Overview of corrosion in my country's natural environment and its hazards
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Our country has a vast territory, long coastline, many soil types, and large differences in atmospheric environment. Therefore, it is necessary to carry out corrosion investigations in various typical environments and establish environmental corrosion test stations in different regions, accumulate atmospheric, soil and seawater corrosion data of various materials, form my country's natural environment corrosion data system, and establish a usable database. This is not only * * basic data that is indispensable for the national economy and is also a * * An important symbol of the level of science and technology. According to the purpose, tasks and priorities of the project, a natural environment corrosion investigation was conducted from several aspects. First, a review of the 40 years of progress in the natural environment corrosion test research of materials in my country ； The second is to conduct a general survey and analysis of the corrosiveness of the atmosphere and soil in my country, because the corrosion loss of materials in the atmosphere and soil environment accounts for more than 70% of the total loss. ； The third is to conduct a more detailed investigation and research on typical natural environment corrosion conditions. ； Fourth, the harm and impact caused by typical cases are analyzed ； Fifth, based on my country's actual needs, a more detailed investigation of the western region was conducted. 1. Review of 40 years of research work on natural environmental corrosion testing of materials in my country. In the late 1950s, according to * * The need for planned large-scale economic construction, and the Soviet Union and Eastern Europe at that time * * Make a request for joint testing, * * The Metal Corrosion Group of the Mechanical Group of the Science and Technology Commission organized the research institutes of relevant departments in my country to establish the "National Atmospheric, Seawater, and Soil Corrosion Test Website".鴴こ?笠地远? Patrol Mu Xia Yong こ啒约??Steal the reef nightmare, Zao embarrassment?Leave move?Oyster root?Za 椋?? Agent Song Ye?Mu Bibo Baliaolan?Ci Zacu?Bi Chen??Tao Xi?Huang?Liao Le Xiebu?⒘playing Bo case gum?Ci Zao Jing?Bo Zha Ju Jin?Pun? After about ten years of turmoil, experiments were interrupted, many experimental stations were destroyed, and only a few research units' research teams were able to survive in extremely difficult times. Under certain conditions, we insist on testing, for example, the "20-year exposure test of aluminum and titanium alloys" by the Aeronautical Materials Research Institute, the "20-year exposure test of paint coatings" by the Institute of Metal Chemistry of the Academy of Railway Sciences, the seawater corrosion test of reinforced concrete by the Nanjing Water Conservancy Research Institute, and the Wuhan Iron and Steel Company of the Ministry of Metallurgy. The "15-year atmospheric exposure test of 19 types of low alloy steel" by 6 units including the Iron Research Institute, the soil corrosion test of the Baoshan soil corrosion station responsible for the Shanghai Cable Research Institute of the Ministry of Mechanical Engineering and the Xinjiang Shihezi Station of the Ministry of Petroleum, etc. The results of the long-term exposure test of the above-mentioned materials in the natural environment (atmosphere, seawater, soil) were later used in construction * * They have played a very good role in the construction of the Memorial Hall, Nanjing Yangtze River Bridge, Shanghai Baosteel and other projects. Guangzhou Electrical Equipment Research Institute has made contributions to improving the quality of electricians and electrical products and formulating standards through atmospheric exposure tests. After the 1978 National Science Conference, * * The Corrosion Science Discipline Group of the Science and Technology Commission resumed its activities and included the construction of national atmospheric, seawater, and soil corrosion test websites and the accumulation of material corrosion data into the National Technology and Science Development Plan from 1978 to 1985. * * The atmosphere, seawater, and soil groups of the Corrosion Science Discipline Group of the Science and Technology Commission specifically organized a comprehensive investigation of the current status of corrosion test sites and test work across the country. “During the Sixth Five-Year Plan, * * The Science and Technology Commission listed "Experimental Research on Atmospheric, Seawater, and Soil Corrosion of Common Materials" as a key basic research project. The National Corrosion Testing Website undertook the experimental research task of the project and formulated a test plan for atmospheric corrosion of materials for 20 years, seawater corrosion for 16 years, and soil corrosion for 40 years. From 1983 to 1984, at the National Atmospheric and Seawater Corrosion Site, the first batch of material samples were tested according to the unified test plan and test procedures. At the same time, the construction of industrial atmosphere, low-temperature rural atmospheric corrosion test station and Zhoushan seawater corrosion test station began. my country's material natural environment (atmosphere, seawater, soil) corrosion testing has been resumed after a 15-year interruption, and has since begun a new period of large-scale testing organized by the country and conducted according to a unified plan. It also marks a new stage of the national corrosion testing website from restoration to construction. Currently, press * * In accordance with the requirements of international standards, 36 material natural environment (atmosphere, seawater, soil) corrosion test stations have been built in typical natural environments across the country, including 10 atmospheric corrosion test stations, 4 seawater corrosion test stations, and 22 soil corrosion test stations, including 5 central test stations and 4 acidic soil stations. The materials atmospheric corrosion test station, soil station and freshwater corrosion test station in the western region of my country are planned to be rebuilt during the "Tenth Five-Year Plan" period to meet the needs of development and construction in the western region. Through the "Sixth Five-Year Plan"” * * Project funding from the Science and Technology Commission and“ * * ”By the time of the "Ninth Five-Year Plan"” * * Funded by major projects of the Natural Science Foundation of China and jointly supported by relevant departments, 353 types of corrosion test materials in six categories (ferrous metals, non-ferrous metals, concrete, polymer materials, protective layers, cables, optical cables) and more than 90,000 test pieces (see Table 1) have been put into the National Materials Natural Environment Corrosion Test Site (see Table 1). After 4 cycles of testing, 8-10 years of atmospheric and seawater corrosion test materials have been accumulated.: There are more than 400,000 pieces of corrosion data and natural environmental factor measurement data for 30-35 years of medium and alkaline soil corrosion, 5 years of acidic soil corrosion, and 20 databases have been established. The data has been reviewed by experts and has been * * It has been applied in construction and achieved significant social and economic benefits. “Material natural environmental corrosion” as * * It is an important basic work that must be persisted in the construction for a long time. Accumulating the corrosion data of materials in my country's typical natural environment (atmosphere, seawater, soil) is the main task, because "the natural environment corrosion data of materials” * * The scientific basis for the rational selection of materials in national capital construction, especially in the construction of major projects, is also * * The basis for the formulation of relevant national standards and specifications, it is * * The research and development of new materials plays an important role in improving the quality of materials and products, saving materials, saving energy, and protecting resources and the environment. 2. Overview of atmospheric and soil corrosiveness across the country 1. Classification of natural environment and climate conditions in my country Among the various environmental data tested by corrosion researchers, the relative humidity (RH) of the atmosphere has the greatest impact on corrosion. In the national standard GB/R15957--1995 "Classification of Corrosivity of Atmospheric Environments", the atmospheric environment is divided into three types according to the size of RH.: (1) Dry type (ＲＨ＜60%) (2) Ordinary type (ＲＨ６0-75%) (３) Humid type (ＰＨ＞７5%) According to climatic conditions, our country can be divided into: (1) Temperate climate zone—including the vast area north of the Yangtze River Basin in my country. The region can be subdivided into three districts: northern, central and southern. Among them, the northern temperate climate zone is only the Mohe area of Heilongjiang Province in the northernmost part of my country, accounting for less than one percent of the country's area.: The central temperate climate zone is the vast area north of the Yellow River, accounting for about 30% of the land area.: The southern temperate climate zone is the Yellow River Basin and the vast area north of the Huaihe River, accounting for about 15% of the land area. The western part of the temperate climate zone is a large arid zone, accounting for 3/4 of the entire region, and about 1/4 of the eastern part is a subhumid zone. (2) The subtropical climate zone - south of the Huaihe River includes the Yangtze River Basin, the Pearl River Basin and the vast area between the Yangtze River and the Pearl River, accounting for about 30% of the land area. Except for some sub-humid areas in the north, most of the rest of the area is humid. (3) Tropical climate zone - south of the Pearl River Basin, including Hainan Island, Leizhou Peninsula, Xishuangbanna and other places, accounting for less than 1% of the country's area. This area is characterized by year-round hot and humid weather. (4) Plateau climate zone 1 is dominated by Tibet, including most areas in western Sichuan and Qinghai Province, accounting for about 20% of the country's area. To sum up, it can be seen that the western region, which accounts for 50% of my country's territory, is a dry climate zone and a plateau climate zone, with a relative atmospheric humidity of RH <60%, so the corrosion phenomenon is very slight in these areas. Few corrosion tests have been carried out based on the climate characteristics of the above-mentioned areas. Only some units have been found to have conducted outdoor exposure tests in the Baotou area (RH = 52%). With Baotou as the representative, people can have a preliminary understanding of the atmospheric corrosion profile in the above-mentioned areas. 2. The atmospheric corrosiveness profile of various regions in my country only takes the commonly used structural material A3 steel as an example. The corrosion rate values tested by the National Atmospheric Corrosion Test Website and relevant units engaged in corrosion research in recent years are analyzed and compared in order to understand the atmospheric corrosiveness profile of various regions in my country. See figure and table. It can be seen from the figure that the order of corrosiveness from light to heavy is:: one year: Baotou-Qionghai-Beijing-Wanning-Wuhan-Shenyang-Anshan-Guangzhou-Qingdao-Chengdu-Jiangjin 2 years: Baotou-Qionghai-Beijing-Shenyang-Wuhan-Anshan-Wanning-Guangzhou-Qingdao-Chengdu-Jiangjin four years: Baotou-Beijing-Shenyang-Qionghai-Anshan-Wuhan-Guangzhou-Chengdu-Qingdao-Jiangjin-Wanning eight years: Baotou-Shenyang-Anshan-Beijing-Wuhan-Guangzhou-Jiangjin-Chengdu-Qingdao-Qionghai-Wanning It can be seen from the above statistical data: (1) In the ranking of the corrosion rates of the 11 cities, it can be seen that Baotou has always been at the lowest corrosion rate. Since its average atmospheric relative humidity is about 52%, it represents the atmospheric corrosion conditions in dry climate areas. (2) At the beginning of the test, there was no obvious pattern in the order of corrosion rates. The corrosion rate of Qionghai on Hainan Island was lower than that of Beijing, and Wanning was lower than Wuhan and Guangzhou. However, by the eight-year period, the order of corrosion rates had changed significantly, that is, from north to south, Shenyang, Anshan, Beijing, Wuhan, Guangzhou, and Qionghai were arranged according to the geographical latitude of each pilot location. The corrosion rate also showed a regular arrangement from low to high. (3) Typical environments have a significant impact on atmospheric corrosion. The industrial atmosphere has a greater impact at the initial stage of the test. As time goes by, the impact gradually weakens. ； As time goes by, the influence of the ocean atmosphere increases rapidly. This can be confirmed from the following arrangement change rules: 1) Anshan (industrial atmosphere in the mid-temperate subhumid zone) was ranked later in the early stage of the experiment. In the later period of the experiment, Anshan gradually moved forward and was ranked before Beijing (urban atmosphere in the mid-temperate subhumid zone). 2) Qingdao (marine atmosphere in the south temperate subhumid zone) ranked before Chengdu (urban atmosphere in the humid subtropical zone) in the early stage of the experiment, and ranked behind Chengdu in the later period of the experiment. 3) Wanning (ocean atmosphere in the humid tropical zone) ranked before Wuhan (urban atmosphere in the humid north subtropical zone) in the early stage of the test, and ranked last in the later period of the test, becoming the most severely corroded area. 3. Atmospheric corrosivity characteristics and regional division of my country's natural environment (1) Atmospheric corrosivity characteristics 1) The vast area in western my country (accounting for about 1/2 of the country's land area) is a relatively arid area. The relative humidity of the atmosphere is less than 60% all year round, and the corrosion phenomenon is very slight. 2) There is an obvious atmospheric corrosion phenomenon in eastern my country, and the distribution of corrosion rates varies with the latitude of the region. The general trend is that the corrosion rate gradually increases from north to south as the latitude decreases. 3) The eastern part of my country can be roughly divided into southern and northern parts by the Yangtze River. Although there is corrosion in the northern part, it is mostly at a minor level. ； Most of the vast areas in the south have moderate corrosion levels, and only a few areas in the southernmost part have slightly severe corrosion. 4) In a typical climate environment, the marine atmosphere has the greatest impact on corrosion. Therefore, coastal cities do have significantly more corrosion than inland cities, but this impact gradually weakens beyond 20 kilometers away from the coastline. ； The impact of industrial atmosphere on corrosion is second, and this impact gradually weakens as time goes by. (2) Division of Atmospheric Corrosive Areas Within my country’s 9.6 million square kilometers of territory, the atmospheric corrosive areas can be roughly divided into the following five areas:: 1) Weak corrosion zone (RH<60%, annual average corrosion rate<8.0μm/a). Including Xinjiang, Tibet, Qinghai, Ningxia, Gansu, Inner Mongolia and other vast western regions, accounting for about 50% of my country's territory. 2) Corrosion zone (RH=60-70%, annual average corrosion rate 8-10μm/a). The vast area north of the Yellow River accounts for about 15% of my country's territory. 3) Light corrosion zone (RH=70-75%, annual average corrosion rate 10-15μm/a). The vast area south of the Yellow River and north of the Yangtze River accounts for about 14% of my country's territory. 4) Medium corrosion zone (RH=75-80%, annual average corrosion rate 15-201μm/a). The vast area south of the Yangtze River accounts for about 20% of my country's territory. 5) Strong corrosion area (RH>80%, annual average corrosion rate 20-30μm/a). Hainan Island, Leizhou Peninsula and Xishuangbanna tropical humid areas account for about 1% of my country's territory. 4. my country's soil corrosiveness status The National Soil Corrosion Test Website has formulated standards for classifying the corrosivity of carbon steel based on the corrosion status of my country's soil. It is divided into five levels according to the corrosion weight loss per square decimeter per year or the average annual depth, as shown in Table 1. Based on years of work on the soil corrosion test website, the corrosion data and main physical and chemical properties of carbon steel obtained in some typical areas are introduced in Table 2. It can be seen from Tables 1 and 2 that the soils with corrosion rates above level V (greater than 7g/dm·a) are red soil in Shenzhen and brown desert soil in Karamay, Xinjiang. Corrosion rates between level IV and level V (corrosion rate between 5 and 7 g/dm·a) include the Gobi gravel soil in Xinjiang, the desert soil in Lunnan No. 2 in the Tarim Basin, and the gray brown soil in Dunhuang. Desert soil, gray soil in Wumen, red soil in Guangzhou, red soil in Yingtan, brick red soil in Wenchang, Changjiang, and Tongshi in Hainan, and meadow alkaline soil in Dawa, Liaoning. Those with corrosion rates in grades III to IV (corrosion rates between 3 and 5 g/dm·a) include Dagang's coastal salt soil, Jinan's alluvial soil, Changxindian's meadow cinnamon soil, Liaoning's Benxi's brown soil, Chengdu's meadow soil, Qinghai's Lenghu's gravelly lime-brown desert soil, and Xi'an's black loam soil. Those with corrosion rates in Level II (corrosion rate 1-3g/dm·a) include soda salt soil in Daqing, black tide soil in Shenyang, coastal salt soil in Donggang, Liaoning, purple soil in Luzhou, Sichuan Province, and coastal salt soil in Yinggehai, Hainan Province. The wind-sand soil in Zhanggutai, Liaoning Province has a corrosion rate of Grade I. 3. The impact of typical atmospheric environment on material corrosion. Through the reasonable layout of the regional environment, typical metal material specimens are used to hang up in the atmosphere, and the main corrosion factors in the environmental medium are measured at the same time. After obtaining the data according to a certain test period, relevant analysis, principal component analysis, pattern recognition and graphics processing, network point encryption, data smoothing and other technologies are used to draw a regional corrosion map. 1． Industrial Atmospheric Environment Industrial atmosphere refers to the gases emitted by people in production or life that pollute the atmospheric environment, forming an atmospheric environment containing a variety of pollutants. In this atmospheric environment, corrosion becomes significantly accelerated. Common contaminants include: CO, SO, HF, HS, NO, Cl, HCl, dust reduction, etc. The Institute of Corrosion of the Chinese Academy of Sciences conducted a corrosion investigation in Shenyang, a typical industrial city. It collected meteorological data and air pollution data from Shenyang urban area in the past two years, and set up 3 atmospheric corrosion exposure test points within 164 square kilometers of the urban area. At 6 locations, A3 steel was used as a test piece, and a 2-year exposure test was conducted. A correlation analysis was conducted on the average corrosion rate and the average S02 content. Through the internal difference method, an atmospheric corrosiveness level map in Shenyang urban area was drawn (Figure 1). In more than two years of on-site exposure tests and environmental factor tracking, regression analysis was conducted on the measured data. The results showed that only SO has a clear correlation with corrosion (Figure 2), while the relationship with NO, dust, etc. is not obvious. Therefore, it can be said that under general conditions, the so-called industrial atmosphere for corrosion refers to the atmosphere whose main characteristic is SO content. ； In the analysis of the rust layer of the test piece at the seriously polluted point, it was found that there were obvious FeS and FeS particles, which also proved that SO played a significant role. The above-mentioned surveys adopt the census method. Some pilots are selected in areas with concentrated factories and serious pollution, while some pilots are selected in suburban areas with very slight pollution. Through comparison, we can also see the extent of the impact of pollutants on corrosion. As can be seen from Table 1, the SO concentration values in the two locations are quite different. In the comparison of carbon steel corrosion rates, the corrosion rate in the high-concentration area is 2.49 times that of the low-concentration area in one year, and 1.76 times in two years. ； It can also be seen that the influence of SO2 on corrosion gradually weakens over time. 2. Marine atmospheric environment Marine atmosphere refers to the atmospheric environment containing a large amount of salt gas formed due to the evaporation of sea water. Due to the high salt spray content in this gas, it has a strong corrosive effect on metals. This kind of corrosion mostly occurs on ships at sea and on coastal terminal facilities. Many coastal cities in my country are affected by the ocean atmosphere, and the corrosion phenomenon is very serious. However, as the coastline expands inland, the salt spray content in the atmosphere will gradually decrease, and the corrosion phenomenon will also be relatively weakened, until it transitions to a general atmospheric corrosion environment. During the corrosion investigation on Hainan Island, testers from the Institute of Corrosion of the Chinese Academy of Sciences combined with actual outdoor exposure tests to extend from the coastline to the inland from different angles in a large range. On this extension line, they tested the corrosion rate of plain carbon steel samples at different distances from the coastline, thus gaining a preliminary understanding of the scope of influence of the ocean atmosphere. The test results of corrosion weight loss are shown in Figure 3. If compared with the geographical location of each station, it can be seen that the corrosion rate is high in the northeastern region, while the corrosion rate is low in the southwest region. Among them, the corrosion weight loss value of Dongfang Station is particularly high, which is abnormal. Outside the east wall of the station is a large salt field and is polluted by mine dust. After repeated research, it was decided to treat this station as a special case. The measured corrosion rate values for two years were marked on the locations of each test station, and equal corrosion rate lines were drawn using the interpolation method to form an atmospheric corrosion map of Hainan Province (see Figure 4). Among them, Dongfang Station is marked separately as a special case, and its surrounding area is still classified as a low-corrosion area according to the rules of the entire island. It can be seen from Table 2 that Haikou, Wenchang, Lingao, Qionghai and other places are all within 15km from the coastline, and their corrosion is relatively high in the first year, with an average of 62.5μm/ a, and after extending inland, the nearest distance from the coastline in Ding'an, Chengmai, Tunchang and other places is 25km, and the farthest distance is 55km. The corrosion rate generally decreases to the corrosion rate of the general atmospheric environment, falling to about 34μm/a in the first year and about 24.5μm/a in the second year. Significant changes in the corrosion rate occur between 15Km and 25Km away from the coastline. Therefore, it is appropriate to define the impact range to about 20km. (1) Influence of meteorological factors According to the climate characteristics of Hainan, six main meteorological parameters were selected for recording: temperature (X), relative humidity (X), number of days with relative humidity greater than 80% (X), sunshine time (X), rainfall (X) and exposure time (X), and the annual average and annual cumulative total were calculated (statistical results are omitted). The corrosion rate value Y (two-year results) measured at each test station was compared with the environmental factor value xi, and the correlation between the two was sought. The stepwise regression method was used to delete the variables x, x, and X with insignificant effects, and the regression equation was obtained.: y=-100.5789+1.7505x2+3.3797x-8.9248x The correlation coefficient R=0.86, F=13.91>F00.1(1,15)=8.68, passed the F test, which shows that the corrosion rate of A3 steel has a significant correlation with relative humidity, the number of days when the relative humidity is greater than 80%, and the amount of rainfall. (2) Impact of Cl- concentration As far as environmental pollution is concerned, Hainan Province is basically a pollution-free zone, and the concentrations of SO2 and NOx in the atmosphere are far less than the first-level pollution standard (annual daily average SO2 of 0.02 mg/standard meter 3 ； NOx annual daily average 0.05 mg/standard meter 3) ； Therefore, only the influence of Cl- concentration on the corrosion of A3 steel is discussed. Judging from the C1- test (cumulative method) results of each experimental station, a certain amount of C1- can be measured at all coastal stations, while at inland stations such as Tongshi and Ledong, the C1- content is very small. Then examine the corrosion rates measured at each test station. When extending from the coast to the inland, its attenuation roughly corresponds to the attenuation of C1- concentration. Due to the different geographical and climatic characteristics of various parts of the province, the magnitude of attenuation varies greatly. The terrain in the northeast is flat, and the northeast monsoon is strong. Therefore, the corrosion rate in the coastal areas of the northeast is high, which is very different from that in the interior. ； The southwest is mountainous, the southwest monsoon is weak, the corrosion rate in coastal areas is relatively low, and the difference with the inland is much smaller. 4. Typical cases and hazards of natural environment corrosion The hazards of corrosion are well known. It often causes catastrophic consequences such as major economic losses, casualties, production shutdowns, and environmental pollution. Corrosion in natural environments (compared to corrosion in industrial environments) is widespread and widespread. construction, transportation, machinery, * * The system is mainly corroded by the natural environment. For example: * * The Great Hall was built in 1959. It was partially repaired in the 1980s and was overhauled in 1994 and 1995. The main steel bars of the beams and columns were severely corroded. The repair fee for each meter of beams was 1,300 yuan, and the total repair cost was hundreds of millions of yuan. Zhanjiang Wharf, built in 1956, was obviously damaged by corrosion in 1963 and began to be repaired. Inspection in 1979 (23 years ago) 21% of the steel bars were cracked ； Inspection in 1988 (32 years), 91% of the steel bars were cracked ； It was demolished in 1988, and the cost of demolition and reconstruction this time amounted to tens of millions of yuan. A salt factory in Qinghai was built with an investment of 30 million yuan in 1989. The factory was located in a saline-alkali land and produced salt. The factory building was severely corroded and production ceased after 6 years, resulting in direct and indirect losses of nearly 100 million yuan. Corrosion in the natural environment causes mechanical failures in ships, aircraft and vehicles, with very serious consequences. For example, the Maritime Shipbuilding Ship was delivered for use in July 1968. The hull was found to be tilted in September and October of the same year. Water leakage occurred in December. After inspection, it was found that there were corrosion pits of varying depths everywhere on the underwater hull, and there were many Corrosion and perforation, especially the corrosion damage of the shell plates and welds below 300mm below the waterline (light-load waterline during construction), were more serious. Some welds had been completely broken through. In the end, they had to return to the factory to replace the steel plates, which cost 170,000 yuan. For another example, the ship ??? was put into service in October 1991, and severe corrosion in the bilge was discovered in January 1994. In the main engine room, auxiliary engine room and tail shaft room, 217 ulcer-shaped corrosion pits with a diameter of 8-20 mm and a pit depth of 3-6 mm were found. The annual ulcer corrosion rate is 1.5-3 mm/year, and the maximum ulcer corrosion rate is 4.5 mm/year. Among them, one place on the left side of the left main engine gear box has been corroded and perforated, with a pit diameter of 80 mm and a hole diameter of 20 mm. The rest are ulcer-shaped corrosion pits, which are oval in shape, and some corrosion pits are in the shape of steps. The ship is one of the main transport ships in the South China Sea. It was forced to suspend sailing for inspection and repairs due to severe corrosion. It was put on schedule twice, with a total schedule of nearly half a year and a cost of more than one million yuan, which seriously affected the completion of combat readiness transportation tasks. According to statistics from the Type 63 amphibious tank's use tests in coastal areas, after the vehicle was exposed in the coastal salt spray zone, external fasteners such as nuts used for the road wheels and driving wheels, track pins, refueling bolts, etc., corroded and died, making disassembly difficult. ； The movable parts of the internal control device will rust, which will increase the friction resistance of the movable joints and make operation difficult. ； The hinge of the sight folding device and the ruler setting mechanism are corroded, causing the artillery and aiming to be out of sync. ； The control console was damaged due to a short circuit in the cable plug and socket, and the artillery auxiliary relay was burned out due to a short circuit. ； The artillery firing contact point on the upper and lower machine runner parts was sometimes not completely separated from the contact ring due to corrosion, resulting in two misfires during the test. Although there is a certain seal between the upper and lower seats of the turret, water splashing and intrusion at sea often occur. The pin raceways and balls of the turret seat are easily corroded by seawater and salt spray. Because the pin raceways and balls of the turret seat ring are subject to contact stress, paint cannot be used to prevent corrosion, so it is a difficult part to prevent corrosion. The consequences of corrosion will affect the smoothness of the turret's rotation and reduce combat performance. Due to the severe corrosion of the vehicle, special repairs were required after sea training. The cost of repairing the vehicle was as high as 50,000 yuan. A survey conducted by a certain armored regiment showed that approximately 1.2 million yuan is invested in anti-corrosion costs every year, accounting for only about 25% of the required costs. The cost of replacing or repairing corroded parts of each vehicle is about 1,800 yuan, and the maintenance cost after training is as high as 50,000 yuan. At present, the corrosion protection treatment of equipment has high frequency and heavy workload, which takes up a lot of time and manpower. Corrosion causes equipment damage or performance reduction, seriously affecting combat effectiveness. The strength of anti-corrosion maintenance work accounts for more than 80% of the entire military strength, of which more than 40% of the strength is invested by agencies and almost 100% by detachments. The labor consumption for anti-corrosion accounts for about 90% of the labor consumption of all maintenance work. In terms of cost, surface anti-corrosion costs account for more than 70% of all maintenance costs. For pontoon equipment with a long service life, the annual anti-corrosion costs can reach more than 80% of all maintenance costs. Corrosion increases the maintenance workload and lengthens the repair time, shortens the number and time of ships in operation, and consumes the training and learning of the crew. * and rest time, and after corrosion, the ship's tactical and technical performance such as speed, endurance, and vitality were reduced, and its combat effectiveness was reduced. Many ships suffered extremely serious local corrosion damage and were scrapped.
External corrosion of equipment, devices, and pipelines in energy and chemical systems belongs to natural environment corrosion, while internal corrosion belongs to industrial environment corrosion. For example, in May 1971, a natural gas pipeline on the Weicheng Line in Sichuan corroded and burst, causing an explosion and combustion, resulting in a direct economic loss of 70 million yuan. From May 1971 to February 1986, corrosion in Sichuan's natural gas pipeline network led to 83 explosions and combustion accidents, of which 24 people were killed or injured in the first accident. Corrosion often causes work and production to stop, seriously affecting normal production. For example, in 1986, more than 20 drill pipe puncture accidents occurred in Xinjiang Feng 30 Well within two months, resulting in continuous drilling suspensions. In 1995, the oil pipeline between China and North Korea burst due to corrosion, resulting in a two-day interruption to the entire oil pipeline. Another example is the Zhongyuan Huzhuang Oilfield, which was put into production in November 1988 and February 1993. It was drilled more than 780 times, leaked more than 10,000 tons of oil, and was forced to shut down the well more than 50 times, affecting more than 4,000 tons of production. In addition to the serious consequences mentioned above, corrosion often causes serious environmental pollution such as damage to groundwater resources, damage to the ecological environment, and waste of natural resources. For example, underground oil pipelines in the Zhongyuan Oilfield corroded and ruptured, causing a large amount of crude oil to leak, resulting in farmland damage and serious environmental pollution. Natural environmental corrosion exists in all sectors of the national economy, and people's lives are also affected by natural environmental corrosion. At present, my country's township and village enterprises are developing rapidly, and the vast majority of enterprises in the energy structure use coal as their main energy source, which results in an increase in the concentration of sulfur oxides in the atmosphere and a large increase in acid precipitation, causing acid rain pollution. In addition to the old acid rain areas in southwest my country, it has now expanded to provinces and cities where township enterprises have developed rapidly (acid rain areas in Zhejiang Province have reached more than 60%, and southern Jiangsu has also become an acid rain area). Environmental pollution not only makes the environmental adaptability of materials * * Reduce, and directly affect the service life of equipment, equipment and buildings, and even cause corrosion accidents. Chongqing and Nanjing both have subtropical monsoon climates with similar temperature, humidity, rainfall, and geography. The difference is that the air pollution and precipitation acidity are significantly different.: The air pollution in Chongqing is heavier than that in Nanjing, and the hydrogen ion concentration in its rainwater is more than 100 times greater than that in Nanjing. This provides comparable conditions for investigating the differences in the impact of acid rain (including air pollution). The results of the investigation of the two cities are as follows: (1) The harm of acid rain to bridges. The Chongqing Jialing River Bridge is a highway bridge with a steel beam structure. The steel beams need to be derusted and painted every year, and the validity period is only one year. During the bridge overhaul in 1978, it was found that some parts of the steel beams were seriously corroded by 2 to 3 mm. The support parts of the bridge are required to be derusted once every 1 to 2 years, but now they must be derusted once every six months. The Chongqing Yangtze River Bridge built in 1980 is a prefabricated highway bridge. Due to the rapid corrosion of metal in Chongqing, the hanging beam supports of the girder are made of stainless steel (which is not available in similar bridges in other cities). However, due to the impact of expansion and contraction of rainwater, the stainless steel supports and connecting plates have already developed large areas of rust spots. The Nanjing Yangtze River Bridge is a steel beam structure dual-purpose railway and highway bridge. According to conventional reasoning, due to the influence of steam locomotives (smoke), the corrosion rate of the steel beams should be faster than that of the Chongqing Jialing River Bridge. However, the survey results show that: The anti-rust effect of the bridge's steel beams can last five years. During the annual inspection, although some parts were dirty from smoke, they were wiped off and found to be free of rust. The length of the steel beams of the Nanjing Yangtze River Bridge is about four times that of the Jialing River Bridge, but the annual maintenance cost for the steel structure is only 60% of that of the Chongqing Jialing River Bridge. (2) The harm of acid rain to street lamps. Mercury lamps in urban areas of Chongqing are replaced every five years on average. The corrosion of wires is also serious, and the wires need to be replaced every ten years on average. Mercury lamps in urban areas of Nanjing are replaced every ten years on average. The wires have not been replaced since liberation (the corrosion is not serious), which means the maintenance cycle is more than twice as long. (3) The harm of acid rain to public vehicles. The corrosion of vehicle shells caused by acid rain is very obvious. According to surveys, the iron shells (1 mm thick) of Chongqing's passenger cars will rust through in just one year, no matter how well they are protected. In Nanjing, it takes more than three years to rust. 5. Investigation of Environmental Corrosion in Western my country It is important to implement my country’s Western Development Strategy and accelerate economic development in the central and western regions. * * * * according to * * Comrade Comrade Comrade Xi Jinping's strategic thinking on the "two overall situations" in my country's modernization drive is a major decision made with a long-term vision, an overall view, and an orientation toward the new century. This is a large-scale systematic project and a great and arduous historical task. Materials are the backbone and important foundation in infrastructure construction and economic development in the western region. Any infrastructure, equipment and industrial products are inseparable from the use of materials. When all materials are stored, transported, and used in a certain environment, including the natural environment (atmosphere, soil, water), they will be corroded and damaged by environmental factors, leading to a decline in the quality and performance of engineering construction and products, a reduction in reliability, and a reduction in service life. In severe cases, it can cause catastrophic damage accidents. This survey aims to: ①Understand the characteristics of the natural environment (atmosphere, soil, water) in western my country: ②Investigate the corrosion (aging) damage of materials in typical western environments: ③On the basis of the above tasks, in response to the needs of the construction and development of the western region, we purposefully formulate a corrosion test plan for materials in the western environment, carry out material corrosion data accumulation and regular research, study appropriate control methods and measures, and ultimately provide reliable and scientific basis for the rational selection of materials and corrosion control methods for the processing and manufacturing of infrastructure projects, equipment, facilities, etc. in the western region. 1. Atmospheric environment characteristics and material corrosion damage conditions in the western region The western region includes 13 provinces and municipalities directly under the central government, including Sichuan, Guizhou, Yunnan, Tibet, Guangxi, Shaanxi, Gansu, Qinghai, Ningxia, Shanxi, Xinjiang, Inner Mongolia and Chongqing. It covers an area of approximately 6.8 million square kilometers and belongs to six different climate types: humid heat, subhumid heat, cold temperature, warm temperature, dry heat and cold. Due to its unique geography, landform, geothermal and forest vegetation, as well as different population distribution and industrial base, the atmospheric environmental conditions in the western region are very different from those in central and eastern my country. Their atmospheric environment can be roughly divided into the following typical types:: Deep inland, an inland desert with little rain, strong and frequent winds, and an arid atmospheric environment ； Above 1,000 meters above sea level, plateau atmospheric environment with strong solar radiation ； High temperature, high humidity and rainy tropical rainforest environment ； Acid rain atmospheric environment with acidic wet deposition and acidic dry deposition. The corrosion damage rate and damage type of materials in the natural environment are strongly dependent on the conditions of the service environment. For materials, equipment, facilities and product parts used, stored and transported in the atmosphere, this corrosion damage is closely related to the temperature, humidity and conversion frequency of the atmospheric environment, pollutants contained in the atmosphere, such as SO2, Cl-, CO2, NOx... and other environmental factors and the type of atmospheric environment determined by them. Between 1960 and 1964, the American Society for Testing and Materials (ASTM) conducted unified tests on high-purity zinc sheets in 45 regions with different environmental conditions around the world. It was found that the lowest corrosion rate was in the northwest of Canada, which was 0.152μ/a, while the largest was in the coastal area of the Panama Canal Zone, reaching 15.42μ/a. a. Even in the same area, such as the Kure Coast in the United States, corrosion rates at different heights and distances from the coast vary greatly. It can be seen that in the unique atmospheric environment in western my country, the corrosion damage of materials, equipment and products must be quite different from that in the central and eastern environments. Among them, the more typical atmospheric environment can be divided into the arid atmospheric environment of the inland desert, which is deep inland, arid and less rainy, with strong winds and frequent heavy rains. ； Plateau atmospheric environment with strong ultraviolet radiation above 1,000 meters above sea level: High temperature, high humidity and rainy tropical rainforest climate ； Acid rain atmospheric environment with acidic wet deposition and acidic dry deposition, etc. (1) Acid rain atmospheric environment and material corrosion damage 1) Acid rain atmospheric environment characteristics Central Guizhou Province and Sichuan Province are areas with severe acid rain in my country. Among them, major cities such as Guiyang, Zunyi, Anshun, Duyun, Chongqing, and Dazu are particularly polluted. At present, my country's acid rain areas are basically stable, accounting for about 30% of the country's land area. The main characteristics of the atmospheric environment of acid rain are that the pH value of rainwater is lower than 5.6, which is acidic, and the SO2 content in the atmosphere is relatively high. Taking Guiyang as an example, the annual average pH value of precipitation acidity is about 4.2, and the pH value of water in winter is generally below 4.0. It is the city with the most severe SO2 pollution in the atmosphere in the country. First, the pH value of rainwater in Chongqing is around 4.016, reaching 3.0 in winter. Sulfate ions account for 70-90% of the total anions, which is a typical sulfuric acid type acid rain. Table 1 lists the average values of the main atmospheric environment parameters in each acid rain urban area. Huitong is a non-acid rain city with the same climate environment. Table 2 shows the continuous tracking results of the rainwater pH value of the atmospheric environment in Jiangjin, which is an acid rain environment, and Wuhan, Qingdao and other places in non-acid rain areas. Table 3 shows the comparative data of SO2 content in the atmosphere in the above areas. The above data shows that in my country's acid rain areas (Sichuan, Guizhou, and Chongqing), both acidic wet deposition and acidic dry deposition are much higher than in other mainland cities. This kind of industrial pollution will have a great impact on the corrosion and damage of materials. In the process of burning coal or fuel oil, the SO produced can generate sulfuric acid through catalytic oxidation in the gas phase or liquid phase. The latter can have a strong corrosive reaction with metal materials and cause serious damage to the materials. Chongqing and Jiangjin City under its jurisdiction are both in severe acid rain atmospheric environments. The metal corrosion rate in this area is * * Higher than other non-acid rain areas. The previous table lists the comparison of the corrosion rates of the four major categories of standard materials measured in Jiangjin and other non-acid rain areas in my country. The following table lists comparative data on corrosion damage of 13 metal materials in Jiangjin and other non-acid rain areas. The data in the previous table and the table below show that for the four materials including carbon steel, aluminum, zinc, and copper, the corrosion rate in the acid rain environment of Jiangjin is significantly higher than that of other non-acid rain areas, and also higher than that of Qingdao in the marine atmospheric environment. For different grades of metal, the severity of corrosion damage in acid rain areas is also different than in other non-acid rain areas. Taking Beijing as an example, for aluminum, the damage is 13-20 times higher than in Beijing. ； For copper, 3-4 times higher ； For ferrous metals, it is 2-3 times higher. It is worth noting that in acid rain areas, the corrosion damage of weathering steel and stainless steel is almost the same as the corrosion situation in Qingdao area with marine atmospheric environment. Therefore, when selecting these materials in acid rain areas, careful consideration must be made and economic comparison analysis must be conducted. ②Corrosion of the protective coating (plating) layer in acid rain areas destroys automobiles, motorcycles, bicycles, trains, electrical appliances, and many mechanical equipment, power and communication equipment, infrastructure construction facilities, factory buildings, etc., all of which are protected by coating metal, non-metallic or organic coatings. On the one hand, it provides a beautiful appearance, and more importantly, it prevents metal corrosion and rust. During the investigation, it was found that acid rain destroys these protective layers, especially the metallic protective layers, very quickly. For example, in a non-acid rain environment, the protective life of electroplated Cu/Ni/Cr products with average corrosion resistance can be maintained for more than 2 years, while the corrosion-resistant system using a thick Ni layer/microporous Cr layer or a dual Ni/microporous Cr system can last for 5-10 years. However, in the acid rain environment of Jiangjin, even if a corrosion-resistant dual Ni/microporous Cr system is used, severe corrosion will occur after only one year of use. For electro-galvanized products, in the Beijing area, the corrosion rate of the galvanized layer is only about 0.3 μm/a, while in the acid rain environment of Jiangjin it can be as high as 2.0 μm/a. The corrosion rate of tinplate plates commonly used in buildings is 0.3-0.5μm/a in Beijing, and as high as 2-4μm/a in Jiangjin. As far as anti-corrosion coatings of paints are concerned, acid rain will quickly damage the gloss, color and powdering of the paint film. For ordinary paints, obvious loss of gloss and discoloration will occur after 1-2 years of use, and obvious powdering defects will appear after 3 years. ③Corrosion damage of building materials in acid rain environment. According to survey data provided by the Shenyang Corrosion Institute of the Chinese Academy of Sciences and Harbin Institute of Technology, acid rain can cause serious corrosion damage to marble, concrete and other building materials, and lead to large economic losses. Chongqing * * The Great Hall was built in 1954. In less than 30 years, its maintenance cost reached 3 million yuan. After two years, the appearance of residential buildings in Chongqing and Guiyang generally turned gray and black. The exposed stones along the riverside barrier of Jiaxiu Tower in Guiyang are as deep as 0.5-1.0cm. In the gymnasium built in 1956, the cement bars on the playing field were corroded by rainwater, and the steel bars and stones were exposed to a depth of 0.5 to 1.0 cm, which is equivalent to an annual corrosion rate of 200 to 400 μm. Decorative materials such as calcite will change color after half a year. Marble will lose its luster after one year, especially in areas exposed to rain. from Guiyang * * The marble base of the large statue has long lost its original luster. The following is a comparative test on the effects of acid rain on marble and concrete conducted in Guiyang, Chongqing, Chengdu and Huiyong, where Huitong is used as a comparative test point where pollution is not serious. Table 1 shows the two-year test results. Table 2 shows the pH value of the test site and the deposition of SO in the atmosphere. Huitong is a basic comparison environment where acid rain is not serious. From this, it can be seen that as the SO deposition amount and the pH value of rainwater increase, the corrosion damage of marble becomes more serious, and the surface gloss is also more damaged. This is basically the case with concrete damage. In addition, due to SO pollution, the acidic substance HSO is produced, and the presence of sulfuric acid will inevitably lead to serious damage to ancient buildings and cultural relics. For example, the Dazu Rock Carvings are now in ruins due to the erosion of rainwater. The stone carvings of Arhats from the Song and Yuan dynasties in Chongqing were also seriously damaged by wind and rain erosion. Under the action of SO and sulfate, concrete and reinforced concrete interact with calcium aluminate hydrate to form calcium sulfoaluminate by-products in the hydrated cement slurry framework. Its molar volume ratio is 227% of the original calcium aluminate, causing the concrete to undergo swelling and cracking damage. In addition, after the concrete is damaged, it loses its protective effect on the steel bars. Under the action of atmospheric acidic substances, it causes the corrosion of the steel. At the same time, the molecular volume of the corrosion products is 2-4 times larger than that of the steel, causing further expansion and cracking of the concrete. As a result of this repeated action, concrete and reinforced concrete structures are severely damaged under the acid rain atmosphere. ④The assessment of the severity of atmospheric corrosion in acid rain areas is based on the standard method (ISO-9223) developed by the International Standards Organization. Based on the atmospheric corrosion rate data of four standard materials: carbon steel, zinc, aluminum and copper in different regions, the severity of atmospheric corrosion in various regions of the world is divided into five levels (Table 1). According to the data obtained from this survey, the severity of atmospheric corrosion is classified according to ISO9223. Compared with other areas of the country, the severity of atmospheric corrosion in Jiangjin's acid rain environment is very serious. It is basically at level 4-5 based on four types of materials (Table 2). The acid rain situation in Jiangjin in Sichuan, Guizhou, and Chongqing is relatively representative.
(2) Desert atmospheric environment characteristics and material corrosion (aging) damage Various landforms (desert, sandy land, Gobi, etc.) formed by wind blowing, transporting and accumulating surface materials are called aeolian landforms. my country's aeolian landforms are mainly concentrated in the arid and semi-arid (steppe) zones of northwest, northern North China, and western Northeast China between 75-125 degrees east longitude and 35-50 degrees north latitude, with the exception of a very small part scattered in humid areas, which is negligible. Its area, including the Gobi, totals 1.095 million square kilometers, accounting for approximately 11.4% of the country's total area. 1) Characteristics of desert atmospheric environment my country’s aeolian landform has the following characteristics: ①Most of them live inland, roughly west of Wushaoling and Helan Mountains, and are relatively concentrated, accounting for 90% of the total area. East of this line are more scattered, accounting for only 10% of the total area. ②Desert areas are dry, with little rainfall, and winds are strong and frequent. The precipitation is mostly below 400mm. To the west of the Helan Mountain, it is below 200mm. Among them, the Badain Jaran Desert is below 50mm, while the central and eastern parts of the Gobi and Taklimakan Deserts in eastern Xinjiang are even less than 10mm. The dryness of aeolian landforms is above 1.5. The dryness degree in the east of Helan Mountain is 1.5-4.0, and in the west it is above 4.0. The dryness degree in eastern Xinjiang and the Tarim Basin is as high as 2.0-6.0. It is extremely common for the wind strength in the entire region to exceed level 5-6. ③Except for a few distributed in inland plateaus, most of them are located in huge inland basins, such as the Taklimakan Desert in the center of the Tarim Basin, the Gurbantunggut Desert in the Junggar Basin, etc. Most of these basins are river alluvial or alluvial lake plains, which are mainly composed of loose sandy sediments with large thickness. In arid and windy climates, they are easily eroded, transported, and accumulated by the wind. In severe cases, frequent sandstorms may form. The climate of the Tarim Basin is extremely dry, with a dryness degree of 24-64 or above. The famous Taklimakan Desert is located in its center. It is the largest desert in my country, covering an area of approximately 327,000 square kilometers, accounting for 43% of the total desert area in my country (excluding Gobi), and is also one of the largest deserts in the world. Its main feature is that mobile sand accounts for 85% of the entire desert area. ； The sand dunes are tall and complex in shape. The interior of the desert is dominated by huge exposed sand dunes, generally with a height of 100-150 meters. Among them, those with a height of more than 50 meters account for 80% of the desert's mobile sand dunes. This determines that although these deserts are moving sand dunes, they move very slowly due to their high and dense shape. The center of the Junggar Basin is the Gurbantunggut Desert, covering an area of 47,000 square kilometers. It is the second largest desert in my country, with an annual rainfall of 70-150mm and a dryness degree of 2.0-10.0. The desert in eastern Xinjiang refers to the desert between the Altun Mountains and the Tianshan Mountains to the west of the Hexi Corridor and to the east of the Turpan Basin. The annual precipitation is 10-30mm, and the dryness is as high as 29-60. It is one of the extremely arid areas in my country. The Qaidam Basin is located in the northwest of Qinghai, at an altitude of 2,500-3,000 meters. It is the area with the highest desert distribution in my country. The dryness increases from east to west, with 2.1-9.0 in the east and 9.0-20.0 in the west. The deserts in the Hexi Corridor include some sporadic deserts to the west of Wushaoling in Gansu, to the east of Guyumenguan, and between the Qilian Mountains and Lishan Mountains. Their area is less than 1,000 square kilometers, and they are distributed near oases in the middle and lower reaches of the river. They are all mobile sand dunes. 2) Material corrosion in desert atmospheric environment The investigation team visited the Urumqi Petrochemical Plant, Dushanzi Petrochemical Plant and Karamay Petrochemical Plant in the Gurbantunggut Desert in the Junggar Basin in northern Xinjiang, and the Korleta Petrochemical Plant on the edge of the Taklimakan Desert in the Tarim Basin in southern Xinjiang to investigate the corrosion situation of production equipment. Among them, Tower Petrochemical was founded in 1998. Due to various reasons, it has never been put into production and operation. The factory buildings and equipment have been idle and have not been directly affected by chemical production conditions. It can be said that the entire factory is exposed to atmospheric exposure corrosion in the desert environment. The corrosion situation can well illustrate the impact of the desert environment on materials. ①The sand and dust conditions containing high salt content in the atmosphere have led to special corrosion phenomena of non-ferrous metals and stainless steel. Investigation found that in the Korla area, the corrosion rate of carbon steel is lower than that in the central and eastern regions of my country. For example, the corrosion rate of A3 steel is about 20 μm/α, which is 51.8% higher than that in Wuhan area. 3μm/α is 1.5 times lower, but for non-ferrous metals, aluminum and zinc, it is higher. In Korla, the corrosion rate of zinc is 1.76μm/d, and that of aluminum is 1.34μm/d, while in Wuhan, they are 1.22μm/α and 0.058μm/α respectively. For copper, the corrosion rate is comparable to that of Wuhan. In the Tower Petrochemical Plant, the outer flue protection plate of the boiler in the power plant was made of aluminum plate. However, after only two years, very dense and small pitted corrosion appeared on the aluminum plate. The corrosion points protruded and spread all over the entire plate surface. The corrosion was very serious. Similarly, the polypropylene branch of the plant was built in June 2000 and has only been in place for one year. The piping system is protected by hot-dip galvanized sheets. However, during on-site inspection, it was found that the hot-dip galvanized sheets were severely corroded. During the equipment corrosion investigation at the Tower Petrochemical Plant, it was also found that stainless steel products were also damaged by corrosion. For example, the stainless steel expansion joints used in the flue pipelines had suffered from very serious pitting corrosion. In Korla City, obvious corrosion can also be seen on some stainless steel lamp posts and guardrails. In the desert environment, zinc, aluminum products and stainless steel materials will corrode and damage so quickly, which is unexpected and incredible. Based on the investigation and analysis of the environment, the members of the investigation team also conducted a preliminary analysis and discussion on the causes of the above phenomenon. According to soil analysis and measurements on the ground around Korla, the soil contains a large amount of salt compounds. Within the depth range of 0-1Ocm on the surface of meadow soil, the total salt content reaches 22%, while other desert soils and silt soils have 7.10% and 3.0% respectively. They are chlorides of magnesium, sodium, potassium, calcium, etc., as well as sulfates. Measurement data from the local environmental protection department in the spring and autumn of 1993 showed that the monthly sedimentation amounts of sand and dust were as high as 45.97T/km2 and 32.99T/km2 respectively. This salty dust stains the metal surface. * * It increases the hygroscopicity of the metal surface. Even when the relative humidity of the atmosphere is less than 60%, it is easy to form an invisible water film on the metal surface, causing metal corrosion reactions to occur. ； On the other hand, the increase in salts in the water film also * * aggravates the corrosion reaction process. Especially for metals with easily passivated surfaces such as aluminum and stainless steel, C1- ions promote the destruction of the passivation film and easily cause pitting corrosion. This may be one of the possible reasons why stainless steel, aluminum and other corrosion-resistant materials have suffered severe corrosion in Korla in the desert environment. Although the corrosion rate of carbon steel and low alloy steel in desert areas is lower than that in central and eastern atmospheric environments, attention should still be paid to the corrosion damage of equipment. In the Ta Petrochemical Plant, it was found that many doors and windows in the plant were completely rusted, and the cable boxes were also completely rusted, with the corrosion area reaching 100%. The corrosion of pipelines, valves and flanges is also serious. A gas separator labeled D-5 also had its outer surface completely corroded. There is a pedestrian bridge in the factory area. The bottom side is still intact, but the back side is stained with rust. In one factory, the fasteners used in its heat exchange equipment were all corroded and seized within 1-2 years of production. As a result, when the equipment was repaired in the future, it was often necessary to use electric power.
1) Tropical rainforest environment and climate characteristics Tropical rainforest climate characteristics are: no winter, large annual accumulated temperature, small annual temperature difference, high temperature, rainy days, distinct dry and wet seasons, abundant sunshine, large daily temperature difference, and many foggy days. During the wet season, there is more rainfall, low wind speed, less sunshine, high temperature and high humidity. During the dry season, there are few clouds and rain, strong sunlight, and heavy fog and dew. It has obvious effect on the corrosion damage of metal materials. The annual average temperature in Xishuangbanna is between 18 and 22 degrees, the coldest daily average temperature is about 15 degrees, and the hottest month is 25.5 degrees Celsius. Therefore, the annual accumulated temperature is large and the annual temperature difference is small, but the daily temperature difference is as high as more than 27 degrees Celsius. The dry season is generally from November to April of the following year, and the wet season is from May to October. The annual rainfall is generally between 200 and 1900mm. This not only effectively increases the temperature on cold days but also makes up for the lack of precipitation during this period. According to statistics, the number of sunshine hours in Xishuangbanna is about 2,000 hours, and the number of foggy days is generally about 130. Menglun is the area with the most foggy days in Xishuangbanna, up to 173 days. Table 1 shows the measurement results of atmospheric environmental parameters in Xishuangbanna, Yunnan. Table 2 shows the meteorological factors in some areas of Xishuangbanna. It can be seen from the table that most of the environmental factors in the main counties and towns in Xishuangbanna are at the same level and have a relatively typical tropical rainforest climate environment. (2) Material corrosion damage in tropical rain forest environment ① Mildew of organic materials and fogging of optical glass are typical characteristics of material corrosion in tropical rain forest environment. The atmospheric humidity RH in the tropical rainforest reaches more than 85% all year round, and the temperature is around 30°C. In this special environment, mold is suitable for growth, and organic materials provide rich nutrients for mold. Therefore, in the tropical rainforest environment, organic materials such as leather, wood, and paint are very easy to grow mold, deteriorate, and rot. Investigations have shown that if the above-mentioned materials are not properly treated, their performance will be seriously damaged in one or several years. Due to the large temperature difference between day and night in tropical rainforests and the humid and hot environment, the surfaces of optical telescopes and observation lenses are prone to fogging and mold growth, resulting in a decline in the optical performance of the lenses and affecting observation, measurement and weaponry technical combat capabilities. ②Atmospheric corrosion of metal materials in tropical rain forest environment. Before and after the investigation, the Wuhan Materials Protection Research Institute conducted tests on metal corrosion conditions in the tropical rainforest climate of Xishuangbanna for half a year. In order to compare with other climate environments, comparative tests were also conducted in Xisha (island atmosphere), Hailar (cold zone), Wudaoliang (high-altitude mountainous area), Korla (desert) and Wuhan. The test results were listed in the previous table. The results show that compared with several places (Hailaer, Wudaoliang, Xishuangbanna) with light air pollution (or even no pollution), the corrosion of ferrous metals, such as A3 steel, is still more serious in the tropical rainforest environment, which is twice that in the cold climate environment and six times that in the plateau environment. The corrosion rate of copper is 4 times and 2 times that of the above two areas respectively. For zinc, it is 5 times and 7 times respectively. Aluminum is 10 times that of plateau environment. Hainan Jiji also has a humid and hot climate with less air pollution. The corrosion rate of A3 steel there is about 29 micron/a. Beijing has a temperate subhumid semi-rural climate, and the corrosion rate of A3 steel is about 32 micron/a. From this point of view, in a tropical rainforest environment without industrial pollution, the degree of corrosion damage of carbon steel is similar to that in Beijing and Qionghai. With the development of economy in the future, it is bound to cause certain pollution to the environment. With the increase of corrosive substances in the atmosphere, the corrosiveness of metals will inevitably increase under high temperature, high humidity, and rainy climate conditions. It is very necessary to conduct in-depth experiments and research on materials in tropical rainforest environments. (5) Corrosion conditions of materials in Qinghai Salt Lake and saltwater lake environments 40,000 years ago, the Salt Lake area was an inland saltwater lake. It gradually evaporated and dried up, and a large amount of salt accumulated on the surface of the earth. Later, due to flooding, the salt layer was divided into four layers. The Salt Lake area has very little precipitation, with only tens of millimeters of annual precipitation, while the evaporation is more than 3,000 millimeters. There are ten brine lakes around the Qarhan Salt Flats. The average salt content in the brine is as high as 37%, and the highest brine lake has a content of 42.5%, which is more than ten times that of seawater. Due to the extremely high concentration of salt, the oxygen content in the water is reduced, so that ferrous metals used in salt brine for a long time will not cause serious corrosion. However, brine and soil with high salt content will cause serious corrosion damage to cement and non-ferrous metals (such as aluminum). Whenever it rains in the Salt Lake area, the rain will cause severe corrosion damage to metals, because many roadbeds in the Salt Lake area are made of salt blocks. When it rains, the muddy water splashed by rainwater contains a large amount of salt, which causes serious corrosion damage to traffic vehicles and construction machinery, such as short circuits in electrical connectors and pitting corrosion in metals. Therefore, after using the car on rainy days, the driver must rinse the car thoroughly immediately. In the production workshop in the Salt Lake area, if the production is temporarily suspended or the machinery and equipment are temporarily shut down and idle during construction, serious corrosion will occur in the equipment, and the degree of damage will be greater than the corrosion when the machinery is operating in a salt brine environment. Imported mining ships in brine mining areas have been used for more than ten years without requiring major repairs, and the hull paint has not been overhauled. (6) The corrosion damage of concrete structures and highway traffic deserves attention. In the western region, the corrosion damage of concrete is more prominent. The Karamay Petrochemical Plant reported that exposed steel bars in concrete overpasses in the city are relatively common. Because concrete is prone to cracking, buildings generally require veneer protection, which is more serious than other areas in the country. This phenomenon is consistent with reports in the United States. Among the 66 reinforced concrete bridges used in desert areas in the United States, 20 have corroded steel bars in less than 10 years of use, resulting in high maintenance costs. Cracked concrete and exposed steel bars can be seen everywhere on docks, telephone poles, and guardrails on the shores of Qinghai Lake. Some cracks are crack-shaped, and some are strip-shaped, about 1 meter long and several centimeters deep. The steel bars inside are completely rusted, and some are falling off in pieces. The phenomenon of concrete cracking also exists in Xi'an and other areas. For example, the on-campus library building of Chang'an University in Xi'an was built in 1985. In 1998, large pieces of cement fell off, and the steel bars were severely corroded, and they could even be pulled out by hand. The building was severely damaged, endangering the safety of the building and had to be reinforced and repaired. The corrosion damage of highway bridges in the atmospheric environment is also a matter of greater concern in the western region. We learned from relevant experts from the Highway College of Chang'an University in Xi'an that the design life of bridges with reinforced concrete structures is 70 years. However, due to the lack of attention to protection, many bridges do not take any protective measures for the concrete. As a result, many bridges in the western region have corrosion problems of steel bars within two or thirty years of use, resulting in a decrease in load capacity. Once the steel bars are corroded, repair work is particularly difficult and the results are not ideal. Rebar is key to ensuring the reliability of highway bridges. For a large number of suspension bridges or cable-stayed bridges, the steel cables are prone to fracture under the combined effects of tensile stress, fatigue, and atmospheric media, leaving potential safety hazards. Therefore, according to common practice, it is generally required to replace the steel cable after about 10 years of use. However, this replacement standard has no reliable basis and relies mainly on regular testing. In addition to steel bars, corrosion damage to highway bridge ancillary facilities also deserves attention, such as railings, signs, and isolation nets. Five years after the Xibao Line was opened to traffic, the galvanized steel wire isolation mesh is ready to be replaced for the second time. In highway bridges, due to failure of expansion joints, they need to be replaced every 8 to 10 years. Experts from the Highway Academy reported that for the protection of bridge steel structures, the previous selection of protective materials and methods lacked reliable data and was relatively blind. For example, bridges protected by paint usually need to be repaired every 2-3 years. However, after seeing more than ten years of material corrosion data on the website provided by Wuhan Material Protection Institute, I was inspired to use thermal spraying Zn, Al and other protection methods. The protection effect has been significantly improved, and frequent maintenance is no longer required. Therefore, experts attach great importance to the development of material corrosion tests and research work, believing that this kind of basic research will have an important impact on the quality of my country's engineering construction. From the results of this investigation, it can be seen that natural environmental corrosion has a great impact on * * The hazards and impacts of construction are serious. It has the following characteristics: First, corrosion in natural environments (compared to corrosion in industrial environments) is widespread and widespread. construction, transportation, machinery, * * The system is mainly corroded by the natural environment. External corrosion of equipment, devices, and pipelines in energy and chemical systems belongs to natural environment corrosion, while internal corrosion belongs to industrial environment corrosion. Second, the loss caused by natural environment corrosion accounts for the largest proportion of the total loss. According to statistics, the steel used in the atmosphere accounts for about 60% of the total production, the corrosion loss of materials in the atmospheric environment accounts for more than 50% of the total loss, the soil accounts for about 20%, and the water environment accounts for more than 10%. Therefore, the natural environment corrosion loss of materials accounts for more than 80% of the total loss. Third, corrosion in different natural environments varies greatly. The corrosion rate of plain carbon steel Q235 in the ocean atmosphere (Zhanjiang) is 30 times higher than that in the atmosphere (Lhasa) ； The corrosion rate of the galvanized layer in the marine industrial atmospheric environment of the Yangtze River Delta (the environment under Baosteel's ironmaking shed) is 147 times that of Beijing. ； The corrosion rate of amphibious armor steel plates in seawater in the South China Sea is 10 times greater than that in fresh water ； The corrosion rate (maximum pitting corrosion rate) of carbon steel in Xinjiang's saline soil is 9 times greater than that of Daqing's soda salt soil, and 5 times greater than that of Chengdu's meadow soil.: The cable sheathing material corroded and perforated in one year at the Xinjiang Soil Center Station. Fourth, my country's township and village enterprises are currently developing rapidly. The vast majority of enterprises in the energy structure use coal as their main energy source, which has caused an increase in the concentration of sulfur oxides in the atmosphere and a large increase in acid deposition, causing acid rain pollution. In addition to the old acid rain areas in southwest my country, it has now expanded to provinces and cities where township enterprises have developed rapidly (acid rain areas in Zhejiang Province have reached more than 60%, and southern Jiangsu has also become an acid rain area). The corrosion rate of materials in acid rain-polluted areas increases rapidly. The corrosion rate of carbon steel Q235 in acid rain areas (Chongqing) is 2.4 times that of Beijing, the corrosion rate of pure zinc is 2 times that of Beijing, brass is 4 times that of Beijing, and high-strength aluminum alloy (LYl2) is 20 times that of Beijing. The corrosion rate of building materials (concrete, marble) in acid rain areas increases by 1.5 times, and the service life of coating (plating) layers in acid rain areas is reduced. It is only 1/6-1/10 of Beijing's. Environmental pollution not only makes the environmental adaptability of materials * * Reduce, and directly affect the service life of equipment, equipment and buildings, and even cause corrosion accidents. Fifth, there are many factors affecting corrosion in the natural environment and their interactions are complex. Corrosion damage accidents are mostly the result of the combined effects of chemical, physical, microbial and other factors in the natural environment. It has become a hot and difficult issue that experts in the field of international corrosion and protection pay attention to.