Analysis of Basic Corrosion System of Petrochemical Equipment

1 Corrosion characteristics and basic corrosion system of refinery equipment 1.1 Oil refinery equipment and its corrosion characteristics The large-scale development of China's oil refining industry began after the discovery of Daqing Oilfield in the 1960s. Refineries are smaller in scale and more dispersed, with varying levels of development. China's oil fields are widely distributed, and the major properties of crude oil vary greatly, which determines the differences in the degree of corrosion and characteristics of the refinery installations. Since the 1990s, the nature of imported crude oil imported from foreign original pools has also been greatly different. However, a notable feature is the high content of crude sulfur and heavy metals in the Middle East. In sum, the crude oil processed by various refineries in China is mainly divided into high sulfur and high acid. Low sulfur, low acid, high sulfur, high sulfur, low sulfur and four types of acid; equipment is small and dispersed, corrosion is affected by random factors, and it can cause large area corrosion to the equipment. 1.2 Refinery basic corrosion system analysis 1.21 Light oil part HC+ BS) "BO Corrosion System This corrosive environment is mainly found in the atmospheric and vacuum distillation units at the top of the cyclical return of atmospheric pressure. The temperature below 150C is responsible for the formation of this corrosive environment from three sources: The first is in crude oil. Inorganic salts are mainly sodium chloride, calcium chloride, and magnesium chloride, and it is generally believed that magnesium chloride and calcium chloride are heated to above 100° C. and undergo hydrolysis in the presence of water, and HCl gas generation studies show that even at lower temperatures, if In the presence of naphthenic acid, sodium chloride may also be hydrolyzed and become the main source of HCl produced in crude oil. Secondly, sulfur and sulfides in crude oil and crude oil are decomposed from sulfides above 260C. Hydrogen Sulphide Hydrogen Sulphide Hydrogen Sulphide Hydrogen Sulphide Hydrogen Sulphide Hydrogen Sulfide Hydrogen Sulphide Hydrogen Sulphide Hydrogen Sulphide Hydrogen Sulphide Hydrogen Sulphide Hydrogen Sulphide Hydrogen Sulphide Hydrogen Sulphide Hydrogen Sulphide Hydrogen Sulphide Hydrogen Sulphide Hydrogen Sulphide Environmental hydrogen sulfide interacts with hydrochloric acid to make the corrosion rate exponentially more powerful.

Many domestic oil refineries have been exposed to this type of corrosion, such as the accidents of perforation at the top of the atmospheric pressure tower at the Shengli Heavy Oil Plant and the Zhongyuan Oil Refinery. The Jianghan Petrochemical Plant also experienced atmospheric pressure at the top of the tower. Head Corrosion Phenomenon 1.2.2 Sulfide Corrosion System Sulfide Corrosion by High-Temperature Sulfide Corrosion, Low-Temperature Sulfide Stress Corrosion Cracking, and Mid-Temperature Sulfide Dew Point Corrosion High-Temperature Sulphide Corrosion refers to Heavy Oil Sulfur, Vulcanization at temperatures above 240C. Material and hydrogen sulfide formed a corrosive environment. The typical high-temperature sulfide corrosion environment exists in the atmospheric distillation tower in the atmospheric pressure distillation tower under the tower and the bottom of the pipeline, atmospheric pressure heavy oil and vacuum residue high temperature heat exchanger. Carbon steel corrosion rates are generally high at these high temperature sulfide sites. The measured data of domestic industrial installations show that the corrosion rate is all above 1.1mm/a. For example, the corrosion cracking of perforated low-temperature sulfides occurred twice in 1994 and 1997 in Maoming Refinery Coking Plant, referring to the corrosion of H2S+H2O. The environment, namely wet hydrogen sulfide corrosion environment. Typical examples of such corrosive environments are refinery secondary processing units and hydrodesulfurization unit high pressure separation units and their downstream process equipment.

Domestic corrosion surveys have shown that the uniform corrosion of wet H 2 S to carbon steel process equipment increases with increasing temperature. The absorption rate of the stable tower in the Zhongyuan Refinery is 1mm/a. The Shengli refinery absorbs the hydrogen bubbling and bubble cracking on the tower wall of the desorption tower. The dew point corrosion of the sulfide is also a common corrosion system in domestic refineries. 1.2 .3 Naphthenic Acid Corrosion System The corrosion of naphthenic acid is mainly related to the flow rate of acid, temperature and material in the raw material. In the process equipment, the flow velocity of the material is not the main factor except the individual parts, mainly the acid value in the raw material. And temperature.

The corrosion reaction of naphthenic acid in a high-temperature anhydrous environment is as follows: Fe(RCOOH)2 is an oil-soluble corrosion product that cannot form a protective film on the surface of metal equipment, and there is also a FeS protective film formed by the corrosion of sulfides. Destructive effect. As a result, new surfaces appear on the metal surface of the device, allowing corrosion to continue.

Naphthenic acid corrosion mainly occurs in the above 250C Liaohua Refinery. In October 1988, Liaohe high-acid crude oil was processed. In September 1989, the towers and tower walls in the feed section of the atmospheric tower were corroded to a thickness of 2 to 3mm. , Heavy-duty tower sideline pumps also have serious corrosion, replacing more than a dozen times a year.

1.2.4 Hydrogen Damage System Hydrogen damage refers to equipment damage caused by hydrogen, mainly hydrogen embrittlement and hydrogen corrosion. Hydrogen embrittlement occurs mainly at low temperatures. Hydrogen Corrosion refers to the case where the temperature is above 200C and the hydrogen hot corrosion caused by the partial pressure of hydrogen > 0.5MPa is typical for a reactor in a hydrocracking unit, a reactor in a hydrodesulfurization unit, and a platinum reforming unit for a platinum reforming unit. Hydrogen dissolved in steel, such as reforming reactor, reacts chemically with carbon decomposed by unstable carbides at high temperatures and forms methane bubbles distributed along grain boundaries. Hydrogen eroding results in decarburization of steel (surface and interior ) Decreased steel strength, ductility, and fracture toughness. Hydrogen corrosion phenomenon is a common damage method for high-temperature and high-pressure hydrogen equipment. The above four corrosion systems are common corrosion systems in domestic refineries, which can lead to extensive corrosion of equipment. In addition, high-temperature BS+B corrosion systems, RN2-CO2-BS+ Type B Corrosion System, BS+NH+H+BO Corrosion System CO2+BO Corrosion System The heavy metal corrosion system and the composite system composed of the above systems are common corrosion systems.

1.3 Protection Measures for Refinery Equipment 1.3.1 Anticorrosion Technology for Refinery Processes In response to the various corrosion characteristics of refinery installations, various refineries in China have adopted various proven process protection technologies as follows: Crude oil pretreatment technology In the aging of domestic oil fields, a large amount of water injection and chemical reagents have to be used to increase the recovery rate, which has brought difficulties to the operation of electric desalination plants. Some refineries have adopted new crude oil pretreatment devices, such as those developed by Luoyang Petrochemical Engineering Company. Crude oil pretreatment equipment has been applied to engineering practice, thus reducing backmixing and improving the effect of desalination and dehydration. With the same volume of desalting tank, the processing capacity can be increased by 20% to 50%, and solid impurities can be removed.

Crude petroleum electrical desalting technology According to incomplete statistics, about 30% of the refinery desalination index reached less than 3mg/L after desalination, 50% can reach 5mg/L or less, and the remaining 20% ​​above 5mg/L chemical protection in order to be effective Prevention: Corrosion of KS-HCl-BO and H2S-BO type, 9 or more refineries adopt the method of injection inhibitor and neutralizer to reduce the oil and gas pipelines in the atmospheric tower and hydrocracking dephlegmator. Corrosion of cold-exchange equipment and residual oil Demetallization The Luoyang refinery uses this technology to remove more than 70% of CaMgFe in crude oil, and the CaMgFe removal rate in residual oil is over 60%, eliminating the need for catalytic fractionation towers. Salt problems, but also improve the desalination effect.

Circulating water quality is stable The water quality in different parts of China is very different. Each refinery develops water stabilizers with different formulas according to the local water quality conditions. Its scale inhibition, corrosion inhibition and biochemical properties are good, such as Liaoyang Petrochemical Fiber Company and Anshan Refinery. , According to the local water quality, the application of unique formulas, so that the stability of circulating water quality problems basically solved, but the cycle rate should be improved Cathodic protection of underground pipe network Fujian Refining and Chemical Company will use all the underground pipe network cathode protection, effectively prevent the buried pipeline Corrosion Leakage Problems Electrochemical Protection Technology of Tank Coatings Luoyang Petrochemical Plant used sacrificial anode coating technology on several injection pots in 1995. After several years of application, it proved to be effective in slowing the corrosion of oil tanks. Changling Refinery, Guangzhou The petrochemical plant has also begun to use this technology to jointly protect magnesium anode coatings for heat exchangers. Anqing Petrochemical Plant has adopted magnesium anode coating and joint protection technology on more than 60 cold exchange equipments, which has extended the life of heat exchanger tube bundles by 2 Times, and less scaling, improve thermal efficiency.

Using the oil-phase anti-scaling inhibitor, the Tianjin refinery injected 50 to 100 mg/L anti-scaling corrosion inhibitor into the oil slurry circulation system, which solved the plugging problem of the oil steam generator heat exchanger.

1.3.2 Material Protection Techniques for Refineries In the early stage of refinery design, most of the refineries were selected based on the processing of less corrosive Daqing crude oil. At present, a set of methods suitable for the selection of crude oil properties has been explored, and some design materials suitable for high-sulfur, high-acid crude oil new materials and protective technologies for sulfur-containing crude oil processing plants have been accumulated in refineries that process sulfur-containing crude oil. Based on many experiences, and based on many years of experience, the company has formulated the selection criteria for the processing of high-sulfur and high-acid crude oil equipment, and has implemented the SB42nSUS405 composite steel plate (equivalent to Q235+) for the atmospheric and vacuum towers of Maoming Refinery. 0Cr13), proved to be suitable for the processing of Middle Eastern high-sulfur original pools with low sulfur dew point corrosion resistant ND steel as air preheater material after several years of operation, which can effectively prevent sulfuric acid dew point corrosion. Jinan refinery uses ND steel to manufacture heavy oil catalytic cracking unit The coal is in good condition and its life is 3 times that of carbon steel.

Design of High Acid-Valued Crude Oils Crude oils produced in Liaohe Oilfield, Shengli Oilfield, and some Xinjiang oilfields have naphthenic acid contents above 0.5 mgKOH/L, and some of the refineries with these crude oils have caused severe corrosion problems. Jinzhou Refinery The company used 316L to solve the problem of high temperature naphthenic acid corrosion in the vacuum distillation unit minus the two-reduction three-wire mesh tray and other internal components. The carbon steel powder embedded aluminizing technology can withstand high temperature sulfur corrosion, naphthenic acid corrosion The naphthenic acid resistance is comparable to 316L. In 1992, the Guangzhou Petrochemical Plant replaced the originally severely corrosive desulfurization absorption trays with aluminized materials. After two years of operation, there was no serious corrosion phenomenon. The refinery used the aluminized heat exchanger tubes for vacuum residue heat exchange. More than four years without leakage, solve the problem of corrosion and blockage. Slurry induction Aluminizing This technology is characterized by high temperature oxidation resistance, improved heating furnace and heat transfer efficiency. Shijiazhuang Refinery Coking Furnace, using CbM. Aluminizing furnace tube, can improve the oxidation resistance more than four times, heat transfer intensity increased by more than 10%, basically solved the problem of high temperature oxidation of the coke furnace tube, electroless nickel-phosphorus plating can resist High Temperature Sulfur High Temperature Naphthenic Acid and BSHCl Corrosion This technology has been widely used in domestic refineries. Jinling Petrochemical Company's Equipment Institute has a great advantage in this technology. Guangzhou Petrochemical Plant adopts nickel and phosphorus plating technology in places where the corrosion of KSHCl is severe, such as pipeline elbows, plates, heat exchangers, etc., which basically solved these serious parts of corrosion. Corrosion problems of non-metallic coatings Currently all domestic refineries have used anti-static coatings to protect crude oil and petroleum product tanks, extending the service life of tanks. For example, the protective coating for the water cooler of the Tianjin Refinery has no crack cracking during the two-cycle coating operation, and there is no fouling on the pipe wall, which has played an anti-corrosion effect.

3.3 Corrosion monitoring and standardization management of refineries In recent years, refineries have also made great progress in corrosion monitoring and standardization management. A series of mature on-line monitoring methods have been introduced and developed, and standardized management of microcomputers has begun. 2 Petrochemical equipment corrosion Characteristics and Basic Corrosion System 2.1 Petrochemical Equipment Corrosion Characteristics There are more than 200 sets of chemical production equipment in the Sinopec system at present, and there are generally different degrees of corrosion. From the point of view of the production facilities, there are styrene and corrosion chemicals in chemical plants that require compliance. The production equipment of phenolacetone vinyl chloride, m-cresol, alkylbenzene alkylation caustic soda, etc., from the corrosive medium, is mainly an acidic catalyst contacted by chemical production equipment, Cl- and concentrated alkali solution in the production of caustic soda, and urea production. Ammonium solution, hydrofluoric acid in alkylbenzene equipment, etc. The types of materials used in petrochemical production facilities are numerous, and the production itself is characterized by complex technology, high risk, and strong continuity. If the equipment is poorly designed, manufactured, installed, operated, or repaired, or in the process of protective construction, Slight negligence, are likely to increase the occurrence of corrosion hazards 2 Basic corrosion systems and countermeasures for petrochemical equipment 2.21 Corrosion systems and countermeasures for ethylene crackers The corrosion problems existing in ethylene plants are the carburizing and cracking of cracking furnace tubes and the system. Coking and furnace tube bending deformation, and second, diluted steam generation system corrosion China's ethylene plant most of the furnace tube wall there are varying degrees of carburizing and furnace tube bending deformation of some early production equipment, such as Daqing 300,000 tons Since the ethylene plant started operation in 1986, there have been a number of furnace tube damage accidents. By 1995, a total of 172 furnace tubes were replaced. The majority of furnace tube failures were due to carburization, high temperature corrosion creep, and thermal fatigue. factor.

Dilution steam generating system is another unit where ethylene cracking equipment often corrodes. Sulfide is present in the cracked raw materials. C2H2S and organic acid substances are generated during the cracking process. These substances are easily deposited on the surface of steam generator shell pipes. Both corrosion and corrosion of olefin plants such as Qilu Petrochemical and Yangzi Petrochemical have resulted in relatively severe corrosion leakage in the diluted steam generation system.

Countermeasures: 1 Strictly operate the process to prevent the furnace tube from overheating, reduce the number of stop and stop work 2 Improve the stress state of the furnace tube and reduce the bending stress on the furnace tube. 3 Strengthen the inspection and analysis of the furnace tube, establish the standard of its rejection 4 Study the method of removing the carbon dioxide from the furnace tube 5 Use the advanced alloy furnace tube 6 Improve the structure of the furnace tube and furnace components, Reduce the corrosion of secondary stress dilution steam generation system The main reason is that the corrosion caused by the process water containing acidic substances can adjust the pH to make the pH of the process water neutral or slightly alkaline, which will greatly reduce the corrosion. At the same time, the filtration of the process water is added to remove the impurities in the process water. Prevent deposits on the heat transfer surface from scaling.

22.2 Corrosion Systems and Countermeasures for High-Temperature Hydrochloric Acid High-temperature hydrochloric acid corrosion systems mainly occur in the production of isocyanate isomerization units using aluminum trichloride as a catalyst, such as styrene units, phenolacetone units, m-cresols, etc. due to aluminum trichloride catalysts. Hydrolysis to produce hydrochloric acid raises the reaction temperature, sometimes up to 180C, causing strong corrosion to the device. For example, in the 16 static equipments of the Qilu Petrochemical vinyl chloride plant in 1991, there were 13 stainless steel equipments related to the hydrochloric acid medium. The system exists in the reactor, condenser heater, reboiler isostatic equipment, pumps, valves and other moving equipment.

Countermeasures: 1 Non-metallic materials are the best protective materials for hydrochloric acid corrosion. At present, domestic non-metallic equipment such as enamel kettles and graphite heat exchangers such as polytetrafluoroethylene (PTFE), which have good acid resistance and temperature resistance, are limited in quality, and seals are not matched to limit the application of non-metallic materials. In the future, the manufacturing technology and protective construction quality of non-metallic protective equipment should be improved. 2) The domestic production of Hastelloy alloy pumps and valves is to be solved. 3) Strict control technology. 2.2.3 High-temperature sulfuric acid corrosion system. High temperature (above 80C). In the processing equipment, caustic soda plant in the chlorine drying part, such as isobutylene plant, butadiene, butadiene butadiene rubber plant, viscose production equipment, etc. which high temperature dilute sulfuric acid corrosion is a domestic long-term problem that has not been solved currently only a set of isobutylene The equipment, although the cost of protection and renovation was added to the heart of the investment cost of the original equipment, and some of the pipe sections used zirconium, the production was still very passive. In viscose production, heat exchangers and mirabilite crystallizers also have serious high-temperature (about 110C) dilute sulfuric acid corrosion. They are now protected by lead pipes and lead linings. They must be blocked or repaired within 2 to 3 months. .

In addition, some manufacturers of high-temperature concentrated sulfuric acid and alternating sulfuric acid is also quite serious corrosion measures: 1 to solve the sulfuric acid corrosion generally use non-metallic materials, but to strictly control the construction quality, the domestic production plant and construction team is numerous, in the choice of manufacturing and construction units Must be careful to strengthen the study of high-temperature dilute sulfuric acid materials, and the development of the appropriate pumps, valves, so that the formation of a series of varieties.

24 Hydrogen fluoride and hydrofluoric acid corrosion systems Hydrogen fluoride gas and hydrofluoric acid corrosion are completely different in nature. Corrosion Hydrogen fluoride gas is chemically etched. Metal fluorides and hydrogen metal are generated in hydrofluoric acid solution. Corrosion is an electrochemical process. The corrosion types of equipment controlled by electrochemical factors are: uniform corrosion, pitting corrosion, trench corrosion, hydrogen embrittlement with hydrogen bulging, and stress corrosion. More than 10 sets of hydrofluoric acid alkylation equipment in China, most of which are due to serious corrosion problems, open Stopped, and some due to corrosion problems, completely in the state of long-term shutdown measures: 1 strict selection of suitable materials. 2 strictly control the composition of the reaction medium. 3 The use of non-metallic protective layers, such as fluoroplastics, rubber graphite ceramics, etc., is currently the most important corrosion system that restricts China's petrochemical production. In addition, in the petrochemical production process, there is also a carbon dioxide electrochemical corrosion system. , Alkali corrosion systems, chloride ion corrosion systems, water corrosion systems and other common corrosion systems 3 Petroleum chemical fiber equipment corrosion characteristics and basic corrosion system 1 Petrochemical fiber equipment corrosion characteristics Chemical fiber production process is divided into raw materials production polymerization, spinning, fiber processing The corrosive media in the four parts of chemical fiber production vary according to the production type and process route. The media involved in the production process are corrosive and are generally mixed with multiple media, combined with high temperature and high pressure and a certain flow rate and pressure. Gas, so that the chemical fiber production equipment corrosion is very complicated. After more than 20 years of exploration, the basic understanding of the domestic chemical fiber equipment corrosion system, mainly some acidic systems.

3.2 Basic corrosion system of petroleum chemical fiber equipment 3.21 Corrosion system of organic acid In chemical fiber production, organic acids such as maleic acid acetate are often exposed. These organic acids are weak acids, and corrosion is not severe under normal circumstances. However, with the increase of temperature, some solid particles and impurities are mixed in. Corrosion is obviously aggravated. This corrosion usually occurs in the centrifuges and pipes of polyester high-temperature oxidation method, polyester Oxidation towers and dehydration towers for low temperature oxidation processes, recovery towers for acetic acid plants, and distillation towers often cause pitting corrosion, intergranular corrosion, fatigue, and general corrosion and localized corrosion.

In the acetaldehyde production facilities in Yangtze, Daqing, and Shanghai, many key equipment such as acetic acid evaporators, distillation towers, and reboilers all use 316L stainless steel to manufacture tower materials. Corrosion is slight, but the internals of these devices , support rings, fasteners, etc. have crevice corrosion and stress corrosion cracking 3.2.2 inorganic acid corrosion system sulfuric acid corrosion system occurs in the Vinylon finishing process acetalization equipment, acrylic production and recycling equipment, nylon 6 production of caprolactam and other equipment, The main manifestations are stress corrosion corrosion and weld corrosion and other electrochemical corrosion morphology. Hydrochloric acid corrosion systems generally occur in nitric acid plant reactors, demister catalyst regenerators and condenser nitric acid corrosion systems that occur in nylon 66 nitric acid equipment and adipic acid devices, showing high temperature corrosion fatigue cracking Phosphoric acid and chromic acid corrosion The system mostly occurs in the adipic acid device and alcohol ketone device in nylon 66. The hydrocyanic acid corrosion system mostly occurs in the recovery tower and the analytical tower of the acrylonitrile eye device, which is characterized by corrosion fatigue cracking. In addition, there is adipic acid corrosion system terephthalic acid corrosion system and sodium hydroxide corrosion system in the chemical fiber equipment.

3 Corrosion countermeasures for petroleum chemical fiber equipment To reduce the occurrence of crevice corrosion in the structural design, sealants with corrosion inhibitors can be used to seal gaps in the gaps in the tower internals.

For corrosion of maleic acid and other organic acids, the use of 316L stainless steel is generally satisfactory for corrosion resistance. If problems occur, the reason may be due to unreasonable process or structural design, such as erosion, solid particle wear and other factors. Therefore, in the design of the structure to avoid scouring, and to take measures such as filtration, to reduce the solid particles in the medium selection of titanium, hard lead, enamel ceramics, rubber lining, tiles and other lining materials 4 large nitrogen fertilizer equipment corrosion characteristics and basic corrosion system 1 Nitrogen Equipment Equipment Corrosion Characteristics The basic raw materials of large nitrogen fertilizers are carbon-containing compounds, air and water. In the large nitrogen fertilizer industry, due to the high temperature and high pressure corrosion environment, coupled with huge equipment, there is generally no spare equipment. Once corrosion damage occurs, it will cause huge Economic losses and even safety accidents, corrosion is often the key technology that restricts production, directly related to economic benefits.

4.2 Basic corrosion system of large-scale nitrogen fertilizer installations 4.2.1 Corrosion of large-scale ammonia synthesis plants BHT-N2-NB system; (6) Ambient temperature ammonia system; (7) The main corrosion types of water system are: uniform corrosion stress corrosion hydrogen corrosion and Nitriding corrosion, pitting high temperature creep and high temperature oxidation corrosion 4. 2.2 high temperature methylamine solution corrosion and countermeasures Large urea plant corrosion is mainly caused by high temperature methylamine medium, the corrosion site is mainly manifested in high pressure equipment, The status will be directly affected by the long-term safe operation of the urea plant. The urea reactor is the main reactor for urea synthesis. So far, the longest operating time has been for more than 20 years. Corrosion is mainly manifested in the lining of the tower. The corrosion of the inner parts of the tower is reduced and the weld seam is selectively corroded. In addition, many plants, such as the Dongting Nitrogen Fertilizer Plant, have undergone severe selective corrosion at the ear seat of the synthetic tower seat.

The CO2 stripper is the key equipment for the stripping reaction in urea high pressure equipment. Most of the factories put into operation in the 1970s had replaced their new stripper towers because of corrosion. The ubiquitous corrosion is mainly manifested in the following: the stripper tower is prone to condensate corrosion, while the Wuhua petrochemical and Ningxia plant stripper using heavy oil as the raw material, due to the excessive content of HzS in the C2 raw material gas, the corrosion of the lower head lining is reduced. Ammonium condensers are the most severe equipment for urea plants.

In addition to the recently put into operation of fertilizer plants, the vast majority of plants have been replaced, but also the earliest replacement of the four major high-pressure vessels. The corrosion of the shell-shell reactor is mainly caused by the high Cl- content of the cooling water in the condenser. On the upper tube plate side, the Cl- and other salts in the water are evaporated and concentrated, and the local content is as high as 2000mg/L or higher. Under conditions of high oxygen content in the water, stress corrosion cracking is likely to occur. Jinling Plant, Guangzhou Petrochemical, Anqing Plant, Daqing Plant, etc. The replacement of the ammonium-monomer condenser was not caused by the stress corrosion of the tube near the upper tube plate.

The problems with high-pressure scrubbers are the problems of embrittlement and stress corrosion cracking of explosion-proof space linings. In addition, some plant beam corrosion reductions are severe. Countermeasures: 1 For newly-manufactured equipment, whether imported from abroad or domestically produced We must strictly control the quality and conduct strict supervision and inspection work. In-service equipment is regularly subjected to rigorous physical and chemical non-destructive testing, to keep abreast of equipment conditions, and strengthen equipment management. (2) For locations where condensate corrosion is likely to occur, intensify thermal insulation to avoid corrosion caused by gas condensation. 3 For locations where stress corrosion occurs, duplex stainless steel materials may be used. 4 Corrosion of lining and column pipe welds is common for four high pressure vessels. Study the causes of corrosion, and solve the related repair technologies. In addition, further detailed work is done on the extubation and repair technology of the heat exchanger tubes currently promoted and applied, and the quality of extubation repairs is improved.

5 Conclusions From the current status of China's petrochemical equipment anti-corrosion projects, various anti-corrosion technologies are being applied to practical projects, especially the basic theoretical research of anti-corrosion problems in the oil refining industry and the development of engineering application projects. In engineering practice, the control of random factors should be strengthened to avoid significant corrosion accidents caused by random factors. At the same time, the basic corrosion and engineering protection measures for chemical, chemical fiber and fertilizer equipment should be strengthened. (Continued on page 63) By approaching the surface of the steel, the reduction reaction of H is suppressed, and the central atoms N and 0 having unshared electron pairs undergo full-scale chemical adsorption of the Me atoms or ions on the surface of the steel. The positively charged antimony ions adsorb P03- in the solution. And Mo4-, and further with Fe (BP4) 2 and Zn (BP4) 2 on the surface of the iron and steel to produce a synergistic effect between the organic phosphate complex film and ions, but also to make the adsorbed TEA molecules Hydrocarbon chains with hydroxyl groups are tighter on the surface of the steel, which forms a chelating insoluble film covering the original bare part, which in turn makes the adsorption more stable. Therefore, the introduction of TEA in the formulation shows greater advantages. Promote the role, but also play a role in buffering the pH balance of the solution, but also improve the film's dense and anti-alkaline.

The role of 3.3.40P emulsifier This formula adds a small amount of 0P emulsifier, mainly used to improve the phosphating solution on the surface of the workpiece lubrication performance, reduce the pre-treatment requirements; can also increase the cathode polarization, is conducive to obtain crystal fine phosphorus Film.

The test results show that: The total amount of the phosphating agent in the range of 20. 7 ~ 68.6g / L, can form a thin and corrosion-resistant phosphate film When the solution concentration, temperature is higher, can be appropriately shortened phosphating Processing time; and the phosphate film corrosion resistance requirements of the workpiece, it should be appropriate to increase the concentration of phosphating solution after phosphating the workpiece without washing, drying directly, better corrosion resistance.

4 Conclusion Accelerators, TEACIT and other compound accelerators as film-forming aids and stabilizers can produce synergistic effects with the main components of the phosphating solution, and are directly involved in the formation of complex phosphates of iron heteropolyferromolybdate and alcoholamine phosphate. membrane. This not only maintains the stability of the solution, but also improves the corrosion resistance of the phosphating film.

Compared with the phosphating solution containing N2-, N3-, Cl3- and N, Mn2+, the phosphating solution has no strong oxidant to promote the dissolution of the matrix metal, and no alkali metal ions promote the hydrolysis of the second-generation zinc phosphate, so the metal The low dissolved amount, low consumption of effective components of the phosphating solution, slow formation of sludge, long service life not only reduces the number of bath replacements and wastewater treatment costs, but also does not generate toxic gas NOx during the phosphating process, and there is no problem of environmental pollution. The liquid set is characterized by surface modulation, phosphating, and passivation. It has no special requirements before and after treatment. The process is simple, easy to operate, easy to manage, wide range of acidity, low dosage, low dosage, and low price. It has application prospects.