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Corrosion Behavior of the Metal and Coating Systems in the Petrochemical Atmospheric Environment

Author: HuZhangZhi
Tutor: ZhangSanPing
School: Research Institute of Mechanical
Course: Materials Science
Keywords: Petrochemical atmospheric outdoor exposure test rust layer thin film electrochemical impedance
CLC: TG172.3
Type: Master's thesis
Year: 2011
Downloads: 97
Quote: 2
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Abstract


In recent years, with the rapid development of national economy, energy consumption increased and the dependence for oil is enhanced, while chinese crude oil resources are relatively short, the deep exploitation makes the tendency of low-grade crude oil serious, and most imported crude oil are high sulfur and high acid, so the content of corrosive gases in petrochemical industry rises day by day, the corrosion problem of equipment is getting more and more serious. At present, there are no standards or regulations of equipment protection teconology except for steel pipelines and storage tanks in national petrochemical industry. Therefore, studying the corrosion behavior of metal and coating system in the petrochemical atmospheric environment, understanding the law of corrosion and corrosion resistance of different metal and coating system, not only have important significance, but also have great value in application, for the reasonable selection of protective measures, prolonging the using life of equipments and materials and reducing the economic loss caused by corrosion.In this paper, atmospheric exposure tests were carried out in the desulfurization tower, testing centers of the petrochemical plant and atmospheric corrosion of Wuhan National Field Research Stationt with Q235 carbon steel, copper, aluminum, zinc and 20 species of coating system. Rust and corrosion products were analyzed by SEM and XRD. Weatherability and corrosion resistance of the coating system were studied by means of neutral salt spray accelerated test and aging test in laboratories, besides the electrochemical corrosion behavior of the carbon Q235 steel in thin electrolyte film.The results show that the corrosion of materials in petrochemical atmosphere is a complex process. The corrosion rate of metal in the desulfurization tower research station was higher than the other two stations. The corrosion of Q235 carbon steel in the desulfurization tower was extremely serious, the corrosion rate reached for the C5 level, compared with C3 level in the other two research stations. The characteristics of coating system were compared between outdoor exposure tests and indoor accelerated tests, the results indicated that sprayed aluminum coating has a excellent corrosion resistance, fluorocarbon coating has a great weathering resistance, and zinc-rich and sprayed aluminum primer system possess good corrosion resistance.The rust layer of carbon steel in the three research sites had a various shapes, and corrosion products were also different, the growth of which had a certain protective function to the substrate. In the petrochemical plant, the corrosion of carbon steel is not uniform corrosion, as there are some cracks between the rust layer and magnesium substrate. We can see that the surful content in the rust layer is very low through the section of line scans. The surface of carbon steel had massive prosperous undulation pellet in the initial period, with the further occurrence of corrosion, the pellets connected for an entire piece of rust layer. However, the corrosion could not be completely hindered, since there were some cracks in the rust layer.In the thin film containing chloride ion, sulfate ion and the same concentration mixture of the two ions, the chloride ion did a more enormous implication in the corrosion of carbon steel, compared with sulfate ion. The corrosion rate of the Q235 carbon steel in various densities sodium sulfate solution and thin film thickness were studied, the results indicated that:the corrosion rate decreases with the film thickness increases, and then increases; different concentrations of sodium sulfate solution resulted in a different corrosion rate rules. Under the 7μm liquid film, the corrosion rate decreased with the increasing concentration of sodium sulfate solution. In the remaining test of the thin film’s thickness and the bulk solution’s concentration, the corrosion rate increased with the concentration increased, and then decreased.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metal corrosion protection,metal surface treatment > Various types of metal corrosion > Atmospheric corrosion, corrosion of gas
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