Hot water boiler plays an important role in industrial production and people's life. However, the corrosion of hot water boiler system in operation, shutdown corrosion and scaling of corrosion products caused by it are long-standing problems. Because the working condition of hot water boiler is very different from that of steam boiler, and the hot water boiler room is simpler than that of steam boiler room, many effective technologies of steam boiler are difficult to be applied to hot water boiler. The anti-corrosion and anti-scaling technologies for hot water boilers under development are not mature enough, and some are mature but not widely used. These conditions lead to serious corrosion of hot water boilers at present. In foreign countries, this problem has not been well solved. Generally, after two or three years of use, there will be obvious metal corrosion and red water or leakage. The corrosion of hot water boilers in China is serious. According to the statistics of Liaoyang Boiler Inspection Institute, among the 800 heating boilers in use, 755 boilers are corroded, accounting for 95%, of which serious corrosion accounts for about 10%- 15%, corrosion leakage accounts for about 5%-8%, and the normal maintenance cost caused by corrosion is nearly one million yuan. The design life of hot water boilers in China is 12 years. Due to corrosion and other reasons, it will be scrapped after only 5-8 years of operation, which is only 1/2 ~ 1/3 of the design life.

Corrosion will cause huge economic losses. For hot water boilers, corrosion not only leads to a decrease in service life and a substantial increase in maintenance costs, but also occurs in the coldest winter heating period, and the interruption of heating will directly affect the normal life of residents. In order to change this situation, it is imperative to research and develop anti-corrosion and scale inhibition technology for hot water boilers.

The corrosion of hot water boiler and its serious present situation are related to operation corrosion and shutdown corrosion.

In order to prevent the operation corrosion of hot water boiler, people have tried to introduce effective technologies such as thermal oxygen removal and vacuum oxygen removal into hot water boiler for many years, but they failed because of the lack of implementation conditions in hot water boiler room. There are also many problems to be solved, such as desorption deoxygenation, redox resin deoxygenation, sodium sulfite method and zinc plating method, which are specially developed for hot water boilers. High-dose sodium nitrite method has been successfully applied in Japan, but it has not been popularized in other countries because of well-known toxicity problems and insufficient dose, which may cause pitting corrosion of boiler metal.

Corrosion during boiler shutdown is more serious than operation corrosion, which often causes large-scale corrosion damage and local corrosion perforation. The hot water boiler system has short operation period and long shutdown period. Red water and leakage accidents caused by corrosion have occurred from time to time. Some protection methods have been developed to prevent and reduce off-service corrosion. The main methods are the traditional dry method and wet method, and the successfully studied TH-90 1 method. Under the condition of strict implementation, the traditional dry method and wet method can also achieve good results, but due to the complicated operation of the traditional method and the fact that small and medium-sized boiler rooms often do not fully meet the implementation conditions, the effect is not ideal. TH-90 1 method is efficient, convenient and has a long protection period. It has been widely used in the whole country, and the protection of hot water boiler itself is undoubtedly successful. However, it is difficult to protect the complex pipe network, heat exchanger and radiator of hot water boiler system because TH-90 1 corrosion inhibitor cannot be placed. Due to the great difference in environmental conditions between boiler operation period and shutdown period, there are technical problems to be solved in operation corrosion and shutdown corrosion. At present, the research, development and application of anti-corrosion and scale inhibition of hot water boilers at home and abroad are either aimed at operating boilers or stopping boilers. It has become a traditional mode to treat boiler operation and stopping separately. Therefore, it is necessary to study an effective and simple protection method for the whole system shutdown of hot water boilers.

With the acceleration of urbanization and industrialization in China, the scale of heating systems of industrial boilers and hot water boilers, which are closely related to production and life, has also increased rapidly. Due to the limitation of boiler water treatment technology and other reasons, corrosion and scaling problems generally exist in industrial boilers, which leads to the shortening of boiler life and the increase of maintenance and operation costs.