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Common corrosion locations, forms and causes of corrosion in tower equipment 1. HCl-H2O (hydrogen chloride) corrosion corrosion locations: Five-layer trays at the top of the atmospheric tower, tower body, partial volatilization line and condensation cooling system at the top of the atmospheric tower ； Part of the decompression tower evaporation line and condensation cooling system. Corrosion form: General corrosion, uniform thinning of carbon steel components ； Pitting corrosion of Cr13 steel and chloride stress corrosion cracking of 1Cr18Ni9Ti stainless steel. Causes of corrosion: When the chlorine salt contained in crude oil is heated to above 120°C, it begins to hydrolyze to generate HCl. When it meets water droplets at the low temperature part of the tower top, it forms hydrochloric acid, creating an extremely corrosive dilute hydrochloric acid corrosion environment. Chemical corrosion occurs with the equipment body. The presence of hydrogen sulfide further aggravates corrosion. protective measures: Mainly focus on process protection, supplemented by material anti-corrosion. Process protection is "one removal and four injections"”: Crude oil is deeply desalted. After desalting, the crude oil is injected with alkali, ammonia (or amine), corrosion inhibitor, and water are injected into the overhead distillation line. The principle of this anti-corrosion measure is to remove impurities in crude oil, neutralize the generated acidic corrosive medium, change the corrosive environment and form a protective barrier on the surface of the equipment. Material anti-corrosion means improving the material grade on the basis of process protection. For example, 20R+0Cr13 composite plates are used to manufacture the shell of the 5-layer tray at the top of the atmospheric tower. 2. S-H2S-RSH (mercaptan) corrodes high-temperature sulfur corrosion parts: The coking fractionation tower bottom system is the most serious, followed by the distillation vacuum tower bottom system, and the catalytic fractionation tower bottom system. Corrosion form: Chemical corrosion, uniform thinning. Causes of corrosion: Hydrogen sulfide, mercaptans and elemental sulfur can all react directly with metals at 350~400°C, and the elemental sulfur decomposed by hydrogen sulfide at 340~400°C is more active, making corrosion more intense. protective measures: Mainly use corrosion-resistant steel. Such as 20R+0Cr13 composite board. 3. RNH2-CO2-H2S-H2O (wet hydrogen sulfide) corrodes the corroded parts: The bottom of the regeneration tower of the desulfurization unit, the reboiler of the regeneration tower and the rich liquid system pipeline have a temperature of 90~120°C and a pressure of 0.2MPa. Corrosion form: Stress corrosion cracking and uniform thinning caused by carbonates and amines in alkaline media (PH8~10.5). Causes of corrosion: Polyamine-type substances generated by the irreversible reaction of ethanolamine and carbon dioxide are the most common degradation substances that promote equipment corrosion. They degrade and release carbon dioxide at 120 degrees. Free or combined CO2 can cause corrosion. Severe corrosion occurs in high-temperature areas with water (90°C) and above. When the concentration is 20~30%, the corrosion is particularly serious. The corrosion of the mixture of hydrogen sulfide and carbon dioxide is lighter than the corrosion of the corresponding concentration of carbon dioxide, and decreases as the hydrogen sulfide concentration increases. That is, hydrogen sulfide has the effect of inhibiting carbon dioxide corrosion. 4. Corrosion protection measures for Fe+2CO2+2H2O, Fe(HCO3)2+H2Fe(HCO3), (heating) FeCO3+CO2+H2, Fe+H2CO3, FeCO3+H2: Equipment and pipelines with operating temperatures higher than 90 degrees should be subjected to stress relief heat treatment after welding. The hardness of the welds and heat-affected zones should be controlled to be less than HB200. The heat exchange equipment tube bundle should be made of 18-8 steel. The operating conditions should be improved, the operating temperature should be controlled, and corrosion inhibitors should be injected into the monoethanolamine system. 5. RCOOH (naphthenic acid) corrodes the corroded parts: The parts below the oil transfer line at the outlet of the pressure reducing furnace and the feeding section of the pressure reducing tower are the most important. The oil transfer line at the outlet of the atmospheric pressure furnace and the feeding section of the atmospheric pressure furnace come next. The oil collection tank of the coking fractionation tower comes second. Corrosion form: The surface of corroded steel is smooth and free of scale, and corrosion only leaves sharp holes in areas with low medium flow rates. ； Corrosion in areas with high flow rates will result in pits or grooves with sharp edges. Causes of corrosion: Naphthenic acid does not corrode strongly at low temperatures. Once it boils, especially in a high-temperature, water-free environment, corrosion will be most intense.: 2RCOOH+Fe--Fe(RCOO)2+H2 When the acid value is greater than 0.5mgKOH/g crude oil and the temperature is 270~280℃ and 350~400℃, naphthenic acid corrosion is the most serious. protective measures: Mainly use corrosion-resistant steel, such as 316L, etc. ； The inner wall welds of equipment pipes and furnace pipe elbows should be smoothed to keep the inner walls smooth to prevent pre-generated eddy currents from aggravating corrosion. ； Appropriately increase the diameter of the furnace outlet oil transfer line and reduce the flow rate. 6. Hydrofluoric acid corrosion corrosion parts: Mainly the equipment and pipelines in contact with the medium in the alkylation unit, mainly the alkylbenzene unit in the washing plant. Corrosion form: for uniform corrosion ； Hydrogen bubbling and hydrogen embrittlement ； There are 4 types of stress corrosion and crevice corrosion. Causes of corrosion: The corrosion of metal materials by hydrofluoric acid is electrochemical corrosion. The corrosion is carried out according to the electrochemical process, that is, the anode produces metal dissolution (uniform corrosion) and the cathode precipitates hydrogen, leading to hydrogen bubbling, hydrogen embrittlement and stress corrosion cracking. protective measures: Material selection: Carbon steel has better corrosion resistance in hydrofluoric acid media with a concentration greater than 75% below 65°C, but killed steel plates should be used. When the temperature is greater than 71°C and lower than 136°C, Monel alloy can be used in hydrofluoric acid medium of any concentration. However, the corrosion resistance will be reduced when the medium contains harmful impurities such as oxygen or iron salts. Special requirements for manufacturing: All carbon steel and Monel equipment in contact with hydrofluoric acid medium should undergo stress relief heat treatment after welding. The weld hardness should not be greater than HB235.