RU2520164C2 - Forecast method of durability of industrial corrosion-protection paint coatings for metal surfaces - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: proposed technical decision relates to forecast of durability (service life) of paint coatings intended for protection of metal surfaces of industrial facilities against corrosion, including structures for storage of different liquids, and namely oil products. The method provides for accelerated electrochemical tests of metal specimens with coatings in time at superimposition of the specified AC frequencies in electrolyte medium with further determination of frequency coefficient of variation of electrical capacity of specimens (K_f), as per the value of which protective properties of the above coatings are assessed. The proposed method consists in the fact that the above tests are performed at least at two time intervals, which are selected based on the following experimentally defined total dependence of frequency coefficient of variation of electrical capacity of the test specimens (K_f) on duration time of electrochemical tests of metal specimens with coatings (t). Duration of time intervals of electrochemical tests is determined as per the nature of graphic dependence of frequency coefficient (K_f) as a function of test time (t). Forecast of durability of the test coatings is composed by determining their probable operating life (T) based on the following expression: $$T={\left[\frac{(-\ln K_{fm})}{b_1}\right]}^{\frac{1}{n_1}},where$$

, T - probable operating life of industrial corrosion-protection paint coatings for metal surfaces, K_fm - frequency coefficient of variation of electrical capacity of test specimens, which is determined at the end of the second time interval of electrochemical tests, b₁ and n₁ - parameters determined by the nature of industrial corrosion-protection paint coatings and at the end of the second time interval of electrochemical tests.

EFFECT: obtaining a real-time forecast of durability of industrial corrosion-protection paint coatings on meal surfaces by detecting the law of influence of AC frequencies on protective properties of coatings at accelerated electrochemical tests.

4 dwg, 4 tbl

Description

The proposed technical solution relates to the field of predicting the durability (service life) of coatings designed to protect metal surfaces of industrial facilities from corrosion, including the construction of steel tanks for light oil products, and can be used in the oil, oil refining and other industries during anti-corrosion protect the inner surface of containers for storing various liquids, in particular petroleum products.

To assess the corrosion resistance of coatings based on paints and varnishes, full-scale and accelerated climatic tests are carried out. Although full-scale tests are the most reliable, however, their duration does not allow us to predict in advance the operational properties of paints and varnishes. Accelerated test methods for coatings are carried out under the influence of various factors, allowing these tests to be performed at shorter periods of time, including using thermostats and / or in special environments to check the chemical resistance of protective coatings.

Accelerated corrosion testing and forecasting the service life of coatings are given in GOST 9.401-2004 “Unified system of protection against corrosion and aging. Varnish-and-paint coatings. General requirements and methods of accelerated tests for resistance to climatic factors, ”which provides for a large number of cyclic research methods, including exposure of samples in chambers of cold, salt fog, moisture, sulfur dioxide, etc. According to these data, it is considered to be the operation of the coating for a period of one year if it has successfully passed 12-14 required cycles.

The disadvantage of this method of assessing the durability of coatings is the duration of the cycles, which creates difficulties in assessing modern types of coatings whose protective properties are preserved for more than 10 years of operation.

International requirements for anticorrosive protection by paints and varnishes are set out in the standard ISO 12944-6: 1988 “Varnishes and paints. Corrosion protection of steel structures against corrosion using protective paints and varnishes. Part 6. Laboratory test methods for determining performance. ” The requirements set forth in this document are based on an assessment of the protective properties of coatings for continuous exposure to salt fog and condensed moisture, as well as to the effects of a number of chemical media, including sulfur dioxide.

Tests in salt fog according to various studies do not coincide with data obtained under field conditions [Gardner G. ASTM new coatings test method addresses interactive effects of weathering and corrosion // JPCL. 2002. September. P. 58-62], and the estimated service life of the coatings is not specifically indicated and is determined by the durability of the protective paint system until the first overhaul of the coating. Cyclic testing is not excluded, which increases the study time of coatings.

There is also a method of accelerated testing of coatings designed for anticorrosive protection of the inner surfaces of stationary steel tanks for storing light oil products - GOST 9.409-88 "Unified system of protection against corrosion and aging. Varnish-and-paint coatings. Methods of accelerated testing for resistance to the effects of petroleum products. " In accordance with Appendix 1 of GOST 9.409-88, the protective properties of non-conductive coatings are assessed by the capacitive-ohmic method, the essence of which is to measure the parameters of the sample (capacitance C and resistance R) in the electrolyte at given AC frequencies. The condition and protective properties of the coating are evaluated based on the frequency dependences of the capacitance and resistance and their changes during the test. Regardless of the connection of elements of the equivalent circuit in the equalizing arm of the AC bridge, the absence of a dependence of the capacitance on the frequency of the current and the simultaneous change in resistance, which is inversely proportional to the frequency of the current, indicate a low porosity of the coating. A change in capacitance with a current frequency and constant resistance indicate a high porosity and permeability of the coating. For the test result of at least 3 parallel samples, the arithmetic mean value of the frequency coefficient K _{f of the} ratio of capacitances at various frequencies of alternating current and the dielectric loss tangent tgδ, which is practically unchanged during the study of resistant coatings, is taken.

However, this method, although it is a standard method for determining the protective properties of coatings, but at the same time does not allow a fairly long-term forecast of the operational properties of coatings to be made.

The technical problem in the development of the proposed method is to obtain an operational forecast of the durability of industrial anticorrosive coatings on metal surfaces by identifying patterns of the influence of AC frequencies on the protective properties of coatings under accelerated electrochemical tests.

As a result of solving this problem, an operational method for predicting the durability of modern types of coatings for metal surfaces, including with a service life of more than 10 years, was developed. In addition, without requiring large material and time costs, this method allows you to make the most correct choice of the paint material with the greatest resources in an aggressive operating environment as soon as possible. The developed predictive assessment of industrial coatings is confirmed by the practice of its application in a number of industrial objects of corrosion protection in various industries and regions of the Russian Federation.

The proposed method for predicting the durability of industrial anticorrosive coatings for metal surfaces is carried out on the basis of the known method, which provides for accelerated electrochemical testing of metal samples with coatings in time when applying specified AC frequencies in the electrolyte environment and then determining the frequency coefficient of change in the electric capacitance of the tested samples K _f , the value of which assesses the protective properties of varnish GOVERNMENTAL coatings. According to the proposed method, accelerated electrochemical tests of metal samples with the indicated coatings are carried out for at least two time intervals, the selection of which is carried out on the basis of the following experimentally established general dependence of the frequency coefficient of the change in the electrical capacitance of samples K _f on the time of electrochemical tests t:

$$K_f=e^{-b{t}^n},\text{Where}\text{(one)}$$

K _f is the frequency coefficient of change in the electrical capacitance of the tested samples,

e is the base of the natural logarithm,

b and n are the parameters due to the nature of industrial anti-corrosion coatings,

t is the time of electrochemical testing of metal samples with industrial anticorrosive coatings.

The duration of the first time interval of electrochemical tests is limited by the period of a sharp decrease in the frequency coefficient K _f with the greatest influence of the parameters b and n, due to the nature of industrial anticorrosion coatings. The duration of the second time interval of electrochemical tests is limited by the initial period of deceleration of the decrease in the frequency coefficient K _f with a weakened effect of these parameters.

The numerical values of the parameters b and n for the selected time intervals of the electrochemical testing of the samples are determined based on the experimental graphical dependence of the frequency coefficient K _f on the test time and on the basis of the general mathematical dependence of the frequency coefficient K _f represented by expression (1).

The forecast of the durability of these coatings is made by determining the possible life of the coatings T according to the measurement results obtained in the second time interval of the electrochemical testing of the samples, based on the following expression:

$$T={\left[\frac{(-\ln K_{fm})}{b_{\mathrm{one}}}\right]}^{\frac{\mathrm{one}}{n_{\mathrm{one}}}},gde(2)$$

T is the possible life of industrial anticorrosive coatings for metal surfaces,

K _fm - the magnitude of the frequency coefficient of change in the electrical capacitance of the tested samples, determined at the end of the second time interval of electrochemical tests,

b ₁ and n ₁ - parameters due to the nature of industrial anticorrosion coatings at the end of the second time interval of electrochemical tests.

Having taken in expression (2) the value of the frequency coefficient of change in the electric capacitance of the test samples, determined at the end of the second temporary test K _fm , equal to 0.7, as the maximum allowable in ensuring the protective properties of industrial anticorrosive coatings, determine the predicted duration of their durability.

In accordance with GOST 9.409-88 “Unified system of protection against corrosion and aging. Varnish-and-paint coatings. Accelerated Resistance Testing Methods for Petroleum Products ”, the criterion characterizing the dependence of the electrical capacitance of a metal sample with a paint and varnish coating, adopted the frequency coefficient of change in electrolytic capacitance K _f when the alternating current frequencies of 20,000 Hz and 2000 Hz.

, где $$K_f=\frac{C_{\mathrm{one}}}{C_2}$$

where

C ₁ and C ₂ are the capacitances of the test samples at current frequencies of 20,000 Hz and 2,000 Hz, respectively. The higher the K _f value, the higher the protective properties of the coating.

For satisfactory protective properties of the coating, the value of K _f should not be lower than 0.7. At values of K _f <0.7, most likely, the coating swells in the liquid electrolyte and the spatial-spatial “crosslinking” of the coating structure is destroyed, causing a loss of its protective properties.

The value of K _f as a function of test time is a monotonous falling dependence with a relatively high rate of change in the initial stage and a gradual deceleration over the entire interval of observation of this value during the operation of the coating, lasting for several years.

If at the very beginning of electrochemical testing of coatings the frequency coefficient of change in the electric capacitance of the samples is K _f = 1, then its value decreases monotonically and, when K _f <0.7 is reached, the coatings lose their protective properties. Therefore, the time intervals of electrochemical tests of metal samples are selected at which the frequency coefficient K _f decreases sharply at first (the first time interval of the tests), and then the recession period (second time interval of the tests) begins, after which the frequency coefficient of the samples begins to approach very slowly to a value of 0.7.

The electrochemical tests of metal samples with paint coatings in an electrolyte medium over a period of 0-36 days allowed us to establish the regularity with which the frequency coefficient K _f changes in time, while the nature of the curve K _f as a function of test time t corresponds to expression (1) laid the basis of the proposed method.

Expression (1) includes b and n parameters due to the nature of the protective coatings. Their numerical values for the first time interval of electrochemical tests are determined on the basis of the general mathematical dependence (1) and the experimental graphical dependence of the frequency coefficient K _f on the test time, allowing extrapolation to determine the values of K _f at any time t of the test. Arbitrarily choosing the values of the function K _f on the graph for its two values K _f1 and K _f2 corresponding to time instants t ₁ and t ₂ inside the test time interval t, we obtain expressions for calculating b and n parameters.

$$n=\frac{\left[\ln \left(\frac{\ln K_{f\mathrm{one}}}{\ln K_{f2}}\right)\right]}{\ln \left(\frac{t_{\mathrm{one}}}{t_2}\right)}(3)$$

или $$b=-\frac{\ln K_{f2}}{t_2^n},где(4)$$

$$b=-\frac{\ln K_{f\mathrm{one}}}{t_{\mathrm{one}}^n}$$

or $$b=-\frac{\ln K_{f2}}{t_2^n},gde(\mathrm{four})$$

K _f1 and K _f2 are the frequency coefficients of the change in the electrical capacitance of the test samples at time t ₁ and t ₂ respectively, inside the first time interval of electrochemical tests t,

t ₁ and t ₂ are times in the first time interval of electrochemical tests t,

b and n are parameters due to the nature of industrial anti-corrosion coatings.

Having experimentally determined by the nature of the indicated graphical dependence the initial period of deceleration of a sharp decrease in the frequency coefficient K _f in the test time t, we choose the second interval of electrochemical tests t _m , which is also limited by a sufficiently short period of time, after which the value of the frequency coefficient K _{fm is} very slow and practically imperceptibly in time approaches a value of 0.7, below which, as noted above, the protective properties of anticorrosive coatings are coated th is considered terminated.

In the second test time interval t _{m, the} initial period of deceleration of a sharp decrease in the frequency coefficient K _f in time means the beginning of stabilization of coatings at which the parameters due to the nature of industrial anticorrosive coatings change their numerical values, assuming the values n ₁ and at the end of the second test interval b ₁ . The value of the frequency coefficient K _f , obeying the mathematical dependence (1), at times t _m1 and t _m2 inside the second time interval of the test t _m is expressed as follows:

, $$K_{f{m}_2}=e^{-b_1{t}_{m2}^{n1}},где(5)$$

$$K_{f{m}_{\mathrm{one}}}=e^{-b_{\mathrm{one}}{t}_{m\mathrm{one}}^{n\mathrm{one}}}$$

, $$K_{f{m}_2}=e^{-b_{\mathrm{one}}{t}_{m2}^{n\mathrm{one}}},gde(5)$$

K _fm1 and K _fm2 are the frequency coefficients of the change in the electric capacitance of the test samples at times t _m1 and t _m2, respectively, inside the second time interval of the electrochemical tests t _m ,

e is the base of the natural logarithm,

b ₁ and n ₁ - parameters due to the nature of industrial anticorrosive coatings at the end of the second time interval of electrochemical tests t _m ,

t _m1 and t _m2 are times of electrochemical testing of samples in the second test time interval t _m .

Having determined the numerical values of the parameters b ₁ and n ₁ from the data of the experimentally obtained graphical dependence of the frequency coefficient K _f in time and from expressions (5), the possible service life of industrial anticorrosive coatings T is calculated by the formula (2).

$$T={\left[\frac{(-\ln K_{fm})}{b_{\mathrm{one}}}\right]}^{\frac{\mathrm{one}}{n_{\mathrm{one}}}},gde(2)$$

T - the possible life of industrial anticorrosive coatings,

K _fm is the magnitude of the frequency coefficient of change in the electrical capacitance of the test samples at the end of the second time interval of the electrochemical tests t _m ,

b ₁ and n ₁ - parameters due to the nature of industrial anticorrosive coatings at the end of the second time interval of electrochemical tests t _m .

Taking in the expression (2) the value of the frequency coefficient K _fm equal to 0.7, make a forecast of the durability of the coatings.

Figure 1 shows a graphical dependence of the frequency coefficient of change in the electric capacitance of the tested samples K _f from the test time for various types of industrial anti-corrosion coatings.

Curve 1 characterizes the protective properties of epoxy coatings, curve 2 is the same for coatings based on a copolymer of vinyl chloride with vinyl acetate, curve 3 is the same for modified epoxy and epoxy coal coatings.

Figure 2 shows the nomogram of the dependence of the parameter b, due to the nature of industrial anti-corrosion coatings, on the magnitude of the frequency coefficient of change in the electrical capacitance of the tested samples K _f .

Figure 3 shows the nomogram of the dependence of the parameter n, due to the nature of industrial anti-corrosion coatings, on the magnitude of the frequency coefficient of change in the electric capacitance of the tested samples K _f .

Figure 2 and 3 illustrate the nature of the change in the parameters b and n of industrial anti-corrosion coatings from the frequency coefficient K _f during accelerated electrochemical testing of samples with coatings.

Figure 4 presents the possible life of various types of industrial anticorrosive coatings depending on the magnitude of their frequency coefficient K _fm at the end of the second time interval of electrochemical tests t _m .

The possible service life of the coatings (T) is calculated by the value of the frequency coefficient K _fm , determined at the end of the second time interval of the electrochemical tests for each individual type of paint coating.

To implement the proposed method for predicting the durability of industrial anticorrosive coatings using the following equipment and reagents:

- AC bridge type R-571, R-5021, R-568, R-5016, R-5083, etc .;

- electrolytic cell in the measurement scheme in accordance with the requirements of GOST 9.509-89 “Unified system of protection against corrosion and aging. Means of temporary anticorrosive protection. Methods for the determination of protective ability ", Appendix 4;

- electrolyte - sodium sulfate anhydrous according to GOST 4166-76 "Reagents. Sodium sulfate. Technical conditions ";

- distilled water according to GOST 6709-72 "Distilled water. Technical conditions. "

Balancing the AC bridge and taking readings is carried out in accordance with the technical documentation for the device.

The following industrial anticorrosion paints and varnishes are used as coatings applied to metal samples:

- HS-717 enamel (TU 6-10-961-76) based on a washed copolymer of vinyl acetate with vinyl chloride;

- Vinikor-62 enamel (TU 2312-001-54359536-2003) is made on the basis of epoxy and vinyl resins;

- EP-0010 putty (GOST 28379-89) based on epoxy resin;

- EP-525 enamel (GOST 22438-85) on an epoxy basis;

- enamel B-EP-651 (TU 2312-020-50928500-2007) based on a modified epoxy resin; B-EP-68 paints (TU 6-10-2037-85), B-EP-610 (TU 2312-003-27524984-98),

- Modified epoxy composition Polak EP-41 (TU 2312-009-29216933-2001) based on epoxy-coal tar, etc.

Standard metal samples are prepared in the amount of three samples for each type of steel coatings, St.3, dimensions 75 × 150 × 0.8 ÷ 1.0 mm in accordance with GOST 8832-76 “Paint and varnish materials. Methods for obtaining paint coatings for testing ”and ISO 1514-84“ Varnishes and paints. Standard test records. ” Previously, metal plates are mechanically or manually cleaned of rust and scale. Then washed in white spirit or nefras, dried and wiped the surface of the samples. Then the samples are stained with uniform movements of the applicator. For coating, the applicator adjusts the height of its slit, thereby providing the required thickness of the coating layer. In this case, the applicator is placed on the edge of the sample and moved at a speed of 5-10 cm / sec with slight pressure, creating a continuous uniform coating layer on the surface of the sample. Samples are dried in accordance with GOST 19007-73 “Materials for paint and varnish. The method of determining the time and degree of drying ”to degree 3. After drying, the painted metal samples are kept in air at room temperature for at least 10 days.

To conduct accelerated testing of coatings in contact with light petroleum products, prepared samples are placed in containers with liquid fuels under thermostated conditions at elevated temperatures with holding in time with periodic shaking of the fuel tanks:

- in aviation kerosene and diesel fuels at a temperature of 40 ± 0.5 ° C for 110 hours;

- in gasolines at 28 ± 0.5 ° C for 110 hours.

At the same time, full-scale tests are carried out, in which metal samples are coated during the process of anticorrosion work at anticorrosion protection facilities (for example, when protecting the surfaces of steel ground tanks) and are kept in motor fuel under the same conditions as the object itself. After a required period of time, these samples are removed and then electrochemical tests of colored samples are carried out simultaneously in three electrolytic cells filled with a 3% solution of electrolyte (sodium sulfate), for which the cells are held for 30 minutes and the P-5016 AC bridge is balanced. During the tests, the painted samples are exposed to alternating electric current with a frequency of 2000 and 20,000 Hz and the electric capacitances (C ₁ and C _2, respectively) and the resistance (R) of the samples are measured. With a decrease in resistance R, a smooth increase in the electric capacitance is observed, which characterizes the high protective properties of the coatings. According to the data obtained, the values of the frequency coefficients K _{f are} determined separately for each type of coating and graphical dependences of the frequency coefficient K _f on the test time t are constructed (Fig. 1).

Figure 1 shows the averaged results of electrochemical tests of metal samples with coatings, conducted over 36 days, where:

- curve 1 characterizes the protective properties of epoxy coatings, in which a sharp change in the value of K _f stops when the value of K _f = 0, 82;

- curve 2 characterizes the protective properties of coatings based on a copolymer of vinyl chloride with vinyl acetate, in which a sharp change in the value of K _f stops when the value of K _f = 0,86;

- curve 3 characterizes the protective properties of the modified epoxy and epoxy-coal coatings, in which the change in the frequency coefficient K _f slows down when K _f = 0.89 is reached.

The graphical dependence of the magnitude of the frequency coefficient K _f as a function of the time of the electrochemical tests t shown in Fig. 1 is represented by monotonous dropping curves 1, 2, 3, the initial sections of which illustrate the relatively high rate of decrease in the value of K _f and its gradual deceleration in time over time all subsequent observation interval for this value during prolonged operation of coatings, and only on reaching the value K _f <0,7 coatings lose their barrier properties that should be considered when leaving prediction durability of coatings. These data are also confirmed by full-scale tests conducted at the objects of anticorrosive protection, including on the painted surfaces of steel fuel tanks. Thus, curves 1, 2, 3 in FIG. 1 are a graphical display of the overall analytical dependence (1), which is the basis for predicting the durability of industrial anticorrosive coatings.

The nomograms in FIGS. 2 and 3 illustrate the nature of the change in the parameters b and n, due to the nature of industrial anti-corrosion coatings, depending on the frequency coefficient K _f during accelerated electrochemical testing of samples with coatings.

The essence of the proposed method is illustrated by the following examples.

Example 1

The forecast of the durability of the coating based on enamel EP-525 (GOST 22438-85), the coating thickness is 200 microns.

Metal samples are prepared in the same way as described above, painted with enamel EP-525, dried for at least 10 days and kept in contact with TS-1 aviation kerosene at a temperature of 40 ± 0.5 ° C for 110 hours, after which, through a bridge alternating current of the R-5083 brand conduct accelerated electrochemical tests of the sample with previously prepared electrolytic cells filled with a 3% sodium sulfate solution, with alternating current being applied at a frequency of 2000 and 20,000 Hz. During the tests, their electric capacitances (C ₁ and C _2, respectively) and the resistance (R) of the samples are measured. Using the averaged measurement data presented in Table 1, a graphical dependence of the frequency coefficient K _{f is} constructed as a function of test time t, similar to curve 1 in Fig. 1 and described by the general expression (1). The duration of the first test time interval t is determined by the nature of the obtained curve 1 in the area corresponding to the sharpest change in the frequency coefficient K _f in time, the duration of which for the enamel EP-525 is on average t = 28 days. During this period, the parameters b and n, due to the nature of the enamel EP-525, have the greatest influence on the frequency coefficient K _f .

Then choose the second test time interval t _m , which is limited to the initial period of deceleration of a sharp change in the magnitude of the frequency coefficient K _f . For enamel EP-525, the beginning of the second time interval of electrochemical tests t _m falls on the 36th day of testing and then lasts up to 100 days.

Table 1 presents the results of electrochemical tests of samples stained with enamel EP-525 averaged for three electrolytic cells.

Table 1 The averaged results of accelerated electrochemical tests of enamel EP-525 The duration of the electrochemical tests, days (t / t _m ) Frequency of alternating current, Hz 2000 AC frequency, Hz 20000 K _f C _20,000 C ₂₀₀₀ C ₂ R C ₁ R 0.02 80.0 21.0 74.0 1.8 0.93 0.12 83.0 19.0 77.0 1.7 0.93 one 90.0 15.0 83.0 1.4 0.92 four 101.0 11.0 91.0 1,1 0.90 8 110.0 8.1 98.0 0.94 0.89 fourteen 122.0 5.7 105.0 0.76 0.86 eighteen 128.0 5,0 109.0 0.69 0.85 21 136.0 4.3 113.0 0.62 0.83 28 144.0 3,7 118.0 0.55 0.82 36 144.9 3.6 119.0 0.54 0.82 fifty 145.0 3,5 119.0 0.53 0.81 one hundred 145.0 3,5 119.0 0.53 0.80

According to table 1, a graphical dependence of the frequency coefficient K _f on the test time is obtained, similar to curve 1 in figure 1, by which extrapolation is used to find the numerical values of the frequency coefficients K _f at any point in time of electrochemical testing of samples from 0.02 to 100 days or more .

Then, on curve 1 of FIG. 1, two test times t ₁ and t ₂ are arbitrarily selected for the first test time interval t and the corresponding numerical values of the frequency coefficients K _f1 and K _{f2 are} determined by extrapolation (or according to table 1). So, at t ₁ = 14 days, K _f1 = 0.86; at t ₂ = 28 days, K _f2 = 0.82.

After that, using expressions (3) and (4), calculate the values of the parameters n and b, due to the nature of the enamel EP-525 in the first test time interval t:

n = 0.290570, b = 0.070055.

In the second test time interval t _m , stabilization of the coatings begins and, as a result, the values of the parameters n and b change, acquiring the values of n ₁ and b ₁ at the end of the second test interval. To determine their numerical values on the plot of curve 1 of Fig. 1 in the test time interval t _m , two time instants t _m1 and t _m2 are also randomly selected and the corresponding numerical values of the frequency coefficients K _fm1 and K _{fm2 are} determined by extrapolation (or according to table 1) . So, at t _m1 = 28 days, K _fm1 = 0.82, and at t _m2 = 100 days, K _fm2 = 0.80.

Then, using expressions (3) and (4), calculate the numerical values of the parameters n ₁ and b ₁ , due to the nature of the enamel EP-525 at the end of the second time interval of electrochemical tests t _m :

n ₁ = 0.114788, b ₁ = 0.131525.

Based on the results of electrochemical tests obtained in the second time interval t _m , the possible life of the enamel EP-525 (T) is calculated by the formula (2):

$$T={\left[\frac{(-\ln K_{fm})}{b_{\mathrm{one}}}\right]}^{\frac{\mathrm{one}}{n_{\mathrm{one}}}},gde(2)$$

K _fm - the magnitude of the frequency coefficient of change in the electrical capacitance of the tested samples at the end of the second time interval of the electrochemical tests t _m is 0.80.

To make a forecast of enamel endurance EP-525, the frequency coefficient K _{fm is} taken equal to 0.7 as the maximum permissible value, at which the protective properties of the coating still appear. Substituting the value of K _fm = 0.7 in the calculation formula (2), get:

T = 5949 days = 16.3 years.

Thus, the maximum life of a coating for a metal surface using enamel EP-525 is 16.3 years.

Example 2

The forecast of the durability of the coating based on the HS-717 enamel (TU 6-10-961-76), the coating thickness is 90 microns.

The protective properties of the coating created by this enamel on a metal surface in order to predict the durability of the coating is determined by conducting accelerated electrochemical tests similarly to example 1.

Prepared metal plates are painted with HS-717 enamel, dried for at least 10 days, and kept in gasoline at a temperature of 28 ± 0.5 ° C for 110 hours with periodic shaking of gasoline containers. Three electrochemical cells are filled with electrolyte and, using the P-5083 alternating current bridge, affect the prepared samples with alternating current with a frequency of 2000 and 20000 Hz.

Table 2 presents the results of electrochemical tests of samples stained with HS-717 enamel averaged for three electrolytic cells.

table 2 The averaged results of accelerated electrochemical tests of the HS-717 enamel The duration of the electrochemical tests, days (t / t _m ) Frequency of alternating current, Hz 2000 AC frequency, Hz 20000 K _f C _20,000 C ₂₀₀₀ C ₂ R C ₁ R 0.02 55.5 25.0 55.0 2.40 0,990 0.12 57.0 24.0 56.0 2.20 0.980 one 68.7 13.0 67.0 1.10 0.975 four 72.0 9.9 69.0 1.00 0.960 8 77.0 8.0 72.0 1.00 0.940 fourteen 85.0 5.9 76.0 0.89 0.895 21 92.0 4,5 80.0 0.75 0.870 24 93.0 4.1 79.0 0.72 0.860 36 95.0 3,5 82.0 0.69 0.860 58 100.0 3.7 85.0 0.67 0.850 86 105.0 3.8 88.0 0.68 0.840

According to the test results presented in table 3, build a graphical dependence of the frequency coefficient K _f as a function of test time t, similar to curve 2 in figure 1 and described by the general expression (1). The duration of the first test time interval t is determined by the nature of curve 2 of FIG. 1, in which the portion of the curve reflecting the most dramatic change in the frequency coefficient K _f in time t is 36 days.

The second test time interval t _m for curve 2 of FIG. 1 is limited to the beginning of the recession period of a sharp decrease in the frequency coefficient K _f , which is already observed on the 36th day of testing and lasts up to 86 days.

The calculations for predicting the durability of the enamel XC-717 are carried out analogously to example 1, leading to the following results.

For the first time interval of tests t, which amounted to 36 days:

at t ₁ = 14 days K _f1 = 0.895;

at t ₂ = 36 days K _f2 = 0.86;

respectively, n = 0.325257, b = 0.047185.

For the second test time interval t _m :

at t _m1 = 36 days K _fm1 = 0.86;

at t _m2 = 86 days K _fm2 = 0.84;

respectively, n ₁ = 0.16648, b ₁ = 0.083057.

From the expression (2), taking K _fm = 0.7, T = 6333.3 days = 17.35 years.

Thus, the forecast durability of the enamel XC-717 is 17.35 years.

Example 3

The forecast of the durability of the coating based on enamel B-EP-651 (TU 2312-020-50928500-2007), the coating thickness is 300 microns.

Metal samples prepared in the same way as described above are stained with B-EP-651 enamel, dried for at least 10 days and kept in diesel fuel at a temperature of 40 ± 0.5 ° C for 110 hours, after which accelerated electrochemical tests are carried out in the sequence indicated in examples 1, 2.

Table 3 presents the results of electrochemical tests of samples stained with B-EP-651 enamel averaged for three electrolytic cells.

Table 3 The averaged results of electrochemical tests of enamel B-EP-651 The duration of the electrochemical tests, days (t / tm) Frequency of alternating current, Hz 2000 AC frequency, Hz 20000 K _f C _20,000 C ₂₀₀₀ C ₂ R C ₁ R 0.02 308 3.5 305 0.73 0.99 0.12 316 3.4 313 0.68 0.99 one 384 1.8 376 0.35 0.98 four 414 1.7 397 0.30 0.96 8 491 1.4 457 0.24 0.93 fourteen 520 1.3 478 0.22 0.92 21 539 1.3 491 0.21 0.91 24 533 1,2 498 0.20 0.90 36 569 1,1 506 0.21 0.89 55 583 1,0 507 0.18 0.87 84 586 1,1 510 0.19 0.87

Using the averaged measurement results presented in Table 3, a graphical dependence of the frequency coefficient K _{f is} constructed as a function of test time t, similar to curve 3 in FIG. 1 and described by the general expression (1). The duration of the first test time interval t is determined by the nature of this curve in the area reflecting the most abrupt change in the value of the frequency coefficient K _f in time t, which is 36 days.

The second test time interval t _{m is} limited to the initial period of deceleration of a sharp decrease in the frequency coefficient K _f , which for enamel B-EP-651 falls on the curve 1 section of Fig. 1, corresponding to the 36th day of testing and then to 84 days.

Calculations for the prediction of durability of enamel B-EP-651, similar to example 1, lead to the following results.

For the first time interval of tests t = 36 days:

at t ₁ = 14 days K _f1 = 0.92;

at t ₂ = 36 days K _f2 = 0.89;

respectively, n = 0.354439, b = 0.0327218.

For the second time interval of tests t _m , the beginning of which falls on 36 days and lasts up to 84 days, the following results were obtained:

at t _m1 = 36 days K _fm1 = 0.89;

at t _m2 = 84 days K _fm2 = 0.87;

respectively, n ₁ = 0.21029, b ₁ = 0.05485.

From expression (2), taking K _fm = 0.7, T = 7354 days = 20.1 years.

Thus, the forecast of durability of enamel B-EP-651 is 20.1 years.

Table 4 presents the general forecast of the durability of industrial anticorrosive coatings according to the results of accelerated electrochemical tests described in examples 1-3.

As a result of similar electrochemical tests of a wide range of industrial anticorrosive coatings, the main parameters for predicting their durability are determined.

In the corresponding graphical dependence shown in Fig. 4, the possible service life of the paint coatings (T) calculated by the value of the frequency coefficient K _fm determined at the end of the second time interval of the electrochemical tests for each individual type of paint material is reflected.

Claims (1)

A method for predicting the durability of industrial anticorrosive coatings for metal surfaces, involving accelerated electrochemical testing of metal samples with coatings in time when applying the specified AC frequencies in the electrolyte medium, followed by determining the frequency coefficient of change in the electric capacitance of the samples K _f , the value of which evaluates the protective properties of these coatings characterized in that the conduct of accelerated electrochemical tests Nij metal samples is performed by at least two time intervals, the selection of which is performed based on the following experimentally determined general coefficient changes depending on the frequency capacitance test specimens (K _f) from the time of the electrochemical testing metal samples coated (t):

K _f is the frequency coefficient of change in the electrical capacitance of the tested samples,
e is the base of the natural logarithm,
b and n are the parameters due to the nature of industrial anti-corrosion coatings,
t is the time of electrochemical testing of metal samples with coatings,
the duration of the first time interval of electrochemical testing of samples is limited by the period of a sharp decrease in the frequency coefficient K _f with the greatest influence of parameters b and n due to the nature of industrial anticorrosion coatings, the duration of the second time interval of electrochemical tests is limited by the initial period of slowdown in the decrease in the frequency coefficient K _f when weakened by the influence of these parameters, the numerical values of b and n parameters for GOVERNMENTAL slots electrochemical test calculated from the experimental graphic dependence of the frequency change ratio of electrical capacitance of samples (K _f) in time and reduced dependence (1), the forecast coatings subjects durability constitute by determining the possible period of operation (T) from the measurements obtained in the second time interval of electrochemical tests, based on the expression:

T is the possible life of industrial anticorrosive coatings for metal surfaces,
K _fm is the frequency coefficient of change in the electrical capacitance of the test samples, determined at the end of the second time interval of electrochemical tests,
b ₁ and n ₁ - parameters due to the nature of industrial anti-corrosion paint coatings at the end of the second time interval of electrochemical tests,
in which the value of the frequency coefficient of change in the electrical capacitance of the test samples, determined at the end of the second time interval of the electrochemical tests (K _fm ), is taken equal to 0.7, as the maximum allowable in ensuring the protective properties of industrial anticorrosive coatings.

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