JPH1192980A - Corrosion protection method of seawater cooling water series equipment by constant potential external power source system and electric corosion protection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device for efficiently executing electric corrosion protection by controlling an energizing method of corrosion protective current in an existing electric corrosion protection device of constant potential external power source system provided at a seawater cooling water series equipment. SOLUTION: In the electric corrosion protection method by the constant potential external power source system for preventing corrosion of seawater cooling water system equipment constituted of plural different kinds of metals inclusing corrosion resistant metals, (1) procedures, that the corrosion protective current is supplied and energizing is stopped when the corrosion protective current increases and reaches prescribed current value, supply of the corrosion protective current is restarted after elapse of prescribed period of time since stop of energizing, are repeated, otherwise (2) procedures, that the corrosion protective current is supplied and energizing is stopped when the corrosion protective current increases and reaches a maximum output current value of a constant potential DC power source apparatus 1, supply of the corrosion protective current is restarted after elapse of prescribed period of time since stop of energizing, are repeated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a seawater cooling water system device (for example, a condenser) comprising a plurality of dissimilar metals including metals having corrosion resistance in seawater used in thermal power plants and chemical factories. , Heat exchanger, seawater intake screen,
The present invention relates to a cathodic protection method and a cathodic protection device using a constant-potential external power supply method applied to a ball collector, etc., and particularly to a constant-potential external power supply cathodic protection provided in a seawater cooling water system device currently used. TECHNICAL FIELD The present invention relates to a method and an apparatus for efficiently performing electrolytic protection by controlling the passage of anticorrosion current of the apparatus.

[0002]

2. Description of the Related Art For example, in a conventional condenser, a titanium alloy is used for a cooling pipe 11 of a condenser 10 as shown in a sectional view of FIG. Metals that exhibit almost perfect corrosion resistance in seawater are often used for parts. On the other hand, a copper alloy such as naval brass is used for the tube sheet 12 of the condenser 10, and a steel sheet 1 whose surface is coated with rubber lining or anticorrosion coating 16 is used for the water chamber 13 of the condenser.
For example, a metal having low corrosion resistance in seawater such as 7 is used. In FIG. 4, reference numeral 1 denotes a constant potential DC power supply,
Is a durable electrode made of a lead silver electrode or a titanium platinum electrode or an iron electrode, and 15 is a reference electrode made of silver chloride or zinc. In this conventional condenser, the rubber lining 16
There is no problem while the sound is healthy, but when the rubber lining 16 is deteriorated and damaged, dissimilar metals such as the steel alloy 17 and the titanium alloy of the cooling pipe or the copper alloy of the tube sheet 12 and the titanium alloy of the cooling pipe occur, It causes corrosion. In order to prevent this corrosion, corrosion prevention current is passed to prevent corrosion. However, hydrogen embrittlement occurs when titanium alloy is excessively polarized by cathodic protection. A constant-potential external power supply type anti-corrosion device that automatically controls the anti-corrosion current so as to maintain a potential in a range necessary for anti-corrosion is installed.

[0003] Similarly, the body of a ball collector (not shown) is made of a metal that does not show much corrosion resistance in seawater, such as a steel lining or a steel plate coated with anticorrosive paint on the surface. The body portion of the collector where the rubber lining or the like has deteriorated is in contact with the collection grid made of high-grade stainless steel, so that corrosion of the different metals between the steel and stainless steel occurs. Excessive polarization of this collection grid made of high-grade stainless steel may cause hydrogen embrittlement cracking, so strict control of the anticorrosion potential is required. A constant-potential external power supply type anti-corrosion device that automatically controls the anti-corrosion current to maintain the current is installed.

In general, a corrosion protection current required to protect a structure composed of a plurality of dissimilar metals is determined by a product of a corrosion protection target area for each type of metal and a corrosion protection current density required per metal unit area. It can be obtained by the sum of the anticorrosion currents. The above calculations are also applied to seawater cooling water system equipment such as condensers and ball collectors composed of multiple dissimilar metals including corrosion-resistant metals such as titanium alloys and high-grade stainless steel and metals with poor corrosion resistance such as brass and steel. A constant-potential cathodic protection device with sufficient capacity to supply the anticorrosion current determined in step 1 is installed, but the corrosion-resistant metal forms an oxide film with a very high electrical resistance called a passive film in the seawater on the surface. As a result, the anticorrosion current is small, and the anticorrosion current capacity of the anticorrosion device can be designed to be considerably smaller than that of a seawater cooling water system device that does not contain such a corrosion-resistant metal.

[0005]

In recent years, it is composed of a plurality of dissimilar metals including corrosion-resistant metals, such as thermal power plants and chemical factories constructed along the coasts of Tokyo Bay, Osaka Bay, Ise Bay, etc., especially in large cities. In the seawater cooling water system equipment, the current required for anticorrosion increases drastically due to the deterioration of seawater quality, and the anticorrosion current is insufficient with the current capacity of the cathodic protection device based on the conventional design, and the anticorrosion control potential cannot be maintained. In some cases, corrosion has occurred. The present inventors have conducted a polarization test and found that the anticorrosion current required for such a seawater cooling water system device may reach several times to ten and several times the conventional design value.

FIG. 3 is a graph showing the relationship between the anticorrosion current and the anticorrosion potential supplied from the existing constant-potential external power supply type cathodic protection device provided in the currently used seawater cooling water system equipment. Become. When the anticorrosion current increases and the anticorrosion current reaches the maximum output current value of 170 A of the constant potential DC power supply device, it is impossible to increase the anticorrosion current any more due to the capacity of the existing cathodic protection device, and at the same time anticorrosion When the potential shifts to a value higher than the potential set value of -600 V and the anticorrosion potential deviates from the lower limit of -450 V of the anticorrosion control potential, an "insufficient potential" alarm is issued. That is, at the beginning of energization, a potential set value within the range of the anticorrosion control potential is secured even with a small anticorrosion current, but the anticorrosion current temporarily increases and exceeds the maximum output current value of the constant-potential DC power supply. ,
It was found that when the anticorrosion current became insufficient, the potential deviated from the potential set value and shifted to noble, and further shifted to noble so that the anticorrosion control potential could not be maintained. If the existing cathodic protection device is replaced with a cathodic protection device having a capacity several times to several tens times, the anticorrosion current can be increased and the anticorrosion control potential can be maintained as shown by the two-dot chain line A in FIG. However, replacing existing cathodic protection devices with cathodic protection devices of several to several tens of times more would not only require enormous costs but also increase the number of electrode devices etc. in the seawater cooling water system equipment main body. There is a difficult problem that large-scale remodeling must be performed.

[0007]

SUMMARY OF THE INVENTION Accordingly, the present inventors have solved these difficult problems by using the existing constant-potential external power supply type cathodic protection system provided in the currently used seawater cooling water system equipment as it is. As a result of conducting test research to solve the problem, (a) the anticorrosion current is increased for a while to maintain the anticorrosion control potential. When restarted, the anticorrosion current required to maintain the anticorrosion potential is significantly reduced from before the current was stopped, and then temporarily increased again. A procedure in which the time until the current value increases and reaches a predetermined current value is measured in advance, the energization is stopped when the measured time elapses after the energization starts, and the energization of the anticorrosion current is restarted after the elapse of the predetermined time from the energization stop. (C) When the anticorrosion current reaches a predetermined current value that is equal to or less than the maximum output current value of the constant-potential DC power supply, the application of the anticorrosion current is stopped by repeating It is possible to maintain the anticorrosion control potential by repeating the procedure of starting energization again after standing for a period of time, and (d) stopping energization when the anticorrosion current reaches the maximum output current value of the constant-potential DC power supply, for a predetermined period. The anticorrosion control potential can be maintained even when the procedure of restarting the energization is repeated after the elapse, and (e) the anticorrosion potential of the seawater cooling water system equipment is reduced by the shortage of anticorrosion current accompanying the increase in anticorrosion current. The power supply may be stopped before the power supply deviates, and the power supply of the anticorrosion current may be restarted after a predetermined time has elapsed from the power supply stop. (G) The time for stopping the power supply is within a range of 30 minutes to 3 hours. It is enough, it's like it was found.

The present invention has been made based on the results of such research, and (1) a constant-potential external power supply system for protecting seawater cooling water system equipment composed of a plurality of dissimilar metals including corrosion-resistant metals. In the anticorrosion method, the method of stopping the energization when a predetermined time has elapsed since the start of the anticorrosion current energization, and repeating the procedure of resuming the energization of the anticorrosion current after the elapse of the predetermined time from the stop of the energization, a method of electrolytic anticorrosion of a seawater cooling water system device by a constant potential external power supply system. (2) In a cathodic protection method using a constant potential external power supply method for protecting seawater cooling water system equipment composed of a plurality of dissimilar metals including corrosion resistant metals, the maximum output current of the constant potential DC power supply increases due to an increase in the corrosion protection current. A constant-potential external power supply that repeats the procedure of stopping the energization when a predetermined current value equal to or less than the value is reached and restarting the application of the anticorrosion current after a lapse of a predetermined time from the stop of the energization Corrosion protection method for seawater cooling water system equipment by the formula, (3) an anticorrosion current is increased in a cathodic protection method using a constant-potential external power supply system for protecting seawater cooling water system equipment composed of a plurality of dissimilar metals including corrosion-resistant metals. Seawater cooling water system equipment using a constant-potential external power supply system that repeats the procedure of stopping the energization when the maximum output current value of the constant-potential DC power supply device is reached and restarting the application of the anticorrosion current after a lapse of a predetermined time from the stop of the energization (4) In a cathodic protection method using a constant-potential external power supply system for protecting seawater cooling water system equipment composed of a plurality of dissimilar metals including corrosion-resistant metals, there is a shortage of anticorrosion current accompanying an increase in anticorrosion current. The procedure of stopping the energization before the anticorrosion potential of the seawater cooling water system device deviates from the anticorrosion control potential, and resuming the energization of the anticorrosion current after a lapse of a predetermined time from the stop of energization is repeated. Cathodic protection method of seawater cooling water system equipment by potential external power supply system, and it has the characteristics to.

The above-described anticorrosion method of the present invention can be achieved by manual operation. However, when the anticorrosion current temporarily increases and reaches a preset current value, or when the anticorrosion current is insufficient, the seawater cooling water system is supplied to the constant potential DC power supply. If a device is provided that stops the application of the output current when the potential of the device deviates from the anticorrosion management potential or when a predetermined time has elapsed from the start of energization, and starts the energization after a lapse of a predetermined period from the stop of energization, The anticorrosion method according to the present invention can be achieved without monitoring the anticorrosion current or potential of the anticorrosion device.

Therefore, the present invention comprises (5) a transformer for stepping down a commercial AC voltage to a predetermined voltage, a rectifier for converting AC to DC, and a potential control circuit for controlling the anticorrosion potential of the anticorrosion target to be constant. A constant-potential external power supply system basically comprising a constant-potential DC power supply device, an electrode device for supplying an anticorrosion current to seawater cooling water system equipment, and a reference electrode device for measuring the potential of the seawater cooling water system equipment. In the cathodic protection device, a plurality of devices including a corrosion-resistant metal including a control device that stops energization after a lapse of a predetermined time from the start of anticorrosion current energization to the constant-potential DC power supply device and a control device that restarts energization after a lapse of a predetermined period from the stop of energization (6) A constant voltage external power supply type anticorrosion system for seawater cooling water system equipment composed of dissimilar metals, (6) a transformer that steps down a commercial AC voltage to a predetermined voltage, and a rectifier that converts AC to DC A constant-potential DC power supply comprising a potential control circuit for controlling the anticorrosion potential of the anticorrosion target to be constant, an electrode device for supplying anticorrosion current to the seawater cooling water system equipment, and measuring the potential of the seawater cooling water equipment. In a constant potential external power supply type anticorrosion device basically comprising a reference electrode device, a predetermined current value equal to or less than a maximum output current value of the constant potential DC power supply device when an output current increases to the constant potential DC power supply device. A control device that stops energization when the current reaches the control unit, and a control device that restarts energization after a predetermined time has elapsed from the stop of energization. Power supply type cathodic protection device,
(7) a transformer for stepping down a commercial AC voltage to a predetermined voltage;
A constant-potential direct-current power supply comprising a rectifier for converting alternating current to direct current and a potential control circuit for controlling the corrosion prevention potential of the anticorrosion target to be constant, an electrode device for supplying a corrosion protection current to seawater cooling water system equipment, and the seawater cooling. In a constant-potential external power supply type anticorrosion device basically consisting of a reference electrode device for measuring the potential of water system equipment, the output current increases to the constant-potential DC power supply and the maximum output of the constant-potential DC power supply is increased. A seawater cooling water system device comprising a plurality of dissimilar metals including a corrosion-resistant metal, comprising a control device that stops energization when the current value is reached, and a control device that restarts energization after a predetermined time has elapsed from the stoppage of energization. (8) a transformer for stepping down a commercial AC voltage to a predetermined voltage, a rectifier for converting AC to DC, and a potential control circuit for controlling the corrosion prevention potential of an object to be protected at a constant level. A constant-potential external power supply basically consisting of a constant-potential DC power supply device composed of an electrode device for supplying an anticorrosive current to seawater cooling water system equipment and a reference electrode device for measuring the potential of the seawater cooling water system equipment In the anticorrosion system, the anticorrosion current is insufficient beyond the maximum output current value of the constant-potential DC power supply device, and the energization is stopped before the potential of the seawater cooling water system device deviates from the anticorrosion management potential and shifts to noble. A constant-potential external power-supply type cathodic protection device for seawater cooling water system equipment comprising a plurality of different metals including a corrosion-resistant metal, comprising a control device and a control device that restarts power supply after a lapse of a predetermined time from the stop of power supply. It has.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a method for preventing corrosion of a seawater cooling water system apparatus by a constant potential external power supply system and a constant potential external power supply type anticorrosion apparatus of the present invention will be specifically described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of a constant-potential external power supply type anticorrosion device used in the anticorrosion method of the present invention. In FIG. 1, reference numeral 1 denotes a constant potential DC power supply, the main circuit of which is an input switch 2 for introducing a commercial AC current to the constant potential DC power supply 1, and a transformer for stepping down the commercial AC voltage to a predetermined voltage. And a rectifier 4 for converting an AC current into a DC current for anticorrosion. 5
Is a controller for setting an optimum anticorrosion potential and transmitting a current control signal to a DC circuit in order to maintain the same, 6 is a shunt resistor for detecting the DC current value, 7 is a predetermined set value of the anticorrosion current or When the maximum output current value is reached,
Alternatively, the anti-corrosion detection circuit sends a “power OFF” signal to the electromagnetic switch 8 and a “timer ON” signal to the timer 9 before the potential of the anti-corrosion target deviates from the anti-corrosion control potential.
10 is a condenser, 11 is a cooling pipe made of titanium alloy, 1
2 is a tube sheet made of Naval brass, 13 is a water chamber made of steel and the inner surface is covered with a rubber lining. Reference numeral 14 denotes a durable electrode such as a lead silver electrode or a titanium platinum electrode or an iron electrode, and 15 denotes a reference electrode such as silver chloride or zinc.

When the anticorrosion method of the present invention is performed by such a constant potential external power supply type anticorrosion device, the input switch 2 is turned on to introduce an alternating current to the constant potential DC power supply device 1, and the controller 5 performs corrosion protection. After setting the control potential, the electromagnetic switch 8 is turned on, and the cooling pipe 11 is connected via the seawater from the durable electrode 14 connected to the positive electrode of the DC output circuit.
An anticorrosion current is supplied to the tube sheet 12 and the water chamber 13. Cooling pipe 1
1. The potentials of the tube sheet 12 and the water chamber 13 are detected by the reference electrode 15, and this potential signal is fed back to the controller 5 so that the potentials of the cooling pipe 11, the tube sheet 12 and the water chamber 13 are always kept at the anticorrosion control potential. The anticorrosion current is controlled so that

As the time elapses, the anticorrosion current temporarily increases and reaches a current value set in the anticorrosion insufficient detection circuit 7,
Alternatively, if the anticorrosion shortage detection circuit 7 detects that the anticorrosion current reaches the maximum output current value of the DC power supply device, the potential of the seawater cooling water system equipment shifts to noble, and deviates from the anticorrosion control potential, the anticorrosion protection circuit 7 detects that The switch 8 is opened to stop the supply of the anticorrosion current, and the timer 9 differentially operates. When the set time of the timer 9 elapses, the electromagnetic switch 8 is closed by the signal from the anticorrosion insufficient detection circuit 7 and the supply of the anticorrosion current is started again. The electromagnetic switch 8 may be placed on the DC output circuit as shown in this figure, but may be placed on the AC input side. Also, the electromagnetic switch 8 is configured so that the anticorrosion current does not flow from the rectifier 4 by the signal from the controller 5. Then, the electromagnetic switch 8 can be omitted.

Next, embodiments of the present invention will be described more specifically with reference to the drawings. A constant potential external power supply type cathodic protection system shown in FIG. 1 is installed for one series of condensers of a power plant consisting of two series using titanium alloy cooling pipes,
An energization test was performed for 30 days, and a conventional constant potential external power supply type anticorrosion device was installed as a conventional example in the other series to energize. Note that the maximum output current of the DC power supply device per condenser water chamber is 170 A in both the embodiment and the conventional example.
A platinum titanium electrode was used as the electrode 14 and a silver chloride reference electrode was used as the reference electrode 15.

[Embodiment] The anticorrosion control potential of the seawater inlet and outlet water chambers was set to -600 mV, and the maximum output current was 3
When maintained for 0 minutes, the signal from the anticorrosion insufficient detection circuit 7 opens the electromagnetic switch 8 to stop the supply of the anticorrosion current, and after one hour, closes the electromagnetic switch 8 and restarts the supply of the anticorrosion current. The timer 9 was set and the energization of the constant potential DC power supply 1 was started. The change of the anticorrosion current and the potential is shown in the graph of FIG. The anticorrosion current immediately after the start of energization was 40 A for the seawater inlet water chamber and 14 A for the seawater outlet water chamber. Thereafter, the current gradually increased in both water chambers, and the maximum output of the seawater outlet water chamber was reached on the eleventh day after the start of energization. The supply of anticorrosion current was stopped for one hour because the current was reached. The anticorrosion current of the seawater inlet water chamber at the time of stoppage was 142A. The anticorrosion current in the seawater outlet water chamber was reduced to 150 A immediately after the resumption of power supply, and the corrosion protection current was reduced to 120 A in the seawater inlet water chamber. In addition, the second current supply stop is on the 23rd day, the third current supply is on the 30th day, and the anticorrosion current immediately after the current supply is resumed is 2 times smaller than before the current supply was stopped.
It decreased by about 65A from 0A. During the test period, the potential of the seawater inlet water chamber and the outlet water chamber both maintained the anticorrosion control potential of -600 mV.

[Conventional example] The anticorrosion control potential of the seawater inlet water chamber and outlet water chamber was set to -600 mV, and ordinary constant potential cathodic protection was performed. The change of the anticorrosion current and the potential is shown in the graph of FIG. The anticorrosion current immediately after the start of energization is 44 A for the seawater inlet water chamber.
Then, the seawater outlet water chamber was 20A, but then the current in both water chambers gradually increased, and the seawater inlet water chamber reached the maximum output current on the 12th day from the start of energization, and then the potential in both water chambers gradually became higher. On the 15th day, the potential of the seawater inlet water chamber deviated from -450 mV, which is the lower limit of the anticorrosion control range, and the "potential shortage" alarm built in the constant potential DC power supply was issued, and the power supply was stopped.

[0017]

As described above, if the anticorrosion method using the constant potential external power supply system according to the present invention is used, even if the anticorrosion current exceeds the capacity of the cathodic protection device, the current is temporarily supplied. And restarting the energization after that, it is possible to maintain the anticorrosion control potential of the seawater cooling water system equipment again within the capacity of the anticorrosion device, so it is necessary to newly install a large-capacity anticorrosion device. In addition, when the anticorrosion current exceeds a predetermined set value, when the anticorrosion current is insufficient and deviates from the anticorrosion control potential, or when the anticorrosion current is started, the energization is stopped every elapse of a predetermined time, and the energization is performed after the elapse of the predetermined time. The use of a constant-potential DC power supply device incorporating a circuit for resuming the process of the present invention has an excellent effect that the anticorrosion method of the present invention can be achieved without monitoring the anticorrosion current value and potential.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a constant potential external power supply type anticorrosion device of the present invention.

FIG. 2 is a graph showing transition of the anticorrosion current and the potential of the condenser when the anticorrosion method of the present invention is applied by the constant potential external power supply type anticorrosion device of the present invention.

FIG. 3 is a graph showing transition of anticorrosion current and potential when a condenser is anticorrosively protected by a conventional constant potential external power supply type anticorrosion device.

FIG. 4 is a schematic sectional view showing the structure of a conventional condenser.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Constant potential DC power supply 2 Input switch 3 Transformer 4 Rectifier 5 Controller 6 Shunt resistor 7 Corrosion protection insufficient detection circuit 8 Electromagnetic switch 9 Timer 10 Condenser 11 Cooling pipe 12 Tube plate 13 Water chamber 14 Electrode 15 Reference electrode 16 Rubber Lining 17 Steel plate

Claims (8)

[Claims] Claims: 1. An anticorrosion method using a constant-potential external power supply system for anticorrosion of a seawater cooling water system device composed of a plurality of dissimilar metals including a corrosion-resistant metal, comprising:
An electrolytic protection method for a seawater cooling water system device using a constant potential external power supply method, wherein a procedure for restarting the application of the anticorrosion current is repeated after a predetermined time has elapsed from the stop of energization. 2. An anticorrosion method using a constant-potential external power supply method for anticorrosion of a seawater cooling water system device composed of a plurality of dissimilar metals including a corrosion-resistant metal. A constant-potential external power supply characterized by repeating the procedure of stopping energization when a predetermined current value equal to or less than the maximum output current value of the DC power supply device is reached and restarting energization of the anticorrosion current after a lapse of a predetermined time from the stoppage of energization. Corrosion protection method for seawater cooling water system equipment by the method. 3. An anticorrosion method using a constant-potential external power supply system for anticorrosion of a seawater cooling water system device composed of a plurality of dissimilar metals including a corrosion-resistant metal. A seawater cooling water system using a constant potential external power supply system, in which the power supply is stopped when the maximum output current value of the DC power supply device is reached, and the procedure for restarting the supply of the anticorrosive current is repeated after a lapse of a predetermined time from the stoppage of the power supply. The method of cathodic protection of equipment. 4. An anticorrosion method using a constant-potential external power supply system for anticorrosion of a seawater cooling water system device composed of a plurality of dissimilar metals including a corrosion-resistant metal. The anti-corrosion current is insufficient due to exceeding the maximum output current value of the DC power supply, the electric potential of the seawater cooling water system equipment is shifted to noble, and the energization is stopped before the anti-corrosion management potential is deviated, and after a predetermined time has elapsed from the stop of energization An electrolytic protection method for a seawater cooling water system device using a constant potential external power supply method, characterized by repeating a procedure for resuming the application of a corrosion prevention current. 5. A constant-potential DC power supply comprising a transformer for stepping down a commercial AC voltage to a predetermined voltage, a rectifier for converting AC to DC, and a potential control circuit for controlling the corrosion protection potential of an object to be protected to a constant value. A constant-potential external power supply type anticorrosion device basically comprising an electrode device for supplying an anticorrosion current to the device and the seawater cooling water system device, and a reference electrode device for measuring the potential of the seawater cooling water system device. A plurality of heterogeneous metals including a corrosion-resistant metal, comprising: a control device that stops energization after a lapse of a predetermined time from the start of the application of the anticorrosion current to the potential DC power supply device; A constant-potential external power type cathodic protection system for seawater cooling water system equipment made of metal. 6. A constant-potential DC power supply comprising: a transformer for stepping down a commercial AC voltage to a predetermined voltage; a rectifier for converting AC to DC; and a potential control circuit for controlling the corrosion prevention potential of the anticorrosion target to be constant. A constant-potential external power supply type anticorrosion device basically comprising an electrode device for supplying an anticorrosion current to the device and the seawater cooling water system device, and a reference electrode device for measuring the potential of the seawater cooling water system device. A control device that stops energization when the output current of the potential DC power supply increases and reaches a predetermined current value equal to or less than the maximum output current value of the constant potential DC power supply, and restarts energization after a lapse of a predetermined time from the stop of energization A constant-potential external power supply type anticorrosion device for a seawater cooling water system device comprising a plurality of dissimilar metals including a corrosion-resistant metal, comprising a control device. 7. A constant potential DC power supply comprising a transformer for stepping down a commercial AC voltage to a predetermined voltage, a rectifier for converting AC to DC, and a potential control circuit for controlling the corrosion protection potential of the object to be protected to a constant value. A constant-potential external power supply type anticorrosion device basically comprising an electrode device for supplying an anticorrosion current to the device and the seawater cooling water system device, and a reference electrode device for measuring the potential of the seawater cooling water system device. A control device that stops energization when an output current of the potential DC power supply increases and reaches a maximum output current value of the constant potential DC power supply, and a control device that restarts energization after a predetermined time has elapsed from the stop of energization. A constant-potential external power type cathodic protection system for seawater cooling water system equipment comprising a plurality of dissimilar metals including corrosion-resistant metals. 8. A constant potential DC power supply comprising a transformer for stepping down a commercial AC voltage to a predetermined voltage, a rectifier for converting AC to DC, and a potential control circuit for controlling the corrosion protection potential of an object to be protected to a constant value. A constant-potential external power supply type anticorrosion device basically comprising an electrode device for supplying an anticorrosion current to the device and the seawater cooling water system device, and a reference electrode device for measuring the potential of the seawater cooling water system device. A control device that stops the energization before the output current of the potential DC power supply increases and exceeds the maximum output current value and the anticorrosion current runs short, and the potential of the seawater cooling water system equipment shifts to noble and deviates from the anticorrosion management potential. And a control device that restarts energization after a lapse of a predetermined time from the stoppage of energization. A constant-potential external power-supply type cathodic protection device for seawater cooling water system equipment composed of a plurality of different metals including corrosion-resistant metals.