Cathodic protection method for metal structures and cathodic protection metal structures

Abstract

To provide an electrical protection method for a metallic structure which facilitates construction and with which a large amount of sacrificial anodes can be bonded to the metallic structure.SOLUTION: A metallic structure 2 is subjected to electrical protection by joining, to the metallic structure 2, a clad material 3 in which a first metal material 3a joinable to the metallic structure 2 and a second metal material 3b serving as a sacrificial anode with respect to the metallic structure 2 are joined together.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for electrochemically protecting a metal structure and an electrochemically protected metal structure.

Background Art

[0002] To transport various fluids such as oil, gas, and water, pipelines are buried underground. Steel pipes such as carbon steel pipes and stainless steel pipes are often used for pipelines. If steel pipes are left for a long time as they are, they will corrode and become unusable. Therefore, it is necessary to protect steel pipes from corrosion. The same applies to steel structures such as offshore steel structures and steel sheet piles.

[0003] As a method for protecting such metal structures from corrosion, a method of applying paint or coating to the metal structure and electrochemically protecting the metal structure is known. Electrochemical protection is a corrosion protection method that prevents ionized metal from flowing out from a defect part into the soil or the like, which is an electrolyte, in the unlikely event that a defect part occurs in the metal structure. That is, against the corrosion current that tries to flow out from the metal structure to the electrolyte, a current sufficient to overcome this is made to flow into the metal structure from the outside, thereby preventing the metal structure from corroding.

[0004] There are two types of electrochemical protection methods: the external power source method and the galvanic anode method. The external power source method is a method of flowing a corrosion protection current into a metal structure from a DC power supply device through an auxiliary anode. The galvanic anode method utilizes the ionization tendency of metals. A metal (such as Zn, Al, Mg, etc.) with a greater ionization tendency than the metal structure is electrically connected to the metal structure. Instead of the metal structure being ionized, the metal with a greater ionization tendency is ionized to prevent the corrosion of the metal structure. That is, a battery is formed with the metal structure to be protected as the cathode and a metal with a greater ionization tendency than the metal structure as the sacrificial anode, and a corrosion protection current is made to flow into the metal structure due to the potential difference between the two electrodes.

[0005] As a galvanic anode type cathodic protection method, Patent Document 1 discloses a method in which a sacrificial anode made of Zn, Al, Mg, etc. is installed isolated from the steel pipe, and the sacrificial anode and the steel pipe are connected by an electric wire. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 60-36680 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, conventional cathodic protection methods have the drawback of being time-consuming to connect the wires to the steel pipes. Furthermore, if the number of sacrificial anodes that can be installed is limited due to the installation environment, the sacrificial anodes may be consumed prematurely, making it impossible to continuously supply corrosion protection current to the metal structure over a long period.

[0008] This invention has been made in view of the above problems, and aims to provide a method for cathodic protection of metal structures and a cathodic protection metal structure that is easy to implement and can bond a large amount of sacrificial anode to the metal structure. [Means for solving the problem]

[0009] To solve the above problems, one aspect of the present invention provides a first metal material that can be joined to a metal structure and a second metal material that serves as a sacrificial anode for the metal structure. Metallized interface This is a method for electrochemical corrosion protection of a metal structure, which involves joining a clad material to the metal structure and then electrochemically protecting the metal structure from corrosion.

[0010] Another aspect of the present invention provides a first metal material that can be joined to a metal structure and a second metal material that serves as a sacrificial anode to the metal structure. Metallized interface This is an electrochemically protected metal structure in which joined clad materials are joined to the aforementioned metal structure. [Effects of the Invention]

[0011] According to the present invention, since the metal structure can be protected from cathodic corrosion by joining a cladding material to it, the application of cathodic protection is easy. Furthermore, since a large amount of sacrificial anode can be joined to the metal structure, a corrosion-preventive current can be supplied to the metal structure over a long period of time. [Brief explanation of the drawing]

[0012] [Figure 1] This is a cross-sectional view along the pipe axis of a cathodic protection metal structure (cathodic protection coated steel pipe) according to the first embodiment of the present invention. [Figure 2] This is a cross-sectional view along the pipe axis of a cathodic protection metal structure (catechodic protection coated steel pipe) according to a second embodiment of the present invention (Figure 2(a) shows the state before joining the cathodic protection coated steel pipe and the coated steel pipe, and Figure 2(b) shows the state after joining). [Figure 3] This figure shows a steel pipe coated with cathodic protection coating as viewed from the axial direction of the pipe (Figure 3(a) shows a ring-shaped cladding material, Figure 3(b) shows an arc-shaped cladding material, and Figure 3(c) shows an I-shaped cladding material). [Figure 4] This is a schematic diagram of a third embodiment of the present invention, a cathodic protection metal structure (catenically protection marine steel structure). [Modes for carrying out the invention]

[0013] Hereinafter, with reference to the attached drawings, embodiments of the present invention regarding a method for cathodic protection of metal structures and a cathodic-protected metal structure will be described. However, the method for cathodic protection of metal structures and the cathodic-protected metal structure of the present invention can be embodied in various forms and are not limited to the embodiments described herein. These embodiments are provided with the intention that those skilled in the art will be able to fully understand the invention by making full disclosures in the specification. (First Embodiment)

[0014] Figure 1 shows a cross-sectional view along the pipe axis of a cathodic protection metal structure (catechodic protection coated steel pipe 1,1) according to the first embodiment of the present invention. The cathodic protection coated steel pipe 1,1 of this embodiment is installed in the ground by the open-cut method and used as a pipeline for transporting various fluids such as water, gas, and oil. The cathodic protection coated steel pipe 1 comprises a steel pipe 2, a cladding material 3, and a coating 5. The steel pipe 2 is pre-coated with the coating 5 at the factory. The cladding material 3 is welded to the outer surface of the bare portion 2a of the steel pipe 2 that is not coated with the coating 5. The cladding material 3 may be welded to the outer surface of the bare portion 2a at the factory beforehand, or it may be welded to the outer surface of the bare portion 2a at the site of the open-cut method.

[0015] The steel pipe 2 is made of a metal primarily composed of iron, and can be carbon steel pipe, stainless steel pipe, alloy steel pipe, etc. The coating 5 is made of polyethylene, polyurethane, polypropylene, asphalt, or epoxy resin. At the end of the steel pipe 2, a bare section 2a is formed where the coating 5 is not applied.

[0016] The clad material 3 comprises a first metal material 3a that can be joined to the bare portion 2a of the steel pipe 2, and a second metal material 3b that acts as a sacrificial anode for the steel pipe 2. The first metal material 3a and the second metal material 3b of the clad material 3 are joined by methods such as explosive bonding and rolling bonding. The interface between the first metal material 3a and the second metal material 3b of the clad material 3 is joined metallographically. The first metal material 3a is positioned on the inner circumference side, and the second metal material 3b is positioned on the outer circumference side.

[0017] The first metal material 3a of the clad material 3 is welded to the outer surface of the bare portion 2a of the steel pipe 2 by fillet welding or the like. The shape of the clad material 3 in a view along the pipe axis may be a ring shape extending around the entire circumference of the outer surface of the steel pipe 2, or an arc shape following a part of the outer surface of the steel pipe 2. The clad material 3 may also be joined to the bare portion 2a of the steel pipe 2 using joining means such as bolts and nuts, screws, or adhesives.

[0018] The material of the first metal material 3a needs to be a metal with a smaller ionization tendency than the second metal material 3b. Also, depending on the use of the electrically corrosion-resistant coated steel pipe 1, it is desirable that the material of the steel pipe 2 is the same type so as not to cause welding defects. For example, when the steel pipe 2 is carbon steel, it is desirable that the first metal material 3a is also carbon steel. When the steel pipe 2 is stainless steel, it is desirable that the first metal material 3a is also stainless steel.

[0019] The second metal material 3b of the clad material 3 is a metal that is more likely to ionize than the steel pipe 2 (in other words, a base metal compared to the steel pipe 2). For example, when the steel pipe 2 is carbon steel, the second metal material 3b is Mg, Mg alloy, Al, Al alloy, Zn, Zn alloy, etc. When the steel pipe 2 is stainless steel, the second metal material 3b is Mg, Mg alloy, Al, Al alloy, Zn, Zn alloy, Fe, Fe alloy, etc.

[0020] The steel pipes 2, 2 of the electrically corrosion-resistant coated steel pipes 1, 1 are joined by welding, friction stir welding, etc. The symbol 4 is the weld metal. After joining the steel pipes 2, 2 together, backfilling is performed, and the electrically corrosion-resistant coated steel pipes 1, 1 are buried in the ground. The operation and effects of the electrical corrosion prevention method of this embodiment will be described below.

[0021] When the electrically corrosion-resistant coated steel pipes 1, 1 are buried in the ground, which is an electrolyte, instead of the steel pipe 2 ionizing (corroding), the second metal material 3b, which has a greater ionization tendency than the steel pipe 2, ionizes. Since the second metal material 3b is electrically connected to the first metal material 3a and the first metal material 3a is electrically connected to the steel pipe 2, due to the potential difference between the second metal material 3b and the steel pipe 2, a corrosion prevention current flows from the second metal material 3b into the steel pipe 2. Therefore, the steel pipe 2 can be electrically corrosion-protected.

[0022] Since the first metal material 3a of the clad material 3 is welded to the steel pipe 2, even if the second metal material 3b of the clad material 3 is consumed, the clad material 3 can maintain the state of being joined to the steel pipe 2.

[0023] Since the steel pipe 2 is mainly composed of iron and the first metal material 3a of the clad material 3 is mainly composed of iron, it is possible to prevent the occurrence of welding defects. (Second Embodiment)

[0024] Figure 2 shows a cross-sectional view along the pipe axis of a cathodic protection metal structure (catechodic protection coated steel pipe 11 and coated steel pipe 20) according to a second embodiment of the present invention. Figure 2(a) shows the state before joining the cathodic protection coated steel pipe 11 and the coated steel pipe 20, and Figure 2(b) shows the state after joining.

[0025] In pipelines used to transport various fluids such as water, gas, and oil, one method for replacing existing pipelines is pipe-in-pipe. Pipe-in-pipe is a construction method in which a new pipeline (cathodic protection coated steel pipe 11 and coated steel pipe 20) is laid inside the existing outer pipe 14. The outer pipe 14 may be made of steel, stainless steel, cast iron, or concrete. The outer pipe 14 may or may not have its outer surface painted or coated.

[0026] Reference numeral 20 in Figure 2(a) denotes a coated steel pipe in the process of being laid or a coated steel pipe that has been laid. The coated steel pipe 20 comprises a steel pipe 15 and a coated covering 16. Reference numeral 17 denotes a piping smoother for facilitating the pulling-in of the coated steel pipe 20.

[0027] The cathodic protection coated steel pipe 11 comprises a steel pipe 12, a cladding material 13 welded to the bare outer surface 12a of the steel pipe 12, and a coating 18. The cladding material 13 comprises a first metal material 13a that can be joined to the steel pipe 12 and a second metal material 13b that acts as a sacrificial anode for the steel pipe 12. The configuration of the cladding material 13 is the same as that of the cladding material 3 of the cathodic protection coated steel pipe 1 of the first embodiment. The cladding material 13 is positioned at the end of the steel pipe 12 and protrudes from the end of the steel pipe 12 in the direction of the pipe axis.

[0028] Figures 3(a) to 3(c) show the electrochemically protected coated steel pipe 11 viewed from the direction of the pipe axis. As shown in Figure 3(a), the cladding material 13 in the view along the pipe axis may be in the shape of a ring extending around the entire circumference of the outer surface of the steel pipe 12, as shown in Figure 3(b), it may be in the shape of an arc along a part of the outer surface of the steel pipe 12, or it may be in the shape of an I, as shown in Figure 3(c).

[0029] It is desirable that the cladding material 13 be equally distributed around the steel pipe 12. As shown in Figure 3(a), if there is one cladding material 13, a ring-shaped cladding material 13 is placed around the entire outer surface of the steel pipe 12. As shown in Figure 3(b), if there are two cladding materials 13, they are placed above and below the steel pipe 12, or on the left and right sides. As shown in Figure 3(c), if there are four cladding materials 13, they are placed above, below, to the left and right of the steel pipe 12, or arranged to cross diagonally. Note that the number of cladding materials 13 is not limited to the above, and there may be three or six or more, for example.

[0030] As shown in Figures 2(a) to 2(b), when the electrochemically protected coated steel pipe 11 having the clad material 13 is pushed into the coated steel pipe 20, the clad material 13 aligns the steel pipes 12 and 15 with each other.

[0031] After aligning the steel pipes 12 and 15, they are joined together from the inner side by welding, friction stir welding, or the like. Reference numeral 19 denotes the weld metal.

[0032] After joining the steel pipes 12 and 15 together, the space between the outer pipe 14 and the electrochemically protected coated steel pipe 11 and coated steel pipe 20 is filled with a filler material that is an electrolyte such as mortar, air mortar, or water. The operation and effects of the cathodic protection method of this embodiment will be explained below.

[0033] If the space between the outer tube 14 and the cathodic protection coated steel tubes 11 and 20 is filled with an electrolyte filler, the second metal material 13b, which has a greater ionization tendency than the steel tubes 12 and 15, will ionize instead of the steel tubes 12 and 15 ionizing (corrosing). As a result, a corrosion protection current flows from the second metal material 13b to the steel tubes 12 and 15, thereby providing cathodic protection for the steel tubes 12 and 15.

[0034] If the outer pipe 14 has electrical insulation properties due to coating or painting, even if cathodic protection equipment is installed on the outside of the outer pipe 14, it is not possible to allow a corrosion-preventive current to flow into the steel pipes 12 and 15 inside the outer pipe 14. According to the cathodic protection method of this embodiment, even if the outer pipe 14 has electrical insulation properties, the cladding material 13 can allow a corrosion-preventive current to flow into the steel pipes 12 and 15.

[0035] On the other hand, if the outer pipe 14 does not have electrical insulation properties (in other words, if the outer pipe 14 is an unprotected steel pipe, cast iron pipe, concrete pipe, etc.), a corrosion-preventive current can be passed from an electrochemical corrosion protection device installed on the outside of the outer pipe 14 to the steel pipes 12 and 15 inside the outer pipe 14. However, since the inner surface of the outer pipe 14 thins in proportion to the magnitude of the corrosion-preventive current, there is a concern that the strength of the electrochemical corrosion-preventive coated steel pipes 11 and 20, based on a strength design that uses the outer pipe 14 as a protective pipe, may be insufficient. According to the electrochemical corrosion protection method of this embodiment, the corrosion-preventive current is introduced into the steel pipes 12 and 15 by the cladding material 13, so this concern can be eliminated.

[0036] Furthermore, when constructing a pipe-in-pipe system, the sizes of the cathodic protection coated steel pipes 11 and 20 are often made closer to the size of the outer pipe 14 in order to improve the flow performance of the cathodic protection coated steel pipes 11 and 20. In this case, it becomes difficult to paint the bare parts 12a and 15a of the steel pipes 12 and 15, or to cover the bare parts 12a and 15a with heat-shrinkable tubing. According to the cathodic protection method of this embodiment, since the cladding material 13 allows a corrosion protection current to flow into the bare parts 12a and 15a of the steel pipes 12 and 15, the risk of corrosion of the bare parts 12a and 15a can be reduced even if the bare parts 12a and 15a of the steel pipes 12 and 15 cannot be covered with paint.

[0037] Since the steel pipes 12 and 15 of the cathodic protection coated steel pipe 11 and the coated steel pipe 20 are joined from the inner side, the steel pipes 12 and 15 can be joined even if the gap between the outer pipe 14 and the cathodic protection coated steel pipe 11 and the coated steel pipe 20 is small. In addition, the thermal influence on the second metal material 13b on the outer circumference of the cladding material 13 can be reduced.

[0038] Since the clad material 13 is placed at the end of the steel pipe 12, the clad material 13 can be given a centering function.

[0039] Since the cladding material 13 is evenly distributed around the steel pipe 12, the steel pipe 12 can be uniformly protected from cathodic corrosion in the circumferential direction. (Third embodiment)

[0040] Figure 4 shows a third embodiment of the present invention, an electrochemically protected metal structure (electrochemically protected marine steel structure). The electrochemically protected marine steel structure comprises a marine steel structure 21 and a cladding material 23. Reference numeral 22 denotes seawater.

[0041] The cladding material 23 comprises a first metal material 23a and a second metal material 23b. The offshore steel structure 21 is a metal mainly composed of iron, such as carbon steel, stainless steel, or alloy steel. The first metal material 23a of the cladding material 23 is a metal mainly composed of iron, such as carbon steel, stainless steel, or alloy steel. The first metal material 23a of the cladding material 23 is welded to the offshore steel structure 21. The second metal material 23b of the cladding material 23 is a metal that is more easily ionized than the offshore steel structure 21, such as Mg, Mg alloy, Al, Al alloy, Zn, or Zn alloy.

[0042] When the offshore steel structure 21 is placed in seawater 22, which is the electrolyte, the second metal material 23b of the cladding material 23, which has a greater tendency to ionize than the offshore steel structure 21, ionizes instead of the offshore steel structure 21 ionizing (corroding). As a result, a corrosion-preventive current flows from the second metal material 23b of the cladding material 23 to the offshore steel structure 21, thus protecting the offshore steel structure 21 from corrosion. The same applies to steel structures installed in rivers and other bodies of water. [Explanation of Symbols]

[0043] 1.11... Cathodic protection coated steel pipes (catechodic protection metal structures) 2,12,15…Steel pipe (metal structure) 3,13…Clad material 3a, 13a...first metal material 3b,13b…Second metal material 14...Outer tube 21…Marine steel structures (metal structures) 23…Clad material 23a...first metal material 23b…Second metal material

Claims

1. A method for electrochemical corrosion protection of a metal structure, comprising joining a clad material to a metal structure, wherein a first metal material that can be joined to the metal structure and a second metal material that acts as a sacrificial anode to the metal structure are joined at the interface in a metallographic manner, and thereby electrochemically protecting the metal structure.

2. The method for cathodic protection of a metal structure according to claim 1, characterized in that the first metal material of the cladding material is welded to the metal structure.

3. The aforementioned metal structure is made of a metal whose main component is iron. The method for cathodic protection of a metal structure according to claim 1 or 2, characterized in that the first metal material is a metal mainly composed of iron.

4. A clad material is formed by joining a first metal material that can be joined to a steel pipe and a second metal material that acts as a sacrificial anode to the steel pipe, and this clad material is joined to the outer surface of the steel pipe, thereby providing cathodic protection to the steel pipe. A method for electrochemical corrosion protection of a metal structure, wherein the cladding material is in the shape of a ring extending around the entire circumference of the outer surface of the cylindrical steel pipe, or in the shape of an arc or I along a part of the outer surface of the cylindrical steel pipe.

5. A clad material is formed by joining a first metal material that can be joined to a steel pipe and a second metal material that acts as a sacrificial anode to the steel pipe, and this clad material is joined to the outer surface of the steel pipe, thereby providing cathodic protection to the steel pipe. A method for cathodic protection of a metal structure, wherein the cladding material is placed at the end of the steel pipe, and the cladding material is used to center the steel pipes.

6. A clad material is formed by joining a first metal material that can be joined to a steel pipe and a second metal material that acts as a sacrificial anode to the steel pipe, and this clad material is joined to the outer surface of the steel pipe, thereby providing cathodic protection to the steel pipe. A method for cathodic protection of a metal structure, comprising inserting the steel pipes to which the cladding material is joined into an outer pipe, joining the steel pipes together, and filling the space between the outer pipe and the steel pipes with an electrolyte.

7. The method for cathodic protection of a metal structure according to claim 6, characterized in that the steel pipes are joined together from the inner side.

8. The method for cathodic protection of a metal structure according to claim 4, characterized in that the cladding material is equally distributed around the steel pipe in the circumferential direction.

9. A metal structure for cathodic protection, in which a clad material is formed by joining a first metal material, which can be joined to a metal structure, and a second metal material, which acts as a sacrificial anode for the metal structure, at the interface between them in a metallographic manner, and then joining the clad material to the metal structure.

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