Selection of anti-corrosion materials for petroleum storage tanks in coastal areas

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Petroleum is the foundation of industry and the lifeblood of the economy. For the stable development of the industrial economy, my country has built a considerable number of crude oil storage tanks in coastal areas in recent years. The corrosion of these storage tanks in the marine atmospheric environment is more serious than in inland areas. Data show that the corrosion of ordinary carbon steel in the ocean atmosphere is 50 to 100 times greater than in the desert atmosphere. The relative humidity in the marine atmosphere is relatively high, and the marine atmosphere contains high sodium chloride particles. Therefore, for marine steel structures, the relative temperature of the air is higher than its critical value. The surface of steel in the ocean atmosphere can easily form a water film with strong corrosive effects. Oxygen in the air can easily reach the surface of steel and cause corrosion. At the same time, the salt in the atmosphere dissolves in the water film to form an electrolyte, which accelerates the corrosion process. Compared with the condensed water film in clean atmosphere, the corrosion rate is increased by 8 times. There are many factors that affect corrosion in the marine atmospheric environment, such as atmospheric temperature, relative humidity, salt content, light conditions, etc. Among these influencing factors, relative humidity and salt content are relatively important. High relative humidity promotes the formation of water film on the surface of steel, which is conducive to the corrosion process of oxygen concentration electrodes. High salt content leads to high electrolyte concentration in the water film. The three interact with each other, and the comprehensive performance is accelerated corrosion of steel. In water film electrolytes, the most influential one is chloride ion corrosion, which is a typical electrochemical corrosion process. The sodium chloride particles in the ocean atmosphere dissolve in the water film and ionize to produce chloride ions. The chloride ions are adsorbed on the inner layer of the water film and reach the steel surface through the weak points of the steel surface protective film. A corrosion cell forms and electrochemical corrosion begins. Since the typical characteristic of chloride ion corrosion is pitting corrosion, the corrosion points continue to develop in depth. Even ordinary stainless steel has difficulty preventing chloride ion corrosion. The result of the electrochemical corrosion reaction is that iron is continuously consumed to form ferrous hydroxide, which accumulates on the surface of the corrosion pit, while chloride ions are repeatedly used without being reduced. At the same time, the pH value in the pit drops below 4, causing chemical corrosion and aggravating the corrosion process. Some needle-shaped small hole corrosion phenomena are often found on the surface of petroleum equipment. In fact, they are the result of chloride ion corrosion. Although the corrosion area is not large, the depth is very deep, and corrosion penetration often occurs. In order to reduce the effects of electrochemical corrosion, the coating must have the function of conducting micro electricity. In addition, the concrete buildings in the tank area will also suffer from pulverization, embrittlement, and reduction in concrete strength due to the corrosion of salt media in the atmosphere. The physical properties and corrosivity of crude oil from different origins are different. The corrosiveness of crude oil can be evaluated from five indicators, namely crude oil acid value, sulfur content, salt content, nitrogen content and water content. Among them, a sulfur content of 2.0% is high-sulfur crude oil. The main forms of sulfur in crude oil include elemental sulfur, hydrogen sulfide, mercaptans, thioethers, disulfides, thiophene compounds, and sulfur-containing compounds with large molecular weight and complex structures. It can be classified into three categories according to its corrosiveness:: 1. It is a highly corrosive acidic sulfide that easily reacts with metals at room temperature. Its main components are sulfur, hydrogen sulfide and low molecular mercaptans. Mercaptans decompose into olefins and hydrogen sulfide when heated, making them more corrosive. 2. Mainly sulfide and disulfide. They are neutral at room temperature and do not corrode equipment. After being heated, they decompose to produce a corrosive substance - hydrogen sulfide, which also causes strong corrosion to metals. 3. Mainly thiophene and its homologues, alkyl sulfides, cyclic sulfides, alkyl sulfate esters, sulfonic acid, sulfonate, etc. These substances can cause severe corrosion to metals. In addition, there are many impurities in crude oil, and the precipitated water and impurities are retained at the bottom of the tank. The precipitated solution is acidic and highly corrosive, resulting in serious corrosion of steel, mainly pit corrosion, and some can form perforations. SY/T0088-95 "Technical Standard for Cathodic Protection of Steel Tank Outer Walls", GB1338 Relevant standard documents such as "Static Electricity Safety Regulations for Liquid Petroleum Products", GB6950-2001 "Technical Specifications for Electrostatically Conductive Coatings on Petroleum Tanks", GB/T16906-1997 "Resistivity Measurement Method for Electrostatically Conductive Coatings on Petroleum Tanks" all have clear provisions on the electrostatic conductive function of anticorrosive coatings on the inner walls of crude oil storage tanks, requiring that the surface resistivity of electrostatically conductive coatings on petroleum storage tanks should be 105Ω--108Ω. According to Zhisheng Weihua Tanggong, the pigments used in ZS-inorganic anti-corrosion coatings are composed of highly dispersed and activated passivated metal particles, nano-metal amphoteric oxides, ultra-fine rare earth ultra-fine powders, etc. The activated anti-corrosion pigments play the role of anti-corrosion and enhanced polarization, have high acid and alkali resistance and corrosion resistance, and play a very good role in neutralizing and preventing the potential of the substrate from rising. The coating reacts quickly with the atoms or ions of the material on the surface of the object to form a triple protective effect of physics, chemistry and electronics, and is firmly bonded to the surface of the substrate through chemical bonds and ionic bonds. It has good substrate protection performance for physical anti-corrosion, chemical anti-corrosion and electronic anti-corrosion of the base material. At the same time, this is also a high-solid coating that is easy to construct, has no pollution to the environment and has a long service life. It can not only be used for the anti-corrosion of the inner and outer walls of petroleum storage tanks, but can also be painted on concrete surfaces for protection. For lightweight oil tanks, in order to reduce the opening frequency of the small breathing valve and reduce the loss of oil evaporation, ZS-sunscreen and cooling coating can be used. For crude oil storage tanks in areas with lower temperatures, anti-corrosion-insulation-sunscreen composite coating solutions can be used for construction.