CA1088458A - Method of corrosion protection of objects in contact with conducting medium - Google Patents
Method of corrosion protection of objects in contact with conducting mediumInfo
- Publication number
- CA1088458A CA1088458A CA258,476A CA258476A CA1088458A CA 1088458 A CA1088458 A CA 1088458A CA 258476 A CA258476 A CA 258476A CA 1088458 A CA1088458 A CA 1088458A
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- Canada
- Prior art keywords
- cathode
- conducting medium
- corrosion
- potential
- current
- Prior art date
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Abstract
METHOD OF CORROSION PROTECTION OF OBJECTS IN CONTACT
WITH CONDUCTING MEDIUM
Abstract of the Disclosure According to the method, polarizing current is periodically applied between the auxiliary electrode and the object to be protected from corrosion in order to maintain the latter's potential within prescribed limits.
During the time intervals when the supply of polarizing current is discontinued, the auxiliary electrode (the cathode) is shorted out by the object being protected.
WITH CONDUCTING MEDIUM
Abstract of the Disclosure According to the method, polarizing current is periodically applied between the auxiliary electrode and the object to be protected from corrosion in order to maintain the latter's potential within prescribed limits.
During the time intervals when the supply of polarizing current is discontinued, the auxiliary electrode (the cathode) is shorted out by the object being protected.
Description
5~
r~he prese~t invention rela~es to corrosion protection of metals and, more par-ticularly, -to methods o~ anodic protection from corrosion of ai~`~erent objects in contact with aggressive conducti~g media, which objects are made ~rom materials passivating in such media.
'~he invention is the mos~ advantageous ~or the corrosion protection o~ equipment in the chemical, ~ood, textile, and pulp and paper industries.
'~here are other methods of corrosion protection, but the method o~ anodic electrochemical protection proves to be the mos~ e~ective in a number o~ cases.
'l~he essence o~` this me~hod ls as ~ollo~s.
Upon comln~ lnto contac~ with an aggressive medium, a metal is corroded and acquires a potential which is called a steady-state potentlal. I~ the metal's potential is some-how altered towards the positive side, the ra~e o~ corrosion slows down substantially at certain values o~ the potential~
~his phenomenon is re~erred to as passlvation o~ metals, while the proce~s of bringi~g a metal's potential within a passiva-tion range is called a passivation process. ~h0 range of potentials within which metals are passive is called the passive range. 'l~he ex-tent o~ this range depends upon the metal and ~he aggressive medium which is in contact with the metal. By shi~ting ~he electrical pote~tial o~ a metal into the passive ran~e, the metal can be protectod ~rom corrosion.
:` :
r~he prese~t invention rela~es to corrosion protection of metals and, more par-ticularly, -to methods o~ anodic protection from corrosion of ai~`~erent objects in contact with aggressive conducti~g media, which objects are made ~rom materials passivating in such media.
'~he invention is the mos~ advantageous ~or the corrosion protection o~ equipment in the chemical, ~ood, textile, and pulp and paper industries.
'~here are other methods of corrosion protection, but the method o~ anodic electrochemical protection proves to be the mos~ e~ective in a number o~ cases.
'l~he essence o~` this me~hod ls as ~ollo~s.
Upon comln~ lnto contac~ with an aggressive medium, a metal is corroded and acquires a potential which is called a steady-state potentlal. I~ the metal's potential is some-how altered towards the positive side, the ra~e o~ corrosion slows down substantially at certain values o~ the potential~
~his phenomenon is re~erred to as passlvation o~ metals, while the proce~s of bringi~g a metal's potential within a passiva-tion range is called a passivation process. ~h0 range of potentials within which metals are passive is called the passive range. 'l~he ex-tent o~ this range depends upon the metal and ~he aggressive medium which is in contact with the metal. By shi~ting ~he electrical pote~tial o~ a metal into the passive ran~e, the metal can be protectod ~rom corrosion.
:` :
- 2 - ~
3451~
rL'he electrical potential o~ a metal liable to corrosion can be brought i~to the passive ra~ge with a view o-P reducing the rate o~ corrosion by appiyin~ electric curre~t, which thls case is re~errea to as polarizing current; between the metal to be protected from corrosion~ whlch in ~his case is an a~ode, and a~ auxiiiar~ electrode which is a cathode. ~`he same e~`ect can be produced by adding into the corrodin$ solution ~r agents ~hm~ ~re called passiva-tors.
Passivation o~ a metal by means o~ polarizing curre~t is re-~erred to as anodic corrosion protection; the bringing o~
the metal's electric po-tential into the passive ran~e is called anodic polarization.
~ ne impleme~tion of the ~oregoing method in lndustrlal conditions calls ~or some ~ to reliably maintain the passive state of objects ~o be protected ~rom corrosion.
l~ormall~, the passivation of ~etals is e~fected a~d their passive s-tate i.s maintained by electrical potential adjus-tment devices which cha~ge either the ma~nitude o~ the current applied between an object ~ be ~xotected ~rom corrosion ~the anode) and ~n auxiliar~ electrode (the cathode), or bhe t1me lnter~als Detween whlch ~aid current is applied. ~he same ef~ct a~be a-ttained by using the current of a ~oltaic couple made up by the object being protected and an auxiliary elec-trode (the protector) which is in con~act with an aggressive medium.
:.
., .
, ~ ~
.
, ~L08845~
There is known an anodic corrosion protection method carried out with the aid of a periodic-action potential regulator (cf. US Patent No. 3,442,779, Cl. 204-1~7). According to this method, use is made of a cathode and a reference :
electrode which makes it possible to check the potential of .
an article being protected from corrosion. Said article, cathode and reference electrode are in contact with a corroding medium. The range within which the article's potential is ..
altered is set by a setting device of the potential regulator and is found within the passive potential range.
According to the method under review, polarizing current is applied when the potential of -the object being protected from corrosion drops to the lower limit of the predetermined potential adjustment range.
A positive shift in the potential of the object takes place under the action of the polarizing current. As soon as the upper limit of the potential adjustment range has been reached, the supply of polarizing current is discontinued. Then, the potential of the object being protected from corrosion again gradually drops to reach the lower limit of the potential adjustment range, which necessitates a repeated application of polarizing current. The time interval between individual applications of polarizing current is determined by the rate of a drop of the potential from the upper to the lower limit - :~ .
of the potential adjustment range, as well as by the properties ~,. .
.... .....
:, - . . : . , . . , . : , ~L~889L58 of the metal from which the object which is to be protected from corrosion is made, the type of the aggressive medium, and changes in the temperature and level of the conducting medium.
Normally, the intervals at which polarizing current is applied : vary from a few seconds to many minutes. :.
- .:
The method under review ensures corrosion protection .:
in any technological conditions, yet the relatively high switching .
frequency reduces the service life of the potential regulators and thus affects the reliability of corrosion protection.
; 10 Besides, this method does not work in cases of power failure.
There is further known a method of anodic corrosion protection, whereby an article liable to corrosion (the anode) is passivated and malntained in the state of passivation by the current of a voltaic couple produced by bringing into con-tact the article to be protected from corrosion and a cathodic protector (cf. N.D. Tomashov, G.P. Chernova, "Passivnovst i . :
zashchita metallov ot korrozii" / "Passivation and Corrosion Protection of Metals" /, Moscow, 1965. p. 153; M. Stern, H.
Wissenbery, J. Electrochem. Soc., 1959, 106, 751). The protector is made of noble metals (plat:inum, palladium, gold), corrosion-resistant stainless steels, metal oxides, or graphite.
The operation of the voltaic couple and, consequently, the reliability of corrosion protection, are largely determined by the area ratio of the protector and the object to be ' ' -~ .
s~
protected from corrosion.
This method of corrosion protection is highly reliable, easy to implement and independen L of external power supply sources. On the other hand, the protectors' area must be sufficiently large both to maintain the passive state of an article to be protected from corrosion and ensure passivation in the initial period and if the stable passive state of the article is for some reason disturbed. Successive utilization of cathodic protectors is possible only when their area is com-parable with, and even in excess of, the area of an object to be protected from corrosion. The latter consideration casts doubt upon technical feasibility and practical expediency of using cathodic protectors for anodic protection. This a].so accounts ~or the fact that cathodic pro-tectors have not found extensive application in the field of anodic corrosion protection.
It is an extremely complicated and arduous task to bring the equipment to be protected from corrosion into the passive state. This task also makes it necessary to disconnect the equipment from the production line. The above factors make it clear that successful implementation of the anodic protection method is only possible if there are reliable ways to maintain the passive state of an object to be protected from corrosion.
"
.,. ~,.
' ,' ~C~88~5~3 The fore~oing methods of eorxosion protection are -either not reliable enough to justif~ thelr extensive application, or are impractable ~rom the technollgical point of view.
In view of the above considerations, it is an object of the present inventlon to pxovide a highly reliable method of corrosion protection.
It is another object of the invention to provide a corrosion protection method which would malce it possible to prolong the serviee life of the potential adjustment means. ~ -10Aceordingly, the present invention provides a method of proteeting an object in contact with a condueting medium from corrosion by means of anodic polarization of said object, eomprising periodieally passing polarizing eurrent ~rom an external souree bekween an auxiliary eleetrode, i.e. a eathode, and said objeet when the latter~s eleetrieal potential lies outside preseribed limits to bring said objeet into a passive state and eleetrically shortLng said auxiliary electrode to said objeet externally of said eondueting medium, during~ ~me intervals G ~
when said polarizing~is not being passed from said extexnal souree between said auxiliary electrode and said object to ~orm a voltaie eouple and so maintain said passive sta-te under normal operating eonditions, The funetion of the auxiliary eleetrode, with whieh the objeet to be proteeted from corrosion comes into eontact, ean be performed by the eathode and other electrodes whieh .
~ 7-~138g, S~
are in contact with the aggressive conducting medium and can operate as cathodic protectors.
The corrosion protection method does not affect the possibility of changing within a broad range the magnitude or time of application of polarizing current, which is the major advantage of polarizing corrosion protect:ion devices. Besides, the method is highly reliable.
The possibility of changing within broad limits the magnitude or time of application of polarizing current is of utmost importance during the passivation of the metal of objects to be protected from corrosion, or in cases of sharp changes in the parameters of a technological process, which changes can bring the objects being protected from corrosion into the active state. When the technologlcal proces9 goes on normally, the method reliably maintains the passive state of objects being protected from corrosion.
According to the corrosion protection method, the auxiliary electrodes (the cathodic protectors) are only used to maintain the passive state or reduce the rate of a drop in the potential of objects being protected from corrosion in the absence of polarizing current; hence, the area of the auxiliary electrodes may be 50 to 100 times less than that o~
objects being protected from corrosion. This factor makes it possible to employ cathodic protectors for corrosion protection.
.' ' ' ;.
.. ' .:
-:
3Lq~ 5~3 According to the method, the potential regulator .
operates only during the initial period, or when the parameters of technological processes deviate from prescribed values and when the cathodic protectors are no longer able -to maintain the passive state of objects being protected f:rom corrosion. This makes the opera-ting conditions of the periodic-action potential regulators less severe and prolongs their service life.
According to the method, corrosion protection is effect-ed by the cathodic protector current, so the method of the present invention is little affected by power failures.
Other objects and advantages of the present invention will become more apparent from the :Eollowi.ng detailed description of a preEerred embodiment -thereoE to be read in conjunction with the accomapnying draw:incJ which is a block d:iagram of the device for effecting the proposed method.
Referring now to this drawing, in an object 1, which is to be protected from corrosion and is ~-illed with a conducting : medium 2 (for example, sulphur:ic acid or ammonia solution), there is placed a reference electrode 3 which is electrically coupled to a regulator 4 determining the electrical potential of the object 1. The ~otential regul~tor ~ comprises a se-tting device (not shown) and differential amplifier S. The reference electrode 3 is connected to one of the inputs of the amplifier 5, ~
whereas ;
-~
. ~ ,,'.
:
;" .
_g_ ~ ~L(18~9~S8 an auxiliary electrode, or cathode, 6 which is also immersed in the conducting medium 2 is connected to its other input.
The output of the amplifier 5 is connected to the input of a relay 7 which is a final control element. The relay 7 has make contacts 8 which are connected into the clrcuit between rectifier 9 and the auxiliary electrode 6. The relay also has break contacts 10 which are connected into the circuit arranged between the electrode 6 and the object 1.
The reference electrode 3 may be a ealomel, ehlorine-silver, or mereury-sulphate eleetrode.
The auxiliary electrode 6 may be made from a material which can be used as a cathodic protector, for example, platiniæed metal, or graphite.
If at a given instant, the measured value oE the eleetrieal potential of the objeet 1, i.e. of the anode, is below the lower limit of the adjustment range set by the setting deviee (not shown), the error signal (a signal of the difference between the preseribed and aetual potential values), amplified by the amplifier 5, switehes on the relay 7. Said relay 7 through its make eontaets 8 connects the rectifier 9 to the eathode 6 and anode 1. Polarizing current in the anode-cathode eireuit ehanges the potential oE the objeet 1 to a positive value. ~s the potential reaches the upper limit of the potential adjustment range, the relay 7 discontinues the supply of polarizing eurrent to the reetifier 9 and eonneets the eathode 6 through the contaets 10 to the :::
. :
' ',;' --10~ '' 5~3 anode 1, whereby a voltaic couple is ~ormed. ~l'he current o~ voltaic couple (-the anode-cathode protector) slows down the rate o~ the reduc~ion o~ the po~e~tial of the object 1, ~hich is conducive to a stable passive sta-te o~ said object 1 In the course of the passivation o~ the object 19 intervals betwee~ applications o~ polarizing current are increased until the current o~ the voltaic couple is suff'icient to preserve the passi~e state o~ the object 1 being protected ~rom corrosio~. When this state is achieved, the potential regulator 4 remains idle~ ~his operating mode o~ the device can be maintained ~ , until -the passi~e state of the object 1 is disturbed ~or some reason.
1~' the physico-chemical proce~ses u~derway in the techno-logical system, or some other factors disturb tha passive state of the object 1, ~he current of the voltaic couple is insu~icient to restore the passi~e state o~ said ar~icle 1 whose reduced potential again brings into pla~ -the potential regulator 4 which restores the passive state o~ the object 1.
.. ..
.
.: .
3451~
rL'he electrical potential o~ a metal liable to corrosion can be brought i~to the passive ra~ge with a view o-P reducing the rate o~ corrosion by appiyin~ electric curre~t, which thls case is re~errea to as polarizing current; between the metal to be protected from corrosion~ whlch in ~his case is an a~ode, and a~ auxiiiar~ electrode which is a cathode. ~`he same e~`ect can be produced by adding into the corrodin$ solution ~r agents ~hm~ ~re called passiva-tors.
Passivation o~ a metal by means o~ polarizing curre~t is re-~erred to as anodic corrosion protection; the bringing o~
the metal's electric po-tential into the passive ran~e is called anodic polarization.
~ ne impleme~tion of the ~oregoing method in lndustrlal conditions calls ~or some ~ to reliably maintain the passive state of objects ~o be protected ~rom corrosion.
l~ormall~, the passivation of ~etals is e~fected a~d their passive s-tate i.s maintained by electrical potential adjus-tment devices which cha~ge either the ma~nitude o~ the current applied between an object ~ be ~xotected ~rom corrosion ~the anode) and ~n auxiliar~ electrode (the cathode), or bhe t1me lnter~als Detween whlch ~aid current is applied. ~he same ef~ct a~be a-ttained by using the current of a ~oltaic couple made up by the object being protected and an auxiliary elec-trode (the protector) which is in con~act with an aggressive medium.
:.
., .
, ~ ~
.
, ~L08845~
There is known an anodic corrosion protection method carried out with the aid of a periodic-action potential regulator (cf. US Patent No. 3,442,779, Cl. 204-1~7). According to this method, use is made of a cathode and a reference :
electrode which makes it possible to check the potential of .
an article being protected from corrosion. Said article, cathode and reference electrode are in contact with a corroding medium. The range within which the article's potential is ..
altered is set by a setting device of the potential regulator and is found within the passive potential range.
According to the method under review, polarizing current is applied when the potential of -the object being protected from corrosion drops to the lower limit of the predetermined potential adjustment range.
A positive shift in the potential of the object takes place under the action of the polarizing current. As soon as the upper limit of the potential adjustment range has been reached, the supply of polarizing current is discontinued. Then, the potential of the object being protected from corrosion again gradually drops to reach the lower limit of the potential adjustment range, which necessitates a repeated application of polarizing current. The time interval between individual applications of polarizing current is determined by the rate of a drop of the potential from the upper to the lower limit - :~ .
of the potential adjustment range, as well as by the properties ~,. .
.... .....
:, - . . : . , . . , . : , ~L~889L58 of the metal from which the object which is to be protected from corrosion is made, the type of the aggressive medium, and changes in the temperature and level of the conducting medium.
Normally, the intervals at which polarizing current is applied : vary from a few seconds to many minutes. :.
- .:
The method under review ensures corrosion protection .:
in any technological conditions, yet the relatively high switching .
frequency reduces the service life of the potential regulators and thus affects the reliability of corrosion protection.
; 10 Besides, this method does not work in cases of power failure.
There is further known a method of anodic corrosion protection, whereby an article liable to corrosion (the anode) is passivated and malntained in the state of passivation by the current of a voltaic couple produced by bringing into con-tact the article to be protected from corrosion and a cathodic protector (cf. N.D. Tomashov, G.P. Chernova, "Passivnovst i . :
zashchita metallov ot korrozii" / "Passivation and Corrosion Protection of Metals" /, Moscow, 1965. p. 153; M. Stern, H.
Wissenbery, J. Electrochem. Soc., 1959, 106, 751). The protector is made of noble metals (plat:inum, palladium, gold), corrosion-resistant stainless steels, metal oxides, or graphite.
The operation of the voltaic couple and, consequently, the reliability of corrosion protection, are largely determined by the area ratio of the protector and the object to be ' ' -~ .
s~
protected from corrosion.
This method of corrosion protection is highly reliable, easy to implement and independen L of external power supply sources. On the other hand, the protectors' area must be sufficiently large both to maintain the passive state of an article to be protected from corrosion and ensure passivation in the initial period and if the stable passive state of the article is for some reason disturbed. Successive utilization of cathodic protectors is possible only when their area is com-parable with, and even in excess of, the area of an object to be protected from corrosion. The latter consideration casts doubt upon technical feasibility and practical expediency of using cathodic protectors for anodic protection. This a].so accounts ~or the fact that cathodic pro-tectors have not found extensive application in the field of anodic corrosion protection.
It is an extremely complicated and arduous task to bring the equipment to be protected from corrosion into the passive state. This task also makes it necessary to disconnect the equipment from the production line. The above factors make it clear that successful implementation of the anodic protection method is only possible if there are reliable ways to maintain the passive state of an object to be protected from corrosion.
"
.,. ~,.
' ,' ~C~88~5~3 The fore~oing methods of eorxosion protection are -either not reliable enough to justif~ thelr extensive application, or are impractable ~rom the technollgical point of view.
In view of the above considerations, it is an object of the present inventlon to pxovide a highly reliable method of corrosion protection.
It is another object of the invention to provide a corrosion protection method which would malce it possible to prolong the serviee life of the potential adjustment means. ~ -10Aceordingly, the present invention provides a method of proteeting an object in contact with a condueting medium from corrosion by means of anodic polarization of said object, eomprising periodieally passing polarizing eurrent ~rom an external souree bekween an auxiliary eleetrode, i.e. a eathode, and said objeet when the latter~s eleetrieal potential lies outside preseribed limits to bring said objeet into a passive state and eleetrically shortLng said auxiliary electrode to said objeet externally of said eondueting medium, during~ ~me intervals G ~
when said polarizing~is not being passed from said extexnal souree between said auxiliary electrode and said object to ~orm a voltaie eouple and so maintain said passive sta-te under normal operating eonditions, The funetion of the auxiliary eleetrode, with whieh the objeet to be proteeted from corrosion comes into eontact, ean be performed by the eathode and other electrodes whieh .
~ 7-~138g, S~
are in contact with the aggressive conducting medium and can operate as cathodic protectors.
The corrosion protection method does not affect the possibility of changing within a broad range the magnitude or time of application of polarizing current, which is the major advantage of polarizing corrosion protect:ion devices. Besides, the method is highly reliable.
The possibility of changing within broad limits the magnitude or time of application of polarizing current is of utmost importance during the passivation of the metal of objects to be protected from corrosion, or in cases of sharp changes in the parameters of a technological process, which changes can bring the objects being protected from corrosion into the active state. When the technologlcal proces9 goes on normally, the method reliably maintains the passive state of objects being protected from corrosion.
According to the corrosion protection method, the auxiliary electrodes (the cathodic protectors) are only used to maintain the passive state or reduce the rate of a drop in the potential of objects being protected from corrosion in the absence of polarizing current; hence, the area of the auxiliary electrodes may be 50 to 100 times less than that o~
objects being protected from corrosion. This factor makes it possible to employ cathodic protectors for corrosion protection.
.' ' ' ;.
.. ' .:
-:
3Lq~ 5~3 According to the method, the potential regulator .
operates only during the initial period, or when the parameters of technological processes deviate from prescribed values and when the cathodic protectors are no longer able -to maintain the passive state of objects being protected f:rom corrosion. This makes the opera-ting conditions of the periodic-action potential regulators less severe and prolongs their service life.
According to the method, corrosion protection is effect-ed by the cathodic protector current, so the method of the present invention is little affected by power failures.
Other objects and advantages of the present invention will become more apparent from the :Eollowi.ng detailed description of a preEerred embodiment -thereoE to be read in conjunction with the accomapnying draw:incJ which is a block d:iagram of the device for effecting the proposed method.
Referring now to this drawing, in an object 1, which is to be protected from corrosion and is ~-illed with a conducting : medium 2 (for example, sulphur:ic acid or ammonia solution), there is placed a reference electrode 3 which is electrically coupled to a regulator 4 determining the electrical potential of the object 1. The ~otential regul~tor ~ comprises a se-tting device (not shown) and differential amplifier S. The reference electrode 3 is connected to one of the inputs of the amplifier 5, ~
whereas ;
-~
. ~ ,,'.
:
;" .
_g_ ~ ~L(18~9~S8 an auxiliary electrode, or cathode, 6 which is also immersed in the conducting medium 2 is connected to its other input.
The output of the amplifier 5 is connected to the input of a relay 7 which is a final control element. The relay 7 has make contacts 8 which are connected into the clrcuit between rectifier 9 and the auxiliary electrode 6. The relay also has break contacts 10 which are connected into the circuit arranged between the electrode 6 and the object 1.
The reference electrode 3 may be a ealomel, ehlorine-silver, or mereury-sulphate eleetrode.
The auxiliary electrode 6 may be made from a material which can be used as a cathodic protector, for example, platiniæed metal, or graphite.
If at a given instant, the measured value oE the eleetrieal potential of the objeet 1, i.e. of the anode, is below the lower limit of the adjustment range set by the setting deviee (not shown), the error signal (a signal of the difference between the preseribed and aetual potential values), amplified by the amplifier 5, switehes on the relay 7. Said relay 7 through its make eontaets 8 connects the rectifier 9 to the eathode 6 and anode 1. Polarizing current in the anode-cathode eireuit ehanges the potential oE the objeet 1 to a positive value. ~s the potential reaches the upper limit of the potential adjustment range, the relay 7 discontinues the supply of polarizing eurrent to the reetifier 9 and eonneets the eathode 6 through the contaets 10 to the :::
. :
' ',;' --10~ '' 5~3 anode 1, whereby a voltaic couple is ~ormed. ~l'he current o~ voltaic couple (-the anode-cathode protector) slows down the rate o~ the reduc~ion o~ the po~e~tial of the object 1, ~hich is conducive to a stable passive sta-te o~ said object 1 In the course of the passivation o~ the object 19 intervals betwee~ applications o~ polarizing current are increased until the current o~ the voltaic couple is suff'icient to preserve the passi~e state o~ the object 1 being protected ~rom corrosio~. When this state is achieved, the potential regulator 4 remains idle~ ~his operating mode o~ the device can be maintained ~ , until -the passi~e state of the object 1 is disturbed ~or some reason.
1~' the physico-chemical proce~ses u~derway in the techno-logical system, or some other factors disturb tha passive state of the object 1, ~he current of the voltaic couple is insu~icient to restore the passi~e state o~ said ar~icle 1 whose reduced potential again brings into pla~ -the potential regulator 4 which restores the passive state o~ the object 1.
.. ..
.
.: .
Claims (5)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of protecting an object in contact with a conducting medium from corrosion by means of anodic polarization of said object, comprising periodically passing polarizing current from an external source between an auxiliary electrode, i.e. a cathode, and said object when the latter's electrical potential lies outside prescribed limits to bring said object into a passive state and electrically shorting said auxiliary electrode to said object, externally of said conducting medium, during time intervals when said polarizing current is not being passed from said external source between said auxiliary electrode and said object to form a voltaic couple and so maintain said passive state under normal operating conditions.
2. A method as claimed in claim 1, wherein said conducting medium is an electrolyte.
3. A device for protecting an object in contact with a conducting medium from corrosion, comprising means for comparing the potential of the object with a reference potential, a cathode in said conducting medium, an external current source, means for periodically passing anodic polarizing current from said external current source between said cathode and said object when the potential of said object lies outside prescribed limits to bring said object into the passive state, and means for electrically shorting said cathode to said object, externally of said conducting medium, when said polarizing current from said external source is not flowing between said cathode and said object to form a voltaic couple and so maintain said passive state under normal operating conditions.
4. A device as claimed in claim 3, further comprising a reference electrode in said conducting medium and a differential amplifier having one input connected to said reference electrode and another input connected to said object, said differential amplifier controlling means for alternately connecting said external source to said cathode and said object, and shorting said cathode to said object.
5. A device as claimed in claim 4, wherein said means for alternately connecting said external source to said cathode and said object, and shorting said cathode to said object is a relay having make contacts between said source and one of said cathode and said object, and break contacts between said cathode and said object.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA258,476A CA1088458A (en) | 1976-08-05 | 1976-08-05 | Method of corrosion protection of objects in contact with conducting medium |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA258,476A CA1088458A (en) | 1976-08-05 | 1976-08-05 | Method of corrosion protection of objects in contact with conducting medium |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1088458A true CA1088458A (en) | 1980-10-28 |
Family
ID=4106583
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA258,476A Expired CA1088458A (en) | 1976-08-05 | 1976-08-05 | Method of corrosion protection of objects in contact with conducting medium |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1088458A (en) |
-
1976
- 1976-08-05 CA CA258,476A patent/CA1088458A/en not_active Expired
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