Pulsed cathodic protection apparatus and method

Claim 1

A circuit for effecting cathodic protection of an object exposed to an electrically conductive medium, said medium being in electrical contact with anode means located in spaced relationship from said object, which comprises: a. a first lead connecting said anode means to the positive terminal of a source of DC voltage, b. a second lead connecting said object to the negative terminal of said source, c. one of said first and second leads having interposed therein the anodes and cathodes of first and second series-related thyristors poled to conduct current from said positive terminal through said anode means and object to said negative terminal, d. a third lead connected in parallel-circuit relationship relative to said one lead, said third lead having interposed therein the anodes and cathodes of third and fourth series-related thyristors poled to conduct current from said positive terminal through said anode means and object to said negative terminal, e. a fourth lead connected at one end to said one lead at a point between the cathode of said first thyristor and the anode of said second thyristor, the other end of said fourth lead being connected to said third lead at the point between the cathode of said third thyristor and the anode of said fourth thyristor, said fourth lead having capacitor means interposed therein, and f. a gating circuit connected to the gates of all of said thyristors, said gating circuit being adapted to effect simultaneous gating of said first and fourth thyristors, followed by simultaneous gating of said second and third thyristors, and to repeat said gatings in alternation and at a desired relatively high frequency.

Claim 4

A method of effecting pulsed cathodic protection of an object exposed to an electrically conductive medium which comprises: providing in electrical contact with said medium and in spaced relationship from said object an anode means through which current may be passed to said medium and thus to said object, providing a capacitor means, effecting charging of said capacitor means by current flowing from a DC source through a path which includes said medium and also includes said object and said anode means, said current flow being effected in a direction such as to effect cathodic protection of said object, thereafter effecting discharging of said capacitor means through a path which includes said medium and also includes said object and said anode means, the direction of flow of current resulting from said discharging of said capacitor means being such as to effect cathodic protection of said object, and repeating said charging and discharging of said capacitor means rapidly at a desired frequency in order to effect pulsed cathodic protection of said object.

Claim 5

A method of effecting pulsed cathodic protection of an object exposed to an electrically conductive medium which comprises: providing in electrical contact with said medium and in spaced relationship from said object an anode means through which current may be passed to said medium and thus to said object, providing a capacitor means, effecting charging of said capacitor means by current flowing from a DC source through a path which includes said medium and also includes said object and said anode means, said current flow being effected in a direction such as to effect cathodic protection of said object, thereafter effecting discharging of said capacitor means through a path which includes said medium and also includes said object and said anode means, the direction of flow of current resulting from said discharging of said capacitor means being such as to effect cathodic protection of said object, and repeating said charging and discharging of said capacitor means rapidly at a desired frequency in order to effect pulsed cathodic protection of said object.