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In terms of corrosion types, or corrosion mechanisms, the corrosion of chemical processing equipment is highly complex. Chemical materials, equipment environment, medium conditions, and so on are all factors or conditions that contribute to corrosion of equipment. Therefore, the anti-corrosion measures in different environmental conditions also vary. To understand various anti-corrosion measures, it is first necessary to know what types of corrosion exist Corrosion types of petrochemical equipment: Corrosion is classified into metal corrosion and non-metal corrosion based on the type of material. Corrosion is classified into general corrosion and local corrosion based on surface morphology ； Local corrosion includes pitting corrosion, stress corrosion cracking, crevice corrosion, galvanic corrosion, wear corrosion, and so on ； Metal corrosion can be classified by mechanism into physical corrosion, chemical corrosion, electrochemical corrosion, etc. Physical corrosion: The degradation of a material due to purely physical effects, usually caused by dissolution or penetration, such as the dissolution of metal containers in molten metals, or the dissolution and penetration of high-temperature molten salts or caustic alkalis into containers. Chemical corrosion: Damage caused by a direct chemical reaction between a metal and a non-electrolyte. The corrosion process is a pure oxidation-reduction reaction; the corrosive medium collides directly with the atoms on the metal surface to form corrosion products, and no electric current is generated during this reaction, in accordance with the laws of chemical kinetics. Electrochemical corrosion: Damage caused by the electrochemical reaction between a metal and an electrolyte solution. During the reaction process, the anode loses electrons while the cathode gains electrons, along with the flow of electrons (current); this process follows the laws of electrochemical kinetics. The forms of local corrosion in petrochemical equipment mainly include pitting corrosion, intergranular corrosion, stress corrosion, etc. For chemical processing machinery, the interior of the equipment is prone to corrosion by chemical materials, while the exterior is subject to corrosion from the external environment during actual use. Moreover, factors such as oxygen, acids, and bases present in chemical production come into direct contact with the exterior of the machinery, causing corrosion of the equipment as a result of these substances. Prevention of equipment corrosion: The current anti-corrosion techniques mainly include the development of corrosion-resistant materials, surface anti-corrosion methods, corrosion inhibition techniques, and electrochemical protection. From a design perspective: The equipment should be made of metals suitable for the application, and general principles for enhancing its corrosion resistance include: (1) Providing a margin against corrosion to prevent equipment failure due to uniform corrosion ； (2) The external structure should be simple, with a smooth and uniform outer surface, to avoid stress concentration in the load-bearing parts ； (3) Prevent retention of corrosive media and corrosion caused by deposits ； (4) The structural design should minimize gaps between connections to prevent crevice corrosion. (5) To avoid galvanic corrosion, the same material or materials with similar properties should be used as much as possible for components of the same structure. (6) Structural design to prevent erosion corrosion. From a maintenance perspective: the “one removal and four injections” procedure for petrochemical equipment must be properly carried out. The so-called “dehydration” refers to the desalination of crude oil. A small amount of salts in crude oil, upon hydrolysis, produces hydrogen chloride gas, forming an HCl—H2S—H2O corrosive medium that causes corrosion of the trays at the top of atmospheric pressure towers as well as the condensation systems. After desalting crude oil, reducing the generation of hydrogen chloride during crude oil processing can alleviate corrosion. The four \"injections\" refer to the four processes involved in the production of petrochemical equipment: injecting alkali, injecting ammonia, injecting alkaline water, and injecting corrosion inhibitors into the equipment. Alkali injection: The main purpose of injecting alkali into crude oil is to convert MgCl2 and CaCl2 remaining in the crude oil after desalination into NaCl. NaCl is not easily hydrolyzed, and no HCl gas is produced. Thus, the generation of hydrogen chloride is further reduced to effectively control salt corrosion. It also neutralizes some of the petroleum acids and hydrogen sulfide, reducing their corrosive effects. Ammonia injection: After desalination of crude oil by alkali addition, 5–10% of hydrogen chloride remains in the condensation system at atmospheric pressure, causing severe corrosion in the condensation area. Ammonia is injected at the top of the tower with the aim of neutralizing hydrogen chloride gas in the gas phase using ammonia, thereby forming ammonium chloride (NH4Cl) before water vapor condenses into liquid water, and thus preventing the formation of an aqueous solution of hydrogen chloride. Note: Alkaline water. Ammonium chloride, the product of ammonia addition, can clog the equipment (tower). The purpose of adding water is to dissolve ammonium chloride and prevent its deposition, thus avoiding tower clogging. Note: Corrosion inhibitor. A corrosion inhibitor is an organic amine compound that can form a film. Such substances possess surfactant properties, allowing them to adsorb physically or chemically onto metal surfaces to form a water-resistant protective layer that prevents the metal from coming into contact with corrosive aqueous solutions, thus protecting the metal from corrosion. “\"One removal for four coatings\" is a corrosion prevention technique that is widely used in China today, and it is also extensively applied in the field of petrochemical equipment. By using the above method, it is possible to effectively reduce the corrosion of equipment caused by chemical substances such as sulfides in various raw materials used in the production of petrochemical equipment, thereby improving the performance of these devices. During the production of petrochemical equipment, various saline substances or chlorides are often generated. When these substances condense during the production process, they pose a significant corrosion risk to the petrochemical equipment. Therefore, it is very important to implement the \"one removal and four injections\" process during the production of petrochemical equipment, and this aspect needs to be given due attention in such production processes.