Study On Effects Of Air Pollution On Corrosion Of Materials In Chongqing

In the framework of the Sida-funded Program on Regional Air Pollution in Developing Countries (RAPIDC), field exposure of materials was carried out at an urban (GuanYinQiao-GYQ) and a suburb site (TieShanPing-TSP) in Chongqing, China.The relationship between air pollution and atmospheric corrosion rates of carbon steel, zinc, copper, limestone and organic paint at these two sites was investigated. At the same time, based on the database of RAPIDC, order of the effect of environmental factors on atmospheric corrosion rates was analyzed, and Dose-Response Functions of the test materials were obtained. Furthermore, estimating and mapping of the materials corrosion loss in Chongqiong was carried out with the above Dose—Response Functions, then the acceptable SO2 pollution level in urban area was put forward.Through these studies, some main conclusions were drawn as follows: (1) In general, due to the strong effects of urban local sources, the air pollution at GYQ was more serious than that at TSP; accordingly, the atmospheric corrosion rates of materials at GYQ were obviously higher than that at TSP, with the expection of zinc. Due to its relative high sensitivity to precipitation acidity and environmental humidity, the corrosion rate of zinc at TSP was a little higher than that at GYQ. (2) It was clearly that current atmospheric corrsion situation of materials had improved when comparing with that at the end of the 1980s. However, the atmospheric corrosivity at the GYQ site was still the strongest among the member sites of RAPIDC, even the atmospheric corrosivity of TSP was also higher than that of most other urban sites. Consequently, it is necessary to take further measures to control and abate the air pollution in Chongqing. (3) The combined results of the Grey Relational and Principal Component Analysis showed that atmospheric SO2, precipitation acidity and particles were the common main factors that influenced atmospheric corrosion of the tested materials. Among these three factors, SO2 was especially important, and this outcome confirmed the destructive effects of sulfur deposition on corrosion of materials. (4) Based on the analysis of the database of RAPIDC, Dose-Response Functions (DRF) for the tested materials were derived through non-linear regression method. These DRF differed from those simple correlation equation obtained by former researches in that they were able to separate the corrosion contribution of wet and dry deposition and reflect the combined effects of some factors by some extent. The obtained DRF confirmed the dominant effect of dry deposition of SO2 on atmospheric corrosion of materials at most sites. However, in some sites with high frequency of acid rain and abundant rainfall, the effect of wet deposition of H+ is also as important as that of dry deposition of SO2, which is especially true for zinc. (5) With the DRF and routine monitoring environmental parameters, the maps of the atmospheric corrosion rates of carbon steel, zinc, limestone and organic paint were drawn at a relatively coarse scale using the GIS technique. Despite of the type of materials, the visual appearances of the maps were very similar with decreasing values of corrosion attack from south to north. For carbon steel and organic paint,the difference between the south and north was especially obvious.Generally speaking, the main six districts in the old city and some of their surrounding area were the center with the highest corrosion risk in Chongqing. (6) In the view of atmospheric corrosion, the annual average acceptable SO2 pollution level in Chongqing urban area was put forward. According to the type of materials, they were 21μg/m3, 61μg/m3, 33μg/m3, 27μg/m3, respectively for carbon steel, zinc, limestone and organic paint. (7) With the limited available data, economic loss of atmospheric corrosion of zinc in Chongqing was estimated by the approach developed by Dr. Kucera. The results showed that the direct economic loss of zinc corrosion caused by air pollution was more than forty million RMB, which was about 0.1 pecernt of the GDP of the same year.