Sacrificial anode assembly

Abstract

A sacrificial anode assembly for cathodically protecting and/or passivating a metal section, comprising: (a) a cell, which has an anode and a cathode arranged so as to not be in electronic contact with each other but so as to be in ionic contact with each other such that current can flow between the anode and the cathode; (b) a connector attached to the anode of the cell for electrically connecting the anode to the metal section to be cathodically protected; and (c) a sacrificial anode electrically connected in series with the cathode of the cell; wherein the cell is otherwise isolated from the environment such that current can only flow into and out of the cell via the sacrificial anode and the connector. The invention also provides a method of cathodically protecting metal in which such a sacrificial anode assembly is cathodically attached to the metal via the connector of the assembly, and a reinforced concrete structure wherein some or all of the reinforcement is cathodically protected by such a method.A sacrificial anode assembly for cathodically protecting and/or passivating a metal section, includes a cell with an anode and a cathode, a connector attached to the anode of the cell for electrically connecting the anode to the metal section to be cathodically protected; and a sacrificial anode electrically connected in series with the cathode of the cell. The cell is otherwise isolated from the environment such that current can only flow into and out of the cell via the sacrificial anode and the connector. A method of cathodically protecting steel in concrete in which such the sacrificial anode assembly is connected to the steel in an initial step of passivation using a higher current and when the first step is terminated the sacrificial anode alone continues to provide protection.

The invention claimed is: 
     
       1. A sacrificial anode assembly for cathodically protecting and/or passivating a metal section, comprising:
 a cell, which has an anode and a cathode arranged so as to not be in electronic contact with each other but so as to be in ionic contact with each other such that current can flow between the anode and the cathode; 
 a connector attached to the anode of the cell for electrically connecting the anode to the metal section to be cathodically protected; 
 and a sacrificial anode electrically connected in series with the cathode of the cell; 
 wherein there are provided one or more isolating elements which prevent communication of ionic current from the cell to the environment such that current can only flow between the cathode of the cell and the sacrificial anode and between the anode of the cell and the connector; 
 and wherein the sacrificial anode and the cell are connected together so as to form a single unit such that the sacrificial anode is electrically connected in series with the cathode of the cell. 
 
     
     
       2. An assembly according to  claim 1 , wherein the sacrificial anode is of a shape and size corresponding with the shape of at least part of the cell, such that it fits alongside at least part of the cell. 
     
     
       3. An assembly according to  claim 1 , wherein the sacrificial anode forms a container within which the cell is at least partly located. 
     
     
       4. An assembly according to  claim 1 , wherein the sacrificial anode is indirectly connected to the cathode of the cell through an electronically conductive separator. 
     
     
       5. An assembly according to  claim 4 , wherein a layer of a metal is located between the sacrificial anode and the cathode of the cell so as to allow electronic conduction between these components but to prevent direct contact between these components. 
     
     
       6. An assembly according to  claim 1 , wherein the sacrificial anode is zinc, aluminum, cadmium or magnesium, or an alloy of one or more of these metals. 
     
     
       7. An assembly according to  claim 1 , wherein the cell is provided with a porous separator located between the cathode and the anode, which prevents direct contact between the anode and the cathode. 
     
     
       8. An assembly according to  claim 1 , wherein the sacrificial anode forms a container and the cell is located at least partly in the container. 
     
     
       9. An assembly according to  claim 8  wherein the sacrificial anode is in the shape of a generally cylindrical can and the cell is at least partly located in this can. 
     
     
       10. An assembly according to  claim 1  which is at least partly surrounded by an encapsulating material. 
     
     
       11. An assembly according to  claim 10  wherein the encapsulating material is a porous matrix. 
     
     
       12. An assembly according to  claim 11  wherein the porous matrix comprises a cementitious mortar. 
     
     
       13. An assembly according to  claim 12  wherein the porous matrix comprises a mortar having a pH greater than 12. 
     
     
       14. An assembly according to  claim 10  wherein the encapsulating material contains at least one activator to ensure continued corrosion of the sacrificial anode. 
     
     
       15. An assembly according to  claim 14  wherein the activator comprises a humectant. 
     
     
       16. A method of cathodically protecting a metal section steel in an ionically conductive concrete or mortar covering material comprising:
 providing a sacrificial anode; 
 generating a voltage between two connections of a power supply such that current can flow between the negative connection and the positive connection; 
 in a first protection step, electrically connecting one of the connections of the power supply to the metal section steel to be cathodically protected and electrically connecting the sacrificial anode in series with the other connection of the power supply such that the voltage generated by the power supply is added to the voltage generated between the sacrificial anode and the metal steel to produce a voltage greater than the galvanic voltage generated between the sacrificial anode and the metal section steel alone; 
 wherein the power supply is otherwise isolated from the environment such that current can only flow into and out of the power supply via the sacrificial anode and the connector; 
 and, in a second protection step, the voltage generated by the power supply is no longer present and a current flows between the sacrificial anode and the metal steel to continue protecting and/or passivating the metal section steel, where the current is generated solely by the galvanic voltage between the sacrificial anode and the metal steel. 
 
     
     
       17. The method according to  claim 16  wherein the sacrificial anode and the power supply are connected together so as to form a single unit. 
     
     
       18. The method according to  claim 17  wherein the sacrificial anode is of a shape and size corresponding with the shape of at least part of the power supply, such that it fits alongside at least part of the anode and cathode. 
     
     
       19. The method according to  claim 16  wherein the sacrificial anode forms a container within which the power supply is at least partly located. 
     
     
       20. The method according to  claim 16  including surrounding the sacrificial anode by an encapsulating material of a porous matrix. 
     
     
       21. The method according to  claim 20  wherein the porous matrix comprises a cementitious mortar. 
     
     
       22. The method according to  claim 20  including surrounding the sacrificial anode by an encapsulating material wherein the porous matrix comprises a mortar having encapsulating material has a pH greater than 12. 
     
     
       23. The method according to  claim 20  wherein the encapsulating material is pre-cast around the anode. 
     
     
       24. The method according to  claim 20  wherein the encapsulating material is provided after as the sacrificial anode is located at its intended position in the concrete or mortar material. 
     
     
       25. The method according to  claim 16  wherein the sacrificial anode is activated to ensure continued corrosion of the sacrificial anode. 
     
     
       26. The method according to  claim 16  wherein the power supply comprises an electrolytic cell. 
     
     
       27. The method according to  claim 16  wherein the ionically conductive material is a concrete or mortar material in contact with which the metal steel is a steel reinforcing member. 
     
     
       28. A sacrificial anode assembly for cathodically protecting and/or passivating a metal section within an ionically conductive concrete or mortar covering material, comprising:
 a cell, which has an anode and a cathode with an electrolyte therebetween such that current can flow between the anode and the cathode;   a connector attached to the anode of the cell for electrically connecting the anode to the metal section to be cathodically protected;   and sacrificial anode material electrically connected with the cathode of the cell;   wherein there are provided one or more isolating elements which prevent communication of ionic current from the cell to the environment such that current can only flow between the cathode of the cell and the sacrificial anode and between the anode of the cell and the connector;   wherein the sacrificial anode and the cell are connected together so as to form a single unit such that the sacrificial anode is electrically connected in series with the cathode of the cell;   wherein the assembly comprises a container containing at least part of the anode, the electrolyte and the cathode of the cell;   and wherein the sacrificial anode material forms at least part of an outer surface of the container.   
     
     
       29. An assembly according to claim 28, wherein the sacrificial anode is zinc, aluminum, cadmium or magnesium, or an alloy of one or more of these metals. 
     
     
       30. An assembly according to claim 28 wherein the cell and the container are generally cylindrical. 
     
     
       31. An assembly according to claim 28 wherein the container is at least partly surrounded by an encapsulating material. 
     
     
       32. An assembly according to claim 31 wherein the encapsulating material is a porous matrix. 
     
     
       33. An assembly according to claim 31 wherein the encapsulating material comprises a cementitious mortar. 
     
     
       34. An assembly according to claim 33 wherein the encapsulating material has a pH greater than 12. 
     
     
       35. An assembly according to claim 31 wherein the encapsulating material contains at least one activator to ensure continued corrosion of the sacrificial anode. 
     
     
       36. An assembly according to claim 35 wherein the activator comprises a humectant. 
     
     
       37. A method of cathodically protecting steel in an ionically conductive concrete or mortar covering material comprising:
 providing a sacrificial anode;   generating a voltage between two connections of a power supply such that current can flow between the negative connection and the positive connection;   in a first protection step, electrically connecting one of the connections of the power supply to the steel to be cathodically protected and electrically connecting the sacrificial anode in series with the other connection of the power supply such that the voltage generated by the power supply is added to the voltage generated between the sacrificial anode and the steel to produce a voltage greater than the galvanic voltage generated between the sacrificial anode and the steel alone which passivates the steel;   wherein the power supply is otherwise isolated from the environment such that current can only flow into and out of the power supply via the sacrificial anode and the connector;   and, in a second protection step, subsequent to completion of the first step, the voltage generated by the power supply is no longer present and a current flows between the sacrificial anode and the steel to continue protecting and/or passivating the steel, where the current is generated solely by the galvanic voltage between the sacrificial anode and the steel.   
     
     
       38. The method according to claim 37 wherein a porous material is provided at the sacrificial anode so as to provide pores that absorb expansive forces generated by expansive corrosion products. 
     
     
       39. The method according to claim 37 including providing at least one activator which ensures continued corrosion of the sacrificial anode. 
     
     
       40. The method according to claim 39 wherein said at least one activator provides a pH in the encapsulating material sufficiently high for corrosion of the sacrificial anode to occur and for passive film formation on the sacrificial anode to be avoided. 
     
     
       41. The method according to claim 39 wherein said at least one activator provides a pH in the encapsulating material greater than 12. 
     
     
       42. The method according to claim 39 wherein said at least one activator is provided in a porous material at the sacrificial anode. 
     
     
       43. The method according to claim 37 wherein the sacrificial anode is formed of zinc or zinc alloy. 
     
     
       44. The method according to claim 37 wherein an encapsulating material is pre-cast around the sacrificial anode. 
     
     
       45. The method according to claim 37 wherein an encapsulating material is provided around the sacrificial anode as the sacrificial anode is located at its intended position in the concrete or mortar covering material.