Corrosion and ash deposition in the heat tubes of air preheaters in petrochemical heating furnaces
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The image below shows the condition of the heat pipes in the air preheater, which became defective and had to be discarded after being in use for over 2 years. This air preheater is of vertical type with dimensions of 4500×3460×5050; it features 650 vacuum finned tubes with a diameter of Φ30×1, made of ND steel. The flue gas at the inlet and outlet of the heat pipe air preheater is designed to have temperatures of 160°C/300°C, while the actual operating temperatures at the inlet and outlet are around 120°C/300°C. Due to the high concentration of sulfur dioxide gas in the flue gas, it causes severe corrosion of the heat pipes as well as surface scaling. Compared to other areas, the flue gas outlet is the part most affected by corrosion; the temperature there is generally around 120°C, which is relatively low. Within less than a year of operation, some of the fins on the surface of the heat pipes have already corroded, and a large amount of scale has accumulated on the surface of these heat pipes.
In petrochemical heating furnaces, the heat tubes of air preheaters often suffer severe corrosion and scaling due to sulfur dioxide in the high-temperature flue gases. Especially at the flue gas outlet, corrosion is more pronounced due to the relatively low temperature of about 120°C. The fins of heat pipes can corrode and fall off within less than a year of use. Furthermore, a large amount of scale accumulates on the surface of the heat pipe, which not only affects the heat exchange efficiency but may also shorten the service life of the equipment. .
Chinese name: ND steel; Foreign name: ND steel; Alternative names: 09 chromium copper antimony; Material: 09CrCuSb. II. Main applications: ND steel is primarily used in equipment designed to resist sulfuric acid dew point corrosion, such as heat exchangers in electric furnaces, flue pipes, chimneys, boiler air preheaters, economizers, heat exchangers, condensation coolers, evaporators, as well as dust collectors and desulfurization equipment. Furthermore, it can also be used in various devices exposed to flue gases with high sulfur content, as well as in applications where resistance to corrosion by other acidic media is required. III. Performance Features: Excellent corrosion resistance: The addition of elements such as Cu, Cr, and Sb to ND steel gives it very good resistance to sulfuric acid dew point corrosion, which is more than ten times higher than that of ordinary steel plates. Good weldability and formability: ND steel is easy to weld and shape, facilitating processing and manufacturing. Good cost-performance ratio: Compared to stainless steel, ND steel offers a better cost-performance ratio in terms of resistance to sulfuric acid dew point corrosion, making it an ideal material as a substitute for stainless steel. IV. Chemical Composition and Mechanical Properties Chemical composition: The main chemical components of ND steel include C, Si, Mn, Cr, Cu, Sb, etc. The content of C is low, generally not exceeding 0.12%, while the contents of alloying elements such as Cr, Cu, and Sb vary depending on the specific grade. Mechanical properties: The tensile strength, yield strength, elongation, and other mechanical properties of ND steel meet the requirements of relevant ** or industry standards, enabling it to satisfy the needs of various types of equipment.