RU2768625C1 - System of cathodic protection of ship hull against corrosion - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to the field of electrical engineering and electronics in shipbuilding and can be used for cathodic protection of the underwater part of ship hulls, oil and gas production platforms, floating power plants and other offshore structures against corrosion. System comprises comparison electrodes, anodes, a controller and a control and display unit, wherein it is equipped with a module for interfacing with a ship control system, input-output of which is connected to the second input-output of the controller, by the converter currents control module, the first input-output of which is connected to the third input-output of the controller, and second input-output is connected to common bus for control of anode self-contained power supply converters, potentials module, first input-output of which is connected to fourth input-output of controller, and the second input-output is connected to the common potential bus, by the self-contained power supply converters of the anodes, the output of each of which is connected to the corresponding anode, and the input is connected to the corresponding input-output of the common current control bus of the self-contained power supply of the anodes, and the ship hull potential digital sensors, input of each of which is connected to the output of the corresponding comparison electrode, and the output is connected to the corresponding input-output of the common potential bus.

EFFECT: increasing the efficiency of protecting the ship hull against corrosion by increasing the accuracy of installation and maintaining the current values of protective potentials in local areas of the surface, depending on their ability to be polarized by electric current.

1 cl, 3 dwg

Description

The invention relates to the field of application of electrical engineering and electronics in shipbuilding and can be used for cathodic protection of the underwater part of the hulls of sea vessels, oil and gas platforms, floating power plants and other offshore structures from corrosion.

Currently, to prevent corrosion of the underwater part of the hulls of marine vessels, cathodic protection (CPS) systems are widely used, which maintain the required protective potential of the hull by automatically regulating the electric current flowing between the anode submerged in water and the hull of the vessel.

The principle of operation of cathodic protection systems (Corrosion and protection of ships: a Handbook / Lyublinsky EYa. and others - L .: Shipbuilding, 1987. - 376 p.; Bibikov N.N., Lyublinsky E.Ya., Povarova L.V. Electrochemical protection of marine vessels from corrosion. - M: Metallurgy, 1987. - 96 p.) is based on the ability of a metal immersed in sea water to pass into a passive state when its potential shifts in the negative direction from a stationary value.

For efficient operation, the CPS should provide both a high-precision setting of the required value of the protective potential of the ship's hull, and high-precision automatic maintenance of the current value of the protective potential at the level of its required value with an error not exceeding 1% of the required value of the protective potential, based on a comparison of the current value of the potential, removed from the reference electrode installed on the ship's hull, with a given required value.

Known systems for cathodic protection against corrosion of metal structures, mainly ship hull (RU 2110616 C1, 1998; RU 2110617 C1, 1998; RU 2215823 C1, 2003), which in their common part contain a controlled DC source (converter), negative and positive poles which is connected to the ship's hull and the anode, respectively, acting as a sensor of the current value of the ship's hull potential, the reference electrode, the source of the protective potential setting and the control unit.

The number of anode units, controlled converters, switchboards and potential sensors depends on the displacement of the ship.

For example, for a ship with a displacement of 12,000 tons, the cathodic protection system (CPS) consists of 14 anodes connected to two converters, which are divided into anode units equal in number of anodes. The number of anode nodes is equal to the number of converters. For each anode unit, two potential sensors are provided - the main and the backup. A switchboard is provided for each anode unit, to which a cable from the positive pole of the converter and cables from the anode units are connected. The cross-sectional area of the electric cables connected to the anodes is calculated taking into account the length of the route, based on the condition of permissible voltage losses in the cable no more than 5% of the rated output voltage of the converter, and the resistance of the cable connected to individual anodes is chosen such that the current value of each anode differed by no more than 20% from the average value of the anode currents, and the spread of the current strength in the circuits of different anodes did not exceed 30%. These requirements are caused by limitations on the regulation of the anode currents, which is carried out through the power distribution board. This structure of construction of the SKZ continues to be used on ships.

The main disadvantage of such cathodic protection systems is the insufficient accuracy of setting the protective potential, due to the inability to independently control the current of each anode. This circumstance complicates the process of setting and especially adjusting the anode currents during operation, which are limited by the rated current of the converter, which ultimately reduces the effectiveness of cathodic protection, since a reduced protective potential leads to metal corrosion, and when the protective potential is overestimated, the process of saturation of the metal begins. hydrogen, causing the destruction of the metal structure.

The CPS developed by the Central Research Institute of KM "Prometheus" for nuclear icebreakers is widely known (Sudostroenie magazine No. 6 for 2015, "Parameters and operating experience in arctic conditions of cathodic protection systems against corrosion and erosion damage to the hulls of nuclear icebreakers", authors Yu.L Kuzmin, Doctor of Technical Sciences O. A. Stavitsky, A. V. Podshivalov). This RMS includes 38 anodes and 16 reference electrodes. The anodes are divided into eight nodes, and all the anodes of one node are connected to one converter. This RMS is similar in its structure and functionality to the systems described above, so the ability to control the anode currents is also limited. However, unlike the previous SKZ, the anode nodes include 2-3 anodes, which, with 16 reference electrodes, allows you to more accurately and timely monitor the levels of protective potentials, but the correction of the anode currents is carried out according to the average indicator for the entire surface covered by the anode node.

It should be noted that for SCZ the main characteristic of the surface protected from corrosion in sea water is the specific cathodic polarizability "b" (Ohm⋅m ² ), which decreases during operation. For example, as it was registered during the performance tests of the SPS installed on nuclear icebreakers, at the beginning of operation this parameter was 2-3 Ohm⋅m ² , and after 1.5 years 0.5-0.6 Ohm⋅m ² . In this case, the potential of the protected surface, measured by the reference electrodes, and the anode currents, respectively, were changed relative to the initially set values.

A significant spread in the polarizability of the surface protected from corrosion is especially often observed on ships with a large underwater surface, which is caused by uneven wear of the paintwork, mechanical damage, as is clearly manifested on the hulls of icebreakers, as well as the anisotropy of the hull metal and a number of other factors. As a result, when summarizing the data of the previous period of operation, the average value of the specific cathodic polarizability of the surface of each anode unit is determined and the value of the average current density (A/m ² ) is corrected, based on the technical capabilities of controlling the anode currents, the current of which cannot exceed the rated current of the converter. Such a criterion for regulating the protective potential during operation becomes ineffective, since it is redundant for some areas of the protected surface and insufficient for others. At the same time, the CPS must provide, during the entire service life, continuous in time and sufficient cathodic polarization of the entire protected surface, and not individual sections, so that the values of the protective potential in absolute value are within not less than U _min and not more than U _max . During the operation of the SKZ, changes in the protective potential are allowed in the range from minus 0.2 V to minus 1.5 V.

In general, the existing shipboard RMS in terms of their structural design, namely, the combination of anodes into nodes and the supply of power to each anode node through the power distribution board from one converter and the regulation of the protective potential during operation according to the average value of the cathodic polarizability of the surface protected by the current of the anode node , do not provide sufficient protection of the ship's hull in case of manifestation of local types of corrosion, such as pitting, crevice, contact and others, which are detected during inspection during the docking of the ship.

The closest in its technical essence analogue (prototype) in relation to the proposed SKZ is a well-known tool for cathodic corrosion protection of metal structures in water according to patent RU No. 201537, publ. 12/21/2020, IPC C2F13 / 04, containing a reference electrode, an anode, a converter made according to the PWM inverter circuit, a control and indication unit, and current and voltage sensors. Information exchange between the nodes of the tool is carried out in digital form using microcontrollers, which makes it possible to monitor the protective potential of metal structures with high accuracy. The disadvantage of this device, as well as the above-described RMS, is the lack of accuracy in setting and maintaining protective potentials for local areas of the surface of the ship's hull, depending on their polarizability, which reduces the overall effectiveness of the protection of the ship's hull from corrosion.

In this regard, it was necessary to solve the technical problem, which is to increase the effectiveness of the protection of the ship's hull from corrosion in accordance with modern requirements to ensure the accuracy of the installation and maintain the values of the protective potential of the ship's hull.

The technical result of the proposed invention is to increase the efficiency of protecting the ship's hull from corrosion by improving the accuracy of the installation and maintaining the current values of protective potentials in local areas of the surface, depending on their ability to polarize.

The specified technical result is achieved by the fact that the cathodic protection system of the ship's hull against corrosion, containing reference electrodes, anodes and a controller, the first input-output of which is connected to the input-output of the control and indication unit, is equipped with an interface module with the ship's control system, the input-output of which connected to the second input-output of the controller, by the converter current control module, the first input-output of which is connected to the third input-output of the controller, and the second input-output is connected to the common bus for controlling the currents of the autonomous anode supply converters, by the potential module, the first input-output of which connected to the fourth input-output of the controller, and the second input-output is connected to a common potential bus, by anode independent power converters, the output of each of which is connected to the corresponding anode, and the input is connected to the corresponding input-output of the common current control bus of anode autonomous power converters, and digital sweat sensors cial of the ship's hull, the input of each of which is connected to the output of the corresponding reference electrode, and the output is connected to the corresponding input-output of the common potential bus.

Thanks to a new set of essential features in the proposed system of cathodic protection of the ship's hull from corrosion, the cumulative effect of currents of closely spaced anodes on the potential of each local surface area is determined and autonomous regulation of the converter currents is provided with high accuracy corresponding to the given protective potential of the local surface area.

The claimed system of cathodic protection of the ship's hull against corrosion is illustrated by drawings, which show:

in fig. 1 - block diagram of the ship's hull anti-corrosion protection system;

in fig. 2 - general equivalent electrical circuit of the ship's hull RMS against corrosion;

in fig. 3-equivalent electrical circuit for the RMS of the ship's hull against corrosion with three digital potential sensors and three anodes.

The inventive system of cathodic protection of the ship's hull against corrosion, shown in Fig. 1, consists of anodes (6), each of which is connected to an anode autonomous power converter (7), the input of which is connected to a common bus for controlling the currents of the anode autonomous power converters (8), the input-output of which is connected to the converter current control module (4 ). Each reference electrode (11) is connected to a digital ship hull potential sensor (10), the input of which is connected to a common potential bus (9), the input-output of which is connected to the potential module (5). The input-output of the current control module of the converters (4), the input-output of the potential module (5) and the input-output of the control and indication unit (2) are each connected to the corresponding input-output of the controller (3), made on the basis of a microprocessor, while the controller (3) connected to the interface module with the ship's control system (1).

The elements included in the SKZ of the ship's hull against corrosion have the following purpose.

The interface module with the ship's control system (1) is designed to transmit information about the status of the RMS to the ship's automated control system and receive data on the specific electrical conductivity of sea water in the regions where the ship is located, which are fed through the controller (3) to the control and display panel (2). This module is a digital interface element made on the basis of a typical microcontroller and can be structurally combined with the controller (3) through a port with a USB interface, etc.

The control and indication unit (2) is intended for setting and displaying the values of anode currents, setting protective potentials, their correction and indication during operation. The control and indication unit (2) contains elements for entering data on potentials, currents, voltages and a display showing the status of the RMS. Provides display of data coming from the ship's control system. The control and indication unit (2) can be implemented using a microprocessor and on typical elements, and the design is made in accordance with the requirements for the ship's equipment.

The controller (3) is designed to implement the algorithm of the cathodic protection system and provides information exchange between the control and indication unit (2) and the interface module with the ship's control system (1). The block software contains special software modules that set the cycles for polling potential sensors, static processing and polling transducers. The block can be implemented on a typical control microcontroller type 1986 BE91 with built-in FLASH program memory and RAM with 12-bit ADC and DAC, USB, UART, SPI peripheral interfaces, etc.

Converter current control module (4) is designed to transmit and receive via a common current control bus of anode autonomous power converters (8) address commands to set the currents of anode autonomous power converters (7), automatically maintain currents within specified limits and contains interface elements with a common bus control of currents of converters of autonomous supply of anodes (cathode follower).

The potential module (5) receives address messages about potentials from digital sensors of the ship's hull potential (10) in a time cycle set by the controller (3), and consists of a microcontroller and an interface element (matching element) with a common potential bus (9).

The common bus for controlling the currents of the converters of the independent power supply of the anodes (8) and the common bus of potentials (9) provide individual selective receipt of address commands by the converters and the receipt of address messages about the potentials recorded by digital sensors of the ship's hull potential from the general command and message flows.

As anode autonomous power converters (7), controlled power supplies with a digitally regulated output voltage from 12 V to 24 V are used, with an accuracy of maintaining a current of about 1% within the control range, in rare cases up to 36 V with an output current of up to 40 And with a power supply from the mains ~ 3x380 V, for example, type MAA 900-1T1224 BKYUS.436610.007 TU with adjustable output voltage from 12 V to 24 V and output current up to 37.5 A, adjustable sources with PSWM modulation can also be used .

For ships of various displacements and purposes, when designing the SKZ, standard or special anodes can be installed, as is done on icebreakers, silver chloride reference electrodes of the ESKhP-SL type and others, which are installed on the outside of the hull and connected directly or by cable to a digital sensor, galvanically isolated from the ship's electrical network, and also connected to a common potential bus (9). The digital ship hull potential sensor (10) contains an ADC and potential amplification and power supply elements.

In FIG. 3 shows an equivalent electrical circuit of the claimed RMS of the ship's hull against corrosion for the particular case of using three digital potential sensors and three anodes. This scheme is based on the properties of duality (mutual reversibility) of two-terminal networks, and the load of each anode is represented by a parallel connection of the current spreading resistances of each anode over local areas of the surface, on which digital potential sensors are placed.

Based on the assumption that the anode currents add up at each point of the surface, and the digital potential sensor captures the potential proportional to the sum of the flowing currents of the converters, the RMS can be adequately represented by the following system of linear equations (SLE):

where:

-n and m - respectively, the number of digital sensors of potentials and anodes in the SKZ;

- Ij - current of the j-th anode;

- r _ij - current spreading resistance of the "j"-th anode in the circuit of the "i"-th digital potential sensor (transitional resistance);

- U _i …U _m - protective potentials.

For small values of individual transient resistances for remote areas of the surface, this system of linear equations is decomposed into a number of independent equations and the order of the system is reduced.

Let's explain this. Let as a result of measurements, for example, at the stage of commissioning of the RMS at the facility, the following data were obtained for one of the fragments of the protected surface: r ₁₁ = 0.3 Ohm, r ₂₂ = 0.025 Ohm and r ₃₃ = 0.02 Ohm , r ₁₂ =r ₂₁ =r ₃₁ =r ₁₃ =r ₂₃ =r ₃₂ =0.01 Ohm and all other transient resistances associated with the currents of other anodes were set to zero.

The values \u200b\u200bof the protective potentials reduced to the current spreading resistance of the converter are determined and are equal, respectively: U ₁ \u003d 0.7 V, U ₂ \u003d 0.8 V, U ₃ \u003d 0.6 V.

The introduction of the reduced protective potentials to the resistance of the current spreading of the converter is due to the fact that the level potentials recorded by digital sensors indicate only parts of the current spreading over a local area of the surface, but do not pass the entire current.

Using the above data, we will compose the SLE for this fragment of the protected surface:

Substituting the data and solving this SLE, for example, using the Cramer method, we obtain the desired anode currents I ₁ \u003d 22.l A, I ₂ \u003d 32.1 A, I ₃ \u003d 19.4 A (determinant D \u003d 144.5 ⋅ 10 ^-6 , additional determinants: D1=32⋅10 ⁴ , D2=2.33⋅10 ^-4 and D3=28⋅10 ^-6 , Ii=Di/D).

The inventive system of cathodic protection of the ship's hull from corrosion works as follows.

Initially, when the ship hull RMS is put into operation, not including converters, stationary potentials of the ship hull are determined at the locations of digital sensors of the ship hull potentials, and these values are entered into the controller through the control and indication unit. Next, each converter is sequentially turned on/off, the potential values are determined for all sensors and entered into the controller. Thus, the spreading of the current of each converter over the local sections of the ship's hull is determined and the transient resistances between the anodes and sensors are calculated. In FIG. 2 shows the general equivalent electrical circuit of the RMS of the ship's hull against corrosion, from which it follows that the transient resistances between the i-th sensor and the j-th anode r _ij =r _j /k _u , where k _u is the voltage transfer coefficient between them, r _i - internal resistance of the potential sensor. Next, protective potentials are set for all local areas of the surface of the ship's hull, based on the values of stationary potentials, they are entered into the controller, and the required values of the currents of each converter are calculated using the calculation software module of the controller. The obtained values of currents are transmitted to the input of the current control module of the converters.

The converter current control module, in turn, according to the cycle set by the controller, reads from the converters in digital form the current values of the currents that enter its input-output through the common bus for controlling the currents of the converters of the autonomous power supply of the anodes and the controller of this module compares the current value of the current with the task received at its input from the controller, and after calculating the difference in values, changes the converter current in such a way as to reduce this current difference to zero.

An anode isolated from the ship's hull with developed geometric dimensions creates a current spreading zone due to the electrical conductivity of sea water and thereby shifts the potential of this part of the ship's hull surface. A digital sensor of the ship's hull potential located at a distance from the anode converts the value of the ship's hull potential into digital form and transmits the potential value via a galvanically isolated circuit through a common potential bus to the input-output of the potential module, which is connected to the controller.

The reference electrode is a highly sensitive element of the cathodic protection system, is affected by body noise, has a high input resistance of tens of kOhm or more, and for this reason its readings are subject to significant fluctuations. To obtain stable readings of digital sensors of the potential of the ship's hull, the controller sets a time cycle for polling all sensors of the SKZ. The arrays of sensor readings obtained in this way are integrated in the potential module over a significant time interval (of the order of several minutes) with the exception of individual statically outlier values, and upon command from the controller, the potential data from the output of the potential module are sent to the controller.

The general algorithm for regulating the currents of the converters is to perform successive iterations with digital sensors monitoring the shifts of protective potentials.

Claims (1)

The cathodic protection system of the ship's hull against corrosion, containing reference electrodes, anodes and a controller, the first input-output of which is connected to the input-output of the control and indication unit, characterized in that it is equipped with an interface module with the ship's control system, the input-output of which is connected to the second input-output of the controller, the converter current control module, the first input-output of which is connected to the third input-output of the controller, and the second input-output is connected to the common bus for controlling the currents of the autonomous anode power converters, the potential module, the first input-output of which is connected to the fourth input-output of the controller, and the second input-output is connected to a common bus of potentials, by converters of independent power supply of anodes, the output of each of which is connected to the corresponding anode, and the input is connected to the corresponding input-output of the common bus for controlling the currents of converters of independent supply of anodes, and digital ship hull potential sensors, input each of which is connected to the output of the corresponding reference electrode, and the output is connected to the corresponding input-output of the common potential bus.

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