Analysis of the Corrosion Causes in Blast Furnace Gas Pipeline

Blast furnace gas is a byproduct of the ironmaking process, primarily composed of CO, CO2, N2, H2, CH4, etc. The combustible component CO accounts for approximately 25%, while the contents of H2 and CH4 are minimal. CO2 and N2 content is about 15% and 55%, respectively, with a calorific value of around 3,500 KJ/m³.The primary corrosion in the gas used as a corrosion medium is caused by Cl and H2S. The main sources of Cl are: (1) Ore containing chlorides, particularly those washed with seawater, which commonly have higher chloride content. (2) To reduce the low-temperature reduction and sintering powdering rate of sinter, a certain amount of chloride (such as CaCl2) is added. (3) Coke and coal powder contain a certain amount of chloride. (4) Slag from gasification contains chlorides; the addition of flocculants (such as polyaluminum chloride) in wet sludge treatment also introduces Cl, and these sludges are reused in blast furnaces without prior Cl removal. (5) Injection of coal powder and other raw materials. The sulfur in coal powder and other raw materials produces H2S, SO2, and SO3 acidic gases through high-temperature chemical reactions, which dissolve in water to form acidic solutions. The reuse of sinter desulfurization wastewater and coking wastewater also introduces acidic components into the subsequent blast furnace gas. The general location of corrosion in blast furnace gas pipelines is primarily at U-shaped water seals, drain valves, pipe joints, welding points, and expansion joints of compensator stainless steel bellows. It is evident that the corrosion components in the gas are quite complex, and sulfur and chlorine are the two elements that significantly affect the pipe walls. Chlorine is highly reactive and can almost react with all metals at high temperatures. The presence of chlorine can affect the formation speed and structure of metal oxides, increase defects in the surface oxide film, and cause cracks and holes. Chlorine can diffuse into the lattice and voids of metals, causing internal chlorination of the body and increasing the corrosion rate of the pipe wall metal. Blast furnace gas contains sulfur dioxide, sulfur trioxide, and hydrogen sulfide, which raise the dew point of the gas, causing more severe condensation and dew on the inner wall of the pipeline, leading to more severe corrosion. To mitigate the corrosion of blast furnace gas, concentrated alkali can be injected into the gas to absorb some sulfur dioxide, sulfur trioxide, and acidic corrosion mediums, but this will lower the temperature of the blast furnace gas and increase its humidity, making it more prone to condensation. Generally, the most cost-effective method is to apply appropriate anticorrosion coatings to the inner wall of the pipeline. These coatings are typically inorganic anticorrosion coatings, developed and produced by Xuchang Infrared Technology Research Institute Co., Ltd., utilizing interpenetrating polymer network (IPN) anticorrosion technology. Based on silicon-oxygen —Si—O—Si— bonds, organic alkyl side chains are grafted as assistants, and hydroxyl groups are used as terminal chains to chelate an inorganic polymer with IPN structure. The solution has strong stability, the film is denser, and the coating is smooth, controlling microbial contamination, keeping the equipment surface clean, and providing good anticorrosion properties. The inorganic anticorrosion coating, based on the IPN new inorganic polymer, also incorporates dispersed activated metals, nanomaterials, and ultra-micron rare earth element oxides, capable of quickly reacting with iron atoms on the surface of steel structures. The resulting inorganic polymer anticorrosion coating is firmly bonded to the matrix through chemical bonds, providing good adhesion and dual physical-chemical protective effects, suitable for various working conditions. After applying the inorganic anticorrosion coating to the inner wall of the blast furnace gas pipeline, the coating exhibits strong and dense adhesion, high hardness, and can withstand the abrasion and corrosion of blast furnace gas for a long time, with a lifespan generally exceeding 5-8 years.