PSI - Issue 59

Igor Stadnyk et al. / Procedia Structural Integrity 59 (2024) 679–686 Igor Stadnyk et al./ Structural Integrity Procedia 00 (2023) 000 – 000

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If we assume that the corrosion of, for example, evaporation device occurs according to the linear law, its statistical rate is subjected to the normal law of distribution in time of random variables, and the intensity of random failures is described by the exponential law, then the structural models of the probability of failure-free operation and the service life of the device can be written as follows: ( ) (7) ( ) (8) where К av is average corrosion rate, Х max is maximum permissible value of the depth corrosion indicator, , U  is quantile of the random variable,  k is root mean square deviation of the corrosion rate,  a – mean square deviation of the initial parameter of the structural element (thickness of the protective coating); а 0 – the initial value of the structural element parameter; Т – service life of the structural element;  - intensity of failures; t – operating time of the device. The carried out investigations showed (see Fig. 2) that copper plates, which were in mixed environment during visual assessment, had light orange color, close to the color of the original plate. That is, the investigated corrosion action of corrosion inhibitor IGH -3 on the copper plate has insignificant effect, which can be attributed to its slight tarnishing. It is known that the presence of the small amount of corrosive-active elements which do not cause copper plate corrosion during the investigation of the liquid mixture of the medium under standard conditions can cause severe corrosion destruction of the device metal structures. Moreover, the corrosive effect of corrosive-active elements is significantly enhanced due to high temperatures and the presence of vapors (Korniy et al., 2021). Therefore, the investigation was carried out in order to determine corrosive effect on the copper plate of products containing chromium on the laboratory setup, its diagram is shown in Fig. 2. This process took place in the absence of oxygen in the copper plate area. The conditions arising from the movement of the evaporation products of the mixture (inhibitor) through the quartz tube made it possible to establish that, depending on the temperature of the formed medium, the color of the copper plate changed (see Fig. 3). Within the temperature range of the formed medium at 100- 120°C (see Fig. 3, b), the surface of the copper plate acquired pale purple color. Accordingly, the corrosive effect on the copper plate can also be classified as moderate tarnishing. Within the temperature range of 120- 130°С (see Fig. 3, c), the surface of the copper plate acquires silver color, and the corrosive effect on the copper plate can be classified as moderate tarnishing. Taking into account the obtained results, it should be noted that during the dynamics of the movement of the starch-containing medium on the copper plate, energy transformations occur. They prevent formation of corrosive effects in the area of location beyond the process temperature (60- 70°С). Under the influence of medium mixture, the stationary potentials of copper in the device shift towards the side of more negative values, and the increase of extract concentration from 0.4 to 0.8 g/dm 3 does not create conditions for influential values of corrosion effects.

a

b

c

Fig. 3. Type of copper plates: a) initial state; b) initial effect of inhibitor temperature at 100- 120°С; c) after exposure at 120 - 130°C .

Taking into account the above mentioned, we can predict the corrosion destruction of the device surface. If the average rate of corrosion destruction of anti-corrosion coating of the evaporator body К ср = 1 mm/year (typical for most devices of sugar factories), the mean square deviation of the corrosion rate  k = 0.07 mm/year, the mean square