RU2430996C2 - Protective coating - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: protective coating consists of nano structured protective layer of corrosion inhibitor of N-hetero-cyclic alkyl-phosphonic acid and of second external layer consisting of epoxy polymer. Also, the second external layer is obtained from mixture of composition, wt %: monomer of epoxy resin E-40 68.0-72.0; toluol 18.0-20.0; di-butyl-phtalate (DBPH) 2.0-4.0; the said inhibitor of corrosion 2.0-4.0; poly-ethylene-polyamine (PEPA) 4.0-6.0.

EFFECT: raised efficiency of protection of metal from all kinds of corrosion, raised service life and strength of adhesion.

2 cl, 1 tbl, 3 ex

Description

The invention relates to the field of protection of metals from corrosion, in particular to the field of protection against corrosion in mineralized aqueous media containing dissolved oxygen and carbon dioxide, in particular to the protection of structural materials of pipelines, industrial metal structures, equipment, and transport infrastructure facilities made of low-alloyed and low carbon steels.

In all industrialized countries, the losses from the corrosion of metals are very high. Indirect losses arising from accidents due to corrosive causes exceed direct losses.

According to operational data, the average service life of industrial metal structures instead of 10 years according to standard terms in the conditions when they are subject to corrosion, is reduced to 2-3 years. Protective coatings are widely used to extend the life of metal structures and pipes under conditions conducive to the occurrence of corrosion.

Currently, the use of protective coatings of various structures and compositions is widely known.

Known [RF patent 2334158, IPC F16L 58/00, publ. September 20, 2008] a composition for a protective coating, including thiocol, carbon black, thermosetting resin, plasticizer and diphenylguanidine, characterized in that it contains a modified epoxy diane resin as a thermosetting resin, benzylbutylphthalate as a plasticizer and additionally contains manganese dioxide and organic solvent in the following ratio, wt.h .:

Thiokol 55-75

Carbon black 20-42

Modified Epoxy Dian Resin 3-5

Benzyl Butyl Phthalate 35-50

Diphenylguanidine 1-9

Manganese Dioxide 45-64

Organic solvent 25-40.

The disadvantage of this composition is the need to use a large number of components. In addition, this patent does not provide data on the effectiveness of the coating under conditions of local corrosion.

To protect metal products from corrosion, a method is proposed [US Patent No. 3249447, IPC B05D 7/14, publ. 05/03/1966], which consists in applying a film of a composition to a metal product, consisting of a drying organic coating material - paint, enamel varnish (75.0-99.9%) and diaromatic phosphinate of a multivalent metal - calcium, chromium, iron (0, 1-25.0%). The aromatic radical in the diaromatic phosphinate can be phenyl, alkyl substituted phenyl radical (C ₁ -C ₆ ), etc. The protective properties of the composite material are due to improved adhesion of the film to the metal and a decrease in its permeability to water and oxygen.

However, this composition is used to protect metals only from general corrosion and the effectiveness of such protection is low (50-60%).

Known [RF patent 2355821, IPC C23F 11/14, publ. 05/20/2009] composition for protecting metals from corrosion and scaling, including sodium tripolyphosphate and nitrogen-containing compounds, characterized in that it contains benzotriazole and ethanolamine borate as nitrogen-containing compounds in the following ratio, wt.%:

Sodium tripolyphosphate - 10.0-20.0

Benzotriazole - 30.0-40.0

Ethanolamine borate - 40.0-60.

However, such protective compositions are mainly used to combat scaling, and to a lesser extent to combat corrosion.

A known protective coating system for protecting a metal object [RF patent 2341376, IPC B32B 3/02, publ. 06/03/2003] when the system is superimposed on the object. The system is a coating comprising a first layer having a first and second front side and containing moisture absorbing material, and a second liquid impermeable layer, and a corrosion inhibitor source.

This protective coating is a double coating based on synthetic fabrics with the addition of an inhibitor, which significantly limits its scope and it is almost impossible to use it to protect pipelines.

It should be noted that in all of the above patents, protective coatings are used solely to protect against general corrosion.

The prototype of the invention is a coating [RF patent 2348741, IPC C23C 30/00, publ. January 26, 2007], which relates to nanostructured coatings for stainless steel and can be used in the operation of stainless steel as materials for the structural and technological purposes of the petrochemical industry. The coating contains a layer of titanium nitride and an intermediate layer of silicon carbide with a thickness of 5 to 10 nm. The titanium nitride layer has a thickness of 25 to 50 nm, and the silicon carbide layer has a thickness of 5 to 10 nm. The coating has a total thickness of 30-60 nm and the total composition, wt.%: SiC 16.6 and TiN 83.4. The technical result is an increase in the corrosion resistance of materials when working in acidic environments and at elevated temperatures.

The disadvantage of this coating is the complex multicomponent composition and the complex technology of applying inorganic nanomaterials, especially on an irregularly shaped surface. This leads to a significant increase in the cost of the proposed protective coatings, especially for trunk pipelines. In addition, the effectiveness of the protective effect of these coatings under conditions of local corrosion has not been confirmed.

The authors were faced with the task of developing a coating that is distinguished by the effectiveness of protecting the surface of metals from all types of corrosion, the strength of adhesion to the surface of metals and durability.

The essence of the invention lies in the fact that the proposed protective coating, consisting of a nanostructured layer of a corrosion inhibitor deposited on a metal surface, the thickness of which is 10-100 nm, and a second layer 200-400 μm thick, consisting of an epoxy polymer, and this second layer as an inhibitory additive includes one of these corrosion inhibitors.

For applying a nanostructured layer of a corrosion inhibitor, inhibitors are used, which are cyclic derivatives of phosphonic acid of the formula:

HtC (R ₁ R ₂ ) P (O) (OH) ₂ ,

where Ht is a heterocyclic fragment with a nitrogen atom in the ring — pyrrolidine or morpholine;

R ₁ and R ₂ are a hydrogen atom or C ₁ -C _n alkyl radicals, preferably C ₁ -C ₂ .

It can be, for example:

(Pyrrolidin-1-ylmethyl) phosphonic acid,

(1-Methyl-1-pyrrolidin-1-yl-ethyl) phosphonic acid,

(1-Methyl-1-pyrrolidin-1-ylpropyl) phosphonic acid,

(Morpholin-4-ylmethyl) phosphonic acid,

(1-Methyl-1-morpholin-4-yl-ethyl) phosphonic acid,

(1-Methyl-1-morpholin-4-ylpropyl) phosphonic acid,

and linear alkylphosphonic acids, in which the alkyl radical may be without functional groups or contain one or more functional groups, such as hydroxy and amino groups.

It can be, for example:

Isopropenylphosphonic acid

CH ₂ = C (CH ₃ ) P (O) (OH) ₂

Hydroxymethylphosphonic acid

NOSN ₂ P (O) (OH) ₂

N, N ^/ - (polyethylene polyamine) bis (methylphosphonic) acid

(OH) ₂ (O) PCH ₂ [NH (CH ₂ ) ₂ ] _n CH ₂ P (O) (OH) ₂ , where n = 1-10.

A second protective layer, which is a solid polymer film, is applied over this first layer. The composition forming this film includes components, wt.%:

epoxy monomer E-40 - 68.0 ÷ 72.0;

toluene - 18.0 ÷ 20.0;

plasticizer - dibutyl phthalate (DBP) - 2.0 ÷ 4.0;

N-heterocyclic alkylphosphonic acid - 2.0 ÷ 4.0;

polyethylene polyamine (PEPA) - 4.0 ÷ 6.0.

This composition is applied to a layer of a nanoscale inhibitory coating, on which, after drying, an outer second protective film is formed.

To obtain the first layer of nanoscale protective coating on the product is applied aqueous solutions containing 30-60 mg / DM ³ inhibitors or mixtures thereof. These solutions are left on the surface of the products for a period of 15 to 180 minutes, resulting in a first coating layer. Next, the product is removed from solutions, washed with water and dried in air.

The above inhibitors (of the first layer) have the ability to form on the metal surface a nanoscale self-organizing surface layer due to the presence in the molecule of the acid residue -P (O) (OH) ₂ . The inhibitor molecule, adsorbed from the side of the acid group, interacts with the metal. The other end of the molecule - the alkyl group, directed towards the water system, is relatively hydrophobic, therefore, its bond strength with the solution is low. As a result, an almost uniform nanoscale film is formed from phosphonic groups strongly adsorbed on the metal. Experimental studies have established concentration limits for inhibitors of the claimed class. When processing metal surfaces, the concentration of inhibitor in the solution should be from 30 to 60 mg / DM ³ . In the indicated range of concentrations of the studied inhibitors in the solution, their molecules directly interact with the metal to form strong metal-base adsorption complexes.

The result is a first coating layer onto which a second protective layer is applied by spraying or brush coating. After drying, a two-layer coating is formed with high adhesive and anti-corrosion properties.

A second protective layer, which is a solid polymer film, is applied over this first layer. For applying this layer, a composition is prepared separately, wt.%:

Base - epoxy resin monomer E-40 - 68.0 ÷ 72.0;

The solvent is toluene - 18.0 ÷ 20.0;

Plasticizer - dibutyl phthalate (DBP) - 2.0 ÷ 4.0;

Inhibitory Supplement - N-heterocyclic

alkylphosphonic acid - 2.0 ÷ 4.0;

Hardener - polyethylene polyamine (PEPA) - 4.0 ÷ 6.0.

Experimental studies established the concentration limits of the inhibitory additive, which are from 2 to 4 wt.% By weight of the composition. Below this concentration, the protective effect of the second layer decreases, and above 4% there is no improvement in the properties of the protective coating.

The composition immediately after preparation is applied by spraying on top of the first layer in two steps with an interval of 3 hours, necessary for the hardening of each layer. The total polymerization (solidification) time is 6-8 hours.

The protective ability of such a two-layer coating, the first layer of which is nanosized, and the second is an epoxy resin with an inhibitory additive, has a high protective effect for both carbon and low alloy steels. A nano-sized protective substrate provides improved adhesion of the surface of the polymer film to the metal surface, in addition, in the case of carbon steels, it has its own protective effect, and if the continuity (continuity) of the outer layer is violated, it will protect the metal.

Tests for the effectiveness of the protective effect of the developed coating were carried out as follows: tests were carried out on samples of carbon steel grade 20.

Before conducting tests on the strength of applying an inhibitory coating, the surface of the steel samples is ground on SiC abrasive paper with successively decreasing grain sizes. The final grinding is carried out on paper with grain sizes of 10-50 microns. After grinding, the metal surface is washed, dried and degreased with ethyl alcohol. Prepared for testing, steel samples of Art. 20 for applying nanosized protective coatings are immersed in aqueous solutions containing 30-60 mg / dm ^{3 of the} obtained inhibitors or their mixtures for a period of 15 to 180 minutes, as a result, the first coating layer is obtained. Next, the samples are removed from the solutions, washed with water and dried in air.

Testing of the applied two-layer protective coatings was carried out by the method of corrosion tests. The corrosion rate of steel samples was determined: by the gravimetric method — the rate of general corrosion and by the depth-measuring (optical) method — the rate of local corrosion.

Samples of coated steel St 20, previously weighed to an accuracy of 10 ^-4 g, were suspended in vessels filled with test medium — 0.2 M aqueous NaCl solution. The vessels were immersed in a thermostat, in which a temperature of 35 ° C was maintained. According to ISO 12944-6, the test duration was 3000 hours. At the end of the tests, the samples were removed from the test medium, washed, dried. To determine the corrosion rate of the samples, the composite coating (2nd layer) was mechanically removed from them and weighed to an accuracy of 10 ^-4 g. The mass loss Δm = m ₀ -m ₁ , where m _about - the mass of the sample before testing, g; m ₁ is the mass of the sample after testing, g. The rate of general corrosion was calculated by the formula

To ^about = Δm / S · t,

where S is the surface area of the sample; t = 3000 hours - test time. Then, the rate of general corrosion was converted to mm / h. To determine the local corrosion rate of the samples, they were studied using a NEOPHOT-32 computerized optical microscope. By double focusing the light beam, its depth was measured successively on the edge and bottom of the corrosion center. The measurement error did not exceed ± 0.5 μm. Based on the greatest depth of the local corrosion focus and the residence time of the samples in an aggressive environment, the local corrosion rate in mm / year was calculated by the formula

K ^l = 2.92 · h _max · 10 ^-3 / t,

where h _max is the greatest depth of the local corrosion foci found on the surface of the samples exposed in the solution, microns;

t = 3000 hours is the residence time of the samples in the test medium.

In parallel with testing samples with applied composite coatings, tests were carried out on samples of St 20 without coating, for which the rates of total K ^o ₀ and local K ^l ₀ corrosion were also determined.

The coefficient of effectiveness of corrosion inhibitors and composite coatings in% (in the case of general and local corrosion) is calculated by the formula

E ^o = (K ^o ₀ -K ^o ) · 100 / K ^o ₀ ;

E ^l = (K ^l ₀ -K ^l ) · 100 / K ^l ₀ .

Example 1

A steel sample prepared for testing, St 20, without a protective coating, was preliminarily weighed to an accuracy of 10 ^-4 g and placed in a temperature-controlled cell at a temperature of 35 ° C, filled with test medium: 0.2 M aqueous solution of sodium chloride (NaCl). The test time was 3000 hours. At the end of the test, the sample was removed from the medium, washed with water, dried and weighed to an accuracy of 10 ^-4 g. The total corrosion rate of the sample K ^о _{0 was} calculated from the mass difference before and after the tests. Then, with the help of an optical microscope NEOPHOT-32, the depth of the centers of local corrosion of the sample was determined and the rate of local corrosion, K ^o ₀ , was calculated _.

As a result, the following data were obtained: the rate of general corrosion was 0.5 mm / year, the rate of local corrosion was 3 mm / year.

Example 2

Prepared for testing, a sample of steel St 20 was immersed in an aqueous solution containing 60 mg / dm ^{3 of} an inhibitor, hydroxymethylphosphonic acid, for 180 minutes. Next, the sample was removed from the solution, washed with water, dried, weighed to the accuracy of 10 ^-4 g and without applying a second protective polymer layer was placed in a temperature-controlled cell at a temperature of 35 ° C, filled with test medium: 0.2 M aqueous solution of sodium chloride (NaCl) . The test time was 3000 hours. At the end of the test, the sample was removed from the medium, washed with water, dried and weighed to an accuracy of 10 ^-4 g. The total corrosion rate of the sample K ^о _{ing was} calculated from the mass difference before and after the tests. Then, with the help of an optical microscope NEOPHOT-32, the depth of the centers of local corrosion of the sample was determined and the rate of local corrosion, K ^about _ing .

As a result, the following data were obtained: the general corrosion rate K ^l _ing was 0.02 mm / year, the local corrosion rate K ^l _ing was 0.05 mm / year. The coefficient of effectiveness of the inhibitor for total corrosion E ^o = 96%, for local corrosion E ^l = 98.33%.

Example 3

A steel sample of St 20 prepared for testing was immersed in an aqueous solution containing 50 mg / dm ^{3 of the} inhibitor - (pyrrolidin-1-ylmethyl) phosphonic acid for 120 minutes. Next, the sample was removed from the solution, washed with water, dried, weighed to an accuracy of 10 ^-4 g and applied to it by spraying in two doses, with intermediate drying between doses for three hours at a temperature of 20 ° C, composition mixture,%:

Epoxy resin E-40 - 70.0

Toluene - 18.0

DBF - 4.0

(Pyrrolidin-1-ylmethyl) phosphonic acid - 2.0

PEPA - 6.0.

After applying the last layer, the sample was dried for five hours at a temperature of 20 ° C and placed for corrosion tests in a temperature-controlled cell at a temperature of 35 ° C, filled with test medium: 0.2 M aqueous solution of sodium chloride (NaCl). The test time was 3000 hours. At the end of the test, the sample was removed from the cell and dried. Then the protective coating was mechanically removed from the sample and it was weighed with an accuracy of 10 ^-4 g. The total corrosion rate of the sample K ^about _{coating was} calculated from the mass difference before and after the tests. Then, with the help of an optical microscope NEOPHOT-32, the depth of the centers of local corrosion of the sample was determined and the local corrosion rate, K ^l _{coating, was calculated} .

As a result, the following data were obtained: the general corrosion rate K ^о _cover was 0.002 mm / year, the local corrosion rate K ^l _cover - 0.006 mm / year. The coefficient of effectiveness of the inhibitor for total corrosion E ^o = 99.6%, for local corrosion E ^l = 99.8%.

Similarly, other experiments were carried out, examples and results of which are presented in table 1.

As follows from table 1, the results of corrosion tests characterizing the stability of the obtained coatings based on a two-layer system, in which the first is a nanostructured layer of an α-alkylphosphonic acid inhibitor and the second is a polymer layer containing an epoxy base and an inhibitory additive, indicates that all tested two-layer coatings effectively protect the surface of steel samples St 20 from all types of corrosion, and the greatest effect is achieved when protecting the metal from local corrosion - reduced the rate of local corrosion is 300–700 times that of a sample without coating and 60 times that of a sample having a single-layer inhibitor coating. In this case, the rate of general corrosion is reduced by a factor of 100-300 compared to an uncoated sample and several dozen times compared to a single-coated sample. In addition, the use of a corrosion inhibitor in the composition of the second polymer layer improves the adhesion and anticorrosion properties of the coating, as indicated by an increase in the rate of local corrosion by 4–5 times, and in general by 4–8 times for the second coating layer, which does not inhibitor (see table 1, p. 12).

The differences between the developed two-layer protective coatings is that a coating is proposed consisting of an inhibitor nanolayer and a polymer layer including an inhibitor that was not previously known in the field of protection of metals from all types of corrosion, especially from local corrosion.

Thus, the task facing the authors has been achieved - a coating has been developed that is highly effective in protecting the surface of carbon and low alloy steels from all types of corrosion, including local corrosion, adhesion to the metal surface and durability.

Claims (2)

1. A protective coating comprising a nanostructured protective layer, characterized in that it comprises a nanostructured protective layer of a corrosion inhibitor - N-heterocyclic alkylphosphonic acid and a second outer layer consisting of an epoxy polymer, while the second outer layer is obtained from a mixture of the composition, wt.% :
epoxy monomer E-40 68.0-72.0 toluene 18.0-20.0 dibutyl phthalate (DBP) 2.0-4.0 said corrosion inhibitor 2.0-4.0 polyethylene polyamine (PEPA) 4.0-6.0 2. The protective coating according to claim 1, in which the corrosion inhibitor is an N-heterocyclic alkylphosphonic acid of the formula HtC (R ₁ R ₂ ) P (O) (OH) ₂ , where Ht is a heterocyclic fragment with a nitrogen atom in the ring - pyrrolidine or morpholine; R ₁ and R ₂ are a hydrogen atom or alkyl radicals of CH ₃ or CH ₃ and C ₂ H ₅ .