Study of the inhibitory ability of inorganic di- and polyphosphate compositions

The article considers the anticorrosive properties of inorganic di-and polyphosphate compositions in relation to St-3 steel, depending on the pH of the medium, the nature and concentration of phosphate, and the nature of the modifier ion. The research was conducted using GOST-based methods: gravimetry, potentiometry, photocolorimetry, infrared spectroscopy and scanning electron microscopy. On the basis of experimental data, quantitative indicators of corrosion process were determined: the rate of corrosion process, the degree of protection, the depth index, the coefficient of inhibition and the assessment of the stability of the formed film on the ball scale of corrosion resistance against steel. The analysis of experimental data allows to establish the influence of the above factors on the corrosion processes in the systems under study. The experimental data are supplemented by thermodynamic calculations of the corrosion process parameters, the results of which correlate well with the kinetic data of the process under study. In the course of the research work, the analysis of corrosion deposits was also carried out. The regularities established during the work contribute to the creation of effective di-and polyphosphate inhibitors with the highest degrees of protection.

Fireside Corrosion on Heat Exchanger Surfaces and Its Effect on the Performance of Gas-Fired Instantaneous Water Heaters

The heat exchanger in a gas instantaneous water heater is a thermal device used for heat transfer from the high-temperature flue gas to the low-temperature water. The fireside corrosion, due to the reaction of acidic condensate formed on the heat exchanger surfaces and its metallic material, is one of the major hazards for gas instantaneous water heaters. This paper focuses on identifying and quantifying the fireside corrosion on the surface of heat exchangers in gas-fired instantaneous water heaters. Durability tests lasting for 2000 cycles were undertaken for five gas-fired instantaneous water heaters, which were different in terms of the heat input and coating of heat exchangers. The corrosion deposits on the surface of the heat exchangers were surveyed by several methods. The results show that the corrosion deposit grew as the test duration increased. The fins of the heat exchanger with a lead coating had been corroded and copper was exposed. Cu4(OH)6SO4 was the main corrosion product of heat exchangers without a lead coating, whereas PbSO4 was the main corrosion product of heat exchangers with a lead coating. The experiments demonstrate that the corrosion rate decreased with the increase of the heat input. The experiments also show that the thermal efficiency of gas instantaneous water heaters decreased by 2.4% to 6% at the end of the test duration.

Explanation of tuberculation scales formation in steel and iron pipes using the theory of wave motion of a liquid

Electrochemical corrosion of steel and iron pipes in water supply systems is a common problem that causes financial losses to operating companies and deteriorates water quality. A comprehensive study of corrosion deposits formation mechanism is necessary for a better understanding of the processes occurring in pipelines and for scientific justification of monitoring and predicting techniques. The influence of various factors (in particular the water flow velocity) on the formation, growth, and spatial distribution of tuberculation scales on the inner surface of pipes is considered. To study the effect of flow velocity, simple serial tests were carried out on segments of a steel non-galvanized pipe in static and dynamic conditions. The difference in the formation of anode and cathode sections in two dynamic modes is recognized. The first stage of tubercle formation is observed. It was assumed that in pipes with turbulent water flow near metal surface, waves forming tubercles are appeared, and the distribution of the tubercles is depend on water flow velocity.

Corrosion Behavior of Zr-Based Bulk Metallic Glasses by Addition of Ni

Fully amorphous Zr48Cu43-xAl7Ag2Nix(x=0, 2, 4, 6, 8 at. %) alloy system synthesized by Cu mould casting method were utilized to study corrosion behavior due to the poor corrosion resistance of Zr-Cu-Al-Ag alloy system by addition of Ni. High temperature DSC revealed that the Zr-based alloy system still maintained good glass-forming ability and thermal stability with the addition of Ni element. The result obtained from both the immersion test and the potentiodynamic polarization test showed that the addition of Ni element significantly improved the corrosion resistance compared to the Ni-free Zr-based alloy system. SEM graph showed a phenomenon of corrosive pit where there existed corrosion deposits as well as cellular textures and microcracks. In summary, proper addition of Ni could modify the corrosion resistance of the Zr-based alloy system.