Cathodic protection system using impressed current and galvanic action

Abstract

Cathodic protection of steel in a building or other concrete or similar structure is provided by locating an anode in a suitable location adjacent to the steel and providing an impressed current from a power supply to the anode. The anode is formed from a material which is more electro-negative than the steel so that in the event that the power supply falls below the galvanic potential therebetween, current flows under galvanic action to replace the impressed current. A diode in the circuit prevents flow of current across the power supply but allows the galvanic current when the power supply fails open circuit. An additional diode can be provided in the event the power supply fails closed circuit to prevent reverse current flow.

The invention claimed is: 
     
       1. A method for cathodic protection of steel material in a covering material comprising concrete, mortar or masonry material arranged such that at least a part of the steel material is at least partly covered by the covering material; the method comprising:
 providing at least one anode member which is formed of a material which is more electro-negative than the steel material such that galvanic action will generate an electric potential difference therebetween tending to cause a flow of ions; 
 arranging the anode member at least partly in contact with the covering material for communication of ions therebetween; 
 providing an electrical connection arrangement between the at least one anode member and the steel material so that current can flow through said at least one electrical connection arrangement between the at least one anode member and the steel material so that ions flow through the covering material tending to inhibit corrosion of the steel material; 
 providing a DC power supply having a supply potential difference greater than the galvanic potential difference between the anode member and the steel material generated by the galvanic action; 
 connecting the DC power supply into said electrical connection arrangement such that the supply to generate a potential difference causes ions to flow through the covering material tending to inhibit corrosion of the steel material for as long as the power supply is active to generate a supply potential difference greater than the galvanic potential difference between the anode member and the steel material generated by the galvanic action; 
 and said electrical connection arrangement being arranged such that, when the power supply becomes inactive such that the supply potential difference falls below the galvanic potential difference between the anode member and the steel material generated by the galvanic action, current continues to flow through said electrical connection arrangement by the galvanic action to continue to provide cathodic protection to the steel material. 
 
     
     
       2. The method according to  claim 1  wherein the DC power supply is a battery. 
     
     
       3. The method according to  claim 2  wherein the battery has a supply potential difference of the order of or greater than 1.5V. 
     
     
       4. The method according to  claim 2  wherein the covering material comprises a structural material of a building and wherein the battery is buried in the structural covering material of the building. 
     
     
       5. The method according to  claim 4  wherein the structural covering material forms a wall and wherein the battery is buried in a cavity in the wall. 
     
     
       6. The method according to  claim 4  wherein the covering material comprises a structural material of a building and wherein there is provided a plurality of batteries at a plurality of respective locations on the building. 
     
     
       7. The method according to claim  4  6 wherein the building includes a plurality of steel elements of the building and wherein there is provided a separate battery for each element. 
     
     
       8. The method according to  claim 1  wherein the electrical connection arrangement includes a connection which bridges output terminals of the DC power supply and wherein there is provided a diode in the connection to prevent communication reverse flow of current through the electrical connection arrangement across the DC power supply. 
     
     
       9. The method according to  claim 1  wherein there is provided a diode in electrical connection arrangement to prevent flow of current in a reverse direction. 
     
     
       10. A method for cathodic protection of steel material in a covering material comprising concrete, mortar or masonry material arranged such that at least a part of the steel material is at least partly covered by the covering material; the method comprising:
 providing at least one anode member which is formed of a material which is more electro-negative than the steel material such that galvanic action will generate an electric potential difference therebetween tending to cause a flow of ions; 
 arranging the anode member at least partly in contact with the covering material for communication of ions therebetween; 
 providing an electrical connection arrangement between the at least one anode member and the steel material so that current can flow through said at least one electrical connection arrangement between the at least one anode member and the steel material so that ions flow through the covering material tending to inhibit corrosion of the steel material; 
 providing a DC power supply having a supply potential difference greater than the galvanic potential difference between the anode member and the steel material generated by the galvanic action; 
 connecting the DC power supply into said electrical connection arrangement such that the supply to generate a potential difference causes current to flow in the electrical connection arrangement in a required direction so that ions flow through the covering material tending to inhibit corrosion of the steel material when the power supply is active and generates a supply potential difference greater than the galvanic potential difference between the anode member and the steel material generated by the galvanic action; 
 providing in said electrical connection arrangement a connection to allow flow of current across the DC power supply such that, when the DC power supply becomes inactive such that the supply potential difference falls below than the galvanic potential difference between the anode member and the steel material generated by the galvanic action, current continues to flow through said electrical connection arrangement by the galvanic action to continue to provide cathodic protection to the steel material; 
 and providing in said connection a diode arranged to prevent flow of current across said DC power supply in a direction reverse to said required direction. 
 
     
     
       11. The method according to  claim 10  wherein the DC power supply is a battery. 
     
     
       12. The method according to  claim 11  wherein the battery has a potential greater than 1.5V. 
     
     
       13. The method according to  claim 10  wherein the covering material comprises a structural material of a building and wherein the power supply comprises a battery which is buried in the structural covering material of the building. 
     
     
       14. The method according to  claim 13  wherein the structural material forms a wall and wherein the battery is buried in a cavity in the wall. 
     
     
       15. The method according to  claim 13  wherein the covering material comprises a structural material of a building and wherein there is provided a plurality of batteries at plurality of respective locations on the building. 
     
     
       16. The method according to claim  13  15 wherein the building includes a plurality of steel elements each forming a lintel of the building and wherein there is provided a separate battery for each lintel. 
     
     
       17. A method for cathodic protection of steel material in a covering material comprising concrete, mortar or masonry material such that at least a part of the steel material is at least partly covered by the covering material, the method comprising:
 providing at least one anode member which is formed of a material which is more electro-negative than the steel material such that galvanic action generates a galvanic potential difference therebetween;   arranging the anode member at least partly in contact with the covering material for communication of ions therebetween;   in a first step providing a connection between said at least one anode member and the steel material including a DC power supply such that the potential difference between said at least one anode and the steel material is greater than the galvanic potential difference;   and in a second step providing a connection between said at least one anode member and the steel material so that the galvanic potential difference only is applied between the anode member and the steel material.   
     
     
       18. The method according to claim 17 wherein the DC power supply is a battery. 
     
     
       19. The method according to claim 17 wherein the DC power supply includes a rectifier for rectifying an AC power supply. 
     
     
       20. The method according to claim 17 wherein, in the second step, the DC power supply is inactive. 
     
     
       21. The method according to claim 17 wherein the DC power supply is located in the covering material. 
     
     
       22. The method according to claim 17 wherein the covering material forms a wall and wherein the power supply is located in a cavity in the wall. 
     
     
       23. The method according to claim 17 wherein there is provided an electrical connection arrangement including said at least one anode, the steel material and the DC power supply and wherein, when the DC power supply becomes inactive, the electrical connection arrangement is arranged to provide automatically a connection of said at least one anode to the steel material to allow current to flow therebetween caused by the galvanic potential alone.  
     
     
       24. A method for cathodic protection of steel material in a covering material comprising concrete, mortar or masonry material such that at least a part of the steel material is at least partly covered by the covering material, the method comprising:
 providing at least one anode member which is formed of a material which is more electro-negative than the steel material such that galvanic action generates a galvanic potential difference therebetween;   arranging the anode member at least partly in contact with the covering material for communication of ions therebetween;   in a first step providing a connection between said at least one anode member and the steel material including a DC power supply such that the potential difference between said at least one anode and the steel material is greater than the galvanic potential difference;   and in a second step providing a connection between said at least one anode member and the steel material so that the galvanic potential difference only is applied between the anode member and the steel material;   wherein, in the first step, the potential difference is arranged so as to cause an initial migration of ions through the covering material so as to ensure an initial level of protection for the steel material and in the second step, the potential difference is arranged so as to provide a current lower than that in the first step, which current is sufficient to limit the return of migrated ions in the covering material to the position where corrosion occurs.   
     
     
       25. The method according to claim 24 wherein the DC power supply is a battery. 
     
     
       26. The method according to claim 24 wherein the DC power supply includes a rectifier for rectifying an AC power supply. 
     
     
       27. The method according to claim 24 wherein, in the second step, the DC power supply is inactive.  
     
     
       28. The method according to claim 24 wherein there is provided an electrical connection arrangement including said at least one anode, the steel material and the DC power suppjy and wherein, when the DC power supply becomes inactive, the electrical connection arrangement is arranged to provide automatically a connection of said at least one anode to the steel material to allow current to flow therebetween caused by the galvanic potential alone. 
     
     
       29. The method according to claim 24 wherein the DC power supply is located in the covering material. 
     
     
       30. The method according to claim 24 wherein the covering material forms a wall and wherein the power supply is located in a cavity in the wall. 
     
     
       31. A method for cathodic protection of steel material in a covering material comprising concrete, mortar or masonry material such that at least a part of the steel material is at least partly covered by the covering material, the method comprising:
 providing at least one anode member which is formed of a material which is more electro-negative than the steel material such that galvanic action generates a galvanic potential difference therebetween;   providing in the anode member an enhancement material which cooperates with the sacrificial anode material in enhancing the communication of ions between the covering material and the anode material;   arranging the anode member at least partly in contact with the covering material for communication of ions therebetween;   in a first step providing a connection between said at least one anode member and the steel material including a DC power supply such that the potential difference between said at least one anode and the steel material is greater than the galvanic potential difference;   and in a second step providing a connection between said at least one anode member and the steel material so that the galvanic potential difference only is applied between the anode member and the steel material;   wherein there is provided an electrical connection arrangement including said at least one anode, the steel material and the DC power supply and wherein, when in the second step the DC power supply becomes inactive, the electrical connection arrangement is arranged to provide automatically a connection of said at least one anode to the steel material to allow current to flow therebetween caused by the galvanic potential alone.   
     
     
       32. The method according to claim 31 wherein the DC power supply is a battery. 
     
     
       33. The method according to claim 31 wherein the DC power supply includes a rectifier for rectifying an AC power supply. 
     
     
       34. The method according to claim 31 wherein the DC power supply is located in the covering material. 
     
     
       35. The method according to claim 31 wherein the covering material forms a wall and wherein the power supply is located in a cavity in the wall. 
     
     
       36. A method for cathodic protection of steel material in a covering material comprising concrete, mortar or masonry material such that at least a part of the steel material is at least partly covered by the covering material, the method comprising:
 providing at least one anode member which is formed of an anode material which is more electro-negative than the steel material such that galvanic action generates a galvanic potential difference therebetween;   arranging the anode member at least partly buried within with the covering material for communication of ions therebetween;   providing an enhancement material which cooperates with the sacrificial anode material in enhancing the communication of ions between the covering material and the anode material;   providing at the anode member a material which is porous so that corrosion products from corrosion of the anode material during operation are received into pores in the porous material;   and providing an electrical connection arrangement between said at least one anode member and the steel material including a DC power supply such that the potential difference between said at least one anode member and the steel material is greater than the galvanic potential difference.   
     
     
       37. The method according to claim 36 wherein the electrical connection arrangement is arranged such that, when the DC power supply becomes inactive, a connection of said at least one anode to the steel material is provided to allow current to flow therebetween caused by the galvanic potential alone. 
     
     
       38. The method according to claim 37 wherein the electrical connection arrangement is arranged to provide said connection automatically. 
     
     
       39. The method according to claim 36 wherein the DC power supply is a battery. 
     
     
       40. The method according to claim 36 wherein the DC power supply includes a rectifier for rectifying an AC power supply. 
     
     
       41. The method according to claim 36 wherein the DC power supply is located in the covering material. 
     
     
       42. The method according to claim 36 wherein the covering material forms a wall and wherein the power supply is located in a cavity in the wall. 
     
     
       43. The method according to claim 36 wherein the enhancement material comprises a humectant. 
     
     
       44. The method according to claim 36 including maintaining the anode member electrochemically active. 
     
     
       45. A method of at least one of cathodically protecting and passivating a metal section in concrete comprising:
 providing at least one sacrificial anode;   providing a source of DC power with a negative connection and a positive connection;   in a first protection step, electrically connecting one of the connections of the source of DC power to the metal section to be cathodically protected: and electrically connecting the sacrificial anode in series with the other connection of the source of DC power such that the voltage generated by the source of DC power is added to the galvanic voltage, generated between the sacrificial anode and the metal section, to produce a voltage greater than the galvanic voltage generated between the sacrificial anode and the metal section alone; and,   in a second protection step, electrically connecting the sacrificial anode to the metal section with at least one electron conducting conductor that is not in series with the source of DC power to provide a path for electronic current to flow between the sacrificial anode and the metal section, such that the current is generated solely by the galvanic voltage between the sacrificial anode and the metal section.    
     
     
       46. The method as claimed in claim 45 wherein the connection between the sacrificial anode and the source of DC power is an impressed current anode connection.  
     
     
       47. The method as claimed in claim 45 wherein the anode is buried within a cavity in concrete.  
     
     
       48. The method as claimed in claim 47 wherein the cavity comprises a drilled hole.  
     
     
       49. The method as claimed in claim 45 wherein the source of DC power is a battery.  
     
     
       50. A method of protecting and/or passivating steel in concrete comprising:
 providing a sacrificial anode;   forming a cavity in the concrete by cutting a hole;   embedding the sacrificial anode in a porous matrix in the cavity;   providing a source of DC power with a negative connection and a positive connection;   electrically connecting one of the connections of the source of DC power to the steel to be cathodically protected; and   electrically connecting the sacrificial anode in series with the other connection of the source of DC power such that the voltage generated by the source of DC power 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;   wherein the source of DC power is located spaced from the cavity and the connections to the source of DC power comprise an electrical conductor defined by one of wires and cables.    
     
     
       51. The method as claimed in claim 50 wherein the connection between the sacrificial anode and the source of DC power is an impressed current anode connection.  
     
     
       52. A method for cathodic protection of steel material in a covering material comprising concrete, mortar or masonry material such that at least a part of the steel material is at least partly covered by the covering material, the method comprising:
 providing at least one anode member which is formed of an anode material which is more electro-negative than the steel material such that galvanic action generates a galvanic potential difference therebetween; 
 arranging the anode member at least partly buried within with the covering material for communication of ions therebetween; 
 providing an enhancement material which cooperates with the sacrificial anode material in enhancing the communication of ions between the covering material and the anode material; 
 and providing an electrical connection arrangement between said at least one anode member and the steel material including a DC power supply such that the potential difference between said at least one anode member and the steel material is greater than the galvanic potential difference.  
 
     
     
       53. The method according to claim 52 wherein the electrical connection arrangement is arranged such that, when the DC power supply becomes inactive, a connection of said at least one anode to the steel material is provided to allow current to flow therebetween caused by the galvanic potential alone.  
     
     
       54. The method according to claim 52 wherein the electrical connection arrangement is arranged to provide said connection automatically.  
     
     
       55. The method according to claim 52 wherein the DC power supply is a battery.  
     
     
       56. The method according to claim 52 wherein the DC power supply includes a rectifier for rectifying an AC power supply.  
     
     
       57. The method according to claim 52 wherein the DC power supply is located in the covering material.  
     
     
       58. The method according to claim 52 wherein the covering material forms a wall and wherein the power supply is located in a cavity in the wall.  
     
     
       59. The method according to claim 52 wherein the enhancement material comprises a humectant.  
     
     
       60. The method according to claim 52 including maintaining the anode member electrochemically active.