Discuss the causes and hazards of corrosion of industrial water on heat exchange equipment

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1. Causes of corrosion: The corrosion of heat exchange equipment by industrial water, particularly that of cooling equipment, is one of the major problems that have long existed in China’s petrochemical plants. In industrial production, process media with temperatures below 100–150°C are generally cooled using circulating water, that is, through a circulating open-type cooling system. The water is reused continuously: after passing through the heat exchanger, it returns to the top of the cooling tower. A low pressure is created by fans, and the water is cooled due to the latent heat of evaporation; once cooled, it collects at the bottom of the cooling tower and is then pumped back by circulation pumps to various cooling equipment for reuse. In this form of circulating water, the continuous evaporation of water during use leads to the concentration of insoluble salts in it, which can easily cause deposits and scaling on the heat transfer surfaces of the heat exchangers. After passing through the cooling tower, the water becomes saturated with dissolved oxygen; coupled with the concentration of inorganic salts in the water, especially the concentrations of corrosive ions such as Cl- and SO42-, the corrosiveness increases. Additionally, since the temperature of the circulating water is around 30–40°C, microbial nutrients such as N, P, and K concentrate in the water, facilitating the growth and proliferation of microorganisms and causing serious damage. The use of industrial circulating water helps save water, but it also poses two major problems: corrosion and scaling of the cooling equipment. Therefore, oxygen and other dissolved gases, dissolved solids and suspended solids, pH value, water flow velocity and temperature, and the growth of microorganisms are the six major factors that cause corrosion. The forms of corrosion include uniform corrosion as well as localized pitting and scale corrosion; however, pitting is the type that most often causes damage to equipment, as it can lead to perforation and leakage within a very short period of time. 2. Hazards of corrosion: Scaling and corrosion-related leaks in cooling equipment not only increase the energy consumption of the products; moreover, the leaked process gases accumulating at the top of the cooling tower can cause explosions at any time, leading to unimaginable consequences. Severe leaks in the cold exchange equipment led to the shutdown of the entire plant for maintenance, resulting in enormous indirect losses.