The dissertation is devoted to research of processes of corrosion of steel in the conditions of heat transfer, influence on this process of carbonate sediments and ultrasound, development of methods for reducing the rate of corrosion and increasing the efficiency of heat transfer. Influence of the ultrasound intensity (28 kHz, 1.17.5 W/cm2) on CaCO3 nucleation-growth on the surface of a cylinder mild steel electrode rotating at 500 rpm was studied. The deposition kinetics was analyzed by chronoamperometry; the calcareous layer was characterized by gravimmetry, scanning electron microscopy and XRD. The water hardness was found to determine the crystallization kinetics of calcium carbonate influencing both the deposition rate and crystal morphology, so that a porous layer of vaterite was formed in soft water and highly protective calcite scale was built up in hard water. While temperature accelerates crystallization, faster crystallization leads to the formation of a more porous layer with vaterite inclusions due to limitations in calcium supply. Ultrasound accelerates formation of a calcite at intensities lower than 2.23 W/cm2. At higher ultrasound intensities, a significant change in carbonate crystallization occurs. Insufficient calcium concentration in the pre-electrode layer promotes formation of vaterite crystals in the growing calcite layer increasing porosity and scaling time. Application of ultrasound to calcium carbonate crystallization in tap water affects nucleation sites density, mass-transport rate and cavitation erosion of the deposits. Lower intensity ultrasound reduces scale porosity and area density by increasing nucleation site density and accelerating the mass transport. Higher intensity ultrasound promotes cavitation erosion of the formed layer, thus cleaning the surface from the scale. A scale layer with the highest blocking properties formed under applied ultrasound intensity of 1.9 W/cm2. The ultrasound doubled crystallization rate, reduced the scale porosity 5 times and halved its area density comparing to non-sonicated conditions. By the method of polarization curves, it was established that the course of corrosion process on steel practically does not change under the layer of scale both under the influence of ultrasound and without. Thus, the method of polarization resistance can be applied to determine the protective properties of the scum layer in the process of its formation and influence on this process of ultrasound. The corrosion rate variations with scale thickness, scale deposition time and solution composition are measured using linear polarization resistance technique. The deposited scale was formed of calcite crystals of 50-100 m as was established with SEM and XRD. The scale layer of 0.2 mm formed in tap water within 90 hours reduces the steel corrosion rate from 0.8 to 0.1 mm/year and serves as a barrier layer to prevent further corrosion. Increasing the corrosion protection and simultaneously increasing the thermal conductivity of the scale are caused by one fundamentally conjugated group of factors - a decrease in thickness and an increase in the density of calcium carbonate sediment, due to the higher thermal conductivity of the crystalline phases, the increase in thermal conductivity is increased to a greater extent than only due to a decrease in thickness. The coherence of these factors leads to the obligatory reliability of the proposed method of increasing anticorrosion protection when increasing the efficiency of the heat exchanger apparatus. When surface is processed by ultrasound due to different amplitude of fluctuations of scale and steel in the siege there are cracks, which, with prolonged repetition of oscillations, lead to a rejection of thick layers of scale. In the place of the crack, due to the ultrasound, a thin layer of small crystals remains, which creates a reliable barrier for oxygen access and protects the surface from corrosion. The application of ultrasonic devices in the industry has allowed to increase the heat transfer coefficient of tubular heat exchangers by more than 40%. Estimated payback period of ultrasonic devices is 2 months. Cost savings are achieved by increasing the heat transfer coefficient, increasing the efficiency of the boiler and reducing the cost of pumping water due to increasing the through-passage of the heat exchanger channels. The application of the results of the study on the modification of carbonate layers by ultrasound to protect the heat exchange equipment from corrosion and improve heat transfer will allow solving the problem of premature failure of equipment and energy overrun, which will have a significant positive effect on the preservation of the national metal fund from corrosion and the economy of the national energy resources.
