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Anti-corrosion packing, development and application introduces the development process and actual measurement data of new packing in order to improve the corrosion resistance of the packing in the tower and extend the service life. The 304 stainless steel packing with surface film treatment has been running in industrial devices for more than 35,000 hours under high temperature and the coexistence of various corrosive media. It has better corrosion resistance than 316L stainless steel packing. It extends the production cycle of factory equipment and reduces production costs. It has obvious social and economic benefits. -------------------------------------------------------------------------- 1 Introduction The tower is an important equipment in the chemical refining industry. The efficient and long-term operation of the tower directly affects the normal production of the entire device. The internal parts of the tower are the most exposed to corrosive media and the most demanding equipment. Therefore, it is of great economic significance to develop and produce a new type of packing that is corrosion-resistant and can extend the production cycle. The research and development of packing in the tower has done a lot of work in the aspects of high efficiency, low pressure drop, large flux, and multiple specifications. Great progress has been made. However, the improvement of anti-corrosion performance is limited to material selection. The transplantation of chemical-electrochemical anti-corrosion technology into packing manufacturing technology has not yet been reported. In recent years, Sinopec Group Company and China National Petroleum Corporation have both proposed an operation goal of one maintenance every three years. It is a prerequisite to ensure that the tower internal parts will not be shut down for replacement due to corrosion damage within three years. Corrosion control can start from material selection, passivation, adding corrosion inhibitors, cathodic protection, coatings, coatings, linings and other methods. Sinopec Beijing Design Institute, Guangzhou Petrochemical Plant and Shenzhen Chengda Technology Co., Ltd. have cooperated for many years and selected through comparison. In the manufacturing process of tower internal parts, chemical-electrochemical surface treatment technology was transplanted and improved. Packing manufacturing technology with strong corrosion resistance and relatively low cost was researched and developed, thus better meeting the special requirements of the petrochemical industry. 2 Experimental part 2.1 The study of physical properties starts with material selection. The base material is required to be able to form a conversion coating with a dense texture and good impact resistance after treatment. It must be cheap and easy to obtain and easy to process. After many screenings, 0Cr19Ni9 (304) is considered to be more suitable. Of course, 316L can also be used as the base material. Surface autogenous strengthening conversion film technology uses chemical-electrochemical methods to make stainless steel utilize elements contained in the matrix. Through a comprehensive strong oxidation process, a dense film with a specific oxidation valence state (hereinafter referred to as conversion film) is produced on the surface. The formation of the film reduces the corrosion rate (corrosion current) to 10-4 times of the original. The surface electrode potential tends to be near the zero charge potential. The metal surface enters the "passivation zone", thereby blocking chemical corrosion and electrochemical corrosion to a large extent, thus playing a role in corrosion protection. Chengda conversion coating technical indicators. See Table 1. Table 1 Chengda conversion coating technical performance Table 1 data shows that the thickness of the conversion coating is 100-300 times thicker than the natural oxide film of stainless steel. This improves the corrosion resistance in terms of physical properties. The Cr content in the film increases 1-2 times compared with the matrix composition. The Fe content decreases by 50%-70%. The Mo content increases by 1 time. These metals all exist in oxidation state. The film has higher hardness. This has an extremely beneficial impact on improving the wear resistance and erosion resistance of stainless steel. In Table 1, item 3.4.5 is the physical performance data. The test results show that the conversion film can fully withstand the erosion and impact force generated during processing and use. This is because the main component of the conversion film is Cr2O3. Its melting point is above 1000° and has high hardness. During welding, the conversion film will not be damaged except for the fusion part. 2.2 Chemical stability laboratory test data of the chemical stability film. See Table 2. Table 2 The stability of Chengda conversion coating in common chemical media Table 2 data shows that the conversion coating has good stability in most common media. It still lacks stability in reducing acid (HF/HCl) and low concentration H2SO4. 304 stainless steel filler treated with surface conversion coating and 304 stainless steel filler without surface conversion coating. The comparative test results of 316 stainless steel filler in ferric chloride solution are shown in Table 3. Table 3 Comparison table of pitting test results Note: ASTM G48-76.25mm×50mm×1mm material sample. 6% (m) FeCl3 aqueous solution. 30℃±1℃.72h. It can be seen from the results in Table 3 that the corrosion resistance of the 304 stainless steel filler treated with the surface conversion coating is significantly improved compared to the 316 stainless steel filler in the corrosive medium containing chloride ions. The weight loss of the 304 stainless steel filler treated with the surface conversion coating is 2.6%-5.6% (m) compared to the blank sample. The weight loss rate slows down to 1:7.5-1:29 of the blank sample. The pitting corrosion induction period is extended 5 times. 2.3 Stress corrosion cracking behavior test The stress corrosion cracking behavior test of conversion coating stainless steel was carried out according to the ASTM G36-73 (confirmed in 1979) method. The data are shown in Table 4. Table 4 Stress corrosion cracking behavior test results of conversion coating stainless steel Note: The K number in the table is the blank sample without surface conversion coating treatment. The Z number is the conversion coating sample. The test conditions are: atmospheric pressure 0.082MPa, test medium MgCl2· 6H2O(A.R Grade), temperature 155℃±1℃. The test results show: a. After SUS304 stainless steel is treated with surface conversion coating, the initiation period of cracks in boiling MgCl2 stress corrosion medium is extended. b. After SUS304 stainless steel is treated with surface conversion coating, the number of cracks generated in boiling MgCl2 stress corrosion medium is significantly reduced. There is no significant change in the crack expansion rate. c. After SUS304 stainless steel is treated with conversion coating, the film is consistent with the substrate. It does not crack or peel off when subjected to mechanical bending impact. This is incomparable to coatings. The stress corrosion resistance is significantly improved. 3 Industrial Applications 3.1 The industrial application of conversion film fillers in pilot plants began in 1994. A comparative test was first conducted in the naphthenic acid pilot plant of Guangzhou Petrochemical Plant. That is, two different fillers were loaded into the same area of the same equipment. A relatively fragile wire mesh filler was selected to shorten the test time. When the naphthenic acid concentration was 70%-90% (m). Run for 42 hours under acid vapor conditions with a temperature of 130-310°C. Open the tower for inspection. It is found that the packing treated with surface conversion coating has not deformed, softened, corroded, broken, etc. However, the wire mesh packing without conversion coating has developed powdery corrosion and failed. The comparative test results of Guangzhou Petrochemical's naphthenic acid pilot plant provide experience for Maoming Petrochemical's naphthenic acid refining unit using stainless steel conversion film anti-corrosion fillers. In February 1995, the feed concentration of naphthenic acid was 65% (m). The product concentration was 97 %(m). The operating temperature is 270-380℃. The tower was opened for inspection after 10 months of operation in a negative pressure environment with an acid value of 120-220. The packing structure and stiffness have not changed. The surface is intact and there is no obvious corrosion. It is still in use today. 3.2 Large-scale industrial application The refinery of Guangzhou Petrochemical General Plant is a fuel-lubricating oil refining device. It processes crude oil with high sulfur content and high acid value all year round. During the distillation process, not only the temperature is high, but also chloride ions, hydrogen sulfide and organic acids are present. Previously, 304 or 316 stainless steel was used Filling. However, in actual applications, it was found that the corrosion resistance of 304 stainless steel filling in various corrosive media is not ideal. Although 316 has excellent resistance to chloride ion corrosion, it still cannot meet the requirements. And the high cost of 316 stainless steel filling limits the large-scale application of factories. The processing capacity of the distillation (II) unit of Guangzhou Petrochemical Refinery is 250×104t/a. The newly developed Chengda JKB250Y-Ⅱ conversion membrane structured packing has been used in the primary distillation tower. The diameter of the lower part of the primary distillation tower is 4m. The diameter of the lower tower is 2.6m and the total height is 6m. The pressure reduction tower is equipped with three kinds of packing: carbon steel aluminized saddle ring, 304 stainless steel conversion film saddle ring and 304 unconverted saddle ring. The production process conditions are shown in Table 5. Table 5 Industrial application process conditions. The refinery of Guangzhou Petrochemical General Plant opened the tower for inspection after two years and one month of operation. It was found that the 304 stainless steel conversion membrane packing was intact. An application report was submitted. It was also investigated and verified by Sinopec Beijing Design Institute and Shanghai Refinery in conjunction with the director of distillation (1) equipment. It was proved that the application of the conversion membrane packing had indeed achieved the expected results. The conclusion is: a. The conversion film packing in the primary distillation tower is as bright as before. There is no trace of corrosion. The true color of the film is still visible, and there is no coke deposit or coking phenomenon. b. The three types of fillers installed in the same area of the pressure reduction tower have different situations: the filler made of 304 has a rough surface and severe coke deposits. The aluminized carbon steel filler has been severely corroded and most of it has failed. The conversion film filler not only shows no signs of corrosion, but also has a smooth surface with no coke deposits. c. The primary distillation tower does not need maintenance. It can continue to operate with the closed tower. However, the damaged packing of the pressure reduction tower must be replaced. During the second maintenance of the primary distillation tower in 1998, the opening of the tower was observed with the naked eye. Compared with the first maintenance (1996), there were no obvious changes. The closed tower continued to operate. Production is still normal and the process is stable. It is estimated that it can operate for another 2 cycles, that is, the application time is not less than 8 years. 3.3 Due to large-scale industrial applications, it is difficult to obtain accurate data for the device coupon test. Observation with the naked eye always has its limitations. Therefore, Guangzhou Petrochemical also conducted a coupon test at the same time as the industrial application. The results are shown in Table 6. Table 6 The coupon results of the use of conversion film filler in the Guangzhou Petrochemical Refining Distillation (II) Unit Note: Installation time: November 1994, removal time: December 1996, actual operating time: two years and one month. The coupon test provides quantitative data on the corrosion resistance of the conversion film filler for industrial applications. It also proves the reliability of manual observation. It is worth noting that the coupon results in the industrial device are completely consistent with the laboratory coupon results. This once again proves the corrosion resistance of the conversion coating. 3.4 Other industrial device applications April 1996. Jilin Chemical Refinery Vacuum Tower (3800/6000/3400/2200). At the end of 1996 Anqing Petrochemical General Plant Refinery Vacuum Tower (4200/6400/3800). September 2002 Yangzi Petrochemical General The first-stage vacuum tower (tower diameter 5800) of the vacuum distillation unit (renovation) has successively adopted new stainless steel conversion film anti-corrosion packing. The industrial operation is stable. The tower was opened for inspection two years later. Its anti-corrosion performance is similar to that of Guangzhou Petrochemical Refinery: no corrosion, no coke, no coking, and the performance remains good. Jilin Chemical has strict requirements for the iron ion content in the light wax oil, a first-line decompression product, to be less than 1×10-6. After using new fillers, the iron ion content in the light wax oil has been effectively controlled. Long-term monitoring data shows that the iron ion content is generally around 0.04×10-6, which protects the catalyst of the catalytic cracking unit in the next process. Other units using stainless steel conversion membrane fillers have also achieved the expected results. The reduction of coke and coking in the refining process may be related to the reduction of the interfacial tension between the filler surface and the medium, which slows down the colloid, asphaltene, and polycondensation dehydrogenation reactions in the oil. This is of great significance to the refining and petrochemical industries. In the overhaul of ethylene units and hydrocarbon separation units, a large part of the work is to clean up the coke and coking. The application of conversion film technology also provides a useful inspiration for reducing coking in the production process. a. Distillation (II) workshop of Guangzhou Petrochemical General Plant. Preliminary distillation tower. During the renovation in 1994, anti-corrosion packing was used in the entire tower. The packing of this tower has been used for more than 7 years and is still in normal use. b. Distillation (I) workshop of Guangzhou Petrochemical General Plant. 6400 pressure reduction tower. During the transformation in 1997, the first line section was reduced and the third line section was reduced to use anti-corrosion packing. When it was overhauled in 2000, the packing was intact and has not been replaced. It continues to be used to this day. c. Jihua Refinery Atmospheric and Vacuum Workshop. 6400 vacuum tower. Anti-corrosion packing was used in the first-line reduction section during the renovation in 1996. It has not been replaced yet. It has been used for more than 7 years. The iron ion content of the first-line reduction section is only 0.04×10-6, which is 1/25 of the design requirement of 1×10-6. d. Anqing Refinery Atmospheric and Vacuum Pressure Workshop. 6400 vacuum tower. During the renovation in 1995, the entire tower used anti-corrosion packing. During the maintenance in 1999, it was found that the packing in the fourth reduction section and the packing in the washing section showed no obvious corrosion. There was no coking or blocking of the tower. e. The 450×104t/a second atmospheric and vacuum distillation unit (renovation) of the 800×104t/a sour crude oil reconstruction and expansion project of the Yangzi Refinery also used some anti-corrosion fillers in the first-stage vacuum tower (tower diameter 5800). It was put into operation on September 29, 2002. It was calibrated at the end of March 2003. The iron ion content is 0.6×10-6. It fully meets the requirements for hydrocracking raw materials. It is currently in use. 4 Conclusion a. The research and development of new stainless steel anti-corrosion packing and its large-scale industrial application have achieved gratifying results. It has created a new way for the development of corrosion-resistant tower internals and tower packing in my country. b. The new stainless steel anti-corrosion packing has been successfully applied in large-scale industrial applications. The results show that it can extend the production cycle and reduce production costs, reduce iron ions and other contents, and improve product quality. c. The new conversion film anti-corrosion filler is suitable for processes in which chloride ions, hydrogen sulfide and organic acids coexist. Its corrosion resistance is better than 316, while the cost is lower than 316. By reducing the generation of iron ions, it will help improve the quality of semi-finished products, reduce catalyst poisoning in the next process, and avoid hydrogen embrittlement problems and other indirect benefits, which will provide strong support for the application of this filler. d. After the improvement of the surface geometry, the new anti-corrosion filler not only has superior performance in anti-erosion and anti-corrosion properties, but also has the potential to significantly increase the effective surface area, increase the processing capacity, and create favorable conditions for reducing the tower diameter and tower height.