Note: Descriptions are shown in the official language in which they were submitted.
lU90901
The present invention relates to protection of metals
against corrosion, and more particularly to apparatus for anodic
protection of various industrial structures against corrosion,
being in contact with aggressive electrically-conductive media
and made of materials prone to passivation in these media.
The invention is best suitable for corrosion protection
of structures in chemical, food, textile and pulp-and-paper
industries.
Known in the art are various methods and systems for
corrosion protection of industrial structures. The method of
corrosion control by anodic polarization, however, is considered
to be most effective in a number of cases.
Essentially, this method is as follows.
It is well known that when a metal comes into contact
with an aggresive medium,it is attacked by corrosion, with a
potential, known as stationary potenial, being established on the
metal's surface. If the metal potential shifts towards its
positive values, the rate of corrosion, at definite values and
in a number of cases, will sharply decrease. This phenomenon
-2-
109~ 01
is commonly known as the passivity of metal, and the shifting of
its potential towards the range of the indicated values is known
as passivation. The range of the potential values wherein the
passivity takes place is known as the passive region. The
absolute value and extent of this region depend upon the nature
of the corroding metal and aggressive medium to which the metal
is exposed. Consequently, by shifting the metal potential towards
the passive region, it is possible to protect it against corrosion.
This is normally attained either by passing electric current,
known as a polarizing current, from an external power source,
between the metal to be protected, serving as the anode in this
case, and auxiliary electrode serving as the cathode, or els~ by
adding various components, passivators, into the corrosive medium.
The passivity of metal attained by applying the polarizing current
is what, in essence, constitutes the anodic corrosion protection
method, and the process of passivation is, in this case, referred
to as the anodic polarization of metal.
The industrial application of this method requires
apparatus for maintaining the potential of the objects to be
protected within the passive region, which apparatus are to fall
in line with certain specific requirements, the most important
one being their high degree of reliability in maintaining the
potential of the objects in question within a predetermined range.
~0~01
This type of apparatus will ordinarily comprise devices
for controlling the polarizing current with respect to the poten-
tial of the objects being protected, namely, potentiostatic
devices, as well as auxiliary electrodes serving as cathodes and
reference (standard) electrodes being in contact with a corrosive
medium and connected to the potentiostatic devices.
Known in the art is an apparatus for anodic protection
of vessels against corrosion (cf. US Patent No. 3,197,755).
According to this patent, the apparatus comprises an auxiliary
electro~e and two reference electrodes placed in an ago;resive
medium, a controller connected to the auxiliary and reference
electrodes as well as to the vessels being protected. The
apparatus also includes a device for comparing the potential
difference of the reference electrodes, connected to these
electrodes as well as to a change-over switch, the latter being
also connected to the controller. With one of the vessel
potential deviating from a predetermined range, the controller
adjusts,the polarizing current so that the vessel potential
remains within the predetermined range. In case of failure of
one of the reference electrodes, the device for comparing the
potential difference of the electrodes sends an alarm signal
to the operator and actuates the switching device. The latter
10~0~01
switches over the controller to the properly functioning reference
electrode.
The apparatus described above maintains its efficiency
only when one of its elements, the reference electrode, in
this case, is out of order. If, however, any other element or
unit gets out of order (except the reference electrode), the
apparatus will fail to maintain the potential of the vessel being
protected within the predetermined range, thus failing to meet
the most important requirement imposed on structures of this
type, namely, high degree of reliability. Besides, the apparatus
is unable to provide corrosion protection for a plurality of
industrial vessels.
There is also known an apparatus for anodically
protecting several vessels against corrosion, wherein but one
potentiostat i8 used (cf. US Patent No. 3,483,101; Cl. 204-147).
This apparatus comprises one auxiliary electrode and one reference
electrode, arranged in each vessel to be protected and connected
through a cam timing switch to the potentiostat.
To maintain the potential of the vessels being protected
within a predetermined range, the potentiostat, by using the
action of the cam timing switch, is electrically connected in
a stepwise manner to each vessel for equal time periods.
When a potential shift occurs at any one of the vessels, the
1~0901
the potentiostat initiates polarizing current to this vessel, the
"on" cycle of which lasts long enough to maintain the vessel
potential within the preset range. The swi~ching "on-off" cycles
of the cam timing switch is preset in accordance with specific
features of the vessels being protected and remains within the
range of from one to ten minutes per vessel, remaining constant
during the whole operating period. The failure of one of the
appara~us units or elements will impair the desired efficiency
of protection of the vessels connected thereto.
It should also be pointed out that after being in
operation for a certain period of time, an apparatus for anodic
protection may require repair, preventive inspection or replace-
ment of elements (e.g. potentiostats, reference electrodes, etc.).
The prior art systems cannot be repaired or maintained without
the potential of the vessels deviating from a preset range, which
limits the scope of their application.
Besides, the known systems fail to maintain the potenti-
al of the vessels being protected within a predetermined range
in case of disturbances occuring during operation of these
vessels. For example, the concentration of the corrosive
medium is increased, or one of the apparatus elements, for
instance, the potentiostat, is out of order.
lO~O~Oi
It should be noted that the anodic polarization corrosion
protection method fails to find wide industrial application because
heavy polarizing currents are required to convert the metal of
the objects being protected to passive state, or because passivating
agents should be added to the corrosive medium.
The use of heavy polarizing currents requires complex
powerful sources which are not included in the standard set of
such an apparatus. The addition of passivating agents to the
corrosive medium is oftentimes not permitted by the production
process.
It should also be noted that when a production system
is being put into operation, the restrictions mentioned above
could be ignored with no damage to production process. However,
with the systems already in operation, these restrictions assume
primary importance imposing rather strict requirements upon an
apparatus for anodic protection of objects against corrosion,
demanding high degree of reliability in maintaining the vessel
potential within a preset range.
Ordinarily, operation lines may include a plurality of
either similar or dissimilar structures in need of protection
against corrosion.
Therefore, it is preferable that apparatus for anodic
protection should be so designed as to provide for simultanaous
~O~OS~Ol
protection of several structures electrically connected thereto,
functioning either in one or sev-ral operation lines.
Accordingly, it is the primary object of the present
invention to provide an apparatus for anodic protection of
industrial structures against corrosion, wherein a high degree
of reliability in maintaining the structure potential within
a preset range is ensured notwithstanding disturbances in the
operating conditions of these structures, or a break-down of the
apparatus units or elements.
Another object of the invention is to afford corrosion
protection to a plurality of either similar or dissimilar in-
dustrial structures, as well as to complete operation lines.
A further object of the invention is to increase the
number of industrial structures, connected to the apparatus, in
the course of operation without interrupting the production
process, and carry out repair and maintenance of all the apparatus
units with no loss in the efficiency of the structures' protection.
Finally, it is an object of the invention to provide
an apparatus for employment in various branches of industry.
~0 Essentially, the proposed invention resides in that
an apparatus for anodic protection of structures is provided,
wherein the structure potential control circuits and comparator
circuits are made independent.
--8--
~ 0'30~
Accordingly, the present invention provides an
apparatus for anodic protection of metal objects in contact with
electrically conductive media, comprising: a plurality of
self-contained potentiostats for the potential control of each
said object; reference electrodes and auxiliary electrodes
serving as cathodes arranged in contact with said electrically
conductive medium, said reference electrodes being connected
to inputs of said respective potentiostats; a change-over
switch including a control circuit and having first and second
positions, said change-over switch in said first position
connecting said potentiostats to said auxiliary electrodes to
control the potential of said objects; a stand-by power source
electrically connected via said change-over switch when in
said second position to said auxiliary electrodes, the capacity
of said power source being substantially higher than that of
each of said potentiostats; means for sensing the potential of
said objects connected to the control circuit of said change-
over switch and generating a control signal to change-over
said switch to electrically connect said stand-by power source
to the auxiliary electrode of any one of said objects when its
potential deviates from a preset value.
The provision of self-contained potentiostats for
each object being protected makes it possible to maintain the
potential difference at, and carry out polarization of, each
object separately and independently of one another with respect
to their specific features.
.
.~
lO9~0i
The stand-by power source of the apparatus whose capaci-
ty is two to three times higher than that of each self-contained
potentiostat, and the controlled change-over switch, electrically
connecting the potentiostats and stand-by power source to the
objects being protected, make possible the switch-over of each
object being protected to the current of the stand-by power
source, thereby providing for repair and preventive inspection
of the potentiostats, reference electrodes and stand-by power
source with no loss in the efficiency of the objects' protection.
The means for sensing the object potential, generating
a signal for the change-over switch to connect the stand-by
power source to the object being protected having its potential
deviating from a preset value, provides for a high degree of
reliability in maintaining the potential of the objects being
protected notwithstanding a break-down of one of the potentiostatic
devices, or disturbances occurring in the performance character-
istics of these objects.
In accordance with one of the possible embodiments of
the invention, wherein means for sensing the objects potential
comprises a potential comparing device provided with additional
reference (standard) electrodes, each being in contact with the
electrically conductive medium and connected via an interrogating
device to the potential measuring device having one of its outputs
electrically connected via a logical AND-gate to the controlled
change-over switch intended to apply the stand-by power source
current to the object having its potential deviated from a
preset value.
Such an embodiment of the means for sensing the object
potential ensures a high degree of reliability in maintaining
the potential of the objects being protected within a pre-
determined range, both in case of failure of the reference elec-
trodes, or disturbances in the performance characteristics of
--10--
109~01
the industrial objects. The continuous control of all the object
potentials effected by the interrogating device and independent
potential control circuits, make the apparatus for corrosion
protection applicable in systems having a plurality of similar and
dissimilar industrial objects. The number of the latter is
determined mainly by the number of positions of the interrogating
device used.
The employment of a self-contained stand-by power source
(e.g. StQrage battery) ensures a high degree of reliability
in maintaining the object potential within a preset range even
in case of an emergency power supply cut-off, this being an
important factor under conditions of uns~able power supply. The
capacity of the stand-by power source should be sufficient to en-
able simultaneous maintenance of the potential of all the objects
being protected.
Since the potentiostatic devices, as well as the
potential sensing means can be preset at various potential values,
depending upon specific conditions, the herein disclosed apparatus
can advantageously be used in various fields of industry to afford
corrosion protection to structures already in operation as well
as those to be introduced. The apparatus may also be used for
the protection of complete production lines.
Other objects and advantages of the present invention
will be better understood from the following detailed description
of an embodiment thereof taken in conjunction with the accompanying
drawings, wherein:
Fig. I is a block diagram of an apparatus in accordance
with the invention;
~ ig. 2 is a schematic diagram of one of the possible
embodiments of the invention.
The proposed apparatus for anodic protection of objects
I against corrosion comprises potentiostats 2 equal in number to
the objects I, having their positive terminals connected, through
~090.~01
a controlled change-over switch 3 to the objects I, and their
negative terminals to auxiliary electrodes serving as cathodes
and accommodated in each object I.
Each potentiostat 2 has its input connected to a reference
electrode 5 also positioned in each object I. The cathodes 4 and
electrodes 5 are in contact with an electrically conductive medium
6 inside the objects I.
Thus, the potentiostats 2, cathodes 4 and objects I, as
well as the reference electrodes 5, form indepelident potential
control circuits monitoring the potential of the objects I to
be protected.
There is arranged in each object I an additional
electrode 7 connected via an interrogating device 8 to a device
9 intended for measuring the potential of the objects I. The
potential measuring device 9 is connected to one of the inputs
of a logical AND-gate 10, having its second input connected to the
interrogating device 8 and its outputs connected to the change-
over switch 3 and to a means II for sending a signal indicative
of deviation of the potential at the objects I from a preset value.
The apparatus also comprises a stand-by power source 12
connected through the change-over switch 3 to the objects I.
The capacity of this power source, is substantially higher than
that of a power source (not shown) of each self contained
potentiostat 2 and determined by specific conditions. Ordinarily,
the capacity is regarded sufficient if it can provide for
maintaining the potential of at least half of the objects
electrically connected to the apparatus.
Thus, the means for sensing the potential of the objects
I, comprising the potential measuring device 9, additional
reference electrode 7, interrogating device 8 and logical AND-gate
10, is made independent from the potential control circuits
described above.
-12-
lO~O~Oi
The proposed apparatus operates as follows.
The potential at each vbject 1 is adjusted independently
by means of a respective potentiostat 2 and monitored by the
potential measuring device 9 with the help of the additional
reference electrodes 7 electrically connected to and disconnected
from the potential measuring device 9 at regular intervals, by
the interrogating device 8.
In case the potential at any one of the object 1 devi-
ates from a preset value, which may occur due to disturbances
in operating conditions or failure of one of the units, e.g.
potentiostat, 2, the potential measuring device 9 generates a
signal applied to the AND-gate 10. The latter, on obtaining
information from the interrogating device 8 as to which particular
object I has its potential monitored at the moment actuates
the change-over switch 3.
The change-over switch 3 electrically disconnects a
respective potentiostat 2 from the object I, switching it over
to the stand-by power source 12. Simultaneously, the AND-gate 10
actuates the device II, generating a signal indicative of the
potential at a respective object deviating from a preset value,
thus informing the operator of the disturbance. With the failure
having been eliminated, the device II is switched off.
One of the possible embodiments of the invention is
shown in Fig. 2. Elements similar to those shown in Fig. 1
retain the same reference numerals in Fig. 2.
In accordance with the invention, the potentiostats 2
have their positive terminals (not shown) connected to the objects
I being protected, with their negative terminals being connected,
across the opening contacts of switches 13 and opening contacts
14 of an electromagnetic relay 15 to respective cathodes 4.
The stand-by power source 12 has its positive terminal
connected to the objects I being protected and its negative terminal
1~(){~01
connected, via ballast resistors 16 and closing contacts 17 of
the relay 15, to the cathodes 4.
The closing contacts 17 of the relay 15 are shunted
by the closing contacts of the above-mentioned switches 13. The
reference electrodes 5 are directly connected to respective
potentiostats 2, and the electrodes 7 are connected via the
interrogating device 8 to the potential measuring device 9. The
automatic multiple~point potentiometer is used in the embodiment
under consideration to perform the function of the potential
measuring device 9. The function of the interrogating device 8
is performed by the position selector of the said potentiometer.
The AND-gate (shown in Fig. I under reference number 10) is made
of up, in this embodiment, by a closing emergency contact 18 of
said potentiometer, contacts 19 of the position selector switch
of the same potentiometer, and by the electromagnetic relay 15.
The contacts 19 of the position selector are connected to the relay
15. The circuits of the contacts 19 of the position selector
are shunted by series-connected contacts 20 of the relay 15 and
by circuit opening buttons 21, and are associated through these
elements to phase A of the supply voltage. Closing contacts 22
of the relay 15 are connected to respective signal lamps 23 of
the device 11.
The potential of the objects being protected is
maintained by means of the potentiostats 2. Therewith, the
contacts of all the relays and switches are positioned as shown
in Fig. 2.
With the potential at one of the structures deviating
from a preset value, the emergency contact 18 of the above
potentiometer is closed. A respective contact 19 of the potentio-
meter's position selector is closed, too.
The relay 15, corresponding to the object I having itspotential deviated from a preset value, operates on being
-14-
1090~0i
energized viathe contacts18 andl9 and,by its contact 14,switches off
a respectivepotentiostat 2, disconnecting it from a respective cathode
4, and,by its contact 17,switches on the stand-by power source 12,
electrically connectingit through the ballast resistor 16intended for
limitingthepolarizing current to the cathode 4.
At the same time, the contact 22 switches on a
respective signal lamp 23. The contact 20 is used to actuate
a respective relay 15, connecting it through the button 21 to
the supply vol~age. This makes it possible to keep the relay
15 in the on position even after opening of the contact 19, this
being due to the fact that the position selector of the
potentiometer has been shifted to the following position.
After detecting and eliminating the fault, the operator,
by pushing a respective button, breaks the supply circuit of
the relay 15. The contacts are switched over in a reverse
sequence, whereby the apparatus is brought back to the initial
state.
Whenever there is a necessity to carry out repair or
preventive inspection, one of the switches 13 is turned on
disconnecting a respective object I being protected from a
respective potentiostat 2, switching over this object to the
stand-by power source 12.
To bring the apparatus back to the initial state, it
is sufficient to turn the switch 13 back to its previous position.
This being done, a respective object I is electrically
disconnected from the stand-by power source 12 and connected back
to a respective potentiostat 2.
It should be pointed out that the herein disclosed
apparatus may be used for maintaining the potential of the
structures being protected at a preset value in the case of their
cathodic protection. This will only require to reverse the polar-
ity of connecting the potentiostat and stand-by power source to
-15-
~V90~
the ob~ect being protected, serving as the cathode in this case,
and to the auxiliary electrode, serving as the anode.
-16-
