and returns to the electrical equipment; or the induced current generated by electromagnetic field induction flows through the corroded metal and the environmental medium. For example, the electricity used by trams on urban roads may leak through underground metal pipes and flow back to the trams; it is also possible that the current induced by the high-voltage transmission lines on the ground passes through the pipes and the environmental medium. Therefore, the corrosion system of stray current can be approximated as a system similar to a galvanic couple: the anode is the corroded metal; the cathode is an electronic conductor that is far away or even unknown, and the potential difference between it and the corroded metal depends on the strength of the stray source. The electronic current path of such a current loop of a stray current corrosion system is difficult to cut off, because as long as the corroded metal is still in contact with the environmental medium after cutting off, the leakage current of the electrical equipment or the induced current will still flow through the medium and the corroded metal.

[0004] Whether it is galvanic corrosion or stray current corrosion, its outflow position is relatively easy to determine based on the corrosion damage characteristics of the metal surface, but the position of the corresponding cathode or electronic conductor that receives the current is not obvious and difficult to determine, especially the stray current generated by induction is more difficult to determine because the environmental medium is interconnected. At present, the most common practice is to directly coat the metal surface with a protective layer to isolate the anode / environment interface. However, sometimes the direct surface coating is difficult because the metal surface is too deep (such as the inner wall of the pipeline) or too hidden (such as in the gap); more often, the coating is damaged during the use of the component, resulting in severe corrosion damage at the damaged coating. Therefore, actual engineering and industrial applications are still in urgent need of other technologies that can effectively inhibit galvanic corrosion and stray current corrosion. Summary of the invention

[0005] The purpose of the present application is to provide a method for inhibiting metal galvanic corrosion and stray current corrosion, so as 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 inhibit metal galvanic corrosion and stray current corrosion, but the protective layer is still easily damaged, resulting in the inability to effectively inhibit galvanic corrosion and stray current corrosion.

[0006] To achieve the above purpose, the technical solution adopted in the embodiment of the present application is:

[0007] A method for inhibiting metal galvanic corrosion and stray current corrosion, comprising:

[0008] An external cathode and an anode are arranged in the environmental medium around the corrosive metal to be protected, and the external cathode and the 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 regulated by the external power supply, and the anode current or potential of the corroded metal is monitored at the same time until the measured anode current or potential meets a preset condition, wherein the preset condition is that the current direction of the external current is opposite to the current direction of the anode current, so that the anode current or potential meets a certain threshold value, and the anode current flowing therethrough is reduced to zero, or even reversed to protect the corroded metal.

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

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

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

[0013] Providing a reference electrode, inserting the reference electrode into the environmental medium between the corroded metal and the anode, and monitoring the potential of the corroded metal through the reference electrode;

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

[0015] According to the method for inhibiting metal galvanic corrosion and stray current corrosion described above, in the step of setting an additional cathode and anode in the environmental medium around the corroded metal to be protected, and connecting the additional cathode and anode to an external power source through wires to form an external current blocking circuit, neither the cathode nor the anode contacts the corroded metal or the electronic conductor that is directly electrically connected to the corroded metal.

[0016] According to the method for inhibiting metal galvanic corrosion and stray current corrosion described above, in the step of setting an additional cathode and anode in the environmental medium around the corrosive metal to be protected, and connecting the additional 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 method for inhibiting metal galvanic corrosion and stray current corrosion described above, in the step of setting an additional cathode and anode in the environmental medium around the corrosive metal to be protected, and connecting the additional cathode and anode to an external power source through wires to form an external blocking current circuit, the cathode and the anode are both set at positions where the anode current distribution is concentrated in the environmental medium.

[0018] According to the method for inhibiting metal galvanic corrosion and stray current corrosion described above, in the step of setting an additional cathode and anode in the environmental medium around the corroded metal to be protected, and connecting the additional 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 parallel to the surface of the corroded metal.

[0019] According to the method for inhibiting metal galvanic corrosion and stray current corrosion described above, in the step of setting an additional cathode and anode in the environmental medium around the corrosive metal to be protected, and connecting the additional 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 not less than 0.1% of the surface area of ​​the corrosive metal.

[0020] According to the method for inhibiting metal galvanic corrosion and stray current corrosion described above, in the step of adjusting the external current of the blocking current circuit by the external power supply and 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 method for inhibiting metal galvanic corrosion and stray current corrosion described above, in the step of setting an external cathode and anode in the environmental medium around 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 current blocking circuit, the external power source is a DC power source, and the external power source can control the output potential, current or power constantly or variably.

[0022] The beneficial effects of a method for inhibiting metal galvanic corrosion and stray current corrosion provided by the present application are at least:

[0023] The present application uses an impressed current (external current) instead of an insulator to block the corrosion current loop. The present application uses an external power source to regulate the direction of the external current in the environmental medium surrounding the corroded metal to be opposite to the current direction of the original anode current (galvanic current or stray current) of the corroded metal, thereby causing the anode current or potential to meet a certain threshold, thereby blocking the original galvanic current or stray current. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 A flow chart of a method for inhibiting metal galvanic corrosion and stray current corrosion provided in an embodiment of the present application.

[0026] Figure 2 A schematic diagram of a method for inhibiting metal galvanic corrosion and stray current corrosion provided in an embodiment of the present application.

[0027] Figure 3 This is a structural schematic diagram of Example 1 of a method for inhibiting metal galvanic corrosion and stray current corrosion provided in an embodiment of the present application.

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

[0029] Figure 5 A schematic diagram of the effect of external current on galvanic current in Example 1 of a method for inhibiting metal galvanic corrosion and stray current corrosion provided in an embodiment of the present application.

[0030] Figure 6 This is a structural schematic diagram of Example 2 of a method for inhibiting metal galvanic corrosion and stray current corrosion provided in an embodiment of the present application.

[0031] Figure 7 A schematic diagram of the effect of external current on galvanic current in Example 2 of a method for inhibiting metal galvanic corrosion and stray current corrosion provided in an embodiment of the present application.

[0032] Figure 8 This is a structural schematic diagram of Example 3 of a method for inhibiting metal galvanic corrosion and stray current corrosion provided in an embodiment of the present application.

[0033] Fig. 9Schematic diagram of the effect of external current on galvanic current in Example 3 of a method for inhibiting metal galvanic corrosion and stray current corrosion provided in an embodiment of the present application.

[0034] Among them, the reference numerals in the figure are:

[0035] 1. The first ammeter; 2. The second ammeter; 3. The DC power supply; 41. Aluminum bronze; 42. Carbon steel; 43. The first titanium wire; 44. The second titanium wire; 45. The conductor; 46. Epoxy resin; 47. The first NaCl solution; 48. The sink; 51. The magnesium alloy; 52. The stainless steel gasket; 53. The third titanium wire; 54. The fourth titanium wire; 55. The insulating flat washer; 56. The nylon hexagonal nut; 571. The nylon hexagonal screw head; 572. The nylon hexagonal screw tail; 58. The salt spray test chamber; 59. The second NaCl solution; 61. The aluminum bronze tube; 62. The carbon steel tube; 63. The fifth titanium wire; 64. The sixth titanium wire; 65. The PP insulating tube; 66. The flange sealing gasket; 67. The insulating flange cover. DETAILED DESCRIPTION

[0036] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0037] It should be noted that when a component is referred to as being "fixed on" or "disposed on" another component, it may be directly or indirectly located on the other component. When a component is referred to as being "connected to" another component, it may be directly or indirectly connected to the other component. The directions or positions indicated by the terms "upper", "lower", "left", "right", "front", "back", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc. are based on the directions or positions shown in the accompanying drawings and are only for the convenience of description and cannot be understood as limitations on the present technical solution. The terms "first" and "second" are only used for the convenience of description and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features. "Multiple" means two or more, unless otherwise clearly and specifically defined.

[0038] The control of galvanic corrosion is theoretically very simple. It only requires disconnecting the electronic circuit or ion circuit through which the galvanic current flows. However, in practice, such a simple solution is difficult to achieve in many cases. For example, two different metals (such as magnesium alloy and stainless steel) are connected by bolts in an environmental medium (such as seawater) to form a galvanic pair. The potential difference formed between the cathode (such as stainless steel) with a positive self-corrosion potential and the anode (such as magnesium alloy) with a negative self-corrosion potential causes the current to enter the environmental medium from the anode (such as magnesium alloy) in the form of ion current, and then reach the cathode (such as stainless steel) through the environmental medium and transform into electrons. Then, the current from the cathode (such as stainless steel) flows back to the anode (such as magnesium alloy) through the cathode / anode (such as stainless steel / magnesium alloy) interface, forming a complete closed-loop current loop. The current flowing from the anode (such as magnesium alloy) through the anode / environmental medium (such as magnesium alloy / seawater) interface into the environmental medium corresponds to the dissolution corrosion of the anode (such as magnesium alloy), which will be accelerated by the electric field or potential difference applied by the cathode (such as stainless steel) to the 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, so the galvanic corrosion of the anode (e.g. magnesium alloy) can also be understood as the destruction accelerated by the external electric field. The entire current loop can be blocked by insulating the cathode / anode (e.g. stainless steel / magnesium alloy) interface, so 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 avoiding the galvanic corrosion of the anode (e.g. magnesium alloy). However, in practical applications, the connection of the cathode / anode (e.g. stainless steel / magnesium alloy) interface is sometimes used to conduct electrical signals and is not allowed to be insulated; or the interface is added with insulation isolation, which will lead to a significant reduction in the mechanical properties of the connection and is unacceptable; or the addition of such an insulating isolation layer makes the production cost too high to bear. Therefore, in engineering, it is often impossible to solve the above problems by simply isolating the direct electrical connection between the anode and the cathode.

[0039] Stray current corrosion is also a common form of metal damage in practical engineering. It has certain similarities with the above-mentioned galvanic corrosion. Its corrosion acceleration is also caused by an external electric field. The current leaving the corroded metal flows through the environmental medium in the form of ions, and finally returns to other parts of the corroded metal and enters the metal in the form of electrons, forming a closed current loop. The difference between it and galvanic corrosion is that the external potential field is not necessarily other metals or electronic conductors that are directly electrically connected to the corroded metal, but may be other electrical equipment that is not directly electrically connected to the corroded metal. The leakage current passes through the environmental medium and the corroded metal and returns to the electrical equipment; or the induced current generated by electromagnetic field induction flows through the corroded metal and the environmental medium. For example, the electricity used by trams on urban roads may leak through underground metal pipes and flow back to the trams; it is also possible that the current induced by the high-voltage transmission lines on the ground passes through the pipes and the environmental medium. Therefore, the corrosion system of stray current can be approximated as a system similar to a galvanic couple: the anode is the corroded metal; the cathode is an electronic conductor that is far away or even unknown, and the potential difference between it and the corroded metal depends on the strength of the stray source. The electronic current path of such a current loop of a stray current corrosion system is difficult to cut off, because as long as the corroded metal is still in contact with the environmental medium after cutting off, the leakage current of the electrical equipment or the induced current will still flow through the medium and the corroded metal.

[0040] Therefore, in order to suppress galvanic corrosion and stray current corrosion, engineering is more inclined to block or hinder the ion conduction path. Whether it is galvanic corrosion or stray current corrosion, its outflow location is relatively easy to determine based on the corrosion damage characteristics of the metal surface, but the location of the corresponding cathode or electronic conductor that receives the current is not obvious and difficult to determine, especially the inductive stray current is more difficult to determine because the environmental medium is interconnected. If you want to block the ion circuit of such stray current, it is best to choose to do it near the corroded metal where the ion current flows out.

[0041] At present, the most common practice is to directly coat the metal surface with a protective layer to isolate the anode / environment interface. However, sometimes the metal surface is too deep (such as the inner wall of the pipe) or too hidden (such as in the gap), making direct surface coating difficult; more often, the coating is damaged during the use of the component, causing corrosion damage to be severely aggravated at the damaged coating. Therefore, actual engineering and industrial applications are still in urgent need of other technologies that can effectively inhibit galvanic corrosion and stray current corrosion.

[0042] In order to solve the above problems, the present application adds an external loop current in the environmental medium (adds an external electric field to the ion conductive loop) to offset or block the galvanic current or stray current, thereby inhibiting the dissolution of the corrosive metal. Specifically, the present application sets an external cathode and anode in the environmental medium around the corrosive metal to be protected, and connects the cathode and the anode to an external power source through wires to form an external blocking current circuit, adjusts the external current of the blocking current circuit through the external power source, and monitors the anode current or potential of the corrosive metal at the same time until the measured anode current or potential meets the preset condition, wherein the preset condition is that the current direction of the external current is opposite to the current direction of the anode current, so that the anode current or potential meets a certain threshold, so that the anode current flowing through is reduced to zero, or even reversed to protect the corrosive metal.

[0043] It can be foreseen that the present application uses an impressed current (external current) instead of an insulator to block the corrosion current loop. The present application uses an external power source to regulate the current direction of the external current in the environmental medium surrounding the corroded metal to be opposite to the current direction of the original anode current (galvanic current or stray current) of the corroded metal, and makes the anode current or potential meet a certain threshold, thereby blocking the original galvanic current or stray current.

[0044] For this purpose, see Figure 1 , the embodiment of the present application provides a method for inhibiting metal galvanic corrosion and stray current corrosion, the method comprising:

[0045] S10, setting an additional cathode and an anode in the environmental medium around the corrosive metal to be protected, and connecting the additional cathode and the additional anode to an external power source through wires to form an additional blocking current circuit;

[0046] S20, adjusting the external current of the blocking current circuit by means of the external power supply, and monitoring the anode current or potential of the corroded metal at the same time, until the measured anode current or potential meets a preset condition.

[0047] Specifically, the preset condition is that the current direction of the external current is opposite to the current direction of the anode current, and the anode current or potential meets a certain threshold value, so that the anode current flowing through is reduced to zero, or even reversed to protect the corroded metal. The external current is a current applied by the external power source to block the anode current, and the external current applied by the external power source will pass through the external anode, the environmental medium, and finally flow back to the external power source from the external cathode. The external current mainly flows between the external cathode and the anode, which largely avoids the over-protection of the surrounding metal that does not need to be protected as the traditional cathodic protection current may do.

[0048] The size and direction of the external current can be controlled by an external power supply so that the direction of the external current in the environmental medium surrounding the corroded metal is opposite to the direction of the original anode current (galvanic current or stray current) of the corroded metal, thereby blocking the galvanic current or stray current.

[0049] To illustrate the above approach, see Figure 2 , which is a schematic diagram of the present embodiment. In the figure, the corroded metal originally has a dissolution current I g , through the interface of corroded metal (i.e. anode of galvanic pair) / environmental medium, through the environmental medium, through the interface of environmental medium / electronic conductor (where the electronic conductor is the cathode material of different corroded metals, or it can be other parts of corroded metals; it may be close to the corroded metal, or it may be far away, or it is unknown), to reach the electronic conductor (i.e. cathode of corrosion galvanic pair), and then flow back to the corroded metal (i.e. anode of corrosion galvanic pair) in the form of electronic conduction, forming a closed corrosion current loop. When the external blocking current circuit composed of the external anode, cathode, power supply (external power supply), and wire is added, the external current I provided by the power supply e It flows from the positive end of the power supply to the external anode and then splits into two paths: 1) Inner loop current I e i Through the ambient medium, it reaches the external cathode and returns to the negative end of the external power supply; 2) External loop current I e e The current passes through the environmental medium, reaches the corroded metal (i.e., the anode of the corrosion galvanic pair), flows to the electronic conductor (i.e., the cathode of the corrosion galvanic pair or the collector of stray current) in the form of electronic conduction, and passes through the electronic conductor (i.e., the cathode of the corrosion galvanic pair) / environmental medium interface, then flows through the environmental medium, passes through the environmental medium / external cathode interface, and enters the external cathode and I e i The external current I generated by the external blocking current circuit composed of the external anode, cathode, external power supply and wire is e e The original corrosion metal dissolution current I g The direction is opposite, so 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 Can be adjusted by external power supply, with external current I e increases with the increase of ge This is the principle that the dissolution of the corroded metal anode is blocked by the external blocking current. In actual operation, it is only necessary to adjust the external current I e Time Monitoring I g e , when I g e Just reach an acceptable level.

[0052] Optionally, in one embodiment, in the step of setting an additional cathode and anode in the environmental medium around the corroded metal to be protected, and connecting the cathode and the anode to an external power source through wires to form an external blocking current circuit, the cathode, the anode and the external power source do not contact the corroded metal or the electronic conductor that is directly electrically connected to the corroded metal, and the external current is not directly applied to the corroded metal through the wire. In other words, this embodiment is different from the traditional cathodic protection current. The traditional cathodic protection current, whether it is an external power source or flows out from the electronic circuit of the sacrificial anode, needs to be directly applied to the corroded metal through the connection of a wire. Since the external power source, cathode and anode of this embodiment are not directly electrically connected to the corroded metal, it greatly facilitates the application in actual engineering.

[0053] Optionally, in laboratory verification, the corroded metal and the electronic conductor can be completely insulated and isolated, and then short-circuited by 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 the preset conditions. The steps specifically include:

[0054] Providing a first ammeter, connecting the first ammeter between the corroded metal and the electronic conductor, and monitoring the anodic current of the corroded metal through the first ammeter;

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

[0056] In practical applications, the anodic current flowing through the corroded metal can only be inferred by measuring the potential of the corroded metal relative to the external anode or the potential 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, and the potential of the corroded metal relative to the anode is monitored by the anode until the measured potential meets the preset conditions, or a reference electrode is provided, the reference electrode is inserted into the environmental medium between the corroded metal and the anode, and the potential of the corroded metal is monitored by 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 corroded metal relative to the reference electrode meets the preset conditions.

[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, the cathode and the anode are both arranged at positions where the anode current (galvanic current or stray current) in the ambient medium is concentrated, and the distance between the cathode and the anode should be as large as possible.

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

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

[0061] Optionally, in one embodiment, the cathode and the anode are both chemically stable in the environmental medium, insoluble or difficult to dissolve, and have low polarization resistance, or have low oxygen evolution overpotential and low hydrogen evolution overpotential. Wherein, the anode in practical applications can be used but not limited to the anode used in the traditional impressed current cathodic protection system or the electrolysis water oxygen production system or the electrolysis water chlorine alkali system, such as stainless steel, titanium alloy, titanium-plated steel mesh, nickel-plated steel mesh, graphite, even platinum alloy, rare earth compound, high conductivity metal oxide, etc., or can be used but not limited to the commonly used traditional anode, such as stainless steel, titanium alloy, titanium-plated steel mesh, nickel-plated steel mesh, graphite, even platinum alloy, rare earth compound, high conductivity metal oxide, etc.

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

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

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

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

[0066] When the corroded metal cannot be directly electrically connected to the outside world, the anodic current of the corroded metal needs to be estimated by adding a double reference electrode between the corroded metal and the external anode. The closer the potential difference of the external double reference electrode is to 0, the better, indicating that the anodic dissolution of the corroded metal caused by the galvanic or stray current is more effectively suppressed; when the corroded metal cannot be directly electrically connected to the outside world, and it is impossible to add an external reference electrode between the corroded metal and the external anode, the anodic current of the corroded metal can be estimated by measuring the potential difference between the external anode and the cathode and the external current. The potential difference applied by the external power supply should be greater than the self-corrosion potential difference of the external 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 added.

[0067] When the corroded metal cannot be directly electrically connected to the outside world and there is no external electrode between the corroded metal and the external anode, although it is impossible to know how much current the external power supply needs to apply to completely suppress the galvanic corrosion or stray current corrosion of the corroded metal, it can be determined that the greater the external current applied, the better the suppression effect. The potential difference applied by the external power supply is preferably greater than 2V. When the self-corrosion potential difference between the external anode and the cathode is large, it may be possible to short-circuit the external cathode and the anode without the need for an external power supply.

[0068] In order to verify the principle of the present application, the inventors conducted three groups of experiments, which are: Experiment 1 is the blocking of copper-steel galvanic current in 3.5wt.% NaCl solution; Experiment 2 is the blocking of AM60 magnesium alloy-304 stainless steel galvanic current in 5wt.% NaCl salt spray (pH=3.5); Experiment 3 is the blocking of galvanic current of copper pipe-insulating section-carbon steel pipe filled with artificial seawater.

[0069] Experiment 1:

[0070] The engineering background of Experiment 1 is: in engineering applications, it is inevitable to have electrical connections between different metals. In order to study their galvanic corrosion, the different metals are often separated and exposed on the same surface in the laboratory, and then they are connected by wires and ammeters to measure the galvanic current between them. On this basis, this embodiment also adds the cathode and anode of the external blocking current circuit to the measurement surface.

[0071] The galvanic specimens of Experiment 1 are: one Φ1×1cm round rod-shaped QAL10-4-4 aluminum bronze specimen, two TA2 titanium wire specimens (a first titanium wire 43 and a second titanium wire 44), and one Q235 carbon steel specimen, all of which are connected to a wire 45, arranged in a straight line in sequence, and packaged in an 8×2×1.5cm epoxy resin, wherein the aluminum bronze 41 is 12mm away from the axis of the first titanium wire 43, the first titanium wire 43 is 15mm away from the axis of the second titanium wire 44, and the second titanium wire 44 is 12mm away from the axis of the carbon steel 42, see Figure 3 and Figure 4 Their cylindrical end faces are exposed on the bottom surface of the epoxy resin 46, which, after being smoothed by sandpaper, becomes the working surface of the galvanic specimen.

[0072] The experimental assembly of Experiment 1 is as follows: the working surface of the epoxy resin sealed galvanic sample is immersed horizontally downward in a 12×10×7 cm rectangular water tank 48 filled with 700 mL of 3.5 wt.% NaCl solution, and the working surface is 4 cm below the liquid surface of the first NaCl solution 47. The first titanium wire 43, the second titanium wire 44, the DC power supply 3, and the second ammeter 2 are connected in series in sequence through the wires connected to these cylindrical samples; the aluminum bronze 41 and the carbon steel 42 are respectively connected to the first ammeter 1, see Figure 3 and Figure 4 The reading of ammeter 1 represents the anodic current (galvanic current) of the corroded metal; the reading of ammeter 2 represents the external current of the external blocking current circuit.

[0073] The measurement steps of Experiment 1 are as follows: turn on the DC power supply 3, adjust the external current of the external current blocking circuit by adjusting the voltage of the DC power supply 3, wait for 2 minutes after each adjustment of the voltage of the DC power supply, read the current values ​​of the first ammeter 1 and the second ammeter 2, and continuously change the voltage and current of the DC power supply 3. Record the current values ​​of the first ammeter 1 and the second ammeter 2. The entire experiment is carried out in a laboratory with a room temperature of 27 degrees.

[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 or even reverses. This fully proves that the copper-steel galvanic current in 3.5wt.% NaCl solution can indeed be suppressed and blocked by the external current. Figure 5 .

[0075] Experiment 2:

[0076] The engineering background of Experiment 2 is: In engineering applications, magnesium alloys are often connected to other metals through bolts. All engineering metals have an accelerating effect on galvanic corrosion of magnesium alloys, especially steel. Therefore, this embodiment directly simulates the bolt connection between magnesium alloys and steel. For the convenience of current measurement, insulating bolts, nuts, and washers are used in this example. In addition, the current priority application of magnesium alloys is mainly in the atmospheric environment. In order to quickly obtain experimental results, the environmental simulation of this embodiment uses an extremely harsh salt spray test.

[0077] The galvanic sample of Experiment 2 is as follows: prepare a 5.5×3×0.5cm AM60 sheet magnesium alloy sample, drill a circular hole with a diameter of 8mm vertically in the center of the sample for standby use; prepare two Φ1mm TA2 titanium wires (the third titanium wire 53 and the fourth titanium wire 54), one end of each TA2 titanium wire is bent into a circular ring with a diameter of 16mm, and except for the TA2 titanium wire bent into the circular ring, the remaining TA2 titanium wires are covered with heat shrink tubes to avoid contact with environmental salt spray; then prepare 1 M8×20×2 304 stainless steel gasket, 1 M8×60 nylon hexagon screw (including nylon hexagon screw head 571 and nylon hexagon screw tail 572), 1 M8 nylon hexagon nut, and 3 M8×16×1.4 insulating flat washers 55. Put the prepared stainless steel gasket 52, insulating flat gasket 55, the third titanium wire 53 of the ring, insulating flat gasket 55, the fourth titanium wire 54 of the ring, insulating flat gasket 55, and magnesium alloy 51 on the nylon hexagon screw in sequence, and finally use the nylon hexagon nut 56 to tighten from the nylon hexagon screw tail 572 to the nylon hexagon screw head 571, and fix these materials put on the nylon hexagon screw in sequence tightly, among which the outer surface of the ring of the third titanium wire 53 and the fourth titanium wire 54 is aligned with the outer diameter of the insulating flat gasket 55, and the stainless steel gasket 52 and magnesium alloy 51 are respectively connected to the wire, and the joints are sealed with silicone. Such a multilayer structure will be used as a galvanic specimen, refer to Figure 6 .

[0078] The experimental assembly of Experiment 2 is as follows: the prepared galvanic sample is placed on the V-groove of the salt spray test box 58, the stainless steel gasket 52 in the sample is located at the upper end, the angle between the axis of the nylon hexagon screw and the horizontal plane is set to 45°, the third titanium wire 53 in the galvanic sample in the salt spray test box 58, the DC power supply 3 outside the salt spray test box, the first ammeter 1, and the fourth titanium wire 54 in the galvanic sample in the box are connected in series through wires, wherein the third titanium wire 53 is connected to the negative end of the DC power supply, and the fourth titanium wire 54 is connected to the positive end of the DC power supply; the second ammeter 2 outside the salt spray test box is connected to the stainless steel gasket 52 and the magnesium alloy 51 in the galvanic sample in the salt spray test box through wires. In this way, the reading of ammeter 1 represents the external current of the external blocking current circuit; the reading of ammeter 2 represents the anode current (galvanic current) of the corroded metal. The solution used in the salt spray test is a 5 wt. % second NaCl solution 59 with a pH of 3.5 (the pH is adjusted using dilute hydrochloric acid), and the salt spray test temperature is 35° C.

[0079] The measurement steps of Experiment 2 are as follows: first, let the salt spray test chamber 58 run for 12 hours to stabilize the temperature, humidity, salinity and galvanic current in the chamber, turn on the DC power supply 3, and adjust the outflow by adjusting the voltage of the DC power supply 3. After each adjustment for 2 minutes, the external current on the external blocking current circuit and the anode current (galvanic current) on the magnesium alloy-stainless steel galvanic circuit are measured by the first ammeter 1 and the second ammeter 2 respectively.

[0080] The measurement results of Experiment 2 are: Figure 7 Under salt spray conditions, the magnesium alloy-stainless steel galvanic current is very sensitive to the external current of the applied blocking current circuit, further proving that the external current blocking technology can even effectively block the extremely active galvanic corrosion formed by magnesium alloy and stainless steel in extremely harsh salt spray environments. This result is of great significance because galvanic corrosion is currently one of the main obstacles to the engineering application of magnesium alloys.

[0081] Experiment 3:

[0082] The engineering background of Experiment 3 is: surface ships, underwater submarines, offshore platforms, etc., all have pipes made of various metals, and highly corrosive seawater flows through them. In addition to the ion current loop formed by the flowing seawater, there are many other electronic connection channels between these different metal pipes. If only insulating sections are added between different metal pipes, only the resistance of the ion loop is increased, and the electronic loop cannot be blocked, and the suppression of their galvanic corrosion is very limited. Therefore, this example uses an external current blocking technology to completely suppress the galvanic corrosion of the pipeline on the basis of adding insulating sections.

[0083] The electric couple specimens of Experiment 3 are: prepare one QAL10-4-4 aluminum bronze tube, one PP insulation tube, and one Q235 carbon steel tube with flanges of 14 cm outer diameter welded at both ends, a total length of 1 m, and an inner diameter of 3 cm. They are arranged in series, and flange gaskets 9 are inserted between their flanges, and they are fixed by bolts through their flanges. At the same time, prepare two 0.5 m long Φ1 mm TA2 titanium wires (the fifth titanium wire 63 and the sixth titanium wire 64), and bend one end of each titanium wire into a spring-shaped ring with a diameter of 29 mm and 5 turns. Except for the ring part, the remaining titanium wire is covered with a heat shrink tube to insulate it from the ambient medium. The ring of the fifth titanium wire 63 is placed at the mouth of the PP insulating tube 65 near the end of the aluminum bronze tube 61, and the tail end of the fifth titanium wire 63 passes through the flange sealing gasket 66 between the aluminum bronze tube 61 and the PP insulating tube 65. The fifth titanium wire 63 has no direct electrical contact with the aluminum bronze tube 61; the ring of the sixth titanium wire 64 is placed at the mouth of the PP insulating tube 65 near the end of the carbon steel tube 62, and the tail end of the sixth titanium wire 64 passes through the flange sealing gasket 66 between the carbon steel tube 62 and the PP insulating tube 65. Note that the sixth titanium wire 64 has no direct electrical contact with the carbon steel tube 62. The outer mouths of the aluminum bronze tube 61 and the outer mouths of the carbon steel tube 62 are sealed with insulating flange covers 67 respectively. Before the last insulating flange cover 67 is sealed, fill the three pipes connected in series and completely connected with artificial seawater (ASTM D1141-98). For the entire pipeline galvanic specimen, refer to Figure 1 .

[0084] The experimental assembly of Experiment 3 is as follows: the fifth titanium wire 63, the sixth titanium wire 64, the DC power supply 3 and the second ammeter 2 are connected in series in sequence, wherein 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 of the DC power supply; the aluminum bronze tube 61 and the carbon steel tube 62 are connected to the first ammeter 1 with wires. In this way, the reading of the first ammeter 1 represents the galvanic current of the corroded pipeline, and the reading of the second ammeter 2 represents the external current of the external blocking current circuit, see Figure 8 .

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

[0086] The results of the samples in Experiment 3 are: Fig. 9, the galvanic current of the carbon steel pipe-aluminum bronze pipe filled with artificial seawater and with an insulating section almost decreases with the increase of the external current until it disappears. When the external current is 0, although there is an insulating section of 1m between the carbon steel pipe and the aluminum bronze pipe to separate the galvanic pipes, it is far from enough to inhibit their galvanic corrosion, and the galvanic current is as high as more than 800μA. If an external blocking current is added on this basis, the galvanic corrosion can be effectively inhibited. This result once again proves the effectiveness of external current blocking technology in seawater pipeline applications.

[0087] In summary, the present application provides a method for inhibiting metal galvanic corrosion and stray current corrosion, the method comprising: setting an external cathode and anode in the environmental medium surrounding the corroded metal to be protected, and connecting the cathode and the anode to an external power source through wires to form an external blocking current circuit, adjusting the external current of the blocking current circuit by the external power source, and monitoring the anode current or potential of the corroded metal until the measured anode current or potential meets a preset condition, wherein the preset condition is that the current direction of the external current is opposite to the current direction of the anode current, so that the anode current or potential meets a certain threshold value, so that the anode current flowing through is reduced to zero, or even reversed to protect the corroded metal. It can be foreseen that the present application uses an impressed current (external current) instead of an insulator to block the corrosion current loop. The present application regulates the direction of the external current in the environmental medium surrounding the corroded metal through an external power source, so that the current direction is opposite to the original anode current (galvanic current or stray current) of the corroded metal, prompting the anode current or potential to meet a certain threshold, reducing the anode current flowing through to zero, or even reversing it to protect the corroded metal, thereby blocking the original galvanic current or stray current.

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

Claims

1. A method for inhibiting metal galvanic corrosion and stray current corrosion, characterized in that: include: An external cathode and an anode are arranged in the environmental medium around the corrosive metal to be protected, and the external cathode and the anode are respectively connected to an external power source through wires to form an external blocking current circuit; The external current of the blocking current circuit is regulated by the external power supply, and the anode current or potential of the corroded metal is monitored at the same time until the measured anode current or potential meets a preset condition, wherein the preset condition is that the current direction of the external current is opposite to the current direction of the anode current, so that the anode current or potential meets a certain threshold value, and the anode current flowing therethrough is reduced to zero, or even reversed to protect the corroded metal.

2. The method for inhibiting metal galvanic corrosion and stray current corrosion according to claim 1, characterized in that: The step of regulating the external current of the blocking current circuit by the external power supply and monitoring the anode current or potential of the corroded metal until the measured anode current or potential meets the preset condition specifically includes: The external current of the blocking current circuit is adjusted by the external power supply, and the potential of the corroded metal relative to the anode is monitored by the anode until the measured potential meets the preset condition.

3. The method for inhibiting metal galvanic corrosion and stray current corrosion according to claim 1, characterized in that: The step of regulating the external current of the blocking current circuit by the external power supply and monitoring the anode current or potential of the corroded metal until the measured anode current or potential meets the preset condition specifically includes: Providing a reference electrode, inserting the reference electrode into the environmental medium between the corroded metal and the anode, and monitoring the potential of the corroded metal through the reference electrode; The external current of the blocking current circuit is adjusted by the external power supply until the measured potential of the corroded metal relative to the reference electrode meets a preset condition.

4. The method for inhibiting metal galvanic corrosion and stray current corrosion according to claim 1, characterized in that: In the step of setting an additional cathode and anode in the environmental medium around the corrosive metal to be protected, and connecting the additional cathode and anode to an external power source through wires to form an external blocking current circuit, the cathode and anode do not contact the corrosive metal or the electronic conductor that is directly electrically connected to the corrosive metal.

5. The method for inhibiting metal galvanic corrosion and stray current corrosion according to claim 1, characterized in that: In the step of setting an additional cathode and anode in the environmental medium around the corrosive metal to be protected, and connecting the additional 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.

6. The method for inhibiting metal galvanic corrosion and stray current corrosion according to claim 1, characterized in that: In the step of setting an additional cathode and anode in the environmental medium around the corrosive metal to be protected, and connecting the additional cathode and anode to an external power source through wires to form an external blocking current circuit, the cathode and the anode are both set at the position where the anode current distribution is concentrated in the environmental medium.

7. The method for inhibiting metal galvanic corrosion and stray current corrosion according to claim 1, characterized in that: In the step of setting an additional cathode and anode in the environmental medium around the corrosive metal to be protected, and connecting the additional 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 parallel to the surface of the corrosive metal.

8. The method for inhibiting metal galvanic corrosion and stray current corrosion according to claim 1, characterized in that: In the step of setting an additional cathode and anode in the environmental medium around the corrosive metal to be protected, and connecting the additional 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 not less than 0.1% of the surface area of ​​the corrosive metal.

9. The method for inhibiting metal galvanic corrosion and stray current corrosion according to claim 1, characterized in that: In the step of regulating the external current of the blocking current circuit by the external power supply and monitoring the anode current or potential of the corroded metal until the measured anode current or potential meets a preset condition, the potential difference applied by the external power supply is greater than 2V.

10. The method for inhibiting metal galvanic corrosion and stray current corrosion according to claim 1, characterized in that: In the step of setting an external cathode and anode in the environmental medium around 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 current blocking circuit, the external power source is a DC power source, and the external power source can control the output potential, current or power constantly or variably.

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