RU2791539C2 - Device for control and switching of reference electrodes - Google Patents

Abstract

FIELD: electrochemical protection (ECP) of ground and underground structures against corrosion.

SUBSTANCE: invention is intended for cathodic protection of the bottoms of ground steel vertical tanks for storing oil and oil products. The control and switching device for comparison electrodes of the ECP system of the facility includes a power supply, a programmable controller configured to connect to the comparison electrodes, containing a relay board and an associated terminal block, while the relay board is configured to be connected to the comparison electrodes, and the terminal block is configured to switching the reference electrode with a cathodic protection station (CPS).

EFFECT: increased efficiency of ECP of the entire structure, for example, the entire surface of the bottom of a tank for storing oil and oil products from corrosion, by increasing the degree of automation of the ECP system in terms of control and switching of reference electrodes, which ensures timely detection of local underprotection phenomena and/or overprotection of construction sites and prompt elimination of said phenomena by adjusting the output parameters of the RMS (current/voltage) based on the automatic switching of reference electrodes.

1 cl, 2 dwg

Description

The invention relates to the field of electrochemical protection of ground and underground structures against corrosion (ECP) and is intended for cathodic protection of the bottoms of ground steel vertical tanks for storing oil and oil products. The invention can also be used for cathodic protection of technological pipelines, tanks and other underground containers.

Protection of a structure against corrosion using cathodic polarization is to prevent the oxidation of metal atoms on its surface. This can be achieved if the potential of the protected metal relative to the ground is shifted sufficiently to the cathode region. How much it is necessary to shift the potential to the negative region in order to suppress the metal oxidation reaction depends on the conditions under which corrosion occurs. Potential "metal - soil" refers to the class of electrode potentials, which are spontaneously established at any boundary of the metal with the environment. The absolute value of this potential cannot be determined. It is measured with respect to some accepted reference electrode, the potential of which is sufficiently stable. In the technique of cathodic protection, a saturated copper sulfate electrode is used.

When the potential of the protected structure is shifted to the negative area, i.e. to the cathodic side, oxidation reactions are suppressed, and the corrosion rate is significantly slowed down. Depending on the composition of the medium and other conditions, a different amount of potential shift is required to achieve the same corrosion suppression effect. Therefore, in the practice of protecting underground structures, there is a so-called minimum value of the protective potential. This value is chosen based on the operating conditions of the structure according to the reference data. Over the entire length of the pipeline or on the entire surface of the protected structure, the potential must be more negative than the accepted minimum value.

The cathodic polarization of the pipeline is carried out using a direct current supply from a power source - a cathodic protection station (CPS). With one wire, the SKZ is connected to the pipeline, and with the other - to the anode ground electrode.

A well-known scheme of cathodic protection of underground metal structures, including a protected structure - a pipeline, an adjustable DC source, a connecting wire and anode grounding (see Anti-corrosion protection of pipelines and tanks. Textbook. - M.: Nedra, 1978. Authors: Dizenko E.I. ., Novoselov V.F., Tugunov P.I., Yufin V.A., pp. 113 -117). The negative pole of the direct current source is connected to the protected structure - the pipeline, the positive pole - to an artificially created anode - the ground electrode.

To ensure effective protection, it is necessary that the cathodic potential sufficient to suppress corrosion processes be maintained throughout the protected section of the pipeline or on the entire surface of the protected structure.

At the same time, as you move away from the down conductor point (drainage - the place where the “negative” wire from the SKZ is welded to the structure (tank)) the cathode potential decreases. The zone of protective action will be the area on both sides of the down conductor, in which the potential of the protected structure in relation to the ground will be more negative than the accepted value of the protective potential. The highest cathodic potential, i.e. its most negative value will be in the area of the protected structure, located opposite the anode.

Thus, in the case of a long pipeline or a large area of the bottom of the tank, the known cathodic protection system will not be effective enough. a single anode is used for protection.

To increase the efficiency of using cathodic protection installations, a scheme for connecting several anode grounds to one cathode station is used. Each ground is connected to the cathode station using a connecting cable.

From the prior art, a system of electrochemical protection (ECP) of the bottom of a vertical steel tank (RVS) using several horizontal extended anode groundings is known (see RD-91.020.00-KTN-149-06 "DESIGN REGULATIONS FOR ELECTROCHEMICAL PROTECTION OF MAIN PIPELINES AND OPS FACILITIES", regulating the requirements for electrochemical protection of main oil pipelines, technological and auxiliary pipelines of oil pumping stations (OPS), tanks and tank farms, as well as berthing facilities of offshore terminals).

To control the residual corrosion rate and the level of protective potentials on the bottom of the RVS in the known ECP system, installation of corrosion sensors, non-polarizable and bimetallic reference electrodes is provided in an amount that depends on the capacity (volume) of the RVS, which is directly related to the diameter of the bottom and the area of the bottom of the RVS.

So, for a RVS with a volume of 10,000 m ³ in the well-known ECP system, 6 copper sulfate reference electrodes (MES) are provided, and for a volume of more than 10,000 m ³ - 8 MES.

The number of anode ground electrodes in the well-known ECP system also depends on the capacity (volume) of the tank, which is directly related to the bottom diameter and the RVS bottom area. Thus, for a VST with a volume of 10,000 m ³ in the well-known ECP system, 5 main and 5 reserve anodes are provided, and for a VST with a volume of 100,000 m ³ - 24 main and 23 reserve anodes.

Anode ground electrodes are installed evenly under the bottom of the tank. Cables from each anode grounding switch and measuring electrode are led to a terminal box located outside the tank frame.

For effective corrosion protection, cathodic protection stations for pipelines of oil pumping stations and tanks must ensure automatic maintenance of the required value of protective potentials. Those. the ECP system must provide for the entire period of operation continuous cathodic polarization of underground steel structures throughout their entire length (and on their entire outer surface) in such a way that the potential values have a value (in absolute value) not less than the minimum and not more than the maximum value , namely, were in the range - 0.90 to -2.5 V.

If the value of the potential on the protected metal turns out to be less than the minimum value - there is an "underprotection" of the structure, i.e. oxidation of the metal, its corrosion and destruction associated with the fact that the structure, for example, the bottom of the RVS, becomes the anode, and the soil the cathode.

If the value of the potential on the protected metal turns out to be greater than the maximum value, the structure is “overprotected”, i.e. on the surface of the metal, for example, at the border of the metal and the insulation of the outer surface of the RVS bottom, electrochemical processes occur with the release of gas (hydrogen), which in turn leads to adhesion (peeling) of the insulation and acceleration of the corrosion processes of the structure, in particular the bottom of the RVS.

"Underprotection" and "overprotection" of the structure reduce the effectiveness of the cathodic protection of the structure.

From the prior art, a method for controlling the ECP system is known (see PR 13.02-74.30.90-KTN-005-1-00 "RULES FOR CONTROL AND ACCOUNTING OF THE OPERATION OF ELECTROCHEMICAL PROTECTION OF UNDERGROUND COMMUNICATIONS AGAINST CORROSION", approved on March 11, 2000, establishing a unified control procedure and accounting for the operation of ECP facilities).

According to the well-known procedure for monitoring the ECP system, the following parameters are monitored daily: the value of the current of the RMS, the value of the voltage at the output of the RMS and the value of the protective potential at the drainage point of the RMS, i.e. only at one control point (from one MES).

At the same time, the control of the security of the oil pipeline (or structure) as a whole is carried out by seasonal measurements of protective potentials at control and measuring points. Measurements are made at least twice a year during the period of maximum soil moisture: in spring, with the end of measurements before June 1 and in autumn, with the end of measurements before October 1. In corrosive places, determined in accordance with clause 6.4.3. GOST R51164-98, security control is carried out by measuring the protective potential using the remote electrode method at least 1 time in 3 years according to a pre-compiled measurement schedule.

Thus, according to the method of control of the ECP system known from the prior art, the selection of the control electrode (control point) in the RVS terminal cabinet, connected to the control circuit of the SKZ, is done manually during seasonal electrometric measurements 2 times a year (spring/autumn).

The criterion for evaluating the effectiveness of ECP structures against soil corrosion should include the value of the protective potential of the protected structure, which in turn depends on the parameters of the ECP (current / voltage).

At the same time, it should be noted that setting the RMS parameters (current / voltage) on the RVS is a long and laborious process, depending on numerous factors. In addition, even in a perfectly tuned VPS, the value of the protective potential on the entire structure will not remain constant for a long period of time, due to the fact that:

- the value of soil resistivity in the territory of an oil refinery varies significantly throughout the year;

- various malfunctions occur that do not disrupt the operation of the CPS as a whole, but have a local effect on corrosion protection, for example, damage to a section of an extended anode ground electrode or failure of a stationary copper-sulfate reference electrode;

- adjusting the parameters of one SKZ can have a significant impact on neighboring installations and their protection zones in the area of dense underground utilities at oil refineries.

Thus, maintaining the value of the protective potential within acceptable limits at one control point under the VST does not exclude the possibility that at other control points located under the same structure a few meters from it, underprotection or overprotection is observed, which reduces the effectiveness of the corrosion protection of the structure as a whole. .

That is, even after a slight adjustment of the output parameters of the cathodic protection station, it is necessary to carry out repeated measurements on each reference electrode installed under the tank in order to check the values of the protective potential of the entire structure.

Thus, the main disadvantage of the ECP system control mode known from the prior art is the insufficient effectiveness of the cathodic protection of the VST bottoms as a whole from soil corrosion, caused by untimely detection and elimination of local underprotection or overprotection of sections of the VST bottom, which is carried out manually by personnel during seasonal measurements. Twice a year.

The technical problem to be solved by the claimed invention is the timely detection and prompt elimination of local underprotection and/or overprotection of the cathodic protection of protected structure sections in automatic mode.

The technical result of the claimed invention is to increase the efficiency of the electrochemical protection of the entire structure as a whole (the entire bottom of the RVS) from corrosion by increasing the degree of automation of the ECP system in terms of monitoring and switching reference electrodes, which ensures timely detection of local underprotection and / or overprotection phenomena. construction sites and prompt elimination of these phenomena by adjusting the output parameters of the RMS (current / voltage) based on the automatic change of the MES.

The technical problem is solved, and the technical result is achieved by the fact that the device for monitoring and switching the comparison electrodes of the ECP system includes a power supply, a programmable controller configured to connect to the comparison electrodes, containing a relay board configured to connect to the comparison electrodes, connected to the terminal block of the control output of the cathodic protection station, configured to switch the reference electrode with the cathodic protection station.

The invention is illustrated graphically, where in FIG. 1 shows a general view of the claimed device for monitoring and switching reference electrodes, in Fig. 2 - device for control and switching of reference electrodes in the circuit of the ECP system of the RVS bottom.

The positions in FIG. 1, fig. 2 marked:

1 - power supply

2 - controller

3 - relay board

4 - terminal block of the RMS control output

5 - reference electrode

6 - SKZ

7 - terminal box

The control and switching device for reference electrodes shown in Fig. 1 is designed to be included in the circuit of the ECP structure, for the implementation of continuous, continuous, automatic measurement and control of the potential values of the protected structure with respect to all MES connected to it, comparison of the measured potential values with the specified values and switching of the RMS with the MES having the lowest potential located in specified range.

The reference electrode control and switching device corrects the operation of the SKZ by measuring the protective potential relative to each reference electrode installed under the bottom of the RVS or other structure, and connecting the required electrode to the control output of the SKZ.

The reference electrode control and switching device includes a power supply unit (1), a controller (2) configured to be connected to the reference electrodes (5), containing a relay board (3) configured to be connected to the reference electrodes (5), and a control terminal block. output SKZ (4), made with the ability to connect to the SKZ (6).

The control and switching device for reference electrodes can be installed in the terminal cabinet (7) of the ECP system of the protected structure, for example, the bottom of the RVS (Fig. 2).

The power supply unit (1) is designed to power the device for monitoring and switching the reference electrodes, it is made with output protection against short circuit and overload, insulation strength is 3 kV, in an IP67 case.

The controller (2), containing the relay board (3), is configured to connect reference electrodes (5) to it and is designed for automatic measurement and control of protective potentials, reference electrodes (MES) connected to it, automatic selection and signaling to the relay board (3) for switching the selected reference electrode with RMS (6). The controller (2) is programmable and carries out the course of action based on the program.

Prior to installation of the device for control and switching of reference electrodes in the circuit of the ECP system of the facility, the range of values of protective potentials (in absolute value) is entered into the programmable controller (2), within which the protective potential of the MES must lie.

In accordance with the given algorithm, the programmable controller (2) measures the value of the protective potential of the MES connected to it, compares them with pre-set values and sends a command to the relay board (3) to connect to the RMS of the MES with the lowest potential included in the specified range of values or MES, the potential of which is outside the specified range of values.

The RMS control output terminal block (4) is connected to the relay board (3) and is intended for connection to the RMS control output of the MES selected by the controller (2) by switching the relay board (3).

The operation of the device for selecting reference electrodes is as follows (Fig. 2).

Previously, before installing the device for monitoring and switching the reference electrodes in the circuit of the ECP system of the facility, the range of protective potential values (for example, from -0.90 V to -2.5 V) is entered into the programmable controller (2).

The programmable controller (2) measures the protective potentials on the reference electrodes (5) connected to it every 2 seconds (according to the prescribed program) in automatic mode.

Next, the programmable controller (2) selects the reference electrode (5) and sends a signal to the relay board (3), which in turn connects the reference electrode (5) selected by the controller to the RMS control output terminal block (4).

According to the program, the controller (2) selects the reference electrode (5) that goes beyond the lower/upper range of standard potential values previously stored in the controller (2) memory, i.e. reference electrode (5) with a potential less or greater than the potentials in the given range.

Next, the controller (2) sends a command to the relay board (3) to connect the selected reference electrode (5) to the RMS control output terminal block (4).

According to the control output of the RMS, information from the selected reference electrode (5) enters the RMS (6). Based on the received information, the CPS (6) automatically adjusts the output parameters (current and voltage), thereby increasing / decreasing the potential of the selected reference electrode (5), which eliminates the phenomenon of "underprotection" and "overprotection" at the construction site.

If all the potential values on the reference electrodes (5) are within the standard values, the controller (2) will connect the reference electrode (5) with the lowest potential value, after which it will be the control for the RMS, because is the least protected area of the VST bottom (Fig. 2).

Also, in the event of a break in the extended anode ground electrodes, the device will record the drop in the protective potential in a certain area of the surface of the tank bottom and switch the required reference electrode to the control output of the SKZ. This will ensure that the necessary protective potential is constantly maintained on the entire surface of the tank bottom.

Thus, the device for control and switching of reference electrodes performs a constant, continuous measurement and control of the potential values of the protected structure relative to all reference electrodes connected to it, located in different places under the RVS bottom, and not one reference electrode located at the control point, comparison of the measured values of potentials with given values and switching of the RMS with a reference electrode with a potential that is outside the limits of the standard values or has the lowest potential that is in the given range. In comparison with the control mode of the ECP system of the bottom of the tank known from the prior art, when adding a device for monitoring and switching reference electrodes to the ECP circuit, according to the claimed invention, an increase in the degree of automation of the operation of the ECP system is achieved in terms of monitoring protective potentials on the reference electrodes and switching the necessary reference electrode with a cathodic protection station, in connection with which the efficiency of cathodic protection of the entire bottom of the tank as a whole increases, due to the timely detection and prompt elimination of local “underprotection” or “overprotection” of the VST bottom section.

Claims (1)

Device for control and switching of reference electrodes of the electrochemical protection system of the facility, including a power supply unit, a programmable controller configured to connect to the reference electrodes, containing a relay board and an associated terminal block, while the relay board is configured to be connected to the comparison electrodes, and the terminal block is made with the possibility of switching the reference electrode with a cathodic protection station.

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