RU2113544C1 - COMPLEX RUST AND FOULING PROTECTION (Variants) - Google Patents

Abstract

FIELD: rust and fouling protection of wide-purpose marine objects. SUBSTANCE: the method includes application of antirust coating and antifoulding coating in the form of solid current-conducting layer, combination of simultaneous and separate cathode polarization of structure and anode polarization of current-conducting layer, depending on the sea water flow speed and specific contact resistance of antirust coating. EFFECT: enhanced efficiency of rust and fouling protection, enhanced service life and reduced power intensity. 4 cl, 3 dwg , 1 tbl

Description

 The invention relates to the protection against corrosion and fouling of marine objects of general purpose equipment - ships, stationary and floating structures and structures.

 Various protection against corrosion and fouling are known (E.Ya. Lyublinsky, Electrochemical corrosion protection. M: Metallurgy, 1987; Corrosion and corrosion protection. Handbook. L .: Shipbuilding, 1987; Technical, Review, 1992, v. I, N 1, p. 30; 8th International Congress on Marine Corrosion and Fouling, Taranto (Italy). Sept, 1992).

 Among them, the most widely used are electrochemical (cathodic and tread) corrosion protection methods (ECP) in combination with anticorrosive and antifouling coatings. Physico-chemical methods of protection (FZZ) from fouling, carried out by treating seawater with the products of its electrolysis or anodic dissolution of copper, have been used only in confined spaces in which a given protective concentration of biocides can be provided. Conductive coatings are just beginning to be considered as one of the promising anti-fouling agents. It is assumed that they are of interest as an independent element (anode) of one of the varieties of FCP.

 The closest in technical essence to the proposed method of protection is the method, which is a combination of cathodic protection (SC) and paint coatings (LCP) - anticorrosive and antifouling coatings (Corrosion and protection against corrosion, L .: Sudostroenie, 1987). A schematic diagram of the comprehensive protection of the prototype is shown in FIG. 3.

The method of comprehensive protection against corrosion and fouling of the prototype (Fig. 3) is as follows
On the underwater part of the structure (K) is applied anti-corrosion (PCP), then anti-fouling (POP) coating.

 Directly on the underwater part of the hull of floating objects of marine equipment, such as ships (Fig. 3, a), or in the sea on stationary objects of marine equipment, such as platforms (Fig. 3, b), anodes are installed (AI-AII ...) and reference electrodes (ES).

 In the premises of the equipment, on the structure or on the shore, polarization sources (IP - direct current sources) are installed, as a rule, which automatically maintain polarization modes - protective potential.

 Through distribution boards (RC) or directly the negative pole of the switchgear is connected to the housing (K), and the positive - to the anodes (A).

 To measure the potential of the housing, the IP is connected to ES, which are sensors for automatically controlling the polarization modes of the housing.

 Immediately after the structure is immersed in sea water, the process of leaching of biocides from POP begins, regardless of whether there are or are not fouling; if present, fouling is prevented with some protective concentration of biocides.

 The cathodic polarization system of the housing is turned on, which should work continuously until the next docking.

However, the known method has the following significant disadvantages:
the service life of POP is small and ranges from 1 to 3 years;
the effectiveness of the protection does not depend on the biological activity of sea water and is constantly decreasing over time;
at the initial stage of operation of POP (0.5-2.0 g), the prevention of fouling is associated with the death of microorganisms and environmental pollution (sea basins);
the prevention of fouling is associated with the use and irretrievable consumption of scarce and expensive biocides (mainly copper oxide), which are the filler of EPP;
at a flow rate of sea water (v _b ) of more than 3 m / s, when there is no fouling, the highest consumption of biocides is observed;
when the specific transition resistance of the anticorrosion coating (ρ _p ) is more than 10 ³ Ohm • m ² , when the risk of corrosion is small, due to the high barrier properties of the paintwork, the electrochemical protection is not used at full power, since the polarization current is very small or close to zero to maintain the protective potential;
since the ECP, the energy intensity of the power supplies and the number of anodes are calculated taking into account the specified corrosion protection parameters when the paintwork is worn on 20% of the surface, up to this point (2-3 g.) the ECP system is not used at full capacity.

 The aim of the invention is to increase the effectiveness of integrated protection, increase its service life, eliminate the use of biocides in anti-fouling coatings, ensure environmental safety of protection against fouling, increase the efficiency of ECP and auxiliary anodes, use them for dual purposes - additionally as cathodes.

The goal is achieved in that the antifouling coating is made in the form of an electrically conductive layer, it is connected to the positive pole of a direct current source, its anode polarization is effected, which causes electrolytic chlorination of sea water, they ensure the formation of a predetermined concentration on the surface of biocides necessary to prevent fouling, and measure the sea flow rate water (v _b ) and the specific transition resistance of the anticorrosion coating (ρ _p ) and, depending on their values, are carried out separately direct or simultaneous cathodic polarization of the structure and the anodic polarization of the electrically conductive coating.

 Example. In FIG. 1 shows the schematic diagrams that ensure the implementation of the recommended methods of integrated protection against corrosion and fouling of floating (Fig. 1, a), stationary or rarely documented (Fig. 1, b) objects of marine equipment.

 The method of protection against corrosion and fouling according to the invention in accordance with these schemes is as follows.

 Anticorrosive (PCP) and electrically conductive (EPP) coatings are applied to the moving part of the structure (K).

 Auxiliary electrodes (E1-E4 ...) and reference electrodes (ES) are installed directly on the underwater part of the hull of floating objects of marine equipment (Fig. 1, a) or in the sea when protecting stationary structures (Fig. 1, b).

 In the premises of equipment, on structures or on the shore, polarization sources (IP) are installed, as a rule, automatic direct current sources that ensure the maintenance of a given protective potential or protective current density.

 Through the distribution boards (RC), the negative pole of the FE is connected to the structure K or (and) to the electrodes of the E, and the positive pole using the contact electrode of the EP to the EPP and (or) to the electrodes of E.

Depending on the magnitude of v _b and ρ _p , the anodic polarization of the EPP, or the cathodic polarization K, or the simultaneous cathodic polarization of the EPP and the cathodic polarization K are carried out, for which they are used for two purposes - as anodes for polarizing the structure K, or at the same time the first ... the third ... electrodes as anodes and the fourth ... electrodes as cathodes.

Option 1. The method is carried out in accordance with the scheme shown in FIG. 2a, for the case when ρ _p ≤ 10 ³ Ohm • m ² and v _b > 3 m / s. In this case, the anode polarization of the EPP is turned off and the cathodes are used only as anodes and polarize the casing.

Option 2. The method is carried out in accordance with the scheme shown in FIG. _2b , for the case when v _b ≤3 m / s and ρ _p > 10 ³ Ohm • m ² . In this case, the cathodic polarization of the housing K is turned off, and the electrodes are switched to the cathodic polarization mode, and the EPG to the anodic polarization mode.

Option 3. The method is carried out in accordance with the scheme shown in FIG. 2c, for the case when v _b ≤ 3 m / s and ρ _p ≤ 10 ³ Ohm • m ² . In this case, the electrodes use:
E ₁ -E ₃ ... as anodes and relative to them carry out cathodic polarization of the structure K;
E ₂ -E ₃ ... as cathodes and relative to them carry out the anodic polarization of the EPP.

Option 4. The method is carried out in accordance with the scheme shown in FIG. 2d, for the case when the protective potential of the structure K can be provided at the current density of the anodic polarization of the EPP, which is necessary for protection against fouling. In this case, the electrodes are switched off:
the casing is used as a cathode to ensure the parameters of the anodic polarization of the EPP necessary to prevent fouling;
EPPs are used as an anode to provide cathodic polarization parameters for structure K, which are necessary to prevent corrosion.

 Testing of the invention. At the Black Sea corrosion station in Sevastopol, comparative tests of the developed protection method and prototype were carried out. The tests were carried out for 2 years. At the same time, two biologically active seasons were covered - from May to September of each year.

 The test samples were steel sheets measuring 500 x 500 mm. On the entire surface of the sheets on both sides was applied full-time PCP (grade XC-436) and full-time EPP for the prototype.

For the possibility of an accelerated assessment of the method and the reproduction of low values of ρ _p , sheets with aged PKP and POP were used.

 On the surface of each side on the control panel was applied EPP with a size of 400 • 400 mm. Auxiliary electrodes (anodes - cathodes) were platinum-titanium plates. The potential sensor was a chlorine-silver reference electrode with an intrinsic potential of 0.2 V. The measurement results were recalculated with respect to the hydrogen reference electrode. The source of polarization was a potentiogalvanostat.

In all experiments, at the cathodic polarization of the substrate (SC), the optimal protective potential shift ΔE _k = 0.2B was adopted.

 The modes of anodic polarization of EPP are distinguished by significant novelty and are the subject of an independent application for an invention. Therefore, in this invention they are not considered, since to perform the method are not fundamental. In this regard, the regime was used to ensure the prevention of fouling with all the above examples of the invention. In all cases of corrosion and delamination of the PCP and EPP, no fouling was observed, therefore, only fouling was a characteristic.

 The results of comparative experiments are shown in the table.

As can be seen, in all cases, no fouling was detected on the surface of the EPP. At v _b ≤ 3 m / s, on the POP after 8-12 months and on the PCP after 0.5 months, fouling is observed both at the cathodic polarization of steel and at the anodic polarization of the electron beam. After 12 months of testing for POP and PCP, continuous multilayer fouling up to 10 mm thick was observed, consisting of hydroids (60-70%), bryozoans, balyanus, mussels (30-40%).

 Thus, the experimental results fully substantiate the significant advantages of the invention compared to the prototype.

 The significant advantages formulated in the purpose of the invention are explained below.

 Improving the protection against fouling is ensured by the ability to control the anode polarization of the electrically conductive coating, depending on the biological activity of sea water. In this case, unlike anti-fouling coatings, the effectiveness of protection does not depend on the duration of operation of the structure and does not decrease in time.

The service life of the anti-fouling protection is ensured by any given value, but not less than the service life of the anticorrosion coating, for example, from 2 to 5 years. This is ensured by the choice of coating thickness, ensuring its continuity, and also due to the fact that it does not contain leachable biocides. In addition, since the anodic polarization of the electrically conductive coating is switched on only at v _b ≤ 3 m / s, i.e. When parked, the anti-fouling life is approximately doubled.

 The elimination of the need to use biocides in antifouling coatings is provided due to the formation of biocides on the surface of the electrically conductive coating during its anodic polarization in sea water.

Ensuring environmental safety of protection against fouling is achieved as follows:
coatings do not contain toxic substances;
by anodic polarization, a concentration of biocides (products of electrolysis of sea water) is created on the surface of the electrically conductive coating, which is minimally necessary to prevent fouling, in which fouling is not destroyed, but scared away.

EFFECT: reduced energy intensity of cathodic protection due to the fact that it is switched on only when ρ _p ≤ 10 ³ Ohm • m ² , i.e. in the initial period of operation of structures, when the paintwork does not have its own protective barrier properties.

The increase in the efficiency of the auxiliary electrodes is provided by
turning them off as anodes at ρ _p > 10 ³ Ohm • m ² ;
their use as cathodes at v _b ≤ 3 m / s regardless of the value of ρ _p ;
using the first, third ... electrode as the anode and the second, fourth ... as the cathode at ρ _p ≤ 10 ⁰ Ohm • m ² and v _b ≤ 3 m / s.

 Thus, it is fundamentally new also that the cathodic protection system (cathodic polarization) additionally functions as a source of anodic polarization. Therefore, at any object of marine engineering, where the complex protection system has cathodic protection, the possibility of the protection method under consideration is created only by applying an electrically conductive coating and the recommended polarization system.

Claims (4)

1. Comprehensive protection against corrosion and fouling of the structure in sea water, including the application of anti-corrosion and anti-fouling coatings, cathodic polarization of the structure from an external DC source, which ensures the establishment and maintenance of a given protective potential relative to the reference electrodes, characterized in that the anti-fouling coating is made in the form of a continuous an electrically conductive layer, measured speed v _in seawater resistivity and contact resistance anticorrosive coating _n and v values when they are _in> 3 m / s, ρ _n ≤ 10 Ohm • m ² cathodic polarization is carried out with respect to the housing of the auxiliary electrodes. 2. Comprehensive protection against corrosion and fouling of the structure in sea water, including the application of anti-corrosion and anti-fouling coatings, cathodic polarization of structures from an external DC source, which ensures the establishment and maintenance of a given protective potential relative to the reference electrodes, characterized in that the anti-fouling coating is made in the form of a continuous conductive layer, connect it to the positive pole of a DC power source, measure the speed of the sea ode v _in the specific contact resistance and anticorrosive coating ρ _n and v values when they are _in ≤ 3 m / s, ρ _f 10> ³ Ohm • m ² anodic polarization is carried out electrically conductive coating on the subsidiary electrode. 3. Comprehensive protection against corrosion and fouling of the structure in sea water, including deposition of anticorrosion and anti-fouling coatings, cathodic polarization of the structure from an external DC source, providing the establishment and maintenance of a given protective potential relative to the reference electrodes, characterized in that the anti-fouling coating is made in the form of a continuous conductive layer, connect it to the positive pole of a DC power source, measure the speed of the sea ode v _in, the specific contact resistance anticorrosive coating ρ _n, and when the values v _in ≤ 3 m / s, and ρ _p ≤ March ¹⁰ Ohm • m ² carried cathode structure polarization relative to a part installed auxiliary electrodes (e.g. even) and the anodic polarization electroconductive coating relative to other auxiliary electrodes (e.g. odd). 4. Comprehensive protection against corrosion and fouling of the structure in sea water, including the application of anti-corrosion and anti-fouling coatings, cathodic polarization of the structure from an external current source, which ensures the establishment and maintenance of a given protective potential relative to the reference electrodes, characterized in that the anti-fouling coating is made in the form of a continuous electrically conductive layer, connect it to the positive pole of the DC power source, determine the current density of the cathode field polarization for corrosion protection casing i $\genfrac{}{}{0ex}{}{\text{to}}{\text{s}}$ necessary to achieve the protective potential φ $\genfrac{}{}{0ex}{}{\text{to}}{\text{s}}$ , and the current density of the anodic polarization to protect against fouling of the electro-producing layer i $\genfrac{}{}{0ex}{}{\text{a}}{\text{s}}$ and subject to i $\genfrac{}{}{0ex}{}{\text{to}}{\text{s}}$ = i $\genfrac{}{}{0ex}{}{\text{a}}{\text{s}}$ carry out cathodic polarization of the housing relative to the electrically conductive layer.

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