RU1817013C - Method of determination of service life of protective coatings on metals in corrosive media - Google Patents

Abstract

Usage: determination of the service life of protective coatings on metals, mainly oxide, under the Corrosive action of aggressive environments. SUMMARY OF THE INVENTION: at certain intervals from the start of testing a sample batch, individual samples are removed from the array of test samples placed under conditions close to the operational ones. On each sample of the batch, the stationary potential is measured before extraction (pct, then each sample of batch is placed in an electrochemical cell where the potential of the sample is determined, and according to the time interval from the start of the test at which the stationary potential is equal to the potential of the sample, m determined the service life of the protective coatings. 1. 1 table 1

Description

The invention relates to the study of the chemical and physical properties of substances, namely the determination of the service life of protective coatings on metals; predominantly oxide, when corrosive to aggressive media, for example, to determine the service life of a borate coating on aluminum in cooling systems with ethylene glycol aqueous solutions.

 The aim of the invention is to increase the accurate ™ determination of the service life of protective coatings.

The drawing shows the variation of yjtr and yVip values for coverage over time.

The method is based on the following position. If there is a high-quality protective coating on the metal surface

oxide type, a passive region will be observed on the anode polarization curve. By changing the size of the passive region, one can judge the state of the protective coating. Therefore, by determining the difference in the values of rpr - rst of a metal sample with a protective coating at certain intervals, it is possible to establish the moment of violation of the integrity of the protective coating. The time interval from the start of the test, in which there is no massive region on the anode portion of the curve, determines the service life of the protective coating.

The time intervals from the beginning of the test to the measurement of PCT and control can be different and are selected depending on the aggressiveness of the medium, grade of material, us00

 about

with

fishing operation, etc. It is not advisable to set specific time intervals, since they do not change the essence of the invention.

The time of determining the potential of a breakdown of the protective coating rpr, which characterizes the corrosion wear of the protective coating, is commensurate with the time of determination by traditional methods, for example, gravimetric, physical, chemical and metallographic. However, the use of the breakdown potential for determining the service life of protective coatings makes it possible to increase the accuracy of the method. metal surfaces of the anodic and cathodic phases with imperfections in the metal structure, such as vacancies, dislocations along grain boundaries, which is especially characteristic; for example, for aluminum alloys; secondly, the potential of the breakdown is recorded by technical means of measurement.

The method is implemented as follows. An array of samples with a test coating is placed in a stand for corrosion-electrical measurements simulating test conditions as close as possible to operational ones. After a certain period of time from the start of testing on a sample batch of samples, the pc-g is measured under the conditions of the existing test bench. Then this batch of samples is removed from the test bench and the sample potential is determined in a three-electrode cell using the standard method. The obtained values of mouth and RPR are compared with each other. This sequence of measurements is repeated on the rest of the samples with a longer test duration until pst and ctn are equal. The time interval from the start of the test, at which the equality of West and RPR comes, determines the service life of the protective coating.

Example. The service life of the protective oxide coating (borate) was determined on an aluminum alloy AMts in a 66% aqueous solution of ethylene glycol. . .

The working surface of the samples was subjected to grinding and polishing. The protective chemical coating (brratic) was applied according to the existing instructions. The samples prepared for testing were placed in a stand simulating the operating conditions of the product with a protective coating. The temperature of a 66% aqueous solution of ethylene glycol was 70 ° C, pH 3.83, and the velocity of the medium was 2 m / with,

10 h after the start of the tests, the stationary potential was measured under operating conditions at the test bench using a P-340 pH meter. Then the samples (3 samples at one time point) were removed

from the stand and one at a time was placed in a 3-electrode electrochemical cell filled with a 66% aqueous solution of ethylene glycol, kept there for 20 min at 70 ° C and using a P-5827 potentiometer

An anodic polarization curve was taken from the steady state potential to +1.5 V to determine the potential of the sample. The reference electrode is silver-silver, the auxiliary electrode is platinum, and the potential sweep rate is 0.25 tV / s. Then, the operations on measuring γy under operating conditions and removing the anode polarization curves were repeated until they were obtained

stationary potential and sample potential. The research results are summarized in table.

As a result of the tests, equality of the potentials of the stationary and the sample after 4500 hours was obtained. An additional examination of the state of the protective coating in order to verify the method with an MIM-3 microscope confirmed that after 4500 hours there was a violation of the integrity of the protective coating.

The results of electrochemical studies of the protective properties of the borate coating are in good agreement with the on-site corrosion tests of aluminum heat exchangers with a borate coating using a 66% aqueous ethylene glycol solution at a temperature of 70 ° C and a medium velocity of 2 m / s.

Field tests were carried out on a special bench simulating the operating conditions of real cooling systems. Heat exchangers withstood, resource 4000 hours, and after they reveal traces of corrosion

found only on tube boards at soldering points, which could be the result of poor fluxing. The channels of the heat exchangers were without signs of corrosion. Using the proposed method

for determining the service life of protective oxide coatings on metals under the corrosive effects of aggressive media provides, in comparison with existing methods, the following advantages: high accuracy in determining the term

protective coating services through the use of technical means of measurement that make it possible to determine even initial structural failures; the possibility of determining the service life of protective coatings in a cheaper way than field tests, especially when studying corrosion of the internal surfaces of pipelines and heat exchangers that require cutting and, as a result, their single use.

Claims (1)

The claims A method for determining the service life of protective coatings on metals in aggressive environments, which is indoor samples under conditions close to operational, with subsequent determination and at fixed intervals on the extracted solution of samples of the service life of protective coatings, characterized in that, in order to improve the accuracy of determining the service life of coatings, stationary 0 potential, after which each sample is placed in an electrochemical cell, the potential of the coating is determined by urr and the time interval from the start of testing at which the stationary potential is determined 5 is equal to the potential breakdown of the coating, the service life of the protective coatings is determined.