Pulsed cathodic protection system and method

Abstract

A cathodic protection system for protecting buried conducting structures, subject to corrosion such as well casings, pipe lines and the like, utilizes a plurality of pulsed D.C. current sources with the negative output terminal of each source connected to a separate structure and the positive output terminal of the sources connected to a common anode located near the structures. A control circuit synchronizes the operation of the several D.C. sources and sets the frequency and width of the output pulses. The amplitude of the output pulses from each D.C. source may be separately adjusted.

What is claimed is:  
     
       1. In a system for effecting cathodic protection of a plurality of spaced electrically conducting structures, including metal pipe lines or well casings, exposed to an electrically conducting medium, including the ground, the medium being in contact with an anode structure and through which current may be passed to said medium and to the structures, the combination comprising: 
       a plurality of pulsed D.C. current sources, each source being adapted to be connected to a separate conducting structure for supplying a controllable current at a selected frequency pulse between the associated conducting structure and the anode; and  
       a control circuit coupled to each of the current sources for synchronizing the operation of the current sources so that the current pulses from the plurality of current sources occupy substantially the same time frame during each cycle.  
     
     
       2. The cathodic protection system of  claim 1  wherein each current source includes means for adjusting the magnitude of the current supplied therefrom. 
     
     
       3. The cathodic protection system of  claim 2  wherein the control circuit adjusts the frequency of the current pulses supplied by the D.C. current sources and wherein each current source includes an anode/cathode switch. 
     
     
       4. The cathodic protection system of  claim 3  wherein the control circuit sets the pulse width and frequency of the current pulses. 
     
     
       5. The cathodic protection system of  claim 4  wherein the anode/cathode switch employs an isolated gate bipolar transistor to switch the D.C. source across the associated structure/anode load. 
     
     
       6. The cathodic protection system of  claim 3  wherein the anode/cathode switch includes a plurality of silicon controlled rectifirers. 
     
     
       7. The cathodic protection system of  claim 2  wherein each current source includes means for maintaining the current substantially constant once the magnitude thereof is set. 
     
     
       8. The cathodic protection system of  claim 7  wherein the means for maintaining the current constant includes means for measuring the current output. 
     
     
       9. The cathodic protection system of  claim 7  wherein each of the D.C. current sources includes a D.C. to D. C. converter. 
     
     
       10. The cathodic protection system of  claim 7  wherein each of the D.C. current sources include a D.C. source for providing an adjustable current level output and an anode/cathode switch coupled to the control circuit for connecting the output of the D.C. current source to the associated structure and anode unit in accordance with the pulse width and frequency set by the control circuit. 
     
     
       11. A method of protecting a plurality of spaced electrically conducting structures, including well casings or pipelines, exposed to an electrically conducting medium including the ground, the medium being in contact with the structures comprising the steps of: 
       immersing an anode unit into the conducting medium;  
       connecting the negative output terminal of a separate pulsed D.C. source to each conducting structure with each source being adapted to provide pulsed D.C. output current at a selected frequency and pulse width;  
       connecting the positive terminal of each of the pulsed D.C. sources to the anode; and  
       synchronizing the operation of the pulsed D.C. sources so that the current pulses from all of the D.C. sources occupy substantially the same time frame during each cycle.  
     
     
       12. The method of  claim 11  further including the step of individually adjusting the magnitude of the current delivered by the plurality of pulsed D.C. current sources. 
     
     
       13. The method of  claim 12  further including the step of measuring the well head potential of the plurality of structures during the current adjusting step. 
     
     
       14. The method of  claim 11  further including the step of adjusting the frequency and/or the pulse width of the output current pulses. 
     
     
       15. A cathodic protection system in which one or more pulsed dc current source protects one or more spaced electrically conducting structures including metal pipe lines or well casings embedded in the ground along with an anode structure comprising: 
       
         at least one pulsed dc current source, each dc current source having an input circuit and a pair of output terminals with one terminal adapted to be connected to an electrically conducting structure and the other terminal adopted to be connected to the anode structure, dc current source being arranged to produce across the output terminals periodic current pulses at a selected frequency and time frame within each cycle as determined by a control signal applied to its input circuit; and  
       
       
         a frequency control circuit having a plurality of output terminals and being arranged to produce a common controllable frequency output signal on each of the output terminals, one of the output terminals being connected to the input circuit of said at least one dc current source, the remaining output terminals being adapted to be connected to the input circuits of additional pulsed dc current sources. 
       
     
     
       16. The cathodic protection system of  claim 15  wherein the frequency control circuit is arranged to produce substantially square wave output signals and wherein said at least one dc current source is arranged to produce current pulses which coincide with the control circuit output signals. 
     
     
       17. The cathodic protection system of  claim 16  wherein said at least one dc current source includes an anode/cathode switch and wherein the anode/cathode switch employs an isolated gate bipolar transistor. 
     
     
       18. In a system adapted to affect cathodic protection of a plurality of spaced electrically conducting structures including metal pipe lines or well casings, exposed to an electrically conducting medium including the ground, the medium being in contact with an anode structure and through which current may be passed to said medium and to the structures the combination comprising: 
       
         one pulsed dc current source having a pair of output terminals and an input circuit, one of the output terminals being adapted to be connected to one of the conducting structures of the outer terminal being adapted to be connected to the anode, the dc source being responsive to the application of a control signal to the input circuit thereof for supplying current pulses at a selected frequency and time frame within each cycle between the associated conducting structure and the anode, and  
       
       
         a control circuit having a plurality of output terminals, one of the output terminals being connected to the input terminal of said dc source, the other output terminal being adapted to be connected to the input terminals of other dc sources. 
       
     
     
       19. In a system for affecting cathodic protection of a plurality of spaced electrically conducting structures, including metal pipe lines or well casings, exposed to an electrically conducting medium, including the ground, the medium being in contact with an anode structure and through which current may be passed to said medium and to the structures by a plurality of pulsed dc current sources with each source having an input terminal and a pair of output terminals adapted to be connected to a separate conducting structure and the anode, each dc current source supplying controlled current pulses at a selected frequency between the associated conducting structure and the anode in response to a signal on the input terminal thereof, the combination comprising: 
       
         one of said dc sources and a control circuit, the control circuit having a plurality of output terminals, one of the output terminals connected to the input terminal of said one dc source, the other output terminals being adapted to be connected to an input terminal of a separate dc source, the control circuit providing a common output signal on the output terminals for synchronizing the operation of a plurality of dc current sources so that the current pulses from the plurality of current sources occupy substantially the same time frame during each cycle.