Corrosion protection of petroleum refining and chemical processing units during shutdown and standby periods

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Due to adjustments in production plans, petroleum refining and chemical processing plants may be shut down and left idle or in standby mode, to be activated again when production needs arise. Practice has shown that the degree of corrosion on the inner walls of the equipment pipelines in shutdown devices during idle periods is much more severe than during production. This is mainly because the production units that are shut down cannot employ effective anti-corrosion measures, making it difficult to prevent corrosion of the metal surfaces. Without effective anti-corrosion protection measures, large-scale corrosion and perforations will occur, making it difficult to restart the equipment, posing safety risks in production, and even leading to premature disposal of the equipment. I. Comparison of anti-corrosion protection methods during the standby period of petroleum refining and chemical processing units. Traditional anti-corrosion protection methods used during the standby period of such units include dry air protection, nitrogen filling protection, water-based rust prevention methods, and oil-based rust prevention methods ； A new type of anti-corrosion protection method is the use of vapor-phase corrosion inhibitors. The advantages and disadvantages of common corrosion protection methods are shown in the following table: The advantages and disadvantages of corrosion protection methods are as follows: Protection Method, Dry air protection method, Nitrogen flushing protection method, Water-based rust prevention method, Oil-based rust prevention method, Vapor-phase rust prevention method, Conventional method, Protective agents for equipment that is not in use. Requirements and limitations for the equipment to be protected. Size, No restrictions, No restrictions; generally not suitable for protecting very large-sized equipment. No restrictions, generally not suitable for protecting very large-sized equipment. No restrictions. Structure, No restrictions, No restrictions; generally not suitable for protecting equipment with complex structures or deep holes. Hard-sealed rust preventive oils are generally not suitable for protecting equipment with complex structures. No restrictions, No restrictions. Material, No restrictions, No restrictions; attention should be paid to whether these methods are suitable for non-metallic materials and non-ferrous metals. Attention should be paid to whether they are suitable for non-metallic materials and non-ferrous metals. No restrictions; copper components must be wrapped and isolated. Surface condition, Clean and dry, Clean and dry; the surface should be made hydrophilic using a water-based cleaning solution. Clean and dry, Clean and dry. No restrictions. Requirements for packaging during protection, Metal containers or airtight sealing, Metal containers or airtight sealing; oil-resistant paper, plastic film, or containers can be used for full immersion protection. Oil-resistant paper, plastic film, or containers can be used for full immersion protection; plastic film or containers are sufficient for protection, and airtight sealing is not necessary. Special equipment required for protection: Tools for sealing metal containers or envelopes; nitrogen filling devices and sealing tools. Not required. Not required. Not required. Not required. Difficulty of construction during protection: Relatively complex. Complex. Simple. Simple. Simple. Simple. Convenience when opening: Convenient. Convenient. Convenient. Not convenient when using thick oil. Convenient. Convenient. Protection duration: Theoretical protection period is long, but in practice it is effective for only a few months. Theoretical protection period is long, but in practice it is effective for only a few months. Less than 1 year. 1–3 years. 1–3 years. 3–5 years. Safety level in case of leakage: Safe. Can cause injury to personnel and poses safety risks. Causes environmental pollution in case of leakage. Causes environmental pollution in case of leakage. Safe. Safe. Checks required during maintenance: It is necessary to check and maintain positive pressure. It is necessary to check and maintain positive pressure. It is necessary to check and maintain positive pressure. Checks are required. Checks are required. No checks needed. As can be seen from the table above, using protective agents with standby devices enables efficient, safe, and convenient protection of petroleum refining and chemical processing units during periods of inactivity. II. Performance testing of the protective agent HuaRong-911 for equipment on standby 1. Composition of the protective agent HuaRong-911 for equipment on standby: HuaRong-911 is an improved version of the protective agent HL-911, and it is more suitable for providing corrosion protection for large-scale oil refining and chemical processing plants during periods when they are not in use. This protective agent is based on the principle of corrosion inhibition synergy; it is a mixture composed of organic amine salts (such as cyclohexylamine carbonate, dicyclohexylamine hydrochloride, cyclohexylamine chromate, ethylamine, benzylamine, etc.), ammonium salts (such as ammonium hydrogen phosphate, ammonium chromate, ammonium dihydrogen phosphate, etc.), and other additives. It appears as a white crystalline powder, and it protects the metal surfaces inside equipment from corrosion through volatilization and diffusion. 2. Corrosion inhibition performance testing: In accordance with JB/T6071-1992, gas-phase rust prevention tests were conducted (to assess the protective capacity of the protectants used for standby equipment against corrosion in high-temperature and high-humidity conditions for different metals when they are not in contact); humid heat tests were carried out (to evaluate the protective capacity of these protectants against corrosion in high-temperature and high-humidity conditions when different metals are in contact); and gas-phase corrosion inhibition tests were performed (to determine the protective capacity of the protectants over a specified period of time under normal temperature and dew conditions). Tests showed that the weight of the 45# carbon steel corrosion test pieces remained completely unchanged before and after the experiment, proving that the protective agent for dormant equipment can effectively protect carbon steel test pieces under these testing conditions, with a corrosion rate of 0. When actually using the protective agent for shutdown devices, we monitored the actual protective effect by installing test coupons; the measured actual corrosion rate was 0.0013 mm/year. The surface of the carbon steel specimen was as bright as new, with no signs of corrosion or rust, proving that the protective agent designed for equipment on standby can effectively protect carbon steel equipment under actual field conditions. 3. Determination of diffusion distance: The protective agent for shut-down equipment is composed of volatile corrosion-inhibiting substances that can automatically release corrosion-inhibiting gases under normal temperature and pressure. These gases adhere firmly to the metal surface of the equipment being protected through stable chemical adsorption facilitated by nitrogen-containing polar groups, forming a dense protective film that effectively safeguards the equipment and prevents or slows down corrosion. Effective protection can be achieved as long as the corrosion-inhibiting gas can diffuse to the metal surface. Since petroleum refining and chemical processing units have large volumes, the diffusion distance of the volatilized corrosion-inhibiting gases is an important factor in determining whether the protective agent can effectively safeguard the units; for this reason, we conducted tests on vertical diffusion distance and horizontal diffusion distance. A sealed 3m3 container was selected; a DN50 carbon steel pipe 100 m long was connected vertically above the container, and a DN50 carbon steel pipe 20 m long was connected horizontally at the center of the container. Valves were installed at the ends of the pipes for control purposes. Place 10 kg of protective agent for equipment on standby in the container, and close the manhole and the valves at the ends of the pipes. After seven days, the valves at the ends of the vertical and horizontal pipes were opened, and a high concentration of corrosion-inhibiting gas was detected, along with a very strong pungent odor. This proves that the vertical diffusion distance of the corrosion-inhibiting gas emitted by the protective agent is greater than 100 m, and the horizontal diffusion distance is greater than 20 m. III. Typical Applications of the Protective Agent HuaRong-911 for Shut-down Equipment 1. Protection of Shut-down Units in Daqing Petrochemical Company’s Atmospheric and Vacuum Cracking Units. Traditionally, nitrogen filling was used to protect idle atmospheric and vacuum cracking units, but this method led to severe corrosion of the inner walls, along with the formation of numerous corrosion products and uneven corrosion pits. In 1993, Hl-911 was used for corrosion protection; a check was conducted after 6 months, and no signs of corrosion were found on the carbon steel specimens. The rust layer on the surface of the equipment had peeled off, revealing a smooth metal surface, with a corrosion inhibition rate of 100%. 2. Protection for the atmospheric and vacuum distillation unit at Daqing Petrochemical Company’s refinery: In 2000, Huarong-911 was used to provide protection for this unit; the actual volume covered by this protection was approximately 4,000 cubic meters. The expected duration of protection was two years, and the chemical was applied at a dosage of 2.5 kilograms per cubic meter. After two years of protection, inspection showed that the carbon steel specimens were as bright as new; no loose rust deposits formed on the surface of the equipment, and the protective effect of the coating on the metal was also evident in humid conditions. 3. Protection against shutdown was implemented for Unit 1 and Unit 2 of the chemical plant at Daqing Oilfield. Anti-corrosion protection measures were applied to Unit 1 and Unit 2 in 1997 and 1998 respectively, with significant results. 4. Protection against shutdown of the atmospheric and vacuum distillation unit at Liaoyang Chemical Fiber Company’s refinery: Protection measures were implemented for this unit in 1996. This protection is expected to last for four years. The column vessels are added at 3.5 kilograms per cubic meter, while the heat exchange equipment and pipelines are added at 4.5 kilograms per cubic meter. Inspections were conducted annually for four years, with no corrosion detected. Due to the high initial addition amount, no chemicals were added for four years. 5. Protection for the atmospheric and vacuum distillation unit at Jilin Qiange Oil Refinery: Protection measures were implemented for this unit in 1998 and 1999, with good results. 6. Protection shutdown of the third solvent refining unit at Lanzhou Petrochemical Refinery: Protection measures were implemented for the third solvent refining unit in 2000, with significant results. 7. Protection of the catalytic unit at China National Petroleum Corporation’s Dushanzi Petrochemical Branch: Protection measures were implemented in 2011; in 2012, inspections showed that the test samples were as bright as new, indicating good effectiveness of these measures. 8. Protection of the second catalytic unit at the Shijiazhuang Refining and Chemical Plant of Sinopec Corporation. Protection measures were implemented for this unit in 2013, with an expected duration of 3 years. IV. Conclusion Based on experiments and actual industrial applications, it has been proven that the protective agent HuaRong-911 for units that are taken out of service is an effective method for providing corrosion protection during such periods. It possesses the following characteristics: 1. The protective agent can volatilize automatically at room temperature, having a high vapor pressure. The evaporated gases have a corrosion-inhibiting effect on metals, thereby achieving anti-corrosion protection. 2. The protective agent for standby devices has strong permeability and can remove existing scale layers. Prevent and slow down underscale corrosion. 3. The diffusion distance of the protective agent for standby devices can reach over 10 meters, enabling protection of both metal surfaces that are close by and those that are farther away. 4. Although the protective agent for standby devices has an irritating odor, it is harmless to humans, does not pollute the environment, and causes no environmental damage. 5. The protective agent for standby devices is highly soluble in water, and its aqueous solution meets environmental emission requirements when at low concentrations. Therefore, at the end of deactivating the protection, it is not necessary to remove the protective agent; after washing with water, production can proceed. 6. The protective agent for standby devices is economical, safe, convenient, time-saving, labor-saving, and efficient.