EA035712B1 - Method and device for electrochemical protection of structural materials against corrosion - Google Patents

Abstract

The invention relates to a method for protecting constructional metal structures and pipelines against corrosion damage using a low current cathodic protection station, and a device for implementation of the method. The claimed technical result is simplifying the method by eliminating the two-stage determination of the potential of zero charge, increasing the reliability of determining the zero potential, maintaining the protective potential equal to the real potential of the uncharged surface determined with high accuracy and reliability, and maintaining it on the metal by compensating for changes that occur due to a change in the electrical conductivity of the metal-environment system, which leads to higher efficiency of corrosion protection of structural metals. This is achieved by provision of a method for electrochemical protection of structural metals against corrosion, wherein the potential in the metal-solution system is measured, the value of the protective potential is determined, the protective potential is applied to the metal from an external DC source and its level is automatically maintained, a DC source is used to compensate the deviation of the protection potential from the potential of an uncharged metal surface; according to the invention, in case of a change in environmental parameters, the value of zero potential of the metal is measured by the dead point of movement of the pointers of mirror-scale milliamperemeters embedded in the legs of the forward and reverse pulse driver, and the protective potential is set equal to the zero potential of the surface.

Description

The invention relates to a method for protecting structural metal structures and pipelines from corrosion damage using a cathodic protection station for low currents and a device for its implementation.

There is a known method of electrochemical protection of structural metals from corrosion, selected as the closest analogue, in which the stationary potential in the metal solution system is measured, the value of the protective potential is determined, the protective potential is supplied to the metal from an external DC source and its value is maintained, and when the parameters of the surrounding of the medium, the potential of the uncharged surface is measured, and the protective potential is set equal to the potential of the uncharged surface, and the deviation of the protective potential from the changed potential of the uncharged metal surface is compensated using a direct current source. This method uses a method for determining the potential of an uncharged surface of a solid metal electrode, in which the magnitude of the stationary potential of the metal is measured, polarized with an electric current of the forward and reverse directions, the moment of establishing the potential of the uncharged surface is determined, the polarization of the electrode is carried out with a periodic current with different polarity pulses, and at the stages of the flow of the direct and reverse pulses, the external polarizing circuit of the electric current is opened, after opening the polarizing circuit, using an oscilloscope, the time curves of the electrode potential in the electrode-solution system are recorded, the potential decay curves from the positive and negative regions are compared by combining the moments of opening the external circuit when following the direct and reverse pulses, determine the merging point of the decay curves and the potential corresponding to this point is taken equal to the potential of the uncharged surface of the metal electrode (EA 008 848 B1, 31.08.2007).

The disadvantage of the above method is the low efficiency of protection against corrosion destruction, the time range between the circuit break in the area of forward and reverse pulses of periodic current, two-stage method for determining the potential of zero charge.

Known is a device for electrochemical protection of structural metals from corrosion, selected as the closest analogue, containing a device for determining the potential of an uncharged surface of a metal electrode, which consists of a bath with an electrically conductive medium and placed in it auxiliary and test electrodes, a reference electrode with a conductive bridge connected to the tested electrode, an electronic oscilloscope for measuring the potential at the tested electrode, a second electronic oscilloscope connected in parallel with the reference resistor to measure the current flowing from the current source through the switch resistor, an auxiliary electrode, the tested electrode connected, in turn, through the breaker to the current source. It also contains a constant polarizing current source with a regulator and a controlled resistor, a choke and a capacitor for separating periodic and direct current circuits, and a measuring bridge for determining the potential of an uncharged metal surface and monitoring the change in protective potential, consisting of forward and reverse pulses of periodic current, two DC ammeters connected in series with the pulse shapers in the bridge arms, a microammeter connected to the diagonal of the measuring bridge, and a balancing controlled resistor (EA 008848 B1, 08/31/2007).

The disadvantage of the above device is the impossibility of controlling the change in the protective potential in real conditions and maintaining the protective potential equal to the potential of the uncharged surface.

The objective of the invention is to develop an effective method for protecting structural metal structures and pipelines from corrosion damage using a cathodic protection station of the low current mode and a device for its implementation.

The claimed technical result is to simplify the method by eliminating the two-stage determination of the zero charge potential, increasing the reliability of determining the zero charge potential, maintaining the protective potential equal to the real potential of the uncharged surface, determined with high accuracy and reliability, and maintaining it on the metal by compensating for changes that arise in connection with a change in the electrical conductivity of the metal environment, which leads to an increase in the efficiency of corrosion protection of structural metals.

This is achieved by the fact that the method of electrochemical protection of structural metals from corrosion, in which the potential in the metal-solution system is measured, the magnitude of the protective potential is determined, the protective potential is supplied to the metal from an external DC source and automatically maintains its value, and is compensated by a direct current source the deviation of the protection potential from the potential of the uncharged metal surface, according to the invention, when changing the environmental parameters, the value of the potential of the zero charge of the metal is measured along the dead center of the movement of the arrows of milliammeters with a mirror scale, built into the arms of the direct and reverse pulses, and the protective potential is set equal to the potential of the zero charge surface.

This is also achieved by the fact that the device for electrochemical protection of structural metals

- 1 035712 against corrosion, including a device for determining the potential of an uncharged surface of a solid metal, a direct current source with a regulator and a controlled resistor, an inductor and a capacitor for separating circuits of periodic and direct currents, and a measuring bridge for determining and monitoring the potential of an uncharged metal surface according to the invention additionally contains two milliammeters of direct current with a mirror scale connected in series with pulse shapers in the bridge arms.

Moreover, a device for determining the potential of an uncharged surface of a solid metal, including a bath with an electrically conductive medium and placed in it the investigated and auxiliary electrodes, an electric current source, a resistor, instruments for measuring potential and current, a potential comparison electrode with a conductive bridge connected to a device for measuring potential , according to the invention, the source of the polarizing current is a device for obtaining a periodic current with a reverse pulse, the device for measuring the potential is an electronic oscilloscope and / or a digital multimeter, and the studied electrode is connected through a conductive bridge with milliammeters with a mirror scale built into the arms of the direct and reverse pulses.

The authors of the claimed invention have found that to determine the potential of a zero charge of a metal surface, it is sufficient to determine the dead point of the movement of the milliammeter arrow with a mirror scale in the arms of the forward and reverse pulses. In this case, the potential determined by the oscilloscope and / or digital multimeter corresponds to the zero charge potential of the metal electrode with the highest degree of confidence. This allows you to fix the parameters and eliminate the overlap of the slope of the curves when the circuit is broken by the thyratron relay according to the method described in the closest analogue.

In addition, the novelty of the claimed invention lies in the fact that there is no time range between the break of the circuit in the area of forward and reverse pulses of periodic current and there is no need for a two-stage measurement of the potential summed up from the stationary potential and the indicator of the point of meeting of curves (TVC) when the circuit is broken by a thyratron relay ...

The novelty of the claimed invention also lies in the fact that the set current parameters are stabilized in the time interval of the measurement period at the same time both in the forward and reverse direction of the current of the pulse shaper. In this case, an electronic-ionic balance is established in the electric double layer (DOE), which, with a high degree of accuracy, confirms the termination of metal dissolution with the loss of electrons and the correctness of determining the potential of the uncharged surface.

The use in the claimed invention of a device for determining the potential of an uncharged surface allows a high degree of accuracy to determine the potential of an uncharged surface. The use of a measuring bridge consisting of formers of forward and reverse pulses of periodic current, two milliammeters of direct current with a mirror scale, connected in series with the pulse formers in the arms of the bridge, a microammeter included in the diagonal of the measuring bridge, makes it possible to determine the change in the protective potential, and using a controlled resistor and a DC regulator to compensate for this change.

FIG. 1 shows a diagram of the claimed device, which determines the potential of an uncharged surface and includes the following elements: a bath (1) with an electrically conductive medium (2) and auxiliary (3) and investigated (4) electrodes placed in it, a reference electrode (5) located in a cell ( 6) with a conductive solution (7), and through a conductive bridge (8) connected to the test electrode (4), an oscilloscope and / or a digital multimeter (9) to measure the potential at the test electrode (4), an electronic oscilloscope (10) connected parallel to the reference resistor (11) to measure the current supplied to the auxiliary electrode (3) through the switch (12) from the current source (13) connected to the tested electrode (4).

FIG. 2 shows a diagram of the claimed device for electrochemical protection of structural metals from corrosion, which includes the following elements: bath (1) with an electrically conductive medium (2) and auxiliary (3) and investigated (4) electrodes placed in it, reference electrode (5) located in the cell (6) with a conductive solution (7), and through a conductive bridge (8) connected to the test electrode (4), an electronic oscilloscope and / or a digital multimeter (9) for measuring the potential on the test electrode (4), an ammeter (10) for measuring the direct current flowing through the auxiliary electrode (3), the choke (15), the controlled resistor (16) connected to the constant current source (17) with the regulator (18), the second output of the current source (17) through the switch (19), ammeter (10) is connected to an auxiliary electrode (3), an alternating current source (13), connected, in turn, through a capacitor (20), shunted by a contact (21), a breaker (14) with a measuring bridge, state from the formers of forward (22) and reverse (23) pulses of periodic current, switches (24) and (25), milliammeters with a mirror scale (26 and 27) connected in series with the pulse shapers (22 and 23) in the arms of the bridge, microammeter (28) with a switch (29) included in the diagonal of the measuring bridge, and a balancing controlled resistor (30) connected to the tested electrode (4). The second output of the source (13) of alternating current through the switch (12) is connected to the auxiliary electrode (3).

A device for determining the potential of an uncharged surface works as follows.

When the switch (12) is closed, a periodic current with a reverse pulse is supplied to the auxiliary electrode (3) and the tested electrode (4) from the current source (13) through the closed contact of the breaker (14). A current flows through the tested conductive medium (2), the shape and value of which is recorded by an oscilloscope and / or a digital multimeter (9). An electronic oscilloscope (10) at this time records the voltage drop between the investigated electrode (4) and the tested conductive medium (2). A balancing controlled resistor is used to adjust the current supply and determine the dead point of the movement of the milliammeter arrows with a mirror scale built into the arms of the forward and reverse pulses of periodic current. At this time, the readings of the oscilloscope and / or digital multimeter are recorded. These indicators are the parameters of the potential of the uncharged surface.

An example of a specific implementation of the method.

Iron, platinum, and silver electrodes were taken as the studied electrode. The electrodes were placed in a single normal solution of sulfuric acid (reagent grade) at a temperature of 298 K, in which there was a titanium electrode as an auxiliary electrode. The test electrode was exposed polarizing current amplitude at a current density of the forward and reverse pulse 500 A / m ² for 40-45 seconds. The current supply was adjusted and the dead center of the movement of the arrows of milliammeters with a mirror scale built into the arms of the direct and reverse pulses of periodic current was determined. At this time, the readings of the oscilloscope and / or digital multimeter were recorded. The results of measurements carried out using the proposed method and device are shown in table. 1.

Table 1

Test electrode Uncharged surface potential determined by the claimed method Uncharged surface potential determined by the Kosov method Uncharged surface potential determined by other methods The potential of the uncharged surface, calculated according to L.I. Antropov. Iron - 0.3857 ... -0.3866 -0.385 ...- 0.386 -0.37 -0.4 Platinum + 0.3098 ... +0.3104 +0.309 ... + 0.311 +0.28 +0.2 Silver -0.6946 ... -0.6957 -0.694 ...- 0.696 -0.70 ... -0.80 -0.4

Thus, the test results confirm the achievement of the set task - to increase the accuracy of determining the potential of the uncharged surface of a solid metal electrode.

The device for electrochemical protection of structural metals against corrosion works as follows.

The voltage from an adjustable AC source (13) through a switch (12) is fed to an auxiliary electrode (3) located in a bath (1), and through a capacitor (20) and a normally closed contact (21) is fed through a normally closed breaker (14) to the AC bridge, which, with the help of a forward pulse shaper (22), a reverse pulse shaper (23), generates forward and reverse voltage pulses supplied through a controlled resistor (30) to the electrode (4).

With the preliminary connection of the active load, instead of electrodes (3 and 4), the bridge is balanced, the current strength of the forward and reverse pulses is controlled by milliammeters (26 and 27), and the moment of establishing the balance of the components of the periodic current achieved using a balancing controlled resistor (30) is controlled by a microammeter (28).

When a bath (1) with an aggressive solution is connected, a total periodic current flows through the circuit and, using a microammeter 28, the algebraic difference between the forward and reverse currents is recorded according to the formula

Aik ik ia j where ik is the forward current density;

ia is the reverse current density for a given electrode area;

Aik - the difference in current densities, the value of which is estimated using a microammeter 28 with an accuracy of 10 ^-7 A (without amplification).

The magnitude and sign of the difference (Ai _k ) give information about the relative difficulty of the oxidative or reduction reaction in the metal / given aggressive medium system, which serves as a basic indicator for maintaining the protection potential.

With the help of a balancing controlled resistor (30), the dead point of movement is reached

- 3 035712 arrows on milliammeters with a mirrored scale (26 and 27), built into the arms of the forward and backward pulse shaper, on the screen of an electronic oscilloscope and / or digital multimeter (9), with high accuracy determine the potential of an uncharged metal surface in a given aggressive environment with automatic taking into account its heterogeneity, nature and chemical composition.

To establish the value of the current density of the protection from the direct current source (17) controlled by the regulator (18), a constant voltage is applied to the electrodes (3 and 4) of the bath (1) through a controlled resistor (16), when the constant current density changes with the resistor ( 16) or the current regulator (18) set the value of the protection potential (φ ₂ ) equal to the potential of the uncharged metal surface (φ _ε = ₀ ), determined earlier using this device.

When the parameters of the electrically conductive medium (2) change, the balancing of the measuring bridge will be disturbed and a current will flow through the microammeter (28), which will indicate a change in the potential of the uncharged surface of the metal electrode (4). With the help of a regulator (18) and a controlled resistor (16), they achieve such a position when the current passing through the microammeter (28) becomes zero, which will indicate that the supplied potential compensates for the deviation of the protection potential of the metal electrode surface (4) from potential of the uncharged surface (φ _{ε = 0} ).

The method of electrochemical protection of structural metals from corrosion is carried out as follows.

The investigated metal is placed in an aggressive environment. The dead center of the movement of the arrows of milliammeters built into the arms of the direct and reverse pulses of periodic current is determined. Measure the value of the reversal potential of the metal surface charge relative to the selected reference electrode in the metal-solution system - the potential of the uncharged surface. If the parameters of the external environment change, the potential of the uncharged surface is measured again and a polarizing current is supplied to the test metal from a direct current source, compensating for the change in the value of the protective potential by shifting it from a stationary value (φ ^) to (<p _z ).

An example of implementation of the invention.

The tested electrodes, made of iron, aluminum, copper and titanium, are alternately loaded into a 1N aqueous solution of H ₂ SO ₄ , water from the Black Sea and tap water of Chisinau of the following composition (see Table 2).

Table 2. Approximate mineralization of water

Place of water intake Ions, mg / l Total, mg / l Na ⁺ , K ⁺ Ca ²⁺ Mg ²⁺ SG NSOz ' SO ² ' Fe ³⁺ Black Sea g. Odessa 5530 246 648 9629 88 1305 17446 Moldova Chisinau 58.7 97.6 72.5 19.5 od 203 56 0.11 507.51

A titanium anode is placed in the bath (1) and one end of the agar-agar bridge is placed, the second end of the connecting bridge is immersed in a cell (6) with a saturated solution of potassium chloride, where the silver chloride reference electrode (5) was located, the dead points of the movement of milliammeter arrows with a mirror scale (26 and 27) and measure the value that corresponds to the potential of zero charge, while determining the density of the protective current (i _z ), hold the metal under the protective potential for 120 hours at T = 298 K and after weighing evaluate the effectiveness of electrochemical protection of the metal from corrosion destruction (see Table 3 for the results) in each environment.

- 4 035712

Table 3. Test results of the proposed method and device for protecting metals from corrosion destruction at a temperature of 298 K _____

Name of the aggressive environment pH of the environment Metal <Pz, B ic A / m ² iz A / m ² γ = = ie / iz z,% Fe -0.385 0.45530 0.03285 16.36050 92,7 1N solution 2.2 Al -0.510 1.47450 0.06500 22.68555 95.5 H ₂ SO ₄ Cu -0.265 0.29565 0.03120 9.47620 89.4 Ti -0.410 0.01615 0.00085 19.02348 94.7 Fe -0.425 0.34920 0.01885 18.52490 94.8 Black water 7.6..7.7 Al -0.570 0.93843 0.04635 20.24607 89.1 seas Cu -0.160 0.11875 0.00940 12.63121 92.1 Ti -0.470 0.01095 0.00045 23.79418 95.8 Water from Fe -0.495 0.18220 0.00715 25.48325 96.0 7.4 ... 7.8 Al -0.555 0.22945 0.00830 27.64338 95.9 water supply system Cu -0.170 0.06215 0.00290 21.43865 95.3 Chisinau Ti -0.455 0.00573 0.00020 28.64231 96.5

As shown by the results of the implementation of the claimed method and device for the protection of iron, aluminum, copper and titanium in various aggressive environments, the corrosion inhibition coefficient increases when going from 1N sulfuric acid solution to water from a water supply system in Chisinau for Fe from 16 to 25, for Al from 22 to 27, for Cu from 9 to 21, for Ti from 19 to 28; the degree of protection, for example, of iron in an acidic environment when using the proposed method and device is 92.7%, which indicates the effectiveness and appropriateness of the practical application of the invented method of protecting metal from corrosion and the device for its implementation.

The claimed invention has the following advantages:

for corrosion protection, the parameters of the zero charge potential determined in laboratory conditions are used, the set protection parameters are set and automatically maintained with an accuracy of + -1 mV;

protection is carried out with low currents, which practically exclude the evolution of hydrogen on the surface of the protected metal;

when establishing and automatically maintaining the potential of zero charge on the metal surface, a protective film is formed, consisting of metal salts in the electrolyte, with a thickness of 15-25 microns with dielectric characteristics (with a resistance of more than 30 MΩ), which makes it possible to bring the efficiency of SKZMT to 96-98% without the use of passive protection (primers, paints, varnishes, etc.);

form a protective film on the surface of the protected metal, which makes it possible to reduce power consumption by up to 10 times or more;

after 3-4 weeks from the start of the protection of objects (time of formation of a protective film), a dynamic equilibrium is established in the metal / aggressive environment system, at which the destruction of the protected metal and anode stops, and the protected metal itself enters an indifferent state;

the formation of a protective film makes it possible to minimize the contamination of soil and water bodies with corrosion products;

at a potential of zero charge installed on the surface of the protected metal, the tension in the surface layers of the crystal lattice of the metal tends to zero and the strength of the surface layer of the metal takes on the strongest structure (Rebinder effect);

potential propagation over the metal surface during operation with low currents occurs practically without attenuation, which in practice makes it possible to reduce the number of cathodic protection stations on extended objects;

work with low currents allows you to reduce the cross-section of the cables used when installing the Cathodic Protection Station of the Low Current Mode (SKZMT);

there is no need for allowances in the thickness of the walls of metal structures for corrosion and, as a result, for the safety of the subsoil;

the installation is made according to SMD technology, which allows increasing the reliability of the station, reducing its size and weight to max. 7 kg;

double protection built-in at the input and output varistors and suppressors protects the electronics from direct electrical discharge (lightning);

the software is built on the Android operating system;

- 5 035712 setting the operating parameters of protection is carried out over a wireless Bluetoth connection from any gadget running on the Android operating system;

it is possible to use all existing telemetry tools (GPS, GPRS, GSM, RS-485, etc.);

automatic recording and archiving of the protection parameters of the object occurs every 3 seconds 24/7;

double rectification of the current led to the maximum possible decrease in the impulse rate and is equal to no more than 0.1;

the use of a special paste based on silicone to protect electronic boards allows the stations to be used in the most extreme temperature conditions, from -65 to + 90 ° С;

vandal-proof enclosures made of special die-cast aluminum have a maximum protection class of IP69.

Claims (7)

CLAIM 1. The method of electrochemical protection of structural metals from corrosion, in which the potential in the metal-solution system is measured, the value of the protective potential is determined, the protective potential is supplied to the metal from an external DC source and automatically maintains its value, the deviation of the protection potential is compensated using a direct current source from the potential of the uncharged metal surface, characterized in that when the environmental parameters change, the value of the potential of the zero charge of the metal is measured at the dead center of the milliammeter arrows, and the protective potential is set equal to the potential of the zero charge of the surface. 2. The method according to claim 1, characterized in that said milliammeters have a mirror scale. 3. The method according to claim 1, characterized in that said milliammeters are built into the arms of the forward and reverse pulses. 4. A device for electrochemical protection of structural metals against corrosion by the method according to claims 1 to 3, including a device for determining the potential of an uncharged surface of a solid metal, a direct current source with a regulator and a controlled resistor, a choke and a capacitor for separating periodic and direct current circuits, a measuring bridge to determine and control the potential of the uncharged metal surface and two DC milliammeters with a mirror scale connected in series with the pulse shapers in the bridge arms. 5. The device according to claim 4, characterized in that, in said device for determining the potential of an uncharged surface of a solid metal, the source of polarizable current is a device for obtaining a periodic current with a reverse pulse, adjustable in amplitude and duration. 6. The device according to claim 4, characterized in that in said device for determining the potential of an uncharged surface of a solid metal, the test electrode is connected through a conductive bridge with milliammeters. 7. A device according to claim 4, characterized in that in said device for determining the potential of an uncharged surface of a solid metal, the device for measuring the potential is an electronic oscilloscope and / or a digital multimeter.